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Item Open Access Amphiphile-coated magnetic iron oxide nanoparticles for the extraction of contaminants from the aqueous media(University of the Free State, 2023) Mzinjani, Viwe; Azov, V. A; Langner, E. H. G.The availability of clean water to the community/ society is becoming a huge problem for its ecosystem. These toxic contaminants come from surface and subsurface water systems such as dams, rivers, and oceans that are eluted from industrial, domestic, agricultural, and recreational activities. Both organic and inorganic contaminants are found in these water systems in high concentrations, which put aquatic life at tremendous risk and the environment in general. Thus, the need for synthetic materials that can be used to solve this ongoing problem of water contamination is becoming an obvious research goal that needs urgent attention. Nanomaterials such as nanoparticles are currently being investigated as a tool to remove various contaminants in wastewater. Nanoparticles are very small particles with sizes ranging from 1 to 100 nm. Depending on their type, these nanomaterials may demonstrate various unique properties, such as strong catalytic activity, superparamagnetism, quantum confinement, and extremely high surface-to-volume ratios. In this project, the high surface-to-volume property was explored during the adsorption of methylene blue dye in spiked water samples. Magnetic iron oxide nanoparticles were chosen because of their magnetic susceptibility and most availability of iron metal on earth, making them cheaper materials since they can be prepared from cheap iron precursors. Magnetite NPs were prepared using the co-precipitation method, where iron precursors of Fe²⁺ and Fe³⁺ were dissolved in de-ionized water and ammonium hydroxide was used as the precipitating agent under an inert atmosphere. Better adsorption capacities of these nanoparticles can be achieved by functionalizing them with different organic and inorganic molecules. In this study, mono-alkyl phosphate esters of varying alkyl chain lengths were synthesized and used to functionalize the as-synthesized magnetite NPs to render better affinity towards organic dyes (Figure 1). The as-prepared magnetite NPs were characterized using techniques such as TEM, SEM, FTIR, EDS, and PXRD, and the organic functionalization molecules were characterized using NMR (¹H, ¹³C, and ³¹P), FTIR, and mass spectrometry. These characterization techniques confirmed the successful synthesis of the nanoparticles and mono-alkyl phosphate esters of varying alkyl chain lengths. TEM and SEM micrographs showed close to spherical shapes of the prepared nanoparticles with particle diameters ranging from 12 – 16 nm for bare Fe₃O₄ NPs and 17 – 22 nm for functionalized NPs. Comparable particle size was also obtained from the PXRD results using the Scherrer equation (eq. 3.1) where a particle size of 13 nm was obtained. PXRD characteristic peaks confirmed the inverse spinel structure of the Fe₃O₄ NPs. The presence of iron (Fe) and oxygen (O) in the EDS results confirmed the formation of the magnetite nanoparticles and the presence of carbon (C) and phosphorus (P) on the coated nanoparticles confirmed the successful coating of the Fe₃O₄ NPs. FTIR, NMR, and MS results showed comparable results to those found in the literature.Item Open Access The analysis of natural and sulfited commercial quebracho (Schinopsis lorentzii) and Acacia (Acacia mearnsii) proathocyanidin extracts with electrospray ionisation mass spectrometry(University of the Free State, 2013) Jordaan, Maryam Amra; Van der Westhuizen, J. H.Quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood and black wattle (Acacia mearnsii) bark extracts are important renewable industrial sources of proanthocyanidins (PACs). These extracts are used industrially in leather tanning and adhesive manufacturing. These applications are derived from their chemical properties. The poly hydroxy groups of PACs complex with proteins via hydrogen bonds and thus transforms raw skin into leather. The phloroglucinol or resorcinol type A-rings are nucleophilic and polymerise with aldehydes to form natural adhesives. The ortho hydroxy group on the B-ring form insoluble complexes with heavy metals and can be used in water purification applications. The extracts are often treated with sodium hydrogen sulphate (sulfitation) to enhance their industrial usefulness. From a literature search and discussions with role players in the black wattle and quebracho PAC extract manufacturing industry, it became evident that knowledge on the composition of commercial PACs extracts and chemical changes that takes place during sulfitation is unsatisfactory. These PAC extracts are complex due to variable hydroxylation patterns of the constituent flavan-3-ol aromatic rings, different configurations of the C-2, C-3 and C-4 stereogenic centres, different degrees of polymerisation, and the existence of angular oligomers. Gel or paper chromatography fractionations of the complex extracts are hampered by poor resolution due to their hydrophilic polyphenolic nature and efforts to isolate pure compounds have been restricted to the isolation of mainly monomers and a few dimers and trimers. PACs of the commercially important quebracho (Schinopsis lorentzii and Schinopsis balansae) and black wattle (Acacia mearnsii) extracts have a strong and stable interflavanyl bond. This stability is important from an industrial point of view as it leads to durable leather and adhesive products. It is attributed to the absence of 5-OH groups in the aromatic moieties of the extender fisetinidol and robinetinidol flavan-3-ols units. However, from an analytical point of view it is not advantageous. The high temperatures thus required to hydrolyse the interflavanyl bonds with weak acids; leads to decomposition of the intermediate monomers that renders conventional thiolysis and phloroglucinolysis based analytical methods unreliable. In this thesis we used electrospray mass spectrometry (ESI-MS) to investigate the composition of PACs in black wattle extract and the changes that takes place in the chemical composition of quebracho PACs during sulfitation. We furthermore use all the information available from literature on the phytochemistry of flavan-3-ols and PACs and the syntheses of flavan-3-ol oligomers to guide us in our ESI-MS interpretations. Previous research in our group established that quebracho PACs always consist of a catechin starter unit to which one, two or more fisetinidol extender units are attached. The first and second extender units are always attached to the relatively reactive phloroglucinol A-ring of the catechin starter unit to form predominantly dimers and angular trimers. Further extender units are attached to the relatively less reactive resorcinol A-rings of already incorporated fisetinidol extender units. This explains the relatively short degree of polymerisation of quebracho PAC extracts and their popularity as a tanning agent. Large PACs will not penetrate the spaces between skin proteins and cannot act as a tanning agent. In this thesis we established that black wattle PACs have, in addition to catechin starter units, also gallocatechin starter units and, in addition to fisetinidol extender units, also robinetinidol extender units. Acacia PACs are thus more complex combinations of catechin, gallocatechin, fisetinidol and robinetinidol monomers. This contrasts with quebracho PACs that only contain catechin and fisetinidol monomers. The higher degree of hydroxylation of gallocatechin and robinetinidol explains the higher water solubility of black wattle PACs and the less frequent need for sulfitation. We also established that during sulfitation of quebracho PACs, a sulfonic acid moiety is introduced in both the C-2 and C-4 position of the pyran heterocyclic C-ring. In the case of C-2 sulfitation, the heterocyclic ring is opened. This enhances the reactivity of the A-ring towards the reaction with formaldehyde (adhesive formation) and increases water solubility due to removal of rigidity and introduction of a polar sulfonic acid group. In the case of C-4 sulfitation, the interflavanyl bond is broken. Polarity and water solubility is thus not only increased via an additional sulfonic acid moiety, but due to the presence of shorter oligomers and a smaller average chain length. We also developed a chromatographic method to estimate the degree of sulfitation of quebracho PAC extract. We believe that we have made a valuable contribution towards a better understanding of the composition of black wattle and sulfited quebracho PAC extracts and have identified a number of misconceptions.Item Open Access Analysis of zirconium containing materials using multiple digestion and spectrometric techniques(University of the Free State, 2014-10) Lotter, Steven James; Purcell, W.; Nel, J. T.English: The preparation of pure zirconium metal for nuclear applications is difficult due to the non-reactivity of zirconium minerals, such as zircon. The ability to accurately analyse zirconium-containing materials across the whole beneficiation chain is of crucial importance to the zirconium industry as a whole. The development of such an analytical technique is problematic, however, as the very properties which make these materials desirable also make quantification of their components extremely difficult. Certified reference materials for the fluoride-containing Necsa zirconium process products were not available. Therefore in-house reference materials were created by crystallisation of several (cation)xZrF4+x compounds. Potassium catena di-μ-fluoridotetrafluoridozirconate( IV), cesium hexafluoridozirconate(IV) and tetraethyl ammonium catena di-μ-fluorido-bis-(trifluoridozirconate(IV)) monohydrate were prepared and