Hydrogen Bond Cleavage Research Articles

Atomistic simulations of polysaccharide materials for insights into their crystal structure, nanostructure, and dissolution mechanism

AbstractCrystalline polysaccharides are abundant in nature and can be transformed into highly functional materials. However, the molecular basis for the formation of higher-order structures remains unclear. Computer simulation is an advanced tool for modeling macromolecular structures, and the atomistic simulations provide valuable information on the crystalline polysaccharides. Fiber deformation, crystalline transition, and novel nanostructures of cellulose were characterized through molecular dynamics simulations and density functional theory calculations of models of molecular chain sheets extracted from the crystal structure of the cellulose polymorphs. Extended ensemble molecular dynamics simulations were applied to analyze the artificial crystal structure of non-natural amylose analog polysaccharides, revealing the hexagonal packing of double helices through the self-assembly of molecular chains dispersed in aqueous solution. Dissolution simulations of the cellulose and chitin crystalline fibers revealed that the anions of ionic liquids, with their solvation power, played a key role in the cleavage of intermolecular hydrogen bonds in the crystal structure, whereas the cations contributed to irreversible molecular chain dispersion. The good correlation between the actual solubility of polysaccharides and the predicted number of intermolecular hydrogen bonds prompted the development of a platform that combined simulations and machine learning for high-throughput screening of solvents for cellulose and chitin.

Water-polymer interactions and mechanisms of water-driven glass transition decrease in non-isocyanate polyhydroxyurethanes with varying hydration sites

Non-isocyanate polyurethanes (NIPUs) with varying content of secondary amino groups along their chain were studied with respect to water absorption and plasticization. Secondary amino groups promote water uptake. Water sorption isotherms in the water activity range 0–0.97 are discussed in terms of various sorption models. Secondary amino groups act as additional hydration sites, increasing monolayer capacity. The red shift of the IR band assigned to the carbonyl of the urethane and the simultaneous blue shift of the urethane N–H bending band show cleavage of the polymer-polymer hydrogen bonds upon water uptake, due to strong interactions between water molecules and hydroxyurethanes constituting the primary hydration sites. A decrease in glass transition temperature (Tg) is observed with increasing water content. The effect is discussed in terms of plasticization and slaving mechanisms, while a peculiar decrease of Tg at very low hydrations is attributed to a mechanism not following common mixing laws.

Effects of combined fermentation and ultrasonic treatments on the structure and properties of Okara soluble dietary fiber

In this study, okara dietary fiber samples were prepared through a combination of solid-state fermentation using Aspergillus oryzae and ultrasonication. Subsequent infrared and UV–visible spectral analyses revealed that such treatment resulted in an increase in the oligosaccharide content of these samples through the enhanced cleavage of hydrogen bonds. Scanning electron microscopy and X-ray evaluation further confirmed the changes in the structural makeup of these okara SDF (soluble dietary fiber) samples relative to control samples. Following combination treatment, the soluble dietary fiber levels in these samples were three times higher than in control samples at 18.06 g/100 g. This treatment also led to a significant increase in the water holding, oil holding, and swelling capacities of the prepared fiber samples, whereas the capacity for water retention was slightly reduced. Ultrasonication alone failed to impact SDF oil holding capacity, nor did it impact cholesterol absorption at a pH of 2 used to simulate the stomach microenvironment. Together, these data thus offer a valuable reference for further work aimed at extracting soluble dietary fiber from okara.

Degradation mechanisms and toxicity determination of bisphenol A by FeOx-activated peroxydisulfate under ultraviolet light

