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41.
Ben-Dror S Bronshtein I Wiehe A Röder B Senge MO Ehrenberg B 《Photochemistry and photobiology》2006,82(3):695-701
A crucial factor in choosing a porphyrin or analogous photosensitizer for photodynamic therapy (PDT) is its ability to incorporate into the cells. For hydrophobic compounds that partition passively into the cytoplasmic membrane, a partition coefficient between an organic solvent and water, P, is one factor that could be used to predict the molecule's ability to diffuse into biomembranes. We synthesized several porphyrins, modified with two, three or four meso-substituents and studied their spectroscopic and photophysical properties. The octanol-water partitioning coefficients, log P, were calculated as a parameter for hydrophobicity. We found these porphyrins to be very hydrophobic, with log P values in the range of 8.9-11.8. These were correlated with the binding constants of these porphyrins into liposomes, K(b), as well as to their uptake by cells. The correlation between the estimated log P and K(b) is nearly linear but negative, indicating, apparently, that there is lesser binding to liposomes with increased hydrophobicity. On the other hand, all of the studied porphyrins are taken up by cells, but there is no clear correlation between cellular uptake and the log P or K(b). Lipinski's pharmacological "rule of 5" predicts poor permeation of drugs into cells when log P is greater than five. This may be relevant for diffusional binding to liposomes, where aqueous aggregation can interfere strongly with cellular uptake. In such extreme conditions, neither liposome binding nor other rules seem to predict porphyrin behavior in vitro. 相似文献
42.
Evan R. Trivedi Benjamin J. Vesper Hana Weitman Benjamin Ehrenberg Anthony G.M. Barrett James A. Radosevich Brian M. Hoffman 《Photochemistry and photobiology》2010,86(2):410-417
We report the preparation of chiral oxygen atom-appended porphyrazines (pzs) as biomedical optical agents that absorb and emit in the near-IR wavelength range. These pzs take the form M[pz(A4-nBn)], where “A” and “B” represent moieties appended to the pz’s pyrrole entities, A = (2R,3R) 2,3-dimethyl-2,3-dimethoxy-1,4-diox-2-ene, B = β,β′-di-isopropoxybenzo, M is the incorporated metal ion (M = H2, Zn), and n = 0, 1, 2 (-cis/-trans) and 3 ( Scheme 1 ). When dissolved in polar media, H2[pz(trans-A2B2)] 5a does not fluoresce and has a negligible quantum yield for singlet oxygen generation (ФΔ = 0.074 ± 0.001, methanol), as measured by the photo-oxidation of DMA. However, when sequestered in the nonpolar environment of a liposome, it displays strong NIR emission (λ max = 705 nm, Ф f = 0.087) and an extremely high singlet oxygen quantum yield (ФΔ→1). Of this series, H2[pz(trans-A2B2)] 5a is attractive as a potential optical probe, showing strongly fluorescent uptake by cells in culture, while 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide measurements of cell viability show no evidence of dark toxicity. This agent does show significant photoinduced toxicity suggesting that pzs such as 5a have promise as “theranostic” optical agents that can be visualized with fluorescence imaging while acting as a sensitizer for photodynamic therapy.
43.
Leonid Roitman Benjamin Ehrenberg Yeshayahu Nitzan Vladimir Kral Jonathan L. Sessler 《Photochemistry and photobiology》1994,60(5):421-426
Abstract A spectroscopic and photophysical study of three new sapphyrin molecules is presented. The sapphyrin backbone that was derivatized to make them water soluble possesses an absorption band around 700 nm, a desired property for biological photosensitization. We studied the absorption and fluorescence spectra, from which evidence for aggregation in solvents of different polarities was obtained. The extent of aggregation is correlated with the nature of the attached moiety. The absolute quantum yields of singlet oxygen production were measured, with 1,3-diphenyl isobenzofuran as a model target, and were 0.13–0.18 in ethanol. The binding constants to liposomes and to cells were determined spectroscopically and were found to correspond to the hydrophobicities of the compounds, with an additional effect, ascribed to the sugar moiety, which was found in the case of one of the sapphyrins. The efficiency of photodamage to Staphylococcus aureus by sapphyrins and hematoporphyrin was equivalent, on the basis of cells killed per microgram of sensitizer in the incubation mixture. 相似文献
44.
The acid-base properties of Zn-hematoporphyrin IX (ZnHP) and Zn-mesoporphyrin IX (ZnMP) and the effect of pH on their binding to liposomes have been studied. The ionization constants for the two carboxylate groups of ZnHP were calculated by principal component analysis and are 5.7 +/- 0.1 and 6.9 +/- 0.05. The neutral species and the mono- and dianionic forms all bind to liposomes, but a strong pH effect on the binding constant was observed for both the investigated compounds. We also observed a decrease in the binding of the two anionic species when the membranes carried a negative charge. These results indicate that the porphyrins partition into the membrane with their carboxylic moieties near the lipid-water interface so that their deprotonation, leading to a charged molecule, does not prevent the insertion of the tetrapyrrole ring into the lipid environment of neutral liposomes. 相似文献
45.
Ni(NH3)Cl2 and Ni(NH3)Br2 were prepared by the reaction of Ni(NH3)2X2 with NiX2 at 350 °C in a steel autoclave. The crystal structures were determined by X‐ray powder diffraction using synchrotron radiation and refined by Rietveld methods. Ni(NH3)Cl2 and Ni(NH3)Br2 are isotypic and crystallize in the space group I2/m with Z = 8 and for Ni(NH3)Cl2: a = 14.8976(3) Å, b = 3.56251(6) Å, c = 13.9229(3) Å, β = 106.301(1)°; Ni(NH3)Br2: a = 15.5764(1) Å, b = 3.74346(3) Å, c = 14.4224(1) Å, β = 105.894(1)°. The crystal structures are built up by two crystallographically distinct but chemically mostly equivalent polymeric octahedra double chains [NiX3/3X2/2(NH3)] (X = Cl, Br) running along the short b‐axis. The octahedra NiX5NH3 share common edges therein. The crystal structures of the ammines Ni(NH3)mX2 with m = 1, 2, 6 can be derived from that of the halides NiX2 (X = Cl, Br) by successive fragmentation of its CdCl2 like layers by NH3. 相似文献
46.
The electrochemical behavior and structural changes of the positive electrode material LiCrMnO4 are studied for different end-of-charge voltages. A potentiostatic intermittent titration technique (PITT) experiment performed
up to 5.2 V shows three oxidative peaks. Cells charged to 4.88 V, which corresponds to the minimum between the second and
the third oxidative peak, show 89% of capacity retention for the 60th cycle. Compared to that only 23% of capacity are preserved
in the 60th cycle when the cell is charged to 5.2 V. The structural analysis by Rietveld refinement shows that for the former
case, the amount of structural defects is low and their formation is reversible, while the defect amount is significantly
higher for the latter case and the defect formation is only partially reversible.
Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007 相似文献
47.
In this minireview we will describe work where electron paramagnetic resonance spectroscopy has been used as the major methodology to identify and study the function of an amino acidbased free radical in enzyme function. For many redox processes in biochemistry the interplay between redox-active metal ions and free radicals turns out to be a recurring theme. Seen in this perspective, the enzyme we will describe here, ribonucleotide reductase, is related to several other important enzyme systems, including photosystem II. 相似文献
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