Electronic spectral studies of nickel(II) alanine complexes

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The electronic absorption spectrum of hydrated nickel(II) exhibits three bands, a broad band λ max at 658 nm and two sharp bands with λ max at 394 and 302 nm. The electronic absorption spectrum of Ni(II) and D- and L-alanine in aqueous solution shows the same three characteristic bands, but with λ max at 618,370 and 302 nm, with the absorption intensities increased for the first two bands. The three bands are assigned to the three spin-allowed d-d transitions 3A 2g → 3T 2g, 3A 2g → 3T 1g(F) and 3A 2g → 3T 1g(P) of octahedral nickel(II). Information about the Ni(II) complex formation mechanism and nature of the products was obtained from isosbestic points and pH profile studies of electronic spectra and amino acid racemization rates.