ABSTRACT Ultraviolet light (UV)-assisted advanced oxidation processes (AOPs) are commonly used to degrade organic contaminants. However, this reaction system's extensive comprehension of the degradation mechanisms and toxicity assessment remains inadequate. This study focuses on investigating the degradation mechanisms and pathways of bisphenol A (BPA), generation of reactive oxygen species (ROS), and toxicity of degradation intermediates in UV/PDS/ferrous composites (FeOx) systems. The degradation rate of BPA gradually increased from the initial 11.92% to 100% within 120 min. Sulfate radicals ( SO 4 . − ), hydroxyl radicals (.OH), superoxide anions ( O 2 . − ), and singlet oxygen (1O2) were the primary factors in the photocatalytic degradation of BPA in the UV/PDS/FeOx systems. The main reactions of BPA in this system were deduced to be β-bond cleavage, hydroxyl substitution reaction, hydrogen bond cleavage, and oxidation reaction. A trend of decreasing toxicity for the degradation intermediates of BPA was observed according to the toxicity investigations. The efficient degradation of BPA in UV/PDS/FeOx systems provided theoretical data for AOPs, which will improve the understanding of organic contaminants by FeOx in natural industry wastewater.

Study on effect of magnetization on wetting characteristics of water with different ions to coal dust

Coal dust is a significant problem in underground coal mining, and more economical and effective methods are needed to control coal dust. Magnetized water dust removal technology is considered to be an effective method to solve the problem of high concentration dust. In order to further understand the role of ions in magnetic fields in water, the optimal magnetic field parameters for solutions containing various ions were determined by surface tension and contact angle measurements. The wettability experiments have shown that the optimal magnetization effect can be obtained by placing NaCl solution with the concentration of 0.04 mol/L in the 150mT magnetic field for 120 s at room temperature. Subsequently, the influence of various ions in water on the wettability of coal was investigated using a combination of FTIR testing and Zeta potential experiments. The results showed that the order of the influence intensity of different ions on the wettability of water was Na+ > Mg2+ > Ca2+ when the Cl– content was 0.04 mol/l, and Cl– > CO32– > SO42– when the Na+ content was 0.04 mol/L. Furthermore, Lorentz forces can influence various ions, accelerating their migration and enhancing their accessibility to water clusters. Different ions exert force on the dipoles within water molecules, which can promote or suppress hydrogen bond cleavage. When the number of hydrogen bond breaks rises, it leads to an increase in the wetting properties of the solution. The research findings provide a theoretical foundation for the use of magnetization technology in dust suppression with mist spray in underground coal mines.

Melting and Bubble Formation in a Double-Stranded DNA: Microscopic Aspects of Early Base-Pair Opening Events and the Role of Water.

Despite its rigid structure, DNA is a remarkably flexible molecule. Flexibility is essential for biological functions (such as transcription and gene repair), which require large-amplitude structural changes such as bubble formation. The bubbles thus formed are required to have a certain stability of their own and survive long on the time scale of molecular motions. A molecular understanding of fluctuations leading to quasi-stable structures is not available. Through extensive atomistic molecular dynamics simulations, we identify a sequence of microscopic events that culminate in local bubble formation, which is initiated by base-pair (BP) opening, resulting from the cleavage of native BP hydrogen bonds (HBs). This is followed by the formation of mismatched BPs with non-native contacts. These metastable structures can either revert to their original forms or undergo a flipping transition to form a local bubble that can span across 3-4 BPs. A substantial distortion of the DNA backbone and a disruption of BP stacking are observed because of the structural changes induced by these local perturbations. We also explored how water helps in the entire process. A small number of water molecules undergo rearrangement to stabilize the intermediate states by forming HBs with DNA bases. Water thus acts as a lubricant that counteracts the enthalpic penalty suffered from the loss of native BP contacts. Although the process of bubble formation is reversible, the sequence of steps involved poses an entropic barrier, preventing it from easily retracing the path to the native state.

Proton Conduction in Gly-X (X = Ser, Ser-Gly-Ser) and GS50.

In recent years, the use of biomaterials has been required from the viewpoint of biocompatibility of electronic devices. In this study, the proton conductivity of Glycyl-L-serine (Gly-Ser) was investigated to clarify the relationship between hydration and proton conduction in peptides. From the crystal and conductivity data, it was inferred that the proton conductivity in hydrated Gly-Ser crystals is caused by the cleavage and rearrangement of hydrogen bonds between hydration shells formed by hydrogen bonds between amino acids and water molecules. Moreover, a staircase-like change in proton conduction with hydration was observed at n = 0.3 and 0.5. These results indicate that proton transport in Gly-Ser is realized by hydration water. In addition, we also found that hydration of GSGS and GS50 can achieve proton conduction of Gly-Ser tetrameric GSGS and GS50 containing repeating sequences. The proton conductivity at n = 0.3 is due to percolation by the formation of proton-conducting pathways. In addition to these results, we found that proton conductivity at GS50 is realized by the diffusion constant of 3.21 × 10-8 cm2/s at GS50.

