Formation Of Intermolecular Hydrogen Bonds Research Articles

Structural Basis of Botulinum Toxin Type F Binding to Glycosylated Human SV2A: In Silico Studies at the Periphery of a Lipid Raft.

Botulinum neurotoxins are the deadliest microbial neurotoxins in humans, with a lethal dose of 1 ng/kg. Incidentally, these neurotoxins are also widely used for medical and cosmetic purposes. However, little is known about the molecular mechanisms that control binding of botulinum neurotoxin type F1 (BoNT/F1) to its membrane receptor, glycosylated human synaptic vesicle glycoprotein A (hSV2Ag). To elucidate these mechanisms, we performed a molecular dynamics simulation (MDS) study of initial binding kinetics of BoNT/F1 to SV2A. Since this toxin also interacts with gangliosides, the simulations were performed at the periphery of a lipid raft in the presence of both SV2A and gangliosides. Our study suggested that interaction of BoNT/F1 with SV2A is exclusively mediated by N-glycan moiety of SV2A, which interacts with aromatic residues Y898, Y910, F946, Y1059 and H1273 of this toxin. Thus, in contrast with botulinum neurotoxin A1 (BoNT/A1), BoNT/F1 does not interact with protein content of SV2A. We attributed this incapability to a barrage effect exerted by neurotoxin residues Y1132, Q1133 and K1134, which prevent formation of long-lasting intermolecular hydrogen bonds. We also provided structural elements that suggest that BoNT/F1 uses the strategy of BoNT/A1 combined with the strategy of botulinum neurotoxin type E to bind N-glycan of its glycoprotein receptor. Overall, our study opened a gate for design of a universal inhibitor aimed at disrupting N-glycan-toxin interactions and for bioengineering of a BoNT/F1 protein that may be able to bind protein content of synaptic vesicle glycoprotein for therapeutic purposes.

Improving the Mechanical Properties of Damaged Hair Using Low-Molecular Weight Hyaluronate.

Chemical treatments of hair such as dyeing, perming and bleaching could cause mechanical damage to the hair, which weakens the hair fibers and makes the hair break more easily. In this work, hyaluronate (HA) with different molecular weight (MW) was investigated for its effects on restoring the mechanical properties of damaged hair. It was found that low-MW HA (average MW~42 k) could significantly improve the mechanical properties, specifically the elastic modulus, of overbleached hair. The fluorescent-labeling experiments verified that the low-MW HA was able to penetrate into the cortex of the hair fiber, while high-MW HA was hindered. Fourier transform infrared spectrometry (FT-IR) results implied the formation of additional intermolecular hydrogen bonds in the HA-treated hair. Thermos gravimetric analysis (TGA) indicated that the HA-treated hair exhibited decreased content of loosely bonded water, and differential scanning calorimetry (DSC) characterizations suggested stronger water bonding inside the HA-treated hair, which could alleviate the weakening effect of loosely bonded water on the hydrogen bond networks within keratin. Therefore, the improved elastic modulus and mechanical strength of the HA-treated hair could be attributed to the enhanced formation of hydrogen bond networks within keratin. This study illustrates the capability of low-MW HA in hair damage repair, implying an enormous potential for other moisturizers to be used in hair care products.

2,6‐Di(1H‐tetrazol‐1‐yl)pyridine and its cupric chloride complex

Abstract2,6‐Di(1H‐tetrazol‐1‐yl)pyridine (DTP) was prepared by a four‐stage procedure, including step‐by‐step heterocyclization of both amino groups of 2,6‐diaminopyridine with triethyl orthoformate and sodium azide. According to quantum‐chemical calculations and single crystal X‐ray diffraction data, DTP crystallizes in the form of the thermodynamically most stable conformer and has an almost flat molecular geometry. DTP was found to react with CuCl2 ⋅ 2H2O in ethanol to give the [Cu(DTP)Cl2(H2O)]n complex, which is a 1D coordination polymer, formed at the expense of bridging DTP ligand via the tetrazole ring nitrogen atoms N4. Possible coordination cites in DTP molecule are discussed using the data of quantum chemical calculations. The pyridine ring nitrogen atom of DTP does not participate in the formation of either coordination or intermolecular hydrogen bonds. This is explained by the results of quantum chemical calculations showing that this atom is less basic than N3 and N4 atoms of DTP molecule.

