Hydrogen-bonding Associations Research Articles

Tautomerism of quinazolin-4-ones with 2,3-annulated hydrogenated 1,3-diazaheterocycles. Synchronous and asynchronous double proton transfer in cyclic hydrogen-bonded associates

It was shown by quantum chemical methods and 1H NMR spectroscopy that in the series of prototropic tautomeric quinazolin-4-ones with hydrogenated 1,3-diazaheterocycles annulated at positions 2 and 3, namely, imidazole, pyrimidine, or [1,3]diazepine (compounds 1–3, respectively), the 1H-tautomeric form strongly predominates in the gas phase and in solutions regardless of the nature of these cycles. Tautomerization of tricycles 1–3 occurs via the intermolecular mechanism to form as intermediates hydrogen-bonded cyclodimers of these compounds or their cyclosolvates with proton-donor solvents. The key step of the reaction is the intraassociated concerted double proton transfer, which can proceed in nearly synchronous and asynchronous modes. In particular, double proton transfer in cyclodimers of quinazolinones 1–3 is asynchronous and proceeds with the formation of solvate-stabilized polar transition states, which are similar in structure to ionic intermediates of the nonconcerted double proton transfer.

Hydrogen-bond configuration in hydrogen-bond solutions. 1. Alcohol/alcohol solutions

A theory based on the hydrogen-bond configuration is proposed and applied to alcohol/alcohol binary solutions. The theory leads explicit expressions for the mixing Gibbs energy and reproduces the experiments on the crystal–liquid phase-diagrams of pure crystals and co-crystals and mixing heats with the parameters common to these experiments. The mixing entropy arises from the increase in the hydrogen-bonding availability of proton donors to approach hydrogen-bond-free proton acceptors. The mixing heat arises from a balance between the contribution from maintaining the original associations in pure liquids and the contribution from a construction of hydrogen bonds freely to hydrogen-bond-free acceptors. When hydrogen-bond associations between component-1 and component-2 are distinguished statistically from associations in each pure component, we call the solution as a cooperative solution that has at least one stoichiometric cooperative concentration point. Some shorter alcohol/alcohol solutions and some aromatic alcohol/aromatic alcohol solutions, however, have no cooperative point and we call those solutions as the ideal hydrogen-bond solutions of which properties are mainly governed by the ideal-gas-like mixing hydrogen-bond entropy. The hydrogen-bond energies of various combinations of the proton acceptor and the proton donor have been estimated consistently from the fittings of the theory, the shifts by hydrogen bonding of the OH stretching in the Raman or IR spectroscopy, and the sublimation energy of crystals. The present theory reveals the characteristics of hydrogen-bond solutions and gives some predictions.

Influence of Hydrogen Bonding on the Adhesive Properties of Photo-Curable Acrylics

Novel hot melt pressure sensitive adhesives (HMPSAs) were developed from acrylic terpolymers of 2-ethylhexyl acrylate (EHA), hydroxyethyl acrylate (HEA), and methyl acrylate (MA) functionalized with hydrogen bonding and photo-reactive functionalities. The hydrogen bonding and photo-reactive sites were introduced from the reaction of HEA repeat units with cyclohexyl isocyanate and cinnamoyl chloride, respectively. The functionalization reaction conditions were optimized to tailor the degree of urethane and cinnamate groups in order to examine the influence of hydrogen bonding and photo-active groups in low Tg acrylics. The synergy of hydrogen bonding and photo-reactivity resulted in higher peel values and rates of cinnamate photo-reactivity with increasing urethane concentration. The increase in cinnamate photo-reactivity with increasing urethane concentration provides evidence that hydrogen bond associations can promote cinnamate dimerization. Isothermal rheological experiments conducted at 150°C confirmed the melt stability of the cyclohexyl urethane linkage, cinnamate, and the acrylic composition indicating the potential for hot melt adhesive applications.

Hydration of phospholipid interface: carbonyl–water hydrogen bond association

Being largely driven by electrostatic interactions, hydration compensates hydrophobic repulsion and, thus, contributes decisively in structural expressions of molecules in a phospholipid membrane environment. Here, we explore the nature of the aqueous state associated with carbonyl moieties of a phospholipid bilayer. The task is of an obvious difficulty, since water clustering at a membrane interface implies the presence of various aqueous states giving rise to spectral inhomogeneity. The resultant frequency overlap of the optical response from states of differing nature obscures the structural analysis. We extract the information on water next to phospholipid carbonyls by monitoring the O-D stretch perturbation upon direct infrared excitation of lipid carbonyl groups. Modelling the signal with the help of quantum computations and molecular dynamics simulation, we extract the geometry for the optimal placement of water next to carbonyl moieties, and anticipate the time scale of the water molecule displacement, leading to the disruption of the hydrogen bond, upon direct excitation of the C=O group. The picture we provide here is of general and applied value. The practical importance stems from the necessity of experimentally characterizing the hydration of polar moieties in polypeptides (of pharmacological significance) when in a phospholipid environment, a task not yet achieved.

