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Abstract

The ligand acetohydroxamic acid (AHA) suffers hydrolysis at acidic conditions. This reaction has been studied for a long time, due to its implications in different applications, by using indirect colorimetric methods. This work shows how Raman spectroscopy can be very useful as a direct technique for measuring the hydrolysis kinetics of AHA, faster, more versatile and easier compared with the indirect traditional UV–Vis method which needs a complex formation with Fe. Thereby, we present a detailed study of the qualitative and quantitative Raman spectra of 1 mol/L AHA and its hydrolysis products. These results enabled us to perform a complete kinetic study of this molecule at different pH ranging from 0.5 mol/L to 4 mol/L HNO3, i.e. not only at excess acidic conditions but also at limiting nitric acid conditions.

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Complexation study of acetohydroxamic (AHA) ligand with La(III), Nd(III), Eu(III), Er(III), and Lu(III), as representative of lanthanide (Ln) series, has been described, in presence of pure nitrate and combination of nitrate and perchlorate ions using various spectroscopic analysis and density functional theory (DFT) calculations. Nuclear magnetic resonance (NMR) spectroscopy reports the bidentate mode of coordination of Z-Keto tautomer of AHA monomer with La(III). Formation of 1:3 Nd(III)-AHA complexes in presence of pure nitrate and a combination of nitrate and perchlorate ions has been observed from ultraviolet-visible (UV-Vis) spectroscopy analysis. The geometrical parameter analysis exhibit the bidentate mode coordination fashion of the AHA monomer which corroborates the NMR results. The geometrical parameter, frontier orbital(HOMO-LUMO), global reactivity descriptors and local reactivity descriptors analysis supports the findings of the spectroscopy titration methods that stability of Ln-AHA complexes decreases in the presence of pure nitrate ions than in presence of both perchlorate and nitrate ions. The trend of theoretical NMR chemical shifts of AHA and La(III)-AHA complexes support the experimental NMR chemical shifts. This work helps to measure subtle differences in complexation behaviour of AHA with Ln in presence of pure nitrate and a combination of nitrate and perchlorate ions quantitatively, providing information about the Ln-AHA structural environment.Graphic abstractVarious spectroscopic methods (UV-Vis, NMR, and Fluorescence spectroscopy) and density functional theory (DFT) calculations have been implemented for structural characterization of lanthanides (Ln(III))-acetohydroxamic acid(AHA) complexes in the presence of a combination of both perchlorate and nitrate ions and in pure nitrate ions. The Ln(III)-AHA complexes show more stability in the presence of a combination of both perchlorate and nitrate ions than in the presence of nitrate ions which is supported by DFT calculations.
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The infra-red spectra of the crystals of CH3COOH, CH3COOD, CD3COOH and CD3COOD at 0° and at −180°C have been investigated in the 4000—400 cm−1 region. The spectra are interpreted using the one-dimensional crystal approximation and the fundamentals are assigned and compared to those of the respective dimers and monomers. The origin of the multiple bands of the broad νOH and νOD absorptions is discussed.
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Laboratory experiments have been performed using laser Raman spectroscopy to analyze carbon dioxide (CO(2)) and methane (CH(4)) dissolved in water and seawater. Dissolved CO(2) is characterized by bands at approximately 1275 and 1382 Deltacm(-1). Dissolved CH(4) is characterized by a dominant band at approximately 2911 Deltacm(-1). The laboratory instrumentation used for this work is equivalent to the sea-going Raman instrument, DORISS (Deep Ocean Raman In Situ Spectrometer). Limits of quantification and calibration curves were determined for each species. The limits of quantification are approximately 10 mM for CO(2) and approximately 4 mM for CH(4). A ratio technique is used to obtain quantitative information from Raman spectra: the gas bands are referenced to the O-H stretching band of water. The calibration curves relating band height ratios to gas concentration are linear and valid for a range of temperatures, pressures, and salinities. Current instrumentation is capable of measuring the highest dissolved gas concentration observed in end-member hydrothermal fluids. Further development work is needed to improve sensitivity and optimize operational configurations.
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This work presents Raman spectra obtained from thin films of protein materials which are commonly used as binding media in painted works of art. Spectra were recorded over the spectral range of 3250-250 cm(-1), using an excitation wavelength of 785 nm, and several bands have been identified in the fingerprint region that correspond to the various proteins examined. Differences in the C-H vibrations located between 3200 and 2700 cm(-1) can be accounted for with reference to the amino acid composition of the protein-based binding media as well as the presence of fatty acid esters, in the case of egg yolk. In addition, the discrimination of different proteins on the basis of variations in spectra between 3200 and 2700 cm(-1) can be achieved following multivariate analysis of a large data set of spectra, providing a novel and nondestructive alternative based on Raman spectroscopy to other methods commonly used for the analysis of proteins.
  • Andrieux