An empirical potential for the O-H·O Hydrogen bond: Part I. Comparison with ab initio molecular orbital results

An empirical potential energy function has been devised for the O-H·O hydrogen bond, for use with the MMI force field. The energy of the hydrogen bond is described as the sum of van der Waals, electrostatic and Morse components. The function has been used to calculate the potential energy hypersurface of the water dimer, and the results are compared with published ab initio molecular orbital studies. Satisfactory agreement is obtained except for orientations involving very short H·H contacts. The geometry and hydrogen bond energy of the equilibrium linear form of (H₂O)₂ are calculated to be r(O·O) = 2.84 Å, θ = 36°, ΔE = ?5.35 kcal mol^?1, which are close to the values obtained by experiment, and from molecular orbital calculations. The relative importance of the electrostatic component of the empirical hydrogen bond energy is consistent with molecular orbital energy decomposition studies. The empirical function has also been used to calculate the energy of the water trimer in orientations which serve as models for the crystallographic bifurcated hydrogen bond. The results indicate that, in these orientations, the trimer is typically 0–3 kcal mol^?1 more stable than the dimer, a result which is consistent with ab initio calculations.     

AB initio SCF LCAO MO study of the HOH…Cl− hydrogen bond

Ab initio SCF LCAO MO calculations for the [H₂O…Cl]^? complex have been performed. The energy of the linear hydrogen bond has been found to be lower than the energy of the bifurcated one. The difference of the energies is about 3 kcal/mole. The calculated equilibrium distance between the oxygen and chlorine atoms equals 5.75 au. The interaction energy of the chlorine anion and the rigid water molecule amounts to ?19 kcal/mole. The optimization of the OH bond length in the complex (linear hydrogen bond) leads to an interaction energy of ?19.5 kcal/mole (the experimental value equals ?13.1 kcal/mole). As a result of the hydrogen bond formation the OH bond length increases by 0.08 au.     

Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

Cooperativity between the Dihydrogen Bond and the N⋅⋅⋅HC Hydrogen Bond in LiH–(HCN)n Complexes

The cooperativity between the dihydrogen bond and the N???HC hydrogen bond in LiH–(HCN)_n (n=2 and 3) complexes is investigated at the MP2 level of theory. The bond lengths, dipole moments, and energies are analyzed. It is demonstrated that synergetic effects are present in the complexes. The cooperativity contribution of the dihydrogen bond is smaller than that of the N???HC hydrogen bond. The three‐body energy in systems involving different types of hydrogen bonds is larger than that in the same hydrogen‐bonded systems. NBO analyses indicate that orbital interaction, charge transfer, and bond polarization are mainly responsible for the cooperativity between the two types of hydrogen bonds.     

A scheme for rapid prediction of cooperativity in hydrogen bond chains of formamides,acetamides, and N‐methylformamides

A scheme is proposed in this article to predict the cooperativity in hydrogen bond chains of formamides, acetamides, and N‐methylformamides. The parameters needed in the scheme are derived from fitting to the hydrogen bonding energies of MP2/6‐31+G** with basis set superposition error (BSSE) correction of the hydrogen bond chains of formamides containing from two to eight monomeric units. The scheme is then used to calculate the individual hydrogen bonding energies in the chains of formamides containing 9 and 12 monomeric units, in the chains of acetamides containing from two to seven monomeric units, in the chains of N‐methylformamides containing from two to seven monomeric units. The calculation results show that the cooperativity predicted by the scheme proposed in this paper is in good agreement with those obtained from MP2/6‐31+G** calculations by including the BSSE correction, demonstrating that the scheme proposed in this article is reasonable. Based on our scheme, a cooperativity effect of almost 240% of the dimer hydrogen bonding energy in long hydrogen bond formamide chains, a cooperativity effect of almost 190% of the dimer hydrogen bonding energy in long hydrogen bond acetamide chains, and a cooperativity effect of almost 210% of the dimer hydrogen bonding energy in long hydrogen bond N‐methylformamide chains are predicted. The scheme is further applied to some heterogeneous chains containing formamide, acetamide, and N‐methylformamide. The individual hydrogen bonding energies in these heterogeneous chains predicted by our scheme are also in good agreement with those obtained from Møller‐Plesset calculations including BSSE correction. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical Studies on the Hydrogen Bond Transfer and Proton Transfer between Anamorphoses of the Dihydrated Glycine Complex

