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Low-molecular-weight gelators: Elucidating the principles of gelation based on gelator solubility and a cooperative self-assembly model

DOI: 10.1021/ja801804c DOI Help

Authors: A. R. Hirst (University of York) , I. A. Coates (University of York) , T. R. Boucheteau (University of York) , J. F. Miravet (Universitat Jaume) , B. Escuder (Universitat Jaume) , D. K. Smith (University of York) , V. Castelletto (University of Reading) , I. W. Hamley (University of Reading)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society , VOL 130 (28) , PAGES 9113–9121

State: Published (Approved)
Published: June 2008

Abstract: This paper highlights the key role played by solubility in influencing gelation and demonstrates that many facets of the gelation process depend on this vital parameter. In particular, we relate thermal stability (Tgel) and minimum gelation concentration (MGC) values of small-molecule gelation in terms of the solubility and cooperative self-assembly of gelator building blocks. By employing a van’t Hoff analysis of solubility data, determined from simple NMR measurements, we are able to generate Tcalc values that reflect the calculated temperature for complete solubilization of the networked gelator. The concentration dependence of Tcalc allows the previously difficult to rationalize “plateau-region” thermal stability values to be elucidated in terms of gelator molecular design. This is demonstrated for a family of four gelators with lysine units attached to each end of an aliphatic diamine, with different peripheral groups (Z or Boc) in different locations on the periphery of the molecule. By tuning the peripheral protecting groups of the gelators, the solubility of the system is modified, which in turn controls the saturation point of the system and hence controls the concentration at which network formation takes place. We report that the critical concentration (Ccrit) of gelator incorporated into the solid-phase sample-spanning network within the gel is invariant of gelator structural design. However, because some systems have higher solubilities, they are less effective gelators and require the application of higher total concentrations to achieve gelation, hence shedding light on the role of the MGC parameter in gelation. Furthermore, gelator structural design also modulates the level of cooperative self-assembly through solubility effects, as determined by applying a cooperative binding model to NMR data. Finally, the effect of gelator chemical design on the spatial organization of the networked gelator was probed by small-angle neutron and X-ray scattering (SANS/SAXS) on the native gel, and a tentative self-assembly model was proposed.

Subject Areas: Chemistry

Facility: ID2 at ESRF

Added On: 19/08/2009 23:07

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Chemistry Organic Chemistry

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