Photophysical properties and photoinduced electron transfer within host-guest complexes of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin with water-soluble calixarenes and cyclodextrins.

We report the formation of host-guest complexes between water-soluble calix[n]arene-p-tetrasulfonates (n = 4, 6, 8) or 2-hydroxypropyl-cyclodextrins (alpha-, beta-, gamma-) and the tetratosylate salt of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). The binding constants ranging between 10(2) and 10(5) M-1 were calculated from the absorption and fluorescence changes. Calix[4]arene-p-tetrasulfonate has a high binding affinity and forms with TMPyP a 1:1 complex, whereas other calixarenes bind two molecules of TMPyP. Electrostatic attraction is the dominating binding mode. Binding to calixarenes leads to a considerable decrease of the quantum yields of the triplet and excited singlet states and to shortening of the singlet and triplet lifetimes of TMPyP. The quenching mechanism is attributed to electron transfer between calixarene phenolates and excited TMPyP. Photoinduced electron transfer within a novel supramolecular complex calixarene/TMPyP (electron donor)/methyl viologen (electron acceptor) has been proven by absorption and fluorescence measurements. Electrostatic attraction between the cationic donor and cationic acceptor, on the one hand, and the anionic host, on the other, overcomes the electrostatic repulsion forces. In contrast, the interaction of cyclodextrin with TMPyP is hydrophobic in nature and only slightly influences the photophysical properties of TMPyP. The different behavior of TMPyP bound to either of the hosts has been assigned to the specific effects of the dominant binding modes, viz. the electrostatic attraction for calixarenes and the hydrophobic interactions for inclusion complexes with cyclodextrins.

Long-range assemblies on poly(dG-dC)2 and poly(dA-dT)2: phosphonium cationic porphyrins and the importance of the charge.

The present paper describes synthesis and spectroscopic properties of novel cationic meso-tetraphenylporphyrins bearing two (trans) (P2) or three (P3) triphenylphosphonium substituents. The porphyrin aggregation in aqueous solutions is discussed in detail. Porphyrin binding to and self-organization onto long-range assemblies on poly(dA-dT)2 or poly(dG-dC)2 were probed by combination of absorption, fluorescence, circular dichroism (CD), transient and resonance light-scattering (RLS) techniques. The higher hydrophobicity of P2 is manifested by more extensive self-organization. Induced CD and intensive RLS indicate binding to the chiral environment on the nucleic acids exterior and exciton coupling between adjacent porphyrin moieties. The CD spectra of P2 on poly(dG-dC), and poly(dA-dT)2 suggest that the binding geometry is essentially independent of the base sequence. The fluorescence lifetime of about 4 ns was attributed to the long-range assembly. In the case of P3 the distinctly different CD spectra induced by GC or AT base-pair regions reveal that the number of the substituents determines how closely the porphyrin can approach the specific electronic environment on the nucleic acid exterior. The fluorescence lifetime of the P3 assembly is about 2 ns.

Demethylation of tertiary amines by a reconstituted cytochrome P-450 enzyme system: kinetics of oxygen consumption and hydrogen peroxide formation.

Initial reaction rates of oxygen consumption and hydrogen peroxide formation in a cytochrome P-450 catalyzed reaction are practically independent of the nature of tertiary amines that were used as substrates. From the kinetic studies and the substrate conversion results that the amount of water formed in a side reaction is determined by the substrate specificity. Both hydrogen peroxide and water formation lower the efficiency of the monooxygenatic activity of cytochrome P-450.