Contribution Of Water Molecules Research Articles

Impact of water activity on double layer parameters at the mercury/chlorates(VII) interface in the presence of mixed adsorption layers of 6-mercaptopurine\u2013Triton X-100

Adsorption mechanism of 6-mercaptopurine, 6-mercaptopurine–Triton X-100 on the mercury electrode surface from 2, 4 and to 6 mol dm−3 chlorates(VII) was studied as the function of adsorbate bulk concentration. The experimental data obtained from the measurements of differential capacity of the double layer were used, namely the measurements of zero charge potential and surface tension at the zero charge potential. In the case of mixed adsorption layer of 6-mercaptopurine–Triton X-100 domination of 6MP in adsorption equilibria formation as well as competitive adsorption between the 6-mercaptopurine–Triton X-100 molecules were found. Significant contribution of water molecules in the adsorption–desorption processes was also observed.

Kinetic and mechanisms of methanimine reactions with singlet and triplet molecular oxygen: Substituent and catalyst effects

Methanimine reaction with O2 on singlet and triplet potential energy surfaces are investigated using B3PW91, M06-2X, MP2 and CCSD(T) methods. Thermodynamic and kinetic parameters are calculated at M06-2X method. The most favorable channel involves H-abstraction of CH2NH+O2 to the formation of HCN + H2O2 products via low level energy barrier. The catalytic effect of water molecule on HCN + H2O2 products pathway are investigated. Result shows that contribution of water molecule using complex formation with methanimine can decreases barrier energy of transition state and the reaction rate increases. Also, substituent effect of fluorine atom as deactivating group are investigated on the main reaction pathway.

Computer simulation of the surface layer of an ionic micelle with explicit allowance for the contribution of water

Ionic micelles have been simulated in an aqueous solution of single-charged counterions using the molecular dynamics method. It has been demonstrated that the contribution of water molecules needs to be explicitly taken into account when computing the electrical field strength of a micelle. This contribution results in a complex local dependence of the electric charge and gives rise to a charge reversal region in the immediate vicinity of the micelle crown, thereby causing a nonmonotonic behavior of the electric potential. The computations have been performed for both cationic and anionic micelles. A model micelle consists of a rigid hydrocarbon core (impenetreable to water molecules and counterions) and cationic fragments of a surfactant. Data obtained for three molecular models of water (SPC, TIP5P, and two-centered S2 models) have been compared with the results of the continual description of the solvent. For all water models, its local contribution to the electric field around micelles is significant even at large distances from the particle surface.

Ionic strength independence of charge distributions in solvation of biomolecules

Electrostatic forces enormously impact the structure, interactions, and function of biomolecules. We perform all-atom molecular dynamics simulations for 5 proteins and 5 RNAs to determine the dependence on ionic strength of the ion and water charge distributions surrounding the biomolecules, as well as the contributions of ions to the electrostatic free energy of interaction between the biomolecule and the surrounding salt solution (for a total of 40 different biomolecule/solvent combinations). Although water provides the dominant contribution to the charge density distribution and to the electrostatic potential even in 1M NaCl solutions, the contributions of water molecules and of ions to the total electrostatic interaction free energy with the solvated biomolecule are comparable. The electrostatic biomolecule/solvent interaction energies and the total charge distribution exhibit a remarkable insensitivity to salt concentrations over a huge range of salt concentrations (20 mM to 1M NaCl). The electrostatic potentials near the biomolecule's surface obtained from the MD simulations differ markedly, as expected, from the potentials predicted by continuum dielectric models, even though the total electrostatic interaction free energies are within 11% of each other.

Comparison of Protein-water Interactions in Psychrophilic, Mesophilic, and Thermophilic Fe-SOD

Iron superoxide dismutase (Fe-SOD) can eliminate superoxide anion radicals and is widely used in pharmaceuticals, cosmetics and foodstuff. It's significant to determine the factors that influence Fe-SOD thermostability. Previous studies have focused on the relationship between the structural parameters and thermostability of Fe-SOD while the contribution of water molecules was overlooked. In this study, we examined the relationship between hydration waters and Fe-SOD thermostability. The Voronoi polyhedra method was used to explore the distribution of hydration waters around the Fe-SODs and it was interesting to find that the distribution of hydration waters is related to the B-factor of amino acids, i.e., the flexibility of residues can affect the distribution of waters. Protein-water and water-water hydrogen bonds were examined. We found that the hydrogen bond density in thermophilic Fe-SOD was higher than that in mesophilic Fe- SOD. In addition, larger hydrogen bond networks that involve more waters covered the thermophilic Fe-SOD.

Contribution of Water Molecules in the Spontaneous Release of Protein by Graphene Sheets

Applications of graphene sheets in the fields of biosensors and biomedical devices are limited by the aqueous solubility of graphene. Consequently, understanding the role of water molecules in the aggregation or dispersion of graphene in aqueous solution with a biomolecule is of vital importance to its application. Herein, protein is spontaneously released by the layer-to-layer aggregation of two single-layer graphene sheets due to van der Waals force between the sheets. The properties of water molecules, including density and dynamics, are discussed in detail. The dynamic behavior of aggregation of graphene sheets is triggered by the dynamics of water molecules. To stabilize dispersed graphene sheets in aqueous solution, the density of water molecules between the graphene sheets should be larger than 0.83 g cm(-3), and graphene modified by hydroxyl groups could be a good choice. The stability of a model protein on the graphene sheet is studied to investigate the biological compatibility of graphene sheets. To be a material with good biocompatibility, graphene should be functionalized by hydrophilic groups. The results presented herein could be helpful in the research and application of graphene sheets in the fields of biomaterials, biosensors, and biomedical devices.

