Dynamic Hydration Number Research Articles

Hydration of Alkali Metal and Halide Ions from Static and Dynamic Viewpoints.

Ion hydration in aqueous solutions plays a paramount role in many fields. Despite many studies on ion hydration, the nature of ion hydration is not consistently understood at the molecular level. Combining neutron scattering (NS), wide-angle X-ray scattering (WAXS), and molecular dynamics (MD), we quantify the ionic hydration degree (hydration ability) systematically for a series of alkali metal and halide ions based on static and dynamic hydration numbers. The former is based on the orientational correlation of water molecules bound to an ion derived from the positional information from NS and WAXS. The latter is defined as the mean number of water molecules remaining in the first coordination shell of an ion over a residence time of bound water molecules around the ion from MD. The static and dynamic hydration numbers distinguish hydration from coordination and quantify the ionic hydration degree, which provides a valuable reference for understanding various phenomena in nature.

The first evaluation of the dynamic hydration number of hydrated ions confined in mesoporous silica MCM-41

Ion hydration in narrow pores is important in engineering, biology, and chemistry. The structures of hydrated ions confined in nanospaces have been studied by X-ray diffraction and X-ray absorption spectroscopy, and these confined hydrated ions have been found to have anomalous structures. On the other hand, the dynamic behavior has been studied only by molecular dynamics (MD) simulations, which have revealed the unique dynamics of hydration in nanospaces. However, no experimental studies of the dynamics of confined hydrated ions have been carried out. Here, we focus on the dynamic hydration number (nDHN) used in bulk solutions to evaluate the dynamic behavior of electrolyte solutions confined in nanospaces. To evaluate nDHN in nanospaces, we derived the molality dependence of the 2H spin–lattice relaxation time of D2O confined in nanospaces by considering the contribution of water bound to the pore surface. Next, we applied this to electrolyte solutions confined in mesoporous silica MCM-41 and evaluated nDHN. The absolute value of the dynamic hydration number in mesopores is significantly larger than that in the bulk solution; thus, the confinement effect drastically enhances the dynamic hydration properties (positive and negative hydration). This result supports the compressed hydration structure of ions with positive hydration character reported by previous structural and simulation studies. Our new approach for the evaluation of nDHN in nanospaces can be expected to give new insights in the investigation of electrolyte solutions confined in nanospaces from the viewpoint of the experimental verification of dynamic features of the hydration structure.

The effect of sugar stereochemistry on protein self-assembly: the case of β-casein micellization in different aldohexose solutions.

Protein self-assembly applications, such as nanoencapsulation of drugs and nutraceuticals, require deep understanding of the parameters governing the micellization process, including the effects of ionic and non-ionic co-solutes, like salts and sugars respectively, which is often overlooked. Herein, with the aim of shedding light on the effect of nonionic cosolute stereochemistry on protein self-assembly, we studied the ternary system of water-protein-sugar by examining the concentration-dependent effects of three aldohexoses, d-glucose (Glu), d-galactose (Gal) and d-mannose (Man) and that of urea, on the micellization of beta casein (β-Cas), using pyrene as a fluorescent probe for the formation of hydrophobic domains. Pyrene's excitation spectra were recorded for several sets of samples with rising protein concentration (0-5 mg ml(-1)), each set with a different co-solute type and concentration. Critical micellization concentration (CMC) and cooperativity of micellization were evaluated according to changes in pyrene spectra as it partitioned from the aqueous environment to the hydrophobic cores of β-Cas micelles. All sugars examined lowered the CMC of β-Cas with increasing sugar concentration and with a diminishing degree of effectiveness (Glu > Gal > Man) which correlated well with the sugars' dynamic hydration number, defined by Uedaira, and correlated negatively with their hydrophobic to hydrophilic molecular surface ratio. These results support the hypothesis that sugars affect protein self-assembly through both changes in water structure and by hydrophobic interactions, both of which are evidenced to be highly sensitive to sugar stereochemistry.

The influence of different sugars on corn starch gelatinization process with digital image analysis method

The digital image analysis, integral optical density (IOD) method, combined with “the model of response difference of crystallite change (MRDCC)” was applied to dynamically analyze the influence of different sugars on the gelatinization of corn starch. All of the saccharides (ribose, fructose, glucose, sucrose, lactose, trehalose, maltose, raffinose and stachyose) proposed in our research showed protection effect on starch crystalline structure during gelatinization. The protection effect increased with the increase of sucrose concentration (0–20%). Trisaccharide and tetrasaccharide were more effective in inhibiting the gelatinization process than disaccharide; and the protection effect of disaccharides on starch was bigger than that of monosaccharide during gelatinization. The gelatinization inhibition effect had good relationship with nDHN (dynamic hydration number), and the increase of the equatorial OH (e−(OH)) group number of saccharides might increase the inhibition effect on starch gelatinization. However, in addition to the e−(OH) groups, the combination ability of sugar with water molecules might be also related to the size of the sugar molecules and their three-dimensional structure. We believed that owing to the helical structure which formed though hydrogen bonds, tetrasaccharide tended to decrease the hydration ability of saccharide and destabilized the water structure, thus the inhibitory effect of stachyose was almost the same as raffinose.

