Intramolecular and intermolecular hydrogen bonds in aminophenols

IR-Fourier spectroscopy methods are adopted to study intramolecular and intermolecular hydrogen bonds that form in CCl₄ solutions of aminophenol derivatives and in a solid phase of these compounds pressed in KBr. If a hydroxyl group is present in the molecule in the ortho-position to an amino group, then intramolecular interactions between OH and NH groups will take place in aminophenol solutions. Intramolecular O–H⋅⋅⋅O=S=O and N–H⋅⋅⋅O=S=O hydrogen bonds are found in solutions of compounds containing a sulfonamide fragment. Additional acylation of the amino group causes an intramolecular O–H⋅⋅⋅O=C hydrogen bond to form in solutions. Functional groups OH, NH, SO₂, and C=O interact with one another in various ways in the solid phase to form intermolecular hydrogen bonds in aminophenols.     

Manifestation of intramolecular hydrogen bonds in the IR spectra of bioactive aminophenols

The intermolecular interactions in solutions of aminophenols in CCl₄ are studied by the methods of IR Fourier spectroscopy. If the hydroxyl groups of aminophenol molecules occupy the ortho positions with respect to the amino groups of the molecules, the hydroxyl and amino groups are involved in intramolecular interactions with the formation of hydrogen bonds O-H...N and N-H...O. The introduction of two additional tert-butyl groups into the structure of the aminophenol molecule facilitates the formation of O-H...N bonds and impedes the formation of N-H...O bonds. The occurrence of the carbonyl group in the structure of aminophenols leads to the formation of intramolecular hydrogen bonds O-H...O=C. The introduction of the methyl groups into carbonyl-containing aminophenols transforms the O-H...O=C bond into the hydrogen bond N-H...O=C.     

The Infrared and 1H-NMR Spectra of 8-Hydroxyquinoline Adducts of 8-Hydroxyquinoline Complexes of Dioxouranium(VI), Thorium(IV) and Scandium(III)

The ¹H-nmr and infrared spectra of the complexes [M(ox)_n(Hox)] where M = UO₂ (n = 2), Th (n = 4) or Sc (n = 3) and Hox = 8-hydroxyquinoline are discussed. The nmr spectra of the adducts are uninformative with respect to the bonding and structure of these molecules since they dissociate in solution. The solid state ir spectra show that the adducted molecule of 8-hydroxyquinoline is bound to the metal through the phenolic oxygen, the proton forming an intramolecular hydrogen bond between the nitrogen atom of the adducted molecule and the oxygen atom of a neighbouring chelate ring. The mid-and far-ir spectra are reported for the first time and assignments for the δN-H, νM-O and νM-N modes have been made.     

密度泛函理论计算内掺氢分子富勒烯H2＠C60及其二聚体的几何结构和电子结构

采用密度泛函理论中的广义梯度近似(generalized gradient approximation,简称GGA),对内掺氢分子富勒烯H₂＠C₆₀及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H₂＠C₆₀单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C₆₀和C₁₂₀中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化. 关键词： 几何结构 电子结构 密度泛函     

Hydrogen desorption processes in Li-Mg-N-H systems

Li-Mg-N-H systems composed of Mg(NH₂)₂ and LiH with various ratios can reversibly store a large amount of hydrogen under the temperature condition above 150 °C. These composites with 3:6, 3:8 and 3:12 ratio of Mg(NH₂)₂ and LiH have been independently reported by four groups as promising candidates of high performance hydrogen storage materials possessing the reversibility and the high capacity. In any cases, an interaction between NH₃ and LiH plays an important role for the progress of hydrogen desorbing and absorbing reactions. For the hydrogen desorption process, the NH₃ molecule generated from Mg(NH₂)₂ reacts with LiH, forming LiNH₂ and H₂. Especially, under an equilibrium condition, in situ diffraction results indicated that the single phase of LiNH₂·MgNH (LiMgN₂H₃) could be generated other than the separated two phases. As a next step, the NH₃ molecule generated from LiNH₂ reacts with LiH, desorbing H₂. As a result, the dehydrogenated phase was evaluated to be Li₂NH·MgNH (Li₂MgN₂H₂) or separated two phases, in which the final phase should depend on the experimental conditions. Thus, if the amount of LiH is enough to react with NH₃, the hydrogen desorption processes are described by the NH₃ generation from the corresponding amides and the imide.     

