Strength Of Intermolecular Hydrogen Bonds Research Articles

Synthesis and mesomorphic behaviour of hexacatenar di-hydrazine derivatives

A new series of hydrazide derivatives of N,N-bis(3,4,5-tris(heptyloxy)benzoyl) (T7 series) were designed and synthesised. Investigations on the liquid crystalline properties by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarising optical microscopy (POM) showed that the di-hydrazine derivatives exhibited different mesophases, which were ascribed to the different structure of T7 series. The rectangular columnar mesophases of T7-ben remained stable down to room temperature during cooling, T7-fuma was decomposed at 259°C in the first heating, while T7-mal showed simple cubic mesophase and crystalline phase at room temperature during cooling. Comparing Fourier-transformed infrared (FTIR) at room temperature of T7 series, some differences were found in the N–H stretching vibration and C = O stretching vibration bands, indicating that T7 series had some differences in intermolecular hydrogen bond strength, which were caused by the different linking unit of T7 series. Intermolecular hydrogen bonding between –C = O and –N–H groups in crystalline and liquid crystalline phases was confirmed by temperature FTIR spectroscopy and temperature 1H NMR spectroscopy.

Communication: Frequency shifts of an intramolecular hydrogen bond as a measure of intermolecular hydrogen bond strengths

Infrared-ultraviolet double resonance spectroscopy has been applied to study the infrared spectra of the supersonically cooled gas phase complexes of formic acid, acetic acid, propionic acid, formamide, and water with 9-hydroxy-9-fluorenecarboxylic acid (9HFCA), an analog of glycolic acid. In these complexes each binding partner to 9HFCA can function as both proton donor and acceptor. Relative to its frequency in free 9HFCA, the 9-hydroxy (9OH) stretch is blue shifted in complexes with formic, acetic, and propionic acids, but is red shifted in the complexes with formamide and water. Density functional calculations on complexes of 9HFCA to a variety of H bonding partners with differing proton donor and acceptor abilities reveal that the quantitative frequency shift of the 9OH can be attributed to the balance struck between two competing intermolecular H bonds. More extensive calculations on complexes of glycolic acid show excellent consistency with the experimental frequency shifts.

A TD‐DFT study on the hydrogen bonding of three esculetin complexes in electronically excited states: Strengthening and weakening

Time-dependent density functional theory (TD-DFT) method was used to study the excited-state hydrogen bonding of three esculetin complexes formed with aprotic solvents. The geometric structures, molecular orbitals (MOs), electronic spectra and the infrared (IR) spectra of the three doubly hydrogen-bonded complexes formed by esculetin and aprotic solvents dimethylsulfoxide (DMSO), tetrahyrofuran (THF) and acetonitrile (ACN) in both ground state S(0) and the first singlet excited state S(1) were calculated by the combined DFT and TD-DFT methods with the COSMO solvation model. Two intermolecular hydrogen bonds can be formed between esculetin and the aprotic solvent in each hydrogen-bonded complex. Based on the calculated bond lengths of the hydrogen bonds and the groups involved in the formation of the intermolecular hydrogen bonds in different electronic states, it is demonstrated that one of the two hydrogen bonds formed in each hydrogen-bonded complex is strengthened while the other one is weakened upon photoexcitation. Furthermore, it is found that the strength of the intermolecular hydrogen bonds formed in the three complexes becomes weaker as the solvents change from DMSO, via THF, to ACN, which is suggested to be due to the decrease of the hydrogen bond accepting (HBA) ability of the solvents. The spectral shifts of the calculated IR spectra further confirm the strengthening and weakening of the intermolecular hydrogen bonds upon the electronic excitation. The variations of the intermolecular hydrogen bond strengths in both S(0) and S(1) states are proposed to be the main reasons for the gradual spectral shifts in the absorption and fluorescence spectra both theoretically and experimentally.

