Arrangement Of Water Molecules Research Articles

Hydration of DNA

In the past year, some new experimental and theoretical studies have been published which show that many factors influence hydration structure. As the data emerge, it is clear that DNA sequence, size of the grooves, overall conformation and crystal packing are all related to the structural arrangements of water molecules around nucleic acids. Caution in relating these structures to macroscopic properties is still appropriate.

Nuclear magnetic resonance studies of supercooled aqueous electrolyte solutions

The dynamic properties of water molecules coordinated to simple ions (alkali and alkali-earth halides) and hydrophobic ions (tetraalkylammonium (TAA) halides) in supercooled solutions have been investigated with NMR. The study of spin-lattice relaxation rates and self-diffusion coefficients as functions of temperature, pressure Larmor frequency and concentration reveals characteristic features of molecular motions close to the low-temperature limit of the metastable phase (percolation transition and glass transition) and provides certain details of the local arrangement of water molecules in the coordination sphere of these ions. The intramolecular flexibility of the alkyl chains of the hydrated TAA cations has been investigated also. The dynamics of the methyl group reorientation provide a sensitive probe of structural differences in these solutions.

Geometrical arrangement of water molecules in copper–aquoion complex—Influence on shifts and relaxivities in nuclear magnetic resonance

The unrestricted Hartree–Fock cluster procedure has been applied to the Cu2+–(H2O)6 complex to study both its geometry and the hyperfine properties of protons and 17O nuclei in the water molecules of the first hydration sphere. The geometry was studied to understand the Jahn–Teller effect expected for this complex and to explain the observed tetragonal distortion of an elongated nature from extended x-ray absorption fine structure measurements involving four of the H2O molecules being closer to the Cu2+ ion than the other two. The hyperfine properties were studied to attempt to explain observed data in this respect from nuclear magnetic resonance measurements. Our results for the situation in which there is a hole in the dx2–y2 type of state do explain the elongated nature of the tetragonal distortion. The calculated electronic wave functions provide a satisfactory explanation of the 17O hyperfine interaction. For the protons, our results demonstrate the validity of the point ion model commonly used for the dipolar interaction between protons of the hydrated H2O molecules and the unpaired spins in explaining proton nuclear magnetic resonance relaxation data for aquoions. For the proton contact interaction however, theory appears to lead to a higher value than experiment. Possible sources that can lead to an improvement in the predicted proton hyperfine interaction constant are discussed.

Anomalous diffusion of tetramethylurea (TMU) in aqueous solution

The discrepancy between the values of the characteristic size of the tetramethylurea molecule determined by various methods (elastic neutron scattering, physicochemical methods, neutron spin echo) predicts a peculiar arrangement of water molecules around dissolved TMU molecules. A cage-model commonly accepted for clathrates is proposed to explain the observed data.

Hydration properties of lyotropic mesophases in para-nonylphenol decaoxyethylene glycol-water mixtures

The regions of existence and the phase transitions from lyotropic to solution phases occurring in the binary systems p-nonylphenol decaoxyethylene glycol-water have been probed by polarized light. Dielectric and NMR techniques have been applied to study hydration processes occurring at the interfaces. The results indicate the occurrence of interactions among water and polar head groups and suggest some nonspecific arrangement of water molecules at interfaces. It was found that about 9 water molecules interact with hydrophilic sites of the amphiphile in lamellar phase and about 15 water molecules in hexagonal phase.

Observation of an Eclipsed C‐CH3 Bond in a Tricyclic Orthoamide; Experimental and Theoretical Evidence for CH ⃛O Hydrogen Bonds

The inversion of the rotational barrier of a methyl group can be accomplished by a suitable arrangement of water molecules, as shown by X-ray crystal structure investigations of the orthoamide 1. In the trihydrate, the methyl group adopts a nearly elipsed conformation, whereas in the anhydrous compound the normal staggered conformation is found. The H…O bond strengths of the C−H·O hydrogen bonds required for this inversion (ca. 1.8 kcal nol−1) were confirmed by quantum-chemical calculations only when correlation effects were taken into consideration.