Solvation of lithium chloride in aqueous and mixed solutions of an aprotic solvent

The dynamic hydration and solvation numbers of lithium chloride are estimated on the basis of experimental data on the limiting electrodialysis concentration of an electrolyte from aqueous and aqueousorganic solutions containing aprotic solvent N,N-dimethylacetamide. It is established that the dependence of the hydration numbers of the salt on the volume fraction of the aprotic solvent is of an extreme character, and its solvation number on N,N-dimethylacetamide does not depend on the composition of the mixed solution.

In situ measuring osmosis effect of Selemion CMV/ASV module during ED process of concentrated brine from DSW

Continuing our previous work, in which we analyzed the performance of Selemion ASV membrane (Asahi Glass Engineering) used to reduce the content of sulfate ions in concentrated brine from deep sea water (DSW) via a laboratory-scale electrodialysis (ED) apparatus, we analyze in situ the osmosis effect for Selemion CMV/ASV module (Asahi Glass Engineering) during ED process in this work. By recording the liquid volume in both concentrate and dilute tanks, it is found possible that the water flow across the membranes due to the osmosis effect could be estimated through the measurement of ionic volume flow. The analysis reveals that, when a higher DC voltage is applied, water flows from the concentrate to the dilute at initial stage of ED process, and it flows reversely at later stage; however if a lower DC voltage is applied, water flows from the concentrate to the dilute during whole ED process. Via a carpet searching process, a reasonable effective dynamic hydration number for hydrated ions is found as 3.5, and the water permeability of CMV/ASV module is estimated as 0.25214 cm/h.

Dynamics of Hydration of Alkylsulfonate Anions in Aqueous Solutions

The 17O-NMR spin-lattice relaxation times (T1) of water molecules in aqueous solutions of n-alkylsulfonate (C1 to C6) and arylsulfonic anions were determined as a function of concentration at 298 K. Values of the dynamic hydration number, \((\mathrm{S}^{-}) = n_{\mathrm{h}}^{ -} (\tau_{\mathrm{c}}^{-} /\tau_{\mathrm{c}}^{0} - 1)\), were determined from the concentration dependence of T1. The ratios (\(\tau_{\mathrm{c}}^{ -}/\tau_{\mathrm{c}}^{0}\)) of the rotational correlation times (\(\tau_{\mathrm{c}}^{ -} \)) of the water molecules around each sulfonate anion in the aqueous solutions to the rotational correlation time of pure water (\(\tau_{\mathrm{c}}^{0}\)) were obtained from the nDHN(S−) and the hydration number (\(n_{\mathrm{h}}^{ -} \)) results, which was calculated from the water accessible surface area (ASA) of the solute molecule. The \(\tau_{\mathrm{c}}^{ -}/\tau_{\mathrm{c}}^{0}\) values for alkylsulfonate anions increase with increasing ASA in the homologous-series range of C1 to C4, but then become approximately constant. This result shows that the water structures of hydrophobic hydration near large size alkyl groups are less ordered. The rotational motions of water molecules around an aromatic group are faster than those around an n-alkyl group with the same ASA. That is, the number of water–water hydrogen bonds in the hydration water of aromatic groups is smaller in comparison with the hydration water of an n-alkyl group having the same ASA. Hydrophobic hydration is strongly disturbed by a sulfonate group, which acts as a water structure breaker. The disturbance effect decreases in the following order: \(\mbox{--} \mathrm{SO}_{3}^{-} > \mbox{--} \mathrm{NH}_{3}^{ +} > \mathrm{OH}> \mathrm{NH}_{2}\). The partial molar volumes and viscosity BV coefficients for alkylsulfonate anions are linearly dependent on their nDHN(S−) values.