Ternary structure design based on hydrogen bonding for transparent and flame retardant PMMA with good mechanical properties

AbstractThe synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present，but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas‐phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V‐1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties.

New Saccharin Salt of Chlordiazepoxide: Structural and Physicochemical Examination.

Since the formation of organic salts can improve the solubility, bioavailability, and stability of active pharmaceutical ingredients, the aim of this work was to prepare an organic salt of chlordiazepoxide with saccharin. To achieve this goal, the saccharin salt of chlordiazepoxide was obtained from a physical mixture of both components by grinding them with a small volume of solvent and by crystallizing them with complete evaporation of the solvent. The resulting salt was examined by methods such as Powder X-ray Diffraction (PXRD), Single Crystal X-ray Diffraction (SCXRD), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR), and Raman spectroscopy. The results of the studies proved that saccharin salt of chlordiazepoxide crystallizes in the orthorhombic Pbca space group with one chlordiazepoxide cation and one saccharin anion in the asymmetric unit. In the crystal of the title compound, the chlordiazepoxide cation and the saccharin anion interact through strong N–H···O hydrogen bonds and weak C–H···O hydrogen bonds. The disappearance of the N–H band in the FT-IR spectrum of saccharin may indicate a shift of this proton towards chlordiazepoxide, while the disappearance of the aromatic bond band in the chlordiazepoxide ring in the Raman spectrum may suggest the formation of intermolecular hydrogen bonds between chlordiazepoxide molecules. The melting point of the salts differs from that of the starting compounds. Thermal decomposition of the salt begins above 200 °C and shows at least two overlapping stages of mass loss. In summary, the results of the research showed that the crystalline salt of the saccharin and chlordiazepoxide can be obtained by various methods: grinding with the addition of acetonitrile and crystallization from acetonitrile or a mixture of methanol with methylene chloride.

Characterization of carvacrol incorporated antimicrobial film based on agar/konjac glucomannan and its application in chicken preservation

The objective of this study was to fabricate and characterize antimicrobial films based on Agar/Konjac glucomannan (KA) incorporated with carvacrol (CV) (1%, 1.5% and 2%). The physical, structural and antimicrobial properties were studied to evaluate the effects of carvacrol on the composite films. Results indicated that the addition of 2% CV markedly enhanced the tensile strength (36.72 MPa), elongation at break (100.19%), hydrophobic properties and UV barrier properties compared with KA film. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy indicated good compatibility and the formation of intermolecular hydrogen bonds. Additionally, the addition of 2% CV showed strong antimicrobial activities against the most common food spoiling bacteria, Staphylococcus aureus and Escherichia coli. Finally, the potential application of the films was evaluated by the packing test of chicken, where KA-2% CV was able to prolong the shelf life of refrigerated chicken breast from 5 days to 9 days. Overall, the composite films incorporating 2% carvacrol was a promising antimicrobial packing material to displace petrochemical-based plastics to extend the shelf life of foods.

Changes in solution turbidity and color during paracetamol removal in laboratory and pilot-scale semicontinuous ozonation reactors

Injecting ozone by means of a venturi device causes an increase in the mass transfer coefficient with respect to gas dissolution through a microdiffuser. Moreover, it was observed that significant turbidity levels are not formed (<1 NTU) when using a microdiffuser, probably due to the relatively high stirring which avoids formation of intermolecular hydrogen bonds. On the contrary, employing a venturi injector led to the production of high turbidity levels in water (up to 20 NTU). This indicates that formation of supramolecular structures causing this turbidity requires the presence of certain facilitating species which are formed through ozone decomposition mechanisms. The maximum ozone transfer takes place when operating at pH0 9.0, that is, when this value is close to the pKa and employing a dose of R = 115 mol O3/mol Pa0. Under these conditions, the degradation of paracetamol generates color, which is attributed to the presence of condensation products from pyrogallol, catechol, resorcinol, acetamide, oxalic acid and 4-aminophenol. Once paracetamol is fully degraded and solution turns colorless, turbidity grows (>20 NTU). This is attributed to formation of high molecular weight structures from 4-aminophenol and oxamide. Operating with large ozone excess (R = 500 mol O3/mol Pa0), the maximum ozone transfer rate is achieved at pH0 = 12.0. Under these conditions, the pollutant is fully removed together with water aromaticity and oxalic acid (able to form linear structures through hydrogen bonding) is detected during color development. Then, turbidity is formed due to cyclic dimer formation from acetic acid.

