OH-stretching Frequencies Research Articles

Er:YAG Laser Promotes Gingival Wound Repair by Photo-Dissociating Water Molecules

The aim of the present study was to show that rapid wound repair following Er:YAG treatment and its bactericidal effect can also be related to reactive oxygen species (ROS) generation in irradiated tissue. The Er:YAG laser with a wavelength of 2,940 nm (corresponding to the vibrational OH stretch frequency of water) is of great value in dental medicine, owing to its dual ability to ablate soft and hard tissues with minimal damage to surrounding structures. The relatively rapid postoperative healing time seen after ablation of the gingiva is attributed to the very narrow zone of thermal disruption. Water was irradiated with an Er:YAG laser at an energy of 100-130 mJ/cm(2) and 10-30-Hz pulse repetition rate The concentration of OH radicals produced following irradiation was assessed by spin trapping coupled with electron paramagnetic resonance (EPR) spectroscopy. We found that the Er-YAG laser dissociates water and generates OH radicals. The concentration of radicals produced was strongly dependent on the pulse repetition rate and energy density per laser pulse. The dissociation of water needed to generate OH radicals is possibly due to intermolecular vibrational (V-V) energy transfer in water, competing with vibrational relaxation, thus leading to water dissociation. High amounts of oxygen radicals (e.g., hydroxyl groups) have a sterilization effect, whereas low concentrations of ROS stimulate fibroblasts, causing collagen and extracellular matrix formation. ROS formation may explain the wound healing effect of the Er-YAG laser in dentistry.

Pronounced non-Condon effects in the ultrafast infrared spectroscopy of water

In the context of vibrational spectroscopy in liquids, non-Condon effects refer to the dependence of the vibrational transition dipole moment of a particular molecule on the rotational and translational coordinates of all the molecules in the liquid. For strongly hydrogen-bonded systems, such as liquid water, non-Condon effects are large. That is, the bond dipole derivative of an OH stretch depends strongly on its hydrogen-bonding environment. Previous calculations of nonlinear vibrational spectroscopy in liquids have not included these non-Condon effects. We find that for water, inclusion of these effects is important for an accurate calculation of, for example, homodyned and heterodyned three-pulse echoes. Such echo experiments have been "inverted" to obtain the OH stretch frequency time-correlation function, but by necessity the Condon and other approximations are made in this inversion procedure. Our conclusion is that for water, primarily because of strong non-Condon effects, this inversion may not lead to the correct frequency time-correlation function. Nevertheless, one can still make comparison between theory and experiment by calculating the experimental echo observables themselves.

Infrared Identification of Matrix Isolated H2O×O2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hydrogen and minor element incorporation in synthetic rutile

AbstractThe solubility and incorporation mechanisms of H and various trivalent and divalent cations in synthetic rutile have been investigated. Experiments performed using different bulk Fe2O3 contents demonstrate that Fe3+ substitutes onto the main Ti site, charge-balanced by oxygen vacancies. Under more reducing conditions in Fe-poor systems, the concentration of Ti interstitials in rutile is increased, resulting in a decrease in H solubility. Variation in the solubility of different oxides in rutile as a function of ionic radius implies substitution onto the main Ti site, probably charge-balanced by oxygen vacancies. To a lesser degree, substitution of trivalent and divalent cations is locally charge-balanced by H incorporation. Variation in OH-stretching frequencies in infrared spectra as a function of composition implies that octahedral defects and structurally-incorporated H are coupled. However, in all samples, some of the H is also decoupled from substitutional impurities, as is evident from an OH-absorption band at 3279 cm–1. This band corresponds to the main OH band seen in spectra of many natural rutiles, implying that in most rutiles, H defects are decoupled from substitutional defects.

Dispersion of the Raman depolarization ratio of HDO in water and heavy water from 295to368K, and from concentrated NaClO4∕D2O∕H2O