Perfluorinated nanocomposite membranes modified by polyaniline: Electrotransport phenomena and morphology

This work summarizes results on the modification of perfluorinated sulfocationic membranes MF-4SC by in situ chemical polymerization of aniline. The investigation of transport properties of polyaniline/MF-4SC composite membranes after bulk modification – conductivity, diffusion and electroosmotic permeability, proton permselectivity – as well as porosimetry and polarization behavior is carried out as functions of aniline polymerization parameters and acid concentration. The fibrous-cluster model of a composite membrane is proposed for the estimation of transport and structural parameters, taking into account different mechanism of charge transfer in structural fragments of the composite. The atomic force microscopy images and curves of water distribution on the effective pore radii in the composite membranes testify to a morphological transition from the nano- to the microsize of polyaniline inclusions with increasing the aniline polymerization time. This effect is confirmed by the analysis of two-phase model transport and structural parameters. High values of the “true” proton transport numbers of composites are obtained and discussed. The dynamic hydration numbers of protons and chloride co-ions are estimated using the “true” transport numbers of protons and the electroosmotic coefficients of composites. The current–voltage curves of composite membranes in the “free standing” state after bulk and surface modification by polyaniline are investigated. The effect of stabilization of limiting current density is observed for MF-4SC membrane after bulk modification. The effect of current–voltage curves asymmetry is observed for different orientation of the polyaniline layer towards the current direction for an anisotropic composite membrane after surface modification.

Dynamics of the Hydration of Amino Alcohols and Diamines in Aqueous Solution

Abstract The 17O NMR spin–lattice relaxation times (T1) of solvent water molecules in aqueous solutions of amino alcohols (AA), charged amino alcohols (AA+), and charged diamines (DA2+) were determined as a function of concentration at 298 K. The values of the dynamic hydration number, nDHN = nh(τch/τc0−1), were determined from the concentration dependence of T1. The ratios (τch/τc0) of the rotational correlation times (τch) of the water molecules around each solute molecule in the aqueous solutions to that of pure water (τc0) were obtained from the nDHN and the hydration number (nh), which was calculated from the water accessible surface area (ASA) of the solute molecule. The hydrophobic hydration is disturbed by the adjacent polar groups. The effect of disturbance decreases in the following order: NH3+ > OH > NH2. The ASA dependence of the τch/τc0 value for diamines (DA), AA, and diols decreases in the following order: DA > AA > diols. When DA and AA are in a charged state, this order is reversed, namely, diols > AA+ > DA2+. The thermodynamic quantities of hydration for AA and AA+ are linearly dependent on their nDHN values.

Reverse osmosis of ionic aqueous solutions on aMFI zeolite membrane

separation of ions from aqueous solutions was performed by reverse osmosis (RO) on an α-alumina-supported MFI:-type zeolite membrane synthesized by in-situ crystallization. For the 0.1 M chloride single-salt solutions, the separation efficiency in terms of ion rejection was found to increase with the ion valence in the order r Al 3+ > r Mg 2+ > r Na + , while the ion and water fluxes changed in the reverse order. The charge density, size, and apparent dynamic hydration number of the ion as well as the mobility of the hydrated ion were found to have critical influences on ion diffusion and water permeation through the polycrystalline zeolite membrane.

Hydration and association in solutions of tetraalkylammonium iodides

Conductivity, self-diffusion coefficient and viscosity were measured at 298 K for tetraalkylammonium iodides in aqueous solutions, 0.5 M urea solutions and mixtures of water with tert-butanol. The molar conductivity was analysed via the Fuoss–Hsia equation. The limiting molar conductivity, the separation of ions forming the ion pairs and the association constants were determined. In all studied systems the association of opposite ions was weak, but contact ion pairs were present. The hydrodynamic radii of ions, determined from the self-diffusion coefficients, were used to compute the dynamic hydration numbers. As expected, the dynamic hydration numbers were noticeably smaller than the static numbers, because they represented the water molecules located inside the R4N+ ions, between the alkyl chains. Addition of tert-butanol reduced the hydration of Me4N+ and, probably, Bu4N+ ions, but induced aggregation of Bu4N+ cations only.

Dynamic hydration numbers for biologically important ions

The role of ionized groups in biological systems is determined by their affinity for water [Biophys. J. 72 (1997) 65–76]. The tightly bound water associated with biologically important ions increases their apparent size. We define the apparent dynamic hydration number of an ion here as the number of tightly bound water molecules that must be assigned to the ion to explain its apparent molecular weight on a Sephadex ® G-10 size exclusion column, and report the first accurate determination of tightly bound water for 23 ions of biological significance, including H + and HO −. We also calculate the radius of the equivalent hydrated sphere ( r h) for each ion. We find that the ratio of the hydrated volumes of two ions approximates the ratio of the square of the charges of the same two ions. Since the ‘ionic strength’ of the solution also depends upon the square of the charges on the ions, our results suggest that ionic strength effects may largely arise from local effects related to the hydrated volume of the ion—that is, from space filling, osmotic, water activity, surface tension and hydration shell overlap effects rather than from long-range electric field effects.

