Vibrational relaxation study in carbonyl containing molecule: role of hydrodynamic and dispersion forces

The isotropic Raman component of the C = O stretching mode of ethyl acetate (EA) was analyzed using various polar and nonpolar solvents. It was found that the bandshape approaches towards Lorentzian at high dilution using the curve‐fitting method. The isotropic Raman band was also analyzed by estimating the correlation coefficient with reference to the Lorentzian lineshape using a simple method of linear‐curve fitting. The effects of dispersion and hydrodynamic forces on bandwidth were studied in details. The vibrational relaxation rate was studied using certain parameters and it was found that the microscopic based parameter can explain the complexities occurring in solute–solvent interactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational spectra and quantum chemical calculations of uracilyl–pyridinium mesomeric betaine

Modified nucleobases (MNs) are promising molecules with potential application in non‐linear optic (NLO) and drug design against a wide number of diseases. In the present paper we report studies on a cross‐conjugated mesomeric betaine, which can act as a MN, formed by the covalent union of a 4‐dimethylamino pyridinium and a uracilyl groups. The molecule thus formed must be presented by a dipolar canonical formulae in which positive and negative charges are delocalized within separated moieties. Quantum chemistry density functional theory (DFT) calculations, at the B3PW91/6‐31G** level, and Fourier transform (FT) infrared and Raman spectra of this molecule and its N‐deuterated derivative were performed. The calculated structural properties over the ground state optimized structure evidenced a strong separation between the two conjugated systems. Comparison with previous results obtained for the cationic species indicated that N‐protonation clearly affects the degree of conjugation. Assignments of the FT‐IR and FT‐Raman spectra were supported by the DFT wavenumbers, intensities and normal modes, which also evidenced the separation of the two conjugated systems. Significant deviations were found for the stretching force constants of the inter‐ring and the uracilyl skeletal bonds when comparing this molecule with its N‐protonated species. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational and orientational relaxation of thiocyanate ion in crown ether complexes

The IR absorption and Raman spectra of the following complex compounds based on thiocyanates and crown ethers have been studied: KSCN-18-crown-6, KSCN-dibenzo-18-crown-6, NaSCN-dibenzo-18-crown-6, and NaSCN-benzo-15-crown-5. The shape of the contour of the spectral line corresponding to the stretching vibration ₁(CN) of the thiocyanate ion in the indicated compounds in the temperature interval involving solid and liquid phases have been investigated for the first time. The reorientation parameters and molecular-relaxation characteristics of the thiocyanate ion in the crown compounds have been calculated. It is found that an increase in temperature leads to gradual freeing of cations and to the properties of crown compounds becoming identical to those of pure salt melts.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 23–27, January–February, 2005.     

Infrared and Raman spectroscopic studies of L‐valinium picrate

The vibrational assignments of the observed wavenumbers have been made by analyzing the infrared and Raman spectra of L ‐valinium picrate in the crystalline state at room temperature. L ‐Valinium acts as the cation of the crystal and the carbonyl CO group exists in the protonated form in it. Asymmetric deformation and symmetric deformation modes of the isopropyl group have been identified, indicating that the two CH₃ groups are in different environments. The stretching and bending modes of the various functional groups have been shifted owing to the extensive intermolecular hydrogen bonding in the crystal. The symmetry of the picrate anion has not been modified in the crystal by the hydrogen bonding with the cation. Fermi resonance is also observed. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibrational investigation of 1-cyclopentylpiperazine: A combined experimental and theoretical study

FT-IR and Raman spectra of 1-cyclopentylpiperazine(1cppp)have been experimentally examined in the region of 4000–200cm-1.The optimized geometric parameters,conformational equilibria,normal mode frequencies and corresponding vibrational assignments of 1cppp(C9H18N2)are theoretically examined by means of B3LYP hybrid density functional theory(DFT)method together with 6-31++G(d,p)basis set.On the basis of potential energy distribution(PED)reliable vibrational assignments have been made and the thermodynamics functions,highest occupied and lowest unoccupied molecular orbitals(HOMO and LUMO)of 1cppp have been predicted.Calculations are employed for four different conformations in C1 and Cs point groups of 1cppp in gas phase.Comparison between the experimental and theoretical results indicates that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters,vibrational frequencies and assignments.Furthermore,C1(equatorial-axial)point group has been found as the most stable conformer of 1cppp.     

