共查询到20条相似文献,搜索用时 93 毫秒
1.
Bogumil Brzezinski 《Journal of Molecular Structure》1984,118(3-4):311-318
Heteroconjugated NO+H … N NO … H+N and homoconjugated NO+H … ON NO … H+ON intramolecular hydrogen bonds formed in semisalts of mono- and di-N-oxides of N,N′-tetraalkyl-o-xylyldiamines were studied by IR and NMR spectroscopy. All these hydrogen bonds show large proton polarizability. In the case of the heteroconjugated hydrogen bonds the proton transfer equilibrium shifts from compounds 1 to 3 to the left hand side since the interaction of the hydrogen bond with the solvent environment decreases in this series of compounds. With compound 1 the hydrogen bonds are slightly weaker and longer, hence the wavenumber dependence of the intensity of the continuum caused by these hydrogen bonds is slightly changed with compound 1 compared with compound 2. In the case of compound 3 the intensity of the continuum decreases because of increasing screening of the hydrogen bonds. In the series of homoconjugated hydrogen bonds, from compound 4 to 6 the intense continuum vanishes, and only the band of the 0–1 proton transition at 950 cm−1 remains. The vanishing of the continuum is caused by increasing screening of the hydrogen bonds against their solvent environments by bulky groups, and thus, this change demonstrates again that the interaction of the hydrogen bond with large proton polarizabilities is a necessary prerequisite for IR continua to appear. 相似文献
2.
The complexes formed by phenols with 1,3,4,6,7,8-hexahydro-l-methyl-2H-pyrimido[1,2-a]pyrimidine (mTBD), an N-base with guanidine-like character, were studied as a function of the pKa of the phenols by FT-IR spectroscopy. The following phenols were used: 4-cyanophenol (4-CNPh), pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DNPh). In the case of chloroform solutions of 1: 1 mixtures of the phenols with MTBD the corresponding complexes are formed completely. With increasing acidity of the phenols the hydrogen bonds become increasingly asymmetrical. The O … N −O … H+N hydrogen bond in the 4-CNPh-MTBD complex shows large proton polarizability. In the other cases only the polar structure is realized. With increasing phenol MTBD ratio, the formation of chains with two phenol molecules is observed. With decreasing pKa of the phenols the fluctuation is limited to the phenol-phenolate bond and finally, the phenol-protonated MTBD bond begins to dissociate. In acetonitrile solutions, N+H …O− hydrogen bonds are observed in the case of the 1:1 mixture of 4-CNPh with MTBD. A weak continuum indicates the presence of homoconjugated phenol-phenolate bonds with large proton polarizability. In the case of 2:1 mixtures only protonated MTBD and homoconjugated phenol-phenolate bonds are observed, independent of the pKa of the phenols. The results are discussed with regard to the proton pathway in bacteriorhodopsin. 相似文献
3.
The complexes formed by phenols with 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine (mTBD), an N-base with guanidine-like character, were studied as a function of the pKa of the phenols by FT-IR spectroscopy. The following phenols were used: 4-cyanophenol (4-CNPh), pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DNPh). In the case of chloroform solutions of 1:1 mixtures of the phenols with MTBD the corresponding complexes are formed completely. With increasing acidity of the phenols the hydrogen bonds become increasingly asymmetrical. The OH … N −O … H+N hydrogen bond in the 4-CNPh-MTBD complex shows large proton polarizability. In the other cases only the polar structure is realized. With increasing phenol MTBD ratio, the formation of chains with two phenol molecules is observed. With decreasing pKa of the phenols the fluctuation is limited to the phenol-phenolate bond and finally, the phenol-protonated MTBD bond begins to dissociate. In acetonitrile solutions, N+H … O− hydrogen bonds are observed in the case of the 1:1 mixture of 4-CNPh with MTBD. A weak continuum indicates the presence of homoconjugated phenol-phenolate bonds with large proton polarizability. In the case of 2:1 mixtures only protonated MTBD and homoconjugated phenol-phenolate bonds are observed, independent of the pKa of the phenols. The results are discussed with regard to the proton pathway in bacteriorhodopsin. 相似文献
4.