Extraction Equilibria of Trimellitic and [1,1′-Biphenyl]-2,2′-dicarboxylic Acid with 1-Octanol, 50%TBP, and 10%TRPO in Kerosene

To explore the feasibility of extracting aromatic acid products from oxidizing coal, two aromatic acids, trimellitic and [1,1′-biphenyl]-2,2′-dicarboxylic acid, were selected as the solutes, and the extraction equilibrium of the acids were studied with 1-octanol, 50% tributyl phosphate (TBP) in kerosene, and 10% trialkylphosphine oxide (TRPO) in kerosene. The results showed that the degree of extraction of [1,1′-biphenyl]-2,2′-dicarboxylic acid was larger than that of trimellitic acid for all of the solvent, and the extraction capacity with TRPO is more effective than the one with TBP. The extraction behavior of aromatic polyacid is different from that of carboxylic acid, and the reactive extraction function of aromatic acids with TBP and TRPO is not as effective as that of carboxylic acid. 1-octanol could be used to remove [1,1′-biphenyl]-2,2′-dicarboxylic acid from the mixture of trimellitic acid and [1,1′-biphenyl]-2,2′-dicarboxylic acid. Because the weak hydrogen bond association exists between OH in 1-octanol and COOH in aromatic acid, the extractive selectivity of [1,1′-biphenyl]-2,2′-dicarboxylic to trimellitic acid depends on the stoichiometric ratio.

Effect of temperature and water content on the structure of 1,2-propanediol and 1,3-propanediol: Near-infrared spectroscopic study

Effect of temperature and water content on the structure of 1,2-propanediol (12PD) and 1,3-propanediol (13PD) in the liquid phase has been studied by Fourier-transform near-infrared (FT-NIR) spectroscopy. In addition, the spectra of both diols in CCl 4 solutions at various concentrations were measured. The experimental spectra were analyzed by two-dimensional (2D) correlation approach and chemometric methods. The present results give no evidence that 12PD form the intramolecular hydrogen bonding. In contrast, significant amounts of 13PD molecules in diluted CCl 4 solution is involved in the intramolecular hydrogen bonding. At higher concentrations the intramolecular hydrogen bonds are broken and replaced by the intermolecular ones. The structure of pure liquid propanediols is determined by the intermolecular hydrogen bonding. Unlike for monohydroxyl alcohols, addition of water to propanediols leads to faster temperature-induced breaking of the hydrogen-bonded associates. However, variation of water content at constant temperature does not influence the structure of both diols. In this respect behavior of propanediols is similar to that of the monohydric alcohols. The molecules of water in the mixtures are hydrogen bonded to the diols and act as a double proton donor. This bonding appears to be stronger than that in bulk water.

Taking Advantage of Tailored Electrostatics and Complementary Hydrogen Bonding in the Design of Nanostructures for Biomedical Applications

AbstractFour‐armed, star‐shaped poly(D,L‐lactide) (PDLLA) was synthesized and terminally‐functionalized with either adenine or thymine complementary hydrogen bonding groups (PDLLA‐A and PDLLA‐T, respectively). The strong hydrogen bonding led to increased viscosity below the dissociation temperature of the hydrogen bonds. Rheology confirmed that these bonds were thermally reversible, with a sharp reduction in viscosity near 100 °C. PDLLA, PDLLA‐A, and PDLLA‐T were melt electrospun with no significant change in fiber diameter (all between 3.6 and 4.0 µm). However, a blend of PDLLA‐A and PDLLA‐T formed fibers with an average diameter of 9.8 ± 2.0 µm, resulting from the hydrogen bond associations. Also, the phospholipid 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphoethanolamine (POPE) was melt electrospun at 200 °C and formed uniform fibers with average fiber diameter of 6.5 ± 2.0 µm.

