Array Of Hydrogen Bonds Research Articles

A Mechanistic Study of Direct Activation of Allylic Alcohols in Palladium Catalyzed Amination Reactions

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative hydrogen-bonding array between the urea moiety and the hydroxyl group of the allyl alcohol, which strengthens the hydrogen bond between the O-H moiety of the coordinated allyl-alcohol and the carbonyl-moiety of the ligand. This hydrogen bond pattern facilitates the (rate-limiting) C-O oxidative addition step and leads to lower energy isomers throughout the catalytic cycle, clarifying the role of the urea-moiety.

The construction of supramolecular polymers through anion bridging: from frustrated hydrogen-bonding networks to well-ordered linear arrays

The construction of supramolecular polymers has been realized by converting random hydrogen-bonding networks into well-ordered linear hydrogen-bonding arrays through an anion-bridging strategy.

Di-amidosils with tunable structure, morphology and emission quantum yield: the role of hydrogen bonding

Di-amidosil hybrids with variable structure, morphology and photoluminescence properties were obtained using different experimental conditions. A correlation between the emission quantum yield value and the degree of order of the amide–amide hydrogen-bonded array was established for mono- and di-amidosils.

The Structures of Uncommon Cationic N‐alkenyl Purine and Pyrimidine Bases

The structures of 1,3 bis‐(allyl)cytosinium bromide (1), 7,9 bis‐(allyl)adeninium bromide hydrate (2) and 3‐(butenyl)adeninium bromide (3) have been determined. 1 is dimeric via N―H…Br hydrogen bonds, which further associate into ribbons via weaker C―H…Br interactions. 2 is also dimeric, now from N―H…N hydrogen bonds, which build up further through a complex array of hydrogen bonds involving both the anion and water of crystallization (O―H…N, O―H…Br, C―H…Br). 3 does not dimerise but forms polymeric sheets via a series of N―H…N, C―H…N and C―H…Br hydrogen bonds.

Self-assembled multiwalled carbon nanotube films assisted by ureidopyrimidinone-based multiple hydrogen bonds.

Self-assembled functionalized multiwalled carbon nanotube (MWNT) films were successfully constructed, linked by a kind of strong binding strength from the self-complementary hydrogen-bonding array of ureidopyrimidinone-based modules (UPM) attached. Employing the feasible reaction of isocyanate containing ureidopyrimidinone with amine modified MWNTs, the UPMs composed of ureidopyrimidinone and ureido were attached to MWNTs with the content as low as 0.6 mmol/g MWNTs. Upon multiple hydrogen-bonding interactions from incorporation of the AADD (A, hydrogen-bonding acceptor; D, hydrogen-bonding donor) quadruple hydrogen bonds of ureidopyrimidinone and the double hydrogen bonds of ureido group, UPM functionalized MWNTs (MWNT-UPM) can be well dispersed in the polar solvent of N,N-dimethylformamide (DMF), while they tend to self-assemble to give a self-supported film in the apolar solvent of CHCl3. In addition, by using the multiple hydrogen-bonding interactions as the driving force, the layer-by-layer (LBL) MWNT-UPM films with high coverage on solid slides can be processed. Because of the self-association of MWNT-UPM in apolar solvent, it was found that the LBL assembly of MWNT-UPM was more favorable in the polar solvent of DMF than in the apolar solvent of CHCl3. Moreover, the hydrogen-bonding linked MWNT-UPM films showed good stability upon soaking in different solvents. Furthermore, the as-prepared LBL films showed electrochemical active behaviors, exhibiting a remarkable catalytic effect on the reduction of nifedipine.

New Assembly of Acetamidinium Nitrate Modulated by High Pressure

High pressure is an essential thermodynamic parameter in exploring the performance of condensed energetic materials. Combination of high-pressure techniques and supramolecular chemistry opens a new avenue for synthesis of high energy density materials. Herein, we fabricate a new high-pressure-assisted assembly of energetic material acetamidinium nitrate (C2N2H7+·NO3–, AN) with P-1 symmetry after a 0–12 GPa–0 treatment at room temperature, which exhibits a density that is 9.8% higher than that of the initial P21/m phase. Evolution of intermolecular lattice modes in Raman spectra and synchrotron X-ray diffraction (XRD) patterns provide strong evidence for this transition in the 1.3–3.4 GPa range. The mechanism involves relative motions between ionic pairs in the hydrogen-bonded array and distortions of building blocks.

β-sheet-like hydrogen bonds interlock the helical turns of a photoswitchable foldamer to enhance the binding and release of chloride.

