Formation Of Hydrogen Bond Network Research Articles

Development of Glassy Bicontinuous Cubic Liquid Crystals for Solid Proton-Conductive Materials.

Glassy bicontinuous cubic liquid crystals are developed to be a matrix having a hydrophilic infinite periodic minimal surface (IPMS). They function as a scaffold for water, leading to the formation of a 3D continuous hydrogen-bonding network of water molecules along the IPMS. This material design is advantageous for developing novel electrolytes with rigidity and high proton conductivity.

Acid-base high temperature proton exchange membranes prepared from phosphonic acid functionalized siloxane

One kind of acid-base high temperature proton exchange membranes has been prepared from amino trimethylene phosphonic acid (ATMP), epoxycyclohexyethyltrimethoxysilane (EHTMS), and 3-aminopropyltriethoxysilane (APTES) by sol-gel process. The structural characteristics of these membranes with different amount of APTES were investigated by FT-IR, XRD, and SEM. These membranes showed excellent dimensional stability in water with the contribution of flexible ionic network structure and were thermally stable up to about 200 °C. In addition, the proton conductivity of the membranes increased with increasing temperature over the range of 20 to 140 °C, up to a maximum of 2.63 × 10−2 S cm−1 at 140 °C under anhydrous condition. The high proton conductivity was attributed to the formation of hydrogen bond network through the synergistic effect of N and P. The activation energy value of membranes became lower from 0.46 to 0.30 eV because of the acid-base pairs. The variable-temperature FT-IR further proved the formation of hydrogen bond network in the membrane.

Nanocystalline cellulose reinforced sulfonated fluorenyl-containing polyaryletherketones for proton exchange membranes

Sulfonated fluorenyl-containing polyaryletherketones (SFPAEKs) were synthesized through a postsulfonation approach under a mild reaction condition. The composite proton exchange membranes based on SFPAEKs and various amounts of the modified nanocrystalline cellulose (NCC) were prepared by solution casting method. The existence of the multiple hydroxyl and sulfonic acid groups on the chemically modified nanocrystalline cellulose was supposed to benefit the formation of hydrogen-bond network and proton-conducting channels, which would improve the proton conducting ability of the composite membranes. Furthermore, the properties, such as mechanical properties, thermal stability, water uptake, swelling ratio and so on, were thoroughly investigated. In comparison to the pristine SFPAEK, the composite membranes containing a “performance enhanced” NCC component presented the higher proton conductivity and better mechanical properties. It was found that the proton conductivity of the composite membrane with 4wt% of NCC could reach 0.234Scm−1 at 100°C, and this value was higher than that of most of the reported membranes. The results showed that the modified nanocrystalline cellulose reinforced SFPAEK composite membrane would be promising for the application as middle-temperature proton exchange membranes in fuel cells.

Structural Insight into the Critical Role of the N-Terminal Region in the Catalytic Activity of Dual-Specificity Phosphatase 26.

Human dual-specificity phosphatase 26 (DUSP26) is a novel target for anticancer therapy because its dephosphorylation of the p53 tumor suppressor regulates the apoptosis of cancer cells. DUSP26 inhibition results in neuroblastoma cell cytotoxicity through p53-mediated apoptosis. Despite the previous structural studies of DUSP26 catalytic domain (residues 61–211, DUSP26-C), the high-resolution structure of its catalytically active form has not been resolved. In this study, we determined the crystal structure of a catalytically active form of DUSP26 (residues 39–211, DUSP26-N) with an additional N-terminal region at 2.0 Å resolution. Unlike the C-terminal domain-swapped dimeric structure of DUSP26-C, the DUSP26-N (C152S) monomer adopts a fold-back conformation of the C-terminal α8-helix and has an additional α1-helix in the N-terminal region. Consistent with the canonically active conformation of its protein tyrosine phosphate-binding loop (PTP loop) observed in the structure, the phosphatase assay results demonstrated that DUSP26-N has significantly higher catalytic activity than DUSP26-C. Furthermore, size exclusion chromatography-multiangle laser scattering (SEC-MALS) measurements showed that DUSP26-N (C152S) exists as a monomer in solution. Notably, the crystal structure of DUSP26-N (C152S) revealed that the N-terminal region of DUSP26-N (C152S) serves a scaffolding role by positioning the surrounding α7-α8 loop for interaction with the PTP-loop through formation of an extensive hydrogen bond network, which seems to be critical in making the PTP-loop conformation competent for phosphatase activity. Our study provides the first high-resolution structure of a catalytically active form of DUSP26, which will contribute to the structure-based rational design of novel DUSP26-targeting anticancer therapeutics.

