Vibrational spectroscopy of dispersed ReO sites supported on monoclinic zirconia.

Raman and FTIR spectra complemented by Raman/O isotope labelling are exploited for deciphering the structural properties and configurations of the (ReO) phase dispersed on monoclinic ZrO at temperatures of 120-400 °C under oxidative dehydration conditions and coverages in the range of 0.71-3.7 Re nm.

Heterogeneity of the vanadia phase dispersed on titania. Co-existence of distinct mono-oxo VO sites.

The structural and configurational characteristics of the species comprising the (VO) phase dispersed on TiO(P25) are studied under oxidative dehydration conditions by molecular vibrational spectroscopy (Raman, FTIR) complemented by Raman/O isotope exchange and Raman spectroscopy under static equilibrium at temperatures of 175-430 °C and coverages in the 0.40-5.5 V nm range.

Evidence of Self-Association and Conformational Change in Nisin Antimicrobial Polypeptide Solutions: A Combined Raman and Ultrasonic Relaxation Spectroscopic and Theoretical Study.

The polypeptide Nisin is characterized by antibacterial properties, making it a compound with many applications, mainly in the food industry. As a result, a deeper understanding of its behaviour, especially after its dissolution in water, is of the utmost importance. This could be possible through the study of aqueous solutions of Nisin by combining vibrational and acoustic spectroscopic techniques.

Rethinking the molecular structures of WO sites dispersed on titania: distinct mono-oxo configurations at 430 °C and temperature-dependent transformations.

The structural properties of the (WO) phase dispersed on TiO (P25, anatase) at surface densities of 0.5-4.5 W nm ( up to approximately a monolayer) were explored by using Raman and FTIR spectroscopy, Raman/O exchange and Raman spectroscopy in static equilibrium at temperatures of 175-430 °C.

Proton-transfer in 1,1,3,3 tetramethyl guanidine by means of ultrasonic relaxation and Raman spectroscopies and molecular orbital calculations.

In this work, we report on the structure and dynamics of the 1,1,3,3 tetramethyl guanidine (TMG) aqueous solutions in a wide concentration and temperature range by combining vibrational and ultrasonic spectroscopies. The experimental Raman spectra have been compared with the corresponding spectra obtained by ab initio quantum mechanical and density functional theory electronic structure calculations. This comparison indicated that only a single mechanism occurs when dissolving TMG in water and this is the proton transfer reaction, while the formation of byproducts during hydrolysis of TMG is dubious.

Heterogeneity of deposited phases in supported transition metal oxide catalysts: reversible temperature-dependent evolution of molecular structures and configurations.

In situ high-temperature Raman spectroscopy under steady state oxidative dehydrated conditions was used for determining the temperature dependence of the molecular structures and configurations of (MO) (M = Re, Mo, W) sites supported at low submonolayer loadings on TiO(P25). Prior to the Raman analysis, the studied catalyst samples underwent calcination at 450-480 °C for 4-5 h. Regularly repeated random sequences of heating and cooling under flowing 20%O/He (in the absence of incoming water vapor) in the 35-430 °C temperature range were shown to cause drastic changes in the vibrational properties of the M-O stretching modes and in the molecular structures and configurations of the deposited ReO, MoO, and WO sites in a reversible and reproducible manner.

Molybdena deposited on titania by equilibrium deposition filtration: structural evolution of oxo-molybdenum(vi) sites with temperature.

The equilibrium deposition filtration (EDF) method, an advanced catalyst synthesis route that is based on a molecular level approach, can be used for tailoring the oxometallic phase deposited on a porous oxide support. Here, the EDF method is used for synthesizing (MoOx)n/TiO2 catalysts. In situ Raman spectroscopy in the temperature range of 25-450 °C, low temperature (77 K) EPR spectroscopy and DR-UV spectroscopy are used for studying the evolution of the structural configuration of oxo-Mo(VI) species on TiO2 with increasing temperature as well as the influence of the supported (MoOx)n species on the photo-generation of electrons and holes of TiO2.

Glass-forming ability of TeO₂ and temperature induced changes on the structure of the glassy, supercooled, and molten states.

Polarized (VV) and depolarized (VH) Raman spectra are obtained for glassy, supercooled, and molten TeO2 at temperatures up to 1000 K in order to elucidate the temperature evolution of the pertinent structural and vibrational properties. The intrinsic tendency of the system for crystallization is avoided by means of a newly applied protocol, thereby enabling the recording of Raman spectra of pure TeO2 on going from the molten to the supercooled liquid and to the room temperature glass states. Following an appropriate fitting procedure, the revealed bands are assigned to specific modes of structural polymorphs.

Vibrational dephasing and frequency shifts of hydrogen-bonded pyridine-water complexes.

In this paper we present the picosecond vibrational dynamics and Raman shifts of hydrogen-bonded pyridine-water complexes present in aqueous solutions in a wide concentration range from dense to extreme dilute solutions. We studied the vibrational dephasing and vibrational frequency modulation by calculating time correlation functions of vibrational relaxation by fits in the frequency domain. The concentration induced variations in bandwidths, band frequencies and characteristic dephasing times have been estimated and interpreted as effects due to solute-solvent interactions.

