Molecular mobility of trehalose in relation to its bioprotective action.

De Giacomo, Ornela Zulma

De Giacomo, Ornela Zulma

2008-04-10

http://hdl.handle.net/10077/2613

Doctoral Thesis

Contributor(s)

Di Fonzo, Silvia

Abstract

Beyond the myth and despite some mistakenly reported exceptional properties literature is plenty of, the special role of trehalose and its structural organisation at mesoscale in bioprotection seems to be a fact. This justifies the great effort in the scientific community trying to understand the molecular mechanism(s) underlying bioprotection. The comprehension of the bioprotective phenomenon is expected to have a strong impact in several fields ranging from food industry to biomedical and nanopharmaceutical applications. In front of the many different hypotheses stated in the past, the advantages of trehalose nowadays appear to come from a combination of factors and not from a single exceptional property. In this thesis work we present some new important features apparently ignored. The first set of experiments deal with the structural organisation of glassy/amorphous trehalose in the absence of water. While different crystalline polymorphs have already been recognised and characterised, in this work for the first time evidence of the existence of two different glasses is provided. Characterization of the glasses has been carried out by studying the process of physical aging with the result that different molecular mobility and different activation energies are deduced for the two glasses. In addition to discuss the role these findings may have in bioprotection, the other heuristic result is that the existence of two amorphous forms of trehalose may explain one literature ambiguous crystallisation behaviour of the amorphous phase (previously considered random). In the second set of experiments, Brillouin light scattering (BLS) experiments on a wide range of concentrations of water-trehalose solutions at different temperatures were performed to explore the density fluctuations (nanoscale inhomogeneities) in the solution. A traditional acoustic analysis was carried out and the parameters describing propagating and dissipative properties were examined in the framework of two different formalisms for characterising the structural relaxation process present in this frequency range. It was found that an increase in trehalose concentration slows down the dynamics, affecting the characteristic time tau. Moreover, the activation energy of the process has a only slight dependence on temperature for diluted and semi diluted systems, that could be attributed to local hydrogen bonding.