Manifestation of Intermolecular Interactions in the IR Spectra of 8-Azasteroids

We have investigated the intermolecular interactions of 8-aza-D-homogona-1,3,5(10),13-tetrane-12,17a-dione and 2,3-dimethoxy-8-azagone-1,3,5(10),13-tetran-12,17-dione with CHCl₃, binary solvents CHCl₃–CH₃OH, CCl₄–CHCl₃, and CCl₄–CH₃OH and also in the solid phase, which manifest themselves in the IR spectra. When the C=O groups of the studied 8-azasteroids form hydrogen bonding with the OH groups of alcohol, the frequencies (C=O) change insignificantly. We have found that they are higher than the corresponding frequencies in the IR absorption spectra of solid-phase samples, which is attributable not only to the effect of the medium but also to the possible shortened contacts of the C=O groups with the CH₃ and CH₂ groups of the molecules under study.     

Internal hydrogen bond,torsional motion,and molecular properties of 2-methoxyethylamine by microwave spectroscopy: Methyl barrier to internal rotation for 2-methoxyethanol

The microwave spectra of four substituted isotopic species of 2-methoxyethylamine (NH₂, NHD, NDH, ND₂) have been assigned. The molecule is found to exist in a gauche form with an intramolecular hydrogen bond of the NH?O type. The four possible sets of the amino hydrogen r_s corrdinates give different H?H distances, probably because the -NH₂ group is involved in large amplitude vibrations and because of changes in the heavy atom positions arising from the deuteration of the hydrogen bond. For the most abundant species many vibrational states have been analyzed and assigned to the two possible CO torsions in the molecule. A value V₃ = 3150 ± 50 cal/mol was found for the methyl torsional barrier and V₁ = 9 ± 3 kcal/mol for the other CO torsional barrier. A third set of observed vibrational satellites is probably assignable to the CC torsion. The determination of the dipole moment and of the quadrupole coupling constants gave values which were not in good agreement with those predicted from nonhydrogen bonded molecules. In addition a value V₃ = 3100 ± 100 cal/mol was calculated for the CH₃ torsional barrier in the related 2-methoxyethanol, using previous experimental data (Canad. J. Chem.50, 1149–1156 (1972)).     

Investigation of the IR spectra of weakly hydrogen-bonded complex Cl<Subscript>3</Subscript>CH…O(CD<Subscript>3</Subscript>)<Subscript>2</Subscript> in a cryosolution in liquid krypton

The IR absorption spectra of cryosolutions of chloroform, dimethyl ether, and their mixtures in liquefied krypton have been measured. It has been shown that, in solutions of mixtures, Cl₃CH…O(CD₃)₂ complexes with a weak hydrogen bond are formed. The spectral characteristics of individual absorption bands that refer to proton donors and to proton acceptors have been determined. From temperature measurements of the integrated intensities of the bands of monomers and of the complex (T ~ 120–160 K), the enthalpy of the complex formation has been estimated. The measurement data have been analyzed in comparison with the results of ab initio calculations in terms of the МР2/6-311++G(2df, 2pd) approximation. The analysis has been done taking into account peculiarities of the dipole moment function of chloroform and possible effects of the anharmonic interaction between the С–Н stretching vibration and the overtone of the Cl–C–H bending vibration.     

Interaction between nanobuds and hydrogen molecules: A first-principles study

Hydrogen storage materials are crucial for the wide application of hydrogen in fuel cells. In this Letter, the interaction between hydrogen molecules and nanobuds has been studied using the Dmol3 package. The results show that the adsorption energies of hydrogen molecules onto nanobuds range from 0.069 eV to 0.115 eV, and that the adsorption energies are not sensitive to the nanobuds' structures but closely related to the number of carbon atoms around H₂ molecules. The energy barrier of a hydrogen molecule entering C176 is 2.38 eV. Each C176 nanobud can accommodate four H₂ molecules. The stress existing in nanobuds induces alterative charge distribution, which can improve the hydrogen storage performance of nanobuds to a certain extent.     

Surface heterogeneity of polysiloxane xerogels functionalized by 3-aminopropyl groups

DRIFT spectra of xerogels synthesized by co-condensation of tetraethoxysilane (or 1,2-bis(triethoxysilyl)ethane) and 3-aminopropyltriethoxysilane have been measured using termoevacuation in the temperature range 50-350 °C. The disappearance of bands related to the vibrations of water molecule with temperature growth and shifts of absorption band related to the deformation vibrations of amino groups to the high-frequency region have been observed. The formation of a new band in the range of 3650-3660 cm⁻¹ has been attributed to stretching vibrations of silanol groups. The simplest change of surface layer composition in the amino-containing xerogels by water removal results in transformation of one type of hydrogen bond to another. The first type is associated with forming of cyclical structure with participation of 3-aminopropyl and silanol groups and water molecule, [≡Si(CH₂)₃H₂N···HO(H)···HOSi≡], the other type is associated with the interaction of amino groups between each other.     