Role of an intramolecular H-bond in lidocaine conformer distribution and polymorph stability

• Solubility of lidocaine in scCO 2 in wide range of phase diagram was measured. • Analysis of the conformations of lidocaine in scCO 2 was performed. • Stability of intramolecular hydrogen bond in lidocaine molecule was found. In this work, we study conformational equilibria of lidocaine molecules in a saturated lidocaine solution in scCO 2 under heating conditions in the temperature range of 35–80 °C along three isochores corresponding to the scCO 2 density of 1.1, 1.3, and 1.5 of its critical value. It is established that among of 68 conformers obtained by quantum chemical calculations, it is only conformers with an intramolecular hydrogen bond that are realized within the studied range of parameters of state. The IR spectroscopy data show that the lidocaine solubility in scCO 2 increases significantly with the fluid phase temperature and density growth, reaching the concentration about 10 −1 mol·L −1 . However, this does not lead to the formation of intermolecular hydrogen bonds between the lidocaine molecules in the solution. Moreover, the heating changes the conformational equilibrium of lidocaine molecules in the scCO 2 phase, but this change is not related to the destruction of the intramolecular hydrogen bond. Higher scCO 2 phase density is found to reduce the temperature effect on the conformational equilibrium. Finally, we establish that the temperature-induced conformational changes in the lidocaine molecules in the scCO 2 phase are completely reversible. It allows us to assume that, regardless of the SCF solution parameters of state in the considered phase diagram region, lidocaine crystallization from this solution will lead to the formation of the same stable polymorph.

Stretchable, conductive poly(acrylamide‐co‐maleic acid)/triethylene glycol/NaCl double‐crosslinked organohydrogel with excellent antifreezing and sensing properties

AbstractRecently, the wearable electronic devices have attracted extensive attention while the low stretchability and freezing‐induced performance deterioration largely limit the applications in many fields. In this work, the poly(acrylamide‐co‐maleic acid) hydrogels are immersed in the triethylene glycol/sodium chloride/water solution to establish the dual‐crosslinked organohydrogels, which present the extraordinary stretchability (1322 ± 75%) ascribed to the energy dissipation of physical interactions and stability of chemical crosslinked networks. Triethylene glycol forms strong hydrogen bonds with water, which interfere with the formation of intermolecular hydrogen bonds among water molecules at low temperatures and inhibit the formation of ice crystals in the organohydrogel networks. Sodium chloride imparts excellent electrical conductivity to the organohydrogel. As a result, a stretchable electronic sensor based on the organohydrogel is fabricated, which is strain‐sensitive with a wide strain sensing window (0%–440%) and excellent stability. More importantly, the sensor based on the as‐prepared organohydrogel could precisely detect various activities of the human model at −30°C leading to the widely application prospects.