Thermal motion from monte carlo simulations of aqueous ionic solutions

AbstractThe statistical pattern recognition procedure of Marchese and Beveridge for the analysis of Monte Carlo simulations of aqueous ionic solutions [J. Am. Chem. Soc. 106, 3713 (1984)] has been extended to include average hydrogen positions as well as oxygen positions. In addition, thermal ellipsoids have been calculated for each atom and displayed graphically. Application of this procedure to the analysis of a dilute aqueous solution of Zn++ reveals an octahedral arrangement of water molecules within the ion's first hydration shell. The thermal ellipsoids show that most of the water motion is manifest in the hydrogen atoms.

Mössbauer studies of radioactive atoms implanted in frozen solids

Abstract Radioactive atoms of 57Co and 125mTe implanted in frozen N2, H2O, HC1 and Xe were studied by Mossbauer spectroscopy. Results of 57Co in ice show stable arrangements of water molecules around the 57Co atom and a rearrangement after the amorphous crystalline phase transitions. Results on N2, HC1 and Xe show the existence of various charge states produced in the decay after-effects and possible formation of an Fe-N molecule.

X-ray diffraction studies on the arrangement of water molecules in a smectite. I.Homogeneous two-water-layer Na-beidellite

A method of indirect analysis of X-ray diffraction patterns of homogeneous hydrated microcrystalline silicates is introduced. This method is applied to a sodium beidellite of Rupsroth, Bavaria, Germany, hydrated with two water layers to determine all its structural characteristics: namely, the average dimension and size distribution of coherent domains, stacking mode of the layers along the c* direction, levels and number per unit cell of water molecules. A critical analysis on the `concept of homogeneity' of hydrates and a discussion on the conditions of its application to lamellar microcrystalline silicates with a few numbers of layers are made.

Double layer on silver single crystal electrodes in contact with electrolytes having anions which are slightly specifically adsorbed: Part II. The (100) face

Double-layer measurements for a (100) face of silver in NaF, NaClO 4 and KPF 6 solutions are analysed to obtain quantitative data on the structure of the solid electrode-aqueous electrolyte interface. It is found that the specific adsorption increases as O<PF 6 − <F − <ClO 4 − Surface concentrations of the specifically adsorbed ions are calculated for ClO 4 − and F − in NaClO 4 + KPF 6 and NaF + KPF 6 solutions. These specific absorptions are shown to characterize essentially the property of the (100) face. and not that of the defects of the surface. For the (100) Ag/KPF 6 system, the electrical double-layer model in the absence of specific adsorption is verified; the incomplete dissociation of KPF 6 is taken into account. The (100) Ag pzc is −0.865±0.005 V (SCE). The high inner-layer capacities are interpreted considering the influence of the atomic distribution of the ideal (100) place on the arrangement of water molecules at the interface. Weak metal-solvent interactions at the pzc are deduced from the variation of the inner-layer capacity as a function of the electrode charge. For mixed solutions of NAF + KPF 6, and NaClO 4 + KPF 6, the differential capacity is resolved into its components with the aid of diffuse-layer theory. The two components of the total inner-layer capacity, at constant electrode charge and constant amount adsorbed, are also determined. From this analysis, it is shown that the ionic size is responsible for the lowering of the differential capacity in the region of positive charges when fluoride is replaced by perchlorate although the specific adsorption of perchlorate is larger than that of fluoride.

Columns of water molecules and chloride ions in hydrophobic channels in crystals of a potassium complex.

The complex between potassium chloride and a macrobicyclic polyether (L) had been shown to crystallize as complex cations KL+ packed to form channels which contained ‘disordered’ water molecules and chloride ions. Here the arrangement of water molecules and chloride ions is described.

Highly structured water network in crystals of a deoxydinucleoside---drug complex.

X-ray diffraction analysis of crystals of the intercalative complex between the deoxyribonucleoside phosphate d(CpG) and the mutagen proflavine shows a highly structured arrangement of water molecules linked together by newtworks of hydrogen bonds to form four edge-linked pentagons per asymmetric unit. These pentagons have a general role in maximizing hydrogen bonding at 3.4-A intervals. The conformation of the deoxyribose sugar ring at the 3' end of one strand can depend on its local aqueous environment.