Inspired by halorhodopsin's use of photoisomerization to regulate chloride, aryltriazole-based foldamers have been created to "catch and release" chloride ions upon light irradiation of end-appended azobenzenes. The proposed mode of stabilization exploits a β-sheet-like hydrogen-bonding array to cooperatively interlock the ends of a foldamer together with its helical core. We find that the hydrogen-bonding array has a greater influence on stabilizing the helix than the π-stacked seam under the conditions examined (50:50 MeCN/THF). Thus, we show how it is possible to enhance the difference between Cl(-) binding and release using light-dependent control over the foldamer's degree of helix stabilization. Making and breaking three π-π contacts with light caused an 8-fold change in chloride affinity (40 300 M(-1) ⇄ 5000 M(-1)), five π-π contacts produced a 17-fold change (126 000 M(-1) ⇄ 7400 M(-1)), and strategically located hydrogen-bonding units enabled a greater 84-fold differential (970 000 M(-1) ⇄ 11 600 M(-1)). The improved performances were attributed to stepwise increases in the preorganization of the binding pocket that catches chloride while leaving the cis states with just one π-π contact relatively unchanged.

High proton conduction at above 100 °C mediated by hydrogen bonding in a lanthanide metal-organic framework.

A lanthanide metal-organic framework (MOF) compound of the formulation [Eu2(CO3)(ox)2(H2O)2]·4H2O (1, ox = oxalate) was prepared by hydrothermal synthesis with its structure determined crystallographically. Temperature-dependent but humidity-independent high proton conduction was observed with a maximum of 2.08 × 10(-3) S cm(-1) achieved at 150 °C, well above the normal boiling point of water. Results from detailed structural analyses, comparative measurements of conductivities using regular and deuterated samples, anisotropic conductivity measurements using a single-crystal sample, and variable-temperature photoluminescence studies collectively establish that the protons furnished by the Eu(III)-bound and activated aqua ligands are the charge carriers and that the transport of proton is mediated along the crystallographic a-axis by ordered hydrogen-bonded arrays involving both aqua ligands and adjacent oxalate groups in the channels of the open framework. Proton conduction was enhanced with the increase of temperature from room temperature to about 150 °C, which can be rationalized in terms of thermal activation of the aqua ligands and the facilitated transport between aqua and adjacent oxalate ligands. A complete thermal loss of the aqua ligands occurred at about 160 °C, resulting in the disintegration of the hydrogen-bonded pathway for proton transport and a precipitous drop in conductivity. However, the structural integrity of the MOF was maintained up to 350 °C, and upon rehydration, the original structure with the hydrogen-bonded arrays was restored, and so was its high proton-conduction ability.

Investigation of supramolecular synthons and structural characterisation of aminopyridine-carboxylic acid derivatives.

BackgroundCo-crystal is a structurally homogeneous crystalline material that contains two or more neutral building blocks that are present in definite stoichiometric amounts. The main advantage of co-crystals is their ability to generate a variety of solid forms of a drug that have distinct physicochemical properties from the solid co-crystal components. In the present investigation, five co-crystals containing 2-amino-6-chloropyridine (AMPY) moiety were synthesized and characterized.ResultsThe crystal structure of 2-amino-6-chloropyridine (AMPY) (I), and the robustness of pyridine-acid supramolecular synthon were discussed in four stoichiometry co-crystals of AMPY…BA (II), AMPY…2ABA (III), AMPY…3CLBA (IV) and AMPY…4NBA (V). The abbreviated designations used are benzoic acid (BA), 2-aminobenzoic acid (2ABA), 3-chlorobenzoic acid (3CLBA) and 4-nitrobenzoic acid (4NBA). All the crystalline materials have been characterized by 1HNMR, 13CNMR, IR, photoluminescence, TEM analysis and X-ray diffraction. The supramolecular assembly of each co-crystal is analyzed and discussed.ConclusionsExtensive N---H · · · N/N---H · · · O/O---H · · · N hydrogen bonds are found in (I-V), featuring different supramolecular synthons. In the crystal structure, for compound (I), the 2-amino-6-chloropyridine molecules are linked together into centrosymmetric dimers by hydrogen bonds to form homosynthon, whereas for compounds (II-V), the carboxylic group of the respective acids (benzoic acid, 2-aminobenzoic acid, 3-chlorobenzoic acid and 4-nitrobenzoic acid) interacts with pyridine molecule in a linear fashion through a pair of N---H · · · O and O---H · · · N hydrogen bonds, generating cyclic hydrogen-bonded motifs with the graph-set notationR228, to form heterosynthon. In compound (II), another intermolecular N---H · · · O hydrogen bonds further link these heterosynthons into zig-zag chains. Whereas in compounds (IV) and (V), these heterosynthons are centrosymmetrically paired via N---H · · · O hydrogen bonds and each forms a complementary DADA [D = donor and A = acceptor] array of quadruple hydrogen bonds, with graph-set notation , and .

