Comparative study of the water oxidizing reactions and the millisecond delayed chlorophyll fluorescence in photosystem II at different pH

Water splitting activity, the multiline EPR signal associated with S(2)-state of the CaMn(4)-cluster and the fast and slow phases of the induction curve of the millisecond delayed chlorophyll fluorescence from photosystem II (PSII) in the pH range of 4.5-8.5 were studied in the thylakoid membranes and purified PSII particles. It has been found that O(2) evolution and the multiline EPR signal were inhibited at acidic (pK approximately 5.3) and alkaline (pK approximately 8.1) pH values, and were maximal at pH 6.0-7.0. Our results indicate that the loss of O(2) evolution and the S(2)-state multiline EPR signal associated with the decrease of the millisecond delayed chlorophyll fluorescence only in alkaline region (pH 7.0-8.5). Possible correlations of the millisecond delayed chlorophyll fluorescence components with the donor side reactions in PSII are discussed.     

Medicinal flowers. XI. Structures of new dammarane-type triterpene diglycosides with hydroperoxide group from flower buds of Panax ginseng

Six new dammarane-type triterpene diglycosides with a hydroperoxide group, floralginsenosides A, B, C, D, E, and F, were isolated from ginseng flower, the flower buds of Panax ginseng C. A. MEYER, together with seven known dammarane-type triterpene oligoglycosides. The structures of new floralginsenosides were elucidated on the basis of chemical and physicochemical evidence.     

Metal patterning on silicon surface by site-selective electroless deposition through colloidal crystal templating

Site-selective Cu deposition on a Si substrate was achieved by a combination of colloidal crystal templating, hydrophobic treatment, and electroless plating. Uniformly sized nano/microstructures were produced on the substrate using a monolayer coating of colloidal spheres instead of a conventional resist. The Cu patterns obtained were of two different types: networklike honeycomb and isolated-island patterns with a minimum period of 200 nm. Each ordered pattern with the desired intervals was composed of clusters of Cu nanoparticles with a size range of 50-100 nm. By the present method, it is possible to control the periodicity of metal arrays by changing the diameter of the colloidal spheres used as an initial mask and to adjust the shape of the metal patterns by changing the mask structure for electroless plating.     

Photosensitized DNA damage and its protection via a novel mechanism

UVA, which accounts for approximately 95% of solar UV radiation, can cause mutations and skin cancer. Based mainly on the results of our study, this paper summarizes the mechanisms of UVA-induced DNA damage in the presence of various photosensitizers, and also proposes a new mechanism for its chemoprevention. UVA radiation induces DNA damage at the 5'-G of 5'-GG-3' sequence in double-stranded DNA through Type I mechanism, which involves electron transfer from guanine to activated photosensitizers. Endogenous sensitizers such as riboflavin and pterin derivatives and an exogenous sensitizer nalidixic acid mediate DNA photodamage via this mechanism. The major Type II mechanism involves the generation of singlet oxygen from photoactivated sensitizers, including hematoporphyrin and a fluoroquinolone antibacterial lomefloxacin, resulting in damage to guanines without preference for consecutive guanines. UVA also produces superoxide anion radical by an electron transfer from photoexcited sensitizers to oxygen (minor Type II mechanism), and DNA damage is induced by reactive species generated through the interaction of hydrogen peroxide with metal ions. The involvement of these mechanisms in UVA carcinogenesis is discussed. In addition, we found that xanthone derivatives inhibited DNA damage caused by photoexcited riboflavin via the quenching of its excited triplet state. It is thus considered that naturally occurring quenchers including xanthone derivatives may act as novel chemopreventive agents against photocarcinogenesis.     

Unidirectional crystallization of charged colloidal silica due to the diffusion of a base

Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix.     

Stimulated Raman scattering and four-wave Raman mixing seeded by a supercontinuum generated in dibromomethane using picosecond and femtosecond laser sources

Stimulated Raman emission from liquid dibromomethane (vibrational Raman shift frequency, 588 cm⁻¹) is introduced into hydrogen gas (rotational Raman shift frequency, 587 cm⁻¹) as a seed beam, in order to generate numerous rotational lines by four-wave Raman mixing. Unexpectedly, a supercontinuum, which is generated by self-phase modulation in dibromomethane, acted as a seed beam to exclusively generate vibrational lines; the rotational lines are generated only when the supercontinuum is minimal. The former is explained by a competition between the high-gain vibrational and low-gain rotational Raman effects when strongly seeded by a supercontinuum. The latter is explained by stimulated Raman gain under the seed effect exclusively to the first-Stokes rotational line.     

