Aqueous laser-Raman spectroscopy

The composition of aqueous solutions of D-arahino-2-hexulose (d-fructose) has also been studied by laser-Raman spectroscopy.45 (The composition of solutions of D-fructose appears to have been determined by more methods, and more often, than that of any other sugar.20)... 

It may be concluded, from the analysis of the Raman results, that the information provided by Raman spectroscopy is, in essence, similar to that of infrared spectroscopy. The exploitation of the data, namely, the frequencies and intensities due to the molecular vibrations, is of a certain benefit in giving some insight as to the conformations of carbohydrates, and their interactions with the environment. As laser-Raman spectroscopy is applicable to solids, as well as to aqueous solutions, the linear relationship between Raman intensities and mass concentrations, and the specificity and high quality of the spectra experimentally obtained, make this technique particularly promising in investigations of the chemistry and biochemistry of carbohydrates. 

There have been a number of recent investigations in the field of normal Raman spectroscopy with laser excitation of proteins in aqueous solutions . Raman spectroscopy uncovers information of the peptide backbone, geometry of... 

Cerrata, M.K. and Berglund, K.A. (1987) Structure of aqueous solutions of some dihydrogen orthophosphates by laser Raman spectroscopy. Journal of Crystal Growth, 84, 577-588. 

Laser-Raman spectroscopy of D-fructose in aqueous solution has given results for the proportions of furanose and pyranose similar to those from other tech-... 

Raman spectroscopy is a vibrational spectroscopic technique which can be a useful probe of protein structure, since both intensity and frequency of vibrational motions of the amino acid side chains or polypeptide backbone are sensitive to chemical changes and the microenvironment around the functional groups. Thus, it can monitor changes related to tertiary structure as well as secondary structure of proteins. An important advantage of this technique is its versatility in application to samples which may be in solution or solid, clear or turbid, in aqueous or organic solvent. Since the concentration of proteins typically found in food systems is high, the classical dispersive method based on visible laser Raman spectroscopy, as well as the newer technique known as Fourier-transform Raman spectroscopy which utilizes near-infrared excitation, are more suitable to study food proteins (Li-Chan et aL, 1994). In contrast the technique based on ultraviolet excitation, known as resonance Raman spectroscopy, is more commonly used to study dilute protein solutions. 

Laser Raman spectroscopy has been used to obtain spectra of aqueous solutions and of two crystalline forms of hen egg-white lysozyme." ... 

Somasak Naviroj is currently a Ph.D. candidate in the Department of Macromolecular Science, Case Western Reserve University, Cleveland. He is presently studying the molecular structure of composite Interfaces using FT-IR and structure of silanes in aqueous solution by laser Raman spectroscopy. 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

Owens and Iqbal [146] succeeded in an electrochemical hydrogenation of open-ended SWCNTs synthesized by CVD. Sheets of SWCNT bucky paper were used as the negative electrode in an electrochemical cell containing aqueous KOH solution as electrolyte. The authors claimed to have incorporated up to 6 wt. % of hydrogen into the tubes, determined by laser Raman IR spectroscopy and hydrogen release by thermolysis at 135 °C under TGA conditions [146], However, the stability of exohydrogenated carbon nanotubes and the low temperature of hydrogen release at 135 °C [146] is contradictory with the 400-500 °C reported elsewhere [79a, 145],... 

One of the main advantages of Raman spectroscopy over IR is that water is a weak Raman scatterer. The spectrum of water causes little interference so that spectra of solutes can be measured in aqueous solutions. A good example of the reduced interference from water is shown for two pharmaceuticals in Fig. 7-28. The Raman spectra of damp and dry samples of acetaminophen and ibuprofen are shown in the figure. Bands due to water are not observed in the spectra. Near and mid-IR of these same samples exhibited relatively strong absorbances due to water. These Raman spectra were measured on a dispersive instrument and were excited with an Ar-ion laser emitting at 488 nm. The background for the acetaminophen sample is flat, whereas ibuprofen exhibits a background characteristic of fluorescence. 

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