Presence Of Various Salts Research Articles

DSA electrochemical treatment of olive mill wastewater on Ti/RuO2 anode

The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO2 anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO2 anode. Experiments were conducted at 300–1,220 mg L−1 initial chemical oxygen demand (COD) concentrations, 0.05–1.35 V versus SHE and 1.39–1.48 V versus SHE potential windows, 15–50 mA cm−2 current densities, 0–20 mM NaCl, Na2SO4, or FeCl3 concentrations, 80 °C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L−1 and 50 mA cm−2 leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L−1) using lower current densities (15 mA cm−2) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L−1 in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO2 anode seems to be independent of the presence of salts in contrast with Ti/IrO2 where addition of NaCl has a beneficial effect on decolorization.

Organization of butadienyl dyes containing benzodithiacrown-ether or dimethoxybenzene in monolayers at the air/aqueous salt solution interface

Two amphiphilic butadienyl dyes 1 and 2 form stable monolayers at the air/water interface in the presence of various salts. Dye 1 consists of the basic amphiphilic butadienyl chromophore. In dye 2, the dimethoxybenzene part of dye 1 is substituted by benzodithia-15-crown-5. The monolayers have been characterized by surface pressure-area and surface potential-area isotherms as well as Brewster angle microscopy and reflection spectroscopy. In contrast to dye 1, dye 2 interacts specifically with Hg 2+ and Ag + cations forming complexes . No complex formation was observed with alkali and earth alkali metal ions. The nature of the anion (Cl − or ClO 4 −) influences the monolayer behaviour of both dyes. At the air/water interface, besides monomers of the dyes, two types of associates are coexisting in the pure dye monolayers on aqueous salt solutions, attributed to dimers and aggregates, respectively. Their equilibria depend on the nature of both cations and anions in the subphase, as in the case of dye 2, or only anions, as in the case of dye 1. The dimers may be organized as head-to-tail dimers with the intermolecular distances 0.38 and 0.45 nm for dye 1 and dye 2, respectively. According to the extended dipole model, we propose formation of aggregates in which the chromophores are parallel to each other with the same intermolecular distances as in the dimers, and the centers of their transition moments shifted by 0.95 nm (dye 1) and 1.2 nm (dye 2).

Effects of Surfactants and Electrolytes on Adsorbed Layers and Particle Stability

Adsorbed polymer and polyelectrolyte layers on colloidal silica nanoparticles have been studied in the presence of various salts and surfactants using photon correlation spectroscopy and solvent relaxation NMR. Poly(ethylene oxide) (PEO; molar mass 103.6 kg mol (-1)) adsorbed with a relatively high affinity and gave a layer thickness of 4.2 +/- 0.2 nm. While the nonionic surfactant used only increased this thickness slightly, anionic surfactants had a much greater effect, mainly due to repulsions between adsorbed aggregates, leading to expansion of the layer. A nonionic/anionic surfactant mixture was also tested and resulted in a larger increase in layer thickness than any of the individual surfactants. The dominant factor on addition of salt was generally the reduced solvency of PEO, which resulted in a further increase in the layer thickness but in some cases caused flocculation. This was not the case when the surfactant was sodium dodecylbenzenesulfonate; instead screening of the intermicellar repulsions possibly combined with surfactant-cation binding resulted in a reduction in the layer thickness. In comparison the affinity between silica and sodium polystyrenesulfonate was very weak. Anionic surfactants and salts did not noticeably increase the strength of adsorption, but instead encouraged flocculation. The situation was different with a nonionic surfactant, which was able to adsorb to silica itself and apparently facilitated a degree of polyelectrolyte adsorption as well.

