Bis(PheOH) Maleic Acid Amide−Fumaric Acid Amide Photoizomerization Induces Microsphere-to-Gel Fiber Morphological Transition:  The Photoinduced Gelation System

Abstract

The photoinduced gelation system based on 1 (non-gelling) to 2 (gelling) molecular photoisomerization in water results by microspheres (1) to gel fibers (2) transformation at the supramolecular level.

Preparation of dicholesteryl-derivatives: The effect of spatial configuration upon gelation

“…With careful reference to Table 1 and paying more attention to the cis-trans isomerism, it should be not difficult to find that the trans-isomers are more effective gelators. As for FaDC and FaLC, they form 37 gels including 12 room temperature gels compared with 9 gels formed by the cis-isomers, MaDC and MaLC, suggesting that the trans-configuration is more helpful for the gelation, which is consistent with the results of literatures [28][29][30][31][32][33][34][35][36][37]. This may be understood by considering that the change in molecular configuration leads to the weakening of van der Waals interaction between cholesteryl moieties [30] as well as breaking or reforming of the hydrogen bonding [28,29] in cis-isomer, thus making cis-isomers dissolve or form partial gels in most of the solvents which can be gelled by trans-isomers.…”

“…Likewise, the impact of the different inherent chirality of the gelators on the morphology was displayed by the varied morphologies of the xerogels of MaDC/DMSO and MaLC/DMSO, FaDC/cyclohexane and FaLC/cyclohexane, as well as FaDC/benzene and FaLC/ benzene. These findings indicate clearly that the slight change in the spatial configuration of the linkers between the two cholesteryl moieties of each compound shows a significant effect on the morphologies [22,37]. This conclusion is also supported by the results from polarized optical microscopy (POM) studies of the gels of MaDC/DMSO, FaDC/DMSO and MaLC/DMSO (Figure 2).…”

“…As for the chirality, the numbers of the gels formed by D-isomers (21) and L-isomers (25) are very similar, demonstrating that the chirality is not the main factor affecting the gelation ability of the four isomers. It provides the clear-cut evidence that the formation of the gel depends on the configurational properties of compounds even though they have the same chemical composition [37].…”

“…Stereoisomerism, which can be classified into cis-trans isomerism (or geometric isomerism), optical isomerism and conformational isomerism, is of special importance among many properties of the functional groups. As for the cis-trans isomerism, azobenzene-based [28][29][30][31][32][33], stilbene-based [34][35][36] and butene diacid-based [37] gelators have attracted a great deal of attention due to the reversible sol-gel transition of the system achieved by the configurational change induced by light illumination. Žinić and coworkers [34][35][36] reported the first example of gelation induced by configurational isomerization, which is also the first example of gel preparation by converting a non-gelling compound to a gelator induced by light illumination.…”

“…Žinić and coworkers [34][35][36] reported the first example of gelation induced by configurational isomerization, which is also the first example of gel preparation by converting a non-gelling compound to a gelator induced by light illumination. They also prepared bis(phenylalanine) maleic acid (1) and fumaric acid (2) amides and found that in water the non-gelling maleic acid amide (1) could be converted into gelling fumaric acid amide via photochemical treatment [37]. Zhang and colleagues [30] synthesized a series of new symmetric dicholesteryl gelators with an azobenzene unit in the linkers (DCAZO).…”