characterised by X-ray crystallography and qualitative XRD. Coordination numbers for the zirconium atoms in each of these crystals were found to be 8, 6 and 7 respectively. Bridging fluorine bond lengths were determined to be approximately 2.06 and 1.97 Å for the potassium and tetraethyl ammonium complexes while terminal bond lengths were found to be 2.17 (potassium), 2.007 (cesium) and 2.15 (tetraethyl ammonium) Å. ICP-OES lower limits of detection for zirconium in the 3.25% nitric acid matrix were found to be 1.6 ppb with lower limits of quantification being ten times this value. ICPOES zirconium recoveries for these crystals were 101(1) and 100(2)% for the potassium and cesium crystals respectively. Dissolution of various commercial and Necsa process samples was problematic and thus several digestion methods were investigated. Sulphuric acid, ammonium bifluoride and hydrofluoric acid were all investigated along with microwave assistance. A microwave-assisted acid digestion method was developed capable of complete dissolution of all zirconium compounds with ICP-OES analytical recoveries of 102.0(9), 100(2) and 101(3)% for 99.98% zirconium metal foil, ZrC and ZrH2 respectively. In order to circumvent the dissolution step a solid state GD-OES method was developed wherein sample powders were pressed into disks with a binder material, either copper or graphite. Initially instrument response across different samples was inconsistent but after optimisation of several instrument parameters, such as applied voltage and pre-burn time, a calibration curve with a R2 value of 0.9805 was achieved using multiple sample materials. This was achieved using the radio frequency glow discharge source operating at 900 V applied voltage and 14 W applied power with a 5-minute pre-burn period. Results for Necsa process products were largely in line with those achieved by the ICP-OES method.Item Open Access Analysis of zirconium containing materials using multiple digestion and spectrometric techniques(University of the Free State, 2014-10) Lotter, Steven James; Purcell, W.; Nel, J. T.English: The preparation of pure zirconium metal for nuclear applications is difficult due to the non-reactivity of zirconium minerals, such as zircon. The ability to accurately analyse zirconium-containing materials across the whole beneficiation chain is of crucial importance to the zirconium industry as a whole. The development of such an analytical technique is problematic, however, as the very properties which make these materials desirable also make quantification of their components extremely difficult. Certified reference materials for the fluoride-containing Necsa zirconium process products were not available. Therefore in-house reference materials were created by crystallisation of several (cation)xZrF4+x compounds. Potassium catena di-μ-fluorido-tetrafluoridozirconate(IV), cesium hexafluoridozirconate(IV) and tetraethyl ammonium catena di-μ-fluorido-bis-(trifluoridozirconate(IV)) monohydrate were prepared and characterised by X-ray crystallography and qualitative XRD. Coordination numbers for the zirconium atoms in each of these crystals were found to be 8, 6 and 7 respectively. Bridging fluorine bond lengths were determined to be approximately 2.06 and 1.97 Å for the potassium and tetraethyl ammonium complexes while terminal bond lengths were found to be 2.17 (potassium), 2.007 (cesium) and 2.15 (tetraethyl ammonium) Å. ICP-OES lower limits of detection for zirconium in the 3.25% nitric acid matrix were found to be 1.6 ppb with lower limits of quantification being ten times this value. ICP-OES zirconium recoveries for these crystals were 101(1) and 100(2)% for the potassium and cesium crystals respectively. Dissolution of various commercial and Necsa process samples was problematic and thus several digestion methods were investigated. Sulphuric acid, ammonium bifluoride and hydrofluoric acid were all investigated along with microwave assistance. A microwave-assisted acid digestion method was developed capable of complete dissolution of all zirconium compounds with ICP-OES analytical recoveries of 102.0(9), 100(2) and 101(3)% for 99.98% zirconium metal foil, ZrC and ZrH2 respectively. In order to circumvent the dissolution step a solid state GD-OES method was developed wherein sample powders were pressed into disks with a binder material, either copper or graphite. Initially instrument response across different samples was inconsistent but after optimisation of several instrument parameters, such as applied voltage and pre-burn time, a calibration curve with a R 2 value of 0.9805 was achieved using multiple sample materials. This was achieved using the radio frequency glow discharge source operating at 900 V applied voltage and 14 W applied power with a 5-minute pre-burn period. Results for Necsa process products were largely in line with those achieved by the ICP-OES method.Item Open Access Application of the cross-metathesis reaction as alternative methodology for the synthesis of paramethoxycinnamate analogues as sunscreen components(University of the Free State, 2016-01) Swart, Marthinus Rudi; Marais, C.; Bezuidenhoudt, B. C. B.2-Ethylhexyl p-methoxycinnamate [Octyl methoxycinnamate (OMC)] is an organic compound that is commercially used in the cosmetic industry as a UV blocker in sunscreen creams and lotions. Commercial production of this compound, however, is hampered by multiple synthetic steps, high temperatures, tedious work-up procedures, halogenated by-products, and low atom economy. Due to the abundance of naturally occurring essential-oil phenylpropenoids like estragole, eugenol, and safrole, which can easily be transformed into anethole, isoeugenol, and isosafrole by catalytic double bond isomerisation, the possibility of utilizing one of these b-methylstyrenes, i.e. anethole, together with 2-ethylhexyl acrylate in metathesis based methodology for the preparation of OMC looked promising and was investigated. Model metathesis reactions between trans-b-methylstyrene and methyl acrylate over Grubbs 2nd generation catalyst, however, produced only the homometathesis product, trans-stilbene, in very high yields (>99%). Solvent, temperature and reactant ratio studies failed to change the course of the reaction towards the desired cross-metathesis product. Since Forman et al. reported the addition of phenol to the reaction mixture to enhance crossmetathesis over self-metathesis, the reaction was repeated with p-cresol (2 eq.) as additive. In order to prevent secondary metathesis reactions from occurring, the propene side-product was also stripped away by entrainment with argon, which led to the successful formation of methyl cinnamate in 38% yield. In order to determine the general applicability of the new process, the electronic effect, if any, of substituents in the para-position of the b-methylstyrene and the steric/electronic influence of the alkyl group attached to the α,b-unsaturated carbonyl compound on the outcome of the reaction were investigated. Trans-pmethoxy- b-methylstyrene (trans-anethole) (1 eq.) and trans-4- trifluoromethylsulfonyloxy-b-methylstyrene (1 eq.) were therefore reacted with methyl acrylate (2 eq.) under the optimized reaction conditions [Grubbs 2nd generation catalyst (0.5 mol%), p-cresol (0.25 eq.), refluxing DCM (10 mL), 2 hours] and it was found that an electron-donating group in the para-position caused a slight decrease in cross-metathesis product formation (36% vs 38% for unsubstituted trans-b-methylstyrene) whereas an electron-withdrawing group (triflate) in the same position enhanced cinnamate formation (43% vs 38%). The concomitant homo-metathesis reaction followed the opposite trend with the p-triflate suppressing stilbene formation (4% vs 18% for unsubstituted trans-b- methylstyrene) and a p-methoxy group enhancing the formation of the stilbene (50% vs 18%). When the influence of the O-alkyl group attached to the α,b-unsaturated carbonyl moiety was investigated, it was found that the yield of the cinnamate product increased with increasing steric bulk of the alkyl group. For the reaction of unsubstituted trans-b-methylstyrene with methyl acrylate and n-butyl acrylate, respectively, the yield increased from 38 to 55%, while for reaction between trans-anethole and these acrylates it went from 36 to 41%. Substituting the ester O-alkyl moiety in the α,b-unsaturated system with an alkyl group (3-buten- 2-one) and a hydrogen (acrolein), resulted in moderate yields of 34 and 32% for the reactions between the ketone and unsubstituted trans-b-methylstyrene and trans-anethole, respectively, while with acrolein only trace amounts (< 5%) of the cross–metathesis products were obtained. In all these reactions, the respective stilbenes were formed in 18 (for the reaction between methyl or nbutyl acrylate and trans-b-methylstyrene) to 58% (for the reaction of acrolein with trans-b-methylstyrene) yield. Finally, trans-β-methylstyrene and transanethole were reacted with 2-ethylhexyl acrylate to form 2-ethylhexyl cinnamate and the desired 2-ethylhexyl p-methoxycinnamate (OMC), which could be isolated as major products from the reaction in 64 and 47% yields, respectively. Due to the higher reactivity of trans-anethole, the cross-metathesis product (OMC) in this instance was accompanied by 32% of 4,4’-dimethoxystilbene. In an effort to determine how p-cresol addition affects the catalytic cycle of Grubbs 2nd generation catalyst and thus how it influences product formation, a full NMR study of the addition of cresol to the catalyst, the catalyst and trans-b-methylstyrene, the catalyst and methyl acrylate, as well as all the reactants together, was embarked upon. Despite severely restricted rotation, which necessitated the spectra to be recorded at 60 oC, room temp., and -40 oC, all the 1H and 13C NMR resonances in the spectra of the Grubbs II catalyst could be allocated unambiguously to the appropriate protons and carbon atoms. 