PROTEIN INTERACTIONS WITH BIVALENT TIN .1. HYDROLYSIS AND COMPLEXATION OF TIN(II) ION WITH GLYCINE

The complexation between tin(II) ion and glycine was studied in 0.15 m ol/dm(3) NaCl medium at 310 K using potentiometric glass electrode tit rations. 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 r atio 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 co mplex Sn-4(OH)(6)(2+), whose stability constant was determined in sepa rate experiments and found to be -4.30 +/- 0.08, under the same experi mental conditions as for complexation study. The precipitate formed in tin(II)-glycine system at pH ca. 5.0 was characterized by chemical an d TG analysis, I. R. spectra, X-ray powder diffraction, and electron s canning microscopy measurements. It has been shown that the precipitat e has the composition Sn(OH)Gly and crystallizes in a tetragonal syste m with unit cell dimensions a = b = 1.584 nm, c = 0.597 nm. The mechan ism of the complex formation in solution is discussed.