Effect of tetraalkylammonium salts on the micellar behavior of lithium dodecyl sulfate: A conductometric and tensiometric study

The effect of quaternary ammonium bromides R 4NBr (R = H, CH 3, C 2H 5, C 3H 7 and C 4 H 9) on the micellar properties of lithium dodecyl sulfate (LDS) micelles has been studied by conductometric and tensiometric techniques. The degree of the conuterion binding, β, is found to increase with the increasing size of the alkyl chain length of the tetraalkylammonium salts. The thermodynamics of micelle formation of ionic surfactant LDS in the presence of 0.001M of different quaternary salts have been thoroughly assessed by the critical micelle concentration (CMC) measurement in the 288.15–318.15K-temperature range at 10K intervals conductometrically. Results show a shallow minimum of the CMC values typically between 300 to 305K for LDS micelles in presence of various salts. The standard free energy of micellization, Δ G 0 m has been found to decrease upon growth of temperature. The standard enthalpy change on aggregation was calculated by using the Gibbs–Helmholtz equation. Tensiometric results show a significant reduction in the solution surface tension with increasing electrolyte concentration. The surface excess of LDS and its minimum area at the air–water interface in the presence of different R 4NBr environment has been determined. The micellar solution of LDS has been found to exhibit a cloud point phenomenon in the presence of Bu 4NBr. The occurrence of cloud point phenomenon is accounted for in terms of the penetration of butyl chains at the surface layer of one micelle into another due to the hydrophobic effect.

CML24, regulated in expression by diverse stimuli, encodes a potential Ca2+ sensor that functions in responses to abscisic acid, daylength, and ion stress.

Changes in intracellular calcium (Ca(2+)) levels serve to signal responses to diverse stimuli. Ca(2+) signals are likely perceived through proteins that bind Ca(2+), undergo conformation changes following Ca(2+) binding, and interact with target proteins. The 50-member calmodulin-like (CML) Arabidopsis (Arabidopsis thaliana) family encodes proteins containing the predicted Ca(2+)-binding EF-hand motif. The functions of virtually all these proteins are unknown. CML24, also known as TCH2, shares over 40% amino acid sequence identity with calmodulin, has four EF hands, and undergoes Ca(2+)-dependent changes in hydrophobic interaction chromatography and migration rate through denaturing gel electrophoresis, indicating that CML24 binds Ca(2+) and, as a consequence, undergoes conformational changes. CML24 expression occurs in all major organs, and transcript levels are increased from 2- to 15-fold in plants subjected to touch, darkness, heat, cold, hydrogen peroxide, abscisic acid (ABA), and indole-3-acetic acid. However, CML24 protein accumulation changes were not detectable. The putative CML24 regulatory region confers reporter expression at sites of predicted mechanical stress; in regions undergoing growth; in vascular tissues and various floral organs; and in stomata, trichomes, and hydathodes. CML24-underexpressing transgenics are resistant to ABA inhibition of germination and seedling growth, are defective in long-day induction of flowering, and have enhanced tolerance to CoCl(2), molybdic acid, ZnSO(4), and MgCl(2). MgCl(2) tolerance is not due to reduced uptake or to elevated Ca(2+) accumulation. Together, these data present evidence that CML24, a gene expressed in diverse organs and responsive to diverse stimuli, encodes a potential Ca(2+) sensor that may function to enable responses to ABA, daylength, and presence of various salts.

Mass spectrometric analysis of human microsatellite markers

Genotyping based on the analysis of multiple short tandem repeat (STR) loci has been validated for routine use in human identification, parentage testing as well as in diagnosis of hereditary diseases. Currently, the analysis of the polymorphic variations in allele length of these genetic markers depends on electrophoretic separation of fluorescently labeled PCR products. Another technique accepted for sizing and typing of microsatellite markers is capillary electrophoresis which, compared to slab gel electrophoresis, is capable of a more automated procedure with increased resolution of the separation and reduced time for an electrophoretic run. Despite the improvement toward automation and throughput, difficulties remain associated with electrophoretic methods. Mainly the size determination which is correlated to the mobility of an internal standard in the gel matrix is error prone due to sequence-specific effects and unresolved secondary structures. With the introduction of gentle ionization techniques for large biomolecules such as electrospray (ESI) and matrix-assisted laser desorption/ionization (MALDI), mass spectrometry (MS) has become an alternative method for the size determination of DNA fragments. The generation of intact gas phase ions for separation and detection offers the advantage of short analysis time and the ability to obtain molecular weight information without the need for labeling and size standards. However, mass analysis of PCR products is complicated by the presence of various salts as well as of surplus nucleotide triphosphates and primers used in the amplification reaction of relevant regions in the genome. Thus, purification of the PCR reaction is a severe demand for the use of both MALDI and ESI MS.

