Interaction Of Water Molecules Research Articles

Water retention capabilities of collagen, gelatin and peptide as studied by IR/QCM/RH system.

In this study, water retention properties of triple helix collagen, gelatin (separated single chains) and peptide (broken peptide fragments) were studied by using IR micro-spectroscopy equipped with a relative humidity (RH) control system and quartz crystal microbalance (QCM). Adsorbed water ratios (wt%) are found to be in the order of collagen, gelatin and peptide (at about RH=60%, 22wt% for collagen, 14wt% for gelatin and 9wt% for peptide). Free water molecules with longer H bonds are the major adsorbed water species for collagen, gelatin and peptide. IR band shifts and changes in normalized band areas of functional groups are generally larger for collagen than gelatin and peptide, indicating larger interactions of water molecules with functional groups such as aliphatic CH2, CH3, amides, COO- and C-O for collagen. Relations between normalized band areas show that water molecules are interacting with aliphatic CH species and C-O bonds of collagen. Since the fibril structures of collagen triple helices are reported to be cross-linked by sugars, water molecules can be attracted to polar C-O bonds of sugars linking collagen triple helices in fibrils and they are interacting with adjacent aliphatic CH side chains on the surface of fibrils.

Molecular dynamics simulation of water-based nanofluids viscosity

The shear viscosity coefficients of water and water-based nanofluids with copper particles are calculated by the molecular dynamics method. Copper nanoparticles with a diameter of 2, 4 and 10 nm were used in the simulation. The volume fraction of nanoparticles was varied from 1 to 5%. The interaction of water molecules with each other was modeled using the Lennard–Jones potential. The Rudyak–Krasnolutskii and Rudyak–Krasnolutskii–Ivanov potentials were used as nanoparticle–molecule and nanoparticles interaction potentials, respectively. The viscosity coefficient was calculated using the fluctuation–dissipation theorem by the Green–Kubo formula. It is shown that the viscosity of the nanofluid significantly exceeds the viscosity of the coarse-grained suspension and increases with a decrease in the nanoparticles size at their fixed volume fraction. The correlation functions determining the viscosity coefficient of the nanofluid were analyzed in detail. The radial distribution functions of pure water and nanofluids are also presented in the paper. It is shown that the liquid near the nanoparticle is structured much more strongly than in the bulk. This greater ordering of the nanofluid is one of the main factors determining the increase in nanofluids viscosity.

Synthesis and complex study of cerium(IV) fluoride hydrate

By precipitating from an aqueous solution of Ce(SO4)2·4H2O with 40 % hydrofluoric acid obtained a nanosized powder of cerium tetrafluoride hydrate with a composition close to CeF4*0.95 H2O. According to the results of x-ray phase analysis, the crystalline phase has a cubic lattice similar to lattice of PuF4·1.6H2O. The hydrate nanopowder is characterized by XRD, TEM, 1H and 19F{1H}NMR and IR - spectroscopy. Quantum chemical calculations of the IR- spectra of models of the possible interaction of water molecules with a fluorine ions have been carried out. The temperature behavior of the CeF4*0.95 H2O powder was studied by using X-ray powder diffraction analysis up to 300 °C and thermogravimetrically up to 200 °C.

Features of the Structural Organization and Sorption Properties of Cellulose

An improved model of the layered structure of cellulose microfibrils is proposed, taking into account the presence of slit-like pores between its structural elements. The scheme of the formation of donoracceptor intramolecular, intermolecular and interlayer hydrogen bonds of one glucopyranose unit in the cellulose crystallite is presented. The mechanism of specific adsorption interactions of water molecules in a monolayer with active centers located on the hydrophilic surfaces of elementary fibrils is described. The energy of dipole-dipole interactions was calculated depending on the distance between the active center and the adsorbate water molecule. The thermodynamic parameters characterizing the state of the adsorbate in the adsorption layers are determined by the proton magnetic relaxation method and sorption measurements. The possibility of determining the net heat of adsorption in a bilayer taking into account the Arrhenius nature of the correlation times of the thermal molecular motions of the adsorbate was established. An increase in the entropy of adsorbed water during the adsorption process was revealed. It was found that during adsorption, a part of the inner regions of crystallites transitions to their surface with the participation of cellulose hydroxyl groups, and during desorption, the reverse process is observed.