Pathogenicity characterization with implicit and explicit molecular dynamics simulation

The contribution of water molecules in molecular dynamics simulation (MDS) is unquestionably high, particularly for enzymatic interaction which occurred in the cytoplasmic environment. The addition of water molecules to the system will surely influence different direct interaction between active site residues and substrate. We try to theoretically investigate to what extent the pathogenicity characterization will varies in different neuraminidase-sialic acid complex systems. The heating dynamics simulations were produced with and without TIP3P water molecules. The periodic boundary system was made for explicitly added TIP3P water molecules and generalized born molecular volume (GBMV) energy contribution was added for implicit solvent system. Both complexes, neuraminidasesialic acid of A/Tokyo/3/67 and A/Pennsylvania/10218/ 84, which have a different pathogenicity levels were minimized and simulated. The result shows more residues produced hydrogen bonds with substrate when water molecules were not added to the system. The binding free energies also show differences. Overall, even the values of energy differences, but an implicit solvent provides the similar result (HPAI complex has higher activity than LPAI for both systems) in characterization of pathogenic virus neuraminidase activity.

Hydrothermal Dechlorination of a Reclaimed Oil in a Continuous Packed-Bed Reactor

The liquid-phase hydrothermal dechlorination of a reclaimed oil (Cl content = 2280 ppm) derived from waste lubricating oils was investigated at 275–325°C by using a continuous packed-bed reactor. The reaction proceeded readily in aqueous NaOH solutions, especially at higher NaOH concentrations and at higher reaction temperatures. Thus, the chlorine content in the oil decreased to 57 ppm at 325°C when 0.4 mol/L NaOH was used at the weight feed ratio of 1.3 and at the residence time of 8.0 min. However, the reaction did not proceed further even when the concentrated NaOH solutions of more than 0.4 mol/L were used. The rate of the dechlorination could be well described in terms of a homogeneous SN2-type reaction kinetics involving the participation of water molecules and OH– ions. In contrast to the contribution of water molecules to the reaction, that of OH– ions increased at higher NaOH concentrations and at higher reaction temperatures.

Energetics of Water/Cyclodextrins Interactions

The heat capacities of solid γ-CD, 8.1 H2O and α-CD, 6.0 H2O have been measured between 10 and 300 K by adiabatic calorimetry. Using earlier results obtained in similar experiments with anhydrous cyclodextrins and with β-CD, 9.7 H2O, a comparative analysis has been developed. The energetic behaviours of anhydrous and hydrated cyclodextrins (CDs) have been compared in order to investigate the role of water molecules in the stabilization of the cyclodextrin's rings and on their reactivities. Calculations, based on the additivity of thermodynamic properties, provide the energetic and entropic average contributions of water molecules in each cyclodextrin. From these results, we assumed that the water–water and water–CD interactions are rather different according to the cyclodextrin. In the (β-CD, 9.7 H2O) structure, the water molecules seem to be better organised in a relatively independent network. Concerning hydrated α-CD and γ-CD, stronger water–CD interactions probably prevent an optimal organisation of the water–water bonds network. Differential scanning calorimetry was also used to follow the evolution of the thermal behaviour of γ-CD, nH2O versus hydration ratio between 170 and 300 K. Our results indicate that the γ-CD ring needs at least 1.6 water molecules to be stabilized in the solid state.

Contribution of water molecules in the interior of a protein to the conformational stability

Water molecules frequently occur in the interior of globular proteins. To elucidate the contribution of buried water molecules to the conformational stability of a protein, we examined the crystal structures and the thermodynamic parameters of denaturation of six Ile to Ala/Gly mutant human lysozymes, in which a cavity is created at each mutation site by the substitution of a smaller side-chain for a larger one. One or two ordered water molecules were found in the cavities created in some mutants (I106A, I59A and I59G). The cavity volumes for these three mutants were bigger than those that remained empty in the other mutants. The stability of the mutant proteins with the newly introduced water molecules was about 8 kJ/mol higher than that expected from the change in hydrophobic surface area (ΔΔ ASA HP) exposed upon denaturation. It was concluded that a water molecule in a cavity created in the interior of a protein contributes favorably to the stability.

STUDY OF SLOW MOTION OF WATER MOLECULES IN ROCHELLE SALT AND IN AMMONIUM ROCHELLE SALT BY SPIN-LATTICE RELAXATION OF PROTONS IN ROTATING FRAME

Abstract. - Temperature and frequency dependence of spin-lattice relaxation time in rotating frame Tlr of protons in Rochelle salt and in ammonium Rochelle salt was measured. Two groups of water molecules, called by Bjorkstam [I] A, B, C, D and a, D,y, S water molecules were studied and the correlation time zc was determined for both groups. No direct contribution of water molecules to ferroelectric dipoles was found. Measurements of Tlr of protons in 7.8 mol% ammonium Rochelle salt were performed to check our conclusions, obtained for Rochelle salt. Comparison is made with the dielectric measurements on Rochelle salt at 298 OK. Introduction. - The first known ferroelectric Rochelle salt [2] (R. S.) NaKC,H,O,. 4 H,O is still interesting since there are several open questions in the dynamics of crystal lattice, in particular at both ferro- electric transitions. R. S. is one of the few ferro- electrics with two transition temperatures and with the ferroelectric phase between the transition tempera- tures : 24 OC and