Structural investigation of hydrate compounds of the tetraisoamylammonium form of polyacrylate ion exchange resins. Crystal structure of a clathrate hydrate of linear tetraisoamylammonium polyacrylate

A polyhydrate of the tetraisoamylammonium salt of linear (uncrosslinked) polyacrylate (～25 monomeric units in the polyacrylate chain) is described and compared to polyhydrates of cross-linked tetraisoamylammonium polyacrylates (0.5–3% of cross-linking with divinylbenzene or divinylsulfide). Powder X-ray diffraction reveals that the polyhydrate containing a linear polyacrylate molecule has the same structure (hexagonal, a = 12.26 Å, c = 12.71 Å at 3°C) as polyhydrates of the cross-linked polyacrylate molecules. A single crystal of the polyhydrate obtained from an aqueous solution of linear tetraisoamylammonium polyacrylate is studied by X-ray diffraction at ?173°C. The structure is hexagonal; space group P-6m2; the polyhydrate framework is a slightly distorted variant of the hexagonal structure-I of clathrate hydrates.     

Model verification of limiting concentration by electrodialysis of an electrolyte solution

The concentration of LiCl in brine and brine volume are obtained as functions of current density by the method of limiting concentration by electrodialysis. These relationships are used for model calculations of current efficiency, the diffusion, osmotic, and electroosmotic permeability of an MK-40/MA-40 membrane pair, and also salt hydration numbers. These theoretical values of water transport numbers and LiCl hydration numbers are compared with corresponding experimental and literature data. It is shown that the model adequately describes the phenomena of the mass electrotransport occurring in electrodialyzers with noncirculating concentration compartments, and it can be successfully applied in calculating the technological parameters of the process, finding the transport properties of ion-exchange membranes, and determining salt hydration numbers in aqueous electrolyte solutions.     

Evaluation of pozzolanic activity and physico-mechanical characteristics in ceramic powder-lime pastes

Ceramic powder has been used as an artificial pozzolanic addition, in preparing pozzolanic mortars for the historic/traditional structures’ construction. In order to evaluate the pozzolanic activity of ceramic powder, several pastes were prepared, by mixing it with hydrated lime, in different ratios. The pastes were stored in standard conditions (RH=99±1%, T=25±1°C) and evaluated using thermal analysis (DTA/TG), X-ray diffraction (XRD), compressive strength tests and mercury intrusion porosimetry (MIP), in time. The obtained results revealed that the compounds formed were CSH and C₄ACH₁₁ (monocarboaluminate) after 270 days of curing. The calcium hydroxide consumption increases as the initial amount of the ceramic powder in the paste augments. The maximum strength development is obtained for ceramic powder/hydrated lime ratio 3:1.     

The Electrostatic Origin of Low‐Hydration Polymorphism in DNA

In recent years, significant progress has been made towards uncovering the physical mechanisms of low‐hydration polymorphism in double‐helical DNA. The effect appears to be mechanistically similar in different biological systems, and it is due to the ability of water to form spanning H‐bonded networks around biomacromolecules via a quasi‐two‐dimensional percolation transition. In the case of DNA, disintegration of the spanning H‐bonded network leads to electrostatic condensation of DNA strands because, below the percolation threshold, water loses its high dielectric permittivity, whereas the concentration of neutralizing counterions becomes high. In this Concept article arguments propose that this simple electrostatic mechanism represents the universal origin of low‐hydration polymorphism in DNA.     

Hydration Dynamics of Water near an Amphiphilic Model Peptide at Low Hydration Levels: A Dielectric Relaxation Study

A dielectric relaxation study of aqueous solutions of the amphiphilic model peptide N‐acetyl‐leucine amide (NALA) at 298 K over a wide range of hydration levels is presented. The experiments range from states where water builds up several hydration layers to states where single water molecules or small water clusters are shared by several NALA molecules. The dielectric spectra reveal two modes on the 10 and 100 ps timescales. These are largely broadened with regard to the Lorentzian shape caused by simple Debye‐type relaxation, and are well described by the Kohlrausch–Williams–Watts stretched exponential function. The fast mode is assigned to water reorientation comprising bulk water as well as hydration water. Even when all water molecules are in contact with the solute, this fast component is dominant, and its mean relaxation time is retarded by less than a factor of two relative to neat water. The amplitude of the slow process is far higher than expected for the dipolar reorientation of the solute. The observations are consistent with results from molecular dynamics simulations for a similar model peptide reported in the literature. They suggest that the slow relaxation mode is mainly founded in peptide–water dipolar couplings, with some additional contribution from slowly reorienting hydration water molecules. The results are discussed with regard to the hydration dynamics of proteins and the interpretation of dielectric spectra of protein solutions.     