Furazans with Azo Linkages: Stable CHNO Energetic Materials with High Densities, Highly Energetic Performance, and Low Impact and Friction Sensitivities.

Various highly energetic azofurazan derivatives were synthesized by simple and efficient chemical routes. These nitrogen-rich materials were fully characterized by FTIR spectroscopy, elemental analysis, multinuclear NMR spectroscopy, and high-resolution mass spectrometry. Four of them were further confirmed structurally by single-crystal X-ray diffraction. These compounds exhibit high densities, ranging from 1.62 g cm(-3) up to a remarkably high 2.12 g cm(-3) for nitramine-substituted azofurazan DDAzF (2), which is the highest yet reported for an azofurazan-based CHNO energetic compound and is a consequence of the formation of strong intermolecular hydrogen-bonding networks. From the heats of formation, calculated with Gaussian 09, and the experimentally determined densities, the energetic performances (detonation pressure and velocities) of the materials were ascertained with EXPLO5 v6.02. The results suggest that azofurazan derivatives exhibit excellent detonation properties (detonation pressures of 21.8-46.1 GPa and detonation velocities of 6602-10 114 m s(-1) ) and relatively low impact and friction sensitivities (6.0-80 J and 80-360 N, respectively). In particular, they have low electrostatic spark sensitivities (0.13-1.05 J). These properties, together with their high nitrogen contents, make them potential candidates as mechanically insensitive energetic materials with high-explosive performance.

Synthesis and structural characterization of Rh(III) complexes containing diamino ligands of types {D(C6H4NH2)2} and {D(C6H4CH2NHEt)2} (D = O, S) bearing different spacers

The reaction of the diamino ligands of general formula {D(C6H4NH2)2} [D=O (L1); S (L2)] and {D(C6H4CH2NHEt)2} [D=O (L3); S (L4)] with RhCl3·3H2O yielded neutral coordination complexes [RhIII(Ln)Cl3] [n=1 (1); n=2 (2); n=3 (4); n=4 (5)]. Compound 1 in N,N-dimethylformamide solution promoted the formation of the neutral complex [RhIII(L1)(dmf)Cl3] (3). A zwitterionic complex [RhIII(HL4)Cl4] (6) was obtained from the reaction of L4 with RhCl3·3H2O as a minor compound. All complexes were characterized in solution by NMR and by vibrational spectroscopy in solid state. Crystal structures of the chlorohydrates [H2L3]Cl2·H2O, [H2L4]Cl2, and the complexes 2–6 were identified by X-ray diffraction studies. Molecular structures of the complexes revealed different coordination patterns of the diamino ligands Ln as well as the formation of chelate rings of five-, six-, and eight members. The presence of N–H groups in the title compounds enhanced the formation of hydrogen bond networks that were analyzed on the basis of a graph set analysis approach, displaying rings at the first to third level.

Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation.

Effect of 1-ethyl-3-methylimidazolium bromide on interfacial and aggregation behavior of mixed cationic and anionic surfactants

Aggregation behavior and interaction of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB) and their mixtures with an excess of anionic surfactant in the presence of imidazolium-based ionic liquid, 1-ethyl-3-methylimidazolium bromide (EMIm Br) were investigated using surface tension, electrical conductivity, dynamic light scattering (DLS), transmission electron microscopy (TEM) and cyclic voltammetry measurements. Different physicochemical properties such as critical micelle concentration (CMC), degree of counterion dissociation (αdiss), interfacial properties, the standard Gibbs energy of adsorption and the size of aggregates were determined. The effects of ionic liquid (IL) as additive on the interactions between the surfactants; TTAB, SDS and their mixtures were analyzed on the basis of regular solution theory, both for mixed monolayers at the air/liquid interface (βδ) and for mixed micelles (βM). Interaction parameter values suggested that the formation of aggregates is due to the synergistic interactions in the case of SDS/TTAB systems and becomes more affected by adding IL. It was shown that an excess of cationic surfactant and IL resulted in an increase in the nano-aggregate sizes. The synergism observed for three component systems (surfactant–water–IL) revealed the effect of attractive electrostatic interaction, formation of a three-dimensional hydrogen bond network and hydrophobic forces on mixed micelle formation.

Monitoring Backbone Hydrogen-Bond Formation in β-Barrel Membrane Protein Folding.