The influence of physico-chemistry on the retention of chromium ions during nanofiltration

In the present work, we were interested in the treatment by nanofiltration of synthetic solutions containing chromium salts. Two types of solutions (CrCl 3  K 2Cr 2O 7) were treated according to the experimental parameters such as pH, pressure and concentration. With the aim of studying the influence of possible ionic interactions, we have carried out tests on solutions containing the trivalent and hexavalent chromium ions in the presence of various salts (NaCl, KCl, NaNO 3, Na 2SO 4, K 2SO 4) for different concentrations. The results have shown a total chromium retention which varies from 38 to 99% relating to the composition of the solution and operating conditions. For Cr(III), a better retention was obtained in acid medium and for an optimal pressure of 5 bar. The influence of the ionic strength as well as the concentration were found weak. The retention of the Cr(III) ions was not affected by the presence of salts solution. The results for bichromate solutions were strongly dependant of the form in which the Cr(VI) ions were present. The form of HCrO 4 − has given a better retention at low concentrations. When the concentration increases, the phenomenon of repulsion becomes less significant and consequently the ions were less and less retained. The influence of the salt addition on the retention of the Cr(VI) ions have revealed the effect of the interactions of the membrane/solute and solute/solute on the selectivity of the membrane.

Influence of Multivalent Electrolytes on Interionic Correlations: A Grand Canonical Monte Carlo Study of the Electrostatic Stability of Charged Interfaces

We use grand canonical Monte Carlo simulations in the framework of the primitive model to determine the mechanical stability of planar charged interfaces in the presence of various salts of multivalent counterions. Our intent is to determine the influence of salt addition on the strength and the range of interionic correlations. Despite the simplicity of the primitive model, the equation of state of these interfacial systems exhibits complex behavior because the addition of salts of di- and trivalent counterions enhances the interionic correlations and induces the coexistence of two phases composed of differently swollen interfaces. The occurrence of such phase coexistence is related to the inversion of the apparent interfacial charge and the accumulation of salt in the interfacial domain by contrast with the Donnan exclusion phenomenon.

Occurrence of salt, pH, and temperature-tolerant, phosphate-solubilizing bacteria in alkaline soils

An ecological survey was conducted to characterize 4800 bacterial strains isolated from the root-free soil, rhizosphere, and rhizoplane of Prosopis juliflora growing in alkaline soils. Of the 4800 bacteria, 857 strains were able to solubilize phosphate on plates. The incidence of phosphate-solubilizing bacteria (PSB) in the rhizoplane was highest, followed by rhizosphere and root-free soil. Eighteen bacterial strains out of 857 PSB were able to produce halo at 30 degrees C in a plate assay in the presence of 5% salt (NaCl) and solubilize tricalcium phosphate in National Botanical Research Institute's phosphate growth medium (NBRIP) broth, in the presence of various salts, pHs, and temperatures. Among the various bacteria tested, NBRI4 and NBRI7 did not produced halo in a plate assay at 30 degrees C in the absence of salt. Contrary to indirect measurement of phosphate solubilization by plate assay, the direct measurement of phosphate solubilization in NBRIP broth assay always resulted in reliable results. The phosphate solubilization ability of NBRI4 was higher than in the control in the presence of salts (NaCl, CaCl2, and KCl) at 30 degrees C. Phosphate solubilization further increased in the presence of salts at 37 degrees C as compared with 30 degrees C. At 37 degrees C, CaCl2 reduced phosphate solubilization ability of NBRI4 compared with the control. The results indicated the role of calcium salt in the phosphate solubilization ability of NBRI4.http://link.springer-ny. com/link/service/journals/00284/bibs/39n2p89.html

Relative role of anions and cations in the stabilization of halophilic malate dehydrogenase.