Changes in protein structure and dynamics as a function of hydration from (1)H second moments

We report the proton second moment obtained directly from the Free Induction Decay (FID) of the NMR signal of variously hydrated bovine serum albumin (BSA) and hen egg white lysozyme (HEWL) and from the width of the NMR Z-spectrum of the cross-linked protein gels of different concentrations. The second moment of the proteins decreases in a continuous stepwise way as a function of increasing water content, which suggests that the structural and dynamical changes occur in small incremental steps. Although the second moment is dominated by the short range distances of nearest neighbors, the changes in the second moment show that the protein structure becomes more open with increasing hydration level. A difference between the apparent liquid content of the sample as found from decomposition of the FID and the analytically determined water content demonstrates that water absorbed in the early stages of hydration is motionally immobilized and magnetically indistinguishable from rigid protein protons while at high hydration levels some protein side-chain protons move rapidly contributing to liquid-like component of the NMR signal.     

The hydration of nitriles catalyzed by simple transition metal salt of the fourth period with the aid of acetaldoxime

We describe here a method for selective hydration of nitriles into the corresponding amides by employing commercially available acetaldoxime and simple transition metal catalysts such as nickel salts, zinc salts, cobalt salts and manganese salts in water. Nickel salts show the highest catalytic activity, owing to their relatively small diameter of the metal cation. Nitriles having electron‐withdrawing groups could be converted into the corresponding amides in excellent yields using nickel catalyst at room temperature. Heterocyclic nitriles with heteroatom lone pair positioned ortho to the nitrile group show high reactivity; even these special nitriles could be hydrated by transition metal catalyst and water at refluxing temperature in the absence of acetaldoxime. Copyright © 2012 John Wiley & Sons, Ltd.     

Partial amination of cationic exchange resins and its application in the hydration of butene

In this work,the amination of sulfonated polystyrene resin with alkyl secondary amine is investigated.The catalytic activities of the modified resins are determined through the hydration of 1-butene.The optimum chain length and the best range of amination rate are determined.It is found that the single-pass conversion of 1-butene was raised 2% on average,and the relative activity was increased over 30% after modification.A hypothesis about the enhancement of catalytic activities by the inclusion of alkyl chain to wrap up the butene molecule is proposed.     

Hydration‐mediated effects of saccharide stereochemistry on poly(N‐isopropylacrylamide) gel swelling

To shed new light on the mechanisms of saccharide stereochemistry effect on macromolecules in aqueous solutions, we studied the effect of three monosaccharide stereoisomers, glucose, galactose, and mannose, on the swelling of Poly(N‐isopropylacrylamide) (PNIPA) hydrogels. We equilibrated PNIPA hydrogels in sugar solutions of different concentrations at 25 °C, and determined gel volume and mass swelling ratios, and sugar concentration imbalance. The volume‐phase‐transition occurred at molal concentrations of 0.587 ± 0.004 (galactose), 0.724 ± 0.003 (glucose), and 0.846 ± 0.004 (mannose). The same order of sugars emerged for the gel‐swelling and the magnitude of the sugar concentration‐imbalance, which correlated with sugar isentropic molar compressibility and hydration number. The more hydrated the sugar, the worse a cosolvent it is for the polymer, hence the larger the deswelling and the more negative the sugar concentration imbalance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Proton Longitudinal Relaxation Rates of Water in Aqueous Orthophosphoric Acid

Abstract

Longitudinal relaxation rates of water protons were determined for aqueous solutions of orthophosphoric acid at concentrations up to 85% by weight, and their concentration dependence was investigated. An appropriate choice of variables yielded an essentially linear plot for concentrations up to at least 15% by weight. Deviations from linearity are discussed and are interpreted in terms of mass-law effects. The use of parameters of this plot for deriving values for correlation coefficients and for a hydration parameter is illustrated by application to observed data and data from the literature.