All-valence MO study of hydrogen bonding in water

Theoretical hydrogen bond energies and proton barriers for water dimer and trimer calculated by semiempirical all-valence MO methods have been compared. The results of CNDO/2 and INDO calculations are more adequate than those obtained by the MINDO/1 approach.     

An alternative approach to selective sea water oxidation for hydrogen production

Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion^®), which electrostatically repels chloride ions (Cl⁻) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO₂/Ti electrode surface-modified by a perm-selective polymer.     

Influence of isobaric heating of hydrogen bonding in precritical water

IR spectroscopy and statistical mechanic calculations were used to study the influence of isobaric heating (p 250 bar, T 493–633 K) on H-bond distribution in precritical water. As the temperature rises, the intermolecular water H-bond network is much destroyed, and the fractions of H-bonded n-mers are redistributed. At temperatures close to critical, water has a cluster-like structure with prevalence of dimers and trimers.     

Application of SCF-perturbation theory to hydrogen bonding in water dimers

The usefulness of Self-consistent perturbation theory and of a variation perturbation treatment both in semiempirical form (CNDO/2) is tested by application to hydrogen bonding in water dimers. The results are comparable to variational calculations. A splitting of the total energy in various components provides insight into the nature of hydrogen bonding.

---

Zusammenfassung Die Anwendbarkeit von SCF-Störungstheorie und eines Variationsstörverfahrens, beide in semiempirischer Form (CNDO/2), wird an der Wasserstoffbrückenbindung im dimeren Wasser geprüft. Die Ergebnisse sind vergleichbar mit Variationsrechnungen. Eine Aufspaltung der Gesamtenergie in verschiedene Komponenten vermittelt einen Einblick in die Natur der Wasserstoffbrückenbindung.

     

An inelastic neutron scattering study of hydrogen bonding in potassium hydrogen dichloromaleate

The inelastic neutron scattering (INS) spectrum (350–2000 cm^?1) of potassium hydrogen dichloromaleate (solid slate) has been obtained. Two of the normal modes of vibration of the hydrogen bond [γ(OHO) and δ(OHO)] were observed and assigned. No INS band v_as(OHO) was observed in the region 500–1300 cm^?1. This conflicts with expectations from infrared data.     

UV raman examination of alpha-helical peptide water hydrogen bonding

UV resonance Raman spectra (UVRS) of an alpha-helical, 21 residue, mainly Ala peptide (AP) in the dehydrated solid state were compared to those in aqueous solution at different temperatures. The UVRS amide band frequencies of a dehydrated solid alpha-helix peptide show frequency shifts compared to those in aqueous solution due to the loss of amide backbone hydrogen bonding to water; the amide II and amide III bands of the solid alpha-helix downshift, while the amide I band upshifts. The shifts are identical in direction but smaller than those that occur for alpha-helices in aqueous solution as the temperature increases; water hydrogen bonding strengths decrease as the temperature increases. The UV Raman amide band frequency shifts can be used to monitor alpha-helix hydrogen bonding.     

Signatures of the hydrogen bonding in the infrared bands of water

Infrared spectroscopy measurements have been completed over a wide range of frequencies allowing to measure the evolution of both intramolecular and intermolecular vibrational modes in water as a function of temperature. Emphasis is made on the high frequency OH stretching band and the so-called connectivity band that lies in the far infrared region. The substructures of the two infrared bands are analyzed in terms of different levels of connectivity of the water molecules, along the statements of the percolation model. Both band profiles appear to be related to the different degrees of connectivity of water molecules. Comparison of the data with the predictions of the percolation model shows good agreement as for the temperature evolution of liquid water. This work provides additional support to the interpretation of water bands substructures as signatures of its very specific connectivity pattern.     

