Titanium Dioxide/Electrolyte Solution Interface: Electron Transfer Phenomena

Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.     

Stability diagram of rice starch as determined with FTIR

Abstract

In this study, we followed in situ changes in the infrared spectrum at different conditions of pressure and temperature. Cooperative changes were observed when temperature or pressure was increased. Plotting the midpoints of cooperative transitions in a pressure-temperature plane results in an outline similar to the stability curve of proteins. We can assume that it is the first time that the pressure-temperature dependent gelation diagram is determined in situ for starch.     

Pressure stability of insulin: A fourier transform infrared spectroscopy study

High hydrostatic pressure can induce partially unfolded protein conformations that are highly aggregation prone under conditions that normally favour the native state. We investigated the pressure stability of insulin at pH 2 with Fourier transform infrared spectroscopy. We do not observe any cooperative change up to 13 kbar. All spectral changes in the amide I area are fully reversible and are assumed to arise from the elastic effect of pressure, which causes no conformational changes. Moreover, insulin has no higher temperature-induced aggregation tendency when pressure pre-treated.     

Microscopic description of elementary growth processes and classification of structural defects in pentacene thin films

Elementary growth processes such as kink initiation, adding a molecule to a kink, and adding a molecule between two neighboring kinks and between two grains are theoretically studied in pentacene films by adding one molecule at a time to a predefined aggregate. For each molecule, the potential energy surface is calculated using the MM3 molecular mechanics force field, which allowed one to identify useful parameters like the energy barrier for diffusion and the energy to create kinks, as well as defect configurations. Depending on the properties of the potential energy surface and the resulting growth-condition-dependent probabilities of initiating defect configurations in the film, three types of pentacene defects are identified: a thermally activated defect, an intrinsic defect, and a kinetic defect. Upon film growth, most defects relax into the ideal crystal configuration. Bulk defects that resist relaxation have densities lower than 10(16) defects/cm3 at typical growth conditions. Grain boundary defects, on the other hand, are very stable. Moreover, interstitial molecules at grain boundaries are identified as a source of compressive stress.     

Unfolding and Fibrillogenesis of Insulin: Temperature,Pressure and Chemistry

Protein folding or unfolding can lead to the population of intermediates or partially unfolded conformations that have a high aggregation tendency. Some of these states associate in vivo to form fibrillar structures. These fibrils are the hallmark of molecular diseases such as Alzheimer's disease. It has been suggested that in vitro fibril formation is a generic property of all proteins. Insulin has been chosen as a model protein to study the process of fibrillation with Fourier-transform infrared spectroscopy. It is found that the formation of fibrils is preceded by amorphous aggregation. We also investigated the effect of hydrostatic pressure on insulin fibrils. The observed spectral changes are interpreted in terms of fibril dissociation into protofilaments. Preliminary results indicate that pressure is an interesting tool to characterize the interactions that maintain the fibril structure.