sodium-perchlorate and sodium-nitrate

Potentiometric titration and zeta potential measurements are crucial techniques for the characterization of the surface properties of bacterial cells. In this study, we investigated the effects of two commonly used electrolytes, NaNO(3) and NaClO(4), on the viability and acid-base properties of Gram-positive bacteria Bacillus subtilis. B. subtilis are non-pathogenic bacteria which are often used to model the surface properties of pathogenic microorganisms of the same genus, including Bacillus anthracis and Bacillus cereus. The survival rates of bacterial cells treated with NaNO(3) were significantly higher in comparison with microorganisms treated with NaClO(4) (5.2-6.8 and 4.1-4.7 log(10) cfu - colony-forming units, respectively). A decrease in the ionic strength (0.1 M, 0.01 M and 0.005 M) of both electrolytes increased viable bacterial cell counts in NaNO(3) treatments and decreased viable bacterial counts in NaClO(4) treatments. Potentiometric titration revealed three dominant types of cell wall functional groups: the carboxyl group (pK(a) values of 4.58-4.89), the amino group (pK(a) values of 9.62-9.89) and the phosphate group (pK(a) values of 7.12-7.49). An increase in the ionic strength of electrolytes led to a decrease in total site concentrations and a drop in buffering capacity at the examined pH values. Based on zeta potential values, measured as a function of pH and ionic strength, the isoelectric point of B. subtilis was determined at pH 2.2 for 0.005 M and 0.01 M NaNO(3). Zeta potential increased with a rise in pH, and it decreased with an increase in ionic strength.

Topics: Bacillus subtilis; Colloids; Electrolytes; Hydrogen-Ion Concentration; Nitrates; Osmolar Concentration; Perchlorates; Sodium Compounds; Surface Properties

Kinetics of adsorption plays a pivotal factor in determining the bio-availability and mobility of Hg(II) in the environment. The kinetics of Hg(II) adsorption on gibbsite was examined as a function of pH, temperature and electrolyte type. Adsorption of Hg(II) was highly non-linear where the rate of Hg(II) retention was rapid initially and was followed by gradual or somewhat slow retention behavior with increasing contact time. The respective rate constants designated as k(1) (S-1: fast step) and k(2) (S-2: slow step). Always k(1) follows the order: k(1)(CIO)(4) >/= k(1)(NO3)(4) >> k(1)(Cl). Such a relationship was not observed for the S-2 route. A two-step reaction model with pseudo-first order kinetics successfully described the adsorption rates of Hg(II) on gibbsite. Arrhenius and Erying models determined the thermodynamic parameters at activation states, which correspond to S-1 and S-2 routes. In a given system, always the activation energies showed a decrease with the pH. Gibbs free energy (DeltaG(#)), enthalpy (DeltaH(#)), and entropy (DeltaS(#)) values of activation states were almost similar both in NaClO(4) and NaNO(3) which signal a similar Hg(II) adsorptive mechanism on gibbsite. The configurations of different Hg(II)-surface complexes were elucidated by transmission vibration spectroscopy.

Topics: Adsorption; Hydrogen-Ion Concentration; Kinetics; Mercury; Nitrates; Perchlorates; Sodium Chloride; Sodium Compounds; Temperature; Thermodynamics; Water