Salim Abdali

New Insight into Erythrocyte through In Vivo Surface-Enhanced Raman Spectroscopy

The article presents a noninvasive approach to the study of erythrocyte properties by means of a comparative analysis of signals obtained by surface-enhanced Raman spectroscopy (SERS) and resonance Raman spectroscopy (RS). We report step-by-step the procedure for preparing experimental samples containing erythrocytes in their normal physiological environment in a mixture of colloid solution with silver nanoparticles and the procedure for the optimization of SERS conditions to achieve high signal enhancement without affecting the properties of living erythrocytes. By means of three independent techniques, we demonstrate that under the proposed conditions a colloid solution of silver nanoparticles does not affect the properties of erythrocytes. For the first time to our knowledge, we describe how to use the SERS-RS approach to study two populations of hemoglobin molecules inside an intact living erythrocyte: submembrane and cytosolic hemoglobin (Hb(sm) and Hb(c)). We show that the conformation of Hb(sm) differs from the conformation of Hb(c). This finding has an important application, as the comparative study of Hb(sm) and Hb(c) could be successfully used in biomedical research and diagnostic tests.

Pressure effect on crystallization of metallic glass Fe72P11C6Al5B4Ga2 alloy with wide supercooled liquid region

The effect of pressure on the crystallization behavior of metallic glass Fe72P11C6Al5B4Ga2 alloy with a wide supercooled liquid region has been investigated by in situ high-pressure and high-temperature x-ray diffraction measurements using synchrotron radiation. In the pressure range from 0 to 2.4 GPa, the crystallization temperature, Tx, increases with pressure, p, having a slope of 30 K/GPa while a minimum in Tx was detected in the range from 2.4 to 3.9 GPa. With a further increase of p, Tx is independent of p. The Tx vs p behavior can be qualitatively explained by the suppression of atomic mobility and changes of the Gibbs free energy of various phases with pressure.

Angular and energy dependence of ion bombardment of Mo/Si multilayers

The process of ion bombardment is investigated for the fabrication of Mo/Si multilayer x-ray mirrors using e-beam evaporation. The ion treatment is applied immediately after deposition of each of the Si layers to smoothen the layers by removing an additional thickness of the Si layer. In this study the parameters of Kr+ ion bombardment have been optimized within the energy range 300 eV–2 keV and an angular range between 20° and 50°. The optical performance of the Mo/Si multilayers is determined by absolute measurements of the near-normal-incidence reflectivity at 14.4 nm wavelength. The multilayer structures are analyzed further with small-angle reflectivity measurements using both specular reflectivity and diffuse x-ray scattering. The optimal smoothening parameters are obtained by determining the effect of ion bombardment on the interface roughness of the Si layer. The optimal conditions are found to be 2 keV at 50° angle of incidence with respect to the surface. These settings result in 47% reflectivit...

Substrates and mounting techniques for the High-Energy Focusing Telescope (HEFT)

The high energy focusing telescope (HEFT) is a balloon-borne system for obtaining arcminute imagery in the 20 - 100 keV energy band. The hard x-ray optics are baselined to use thin epoxy-replicated aluminum foil substrates coated with graded-d multilayers, and we show some results on x-ray performance of prototype foil substrates. We also propose an extremely promising alternative substrate -- thermally formed glass. The advantages of thermally formed glass substrates, their fabrication and preliminary metrology on sample pieces are discussed. If ultimately feasible, the thermally formed glass is a better substrate due to its superior hard x-ray reflectivity and scattering properties in comparison to similarly coated epoxy-replicated aluminum foil. We also discuss some preliminary work on the HEFT mirror mounting concept and the associated angular resolution error budget.

Ab Initio Calculations and Raman and SERS Spectral Analyses of Amphetamine Species

Abstract For the first time, the differences between the spectra of amphetamine and amphetamine-H+ and between different conformers are thoroughly studied by ab initio model calculations, and Raman and surface-enhanced Raman spectroscopy (SERS) spectra are measured for different species of amphetamine. The spectra of amphetamine and amphetamine-H+ samples were obtained and assigned according to a comparison of the experimental spectra and the ab initio MO calculations, performed using the Gaussian 03W program (Gaussian, Inc., Pittsburgh, PA). The analyses were based on complete geometry minimization of the conformational energy of the S-plus-amphetamine molecule and the S-plus-amphetamine-H+ ion. The harmonic frequency calculations provide information about the characteristic features of the Raman spectra and the nature of the bonding in the molecule. It is concluded that vibrational bands from salt anions with internal bonds (sulfates, hydrogen phosphates, etc.) need to be taken into account when employing these spectra for identification purposes. These results also show how Raman spectroscopy can assist the forensic community in drug profiling studies. Furthermore, because their spectra are different, discrimination between the free and protonated forms of amphetamine salts can be observed. Here, we provide evidence for this difference and show experimentally how it has been overseen.