Aquachloridobis(1,10-phenanthroline-κ2N,N′)zinc(II) chlorideN,N-dimethylformamide solvate

The Zn atom in the title salt, [ZnCl(C12H8N2)2(H2O)]Cl·C3H7NO, is chelated by two phenanthroline mol­ecules and is bonded to one chloride ion and one water mol­ecule, resulting in a ZnN4ClO octa­hedral coordination environment with the Cl and O atoms in a cis conformation. The cations and anions are linked by O—H⋯Cl hydrogen bonds across a center of inversion, forming a hydrogen-bonded dimeric association. The dimethyl­formamide solvent mol­ecule is disordered over two orientations in a 0.56 (1):0.44 (1) ratio.

Solubility switch of gold nanoparticles through hydrogen bond association

Gold nanoparticles (AuNPs) coated with hexafluoroisopropanol moieties were prepared, and their surface was changed through simple hydrogen bond association with various amines, which allow orientation of the solubility of these AuNPs in determined organic solvents.

Association of polyacrylic acids with metronidazole

Intermolecular interactions in mixtures of dilute solutions of poly acids with 1-(β-hydroxyethyl)-2-methyl-5-nitroimidazole were studied by viscometry, potentiometry, and IR spectroscopy. The rheological behavior of dilute aqueous solutions of polyacrylic and polymethacrylic acids and of metronidazole at a total concentration of the components of 0.1 wt % was examined. The composition dependences of the specific viscosity show positive deviations from the additivity with a maximum at approximately 50% relative content of the poly acid. In these mixtures, polyelectrolytic complexes stabilized by hydrogen bonds are formed. The strength of the associates increases with an increase in the temperature to 40°C. Hydrophobic groups in macromolecules of the poly acid play a significant role in stabilization of the complexes. In aqueous solutions metronidazole interacts with acrylic, methacrylic, and hydrochloric acids, and in the solid state it forms linear hydrogen-bonded associates.

Biological implications of the interaction (via silanol groups) of silicon with metal ions.

Since the demonstration, in 1972, of the essentiality of silicon in higher animals, bio-inorganic chemists have speculated about the site and mechanism of action of silicon. Bone and connective tissue have been identified as tissues that are altered in the absence of silicon. Si-C bonds are foreign to biochemistry so organic bonding must be via Si-O-C, but the instability of the ester bond in aqueous solution at pH 7.4 has prompted us to investigate the interactions of silicic acid. Silicic acid could, by hydrogen bonding, alter the conformation of organic macromolecules, since hydrogen bond association can inhibit silanol condensation. However, silanols are also able to interact with metal ions that are basic at physiological pH, e.g. Fe3+ or Al3+ but not Ca2+, and such interactions are known in geochemistry. The observed effects of Si on hard and soft tissue could therefore result from interactions of Si(OH)4 with Fe3+, which is involved in connective tissue synthesis (via enzymes, e.g. prolyl hydroxylase) and damage (via iron-catalysed radical generation), or with Al3+ which exerts toxic effects at sites (bone and brain) at which Si has also been observed. Although we have demonstrated several Fe3+/Si interactions, we have not been able to show their relevance in a biochemical context. Al3+ interacts with Si(OH)4 in aqueous solution and preliminary experiments have suggested that silicic acid can counteract deleterious effects of aluminium, for example the activity of prolyl hydroxylase, an observation with implications not only in osteogenesis but also in Alzheimer's disease and aluminium toxicity in acidified waters.

Charge-Assisted Hydrogen-Bonded Assemblage of an Anionic {M(C2O4)4}4- Building Unit and Organic Cations: A Versatile Approach to Hybrid Supramolecular Architectures

The possibility to construct extended hybrid hydrogen-bonded networks by association of an anionic coordination complex and organic cations acting respectively as a hydrogen-bond acceptor and hydrogen-bond donors is explored. A series of seven architectures developed by charge-assisted hydrogen-bond association of {Zr(C2O4)4}4- (C2O4 = oxalate) and dications bearing N−H donor functions are described. The selected organic modules (i.e., protonated 4,4‘-bipyridine, di(4-pyridyl)ethane, di(4-pyridyl)ethylene, piperazine, m/p-phenylenediamine, terephtalamidine) possess two hydrogen-donor functions to allow them to act as bridges between the inorganic anions. Depending on the nature of the donor group, the number of hydrogens available for bonding, the geometric features, and sizes of the organic modules diverse assembling patterns have been observed ranging from one-dimensional (1-D) to three-dimensional (3-D) interlocked networks. A further, rather surprising hybrid system was realized by assembling the inor...

