Impact of solvent quality on the network strength and structure of alginate gels

AbstractThe influence of the mixture of water and alcohols on the solubility and properties of alginate and its calcium-induced gels is of interest for the food, wound care and pharmaceutical industries. The solvent quality of water with increasing amounts of ethanol (0–20%) on alginate was studied using intrinsic viscosity. The effect of ethanol addition on the rheological and mechanical properties of calcium alginate gels was determined. Small-angle X-ray scattering and transmission electron microscopy were used to study the network structure. It is shown that the addition of ethanol up to 15% (wt) increases the extension of the alginate chain, which correlates with increased moduli and stress being required to fracture the gels. The extension of the polymer chain is reduced at 20% (wt) ethanol, which is followed by reduced moduli and stress at breakage of the gels. The network structure of gels at high ethanol concentrations (24%) is characterized by thick and poorly connected network strands

Peptides in BioNMR Research

Heteronuclear NMR in combination with isotope labelling is used to study folding of polypeptides induced by metals in the case of metallothioneins, binding of the peptidic allosteric modulator ?-TIA to the human G-protein coupled ?1b adrenergic receptor, the development of therapeutic drugs that interfere with the biosynthesis of the outer membrane of Gram-negative bacteria, and a system in which protein assembly is induced upon peptide addition. NMR in these cases is used to derive precise structural data and to study the dynamics

Hierarchical structure function models of biopolymer networks : thesis submitted to the Institute of Fundamental Sciences, Massey University, New Zealand, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physics, Palmerston North, October 2011

This project aimed to bridge the structure-function divide in polysaccharide networks so that the rheological properties of multi-chain assemblies might be predicted from the ne structures of the constituent polymers and their mode of assembly. The polysaccharide pectin is an important constituent of the plant cell wall and when cured into a gel the mechanical properties of its networks have recently come into the focus of research via extensive microrheological studies, in which interesting connections between the gel's mechanical response, gelation conditions and the pectin ne structure were discovered. This tunability makes it therefore a promising model system for further experiments and computer-aided investigations, and accordingly it is the focus of this thesis. Firstly, a small angle X-ray scattering study of di erent microrheologically wellcharacterized ionotropic pectin gels was undertaken to gain insights into the structures of the assembled elementary network strands. The SAXS results paired with molecular modelling con rm that gels which are semi exible from a microrheological point-of-view contain large bundles of aggregated dimers compared to the more exible networks, where predominantly single chain sections and dimers are found to contribute. These later gels can be formed among other ways using a biomimetic methodology exploiting plant enzymes. Secondly, after learning that networks could be experimentally manifest where single chains form the majority of links between nodes, in contrast to the better known hierarchical structures of polysaccharide gels, a computational approach was pursued to investigate the behaviour of biopolymer networks comprised of single polysaccharide chains using the experimentally measured force extension relation for pectin. This exhibits interesting force-induced conformational transitions that have been investigated in their own right. A 2-dimensional model was initially chosen for practical purposes. The study supports the hypothesis that conformational transitions could have biological signi cance as stress-switches in signalling processes, but that they are unlikely to a ect the bulk rheological properties of tissue. Finally, the model was further expanded into 3-dimensions to test quantitatively its predictions of the shear moduli of such systems. To this end a comparison with rheological prestress experiments on enzymatically induced pectin gels was undertaken. The model was found to successfully describe the observed nonlinear rheology for completely percolated, strong gels, based only on the polymer concentration and an experimentally accessible single chain force-extension relationship; for the rst time providing a true bottom-up example to the properties of soft materials

