Chemical and Biolgical Engineering

The surface segregation of a fluorochemical additive from a polyolefin host matrix has been investigated by X-ray photoelectron spectroscopy, optical microscopy, tapping mode atomic force microscopy, imaging time-of-flight secondary ion mass spectrometry, and contact angle analysis. The level of surface enrichment has been found to be governed by the temperature and duration of annealing.

The effect of added salt on the propulsion of Janus platinum-polystyrene colloids in hydrogen peroxide solution is studied experimentally. It is found that micromolar quantities of potassium and silver nitrate salts reduce the swimming velocity by similar amounts, while leading to significantly different effects on the overall rate of catalytic breakdown of hydrogen peroxide. It is argued that the seemingly paradoxical experimental observations could be theoretically explained by using a generalised reaction scheme that involves charged intermediates and has the topology of two nested loops.

This paper aims to use Atomic Force Microscopy (AFM) to characterise the interaction forces between micronised salbutamol particles, an active ingredient frequently used in metered dose inhalers, and also to glass, lactose and a fluoropolymer. The methodology used involves challenging a salbutamol functionalised AFM tip to the surfaces of interest and measuring the force experienced by the cantilever as a function of tip-sample separation. Analysis of this force-distance data allows quantification of the particle-substrate adhesion. This study yields a ranking of adhesion as glass \lactose \salbutamol\polytetrafluoroethylene (PTFE). An increase in the interaction force between the salbutamol particle and PTFE on repeated contact due to tribocharging is also observed.

The introduction of a bio-refinery approach in producing bio-chemicals represents a potential opportunity to cover the increased demand for fine chemicals and reduce the societal dependence on fossil sources for petrochemicals. Valorisation of lignocellulosic material for the production of renewable chemicals has attracted much attention as such chemicals could significantly improve the economics of bio-refineries. The present work has investigated the conversion of brewer's spent grain (BSG), a raw material in the form of food industry wastes into value-added chemical and biofuels. BSG represent around 85% of the total by- products generated from the brewing industry and is available in large quantities throughout the year; however its primary application has been limited to animal feed. Despite this, due to its chemical composition, it has value as lignocellulosic rich material. In this thesis, raw BSG has undergone physical and chemical characterisation to determine the compo...

Isothermal titration calorimetry (ITC) was used to detect phytate binding to the protein lysozyme. This binding interaction was driven by electrostatic interaction between the positively charged protein and negatively charged phytate. When two phytate molecules bind to the protein, the charge on the protein is neutralised and no further binding occurs. The stoichiometry of binding provided evidence of phytate-lysozyme complex formation that was temperature dependent, being most extensive at lower temperatures. The initial stage of phytate binding to lysozyme was less exothermic than later injections and had a stoichiometry of 0.5 at 313 K, which was interpreted as phytate crosslinking two lysozyme molecules with corresponding water displacement. ITC could make a valuable in vitro assay to understanding binding interactions and complex formation that normally occur in the stomach of monogastric animals and the relevance of drinking water temperature on the extent of phytate-protein interaction. Interpretation of ITC data in terms of cooperativity is also discussed.

The positively charged amino acids are commonly used excipients in biopharmaceutical formulations for stabilization of therapeutic proteins, yet the mechanisms for their modulation of protein stability are poorly understood. In this study, both lysine and histidine are shown to affect the thermal stability of myoglobin, bovine serum albumin, and lysozyme through a combination of mechanisms governed by their respective functional side chains and glycine, similar to arginine. This study provides evidence that at low concentrations, lysine and histidine interact with proteins by a combination of (1) direct electrostatic interactions with negatively charged side chains, (2) possible binding to high-affinity hydrophobic binding sites, and (3) glycine-mediated weak interactions with peptide backbone and polar side chains. At high concentrations, lysine and histidine act via (4) glycine-mediated competition for water between the unfolding protein and the excipient and (5) sidechain-mediate...

In a single Isothermal Titration Calorimetry (ITC) experiment, the Gibbs free energy (∆G), the enthalpy (∆H), entropy (∆S), specific heat capacity (ΔCp) and stoichiometry of binding (n) can be identified. Non-sigmoidal binding isotherms are particularly difficult to interpret, yet these are routinely found in ITC studies. ITC binding studies at 25 °C between tannins and bovine serum albumin (BSA) produced biphasic binding isotherms that were suggested to be indicators of positive cooperative binding. However, reducing the temperature to 10 °C produced monophasic binding isotherms, which raised questions regarding the validity of these binding isotherms being classified as positively cooperative binding. The biphasic binding isotherm had two separate temperature dependences, with the initial stage producing a positive ΔCp and the second stage a negative one. Subsequently, this binding isotherm was suggested to essentially be a composite of two crosslinking events. This idea of two di...