Hydrogen-bonding A(LS)2-type low-molecular-mass gelator and its thermotropic mesomorphic behavior

Synthesis and spectroscopic characterization of chiral biphenyl-cholesterol gels

The synthesis of 4-(3-cholesteroxycarbonylpropyloxy)biphenyl (BO4-chol), 4-(7-cholesteroxycarbonylheptyloxy)biphenyl (BO8-chol), and 4,4'-bis(7-cholesteroxycarbonyl heptyloxy)biphenyl (BBO8-chol) is reported. These gelators form 1% and 2% (w/w) stable gels in n-octanol. The gels formed from single cholesterol gelators (BO4-chol and BO8-chol) exhibit lower phase transition temperatures (Tg) (62-65, 68-69 °C) than the gel obtained from the bischolesterol gelator BBO8-chol (96-98 °C). All three gelators form chiral gels in n-octanol as observed by induced circular dichroism (ICD) spectroscopy. The effect of two cholesterol moieties versus one cholesterol unit linked to a biphenyl molecule by a flexible chain, and the effect of the chain length on the gelation ability of these three novel gelators was investigated by circular dichroism (CD), absorption, and fluorescence spectroscopies. The gels obtained from BO4-chol and BO8-chol exhibit biphasic circular dichroism spectra with opposite chirality. The ICD spectra of both BO8-chol and BBO8-chol gels show a positive ICD band followed by a negative band at room temperature. However, while BO8-chol gel ICD absorptions decrease equally as temperature increases, BBO8-chol gel shows an inversion of the Cotton effect bands between 50 and 60 °C until completely disappearing above the phase transition temperature. SEM was used for the investigation of the morphology of the xerogels. On the basis of XRD data and molecular modeling, we propose packing modes for the formation of the organogelator aggregates.

Small-angle X-ray scattering structural study of the nanofiber self-assembly process in supramolecular gels based on glucopyranosides

This paper reports a study of the supramolecular self-assembly process of low molecular mass organic gelators in the formation of nanofiber networks. Methyl 4,6-O-benzylidene-α-D-glucopyranoside derivative compounds were designed to investigate the effect of substituents on the molecules' self-assembly properties. Gelators were prepared using two different substituent groups at position 4 of the aromatic ring: an electron-donating series (with n-alkoxyl groups) and an electron-withdrawing series (with n-alkoxycarbonyl groups), where n = 2, 3, 4, 8 and 16 C atoms. The gelation process in several gelator concentrations was studied in polar and apolar organic solvents. Differential scanning calorimetry revealed that the gelation temperature increases with the molar concentration and decreases with alkyl chain size in both series of gelators. Scanning electron microscopy images of the xerogel showed cylindrical aggregates. In situ small-angle X-ray scattering analysis corroborated a model of self-assembly based on one-dimensional nanofiber growth in a two-phase gel system, while X-ray powder diffraction revealed partial crystallization for the gelator compounds and for some gel samples. The infrared analyses of gels indicated that molecules undergo a self-assembly process via hydrogen bonding, suggesting that both OH groups are involved for samples of the n-alkoxycarbonyl series. On the other hand, the n-alkoxyl series aggregation process depends on the size of the alkyl chain. The compound with the smallest group, n-propoxyl, also undergoes self-assembly using both OH groups. Conversely, the rest of the n-alkoxyl series uses only one hydroxyl group.

New triangular steroid-based A(LS)3 type gelators for selective fluoride sensing application

A new series of triangular steroid-based A(LS)₃ type gelators has been developed which exhibited selective fluoride sensing abilities. The gelation, self-assembly and anion sensing properties of these gelators could be controlled by systematically altering their molecular structures.

Enantiomeric organogelators from d-/l-arabinose for phase selective gelation of crude oil and their gel as a photochemical micro-reactor

Easy access via single steps to each enantiomer of a simple chiral organogelator, their gelation abilities and applications are reported.

Reversible organogels triggered by dynamic K+ binding and release

In this study, a new lipophilic guanosine derivative was synthesized as an organogelator. The self-aggregation behavior of this organogelator was investigated by NMR, XRD and AFM. In solution, the lipophilic guanosine derivative can form a stable ribbon-like structure through NH(1)-N(7) and NH(2)-O(6) hydrogen bonds. However, gelation would occur in some aprotic solvents after the concentration reached a definite value. More interesting, the ribbon-like structure was able to change to G-quartets in the presence of K(+), which led to the transformation from a gel to a sol. Upon the addition of the cryptand [2.2.2], which can efficiently complex with K(+), G-quartets reverted to the original ribbon-like structure and the gel recovered. Subsequently, upon the addition of acids, K(+) was released from the cryptate with the transformation of gel-to-sol simultaneously. Finally, upon the addition of bases which deprotonated [H(+) ⊂ 2.2.2], the liberated cryptand [2.2.2] recaptured K(+) and the gel was regenerated again. This process of interconversion between G-ribbon 1(n) and octamer 1(8)·K(+) was well monitored by circular dichroism spectra.

Fluorescence-enhanced organogels and mesomorphic superstructure based on hydrazine derivatives

New low-molecular-mass organic gelators (LMOGs) bearing hydrazine linkage and end-capped by phenyl, namely 1,4-bis[(3,4-bisalkoxyphenyl)hydrozide]phenylene (BPH-n, n = 4, 6, 8, 10), were designed and synthesized. These organogelators have shown great ability to gel a variety of organic solvents to form stable organogels with the critical gelation concentration as low as 8.7 x 10(-4) mol L(-1) (0.06 wt %). The formed gel has a high gel-sol transition temperature (T(gel)) at low gelation concentration. Aggregation-induced emission (AIE) has been observed after gelation though conventional chromophore units not incorporated in BPH-n. The fluorescence quantum yields of xerogel are 2 orders higher than that of dilute solution. In addition, the BPH-n (n = 6, 8, 10) exhibited thermotropic hexagonal column (Col(h)) mesophase, which are stable at room temperature as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) studies.