Study On The Molecular Gels Formed By Benzylidene-sorbitol Derivatives

Benzylidene-D-sorbitol derivatives such as 1,3:2,4- di-O-benzylidene-D-sorbitol(DBS), 1,3:2,4-di-O-methylbenzylidene-D-sorbitol (MDBS) and 1,3:2,4-di-O-imethylbenzylidene -D-sorbitol (DMDBS) are able to induce gelation in variety organic solvents by molecular self-organization.In this work, DBS, MDBS and DMDBS as gelators were investigated on their abilities of gelation based on molecular structure and the polarity of solvents. Gel's thermal stability were studied by TGS, Which affected by gelator molecular structure and the polarity of solvents. The results indicate that the ability of self-assembly for three gelators is related to the amount of methyl groups which resulted in solvophilic and conformation of molecular structures. The lower minimum gelation concentration (MGC) and higher phase transition temperature for MDBS and DMDBS usually implies the higher ability of self-assembly due to the more methyl groups in comparing with DBS. The increasing polarity of solvents causes the decrease of phase transition temperature of the gels formed by three gelators.The self-organization mechanism of these three gelators was studied by UV spectrum and FT-IR spectrum. UV spectra of the n-octanol gels formed by three gelators indicate that the K bands of benzene rings show red shifts reveal that theπ-πstack is one of the driving forces for the self-assembly of gelators;the extent of red shifts depends on the amount of methyl groups in benzene rings and in accord with the TGS of the gels formed by three gelators. FT-IR spectra suggests that H-bond of OH groups is another driving forces for the self-assembly of gelators.Lowest-energy molecular configurations of DBS, MDBS and DMDBS were obtained by molecular mechanics calculation software Spartan'02 .Combined with the results of UV spectra and FT-IR spectra, the conceptual model for MDBS aggregation was proposed.The Microtopography of gels was observed by FE-SEM and POM. POM images of the gels show that the aggregates of three gelators in propylene carbonate (PC) are spherulite crystalline and other types of crystalline in n-octanol. FE-SEM images show entangled fiber-like aggregates of gelators, which in turn form a three-dimensional network in n-octanol gels.The diffusion behaviors of Fe2+in molecular gels formed by sorbitol derivatives were investigated by the reaction of orthophenanthroline with Fe2+ using spectrophotometry .It is concluded that release of Fe2+ from molecular gels is influenced by different gelators ,the gelators'concentration, temperature and the amount of Fe2+ in gels.