PHOTOREDUCTION OF IRON(III)PORPHYRINS

Abstract— Ferrideuteroporphyrin in benzene, water or micelle solutions containing primary or secondary alcohols as well as in pure or basic 2-propanol solutions is clearly reduced to the ferrous state by continuous light irradiation in the Soret region. Quantum yields range between 4 × 10⁻⁴ and 3 × 10⁻² depending on the solvents used and on the coordination state of the ferric porphyrin. As inferred from laser pulse photolysis experiments, the primary chemical step appears to be the homolytic cleavage of the bond between the ferric ion and a coordinated alcoholate anion leading to the ferrous porphyrin and the alkoxy radical. This cleavage is found to occur within less than 50 ns. The alkoxy radical rearranges leading to the α-hydroxyalkyl radical which reacts with excess ferric porphyrin leading to further reduction. The reaction rate constant for the reaction of α-hydroxyisopropyl radicals is found to be k = (2.1 ± 0.3) × 10⁸ M ⁻¹ s⁻¹ in pure 2-propanol. As expected, this rate is greatly increased in basic 2-propanol where α-hydroxyisopropyl radicals deprotonate.     

PHOTOREDUCTION OF PORPHYRINS TO CHLORINS BY TERTIARY AMINES IN THE VISIBLE SPECTRAL RANGE. OPTICAL AND EPR STUDIES

Abstract— The photoreduction of free base porphyrins by tertiary amines in the visible spectral range leads to the formation of chlorin. The increase of the apparent first order rates to yield chlorin is correlated with the inductive effect on the nitrogen of the amine used. A mechanism involving a charge transfer interaction between the photoexcited singlet of the prophyrin and the amine is proposed. The porphyrin radicals formed recombine to form a light sensitive dimer which disproportionates in the dark to yield chlorin and porphyrin. The mechanism is elucidated by the use of EPR, laser and flash photolysis.     

LASER PHOTOLYSIS STUDIES OF SUPEROXIDE ADDUCTS OF COBALT(II) AND ZINC(II) PORPHYRINS IN DIMETHYLFORMAMIDE

Abstract— Photochemistry of superoxide adducts of cobalt(II) and zinc(II) porphyrins has been studied by laser photolysis. It was found that the former in dimethlformamide photodissociates the superoxide anion radical, O₂^-, with the quantum yield of 0.5 ± 0.05 at the excitation wavelenths 355 and 532 nm, and the latter gives flurescence and the triple state without giving rise to the photodissociation of O₂^-     

SINGLET OXYGEN GENERATION OF PORPHYRINS, CHLORINS, AND PHTHALOCYANINES

The production of singlet oxygen was measured indirectly for three classes of photosensitizers: porphyrins (Photofrin II, TPPS4), chlorins (MACE, DACE), and a phthalocyanine (CASPc). Buffered solutions of sensitizers and singlet oxygen acceptors were irradiated with a CW dye laser and the oxygen depletion was monitored electrochemically with a Clark-type microelectrode. A comparison of oxygen-depletion rate constants and quantum efficiencies yields the order of efficiency of the sensitizers: TPPS4 greater than MACE greater than PII greater than DACE greater than CASPc. For singlet oxygen acceptors the order was: furfuryl alcohol greater than imidazole greater than tryptophan. CHO cell suspensions were also used as acceptors. Here the order of efficiency (per absorbed photon) was PII greater than MACE approximately CASPc. Expressed in terms of oxygen depletion per cell the order was CASPc approximately PII greater than MACE. When performing cell clonogenicity studies the order of efficiencies, expressed as percentage cell kill per unit weight of sensitizer, was CASPc greater than PII greater than MACE approximately DACE. The discrepancy between the efficiencies of sensitizers to generate singlet oxygen and their cytotoxicity was explained in terms of photodegradation (for the chlorins), intracellular localization (for PII), and contributions from a Type I mechanism (for CASPc).     