Dynamics of the Hydration of Halogenoalcohols in Aqueous Solution

Abstract The 17O NMR spin-lattice relaxation times (T1), of the solvent water in aqueous solutions of halogenoalcohols were determined as a function of the concentration at 298 K. The values of the dynamic hydration number, nDHN ≡ nh(τch/τc0 -1), were determined from the concentration dependence of T1. In order to investigate the effect of the halogen atom on hydrophobic hydration, the ratios (τch/τc0), of the rotational correlation times,(τch), of water molecules around the solute to those of pure water,(τc0), were estimated from the nDHN and the coordination numbers (nh), which were calculated from the water-accessible surface area (ASA) of the solute molecule. (i) The τch/τc0 value decreased in the order EtOH > IEtOH ≥ BrEtOH ≥ ClEtOH > FEtOH for monohalogenoethanols, EtOH ≥ Cl3EtOH > Cl2EtOH ≥ ClEtOH and EtOH ≥ F3EtOH > FEtOH for polyhalogenoethanols, and PrOH > ClPrOH and i-PrOH > (CF3)2CHOH for halogenopropanols. (ii) The ASA dependence of the τch/τc0 value for chloroethanols was smaller than that for fluoroethanols. These results are explained by the disturbance of hydrophobic hydration by the halogen atom and the size effect.

Volume phase transitions of poly(acryloyl- l-proline methyl ester) gels in response to water–alcohol composition

The volume phase transitions of poly(acryloyl- l-proline methyl ester (A-ProOMe)) gels in mixtures of water and various alcohols (methyl, ethyl, propyl, and t-buthyl alcohols) were investigated. The poly(A-ProOMe) gels showed two swelling phases (first swell, 0–10 vol%; second swell, 50–80 vol%) and two shrinking phases (first shrink, 10–50 vol%; second shrink, 80–100 vol%) in the presence of each aqueous alcohol under alcohol concentrations ranging from 0 to 100 vol%. The swelling profiles at second swell and second shrink varied in terms of the solvent alcohols; this difference was quantitatively elucidated by taking into account the hydrophobicity of the solvents using dynamic hydration numbers as a parameter of the alcohol's hydrophobicity. The gels showed a shrinking phase in the region of high alcohol concentration (second shrink), which had not been observed in other hydrogels such as NIPAAm. Infrared spectra of the poly(A-ProOMe) revealed that the hydrogen bonding of the amide moiety of poly(A-ProOMe) plays a key role in the gel's sensitivity to the solvent composition, resulting in the sudden shrinking.

Synthesis of lauroyl saccharides through lipase-catalyzed condensation in microaqueous water-miscible solvents

Lauroyl saccharides were synthesized at 50°C through condensation in acetonitrile, acetone and tert-butanol with various water contents using the immobilized lipase Novozym®435. Saccharides used were glucose, galactose, mannose and fructose. The equilibrium yields of the monoesters in acetonitrile were significantly different among the saccharides tested. The apparent equilibrium constants based on the concentrations of substrates and products in acetonitrile could be correlated to the dynamic hydration numbers of the saccharides, indicating that the water activity played an important role during the condensation in the microaqueous water-miscible solvent. However, a significant correlation between the equilibrium constant for lauroyl fructose formation and parameters characterizing the solvent property could not be found.

The study of hydration effects in aqueous solutions of LiCl and CsCl by inelastic neutron scattering

Abstract Data analysis of inelastic neutron scattering experiments in 2.14M aqueous LiCl and CsCl solutions is presented. The diffusion parameters of hydration water molecules (residence time, diffusion coefficients) were extracted from the quasi-elastic component of the scattering law S(Q,ω). It was established that there are about four molecules in the hydration shell of a Li + ion, and their diffusion mobility is strongly hampered. A Cs + ion has about 8 molecules in its hydration shell, and this ion intensifies the diffusion motion of surrounding molecules. The dynamic hydration numbers were estimated: 3.7 for a Li + ion and ∼ 1 for a Cs + ion. The generalized frequency distributions for water molecules hydrating Li + and Cs + ions were obtained from the inelastic part of S(Q,ω). The effects observed indicate essential distortion of the hydrogen-bond (Hz.sbnd;B) network in the vicinity of both ions, but the character of this distortion has different physical natures.

