Techniques for the Characterisation of Molecular Gels

Abstract

Molecular gels represent a case of hierarchical self-assembly of low molecular weight compounds into well ordered fibrillar architectures through non-covalent interactions. The resulting nanomaterials have found applications in multiple fields. In order to facilitate these applications, detailed study of their self-assembly mechanisms and properties at different length scales is required. The hierarchical nature of these materials means that a wide and multidisciplinary set of techniques have been developed and applied for the fundamental study of molecular gels. Different techniques are optimal for characterising aspects of the gel on each length scale – molecular, nano, microscopic and macroscopic. The present chapter uses selected examples to describe the different techniques that have been applied so far for a complete characterization of these systems. In particular, we focus on spectroscopy for probing molecular assembly, microscopy & diffraction/scattering to probe the nanoscale structuring, and calorimetric & rheological studies to provide insight into macroscopic performance. This chapter also focuses on aspects of gel characterisation such as chirality, kinetics and solvent effects.

Multi-component hybrid hydrogels – understanding the extent of orthogonal assembly and its impact on controlled release

“…S8 and S9 † ). 21 In this way, self-assembly kinetics can be followed, and the final CD spectrum gives direct insight into the nanoscale chirality of the self-assembled fibres. On self-assembly, DBS–COOH (0.02% wt/vol) developed a CD band at ca.…”

“…The aim of this study was to characterize and fully understand multi-component systems derived from these units, determining the precise influence of each component on the others, and probing the ability to release heparin. Gel characterization is a challenging task, performed across multiple length scales – from molecular-scale to nanoscale to macro-scale, 21 made more complex when multiple components are present. This study provides fundamental insights into complex multi-component self-assembled soft materials, and the extent to which the individual components can be considered to be orthogonal.…”

Probing the surface chemistry of self-assembled peptide hydrogels using solution-state NMR spectroscopy

“…Solution-state NMR spectroscopy is commonly used to follow the formation of supramolecular hydrogels as it is a powerful, non-invasive and widely available technique. 11,20 However, experimental attention is usually confined only to the mobile gelator present in solution rather than the gel networks themselves, which are usually NMR-silent. [21][22][23] As the molecules assemble, their resonances generally broaden, 21 decrease in intensity and may shift in frequency, 24 thus yielding valuable insights into the molecular interactions responsible for self-assembly, [25][26][27] and the kinetics and thermodynamics of assembly.…”

Low-Molecular-Weight Gels: The State of the Art

“…To understand the molecular packing, techniques such as nuclear magnetic resonance (NMR) spectroscopy, infrared spectroscopy, circular dichroism, fluorescence, and X-ray diffraction are used. 49,50 Although all of these can be informative, there are always caveats. Circular dichroism, for example, is very sensitive to concentration, and so good-quality data can often only be collected at concentrations lower than the mgc.…”