Hydration Radius Research Articles

Temperature Dependence of Triton X-100 Micelle Size and Hydration

Quasi-elastic light scattering spectroscopy was used to measure the mutual diffusion coefficient, D m , of Triton X-100 micelles in aqueous solution and the translational diffusion coefficient, D p , of mesoscopic probes in the same solutions. We apply conventional hydrodynamic treatments of diffusion under the assumption that Triton X-100 minimal micelles are adequately represented as hard spheres. D m and D p measured at a series of surfactant concentrations are used to infer the micelle radius, am, aggregation number, N, and degree of hydration, δ, for temperatures 10≤T≤50 o C. As T is increased toward the cloud point, am and N increase, the increase in N being especially dramatic above 40 o C. δ at first increases but then tends to saturate with increasing T

The intracellular distribution of inositol polyphosphates in HL60 promyeloid cells

1. HL60 promyeloid cells contain high intracellular concentrations of inositol polyphosphates, notably inositol 1,3,4,5,6-pentakisphosphate (InsP5) and inositol hexakisphosphate (InsP6). To determine their intracellular location(s), we studied the release of inositol (poly)phosphates, of ATP, and of cytosolic and granule-enclosed enzymes from cells permeabilized by four different methods. 2. When cells were treated with digitonin, all of the inositol phosphates were released in parallel with the cytosolic constituents. Most of the InsP5 and InsP6 was released before significant permeabilization of azurophil granules. 3. Similar results were obtained from cells preloaded with ethylene glycol and permeabilized by osmotic lysis. 4. Electroporation at approximately 500 V/cm caused rapid release of free inositol. Higher field strengths provoked release of most of the ATP, InsP5 and InsP6, but only slight release of the intracellular enzymes. Multiple discharges released approximately 80-90% of total InsP5 and InsP6. In the absence of bivalent-cation chelators, InsP5 and InsP6 were released less readily than ATP. 5. Treatment of cells with Staphylococcus aureus alpha-toxin caused quantitative release of inositol and ATP, without release of intracellular enzymes. However, inositol phosphates were released much less readily than inositol or ATP. Even after prolonged incubation with a high concentration of alpha-toxin, only approximately 50-70% of InsP2, InsP3 and InsP4 and < or = 20% of InsP5 and InsP6 were released, indicating that the high charge or large hydrated radius of InsP5 and InsP6 might limit their release through small toxin-induced pores. 6. These results indicate that most intracellular inositol metabolites are either in, or in rapid exchange with, the cytosolic compartment of HL60 cells. However, they leave open the possibility that a small proportion of cellular InsP5 and InsP6 (< or = 10-20%) might be in some intracellular bound form.

Influence of various salts on the reversed-phase retention of some dansylated amino acids in TLC

The retention of 14 dansylated amino acid derivatives was determined using aqueous LiCl, NaCl, KCl, RbCl and CsCl solutions as eluents in reversed-phase thinlayer chromatography. The salts exerted typical salting-out effects, the retention of each dansylated amino acid increased with increasing concentration of salt in the eluent. This effect has been tentatively explained by the suppression of the dissociation of the polar groups in the solute molecules resulting in increased apparent lipophilicity. The correlation between the increased retention of dansyl amino acids and the salt concentration was found to be linear. The hydrated radii and energy of hydration of cations as well as the hydrophobicity of free amino acids and the pK value of the α-amino groups simultaneously influenced the retention.

Studies of the Hydrous Silicon–Titanium(IV) Oxide Ion Exchanger. II. Affinity for Various Cations and Thermal Stability

Abstract The affiinity for various cations and the thermal stability were studied on hydrous silicon–titanium(IV) oxide ion exchangers with various titanium contents. An exchanger with 52 mol% Ti shows a higher affinity for an alkali metal ion having a smaller hydrated radius but similar affinity, which depends little on the pH′s of solutions, for alkaline earth metal ions, except for Ba2+. In the sorption of transition metal ions, the formation of a covalent bond is a factor in determining the selectivity of the exchanger, along with the remote coulombic interaction. The composition dependence of the affinities for Cs+, Ba2+, Co2+, Eu3+, and UO22+ was explained in terms of the acid-base properties of the exchangers. The exchangers with 37 to 67 mol% Ti do not suffer from any drastic change in the surface area and in the crystallinity upon heating up to 540 °C, and are much more heat-resistant than the component simple hydrous metal oxides. The degree of the decrease in the exchange capacity upon heat treatment is larger in exchangers with a higher titanium content. The effect of a heat treatment on the acid-base property and the affinity for cations was also studied.

