LASER INTENSITY AND THE COMPARATIVE METHOD FOR DETERMINATION OF TRIPLET QUANTUM YIELDS

Abstract— In the comparative method of determining the triplet quantum yield ø_T by laser flash absorption spectroscopy, general equations are established (1) for describing the dependence of ø_T with laser intensity and (2) for absolute actionometry of a laser pulse. Applications to specific examples are discussed.     

THE TRIPLET AND RADICAL SPECIES OF HAEMATOPORPHYRIN AND SOME OF ITS DERIVATIVES

Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0 -acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).
After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φ_T= 0.92) and photoionises monophotonically (φ_I= 0.03). For the O -acyl derivatives, φ_T approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates ( k ₁˜10⁴s^-1) and oxygen quenching constants ( k _Q˜1.5times10⁹ M ^-1s^-1) for the triplet state have been measured. The difference and corrected spectra for the semi-reduced species in methanol and semi-oxidised species in aqueous Triton X-100 are presented.
The photophysical characteristics in fluid solution of haematoporphyrin and its 0 -acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.     

蒽醌衍生物在不同酸度溶液中的吸收光谱

蒽醌类化合物是一类古老的染料,对光和热非常稳定.某些蒽醌化合物还具有稳定的非晶态和晶态结构,在一定条件下可以进行相互转换,这种材料对强光具有非线性,有潜在的应用背景^[1].为此我们设计合成了两种新的蒽醌类化合物,测试了它们在溶液中的吸收光谱,研究了溶液酸碱性对吸收光谱的影响.     

TRIPLET LIFETIMES OF SOME FLAVINS

Abstract— Using flash photolysis the rate constants of the triplet decay at pH 7.0 (26°C) of 10-hydroxyethyl-isoalloxazine (2700 s⁻¹), 2'-deoxyRF (2300 s⁻¹), 5'-deoxyRF (3200 s⁻¹), 8-hydroxyRF (18 000 s⁻¹) and 8-aminoRF (28 000 s⁻¹) have been measured. The results agree with other evidence that photochemical properties of flavins are influenced by the interaction of the sidechain with the isoalloxazine nucleus. In addition, our data on RF and FMN indicate that the triplet decay rates given in the literature for these compounds have to be corrected to 3200 s⁻¹ (RF) and 4900 s⁻¹ (FMN), respectively. The rate constants for the quenching of the triplet by ground state molecules for all above compounds are given.     

ULTRAVIOLET QUANTUM YIELDS OF PHOTOPHOSPHORYLATION IN Halobacterium halobium*

Quantum yields of photophosphorylation in Halobacterium halobium were determined for ultraviolet spectral bands between 276 and 365 nm, and at 565 nm wavelength, based on integral spectral cell absorptance, bacteriorhodopsin-specific cell absorptance and the corresponding quantum dose rates. In the ultraviolet, there is an almost linear decline of the quantum yields of photophosphorylation from 365 to 276 nm wavelength, despite the peak absorption of bacteriorhodopsin at 280 nm. The cycling quantum yield for 276 nm excitation of bacteriorhodopsin was determined as 4.5 ± 1.8%, which is about one fourth of the value of 19% for solubilized bacteriorhodopsin. Threshold energy fluence rates of 20 W m^?2 for UV-B radiation typify the photophosphorylation as three orders less sensitive than the sensory UV-B avoidance response that needs 0.02 W m^?2 as the threshold. Thus, UV-B avoidance appears as the dominating strategy for survival of the archaic bacterium H. halobium, rather than possible photoenergetic use of UV-B radiation and photorepair of UV-damage.     