SCF-MO-LCGO studies on hydrogen bonding. The water dimer

The hydrogen bond in the water dimer is studied within the SCF-MO-LCAO framework, using a large Gaussian basis set to approximate the wavefunction. A geometry search restricted to structures with linear and bifurcated hydrogen bonds is performed and the associated potential energy curves are displayed. The minimum energy geometry of the water dimer is found to form a linear hydrogen bond with a hydrogen bond distance of 2.04 Å and a binding energy of 4.84 kcal/mole relative to the monomer (exp. 5.0 kcal/mole). No semistable structures are found. The charge density and charge density difference maps are discussed for the structure with a linear hydrogen bond for different subsystem (water) separations, including the minimum energy geometry. The dipole moment of the dimer is computed to be 1.69 a.u. The shift of the IR bands on hydrogen bond formation is explained qualitatively by comparing the potential energy curves of the hydrogen in the OH-bonds of the monomer and the dimer, and the intensity increase of the fundamental OH-stretching band is computed. The shift of the proton magnetic resonance signal is discussed qualitatively by inspecting the charge density change on hydrogen bond formation, and the average diamagnetic shielding is calculated.

---

Zusammenfassung Die Wasserstoffbrückenbindung im dimeren Wasser ist im Rahmen des SCF-MO-LCAO-Verfahrens untersucht worden, wobei die Wellenfunktion durch Gaußfunktionen angenähert wurde. Die Untersuchungen beschränkten sich auf Strukturen mit linearen und gegabelten Wasserstoffbrücken. Die zugehörigen Potentialkurven wurden berechnet und graphisch dargestellt. Danach besitzt das dimere Wasser in der energetisch stabilsten Form eine lineare Wasserstoffbrückenbindung mit einem Brückenbindungsabstand von 2,04 Å. Die Bildungsenergie aus zwei monomeren Wassermolekülen beträgt 4,84 Kcal/Mol. Es wurden keine semistabilen Strukturen anderer Geometrie gefunden. Für das dimere Wasser mit linearer Wasserstoffbrückenbindung sind für verschiedene Brückenbindungsabstände die Elektronendichten und die Elektronendichtedifferenzen, bezogen auf zwei ungestörte Wassermoleküle als Vergleichssystem, graphisch dargestellt und diskutiert worden. Das Dipolmoment des dimeren Wassers wurde zu 1,69 a.u. berechnet. Die Verschiebung der IR-Banden, die bei der Bildung der Wasserstoffbrückenbindung experimentell beobachtet wird, kann qualitativ aufgrund der entsprechenden Potentialkurven erklärt werden. Die dabei gleichfalls beobachtete Intensitätszunahme wurde berechnet. Die Verschiebung des Proton-Kernresonanzsignals konnte qualitativ an Hand der berechneten Ladungsdichtedifferenzen diskutiert und die diamagnetische Abschirmkonstante bestimmt werden.

---

Résumé Etude de la liaison hydrogène du dimère de l'eau dans le cadre SCF-MO-LCAO en utilisant une grande base de fonctions gaussiennes. La géométrie est recherchée parmi les structures à liaisons hydrogène linéaires et fourchues avec production des courbes d'énergie potentielle associées. La géométrie du dimère d'énergie minimum est du type liaison hydrogène linéaire de longueur 2,04 Å et d'énergie 4,84 Kcal/mole (exp. 5,0 Kcal/mole). On ne trouve pas de structures semi-stables. Les cartes de densité de charge et de densité différentielle sont discutées pour différentes distances de séparation du système à liaison hydrogène linéaire. Le moment dipolaire du dimère est évalué à 1,69 u.a. Le déplacement des bandes I.R par formation de liaison hydrogène est expliqué qualitativement en comparant les courbes d'énergie potentielle de la liaison OH dans le monomère et le dimère, et l'on calcule l'augmentation d'intensité de la bande fondamentale de vibration OH. Le déplacement du signal de résonance magnétique du proton est discuté qualitativement par inspection des variations de densité de charge par formation de la liaison hydrogène, et l'on a calculé l'écran diamagnétique moyen.

---

---

These studies were started while the author was visiting the IBM Research Laboratories, San Jose, California 95114, USA.     