Halophilic malate dehydrogenase unfolds at low salt, and increasing the salt concentration stabilizes, first, the folded form and then, in some cases, destabilizes it. From inactivation and fluorescence measurements performed on the protein after its incubation in the presence of various salts in a large range of concentrations, the apparent effects of anions and cations were found to superimpose. A large range of ions was examined, including conditions that are in general not of physiological relevance, to explore the physical chemistry driving adaptation to extreme environments. The order of efficiency of cations and anions to maintain the folded form is, for the low-salt transition, Ca(2+) approximately Mg(2+) > Li(+) approximately NH(4)(+) approximately Na(+) > K(+) > Rb(+) > Cs(+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-), and for the high-salt transition, NH(4)(+) approximately Na(+) approximately K(+) approximately Cs(+) > Li(+) > Mg(2+) > Ca(2+), and SO(4)(2)(-) approximately OAc(-) approximately F(-) > Cl(-) > Br(-) > I(-). If a cation or anion is very stabilizing, the effect of the salt ion of opposite charge is limited. Anions of high charge density are always the most efficient to stabilize the folded form, in accordance with the order found in the Hofmeister series, while cations of high charge density are the most efficient only at the lower salt concentrations and tend to denature the protein at higher salt concentrations. The stabilizing efficiency of cations and anions can be related in a minor way to their effect on the surface tension of the solution, but the interaction of ions with sites only present in the folded protein has also to be taken into account. Unfolding at high salt concentrations corresponds to interactions of anions of low charge density and cations of high charge density with the peptide bond, as found for nonhalophilic proteins.

Fluorescence properties of carbazole-9-yl-acetyl chloride and its application for the simultaneous determination of amino acids and biogenic amines via liquid chromatography with fluorescence detection

A rapid and sensitive derivatization method, using carbazole-9-yl-acetyl chloride (CRA-Cl) as derivatization reagent, for the simultaneous determination of amino acids and biogenic amines with pre-column fluorescence derivatization via liquid chromatography is investigated. The wavelength of maximum emission for the CRA derivatives is 365 nm ( λ ex 335 nm). Fluorescence spectra of non-acyl chloride CRA in the presence of various salts, organic halides and different surfactants are also studied. The quenching constants of NaF, NaCl, NaBr, NaI, and CH 3I to CRA are 9.4, 12.6, 40.4, 56.2, and 102 M −1, respectively. Heavy atoms (above 1.0 μM) will seriously interfere with CRA emission spectra tested in the presence of halogen-salts and iodomethane. On the basis of Stern–Volmer equation for static quenching and a solute–micelle interaction linear relationship, the monomer quenching constant K of hexadecyltrimethylammonium bromide (CTMAB) to CRA is 3.0×10 3 M −1. The binding constants K of micelle of CTMAB and TX-100 to CRA are 5.4×10 3 M −1 and 2.0×10 3 M −1, respectively. In addition, in a kinetic analysis of CRA emission intensity (ln I em) a linear correlation between ln I em and 1/ T was found. The slope of the working curve yields an emission stabilization energy of 17.8 kJ/mol. Derivatization and chromatographic conditions for simultaneous separation of derivatized amino acids and biogenic amines have also been optimized on a reversed-phase C 18 column using a binary gradient. Studies on derivatization conditions indicate that primary and secondary amines react very fast with CRA-Cl in alkaline solution to give the corresponding fluorescent derivatives, which exhibit excellent sensitivity and stability. This method, in conjunction with a multi-gradient program, offers a complete resolution for amino acids and biogenic amines. For rapid separation of biogenic amines in plant tissue, an isocratic elution is used. Excellent response linearity is demonstrated over the injected amounts range 50–250 pmol for biogenic amines. The relative standard deviations ( n=6) at an analytical concentration of pmol level are <5%. Detection limits (signal-to-noise ratio=3) are levels of fmol.