Kinetic investigation of water physisorption on natural clinoptilolite at room temperature

Charge balancing extra-framework cations play a fundamental role in the adsorption/desorption of polar molecules on zeolites. The way cations interact with polar molecules (e.g. water) in combination with the negatively charged framework and the kinetics of such interaction is extremely important for designing novel devices based on these functional materials. Kinetic investigation and mechanistic modeling of these processes can be conveniently performed by electrical tests, based on biasing the clinoptilolite sample with a constant a.c. voltage (20V pp , 5kHz) and monitoring the temporal evolution of the current intensity during the adsorption/desorption processes. According to this kinetic analysis, adsorption is described by the Lagergren pseudo-first-order model with a rate constant of (5.86 ± 0.09)·10 −3 min −1 , while water desorption in dry air follows a first-order kinetic model with a specific rate of (2.02 ± 0.003)·10 −2 min −1 at 25°C. According to these models, the water molecule to be adsorbed is first caught by the cation electric field and then transferred at the cation-framework interface to maximize non-bonding interactions. • Interaction of adsorbate water molecules with cationic sites in zeolites. • The mechanistic water-cation kinetics is based on a two steps process, involving a binary reaction. • Insight of the time evolution of the surface extra-cations from electrical transport properties. • The direct water-cation reaction results one order of magnitude slower than the inverse desorption reaction.

Interactions of Multiple Water Molecules with MIL-53(Al) and Understanding the Mechanism of Breathing: The DFT Study

Geometries and energies of large clusters of the benchmark metal-organic framework MIL-53(Al) with and without water molecules were studied by density functional theory (DFT) using the M06-2X funct...

Platinum Atoms and Nanoparticles Embedded Porous Carbons for Hydrogen Evolution Reaction.

Due to the growing demand for energy and imminent environmental issues, hydrogen energy has attracted widespread attention as an alternative to traditional fossil energy. Platinum (Pt) catalytic hydrogen evolution reaction (HER) is a promising technology to produce hydrogen because the consumed electricity can be generated from renewable energy. To overcome the high cost of Pt, one effective strategy is decreasing the Pt nanoparticle (NP) size from submicron to nano-scale or even down to single atom level for efficient interacting water molecules. Herein, atomically dispersed Pt and ultra-fine Pt NPs embedded porous carbons were prepared through the pyrolysis of Pt porphyrin-based conjugated microporous polymer. As-prepared electrocatalyst exhibit high HER activity with overpotential of down to 31 mV at 10 mA cm−2, and mass activity of up to 1.3 A mgPt−1 at overpotential of 100 mV, which is double of commercial Pt/C (0.66 A mgPt−1). Such promising performance can be ascribed to the synergistic effect of the atomically dispersed Pt and ultra-fine Pt NPs. This work provides a new strategy to prepare porous carbons with both atomically dispersed metal active sites and corresponding metal NPs for various electrocatalysis, such as oxygen reduction reaction, carbon dioxide reduction, etc.

Nanohybrids of a MXene and transition metal dichalcogenide for selective detection of volatile organic compounds

Two-dimensional transition metal carbides/nitrides, known as MXenes, have been recently receiving attention for gas sensing. However, studies on hybridization of MXenes and 2D transition metal dichalcogenides as gas-sensing materials are relatively rare at this time. Herein, Ti3C2Tx and WSe2 are selected as model materials for hybridization and implemented toward detection of various volatile organic compounds. The Ti3C2Tx/WSe2 hybrid sensor exhibits low noise level, ultrafast response/recovery times, and good flexibility for various volatile organic compounds. The sensitivity of the hybrid sensor to ethanol is improved by over 12-fold in comparison with pristine Ti3C2Tx. Moreover, the hybridization process provides an effective strategy against MXene oxidation by restricting the interaction of water molecules from the edges of Ti3C2Tx. An enhancement mechanism for Ti3C2Tx/WSe2 heterostructured materials is proposed for highly sensitive and selective detection of oxygen-containing volatile organic compounds. The scientific findings of this work could guide future exploration of next-generation field-deployable sensors.

Mathematical Study of the Water-Vapor Permeability of the Surface Layer of a Homogeneous Porous Material

Permeability in relation to gases and liquids is one of the most important characteristics of porous materials. A porous material can interact with gases and liquids flowing through it in different ways that depend on a material’s permeability. Studies of the interaction of water vapor with materials with uniformly distributed pores are of considerable practical interest, since many of these materials are used in building and construction. Interest is also due to the possibility of expanding the study results obtained for an individual pore to a porous medium if this medium can be represented as a structure with uniformly distributed pores with sufficient accuracy. The dependence of the permeability of an individual cylindrical pore on its radius, length, and characteristics of the process of water-molecule interaction with the pore walls is studied.