Electrochemical Characterization of an Electroactive Ureidopyrimidinone Derivative, a Four Hydrogen Bond Array Containing a Dimethylaminophenylurea

Electron transfer reactions can be used to perturb the strength of hydrogen bonding interactions between organic molecules. When molecular redox centers are integrated onto hydrogen bond arrays, this combination can become a powerful tool for controlling binding strength in supramolecular complexes. Whether used for sensing devices, molecular machines or self-assembly, the strength of a hydrogen bond can also be enhanced simply by arrangement of hydrogen donor interactions (D) versus hydrogen acceptor interactions (A). Indeed, because of secondary interactions, dimerization constants of the DDAA 4 H-Bond array typically exceed that of the DADA 4 H-Bond array.1 By combining a DDAA 4 H-bond array such as Meijer’s ureidopyrimidinone1with an electroactive center such as the dimethylaminophenylurea, the strength of hydrogen bonding becomes tunable.Cyclic voltammetry investigation, in nonaqueous solvents, of dimethylaminophenylurea (UHH), a DD 2H-bond array, show that without a guest present, there is one reversible oxidation wave in methylene chloride of one electron height. CV Digital simulations as well as UV-vis spectroelectrochemistry indicate a proton transfer from the radical species to the reduced U(H)H, followed by another electron transfer due to potential inversion to give the quinoidal cation, Scheme 1. With the integration of the dimethylphenylamino redox center, this mechanism would certainly complicate the dimerization of Meijer’s DDAA array.Scheme 1. Proposed oxidation mechanism of UHH undergoing an overall one electron transfer due to proton transfer.Due to the acidity of the urea NH that is part of the electroactive center, proton transfer could also occur as part of the electrochemistry associated with the DDAA dimer. We hypothesize that depending on the ratio of arrays substituted with an electroactive center versus those without, the DDAA sequence could change to a DDAD array. With all arrays containing an electroactive center the hydrogen bonding array would form an ADDA homodimer.This presentation will cover cyclic voltammetry studies that includes concentration and scan rate dependence investigations on Meijier’ DDAA dimer equipped with a dimethyphenylurea electroactive center. Digital CV simulations and spectroelectrochemistry will be used to analyze experimental CV ‘s.Figure 1. Meijer’s ureidopyrimidinone (Upy) 4 H-bond system without redox functionality as a DDAA homodimer.Figure 2. Structure of the proposed heterodimer, DDAD array, as a result of half the concentration with an electroactive center and the other half without.

Structural characterization and properties of bis (1,4-H2-1,2,4-triazolium) pentachlorobismuthate (III) and cocrystal of ammonium chloride with tris (1,4-H2-1,2,4-triazolium) hexachlorobismuthate (III)

The crystal structure of two novel 1,2,4-triazolium analogues: [C2N3H4]2[BiCl5] (TBC) and [NH4][C2N3H4]3[BiCl6][Cl] (TCBA), isolated from one system, has been determined. The structure of TCBA is built up from cationic substructures consisting of 1,2,4-triazolium and ammonium cations, [Cl]-, and discrete [BiCl6]3- octahedral anions. The two-component cationic sublayer of TCBA is unique in the case of halobismuthates(III). TCBA adopts the triclinic space group (P1¯) at 100K. Differential scanning calorimetry (DSC) and dilatometric measurements showed that it undergoes reversible first-order phase transition (PT) at 420/405K (heating/cooling) governed by an ’order–disorder’ mechanism. The crystal structure of TBC (Cmca at 100K) contains the [BiCl5]∞2- chains of cis-connected octahedra and a hydrogen-bonded array of 1,2,4-triazolium cations. The statistical disorder of the 1,2,4-triazolium cations is found at low temperatures. No PT is detected between 100 and 400K in TBC.

Peptide turns through just ‘one atom’! A sulfamide group nucleates folding and stabilizes new supramolecular topologies in short peptides

Peptide segments with centrally placed sulfamide groups showed a remarkable tendency to adopt a turn conformation and exhibited supramolecular topologies like ‘helical stacks’ and ‘hairpin sheets’ through a highly coordinated array of strong and weak hydrogen bonds.