β-barrel membrane proteins are key components of the outer membrane of bacteria, mitochondria and chloroplasts. Their three-dimensional structure is defined by a network of backbone hydrogen bonds between adjacent β-strands. Here, we employ hydrogen-deuterium (H/D) exchange in combination with NMR spectroscopy and mass spectrometry to monitor backbone hydrogen bond formation during folding of the outer membrane protein X (OmpX) from E. coli in detergent micelles. Residue-specific kinetics of interstrand hydrogen-bond formation were found to be uniform in the entire β-barrel and synchronized to formation of the tertiary structure. OmpX folding thus propagates via a long-lived conformational ensemble state in which all backbone amide protons exchange with the solvent and engage in hydrogen bonds only transiently. Stable formation of the entire OmpX hydrogen bond network occurs downhill of the rate-limiting transition state and thus appears cooperative on the overall folding time scale.

Monitoring Backbone Hydrogen‐Bond Formation in β‐Barrel Membrane Protein Folding

Abstractβ‐barrel membrane proteins are key components of the outer membrane of bacteria, mitochondria and chloroplasts. Their three‐dimensional structure is defined by a network of backbone hydrogen bonds between adjacent β‐strands. Here, we employ hydrogen–deuterium (H/D) exchange in combination with NMR spectroscopy and mass spectrometry to monitor backbone hydrogen bond formation during folding of the outer membrane protein X (OmpX) from E. coli in detergent micelles. Residue‐specific kinetics of interstrand hydrogen‐bond formation were found to be uniform in the entire β‐barrel and synchronized to formation of the tertiary structure. OmpX folding thus propagates via a long‐lived conformational ensemble state in which all backbone amide protons exchange with the solvent and engage in hydrogen bonds only transiently. Stable formation of the entire OmpX hydrogen bond network occurs downhill of the rate‐limiting transition state and thus appears cooperative on the overall folding time scale.

Initial dissolution of D2O at the gas-liquid interface of the ionic liquid [C4min][NTf2] associated with hydrogen-bond network formation.

We have studied the initial dissolution of D2O at the interfacial surface of the flowing jet sheet beam of the ionic liquid (IL) [C4min][NTf2] using the King and Wells method as a function of both the temperature and collision energy of the IL. The initial dissolution probability of D2O into the IL [C4min][NTf2] was found to follow the general propensity that the solubility of gases into a liquid decreases with temperature. However, a large partial molar enthalpy and entropy for the initial dissolution of D2O in the IL [C4min][NTf2] were observed from the temperature dependence of the initial dissolution probability: ΔHl = -53 ± 8 kJ mol-1, ΔSl = -210 ± 30 J mol-1 K-1. In addition, it was found that the collision energy significantly reduced the initial dissolution probability. We propose that the associated D2O molecules at the interface of the IL [C4min][NTf2] make a hydrogen-bond network around the [NTf2]- anion before dissolution into the deeper portion of the interface layer.

Molecular tectonics: tetracarboxythiacalix[4]arene derivatives as tectons for the formation of hydrogen-bonded networks

A series of thiacalix[4]arene derivatives blocked in the 1,3-alternate conformation and bearing four carboxylic acids have been designed and synthesized. These compounds, owing to the H-bond donor (OH moiety) and acceptor (CO group) nature of the carboxylic acid moieties, behave as self-complementary tectons and lead to the formation of tubular 1D H-bonded networks in the crystalline phase. Upon deprotonation of the self-complementary neutral compounds, i.e. transformation of carboxylic acid moieties into carboxylates, anionic tectons are generated. Due to their propensity to form H-bonded networks in the presence of a dicationic H-bond donor tecton of the cyclic bis-amidinium type, designed to behave as a molecular staple interconnecting two carboxylates moieties, 1- and 2-D H-bonded networks are formed under self-assembly conditions.

Probing the microsolvation of a quaternary ion complex: gas phase vibrational spectroscopy of (NaSO4(-))2(H2O)(n=0-6, 8).

We report infrared multiple photon dissociation spectra of cryogenically-cooled (NaSO4(-))2(H2O)n dianions (n = 0-6, 8) in the spectral range of the sulfate stretching and bending modes (580-1750 cm(-1)). Characteristic absorption bands and structural trends are identified based on a comparison to harmonic spectra of minimum-energy structures. The bare quarternary complex (NaSO4(-))2 exhibits a C2h structure containing two fourfold-coordinated sodium cations in-between the two chelating sulfate dianions. Its stepwise solvation is driven by an interplay of SO4(2-)-H2O and Na(+)-H2O interactions. The first water binds in a tridentate intersulfate-bridging fashion. The second and third water molecules bind to the sulfate groups at either end of the complex, which is followed by the onset of water hydrogen-bond network formation. In contrast to the binary ion pair, NaSO4(-), no clear evidence for the disruption of the quaternary ion complex upon microhydration is found up to n = 8, underlining its remarkable stability and suggesting that the formation of quaternary ion complexes plays a central role in the initial stages of prenucleation in aqueous Na2SO4 solutions.

