COORDINATION OF THE EPSILON-NH2 GROUP OF THE LYSYL RESIDUE IN THE CU-TYRLYS.3H2O SINGLE-CRYSTAL

The crystal and molecular structure of the violet compound (L-tyrosyl- L-lysine)Cu(II).3H2O has been determined by X-ray diffraction. The coo rdination mode of the peptide is the same as previously reported for t he blue (LysTyr)Cu(II).2H2O complex. However, the Cu-alpha-NH2 bond di stance in the violet complex is significantly shorter than that in the blue complex (1.991(7) angstrom and 2.045(8) angstrom respectively). The coordination number is four, not five, since there is no apically bound water molecule in the Cu-TyrLys complex and the aromatic ring is situated close to the basal complex plane. The considerable differenc es in the stereochemistry of the discussed complexes are responsible f or the difference in the d-d transition energy (605 nm and 560 nm resp ectively).