31P NMR studies allowed for the confirmation of a hydrogen bonding complex between cresol and the catalyst, while it also indicated some dissociation of the tricyclohexylphosphine from the catalyst to occur. The liberated tricyclohexylphosphine, however, prefers to react with the acrylate in a 1,4- addition process rather than forming a complex with the cresol as was postulated by Forman et al. This was confirmed by the preparation of the zwitterionic phosphonium salt through reaction of tricyclohexylphosphine with methyl acrylate in the presence of LiCl. Addition of cresol to the reaction mixture enhances the formation of the salt in its protonated form, while it also induces accelerated formation of oligomeric forms of the initially formed monomeric zwitterionic phosphonium salt. Although Forman et al. proposed the addition of phenols to stabilize the Grubbs catalyst by slowing down the dissociation of the tricyclohexylphosphine from the metal and once dissociated, prevents the phosphine from binding to the metal again, this explanation does not allow for the fact that the more reactive styrene analogue becomes less reactive than the acrylate moiety when cresol is added to the reaction mixture, as is evident from the fact that cresol addition enhances cross-metathesis. It was determined during the current study that the crossmetathesis products (cinnamates) are indeed the result of the primary metathesis process and are not formed through secondary metathesis of the stilbene products. In order to explain the formation of the cross-metathesis over homo-metathesis products in the presence of cresol, it is proposed that an associative mechanism rather than a dissociative process is prevailing when cresol is added to the reaction mixture. In this instance the co-ordination number of the ruthenium temporarily increases from 5 to 6 to allow for the additional ligand to be attached to the metal centre. The catalyst complex therefore becomes sterically more crowded and the steric size of the incoming ligand (reactant) would play a decisive role in its ability to react with the metal centre in the first step of the reaction. Since acrylate represents a mono substituted alkene and the alkyl group resides in a remote location with regard to the reaction centre, it would be sterically less demanding when compared to trans-b-methylstyrene and lead to enhanced formation of the cross-metathesis product. This assumption was proven by substituting methyl acrylate with methyl crotonate during the reaction and the resulting drop in cross-metathesis product from 38 to 31% yield observed. Support for this proposal comes from results by Fogg and co-workers, who reported cross-metathesis to be the dominant reaction when b-methylstyrenes were reacted with acrylates over the Hoveyda-Grubbs catalyst. Finally, with a number of cinnamates (OMC, methyl p-methoxycinnamate, methyl cinnamate, n-butyl cinnamate, n-butyl p-methoxycinnamate, and 2- ethylhexyl cinnamate) and 3-buten-2-ones [4-phenyl-3-buten-2-one and 4-(4- methoxyphenyl)-3-buten-2-one] available, it was decided to evaluate the UV-B blocking properties of these compounds through utilization of UV spectroscopy in an effort to determine if OMC would, in principle, be the best sunscreen component of the series. By comparing the UV spectra of OMC to that of the other compounds, it was determined that methyl cinnamate, n-butyl cinnamate, methyl p-methoxycinnamate and n-butyl p-methoxycinnamate could be promising candidates in the development of new and maybe better sunscreen lotions and should be subjected to biological evaluation processes.Item Open Access Atropisomerie in nuwe tipe bifeniel en o-terfeniel gekondenseerde tanniene(University of the Free State, 1984-03) Young, Esme; Ferreira, D.; Roux, D. G.Afrikaans: Chemiese ondersoek van die kernhout van Prosopis gZanduZosa het aan die lig gebring dat dit oor 'n komplekse flavanoïedinhoud beskik. As gevolg van hierdie kompleksiteit, was genoegsame materiaal en 'n aantal goedbeplande skeidingstegnieke van fundamentele belang. Die oorheersende fenoliese komponent van die kernhout is 'n flavan-3-ol met 'n 3' ,4' ,7,8-tetrahidroksi fenoliese substitusiepatroon. Dit dien as voorganger vir 'n verskeidenheid komplekse metaboliese analoë. Die ooreenstemmende flavan-3,4-diol met 'n soortgelyke substitusiepatroon, is slegs in spoorhoeveelhede geïsoleer. Afgesien van die isolasie van "konvensioneel" gekoppelde biflavanoïede gebaseer op elektrofiele aanval by die C4-karbeniumioon vanaf flavan-3,4-diole op die nukleofiele posisies van flavan-3-ole, is 'n nuwe 1-flavaniel-1,3- diarielpropan-2-ol sowel as 'n B-ring gekoppelde flavaniel-2-bensoïelbnsofuraan geïsoleer. Die uniekheid van hierdie ondersoek is egter gasetel in die identifisering van [5,6]-gekoppelde en atropisomeriese l5,51-biflavanoïede gebaseer op 'n bifenielbinding wat na triflavanoïedvlak uitgebrei is met herkenning van vier [5,5:5,6]-o-terfeniel triflavanoïedatropisomere. Die [5,5]-atropisomere is reeds op vryfenoliese vlak skeibeer- terwyl die [5,6]-isomeer en [5,5:5,6]-o-terfeniel atropisomere eers na derivatisering geskei kan word. Die 1H kmr-spektra van hierdie 5,5 -dimere en [5,5:5,6]-trimere vertoon opvallend skerp spektra by kamertemperatuur wat op "starheid" van struktuur by hierdie temperature dui. Hierdie spektra vertoon nie wesenlike verskerping van resonanse by hoër temperature nie. Verdere getuienis vir atropisomere by die [5,5]-gekoppelde dimere is aan die hand van 'n isomerisasie eksperiment verkry. Wanneer die temperatuur genoegsaam verhoog word (170'C in DMSO-oplossing), word die twee strukture onderling omskakelbaar. Die verskynsel word toegeskryf aan onderlinge interaksie tussen die "starre" C4-metileenfunksie en die "buttressing" effek van die meta hidroksi- of metoksisubstituent op die CG-proton. By die [5,6]-gekoppelde isomere, word 'n dinamiese ewewig by die 1H kmr-spektra van die metieleterasetaatderivate bespeur. Die 7-0H (D-ring) van die biflavanoied is traag om metilering te ondergaan as gevolg van sterk waterstofbinding met die π-elektrone van die A-ring. Daar word dus gepostuleer dat atropisomere as gevolg van waterstofbinding in die vryfenoliese toestand van die [5,6]-biflavanoied voorkom. Derivatisering hef hierdie waterstofbinding op en gee aanleiding tot 500 MHz kmr-spektra waarin seinverdubbeling en dus 'n redelike mate van beperking op die rotasiespoed voorkom. Sintese van die opties rein [5,6]-biflavanoied met 3' ,4',7,8- tetrahidroksileringspatroon is uitgevoer deur reduksie van (+/-)-3' ,4' ,7,B-tetrametoksidihidroflavonol, kondensasie daarvan aan die monomeriese (+)-3' ,4' ,7,B-tetrahidroksiflavan-3-ol en daaropvolgende skeiding van die diastereoisomeriese mengsel. Tydens suurkondensasie van (+)-mollisacacidien met die 3' ,4' ,7,B-tetrahidroksiflavan-3-oL is beide [4,6] +cis een [4,6] -trans biflavanoiede in die verhouding 1:6.4 verkry. Hierdie verbindings word vergesél deur 'n nuwe "lineêre" trimeer' {[4,6:4,6] -2,3-trans-3,4-trans:2' ,3'-trans:2",3"-trans-3",4"-cis-triflavanoied} wat ontstaan deur kondensasie van die gevormde [4,6]-3,4-trans-biflavanoied as nukleofiel met 'n verdere molekuul flavan-3,4-diol.Item Open Access Biflavonoied diastereo-isomere en hul biogenetiese voorlopers uit Berchemia SPP.: pogings tot sintese van analoe(University of the Free State, 1976-02) Volsteedt, Francois du Rouan; Roux, D. G.Afrikaans: Hierdie studie behels die struktuurondersoek, omskakelingsreaksies en pogings tot sintese van sommige van die mono- en biflavonoïede uit die kernhout van Berchernia zeyheri met 'n aanvullende studie op die kernhoutstowwe van die taksonomies notiverwante spesie; B discolor. Die verbindings uit B. zeyheri (rooi ivoor) kan in twee groepe geklassifiseer word, nl. mono- en biflavonoïede, almal op dieselfde 4' ,5,7- trihidroksi- (of sy ekwivalent) fenoliese patroon gegrond. Die eerste groep sluit die volgende in: maesopsin {2-(4-hidroksibensiel)-2,4,6-trihidroksibenso[b]furan-3(2H)-oon}; 7-metielmaesopsin (nnut); α,2’,4,4’,6’-pentahidroksicis- en trans-chalkoon; 2,3-trans-aromadendrin (3,4’,5,7-tetrahidroksiflavanoon); kaempferol (3,4’,5,7-tetrahidroksiflavoon); naringenin (4’,5,7-trihidroksiflavanoon) en 4,4’,6-trihidroksiauroon. Uit die beskikbare eksperimentele gegewens kon geen aanduiding van die struktuur van die rooi pigment wat verantwoordelik is vir die besondere voorkoms van die kernhout, verkry word nie. Die relatiewe hoë opbrengs van maesopsin het toegelaat dat verskeie nuwe omskakelings op die tetra-O-metieleter uitgevoer kan word met die doel om soortgelyke reaksies op daardie biflavonoïede, met een of meer maesopsineenhede waarvan genoegsaam verkry kon word, te herhaal. Reduksie met LiA1H4 het die ooreenstemmende 3-ol gelewer; brominering die 7-broomderivaat; en fotolise die 2’-hidroksi-α-metoksi-cis-chalkoonanaloog sowel as 1-(2-hidroksi-4,6-dimetoksifeniel)-2,2-dimetoksi-3-(4-metoksifeniel)-propan-1-oon. 2-(α-Asetoksi-4-metoksibensiel)-2,4,6-trimetoksi- en 2-(4-metoksibensoïel)-2-asetoksi-4,6-dimetoksibesno[b]furan-3(2H)-oon is vir die eerste keer verkry deur oksidasie van sintetiese 2’-hidroksi-α-metoksi-trans-chalkoon met Pb(0Ac)4 in asynsuur. Die struktuur van die cis- en trans-α-hidroksiechalkone is deur sintese en fotolitiese omskakeling bevestig. Die struktuur van die “konvensionele” chalkoon is deur sintese van 2’-hidroksi-4,4’,6’-trimetoksi-trans-chalkoon bevestig. Oksidasie van laasgenoemde met Pb(OAc)4 en Tl(NO3)3 lewer onderskeidelik tri-0-metielauroon en –isoflavoon. Al die biflavonoïede is nuwe natuurprodukte en sluit die volgende opties onaktiewe verbindings in (slegs triviale name genoem): zeyherin en isozeyherin, beide enantiomere pare bestaande uit twee