Synthesis and absolute structure of manzacidin B

[reaction: see text] Four possible stereoisomers of manzacidin B were synthesized using stereochemically defined synthetic routes via the azide 7 and oxazoline 11 starting with the (R)-alpha-methyl Garner aldehyde 5. Comparisons of the spectroscopic data of the synthetic isomers 4a-d with those of the natural manzacidin B revised the proposed structure 3 to (4S,5S,6R)-4d.     

One-electron oxidation of alcohols by the 1,3,5-trimethoxybenzene radical cation in the excited state during two-color two-laser flash photolysis

One-electron oxidation of alcohols such as methanol, ethanol, and 2-propanol by 1,3,5-trimethoxybenzene radical cation (TMB*+) in the excited state (TMB*+*) was observed during the two-color two-laser flash photolysis. TMB*+ was formed by the photoinduced bimolecular electron-transfer reaction from TMB to 2,3,5,6-tetrachlorobenzoquinone (TCQ) in the triplet excited-state during the first 355-nm laser flash photolysis. Then, TMB*+* was generated from the selective excitation of TMB*+ during the second 532 nm laser flash photolysis. Hole transfer rate constants from TMB*+* to methanol, ethanol, and 2-propanol were calculated to be (5.2 +/- 0.5) x 10(10), (1.4 +/- 0.3) x 10(11), and (3.2 +/- 0.6) x 10(11) M-1 s-1, respectively. The order of the hole transfer rate constants is consistent with oxidation potentials of alcohol. Formation of TCQH radical (TCQH*) with a characteristic absorption peak at 435 nm was observed in the microsecond time scale, suggesting that deprotonation of the alcohol radical cation occurs after the hole transfer and that TCQ radical anion (TCQ*-), generated together with TMB*+ by the photoinduced electron-transfer reaction, reacts with H+ to give TCQH*.     

Intramolecular triplet energy transfer via higher triplet excited state during stepwise two-color two-laser irradiation

We studied the energy transfer processes in the molecular array consisting of pyrene (Py), biphenyl (Ph2), and bisphthalimidethiophene (ImT), (Py-Ph2)2-ImT, during two-color two-laser flash photolysis (2-LFP). The first laser irradiation predominantly generates ImT in the lowest triplet excited state (ImT(T1)) because of the efficient singlet energy transfer from Py in the lowest singlet excited state to ImT and, then, intersystem crossing of ImT. ImT(T1) was excited to the higher triplet excited state (Tn) with the second laser irradiation. Then, the triplet energy was rapidly transferred to Py via a two-step triplet energy transfer (TET) process through Ph2. The efficient generation of Py(T1) was suggested from the nanosecond-picosecond 2-LFP. The back-TET from Py(T1) to ImT was observed for several tens of microseconds after the second laser irradiation. The estimated intramolecular TET rate from Py(T1) to ImT was as slow as 3.1 x 104 s-1. Hence, long-lived Py(T1) was selectively and efficiently produced during the 2-LFP.     

Porphyrin light-harvesting arrays constructed in the recombinant tobacco mosaic virus scaffold

We have demonstrated the construction of multiple porphyrin arrays in the tobacco mosaic virus (TMV) supramolecular structures by self-assembly of recombinant TMV coat protein (TMVCP) monomers, in which Zn-coordinated porphyrin (ZnP) and free-base porphyrin (FbP) were site-selectively incorporated. The photophysical properties of porphyrin moieties incorporated in the TMV assemblies were also characterized. TMV-porphyrin conjugates employed as building blocks self-assembled into unique disk and rod structures under the proper conditions as similar to native TMV assemblies. The mixture of a ZnP donor and an FbP acceptor was packed in the TMV assembly and showed energy transfer and light-harvesting activity. The detailed photophysical properties of the arrayed porphyrins in the TMV assemblies were examined by time-resolved fluorescence spectroscopy, and the energy transfer rates were determined to be 3.1-6.4x10(9) s(-1). The results indicate that the porphyrins are placed at the expected positions in the TMV assemblies.     

C-O-bond cleavage of esters with a naphthyl group in the higher triplet excited state during two-color two-laser flash photolysis

A C-O-bond cleavage of esters having a naphthyl group, NpCO-OR and RCO-ONp (Np=alpha- and beta-naphthyl ((alpha)Np and (beta)Np, respectively), R=Ph and Me), was found during the two-color two-laser flash photolysis in acetonitrile. The C-O-bond cleavage occurred when NpCO-OR and RCO-ONp were excited to the singlet excited states (S1). On the other hand, no reaction occurred from the lowest triplet excited states (T1). When NpCO-OR(T1) and RCO-ONp(T1) were excited to the higher triplet excited states (Tn) using the second laser during the two-color two-laser flash photolysis, the C-O-bond cleavage occurred. The C-O-bond cleavage quantum yield (Phi) was estimated from the plots of the T1-state esters disappeared within a laser flash versus the second laser intensities. The C-O-bond cleavage in (beta)NpCO-OPh(Tn) occurred more efficiently than in (alpha)NpCO-OPh(Tn) and that in PhCO-O(beta)Np(Tn) occurred more efficiently than in PhCO-O(alpha)Np(Tn). The Phi value for ester with Ph and beta-Np groups was larger than that for ester with Ph and alpha-Np groups. The Phi value for MeCO-O(alpha)Np(Tn) was similar to those for PhCO-ONp(Tn), while that for MeCO-O(beta)Np(Tn) was much smaller than those for PhCO-ONp(Tn) and MeCO-O(alpha)Np(Tn). On the other hand, no C-O-bond cleavage was observed in NpCO-OMe(Tn). The Phi value depended on the characters of the groups (Np, Ph, and Me) on the ester. Whether R is Ph or Me with or without pi electron, respectively, is important for the C-O-bond cleavage. In other words, electronic delocalization of the T(n) state including Np and ester groups is necessary for the occurrence of the C-O-bond cleavage in NpCO-OR(Tn) and RCO-ONp(Tn).     