Molybdenum(VI) oxosulfato complexes in MoO3-K2S2O7-K2SO4 molten mixtures: stoichiometry, vibrational properties, and molecular structures.

The structural and vibrational properties of molybdenum(VI) oxosulfato complexes formed in MoO(3)–K(2)S(2)O(7) and MoO(3)–K(2)S(2)O(7)–K(2)SO(4) molten mixtures under an O(2) atmosphere and static equilibrium conditions were studied by Raman spectroscopy at temperatures of 400–640 °C. The corresponding composition effects were explored in the X(MoO)(3)(0) = 0–0.5 range.

An operando Raman study of molecular structure and reactivity of molybdenum(VI) oxide supported on anatase for the oxidative dehydrogenation of ethane.

Supported molybdenum oxide catalysts on TiO(2) (anatase) with surface densities in the range of 1.8-17.0 Mo per nm(2) were studied at temperatures of 410-480 °C for unraveling the configuration and molecular structure of the deposited (MoO(x))(n) species and examining their behavior for the ethane oxidative dehydrogenation (ODH).

Raman spectroscopic study of tungsten(VI) oxosulfato complexes in WO3-K2S2O7-K2SO4 molten mixtures: stoichiometry, vibrational properties, and molecular structure.

The dissolution reaction of WO3 in pure molten K2S2O7 and in molten K2S2O7-K2SO4 mixtures is studied under static equilibrium conditions in the XWO3(0) = 0-0.33 mol fraction range at temperatures up to 860 °C. High temperature Raman spectroscopy shows that the dissolution leads to formation of W(VI) oxosulfato complexes, and the spectral features are adequate for inferring the structural and vibrational properties of the complexes formed.

Stoichiometry, vibrational modes, and structure of niobium(V) oxosulfato complexes in the molten Nb(2)O(5)-K(2)S(2)O(7)-K(2)SO(4) system studied by Raman spectroscopy.

The structural and vibrational properties of NbV oxosulfato complexes formed in Nb2O5-K2S2O7 and Nb2O5-K2S2O7-K2SO4 molten mixtures with 0 C2n-; a simple formalism exploiting the relative Raman band intensities is used for determining the stoichiometric coefficient, n, pointing to n = 3 and to the following reaction: Nb2O5 + 3S2O72- --> 2NbO(SO4)33-, which is consistent with the Raman spectra of the molten mixtures.

Thermodynamic analysis of reaction equilibria in ionic and molecular liquid systems by high-temperature Raman spectroscopy.

A formalism for correlating relative Raman band intensities with the stoichiometric coefficients, the equilibrium constant, and the thermodynamics of reaction equilibria in solution is derived. The proposed method is used for studying: (1) the thermal dissociation of molten KHSO(4) in the temperature range 240-450 degrees C; (2) the dinuclear complex formation in molten TaCl(5)-AlCl(3) mixtures at temperatures between 125 and 235 degrees C. The experimental and calculational procedures for exploiting the temperature-dependent Raman band intensities in the molten phase as well as (if applicable) in the vapors thereof are described and used for determining the enthalpy of the equilibria: (1) 2HSO(4)(-)(l) <--> S(2)O(7)(2-)(l) + H(2)O(g), DeltaH(0)=64.

Thermal dissociation of molten KHSO4: temperature dependence of Raman spectra and thermodynamics.

Raman spectroscopy is used to study the thermal dissociation of molten KHSO4 at temperatures of 240-450 degrees C under static equilibrium conditions. Raman spectra obtained at 10 different temperatures for the molten phase and for the vapors thereof exhibit vibrational wavenumbers and relative band intensities inferring the occurrence of the temperature-dependent dissociation equilibrium 2HSO4(-)(l) <--> S2O7(2-)(l) + H2O(g). The Raman data are adequate for determining the partial pressures of H2O in the gas phase above the molten mixtures.

Crystal structure and spectroscopic properties of CsVO2SO4.

Dark crystals of the V(V) compound CsVO(2)SO(4), suitable for X-ray investigations have been obtained from the catalytically important Cs(2)S(2)O(7)-V(2)O(5) system. By cooling of the mixture with the composition X(V)2(O)5 = 0.5, some crystals were obtained in the otherwise glassy sample.

Crystal structure and spectroscopic properties of Na(2)K(6)(VO)(2)(SO(4))(7).

Red-brown crystals of a new mixed alkali oxo sulfato vanadium(V) compound Na(2)K(6)(VO)(2)(SO(4))(7), suitable for X-ray determination, have been obtained from the catalytically important binary molten salt system M(2)S(2)O(7)-V(2)O(5) (M = 80% K and 20% Na). By slow cooling of a mixture with the mole fraction X(V(2)O(5)) = 0.24 from 325 degrees C, i.

Usefulness of routine preoperative chest roentgenograms in elderly patients.

One hundred thirty-six charts of preoperative patients over the age of 59 years were reviewed to determine whether clinical criteria alone are sufficient to identify patients who would not benefit from preoperative chest roentgenograms. Thirty-four percent of the patients without risk factors and 62% of those in the high-risk group were found to have significant abnormalities on chest roentgenograms (P less than 0.05).