Intermolecular hydrogen bond modulating the selective coupling of protons and CO2 to CH4 over nitrogen-doped carbon layers modified cobalt

Photocatalytic reduction of CO2 with H2O to CH4 is a promising route to migrate CO2 emission and complete the carbon neutrality goal. Nevertheless, one of the biggest challenges for this elegant strategy is that the coupling of the protons and CO2 to form CH4 is fiercely competed with proton-proton coupling to form H2, leading to extremely low CH4 selectivity. Herein, we designed and fabricated the nitrogen-doped carbon layers modified cobalt (N-C@Co) photocatalyst achieving the selective coupling of protons and CO2 to CH4 during photocatalytic reduction of CO2. The successful formation of intermolecular hydrogen bonds between the as-prepared N-C@Co and H2O molecule was found to suppress the mass transfer of the generated protons and promote the adsorption and activation of the CO2 molecule. More crucially, it was conducive to suppressing the desorption of the CO intermediate, which was typically deemed as the decisive species for CH4 generation. As a result, the H2 selectivity (9.0 %) and activity (17.3 µmol g−1) of the as-prepared N-C@Co were reduced by a factor of 9.3 and 17.6, respectively, as compared to that of bulk Co. The CH4 selectivity of N-C@Co was boosted 6.1 times from 13.3% of bulk Co to 81.3 % of N-C@Co with the generation rate of 155.7 μmol g−1 in 23 h. This work provides a new insight into the photocatalyst design for improving CH4 selectivity and suppressing the competing H2 and CO generation.

Theoretical study on the interaction of flutamide anticancer drug with cucurbit[n]uril (n = 5–8) as a drug delivery system

AbstractThe supramolecular complexation of flutamide, an anti‐androgen drug with cucurbit[n]uril was studies using density functional theory (DFT). The structural and electronic analysis of the complexes was performed. The negative binding energy of the complexes show that complexation process is exothermic. The thermodynamic results reveal that the process of inclusion complex formation is spontaneous. To gain insightful knowledge about the nature of interactions present between the host‐guest molecules of the complexes, molecular electrostatic potential, non‐covalent interaction–reduced density gradient, and natural bond orbital analysis was done. These results suggest that electrostatic interactions and intermolecular hydrogen bond formation contribute to the stability of these complexes. The coupled‐cluster theory with single, double and perturbatively connected triple excitations calculations for the complexes support the DFT results. The quantitative decomposition of the interaction energies of the complexes was acquired by the local energy decomposition analysis. The atom‐centered density matrix propagation molecular dynamic analysis confirms the stability of the examined complexes.

Effects of konjac glucomannan on pasting, rheological, and structural properties of low-amylose rice starch

Abstract Blend of starch and polysaccharide is a secure and feasible modifying method for starch. Effects of konjac glucomannan (KGM) on pasting, retrogradation, rheological and structural properties of low-amylose rice starch were evaluated. KGM addition reduced the pasting temperature, breakdown and setback values, but raised the peak viscosity. When KGM concentration increased, the storage and loss moduli showed an upward trend. Fourier transform infrared spectroscopy (FTIR) showed redshifts at 3450 and 1640 cm−1 and suggested the formation of intermolecular hydrogen bond between KGM and starch molecules. X-ray diffraction (XRD) indicated that KGM decreased the relative crystallinity from 11.88 to 3.10%. Scanning electron microscopy (SEM) of KGM induced samples showed looser network structures, and confocal laser scanning microscopy (CLSM) detected less cloud-like blurry pastes surrounding around the starch ghosts. KGM addition suppressed the starch retrogradation. These results could be used to broaden the application of KGM in the food industry.

Limited Alcalase hydrolysis improves the thermally-induced gelation of quinoa protein isolate (QPI) dispersions

Gelation is critical in many food applications of plant proteins. Herein, limited hydrolysis by Alcalase was used to promote thermally induced gelation of quinoa protein isolates (QPI). Mechanical properties of various QPI gels were characterised by small and large oscillatory shear deformation rheology while the microstructural features were observed by confocal laser scanning microscopy (CLSM). Both the gel strength and microstructure are strongly related to the hydrolysis time. The maximum gel strength (∼100 Pa) was achieved after Alcalase hydrolysis for 1 min, which was ∼20 folds higher than that of untreated QPI. Extended hydrolysis up to 5 min progressively decreased the gel strength. A string-like interconnected protein network was formed after proteolysis. The change of gel strength with hydrolysis time correlated well to the Gʹ20°C/Gʹ90°C value and results of intrinsic fluorescence and surface hydrophobicity. The Gʹ20°C/Gʹ90°C value is sensitive to hydrogen bonds formation while the intrinsic fluorescence and surface hydrophobicity are associated with protein unfolding and exposure of hydrophobic groups. Therefore, both hydrogen bonding and hydrophobic interactions are critical in improving the gel strength of QPI hydrolysates. Finally, FTIR analysis revealed that protein secondary structures are affected by the proteolysis and formation of inter-molecular hydrogen bonds between polypeptides. This study provides an efficient strategy for improving thermally induced gelation of QPI and enables a deep understanding of QPI gelation mechanism induced by Alcalase hydrolysis.

