Bone diagenesis: New data from infrared spectroscopy and X-ray diffraction

This paper combines non-destructive high-resolution Fourier transform infrared spectroscopic techniques (attenuated total reflectance in the mid-infrared - ATR, and diffuse reflectance in the near-infrared - NIR) with X-ray diffraction and Rietveld analysis, in the study of bone diagenesis. Sixty fossil bones from two Upper Miocene sites in Greece (Pikermi and Chalkoutsi) and one Upper Pleistocene site in Cyprus (Aghia Napa) are investigated in comparison to various mineral and biological apatites. Diagenetic trends, common to all these sites include a subtle but systematic decrease of the unit cell volume and a-axis of carbonate hydroxylapatite, as well as a parallel increase of the coherence length along the c-axis. Chemometric modelling reveals that the changes in the unit cell and the coherence length are highly correlated to (and can be predicted on the basis of) the ATR spectra. Besides using chemometrics as a convenient predictive tool, we have been able to identify that the correlation with the XRD data is primarily based on the intensity of infrared bands at 577, 865 and 1092 cm- 1, as well as on the position of the ν1 phosphate mode at ca. 960 cm- 1. These structural changes constitute the vibrational signature of diagenesis throughout our set of bone samples and can be accounted for by the stabilization of a distorted CO32- species in the B-sites of apatite, and to a lesser extent by the substitution of OH- by F-. NIR spectroscopy allowed for the identification of a well-defined H2O species, absorbing at 5318 and 7240 cm- 1. This species is labile, appears to characterize mostly biogenic apatite, and is therefore considered to be chemisorbed on the surface of the crystallites. © 2008

On the structure of palygorskite by mid- and near-infrared spectroscopy

Journal URL: http://www.minsocam.org/MSA/AmMin/AmMineral.htm

Amyloid-like fibrils from an 18-residue peptide analogue of a part of the central domain of the B-family of silkmoth chorion proteins

Chorion is the major component of silkmoth eggshell. More than 95% of its dry mass consists of the A and B families of low molecular weight structural proteins, which have remarkable mechanical and chemical properties, and protect the oocyte and the del eloping embryo from the environment. We present data from negative staining, Congo red binding, X-ray diffraction, Fourier transform-Raman, attenuated total reflectance infrared spectroscopy and modelling studies of a synthetic peptide analogue of a part of the central domain of the B family of silkmoth chorion proteins, indicating that this peptide folds and self-assembles, forming amyloid-like fibrils, These results support further our proposal, based on experimental data from a synthetic peptide analogue of the central domain of the A family of chorion proteins, that silkmoth chorion is a natural, protective amyloid [Iconomidou et a.,, FEBS Lett, 479 (2000) 141-145].: (C) 2001 Federation of European Biochemical Societies, Published by Elsevier Science B.V. All rights reserved

STRUCTURE AND DYNAMICS OF WATER-SMECTITE INTERFACES: HYDROGEN BONDING AND THE ORIGIN OF THE SHARP O-DW/O-HW INFRARED BAND FROM MOLECULAR SIMULATIONS

International audienceExperimental studies have shown that a sharp, high-frequency IR band at ~3615 cm-1 (in H2O form) and at ~2685 cm-1 (in D2O form) is a common feature for all smectites, and its position correlates with layer charge. In order to explain the molecular origin of this band in terms of total layer charge, charge localization, as well as nature of interlayer cations influencing the position and intensity of this peak, a series of classical molecular dynamics (MD) simulations was performed for several smectite models. The smectite layers were described using a modified CLAYFF force field, where the intramolecular vibrations of H2O were described more accurately by the Toukan-Rahman potential. The power spectra of molecular vibrations of hydrogens were calculated for selected sub-sets of interlayer H2O to analyze quantitatively their contribution to the observed spectral features. The statistics of hydrogen bonds in the smectite interlayers were also analyzed to support the spectral calculations.The simulation results demonstrated clearly that only the H2O molecules in close proximity to the smectite surface are responsible for the sharp vibrational band observed. Other hypotheses for the possible origins of this band were considered carefully and eventually rejected. Two orientations of H2O molecules donating one or two H bonds to the basal oxygens of the smectite surface (monodentate and bidentate orientations, respectively) were observed. In both orientations, these H bonds are quite weak, pointing to a generally hydrophobic character of the smectite surface. Both orientations contributed to the high-frequency band, but the monodentate orientation provided the predominant contribution because surface H2O molecules in this orientation were much more abundant. In good agreement with experiment, only a small difference in the peak position was observed between smectites with different charge localization. The effect of the total layer charge, i.e. the red-shift for higher-charge smectites, was also confirmed. This shift arose from the decrease in the H-bonding distances of H2O in monodentate and bidentate orientation

Polarized resonance Raman and FTIR reflectance spectroscopic investigation of the molecular orientation in industrial poly(vinyl chloride) specimens

Journal URL: http://pubs.acs.org/macromolecules