Volume 225, Issue 6-7 - Many Facets of Raman Spectroscopy

Bi 2 O 3 -rich glasses belonging to the system x Gd 2 O 3 (1− x )[0.857Bi 2 O 3 ·0.143GeO 2 ] with 0.005≤ x ≤0.1, have been obtained by rapid cooling of the melts. Polycrystalline samples have been further obtained by applying a heat treatment at 600ºC for 24 h. Both types of samples were structurally characterized by using X-ray diffraction (XRD), and infrared (IR) and Raman spectroscopic techniques. Local structural units for the investigated samples are identified on the basis of vibrational spectroscopic data. The obtained data reveal the presence of GeO 4 , GeO 6 , BiO 3 and BiO 6 groups as basic structural units of the networks. For the vitroceramic samples some changes occur in their network, mainly reflecting the presence of an ordered structure, but much important is that part of the BiO 6 structural units from Bi 2 O 3 -GeO 2 glass network are converting into BiO 3 units. The IR and Raman results support the idea that the local structure of the glasses and vitroceramics is less affected by the presence of Gd 3+ ions but there is strong long range order influence on developed crystalline phases from vitroceramic samples, as proved by XRD. However, the spectral analyses reveal the formation of a structure with a higher disorder degree for x =0.1 in comparison with the other investigated vitroceramics as a result of the partial replacement of the Bi 3+ ions with Gd 3+ ions. Starting from the Bi 12 GeO 20 sellenite phase in the samples with low gadolinium content ( x ≤0.01), the structure is change to Bi 24 GeO 38 phase, via a BiLa type structure, when the Gd 2 O 3 concentration is increasing up to x =0.1.

In order to obtain a deeper insight into the interaction between cytosine and copper electrode, a surface-enhanced Raman scattering (SERS) study and density functional theory (DFT) simulation have been used. The experimental result shows that a decrease of relative intensity of the band at around 1315 cm −1 is accompanied by a considerable increase of relative intensity of the bands in the 1490∼1600 cm −1 region when the potential is below −0.7 V, and it is explained by the chemical effect (CE). Simultaneously, the geometry and Raman spectra of neutral and cationic Cu-cytosine complexes are calculated and simulated using the B3LYP/lanl2dz basis. The simulation shows that the relative intensities of Raman spectra depend strongly on the molecular active sites involved in the interaction between the copper electrode and the cytosine molecule. Combining the experimental results with theoretical calculations, we conclude that the adsorptive orientation of cytosine on the copper electrode occurs on the N 3 site and the carbonyl site when the potential is above and below −0.7 V, respectively. This study also indicates that a combination of SERS and DFT simulations is a valuable tool for studying interactions of biomolecules with metal.

The wavenumber difference (Δ ν ) of the ring breathing mode ( ν 1 ), ring deformation mode ( ν 12 ) and C–H stretching mode ( ν 3 ) of pyridine (Py) dissolved in both H 2 O and D 2 O at equal mole fractions of the solute (Py) and the solvent (H 2 O/D 2 O) has been determined precisely by using the technique of Raman difference spectroscopy (RDS) in order to analyze the relative shift caused by these two solvents. The spectra of the two systems, for which the difference spectrum is to be generated, were recorded simultaneously and the wavenumber shifts up to almost one hundredth part of the linewidth of a band could be determined precisely. The values of Δ ν for the three modes as a function of mole fraction are compared with the Δ ν obtained by the solvation of Py molecule in the media of dielectric constants equal to that of the mixture of Py and H 2 O/D 2 O at the experimental mole fractions using DFT and MP2 methods. The variation in Δ ν with mole fraction seems to be the result of difference of dielectric constants of Py+H 2 O and Py+D 2 O at equal mole fraction. The absolute peak position and linewidth of the three modes as a function of mole fraction have been discussed in terms of relevant models, which show the effective role of diffusion and concentration fluctuation in the mixture.

Deep UVRR spectra of the aromatic amino acids Phe and Tyr in the wavenumber range 800–1800 cm −1 with λ exc =195–208 nm exhibit a selective enhancement of signals arising from vibrations localized in the aromatic ring. For λ exc >198 nm, the UVRR spectra of Phe and Tyr are dominated by contributions from the in-plane ring stretching modes ν 8 a and ν 8 b at ∼1600 cm −1 . For λ exc ≤198 nm, intense signals from the symmetric ring stretching, in-plane C–H bending and phenyl–C stretching vibrations below 1400 cm −1 are observed. Excellent stray light rejection is achieved by a triple monochromator, which can be used either in the additive or subtractive mode for high-resolution and low-wavenumber measurements, respectively. A home-built circulating free-flow system allows the investigation of sample volumes as small as 1 mL.

We theoretically study interference effects in two-dimensional (2D) vibronic spectra which arise from two electronically excited states taking part in the multi-photon process initiated by femtosecond laser pulses. Therefore, a model is employed which mimiques the situation encountered in many halogen and interhalogen molecules. There, upon excitation from the ground state, an excited bound state and a dissociative state exist which are close in energy. We demonstrate that the different pathways to final states which enter into the third-order polarization result in pronounced interference patterns in the 2D-spectra.

