Study of hydrogen bonding in liquid crystalline solvent by Fourier transform infrared spectroscopy

A hydrogen-bonded complex between an aromatic acid and an enantiopure chiral amine has been dissolved in a nematic solvent, giving rise to a cholesteric medium. Fourier transform infrared (FT-IR) experiments have been performed at various temperatures on both sides of the cholesteric-isotropic transition. Liquid crystalline order provides significant enhancement to the strength of interaction, inducing a discontinuous jump in concentration of the complex at the cholesteric-isotropic transition.     

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding by matrix-isolation infrared spectroscopy

Experimental evidence for intramolecular blue-shifting C-H...O hydrogen bonding is presented. Argon matrix-isolation infrared spectra of 1-methoxy-2-(dimethylamino)ethane exhibit a band at 3016.5 cm-1. Spectral behavior with annealing indicates that this band is assigned to the most stable conformer, trans-gauche-(trans|gauche'), with an intramolecular C-H...O hydrogen bond. Density functional calculations show that this band arises from the stretching vibration of the C-H bond participating in the formation of the C-H...O hydrogen bond. The C-H bond is shortened by 0.004 A, and the C-H stretching band is blue-shifted by at least 35 cm-1 on the formation of the hydrogen bond. The (C)H...O distance is calculated as 2.38 A, which is shorter than the corresponding van der Waals separation by 0.3 A.     

Matrix isolation infrared and ab initio study of the hydrogen bonding between formic acid and water

The infrared spectra of the formic acid-water complexes isolated in argon matrices are reported. Both supersonic jet expansion and a conventional effusive source followed by trapping in solid argon at 10K are used to obtain the matrices. The experimental IR spectra are compared to the data obtained from high level ab initio (MP2) and DFT (B3LYP) calculations with 6-311++G(d,p) and aug-cc-pVTZ basis sets. The complex formation results in red shifts in the C=O and O-H stretching vibrations and a blue shift in the C-O stretching vibration of formic acid. The O-H stretching modes of water also exhibit pronounced red shifts. Both the MP2 and B3LYP calculations located three minima corresponding to cyclic HCOOH...H2O complexes with two hydrogen bond interactions. The binding energies are -10.3, -5.1, and -3.5 kcal mol(-1), respectively, for the three complexes at the MP2/ aug-cc-pVTZ level, corrected for the basis set superposition error (BSSE) using the Boys-Bernardi counterpoise scheme. Comparison of the calculated frequencies of the three complexes with the matrix IR spectrum reveals that the lowest energy complex is formed. In addition, a complex of formic acid with two water molecules is observed.     

Basicity of siloxanes,alkoxysilanes and ethers toward hydrogen bonding

Thermodynamic constants have been determined for hydrogen bonding of phenol to several siloxanes and alkoxysilanes, as well as to Me₃SiSCMe₃ and Me₃SiSSiMe₃. Alkoxysilanes are slightly weaker bases toward phenol than the isostructural ethers. Unstrained siloxanes have low values of △H for hydrogen bonding of 3.5–3.9 kcal/mol and are therefore distincatly weaker bases than either alkoxysilanes or ethers. Siloxanes with small SiOSi bond angles show increased basicity. Me₃SiSCMe₃ (△H 1.9 kcal/mol) and Me₃SiSSiMe₃ (△ 0.8 kcal/mol) are markedly less basic than dialkyl sulfides. The results are discussed using a molecular orbital model.     

On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.     

Geometrical behavior of hydrogen bonding patterns in the alpha-dodecyl-omega-hydroxy-tris(oxyethylene)-water system monitored by near infrared spectroscopy

Changes in the geometry of hydrogen bonding patterns in the alpha-dodecyl-omega-hydroxy-tris(oxyethylene) (C(12)E(3))-water system have been investigated by near infrared (NIR) spectroscopy. In the 5,300-4,600 cm(-1) region, the characteristic bands for C(12)E(3) and water can be separately investigated, since the combination bands of the OH stretching and its COH bending of alcohols are observed at 5,000-4,650 cm(-1), whereas the combination bands of the OH stretching and its HOH bending of water, at 5,300-5,000 cm(-1). The NIR result has revealed that the addition of water to C(12)E(3) promotes the formation of the OHcdots, three dots, centeredOHcdots, three dots, centeredO hydrogen bonds.     