Study of vibrational relaxation and molecular reorientation in liquids: a Raman spectroscopic study

The vibrational relaxation and molecular reorientational processes in liquids have been studied in some carbonyl‐containing molecules using the acetonitrile (ACN) solvent. The vibrational and reorientational processes have been studied in correspondence with correlation times. The screening effect due to dielectric has been studied and the Onsager reaction field model has been tested. The study shows that repulsive types of intermolecular forces play an important role in complex systems. Copyright © 2010 John Wiley & Sons, Ltd.     

二维有摩擦颗粒体系振动态密度与玻色峰的研究

利用颗粒离散元方法,研究了由2048个有摩擦的单分散圆盘颗粒组成的体系在各向同性压缩条件下,颗粒摩擦系数μ对颗粒体系结构与振动特性的影响.结果表明:固定压强下,随μ的增大,区分德拜标度与态密度平台的过渡频率ω*与玻色峰频率ωBP均向低频移动,玻色峰高度D(ωBP)/ωBP逐渐增加.主要原因是μ增大导致颗粒体系无序程度增加(平均配位数减小)而在ωω*处出现了大量额外模式.模式分析表明:低频(ω1.0)模式主要是以平动为主的混合模式,中频(1.0ω4.0)模式主要是以平动为主的混合局域化模式,高频(ω4.0)振动模式几乎为纯转动的局域化模式;并且随μ的增大,低频下平动模式更加局域化,同时低频转动模式的贡献也逐渐增加,暗示在高摩擦系数下低频转动模式产生更重要的影响.     

Vibrational relaxation of a molecule in strong interaction with a reservoir: Nonmonotonic temperature dependence

This theoretical study of the vibrational relaxation of a molecule in interaction with a reservoir uncovers a noteworthy temperature (T) dependence of the time evolution of the relaxation. Its rate increases with T in one interval but decreases in another. The feature arises not for a weak molecule-reservoir interaction but only for coupling strong enough to require polaronic dressing transformations. Our treatment, based on a recent generalization of the well-known Montroll–Shuler equation for relaxation and an explicit calculation of bath correlations from the microscopically specified Hamiltonian, could provide an alternative explanation of an “inverted” T-dependence of relaxation in an experimental report by Fayer and collaborators on W(CO)₆ dissolved in CHCl₃.     

Aggregation of trichogin analogs in weakly polar solvents: PELDOR and ESR studies

The technique of pulsed electron-electron double-resonance is used to study the self-aggregation of spin labeled trichogin GA IV analogs in weakly polar solvents. The dipole-dipole spinspin relaxation of spin labels has been experimentally studied in glassy solutions of spin-labeled peptides frozen to 77 K in the mixtures of chloroform-toluene, chloroform-decalin, tetrachloromethanetoluene, dichloroethan-toluene depending on the label position in peptide and the structure of terminal groups. It is shown that the studied trichogin analogs in weakly polar solvents form aggregates whose structure depends on solvent properties and peptide structure. It is also demonstrated that the distances between spin labels which can be measured in aggregates amount to the values of 2.3, 2.6 and 3.3 nm. The lower estimate is given for the average number of peptide molecules in aggregates to within 3.1–4.3 depending on peptide structure and solvent composition.     

Vibrational spectra and scaled quantum chemical studies of the structure of Martius yellow sodium salt monohydrate

The FT‐IR and Raman spectra of Martius Yellow sodium salt Monohydrate (MYM) [2, 4‐dinitro‐1‐naphthol sodium salt] in solid‐phase have been measured. The geometry, intramolecular hydrogen bonding and harmonic vibrational wavenumbers of MYM have been investigated with the help of B3LYP density functional theory (DFT) methods. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The existence of intramolecular C H···O improper, blue‐shifted hydrogen bonding was investigated by means of the NBO analysis. The infrared and Raman spectra were predicted theoretically from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. Copyright © 2009 John Wiley & Sons, Ltd.     

An ab initio study of some binary complexes containing methyl fluoride and difluoromethane: red-shifting and blue-shifting hydrogen bonds

The properties of a number of hydrogen-bonded complexes of methyl fluoride and difluoromethane with a range of hydrides of the first two rows of the periodic table have been computed using ab initio molecular orbital theory. The aim of this work was to identify possible examples of blue-shifting hydrogen-bonded species analogous to those formed between fluoroform and ammonia, water, phosphine and hydrogen sulphide, reported earlier. The calculations were carried out using the Gaussian-09 program, at the second-order level of Møller–Plesset perturbation theory, and with the aug-cc-pVTZ basis sets of Dunning. The properties studied include the molecular structures, the hydrogen bond energies and the vibrational spectra. The results have been interpreted with the aid of natural bond orbital theory and the quantum theory of atoms in molecules.     

