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PubMed1977

Raman spectroscopic studies of different forms of cholesterol and its derivatives in the crystalline state.

A Raman spectroscopic study has been carried out on a number of cholesterols and cholesterol derivatives in the crystalline state, in order to obtaine some empirical correlations between the Raman spectra and structure of each cholesterol form. Although the Raman spectra of the various cholesterols are highly complex it was found that three regions of the spectrum yield considerable information about the crystalline chain packing in each form. They are: (1) the low frequency region below 300 cm-1, giving information on the inter-and intramolecular vibrations in the cholesteryl moiety; (2) the methylene rocking/deformation region between 1400 and 1500 cm-1 giving information on chain packing in the crystalline state, and (3) the C-H stretching region between 2700 and 3100 cm-1 which appears to indicate that there is a correlation between branching in the side chains of the cholesterols, polarity of the substituent groups in the various derivatives studied and relative chain order in the packing arrangements in the crystalline state. A study of two branched chain aerosol derivatives, bis(di2-octyl) sodium sulphosuccinate and its isomer bis(di-2-ethylhexyl) sodium sulphosuccinate, indicate that branched chain amphiphiles are good Raman spectroscopic models for the cholesterols, similar to previous Raman spectroscopic studies which have found straight chain amphiphiles to be good models for more complex phospholipids.

Cholesterol↗
PubMed2006

Synthesis and characterization of the hexenuronic acid model methyl 4-deoxy-beta-L-threo-hex-4-enopyranosiduronic acid.

A facile synthetic scheme for the preparation of methyl 4-deoxy-beta-L-threo-hex-4-enopyranosiduronic acid utilizing the commercially available methyl alpha-D-galactopyranoside as starting material has been developed. The synthesis sequence comprises six high yielding reaction steps: TEMPO oxidation, acetylation, methanolysis of the lactone, acetylation, beta-elimination, and final removal of the protecting groups. Only one column chromatographic purification is needed throughout the whole sequence. The overall yield is 60%. The final product has been characterized by NMR, Raman, UVRR, FTIR, and HRMS.

Carbohydrate Conformation↗
PubMed2005

Qualitative study of ethanol content in tequilas by Raman spectroscopy and principal component analysis.

Using Raman spectroscopy, with an excitation radiation source of 514.5 nm, and principal component analysis (PCA) was elaborated a method to study qualitatively the ethanol content in tequila samples. This method is based in the OH region profile (water) of the Raman spectra. Also, this method, using the fluorescence background of the Raman spectra, can be used to distinguish silver tequila from aged tequilas. The first three PCs of the Raman spectra, that provide the 99% of the total variance of the data set, were used for the samples classification. The PCA1 and PCA2 are related with the water (or ethanol) content of the sample, whereas the PCA3 is related with the fluorescence background of the Raman spectra.

Alcoholic Beverages↗
PubMed2005

Discrimination of metamorphic diamond populations by Raman spectroscopy (Kokchetav, Kazakhstan).

Metamorphic diamond is a powerful but frequently debated indicator for ultrahigh-pressure metamorphic (UHPM) conditions. Because of their small size, their optical identification needs confirmation. Characteristics of chemically extracted microdiamonds from Kokchetav, identified by different analytical methods, are used here for unambiguous in situ identification by Raman microspectroscopy. Differences appear in the diamond spectra and the Raman analytical method is explored as a helpful tool in the discrimination between diamond populations from four different UHPM lithologies of Kokchetav. Not considering the graphite-coated diamond, out of the reach of the laser wavelength used here, the comparison of these Kokchetav Raman spectra may provide additional information in other UHPM studies.

Diamond↗
PubMed2006

Hydrogen bonding effects on infrared and Raman spectra of drug molecules.

Infrared and Raman spectra of three drug molecules, aspirin, caffeine and ibuprofen, in gas phase and in aqueous solution have been simulated using hybrid density functional theory. The long range solvent effect is modelled by the polarizable continuum model, while the short range hydrogen bonding effects are taken care of by the super-molecular approach with explicit inclusion of water molecules. The calculated spectra are found to compare well with available experimental results. The agreement obtained make grounds for proposing theoretical modeling as a tool for characterizing changes in the bonding environments of drug molecules in terms of particular variations in their IR and Raman spectra.

Aspirin↗
PubMedDate not supplied

Physicochemical properties and O2-coordination structure of human serum albumin incorporating tetrakis(o-pivalamido)phenylporphyrinatoiron(II) derivatives.

Incorporation of tetrakis(o-pivalamido)phenylporphyrinatoiron(II) derivatives with a covalently linked axial imidazole (FeP) into human serum albumin (HSA) provides a new type of artificial hemoprotein (HSA-FeP) that binds and releases dioxygen reversibly under physiological conditions (in aqueous media, pH 7.4, 37 degreesC) and in a fashion similar to hemoglobin and myoglobin. The HSA host adsorbs a maximal eight FeP molecules, and their stepwise equilibrium constants (K1-K8) range from 1.2 x 10(6) to 1.3 x 10(4) M-1. The major binding sites of the synthetic hemes are identical to those of hemin, bilirubin, and long-chain fatty acids. The red-colored solution of HSA-FeP was stored for three months at 4 degreesC and could be kept as a freeze-dried powder for more than six months. The solution properties [[HSA]: 5 wt %, FeP/HSA = 1-8 (mol/mol)] satisfy the physiological requirements for dioxygen infusion for potential clinical use; the specific gravity is 1.013, and the viscosity is 1.1 cP. Mixing the solution with human blood does not induce any coagulation and precipitation. On the basis of the gel permeation chromatography, CD spectroscopy, and IEF measurements, the molecular size, second-order structure, and surface charge distribution of the HSA-FeP conjugate are constant and independent of the binding numbers of heme molecules. Furthermore, the O2-coordination structure of FeP embedded into certain hydrophobic domains of the albumin was confirmed by resonance Raman spectroscopy.

