Infrared and multivariate studies of a biopolymer

Welsh, Calum D.M. (2017) Infrared and multivariate studies of a biopolymer. PhD thesis, University of Nottingham.

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This Thesis utilises vibrational spectroscopy in combination with multivariate and two-dimensional analytical techniques to probe the interactions of a biopolymer in water-based systems.

Chapter 1: This Chapter gives an introduction to the Thesis and briefly outlines the experimental tech- niques used to study biopolymeric systems before covering the theory and implementation of the multivariate and two-dimensional methods used. A brief introduction to carrageenan, the biopolymer of interest, is then given.

Chapter 2: The general experimental procedures are discussed together with the development of a new low-temperature ATR system, which allows very precise control and variation of sample tem- perature. The latter is key to many of the measurements and analyses reported in this thesis. The ATR system is stable to 0.01 C over a temperature range of -30 to 80 C. Many of the tech- niques used within this thesis rely on the Matlab environment. Analysis methods that are not commercially available have been programmed as part of my work. The theoretical background is discussed and the scripts for these functions are included in the Appendix.

Chapter 3: Three commercially available carrageenans, k-, i- and l-carrageenan are studied with infrared spectroscopy. The carrageenan solutions are cooled from ca. 80 to 10 C. k- and i-carrageenan undergo a gelation transition during the cooling and this is investigated with a variety of analysis methods. The gelation transition can be monitored with FTIR allowing insight into the struc- tural rearrangement of the biopolymer as a function of temperature. The spectral transitions are probed with multivariate (PCA & MCR) and two-dimensional (2DCOS, MW2D & PCMW2D) techniques. Structural rearrangement for k- and i-carrageenan is observed, with various sulfate based modes showing the most intense changes to temperature. As cooled from 80 to 10 C, k- and i-carrageenan showed sulfate vibrational modes changing predominantly before vibrations associated with the backbone of the polyelectrolyte (C-O-C), indicating a sequential order to the molecular rearrangement occurring during the gelation transition.

Chapter 4: Investigation of a 2 % i-carrageenan in H2O is frozen and probed with infrared spectroscopy using a modified low-temperature ATR accessory. The sample is cooled past it’s freezing point and is then subjected to short term, constant temperature storage. Changes in structure of the water and carrageenan are observed as a function of time post-freezing. Analysis by multivariate, two-dimensional and band fitting routines is applied, allowing the post freezing spectral perturbations to be monitored. Several spectral changes within the fingerprint region occur at a different rate, these have been proposed as vibrations associated with the backbone and pro- truding groups of i-carrageenan showing di↵erent processes in response to being frozen. Initially post-freezing, large changes in the O-H stretch region for H2O are observed, before subsiding and and followed by changes in the structure of carrageenan. These effects suggests an interaction between i-carrageenan and ice.

Chapter 5: The use of a confocal Raman microscope, installed at Unilever’s Colworth facility has been used to investigate i-carrageenan in frozen systems. A gradient temperature stage allows formation of ice-fronts and a variety of these type of systems are probed. Changes in the concentration of carrageenan are seen dependant on the movement of the ice-front. Progressing an ice front into a gelled (unfrozen) section of the sample results in a large increase in carrageenan concentration at the ice-front. This indicates that the slow growth of the ice crystal is excluding the carrageenan and causing a freeze-concentration effect at the ice-front.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: George, Mike
Howdle, S.M.
Subjects: Q Science > QD Chemistry > QD 71 Analytical chemistry
Q Science > QP Physiology > QP501 Animal biochemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 41503
Depositing User: Welsh, Calum
Date Deposited: 18 Jul 2017 04:40
Last Modified: 07 May 2020 12:15

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