John B. O. Mitchell
Sarah L. Price
《Chemical physics letters》1991,180(6):517-523We have performed Hayes—Stone intermolecular perturbation theory (IMPT) calculations on amide…water and amide…amide complexes in order to estimate the change ΔW in intermolecular interaction energy associated with the hydrogen bond exchange process amide(NH)…water+water…(OC)amideamide(NH)…(OC)amide+water…water. ΔW is found to be small and varies by almost 5 kJ/mol and in sign for the amides formamide, acetamide, N-methyl formamide and N-methyl acetamide. The main variations in the amide hydrogen bond energies occur in the electrostatic and exchange-repulsion contributions. This reflects the variation in the charge distributions of the hydrogen bonding groups between the different amides. Thus, we cannot quantify an isolated hydrogen bond strength with any great accuracy, and care must be used in extrapolating model potentials based on small model systems to peptides and proteins. 相似文献
5.
The relative stabilities of thiourea in water are investigated computationally by considering thiourea–water complexes containing up to 1–6 water molecules (CS(NH2)2(H2O)n=1–6) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H2O molecule is about 33 kJ mol−1 for n=1–5.The C–S bond, N–C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H2O molecules. As the solvation progresses, the C–S distance increases monotonically while the Mulliken populations on the C–S bond reduces monotonically with the addition of each H2O molecule, indicating that the C–S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H2O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea. 相似文献
6.
The Fourier transform infrared spectra of the H-bonded complexes between HCl and 4-aminopyridine, 4-aminopyrimidine, 4-hydroxypyridine, 2-hydroxypyridine, benzimidazole and purine were investigated in Ar matrices. From the analysis of these spectra, the H-bonds N HCl appear to be of the pseudosymmetric type II for 4-aminopyridine, 4-aminopyrimidine and 4-hydroxypyridine, while benzimidazole forms a slightly weaker complex. H-bonding of HCl with the bases 2-hydroxypyridine and purine is of the intermediate type I → II. In the case of 4-aminopyrimidine, additional bonding of the Cl atom of HCl to an amino N---H bond yields a closed complex which explains the type II behaviour. In all other cases, bonding of additional HCl molecules to the 1:1 complexes results in proton transfer towards N---H+…Cl−(HCl)π species, but n is much lower for type II than for the intermediate type I → II complexes. The results allow us to investigate the vibration correlation diagram and the isotopic ratio ν(HCl)/ν(DCl) for B - HCl complexes in Ar matrices into more detail. 相似文献
7.
The infrared absorption of mixtures of dimethyl ether and hydrogen halide (HX) in nitrogen at 13 K display relatively narrow bands in the range 650–800 cm−1 with an isotopic ratio νH/νD larger than 1.4 and weakly halogen dependent; these features are assigned to the antisymmetric O…H…O stretching within the [(CH3)2 O…H…O(CH3)2]+X− ion pair. With HI—ether mixtures, the intensity of the 660 cm−1 band decreases under infrared irradiation of the matrix, which might be due to the transfer of the proton back to the I− anion. 相似文献
8.
The interactions between some acrylic and sulphonic polyanions and some protonated amines (diamines NH2-(CH2)x-NH2, x=2,…,10; linear tri-, tetra-, penta- and hexa-amines) were studied potentiometrically in aqueous solution, at 25°C. For both types of polyanions AL2Hi (L−, monomer of polyanion, A, amine) species are formed, with i=1,…,n (n=number of amino groups in the amine). The stability of these species is strictly dependent on the polyammonium cation charge, and fairly independent of the type of amine (in diamine species maximum stability is observed for x=4, 5). Acrylic and sulphonic polyanion complexes are considerably stronger than analogous species formed by low molecular weight anions. Mean stability can be expressed as log K=2.87ζ2/3, for polyacrylic anions and log K=2.42ζ2/3 for polysulphonic anions (ζ=absolute value for charge product of reactants). 相似文献
9.
Vesa Nevalainen 《Tetrahedron: Asymmetry》1993,4(12):2517-2530
Conformers of 4-coordinate adducts of carbonyl compounds and diaza-, oxaza- and dioxaluminolidines were investigated by means of ab initio MO methods (RHF). Formaldehyde was used as a model of carbonyl compounds. Relative stabilities of the conformers indicate formation of syn adducts of carbonyl compounds and aluminolidines (CC=O and aluminolidine ring syn about the Al---OC=O bond) to be favoured over that of the corresponding anti ones (all syn/anti ratios higher than 99:1, 6–31G//6–31G). The energetic preference for the formation of syn adducts of oxazaaluminolidines was about twice as high as that of diaza- or dioxaluminolidines of which the syn/anti selectivities were found to be practically equal. 相似文献
10.
