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Salt Effects (salt + effects)
Selected AbstractsFormation of Soy Protein Isolate Cold-set Gels: Protein and Salt EffectsJOURNAL OF FOOD SCIENCE, Issue 1 2005Anne Maltais ABSTRACT: The influence of protein and calcium concentration on soy protein cold-set gel formation and rheology has been investigated. Cold-set gels can be formed at soy protein concentrations from 6% to 9% and calcium concentrations from 10 to 20 mM. Gel properties can be modulated by changing the protein and/or CaCl2 concentrations. An increase in CaCl2 concentration from 10 to 20 mM increased gel opacity while an increase in protein concentration from 6% to 9% decreased opacity. Water-holding capacity improved with increasing protein concentration and decreasing CaCl2 concentration. The elastic modulus (G') increased with protein and calcium chloride concentrations. Microscopy revealed an increase in the diameters of aggregates and pores as CaCl2 concentration increased and as protein concentration decreased. Cold-set gels with a broad range of characteristics can be obtained from soy protein. [source] Spectroscopic and Electrochemical Evaluation of Salt Effects on Electron-Transfer Equilibria between Donor/Acceptor and Ion-Radical Pairs in Organic SolventsCHEMPHYSCHEM, Issue 16 2008Sergiy V. Rosokha Dr. Abstract Addition of "inert" tetrabutylammonium hexafluorophosphate (Bu4NPF6) to a solution of TMDO/DDQ in dichloromethane (where TMDO=2,2,6,6-tetramethylbenzo[1,2-d;4,5-d]bis[1,3]-dioxole, donor, and DDQ=diclorodicyano-p-benzoquinone, acceptor) is accompanied by drastic changes in the electronic spectrum, which are related to the appearance of the DDQ,. and TMDO+. ion radicals and a decrease in the concentration of the neutral molecules and the charge-transfer complex [TMDO,DDQ]. These changes point to a considerable rise (of about three orders of magnitude) in the apparent electron-transfer equilibrium constant (KET) for this donor/acceptor pair upon increasing the electrolyte concentration from 0 to 0.5,M. Accordingly, the ion-radical fractions and KET values are higher in dichloromethane, at high electrolyte concentrations, than in acetonitrile (where the effect of Bu4NPF6 is less pronounced). Similar trends of the apparent equilibrium constants are observed for the tetramethyl-p-phenylenediamine/tetracyanoethylene pair. Electron-transfer equilibrium constants for both donor/acceptor dyads obtained from spectral measurements are related to those derived from the redox potentials of the reactants. The effects of media variations on the electron-transfer equilibria are discussed within the ion-pairing and ionic-activity frameworks. [source] Abnormal salt effects on reactions between ions: The coupling of salt and solvent effectsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2009V. I. Martin Salt effects on the reactions [Fe(CN)6]4, + S2O=8 and [Ru(NH3)5py]2+ + S2O have been studied in media of different dielectric constants constituted by mixtures of water with organic cosolvents. It is known that salt and solvent effects are coupled and, consequently, cannot be treated separately. This implies that salt (and solvent) effects need to be carefully analyzed before using them as a tool for mechanistic discrimination. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 582,588, 2009 [source] Micellar and salt effects on the interaction of [Cu(II)-Gly-Gly]+ with ninhydrinINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2007Mohd. Akram The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the kinetics of interaction of copper dipeptide complex [Cu(II)-Gly-Gly]+ with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first- and fractional-order kinetics, respectively, in complex and ninhydrin. The reaction is catalyzed by CTAB micelles, and the maximum rate enhancement is about twofold. The results obtained in the micellar medium are treated quantitatively in terms of the kinetic pseudophase and Piszkiewicz models. The rate constants (kobs or k,), micellar-binding constants (kS for [Cu(II)-Gly-Gly]+, kN for ninhydrin), and index of cooperativity (n) have been evaluated. A mechanism is proposed in accordance with the experimental results. The influence of different inorganic (NaCl, NaBr, Na2SO4) and organic (NaBenz, NaSal) salts on the reaction rate has also been seen, and it is found that tightly bound/incorporated counterions are the most effective. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 556,564, 2007 [source] Fat, wheat bran and salt effects on cooking properties of meat patties studied by response surface methodologyINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 10 2010Hasibe Tekin Summary Response surface methodology was used to investigate the main effects and interactions of composition (processing) variables such as fat (10,30%), wheat bran (5,15%) and NaCl (0,2%) on cooking properties of beef patties. In addition, the ridge analysis was conducted to find the values of processing variables that maximise and minimise the cooking parameters (moisture retention, fat retention, reduction in thickness, reduction in diameter, cooking yield, shrinkage and water-holding capacity). It was found that the moisture and fat retention, reduction in thickness and cooking yield values decreased; however, reduction in diameter and shrinkage values increased, respectively, as the amount of fat increased. However, wheat bran addition increased fat retention, moisture retention, cooking yield and water-holding capacity values of the patties. Increasing NaCl levels decreased water-holding capacity value by its quadratic effect and moisture and fat retention value by its interaction effect with