By utilizing up-to-date knowledge about gelators, we designed and synthesized a novel low-molecular-weight gelator bearing a pyridine-2,6-dicarboxylic acid moiety and two cholesteryl glycinate units. In order to demonstrate the ingenuity of our design, we prepared a series of structurally related compounds and studied their gelation properties. Based on the results, we determined structural features of the gelator molecules which were important for successful gel formation. We showed that the properties of the gel systems (transparency, morphology, etc.) can be tuned by coordination with different metal ions, as well as by changing the solvent. Gelators, and their gels and xerogels were studied by combined NMR spectroscopy, X-ray powder and single crystal diffractions, and electron microscopic techniques. Additionally, a systematic investigation of xerogels derived from silver metallogels revealed an in situ generation of silver nanoparticles.

“The best catalyst is no catalyst.” With growing public concern over global warming and the amount of greenhouse gases, it is important to reduce the amount of chemicals and eliminate waste, to obtain better results in a simple, selective, safe, and environmentally benign fashion compared to conventional tedious chemical synthesis. Herein, we disclose an environmentally benign, rapid, catalyst/promoter/coupling reagent-free cyclization procedure of free amino acids to furnish exclusively cyclic dipeptides (2,5-diketopiperazines, DKPs) in excellent or even quantitative yield, along with their solid state self-assembling properties. This process is extremely simple and highly efficient with little or no traditional synthetic skills and without any chromatographic purification. Synthesis of structurally diverse DKPs has been achieved with a dramatic decrease in the reaction time, the amount/number of solvents used, a significant increase in the yield and nearly complete elimination of waste. As a result, this is an excellent example for the environmentally benign, clean and green chemistry concept. The most exciting outcome of our investigation is an unusual case of chiral self-recognition encountered upon the cyclization of rac-pipecolic acid, which resulted in the formation of the meso-product exclusively.

A wide variety of novel compounds obtained by combining two types of known organogelators, viz., bile acid alkyl amides and pyrene alkanoic acids, were synthesized and screened for their gelation ability. The 3α esters of 1-pyrene butyric acid (PBA) of alkylamides of deoxycholic acid (DCA) turned out to be effective in the gel formation with many organic solvents although the gelation has to be triggered by the addition of a charge transfer (CT) agent 2,4,7-trinitrofluorenone (TNF). The special feature of these molecules is that the organogelation is achieved only after derivatizing the acid moiety of the 1-pyrenealkanoic acids. Additionally, the gelation properties can be fine-tuned by inserting different functional groups at the bile acid side chain. The gels obtained are deep red in colour and optically transparent up to 2% w/v. The SEM studies of the obtained xerogels revealed bundled rod-like morphology without specialized branching.

A detailed understanding of the mode of packing patterns that leads to the gelation of low molecular mass gelators derived from bile acid esters was carried out using solid state NMR along with complementary techniques such as powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarizing optical microscopy (POM). Solid state 13C{1H} cross polarization (CP) magic angle spinning (MAS) NMR of the low molecular mass gel in its native state was recorded for the first time. A close resemblance in the packing patterns of the gel, xerogel and bulk solid states was revealed upon comparing their 13C{1H}CPMAS NMR spectral pattern. A doublet resonance pattern of 13C signals in 13C{1H}CPMAS NMR spectra were observed for the gelator molecules, whereas the non-gelators showed simple singlet resonance or resulted in the formation of inclusion complexes/solvates. PXRD patterns revealed a close isomorphous nature of the gelators indicating the similarity in the mode of the packing pattern in their solid state. Direct imaging of the evolution of nanofibers (sol–gel transition) was carried out using POM, which proved the presence of self-assembled fibrillar networks (SAFINs) in the gel. Finally powder X-ray structure determination revealed the presence of two non-equivalent molecules in an asymmetric unit which is responsible for the doublet resonance pattern in the solid state NMR spectra.

Combined solid-state NMR, powder, and single crystal X-ray diffraction, as well as thermoanalytical studies were performed towards the identification, isolation, and structural characterization of polymorphs present in commercial samples of six natural bile acids. The 13C{1H} cross-polarization (CP) magic angle spinning (MAS) NMR technique was used as a primary tool to identify the mixture of polymorphs present in the natural bile acids obtained from commercial sources. A detailed study including selective crystallization of each polymorphic form of the bile acids in different solvents and mixture of solvents was carried out, and their spectral patterns were compared with the mode of packing and number of molecules present in an asymmetric unit. These studies were strongly supported by other complementary techniques such as powder/single crystal X-ray diffraction and differential scanning calorimetric (DSC) experiments. While a few single crystal X-ray structures are solved in order to confirm the correct polymorphic form, most of the powder X-ray diffraction data were compared with the simulated X-ray patterns obtained from previously reported single crystal structures. Detailed analyses using multiple experimental techniques provided useful insights towards the mode of packing which is responsible for unique spectral patterns in the solid state.

Steroidal compounds have been utilized as carriers and for modification of physico-chemical properties of model biologically active secondary alcohols – juvenoids. Juvenoids are juvenile hormone analogues – environmentally safe insecticides, possessing significant biological activity towards different arthropods groups in focus on insect pest species. Structure modification of juvenoids plays important role to control the rate of liberation and decomposition of juvenoid in digestive system and can also play important role in the mode of action towards selected insect. This study presents an approach to the synthesis of steroidal monomers and dimers carrying one and two molecules of a juvenoid in their structures. The prepared compounds were tested for their inhibition activity on reproduction of the blowfly Neobellieria (Sarcophaga) bullata. These steroid–juvenoid conjugates showed promising possibilities in synthesis of new unique biochemical insecticides. Preliminary biological test results of prepared compounds are presented.

Steroidal compounds have been utilized as carriers and for modification of physico-chemical properties of model biologically active secondary alcohols – juvenoids. Juvenoids are juvenile hormone analogues – environmentally safe insecticides, possessing significant biological activity towards different arthropods groups in focus on insect pest species. Structure modification of juvenoids plays important role to control the rate of liberation and decomposition of juvenoid in digestive system and can also play important role in the mode of action towards selected insect. This study presents an approach to the synthesis of steroidal monomers and dimers carrying one and two molecules of a juvenoid in their structures. The prepared compounds were tested for their inhibition activity on reproduction of the blowfly Neobellieria (Sarcophaga) bullata. These steroid–juvenoid conjugates showed promising possibilities in synthesis of new unique biochemical insecticides. Preliminary biological test results of prepared compounds are presented.