Fundamental OH Research Articles

Cholesterol complexes with some proton acceptors in benzene and toluene solutions

Cholesterol complexes with tri-n-butyl phosphate, tri-n-octylamine, N,N-dimethylacetamide, and cyclohexanone in benzene and toluene solutions were studied using conventional IR spectroscopy. The spectra were recorded in the region of fundamental OH stretching (3,700–3,100 cm−1) at 298 K. The experimental spectra were resolved into bands corresponding to the cholesterol monomer and particular oligomeric and complex species. The formation constants of complexes were determined from the-least squares plots of the linearized expressions of Bjerrum’s formation function. The stoichiometry of complexes was also identified in this way. The identification of the particular resolved bands was performed from their location, and from the dependence of their intensity on the cholesterol monomer and free base concentration.

Water speciation in sodium silicate glasses based on NIR and NMR spectroscopy

Water speciation in hydrated Na 2O·2SiO 2 (NS2), Na 2O·4SiO 2 (NS4), and Na 2O·6SiO 2 (NS6) glasses was analyzed by near-infrared (NIR) spectroscopy and low temperature static 1H nuclear magnetic resonance (NMR) spectroscopy. For each composition 6–9 glasses containing between 0.5 and 7.0 wt.% total water (measured by Karl–Fischer titration) were used to calibrate the molar absorption coefficients for the NIR combination bands near 4500 cm − 1 (OH groups) and near 5200 cm − 1 (H 2O molecules). Noticeable disagreement was found between the water speciation derived from NIR spectra using an internally consistent calibration based on total water content and the water speciation determined by 1H NMR spectroscopy. The discrepancies are more pronounced for the evaluation of NIR peak areas (differences up to 55% in OH group content) than for the evaluation of peak heights (differences up to 35% in OH group content). Based on the NMR data we performed a new calibration for the NIR combination bands of the hydrous sodium silicate glasses. The molar absorption coefficients for the 4500 cm − 1 band ( ε 4500) and the 5200 cm − 1 band ( ε 5200) noticeably decrease with increasing Na 2O content of the glasses from NS6 to NS2. The ε values for both bands also decrease with total water content in NS4 and NS6 glasses. The variation of ε values may be due to changes in the relative abundance of water subspecies, i.e. species exposed to strong or weak hydrogen bonding. Another explanation could be an incomplete separation of the combination bands from the tail of the fundamental OH stretching vibration bands and from the unassigned water-related band at 4000 cm − 1 . Using the NMR-supported NIR calibration we calculated water species concentrations in the sodium silicate glasses as a function of total water content. At a total water content of 6.0 wt.%, the amount of water dissolved as OH groups is noticeably higher in the depolymerized glasses NS2 and NS4 (∼ 3.0 wt.%) than in the less depolymerized NS6 (∼ 2.5 wt.%). This observation implies that non-bridging oxygen, charge-compensated by sodium, promotes the formation of OH groups. No significant difference in water speciation was found between rapidly quenched glasses (∼ 150 K/s) and more slowly cooled glasses (∼ 2 K/s).

Polarized IR studies of silica glasses exposed to polarized excimer radiation

Silica glass exhibits a permanent anisotropic response, polarization-induced birefringence (PIB), when exposed to short-wavelength polarized light. This behavior has been correlated with the OH content of the glass. In this paper we describe polarized infrared studies of silica glasses of different OH content exposed with polarized 157 nm laser light. Changes in the fundamental OH band as a consequence of exposure are shown. We find differential bleaching of a particular OH band where OH species that are oriented parallel to the incident exposing polarization undergo greater bleaching than those oriented perpendicular. The preferential bleaching as a function of exposure time correlates strongly with the evolution of PIB, leading to a bleaching model of OH that is causally linked to PIB.

Dehydroxylation, proton migration, and structural changes in heated talc: An infrared spectroscopic study

