Functionalised peptide-based gels containing a free carboxylic acid can be triggered using divalent cations. In most cases, the peptide must form worm-like micelles (exhibit shear-thinning behaviour/form 1D structures according to small-angle scattering) in order to successfully form gels on addition of a salt. The properties of the gels can be tailored by using different salts, with the properties changing depending on the identity of both the cation and the anion. The most commonly used salt in the Adams group is CaCl2.
CaCl2 triggered gels are prepared by first preparing the pre-gel solution at high pH. This is achieved by suspending a gelator in deionised water and then dissolving it by addition of a predetermined volume of 0.1M NaOH. In most cases, one molar equivalent of NaOH is sufficient. After stirring overnight to ensure complete dissolution, the pH is adjusted to the required pH using 1 M NaOH.
The pre-gel solution is then transferred to the chosen container for gel formation. 2 molar equivalents of 200 mg/mL CaCl2 solution is then pipetted onto the centre of the pre-gel solution. The sample must be left undisturbed for at least 24 hours to give the gel time to form.
Dave Adams Lab 