The conversion between anamorphoses of the dihydrated glycine complex was studied by means of B3LYP/6-31++G**. It was found that proton transfer was accompanied by hydrogen bond transfer in the process of conversion between different kinds of anamorphoses. With proton transfer, the electrostatic action was notably increased and the hydrogen-bonding action was evidently strengthened when the dihydrated neutral glycine complex converts into dihydrated zwitterionic glycine complex. The activation energy required for hydrogen bond transfer between dihydrated neutral glycine complexes is very low (6.32 kJ·mol-1); however, the hydrogen bond transfer between dihydrated zwitterionic glycine complexes is rather difficult with the required activation energy of 13.52 kJ·mol-1 due to the relatively strong electrostatic action. The activation energy required by proton transfer is at least 27.33 kJ·mol-1, higher than that needed for hydrogen bond transfer. The activation energy for either hydrogen bond transfer or proton transfer is in the bond-energy scope of medium-strong hydrogen bond, so the four kinds of anamorphoses of the dihydrated glycine complex could convert mutually.     

An empirical scheme for evaluating in situ bond energy from MNDO data

The in situ bond energy is evaluated from the resonance integral contribution to energy with a correction term of monatomic energy obtained from MNDO calculation. The sum of the in situ bond energies in a molecule is expected to be equal to its atomization energy. Root-mean-square error of heat of formation calculated from in situ bond energy for seventy nine molecules containing hydrogen, carbon, nitrogen, oxygen, and fluorine amounts to 5.5 kcal/mol. Correlations of in situ bond energy with contributional bond energy, bond dissociation energy, isolated stretching frequency, and bond length are performed and discussed.     

Theoretical study on the bromomethane-water 1:2 complexes

Bromomethane-water 1:2 complexes have been theoretically studied to reveal the role of hydrogen bond and halogen bond in the formation of different aggregations. Four stable structures exist on the potential energy surface of the CH3Br(H2O)2 complex. The bromine atom acts mainly as proton acceptor in the four studied structures. It is also capable of participating in the formation of the halogen bond. The properties and characteristics of the hydrogen bond and the halogen bond are investigated employing several different quantum chemical analysis methods. Cooperative effects for the pure hydrogen bonds or the mixed hydrogen bonds with halogen bonds and the possibility of describing cooperative effects in terms of the topological analysis of the electronic density or the charge-transfer stabilization energy are discussed in detail. An atoms-in-molecules study of the hydrogen bond or the halogen bond in the bromomethane-water 1:2 complexes suggests that the electronic density topology of the hydrogen bond or the halogen bond is insensitive to the cooperative effect. The charge-transfer stabilization energy is proportional to the cooperative effect, which indicates the donor-acceptor electron density transfer to be mainly responsible for the trimer nonadditive effect.     

Theoretical investigation of the hydrogen bond interactions of methanol and dimethylamine with hydrazone and its derivatives

The interactions between hydrogen bond donors (dimethylamine (DMA) and methanol (MeOH)) and acceptors (formaldehyde dimethylhydrazone, acetaldehyde N,N-dimethylhydrazone and N-nitrosodimethylamine) were theoretically investigated by DFT. The hydrogen bonding interactions were found on several bonding sites of the acceptors. The important properties of structure, binding energy, enthalpy of formation, Gibbs free energy of formation and equilibrium constant were investigated. Compared to the monomer, the DMA complexes show a small red shift of the NH-stretching vibrational transition but a significantly intensity enhancement. On the other hand, the MeOH complexes have a large red shift but a relatively small intensity enhancement of the OH-stretching transition. Atoms-in-molecules analysis revealed that several types of hydrogen bond interaction were present in the complexes. Since natural bond orbital analysis overestimated the effect of charge transfer, the more reliable localized molecular orbital energy decomposition analysis was performed and it shows that the major contribution to the total interaction energy is the electrostatic interaction. All these parameters suggest that the hydrogen bond donor strength of MeOH is substantially greater than DMA.