The high-temperature dehydroxylation and structural change of talc, Mg3(Si2O5)2(OH)2, has been investigated in detail using infrared (IR) spectroscopy. The data (in the region of 20–12000 cm–1) on quenched samples show that absorptions from structurally incorporated OH and OD, as well as NH4-like species, have similar temperature dependences in dehydroxylation. The OH species exhibit weak variation in frequency on heating, which is inconsistent with thermally induced weakening of O-H bonds. Dehydroxylation in talc is a complex process that involves proton migrations and formation of new OH species. Additional fundamental OH bands near 3665 and 3745 cm–1 became detectable near 900 °C. On further heating the former disappear near 1200 °C, whereas the latter became undetectable near 1350 °C. The occurrence of CO2 is observed in samples quenched between 600 and 1250 °C. The phonon spectrum (20–1500 cm–1) of the dehydroxylate (obtained by annealing the sample at 1000 °C) gives features significantly different from that of talc, indicating the loss of the original layer structure. The IR data imply that the talc dehydroxylate consists of disordered SiO2 and enstatite (MgSiO3). Although MgSiO3 exists dominantly in the form of orthoenstatite, the characteristic bands of clinoenstatite phase are found to coexist in the samples treated at 1000 °C. The IR data from in situ measurements show that protons become mobile at temperatures below the dehydroxylation and an extra OH species near 3500 cm–1 develops on heating. This new species is not quenchable, and it decreases intensity on cooling and disappears at room temperature. The in situ results also indicate external carbon-related substances can diffuse into talc during dehydroxylation.

Anomalous volumetric behavior of water-hexane and water-decane mixtures in the vicinity of the critical region as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with hexane and decane were measured at temperatures and pressures in the 473-648 K and 70-350 bar ranges, respectively. Volumetric concentrations of water and the hydrocarbons in the mixtures were obtained from absorption intensities of the fundamental OH stretching band of HDO and combination transitions of the hydrocarbons. Using both the concentrations, densities of the aqueous mixtures were estimated and compared with densities before mixing, which were calculated using literature densities of the neat liquids. It is found that anomalously large volume expansion on mixing occurs in the vicinity of the critical region of the mixtures.

Influence of molecular hydrogen diffusion on concentration and distribution of hydroxyl groups in silica fibers

To study the hydroxyl (OH)-group contamination mechanisms in silica-based optical fibers, the transmission spectra of substrate tubes and fiber preforms made from various types of silica glasses ("Suprasil F-300," KS-4V, and KUVI) are measured by the method of infrared Fourier spectroscopy in a wavelength region of 2-5 /spl mu/m. Due to the intensity of the fundamental OH stretching vibration band, the absorption coefficient, concentration, and a distribution profile of OH groups across the aforesaid samples are calculated. It is found that using an oxyhydrogen burner in the modified chemical vapor deposition (MCVD) process of manufacturing preforms and fiber drawing, the main source of impurity OH groups can be the molecular hydrogen H/sub 2/ penetrating into glass much deeper than the OH groups diffusing from the substrate tube surface. A simple model explaining the formation and diffusion of OH groups into a fiber core and cladding is proposed. It is shown that heating tubes and preforms in a flame of oxyhydrogen burner during fiber fabrication causes a significant OH-group content growth (almost by two orders of magnitude) near to the outer preform surface. Using substrate tubes made from Suprasil F-300 glass, optical fibers are fabricated having a silica core and fluorosilicate reflecting cladding with optical losses of 0.3 dB/km at 1.55 /spl mu/m and a refractive-index difference between core and cladding /spl sim/1/spl middot/10/sup -2/.

Refined relationship between the position of the fundamental OH stretching and the first overtones for clays

The aim of this paper is to determine a relationship between the wavenumbers of the first OH-stretching overtones (W2νOH) and the wavenumbers of the OH-stretching fundamentals (WνOH) to help to interpret the near-infrared (NIR) spectra. The first overtone (2νOH) bands appear at wavenumbers less than twice those of the fundamental bands (νOH), due to the anharmonic character of vibrations, X = W2νOH/2 - WνOH, with X being the anharmonicity constant. Talc samples with various crystal chemistries are used to solve the equation and the experimental data are well fitted with X = −85.6 cm−1. As far as the authors are aware, it is the first time that the anharmonicity constant for the OH-stretching vibrations is determined for phyllosilicates. The anharmonicity constant remains almost unchanged for several types of clay samples. Therefore the relation, established from talc samples because their absorption bands are narrow and their wavenumber range of OH vibrations is wide, can be used for any other clay minerals.

Characterization of hydrogen bonds in the interactions between HO 2 radical and amides

The hydrogen bonds formed between the hydroperoxyl radical and formamide, acetamide, and urea were characterized using geometric, energetic, along with the AIM analyses of the MP2 densities with the UMP2(full)/6-311G(d,p) method. Energetic analysis at G2MP2 level proved that the studied complexes are stable. The fundamental anharmonic OH vibrational frequencies calculated at this level of theory were 2840, 2749, and 2825 cm −1 for the complexes of HO 2 with formamide, acetamide and urea, respectively. The results allowed the characterization of the hydrogen bonds formed in the complexation of the amides with the hydroperoxyl radical.