On the hydrogen bonding between water and ammonia molecules

The hydrogen bond N·HO between the water and ammonia molecules has been investigated ab initio using the SCF LCAO MO method. The minimal and extended basis sets of Slater type orbitals were used. It was found that the energy of the hydrogen bond is equal to 6.44 kcal/mole and the equilibrium separation of the oxygen and nitrogen atoms in the dimer is 5.72 au. At this intermolecular distance there is only one minimum in the potential energy curve for the motion of proton.     

An NMR study of hydrogen bonding in some azo dyestuffs

The ¹H, ¹³C, and ¹⁵N NMR data reported for compounds 1–4 show that in DMSO solutions all of them exist in the azo form only and do not participate in the azo–hydrazoimine equilibrium. The NMR data for compounds 1 and 2 show the presence of a weak hydrogen bond for the non-protonated forms, between N10 and the 2-NHCH₃ proton. All compounds have also been studied in TFA solutions in which they are protonated. The site of protonation of 1, 2 and 3 is determined to be at N10 in TFA solutions. These results are supported by some ab initio GIAO-CHF molecular orbital calculations.     

The effects of dissolved halide anions on hydrogen bonding in liquid water

It is widely believed that the addition of salts to water engenders structural changes in the hydrogen-bond network well beyond the adjacent shell of solvating molecules. Classification of many ions as "structure makers" and "structure breakers" has been based in part on corresponding changes in the vibrational spectra (Raman and IR). Here we show that changes in O-H vibrational spectra induced by the alkali halides in liquid water result instead from the actions of ions' electric fields on adjacent water molecules. Computer simulations that accurately reproduce our experimental measurements suggest that the statistics of hydrogen-bond strengths are only weakly modified beyond this first solvation shell.     

Theoretical study on the hydrogen bonding of five-membered heteroaromatics with water

The hydrogen-bonding ability of five-membered heteroaromatic molecules containing one chalcogen and two heteroatoms with nitrogen in addition to chalcogen, respectively, have been analyzed using density functional and molecular orbital methods through adduct formation with water. The stabilization energies for all the adducts are established at B3LYP/6-31+G* and MP2/6-31+G* levels after correcting for the basis set superposition error by using the counterpoise method and also corrected for zero-point vibrational energies. A natural bond orbital analysis at B3LYP/6-31+G* level and natural energy decomposition analysis at HF/6-31+G* using MP2/6-31+G* geometries have been carried out to understand the nature of hydrogen-bonding interaction in monohydrated heterocyclic adducts. Nucleus-independent chemical shift have been evaluated to understand the correlation between hydrogen bond formation and aromaticity.     

Transition from patchlike to clusterlike inhomogeneity arising from hydrogen bonding in water

Assembling of water molecules via hydrogen bonding has been studied by molecular dynamics simulations using flexible potential model. The relationship between the number of H-bonds per molecule, n(HB), the size of H-bonded nets, k, and the size of patches of four-bonded molecules, k(4), has been examined for several thermodynamic states of water ranging from ambient to supercritical conditions. Two kinds of structural inhomogeneity have been found: the patchlike associated with the mean n(HB)> 2.0 and the clusterlike for n(HB)< 1.9. In compressed water up to ~473 K patches coexist with less ordered nets, both constituting the gel-like H-bonded network. The size of patches steeply decreases with the increasing temperature and the decreasing density of water. The inhomogeneity resulting from the presence of patches disappears above 473 K. This feature is associated with the rapid increase in the fraction of unbound molecules and with the breakage of the gel-like network into a variety of H-bonded clusters leading to the clusterlike structural inhomogeneity. In contrast to the patchlike inhomogeneity an increase in temperature and a decrease in density make this kind of inhomogeneity more pronounced. A degree of connectivity of H-bonds has been characterized by a parameter P(g) defined as the total fraction of molecules belonging to the H-bonded clusters of size k ≥ 5. The simulation-derived values of P(g) agree well with the predictions of the random bond theory giving the explicit expression for P(g) as a function of the mean n(HB). Going from ambient to supercritical conditions, we have found that the patchlike inhomogeneity is connected with the very slight reduction in P(g), whereas the clusterlike inhomogeneity generates a steep linear decrease of P(g) with the decreasing mean n(HB). The self-diffusion coefficient calculated for the thermodynamic states of water showing the clusterlike inhomogeneity has occurred to be inversely proportional to the density. We have also found that the clusterlike inhomogeneity is associated with the linear correlation between P(g) and the macroscopic properties of water: the static dielectric constant, the viscosity, and the density. The provided relationships allow one to estimate the degree of connectivity of hydrogen bonds from the measured macroscopic quantities.     