Influence of the water content on the kinetics of counter-ion transport in perfluorosulphonic membranes

The high frequency electrical resistance of a Nafion ® 117 perfluorosulphonic membrane has been measured by means of the ac impedance technique. Using a mercury cell, the variations of the membrane conductance as a function of the degree of swelling and of the nature of the counter-ion have been determined. The variations of the conductance with the water content have two different origins: the first is a change in the rate constant of the elementary ion transfer reaction due to interactions between the mobile ions and the fixed sites, and the second is related to a change in the microstructure of the membrane material. An analysis of the membrane conductance on the basis of the absolute rate theory is proposed. It enables one to explain the shape of the impedance diagrams and shows that the variations of the membrane conductance with its water content cannot be accounted for by geometric considerations alone. On the basis of a simple electrostatic interaction model, the energy barrier of the elementary ion transfer jump can be related to the hydration radius of the cation.

Influence of structure and counterions on physicochemical properties of linear alkylbenzene sulfonates

The effects of different inorganic and organic counterions on the physicochemical behavior of three commercial linear alkylbenzene sulfonates (LAS) have been studied. It has been found that the counterion hydration radius of the corresponding commercial linear alkylbenzene sulfonates has great influence on solubility, viscosity, surface tension and critical micelle concentration (CMC). The counterion has no influence on the detergency performance of the finished formulation. The alkyl chain length and the presence of tetralines have an important influence on solubility, viscosity and surface tension.

A calcium‐ and voltage‐dependent chloride current in developing chick skeletal muscle.

1. Depolarization of embryonic chick myotubes from negative potentials elicits a rapid spike followed by a long-duration after-potential. The ionic basis of the long-duration after-potential was examined by making intracellular recordings from cultured myotubes, and by making whole-cell patch-clamp recordings from myoblasts and myoballs. 2. The peak potential of the long-duration after-potential varied with the chloride gradient, suggesting that a conductance increase to chloride is involved in generating the after-potential. However, a calcium current was also implicated, since lowering the extracellular calcium or replacing extracellular calcium with cobalt abolished the after-potential. 3. When extracellular calcium was replaced with strontium or barium, short-duration spikes similar to calcium spikes were observed, but only strontium was able to support activation of long-duration after-potentials. Intracellular injection of calcium or strontium into myotubes bathed in calcium-free extracellular solutions restored the ability of depolarization to evoke an after-potential. Intracellular injection of magnesium, barium, nickel or cobalt did not restore this ability. These experiments strongly suggested that the long-duration after-potential was due to a calcium- and voltage-activated chloride current. 4. Whole-cell voltage-clamp recordings from myoballs and myoblasts showed that a large chloride conductance could be activated by depolarization when the internal free calcium concentration was buffered at levels greater than 10(-7) M. At 2.5 x 10(-7) M-calcium, the voltage dependence of activation was steepest in the range of -30 to -20 mV and the activation kinetics varied with the membrane potential. The time to half-maximal activation ranged from 0.1 s at positive potentials to greater than 1 s at more negative potentials. The time constant for deactivation was approximately 1 s at -50 mV. No inactivation was observed. 5. The selectivity of the chloride current was measured by substituting other anions for chloride. The following permeability series was found: I- greater than NO3- greater than Br- greater than Cl- greater than acetate greater than F- greater than SO4- = glucuronate. Thus anion permeability decreased as the hydration radius increased. 6. Measurements of the resting potential of developing myoblasts and myotubes under 'physiological' conditions (37 degrees C, bicarbonate buffer) suggest that the after-potential acts to depolarize these cells 10-20 mV above their resting potential (approximately -60 mV) for several seconds. 7. We discuss the possibility that the long-duration after-potential may be involved in triggering myoblast fusion and in the generation of bursts of spontaneous contractions in developing myotubes.