Chiromers: conformation-driven mirror-image supramolecular chirality isomerism identified in a new class of helical rosette nanotubes.

Rosette nanotubes are biologically inspired nanostructures, formed through the hierarchical organization of a hybrid DNA base analogue (G∧C), which features hydrogen-bonding arrays of guanine and cytosine. Several twin-G∧C motifs functionalized with chiral moieties, which undergo a self-assembly process under methanolic and aqueous conditions to produce helical rosette nanotubes (RNTs), were synthesized and characterized. The built-in molecular chirality in the twin-G∧C building blocks led to the supramolecular chirality exhibited by the RNTs, as evidenced by the CD activity. Depending on the motifs and environmental conditions, mirror-image supramolecular chirality due to absolute molecular chirality, solvent-induced and structure-dependent supramolecular chirality inversion, and pH-controlled chiroptical switching were observed.

Lamellar Salt-Doped Hybrids with Two Reversible Order/Disorder Phase Transitions

A lamellar bilayer hierarchically structured amide cross-linked alkyl/siloxane hybrid matrix (mono-amidosil, m-A(14)) was doped with a wide concentration range of potassium triflate (KCF3SO3), magnesium triflate (Mg(CF3SO3)2), and europium triflate (Eu(CF3SO3)3). In the K(+)-, Mg(2+)-, and Eu(3+)-based samples with n ≥ 5, 20, and 60 (where n is the molar ratio of amide C═O groups per cation), respectively, the original lamellar structure of m-A(14) coexists with a new lamellar phase with lower interlamellar distance. The texture of the mono-amidosils doped with K(+), Mg(2+), and Eu(3+) ions mimics cabbage leaves, foliated schist, and sea sponges, respectively. In the three series of materials, the cations bond to the oxygen atoms of the amide carbonyl groups. The amide-amide hydrogen-bonded array of m-A(14) is less perturbed by the inclusion of KCF3SO3 and Mg(CF3SO3)2 than by the incorporation of Eu(CF3SO3)3. The degree of ionic association is low for n ≥ 20. The cations coordinate to the oxygen atoms of the triflate ions, forming contact ion pairs at higher salt content. In the Mg(CF3SO3)2- and Eu(CF3SO3)3-containing materials with n = 5 and 10, respectively, crystalline salt is formed. The structural changes undergone by the alkyl chains of selected mono-amidosils in a heating/cooling cycle are reversible, are time-independent, and exhibit two distinct hysteresis domains, one associated with the order/disorder phase transition of the original lamellar bilayer structure of m-A(14) and the second one associated with the order/disorder phase transition of the new lamellar bilayer structure formed in the presence of the salts.

Preparation and Characterization of An Electroactive Ureidopyrimidinone Derivative, A Four Hydrogen Bond Array Containing a Dimethylaminophenylurea

not Available.

Molecular dynamics simulation of oleic acid/oleate bilayers: An atomistic model for a ufasome membrane

When oleic acid and oleate coexist in comparable amounts they form unilamellar vesicles called ufasomes in aqueous phase. Intrinsic pH sensitivity of ufasomes makes it an attractive vehicle for drug delivery. Physical properties of ufasomes have been studied by using spectroscopic techniques but an atomistic model for a ufasome has not been proposed. In this study molecular dynamics simulation was performed on oleic acid/oleate bilayers with the oleate concentration varying from 40 to 70mol%. All the bilayers reached an equilibrium and stayed stable during a 40ns simulation. Area per lipid increased with mol% of oleate probably due to charge repulsion between anionic oleate molecules. Oleate was pulled out toward the aqueous phase so that the carboxyl groups of oleic acid and oleate were separated by 0.392nm in the bilayer of oleic acid/oleate 1:1. Water concentration at the depth of carboxyl group of oleate was five times as high as that of oleic acid. Number of hydrogen bonds between oleic acid and oleate was small in contrast to a proposal that it is an important factor for the bilayer stability. However there was an extensive array of hydrogen bonds between the lipids and water molecules. Acyl chain order was within a normal range for a lipid bilayer but lateral diffusion was an order of magnitude faster in oleic acid/oleate bilayer than in dioleoylphosphatidylcholine bilayer. Cholesterol increased the bilayer thickness and order parameter and decreased the rate of lateral diffusion.

