tetraphenylporphine and octaethylporphyrin

The ultrafast dynamics of copper tetraphenylporphyrin (CuTPP), copper octaethylporphyrin (CuOEP), and of the free base tetraphenylporphyrin (H2TPP), excited in the S2 state have been investigated in the gas phase by femtosecond pump/probe experiments. The porphyrins were excited in the Soret band at 400 nm. Strikingly, the S2-S1 internal conversion in H2TPP is very rapid (110 fs), as compared to that of ZnTPP (600 fs), previously observed. In turn, CuTPP and CuOEP, excited in S2, follow an efficient and different relaxation pathway from that of other open-shell metalloporphyrins. These two molecules exhibit a sequential four-step decay ending on a slow evolution in the nanosecond range (2)S2 → (2)CT → (2)T → (2)Ground State. This latter evolution is linked to the formation of the (2)T, tripdoublet state in CuTPP, observed in the condensed phase. It is shown that an intermediate charge transfer state plays a crucial role in linking the porphyrin centered (1)ππ* and (3)ππ* configurations. A simple model is presented that allows a rapid evolution between these two configurations, via coupling of the porphyrin π system with the free d electron on the copper. The mechanism obviates the need for the spin orbit coupling within the porphyrin. The result is that these copper porphyrins can exhibit an ultrafast apparent intersystem crossing, unprecedented for organic molecules.

Topics: Coordination Complexes; Copper; Electrons; Gases; Metalloporphyrins; Models, Chemical; Porphyrins; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Thermodynamics; Time Factors

In this work, the possibility of application of free base porphyrin as a lipophilic pH chromoionophore for the preparation of optical cation-selective sensors was investigated. The properties of polymeric membranes, containing porphyrins of different structures, namely tetraphenylporphyrin (TPP) and octaethylporphyrin (OEP), were compared. Changes in equilibrium between protonated and deprotonated form of porphyrin, resulting from variations in ACh concentration, were evaluated. The influence of various factors (kind and quantity of anionic additive and porphyrin in the membrane phase, pH of sample solution) on initial equilibrium was studied. The best membrane composition was chosen as: TPP 3 wt.%, KTFPB 175 mol.% relative to ionophore, PVC:o-NPOE (1 : 4) and measuring buffer solution: 0.05 M MES, pH 4.5. Selectivity, response stability, reversibility and repeatability tests were carried out for chosen sensor. Developed sensor allowed for the determination of a model analyte, acetylcholine, at the concentration range of 10(-5) to 10(-2) M, both in stationary and flow-injection system. Sensor response was reversible and repeatable in the mentioned concentration range.

Topics: Acetylcholine; Cations; Flow Injection Analysis; Hydrogen-Ion Concentration; Polyvinyl Chloride; Porphyrins; Spectrophotometry, Ultraviolet; Static Electricity

Photolyses of metastable porphyrin-iron(IV) diperchlorates in laser flash photolysis reactions gave highly reactive transients. The systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetramesitylporphyrin (TMP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP). The new species, which decayed within milliseconds in acetonitrile solutions, were shown to react with organic substrates by oxo-transfer reactions involving insertions into carbon-carbon double bonds of alkenes and styrenes or benzylic carbon-hydrogen bonds of arenes. The order of reactivity was OEP > TPP > TMP. Second-order rate constants for reactions with several substrates at 22 degrees C were determined; representative values of rate constants for the TPP derivative were k = 8.6 x 10(5) M(-1) s(-1) for styrene, k = 2.5 x 10(6) M(-1) s(-1) for cyclohexene, and k = 7.7 x 10(4) M(-1) s(-1) for ethylbenzene. These porphyrin-iron-oxo transients reacted 4-5 orders of magnitude faster than the corresponding iron(IV)-oxo porphyrin radical cations with rate constants similar to those of porphyrin-manganese(V)-oxo derivatives. Rate constants for oxidations of benzylic C-H positions of arenes correlated with the C-H bond dissociation energies, and Hammett correlations for reactions with substituted styrenes had rho(+) values ranging from -0.5 to -0.7, reflecting electrophilic character of the oxidants and their high reactivity. On the basis of their unique UV-visible spectra, high reactivities, and oxo-transfer properties, the new transients are tentatively identified as porphyrin-iron(V)-oxo perchlorates, electronic isomers (or valence tautomers) of well-known iron(IV)-oxo porphyrin radical cations.

Topics: Ferric Compounds; Heme; Iron Compounds; Kinetics; Metalloporphyrins; Oxidation-Reduction; Photolysis; Porphyrins; Reducing Agents; Spectrophotometry, Ultraviolet

The objective of this study is to investigate the solubilization of poorly water-soluble anticancer drugs, octaethylporphine (OEP), meso-tetraphenyl porphine (mTPP) and camptothecin (CPT), in Pluronic and polyethylene glycol-distearoylphosphatidylethanolamine (PEG-DSPE) polymeric micelles. Three different Pluronic and PEG-DSPE polymers with various chain lengths were chosen and micelle formulations were prepared by using various drug:polymer ratios. Formulations were characterized by critical micellization concentration (CMC) values of copolymers, micelle particle size and distribution, zeta potential, loading efficiency and stability. Polymers formed very stable, low CMC micelles with smaller sizes than 100 nm. It was shown that drug loading efficiency highly depends on the polymer type, drug type and their ratios. The most efficient drug loading was obtained by loading mTPP in PEG2000-DSPE and Pluronic F127 micelles. This result is attributed to phenyl groups in mTPP might lead to attraction between alkyl groups in the polymer and increase drug incorporation. PEG-DSPE formulations had higher zeta potential values indicating that they would be more stable against aggregation than Pluronic micelles. From the drug assay aspect Pluronic micelles remained more stable in 3-month long stability test. These results showed that besides their solubilizing effects, polymeric micelles could be useful as novel drug carriers for hydrophobic drugs.

Topics: Antineoplastic Agents; Camptothecin; Chemistry, Pharmaceutical; Drug Carriers; Drug Stability; Hydrophobic and Hydrophilic Interactions; Micelles; Particle Size; Phosphatidylethanolamines; Poloxamer; Polyethylene Glycols; Polymers; Porphyrins; Solubility; Structure-Activity Relationship; Time Factors