Investigations on Carboxy Dibenzylidene Sorbitol Hydrogels Using EPR Spectroscopy

Abstract

Low-molecular-weight organic gelators generate physical gels by the formation of three-dimensional fibrous network structures as a response to various physicochemical stimuli such as heat, light, ultrasound and chemical environments. Dibenzylidene sorbitol (DBS) represents a typical compound able to generate gels because of some prerequisite structural features: the presence of functional groups to form intermolecular hydrogen bonds and of aromatic groups to be involved in p-p interactions, or chirality. Herein, we present the synthesis of three derivatives of DBS-bearing carboxy groups attached to phenyl rings and the corresponding spin-labelled compounds. We studied the formation of physical gels resulting from self-assembly of DBS derivatives with the aim of highlighting the influence of the position of the carboxy group on the gel properties. These types of compounds can form gels in polar solvents (such as water, DMSO) by either temperature treatment or variation of the pH. In this study, the systems were investigated by rheological measurements, SEM analysis and EPR measurements. The results showed that the introduction of carboxy groups into the structure of DBS generates weaker gels compared with the parent gelator, DBS. The spin probes used in this study (spinlabelled DBS derivatives and 5-doxyl stearic acid) demonstrated that assembly of gelator molecules is a highly selective process. The two-component feature of EPR

Cyclodextrins as Bricks for Tuning Polymer Properties

“…In the particular case of gel formation, electron microscopy techniques are used to evidence the gel fibers. An interesting, powerful, but still rarely used approach in studying gels involves EPR spectroscopy [34,79,81,84,85]. The EPR spectroscopy is suitable to study polymer systems and gels as the method can provide insights into local, static, and dynamic properties of these systems.…”

“…By using spin-labeled CDs, it was possible to monitor the gel formation process, while the diffusion of various spin probes can evidence the nonuniform properties of covalent gels [81,88,89]. Other EPR studies explored the self-assembly of pluronic F127 leading to gel phase as a function of temperature and concentration of CD [34,35] or the formation of supramolecular gels resulted by the assembly of lowmolecular-weight gelators [85].…”

Non-covalent interactions evidenced by EPR spectroscopy in cyclodextrin complexes

“…The EPR studies using spin-labelling or the spin probe method have rarely been used to prove the assembly of LMFG based on the changes observed in the dynamics of the paramagnetic moiety. [60][61][62][63] Starting from these literature data, we applied the EPR method to investigate the formation of supramolecular gels resulted by assembly of dibenzylidene sorbitol derivatives 64 and 12hydroxystearic acid. 65 The results show that our approach of using spin-labelled gelators was less sensitive compared to using spin probes like 5-doxyl stearic acid (5-DSA, Fig.…”

Characterization and Tailoring the Properties of Hydrogels Using Spectroscopic Methods

“…Few EPR studies reported in the literature regard the supramolecular gels resulting from assembly of LMWG [109][110][111][112]. One explanation is probably that the self-assembly process represents a reorganization and thus selective process and insertion of a different molecule in the fibrillar assembly is, in general, less probable.…”

“…The behaviour of spin probes in gel systems depends on the solvent used. Thus, it was observed that the spin probe 5-doxyl stearic acid is entrapped in the gel fibres when the solvent composition water/ DMSO was 1:1 (v/v) [111].…”