A Nanoscale Ternary Amide‐rGO Composite with Boosted Kinetics for Reversible H2 Storage

AbstractMetal amides are attractive candidates for hydrogen storage due to their high volumetric and gravimetric hydrogen densities. However, the sluggish kinetics and competing side reactions during hydrogen uptake and release limit their practical use. Here, a novel nanoconfined Li2Mg(NH)2@reduced graphene oxide (rGO) composite is presented, which is fabricated using a melt‐infiltration method with a minimum weight penalty of only 2 wt.%. The presence of rGO ensures close contact between the active phases, effectively preventing aggregation during cycling process. As a result, the reversible capacity of Li2Mg(NH)2@rGO reaches 4.42 wt.%, with no capacity degradation observed after multiple cycling. Theoretical calculations show that rGO catalyzes the hydrogen bond cleavage at the Mg‐amide/Li hydride interface, leading to local dehydrogenation hotspots and significantly improves kinetics of dehydrogenation compared to the bulk counterpart. This study provides a promising strategy for designing metal imide‐based composites to overcome the kinetic limitations and improve their reversible hydrogen storage performance.

Effects of discharge characteristics and evaluation of pressure of shock wave on underwater discharge as pretreatment for enzymatic saccharification

Cellulosic bioethanol produced from wood is a candidate for alternative fuel to fossil fuels. In the cellulosic ethanol production process, pretreatment before enzymatic saccharification should be introduced for acceleration of the process. We proposed a new pretreatment technique for the cleavage of inter-cellulose hydrogen bonds by underwater discharge shock waves. In this study, we quantitatively analyzed the relationship among discharge conditions, shock wave properties, and treatment efficiency to estimate the optimal treatment conditions. The shock wave pressure was measured at several MPa, and optical microscopy results suggested wood flour fragmentation. The relationship between the discharge characteristics and the treatment effect was investigated by measuring the water retention value as an indicator of hydrogen bond cleavage and the amount of glucose as bioethanol intermediate products. The discharge energy of 0.85–1.16 J/pulse did not affect the treatment effect, while an increased discharge frequency in the range of 3.3–7.3 Hz did. The independence of treatment effect on the discharge energy was investigated to arise from the saturation in the discharge-current rising rate and shock-wave pressure.

Changes in the structure of polysaccharides under different extraction methods

Changes in the structure of polysaccharides under different extraction methods

Synthesis and characterization of bioplastic curdlan esters with an introduced flexible carboxylic acid side chain

Curdlan, a linear β-1,3-glucan, was reacted with glutaric anhydride and heptanoyl chloride to afford thermoplastic curdlan esters (CrdE(HepGlu)) with a carboxylic acid side chain. CrdE(HepGlu) with a degree of substitution of the glutaric acid monoester moiety (DSGlu) in the range of 0–0.58 and that of the heptanoate moiety (DSHep = 3 − DSGlu) was prepared. The esterification of the hydroxy groups in the glucan skeleton effectively caused the cleavage of the interchain hydrogen bonds of curdlan and enhanced the formability of CrdE(HepGlu). Moreover, the flexible carboxylic acid side chain moderately affected hydrogen bonding. Thus, the glass transition temperature of CrdE(HepGlu), estimated by differential scanning calorimetry, increased with increasing DSGlu. CrdE(HepGlu) with DSGlu between 0 and 0.58 displayed high solubility in organic solvents and thermoplasticity, enabling the formation of homogeneous and free-standing films by solution casting. The mechanical properties of CrdE(HepGlu) films were evaluated by a stress−strain test, which showed that Young's modulus and the maximum stress increased with increasing DSGlu. CrdE(HepGlu) exhibited higher mechanical strength than non-hydrogen-bonded curdlan triheptanoate and hydrogen-bonded curdlan alkylcarbamates, with thermal stability comparable to that of thermally stable curdlan esters. In addition, these properties can be regulated by controlling DSGlu.