几个新型二茂铁衍生物的合成

二茂铁及其衍生物作为油类消烟剂、燃速催化剂等已得到应用,在药物、合成材料等方面亦具有应用前景。文献曾报道含二茂铁基β-二酮的合成及以它为配体的金属配合物。此类配合物均含两个以上金属原子,它们在有机合成中具有独特的催化活性。 我们将二茂铁甲酰丙酮分别与水扬酰肼、异菸肼、乙二胺及硫代氨基脲在甲醇或甲醇-水介质中进行缩合反应,合成了4个新型二茂铁衍生物,它们含有三个或四个配位功能基团,可作为多齿配体用于金属有机配合物的合成。衍生物的合成路线如下:     

IS SINGLET OXYGEN FORMATION DOMINANT IN TRIPLET QUENCHING PROCESSES? MEASUREMENT OF THE QUANTUM YIELD OF SINGLET OXYGEN FORMATION BY THE TIME-RESOLVED THERMAL LENS METHOD

The quantum yields of singlet oxygen formation (Ø_Δ) by the quenching of triplet states of organic sensitizers are measured at various concentrations of the sensitizers by using the time-resolved thermal lens method. Above a certain concentration, Ø_Δ is independent of the sensitizer concentration. Below the threshold, Ø_Δ gradually decreases as the concentration of the sensitizer decreases. The extrapolation of Ø_Δ to zero concentration indicates that singlet oxygen formation is not necessarily dominant in the quenching process even for the ³ππ* state in benzene.     

THE TRIPLET EXTINCTION COEFFICIENTS OF SOME BACTERIAL CAROTENOIDS

The extinction coefficients of the triplet states of the bacterial carotenoids, neurosporenc (Λ_max 489 nm). sphcroidene (Λ_max 510 nm). spheroidenone (Λ_max 550 nm) and spirilloxanthin (Λ_max 550 nm) in cyclohexane have been determined to be 27.4. 30.9. 6.06 and 9.20 × 10⁴ dm³ mol^?1 cm¹, respectively. These values were obtained by an energy transfer technique using a range of carotenoid concentrations. For the three that had been studied earlier, the extinctions now obtained are suhstantially higher than prcviously reported.     

PHOTOELECTRON QUANTUM YIELDS AND PHOTOELECTRON MICROSCOPY OF CHLOROPHYLL AND CHLOROPHYLLIN

Abstract— The absolute PE quantum yield curves of chls a and b ,.chin, and phytol were examined over the wavelength range 500-180 nm. In the long wavelength region (500-240 nm) quantum yields are below 5 × 10^-6 electrons per incident photon. Below 240 nm the quantum yields rise sharply. The chls and chin exhibit similar yield curves; measured yields were of order 5 × 10^-6 electrons per incident photon at 240 nm, 1 × 10^-4 at 220 nm, and 1 × 10^-3 at 180 nm. These yields are at least 2 orders of magnitude greater than those of the amino acids and more than three orders of magnitude greater than that of phytol over this wavelength region. Photoemission observed in chl thin films is due to the porphyrin moiety of the molecule. High contrast is obtained in PE micrographs of chin deposited on substrates of bovine serum albumin, dipalmitoyl phosphatidylcholine, or starch. Chl is expected to be the dominant photoemissive component of thylakoid membranes and accounts for the image contrast observed previously in PE micrographs of spinach chloroplasts.     

TRANSIENTS OF URACIL and THYMINE DERIVATIVES and THE QUANTUM YIELDS OF ELECTRON EJECTION and INTERSYSTEM CROSSING UPON 20 ns PHOTOLYSIS AT 248 nm

Transients of uracil and a series of 17 correlated pyrimidines, e.g. methylated bases, nucleosides, nucleotides, and polyuridylic acid [poly(U)] were studied after 248 nm excitation by 20 ns laser pulses. The transient absorption spectra in aqueous solution at room temperature reveal the triplet state and the hydrated electron (e-aq), while the corresponding radical cation could not be observed at pH 6-7. Fast loss of the chromophore in the 260-290 nm range within 0.1 microsecond was observed in aqueous solution in some cases [e.g. poly(U), 5'-UMP, uridine, uracil] and in others (thymine, thymidine) virtually not. This photobleaching is assigned to formation of the photohydrate. The concentration of e-aq shows a quadratic dependence on the laser pulse intensity (IL) in the range (0.2-2) x 10(7) W cm-2 and the quantum yield of electron ejection (phi c-) thus depends linearly on IL. This behaviour, suggesting that the photoionization involves a two-step absorption process, was found for poly(U) and all pyrimidine monomers examined. At a constant IL value of 2 x 10(7) W cm-2, phi c- ranges from 3 x 10(-3) for 1,3-dimethylthymine to 4 x 10(-2) for poly(U). The triplet state shows a much larger transient absorbance (delta A, typically in a broad range, e.g. 290-500 nm) than that of the neutral radical resulting from the radical cation. The triplet state in organic solvents (acetonitrile and ethanol) shows generally a significantly larger delta A value than in aqueous solution. The estimated quantum yields of intersystem crossing at room temperature are compared with those of phosphorescence at -196 degrees C.     