Slow dynamics of supercooled hydration water in contact with lysozyme: examining the cage effect at different length scales

ABSTRACT We study by computer simulation the dynamics of hydration water in solution with lysozyme upon approaching the glassy state of water. We calculate the self-density correlation function at different wavelengths to test the Mode Coupling Theory (MCT) of glassy dynamics at different length scales. The results show a strict and clear relation of the behaviour of the structural relaxation with the cage effect. We find a good agreement with the predictions of the MCT in the short and medium scale range, while at increasing length scales the interaction of water molecules with the protein's substrate induces deviations from the MCT behaviour, as found in previous studies. Besides at low temperatures the slow dynamics deviates from MCT due to hopping processes, similar to the bulk, as witnessed by a crossover from a fragile behaviour to a strong behaviour. We show that this deviation is evident at all length scales. Interestingly, we find that in the fragile region the confining cage decreases in radius with temperature while in the strong region it appears stable.

Molecular velocity auto-correlations in glycerol/water mixtures studied by NMR MGSE method

Molecular dynamics in binary mixtures of water and glycerol was studied by measuring the spectrum of water velocity auto-correlation in the frequency range from 0.05−10 kHz by using the NMR method of modulated gradient spin echo. The method shows that the diversity of diffusion signature in the short spin trajectories provides information about heterogeneity of molecular motion due to the motion in the micro-vortexes of hydrodynamic fluctuation, which is especially pronounced for the mixtures with low glycerol content. As concentration of glycerol increases above 10vol%, a new feature of spectrum appears due to interaction of water molecules with the clusters formed around hydrophilic glycerol molecules. New spectrum exposes a rate thickening of molecular friction, according to Einstein–Smoluchowski–Kubo formula, which inhibits rapid molecular motions and creates the conditions for a slow process of spontaneously folding of disordered poly-peptides into biologically active protein molecules when immersed in such a mixture.

Спектры РКР Co(II)- и Cu-5,10,15,20-тетракис[4-(N-метилпиридил)]порфирина в возбужденном dd-состоянии и механизмы его дезактивации в растворе и комплексах с ДНК

A study of the resonance Raman scattering (RRS) spectra of Co(II)- and Cu-5,10,15,20-tetrakis [4-(N-methylpyridyl)]porphyrin (CoIITMpyP4, CuTMpyP4) in various solvents and in complex with DNA was carried out. Additional lines were found in the RRS spectra of CoIITMpyP4 in a dimethylformamide (DMF) solution containing formic acid as an impurity, as well as for its complex with DNA under nanosecond pulsed excitation. At the same time, under the same excitation conditions, such lines are absent in the spectra of CoIITMpyP4 solutions in pure DMF, dimethyl sulfoxide, water, and alcohols. To interpret the experimental data, we performed calculations of the structure and vibrations for the solvate complexes of CoII - and CuTMpyP4 with water, methanol and formic acid in the ground and in excited states. Based on the data obtained, additional lines in the Raman spectra were assigned to the excited dd-state corresponding to the d(z2) d(x2-y2) transition, the lifetime of which increases with the formation of complexes of CoIITMpyP4 with formic acid. According to the calculation results, this correlates with a decrease in the rate constant of the internal conversion kic due to an increase in the energy gap E between the ground and dd states of CoIITMpyP4. In the case of CoII and CuTMpyP4 binding to DNA, the decrease in kic is due to the additional interaction of the extra-liganding water molecule directly or with the participation of several immobilized DNA water molecules with one of its bases. This complicates the conformational rearrangement of the water molecule in the dd-state, which contributes to an increase in E.

Water dimer isomers: interaction energies and electronic structure.

The energetic and electronic structure of various water dimer isomers has been explored through DFT methodology. Six different possible water dimers come in two broad categories, planar and non-planar. In each of the categories, three distinct topologies (i) linear, (ii) ring and (iii) bifurcated, have been obtained. The linear dimer has the highest interaction energy, followed by the ring dimer and then comes the bifurcated dimer. For each of these type, a planar dimer having all six atoms organized in a single plane come very close to, but has a slightly higher energy than the corresponding non-planar counterpart. Bader's atoms in molecules (AIM) theory, reduced density gradient (RDG) method and non-covalent interaction (NCI) analysis reveal that the electron density distribution among the interacting water molecules correlates exactly in the sequence of interaction energies of different isomers of water dimer. Graphical abstractVarious possible water dimer isomers.

