Michel Rougée

Hinding of imidazole and 2-methylimidazole by hemes in organic solvents. Evidence for five-coordination

Abstract By means of absorption spectroscopy we show that in benzene solutions, only one molecule of 2-methylimidazole is bound with a great affinity by deuteroheme (K = 1.25 10 4 M −1 ) and mesotetraphenylheme (K = 2.4 10 4 M −1 ). Besides, two overlapping steps may be distinguished when hemes bind imidazole molecules. The equilibrium constants are K 1 = 4.5 10 3 M −1 and 8.8 10 3 M −1 , K 2 = 6.8 10 4 M −1 and 7.9 10 4 M −1 for deuteroheme and mesotetraphenylheme respectively.

PHOTOPHYSICAL PROPERTIES OF 2‐NITRO‐5,10,15,20‐TETRA‐p‐TOLYLPORPHYRINS

Abstract— Tetraarylporphyrins substituted with nitro groups at fipyrrolic positions are potential candidates for electron‐accepting pigments in model systems for photosynthesis. The photophysics of 2‐nitro‐5,10,15,20‐tetra‐p‐tolylporphyrin and its zinc analog have been studied in order to evaluate this potential. The ground state absorption spectrum, the triplet‐triplet absorption spectrum, the fluorescence emission spectrum, and associated photophysical parameters have been determined. The molecules have short singlet lifetimes and anomalous temperature‐ and solvent‐dependent emission spectra which are consistent with the formation of an intramolecular charge transfer state of the type P+ ‐NO2; in which the nitro group is twisted about its bond to the porphyrin, relative to the ground state conformation.

Fluorescence energy transfer between dimethyldiazaperopyrenium dication and ethidium intercalated in poly d(A-T).

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double‐stranded polynucleotide such as poly d(A‐T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double‐stranded polynucleotide.

Mechanism of action in a 4,5-diarylpyrrole series of selective cyclo-oxygenase-2 inhibitors.

Using semi-empirical AM1 calculation and 6.31G* basis sets, we have calculated the energy of the highest-occupied molecular orbital (E(HOMO)) for anti-inflammatory 4,5-diarylpyrroles which have been shown to have inhibitory activity on cyclooxygenase COX-2, an inducible enzyme expressed during inflammation. We have found a correlation between the E(HOMO) of a molecule and its COX-2 inhibition. However, no correlation was observed between E(HOMO) and the inhibition efficiency of cyclooxygenase-1 (COX-1), the constitutively expressed enzyme, protective to the organism. This result suggests that the inhibitions of the two isoforms follow different molecular mechanisms.

Reaction of carbon tetrachloride with 5,10,15,20-tetraphenyl-porphinatoiron(II)[(TPP)FeII]: evidence for the formation of the carbene complex [(TPP)FeII(CCl2)]

The reaction of 5,10,15,20-tetraphenylporphinatoiron(II)[(TPP)FeII] with carbon tetrachloride in the presence of an excess of reducing agent leads to a complex having properties consistent with the carbene, :CCl2, bound to FeII; this is believed to be the first example of a carbene complex of a metalloporphyrin.