AAAA-DDDD Quadruple Hydrogen-Bond Arrays Featuring NH···N and CH···N Hydrogen Bonds

The X-ray crystal structure of a previously reported extremely strong quadruple NH···N AAAA-DDDD hydrogen-bond array [5·4] (K(a) = 1.5 × 10(6) M(-1) in CH3CN; K(a) > 3 × 10(12) M(-1) in CH2Cl2) features four short linear hydrogen bonds. Changing the two benzimidazole groups of the DDDD unit to triazole groups replaces two of the NH···N hydrogen bonds with CH···N interactions (complex [5·6]), but only reduces the association constant in CH3CN by 2 orders of magnitude (K(a) = 2.6 × 10(4) M(-1) in CH3CN; K(a) > 1 × 10(7) M(-1) in CH2Cl2). Related complexes without the triazole groups range in K(a) from 18 to 270 M(-1) in CH3CN, suggesting that the CH···N interactions can be considered part of a strong AAAA-DDDD quadruple hydrogen-bonding array. The NH···N/CH···N AAAA-DDDD motif can be repeatedly switched "on" and "off" in CDCl3 through successive additions of acid and base.

Vibrational analysis of d-PCL(530)/siloxane-based hybrid electrolytes doped with two lithium salts

The present study has been focused on environmentally friendly sol–gel-derived electrolytes based on a di-urethane cross-linked d-PCL(530)/siloxane network [where d represents di, PCL identifies the poly(ε-caprolactone) biopolymer, and 530 is the average molecular weight in grams per mole] doped with a wide range of concentration of lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide. Fourier Transform Infrared and Raman spectroscopies have been applied to evaluate the extent of ionic association. Characteristic bands of the PCL(530) segments, of the urethane cross-links, and of the anions have been examined to gain insight into the cation/biopolymer, cation/anion, and cation/cross-link interactions. In both electrolyte systems, “free” ions and contact ions have been identified. The addition of salt modifies the hydrogen-bonded array of the host matrix, causing the destruction/formation of the urethane/urethane aggregates.

The Tris‐Urea Motif and Its Incorporation into Polydimethylsiloxane‐Based Supramolecular Materials Presenting Self‐Healing Features

Materials of supramolecular nature have attracted much attention owing to their interesting features, such as self-reparability and material robustness, that are imparted by noncovalent interactions to synthetic materials. Among the various structures and synthetic methodologies that may be considered for this purpose, the introduction of extensive arrays of multiple hydrogen bonds allows for the formation of supramolecular materials that may, in principle, present self-healing behavior. Hydrogen bonded networks implement dynamic noncovalent interactions. Suitable selection of structural units gives access to novel dynamic self-repairing materials by incrementing the number of hydrogen-bonding sites present within a molecular framework. Herein, we describe the formation of a tris-urea based motif giving access to six hydrogen-bonding sites, easily accessible through reaction of carbohydrazide with an isocyanate derivative. Extension towards the synthesis of multiply hydrogen-bonded supramolecular materials has been achieved by polycondensation of carbohydrazide with a bis-isocyanate component derived from poly-dimethylsiloxane chains. Such materials underwent self-repair at a mechanically cut surface. This approach gives access to a broad spectrum of materials of varying flexibility by appropriate selection of the bis-isocyanate component that forms the polymer backbone.

Binding characteristics of homogeneous molecularly imprinted polymers for acyclovir using an (acceptor–donor–donor)—(donor–acceptor–acceptor) hydrogen-bond strategy, and analytical applications for serum samples

This paper demonstrates a novel approach to assembling homogeneous molecularly imprinted polymers (MIPs) based on mimicking multiple hydrogen bonds between nucleotide bases by preparing acyclovir (ACV) as a template and using coatings grafted on silica supports. 1H NMR studies confirmed the AAD-DDA (A for acceptor, D for donor) hydrogen-bond array between template and functional monomer, while the resultant monodisperse molecularly imprinted microspheres (MIMs) were evaluated using a binding experiment, high performance liquid chromatography (HPLC), and solid phase extraction. The Langmuir isothermal model and the Langmuir–Freundlich isothermal model suggest that ACV-MIMs have more homogeneous binding sites than MIPs prepared through normal imprinting. In contrast to previous MIP–HPLC columns, there were no apparent tailings for the ACV peaks, and ACV-MIMs had excellent specific binding properties with a Ka peak of 3.44×105M−1. A complete baseline separation is obtained for ACV and structurally similar compounds. This work also successfully used MIMs as a specific sorbent for capturing ACV from serum samples. The detection limit and mean recovery of ACV was 1.8ng/mL−1 and 95.6%, respectively, for molecularly imprinted solid phase extraction coupled with HPLC. To our knowledge, this was the first example of MIPs using AAD-DDA hydrogen bonds.