Enhancements of hydrogen adsorption energy in M-MOF-525 (M= Ti,V, Zr and Hf): A DFT study

Electric dipole moment and hydrogen adsorption properties of four different Metal–Organic Framework-525, namely M-MOF-525 (M= Ti, V, Zr and Hf) were computed via the first-principles technique. Our calculation results revealed that the bond length between M–O (M= Ti, V, Zr and Hf) of the metal-oxide cluster is proportional to the atomic radius of M in metal-oxide cluster. The increasing of the M–O distance results in enhancement of electric dipole moment of the M-MOF-525. Moreover, it was found that the averaged M-O distances are 2.10, 2.05, 2.24 and 2.25 Å for Ti-, V-, Zr- and Hf-MOF-525, respectively. To investigate the hydrogen adsorption property, all possible hydrogen adsorption sites in the M-MOF-525 must be firstly searched. According to our calculation results, five stable hydrogen adsorption sites were found. For each adsorption site, two orientations of the HH bonding, namely parallel and perpendicular directions, were considered. Based on our calculation results, it was found that the Ti- and V-MOF-525 are unable to bind a hydrogen molecule on their surfaces, whereas a hydrogen molecule can trap on the surface of the Zr- and Hf-MOF-525. This is owing to stronger electric dipole moments of Zr- and Hf-MOF-525 in comparison to Ti- and V-MOF-525. For the Zr-MOF-525, the hydrogen molecule can trap on this structure with hydrogen adsorption energy ranging from 0.04–0.15 eV/H₂. Additionally, the hydrogen binding energies of the Hf-MOF-525 range from 0.06 to 0.16 eV/H₂. According to our computational results, it was obviously seen that hydrogen adsorption energy of the site near metal oxide cluster is always larger than that of the TpCPP linker. Lastly, we also found that the interaction between the hydrogen molecule and the M-MOF-525 host is mainly governed by a weak dispersive interaction.     

Raman Intensity of the v C=O Band in Hydrogen Bonded Complexes Involving Ethylformate and Phenol Derivatives

The hydrogen bonded complexes between carbonyl bases and hydroxylic derivatives have been extensively studied by infrared spectrometry; by comparison very little Raman data have been reported in the literature. Some qualitative measurements on the v _C=O band of acetone dissolved in water-tetrachloride mixtures have been performed by Singurel¹. Quantitative data on the absolute Raman intensity have been obtained for complexes involving cyclohexanone², acetone, acetophenone³ and methylacetate⁴. For these systems, hydrogen bond formation brings about a moderate intensity enhancement of the v _C=O band. In this work the Raman intensity of the v _C=O band of ethylformate (EtFo) complexed with phenol derivatives is investigated.     

Manifestation of structure and intermolecular interactions of biologically active brassinosteroids in infrared spectra

We have analyzed the IR spectra obtained for steroidal phytohormones 24-epibrassinolide, 24-epicastasterone, 28-homobrassinolide, and 28-homocastasterone. The characteristic frequencies of the stretching vibrations of the hydrocarbon groups CH₃, CH₂, and CH and also the C=O groups in the spectra of brassinolides are higher than in the spectra of castasterones, which makes it possible to identify them from the IR spectra. Study of the spectra of these brassinosteroids in different media (pressed samples in KBr, films, solutions in CHCl₃ and CDCl₃) allowed us to establish the presence of intermolecular interactions in which C=O and OH groups, OH-OH groups participate, and also the possible formation of intramolecular hydrogen bonds between the OH groups of the molecules. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 610–616, September–October, 2007.     

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformations of He-jet-cooled trimethyl[(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S₀–S₁ transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C - H ?O < _C^Si C - H \cdots O <_C^{Si} between hydrogen atoms of methyl groups and an oxygen atom and C–H···π between H and the π-electron cloud of the indole ring.     

Spectroscopic properties of pharmacologically active phenols

The IR Fourier-transform spectra of pharmacologically active phenol molecules in solutions in CCl₄ and in the crystalline state have been studied. Phenol derivatives with different directivities and different levels of pharmacological efficiency have been examined. Based on analysis of the IR spectra of screened phenols, the antimicrobial activity of phenols with free hydroxyl groups has been shown to be highest. The high antimicrobial activity of aminophenols is related to the formation of intramolecular hydrogen bonds. For aminophenols that are active against herpesviruses, O-H...N hydrogen bonds are formed in molecules. The main characteristic of the high antiviral activity against A-type influenza is predominance of intramolecular hydrogen bonds of the O-H...O=C type in molecules. Sulfur-containing aminophenols, which manifest activity against HIV infection, are characterized by the occurrence of hydrogen bonds that involve the participation of the OH, NH, and SO₂ groups.     