Degradation by Electron Beam Irradiation of Some Composites Based on Natural Rubber Reinforced with Mineral and Organic Fillers.

Composites based on natural rubber reinforced with mineral (precipitated silica and chalk) and organic (sawdust and hemp) fillers in amount of 50 phr were obtained by peroxide cross-linking in the presence of trimethylolpropane trimethacrylate and irradiated by electron beam in the dose range of 150 and 450 kGy with the purpose of degradation. The composites mechanical characteristics, gel fraction, cross-linking degree, water uptake and weight loss in water and toluene were evaluated by specific analysis. The changes in structure and morphology were also studied by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. Based on the results obtained in the structural analysis, possible mechanisms specific to degradation are proposed. The increasing of irradiation dose to 450 kGy produced larger agglomerated structures, cracks and micro voids on the surface, as a result of the degradation process. This is consistent with that the increasing of irradiation dose to 450 kGy leads to a decrease in crosslinking and gel fraction but also drastic changes in mechanical properties specific to the composites’ degradation processes. The irradiation of composites reinforced with organic fillers lead to the formation of specific degradation compounds of both natural rubber and cellulose (aldehydes, ketones, carboxylic acids, compounds with small macromolecules). In the case of the composites reinforced with mineral fillers the degradation can occur by the cleavage of hydrogen bonds formed between precipitated silica or chalk particles and polymeric matrix also.

Structural Analysis of an Octameric Resorcinarene Self-Assembly in Toluene and its Morphological Transition by Temperature.

Calix[4]resorcinarene derivatives such as C-undecylcalix[4]resorcinarene self-assemble into a hexameric capsule-like structure. This structure is expected in any apolar solvent, but we recently found a self-assembled octameric form of resorcinarene in toluene. To understand this unexpected form, we performed small-angle X-ray scattering (SAXS) measurements of the octameric self-assembly. In ab initio shape reconstruction and model fitting of the SAXS profile, a core-shell spherical structure resembling a reverse micelle was found in the octameric self-assembly. The shell and core were composed of alkyl chains and resorcinol moieties, respectively. We also evaluated the temperature dependence of the octameric self-assembly. Above 95 °C, the structure began directly decomposing into unimers, implying the partial cleavage of hydrogen bonds in the octamer core. Meanwhile, below 25 °C, the spherical structure of the octamer partially transformed to a cylindrical structure. This morphological transition could be understood by packing parameter theory, which is often applied to suspected micellar structures.

Efficient cleavage of strong hydrogen bonds in sugarcane bagasse by ternary acidic deep eutectic solvent and ultrasonication to facile fabrication of cellulose nanofibers

From the perspective of green chemistry, it is of great significance to produce cellulose nanofibers (CNFs) with more environmentally friendly and sustainable materials. This study investigated the efficient cleavage of strong hydrogen bonds occurred in sugarcane bagasse (SCB), ultrafast fabrication of CNFs through a 20 min microwave-assisted ternary carboxylic acid deep eutectic solvent (Mw-TCADES) deconstruction and sweep frequency ultrasonic (SFU) separation pretreatment. It also investigated the subsequent high-intensity ultrasonication (HIU) fibrillation process. After pretreating SCB with two different TCADES (choline chloride: oxalic acid: AlCl3·6H2O, and choline chloride: lactic acid: AlCl3·6H2O, molar ratio 1:1:0.2), the cellulose content of the SCB was 56.2 and 62.6%, respectively. The CNFs obtained after the two Mw-TCADES treatments contained 0.74 and 0.84 mmol/g carboxylic acid groups, and the crystallinity was 58.05 and 60.71%, respectively. Meanwhile, the CNFs obtained under the optimum treatment conditions (Mw-TCADES, 100 °C, 20 min and HIU) showed high thermal stability, which exhibited promising potential for further applications. Under the optimum conditions, the CNFs had a length of about 400–600 nm, width of around 15–17 nm, and a height of about 6–7 nm. The results showed that the TCADES can be used effectively as an alternative to the traditional acid–base pretreatment method and provide a green and efficient method for the utilization of lignocellulosic materials and the separation of CNFs.