Click Chemistry Finds Its Way in Constructing an Ionic Highway in Anion-Exchange Membrane.

To find the way to construct an ionic highway in anion-exchange membranes (AEMs), a series of side-chain-type alkaline polymer electrolytes (APEs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymer backbones were synthesized via Cu(I)-catalyzed click chemistry. The resulting triazole groups and quaternary ammonium (QA) groups facilitate the formation of a continuous hydrogen bond network, which will lead to high hydroxide conductivity according to Grotthuss-type mechanism. Microphase separation induced by long alkyl side chains contributes at the same time to further improving the hydroxide conductivity of the resultant AEMs. Hydroxide conductivity as high as 52.8 mS/cm is obtained for membrane TA-14C-1.21 (IEC = 1.21 mmol/g) with the longest pendant chain at 30 °C, and the conductivity can be increased to 140 mS/cm when the temperature was increased to 80 °C. Moreover, the corresponding water uptake is only 8.6 wt % at 30 °C. In the meantime, the membrane properties can be tuned by precisely regulating the hydrophilic/hydrophobic ratio in the cationic head groups. Compared with AEMs containing triazole and quaternized trimethylammonium head groups, enhanced dimensional stability and mechanical properties are obtained by tuning side-chain chemistry. However, the alkaline stability of the membrane is not as stable as anticipated, probably because of the existence of the triazole ring. Further study will be focused on increasing the alkali stability of the membrane. We envisage that the side-chain-type APEs meditated by click chemistry bearing long hydrophobic side chains pendant to the cationic head groups hold promise as a novel AEMs material.

Building hydrogen-bonded networks from metal complexes containing the heterotopic (N or O) ligand 4,4′-bipyridine-N-monoxide

The heterotopic ligand 4,4′-bipyridine-N-monoxide (BIPYMO) has a rigid, linear structure and contains both a pyridine N-donor and a pyridine-N-oxide O-donor which are capable of coordinating to a metal centre or alternatively acting as a hydrogen bond acceptor. The hydrogen bonding capacity of BIPYMO is first demonstrated by the formation of hydrogen-bonded networks with water and some simple dicarboxylic acids (fumaric = FUM, terephthalic = TPA). It is then shown that BIPYMO can coordinate through the pyridine N-donor to Pd(II) and through the pyridine-N-oxide O-donor to Fe(II), Co(II) and Mn(II). In each case, the peripheral, uncoordinated N- or O-atoms act as a hydrogen bond acceptors and interact with a metal-bound and hydrogen bond donor (H2O, fumarate = FUM, malonate = MAL, isophthalate = IPA) to form a solid-state, network through a combination of metal–ligand coordination and hydrogen bonding. Single-crystal X-ray structures of {(BIPYMO)(H2O)2}n, {(BIPYMO)(FUM)}n, {(BIPYMO)(TPA)}n, {[Pd(BIPYMO)2(MAL)2](H2O)}n, {[Pd(BIPYMO)2(IPA)2](H2O)2}n and {[M(BIPYMO)2(FUM)2(H2O)2]}n (M = Mn, Fe, Co), show how the individual building blocks are organised via hydrogen bonding through uncoordinated pyridine N-atoms or pyridine-N-oxide O-atoms to form supramolecular networks.

Regioselective Monoesterification Study of the Diol in 1-C-(4,6-O-Benzylidene-β-D-glucopyranosyl) Acetone

1-C-(4,6-O-Benzylidene-β-D-glucopyranosyl) acetone has been studied in a catalytic system consisting of triethylamine-p-dimethylaminopyridine (TEA-DMAP) in the presence of a number of esterification reagents in dichloromethane. It was found that all-protected and monoprotected products form simultaneously. However, the regioselectivity tends to favor the 3-substituted derivative. Structural parameters have been determined by 1H NMR, 13C NMR, 1H-1H correlation spectroscopy, and elemental analysis. Furthermore, a possible mechanism for the formation of intramolecular hydrogen-bond networks between the carbonyl group and 2-OH was described. The energy changes of the transition state in this reaction, as determined by a molecular modelling study, provided further evidence to assign the relative reactivities of each individual hydroxyl group.