The dispersion of the Raman depolarization ratio rho(L) was measured for HDO in H(2)O and in D(2)O. rho(L) for the decoupled OD stretch displays a maximum at 2575 +/- 15 cm(-1) at 296 K and a minimum at 2675 +/- 15 cm(-1), in agreement with the isosbestic point 2570 +/- 10 cm(-1), and the enthalpy dispersion maximum, 2650-2675 cm(-1), respectively. However, three extrema were uncovered in rho(L) for the OH stretch of HDO in D(2)O, and their positions agree with the frequencies of a minimum and a maximum in the enthalpy dispersion and with the isosbestic frequency. The frequency of the rho(L) maximum (OH stretch) lies just above the frequency corresponding to the joint angle-frequency probability maximum. [Lawrence and Skinner, J. Chem. Phys. 118, 264 (2003)]. The low- and high-frequency minima in rho(L) (OH stretch), correspond, respectively, to very strong H-bonds, and extremely weak, long, bent H bonds. The frequencies of the maxima and minima in rho(L) for the decoupled OH and OD stretches are independent of temperature within experimental error between 295 and 368 K. rho(L) was also measured for the OD stretch from saturated NaClO(4) in D(2)OH(2)O; it displays a maximum at 2560 +/- 20 cm(-1) and a sharp minimum at 2650 +/- 5 cm(-1). The shape of the dispersion of (betaalpha)(2) approximately rho(L) for HDO in D(2)O was calculated with the aid of the molecular dynamics results of Lawrence and Skinner. beta(2) is the anisotropic polarizability and alpha is the isotropic polarizability. A maximum resulted in the calculated dispersion at 3400 +/- 10 cm(-1), in excellent agreement with the measured maximum of 3395 +/- 15 cm(-1). The H-bond angles decrease far below 180 degrees as the OH-stretching frequency increases to 3700 cm(-1) and above. Such small H-bond angles, and very large O-O distances, are tantamount to broken H-bonds and are thought to produce the minimum in rho(L) near 2650 cm(-1).

Infrared Identification of Matrix Isolated H2O·O2

Theoretical studies of the H2O.O2 complex have been carried out over the past decade, but the complex has not previously been experimentally identified. We have assigned IR vibrations from an H2O.O2 complex in an inert rare gas matrix. This identification is based upon theoretical calculations and concentration dependent behavior of absorption bands observed upon co-deposition of H2O and O2 in argon matrixes at 11.5 +/- 0.5 K. To aid assignment, we have used a harmonically coupled anharmonic oscillator local mode model with an ab initio calculated dipole moment function to calculate the OH-stretching and HOH-bending frequencies and intensities in the complex. The high abundance of H2O and O2 makes the H2O.O2 complex likely to be significant in atmospheric and astrophysical chemistry.

Solvated electron in [formula omitted] dodecahedral cavity: calculated stretch frequencies and vertical dissociation energy

A highly stable ( H 2 O ) 20 - dodecahedral cluster was identified by applying the density functional theory and 6-311++G** and aug-cc-pVDZ basis sets. This cluster has four non-H-bonding H atoms turned toward cavity and has vertical electron dissociation energy of around 1.32 eV. The examination of singly occupied molecular orbital suggests that the extra electron is located inside of the dodecahedral cage and is surrounded by 20 water molecules. Calculation of OH stretch frequencies suggests intensity maxima at around 2914 cm −1 for inward turned H atoms and around 3073 cm −1 for H-bonded H atoms. The six dangling H atoms (projected outward) show negligible intensity at around 3700 cm −1.

Use of DFT to achieve a rational understanding of acid–basic properties of γ-alumina surfaces

In a recent priority communication [M. Digne et al., J. Catal. 211 (2002) 1], we proposed the first ab initio constructed models of γ-alumina surfaces. Using the same density-functional approach, we investigate in further detail the acid–basic properties of the three relevant γ-alumina (100), (110), and (111) surfaces, taking into account the temperature-dependent hydroxyl surface coverages. The simulations, compared fruitfully with many available experimental data, enable us to solve the challenging assignment of the OH-stretching frequencies, as obtained from infrared (IR) spectroscopy. The precise nature of the acid surface sites (concentrations and strengths) is also determined. The acid strengths are quantified by simulating the adsorption of relevant probe molecules such as CO and pyridine in correlation with surface electronic properties. These results seriously challenge the historical model of a defective spinel for γ-alumina and establish the basis for a more rigorous description of the acid–basic properties of γ-alumina.

Quantum chemical calculation of infrared spectra of acidic groups in chabazite in the presence of water.