A novel one-dimensional supramolecular inclusion compound linked by hydrogen bonding interaction

Crystal structure analysis shows the cucurbit[6]uril host and its tetrahydrofuran (THF) guest in the Pmn2₁ crystal lattice. The crystal data and refinement parameter for the title compound are: a = 14.027(3), b = 11.807(3), c = 16.760(4) Å, V = 2774.7(9) ų. For Z = 2 and Mw = 1529.52, the calculate density Dcal = 1.825 g/cm³. Hydrogen bonding interaction assembled the adjacent {[La(H₂O)₆Cl](C₄H₈O@C₃₆H₃₆N₂₄O₁₂)}²⁺ cations into a novel one-dimensional superamolecular chain.     

Oxonium ions from aqua regia: isolation by hydrogen bonding to crown ethers

The preparation and structures of a variety of oxonium ion tetrachloroaurate(III) salts isolated from aqua regia are reported. The new compounds are [(H(5)O(2))(2)(12-crown-4)(2)][AuCl(4)](2) (1), [(H(7)O(3))(15-crown-5)][AuCl(4)] (2), [(H(5)O(2))(benzo-15-crown-5)(2)][AuCl(4)] (3), [(H(3)O)(18-crown-6)][AuCl(4)] (4), [(H(5)O(2))(dibenzo-24-crown-8)][AuCl(4)] (5), [(H(5)O(2))(4-nitrobenzo-15-crown-5)(2)][AuCl(4)] (6), [(H(3)O)(4-nitrobenzo-18-crown-6)][AuCl(4)] (7), [(H(11)O(5))(tetrachlorodibenzo-18-crown-6)(2)][AuCl(4)] (8), and [(H(7)O(3))(dinitrodibenzo-30-crown-10)][AuCl(4)] (9). A significant correlation between the degree of proton hydration and crown ether size is observed. Aryl crown ethers are nitrated in concentrated aqua regia, but nonnitrated products may be obtained in a dilute solution of aqua regia by reaction with aqueous HAuCl(4).     

The effect of cooperative hydrogen bonding on the OH stretching-band shift for water clusters studied by matrix-isolation infrared spectroscopy and density functional theory

Infrared spectra of the water clusters have been measured in the N2 + O2 matrix. The aggregation process of water in the matrix has been monitored by annealing the deposited samples up to 40 K and UV irradiation. The monomer, dimer, cyclic trimer and cyclic pentamer are found as water clusters in the matrix. For the hexamer, several structures such as chair, cage, prism, bag 1 and/or book 1 are likely to exist. By UV irradiation, the cyclic pentamer is predominantly formed from the monomer and dimer. On the other hand, by annealing the deposited sample, several hexamers are formed. The theoretical calculation for water clusters has revealed that the formation of one hydrogen bonding in a hydrogen-bonded chain cooperatively enhances or diminishes the strength of another hydrogen bond. Both proton donor (D) and acceptor (A) participating in a hydrogen-bonding pair DA are capable of forming hydrogen bonding with the other water molecules; D can additionally accept two protons and donate one proton, and A can additionally donate two protons and accept one proton. We have proposed the classification of hydrogen-bonding patterns considering the cooperativity, denoting as d'a'DAd'a', where d and a are integers indicating the number of proton donors and acceptors to D (the single prime) and A (the double prime), respectively. Then, a magnitude given by MOH = -d' + a' + d' - a' has been introduced, which is very useful for connecting the hydrogen-bonding patterns to their OH wavenumbers. As a result, it is revealed that the OH stretching bands of water clusters are characterized by eight indicators (free and MOH = -2, -1, 0, 1, 2, 3 and 4). The classification proposed here is applicable to the OH band analysis for the hydrogen-bonded water and alcohols in a condensed phase.     

