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The decrease in ionized calcium by bicarbonate was examined with a calcium ion-sensitive potentiometric method. In the physiological concentration range, calcium ion concentration is about 80% of total (ultrafiltrable) calcium. In complex aqueous physiological solutions, bicarbonate is mainly responsible for the decrease in calcium ion concentration. [ABSTRACT FROM AUTHOR]

The thermodynamic formulation of isotope interaction (coupling of abundant and tracer isotope flows) has been tested in a highly permselective anion exchange membrane in the absence of significant electroosmosis. A previous study of Cl permeation has now been extended to include permeation of I, Acetate, and SO in different bath concentrations, with the use of both electrical and chemical driving forces. The flux ratios were 'abnormal' according to the usual criteria for simple passive flow, but were closely predicted by the theoretical expression incorporating the influence of isotope interaction. In the absence of coupled flows of other chemical species the extent of isotope interaction can be determined either from the flux ratio or from the measurement of a single unidirectional flux at two settings of the electrochemical potential difference. Direct evidence of negative isotope interaction was presented. [ABSTRACT FROM AUTHOR]

The operation of a seven-compartment model is described with respect to flows of Na within and across this system, simulating published results obtained on frog skin. The seven compartments represent: one outside and one inside solution compartment; the subcorneal space; the first reacting cell layer (1. RCL); the remaining cell compartment; the non-, or slowly exchangeable Na compartment; the extracellular space. Assuming reasonable volumes for the epidermal compartments and further chosing, by trial and error, appropriate rate constants, a set of seven simultaneous linear differential equations was solved by the application of the Continuous System Modeling Program (CSMP), using an IBM 1130 computer. Initial conditions for influx, backflux and net flux were taken which correspond to [Na]; [Na]=115 mm. Print-out data were obtained at 0.5-min intervals for 30 min, when steady states were obtained in 13 models studied, varying certain k's thus simulating actions of chemical agents (hormones; drugs). Simulation was achieved with regard to rate of influx, backflux and net flux, steady-state time (30 min), and electrical potentials. In addition, this approach gave detailed information on Na pool sizes and their variations with changes in k's. These results are compared to published data on frog skin and good agreement between operation of skin epidermis and model was found. [ABSTRACT FROM AUTHOR]

Stoichiometric dissociation constants of complexes between the fully deprotonated 3-phosphoD-glyceric acid and Mg2+, Mn2+, Ca2+ Co2+, Zn2+, and Ni2+, respectively, were determined in 0.25 M NaCl at 25 °C. Potentiometric titrations of the ligand with these divalent, metal ions were performed over a pH range close to the pK for the final deprotonation step of the ligand. The observed pH changes were utilized to estimate the dissociation constants; both algebraic and graphical techniques were employed in the estimations. Under the experimental conditions 1:1 complexes were the predominant products. [ABSTRACT FROM AUTHOR]

We have performed potentiometric titrations and chemical modifications of demetallized concanavalin A and of the Ni2+ concavalin A complex. Two protons are released upon binding of one Ni2+ ion per concanavalin A subunit. The pH-dependence of proton release indicates that two ionizable groups with pKa 6.8 are ligands for binding of the transition-metal ion. Ethoxyformylation of histidines causes the destruction of the transition-metal-binding site unless it is occupied by a transition-metal ion. For each transition-metal site thus protected two otherwise ethoxyformylated histidines are rendered inert to the chemical modification. On photooxidation in the presence of rose bengal, protection of histidines and of the transition-metal-binding capacity was also observed to occur when Ni2+ ions were present. Two histidine residues in concanavalin A are, therefore, very likely metal-ion ligands in the binding site. [ABSTRACT FROM AUTHOR]

A method is described for enthalpy titration of proteins, using a flow microcalorimeter in combination with a device for continuous pH measurements. The calorimetric titration of lysozyme between pH 1.5 and 12 has been carried out as well as the corresponding potentiometric titration. Enthalpy values for the titrated groups are estimated and discussed in comparison with reported data for free amino acids. [ABSTRACT FROM AUTHOR]

The corrosion of some gold base alloys was studied in artificial saliva through the use of electrochemical methods, primarily potentiokinetic curves. The effects of various alloying elements were investigated. [ABSTRACT FROM AUTHOR]

This article reports on the analysis of tongue and oral tissue for changes related to aging. The article discusses aging tissues in relation to oxidizing and reducing particles, extracellular compartments, and physical and chemical dynamics. Information is also provided on research conducted through potentiometric techniques.

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