Absence in amphotericin B-spiked human plasma of the free monomeric drug, as detected by SERS.

Using surface enhanced Raman spectroscopy (SERS) which enables us to specifically detect traces of monomeric amphotericin B (AmB), we were able to show that in a 10(-5) M AmB suspension, the concentration of free drug was below 10(-8) M in the presence of low density lipoproteins (LDL) or plasma. The affinity constant of AmB for LDL determined from electronic absorption data, was found to be 4 x 10(6) M(-1). Therefore, since AmB appears to be in the majority bound to lipoproteins under in vivo conditions, its toxicity should not result from the induction of host-cell transmembrane permeability but rather from the internalization of the AmB-LDL complex.

Free radicals in melanin-cationic porphyrin complexes in the dark and under light irradiation.

Electron Paramagnetic Resonance (EPR) spectroscopy was employed in the study of the interaction between L-3,4-dihydroxyphenylalanine (L-Dopa) melanin and the cationic porphyrins meso-tetrakis(1-methylpyridinium-4yl)-porphyrin (TMPyP), meso-tetrakis-(1-benzylpyridinium-4-yl)-porphyrin (TBzPyP), and their respectives complexes ZnTMPyP and ZnTBzPyP. By monitoring signal intensities and progressive microwave power saturation it was shown that the interaction increases the equilibrium concentration of free radicals in L-Dopa melanin in the dark. The extent of increase is dependent on the presence of molecular oxygen and on the type of porphyrin. Not all interacting sites available for complexation in L-Dopa melanin are involved in the formation of free radicals. It was also observed that the interaction with porphyrins promotes an increase in the number of photoinduced free radicals in L-Dopa melanin during illumination with visible light.