APPLICATION OF IMAGE ANALYSIS USING TEXTURES OF Py14BA:nFA FOR MESOGEN PARAMETERS

Thermal and optical properties of two supra molecule mesognes: Py14BA:nFAs (n=14 and 16) (4-Pyridyl)- benzylidene-4’- n-tetradecyl aniline(PyB14A):aliphatic carboxylic acids (nFA where n = 14 and 16) are investigated. This study is carried out with a polarizing optical microscope and image analysis method. It is based on the temperature dependence of intensities of the mesogen textures. Intermolecular hydrogen bond formation between the two nonmesogens gives rise to mesogen complexes Py14BA:nFAs (n=14 and 16). The properties of these mesogen complexes are computed from the images (textures) through MATLAB software. Transition temperatures, heat enthalpy, thermal stability factor, Birefringence dispersion, Phase retardation, Transient transmission and order parameter studies are carried out. The results manifest that hydrogen-bonded mesogens exhibit good thermo-optical properties.

Interaction between Negatively Charged Fish Gelatin and Cyclodextrin in Aqueous Solution: Characteristics and Formation Mechanism.

The effect that ratios of fish gelatin (FG) to α/β/γ cyclodextrins (α, β, γCDs) had on the phase behavior of a concentrated biopolymer mixture were comparatively investigated. This showed that the formed biopolymer mixture had the highest gel strength at ratios of FG–CD = 90:10. FG could interact with CDs to form stable soluble complexes with lower values of turbidity, particle size and ζ-potential. All of the FG–CD mixture solutions exhibited pseudo-plastic behaviors, and FG–αCD samples had the highest viscosity values than others. The addition of CDs could unfold FG molecules and make conformation transitions of FG from a random coil to β-turn, leading to the environmental change of hydrophobic residues and presenting higher fluorescence intensity, especially for βCDs. FTIR results revealed that the formation of intermolecular hydrogen bonds between FG and CD could change the secondary structure of FG. These findings might help further apply FG–CD complexes in designing new food matrixes.

A DFT and MP2 mechanistic and kinetic study on hypohalogenation reaction of cysteine and N-acetylcysteine in aqueous solution

A theoretical study simulating the hypohalogenation reaction of cysteine (CSy) and N-acetylcysteine (NAC) has been performed with the objective of obtaining the energetic, electronic and kinetic properties for the reactions at room temperature and body temperature and considering neutral and basic conditions in aqueous medium. The study has been performed using the M06-HF, M06-2X, MPWB1K, BHANDHLYP density functional methods and with the MP2 method along with either the 6-311+G(d, p) basis set or the extended 6-311++G(3df,3pd) basis set. The results of the study indicate that all reactions proceed through the formation of the reactant complex structure, which is stabilised by the formation of intermolecular hydrogen bond between the reactant species. The reactions are also thermodynamically preferred to take place at room temperature. The reaction involving hypochlorous acid is faster and more thermodynamically preferred to the reaction involving hypochlorite anion, both at room temperature and at body temperature. The relative magnitude for the rate constant involving CSy and NAC is dependent on the pH of the solution. A comparison of the calculation methods utilised for the study suggests that the best methods for estimation of the rate constant are those containing both the HF-like exchange and the kinetic density components.