Thermal loss mechanism in the generation of multifrequency laser emission via stimulated Raman scattering and four-wave Raman mixing studied by photothermal refraction spectroscopy

The heat produced in conjunction with the processes of stimulated Raman scattering and four-wave Raman mixing in hydrogen was measured by photothermal refraction spectroscopy. Many vibrational, rotational, and vibrationally shifted rotational Raman lines are exclusively/simultaneously generated by changing the polarization of the laser beam and the hydrogen pressure. Thermal loss occurs predominantly from vibrational Raman scattering, which can be ascribed to a large Raman shift frequency of 4155 cm^-1 for the vibrational transition. In contrast to stimulated Raman scattering, little or no thermal loss is observable during the process of four-wave Raman mixing. Received: 12 April 1999 / Revised version: 12 July 1999 / Published online: 20 October 1999     

Guanine-specific DNA damage photosensitized by the dihydroxo(tetraphenylporphyrinato)antimony(V) complex

The dihydroxo(tetraphenylporphyrinato)antimony(V) complex (SbTPP) demonstrates bactericidal activity under visible-light irradiation. This phototoxic effect could be caused by photodamage to biomolecules, but the mechanism has not been well understood. In this study, to clarify the mechanism of phototoxicity by SbTPP, DNA damage photosensitized by SbTPP was examined using [(32)P]-5'-end-labeled DNA fragments. SbTPP induced markedly severe photodamage to single-stranded rather than to double-stranded DNA. Photo-irradiated SbTPP frequently caused DNA cleavage at the guanine residue of single-stranded DNA after Escherichia coli formamidopyrimidine-DNA glycosylase or piperidine treatment. HPLC measurement confirmed the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidation product of 2'-deoxyguanosine, and showed that the content of 8-oxodG in single-stranded DNA is larger than that in double-stranded DNA. The effects of scavengers of reactive oxygen species on DNA damage suggested the involvement of singlet oxygen. These results have shown that the mechanism via singlet oxygen formation mainly contributes to the phototoxicity of SbTPP. On the other hand, SbTPP induced DNA damage specifically at the underlined G of 5'-GG, 5'-GGG, and 5'-GGGG in double-stranded DNA. The sequence-specificity of DNA damage is quite similar to that induced by the type I photosensitizers, suggesting that photo-induced electron transfer slightly participates in the phototoxicity of SbTPP. In conclusion, SbTPP induces DNA photodamage via singlet oxygen formation and photo-induced electron transfer. A similar mechanism can damage other biomacromolecules, such as protein and the phospholipid membrane. The damage to biomacromolecules via these mechanisms may participate in the phototoxicity of SbTPP.     

Structure-activity relationships of neuromedin U. V. study on the stability of porcine neuromedin U-8 at the C-terminal asparagine amide under mild alkaline and acidic conditions

Porcine neuromedin U-8 (X-Asn-NH(2), X=H-Tyr-Phe-Leu-Phe-Arg-Pro-Arg) is occasionally unstable in the biological fluids used for bioassay as well as in the acidic solutions used for purification of synthetic peptides. In this study, HPLC examination of an incubate solution of X-Asn-NH(2) revealed that the main decomposition products in Tyrode's solution (pH 7.4) were either alpha- or beta-monocarboxylic acid analogs (X-Asn-OH or X-Asp-NH(2)), and that no dicarboxylic acid analog (X-Asp-OH) was produced. Further investigation, employing a model peptide (Y-Asn-NH(2), Y=Benzoyl-Pro-Arg) incubated in a 0.1 M sodium bicarbonate solution at 60 degrees C, revealed that the decomposition of C-terminal Asn-NH(2) occurred through the formation of an aminosuccinimide intermediate (Y-Asu), at a rate faster than that of Y-Asn-Ser peptide but slower than that of Y-Asn-Gly peptide. Mild acid hydrolysis of X-Asn-NH(2) examined in a 1 M HCl solution at 60 degrees C yielded X-Asn-OH and X-Asp-NH(2), which further decomposed to yield X-Asp-OH. The C-terminal degradation of X-Asn-NH(2) resulted in reduced biological and immunochemical binding activities.     

Targeting of sebocytes by aminolevulinic acid-dependent photosensitization

Photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX has been developed as a very useful therapeutic modality. Recently, several authors have reported on the efficacy of this procedure for acne. This approach is based on the fact that 5-aminolevulinic acid-induced protoporphyrin IX has strong selectivity for sebaceous glands. We used the immortalized human sebaceous gland cell line SZ95 to investigate cellular mechanisms of photodynamic therapy using 5-aminolevulinic acid-induced protoporphyrin IX. Quantification of induced protoporphyrin IX production showed dependence on the applied 5-aminolevulinic acid dose. When SZ95 sebocytes were differentiated by arachidonic acid treatment, there was no difference between them and the control cells with respect to both the amount of 5-aminolevulinic acid-induced protoporphyrin IX and the phototoxic effects. We altered protoporphyrin IX formation rates by growing cells scattered as single cells in the culture dishes. Single cells produced significantly lower protoporphyrin IX levels than those grown with intercellular contacts. Intracellular localization of protoporphyrin IX was imaged using confocal laser scanning microscopy. The differentiation-specific lipid droplets were virtually excluded from protoporphyrin IX fluorescence. In addition to weak mitochondrial and strong membrane fluorescence, distinctive spots with strong fluorescence were observed. These did not colocalize with fluorescent probes for mitochondria, lysosomes or the Golgi apparati.