No abstract

A molecular modelling approach has been used to study the relative binding of a winter flounder antifreeze peptice (AFP) to the faces and the internal planes, in particular the c-face and the 2021 plane, of the ice (Ih) crystal. The in vacm binding energies of the peptide molecule with the two surfaces differ by a factor of more than three, which could account for the suggested higher affinity of the molecule for the 2021 plane than for the c-face or the prism face. The propensities of the molecule to hydrogen bond with these surfaces are not so different. The key difference in the mode of attachment of the molecule to the various surfaces appears to stem from their geometrical features: the c-face and the prism face are flat, precluding intimate physical contact to be made with the peptide, but the 2021 plane contains 'ridges' and 'valleys' which produce a near-perfect steric match for the structure of the peptide molecule, so accommodating it in the 'lock and key' fashion.

Small drops of the pure linear alcohol ethoxylates C12E5 and C12E6 were injected into water at temperatures below their cloud points, and the times required for their dissolution were measured using videomicroscopy. Separately the rates of growth of the various liquid crystalline intermediate phases formed during penetration experiments with these surfactants in vertical linear cells were measured using videomicroscopy. It was found from both types of experiments that the dissolution process was controlled by diffusion, not by kinetics of phase transformation at interfaces. Effective diffusivities of the various phases were calculated from the data obtained and were found to be of order 10 -10 m 2 /s. Finally, interferometry was used to measure concentration distributions as a function of time during dissolution of the lamellar phase of C12E5. Diffusivity in the micellar solution was found to increase with increasing surfactant concentration with a further increase occurring at the concentration where the lamellar phase formed. The results were consistent with the effective diffusivities determined from the videomicroscopy experiments and with available values in the literature obtained by other techniques.