Guanidinium 2-carboxy-6-nitrobenzoate monohydrate: a two-dimensional hydrogen-bonded network structure

In the structure of the title compound, CH6N3+·C8H4NO6−·H2O, obtained from the reaction of guanidine carbonate with 3-nitro­phthalic acid, the 2-carboxylic acid group is deprotonated and participates in an asymmetric cyclic R21(6) hydrogen-bonding association with the guanidine cation together with a bridging water mol­ecule of solvation. A conjoint R12(7) facial association involving a nitro O-atom acceptor together with a further five guanidinium N—H⋯O hydrogen bonds, as well as a strong carbox­yl–water O—H⋯O inter­action [2.528 (3) Å], give a two-dimensional network structure.

Explicit-Solvent Molecular Dynamics Simulations of the Polysaccharide Schizophyllan in Water

Schizophyllan is a β(1→3)-D-glucan polysaccharide with β(1→6)-branched lateral glucose residues that presents a very stiff triple-helical structure under most experimental conditions. Despite the remarkable stability of this structure (which persists up to 120°C in aqueous solution), schizophyllan undergoes a major change of state around 7°C in water that has been hypothesized to result from an order-disorder transition in the lateral residues. This hypothesis is only supported by indirect experimental evidence and detailed knowledge (at the atomic level) concerning hydrogen-bonding networks, interactions with the solvent molecules, orientational freedom of the lateral residues, and orientational correlations among them is still lacking. In this study explicit-solvent molecular dynamics simulations of a schizophyllan fragment (complemented by simulations of its tetrasaccharide monomer) are performed at three different temperatures (273K, 350K, and 450K) and with two different types of boundary conditions (finite nonperiodic or infinite periodic fragment) as an attempt to provide detailed structural and dynamical information about the triple-helical conformation in solution and the mechanism of the low-temperature transition. These simulations suggest that three important driving forces for the high stability of the triple helix are i), the limited conformational work involved in its formation; ii), the formation of a dense hydrogen-bonding network at its center; and iii), the formation of interchain hydrogen bonds between main-chain and lateral glucose residues. However, these simulations evidence a moderate and continuous variation of the simulated observables upon increasing the temperature, rather than a sharp transition between the two lowest temperatures (that could be associated with the state transition). Although water-mediated hydrogen-bonded association of neighboring lateral residues is observed, this interaction is not strong enough to promote the formation of an ordered state (correlated motions of the lateral residues), even at the lowest temperature considered.

Surface and Interfacial Segregation in Blends of Polystyrene with Functional End Groups and Deuterated Polystyrene

The effect of chain-end chemistry on surface and interfacial segregation in symmetric blends of polystyrene (hPS)/deuterated polystyrene (dPS) has been investigated by X-ray photoelectron and secondary ion mass spectroscopy in conjunction with neutron reflectivity measurements. Alpha,omega-fluoroalkyl- and alpha,omega-carboxy-terminated polystyrenes (alpha,omega-hPS(Rf)2 and alpha,omega-hPS(COOH)2) were used as end-functionalized polymers; the former possesses chain ends with lower surface energies, and the latter possesses higher surface energies compared with that of the main chain. In the case of an alpha,omega-hPS(Rf)2/dPS blend film, alpha,omega-hPS(Rf)2 was enriched at the surface owing to the surface localization of the Rf groups, although the surface energy of the hPS segments was slightly higher than that of the dPS ones. On the contrary, in the case of an alpha,omega-hPS(COOH)2/dPS blend film, dPS was preferentially segregated at the surface. This may be due to a surface depletion of COOH ends and an apparent molecular weight increase of alpha,omega-hPS(COOH)2 produced by a hydrogen-bonded intermolecular association of COOH ends in addition to the surface energy difference between hPS and dPS segments. Interestingly, both Rf and COOH chain ends were partitioned to the substrate interface for the alpha,omega-hPS(Rf)2/dPS and alpha,omega-hPS(COOH)2/dPS blend films, resulting in the segregation of the hPS component at the substrate interface for both blends. The results presented imply that surface and interfacial segregation in polymer blends could be regulated by incorporating functional groups into the end portions of one component.

IR-spectroscopic studies of hydrogen-bonding solutions: Lineshape analysis of ethanol + hexane system

IR (infrared) line shapes of OH stretching bands in hydrogen-bonding states of ethanol–hexane solutions have been examined using a theoretically rigorous Voigt function, instead of the commonly used empirical Lorentz–Gauss equation. An efficient and numerically-stable computer code with the Voigt function has been developed in order to analyze hydrogen-bonding effects in IR absorption spectra. Although the Voigt function is not an analytically-closed form, a numerical computer subroutine, with only three adjustable parameters for each IR band (or peak), provides a unique solution in a least-squares analysis of the line shapes. On the other hand, the Lorentz–Gauss equation is an analytical function with four adjustable parameters for each IR peak. However, this function makes non-linear least-squares analyses almost impossible due to the existence of strong correlations among the parameters. Example analyses, using the ethanol–hexane system, are given. The degree of hydrogen-bonding associations of ethanol and an effective IR-absorbance coefficient for hydrogen-bonded clusters have been estimated, and results are quite reasonable, compared with those in the literature.