The Halochromism of the 1-Methyl-8-Oxyquinolinium Dye

The halochromic behaviour of the title dye (1) was studied in methanol, ethanol, 2-propanol, 1-butanol, 2-butanol, dimethyl acetamide, dimethyl sulfoxide, acetone and acetonitrile, in the presence of sodium iodide, potassium perchlorate and lithium perchlorate. The observed shifts of the charge-transfer band of 1, caused by the addition of increasing concentrations of the salts, was interpreted in terms of dye-salt and solvent-salt interactions and compared with the behaviour of other solvatochromic dyes which exhibit cationic halochromism. The phenomenon of halochromism is related to the more thoroughly investigated solvatochromic behaviour of dyes exhibiting a medium-sensitive absorption arising from an internal charge transfer. 1–8 The position of the charge- transfer band of a halochromic dye in solution is sensitive to the nature and concentration of an added salt. We may distinguish two kinds of behaviour, a cationic and an anionic halochromism, depending on which species is mainly responsible for the spectral changes induced by the salt added to the dye solutions.3 The halochromic shifts may be explained in terms of dye-salt associations.9.10 Most studies have been concerned with the halochromism of pyridinium phenoxides. For these compounds, which exhibit cationic halochromism, it is the association of the dye with the metal cation which determines the spectral shifts in solution. The 1-methyl-8-oxyquinolinium betaine 1 (QB) was originally described by Ueda and Schelly 11. More recently, solvatochromic shifts of this dye in 28 solvents were recorded and compared to the solvatochromic behaviour of the widely employed ET(30) polarity probe 212. A good correlation of the transition energies of the solvatochromic band of 1 (ET(QB)) was obtained with the corresponding ET(30) values in these media, with a correlation coefficient of 0.9935. In the present communication we studied the spectral properties of organic solutions of dye 1 in the presence of various salts. Because of the similarity of its solvatochromic behaviour with that of the ET(30) dye, it seemed natural to compare the halochromic properties of 1 with those of other pyridiniophenolate dyes previously studied by us and others. 1,6,8

Ion specific differences in salt induced precipitation of kraft lignin

Kraft lignin (KL) precipitation, measured as turbidity, in alkaline solutions (pH = 10.5) at 70degreesC in presence of various salts was investigated. Special concern was devoted to study ion speci ...

Thermal denaturation and gelation of rubisco: effects of pH and ions

In order to understand the mechanism of thermal gelation of rubisco, its native and heat denatured states were characterized by absorbance, fluorescence and circular dichroïsm spectroscopies as well as by differential scanning calorimetry in the presence of various salts. It appears that during the denaturation process, divalent anions are released while divalent cations are fixed by the protein, while it is disorganized and while the environment of its aromatic chromophores becomes more hydrophilic. The pH transition of gelation is shifted 1–2 pH units higher than the transition of denaturation temperature which occurs near the isoelectric point of the native molecule. This shift probably corresponds to the breaking of saline bridges within the protein molecule. Finally, a large effect of divalent cations on the phase diagram indicates that a particular denatured state is attained when these cations are in the denaturation medium.