wheat bran. [source] Effects of salts on protein,surface interactions: applications for column chromatographyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2007Kouhei Tsumoto Abstract Development of protein pharmaceuticals depends on the availability of high quality proteins. Various column chromatographies are used to purify proteins and characterize the purity and properties of the proteins. Most column chromatographies require salts, whether inorganic or organic, for binding, elution or simply better recovery and resolution. The salts modulate affinity of the proteins for particular columns and nonspecific protein,protein or protein,surface interactions, depending on the type and concentration of the salts, in both specific and nonspecific manners. Salts also affect the binding capacity of the column, which determines the size of the column to be used. Binding capacity, whether equilibrium or dynamic (under an approximation of a slow flow rate), depends on the binding constant, protein concentration and the number of the binding site on the column as well as nonspecific binding. This review attempts to summarize the mechanism of the salt effects on binding affinity and capacity for various column chromatographies and on nonspecific protein,protein or protein,surface interactions. Understanding such salt effects should also be useful in preventing nonspecific protein binding to various containers. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1677,1690, 2007 [source] A SERS probe of adenyl residues available for intermolecular interactions.JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2001Part I, adenyl, fingerprint' This work validated a SERS probe able to compare adenyl reactivity in DNA and RNA. A Creighton silver colloid including adenine (A) [or 2, -deoxyadenosine 5, -phosphate (pdA)] from 2 × 10,3 to 2 × 10,8M is stabilized in the absence or presence of chloride. Concentration-dependent SER spectral profiles reveal how A may interact with (Ag)n+ sites. At concentration ,2 × 10,5M adsorption of (A)n clusters prevents the colloid from undergoing salt effects. Adsorption via N1/N3 is allowed whereas C6NH2 is involved in self-association. At [A] <2 × 10,5M with chloride, hydrogen bonding between chloride and the C6NH2 group enhances C6N electronegativity, which assists C6N/N7 cooperative adsorption. Complex A(Cl,) entities compete with individual chloride ions for adsorption on silver. Very similar C6N/N7 adenyl adsorption occurs for pdA but only above 2 × 10,5M. Chloride,adenyl bonding is reduced and pdA self-association is weaker than adenine self-association. Steric factors, repulsive electrostatic forces and phosphate competitive reactivity with respect to chloride may explain the much higher pdA concentration needed to saturate the silver surface compared with A. Mg2+,phosphate complexation entails concentration-dependent opposite effects on adenyl reactivity with (Ag)n+ sites. Cytosine, thymine and guanine base or corresponding nucleotides deliver weaker SER spectra and much higher SERS responses for chloride adsorption compared with A or pdA. This reveals a weaker adsorption of the oxo bases, assumed to result from alternative oxo and nitrogen interactions with the (Ag)n+ sites. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sequence-dependent Interactions of Cationic Naphthalimides and PolynucleotidesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Sun McMasters The binding interactions of three naphthalimide derivatives with heteropoly nucleic acids have been evaluated using fluorescence, absorption and circular dichroism spectroscopies. Mono- and bifunctionalized naphthalimides exhibit sequence-dependent variations in their affinity toward DNA. The heteropoly nucleic acids, [Poly(dA-dT)]2 and [Poly(dG-dC)]2, as well as calf thymus (CT) DNA, were used to understand the factors that govern binding strength and selectivity. Sequence selectivity was addressed by determining the binding constants as a function of polynucleotide composition according to the noncooperative McGhee,von Hippel binding model. Binding affinities toward [poly(dA-dT)]2 were the largest for spermine-substituted naphthalimides (Kb = 2,6 × 106 m,1). The association constants for complex formation between the cationic naphthalmides and [poly(dG-dC)]2 or CT DNA (58% A-T content) were 2,500 times smaller, depending on the naphthalmide,polynucleotide pair. The binding modes were also assessed using a combination of induced circular dichroism and salt effects to determine whether the naphthalimides associate with DNA through intercalative, electrostatic or groove-binding. The results show that the monofunctionalized spermine and pyridinium-substituted naphthalimides associate with DNA through electrostatic interactions. In contrast, intercalative interactions are predominant in the complex formed between the bifunctionalized spermine compound and all of the polynucleotides. [source] pH and salt effects on interpolymer complexation via hydrogen bonding in aqueous solutionsPOLYMER INTERNATIONAL, Issue 9 2004Dr Vitaliy V Khutoryanskiy Abstract The effect of inorganic salts addition on the complex formation of poly(acrylic acid) with various non-ionic polymers such as poly(vinyl pyrrolidone), poly(acrylamide), poly(ethylene oxide), pol(vinyl methyl ether), poly(vinyl alcohol), poly(N -isopropylacrylamide), poly(2-hydroxyethyl vinyl ether), hydroxypropylcellulose and hydroxyethylcellulose has been studied in aqueous solutions. It was found that, depending on the nature of the polymers and pH medium, addition of inorganic salts could increase or decrease the critical pH values of complexation. A new classification of interpolymer complexes