Quantitative determination of acyclovir in plasma by near infrared spectroscopy

The aim of this study was to assess the feasibility of near infrared spectroscopy (NIRS) for analysis of acyclovir in plasma. This methodology was based on the direct measurement of the transmission spectra of liquid samples and a multivariate calibration model (partial least squares, PLS) to determine the acyclovir concentration in plasma sample. The PLS calibration set was built on using the spiked samples by mixing different amounts of acyclovir. Concentration of acyclovir in the plasma samples was calculated employing a 6-factors PLS calibration using the spectral information in the range of 6102-5450 cm^− 1. The root mean square errors of prediction (RMSEP) found was 1.21 for acyclovir. The developed PLS-NIRS procedure allows the determination of 120 samples/h does not require any sample pretreatment and avoids waste generation.     

1H nmr study of hydrogen bonding of fluorinated alcohols with ethers

The hydrogen bonding of TFE and HFIP with t-BuOCH₃ (1) and PhOCH₃ (2) was studied using ¹H nmr. The Δ δ values of carbon-bound hydrogens in 1 and 2 show good linear correlation with the alcohol acidity.     

Computational study of hydrogen bonding interaction between formamide and nitrosyl hydride

The hydrogen bonding interaction of formamide–nitrosyl hydride complex has been investigated using density functional theory (DFT) and ab initio method. The natural bond orbital (NBO) analysis and atom in molecules (AIM) theory were applied to understand the nature of the interaction. Two stable geometries are found on the potential energy surface, a six-membered cyclic structure of complex A and a seven-membered cyclic structure of complex B, characterized by AIM analysis. Complex A is less stable than complex B. It is confirmed that there are contractions of CH (compared with the monomer HCONH₂), NH bonds (compared with the monomer HNO) and the corresponding stretching vibrational frequencies are blue-shifted, while there is an elongation of the NH bond and the corresponding stretching vibrational frequency is red-shifted, relative to those of the monomer HCONH₂. From NBO analysis, it is evident that the electron densities in the σ^* (CH) and σ^*(NH) of the complex A are less than those of the monomers HCONH₂ and HNO, which strengthen CH and NH bonds. Furthermore, the increases in s-characters of X also strengthen XH bonds.     

Molecular mechanics study of conformational trends in simple alcohols and ethers. II. Intramolecular hydrogen bonding

In this article we present an extension of our modified MM2(80) force field MM2MOD in which a potential function for hydrogen bonding in alcohols and ethers is included. The results of applying MM2(85), MM2(87), and MM2MOD on ethylene glycol, 2-methoxyethanol and 1,3-propanediol are reported and compared with available experimental data and ab initio results. It is concluded that hydrogen bonding plays an important role in determining the molecular conformations of these systems. © 1992 by John Wiley & Sons, Inc.     

Pressure-dependent Fourier transform infrared spectroscopy of a poly (ester urethane)

The effects of hydrostatic pressure upon (1) a segmented poly (ester urethane), (2) a hydrolytically degraded sample of the same polymer, and (3) models for the polyurethane and polyester segments in this polymer have been studied by Fourier transform infrared spectroscopy using high-pressure diamond anvil cells (DACs). The pressure responses of the vibrational frequencies of specific functional groups of the poly (ester urethane) in the 0-100-kbar range are compared with data for individual segment models and the partially degraded sample. The results indicated that the polymer is highly stable in this pressure regime, with no measurable degradation or phase changes. Differences in the pressure dependency of specific infrared bands between the poly (ester urethane) sample and the partially degraded sample are slight and consistent with changes in hydrogen-bonding interactions and shorter chain lengths in the degraded sample.     

