Complete systematic study of reactions between copper(II) ions and tripeptides containing glutamic acid, glycine and histidine

For the first time, a complete systematic study of the reactions between Cu2+ and tripeptides containing glutamic acid (Glu, E), glycine (Gly, G), and histidine (His, H) is explored and reported in this thesis. This study revealed that the high-order interaction between the peptide residues is the major factor that controls peptide systems. The results of this project have implications in different fields including experimental design, multi-way data analysis, knowledge of peptide and metallo-peptide properties, and peptide-modified bio-sensors for copper sequestration.Potentiometric pH titration and visible spectroscopy were chosen as the most suitable analytical techniques for this purpose. The experiments provided data on acid dissociation constants (pKa), copper-complex formation constants (logβ), copper speciation and their spectral parameters (maximum absorption wavelength) for the full tripeptide set. The quantum mechanical modelling method PM6 was used to optimise the geometry of copper complex species with the various tripeptides. The outputs provided information about the copper complex geometries, the peptide’s copper anchoring atoms and thus the copper binding mode. The optimised geometries were mostly distorted structures and varied between tetrahedral (or trigonal planar) and square planar shapes in which the copper was tetra-bound to the peptide via 3 or 4 nitrogen atoms (3N and 4N). The mathematical model generalized multiplicative analysis of variance (GEMANOVA) was used to perform multi-way modelling of the pKa and logβ values determined by potentiometry. GEMANOVA generates parsimonious models of high-order interactions. For this reason, GEMANOVA models were used to explain and quantify the effects of the interactions between the positions and the kinds of the tripeptides residues on the magnitude of the pKa and logβ values.Principal components analysis (PCA) and multivariate curve resolution–alternating least square (MCR-ALS) methods were used to decompose the spectroscopic data into their pure components. PCA and MCR-ALS were used to confirm the presence or absence of the copper complex species identified in the visible spectra including the bis-complex (metal:ligand 2:1) and dimer species (2:2) that can be formed with tripeptides containing His at N-terminus and central position