based on critical pH values and ionic strength effects is suggested. Copyright © 2004 Society of Chemical Industry [source] Structural effects of monovalent anions on polymorphic lysozyme crystalsACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2001M. C. Vaney Understanding direct salt effects on protein crystal polymorphism is addressed by comparing different crystal forms (triclinic, monoclinic, tetragonal and orthorhombic) for hen, turkey, bob white quail and human lysozymes. Four new structures of hen egg-white lysozyme are reported: crystals grown in the presence of NapTS diffracted to 1.85,Å, of NaI to 1.6,Å, of NaNO3 to 1.45,Å and of KSCN to 1.63,Å. These new structures are compared with previously published structures in order to draw a mapping of the surface of different lysozymes interacting with monovalent anions, such as nitrate, chloride, iodide, bromide and thiocyanate. An analysis of the structural sites of these anions in the various lysozyme structures is presented. This study shows common anion sites whatever the crystal form and the chemical nature of anions, while others seem specific to a given geometry and a particular charge environment induced by the crystal packing. [source] Continuum molecular electrostatics, salt effects, and counterion binding,A review of the Poisson,Boltzmann theory and its modificationsBIOPOLYMERS, Issue 2 2008Grochowski Abstract This work is a review of the Poisson,Boltzmann (PB) continuum electrostatics theory and its modifications, with a focus on salt effects and counterion binding. The PB model is one of the mesoscopic theories that describes the electrostatic potential and equilibrium distribution of mobile ions around molecules in solution. It serves as a tool to characterize electrostatic properties of molecules, counterion association, electrostatic contributions to solvation, and molecular binding free energies. We focus on general formulations which can be applied to large molecules of arbitrary shape in all-atomic representation, including highly charged biomolecules such as nucleic acids. These molecules present a challenge for theoretical description, because the conventional PB model may become insufficient in those cases. We discuss the conventional PB equation, the corresponding functionals of the electrostatic free energy, including a connection to DFT, simple empirical extensions to this model accounting for finite size of ions, the modified PB theory including ionic correlations and fluctuations, the cell model, and supplementary methods allowing to incorporate site-bound ions in the PB calculations. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 93,113, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Do electrostatic interactions destabilize protein,nucleic acid binding?BIOPOLYMERS, Issue 2 2007Sanbo Qin Abstract The negatively charged phosphates of nucleic acids are often paired with positively charged residues upon binding proteins. It was thus counter-intuitive when previous Poisson,Boltzmann (PB) calculations gave positive energies from electrostatic interactions, meaning that they destabilize protein,nucleic acid binding. Our own PB calculations on protein,protein binding have shown that the sign and the magnitude of the electrostatic component are sensitive to the specification of the dielectric boundary in PB calculations. A popular choice for the boundary between the solute low dielectric and the solvent high dielectric is the molecular surface; an alternative is the van der Waals (vdW) surface. In line with results for protein,protein binding, in this article, we found that PB calculations with the molecular surface gave positive electrostatic interaction energies for two protein,RNA complexes, but the signs are reversed when the vdW surface was used. Therefore, whether destabilizing or stabilizing effects are predicted depends on the choice of the dielectric boundary. The two calculation protocols, however, yielded similar salt effects on the binding affinity. Effects of charge mutations differentiated the two calculation protocols; PB calculations with the vdW surface had smaller deviations overall from experimental data. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 112,118, 2007. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Protein instability during HIC: Hydrogen exchange labeling analysis and a framework for describing mobile and stationary phase effectsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2007Yunzhi Xiao Abstract Unfolding of marginally stable proteins is a significant factor in commercial application of hydrophobic interaction chromatography (HIC). In this work, hydrogen-deuterium isotope exchange labeling has been used to monitor protein unfolding on HIC media for different stationary phase hydrophobicities and as a function of ammonium sulfate concentration. Circular dichroism and Raman spectroscopy were also used to characterize the structural perturbations experienced by solution phase protein that had been exposed to media and by protein adsorbed on media. As expected, greater instability is seen on chromatographic media with greater apparent hydrophobicity. However, increased salt concentrations also led to more unfolding, despite the well-known stabilizing effect of ammonium sulfate in solution. A thermodynamic framework is proposed to account for the effects of salt on both adsorption and stability during hydrophobic chromatography. Using appropriate estimates of input quantities, analysis with the framework can explain how salt effects on stability in chromatographic systems may contrast with solution stability. Biotechnol. Bioeng. 2007;96: 80,93. © 2006 Wiley Periodicals, Inc. [source] | |||||||||||||