Infrared and Raman spectra of the BaF(HF2) crystal and its 10 and 50% deuterated derivatives at 300 and 90 K have been investigated in the 4000 to 20 cm−1 range. An assignment of internal and lattice vibrations has been proposed. Vibrational spectra are consistent with a centrosymmetric P21/m space group and Z=2. They show that the (FHF)− ion is not centrosymmetrical, in spite of a short F…F distance; a force field calculation has been performed in order to determine the F---H and H…F distances, which are equal to 1.08 and 1.20 Å, respectively, in agreement with the 1H and 19F NMR data. The ν3(H)/ν3(D) isotope frequency ratio indicates a negative or zero isotope effect on the F…F distance, which is observed for the first time for a strong asymmetric hydrogen bond. 相似文献
11.
Piotr Barczyski Anna Komasa Magorzata Ratajczak-Sitarz Andrzej Katrusiak Bogumil Brzezinski 《Journal of Molecular Structure》2006,800(1-3):135-139
Bis(8-oxy-1-methylquinolinium) hydroiodide has been studied by X-ray diffraction, FT-IR, 1H and 13C NMR spectroscopy. In the crystalline state a homoconjugated OH O− hydrogen bond is formed. As indicated by the X-ray data this hydrogen bond is very short (2.457 Å) and structurally symmetrical. The existence of this bond is manifested in the FT-IR spectra by an intense and broad band in the 1500–400 cm−1 region. This type of absorption indicates that this hydrogen bond can be described by one very broad potential energy minimum in which the proton shows a large proton polarizability due to its fast fluctuations, i.e., it shows the so-called Zundel’s polarizability. 相似文献
12.
Rita Terzian Nick Serpone Marye Anne Fox 《Journal of photochemistry and photobiology. A, Chemistry》1995,90(2-3):125-135
Photo-oxidations of environmental organics in illuminated TiO2 dispersions have implicated surface-bound •OH radicals and/or valence band holes. To explore the implications of the former oxidizing entity, six isomeric xylenols (dimethylphenols) were examined by pulsed (nanoseconds to milliseconds) radiolysis methods. The spectral and kinetic characteristics of formation and decay of the transients formed by the reaction of N3•, •OH and H• radicals with these xylenols were assessed in buffered (pH 4, 10−3 M phosphate) aqueous media, where the xylenols exist in their protonated form (pK ≈ 10.19–10.65). The products from the reaction of N3• with 2,6- and 3,4-xylenol were exclusively the corresponding dimethylphenoxyl radicals, formed via electron transfer followed by deprotonation. In contrast, except with 3,4-xylenol, the principal radical intermediates formed initially upon reaction with •OH were the corresponding •OH adducts, the dihydroxydimethylcyclohexadienyl radicals. 3,4-Xylenol was examined in the pH range 4–10. At pH 8 the initial •OH adduct (dihydroxy-3,4-dimethylcyclohexadienyl radical) was subsequently transformed (about 20%–40%) via water elimination into the dimethylphenoxyl radical. In contrast, at pH 9 and 10 the •OH adduct and the dimethylphenoxyl radical were formed concurrently (about 60% •OH adduct and about 40% dimethylphenoxyl species), the latter through an inner-sphere electron transfer pathway. The switch in behaviour from pH 8 to pH 9 suggests that the pKa of the dihydroxy-3,4-dimethylcyclohexadienyl radical is about 8–9, about 2 pK units below the pKa of the parent substrate (10.4). A mechanism for the conversion of the •OH adduct to the dimethylphenoxyl radical is proposed. Reaction of 2,6-xylenol with H• radicals gave exclusively the H• adduct (hydroxycyclohexadienyl radical), whose spectral characteristics are similar to those of the related •OH adduct. 相似文献
13.