I-2,II-7-gekoppelde bensokumaranonieleenheid verbind en neo- en isoneoberchenin wat slegs verskil t.o.v. die I-3,II-5-interflavonoïedbinding van voorafgaande twee. Al vier is enantiomere pare. ‘n Verdere biflavonoïed, rhamnin, saamgestel uit ‘n naringenieleenheid en ‘n terminale α-hidroksichalkooneenheid (I-3,II-3’-gekoppel), lewer vir die eerste keer direkte bewys (met die moontlikheid van ringopening in ag geneem) van inkorporasie van ‘n α-hidroksichalkoon as biogenetiese voorloper. Die bestaan van die verbinding dui aan dat ringsluiting van die terminale eenheid by berchenin en isoberchenin na intermolekulêre koppeling plaasvind. Twee verdure biflavonoïede, laktoon A en B genoem, identies aan die zeyherins behalwe dat die terminale eenheid (maesopsin) ’n bensielsuuromskakeling onder die toestande van metilering ondergaan het en derhalwe nie as natuurprodukte beskou word nie, is as enantiomorfe mengsels verkry. Hul dien egter as ‘n indirekte bewys vir α-hidroksichalkone as biogenetiese voorlopers, en dat siklisering by die zeyherins soos in die geval van berchenins moontlik eers na intermolekulêre koppeling geskied. Geeneen van die pare biflavonoïede ondergaan onderlinge omskakeling by ca. 150° (ontbinding) nie, sodat hul nie rotasie isomere verteenwoordig nie, maar wel diastereoisomere. Bibensokumaranonielmetaan, moontlik ‘n rotameriese mengsel volgens duplisering van seine in die KMR-spektrum van die 0-metieleter, bestaan uit twee maesopsineenhede, unike I-5,II-7 oor ‘n CH2-brug verbind. ‘n Verbinding verwant aan laasgenoemde, n. 2,7-bi(4-hidroksibensiel)-2,4,6-trihidroksibenso[b]furan-3(2H)-oon is ook geïsoleer. Al die biflavonoïede is uniek in die opsig dat hul 5-ledige heterosikliese ring(e) of ‘n α-hidroksichalkoon as eenhede bevat. As gevolg van ‘n gebrek aan material is slegs enkele omskakelings op sommige van die biflavonoïede uitgevoer. Reduksie van 0-metielzeyherin met KBH4 skakel slegs die karbonielgroep van die terminale eenheid na die alcohol om. Dieselfde resultaat is op die berchenins verkry. Fotolise van 0-metielzeyherin lei tot omskakeling van die terminale eenheid na ‘n ketalstruktuur soortgelyk as die verkry uit die fotolise van 0-metielmaesopsin. Deur die uitskakeling van suurtoestande en hitte is die 0-metieleters van maesopsin, zeyherin, isozeyherin, berchenin en isoberchenin na voltooiing van die ondersoek as opties aktiewe verbindings geïsoleer na metilering met diasometaan. In ‘n poging tot sintese van ‘n biflavonoïed is gevind dat wanneer ‘n gesubstitueerde fenol i.p.v. ‘n flavonoïedeenheid gebruik word onder toestande wat fenolkoppeling bevorder [alkalise K3Fe(CN)6], die reaksie van die verwagte afwyk deurdat koppeling in die β- i.p.v. die α-posisie van die chalkoon plaasvind. In die spesifieke geval koppel 2’,4-dihidroksi-4’,6’-dimetoksi-trans-chalkoon in die β-posisie met 3,5-dimetoksifenol in teenwoordigheid van K3Fe(CN)6 om vier diastereoisomere 2-[α-(4-hidroksi-2,6-dimetoksifeniel)-4-hidroksibensiel]-4,6-dimetoksiebenso[b]furan-3(2H)-one en 4’-hidroksie-4,6-dimetoksiauroon in goeie opbrengste te lewer. Die volgende verbindings is uit die kernhout van die verwante B. discolour geïsoloeer: maesopsin, alfitonien {2-(3,4-dihidroksibensiel)-2,4,6-trihidroksibenso[b]furan-3(2H)-oon}; α,2’,4,4’,6’-pentahidroksi- en α-2’,3,4,4’,6’-heksahidroksitrans-chalkoon (beide nuwe natuurprodukte); (-)-epi- en (+)-katesjien; kaempferol (3,4’,5,7-tetrahidroksiflavoon), kwersitien (3,3’,4’,5,7-pentahidroksiflavoon), 3,4’,5-trihidroksidihidrostilbeen, asook twee verbindings waarvan nog geen struktuurtoeseggings moontlik was nie. Fotolise van die heksametoksi-trans-chalkoon, derivaat van bogenoemde α-heksahidroksichalkoon, het die cis-isomeer gelewer. Slegs ‘n ketalanaloog is na die foto-oksidatiewe omskakeling van penta-0-metielalfitonien geïsoleer, in teenstelling met die addisionele cis-α-metoksichalkoon verkry by die fotolise van tetra-0-metielmaesopsin. Skrille kontras bestaan dus tussen die inhoudstowwe van die twee spesies. Benewens ‘n aanvullende katekoloksigeneringspatroon is die opvallendste egter die afwesigheid van die verwagte biflavonoïede by B. discolour op grond van taksonomiese verwantskap. Alhoewel twee α-hidroksichalkone in die kernhout voorkom dui die afwesigheid van biflavonoïede in teenstelling met die geval van B. zeyheri moontlik op ‘n verskil in die redokspotensiaal van die twee spesies se ensiemsisteme en/of dat ‘n α-hidroksichalkoon slegs tesame met ‘n “konvensionele” chalkoon, soos in die geval van rooi ivoor, as biogenetiese voorlopers vir biflavonoïede optree. Die aanwesigheid van α-hidroksichalkone en verwante hemiketale in hoë konsentrasie dui op ‘n chemotaksonomiese verwantskap tussen twee spesies.Item Open Access Bulky metal complexes as model nanoscale catalysts(University of the Free State, 2012-11) Young, Cyril; Roodt, Andreas; Bezuidenhout, BenEnglish: The lifestyle of modern society has created a massive demand for various chemicals such as fuels, chlorine-free refrigerants, high-strength polymers, stain-resistant fibres, cancer treatment drugs and thousands of other products. The demand for these compounds can only be met through the use of catalysts. Heterogeneous catalysis has become a fundamental part of the industrial scale production of these chemicals. Although heterogeneous catalysis is better suited for these processes than its homogeneous counterpart, some of the systems are plagued by poor distribution of the active metal species throughout the support. The aim of this study was to investigate the feasibility of synthesising robust, planar, bridging ligands that could act as spacers between active metal species in the deposition of active catalysts onto heterogeneous supports. By choosing different building blocks, for the simple Schiff base reaction, the distance and proximity between active metal species could theoretically be controlled for a desired application. 1,10-Phenanthroline and diamide type ligands (Figure 1) were identified as possible candidates for this application Figure 1: Different ligand systems identified as possible dispersion spacers. (A) represents the diamide type ligands and (B) the 1,10-phenanthroline ligands. The aim of this study was pursued by the identification and synthesis of building blocks such as 5,6-diamino-1,10-phenanthroline and 1,10-phenanthroline-5,6-dione which could act as bridging ligands and could be used to construct larger bridging systems. The bridging ligands and building blocks were coordinated to square planar metal centres such as platinum and palladium. This would enhance the possibility of creating a single layer network on the surface of the support. The ligands and complexes were characterised using solid state techniques and single crystal X-Ray Diffractometry to investigate the planarity of these species and the coordination mode to some of the diamide type complexes that have not found many applications in this field. The Heck coupling was identified as a standard reaction which could be utilised to test the catalytic properties of the palladium species. The catalytic activity of a range of diamide and 1,10-phenanthroline type ligands was evaluated after the optimisation of the Heck coupling. It was found that reducing the electron density on the five and six position of the phenanthroline ring drastically enhances the catalytic capabilities of these compounds. The diamide type complexes and larger bridging ligands showed less promising results.Item Open Access The characterisation and kinetic study of rhodium(I) and iridium(I) triazole complexes(University of the Free State, 2000-11) Muller, Alfred Johannes; Basson, S. S.; Purcell, W.English: A number of triazolecyclooctadienemetal(l) complexes of the type [M(LL')(cod)] (where M = Ir or Rh and LL' represents the different bidentate N-N'- donor atom ligands, such as bpt-Nl+ and bpt) as well as their oxidative addition products [M(LL')(cod)(Me)(I)] have been prepared and characterised by IR, ¹H NMR and elemental analyses. It was found that in general these complexes are monomeric containing one LL' and cod ligand respectively. The oxidative addition between CH31 and the studied metal(l) complexes have been investigated on a UVNis . spectrophotometer. Under pseudo-first order conditions linear relationships were found indicating second order kinetics. All of the kinetic data had zero intercepts (within experimental error) indicating that no reverse reactions occur. The reactions were carried out in different solvents to study the influence of solvent properties on the reaction rate. The reactions were also conducted at different temperatures to calculate the activation parameters. These indicated an associative mechanism as what is usually expected from these types of complexes. The ability of the LL' bidentate ligands to increase the Lewis basicity of the metal center are reflected in the values of the second order rate constants. From this we can compile the following series indicating the different bidentate ligands' donating capabilities: macsm> AnMetha > hpt > bpt-Nl+ > sacac> tfaa > cupf > bpt' The activation ability of the bpt-Nl+ ligand for oxidative addition to the metal center is better than that of the bpt ligand given the correct solvent and metal center are chosen. It seems that in the case of the [M(bpt-NH)( cod)] complexes the rhodium analogue is more reactive, while the opposite case' is observed for the- [M(bpt)(cod)] complexes. Thus the bpt-Nl+ ligand is the better 0- donor in the rhodium complex, while the bpt ligand is the better 0- donor in the iridium complex.Item Open Access Characterisation and substitution kinetics of hromium(III)- and obalt(III)nitrilotriacetato complexes(University of the Free State, 2000-11) Visser, Hendrik Gideon; PurcelI, W.; Basson, S. S.English: The synthesis and reactions of Co(llI) and