Water interactions with varying molecular states of bovine casein: 2H NMR relaxation studies

The caseins occur in milk as spherical colloidal complexes of protein and salts with an average diameter of 1200 Å, the casein micelles. Removal of Ca 2+ is thought to result in their dissociation into smaller protein complexes stabilized by hydrophobic interactions and called submicelles. Whether these submicelles actually occur within the micelles as discrete particles interconnected by calcium phosphate salt bridges has been the subject of much controversy. A variety of physical measurements have shown that casein micelles contain an inordinately high amount of trapped water (2 to 7 g H 2O/g protein). With this in mind it was of interest to determine if NMR relaxation measurements could detect the presence of this trapped water within the micelles, and to evaluate whether it is a continuum with picosecond correlation times or is associated in part with discrete submicellar structures with nanosecond motions. For this purpose the variations in 2H NMR longitudinal and transverse relaxation rates of water with protein concentration were determined for bovine casein at various temperatures, under both submicellar and micellar conditions. D 2O was used instead of H 2O to eliminate cross-relaxation effects. From the protein concentration dependence of the relaxation rates, the second virial coefficient of the protein was obtained by nonlinear regression analysis. Using either an isotropic tumbling or an intermediate asymmetry model, degrees of hydration, ν , and correlation times, τ c , were calculated for the caseins; from the latter parameter the Stokes radius, r, was obtained. Next, estimates of molecular weights were obtained from r and the partial specific volume. Values were in the range of those published from other methodologies for the submicelles. Temperature dependences of the hydration and Stokes radius of the casein submicelles were consistent with the hypothesis that hydrophobic interactions represent the predominant forces responsible for the aggregation leading to a submicellar structure. The same temperature dependence of r and ν was found for casein under micellar conditions; here, the absolute values of both the Stokes radii and hydrations were significantly greater than those obtained under submicellar conditions, even though τ c values corresponding to the great size of the entire micelle would result in relaxation rates too fast to be observed by these NMR measurements. The existence of a substantial amount of trapped water within the casein micelle is, therefore, corroborated, and the concept that this water is in part associated with submicelles of nanosecond motion is supported by the results of this study.

The effects of whey cations on the kinetic parameters of a model for the enzymic hydrolysis of lactose

AbstractThe effects of whey cations (Ca2+, Mg2+) on the enzymic hydrolysis of lactose have been studied, at temperatures in the range 30–50°C, in a continuous stirred tank reactor (CSTR), using an immobilized β‐galactosidase (Novozym 231). A model for the variation of Vmax (the maximum rate in the Michaelis—Menten expression) in the presence of the ionic environment has been developed based on the Gouy electrical double layer concept and the liquid phase bimolecular process. In the presence of one cation (Mg2+), the mean value of the model parameter av, an approach distance including the hydration radius of the protein, was 27 × 10−10 m, almost identical to the value obtained by the crystal density method. When two cations (Mg2+ and Ca2+) were present simultaneously the value of Vmax as a function of the ionic strength showed a maximum which may be explained by the Stern adsorption modification of the Gouy theory.

Ion-exchange and surface properties of titania gels from Ti(III) solutions

The present investigation deals with the surface properties, thermal behavior, and ion-exchange characteristics of titania gels prepared from titanous chloride under different conditions of pH and temperature. The surface properties, exchange characteristics, and structures of these gels were studied with the aid of thermogravimetric analysis, nitrogen adsorption, visible spectrophotometry, and X-ray diffraction. Studies of the exchange behavior of four different cations, Cu 2+, Ni 2+, Co 2+, and Cr 3+, do not suggest a clearcut relationship between the extent of surface area and the ion-exchange properties. It is suggested that the “bridged OHs” on the titania surface are responsible for the cation-exchange properties of the gels. A high pH of preparation would lead to a large number of available exchangeable OH groups, whereas a low pH of preparation would lead to the formation of gels with low exchange capacities because of minimal exchangeable sites. In the case of the trivalent Cr 3+ ion and its large hydrated radius the size of the pores seems to play a crucial role in terms of selectivity. Thermogravimetric studies reveal the presence of two types of water (interstitial and rigidly bound water in the form of hydroxyl ions) in samples prepared at a high pH. An additional weight loss appears in the case of samples prepared at a low pH and seems to arise from the loss of coordinately bound water ligands.

Cytoplasmic gel and water relations of axon.