The 1:1 and 2:1 complexes between water and trans- and cis-isomers of nitrous acid have been isolated in argon matrices and studied using FTIR spectroscopy and DFT(B3LYP) calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra indicate that 1:1 complexes trapped in solid argon involve very strong hydrogen bond in which acid acts as the proton donor and water as the proton acceptor. The perturbed OH stretches are −248, −228 cm−1 red shifted from their free-molecules values in complexes formed by trans- and cis-HONO isomers, respectively. The calculated spectral parameters for the two complexes are in good agreement with experimental data. The calculations also predict stability of two more 1:1 weakly bound complexes formed by each isomer. In these the water acts as the proton donor and one of the two oxygen atoms of the acid as the acceptor. The experimental spectra demonstrate also formation of 2:1 complex between water and trans-HONO isomer in an argon matrix. The performed calculations indicate that the complex involves a seven-membered ring in which OH group of HONO forms very strong hydrogen bond with the oxygen atom of one water molecule and nitrogen atom acts as a weak proton acceptor for the hydrogen atom of the second water molecule of the water dimer. The observed perturbations of the OH stretch of trans-HONO (750 cm−1 red shift) is much larger than that predicted by calculations (556 cm−1 red shift); this difference is attributed to strong solvation effect of argon matrix on very strong hydrogen bond. 相似文献
14.
The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP-PCP) and its deuterated analogue (MP-PCP-d) were determined at 80 K by X-ray diffraction. The MP-PCP complex crystallizes in the space group P
with a = 7.267(7), b = 8.966(9), c = 13.110(14)Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP-PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12)Å, β = 101.38(9)° and Z = 4. The O… H … N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D … N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond. 相似文献
15.
Calculations with Hartree—Fock electron densities for the rare gas atoms He through Xe show that the gradient expansion for the kinetic energy functional, T[] = T0[] + T2[] + T4[] + … = ∫t() dτ, approximates the kinetic energy by averaging over the shell structure present in the true local kinetic energy density, t(), and that the accuracy of the gradient expansion improves with increasing atomic number. Components of t(), t0(), t2() and t4(), are exhibited and discussed. The defined function t() is everywhere positive. 相似文献
16.
A calorimetric study was performed for adducts of general formula CdBr2·nL (n=1 and 2; L=ethyleneurea (eu) and propyleneurea (pu)). The standard molar reaction enthalpy in condensed phase: CdBr2(c)+nL(c)=CdBr2·nL(c); ΔrHmθ, were obtained by reaction–solution calorimetry, to give the following values for mono- and bis-adducts: −19.54 and −34.59; −7.77 and −19.05 kJ mol−1 for eu and pu adducts, respectively. Decomposition (ΔDHmθ) and lattice (ΔMHmθ) enthalpies, as well as the mean cadmium---oxygen bond dissociation enthalpy, DCd---O, were calculated for all adducts. 相似文献
17.
Jarosaw Ja
wiski 《Journal of Molecular Structure》2005,750(1-3):7-17
1H, 13C and 15N NMR spectroscopy has been applied for investigation of amine adducts with rhodium(II) tetraacetate dimer and rhodium(II) tetratrifluoroacetate dimer in CDCl3 solution. Subsequent formation of two adducts, 1:1 and 2:1, was proved by NMR and VIS titration experiments, and by NMR measurements at reduced temperatures, from 233 to 273 K. The adduct formation shift, defined as Δδ=δadduct−δligand and characterizing complexation reaction, varies from ca. 0 to +1.6 ppm for 1H, from ca. −10 to +6 ppm for 13C and from −4.4 to −39 ppm for 15N NMR. Formation of N–Rh bond slows the inversiof on the nitrogen atom and generates, in the case of N-methyl-(1-phenylethyl)-amine, a nitrogenous chiral center in the molecule. VIS spectra of amine-dirhodium salt mixture contain two bands in the 532–597 nm spectral range, assigned to 1:1- and 2:1-adducts. 相似文献
18.