Hydroxide in kyanite: A quantitative determination of the absolute amount and calibration of the IR spectrum

Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by ^(15)N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H_2O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750–3100 cm^(−1) region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle-derived olivine analyzed to date contains 240 ppm wt. H_2O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra.

DISORDERED Mg-BEARING OLENITE FROM A GRANITIC PEGMATITE AT GOSLARN, AUSTRIA: A CHEMICAL, STRUCTURAL, AND INFRARED SPECTROSCOPIC STUDY

The core and rim of a short prismatic dark brown tourmaline crystal (10 mm in diameter) from a granitic pegmatite near Goslarn, Lower Austria, were structurally and chemically characterized, including H2O determination and Mossbauer analysis. The optimized formula, calculated using chemical and structural data for the core, is X (Na0.64Ca0.11K0020.23) Y (Al1.58Mg0.91Fe 2+ 0.41Ti0.10) Z (Al4.90Mg1.10) T (Si6.00) B3O27 [(OH)3.07O0.90F0.03], with a 15.9149(3), c 7.1757(2) A, R = 0.014. The optimized formula for the rim is X (Na0.71Ca0.10K0010.18) Y (Al1.42Mg1.10Fe 2+ 0.39Ti0.09) Z (Al4.94Mg1.06) T (Si5.95Al0.05) B3O27 [(OH)3.05O0.92F0.03], with a 15.9238(4), c 7.1822(2) A, R = 0.014. Mg and Al are highly disordered in this sample of tourmaline, and the O1 site is occupied by ~[O0.9(OH)0.1]. Such samples of magnesian olenite provide a very good example of disorder driven by the short-range requirements of O 2– at the O1 site that is associated with the ~2Al + Mg configuration at the coordinating Y sites. To date, these tourmaline samples have the highest Al content at the Y site (up to ~1.6 apfu) for Mg-rich tourmaline. Three quadrupole-splitting distributions were used to represent the contributions of Y-site Fe 2+ in the Mossbauer spectrum. The absence of Fe 3+ reflects the low fugacity of oxygen in this pegmatite. The infrared (IR) spectrum shows four bands. These bands, at ~4528, 4457, 4358 and 4241 cm –1 , are combinations of OH stretching + MOH bending motions. In the fundamental OH region, only three bands at ~3737, 3630 (sh) and 3552 cm –1 are clearly observed. The relatively sharp bands and the very low R-values of the crystal-structure refinements indicate a high degree of crystallinity. The strong band at ~3552 cm –1 can be assigned to O–H3 stretching, which is in agreement with an occupancy of ~(OH)3 at the V site. The band at ~3630 cm –1 , which can be assigned to O–H1 stretching, is relatively small. This is in agreement with the occupancy of ~[O0.9(OH)0.1] at the W site. We assess the assignment of Mg-rich tourmaline to dravite or olenite, and different methods to approximate the Al–Mg order, where there is no possibility for a single-crystal determination of the structure.

Theoretical Analysis on the Fundamental and Overtone OH Stretching Spectra of Several Simple Acids and Alcohols

We calculated the fundamental and overtone OH stretching vibrational spectra for the following alcohols and acidsmethanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, 2,2,2-trifluoroethanol, acetic acid, trifluoroacetic acid, and nitric acidunder the local mode model. We obtained the potential energy surface (PES) and the dipole moment function (DMF) by hybrid density functional theory method and performed vibrational calculation using the grid variational method. The theoretical results were in good agreement with the experimental observations. It was found that the molecular shape, such as the rotational conformation, is very important in the description of the OH stretching vibrational spectra. For alcohols with rotational conformers, such as ethanol, 1-propanol, and 2-propanol, we found that the isomer with the alkyl group in the trans position of the vibrating OH bond has a larger transition energy and a slightly stronger absorption intensity. We analyzed the first and second derivative terms of the DMF of these molecules to obtain insight on the difference in the absorption intensities. In addition, for the fundamental spectra, we investigated the difference between the local and normal mode vibrational calculation results.

Hydroxide in olivine: A quantitative determination of the absolute amount and calibration of the IR spectrum

Olivine is an important host of hydrogen in the Earth's upper mantle, and the OH abundance in this mineral determines many important physical properties of the planet's interior. To date, natural and experimentally hydrated olivines have been analyzed by uncalibrated spectroscopic methods with large (±100%) uncertainties in accuracy. We determined the hydrogen contents of three natural olivines by 15N nuclear reaction analysis and used the results to calibrate the common infrared (IR) spectroscopic method for quantitative hydrogen analysis of olivine. OH content (expressed as parts per million H2O by weight) is 0.188 times the total integrated absorbance of the fundamental OH stretching bands in the 3750–3100 cm−1 region. The results indicate that an upward revision of some previous determinations by factors of between 2 and 4 is necessary. The most hydrous naturally occurring mantle‐derived olivine analyzed to date contains 240 ppm wt. H2O. Retrospective application of this calibration to experimentally hydrated olivines may be limited by spectral differences in some cases and by the previous use of nonpolarized IR spectra.