PHOTOREDUCTION OF ZINC PORPHIN BY ASCORBIC ACID*

Abstract— Zinc porphin is photoreduced to zinc chlorin through an intermediate dihydroporphin (PH₂) by ascorbic acid in ethanol containing 1% to 10% (v/v) piperidine. Under the same conditions zinc chlorin is more slowly photoreduced to zinc tetrahydroporphin. The reactions leading to chlorin are photosensitized by the product chlorin and so are autocatalytic in red light. Quantum yields for these reactions range up to 0.05.Other aliphatic amines catalyze these reactions, but at rates peculiar to the amine. The immediate product of reduction of zinc porphin, PH₂, is distinguished by an intense band at 437 nm; it reverts to porphin in the dark in the presence of oxygen or dehydroascorbic acid. Its conversion to chlorin is effected by light absorbed by porphin or chlorin, but not by light absorbed by PH₂ itself. A suggested structure for PH₂, compatible with the observed reactions, has added hydrogens on one bridge carbon and one β-pyrrole carbon. The possibility of an analogy between these reactions and the biochemical conversion of protochlorophyll to chlorophyll is discussed.     

ZINC TETRAPHENYLPORPHYRIN-SENSITIZED PHOTOREDUCTION OF ANTHRAQUINONESULFONATE IN AQUEOUS MICELLAR SOLUTIONS*

Abstract— Zn-tetraphenylporphyrin (ZnTPP), solubilized in non-ionic surfactant micelles, was found to sensitize photoreductions of some sodium anthraquinonesulfonatesz in the presence of ascorbic acid under anaerobic conditions. The reaction rate was increased by the addition of an anionic surfactant, while retardation was observed with a cationic surfactant. The pH-reaction rate profiles showed maxima located in the order corresponding to pK_a-values for the semiquinone of each anthraquinone-sulfonate. A reaction scheme involving the formation of ZnTPP⁺ at the primary step, followed by back-reduction with ascorbic acid, is proposed. The reaction scheme is in good agreement with the results of flash photolysis. The surfactant micelles are suggested to aid the charge-separation between the ionic species just after the redox reaction involving the photoexcited ZnTPP and anthraquinonesulfonates.     

非对称取代卟啉锌、镉的生成反应动力学及动力学盐效应研究

本文报道应用停流方法对非对称取代卟啉［5-(4-乙酰氨基苯基)-10,15,20-三(4-甲基苯基)卟啉］(H₂T(p-CH₃)₃(p-NHCOCH₃)PP)与Zn(Ⅱ)、Cd(Ⅱ)在丙酮中的生成反应动力学进行了研究,提出了反应机理,并用非线性拟合和线性拟合的方法求得了生成反应各基元步骤的动力学参数,同时还探讨了温度,溶剂效应、动力学盐效应对反应体系的影响,并对锌、镉两种卟啉在生成机理及生成反应速率上的差异给予了解释。     

PHOTOREDUCTION OF NAD TO NADH IN SEMICONDUCTOR DISPERSIONS

Abstract— Band gap illumination of TiO₂ (anatase) dispersions in weakly alkaline solutions of nicotinamide-adenine-dinucleotide (NAD⁺) leads in the presence of rhodium trisbipyridyl complex [Rh(bipy)³⁺₃], to continuous generation of biologically active cofactor NADH. Effects of pH, NAD⁺ and Rh(bipy)³⁺₃ concentration on the efficiency of this photoconversion process are investigated. The reaction proceeds already in aqueous solution in the absence of external electron donors but it is enhanced significantly in the presence of 10% methanol.     

ENERGY RELAXATION MECHANISM IN Ni(II), Pd(II), Pt(II) and Zn(II) PORPHYRINS

Abstract—Picosecond absorption spectroscopy was used to determine the intramolecular energy relaxation processes occurring in Ni(II). Pd(II), Pt(II), and Zn(II) protoporphyrin IX dimethyl ester. Picosecond data on the rate of ground state repopulation and the kinetics of a transient intermediate made it possible to determine the lifetimes of the excited singlet state of Ni, Pd, and Zn porphyrins as 10±2ps, 19±3ps, and 2.6±0.5 ps, respectively, and<8 ps for Pt porphyrin. On the basis of these data. the nonfluorescent and nonphosphorescent property of Ni porphyrin can be interpreted in terms of internal conversion to a lower lying singlet d-d level which is not the case for the strongly phosphorescent Pd and Pt porphyrins.     