NMR studies on dynamic behavior of water molecules in tetraalkylammonium bromide-D2O solutions at 5–25°C+

Abstract The spin-lattice relaxation times (T 1 ) of D and 17 O nuclei of D 2 O molecules in tetraalkylammonium bromides (R 4 NBr; R=Me, Et, Pr, Bu), dilute aqueous solutions were measured at the concentration of 0.2 to 1.0 mol/kg and at the temperature of 5 to 25 °C. The relative spin-lattice relaxation rate, R 1 /R 1 0 (R 1 =1/T 1 ) at 25 °C increased linearly with increasing concentration of tetraalkylammonium bromide solutions. But, it varied nonlinearly against the concentration below 20 °C and the deviation increased with decreasing temperature. The dynamic hydration number (n DHN ) of D and 17 O nuclei of a D 2 O molecule in the hydration sphere of tetraalkylammonium ions had good correlation with the molecular size, except for the Bu 4 N + ion. The deviation of n DHN of Bu 4 N + ion at low temperature reflected the caging effect due to the association through hydrogen bonding among water molecules as the association increases at lower temperature. It was suggested that the rotational anisotropy ( τ + D / τ + 170 ) of water molecules can be used as a new indicator to classify three types of hydration; negative, positive, and hydrophobic hydrations.

Dynamics of hydration of alcohols and diols in aqueous solutions

The 17 O NMR spin–lattice relaxation times, T 1 , of the solvent water in aqueous solutions of nine alcohols and five diols have been determined as a function of the concentration at 25°C. For the alcohol solutions, the concentration dependence of T 1 has been determined in the temperature range from 1 to 50°C. The value of n h [(τ c h / τ c 0 )-1] which has been obtained from the concentration dependence of T 1 has been defined as the dynamic hydration number (n DHN ). The values of the coordination numbers n h , have been estimated on the basis of the water-accessible surface areas (ASA) of the solute molecules. The rotational correlation times, τ c h , of water molecules around the solute molecules have been estimated and compared with that of pure water τ c 0 . The value of τ c h /τ c 0 =2.22 for Bu t OH at 25°C is the largest among the solutes investigated. The τ c h /τ c 0 values of the n-alcohols and diols increase with increasing ASA and become almost constant. The τ c h /τ c 0 values decrease with increasing temperature and approach constant value above 40°C. The temperature dependence of τ c h /τ c 0 for Bu t OH is the largest. The activation energy of τ c h for n-alcohols has the maximum value at ASA≈240 A 2 . These results are discussed by considering the molecular sizes. The τ c h /τ c 0 value for a diol was smaller than that of the corresponding n-alcohol. This result supports the concept that hydrophobic hydration is distributed by the OH groups of the solute molecules. The thermodynamic properties of hydration for n-alcohols, butanol isomers and diols are linearly dependent on their n DHN .

Effects of hydroxy compounds on gel formation of gelatin

Network formation of gelatin gel is known to consist of three-dimensionally cross-linked triple helices among polypeptide chains. The effects of added low molecular weight mono-ols, diols and polyols on the higher-order structure formation of gelatin chains were investigated using the following measurements: melting temperature, viscoelasticity and spin-lattice relaxation time (Ti) of H217O of gels, and circular dichroism spectra of diluted gelatin solutions. Furthermore, hydration behaviors of these hydroxy compounds were evaluated from the dynamic hydration numbers (nDHN) derived from T1 of H217O in the solutions. It was found that network structures of gelatin gels containing hydoxy compounds were influenced by the number and position of hydroxyl groups as well as the number of carbon atoms of these coexisting compounds. The effect of hydroxyl groups of hydroxy compounds was considered to stabilize the helices among gelatin chains. Especially, the addition of polyols with large number of hydroxyl groups increased the number of cross-linking junctions in the gel networks, which consist of the aggregation among the helices. On the contrary, the effect of carbon atoms of hydroxy compounds is to disturb the formation of the helices and the aggregation among the helices.

Influences of Polyols on Thermal and Dynamic Viscoelastic Properties of Rice Starches during Gelatinization

AbstractThe thermal and dynamic viscoelastic characteristics of indica (KSS7) and japonica (TNu67) rice starches (starch:water = 1:2) during gelatinization have been investigated in polyol solutions, with DSC and dynamic rheometry. The results indicate that the increments of some critical temperatures (To, Tp, TG′ and TG′max) in the thermograms and rheograms of rice starches are correlated well with the dynamic hydration number of polyol added. This firmly implies the importance of polyol‐water interaction in delaying the initial gelatinization. Polyol‐starch interactions appear to be different for low‐MW polyol and maltodextrin (DE = 8 ∼14) studied. As suggested by the changes in ΔH, tanδ and G′95 values, the action from the plasticization of polyol presumably occurs during final gelatinization. These interactions and the plasticization of water and polyol cosolvents depend considerably on the granular structure of starch.