Binding Sites↗
PubMed1995

Resonance Raman evidence that the thioester-linked 4-hydroxycinnamyl chromophore of photoactive yellow protein is deprotonated.

Resonance Raman spectra of the ground state of photoactive yellow protein (PYP), a photoactive pigment found in Ectothiorhodospira halophila, have been obtained with excitation at 413.1 nm using a microspinning sample cell. The resonance Raman spectra of the thioester-linked 4-hydroxycinnamyl chromophore in the protein are compared with the preresonance Raman spectra of the 4-hydroxycinnamyl phenyl thioester and 4-hydroxycinnamic acid model compounds at various pH values. Bands at 1568, 1542, 1500, 1434, and 1166 cm-1 in the Raman spectrum of the anionic form of the 4-hydroxycinnamyl phenyl thioester are shown to be characteristic for the deprotonation of the chromophore. The observation of bands in PYP exhibiting very similar frequency and intensity patterns provides strong evidence that the chromophore in PYP is stabilized as a phenolate anion at pH 7.4, in support of conclusions from crystallographic studies. Furthermore, the insensitivity of the PYP Raman spectrum to placement of the protein in D2O buffer is consistent with the absence of the exchangeable phenolic proton on the cinnamyl chromophore. These results establish the feasibility of elucidating the molecular mechanism of light-to-information transduction by this new photosensory pigment with resonance Raman spectroscopy.

Bacterial Proteins↗
PubMed2003

Resonant Raman quantification of zeaxanthin production from Flavobacterium multivorum.

Resonant Raman scattering was used as a novel, rapid, non-destructive optical technique to measure zeaxanthin levels in Flavobacterium multivorum ATCC 55238. Culture broth, after bacterial growth for 40 h, exhibited characteristic resonance Raman vibrational modes at 1159 cm(-1) (C-C stretch) and 1525 cm(-1) (C=C stretch) upon excitation at 488 nm. A striking correlation was observed between the carotenoid level as estimated by HPLC and by resonance Raman spectroscopy.

Chromatography, High Pressure Liquid↗
PubMed2002

Single-pulse coherently controlled nonlinear Raman spectroscopy and microscopy.

Molecular vibrations have oscillation periods that reflect the molecular structure, and are hence being used as a spectroscopic fingerprint for detection and identification. At present, all nonlinear spectroscopy schemes use two or more laser beams to measure such vibrations. The availability of ultrashort (femtosecond) optical pulses with durations shorter than typical molecular vibration periods has enabled the coherent excitation of molecular vibrations using a single pulse. Here we perform single-pulse vibrational spectroscopy on several molecules in the liquid phase, where both the excitation and the readout processes are performed by the same pulse. The main difficulty with single-pulse spectroscopy is that all vibrational levels with energies within the pulse bandwidth are excited. We achieve high spectral resolution, nearly two orders of magnitude better than the pulse bandwidth, by using quantum coherent control techniques. By appropriately modulating the spectral phase of the pulse we are able to exploit the quantum interference between multiple paths to selectively populate a given vibrational level, and to probe this population using the same pulse. This scheme, using a single broadband laser source, is particularly attractive for nonlinear microscopy applications, as we demonstrate by constructing a coherent anti-Stokes Raman (CARS) microscope operating with a single laser beam.

Lasers↗
PubMed2005

Raman spectroscopy of hot desert, high altitude epilithic lichens.

Twenty-three highly-coloured lichen specimens belonging to the genera Candelariella, Aspicilia and Xanthoria from high altitude sites in the Atacama Desert, Chile, 2300-4500 metres, have been analysed non-destructively by Raman spectroscopy. The vibrational band assignments in the spectra of the specimens, which were still attached to their limestone or sandstone substrata, were accomplished by comparison with the chemical compositions obtained from wet chemical extraction methods. Carotenoids and chlorophyll were found in all specimens as major components and the characteristic spectral signatures of calcium oxalate monohydrate (whewellite) and dihydrate (weddellite) could be identified; chemical signatures were found for these materials even in lichen thalli growing on the non-calcareous substrata, indicating probably that the calcium was provided here from wind- or rain-borne sources. The Raman spectral biomarkers for a variety of protective biomolecules and accessory pigments such as usnic acid, calycin, pulvinic acid dilactone and rhizocarpic acid have been identified in the lichens, in broad agreement with the chemical extraction profiles. The present study indicates that some form of non-destructive taxonomic identification based on Raman spectroscopy was also possible.

Altitude↗