Vibrational and Electronic Spectroscopy of Sulfuric Acid Vapor

We have measured and analyzed the infrared (IR), near-infrared (NIR) and vacuum ultraviolet (VUV) absorption spectra of vapor-phase sulfuric acid (H2SO4). Transitions associated with the fundamental vibrations and the first and second OH stretching overtones of this molecule have been identified. Our measured vibrational spectrum extends and complements those in the literature and agrees well with ab initio calculated spectra. We have calculated the fundamental and overtone OH stretching intensities with the use of a simple anharmonic oscillator local-mode model with ab initio calculated dipole-moment functions. Theory and experiment have been used to investigate the OH stretching vibrational overtones of H2SO4 and indicate that the OH stretching mode in H2SO4 is an important aspect of the spectroscopy of this atmospheric chromophore. We have attempted to measure the VUV spectrum of vapor-phase sulfuric acid and, in the absence of observed bands, give upper bounds to the photoabsorption cross section. We conclude that H2SO4 absorbs in the IR and NIR regions, with the OH stretching vibration playing the dominant role, and that the electronic excitation of H2SO4 will only be significant at very high energies, well above those available from the sun in the earth's atmosphere.

Physical properties of selected illites, beidellites and mixed-layer illite–beidellites from southwestern Idaho, and their infrared spectra

The silver–gold ore deposits of the De Lamar mine, the mines in Florida Mountain and the mines in War Eagle Mountain occur in conjunction with large seams of clay minerals, which consist mainly of mixed-layer illite–beidellite. When saturated with groundwater, these clay seams have caused slope failures during mining and processing of ore. The illite–beidellite clays have effective internal friction values, Ø e, as low as 4° and cementation C values of about 1.0 kg f/cm 2. The Fe-beidellite used for the clay core of the mill pond dam has an average Ø e value of 8.3° and C value of 0.79 kg f/cm 2, with an average permeability ( K-value) of 5.6×10 −7 cm/s. The fundamental OH spectra of beidellite, illite and muscovite are similar with beidellite having bands near 3635, 3654 and 3653 cm −1. Montmorillonite has one Al–OH libration band near 915 cm −1, whereas beidellite has a second band near 942 cm −1. In like manner, illites and muscovites have bands from 928 to 933 cm −1, as well as the Al–OH libration bands from 912 to 917 cm −1. The OH libration bands vary both in position and intensity with particle orientation and heating. Combination bands for Fe-bearing muscovite show moderate bands at 4451 cm −1 for ferrous muscovite and at 4471 cm −1 for ferric muscovite. These bands also are present for illites. The dominant Al–OH combination band wave numbers of muscovites form a linear relationship with the Al 2O 3 muscovite contents, but not so precisely for illites. Chemical analysis of illites indicates that the compositions are a continuum into muscovites. Illites from the Miller–Walters mine contain a rather large amount of certain trace elements, whereas the adjacent beidellites do not.

Hydroxyl groups in GeO2 glass

The shape of the fundamental OH stretching band of GeO2 glass was analyzed before and after hydrostatic compression at 5.2 GPa. The results were interpreted using quantum-chemical modeling of the incorporation of OH groups and H2O molecules into the GeO2 glass network.

Infrared spectroscopy of ArOH: A direct probe of the Ar+OH X2Π potential energy surface

An infrared-ultraviolet (IR-UV) double-resonance technique has been implemented to obtain the infrared spectrum of ArOH in the vicinity of the fundamental OH stretch at 2.8 μm. A rotationally resolved spectrum of the fundamental OH stretching band of ArOH is observed at 3567.85(1) cm−1 (origin). A combination band, involving both OH stretch and intermolecular bending excitation, is identified at 3577.00(1) cm−1 (origin). The intermolecular energy of the excited bending state provides a direct measure of the anisotropy of the Ar+OH X2Π interaction potential. The rotational structure of the combination band reveals a large splitting between parity components with the same total angular momentum in the excited bending state [0.69(1) cm−1 for J=32]. The experimentally derived parity splitting is compared with previous experimental and theoretical determinations of this parameter. The parity splitting associated with the excited bending state reflects the change in the intermolecular potential when the pπ orbital containing the unpaired electron of OH lies in or out of the ArOH plane.