Der Polarisationszustand der Fluoreszenz von uranhaltigen Borosilicatgläsern

Es werden Reintransmissionsgrad, relative spektrale Energieverteilung der Fluoreszenz und Fluoreszenzvermögen uranhaltiger Borosilicatgläser bestimmt. Bei Anregung durch polarisierte Strahlung zeigt das Fluoreszenzlicht einen frequenzabhängigen Polarisationsgrad, der von der Lage der Beobachtungsrichtung bezüglich der Polarisationsrichtung der anregenden Strahlung bestimmt wird. Auf Grund der polarisationsoptischen Analyse läßt sich die beobachtete Fluoreszenz als reine Dipolstrahlung linearer Oszillatoren deuten. Aus der Konzentrationsdepolarisation ist zu folgern, daß eine strahlungslose Weitergabe der Anregungsenergie über Molekülabstände von mindestens 10^-6 cm erfolg

Biodegradable nanofilms on microcapsules for controlled release of drugs to infected chronic wounds

Systemic antibiotic and topical antimicrobial overexposure strongly contributes to the development of bacterial resistance. We have assembled nanofilms as a lid for drugs, which respond to the Staphylococcus aureus protease V8, while remaining intact when exposed to a human wound protease. Hollow microcapsules, loaded with a model drug and with the nanofilm as shell were assembled by template assisted assembly. With a poly-L-glutamic acid-based film, the Glu-X specific V8 caused the film to degrade, leading to release of the model drug, while the human wound protease did not affect the microcapsules. This is an example of triggered release of an active with the wound infection being the trigger

Using fluorescent probes and FRAP to investigate macromolecule diffusion in steam-exploded wood

Diffusion of fluorescently labeled dextran of varying molecular weight in wood pretreated by steam explosion was studied with a confocal microscope. The steam explosion experiments were conducted at relatively mild conditions relevant for materials biorefinery at a pressure of 14 bars for 10 min. The method of fluorescence recovery after photobleaching (FRAP) was used to perform diffusion measurements locally in the wood microstructure. It was found that the FRAP methodology can be used to observe differences in the diffusion coefficient based on localization in the microstructure, i.e., earlywood, latewood, and cell wall. Microscopic changes due to steam explosion were seen to increase diffusion of the smaller 3-kDa dextran diffusion probe in the earlywood, while the latewood structure was not affected in any significant way. Macroscopic changes to the structure in the form of ruptures due to the steam explosion pretreatment were observed to increase the rate of diffusion for the larger 40-kDa dextran probe

Rheology of natural and imitation mozzarella cheese at conditions relevant to pizza baking

The rheology of mozzarella and imitation cheese was studied at 60 °C, with small amplitude oscillatory shear (SAOS), shear and extensional flow measurement at low strain rates in the range 0.01-1 s-1. These conditions were chosen to replicate those experienced by the cheese during pizza baking and consumption. The extensional viscosity measurements were carried out by means of hyperbolic contraction flow, an alternative method to traditional extensional measurements. The extensional viscosity measured by hyperbolic contraction flow was related to the cheese elasticity and consequently to its stretchability, a major quality characteristic when this is consumed on pizza pies. The rheology of the two cheese materials could be explained by the structural observations made by confocal laser scanning microscopy (CLSM)

Foaming behavior of water-soluble cellulose derivatives: hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose

Hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose could be interesting candidates for production of lightweight, foamed packaging material originating from non-fossil, renewable resources. The foaming ability of nine different grades of the two cellulose derivatives, using water as the blowing agent, was investigated using a hot-mold process. The foaming process was studied by evaluating the water loss during the heating, both in a real-time experiment and by thermal gravimetric analysis. Further, the development of the rheological properties of the derivative-water mixtures during a simulated foaming process was assessed using dynamical mechanical thermal analysis and viscosity measurements. Five of the studied derivatives showed promising properties for hot-mold foaming and the final foams were characterized with regard to their apparent density. It was concluded that the foamability of these systems seems to require a rather careful tailoring of the viscoelastic properties in relation to the water content in order to ensure that a network structure is built up and expanded during the water evaporation

Le Grand écho du Nord de la France

04 mars 19021902/03/04 (A84,N63).Appartient à l’ensemble documentaire : NordPdeC