Cellulose nanocrystals from bleached rice straw pulp: acidic deep eutectic solvent versus sulphuric acid hydrolyses

The present work aims to investigate the feasibility of oxalic acid-choline chloride deep eutectic solvent (OA-ChCl DES), which serves as a promising green solvent that utilized in the acidic deep eutectic solvent (DES) hydrolysis. Oxalic acid-choline chloride DES cellulose nanocrystal (OA-ChCl DES CNC) was isolated from the bleached DES treated pulp (BP) through the acidic DES hydrolysis using 1:1 molar ratio of OA-ChCl DES. The functional groups, crystallinity index, morphological structure, particle size, zeta potential, thermal stability and surface chemistry of the OA-ChCl DES CNC were compared with the sulphuric acid cellulose nanocrystal (SA-CNC) that prepared via sulphuric acid hydrolysis. The findings revealed the presence of negatively charged carboxyl groups on OA-ChCl DES CNC surface after the acidic DES hydrolysis. The physicochemical analyses verified that the OA-ChCl DES CNC was in nano-sized range with polydispersity index (PdI) of 0.56, indicating slightly monodispersed nanoparticles. A stable OA-ChCl DES CNC colloidal suspension with zeta potential value of −52.1 ± 5.2 mV was obtained. The OA-ChCl DES CNC outweighed the SA-CNC in term of thermal stability (288 °C) despite having a slightly lower crystallinity index (76.7%). In fact, the OA-ChCl DES CNC with a yield of 55.1% was achieved through the acidic DES hydrolysis, suggesting that the OA-ChCl DES was capable of promoting efficient cleavage of strong hydrogen bonds in BP.

Temperature-Dependent Low-Frequency Vibrations of Thiamine Crystal Containing Hydrated Ions

Low-frequency vibrations of crystalline molecules are very sensitive to the local environment in which the molecules, for example, hydrated ions captured in crystals, find themselves. We present low-temperature X-ray crystallographic measurements on the harvested thiamine crystal containing hydrated ions and its temperature-dependent terahertz spectra and synchrotron infrared microspectra. It is found from the X-ray structure that the hydrated ions and hydration water are in a similar environment to liquid, although those are captured in crystals. The vibrationally resolved THz spectra of two states in the present organic crystals containing hydrated ions are well explained by the difference in the hydrogen-bonded pattern. Peak assignments were performed based on highly accurate first-principles calculations incorporating relativistic effects and dispersion corrections. The temperature dependences are observed for the vibrations around the chloride ions and hydration water due to the loose binding of chloride ions, the bond elongation with increasing temperature, and the cleavage of weak hydrogen bonds.

Statics and dynamics of ferroelectric domains in molecular multiaxial ferroelectric (Me3NOH)2[KCo(CN)6

Statics and dynamics of ferroelectric domains in molecular perovskite multiaxial ferroelectric (Me3NOH)2[KCo(CN)6].

Acoustic and hydrodynamic cavitation assisted hydrolysis and valorisation of waste human hair for the enrichment of amino acids