Pairwise Substitution Effects, Inter- and Intramolecular Hydrogen Bonds in Methoxyphenols and Dimethoxybenzenes. Thermochemistry, Calorimetry, and First-Principles Calculations

Methoxyphenols are the structural fragments of different antioxidants and biologically active molecules, which are able to form strong intermolecular and intramolecular hydrogen bonds in condensed matter. In the present work, thermochemical, Fourier transform infrared (FTIR)-spectroscopic and quantum-chemical studies of methoxyphenols and its H-bonded complexes in solution and gas phase have been carried out. Thermodynamic properties (standard molar enthalpies of formation, vapor pressure, vaporization enthalpies, sublimation enthalpies, and fusion enthalpies) of 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, and 1,4-dimethoxybenzene have been studied in this work. To verify the experimental data, ab initio calculations of all compounds have been performed using density functional theory (DFT), MP2, and G3 methods. The quantitative analysis of ortho, meta, and para pairwise-substituent effects in methoxyphenols has been performed. Solution enthalpies of methoxyphenols at infinite dilution in proton acceptor solvents have been measured. Calorimetric data shows that intermolecular hydrogen bond strength in complexes of 2-methoxyphenol with organic bases is less than that for 4-methoxyphenol. Two experimental approaches for determination of enthalpy of intramolecular hydrogen bonds in ortho-methoxyphenols were proposed. The new results help to resolve uncertainties in the available thermochemical data on methoxyphenols and dimethoxybenzenes and to realize relations among properties and structures for these compounds.

Prediction of relative pK a values of amines by quantum chemical calculations

An approach based on the cluster-continuum model is used to calculate some relative pK a values. For this purpose, one and two explicit water molecules are combined with the polarizable continuum model (PCM), conductor-like polarizable continuum model (CPCM), and integral equation formalism polarizable continuum model (IEF-PCM) to accurately predict solvation free energies. Pure continuum model results are also presented for comparison. B3LYP/6-31+G* level of theory is used for prediction of both gas-phase and solvation free energies during all calculations. Atoms in molecules analyses are also presented to characterize the strength of intermolecular hydrogen bonds between the solvent molecules and the bases. Results are in line with previous studies and show that introducing explicit solvent molecules has a drastic effect on the prediction of acidity constants of amines.

FTIR study of H-bonds cooperativity in complexes of 1,2-dihydroxybenzene with proton acceptors in aprotic solvents: Influence of the intramolecular hydrogen bond

FTIR spectroscopic study of hydrogen bonding of 1,2-dihydroxybenzene (catechol) with proton acceptors has been carried out. The influence of intramolecular and intermolecular hydrogen bonds on the strengths of each other in complexes of 1,2-dihydroxybenzene with various proton acceptors has been analyzed. It was shown that intramolecular hydrogen bond is strengthened when 1,2-dihydroxybenzene interacts with bases (ethers, amines, nitriles, etc.) in inert solvents. The contribution of the cooperativity of intramolecular hydrogen bonds in the frequency of stretching vibrations of O–H groups linearly depends on the proton acceptor ability of the bases. The solvent effect on hydrogen bond cooperativity in 1,2-dihydroxybenzene–base complexes has been studied. The approach to determine the influence of cooperative effects on the formation of intermolecular complexes with 1,2-dihydroxybenzene is proposed. It was shown that the strength of intramolecular hydrogen bonds in the complexes of 1,2-dihydroxybenzene with bases due to cooperativity of interactions increases by 30–70%, and the strength of intermolecular hydrogen bond by 7–22%.

Synthesis of Chalcone and Flavanone Derivatives from Condensation of 2’-Hydroxyacetophenones and Benzaldehyde over Basic <i>β</i>-Zeolites

The basic strength of alkali metal ion-exchanged β-zeolites was assessed based on the extent of Knoevenagel reaction using malonic acid derivatives and benzaldehyde. Preparation of chalcone and flavanone derivatives from the condensation of 2’-hydroxyacetophenones and benzaldehyde were carried out over the zeolites. The conversions of chalcone and flavanone derivatives and the selectivity of flavanone derivatives increased with the basic strength of the catalyst. A cyclization from chalcone to flavanone was controlled with intermolecular hydrogen bond strength of chalcone derivatives.

