Speed versus stability – structure–activity effects on the assembly of two-component gels

Abstract

Article:Rohner, Stefan S., Ruiz-Olles, Jorge orcid.org/0000-0002-3037-5722 and Smith, David K. orcid.org/0000-0002- 9881-2714 (2015) Speed versus stability-structure-activity effects on the assembly of two-component gels. RSC Advances.This paper reports the structural modification of a two-component gelation system comprising a 1:1 complex formed between a peptide carboxylic acid and phenylethylamine. Changing amino acids has a profound effect on the speed of gel formation and the minimum gelation concentration (MGC) yet the thermal stability of the gel remains unchanged.Variable temperature NMR studies demonstrate that at room temperature, the speed at which the gel forms is controlled by the solubility of the acid-amine complexes, which mediates the initial nucleation step required for gel assembly.On increasing the temperature, however, a thermodynamic enthalpy-entropy balance means all of the gels break down at around the same temperature. Those gels which are more favourably and rapidly formed at room temperature on enthalpic grounds are also more temperature sensitive as a consequence of the greater entropic cost of efficient packing within the gel fibres. This constitutes a rare example in which the time required for gelation can be structurally controlled, with NMR providing unique insight into the dynamics of these gel-phase materials. We suggest that in the future, combining solvent and solute (gelator) solubility parameters may provide further insight into these materials.

Gels with sense: supramolecular materials that respond to heat, light and sound

“…Similarly divergent trends in gelation kinetics and gel stability were described by Rohner et al, in a study of 1:1 toluene gels of phenylethylamine and a range of peptide carboxylic acids. 91 The least soluble peptides exhibited the lowest CGC values and gelation times as expected, but converted to sols at roughly the same temperature as more soluble analogues, due to a tendency for more enthalpically favoured structures to exhibit larger entropies of dissociation.…”

Investigating hydrogel formation using in situ variable-temperature scanning probe microscopy

“…In situ imaging of this nature will be vital to resolve if the gel structure changes over time, and may be useful to apply to other systems where kinetic effects are being investigated. 16 , 17 …”

Selective aliphatic/aromatic organogelation controlled by the side chain of serine amphiphiles

“…In this regard, solvent polarity, solubility parameters and structural relationships have been investigated. [13][14][15][16][17][18][19][20] These studies highlight the impact that subtle structural modications can have in gelation efficacy. [21][22][23] Despite these efforts and the recent advances in the understanding of kinetic and thermodynamic aspects of the selfassembly process 24,25 it is not yet possible to formulate a model for the design of functional molecular gels.…”