Hair waste in large amount is produced in India from temples and saloons, India alone exported approximately 1 million kg of hair in 2010. Incineration and degradation of waste human hair leads to environmental concerns. The hydrothermal process is a conventional method for the production of hair hydrolysate. The hydrothermal process is carried out at a very high temperature and pressure, which causes the degradation of heat-sensitive essential amino acids, thereby depleting the nutritional value. This work deals with alkaline hydrolysis of human hair using acoustic and hydrodynamic cavitation, and comparison with the conventional method. The optimal operating conditions for highest efficiency was observed, for the hydrolysis of 1 g of sample hairs in 100 mL of solution, at 4:1 (KOH: hair) ratio, soaking time of 24 h, the ultrasonic power density of 600 W dm−3 (20 KHz frequency and input power 200 W) or hydrodynamic cavitation inlet pressure of 4 or 7 bars. Cavitation results in rupture of disulfide linkages in proteins and mechanical effects lead to cleavage of several hydrogen bonds breaking the keratin sheet structure in hair. Breakdown of bonds leads to a decrease in viscosity of the solution. 10% and 6% reduction in viscosity is obtained at optimal conditions for ultrasonic and hydrodynamic cavitation treatment, respectively. FTIR analysis of produced hair hydrolysate confirmed that the disulfide bonds in hair proteins are broken down during cavitation. The amino acid of hair hydrolysate, prepared using cavitation, has a relatively higher digestibility and nutritional value due to the enhancement of amino-acid content, confirmed using amino acid analysis. Cavitation assisted hair hydrolysate has a potential application in agricultural engineering as a fertilizer for improvement of the quality of the soil and land. Cavitation based hair hydrolysate can also be used as an environmentally friendly and economical source of essential amino acids and digestibles for animal or poultry feed.

Facile One-step Fabrication of Functional Cellulose Nanocrystals with High Efficiency under Microwave-ultrasound Synergy

The use of cellulosic biomass for the manufacture of functional cellulose nanocrystals (FCNs) in a mild and green process is limited due to the multiple hydrogen bonds between cellulose. Based on the mechanochemical mechanism, an efficient and green approach to cleave hydrogen bonds and fabricate FCNs was realized via microwave-ultrasound synergy. In the one-step process, impact force, crash force, friction, chemical action, and thermodynamic interaction combined to create synergistic effects, accelerating the cleavage of hydrogen bonds and formation of FCNs synchronously. One-step purification of FCNs was implemented after reaction for the recovery of byproducts, which was critical to cost reduction and waste liquor treatment. FCNs with high crystallinity of 80%, high charge density, and good dispersion stability were obtained. Thus, a facile versatile green avenue for the large-scale production of FCNs was achieved in the study, and is expected to carry significant benefits in terms of economy and sustainability.

Mechanistic examination of Cα -Cβ tyrosyl bond cleavage: Spectroscopic investigation of the generation of α-glycyl radical cations from tyrosyl (glycyl/alanyl)tryptophan.

In this study, dissociative one-electron transfer dissociation of [CuII (dien)Y(G/A)W]•2+ [dien = diethylenetriamine; Y(G/A)W = tyrosyl (glycyl/alanyl)tryptophan] was used to generate the tripeptide radical cations [Y(G/A)W]•+ ; subsequent loss of the Tyr side chain formed [Gα • (G/A)W]+ . The π-centered species [YGWπ • ]+ generated the α-centered species [Gα • GW]+ through Cα -Cβ bond cleavage, as revealed using infrared multiple photon dissociation (IRMPD) measurements and density functional theory (DFT) calculations. Comparisons of experimental and theoretical IR spectra confirmed that both the charge and spin densities of [Y(G/A)Wπ • ]+ were delocalized initially at the tryptophan indolyl ring; subsequent formation of the final [Gα • (G/A)W]+ structure gave the highest spin density at the α-carbon atom of the N-terminal glycine residue, with a proton solvated by the first amide oxygen atom. The IRMPD mass spectra and action spectra of the [Gα • (G/A)W]+ species were all distinctly different from those of their isomeric [G(G/A)Wπ • ]+ species. The mechanism of formation of the captodative [Gα • (G/A)W]+ species-with the charge site separated from the radical site-from [Y(G/A)Wπ • ]+ has been elucidated. DFT calculations suggested that the Cα -Cβ bond cleavage of the tyrosine residue in the radical cationic [Y(G/A)Wπ • ]+ precursor involves (a) through-space electron transfer between the indolyl and phenolic groups; (b) formation of proton-bound dimers through Cα -Cβ cleavage of the tyrosine residue; and (c) a concerted proton rearrangement from the phenolic OH group to the carboxyl group and formation of the α-carbon-centered product [Gα • (G/A)W]+ through hydrogen bond cleavage. The barriers for the electron transfer (a), the Cα -Cβ cleavage (b), and the protonation rearrangement (c) were 12.8, 26.5, and 10.3 kcal mol-1 , respectively.