Conformational,electronic and antioxidant properties of lucidone,linderone and methyllinderone: DFT,QTAIM and NBO studies

Theoretical studies on lucidone, linderone and methyllinderone were performed to investigate factors that contribute to structural stability and to elucidate the antioxidant properties and mechanisms. The study was performed in different media utilising the density functional theory with different functionals and the 6-311+ G(d,p) basis set. The antioxidant activity has been considered through the electron transfer and metal chelation mechanisms. The results show that the stability of the tautomers and conformers is due to the presence of several intramolecular hydrogen bonds. The ionisation potential values suggest that the antiradical activity increases with the increase in the number of OCH₃ groups substituted on the cyclopentene-1,3-dione ring. In vacuo, the spin density of the Fe(II) cation upon ligand coordination decreases to 3.0?3.5, whereas the ligand spin density approaches 1, indicating that it is oxidised to a radical cation. The metal ion affinity (MIA) is influenced by the position and number of OCH₃ substituted on the acylcyclopentene-1,3-dione ring. A very favourable MIA, in vacuo, is obtained when Fe(II) is chelated between the sp² O and sp³ O atoms. An estimation of MIA in an aqueous solution shows a remarkable decrease with respect to the results in vacuo.     

Raman spectroscopic studies of vibrational relaxation and non‐coincidence effect in substituted benzaldehyde binary mixtures

The molecular interaction in the binary mixture of 3‐phenoxybenzaldhyde (3Phbz) and 4‐ethoxybenzaldehyde (4Etob) was analysed in four different solvents. The concentration dependence of vibrational relaxation of the CO stretching band of 3Phbz in different solvents was investigated by varying the concentration of the solute molecule in the solvents by performing Raman spectroscopic measurements. The self‐associated nature and the formation of hydrogen‐bonded complexes in the solute molecule, 4Etob, were considered to analyse the wavenumber separation between the peaks of hydrogen‐bonded and free carbonyl groups. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrasonic absorption studies in solutions of ortho and para hydroxy benzoic acid in dioxan

Ultrasonic absorption was measured in ortho and para hydroxy benzoic acid (OHBA and PHBA) in dioxan at room temperature for various solute concentrations. The variation of ultrasonic absorption in both solutions with the solute concentration showed two maxima, one at lower solute concentration and the other at higher solute concentration. The first maximum is explained as due to formation of hydrogen bonds between the O-H groups of OHBA and PHBA molecules and the oxygen of dioxan molecules and the second maximum as due to the COOH group of the OHBA/PHBA molecules and oxygen of dioxan molecules. In both systems the measured absorption is explained on the basis of Hall’s two-state model.     

Photophysical properties of substituted intramolecularly hydrogen bonded compounds: A combined experimental and theoretical study

Photophysical properties of prototype excited state intramolecular proton transfer (ESIPT) system 4-methyl-2,6-diformyl phenol (MFOH) and its derivatives were studied by steady state and time-resolved fluorescence spectroscopy as well as by ab-initio quantum chemical calculation. It has been found that nonradiative decay process is the most important deactivation channel in all the cases and the hydrogen bonded enol conformer is stable in the ground state whereas, the proton transferred keto form is energetically favoured in the S₁(ππ^*) state. However, the net gain in stabilization in the process of ESIPT is almost unaffected by the substitution. The reversal of stability in the excited state was explained on the basis of the nature of frontier molecular orbital in all the cases. Intrinsic reaction coordinate analysis showed that drastic change in nonbonded interoxygen distance R(O-O) in the proton transfer pathway causes the switch over from the enol to keto configuration. A close comparison of several properties like molecular geometry, hydrogen bond strength and atomic charge in different derivatives of MFOH were found to be consistent and in good agreement with the experimental results obtained from time-resolved fluorescence experiments.     

Vibrational spectra and structural studies of nonlinear optical crystal ammonium D,L‐tartrate: a density functional theoretical approach

Single crystals of ammonium D , L ‐tartrate, a potential nonlinear optical (NLO) material of interest, were grown by the slow evaporation technique. The crystal structure was determined by single‐crystal X‐ray diffraction. Fourier transform infrared and Raman spectra of the crystallized molecule were recorded and analyzed. The geometry, intermolecular hydrogen bonding, first hyperpolarizability and harmonic vibrational wavenumbers were calculated with the help of B3LYP density functional theory method. The red shift of hydroxyl and NH₄⁺ stretching wavenumbers indicate the formation of inter‐ and intramolecular hydrogen bonding. Simultaneous activation of CH stretching wavenumbers shows the presence of intramolecular charge transfer in the molecule. Natural bond orbital analysis was carried out to demonstrate the various inter‐ and intramolecular interactions that are responsible for the stabilization of this molecule, leading to high NLO activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational spectral studies on charge transfer and ionic hydrogen‐bonding interactions of nonlinear optical material L‐arginine nitrate hemihydrate

