Protein interactions with bivalent tin .1. Hydrolysis and complexation of tin(II) ion with glycine
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The complexation between tin(II) ion and glycine was studied in 0.15 mol/dm(3) NaCl medium at 310 K using potentiometric glass electrode titrations. In the pH range 1.1-4.5 and concentration range of the tin(II) between 0.2 and 5.0 mmol/dm(3), with variable glycine-to-tin molar ratio up to 10:1, the experimental data were explained by the formation of the following complexes and their overall stability constants: log(beta +/- sigma): Sn(HGly)(+), (12.78 +/- 0.08); Sn(Gly)(+), (10.02 +/- 0.07); Sn(OH)Gly, (7.34 +/- 0.03), as well as the pure hydrolytic complex Sn-4(OH)(6)(2+), whose stability constant was determined in separate experiments and found to be -4.30 +/- 0.08, under the same experimental conditions as for complexation study. The precipitate formed in tin(II)-glycine system at pH ca. 5.0 was characterized by chemical and TG analysis, I. R. spectra, X-ray powder diffraction, and electron scanning microscopy measurements. It has been shown that the precipitate has the compositio...n Sn(OH)Gly and crystallizes in a tetragonal system with unit cell dimensions a = b = 1.584 nm, c = 0.597 nm. The mechanism of the complex formation in solution is discussed.