Anion Detection Driven by a Surprising Internal Hydrogen-Bonding Association in a Dinuclear Rhenium(I) Complex

A neutral dinuclear rhenium(I) bipyridinetricarbonyl bromide complex has been investigated with a range of anions, giving a remarkable binding affinity for dihydrogenphosphate. These studies highlight that anion sensing can be achieved with structurally simple species provided that the compound adopts an unconventional conformation, through, for example, intramolecular hydrogen bonding in solution.

Ruthenium Complex Fragments as Constituents of Trinuclear Photoactive Supramolecular Assemblies Based on Hydrogen Bond Association

AbstractThe reaction of the octahedral complexes cis‐ or trans‐[Ru(C≡N‐tBu)4(CN)2], (Ru(CN)2), with the photochemically active [bis(bipyridyl)bibenzimidazole‐ruthenium(II)], (RubiH2), component via hydrogen bond association results in the formation of supramolecular aggregates with modified photophysical properties. The first structural characterization of a supramolecular adduct is reported, in which the N–H functions of the ruthenium bound bibenzimidazole ligand via hydrogen bonds serve as an interface directly toward a cyanide ligand acting as a bridge to another transition metal. In addition, the maximum stoichiometry of the supramolecular associates is estimated by NMR titration experiments and association constants of the hydrogen bonded adducts are determined by the decay of the emission intensity during the titration experiments.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Molecular Recognition of Adeninium Cations on Anionic Metal−Oxalato Frameworks: An Experimental and Theoretical Analysis

Reactions of adenine with water-soluble oxalato complexes at acidic pH give the compounds (1H,9H-ade)2[Cu(ox)2(H2O)] (1) [H2ade=adeninium cation (1+), ox=oxalato ligand (2-)] and (3H,7H-ade)2[M(ox)2(H2O)2].2H2O [M(II)=Co (2), Zn (3)]. The X-ray single crystal analyses show that the supramolecular architecture of all compounds is built up of anionic sheets of metal-oxalato-water complexes and ribbons of cationic nucleobases among them to afford lamellar inorganic-organic hybrid materials. The molecular recognition process between the organic and the inorganic frameworks determines the isolated tautomeric form of the adeninium cation found in the crystal structures: the canonical 1H,9H for compound 1, and the first solid-state characterized 3H,7H-adeninium tautomer for compounds 2 and 3. Density functional theory calculations have been performed to study the stability of the protonated nucleobase forms and their hydrogen-bonded associations by comparing experimental and theoretical results.

Chiral solvating properties of ( S)-1-benzyl-6-methylpiperazine-2,5-dione

In CDCl 3 solution, enantiopure ( S)-1-benzyl-6-methylpiperazine-2,5-dione ( S)- 1a formed diastereomeric C O⋯ H–N hydrogen-bonded associates with racemic ( RS, Z)-1-benzyl-3-[(dimethylamino)methylidene]piperazine-2,5-diones 2a and 2b, ( RS)- tert-butyl pyroglutamate ( RS)- 2c and ( RS)- N-benzoylalanine methyl ester ( RS)- 2d. This resulted in splitting (doubling) of the characteristic signals in the 1H NMR and 13C spectra of racemic compounds 2a– d in the presence of 1 equiv of ( S)- 1a. The formation of hydrogen-bonded dimers in CDCl 3 solution was studied by 1H NMR, 13C NMR and 2D NMR and confirmed by the intermolecular NOE observed between the hydrogen-bonded amide protons from each of the monomeric units, ( S)- 1a and 2a– c. On the other hand, a slightly different binding mode was proposed for association of ( S)- 1a with alaninamide ( RS)- 2d. Enantiomer compositions of known (weighed) mixtures of both enantiomers of tert-butyl pyroglutamate 2c were re-determined by 1H NMR in the presence of ( S)- 1a in CDCl 3. The experimental values were in good agreement with the theoretical values, thus indicating the potential applicability of ( S)- 1a and related diketopiperazines as chiral solvating agents in NMR spectroscopy.