Elucidation of Salt Effects on the Indicator Acidity in Acetonitrile

Abstract The salt effects on the proton-transfer from CF3COOH to an acid-base indicator, ‘Methyl Yellow’ [p-(dimethylamino)-azobenzene], were examined in acetonitrile by means of spectrophotometry. The addition of LiClO4 to the indicator (Ind) and CF3COOF mixture (both 2.0 × 10−4 mol dm−3) caused an increase and a successive decrease in the absorbance (λmax = 514 nm) of IndH+. The promoted increase of the IndH+ concentration with increasing concentration of LiClO4 was explained on a quantitative basis concerning the formation of a triple cation, CF3COO−(Li+)2, as well as an ion pair, CF3COO−Li+: Ind–CF3COOH + 2 Li+ IndH+ + CF3COO−(Li+)2. The successive decrease in the absorbance at 514 nm with a large excess of LiClO4 was attributed to an ion-exchange reaction: IndH+ + Li+ IndLi+ + H+. The addition of NaClO4 to Ind–CF3COOH caused only an increase in the IndH+ concentration, and no deprotonation from IndH+. Alkaline-earth metal ions (M2+ = Mg2+, Ca2+, Sr2+, and Ba2+) promoted protonation by the formation of complex species, CF3COO−M2+. Although distinct deprotonation from IndH+ was observed with Mg(ClO4)2, no deprotonation occurred with Ba(ClO4)2. The effects of the chloride ion (Et4NCl) on deprotonation from IndH+ (In + CF3SO3H) were explained by the formation of homoconjugated species (HCl2−), and not by the mere formation of HCl. The apparent changes in pH or the Hammett acidity function with the presence of various salts were elucidated by the ‘complex’ formation in acetonitrile.

Cleavage of DNA by the insulin-mimetic compound, NH4[VO(O2)2(phen)

The kinetics and mechanism of cleavage of DNA by the insulin-mimetic peroxo-vanadate NH4[VO(O2)2(phen)], pV, are described. In the presence of low energy UV radiation or biologically common reducing agents, pV decomposes into the monomer, dimer, and tetramer of vanadate and an uncharacterized compound of V4+ as shown by 51V NMR, ESR, and absorption spectra. The rate of photodecomposition of pV is reduced in the presence of calf thymus DNA, indicating that a decomposition product of the peroxo-vanadate, that is important in the destruction pathway of the complex, is interacting with DNA. This species, probably a short-lived complex of V4+, may also be responsible for the observed catalytic decomposition of pV in the absence of DNA by ascorbate. If closed circular pBR322 DNA is present when the peroxo-vanadate is destroyed by either UV radiation or reducing agents, the polymer may have its sugar-phosphate backbone broken. Closed circular DNA (form I) is converted into nicked circular DNA (form II) and linear DNA (form III). The amounts of the various forms produced as a function of irradiation time and peroxo-vanadate concentration were fit to a kinetic model to derive rate constants for the conversions. The kinetic analysis shows that pV is a single-strand nicking agent which exhibits some base and/or sequence preference. Furthermore, the pH dependences of the rates for conversion of form I to form II and for conversion of form II to form III are different, indicating that the nature of the chemistry at the site of cleavage on DNA influences further cutting by activated pV. Reduced amounts of DNA breakage in the presence of various salts and metal binding ligands indicate that a short-lived reactive complex of V4+, not the V4+ species detected by ESR at long irradiation times, is important in the cleavage process. The susceptibility of pV to decomposition by biologically common reducing agents suggests that metabolites of the agent, and not the compound itself, are responsible for its insulin-mimetic effects.

Polymerization and thermal behaviors of poly[dimethyl(acrylamidopropyl)ammonium propane sulfonate] poly (DMAAPS)

AbstractThe conversion in the free radical polymerization of zwitterionic sulfobetaine monomer [dimethyl(acrylamidopropyl)ammonium propanesulfonate] (DMAAPS) was investigated under various conditions, such as, monomer concentration, reaction time and temperature, and various salts. The high conversion of DMAAPS monomer could be achieved under lower temperature. The conversion of DMAAPS is enhanced in the presence of various salts in aqueous solution, but is not very significant because the reactivity of DMAAPS is very rapid even at lower temperature and lower concentration of the monomer. The thermal behavior of poly(DMAAPS) was also studied under nitrogen and air atmosphere at various heating rates. The kinetic parameters such as activation energy, preexponential factor, and reaction order were determined by Ozawa's method. Thermal degradation of such a polymer occurs in two and three stages in nitrogen and air atmospheres, respectively. © 1995 John Wiley &amp; Sons, Inc.

Stability studies on maize leaf phosphoenolpyruvate carboxylase: the effect of salts.