The standard enthalpies of formation of l-asparagine and l-α-glutamine

The energies of combustion of l-asparagine and l-α-glutamine were measured in a static bomb adiabatic calorimeter. Corrections were made for the heats due to the ignition of sample and for the nitric acid formation. The derived enthalpies of formation in solid state of asparagine monohydrate, nonhydrated asparagine and glutamine are respectively −1084.1 ± 3.0, −788.1 ± 4.7 and −834.3 ± 4.6 kJ mol −1. The data of enthalpy of formation are compared with the literature values and with estimated values by means of group additivity, using parameters recommended by Domalski and Hearing. The discrepancies between experimental and calculated values are explained by considering the number and strength of intermolecular hydrogen bonds. The dehydration of asparagine monohydrate and the possible melting of the three amino acids were investigated by means of DSC. Glutamine melts without considerable decomposition at about 182 °C, while asparagines decompose during the fusion process (208 °C).

A new method for quick predicting the strength of intermolecular hydrogen bonds

A new method is proposed to quick predict the strength of intermolecular hydrogen bonds. The method is employed to produce the hydrogen-bonding potential energy curves of twenty-nine hydrogen-bonded dimers. The calculation results show that the hydrogen-bonding potential energy curves obtained from this method are in good agreement with those obtained from MP2/6-31+G** calculations by including the BSSE correction, which demonstrate that the method proposed in this work can be used to calculate the hydrogen-bonding interactions in peptides.

Structural aspects of the intermolecular hydrogen bond strength: H‐bonded complexes of aniline, phenol and pyridine derivatives

AbstractThis short review is devoted to the description of the effect of the nature and the strength of intermolecular hydrogen bonds on structural properties of H‐bonded complexes of aniline, phenol and pyridine derivatives. Several hundreds of such complexes, playing an important role in organic chemistry and biochemistry, have been identified and described in the literature. In the introductory part, the idea of the H‐bond is discussed in terms of its historical development, followed by presently accepted classification of H‐bonds. Critical review of quantum methods usually used for the calculations of the geometry of H‐bonded complexes and the energies of H‐bonds is then presented. In the second part, the H‐bond‐induced geometrical, hybridization and aromaticity index changes are discussed. All correlations based on quantum calculations are compared with those derived from the available crystal structure data. Although the experimental data are more scattered than the calculated ones, their agreement is impressive. This unequivocally shows the power of the calculation methods developed in recent years. Copyright © 2008 John Wiley & Sons, Ltd.

Quantum chemical studies on the potentially important imidates

The conformational space for the imidates 1–5 was explored with the Monte Carlo conformational search varying all the torsional degrees of freedom. Geometry optimization of the most stable conformers of imidates 1–5 were performed at the level B3LYP/6-31+G(d). Computed geometrical parameters were compared with the X-ray reported results. Hydrogen bonding, both intra- and intermolecular with methanol as solvent were computed at different computational levels in gas phase and DMSO. Intramolecular hydrogen bond strength does not exceed the limit of 8.50 kcal/mol due to geometry restrictions while, on the other hand, intermolecular hydrogen bond strength approaches 30.00 kcal/mol. Transition states of the inter-conversion between the most stable conformers (rotamers) were located and activation barrier of the inter-conversion processes was computed at different levels in gas phase and DMSO. Infrared spectra of these compounds were simulated and compared with experimental results. The carbonyl of the ester group shows bond stretching vibrational frequency at 1706–1812 cm −1 which agrees well with the experimentally recorded values at 1708–1740 cm −1.

Characterization of Peptide–Pyrazole Interactions in Solution by Low‐Temperature NMR Studies

Complexation of the amino- and carboxyl-protected tripeptide Piv-L-Val-L-Val-L-Val-tBu with 3-methylpyrazole and 3-amino-5-methylpyrazole was studied by low-temperature NMR experiments in a freonic solvent. The peptide forms an extended beta-type structure at all temperatures and associates through hydrogen bonding with the two pyrazole-based beta-sheet ligands. A detailed structural characterization of the formed complexes by one- and two-dimensional NMR experiments under slow exchange conditions was made possible by employing very low temperatures. The tripeptide associates to stable antiparallel dimers that are symmetrically capped on both sides by two pyrazole receptors to form 2:2 complexes. Amide groups of two neighboring residues in an extended conformation are involved in cyclic hydrogen bonds to the pyrazole. Based on amide chemical shift changes, the relative strength of intermolecular hydrogen bonds can be assessed and correlated with the electronic effects of the substituents on the pyrazole.

