Search

Abstract: Copper is known to exert diverse effects on the self-association of proteins and has been found in amyloid deposits that are involved in neurodegenerative disease processes. The effects of the metal ion on the protein during fibrillation were investigated by fluorescence, circular dichroism spectroscopy and fluorescence microscopy. We report for the first time, the complete reduction of Cu(II)→Cu(I) in vitro during fibrillation of hen egg white lysozyme at pH 7. This was confirmed by the lack of any signal for Cu(II) in electron paramagnetic resonance spectroscopy and quantification of Cu(I) was achieved by a bathocuproine disulfonate based assay. [Copyright &y& Elsevier]

The interaction of l-tryptophan (Trp) with silver colloids was investigated at between pH values of 6.11 and 10.6 of the sol. The measurements of surface-enhanced Raman bands of Trp in the colloidal solution indicate the evolution of interaction between the metal particles and the molecules with increasing pH values for the sol. The experimental observations were explained using the estimated atomic charge distribution in the zwitterionic and anionic forms of the residue, obtained by density functional theory calculations. The variation in the ratio of the spectral intensities of the Fermi resonance bands with the pH reflects the effect of the colloidal environment on Trp. The results obtained can be used as a marker for describing the nature of the interaction of silver colloids with the specific terminus of the residue, at varying pH environments. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this article, we discuss metal–protein interactions in the Ag–lysozyme complex by spectroscopic measurements. The analysis of the variation in relative intensities of SERS bands reveals the orientation and the change in conformation of the protein molecules on the Ag surface with time. The interaction kinetics of metal–protein complexes has been analyzed over a period of 3h via Raman measurements. Our analysis indicates that the Ag nanoparticles most likely interact with Trp123 which is in close proximity to Phe34 of the lysozyme molecule. [ABSTRACT FROM AUTHOR]

Abstract: Surface enhanced Raman spectra of Phenylalanine (Phe) in Ag colloidal solution have been recorded for Phe solutions at different pH. Spectral line-shape analyses of three enhanced modes have been carried out between pH 4.5 and 10.5. The variation of line-width with pH reveals two mechanisms in solution: (i) the fluctuation of pH in microscopic volume and (ii) the motional narrowing caused by the intermolecular ionic interaction. The different charge states of the reference molecule are responsible for the observed bond softening with decrease in pH. The ‘Raman shift’ and the ‘Raman activity’ of the vibrational modes with maximum enhancement have been explained by carrying out DFT calculations. [Copyright &y& Elsevier]

The phase stability of zirconia (ZrO 2) under external perturbation draws the attention of researchers, as it governs the practical use of this material in technological applications. In this article, the phase transition in zinc oxide (ZnO) doped ZrO 2 is addressed by exploiting complementary methodologies, X-ray diffraction, and Raman spectroscopic measurements. We have observed a pressure-induced partial phase transformation in the doped ZrO 2 system for a compacting pressure of less than 1 GPa. It is noteworthy that the level of compacting pressure used in this study is much lower than the range of pressure, reported in the literature, for observing phase transition in pure and doped ZrO 2 using other high-pressure experiments. To understand the underlying dynamics of low pressure-induced phase transformation, we carried out density functional theory calculations for the doped supercell. We have discussed the local bonding environment around the dopant metal ion (Zn2+ in the present case), which, we believe, leads to the phase evolution in a real system. [ABSTRACT FROM AUTHOR]

Sapphire-supported hBN films of different thicknesses are grown using metalorganic vapour phase epitaxy technique by following a flow modulation scheme. Though these wafer-scale films are potential candidates for real device applications, they exhibit wrinkling. The wrinkles are a key signature of strain distribution in the films. We utilized Raman imaging to study the residual strain distribution in the wrinkled hBN films. An increase in the overall compressive strain in the films with an increase in the layer thickness is observed and explained. An empirical relation is proposed for estimating the wrinkle mediated strain relaxation from the morphology of the films. Furthermore, we show that the residual strain can be partially released by the delamination of the films. [ABSTRACT FROM AUTHOR]

We have investigated the nonthermal effect of 10 GHz/22 dBm microwave radiation on hen egg-white lysozyme (HEWL) over different irradiation times, ranging from 2 min to 1 h. To ensure a control over the radiation parameters, a pair of microwave rectangular waveguides is used to irradiate the samples. Optical spectroscopic measurements, which include UV-visible absorption spectroscopy, Raman spectroscopy, and far UV CD spectroscopy, reveal the exposure of the buried tryptophan (Trp) residues of the native molecule between 15 and 30 min of radiation. The higher duration of the perturbation leads to a compact structure of the protein and Trp residues are buried again. Interestingly, we do not find any change in the secondary structure of the protein even for 1 h duration of radiation. The relaxation dynamics of the irradiated molecules also has been discussed. We have shown that the molecules relax to their native configuration in 7-8 h after the radiation field is turned off. The structural rearrangement over the above timescale has further been probed by a model calculation, based on a modified Langevin equation. Our coarse-grained simulation approach utilizes the mean of atomic positions and net atomic charge of each amino acid of native HEWL to mimic the initial conformation of the molecule. The modified positions of the residues are then calculated for the given force fields. The simulation results reveal the nonmonotonous change in overall size of the molecule, as observed experimentally. The radiation parameters used in our experiments are very similar to those of some of the electronic devices we often come across. Thus, we believe that the results of our studies on a simple protein structure may help us in understanding the effect of radiation on complex biological systems as well. [ABSTRACT FROM AUTHOR]