The solution stability of phosphoenolpyruvate carboxylase (PEPC) has been determined in the presence of various salts by temperature-accelerated enzyme inactivation and also by using high-performance size-exclusion chromatography. Kosmotropic (water structuring) anions in the Hofmeister series (HPO(4)2-, citrate3-, SO(4)2-, F-, OAc-) and glutamate stabilized the enzyme most effectively, while Cl- (a borderline Hofmeister anion) and Br- (a chaotropic anion) were destabilizing. The effects of the cations on PEPC stability ranged from relatively inert (Na+, K+) to destabilizing ((CH3)4N+, NH4+, Li+). The observed stabilization of PEPC by specific salts has been interpreted in terms of the positive surface tension increment and the water-structuring effects conferred on the solution by the specific stabilizing reagents. Both these effects enhance hydrophobic interactions of proteins and increase the energy required to enlarge the surface area of the solvent cavity in which the protein resides. The destabilization of PEPC by some salts at a concentration of 0.5 M was associated with the dissociation of the tetrameric enzyme into its dimeric and monomeric forms, a process most probably occurring as a result of ion-peptide dipole binding, which promotes protein-solvent interaction and a subsequent reduction in the free energy of cavity formation. The stabilization of enzyme activity by kosmotropic salts depended on the salt concentration with maximum stabilization of PEPC in solution at 52 degrees C observed with 0.6-0.8 M sodium glutamate, 2 M KF, and 2.2 M KOAc. Higher concentrations of these salts resulted in decreased activity. This reduction in activity of PEPC in the presence of high concentrations of kosmotropic salts appears to be associated with irreversible conformational changes of the tetrameric enzyme.

Enhancement of canine taste responses to umami substances by salts

The effects of salts on canine taste responses to umami substances were examined by recording the activity of the chorda tympani nerve. 1) The responses to monosodium glutamate (MSG), disodium 5'-guanylate (GMP), and that induced by the synergism between MSG and GMP were enhanced by the presence of various salts. 2) The effective salts were those carrying inorganic cations such as Na, K, and Mg, while CaCl2 had no enhancing effect. Salts carrying organic cations such as tris(hydroxymethyl)aminomethane (Tris), choline, N-methyl-D-glucamine, and 1,3-bis[tris(hydroxymethyl)-methylamino]propane also produced positive results. 3) The dependence of the umami responses on NaCl and MgCl2 concentrations showed a bell-shaped response curve with the maximal enhancing effect being seen at 100 mM NaCl and 3-10 mM MgCl2. 4) The degree of the enhancement depended not only on the species of the cation, but also on that of anion. For example, 100 mM NaCl showed a much larger enhancing effect than Na phosphate, Na2SO4, and Na4Fe(CN)6 at equimolar Na+. 5) The enhancing effects of salts on the responses to the umami substances could not be simply explained in terms of the permeability of cation and anion of salts. It was speculated that the binding of both cations and anions to the receptor membranes leads to changes in the interaction of the umami substances with the receptor proteins.

Large enhancement of canine taste responses to amino acids by salts.

The effects of salts on the canine taste responses to amino acids were examined by recording the activity of the chorda tympani nerve. 1) The tonic responses to most amino acids examined were significantly enhanced by the presence of various salts. 2) The degree of the enhancement varied with the species of amino acid and salt. The responses to most amino acids were enhanced by sodium, potassium, and calcium salts, but not enhanced by magnesium salts. The response to methionine, for example, was enhanced by NaCl, but not by Na phosphate of equimolar Na+. 3) The responses to glycine and alanine were suppressed by high concentrations of NaCl. 4) The presence of salts (NaCl and CaCl2) enhanced the responses to amino acids without affecting the thresholds for the amino acids, suggesting that the presence of the salts did not change the affinity of amino acids to the receptor sites. 5) The enhancing effects of salts on the responses to amino acids could not be explained in terms of permeability of cation and anion of salts. It was speculated that the binding of cation and anion of salts on the receptor membranes induces exposure of the receptor sites for amino acids available for binding of amino acids.