Microcalorimetric studies. Part 2.—Enthalpies of reaction of Cu(II), Ni(II) and Zn(II) with glycine, serine, threonine and histidine

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Abstract
Measurements are reported of the enthalpies of reaction of Cu(II), Ni(II) and Zn(II) with neutralized glycine, serine, threonine and histidine solutions over a broad range of pH. There is a sharp change in enthalpy of reaction above pH∼10 in Cu-serine and Cu-threonine solutions, possibly due to the formation of hydroxypolynuclear complexes in more alkaline solutions. Ni-serine and Zn-serine systems do not show a similar change in enthalpy of reaction at high pH, but precipitation may occur. The enthalpies of formation of the bis-histidino complexes with Cu(II), Ni(II) and Zn(II) are reported; using measured enthalpies of ionization of the histidine acids, reaction enthalpies of Ni(II) with histidine over a range of experimental conditions were calculated, and compare satisfactorily with the observed results.

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