Abstract
To investigate the effect of spatial configuration on the gelation properties of low molecular mass gelators (LMMGs), four novel di-cholesteryl derivatives have been specially designed and synthesized by introducing the cis-/trans-isomers of butene diacid and the optical isomers of D/L-phenylalanine into the linker between two cholesteryl moieties. These isomers have been denoted as MaDC, FaDC, MaLC and FaLC, respectively. The gelation properties of the compounds were examined in 26 organic solvents, and it was found that the trans-configuration is more favorable for the gelation, but the chirality of the linker shows little effect to the gelation. FaDC has the strongest gelation ability among the four isomers. Interestingly, FaDC and FaLC display phase-selective gelation of benzene, toluene and xylene from their mixtures with water at room temperature, which establishes a foundation for the purification of water contaminated by oil or aromatic solvents. SEM and CD spectroscopy studies revealed that the spatial configuration of the linkers of the gelators affects significantly the aggregation mode, the morphologies and the chirality of the network of the gels. Moreover, the different aggregation behaviors also have an impact on mechanical properties of the gels, which are consistent with the results from rheological studies. Furthermore, temperature- and concentration-dependent 1H NMR and FTIR measurements demonstrated that intermolecular hydrogen bonding and π-π stacking are the main driving forces for the formation of the gels.
Highlights
Scanning electron microscopy (SEM) and Circular dichroism (CD) spectroscopy studies revealed that the spatial configuration of the linkers of the gelators affects significantly the aggregation mode, the morphologies and the chirality of the network of the gels
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]
Gelation test revealed that FaDC has the strongest gelation ability among the four isomers
Summary
Cholesterol, boc-D-phenylalaninate, boc-L-phenylalaninate, maleic acid, fumaric acid, dicyclohexylcarbodimide (DCC), and N,N-dimethylamino-pyridine (DMAP) were supplied from the Sinopharm Chemical Reagent Co., Ltd, and used without further purification. The FTIR spectra of solution and gel samples were recorded in transmission mode using a Bruker Equinox 55 infrared spectrometer. The gel sample for measurement was prepared by coating it on a KBr slice as a smooth film and freeze-dried. The first step of an experiment consists of determining the so-called linear viscoelastic region of the gel. This was done by measuring the storage modulus G′, associated with the energy storage, and the loss modulus G′′, associated with the loss of energy, as a function of the stress amplitude. The purification efficiency was determined by fluorescence measurement conducted on a time-correlated single-photon-counting FLS 920 fluorescence spectrometer (Edinburgh).
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