Linking micellar structures to hydrogelation for salt-triggered dipeptide gelators

• Published in: Soft matter 2016-04, Vol.12 (15), p.3612-3621
• Main Authors: Cardoso, Andre Zamith, Mears, Laura L. E, Cattoz, Beatrice N, Griffiths, Peter C, Schweins, Ralf, Adams, Dave J
• Format: Article
• Language: English
• Subjects: Calcium; Confocal; Dipeptides - chemistry; Hydrogels; Hydrogels - chemistry; Hydrogen-Ion Concentration; Joining; Micelles; Naphthalenes - chemistry; Salts - chemistry; Styrene acrylonitrile resins; Transformations
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c5sm03072b

Some functionalised dipeptides can form hydrogels when salts are added to solutions at high pH. We have used surface tension, conductivity, rheology, optical, confocal and scanning electron microscopy, 1 H NMR and UV-Vis spectroscopy measurements to characterise fully the phase behaviour of solutions of one specific gelator, 2NapFF, at 25 C at pH 10.5. We show that this specific naphthalenedipeptide undergoes structural transformations as the concentration is increased, initially forming spherical micelles, then worm-like micelles, followed by association of these worm-like micelles. On addition of a calcium salt, gels are generally formed as long as worm-like micelles are initially present in solution, although there are structural re-organisations that occur at lower concentrations, allowing gelation at lower than expected concentration. Using IR and SANS, we show the differences between the structures present in the solution and hydrogel phases. The hierarchical structure of a dipeptide micellar phase is characterised and linked with the corresponding salt-triggered hydrogel phase.