Supramolecular Gels

Gels are ubiquitous solid-like materials found in everyday applications such as contact lenses, lithium grease, jelly and hair gels. They are generally based on polymers of low crystallinity and can be recognised by a simple ‘inversion test’ – the material doesn’t flow when turned upside down. Commonly gels comprise two-or-more component mixture comprising a gelator (ca. 1–2 % by weight or lower) and a fluid component that is immobilised by surface tension. Gels have a fibrous structure that spans the entire sample in one continuous, three dimensionally cross-linked network and are solid-like in their rheological properties. While most gels are based on polymeric components, this is growing recent interest in a class of gelators termed low molecular weight gelators (LMWG) that are based on small molecular species that form gel fibres by supramolecular interactions such as hydrogen bonding and hydrophobic effects. We have synthesized and characterized various hydrogen-bond functionalized pyridyl based ligands, which were excellent hydrogelators.( Langmuir 2004, 20, 10413, Chem. Mater. 2004, 16, 2332, Chem. Comm.2005, 4059-4061).

Multi-component gels based on enantiomers were prepared by mixing the equal amount of pure enantiomers as well as varying individual enantiomer concentrations. The enhanced thermal and mechanical strength may be attributed to the enhanced intermolecular forces and the combination of both self-sorted and co-assembled enantiomers in the mixed gel.Langmuir 2018, 34, 12957−12967

In collaboration with Steed´s group, we reported the synthesis of a bis(urea) gelator designed to specifically mimic the chemical structure of the highly polymorphic drug substance ROY. In this work, we have shown LMWGs that are structurally similar to crystallisation substrate will enable selective crystallisation of the particular polymorphs.Chem. Sci., 2017, 8, 78-84

We have extended this technique to inorganic complexes and have isolated different forms of copper(II) isonicotinate-N-oxide complex and studied their phase interconversion via solvent-mediated crystal to crystal transformation. Gel phase crystallisation performed in hydrogels, low molecular weight gels and gels of tailored gelators showed crystal habit modification. Crystallisation in aqueous ethanol resulted in concomitant formation of blue (form-I) and green (form-II/IV) crystals while use of LMWGs (Val-TMA) results in selective crystallisation of the blue form-I under identical conditions New. J. Chem, 2018, 42, 19963 - 19970.

 

We have reported the gelation ability of metallogels based on metal complexes of N-(4-pyridyl)nicotinamide (4PNA) and the studies revealed that copper(II) complexes of 4PNA formed gels selectively. In this study, we have proved the existence of crystalline state in the supramolecular gel matrix. The formation of crystalline materials in gel state is very important due to the potential applications in utilising LMWGs as cell growth media and a medium to control crystal growth CrystEngComm, 2015, 17, 8130-8138

 

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