     

Molecular mechanics study on conformation of perylene-quinonoid photosensitizers

Using molecular mechanics method,values of the heat of formation (HF) of different conformations,of perylenequinonoid photosensitizes hypocrellin A (HA) and hypocrellin B (HB) were calculated and the variance of HF after phenolic protons' dissociation were calculated as well The following was found:(i) The HF values of lour conformational isomers of HA and HB are similar to each other,so the four isomcrs can transform to each other room temperature,(ii) There exists the difference between the ability of dissociation of phenolic protons of HA and that of HB,the former is higher than the latter (iii) There exist two intramolecular hydrogen bonds in HA and HB The bond energy is approximately 8 kJ/mol and the energy of conformation Ⅰ is lower than that of conformationⅡ The bond energy of HA is lower than that of HB.(iv) There exists a low energy snot when phenolic hydroxyl bond twists 180° from the position where hydrogen bond is formed,which suggests that this kind of conformation probably exists,(v) Th     

Studies on the Effect of Structure to Property Stability of Glucomannan

1 INTRODUCTION Directive action of hydrogen bond paves the way for new fields of biological activity, molecular re- cognition and crystal engineering[1]. Hydrogen bond plays an important role in the physical and chemical properties, such as melting point, boiling point, solu- bility, acid strength, viscosity and hardness degree[2]. At present, the popular tools used to investigate hy- drogen bond include wet melting point method, chromatography analysis method, spectrum method and diffract…     

An Experimental Exploration of C−H⋅⋅⋅X Hydrogen Bond in [CHCl3−X(CH3)2] Complexes (X=O,S, and Se)

Among the conglomeration of hydrogen bond donors, the C−H group is prevalent in chemistry and biology. In the present work, CHCl₃ has been selected as the hydrogen bond donor and are X(CH₃)₂ are the hydrogen bond acceptors. Formation of C−H⋅⋅⋅X hydrogen bond under the matrix isolation condition is confirmed by the observation of red-shift in the C−H stretching frequency of CHCl₃ and comparison with the simulated spectra. Stabilisation energy of all the three complexes is almost equal although the observed red-shift for the C−H⋅⋅⋅O complex is less compared to the C−H⋅⋅⋅S/Se complexes. The nature and origin of the hydrogen bond have been delineated using Natural Bond Orbital, Atoms in Molecules, Non-Covalent Interaction analyses, and Energy Decomposition Analysis. Charge transfer is found to be proportional to the observed red-shift. This work provides the first impression of C−H⋅⋅⋅Se hydrogen bond and its comparison with C−H⋅⋅⋅O/S hydrogen bond interaction under experimental condition.     

氨基酸侧链与氧化鸟嘌呤碱基对体系的氢键作用

应用量子化学方法,分别在气相和水溶液中对氨基酸侧链与氧化鸟嘌呤碱基对(8-oxo-G∶C)形成的三体复合物的氢键键能、几何结构、电荷分布及二阶稳定化能进行了研究.结果表明,水溶液的存在削弱了复合物中的氢键强度,电荷分布变化明显,水溶液中形成氢键位点的电荷变化量约为气相中的10倍,而几何结构变化不明显、对于酶与DNA之间的相互作用的研究需在水溶液中进行.水溶液对带电三体复合物中8-oxo-G∶C与氨基酸侧链间的氢键有较大影响,键能平均减小了69.23 k J/mol,不带电复合物仅减小了3.60k J/mol.水溶液中三体复合物中8-oxo-G∶C间的氢键受侧链的影响不大,且与侧链带电与否无关,带电复合物和不带电复合物的氢键强度分别减小了24.57和30.05 k J/mol,且二阶稳定化能越大,其对应的氢键键长越短.     

取代基对N-H…O=C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N—H…O=C氢键强度, 探讨了氢键受体分子中不同取代基对N—H…O=C氢键强度的影响. 研究表明, 不同取代基对氢键三聚体中N—H…O=C氢键强度的影响是不同的: 取代基为供电子基团, 氢键键长r(H…O)缩短, 氢键强度增强; 取代基为吸电子基团, 氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明, N—H…O=C氢键强度越强, 氢键中氢原子的正电荷越多, 氧原子的负电荷越多, 质子供体和受体分子间的电荷转移越多. 供电子基团使N—H…O=C氢键中氧原子的孤对电子n(O)对N—H的反键轨道滓*(N—H)的二阶相互作用稳定化能增加, 吸电子基团使这种二阶相互作用稳定化能减小. 取代基对与其相近的N—H…O=C氢键影响更大.     