Transformation of the Near-Infrared Bands of Cellulose Surface Hydroxyls under the Influence of Adsorbed Water Molecules

Near-infrared absorption spectra of sulfite cellulose with a varied adsorbed water content were studied. Analysis of the spectra has been made on the basis of previously published relations and results of the cellulose surface hydroxyls' interaction with absorbed water. Spectra of the OH overtone region of 1.3–1.65 μm were deconvoluted to components of cellulose volume and surface hydroxyls as well as to those of absorbed water. Besides the 1.53–1.55 μm component of “bound” water, the 1.42–1.44 μm component of “free” water starts to grow as the surface coverage exceeds 1.5. Comparison of the peak positions of these water components with those of liquid water suggests that bound water is constituted of hydrogen-bonded molecules. The 1.42–1.44 μm component of free water implies nonhydrogen-bonded and partially hydrogen-bonded molecules. The whole 1.363 μm band and a part of the 1.424 μm band of surface hydroxyls turn into the 1.52–1.53 and 1.57–1.59 μm peaks, respectively, after attachment of H2O molecules. The red shift of the surface bands by approximately 780 cm−1 caused by the adsorbate is consistent with a shift of the fundamental OH band of silica gel. The possible chemical, morphological, and physical causes of the two 1.363 and 1.424 m surface hydroxyl bands are discussed.

Self-association of cholesterol in benzene and toluene solutions

The self-association of cholesterol in dilute benzene and toluene solutions was investigated by conventional infrared spectroscopy. The sample spectra, recorded in the fundamental OH stretching range, were resolved into the bands of functionally different OH groups of associated cholesterol and its predominant species identified by analysis of their absorbances. The formation constants of oligomers were derived from monomer absorbances measured as a function of cholesterol concentration. In addition to the monomers A 1, open à 2 (Δ H̃ 2=−11±1 kJ mol −1) and cyclic dimers  2 (Δ Ĥ 2=−24±2 kJ mol −1) in benzene and open dimers à 2 (Δ H̃ 2=−12±1 kJ mol −1) and tetramers A 4 (Δ H 4=−47±6 kJ mol −1) in toluene were established as the prevailing species.

Self-association of cholesterol in some chlorinated hydrocarbon solvents

The self-association of cholesterol in dilute solutions in 1,2-dichloroethane, trichloromethane and tetrachlorormethane and over the temperature range 298–328 K was investigated using conventional infrared spectroscopy. The information on the size of the predominant cholesterol species was obtained by numerical processing of the solution spectra, recorded in the fundamental OH stretching range. Formation constants were derived from monomer absorbances measured as a function of cholesterol concentration. The following prevailing species and their enthalpies of formation were established: the monomer A 1 and monomer-solvent complex A 1* (Δ H 1*=−9±3 kJ mol −1) in 1,2-dichloroethane; the monomer and open dimer ( Ã 2) (Δ H̃ 2=−15.0±1.2 kJ mol −1) in trichloromethane; the monomer, open trimer ( Ã 3) (Δ H̃ 3=−31±3 kJ mol −1) and cyclic hexamer ( Â 6) (Δ Ĥ 6=−70±10 kJ mol −1) in tetrachloromethane.

Self-Association of Medium-Chain Alcohols in n-Decane Solutions

Self-association of medium-chain alcohols in n-decane solutions has been studied by infrared absorption of the fundamental OH stretching vibration. The alcohols investigated were 1-propanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-butanol, 1-pentanol, and 1-hexanol. Infrared spectra were acquired for varying alcohol molalities, the highest concentration being 0.2 mol/kg. The spectra for each alcohol were collected in a data matrix. The bilinear multicomponent data were successfully resolved into spectra and concentration profiles by a multivariate method. The result indicates that monomers dominate the spectral variance in the low-molality region, while cyclic oligomers dominate in the upper concentration range. It further indicates that minor amounts of open-chain aggregates may be present. The monomer and cyclic tetramer appear to be the dominant species, while the amount of open-chain aggregates was negligible even in the low-molality region. The equilibrium constants for the monomer–tetramer association reactions ( K1–4) were calculated by a least-squares method. The calculated values for the equilibrium constants, based on the molality, range from 138 to 106 for the linear alcohol molecules. The result shows that 1-butanol, 1-pentanol, and 1-hexanol have similar constants, while 1-propanol displays a markedly higher value. The equilibrium constants obtained for 2-methyl-1-propanol and 2-methyl-2-propanol were 77 and 39, respectively. The considerably lower values for the branched alcohol molecules indicate that steric interaction between the chain prevents self-association into larger aggregates.