The threshold photoelectron spectrum of NTCDA (1,4,5,8-naphthalene-tetracarboxylic dianhydride) has been recorded using synchrotron radiation. An ionization energy of 9.66 eV was observed. The experiments are supported by DFT computations that yield a value of 9.51 eV, in good agreement with the measured value. Several bands corresponding to excited electronic states of the cation are also visible and can be assigned with the aid of computations.

Raman spectra of neat paraldehyde (prldh) and its binary mixtures with methanol (M) with varying mole fractions of prldh from 0.1 to 0.8 were recorded in order to explore the hydrogen bonding patterns of prldh and their influence on spectral features of some selected vibrational bands of prldh in the region 400–1200 cm −1 . Only few vibrational bands of paraldehyde show a significant change in their peak position in going from neat prldh to the complexes. One peculiar feature in this study is that the solvent band which occurs at ∼1034 cm −1 shows significant red shift of >4 cm −1 at higher mole fractions of prldh. This red shift is caused due to the hydrogen bonding between the O atom of the prldh ring and H atom of the methanol molecules. The Raman band at ∼1097 cm −1 band shows a blue shift of ∼5 cm −1 upon dilution and its linewidth also shows an increase of ∼5 cm −1 in going from neat prldh to extreme dilution. The line broadening upon dilution clearly indicates that the diffusion mechanism plays a dominant role in the dephasing of this vibrational mode. Density functional theoretic (DFT) calculations were performed employing B3LYP functional and high level basis set, 6-311++G(d,p) to obtain the ground state geometry of neat prldh and its hydrogen bonded complexes with methanol in gas phase. Basis set superimpose error (BSSE) correction was also introduced using the counterpoise method. In order to realize a condition quite close to the experiment, the polarizable continuum model (PCM, specific plus bulk solvation) calculations were also performed. For a detailed vibrational assignment of the normal modes, potential energy distribution (PED) calculation was also performed.

The interaction of urea with myoglobin, as a benchmark system for heme-containing proteins, is studied via femtosecond coherence spectroscopy. The work focuses on the effect of urea on the appearance of low-wavenumber oscillations, which are a measure of the geometrical structure of the heme group and its interaction with the polypeptide chain. Pursuing this approach, structural alterations ( i.e. changes in the vibrational dynamics of the heme group) are detected at denaturant concentrations below the full denaturation limit of 6 M urea for myoglobin. In particular, the low-wavenumber oscillation associated with the heme-doming ( i.e. the out-off-plane vibration of the propyrin macrocycle) is found to appear spectrally shifted with a concentration of only 3 M urea. These results suggest that the local environment around the heme is already altered despite the fact that macroscopic unfolding as manifested in the thermodynamic properties of the polypeptide chain is not complete at these urea concentrations.

A wavenumber and intensity calibration procedure of Raman spectra by using chemometric techniques is presented. This approach allows the fine tuning of calibration parameters and routines with the final goal to eliminate setup dependent differences within experimentally recorded Raman spectra. This seems to be necessary since more and more Raman databases are needed for different analytical tasks, like identification of minerals or bacteria. Minimizing the impact of the applied experimental Raman setup on the reference (database stored) Raman spectra allows the databases to be enlarged very easily by feeding the database with Raman spectra recorded with different setups. Furthermore the chemometric analysis performance increases due to the larger number and better quality of reference spectra.

Biological rhythms, which regulate the biological cycles of life, are of great interest in biomedicine. The effect of biological rhythms on bone is controversial at the moment. Raman spectroscopy was applied to assess the bone compositional information of hamsters under different photoperiods, designed as long day photoperiod of 16 h light and 8 h dark (LD, 16L : 8D) and short day photoperiod of 8 h light and 16 h dark (SD, 8L : 16D). After three months under such well-defined conditions, the hamsters in the two groups exhibited differences in body weight, fur color and testis size. In addition, for the first time to our knowledge bone compositional variations were observed in both mineral constituents and collagen secondary structures in hamsters conditioned under the different photoperiods. The collagen secondary structure in the SD hamsters was characterized by a higher ratio of mature intra-fibril cross-links indicating a more stable form of collagen. It is hypothesized that increased bone turnover rate and resorption led to the alteration of collagen cross-links in the SD group.

Fairly monodisperse “dog bone” shaped gold nanorods were obtained clean and in high yield. Their average aspect ratio could be adjusted from ∼ 2 to ∼ 3 by altering the amount of silver nitrate present in the growth solution. They were coated with a uniform, ultrathin shell of silica and used to detect parathion pesticide on an orange peel by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS).

Diazines form various types of hydrogen bonds with water, wherein C–H groups are sometimes involved directly and sometimes indirectly. On hydrogen bond formation, the wavenumber of C–H stretching vibration are usually red shifted (normal hydrogen bond) but blue shift of C–H modes (anomalous hydrogen bond) is also possible in some cases. The Raman spectra of the C–H stretching bands of three diazines; pyrimidine, pyridazine, and pyrazine in pure form and at many concentrations in mole fractions of diazines in the mixture of diazines + water have been measured to analyze the wavenumber shifts experimentally. Theoretical wavenumber shifts have been calculated and NBO analysis has been performed using DFT methods to understand the cause of the shifts. All the four C–H stretching bands of diazines are blue shifted on dilution with water both experimentally and theoretically. The NBO calculations reveal that the cause of the shift is decrease in the charge density in the antibonding orbital of C–H bond on complex formation.