Development of alginate-chitosan composite scaffold incorporation of bacterial cellulose for bone tissue engineering

On account of the excellent biocompatibility and biodegradability of natural polymers, such as alginate, chitosan (CS), and bacterial cellulose (BC), we developed the alginate/bacterial cellulose-chitosan (Alg/BC-CS) composite scaffolds through the incorporation of BC into alginate matrix and the surface coverage of CS, using hydroxyapatite/D-glucono-δ-lactone (HAP/GDL) complex as the gelling system. The effects of the addition of BC on the scaffold morphology, porosity, mechanical property, swelling, degradability, protein adsorption, and release properties, and cytocompatibility were investigated. The fabricated Alg/BC-CS composite scaffolds revealed the regular 3D morphology due to the homogeneous cross-linking by HAP/GDL complex. The incorporation of the BC significantly reduced their pore size, making Alg/BC-CS composite hydrogel more beneficial to favor tissue ingrowth and ensure mechanical integrity. Moreover, the tight fiber network structure and good barrier properties of BC and its formation of intermolecular hydrogen bonds with alginate could effectively control swelling behaviors and inhibit the degradation of Alg/BC-CS composite scaffolds. Meanwhile, the resultant Alg/BC-CS composite scaffolds showed good apatite formation ability, protein adsorption, and release performance, as well as excellent cytocompatibility, so they could exhibit great application potentials for bone tissue engineering.

Diversity of N-triphenylacetyl-L-tyrosine solvates with halogenated solvents.

The structure of N-triphenylacetyl-L-tyrosine (C29H25NO4, L-TrCOTyr) is characterized by the presence of both donors and acceptors of classical hydrogen bonds. At the same time, the molecule contains a sterically demanding and hydrophobic trityl group capable of participating in π-electron interactions. Due to its large volume, the trityl group may favour the formation of structural voids in the crystals, which can be filled with guest molecules. In this article, we present the crystal structures of a series of N-triphenylacetyl-L-tyrosine solvates with chloroform, namely, L-TrCOTyr·CHCl3 (I) and L-TrCOTyr·1.5CHCl3 (III), and dichloromethane, namely, L-TrCOTyr·CH2Cl2 (II) and L-TrCOTyr·0.1CH2Cl2 (IV). To complement the topic, we also decided to use the racemic amide N-triphenylacetyl-DL-tyrosine (rac-TrCOTyr) and recrystallized it from a mixture of chloroform and dichloromethane. As a result, rac-TrCOTyr·1.5CHCl3 (V) was obtained. In the crystal structures, the amide molecules interact with each other via O-H...O hydrogen bonds. Noticeably, the amide N-H group does not participate in the formation of intermolecular hydrogen bonds. Channels are formed between the TrCOTyr molecules and these are filled with solvent molecules. Additionally, in the crystals of III and V, there are structural voids that are occupied by chloroform molecules. Structure analysis has shown that solvates I and II are isostructural. Upon loss of solvent, the solvates transform into the solvent-free form of TrCOTyr, as confirmed by thermogravimetric analysis, differential scanning calorimetry and powder X-ray diffraction.

Competition between inter and intramolecular hydrogen bond evidenced by vibrational circular dichroism spectroscopy: The case of (1S,2R)-(-)-cis-1-amino-2-indanol.

The infrared (IR) absorption and vibrational circular dichroism (VCD) spectra of an intramolecularly hydrogen-bonded chiral amino-alcohol, (1S,2R)-(-)-cis-1-amino-2-indanol, are studied in DMSO-d6 . The spectra are simulated at the density functional theory (DFT) level within the frame of the cluster-in-the-liquid model. Both IR and VCD spectra show a clear signature of the formation of intermolecular hydrogen bonds at the detriment of the intramolecular OH … N interaction present in the isolated molecule. Two solvent molecules are necessary to reproduce the experimental spectra. Whereas the first DMSO molecule captures the main spectral modifications due to hydrogen bond formation between the solute and the solvent, the second DMSO molecule is necessary for a good description of the Boltzmann contribution of the different complexes, based on their Gibbs free energy.

Diradicals or Zwitterions: The Chemical States of m -Benzoquinone and Structural Variation after Storage of Li Ions

Diradicals or Zwitterions: The Chemical States of <i>m</i> -Benzoquinone and Structural Variation after Storage of Li Ions