The near infrared Fourier‐transform (NIR FT)‐Raman and Fourier‐transform infrared (FT‐IR) spectroscopies supported by HF/6‐31G(d) computations have been employed to derive equilibrium geometry, vibrational wavenumbers and the first hyperpolarizability of the nonlinear optical (NLO) material, L ‐arginine nitrate (LAN) hemihydrate. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz–Perry powder second harmonic generation (SHG) experiments. The changes in the atomic charge distribution among different groups due to the presence of strong electronegative atoms and the shrinking of N O bonds of nitrate anion and C N bonds of guanidyl group have been analyzed. The splitting of the carboxylate stretching modes, blue shifting of methine vibrations and the electronic effects such as backdonation and induction on the methylene hydrogen atoms have also been examined in detail. The intense low wavenumber H‐bond Raman vibrations due to electron–phonon coupling and nonbonded interactions in making the LAN molecule NLO active have been discussed based on the vibrational spectral features. The natural bond orbital (NBO) analysis and HF computations confirm the occurrence of strong intra‐ and intermolecular N H·O and O H·O ionic hydrogen bonding between charged species providing the noncentrosymmetric structure in the LAN crystal. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural and aromatic aspects of tautomeric equilibrium in hydroxy aryl Schiff bases

The synthesis and X‐ray measurements of four Schiff bases were carried out at 100 K. The HOMA and HOSE aromaticity indices were estimated on the basis of the experimental data. The aromaticity of the phenyl ring and the chelate chain was analysed. A comparison of the aromaticity of naphthalene and phenyl derivatives of hydroxy aryl Schiff bases is presented. The balance between the aromaticity of adjacent rings of the naphthalene fragment and its effect on proton transfer is defined. Research on the interrelations between aromaticity and the intramolecular proton transfer in hydroxy aryl Schiff bases is shown. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular dynamics simulation studies of cryoprotective agent solutions: the relation between melting temperature and the ratio of hydrogen bonding acceptor to donor number

Molecular dynamics simulations have been carried out for glycerol–water–sodium chloride ternary solution due to its important role in cryopreservation engineering. The radial distribution functions for atom pairs potentially related to C–H ··· O and O–H ··· O hydrogen bonds were calculated. The radial distribution functions for the H (connected to C)–O atom pair do not exhibit peaks between 2 and 3 Å, whereas the radial distribution functions for the C–O atom pair exhibit distinct peaks between 3 and 4 Å. The reason for this is because most C–H ··· O geometries are bent and deviate from linearity. The ratios of acceptor to donor numbers for water and glycerol molecules decrease as the solute concentration increases. A characteristic concentration has been found that divides solutions with different mechanisms. Below the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for water molecules, whereas above the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for glycerol molecules. Further studies indicate that the relations are independent of hydrogen bonding criteria and temperature.     

The equilibrium and kinetics of intermolecular hydrogen bonding in nitroarene anion radical–alcohol system: 1,3‐dinitro‐benzene anion radical – R–OH (R═CH3–, C2H5–, (CH3)2 CH–)

To explore the possibility of hydrogen bonding of a stable anion radical with DNA – component sugar, hormones, steroid, and so on (through hydroxyl group), as a first step, the possibility of hydrogen bonding of 1,3‐dinitrobenzene anion radical (1,3‐DNB^??) with aliphatic alcohols was studied. It was found that 1,3‐DNB^?? anion radical undergoes hydrogen bonding with alcohols: methanol, ethanol, and 2‐proponal. The hydrogen‐bonding equilibrium constant K_eq and the (hydrogen‐bonding) rate constants k₂ were evaluated through the use of linear scan and cyclic voltammetry theory and techniques. The K_eq was found to be in the range of 1.4–6.0 m ^?1, whereas the rate constants k₂ were found to be in the range of 1.5–3.6 m ^?1 s^?1, depending upon the hydrogen‐bonding agent and the equation used for the calculation of the rate constants. The hydrogen‐bonding number n was found to be around 0.5 or 1.0. The implication of this study in, for example, the replication of DNA, the prevention of the formation of super oxide, and so on is discussed. Copyright © 2012 John Wiley & Sons, Ltd.