SOLVENT DEPENDENCE OF THE QUANTUM YIELD OF TRIPLET STATE PRODUCTION OF 9-PHENYLANTHRACENE

Abstract— Values of φ T , the quantum yield of triplet state production of 9-phenylanthracene, have been determined in four different solvents by measuring the effects which 'heavy atom quenchers' have on the fluorescence intensity and the triplet state absorption of the solute. A variety of quenchers have been used including organic and inorganic halides and the rare gas, Xenon. There is a converse solvent dependence of φ F and φ T , and for each of the four solvents used φ F +φ T has been found to be unity within experimental error.     

A METHOD FOR THE CORRECTION OF QUANTUM YIELDS OF FLUORESCENCE IN SOLUTIONS

Abstract— The correction factors due to the overlap of absorption and emission spectra have been calculated for various concentrations of fluorescein dye at pH 12 by using the experimentally obtained value of apparent molar absorptivity, ε₂, for the fluorescence radiation. The observed fluorescence intensities for the same-surface detection for a given geometry have been corrected for the secondary emission effect thus calculated, and also for refraction and dilution effects, to give corrected relative quantum yields for the solutions. These have been converted to the absolute values by comparison of the integrated fluorescence quantum spectrum of a dilute solution of fluorescein with that for quinine sulphate in 0.1 N H₂SO₄. The corrected quantum yields compare well with values given in the literature.     

SYNTHESIS OF SOME SULFUR-CONTAINING SPIROINDOLE DERIVATIVES

Abstract

The synthesis of some new sulfur-containing spiroindole derivatives is reported. Fluorinated 3′-aryl-2′-phenylimino-spiro[3H-indole-3,6′[4,5′-pyrazolin][4,3-d]thiazolo]2(1H)-ones were prepared by the reaction of 5-(2-oxo-3-indolinylidene)-3-aryl-2-phenylimino-4-thiazolidinones with hydrazine hydrate. The compounds have been characterized on the basis of elemental and spectral studies.     

APPARATUS FOR THE MEASUREMENT OF QUANTUM YIELDS AND RATES OF PHOTOCHEMICAL REACTIONS

Abstract— A versatile irradiation apparatus for the quantitative study of photochemical reactions is described, which incorporates a commercial monochromator and utilizes a calibrated thermopile for the continuous measurement of light absorption during irradiation. The operating characteristics are discussed, and illustrative applications are cited. Using this apparatus, the quantum yield of the potassium ferrioxalate actinometer at 366 nm and 25C was determined as 1.27 ± 0.01 for a 6.0 times 10^-3 M solution, in excellent agreement with reported values of 1.26.     

BIOLOGICAL PROPERTIES OF SOME BENZOPSORALEN DERIVATIVES

Abstract— The biological activity of some benzopsoralen derivatives, prepared with the aim of obtaining new drugs for photochemotherapy, has been studied. The more interesting compounds are 4-hydroxy-methyl-4',5'-benzopsoralen and 4-hydroxymethyl-4',5'-tetrahydro-benzopsoralen, which were found to be active in the dark also: DNA and RNA synthesis were both inhibited in Ehrlich cells, even if in a partially reversible fashion, while protein synthesis remained unaffected. In Chinese hamster ovary cells cultured in vitro , the clonal growth was strongly inhibited by incubation in the dark with both drugs, while a number of chromosomal aberrations was observed in the fraction of growing cells. Using alkaline elution, DNA strand breaks were detected. In addition, in the presence of aphidicolin, a specific inhibitor of DNA polymerase, the clonal growing capacity was completely restored; in contrast, the number of DNA strand breaks remained unchanged. All these results suggest that DNA topoisomerases are probably the target of these two benzopsoralens. These compounds are also good sensitizers; by UV-A irradiation they have a good capacity to produce singlet oxygen, but they appeared to be unable to induce erythemas on guinea-pig skin. Under UV-A light, they induced a strong inhibition of DNA synthesis in Ehrlich cells. Thus, benzopsoralens appear to be capable of inducing strong antiproliferative effects by two different mechanisms, by UV-A irradiation and in the dark.     

