1981 年 101 巻 2 号 p. 118-124
The coordination sites of tetracyclines to Cu2+ in a solution at pH 5 were examined by the methods of circular dichroism (CD) spectra, absorption spectra and optical rotation. The results obtained were as follows : 1) The CD spectrum of tetracycline (TC)-Cu2+ complex showed a positive peak at 400 nm, whereas that of tetracyclinenitrile (TN)-Cu2+ complex didn't show any positive peaks in the range over 350 nm. 2) Bathochromic shifts in the absorption spectra of TC and TN induced by the addition of Cu2+ at pH 5 were observed. 3) With an increase in the molar ratio of Cu2+ to TC or oxytetracycline (OT), the optical rotation changed from negative to positive. On the other hand, the optical rotation of TN-Cu2+ complex was independent of the molar ratio of Cu2+ to TN. 4) The CD spectrum of TC-Cu (ethylenediamine)2+ or OT-Cu (ethylenediamine)2+ complex showed a positive peak at 400 nm or 390 nm. 5) The curves obtained by the plots of the optical rotation against the molar of Cu (ethylenediamine)2+ to TC or OT were similar to that obtained by the plots against the molar ratio of Cu2+ to OT. Therefore, at pH 5, tetracyclines may bind to Cu2+ at both C11-C12 β-diketone site and C2 carboxamide site through bending of A ring over B and C rings.