Cr(lIl) complexes with nitrilotriacetic acid (nta) as tetradentate ligand have widespread interest, mainly because of the fact that these complexes can be usedas biological model complexes and because nta labilises usually inert metal centres. Mori et al (1958:940) and Uehara et al. (1967:2317) were the first to prepare different Co(III)-nta and Cr(III)-nta complexes respectively. Since then these complexes have been used in several kinetic and synthetic studies (Visser et al. 1997:2581; Visser et al. 1994:1051 and Thacker & Higginson, 1975:704). However the identity and purity of these complexes were questionable and had not been solved up to the time of this study. The question regarding the identity of the different Co(III)-nta species in solution at different pH levels have largely been accounted for in this study (refer to Scheme 1). Scheme 1 Complexes and reactions of Co(III)-nta. (Refer to PDF attached) The identity of the complex first prepared by Mori et al (1958:940) was finally characterised with X-ray crystallography as being [Co(nta)(1l-0H)]22-. Crystals of CS2[Co(nta)(J.l-OH)].4H20 crystallises in the orthorombic space group 141/a (R1= 0.0322). The Co-N bonding distance was determined as 1.922(6) A. [Co(nta)(J.l-OH)]}- undergo bridge-cleavage upon acidification with H+ ions to form [Co(nta)(H20)2]. The pKa of this reaction was determined as 3.09(3). Further acidification of [Co(nta)(H20)2] leads to the stepwise dissociation of nta. The formation of an ion associated species between [Co(nta)(H20)2] and H+ions upon addition of acid is postulated. This ion associated species dissociates in the rate determining step to form the tridentate nta complex, [Co(,,3-nta)(H20hr. The value of k1 at 25.9 °C was determined as 0.13(1) S-1. Another acid-base equilibrium is observed when the pH of a [Co(nta)(H20)2]solution is increased. It was concluded that the newly formed species is not the dimer, but rather [Co(nta)(H20)(OH)]" which reverts back to the dimer at pH 6 - 7 after several days. This second pKawas determined as 6.52(2). The substitution reactions between [Co(nta)(H20)2] and NCS- ions have been investigated, At pH = 2.00 NCS-ions substitute the aqua ligands in a stepwise fashion. The substitution of the first aqua ligand (k1= 2.4(1) x 10-2M-1 S-1at 24.7 °C) is about 120 orders of magnitude faster than the rate of substitution of the second aqua ligand (~ = 1.98(6) X 10-4M-1S-1at 24.7 °C). The [Co(nta)(H20)OHr complex reacts about 70 times faster at 24.7 "C with NCS- than [Co(nta)(H20)2] with NCS- (k2 = 1.68(5) M-1S-1vs. 2.4(1) x 10-2 M-1 S-1for k1 at 24.7 °C). This clearly indicates that the hydroxo ligand labinses the eis-aqua bond so that an increase in rate is observed. Hydroxide is not substituted by NCS- ions at higher pH so that only one reaction is observed spectrophotometrically. [Co(nta)(wOH)]i- undergo bridge cleavage at higher pH upon addition of various ligands like en, dmap or py. As a result of this several [Co(nta)(LL')] and [Co(nta)(L)2] (LL' = various N,N and N,O donors and L = dmap, py) complexes have been synthesised. The X-ray crystallographical structure determination of [Co(nta)(N,N-Et2en)] is a result of one of the synthetic studies. Crystals of [Co(nta)(N,N-Et2en)] crystallises in the orthorombic space group Pbcm (R1 = 0.0309). The Co-N bonding distance was determined as 1.950(4) A. The bridge cleavage reactions of u-hydroxo bridged Co(III)-complexes have not been studied to our knowledge. The substitution reactions between [Co(nta)(1l-0H)]l- and various ligands like dmap, py, en and N,N-Et2en have been investigated at pH 9 - 11.5. It is suggested that [Co(nta)(1l-0H)]/- equilibrates rapidly in aqueous basic solutions with a mono-u-hydroxo bridged species and that both these species react with the incoming ligand to form ion associated species (rapid) which dissociates in the rate determining step to the products. The existence of the formed mono-u-hydroxo bridged complex was confirmed by the fact that the value for the equilibrium constant, pKoH, was determined as 3.3 for all the reactions studied. This mono-u-hydroxo species is more labile towards substitution than the dimer itself as is illustrated by the fact that k1 < k2 for all the reactions studied. The values of k1 varied between 8.7(7) X 10-5 S-1 and 3.3(7) x 10-3 S-1 and those of k2 between 6.8(2) x 10-4S-1 and 5.7(2) x 10-2S-1. The synthesis and characterisation of Cs2[Co(nta)(C03)].H20 was also undertaken. This complex crystallises in the monoclinic space group P21/c (R1 = 0.0249) and can be used as an alternative to [Co(nta)(1l-0H)]l- for the synthesis of different Co(III)-nta complexes. The Co-N bonding distance was calculated as 1.920(2) A. The uncertainty surrounding the identity of the Cr(III)-nta complexes first prepared by Uehara et al. (1967:2317) have been erased with the X-ray crystal structure determination of Cs2[Cr(nta)(j.l-OH)].4H20. CS2[Cr(nta)(1l-0H)].4H20 crystallise in two different space groups, tetragonal 141/a (R1 = 0.0354) and monoclinic P21/c (R1 = 0.0354). The Cr-N bonding distances were 2.048(9) and 2.061 (3) A respectively. The strain experienced by the glycinato rings of coordinated nta decreases in the order G > R for all the complexes studied. The R rings in all the complexes are almost perfectly planar in all cases, while the G rings are non-planar.Item Open Access Chemical analysis and evaluation of a homemade pest control mixture used by a local farmer from Maloti-A-Phofung municipality of the Afromontane region in the Free State(University of the Free State, 2022) Sebotsa, Maria Mojabeng; Molefe, N. F.; Mosoabisane, M. F. T.The indigenous community of the Afromontane region has developed and adopted strategies for survival to reduce diseases and eliminate ticks and pests on crops at a lower cost. Biopesticides are efficient in eradicating various plant pests, affordable, quickly biodegradable, with multiple mechanisms of action, freely available supplies, and low toxicity to non-target organisms. The phytochemical composition of different plants is thought to be responsible for their various modes of action. Synthetic pesticides are expensive for small-scale farmers in undeveloped regions like the Afromontane region. Investigating agrochemical alternatives will benefit small-scale farmers who cannot access these due to their high cost. This study aims to analyse and evaluate the effectiveness of homemade pest control used by a small-scale farmer in the Afromontane region. The homemade pest control mixture used by local farmers was collected, then sequentially extracted and sonicated using hexane, chloroform, ethyl acetate, methanol and water. The extracts were screened for active compounds by phytochemical analysis and characterized using ultraviolet-visible (UV-Vis) spectroscopy, Fourier-Transform Infrared Spectroscopy (FTIR), and liquid chromatography-tandem mass spectrometry (LC-MS/MS. Biological testing was used to examine for antibacterial and antifungal activities. Saponins, phenolic compounds, and terpenes were found in all of the extracts after phytochemical analysis of the samples. Through using FTIR spectroscopy, the functional groups of the extracts were detected while UV/Vis spectroscopy identified the presence of chromophore at a region of 220-300 nm. LCMS/MS was performed to dereplicate the analyte components with a focus on their collision induced dissociation (CID) spectra. LC-MS/MS and molecular networking enabled annotation of metabolites active in the different extracts of the homemade pesticide. Based on the connectivity of the molecular network, the homemade pest control molecular networking nodes were grouped into five clusters (1–5). Cluster 1 consists of features annotated as flavonoids, cluster 2 corresponds to compounds of the alkaloids and flavonoids, cluster 3 corresponds to amino acids and alkaloids, cluster 4 consists of fatty acids and alkaloids and cluster 5 consists of features annotated as isoflavonoids. The annotated compounds exhibited various characteristics; some were insecticidal, while others showed antimicrobial activities. The antibacterial and antifungal properties of the sequential and ultrasonic extracts were examined using microdilution. Among the tested extracts, chloroform sequentially and sonicated extracts, methanol sequentially and sonicated extracts showed the best antibacterial activity with the MIC values of 0.09-0.195 mg/ml. The antibacterial activity for sequential chloroform extract showed the best activity against all the bacterial strains, with MIC values ranging between 0.098-0.39 mg/ml. Most of the extracts tested were ineffective against the fungal strains for antimitotic activity. Only a sonicated methanol extract showed the best antifungal activity. The sonicated methanol extract showed good activity (0.39-0.78 mg/ml) against Candida albicans, C. vulgaris and Trichophyton mucoides. In the case of water extracts, no activity was observed in the gram-negative bacteria and antifungal activity. The growth of Fusarium culmorum was suppressed by the sequence water extract and sonicated hexane extract. The current study's phytochemical and annotated compounds revealed that homemade pest-control bioactive compounds such as saponins, terpenoids, alkaloids, isoflavonoids and amino acids have antimicrobial properties against a variety of pathogens. Overall, the findings indicate that the mixture contains phytoconstituents that are effective against plant pathogens and capable of killing insect pests.Item Open Access Chemical kinetics, electrochemistry and structural aspects of ferrocene-containing b-diketonato complexes of rhodium(I) and iridium(I)(University of the Free State, 1999) Conradie, JeanetEnglish: Synthetic routes to prepare new Rh(I)-β-diketonate complexes [Rh(FcCOCHCOR)(CO)2] and [Rh(FcCOCHCOR)(CO)(PPh3)] with Fc = ferrocenyl and R = Fc, C6H5, CH3 and CF3 have been developed and optimized. Optimized synthetic routes to iridium(I) complexes, [Ir(R'COCHCOR)(cod)], with R' = Fc and R = C6H5, CH3 and CF3, or with R' = CF3 and R = CH2CH3, CH(CH3)2 and C(CH3)3 have also been developed. 