Computational evidence for methyl-donated hydrogen bonds and hydrogen-bond networking in 1,2-ethanediol-dimethyl sulfoxide

The 1:1 complex of 1,2-ethanediol with dimethyl sulfoxide was studied using density functional theory. A network of three hydrogen bonds holds the complex together, including two in which each methyl group donates to the same hydroxyl oxygen. Four lines of evidence support the existence of methyl-donated hydrogen bonds. The interaction energy is 36 +/- 5 kJ/mol using Becke's three parameter hybrid theory with the 1991 nonlocal correlation functional of Perdew and Wang, and a moderately large basis set (B3PW91/6-311++G**//B3PW91/6-31+G**). To determine the energy of each hydrogen bond, a relaxed potential energy scan was performed in a smaller basis set to break the weaker hydrogen bonds by forced systematic rotation of the methyl groups. Two cross-checking analyses show cooperative effects that cause individual hydrogen bond energies in the network to be nonadditive. When one methyl hydrogen bond is broken, the remaining interactions stabilize the complex by storing an additional 2-3 kJ/mol. With all hydrogen bonds intact, the O[bond]H...O[bond]S hydrogen bond contributes 26 +/- 2 kJ/mol stability, and each weak methyl bond stores 5 +/- 2 kJ/mol.     

Investigating hydrogen bonds in liquid ethylene glycol structure by means of molecular dynamics

Models of liquid ethylene glycol are built by means of molecular dynamics at temperatures ranging between 268 and 443 K, with 1000 molecules in rectangular parallelepiped basic cells. The dependences of structures of O-H…O hydrogen bonds on modeling time and temperature are analyzed. It is found that the hydrogen bonds emerge at different sites of a model, thus forming a hydrogen bonds network that is continuously rebuilt under the action of thermal fluctuations. The number of hydrogen bonds in the models is observed to decrease when the temperature is raised. The energy of hydrogen bond formation is found to be ?20.0 ± 2.6 kJ mol^?1, the average bond lifetime is 370 ps at 268 K and 147 ps at 323 K, and the activation energy of hydrogen bond rupture at these temperatures is ～12.1 kJ mol^?1. It is concluded that the data on the breaking of H-bonds at temperatures of 323 to 443 K can be explained by the molecules moving away from each other as a result of diffusive motion, accompanied by rearrangement of the hydrogen bonds network. The concentration of dimers in the models is shown to be rather low, while the average energy of forming a dimer from two ethylene glycol molecules is ?35.4 kJ mol^?1.     

Correlated proton motion in hydrogen bonded systems: tuning proton affinities

The theorem of matching proton affinities (PA) has been widely used in the analysis of hydrogen bonds. However, most experimental and theoretical investigations have to cope with the problem that the variation of the PA of one partner in the hydrogen bond severely affects the properties of the interface between both molecules. The B3LYP/d95+(d,p) analysis of two hydrogen bonds coupled by a 5-methyl-1H-imidazole molecule showed that it is possible to change the PA of one partner of the hydrogen bond while maintaining the properties of the interface. This technique allowed us to correlate various properties of the hydrogen bond directly with the difference in the PAs between both partners: it is possible to tune the potential energy surface of the bonding hydrogen atom from that of an ordinary hydrogen bond (localized hydrogen atom) to that of a low barrier hydrogen bond (LBHB, delocalized hydrogen atom) just by varying the proton affinity of one partner. This correlation shows clearly that matching PAs are of lesser importance for the formation of a LBHB than the relative energy difference between the two tautomers of the hydrogen bond.     

Molecular orbital theory of the hydrogen bond. VIII. Hydrogen bonding in H2OH2CO in relaxed singlet and triplet n → π* states

Ab initio SCF CI calculations with a minimal STO-3G basis set have been performed on the hydrogen bonded dimers in which H₂O is the proton donor to H₂CO in its relaxed singlet and triplet n→π^* states. Two dimers which are easily interconverted are found in the singet n→π^* state with hydrogen bond energies of 1.82 and 1.71 kcal/mole. The equilibrium dimer in the triplet state has a hydrogen bond energy of 2.97 kcal/mole. In both states, hydrogen bond formation occurs at the carbon atom. The structures of the dimers and the nature of the intermolecular surfaces in the regions of hydrogen bond formation are examined. Electron densities and distributions are also discussed.     

Evaluation of the individual hydrogen bonding energies in N-methylacetamide chains

The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction. The calculation results indicate that compared with MP2 results, B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ mol^?1 for both the terminal and central hydrogen bonds, whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds, but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol^?1 for the hydrogen bonds near the center. Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends. The weakest individual hydrogen bonding energy is about ?29.0 kJ mol^?1 found in the dimer, whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as ?62.5 kJ mol^?1 found in the N-methylacetamide decamer, showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains. The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H?O=C bond, corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital, and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.