Showing papers by "Raymond Bonnett published in 1997"

Cleavage of (octaethyl-2,3-dihydroxychlorinato)nickel( II ) to give the novel 2,3-dioxo-2,3-secochlorin system

Abstract: Treatment of (octaethyl-2,3-dihydroxychlorinato)nickel(II) with lead tetraacetate in benzene causes cleavage of the 2–3 bond to give the nickel(II) 2,3-secochlorin-2,3-dione system 7, a previously unknown structural type. The structure is established by elemental analysis and spectroscopic methods, and confirmed by X-ray analysis. The dione gives a bis(2,4-dinitrophenylhydrazone). Treatment with base causes an aldol-type condensation to occur to give the (2-oxo-2a-homoporphyrinato)nickel(II) 8. This substance is rather unreactive, and it has not been possible to prepare carbonyl derivatives. This lack of reactivity is rationalised in terms of charge delocalisation which reduces carbonyl double-bond character. These novel pathways are discussed in relation to the known (and different) pathways of chlorophyll catabolism which have recently been uncovered.

Post-exposure processes in Temoporfin-photosensitized cells in vitro: reliance on energy metabolism.

Abstract: The progressive responses to photodynamic treatment (λ > 590 nm) mediated by Temoporfin have been investigated in vitro on two rodent cell lines: BHK and murine hepatoma MH22 cells. Comparisons are made of twoo light exposure/post-exposure incubation media: Dulbecco's minimal essential medium (DMEM) and phosphate-buffered saline (DPBS) depleted of energy sources. Enhancement of lipid peroxidation is an early response to Temoporfin photosensitization in either experimental set. It is restored to the initial level by subsequent incubation in DMEM, but not in DPBS. The decrease in MTT specific activity and especially lactate dehydrogenase leakage from the cells are faster in DPBS and continue to proceed during the post-exposure incubation in the both media. The intracellular ATP pool is completely depleted within 3 h of post-exposure incubation in DPBS, but not in DMEM where, in contrast, an initial increase in ATP is observed. Based on these preliminary observations, it is presumed that ATP synthesized by injured mitochondria and activated glycolysis is being used to restore the deteriorated cell functions and/or to allow reactions involved in apoptosis to proceed.

Immobilized photosensitizers: photosensitizer films with microbicidal effects

Abstract: The concept of the photodynamic surface is developed. Such surfaces are prepared by incorporating a suitable photosensitizer into a translucent thermoplastic polymer which can for subsequent evaluation and application be presented as a film, fiber, extrudate, molding or bead. The potential applications of such 'photosterile' materials in domestic, medical and industrial situations where it is desirable to maintain microbial populations at a low level are outlined. Polymer containing porphyrin and phthalocyanine sensitizers have been prepared by impregnation (dyeing), codissolution and casting, and copolymerization. Regenerated cellulose impregnated with 5,10,15,20-tetrakis(N- methylpyridinium)porphyrin tetra-p-tosylate has photobactericidal activity against S. aureus, E. coli., P. vulgaris and B. subtilis. The film retains both its mechanical strength and its photobactericidal properties after 50 h exposure to a xenon arc lamp. The effect is photobactericidal and not photobacteriostatic. A potential application in the development of safer domestic wiping cloths has been identified. The mechanisms of the microbicidal effect are considered to be (1) direct cell damage by singlet oxygen generated at the impregnated surface and diffusing to the microbial wall and/or (2) the controlled and slow release of the photosensitizer into solution and the microbial cell.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Gd-meso-tetraphenylporphyrins: synthesis, encapsulation into liposomes, and characterization of the resulting preparations

Abstract: POPC, DPPC/DMPC and POPC/OOPS liposomes containing gadolinium(III) meso-tetraphenylporphyrin and gadolinium(III) meso-tetra(4-pyridyl)porphyrin have been prepared by different techniques, their porphyrin and lipid contents have been evaluated, and the size and stability of the liposomes have been determined. The results show the influence of the method of preparation on the amount of Gd-porphyrin incorporated, and that of the lipid composition on the incorporation efficiency and stability of the Gd(III) porphyrin trapped in the liposomes, as well as the presence of strong lipid to porphyrin association at least in the case of the DPPC/DMPC liposomes.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Novel Chlorins with a δ-Lactone Ring Fused at Ring D.

Abstract: Reaction of purpurins ( 1a,b ) with DDQ resulted in oxidative ring closure at ring D to give novel δ-lactones ( 2a,b ), mild treatment of which with TFA/methanol gave chlorins ( 3a,b ) possessing a hydroxy group at C-18. Prolonged treatment of ( 3a,b ) with TFA resulted in their dehydration and the formation of porphyrins ( 4a,b ). © 1997 Elsevier Science Ltd.

Cleavage of (Octaethyl-2,3-dihydroxychlorinato)nickel(II) to Give the Novel 2,3-Dioxo-2,3-secochlorin System.

Abstract: Treatment of (octaethyl-2,3-dihydroxychlorinato)nickel(II) with lead tetraacetate in benzene causes cleavage of the 2–3 bond to give the nickel(II) 2,3-secochlorin-2,3-dione system 7, a previously unknown structural type. The structure is established by elemental analysis and spectroscopic methods, and confirmed by X-ray analysis. The dione gives a bis(2,4-dinitrophenylhydrazone). Treatment with base causes an aldol-type condensation to occur to give the (2-oxo-2a-homoporphyrinato)nickel(II) 8. This substance is rather unreactive, and it has not been possible to prepare carbonyl derivatives. This lack of reactivity is rationalised in terms of charge delocalisation which reduces carbonyl double-bond character. These novel pathways are discussed in relation to the known (and different) pathways of chlorophyll catabolism which have recently been uncovered.