1H and 31P NMR studies indicated that for complexes of the type [Rh(β-diketonato)(CO)(PPh3)] with an unsymmetrical β-diketonato ligand, at least two main isomers exist in solution. The structure of one isomer of [Rh(fctfa)(CO)(PPh3)], as well as crystal structures of FcCOCH2COCF3, [Rh(fctfa)(CO)2] and [Rh(fctfa)(CO)(PPh3)(CH3)(I)] were solved. The chemical kinetics of the oxidative addition of iodomethane to [Rh(FcCOCHCOR)(CO)(PPh3)] has been studied utilizing IR, UV/visible, 1H NMR and 31P NMR techniques. The NMR studies revealed that the rate of oxidative addition of iodomethane to the different [Rh(FcCOCHCOR)(CO)(PPh3)] isomers was the same. A complete general reaction sequence for the oxidative addition of iodomethane to all [Rh(bidentate ligand)(CO)(PPh3)] complexes is: First set of reactionsSecond set of reactionsThird set of reactions{[Rh(III)-alkyl1] [Rh(III)-acyl1] }K2=k2/k-2Rh(I)+ CH3I k1k-1k3k-3k4k-4[Rh(III)-alkyl2][Rh(III)-acyl2] 1H and 31P NMR studies further showed that all rhodium-containing complexes in the above mentioned reaction scheme, are actually composed of at least two main isomers, that is Rh(I)A the rate of substitution becomes faster when the group electronegativity of the R groups increases. This tendency is, as expected, exactly the opposite to what was observed during oxidative addition. A general reaction mechanism for both Rh and Ir complexes was presented. An additional study on the rate of the β-diketonato substitution with 1,10-phenanthroline in complexes of the type [Ir(CF3COCHCOR)(cod)] with R = CH3, CH2CH3, CH(CH3)2 and C(CH3)3 showed that the size of R does not hamper the rate of substitution. All substitution reactions were independent of a solvent step. The cyclic voltammetry study of all the ferrocene-containing β-diketonato complexes of rhodium(I) and iridium(I) synthesized, exhibited a single electrochemically reversible redox couple corresponding to the formal reduction potential of the ferrocenyl group of the β-diketonato ligand coordinated to the rhodium or iridium complexes, as well as an electrochemically irreversible anodic oxidation peak which corresponds to the oxidation of the metal = Rh or Ir. The 31P NMR study on different six-membered chelate complexes, [Rh(L,L'-BID)(CO)(PPh3)], and related Rh(III) complexes, indicated a general decrease in coupling constants 1J(31P-103Rh) as the Rh-P bond length, determined by X-ray crystallography, increases according to the relationship d(Rh-P) = -0.0014(1) x 1J(31P-103Rh) + 2.49(2). The Rh-P bond lengths, d(Rh-P), varied between 2.23 Å and 2.36 Å. The electron density on the Rh(I) and Ir(I) metal centres was manipulated over a wide range by changing the R group on the coordinated ligand (FcCOCHCOR)- from the highly electron donating Fc group (χFc = 1.87) to C6H5, (χC6H5 = 2.21) to CH3(χCH3 = 2.34) to the strongly electron withdrawing CF3 group (χCF3 = 3.01). The effect of the different R groups on the β-diketonato ligand (FcCOCHCOR)- coordinated to the rhodium(I) and iridium(I) complexes was not only observed in kinetic rate constants, but also in formal reduction potentials of the ferrocenyl group, the oxidation potential of Rh(I) or Ir(I), pKa-values, IR stretching frequencies, and crystallographic bond lengths.Item Open Access Chemical profile of walnuts (Juglans regia L.) and synthesis of stilbenes from Arformosia elata(University of the Free State, 2007-01) Sonopo, Molahlehi Samuel; Kamara, B. I.; Bezuidenhoudt, B. C. B.Firstly, this study presents an in-depth investigation on Walnuts (the nuts of Juglans regia L.). Walnuts (Juglans regia L.) are members of the relatively small Juglandaceae family, which have shown positive results in humans, in the treatment of metabolic syndrome. Besides the very high content of unsaturated fatty acids (60-70%) in Walnuts (Juglans regia L.), previous investigations have revealed tannins as the only phenolics present. Generally, plants have had their biological activities attributed to the presence phenolics, specifically the flavonoids, which are the most abundant polyphenols in nature. Since Walnuts leave behind an astringent taste in the mouth after ingestion, a characteristic associated with presence of phenolics, especially tannins, it was reasonable to assume that Walnuts may also contain flavonoids. Besides having well-established biological activities such as, antioxidant, anticancer, and anti-inflammatory properties, flavonoids are believed to augment the ability of Walnuts to act as a possible candidate for treatment of metabolic syndrome. In the previous studies, isolation of flavonoids has not been reported. Therefore, in this study we carried out an in-depth investigation to establish the presence of flavonoids in the Walnuts Juglans regia L. Pure compounds were obtained after repeated column and preparative thin layer chromatography and characterized by extensive NMR spectroscopic methods. The phenolics isolated in this study as peracetate and permethyl derivatives from the Walnuts Juglans regia L. are: catechin, gallocatechin, penta-O-acetyl-O-β-D-xylopyranosylellagic acid, gallic acid, methyl gallate, pedunculagin, casuarinin, hexaacetoxy-4-O-β-D-glucopyranosylnapthalene and 2,3-O-(S)-heptamethoxy-β-D-glucopyranosyldiphenoyl. Tetra-O-acetyl-9-β-D-glucopyranosylmegastigmen-3-one, tetraacetoxy-3-O-β-D- glucopyranosylsitosterol, glucose and sucrose were isolated as non-phenolics. Secondly, the study exploits methods to synthesize stilbene monomers and dimers isolated from Afrormosia elata. Afrormosia elata (Pericopsis elata) Harms, Fabaceae, is a tree native to the Guinean equatorial forests of West and Central Africa. The bark of this tree is used as a treatment for cancer by the local population. Stilbenes are a class of polyphenols with very 26 limited taxonomic distribution and varied biological activities which include, blood sugar reduction, antibacterial, antifungal, antioxidant, anti-HIV and anti-inflammatory. They posses COX-1 and COX-2 inhibitory effects, affect lipid peroxidation, LDL oxidation, function as phytoalexins, and have chemopreventative effects on cancer. The reported biological activities of stilbenes highlight the importance of stilbenoids as a resource for development of new drugs and pesticides. Since the occurrence of these stilbenoids in plants is in extremely low concentrations, we attempted synthesis of dimeric stilbenes with the aim of developing methods which may yield qualitative amounts. Syntheses of the monomeric stilbenes preceded that of the dimers. The classic Wittig reaction and the most recently developed metathesis reactions were the routes used to synthesize the monomers,while the route via the Heck coupling was considered for synthesis of the dimeric stilbenes.Item Open Access Comparison of injection moulded, natural fibre reinforced composites with PP and PLA as matrices(University of the Free State (Qwaqwa Campus), 2010-12-07) Mofokeng, Julia Puseletso; Luyt, A. S.Poly(lactic acid) (PLA) and polypropylene (PP) were comparatively investigated as matrices for injection moulded composites containing small (1-3 wt.%) amounts of short sisal fibre. The polymers and fibres were mechanically mixed, followed by extrusion at 190 C and injection moulding at the same temperature. The morphology, thermal and mechanical properties, and degradation characteristics were investigated using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, polarised optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and tensile testing. From the POM photos it seems as if the fibres are equally well dispersed in the PLA and PP matrices. The SEM photos, however, show more intimate contact and better interaction between the fibres and PLA. This improved interaction was confirmed by the FTIR results that show the presence of hydrogen bonding interaction between PLA and the fibre. This improved interaction did not seem to have a significant influence on the yield stress, stress at break or tensile modulus of PLA. In the case of PP, however, the stress at break reduced observably, while the tensile modulus almost doubled in the presence of the fibre. The thermal stability (as determined through TGA) of both polymers increased with increasing fibre content, with a more significant improvement in the case of PP. The DSC results show a significant influence of the presence of the fibre on the crystallization behaviour of PLA, because both the melting temperature and melting enthalpy decreased with increasing fibre content, even at low fibre contents of 1-3%. This is the result of the strong interaction between PLA and the fibre, which immobilizes the PLA chains. The influence of the fibre on the melting characteristics of the PP was negligible. Both the storage and loss moduli of the PLA decreased with increasing fibre content below the glass transition of PLA, but the influence on the loss modulus was more significant. The DMA results clearly show cold crystallization of PLA around 110 C, and the presence of fibre gave rise to higher modulus values between the cold crystallization and melting of the PLA. The presence of fibre also had an influence on the dynamic mechanical properties of PP. The biodegradation of PLA and its composites was determined by keeping the samples in water at an elevated temperature for up to 10 days. The composites initially showed a larger mass loss than pure PLA, but after 10 days the pure PLA seemed to be more degraded. The SEM results of biodegraded samples show complete collapse of the surface of the PLA matrix after ten days.Item Open Access Comparison of the influence of CeYAG and MCM-41 as nanofillers on the properties of polycarbonate and poly( methyl methacrylate)(University of the Free State (Qwaqwa Campus), 2016-01) Sibeko, Motshabi Alinah; Luyt, A. S.This study reports on the morphology of poly( methyl methacrylate) (PMMA) and polycarbonate (PC) filled with mesoporous silica (MCM-41) and cerium doped yttrium aluminum garnet (Ce:YAG) at contents in the range of 0.1 to 5 wt.