The changes in the spectra of the acidic group in chabazite are studied by quantum chemical calculations. The zeolite is modeled by two clusters consisting of eight tetrahedral atoms arranged in a ring and seven tetrahedral atoms coordinated around the zeolite OH group. The potential energy and dipole surfaces were constructed from the zeolite OH stretch, in-plane and out-of-plane bending coordinates, and the intermolecular stretch coordinate that corresponds to a movement of the water molecule as a whole. Both the anharmonicities of the potential energy and dipole were taken into account by calculation of the frequencies and intensities. The matrix elements of the vibrational Hamiltonian were calculated within the discrete variable representation basis set. We have assigned the experimentally observed frequencies at approximately 2900, approximately 2400, and approximately 1700 cm(-1) to the strongly perturbed zeolite OH vibrations caused by the hydrogen bonding with the water molecule. The ABC triplet is a Fermi resonance of the zeolite OH stretch mode with the overtone of the in-plane bending (the A band) and the overtone of the out-of-plane bending (the C band). In the B band the stretch is also coupled with the second overtone of the out-of-plane bending. The frequencies at approximately 3700 and approximately 3550 cm(-1) we have assigned to the OH stretch frequencies of a slightly perturbed water molecule.

Hydrogen Bond Dynamics in Water and Ultrafast Infrared Spectroscopy: A Theoretical Study

Molecular Dynamics simulations are used to examine several key aspects of recent ultrafast infrared experiments on liquid water dynamics in an amplified and extended version of a recent communication [J. Phys. Chem. A 2002, 106, 11993]. It is found that the relation between the OH stretch frequency and the length of the hydrogen bond in which the OH is involved is characterized by considerable dispersion. This dispersion, which is in part related to the varying OHO angle of the hydrogen bond, precludes a one-to-one correspondence between the OH frequency and the hydrogen bond length. Further, it is found that the time scale currently interpreted in terms of a stochastic modulation by the surrounding solvent of a highly frictionally damped hydrogen bond system is largely governed by hydrogen bond-breaking and -making dynamics, while the motion of an intact hydrogen-bonded complex is underdamped in character. A detailed analysis of these issues is provided for calculated spectral dynamics after creation of a hole in the ground vibrational state, in terms of a three time analysis (in addition to the H-bond period). Further, the validity of describing the OH frequency fluctuations as a Gaussian random process is examined, as is the character of the associated autocorrelation function of the OH frequency shift.

Investigation of Water Structure at the TiO2/Aqueous Interface

TiO2 thin films coated on SiO2 substrates were prepared for the investigation of water structure at the TiO2/aqueous interface by vibrational sum-frequency spectroscopy (VSFS). The films were first characterized by X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. Film thickness could be readily varied between 0.9 and 5.9 nm with the thinnest film displaying the least degree of surface roughness. The 0.9 nm films were employed in the VSFS investigations and showed characteristic 3200 and 3400 cm-1 OH stretch frequencies of highly aligned interfacial water. Such peaks were reminiscent of those known from SiO2/aqueous interfaces; however, the chemistry at TiO2/aqueous interfaces was significantly richer. In the presence of Cl anions, the surface had an isoelectric point near pH 5.5 and showed the least degree of water organization near this pH. Almost equally strong 3200 cm-1 features could be produced at pH 2.0 and 12.0. On the other hand, the spectra were dramatically altered in the presence of phosphate-buffered saline. The phosphate ions specifically bound to the substrate surface and shifted the isoelectric point of the interface to pH 2.0. In this case, the intensity of the 3400 cm-1 peak was significantly increased in comparison with the Cl ion data at both neutral and acidic pH values. This is presumably because of a lack of sites directly adjacent to the oxide for forming tetrahedrally coordinated water when phosphate ions are present.

The heterogeneity of the hydroxyl groups in chabazite

Two different clusters that have the topology of chabazite but different shapes have been used as a model for the Brønsted sites in chabazite. One of the clusters consists of eight tetrahedral atoms (8T) arranged in a ring and the other represents an intersection of two 8T rings. The adsorption of water and methanol on the two stable proton positions in chabazite has been studied using the B3LYP functional. The coordination of water and methanol with respect to the zeolite fragments were found to be similar, but with methanol situated closer to the acid site than water. The anharmonic zeolite OH stretch frequencies were found to be in the range of 2170–2500 cm−1 and 1457–2074 cm−1 in the presence of water and methanol, respectively. As a measure of the acidity of the bridging hydroxyl groups in chabazite the shift of the zeolite OH stretch frequency upon adsorption has been used. We have found that the proton attached to the oxygen atom O1 to be more acidic than the proton attached to the oxygen atom O3. Also, in the closed ring clusters the zeolite hydroxyl groups are more acidic than in the open clusters. This is not due to a steric effect as the orientation of the adsorbates with respect to the zeolite site is very similar for both clusters. The anharmonicities of the zeolite O–H bond account for about 40% in the redshift upon the adsorption of water or methanol.