A previous method of measuring the swelling pressure (delta IIg) of the cytoplasmic gel of the giant axon of Loligo vulgaris was refined. The estimates of delta IIg made with the improved method were consistent with those made with the earlier method. In these methods the activity of the solvent in the gel is measured by increasing the activity of the solvent in the internal phase of the gel by application of hydrostatic pressure to the gel directly. Comparable values for the activity of the solvent in the gel were obtained also by an alternate method, in which the deswelling of the gel is measured upon decreasing the activity of the solvent in the external phase by addition of a nonpenetrating high mol wt polymer (i.e., Ficoll). Additional support was obtained for the earlier suggestion that delta IIg contributes to the swelling and shrinkage pattern of the whole axon. In part, the new evidence involved two consecutive direct measurements of intraxonal pressure. The first measurement was that of a mixed pressure composed of delta IIg and delta IIm (delta IIm being the effective osmotic pressure due to the intra-extraxonal gradient in the activity of mobile solutes). The subsequent measurement was that of delta IIg alone. The latter measurement was made feasible by destroying the axolemma, thereby eliminating the contribution of delta IIm. An estimate of delta IIm was obtained by subtracting delta IIg from the total pressure measured initially. The delta IIm determined by the above method was two orders of magnitude smaller than the theoretical osmotic pressure. This is consistent with the delta IIm determined previously, where osmotic intra-extraxonal filtration coefficients were compared to the hydrostatic. The mixed pressure experiments lend credence to the idea that the substantial contribution of delta IIg to the water relations of the whole axon is due to delta IIg being of the same order of magnitude as delta IIm. The degree of free swelling of axoplasmic gels was studied as a function of pH, salt concentration, and hydration radius of the anion of the salt used. The swelling increased with an increase in the reciprocal of the hydration radius, a decrease in salt concentration, and at pH below or above similar to 4.5. The nature of the constraints to the free swelling of axoplasm in axons immersed in seawater was studied. With the seawater employed, these constraints appeared to be due more to the retractive forces of the sheath than to delta IIm.

Calcium and Cation Sorption by Cladophora from the Great Lakes

In evaluating Cladophora as a scavenger of exotic cations, the study of calcium sorption leads to an understanding of the alga's cationic sorption in general. Total calcium uptake by Cladophora grown in batch cultures under defined conditions was directly proportional to concentration of the ion in the medium at low levels (2-20 mg Ca/l) but became saturated at high levels (13 mg Ca/g algae at 20-100 mg Call). This uptake was largely an ion-exchange reaction, favoring polyvalent cations of small hydrated radius. Therefore, strontium uptake mimicked that of calcium, but the plant preferentially adsorbed strontium over calcium by a factor of 1.25. Because exotic cations bound to Cladophora could largely be lost through ion-exchange and dilution in the absence of their source, such accumulations may not be so important as was previously thought. Analysis of variance of calcium and strontium sorption data showed that Cladophora samples from each of the Great Lakes had the same cationic sorptive capacity. Results from experiments with a Lake Michigan isolate should, therefore, be applicable to natural populations of the alga. Turbulence and pH contributed to the variability of calcium sorption by Cladophora through affecting diffusion gradients and solubility of calcium respectively.

Crystalline insoluble acid salts of tetravalent metals — XIII Ion exchange of crystalline zirconium phosphate with alkaline earth metal ions

Titration curves of crystalline zirconium phosphate with alkaline earth metal hydroxides are strongly affected by hydrolysis of the exchanger and precipitation of insoluble phosphates. The degree of conversion of the exchanger at which phosphate precipitation begins depends on the alkaline earth metal ion, and the following values have been obtained: 70% for Ca 2+, 80% for Sr 2+ and 10% for Ba 2+. No exchange has been found with Mg(OH) 2, and this is probably due to steric reasons owing to its large hydrated ionic radius. X-ray diffraction shows that the exchange of Ca 2+ and Sr 2+ occurs with formation of the phases ZrCa 0·63(PO 4) 1·26(HPO 4) 0·74. 3H 2O and ZrSr 0·5PO 4. 3·5H 2O, with interplanar distances 9·98 and 10·2 A, respectively. Owing to their immiscibility with Zr(HPO 4) 2. H 2O a plateau in their titration curve is found. The results are compared with those reported by other authors.