X-ray calibration of the SODART flight telescopes

The on- and off-axis imaging properties and effective area of the two SODART flight telescopes have been measured using the expanded beam x-ray facility at the Daresbury synchrotron. From on-axis measurements the encircled power distribution and the point spread function at three energies 6.627 keV, 8.837 keV and 11.046 keV have been measured using a one-dimensional position sensitive detector. We found that the point spread function can be presented well by a function which is a sum of a Gaussian divided by the radius and two exponential terms where the first has a 1/e value close to 2 arcmin and the other a 1/e value of ca. 15 arcmin. The data have been used to calculate the half power diameter (HPD) for three different SODART focal plane detectors, the high energy proportional counter (HEPC) with a field of view (FOV) of 65 arcmin, the low energy proportional counter (LEPC) with a FOV of 33 arcmin and the 19 element solid state detector array (SIXA) with a FOV of 18 arcmin. We found that the HPD decreases with increasing energy due to poorer figure of the outermost mirrors. The HPD falls in the range from 2.4 to 3.8 arcmin depending on energy and FOV. Data have also been obtained on the on- and off-axis effective area at all three energies and compared to that obtained from a raytracing of an ideal telescope configuration. We found that the measured on-axis effective area integrated over a FOV of 105 arcmin is ca. 65% of the area predicted from an ideal geometry. Finally the one- dimensional detector data has been used to obtain the radial dependence of the on-axis HPD and the on-axis effective area and the data from the two-dimensional position sensitive detector has been used to obtain the azimuthal dependence of the on-axis HPD and the on-axis effective area.

Conformational determination of [Leu]enkephalin based on theoretical and experimental VA and VCD spectral analyses

Conformational determination of [Leu]enkephalin in DMSO-d6 is carried out using VA and VCD spectral analyses. Conformational energies, vibrational frequencies and VA and VCD intensities are calculated using DFT at B3LYP/6-31G* level of theory. Comparison between the measured spectra and the spectral simulations of the low energy conformations of the neutral species enable conformational determination of the molecule. In an earlier study, based only on VA spectroscopy, the results led to the conclusion that [Leu]enkephalin had only a single β-bend conformation of the neutral species in DMSO-d6. The present work shows the importance of using VCD in addition to VA in determining the conformation of chiral molecules and which one of the examined three single β-bend structures is the most stable in DMSO-d6.

Novel chiroptical analysis of hemoglobin by surface enhanced resonance Raman optical activity spectroscopy

The metalloprotein hemoglobin (Hb) was studied using surface enhanced resonance Raman spectroscopy (SERRS) and surface enhanced resonance Raman optical activity (SERROA). The SERROA results are analyzed and compared with the SERRS, and the later to the resonance Raman (RRS) performed on Hb. The SERRS measurements careful optimization, with respect to the concentration and volume ratio of the analyte to colloids, enables for the first time SERROA of this molecule. We observed that the most intense SERROA signals were attributed the nu(4), nu(20), and nu(21) vibrations, which are sensitive to the redox state of the hemes iron ion, and to the presence of its sixth site, bound to exogenous ligand; O(2), NO or CO. However, in this study, the SERROA signals corresponding to these vibrations appear more sensitive to the Hb oxygen-binding properties than they appear in the SERRS or RRS. Moreover, the SERROA signal of Hb has successfully been monitored as a function of time, and was observed to be stable for 4-5 min. To our knowledge, the SERROA results of Hb, and its comparison to SERRS and RRS, are here reported for the first time.

Surface enhanced Raman optical activity as an ultra sensitive tool for ligand binding analysis

The Surface Enhanced Resonance Raman Scattering (SERRS) and Surface Enhanced Resonance Raman Optical Activity (SERROA) spectra of myoglobin and the myoglobin-azide complex were measured on very dilute samples (100 nM protein) in order to analyze the sensitivity of SERROA spectroscopy when inducing small structural changes. While the SERRS spectra of the two compounds were virtually identical, comparison of the SERROA spectra revealed several differences, includ- ing frequency shifts and changes in signal intensity, consistent with structural change in the porphyrin prosthetic group of the protein upon azide complexation. Application of this method allows for rapid analysis of ligand binding in metalloproteins in dilute aqueous solution and could in the future, when combined with theoretical studies, increase the obtainable structural resolution of proteins beyond that of X-ray analysis.

Energy levels and quantum states of [Leu]enkephalin conformations based on theoretical and experimental investigations

This paper describes a theoretical and experimental study of [Leu]enkephalin conformations with respect to the quantum states of the atomic structure of the peptide. Results from vibrational absorption measurements and quantum calculations are used to outline a quantum picture and to assign vibrational modes to the different conformations. The energy landscape of the conformations is reported as a function of a Hamming distance in Ramachandran space. Molecular dynamics simulations reveal a pronounced stability of the so-called single-bend low-energy conformation, which supports the derived quantum picture of this peptide.