Strong Similarities in the Local Hydration Environments of the Bromide Ion and the Cl-·CCl3• Ion−Radical Complex: Factors Contributing to Intramolecular Distortions in the Primary Hydration Shell

We report the infrared photofragmentation spectra of the Cl-·CCl3·nH2O, n = 1−3 complexes and compare the observed pattern of OH stretching vibrations with those displayed by the X-·nH2O, [X = Cl, Br] clusters. The predissociation spectra reveal hydrogen bonded networks in the di- and trihydrate clusters. Addition of the CCl3• radical to the Cl-·nH2O complexes causes a significant blue shift in the OH stretching vibrations involving the hydrogen atoms bound to the ion. As a result, the Cl-·CCl3·nH2O spectra appear remarkably similar to those observed previously for the bromide hydrates. We trace this effect to partial charge delocalization onto the CCl3• radical through an analysis of the electronic structure carried out with density functional calculations. Two important factors contributing to the ion-bound OH stretch frequencies are the radius, (ri), and excess charge, (qi), associated with the halide. The red shifts displayed by the water molecule in a number of halide−water complexes are found to be ...

Ultrafast hydrogen-bond dynamics in the infrared spectroscopy of water.

We investigated rearrangements of the hydrogen-bond network in water by measuring fluctuations in the OH-stretching frequency of HOD in liquid D2O with femtosecond infrared spectroscopy. Using simulations of an atomistic model of water, we relate these frequency fluctuations to intermolecular dynamics. The model reveals that OH frequency shifts arise from changes in the molecular electric field that acts on the proton. At short times, vibrational dephasing reflects an underdamped oscillation of the hydrogen bond with a period of 170 femtoseconds. At longer times, vibrational correlations decay on a 1.2-picosecond time scale because of collective structural reorganizations.

Structure of the aqueous solvated electron from resonance Raman spectroscopy: lessons from isotopic mixtures.

The structure and thermodynamics of the hydrated electron are probed with resonance Raman spectroscopy of isotopic mixtures of H(2)O and D(2)O. The strongly enhanced intramolecular bends of e(-)(H(2)O) and e(-)(D(2)O) produce single downshifted bands, whereas the e(-)(HOD) bend consists of two components: one slightly upshifted from the 1,446 cm(-1) bulk frequency to 1,457 cm(-1) and the other strongly downshifted to approximately 1,396 cm(-1). This 60 cm(-1) split and the 200 (120) cm(-1) downshifts of the OH (OD) stretch frequencies relative to bulk water reveal that the water molecules that are Franck-Condon coupled to the electron are in an asymmetric environment, with one proton forming a strong hydrogen bond to the electron. The downshifted bend and librational frequencies also indicate significantly weakened torsional restoring forces on the water molecules of e(-)(aq), which suggests that the outlying proton is a poor hydrogen bond donor to the surrounding solvent. A 1.6-fold thermodynamic preference of the electron for H(2)O is observed based on the relative intensities of the e(-)(H(2)O) and e(-)(D(2)O) bands in a 50:50 isotopic mixture. This equilibrium isotope effect is consistent with the downshifted vibrational frequencies and a relative reduction of the zero-point energy of H(2)O bound to the electron. Our results enhance the cavity model of the solvated electron and support only those models that contain water monomers as opposed to other molecular species.

Hydrogen Bond Dynamics in Water and Ultrafast Infrared Spectroscopy

Molecular dynamics simulations are used to examine two key aspects of recent ultrafast infrared experiments on liquid water dynamics. It is found that the relation between the OH stretch frequency and the length of the hydrogen bond in which the OH is involved, currently assumed to be one-to-one, is instead characterized by considerable dispersion and that the time scale currently interpreted in terms of a stochastic modulation by the surrounding solvent of a highly frictionally damped hydrogen bond system is shown to be governed by hydrogen bond-breaking and -making dynamics, whereas the motion of an intact hydrogen-bonded complex is underdamped in character.