%. The interactions between the polymer and fillers in these composites, and their thermomechanical, mechanical and thermal degradation properties were studied. The techniques used were small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), CP-MAS-NMR spectroscopy, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), impact testing and luminescence spectroscopy. The samples containing more than 0.5 wt.% of filler were Jess transparent than those containing smaller amounts, due to the presence of agglomerates. MCM- 41 particles were well dispersed at low loadings, but formed agglomerates at higher loadings, while the Ce:Y AG particles were not too well dispersed in both polymers at low loadings. Mixing with PMMA and PC did not alter the pore dimensions in the MCM-41 structure, and it maintained its hexagonal structure, even though the polymer chains partially penetrated the pores during composite preparation. Both polymers have carbonyl groups that had hydrogen bond interactions with the silanol group (Si-OH) on the surfaces of the MCM-41 particles. In the case of Ce: Y AG the interaction was through electron donor-acceptor interaction between the carbonyl oxygen lone pair in the polymers and the yttrium cation (Y3+). PMMA, however, showed a stronger interaction than PC. The addition of MCM-41 and Ce:Y AG increased the storage and loss modulus of PMMA and PC above the glass transition temperature. In the presence of MCM- 4 I the increase in modulus was due to the interaction of the polymer chains with the porous filler which restricted the mobility of the polymer chains and increased the stiffness of the composites. The impact strength of the polymer increased with the addition of MCM-41 and Ce: Y AG, but the concentration corresponding to the maximum increase depended on the type of filler. The combination of blue LEDs with the PMMA/Ce:YAG composites loaded with 5 wt.% and PC/Ce:YAG composites loaded with 2 wt.% gave off light in the white region, making them suitable for applications in white light emitting diodes.Item Open Access Comparison of the spectroscopically measure catalyst transformation and electrochemical properties of Grubbs' first- and second-generation catalysts(American Chemical Society, 2021) Swart, Marthinus R.; Marais, Charlene; Erasmus, ElizabethAccording to UV–vis spectroscopy (0.10 mM, CH2Cl2 at 25 °C), the catalyst transformation (which could possibly include ligand dissociation with active catalyst formation, dimer formation, and decomposition) rate constants (kobs) of Grubbs’ first (1) and second (2) generation catalysts are 7.48 × 10–5 and 1.52 × 10–4 s–1, respectively. From 31P NMR (0.1 M, CD2Cl2, at 25 °C), the catalyst transformation was 5.1% for 1 and 16.5% for 2 after 72 h. However, due to the larger concentrations of the NMR samples compared to the UV–vis samples, the extent of transformation did not correspond. The oxidation potential of the RuII/RuIII couple of 2 (E°’ = 27.5 mV at v = 200 mV s–1) was considerably lower than that of 1 (E°’ = 167 mV at v = 200 mV s–1). In the case of 1, a second reduction peak appeared at slow scan rates. This may probably be ascribed to an electrochemically active compound that was formed from the intermediate cation 1•+ and the subsequent reduction of the latter. The oxidation/reduction of 1 proceeds according to an ErCi electrochemical mechanism (Er = electrochemically reversible step, Ci = chemically irreversible step), whereas 2 proceeds according to an ErCr electrochemical mechanism (Er = electrochemically reversible step, Ci = chemically reversible step).Item Open Access Computational and characterization studies of homogeneous and heterogeneous tris(beta-diketonato) complexes with catalytic applications(University of the Free State, 2017-06) Gostynski, Roxanne; Conradie, J.; Erasmus, E.English: Nine [Mn(β-diketonato)3] [β-diketonato = dipivaloymethanato (dpm), 1; acetylacetonato (acac), 2; benzoylacetonato (ba), 3; dibenzoylmethanato (dbm), 4; trifluoroacetylacetonato (tfaa), 5; thenoyltrifluoroacetonato (tfth), 6; trifluorofuroylacetonato (tffu), 7; trifluorobenzoylacetonato (tfba), 8 and hexaflouroacetylacetonato, 9] complexes were synthesized by adapted methods from literature. An attempt was made to graft [Mn(β-diketonato)3] complexes 2-9 onto two dimensional (2-D) Si-wafer supports (S5-S12) via a silane linker. The X-ray photoelectron spectroscopy (XPS) Mn:F atomic ratio results of fluorine containing [Mn(β-diketonato)3] complexes grafted onto amino-functionalized Si-wafer (S9-S12) gave an indicaton that the [Mn(β-diketonato)3] complexes decomposed during the grafting process. Studying Mn2O3 on the hydroxylated Si-wafer surface by the use of XPS, it was confirmed that the Mn 2p photoelectron lines observed for S5-S12 consist mostly of Mn2O3 that has no interaction with the silane linker. Eight [Mn(β-diketonato)3] complexes 1-8 was wet impregnated onto various three dimensional (3-D) solid supports (S12- S28) to form [Mn(β-diketonato)3] model catalysts. Additionally a selection of [M(acac)3] complexes ([Co(acac)3], 12; [Rh(acac)3], 13, and [Ir(acac)3], 14) were grafted onto two dimensional (2-D) Si-wafer supports (S29-S31). While [M(acac)3] complexes ([Cr(acac)3], 10; [Fe(acac)3], 11; [Co(acac)3], 12; [Rh(acac)3], 13, and [Ir(acac)3], 14) were wet impregnated onto various three dimensional (3-D) solid supports (forming S32-S36). The model 2-D and 3-D catalysts were studied and characterized by the means of XPS, TGA and computational chemistry calculations. Selected model 2-D (S5, S7, S8, S12 and S29-S31) and Mn(acac)3 immobilized onto SiO2 (3-D catalysts, S14 as is and heat treated at 100, 130, 250 and 350 °C) were tested for the catalytic self-solvating reaction between ethanol and hexamethylenediisocyanate (HDI) to form hexamethylenediurethane (HDU) to mimic the industrial production of polyurethane. The model 2-D [Mn(β-diketonato)3] (S5, S7, S8 and S12) catalysts showed that as the total group electronegativity, 3(R + R'), increase a general decrease in turnover frequency (TOF) was observed. The model 2-D [M(acac)3] catalysts (S29-S31) showed that with an increase in the metal centre’s Pauling electronegativity a general increase in TOF was observed. The catalytic test on the Mn(acac)3 immobilized onto SiO2 showed that the sample heat treated at 100°C before hand has the highest TOF, which is most probably due to the loss of only one -diketonato ligand making it more active. The chromium(0) Fischer carbene complexes (Cr-FCCs) ([Cr(CO)4(PPh3)=C(OEt)(Fu)], C1; [Cr(CO)5=C(NHCy)(Fu)], C2; [Cr(CO)5=C(NHCy)(Th)], C3 and [Cr(CO)5=C(OEt)(ThTh)], C4) study was in collaboration with the research group of Dr. M Landman at the University of Pretoria. The four Cr(0) FCCs, were obtained and characterized by electrochemistry, XPS and computational chemistry calculations in this study. Penta-carbonyl Cr-FCCs [Cr(CO)5=C(OEt)(Fu)], C5, and [Cr(CO)5=C(OEt)(Th)], C6, were also supplied and anchored onto an amino-functionalized Si-wafer to create an immobilized Cr-FCCs C7 and C8. XPS results showed that the Cr(CO)5=C(OEt)(Fu)], C5, and [Cr(CO)5=C(OEt)(Th)], C6, was successfully anchored onto an amino-functionalized Si-wafer (C7 and C8). The electrochemical study of C1-4 showed that the oxidation potential (Epa) is influenced by the varied substituents on different sites of the Cr-FCCs. The oxidation order of the Cr-FCCs is: [Cr(CO)5=C(OEt)(ThTh)], C4 > [Cr(CO)5=C(NHCy)(Th)], C3 > [Cr(CO)5=C(NHCy)(Fu)], C2 > [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1. The reduction followed the same trend except for the [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1, complex that is reduced at a higher potential than the aminocarbene complexes, [Cr(CO)5=C(OEt)(ThTh)], C4 > [Cr(CO)4(PPh3)=C(OEt)(Fu)], C1 > [Cr(CO)5=C(NHCy)(Th)], C3 > [Cr(CO)5=C(NHCy)(Fu)], C2. The electronic energies of the different conformations obtained by the computational study showed that certain conformations are preferred over others. The computational results were in good agreement with experimental characterization method results. Computational study of HOMO and LUMO orbitals of the Cr- FCCs confirmed that the oxidation process is metal based and the reduction is based across the carbene ligand. The correlation of the oxidation potential (Epa) of the Cr0/Cr+1 redox couple and reduction potential (Epc) of the ligand based reduction with the HOMO energy (EHOMO) and LUMO energy (ELUMO) respectively, showed that with decreasing molecular orbital energy (HOMO and LUMO) an increase to more positive Epa and Epc potentials are obtained.Item Open Access Computational, structural and electrochemical properties of metal (III) tris-betadiketonato complexes(University of the Free State, 2012) Freitag, Roxanne; Conradie, JEnglish: A series of MnIII(β-diketonato)3 complexes (β-diketonato = acac, ba, dbm, tfaa, tfth, tffu, tfba and hfac) were synthesized and characterized with the aid of mass spectroscopy, elemental analysis, X-ray diffraction (crystallography) and melting point measurements. The electrochemical study (cyclic voltammetry) showed that for MnIII(β-diketonato)3 complexes with more electron withdrawing R and R' groups on the β-diketonato ligands (RCOCHCOR')-, the redox potential of the [MnIII(β-diketonato)3] + e- [MnII(β-diketonato)3] redox reaction was found to shift to more positive potentials. The reduction