Synthesis, characterization and electrochemical studies of osmocenyl alcohols with biomedical applications

Abstract

English: A series of osmocene-containing carboxylic acids, Oc(CH2)mCOOH where m = 1, 2 and 3, and osmocene-containing alcohols, Oc(CH2)nOH where n = 1, 2, 3 and 4, were obtained in multiple synthetic steps and characterised with the aid of infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, elemental analysis and melting point measurements. New methods were developed for the synthesis of these osmocene-containing carboxylic acids and alcohols. The structures of 2-osmocenylacetonitrile (monoclinic, P21/c, Z = 4, R = 0.057) and 2-osmocenylethanol (trigonal, P-3, Z = 18, R = 0.092) were determined by single crystal X-ray crystallography. The alcohol, 2-osmocenylethanol, showed an extensive hydrogen bonding network involving the OH functionalities of six neighbouring molecules, arranged in a hexagonal pattern. Electrochemical studies, utilising cyclic voltammetry, were performed on all compounds synthesised, including precursor compounds. Electrochemical experiments were conducted in DCM and 0.1 M [NBu4][B(C6F5)4] as supporting electrolyte. A trend was observed between the number of –CH2– spacers and the formal reduction potentials (E°´) for both the carboxylic acids and alcohols. The formal reduction potentials for both the carboxylic acids and the alcohols were found to decrease as the number of –CH2– spacers increased. Dimerisation of the osmocenyl moiety, similar to the known dimerisation of ruthenocene, was observed. It was found that the degree of dimerisation diminishes as the number of –CH2– groups increases for both the osmocenecontaining carboxylic acids and alcohols. The formal reduction potentials for 2-osmocenylethanoic acid, 3-osmocenylpropanoic acid and 4-osmocenylbutanoic acid are 418 mV, 357 mV and 317 mV, respectively. The formal reduction potentials for osmocenylmethanol, 2-osmocenylethanol, 3-osmocenylpropanol, and 4-osmocenylbutanol, are 410 mV, 340 mV, 313 mV and 321 mV, respectively. Dimerisation was observed electrochemically for 2-osmocenylethanoic acid, 3-osmocenylpropanoic acid, 2-osmocenylethanol and 3-osmocenylpropanol. No dimerisation was observed electrochemically for 4-osmocenylbutanoic acid and 4-osmocenylbutanol.

Afrikaans: 'n Reeks osmoseenbevattende karboksielsure, Oc(CH2)mCOOH met m = 1, 2 en 3, sowel as osmoseenbevattende alkohole, Oc(CH2)nOH met n = 1, 2, 3 en 4, is in veelvuldige stappe gesintetiseer en gekarakteriseer deur gebruik te maak van infrarooi spektroskopie, 1H kernmagnetiese resonansspektroskopie, elementele analise en smeltpunt bepalings. Nuwe metodes vir die sintese van hierdie osmoseenbevattende karboksielsure en alkohole is ontwikkel. Die strukture van Oc(CH2)CN (monoklinies, P 21/c, Z = 4, R = 0.057) en OcCH2CH2OH (trigonaal, P-3, Z = 6, R = 0.092) is met behulp van enkelkristal X—straalkristallografie bepaal. Die alkohol vertoon ‘n uitgebreide waterstofbindingnetwerk bestaande uit die OH funksionele groepe van ses naasliggende molekule gerangskik in ‘n heksagonale patroon. ‘n Elektrochemiese studie, wat gebruik maak van sikliese voltammetrie, van alle gesintetiseerde verbindings is uitgevoer. Elektrochemie is uitgevoer in DCM en 0.1 M [NBu4][B(C6F5)4] as hulp elektroliet. 'n Tendens is gevind tussen die aantal -CH2- eenhede en die formele reduksiepotensiaal (E°') vir beide die karboksielsure en alkohole. Die formele reduksiepotensiaal vir beide die karboksielsure en alkohole neem af soos die aantal -CH2- groepe toeneem. Die graad van dimerisasie van die osmoseniel groep is soortgelyk gevind aan die van die rutenoseniel groep. Dit is gevind dat dimerisasie afneem namate die aantal -CH2- groepe toeneem, vir beide die karboksielsure en alkohole. Die formele reduksiepotensiaal van 2-osmoseniel asynsuur, 3- osmoseniel etanoësuur en 4-osmoseniel propanoësuur is 418 mV, 357 mV en 317 mV onderskeidelik. Die formele reduksiepotensiaal vir osmosenielmetanol, 2-osmosenieletanol, 3- osmosenielpropanol, en 4-osmosenielbutanol, is 410 mV, 340 mV, 313 mV en 321 mV onderskeidelik. Dimerisasie is elektrochemies waargeneem vir 2-osmoseniel asynsuur, 3- osmoseniel etanoësuur, 2-osmosenieletanol en 3-osmosenielpropanol. Geen dimerisasie is elektrochemies waargeneem vir 4-osmoseniel propanoësuur of 4-osmosenielbutanol nie.