On the nature of phase transition in the potassium ferrocyanide crystal family

A model of arrangement of water molecules in the lattice on the basis of NMR data for homogeneous KRCT crystal is suggested. The influence of twinning on the value and direction of spontaneous polarization is discussed.The ferroelectrical phase transition is connected with the ordering of a part of water molecules in crystal.

Water on the Surfaces of Clay Minerals: Orientation, Diffusion and Proton Exchange

Abstract The surface of clay minerals such as montmorillonite and vermiculite offersan unique environment for the study of water molecules arrangement and of their interaction with cations since

Arrangement of water molecules in cavities and channels of the lattice of [Phe4Val6]antamanide dodecahydrate.

The synthetic, biologically active, [Phe4Val6] analog of natural antamanide has been crystallized from a solution containing calcium nitrate, acetone, and acetonitrile. The crystal does not contain any Ca2+ ions but does contain 12 water molecules per peptide molecule. The conformation of this dodecahydrate is identical to the trihydrate crystallized from n-hexane/methyl acetate. The packing in both crystals is very similar, governed by parallel bands of phenyl and pyrrolidine ring stacking and by continuous channels for the solvement molecules, water in this case and n-hexane/methyl acetate in the previous study. The two structures are not ideally isomorphous, since the c cell parameter differs by more than 1.0 A in the two cells. There are three functions for H2O molecules: the three intrinsic H2O molecules in the interior of the peptide ring, the H2O bound to the exposed C=O groups, and the H2O molecules that fill space in the solvent channels. There are no direct hydrogen bonds between neighboring peptide molecules and there are only two intramolecular NH-O=C bonds (of the 5 leads to 1 type).

The interaction between sodium carboxymethylcellulose and water

A differential scanning calorimeter has been used to study the nonfreezing of water in a series of solutions of sodium carboxymethylcellulose. In particular, the effects of molecular weight, degree of substitution, and particle size have been investigated. The results show that large amounts of water are associated with all the samples of sodium carboxymethylcellulose, suggesting a multilayer arrangement of water molecules about the solute. A change in degree of substitution has some effect on the hydration, but it appears less significant than a change in molecular weight.

Chromium(II) chemistry. Part IV. Double sulphates

The double salts M2SO4,CrSO4,6H2O (M = NH4, Rb, or Cs) have been found to be high-spin compounds which obey the Curie law. Their spectroscopic and thermal properties are compatible with a tetragonally-distorted, octahedral arrangement of water molecules about the chromium(II) ion. The compounds M2SO3,M2SO4,2H2O M = Na or K) have similar properties, but are more distorted because sulphato-groups are present. The corresponding caesium dihydrate is almost diamagnetic, and this and its spectroscopic properties are consistent with a sulphato-bridged binuclear structure like that of chromium(II) acetate monohydrate.

Jahn-Teller Theorem and the Arrangement of Water Molecules around Paramagnetic Ions in Aqueous Solutions

IT is well known from X-ray studies that in many of the highly hydrated salts of the iron and the rare earth groups the cation is surrounded by an octahedron of water molecules. This distribution fits well with the observed magnetic properties of these salts; first, it gives an electric field of predominantly cubic symmetry about the central cation, as required by the magnetic data, and secondly, it gives the potential of the electric field the proper sign demanded by the magnetic data. The magnetic data, however, further require (1) that the field, though predominantly cubic in symmetry, should deviate from it considerably, since the cation in these crystals exhibits, in general, a strong magnetic anisotropy, and (2) that for a given cation the magnitude and the asymmetry of the electric field about it should be nearly the same in the different hydrated salts containing the ion, since the magnetic anisotropy of the ion is found to be of the same order of magnitude in all these salts. These requirements will be satisfied in a simple manner if the octahedron, instead of being regular, deviates from it slightly—a small deviation is permitted by the available X-ray data—and the deviation is determined by the nature of the cation in the centre. This arrangement appears very probable in view of the important theoretical result obtained recently by Jahn and Teller1, namely, that if the electronic state of the central ion is degenerate, the system will be stable only if there is enough asymmetry in the system to remove the degeneracy (except, of course, the special two-fold degeneracy of Kramers). This minimum asymmetry required for stability supplies then the mechanism by which the cation can in a manner determine the geometry of distribution of the water molecules around it.