INTERACTION OF CU(II) 3,5-DIISOPROPYLSALICYLATE WITH HUMAN SERUM-ALBUMIN - AN EVALUATION OF SPECTROSCOPIC DATA

The copper(II) complex of 3,5-diisopropylsalicylate is a lipophilic wa ter-insoluble binuclear complex, Cu(II)(2)(3,5-DIPS)(4), that has attr acted interest because of a wide range of pharmacological activities. This study was undertaken to examine bonding interactions between the complex and human serum albumin (HSA) to help elucidate the mode of tr ansport of the complex in vivo. Electron paramagnetic resonance, numer ical magnetic resonance and UV-visible absorption spectroscopic studie s were performed using 200 mu M aqueous solutions (pH 7.5) of HSA to w hich had been added up to three molar equivalents of CuCl2, CuSO4, or Cu(II)(2)(3,5-DIPS)(4). Both EPR and UV-visible spectra demonstrated t he presence of more than one copper bonding site on HSA, and proton NM R spectra showed that the 3,5-DIPS ligand is also bonded to HSA. These results indicate that there is no observable direct coordination of t he ligand to copper in the presence of HSA, and that the majority of t he copper and 3,5-DIPS bond to HSA at separate sites. Addition of soli d Cu(II)(2)(3,5-DIPS)(4) to HSA at pH 7.5 similarly resulted in spectr a that suggest that there are no ternary Cu(II)(3,5-DIPS), Cu(II)(3,5- DIPS)(2), or Cu(II)(2)(3,5-DIPS)(4) complexes formed with HSA. It is c oncluded that any ternary complexes formed in the presence of HSA are below the spectroscopic detection limits and represent less than 5% of the total copper.