Structural and spectroscopic characterization of 1-(diaminomethylene) thiouron-1-ium benzoate and bis(1-(diaminomethylene)thiouron-1-ium) phthalate trihydrate

Two single crystals of 1-(diaminomethylene) thiouron-1-ium benzoate (1) and bis(1-(diaminomethylene)thiouron-1-ium) phthalate trihydrate (2) were grown using a solution growth technique. The compound 1 crystallises in the centrosymmetric P21/c space group of the monoclinic system, whereas the compound 2 in the centrosymmetric Pbcn space group of orthorhombic system. The solid-state organisation of 1 and 2 has been analysed with respect to cation-anion and hydrogen bonding interactions. The oppositely charged units interact via almost linear hydrogen bonds with the graphs of R22(8) and R21(6) forming molecular complexes. In the crystal 1 the R22(8) motif is formed by donation to the carboxylate group from amine group joined to C1 and from imine group and R21(6) motif is formed by donation to the O2 from amine group joined to C2 and from imine group, whereas in crystal 2 the graphs are formed oppositely. Interactions between the hydrogen-bonded molecular complexes in 1 lead to formation of layered 2D structure, whereas in 2, due to presence of hydrated water molecules lead to formation of 3D hydrogen-bonded supramolecular network. The obtained deuterated analogues of 1 and 2 crystallise similar as H-compound in the monoclinic and orthorhombic system with quite similar lattice parameters. The compounds were also characterised by the FT-IR and Raman spectroscopies. The characteristic bands of the functional and skeletal groups are discussed.

The structural and mutational analyses of O-ureido-L-serine synthase necessary for D-cycloserine biosynthesis.

We have recently been successful in cloning a gene cluster necessary for the biosynthesis of D-cycloserine (D-CS) from D-CS-producing Streptomyces lavendulae ATCC11924. Although dcsD, one of the ORFs located on the gene cluster, encodes a protein homologous to O-acetylserine sulfhydrylase that synthesizes L-cysteine using O-acetyl-L-serine together with sulfide, it functions to form O-ureido-L-serine as a D-CS biosynthetic intermediate, using O-acetyl-L-serine together with hydroxyurea (HU). In the present study, using crystallographic and mutational studies, three amino acid residues in DcsD that are important for the substrate preference toward HU were determined. We showed that two of the three residues are important for the binding of HU into the substrate-binding pocket. The other residue contributes to the formation of a loose hydrogen-bond network during the catalytic reaction. Information regarding the amino acid residues will be very useful in the design of a new catalyst for synthesizing the β-substituted-L-alanine derivatives. The atomic coordinates and structure factors of wild-type DcsD and l-OUS-bound K43A mutant of DcsD have been deposited in the Protein Data Bank under accession codes 3X43 and 3X44, respectively.

Orientation and Order of the Amide Group of Sphingomyelin in Bilayers Determined by Solid-State NMR

Sphingomyelin (SM) and cholesterol (Chol) are considered essential for the formation of lipid rafts; however, the types of molecular interactions involved in this process, such as intermolecular hydrogen bonding, are not well understood. Since, unlike other phospholipids, SM is characterized by the presence of an amide group, it is essential to determine the orientation of the amide and its order in the lipid bilayers to understand the nature of the hydrogen bonds in lipid rafts. For this study, 1′-13C-2-15N-labeled and 2′-13C-2-15N-labeled SMs were prepared, and the rotational-axis direction and order parameters of the SM amide in bilayers were determined based on 13C and 15N chemical-shift anisotropies and intramolecular 13C-15N dipole coupling constants. Results revealed that the amide orientation was minimally affected by Chol, whereas the order was enhanced significantly in its presence. Thus, Chol likely promotes the formation of an intermolecular hydrogen-bond network involving the SM amide without significantly changing its orientation, providing a higher order to the SM amide. To our knowledge, this study offers new insight into the significance of the SM amide orientation with regard to molecular recognition in lipid rafts, and therefore provides a deeper understanding of the mechanism of their formation.

A theoretical investigation on anomalous switching of single-stranded deoxyribonucleic acid (ssDNA) monolayers by water vapor**Project supported by the National Natural Science Foundation of China (Grant Nos. 21264016, 11464047, and 21364016), the National Basic Research Program of China (Grant No. 2012CB821500), and the Natural Science Foundation of Xinjiang Uygur Autonomous Region, China (Grant No. 2013211A053).

In this paper, we use a molecular theory to study the anomalous switching of ssDNA monolayers. Here, both ssDNA–water and water–water hydrogen bonds and their explicit coupling to the ssDNA conformations are considered. We find that hydrogen bonding becomes a key element in inducing the anomalous switching of ssDNA monolayers. This finding accords well with the experimental observations. Based on our theoretical model, we predict that the anomalous switching induced by water vapor will be applicable to a wide range of hydrogen bonds polymers, and ssDNA–water hydrogen bonds and water–water hydrogen bonds hybridization will lead to the hydrogen-bond network formation of 3D ssDNA monolayers.