Studies on thermal stability of high-power short time microwave dried paprika (Capsicum annuum L.) considering the interaction of water molecules with sorption sites

The moisture adsorption isotherms of high-power short time microwave dried paprika (Capsicum annuum L., a pulverized product of dried red pepper) were determined for thermodynamic analysis and assessment of its stability at elevated temperatures. The thermal stability of paprika was evaluated based on alterations in quality characteristics due to the interaction of water molecules with sorption sites during the adsorption process. The GAB model constants revealed the physical significance and the exothermic interaction of the water molecules with the sorption sites on the surfaces of the paprika. The differential enthalpy was found to decrease with increasing water activity due to the existence of highly active polar sites on the surface of paprika at low water activity. The differential entropy decreases due to a rise in water activity as molecular water movement was highly restricted at an elevated water activity. The safe water activity levels corresponding to monolayer moisture content (M o) of paprika at 30°, 40°, 50°, and 60 °C were found to be 0.58, 0.49, 0.43, and 0.30, respectively. Moreover, the acceleration in quality degradation of paprika was found to increase beyond M o at the respective adsorption temperature.

Role of trapped water on electroresponsive characteristic of silica-graphene oxide composite microspheres

Electroresponsive microspheres containing nanosilica and graphene oxide (GO) sheets have been achieved by the one-step evaporation induced assembly of mixed colloids using spray drying. The interlocking of the nanostructured constituents by the attractive capillary force during drying of dispersion droplets results in the formation of powder grains with correlated nanoparticles and nanosheets. The presence of GO sheets arrests the buckling of the drying droplets during evaporative assembly and results in well-defined spherical shaped grains. Interestingly, this approach of random jamming in colloidal droplets is capable of preventing the spontaneous stacking of the GO sheets and, therefore, facilitates a way to confine the atomic-thick GO sheet in the solid matrix. A plausible mechanism for the formation of silica-GO binary composite microspheres is elucidated. Microspheres dispersed in insulating oil show interesting electroresponsive characteristics where the microspheres form a chainlike percolation path under the applied electric field. It has been established that the adsorbed water in the microspheres plays a profound role as far its electroresponsive behavior is concerned. GO sheets in the microspheres allow for tuning of electroresponse strength owing to the increased interaction of water molecules to the oxygen-containing functional groups anchored on the GO sheets.

Study on the influence mechanism of Mg2+ modification on vermiculite thermal expansion based on molecular dynamics simulation

The thermal insulating performance of expanded vermiculite is closely related to expansibility. A novel method of Mg2+ modification was proposed to improve the vermiculite expansion ratio. The modification process was characterised by energy dispersive X-Ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric-differential scanning calorimeter and scanning electron microscopy. Moreover, the thermal expansion experiment was performed to investigate the expansion behaviours of Raw-V and Mg–V samples at various temperatures. The result indicated that the introduction of Mg2+ could increase the vermiculite interlayer water content through hydration interaction, and the expansion ratio increased 13.7% under the heating temperature of 900 °C after modification. To explain the interaction of magnesium ion and water molecules, a molecular dynamics model was developed, and the simulation results were validated using the binding energy calculation. The results of this study can provide a new perspective and theoretical guidance for the commercial process of vermiculite expansion.

Molecular simulation of viscosity of nanofluids based on water with metal particles

Shear viscosity coefficient of water-based nanofluids with copper particles is simulated with the molecular dynamics method. The interaction of water molecules with each other was modeled with Lennard-Jones potential. The viscosity coefficient was calculated on the basis of the fluctuation-dissipation theorem by the Green–Kubo formula. The selection of parameters of the potential corresponding to the experimental values of water viscosity and density at a given temperature of 25°C at the atmospheric pressure is performed. Rudyak–Krasnolutskii (RK) and Rudyak–Krasnolutskii–Ivanov (RKI) potentials described interaction between nanoparticles and water molecules and nanoparticles with each other, respectively. Diameters of copper nanoparticles used were 2 and 4 nm. Volume concentration of the nanoparticles varied from 1% to 5%. It is shown that the viscosity of the nanofluids exceeds significantly the viscosity of suspensions with macroscopic particles and increases with a decrease in the size of nanoparticles at a fixed volume concentration. The paper also presents the calculation data of pair distribution functions for pure water and nanofluid. It is shown that the water near the nanoparticle is much more structured than in the free volume. This large ordering in the nanofluids is one of the key factors of their higher viscosity compared to pure water.