A systematic study of the proton transfer in the 7-azaindole–water clusters (7-AI(H2O)n; n=1–4) in both the ground and first excited singlet electronic states is undertaken. DFT(B3LYP) calculations for the ground electronic state shows that the more stable geometry of the initial normal tautomer presents a cyclic set of hydrogen bonds that links the two nitrogen atoms of the base across the waters. For the n=4 cluster the water molecules adopt a double ring structure so that two cycles of hydrogen bonds are found there. From this structure full tautomerization implies only one transition state so that a concerted but non-synchronous process is predicted by our theoretical calculations. This behavior is found both in the ground and the excited states where CIS geometry optimizations and TD(B3LYP) energy calculations are performed. The difference between both states is the height of the energy barrier that is much lower in the excited state. Another clear difference between both electronic states is that full tautomerization is an endergonic process in the ground state whereas it is clearly exergonic (then favorable) in the excited state. This is so because electronic excitation implies a charge transfer from the five-member cycle to the six-member one of 7-azaindole so that the proton transfer from the pyrrolic side to the pyridinic one is favored. These results clearly indicate that full tautomerization will not likely occur in the ground state but it will be quite easy (and fast) in the excited state. Reaction is already feasible in the S1 1:1 complex but it is faster in the 1:2 complex. However the reaction slows again for the 1:3 complex and, finally, reaches a new maximum for the largest cluster studied here, the n=4 case. These results, which are in agreement with experimental data, are explained in terms of the number of hydrogen bonds that are involved in the transfer. The proton transfer through a ring formed by the substrate and two water molecules is found to be the more efficient one, at least in this system. 相似文献
19.
The density functional theory and Hartree–Fock methods were used to investigate the proton transfer reaction for a series of model clusters of zeolite/(H2O)n; n=1,2,3, and 4. Without promoted water, the hydrogen-bonded dimer of the water/zeolite system exists as a simple hydrogen-bonded complex, ZOH.(H2O)2, and no proton transfer occurs from zeolite to water. The third promoted water, ZOH(H2O)2H2O, was found to induce a pathway for proton transfer, but at least addition two promoted molecules, ZO(H3O+)H2O(H2O)2, must be involved for complete proton transfer from zeolite to H2O. The results show that the hydronium ion in water cluster adsorbed on zeolite, ZO(H3O+)(H2O)3, can considerably affect the structure and bonding of the hydrogen-bonded dimer of water. The OO distance is contracted from 2.818 Å found in the neutral complex, ZOH(H2O)4, to 2.777 Å for ion-pair complex, ZO(H3O+)(H2O)3. The distance between the oxygen of the hydronium ion and the zeolitic acid site oxygen is predicted to be 2.480 Å which is in good agreement with the experimentally observed value of 2.510 Å. The corresponding density functional adsorption energy of the high coverages of adsorbing molecules on zeolite is calculated to be −9.14 kcal/mol per molecule at B3LYP/6-311+G(d,p) level of theory and compares well with the experimental observation of −8.20 kcal/mol. 相似文献
20.
Kaoru Tsuchiya Akihiro Takahashi Naoto Takeda Naoki Asakawa Shigeki Kuroki Isao Ando Akira Shoji Takuo Ozaki 《Journal of Molecular Structure》1995,350(3):233-240
13C cross polarization-magic angle spinning NMR spectra were measured for a series of peptides containing
-valine,
-leucine and
-aspartic acid residues, for which the crystal structures were already determined by X-ray diffraction, in order to investigate the relationship between hydrogen-bond lengths (RN…O) and 13C chemical shifts of amide carbonyl carbons in the peptides. From these experimental results, it was found that the isotropic 13C chemical shifts (δiso) of the amino acid residues move linearly downfield with a decrease in RN…O within the hydrogen-bonded length range considered here and also shown in our previous work on glycine and
-alanine residues as expressed by δiso(ppm) = a − bRN…O(Å) where a and b are 215.4 (ppm) and 14.2 (ppm Å−1) for the
-valine residue, 202.2 (ppm) and 10.0 (ppm Å−1) for the
-leucine residue, and 199.0 (ppm) and 9.6 (ppm Å−1) for the
-aspartic acid residue, respectively. Using these relations, the RN…O values of some polypeptides in the crystalline state were determined through the observation of the amide carbonyl carbon chemical shifts. These values were compared with those determined by the X-ray diffraction method. Furthermore, quantum-chemical calculation of the 13C shielding constant for a model compound was carried out by the finite perturbation theory INDO method in order to ascertain the 13C shielding behavior in the formation of hydrogen bonds. 相似文献