In this study, the metastable zone width of potassium tetraborate tetrahydrate was determined for four different temperatures and cooling rates. The induction period of potassium tetraborate tetrahydrate in aqueous solution was examined according to polythermal method by using visual observation. The induction period, which changes inversely proportional to the nucleation rate has been used to determine the interfacial tension between the potassium tetraborate tetrahydrate and aqueous solution. By using interfacial tension, the nucleation parameters such as Gibbs free energy change for the formation of critical nucleus, ∆G*, free energy of formation, ∆G, radius of critical nucleus, r and number of molecules in the critical nucleus, i* has been calculated. The effect of Li + and Ca 2+ impurities on metastable zone width has been studied. The metastable zone width of aqueous solution of potassium tetraborate tetrahydrate decreases with increasing impurity concentrations. The equilibrium saturation concentration change is high in the presence of Ca 2+ ions while it is low in the presence of Li + ions.

Glucose‐6‐phosphate dehydrogenase (D‐glucose‐6‐phosphate: NADP+ oxidoreductase, EC 1.1.1.49; G6PD) was purified from coriander (Coriandrum sativum) leaves; the kinetic behavior and some properties of the enzyme were also investigated. The purification was done at 4C and involved two steps: ammonium sulfate fractionation, and DEAE‐Sephadex A50 ion exchange chromatography. The enzyme was obtained with a yield of 26.4% and had a specific activity of 1.826 U/mg protein. Optimum pH, stable pH, optimum temperature, molecular weight, KM and Vmax values for NADP+ and glucose 6‐phosphate (G6‐P) were also determined. The overall purification was about 74‐fold. SDS‐PAGE of the purified enzyme showed a single band. Enzymatic activity was spectrophotometrically measured according to Beutler's method at 340 nm. The molecular mass was estimated to be 74.4 kDa by SDS‐PAGE and 73.2 kDa by Sephadex G‐200 gel filtration column chromatography. The enzyme had an optimum pH at 8.5 and was stable at pH 8.0 in 0.1 M Tris‐HCl buffer. The optimum temperature was at 30C. The KM values for NADP+ and G6‐P were 0.026 mM and 0.116 mM, respectively. The Vmax values for these substrates were 0.035 EU/mL and 0.038 EU/mL, respectively.

In this study, 6-phosphogluconate dehydrogenase (E.C.1.1.44; 6PGD) was purified from parsley (Petroselinum hortense) leaves, and analysis of the kinetic behavior and some properties of the enzyme were investigated. The purification consisted of three steps that are preparation of homogenate ammonium sulfate fractionation and on DEAE-Sephadex A50 ion exchange. The enzyme was obtained with a yield of 49% and had a specific activity of 18.3 U (mg proteins)(-1) (Lehninger, A.L.; Nelson, D.L.; Cox, M.M. Principles of Biochemistry, 2nd Ed.; Worth Publishers Inc.: N.Y., 2000, 558-560). The overall purification was about 339-fold. A temperature of +4 degrees C was maintained during the purification process. Enzyme activity was spectrophotometrically measured according to the Beutler method at 340 mn. In order to control the purification of the enzyme, SDS-polyacrylamide gel electrophoresis was carried out in 4% and 10% acrylamide for stacking and running gel, respectively. SDS-polyacrylamide gel electrophoresis showed a single band for enzyme. The molecular weight was found to be 97.5 kDa by Sephadex G-150 gel filtration chromatography. A protein band corresponding to a subunit molecular weight of 24.1 kDa was obtained on SDS-polyacrylamide gel electrophoresis. For the enzymes, the stable pH, optimum pH, and optimum temperature were found as 8.0, 8.0, and 50 degrees C, respectively. In addition, KM and Vmax values for NADP+ and G6-P at optimum pH and 25 degrees C were determined by means of Lineweaver-Burk plots.

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A potentiometric titration technique has been used to determine the stability constants for the various complexes of Co(II) and Cu(II) with L-asparagine and from DNA base, e.g. adenine. Stability constants of ternary systems have been evaluated by the method suggested by IrwingRossotti. In addition, the conditional constants were calculated as a function of pH. The maximum values of the conditional formation constants were found to be in accordance with the mixed-ligand complex formation constants in a determined pH region. Furthermore, the molar fractions of different species from mixed complexes were calculated by means of formation constants. The values of stability constants of mixed-ligand complexes at 25°C are as follows: log K= 5.25 for Co(II)-L-asparagine-adenine; log K= 9.30 for Cu(II)-L-asparagine-adenine. The ionic strength was kept constant at I = 0.20 with NaClO 4 .