Study of peptide-mineral interactions

The studies of peptide-mineral interactions presented within this thesis aimed to identify and understand the effect(s) induced by peptides/selected motifs on amorphous silica and crystalline zinc oxide (ZnO) formation. The effect of imidazole functionality on silica formation was studied using polyvinylimidazole (PVI) and polyhistidine (P-His). The effect of zinc oxide-binding peptides (ZnO-BPs) on the morphology and formation of ZnO were studied using G-12 (GLHVMHKVAPPR) and EM-12 (EAHVMHKVAPRP), and their derivatives, GT-16 (GLHVMHKVAPPRGGGC) and EC-12 (EAHVCHKVAPRP) respectively. The influence of these additives on reaction kinetics, their effect on the precipitates, and their level of incorporation into the precipitates were investigated. This series of studies revealed three common characteristics of peptide-mineral (ZnO-BPs-ZnO and imidazole-silica) interactions. Firstly, a specific functionality of the biomolecule was responsible for the effect induced while a supporting functionality enhanced the effect. The imidazole group of PVI and P-His catalysed the condensation of monosilicic acid but the peptide backbone and more flexible imidazole enhanced the catalytic capability of P-His with respect to PVI having a similar concentration of imidazole groups. The presence of G-12 and GT-16 reduced the aspect ratio of ZnO crystals formed via an adsorption-growth inhibition mechanism. However the addition of a GGGC-tag on GT-16 weakens the adsorption of GT-16 on the (10-10) face of ZnO crystals. This gave rise to selective adsorption of GT-16 on the (0002) face, with a greater reduction of the crystal aspect ratio. For the EM/EC-12 peptides, metal ion complexation that leads to a delay/suppression of ZnO formation was higher for EC-12 compared to EM-12 and was caused by the more efficient complexation of Zn2+ with the peptide containing cysteine. Secondly, additives can interact with different species in the reaction. Imidazole interacts with neutral monosilicic acid via hydrogen bonds but protonated species of imidazole interact with anionic polysilicic acid via electrostatic interactions. Although EM-12 only interacts with Zn2+ in solution, EC-12 was able to interact reversibly with the solid phases formed in the course of reaction. Thirdly, the type of interaction and interacting species determine the level of additive incorporation and its effect on the concentration of reactants remaining in solution when equilibrium is reached. Peptide-surface interactions generally result in incorporation of the peptide into the solid phase (G-12, GT-16, and EC-12) as opposed to the situation where complexation of reactant species in solution shown by EM-12 did not result in peptide incorporation. The use of peptides/motifs (hiomolecules) isolated from combinatorial libraries for silica and ZnO synthesis has been shown to he a promising approach for morphology and reaction control. It is particularly exciting when their use can he extended to the generation of ZnO which has non-biological origin. By understanding the phenomenal complexity of the behaviour of biomolecules in (hio)mineralising systems, the ground rules in their interactions (with species in (hio)mineralising systems) can be generated and exploited for the synthesis of novel nanomaterials with properties tailored for specific applications.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Nottingham Trent University

Year dc:date.issued

2010

Author dc:creator

• Keat, LM

Language dc:language

en