Flexible simple point-charge water model with improved liquid-state properties

In order to introduce flexibility into the simple point-charge (SPC) water model, the impact of the intramolecular degrees of freedom on liquid properties was systematically studied in this work as a function of many possible parameter sets. It was found that the diffusion constant is extremely sensitive to the equilibrium bond length and that this effect is mainly due to the strength of intermolecular hydrogen bonds. The static dielectric constant was found to be very sensitive to the equilibrium bond angle via the distribution of intermolecular angles in the liquid: A larger bond angle will increase the angle formed by two molecular dipoles, which is particularly significant for the first solvation shell. This result is in agreement with the work of Hochtl et al. [J. Chem. Phys. 109, 4927 (1998)]. A new flexible simple point-charge water model was derived by optimizing bulk diffusion and dielectric constants to the experimental values via the equilibrium bond length and angle. Due to the large sensitivities, the parametrization only slightly perturbs the molecular geometry of the base SPC model. Extensive comparisons of thermodynamic, structural, and kinetic properties indicate that the new model is much improved over the standard SPC model and its overall performance is comparable to or even better than the extended SPC model.

Characterization and evaluation of whey protein-based biofilms as substrates for in vitro cell cultures

Whey proteins-based biofilms were prepared using different plasticizers in order to obtain a biomaterial for the human keratinocytes and fibroblasts in vitro culture. The film properties were evaluated by Fourier Transform Infrared Spectroscopy (FTIR) technique and mechanical tests. A relationship was found between the decrease of intermolecular hydrogen bond strength and film mechanical behavior changes, expressed by a breaking stress and Young modulus values diminishing. These results allow stating that the film molecular configuration could induce dissimilarities in its mechanical properties. The films toxicity was assessed by evaluating the cutaneous cells adherence, growth, proliferation and structural stratification. Microscopic observation demonstrated that both keratinocytes and fibroblasts adhered to the biofilms. The trypan blue exclusion test showed that keratinocytes grew at a significantly high rate on all the biofilms. Structural analysis demonstrated that keratinocytes stratified when cultured on the whey protein-based biofilms and gave rise to multi-layered epidermal structures. The most organized epidermis was obtained with whey protein isolate/DEG biofilm. This structure had a well-organized basal layer under supra-basal and corneous layers. This study demonstrated that whey proteins, an inexpensive renewable resource which can be obtained readily, were non-toxic to cutaneous cells and thus they could be useful substrates for a variety of biomedical applications, including tissue engineering.

A Fourier-transform infrared spectroscopy study of sugar glasses

Fourier-transform infrared spectroscopy (FTIR) was used to study the hydrogen-bonding interactions that take place in vitrified carbohydrates of different chain lengths. The band position of the OH stretching band ( νOH) and the shift in band position as a function of temperature were determined from the FTIR spectra as indicators for the length and strength of intermolecular hydrogen bonds, respectively. Differential scanning calorimetry (DSC) was used to corroborate the FTIR studies and to measure the change in heat capacity (Δ C p) that is associated with the glass transition. We found that with increasing T g, the band position of νOH increases, the wavenumber–temperature coefficient of νOH in the glassy state, WTC g, increases, whereas Δ C p decreases. The positive correlation that was found between νOH and the glass transition temperature, T g, indicates that the length of the hydrogen bonds increases with increasing T g. The increase in WTC g with increasing T g indicates that the average strength of hydrogen bonding decreases with increasing T g. This implies that oligo- and polysaccharides (high T g) have a greater degree of freedom to rearrange hydrogen bonds during temperature changes than monosaccharides (low T g). Interestingly, WTC g and Δ C p showed a negative linear correlation, indicating that the change in heat capacity during the glass transition is associated with the strength of the hydrogen-bonding network in the glassy state. Furthermore, we report that introduction of poly- l-lysine in glassy sugar matrices decreases the average length of hydrogen bonds, irrespective of the size of the carbohydrate. Palmitoyl–oleoyl-phosphatidylcholine (POPC) vesicles were found to only interact with small sugars and not with dextran.