An alternative model for anomalous water

An alternative model for the structure of anomalous water is proposed, in which all hydrogen atoms are involved in hydrogen bonds. Such a model seems to agree well with the main experimental properties of that substance. In particular, IR and Raman spectra can be estimated in agreement with the measurements of Lippincott and coworkers.     

Ab initio study of hydrogen bonding in the phenol–water system

Three hydrogen-bonded minima on the phenol-water, C₆H₅OH—H₂O, potential energy surface were located with 3–21G and 6–31G** basis sets at both Hartree–Fock and MP2 levels of theory. MP2 binding energies were computed using large “correlation consistent” basis sets that included extra diffuse functions on all atoms. An estimate of the effect of expanding the basis set to the triple-zeta level (multiple f functions on carbon and oxygen and multiple d functions on hydrogen) was derived from calculations on a related prototype system. The best estimates of the electronic binding energies for the three minima are –7.8, –5.0, and –2.0 kcal/mol. The consequences of uncertainties in the geometries and limitations in the level of correlation recovery are analyzed. It is suggested that our best estimates will likely underestimate the complete basis set, full CI values by 0.1–0.3 kcal/mol. Vibrational normal modes were determined for all three minima, including an MP2/6–31G** analysis for the most strongly bound complex. Computational strategies for larger phenol–water complexes are discussed. © John Wiley & Sons, Inc.     

Unusual hydrogen bonding behavior in binary complexes of coinage metal anions with water

We have studied the interaction of atomic coinage metal anions with water molecules by infrared photodissociation spectroscopy of M-.H2O.Ar(n) clusters (M=Cu, Ag, Au; n=1, 2). We compare our observations with calculations on density-functional and coupled cluster levels of theory. The gold anion is bound to the water molecule by a single ionic hydrogen bond, similar to the halide-water complexes. In contrast, zero-point motion in the silver and copper complexes leads to a deviation from this motif.     

Carbohydrate intramolecular hydrogen bonding cooperativity and its effect on water structure

Molecular dynamics (MD) simulations combined with water-water H-bond angle analysis and calculation of solvent accessible surface area and approximate free energy of solvation were used to determine the influence of hydroxyl orientation on solute hydration and surrounding water structure for a group of chemically identical solutes-the aldohexopyranose sugars. Intramolecular hydrogen bond cooperativity was closely associated with changes in water structure surrounding the aldohexopyranose stereoisomers. The OH-4 group played a pivotal role in hydration as it was able to participate in a number of hydrogen bond networks utilizing the OH-6 group. Networks that terminated within the molecule (OH-4 --> OH-6 --> O-5) had relatively more nonpolar-like hydration than those that ended in a free hydroxyl group (OH-6 --> OH-4 --> OH-3). The OH-2 group modulated the strength of OH-4 networks through syndiaxial OH-2/4 intramolecular hydrogen bonding, which stabilized and induced directionality in the network. Other syndiaxial interactions, such as the one between OH-1 and OH-3, only indirectly affected water structure. Water structure surrounding hydrogen bond networks is discussed in terms of water-water hydrogen bond populations. The impact of syndiaxial versus vicinal hydrogen bonds is also reviewed. The results suggest that biological events such as protein-carbohydrate recognition and cryoprotection by carbohydrates may be driven by intramolecular hydrogen bond cooperativity.     

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.