potential of the the MnIII/MnII couple was correlated to electronic parameters (acid dissociation constant (pKa) of the uncoordinated b- diketones (RCOCH2COR'), the total group electronegativities [Σ(cR + cR')] and total Hammett sigma meta constant [Σ(σR + σR')] of the R and R' side groups of the b-diketonato ligands (RCOCHCOR') and the calculated electron affinity of Mn(β-diketonato)3 complexes. DFT computational studies were done on the Mn(acac)3 and Mn(dbm)3 complexeto understand the Jahn-Teller distortion that that MnIII(β-diketonato)3 complexes undergo. Electrochemical (cyclic voltammetry) studies were done on M(acac)3 complexes where M = V, Cr, Mn, Fe and Co. The reduction potential of the MIII/MII couple was correlated to electronic parameters such as the metal electronegativity (cPauling and cMulliken), calculated electron affinity and LUMO energy. DFT computational studies were done on the symmetry of V(acac)3 to investigate the Jahn-Teller distortion of the V(acac)3 complex. A DFT computational study was used to illustrate the d-orbital occupations of the M(acac)3 complexes ( M = V, Cr, Mn, Fe and Co).Item Open Access Conformational analysis of oligomeric profisetinidins(University of the Free State, 2007-02) Potgieter, Eleonora Deborah; Ferreira, D.; Brandt, E. V.English: The profisetinidins are an important class of condensed tannins, or proanthocyanidins. Historically, studies towards the structure and conformation of proanthocyanidins were done on their peracetate and permethyl acetate derivatives. A current upsurge in industrial and biological applications of proanthocyanidins has prompted the present efforts at detailed analysis of the conformational behaviour of the naturally occurring free phenolic oligomeric profisetinidins. Studies towards the structure and conformational analysis of a small number of free phenolic dimeric procyanidins that are 4→8 coupled and only one free phenolic dimeric profisetinidin, fisetinidol-(4α→8)-catechin, have hitherto been reported. This study centres on the use of 1H, 13C, gradient COSY, COSY 45, COSY 90W, NOESY PH and HMQC NMR experiments in different solvents and at different temperatures to assign the hydrogen and some carbon resonances of the free phenolic profisetinidins that are found in commercially important southern hemisphere trees, namely Black Wattle (Acacia mearnsii) and Quebracho (Schinopsis balansae). These results, together with data obtained from CD spectra in methanol, were then used to study the conformations of these compounds. Dimers with 2,3-trans-3,4-trans (2,4-cis) configuration, namely fisetinidol-(4α→8)-catechin, fisetinidol-(4α→6)-catechin, ent-fisetinidol-(4β→8)-catechin and ent-fisetinidol-(4β→6)- catechin all displayed sets of duplicate resonances on 1H NMR spectra, indicating the presence of rotamers on an NMR time-scale at ambient temperatures. The proton resonances of the rotamers of the 4→6 linked dimers displayed insignificant chemical shift differences due to the similar magnetic environments and linear shape of both rotamers. The proton resonances of the rotamers of the 4→8 linked dimers displayed significant chemical shift differences due to the presence of compact and extended rotamers resulting in large changes in magnetic environment due to anisotropic effects. The type of solvent, temperature as well as the relative presence of water or cadmium nitrate had a strong influence on the relative concentrations of the rotamers, the conformations of the heterocyclic C- and F-rings as well as the visibility of hydroxy groups. The F-rings all displayed A/E- conformational exchange with line shapes indicating possible skewed boat conformations in some instances. The C-ring conformations ranged from rings with A/E conformational exchange to preferred E-conformers. The dimers with 2,3-trans-3,4-cis (2,4-trans) configuration, namely fisetinidol-(4β→8)- catechin, fisetinidol-(4β→6)-catechin and ent-fisetinidol-(4α→8)-catechin displayed only one set of resonances on 1H NMR spectra at ambient temperatures. The presence of intramolecular hydrogen bonding and limited conformational exchange was confirmed by the following observations: a) Selective broadening of proton resonances in both the heterocyclic and aromatic regions of 1D NMR spectra. b) Sharpening of resonances in 1D spectra at elevated temperatures. c) The presence of abundant coupling between heterocyclic and aromatic ring protons as observed on 2D spectra. d) Coupling between 2-HC and 4-HC on 2D NMR spectra. The C-rings had preferred A-conformations, with the F-rings displaying A/E conformational exchange with line shapes indicating possible skewed boat conformations in some instances. 2D NMR experiments afforded estimations, in some cases, of the angles between the plane of the B-ring and the 2-CC→2-HC bond, the plane of the D-ring and the 4-CF→4-HF bond as well as the plane of the D-ring and the 4-CC→4-HC. The resonances of 4-CC of the 2,3-trans-3,4-trans dimers displayed significant chemical shift differences (± 41 ppm) compared to 4-CC of the 2,3-trans-3,4-cis dimers (± 31 ppm).This could serve as a possible indicator of the relative configurations of the C-rings of 2,3-trans profisetinidins dimers. CD studies of al seven abovementioned dimers, as well as four trimers from Acacia mearnsii displayed complex curves with a number of strong Cotton effects. Although some trends were observed, it was abundantly evident that the chiroptical characteristics of this class of compounds are too complex to be interpreted in terms of the empirical quadrant rule.Item Open Access The constitution of oligomeric benzofuranoids(University of the Free State, 1999-05) Bekker, Riaan; Brandt, E. V.; Ferreira, D.English: Berchemia zeyheri is known for its unique red heartwood, a property that was probably responsible for the first phytochemical investigation into the flavonoid content of this tree. The heartwood contains a unique series of biflavonoids with one of more benzofuranoid moieties. These are usually found in diastereomeric mixtures, the biogenetic origin and stereochemistry of which have hitherto been unknown. This investigation thus represents a renewed effort to solve some of the intricate problems associated with these compounds. The high concentration of maesopsin in the heartwood made extensive enrichment and fractionation by the use of Craig countercurrent distribution techniques and Sephadex LH- 20 gelchromatography necessary. The two diastereomers of 4',5, 7-tri-O-methylnaringenin-(3a~ 7)-2,4,4',6-tetra-Omethylmaesopsin were, for the first time, successfully isolated and separated. Reduction of these diastereomers with Na(CN)BH3 gave two enantiomeric pure fragments. The conformations of the heterocyclic rings of these fragments were established by molecular mechanics (MMX and GMMX) and semi-empirical methods (AMI). These results allowed the absolute configuration of the fragments to be deduced from CD-curves of the compounds by application of Snatzke's rule for a,~-unsaturated five-membered cyclic rings. A n.O.e. correlation observed for one of the diastereomers only, correlates the stereocenter of the maesopsin moiety, of known absolute configuration, with a specific configuration of the naringenin unit, thus defining the absolute configuration of the dimer. These results also allowed the determination of the absolute stereochemistry of two regioisomers of the above dimers, 4',5, 7-tri-O-methylnaringenin-(3a~5)-2,4,4',6-tetra-Omethylmaesopsin and its epimer. The 13CNMR spectra of these related dimers were also studied and fully elucidated by means of HMQC and HMBC experiments. The structure and stereochemistry of two novel isoflavanone-benzofuranone biflavonoids, 4',5,7-tri-Omethyldihydrogenistein-fêcc-» 7)-2,4,4',6-tetra-O-methylmaesopsin and its epirner, were similarly determined. Resolution of maesopsin, the main metabolite in the heartwood, by means of HPLC using a chiral column, for the first time gave access to the two enantiomers of this benzofuranoid. 4,4',6- Tri-O-methyl-2-deoxymaesopsin-(2~ 7)-2,4,4',6-tetra-O-methyl-maesopsin and its epimer, consist of two benzofuranoid constituent units. An X-ray crystal structure was obtained for the one diastereomer, but due to the presence of a symmetric Pbea point group, only the relative configuration could be determined. After the racemic nature of each of the diastereomers was determined, each epimer was resolved with HPLC into its constituent enantiomers. The information obtained from the CD curves and crystal structure allowed the determination of the absolute stereochemistry of each of the enantiomers. Four further epimeric biflavonoids were isolated as the hepta-O-methyl ethers. Evidence obtained from 13C NMR data suggested the presence of a y-lactone functionality in the upper benzofuranoid moiety, identifying the dimers as the epimers of 4,6-dimethoxy-3-( 4- methoxy-benzyl)benzo[b ]furan-2(3H)-one-(2~5)-2,4,4',6-tetra-O-methylmaesopsin and the (2~ 7)-coupled regio-isomer. In order to supplement the above data, an asymmetric synthesis of maesopsin was attempted. The first attempt involved the oxidation of 2-( 4-methoxybenzyl)-4,6- dimethoxybenzo[b ]furan-3(2H)-one, obtained by reduction of the corresponding aurone, with AD-mix-a, a stereoselective catalyst, or chiral oxaziridine. The former afforded the desired product in low yield but no stereo selectivity while the latter method realized a much-improved yield, but still with no selectivity. This lack of selectivity is attributed to equilibrium of the product with the a-diketone. Attempts to prevent the formation of this equilibrium product were unsuccessful. A second synthetic attempt involved benzylation of 2,4,6-trimethoxybenzo[b]furan-3-(2H)-one with (-)-sparteine as chiral auxiliary, but again resulted in high yields but no stereo selectivity.