SENSITIZED TRIPLET FORMATION OF CHLOROPHYLL-A AND ß-CAROTENE

The naphthalene-sensitized formation of triplet excited chlorophyll-a (Chl-a) and all-transß-carotene has been studied by pulse radiolysis. The rate constants for transfer of triplet energy from naphthalene to Chl-a and all-transß-carotene in benzene at 25°C are (3.6 ± 0.6)·10⁹M^-1 s^-1 and (10.7 ± 1.2)·10⁹M^-1 s^-1, respectively. The decays of the excited triplet states of naphthalene, Chl-a and all-transß-carotene all follow a mixed first-and second-order mechanism. The first-order rate constant for triplet decay is strongly dose dependent for naphthalene but only slightly dependent and independent of dose for Chl-a and all-transß-carotene, respectively. The rate constants for triplet-triplet annihilation are (1.4 ± 0.3)·10⁹M^-1 s^-1 for Chl-a and (3.6 ± 0.4)·10⁹M^-1 s^-1 for all-transß carotene. The nearly constant ratio k(ß-carotene)/k(Chl-a) for the bimolecular triplet energy transfer rate constants is discussed in terms of the molecular shapes of the two molecules. The energetics of the triplet-triplet annihilation of all-transß-carotene are discussed, and it is proposed that production of the excited ¹A_B state may be a major route in the annihilation process.     

QUANTUM YIELD OF SINGLET OXYGEN PRODUCTION BY XANTHENE DERIVATIVES

The singlet oxygen quantum yield (φ₁o₂) of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents φ₁o₂ was enhanced with increasing halogenation. Tryptophan and 2,2,6,6-tetramethylpiperidone were found to be unadapted for the determination of φ₁o₂, in our systems; however, the use of 9.10-dipropionic anthracene acid andp-nitrosodimethylaniline in conjunction with imidazole derivatives was suitable for ¹O₂ detection in water. Both methods lead to results in excellent agreement. As in ethanol. φ₁o₂, was equal to the triplet state quantum yield (φ_T), the comparison between the two solvents showed that φ_T in water was greater than in ethanol. The comparison between our values obtained with polychromatic light with published data obtained with monochromatic light suggests that the triplet quantum yield of fluorescein derivatives is wavelength independent.     

ACTINOMETRY IN MONOCHROMATIC FLASH PHOTOLYSIS: THE EXTINCTION COEFFICIENT OF TRIPLET BENZOPHENONE AND QUANTUM YIELD OF TRIPLET ZINC TETRAPHENYL PORPHYRIN

Abstract— The extinction coefficient ε_T, of triplet benzophenone in benzene has been directly determined by absolute measurements of absorbed energy and triplet absorbance, Δ D ⁰_T, under demonstrably linear conditions where incident excitation energy, E ₀, and ground state absorbance, A ₀, are both extrapolated to zero. The result, 7220 ± 320 M ^-1 cm^-1 at 530 nm, validates and slightly corrects many measurements relative to benzophenone of triplet extinction coefficients made by the energy transfer technique, and of triplet yields obtained by the comparative method.
As E ₀ and A ₀ both decrease, Δ D ⁰_T becomes proportional to their product. In this situation, the ratio R = (1/ A ₀)(dΔ D ⁰_T/d E ₀) = (ε_T - ε_G)φ_T. Measurements of R , referred to benzophenone, give (ε_T - ε_G)φ_T for any substance, without necessity for absolute energy calibration.
Both absolute and relative laser flash measurements on zinc tetraphenyl porphyrin (ε_T - ε_G at 470 nm = 7.3 × 10⁴ M ^-1 cm^-1) give φ_T= 0.83 ± 0.04.