Ab initio density functional investigation of the (001) surface of mordenite

Structural and acidic properties of the (001) surface of mordenite have been studied using density functional theory including generalized gradient corrections to the exchange-correlation functional. Our calculations, in agreement with experimental results, show that the surface structure of mordenite differs only moderately from the bulk structure, no reconstruction of the surface has been found. Part of the terminal silanol groups form weak hydrogen bonds with other framework oxygen sites, the lengths of hydrogen bonds vary in the range 1.9–2.6 Å depending on the position of the Al site. The OH-stretching frequencies for various acid sites in the mordenite framework have been calculated. In agreement with experiment, calculated OH-stretching frequencies of terminal silanol groups are shifted by about 100 cm−1 with respect to the Brønsted acid sites. Those silanol groups whose OH-stretching frequencies are modified by the presence of hydrogen bonds are shown to absorb in the region typical for the Brønsted acid sites.

Ab initio quantum mechanical modeling of infrared vibrational frequencies of the OH group in dioctahedral phyllosilicates. Part II: Main physical factors governing the OH vibrations

The physical factors responsible for the variability observed in OH infrared (IR) fundamentals in dioctahedral phyllosilicates, due to octahedral substitution of Al3+ by Mg2+, Fe2+, and Fe3+, are discussed here. The data analyzed consist of experimental frequencies as well as frequencies modeled using Density Functional Theory (DFT) calculations. The charge of the octahedral cations surrounding the OH is one of the main factors affecting both the OH stretch and the in-plane bend; cationic electronegativity and ionic radius play important roles in the stretch and bend modes, respectively. The mass of the octahedral cations does not affect the OH fundamental vibrations. The nature of the octahedral cations alone can explain most of the variability observed in the OH in-plane bend, making this fundamental vibration the most suitable for assessing octahedral composition. Discrepancies between modeled and experimental OH stretch frequencies indicate the existence of other factors governing this fundamental vibration. Further DFT calculations indicate that apical O atoms of the tetrahedral sheet with unsatisfied charges due to octahedral and/or tetrahedral substitutions can explain these discrepancies. The modeling results are utilized to predict the frequency of the OH stretch and in-plane-bend combination band that occurs near 4545 cm−1 (2.2 μm) in phyllosilicates. This band can be observed in imaging spectrometer data, allowing for the detection and analysis of phyllosilicates and other minerals in large natural systems. The modeling results confirm that the variability observed in the combination band of dioctahedral phyllosilicates reflects octahedral and, to a certain degree, tetrahedral composition, but not interlayer composition.

Hydrogen bonding in a sterically hindered alcohol

Quantum Cluster Equilibrium (QCE) theory is presented for liquid 2,2-dimethyl-3-ethyl-3-pentanol (DMEP). The cluster equilibria that dictate phase composition are determined by the rigorous techniques of quantum statistical thermodynamics in the canonical ensemble, based on the ab initio partition function. The validity of the resulting QCE cluster distribution is demonstrated by comparison with experimental temperature dependent NMR hydroxyl proton chemical shifts and OH-stretch vibrational frequencies. The results indicate that liquid DMEP is built upon monomers and dimers only.

Infrared spectroscopy of ethanol clusters in ethanol–hexane binary solutions

Temperature and concentration dependent infrared spectra were recorded for binary solutions of ethanol–hexane, ethanol–carbon tetrachloride, and ethanol–cyclopentane. The temperature range covered was 198 K to 298 K; concentrations ranged from 0.45 mole percent to 4.0 mole percent ethanol. Changes in the OH stretch frequency are consistent with the formation of ethanol clusters (EtOH)n, where n ranges from 2 to 6. The geometry, OH stretch frequency and proton chemical shift for 14 different ethanol clusters ranging from monomer to hexamer in cyclic and linear arrangements were investigated using density functional methods (B3LYP/6-31+G*). These clusters include both gauche and anticonformers of the monomer unit. The OH stretch frequency calculations were compared to experimental Fourier transform infrared measurements made as a function of concentration and temperature for dilute ethanol in hexane binary mixtures. Analysis of the O–H stretch frequency data (3100 to 3700 cm−1) indicate the presence of small clusters of ethanol. The data indicate that at the lower temperatures the clusters are primarily cyclic tetramers, pentamers, and hexamers. This infrared data is in excellent agreement with recent concentration and temperature dependent nuclear magnetic resonance chemical shift investigations that indicate a dramatic change in cluster size with concentration and temperature.