Low-temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline L-alanine

The 400-4000 cm(-1) FTIR spectra of pure NH and isotopically substituted (10 and 90% doped ND/NH) polycrystalline L-alanine were recorded in the temperature range 10-300 K. The observed temperature dependence and isotopic shifts behavior enabled to identify, in the spectra of the doped crystals, three well-separated bands ascribable to either the NH or ND stretching vibrations associated with the three different types of hydrogen bonds existing in the crystal. The observed red shifts of these bands relative to the frequency of a reference "free" NH (or ND) stretching mode were found to correlate well with the H-bond distances found in the crystal and provide an indirect way of estimating the enthalpies associated with each type of H-bond found in the crystal. In the low-frequency deformation and torsional spectral region (below 2000 cm(-1)), several bands, which were found to be affected by isotopic substitution, were identified as belonging to the NH3(+) group. Several bands show splitting at low temperatures, indicating the occurrence of a significant reorganization in the crystal structure, which with all probability results mainly from changes in the proton positions. Finally, the literature assignments of the IR spectra of both crystalline NH3(+) and ND3(+) L-alanine were revised taking into consideration their temperature dependence and behavior upon deuteration.     

Low temperature FTIR spectroscopy and hydrogen bonding in cytosine polycrystals

The FTIR spectra of both the pure NH and isotopically substituted ND (<10% and >90% D) polycrystalline cytosine were recorded in the range 400-4000 cm(-1) as a function of temperature (10-300 K). For the first time, uncoupled NH(D) stretching mode bands of amine and imine groups were observed in the spectra of isotopically diluted cytosine at low temperatures. These bands correspond to the three distinct H-bonds that are present in the crystal, in agreement with the available data obtained by structural methods. At least nine bands were observed below 1000 cm(-1) and, in consonance with their temperature and isotopic exchange behavior, were assigned to the NH proton out-of-the-plane bending modes. Six of these bands were found to correspond to additional "disordered" H-bonds, which could not be observed by structural methods. Empirical correlations of spectral and thermodynamic parameters enabled to estimate the contribution of the H-bonds to the sublimation enthalpy of the crystal, in agreement with independent experimental data.     

复方氯丙那林质量检控的近红外光谱快速分析

基于近红外光纤漫反射技术,利用偏最小二乘法分别建立了复方氯丙那林胶囊的三种药效成分盐酸氯丙那林、盐酸溴己新和盐酸去氯羟嗪的快速同时测定方法。所建立的盐酸氯丙那林、盐酸溴己新和盐酸去氯羟嗪的定量分析多元校正模型的相关系数分别为99.7%、99.4%和99.0%,校正集的均方根残差分别为0.028、0.145和0.250,预测均方根误差分别为0.055、0.120和0.210。由于该方法是在不经任何预处理的情况下的光纤快速同时分析,因此可用于复方氯丙那林的过程质量控制。     

Nonconventional hydrogen bonding between clusters of gold and hydrogen fluoride

The bonding patterns between small neutral gold Au(3 < or = n < or = 7) and hydrogen fluoride (HF)(1 < or = m < or = 4) clusters are discussed using a high-level density functional approach. Two types of interactions, anchoring Au-F and F-H...Au, govern the complexation of these clusters. The F-H...Au interaction exhibits all the characteristics of nonconventional hydrogen bonding and plays a leading role in stabilizing the lowest-energy complexes. The anchor bonding mainly activates the conventional F-H...F hydrogen bonds within HF clusters and reinforces the nonconventional F-H...Au one. The strength of the F-H...Au bonding, formed between the terminal conventional proton donor group FH and an unanchored gold atom, depends on the coordination of the involved gold atom: the less it is coordinated, the stronger its nonconventional proton acceptor ability. The strongest F-H...Au bond is formed between a HF dimer and the singly coordinated gold atom of a T-shape Au4 cluster and is accompanied by a very large red shift (1023 cm(-1)) of the nu(F-H) stretch. Estimations of the energies of formation of the F-H...Au bonds for the entire series of the studied complexes are provided.