Molecular dynamics of aqueous salt solutions in clay nanopores under the thermodynamic conditions of hydraulic fracturing: Interplay between solution structure and molecular diffusion

Shale gas has become an important unconventional energy resource and is extracted by hydraulic fracturing of shale rocks. In shale rocks, kerogen and clays are present, the former providing storage for hydrocarbons, the latter preventing hydrocarbon transport. Clays are hydrophilic and have a layered structure. They can adsorb aqueous salt solutions in the interlayer space, and the interlayer ions contribute to a very high salinity of the flow-back water. We used montmorillonite (MMT) as a proxy of clays and study the interplay between the interlayer structure and the molecular diffusion of the aqueous salt solutions confined in the clay nanopores. We considered water with monovalent Na and divalent Ca ions in the MMT slit pores under a typical shale gas reservoir condition of a temperature of 365 K and a pressure of 275 bar. The confined systems were electrostatically balanced by Cl ions. We varied the amount of water to cover one-, two-, three-, and four-layer hydrate states. We quantified the solution structure in terms of the interlayer atomic density profiles, complemented by the charge density and water orientation profiles. We further evaluated the in-plane self-diffusivity of water and ions to provide insight into the diffusion behaviour of the concentrated water-NaCl and water-CaCl2 solutions in the interlayer galleries of the Na- and Ca-MMT pores. We found that the interlayer water structure displays an attraction of water hydrogens to the clay surfaces as a result of the strong H-bond interactions of water molecules with the surface oxygens and formation of a diffusive layer inside wide clay pores. The presence of divalent Ca ions has more pronounced effects on the interlayer water structures than the monovalent Na ions. Divalent Ca ions exhibit a preference for inner-sphere complexes over outer-sphere complexes due to the strong adsorption on the clay surfaces while Na ions show the opposite trend. The diffusion of water and ions in the clay pores is reduced in comparison with the diffusion in the bulk, especially for the one-layer hydrate states. The presence of the salts in the clay pores further decreases the water diffusion, with a stronger decrease for the divalent CaCl2 than the monovalent NaCl. The diffusion of small Na+ and Ca2+ is lower than large Cl− due to the low mobility of the adsorbed cations and the distribution of Cl ions inside the pores where they can diffuse faster.

The role of nuclear quantum effects in the relative stability of hexagonal and cubic ice.

At atmospheric pressure, hexagonal ice (Ih) is thermodynamically stable relative to cubic ice (Ic), although the magnitude and underlying physical origin of this stability difference are not well defined. Pure Ic crystals are not accessible experimentally, and hence computer simulations have often been used to interrogate the relative stabilities of Ih and Ic; however, these simulations are dominated by molecular interaction models that ignore the intramolecular flexibility of individual water molecules, do not describe intermolecular hydrogen-bonding with sufficient accuracy, or ignore the role of nuclear quantum effects (NQEs) such as zero-point energy. Here, we show that when comparing the relative stability of Ih and Ic using a flexible, anharmonic molecular interaction model, while also accurately accounting for NQEs, a new picture emerges: Ih is stabilized relative to Ic as a result of subtle differences in the intramolecular geometries and intermolecular interactions of water molecules which are modulated by NQEs. Our simulations hence suggest that NQEs are a major contributor to the stabilization of Ih under terrestrial conditions and thus contribute to the well-known hexagonal (sixfold) symmetry of ice crystals.

Unraveling the Origin of the Apparent Charge of Zwitterionic Lipid Layers.

The structure of water molecules in contact with zwitterionic lipid molecules is of great biological relevance, because biological membranes are largely composed of such lipids. The interaction of the interfacial water molecules with the amphiphilic lipid molecules drives the formation of membranes and greatly influences various processes at the membrane surface, as the field that arises from the aligned interfacial water molecules masks the charges of the lipid headgroups from the approaching metabolites. To increase our understanding of the influence of water molecules on biological processes we study their structure at the interface using sum-frequency generation spectroscopy and molecular dynamics simulations. Interestingly, we find that water molecules at zwitterionic lipid molecules are mainly oriented by the field arising between the two oppositely charged molecular moieties within the lipid headgroups.