Complexation in two-component chlortetracycline-melanin solutions

Abstract

UDC (541.14+541.15):615.015The spectra and kinetics of fluorescence of two-component solutions of the chlortetracycline (CHTC)-DOPAmelanin (melanin or ME) system in water have been investigated. The data obtained have been compared to similar data for solutions of CHTC-melanosome from bull eye (MB), which contains natural melanin, in Kphosphate buffer at pH 7.4. The overall results indicate the occurrence of complexation between molecules of CHTC and ME as they are being excited. The studies of complexation in the solution of CHTC-MB in the buffer are complicated by the formation of a CHTC-buffer complex. The effect of optical radiation in the range 330-750 nm on the CHTC-ME complex shows selectivity: the greatest change in the spectrum occurs when the wavelength of the exciting radiation coincides with the long-wavelength band maximum of the fluorescence excitation spectrum of the CHTC-ME complex in aqueous solution. In this range, CHTC and especially ME show high photochemical stability. The nature of the radiation effect on the studied compounds in the hard UV range (λ < 330 nm) differs greatly from that in the range 330-750 nm. It is apparently accompanied by significant photochemical transmutations of all system components. By comparing the characteristics of the CHTC-ME systems with those of the related drug doxycycline (DC-ME), the conclusion has been made that the chlorine atom plays a vital role in formation of the short-wavelength band in the fluorescence spectrum of the CHTC-ME complex.

Hetero-association of aromatic molecules in aqueous solution

“…[100,202]) or with the influence of hetero-association on photo-transformation of the main aromatic drug in the presence of another aromatic compound (predominantly grouped around the photosensitising properties of particular compounds of medical interest, such as Riboflavin and a few other drugs (e.g. [131,[247][248][249])). These results, however, give little insight into the kinetics of hetero-association; the influence of metal ions on the stability of hetero-complexes may be based on the intuitive assumption that metal ions enhance the stability of hetero-complexes by analogy with self-association [17], though information on hetero-complexes is generally unknown and needs to be investigated; 36 M.P.…”