Study of the NMR spectra of hydrogen isotopic analogs and estimation of the magnetic moment of the triton

Nuclear magnetic resonance spectra of the hydrogen isotopic analogs TH and TD on the triton resonance and HT, HD, and H₂ on the proton resonance in the gas phase have been studied. The triton and proton spectra from a single sample have been recorded simultaneously by using the inductivity of a common receiver LC circuit. The energies of the interaction between the magnetic moments of the nuclei of the hydrogen isotopic analogs have been determined: J _tp = 299.3(1) Hz, J _td = 45.5(1) Hz, and J _pd = 43.3(1) Hz. The ratio of the resonance frequencies of the HT molecule nuclei: F _t (TH)/F _p (HT) = 1.066693898(2), which is equal to the ratio of the magnetic moments of the nuclei in the bound state, has been obtained. If the value Δσ(TH) = 2.04 × 10⁻⁸ calculated previously is used for the difference in the screening of nuclei in the HT molecule, then the ratio of the magnetic moment of the triton to the magnetic moment of the proton is μ _t /μ _p = 1.066693920(2), where the statistical standard deviation of the data is given in the parentheses in the units of the last digit.     

用密度泛函方法研究质子化苯基丙酮-水团簇

应用密度泛函B3LYP/631+G(d,p)计算方法,对质子化苯基丙酮水团簇这个弱相互作用体系进行了全自由度能量梯度优化,得到该系列团簇的稳定结构.结果表明,H+C8H8OH2O团簇的形成过程为一无能垒的反应过程,在质子与C8H8O分子中O原子的距离为1.015时达到平衡几何.对H+C8H8O(H2O)n(n=1,2,3)团簇,质子位于C8H8O分子和水分子之间,且随着团簇尺寸的增加,质子与C8H8O分子中O原子之间的距离也增加;C8H8OH+H2O可以视为溶剂壳.而对H+C8H8O(H2O)n(n=4,5,6,7,8)团簇,质子位于两个水分子之间,形成H5O2+结构,即C8H8OH5O2+为该系列团簇的中心结构,新增加的水分子以从不同方向进攻这个中心的方式形成更大尺寸的团簇.     

Ti原子在Al(110)表面吸氢过程中催化作用的第一性原理研究

运用第一性原理方法对H₂分子在Ti掺杂和纯的Al(110)表面的吸附情况进行了研究,发现有Ti原子掺杂时,存在一个H₂分子的吸附路径,即位于Al(110)面顶位Ti原子上方的H₂分子会发生解离,并与Ti原子形成TiH₂分子,然后TiH₂分子向能量更低的空位移动并接近Al(110)表面.态密度与电荷布居分析显示,吸附完成后H原子与表面Al原子存在较强的共价键作用,这为Al-H类物质及Na_{3 关键词： 钛 吸附 解离能 第一性原理}     

High-pressure X-ray diffraction study of dimedone

Abstract

Dimedone (i.e. 5.5-dimethyl-I,3-cyclohexanedione) crystals, C₈HI₁₂O₂, have been studied at high pressures by X-ray diffraction using a Merrill-Bassett diamond-anvil cell. The unit-cell dimensions have been measured to 1.20(5) GPa and the structure has been determined at 0.95(5) GPa. The crystal compressibility is strongly anisotropic and non-linear, relatively strong compressibility of the crystals is observed along the helices of the hydrogen-bonded molecules. Small anomalous changes of the unit-cell dimensions are observed between 0.1 and 50 MPa. The main structural changes are compression of intermolecular contacts, but also an alongation of the O=C bond—accompanied with the compression of the hydrogen bond involving the carbonyl oxygen atom—has been observed. This elongation is consistent with similar effects reported on compression of the hydrogen bonds in 1,3-cyclohexanedione and 2-methyl-1,3-cyclopentanedione. Crystal data for the dimedone structure at 0.95 GPa: monoclinic, P2₁/c, a=9.909(6), b= 6.505(3), c=12.313(6) Å, β=14.51°, V=722.1(5) Å, Z=4, R=0.139 for 336 independent reflections.     

X-ray photoelectron spectroscopic investigations of modifications in plasmid DNA after interaction with Hg nanoparticles

The electronic structure of plasmid DNA both prior to and after its conjugation with Hg nanoparticles (NP) has been investigated here. The DNA molecules undergo severe perturbation on their interaction with Hg-NP. The circular plasmid DNA becomes predominantly linearised on interaction with 10 mM Hg salt solution. These perturbations are also reflected in the electronic structure of C1s and O1s suggesting severe modifications in the exocyclic groups, of the nucleic acid bases, participating in the hydrogen bondings. The results reflect the rupturing of the purine-pyrimidine bonds after interaction with the NP. The study also suggests selective and specific interactions of DNA bases with the Hg nanoparticles leading to the formation of metal-purine-pyrimidine complexes through rupturing of G-C base pairs. Hg-NP exclusively interact with the nitrogen bases of the DNA molecule and do not cause any significant modification to the phosphate backbone of DNA.