REACTIONS OF 1,3-OXAZOLIDINE-2-THIONE WITH ZINC(II), CADMIUM(II) AND MERCURY(II) HALIDES

Abstract

The reactivity of 1,3-oxazolidine-2-thione towards II B group metals is considered. Cadmium halides, mercury chloride and bromide react to give coordination compounds, whose stereochemistry is tentatively assigned by their i.r. spectra.

Otherwise zinc halides and mercury iodide induce a ring opening.     

THE CRYSTAL AND MOLECULAR STRUCTURE OF IODO(TRIETHYLENETETRAMINE) ZINC(II) IODIDE

Abstract

Crystals of [Zn(trien)I]I (trien=triethylenetetramine C₆N₄H₁₈) are orthorhombic. The space group is P2₁2₁2₁, with four molecules in the unit cell of dimensions a=11.97(1), b=13.72(1), c=8.12(1)Å. A total of 2029 independent reflections was measured with a Siemens A.E.D. automatic diffractometer using MoK_α radiation. The structure was refined by full-matrix least-squares to a conventional R factor of 0.041 for 1435 observed reflections. The coordination around the central zinc atom is square pyramidal with the zinc atom 0.71 Å above the plane of the four nitrogen atoms of the ligand molecule. The values of coordination bond lengths, Zn-N(prim) 2.13 Å, Zn-N(sec) 2.19 Å, Zn-I 2.59 Å fall all in the range expected for covalent bonds. The molecular structure is discussed in comparison with that of [Cu(trien)SCN]CNS.     

铁(Ⅲ)—邻菲罗啉溶液体系的光化学还原 Ⅱ.气相色谱法研究光化反应机理

关于Fe(Ⅲ)—邻菲罗啉(phen)溶液的光化学还原现象的记载可追溯到十九世纪末。本世纪以来,许多化学家用多种不同的方法对其进行了研究,但对其反应机理至今仍无定论。我们在前文研究的基础上,用气相色谱法(GC)对溶液体系光化反应后的气相组成进行了分析,并测定吸光度A_(510)值以及反应前后pH值的变化,从而推论在溶液中发生的反应。本文提出的关于光化反应是通过在溶液中形成的DAC(电子给予体—接受体配合物)来进行的假定,有待于用其他动力学方法加以研究。     

INCREASED QUANTUM YIELD OF PHOTOREDUCTION OF DYES (A CATALYTIC EFFECT)

Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet ³ TH ⁺ to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 10^2- M ) is added to thionine and azulene (3 × 10^-4 M ), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.
At very high ATU concentrations (≥ 10^-1 M ), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10^-4 M ).     

铁(Ⅲ)-邻菲罗啉溶液体系的光化学还原 Ⅱ.气相色谱法研究光化反应机理

关于Fe(Ⅲ)-邻菲罗啉(phen)溶液的光化学还原现象的记载可追溯到十九世纪末。     

SINGLET AND TRIPLET REACTIVITY IN THE PHOTOREDUCTION OF OXONINE(3,7-DIAMINOPHENOXAZIN-5-IUM CHLORIDE) BY IRON (II)