Thermal and Infrared Spectroscopic Studies on Hydrogen-Bonding Interaction between Poly(3-hydroxybutyrate) and Catechin

The effects of catechin on the properties of bacterially synthesized isotactic poly[(R)-3-hydroxybutyrate] (i-PHB) and chemosynthesized highly-syndiotactic poly[(R,S)-3-hydroxybutyrate] (s-PHB) were investigated by differential scanning calorimetry and Fourier transform infrared (FT-IR). In both PHB/catechin blend systems, the composition-dependent single glass transition temperature was observed. By using FT-IR, the formation of intermolecular hydrogen bonds was found between the carbonyl of PHB and the hydroxyl of catechin. The strength of intermolecular hydrogen bonds of s-PHB/catechin blends, i-PHB /catechin blends and pure catechin is in this order, i.e., s-PHB/catechin blends < i-PHB/catechin blends < pure catechin. The crystallization of either i-PHB or s-PHB was found to be restrained by the existence of catechin, and both i-PHB and s-PHB are miscible with catechin in the amorphous phase due to the intermolecular hydrogen-bonding. The effect of different stereochemical structures of i-PHB and s-PHB on the PHB-catechin interaction has been discussed.

Effect of the solvent nature and the number of electrophilic substituents in the molecule on hydration of nitro derivatives of phenanthrene-9,10-quinone

Solvates (1⩺2) of 10,10-dihydroxy-2,4,7-trinitro-9,10-dihydrophenanthren-9-one with DMSO and of 10,10-dihydroxy-2,7-dinitro-9,10-dihydrophenanthren-9-one with HMPA were prepared. The crystal structure of 2,5-dinitrophenanthrene-9,10-quinone was established. The results of X-ray diffraction analysis and IR spectroscopy of a series of mono-, di-, and trinitro derivatives of phenanthrene-9,10-quinone demonstrated that the ability of carbonyl groups to participate in nucleophilic addition of water increases as the number of nitro groups in substituted phenanthrene-9,10-quinone increases. The nature of the solvent (HMPA, DMF, or DMSO) affects hydration of phenanthrenequinones primarily due to the difference in the strength of intermolecular hydrogen bonds stabilizing di- and tetrahydroxy-dihydrophenanetherenes.

Characterization of Factors Affecting Properties of Rice Cake and Its Structure.

In the manufacturing process, the relationship between the expansibility of glutinous rice crackers and the properties of gelatinized and retrograded rice flour gel (rice cake) has not been fully clarified. We analyzed glutinous paddy rice from various angles using proximate analysis, amylography, measurement of degree of dispersion and differential scanning calorimetry. The tendencies, depending on cultivars, as measured were related. In particular, it was suggested that the amount and strength of intermolecular hydrogen bonds in rice was related to the expansion volume of rice cake because the enthalpy and peak temperature of DSC is closely related to its volume. Accordingly, it was suggested that DSC might be usable as a common standard for characterization of the factors affecting the properties of rice cake and its structure from the viewpoint of rice cracker expansibility.

Propriétés thermodynamiques en phase condensée des ortho, méta et para fluorotoluéne, crésol et toluidine

The fusion thermodynamic properties and condensed phase heat capacities for isomers of fluorotoluene, cresol and toluidine were determined using microcalorimetry. The lower melting points and enthalpies of fusion for the meta isomer are explained by the lower strength of intermolecular hydrogen bonds. The increase in heat capacity in the liquid state and greater significance of the fusion heat capacities for cresol and toluidine indicate molecular association in these compounds.

Hydrophobic interactions affect hydrogen bond strengths in complexes between peptides and vancomycin or ristocetin.

A study on complexes of the glycopeptide antibiotics vancomycin and ristocetin with various dipeptides and tripeptides shows that the intermolecular hydrogen bond strengths of the complexes are reasonably well correlated with their free energy of formation. Such correlation is not anticipated on the basis of a purely hydrophobic interaction of the peptide side-chains with the antibiotics. It is also shown that the free energy changes observed are very different from those expected as a result of hydrophobic forces. These facts suggest that addition of a hydrophobic group not only allows hydrophobic bonding but also strengthens existing hydrogen bonds. The increased hydrogen bond strength can be an important factor in determining the overall binding energy.