0 Quai Ernest Ansermet

Genève, Switzerland

0 Quai Ernest Ansermet

Genève, Switzerland
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Bouhekka A.,0 Quai Ernest Ansermet | Bouhekka A.,Oran University of Science and Technology - Mohamed Boudiaf | Bouhekka A.,University of Hassiba Ben Bouali Chlef | Burgi T.,0 Quai Ernest Ansermet
Acta Chimica Slovenica | Year: 2012

A Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy study of the photodegradation of adsorbed bovine Serum Albumin (BSA) on porous TiO2 films was carried out. The experiments were performed in a flowthrough cell in water at concentrations of 10-6 mol/L at room temperature. The curve fitting method of the second derivative spectra allowed us to explore details of the secondary structure of pure BSA in water and conformation changes during adsorption and illumination processes. The results clearly demonstrate that the amount of adsorbed BSA decreased under UV illumination although adsorption without illumination is considered as irreversible. The influence of irradiation on the adsorption is not yet well understood. Also, during illumination of adsorbed BSA dissolved CO2 at 2341 cm-1 was observed, which indicates that part of the BSA is mineralized. The analysis of second derivative of infrared spectra was used to obtain direct quantitative information on the secondary structure components of BSA which show that the percentage of α-helix decreases from around 63% to 54% during UV light illumination whereas the percentage of β-turn increases.


Bouhekka A.,0 Quai Ernest Ansermet | Bouhekka A.,Oran University of Science and Technology - Mohamed Boudiaf | Bouhekka A.,University of Hassiba Ben Bouali Chlef | Burgi T.,0 Quai Ernest Ansermet
Applied Surface Science | Year: 2012

In this work in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy in a flow-through cell was used to study the effect of visible light irradiation on bovine serum albumin (BSA) adsorbed on porous TiO 2 films. The experiments were performed in water at concentrations of 10 -6 mol/l at room temperature. The curve fitting method of the second derivative spectra allowed us to explore details of the secondary structure of pure BSA in water and conformation changes upon adsorption as well as during and after illumination by visible light. The results clearly show that visible light influences the conformation of adsorbed BSA. The appearance of a shift of the amide I band, in the original spectra, from 1653 cm -1 to 1648 cm -1, is interpreted by the creation of random coil in the secondary structure of adsorbed BSA. The second derivative analysis of infrared spectra permits direct quantitative analysis of the secondary structural components of BSA, which show that the percentage of α-helix decreases during visible light illumination whereas the percentage of random coil increases. © 2012 Elsevier B.V. All rights reserved.


Knoppe S.,0 Quai Ernest Ansermet | Knoppe S.,Catholic University of Leuven | Burgi T.,0 Quai Ernest Ansermet
Physical Chemistry Chemical Physics | Year: 2013

The ligand exchange reaction between monodisperse Au25(2-PET) 18 (2-PET: 2-phenylethylthiolate) clusters and 1,1′-binaphthyl- 2,2′-dithiol (BINAS) was long thought to induce decomposition of the cluster (Si et al., J. Phys. Chem. C, 2009). We repeated the experiment and analyzed the reaction products using MALDI-TOF mass spectrometry. The spectra clearly indicate successful ligand exchange, bidentate binding of the BINAS ligand and intact Au25 clusters. The reaction products are identified as Au25(2-PET)18-2x(BINAS)x (x = 1-4) for a 24 h reaction with a 50-fold molar excess of BINAS. Two likely binding motifs are discussed. Analysis of atomic distances in both the cluster and the free ligand indicates interstaple binding connecting the central sulfur atom of the protecting (SRAu)2SR with the outer sulfur atom of a second unit. The results presented have implications on the binding position of BINAS in Au 38(SR)24-2x(BINAS)x clusters. © 2013 the Owner Societies.


PubMed | 0 quai Ernest Ansermet
Type: Journal Article | Journal: The EMBO journal | Year: 2010

D1 and D2, two chloroplast proteins with apparent mol. wt of 32 000-34 000, play an important role in the photosynthetic reactions mediated by the membrane-bound protein complex of photosystem II (PSII). We have isolated and characterized an uniparental, non-photosynthetic mutant of Chlamydomonas reinhardtii and show that the mutation is in the chloroplast gene psbD, coding for D2. A 46 bp direct DNA duplication in the coding region of the mutant gene causes a frame-shift which results in a psbD transcript coding for 186 amino acid residues instead of the normal 352. The truncated D2 peptide is never seen, even after pulse-labeling, suggesting that the mutant protein is very unstable. In addition, little or no D1 protein is detected in this mutant although the gene and normal levels of mRNA for D1 are present in mutant cells. All other core PSII proteins are synthesized and inserted into the membrane fraction, but never accumulate. These results suggest that D2 contributes not only to the stabilization of the PSII complex in the membrane, but also may play a specific role in the regulation of the D1 protein, either at the translational or post-translational level.

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