The oxazine dye, oxonine (3,7-diaminophenoxazin-5-ium chloride), 1, is photoreduced by Fe (II) sulfate in dilute sulfuric acid. The reaction mechanism is analogous to that for the photo-reduction of thiazine dyes by Fe (II), the most important difference being that reduction of oxonine occurs predominantly from its excited singlet state, S1, rather than from the triplet state, T1. The latter is formed with an intersystem crossing (isc) quantum yield of ca 1.7 x 10(-3). The quenching of S1 by Fe (II) has a rate constant kSQ = 2.2 +/- 0.1 x 10(9) M-1 s-1 and affords the one electron reduced product, semioxonine (R), with a limiting quantum yield, phi SR, of 0.26 +/- 0.02. In contrast, quenching of T1, generated by bromide ion quenching of S1 or by diacetyl sensitization, occurs with KTQ approximately 1.2 x 10(6) M-1 s-1, extrapolated to zero ionic strength, and affords R with a limiting probability, phi TR = 1.1 +/- 0.2. Three possible reasons for the lower quantum yield of the more exothermic S1 reduction are discussed. These are energy transfer from S1 to Fe (II), different rates of escape of R from the encounter complex as a consequence of the different states of protonation of R as initially formed from S1 and T1, and spin allowed back electron transfer in an exciplex formed between S1 and Fe (II). Evidence is also presented for a very low probability (ca 1%) induced isc from the encounter of S1 with paramagnetic Fe (II). Rate parameters for other processes important to the overall reduction mechanism such as disproportionation of R to leucooxonine L and oxonine, k(R)DIS = 1.7 +/- 0.2 x 10(9) M-1 s-1, oxidation of R by Fe (III), k(R)OX = 1.5 +/- 0.1 x 10(5) M-1 s-1, and oxidation of L by Fe (III), kLOX = 1.1 +/- 0.1 x 10(3) M-1 s-1, have also been measured. These results are contrasted with those for the closely related thionine/Fe(II) photoredox reaction, the most well understood system for photogalvanic energy conversion.     

ZINC(II), CADMIUM(II), MERCURY(II) AND LEAD(II) SEMIQUINONE-TYPE COMPLEXES OF A NEW SCHIFF-BASE LIGAND: ANTIBACTERIAL STUDIES

Abstract

A new Schiff-base ligand LH₂, has been prepared by reaction of 2,9-diformv 1-1,10-phenan-throline with 2,3-diamino-l,4-naphthoquinone. The formation and characterization of complexes of Zn(II), Cd(II), Hg(II) and Pb(II) with the semi-oxidized ligand LH is described. The M(LH)X₂ (X = CI, Br and AcO) radical species are paramagnetic and the observed EPR signals in the solid state at room temperature, with g values close to the electron free g value are proof of the semiquinonic character of the ligand. The antibacterial activity of the ligand and the metal complexes prepared were tested against four bacteria strains and compared with the activity of penicillin.     

四（烷硫基苯基）卟啉及其金属配合物的合成

某些人工合成的金属卟啉,由于其活化分子氧的功能,被广泛用作生物模拟氧化反应中的催化剂。金属四苯基卟啉及其衍生物是用得最普遍的模型化合物。文献中巳报道过各种四苯基卟啉衍生物的合成方法,但尚未见带烷硫基的四苯基卟啉衍生物的系统合成方法。本文报道这类四苯基卟啉衍生物及其金属配合物的合成。 本文采用通常的一步法合成四苯基卟啉衍生物,即首先参照文献方法合成烷硫基苯甲     

PHOTOPHYSICAL PROPERTIES OF meso-TETRAPHENYLPORPHYRIN and SOME meso-TETRA(HYDROXYPHENYL)PORPHYRINS

Abstract— The o-, m-, and p-isomers of 5, 10, 15, 20- tetra(hydroxyphenyl)-porphyrin have been of recent interest as potential second-generation sensitisers in tumour phototherapy. Fluorescence spectroscopy, nanosecond laser flash photolysis and pulse radiolysis have been used to characterise the singlet and triplet excited states of tetraphenylporphyrin and the o, m-, and p-isomers of tetra(hydroxyphenyl)porphyrin. This has included evaluation of fluorescence yields and lifetimes, triplet spectra, lifetimes, oxygen quenching rate constants, extinction coefficients, and yields and singlet oxygen yields. Whilst the fluorescence quantum yields were low, the triplet yields were all 0.7 ± 10% and the singlet oxygen yields 0.6 ± 10%: all these parameters are in the ranges shown by other efficient porphyrin photosensitisers. The similar photophysical properties found for these compounds suggest that their differing tumour sensitising efficiencies are likely to be due to other factors.