Water vibrational spectroscopic studies

Vibrational, spectroscopic studies of water and carbohydrate solutions have been performed, in order to provide information on the nature and variety of hydrogen bonding between molecules (see Sections 11,3 and V,2). It is generally accepted208,209 that i.r.- and Raman-spectral results concerning... 

Although we have presented here only two examples of pressure tuning vibrational spectroscopic studies with aqueous surfactants, we hope that they are sufficient to demonstrate the uniqueness of pressure as a physical parameter in the investigation of the structural and dynamic properties of aqueous surfactants. For many systems, the vibrational spectra at atmospheric pressure are very similar. Yet, the pressure tuning of these spectra will be able to provide additional information about the structure of the surfactant molecules and about their aggregation in water. 

Baldelli, S., Influence of water on the orientation of cations at the surface of a room-tenperature ionic liquid A sum frequency generation vibrational spectroscopic study, J. Phys. Chem. B 107, 6148-6152 (2003). 

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

One of the most important problems that has been actively studied during the past few years is the hydration of biological molecules, especially carbohydrates, and the effect of hydration on the conformation of the solute molecule, as well as the effect of the latter on the water structure. Different theoretical and experimental methods have been utilized, and the discrepancies between the results, expressed as numbers of hydration, are considerable. In addition, the water molecule is a reactant in a number of biochemical reactions. The kinetics of these reactions is influenced both by the conformation of the carbohydrate and the structure of the water. These questions will be discussed, with particular reference to the contribution of the vibrational, spectroscopic information to an understanding of such complex mechanisms. 

Many of the important chemical reactions controlling arsenic partitioning between solid and liquid phases in aquifers occur at particle-water interfaces. Several spectroscopic methods exist to monitor the electronic, vibrational, and other properties of atoms or molecules localized in the interfacial region. These methods provide information on valence, local coordination, protonation, and other properties that is difficult to obtain by other means. This chapter synthesizes recent infrared, x-ray photoelectron, and x-ray absorption spectroscopic studies of arsenic speciation in natural and synthetic solid phases. The local coordination of arsenic in sulfide minerals, in arsenate and arsenite precipitates, in secondary sulfates and carbonates, adsorbed on iron, manganese, and aluminium hydrous oxides, and adsorbed on aluminosilicate clay minerals is summarized. The chapter concludes with a discussion of the implications of these studies (conducted primarily in model systems) for arsenic speciation in aquifer sediments. 

AI-water complexes with more than three waters have received less attention because it is believed that such large complexes cannot be directly involved in the tautomerization. Moreover, these complexes are difficult to be spectroscopically assigned due to the complexity of their electronic [11] and vibrational [10] structures. 7AI with four waters was studied by Fohner et al. [27] using ultrafast pump-probe spectroscopy combined with theoretical calculations. Their results revealed that the proton-transfer rate increases compared to that of 7AI with two and three waters. Their deuteration studies provided proof for the occurrence of proton transfer (PT), although it was not conclusively confirmed that the proton transfer resulted in a complete tautomerization of the 7AI monomer. For even bigger clusters of 7AI with five waters, there are no experimental investigations available only a theoretical study was reported on the second hydration shell effect [45]. 

Dimerization enthalpy and absorption intensities for monomer and dimer. Mol Phys 74 639-647 Bondarenko GB, Gorbaty YE (1997) In situ Raman spectroscopic study of sulfur-satrrrated water at 1000 bar between 200 and 500°C. Geochim Cosmochim Acta 61 1413-1420 Bopp P (1986) A study of the vibrational motions of water in an aqueous CaCl2 solutioa ChemPhys 106 205-212... 

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