Steric stabilization and the Hofmeister series

The relevance of ion hydration and the Hofmeister series to the flocculation of poly (vinyl acetate) hydrosols, stabilized solely by poly(ethylene oxide) chains, has been examined. For these enthalpically stabilized dispersions, the flocculation potency of an electrolyte is determined by its ability to convert water into a theta-solvent for the stabilizing moieties. The order of decreasing flocculation effectiveness for the anions studied (SO 4 = > Cl − > NO 3 − > CNS − > Br − > I −) parallels that of the Hofmeister series. The order for cations (Rb + = K + = Na + = Cs + > NH 4 + = Sr ++ > Li + = Ca ++ = Ba ++ = Mg ++) is in direct conflict with the postulate that the more highly hydrated ions are the more effective flocculants. In general, monatomic anions and cations are less potent flocculants if their effective primary hydration radius (region A) is large. The results have been interpreted in terms of the influence which the positively hydrated ions exert on the structure of the water in their immediate neighborhood (region B), rather than simply in terms of dehydration of the stabilizing species. Preliminary measurements of the entropy and enthalpy of dilution parameters for poly (ethylene oxide) in electrolyte solutions support this interpretation.

On the hydration of simple ions and polyions

Hydration of polymeric ions is investigated by examination of salting-out behaviour in relation to dielectric saturation effects and to the significance of partial molal volumes of polysalts. The validity of previous distribution theories of salting-out is examined and limitations are shown to arise from an unjustified expansion of an exponential distribution factor, and neglect of solvent dielectric saturation effects in the primary solvation shell of the ion where, relatively, the maximum salting-out effect is developed. A new theory is proposed, as a basis for extension to the case of polyions, in which the calculation of the salting-out behaviour is carried out over two regions: ( a ) in the primary hydration shell where a high degree of solvent dielectric saturation prevails and the exponential distribution function must be retained, and ( b ) beyond the primary region where weaker polarization occurs and Kirkwood’s theory of dielectrics can be applied. Comparison of the predictions of various forms of the salting-out equation with experimental data is made. Comparative calculations of the variation of solvent dielectric constant with distance from ions of various geometries have been carried out. The cases examined are those for simple spherical ions, linear polyions and planar colloidal ions having various charge densities. The dependence of solvent dielectric constant on distance from the ions enables a semi-empirical primary hydration radius r d to be evaluated. Values of r d for various simple and polymeric ions are examined in relation to salting-out by polyions and their corresponding monomers and in relation to hydration radii deduced by other methods. In the case of the polyions and planar ions, the extent to which increasing charge density causes increased dielectric saturation can be evaluated. Experimental studies on hydration of polyions and corresponding monomer salts have been carried out by examination of the salting-out of selected non-electrolytes by the polysalts, and by partial molal volume measurements. The effect of variation of the degree of neutralization or charge density has been examined; in general, it is found that the salting-out and partial molal volume behaviour varies with degree of ionization in the expected manner but differs from the corresponding behaviour of the monomer salts owing to stronger electrostriction effects due to condensation of the ionic charge into a chain configuration. The results are examined in relation to the dielectric saturation calculations for polyions, and theoretical salting-out equations are developed for the polyion case, and applied to the present experimental results. The partial molal volume data for the same materials lead to complementary information on the effective hydration radius and solvation numbers of the polysalts.

La structure de la sérum albumine de boeuf en solution à pH 5,3 et 3,6: Étude par diffusion centrale absolue des rayons X

The reversible denaturation of bovine serum albumin (BSA) at acidic pH has been studied by small-angle X-ray scattering experiments, performed on an absolute scale. Near the isoionic point (pH 5.3) BSA is a compact molecule; the molecular weight, radius of gyration, volume, external surface and internal hydration have been determined. All these parameters agree closely with results obtained with other techniques. Important changes in X-ray diffraction are observed at pH 3·6. 1. The intensity varies evenly over a large range of diffraction angle, as it does at pH 5·3, but at very small angles it suddenly rises to large values. 2. The radius of gyration increases from 30·6 A to 68·5 A. 3. The molecular weight does not change. 4. The molecule swells, but the experimental observations are not compatible with a uniform compact particle. Several possible interpretations of these observations are discussed and a model which explains satisfactorily the mechanism of the transformation is proposed. The molecule is a compact particle at isoionic pH. At acidic pH one part of the polypeptide chain (about 35%) unravels, and assumes a loose random-coil like structure; the rest of the molecule remains folded in a compact particle. This model is shown to agree quantitatively with the X-ray experiments, and the dimensions of both the compact nucleus and the loose chain are determined. Other experimental observations (namely hydrodynamic properties and optical rotation measurements) are discussed, and are shown to be consistent with the model.