Electrochemically assisted visible light photocatalysis in a heterosupramolecular system consisting of alpha-Fe2O3 and surfactant molecular assembly

The synergy of an anodic-biased alpha-Fe2O3 film and a cationic surfactant molecular assembly leads to a high visible light induced activity for 2-naphthol oxidation and high stability. An abrupt increase in the photocatalytic activity at a surfactant concentration of ca. 0.2 mmol dm(-3) results from the adsolubilization of 2-naphthol into the hydrophobic nanospace of the surfactant bilayer formed on the alpha-Fe2O3 surface. Also, the surfactant bilayer provides sustainable photocurrent during the reaction.     

Superconvergence of finite difference approximations for convection–diffusion problems

An Erratum has been published for this article in Numerical Linear Algebra with Applications 8 (4) 2001, iii–iv. We are concerned with numerical solutions of convection–diffusion equations. The convergence behaviour of numerical solutions is considered by using the finite difference approximation with respect to spatial variables and implicit method with respect to time variable. It is shown that superconvergence occurs near a part of the boundary which has Dirichlet's data. Copyright © 2001 John Wiley & Sons, Ltd.     

用长气体靶研究22Na+α共振散射

在日本东京大学CRIB 次级束装置上,用长气体靶开展了22Na+ α共振散射的厚靶实验研究。针对长气体靶实验中的两体运动学重构问题,提出了一套包括构建空间复杂几何关系、计算能量损失以及反应运动学的逐事件分析方法;对22Na+α共振散射的实验数据进行了重构分析,得到了E_c.m. = 4.2 ~ 5.4 MeV 区间22Na( α,α ) 的激发函数,从实验的激发函数中观测到了复合核26Al 5 个较为明显的共振峰。鉴于26Al 共振态的衰变模式比较复杂,本工作发现的26Al新共振态的能级性质有待进一步的理论分析。The 22Na+α resonant scattering is studied via a conventional thick target inverse kinematic method with an extended gas target. A data analysis method is proposed for the two-body reaction kinematic reconstruction, in which the spatial geometry, the reaction kinematics and the energy losses are considered. The experimental data of 22Na+ αresonant scattering have been thus reconstructed, and the excitation function is obtained in the energy interval of Ec.m. =4.2~5.4 MeV. Five resonant states in 26Al are observed in the experimental excitation function. Since several decay modes coexist for the observed 26Al resonant states, multi-channel theoretical analysis is thus needed to reveal their structure and decay features.     

Efficient formation of giant liposomes through the gentle hydration of phosphatidylcholine films doped with sugar

Giant liposomes, or giant vesicles, are cell-size (approximately 5-100 microm) compartments enclosed with phospholipid bilayers, and have often been used in biological research. They are usually generated using hydration methods, "electroformation" and "gentle hydration (or natural swelling)", in which dry lamellar films of phospholipids are hydrated with aqueous solutions. In gentle hydration, however, giant liposomes are difficult to prepare from an electrostatically neutral phospholipid because lipid lamellae cannot repel each other. In this study, we demonstrate the efficient formation of giant liposomes using the gentle hydration of neutral phospholipid (dioleoyl phosphatidylcholine, DOPC) dry films doped with nonelectrolytic monosaccharides (glucose, mannose, and fructose). A mixture of DOPC and such a sugar in an organic solvent (chloroform/methanol) was evaporated to form the films, which were then hydrated with distilled water or Tris buffers containing sodium chloride. Under these conditions, giant liposomes spontaneously formed rapidly and assumed a swollen cell-sized spherical shape with low lamellarity, whereas giant liposomes from pure DOPC films had multilamellar lipid layers, miscellaneous shapes and smaller sizes. This observation indicates that giant unilamellar vesicles (GUVs) of DOPC can be obtained efficiently through the gentle hydration of sugar-containing lipid dry films because repulsion between lipid lamellae is enhanced by the osmosis induced by dissolved sugar.     

siRNA-mediated Knockdown of the Heme Synthesis and Degradation Pathways: Modulation of Treatment Effect of 5-Aminolevulinic Acid-based Photodynamic Therapy in Urothelial Cancer Cell Lines

Photodynamic therapy mediated by 5-aminolevulinic acid (ALA-PDT) has been developed as a therapeutic modality for refractory superficial bladder cancers. Here, in experiments using urothelial cancer cell lines, we investigated the effects of siRNA modulating heme-synthetic and degradation pathways for ALA-PDT. Targeted knockdown of ferrochelatase (FECH) suppressed heme synthesis and significantly increased intracellular protoporphyrin IX (PpIX) accumulation, leading to enhanced phototoxicity in four of five cell lines. Heme oxygenase-1 (HO-1) is recognized as important for cytoprotection against oxidative stress such as PDT. Targeted knockdown of HO-1 leads to decreased intracellular PpIX accumulation, resulting in a failure to enhance ALA-PDT effect in four cell lines. Knockdown of HO-1 caused marked growth inhibition in UM-UC-2 overexpressing HO-1, whereas no inhibitory effect was observed in UM-UC-3 lacking HO-1 expression. Moreover, HO-1 protein levels and (GT) _n repeat polymorphism of the HO-1 gene promoter region were examined with the implication that the constitutive expressions of HO-1 protein were associated with a shorter (GT) _n repeat. Our results suggested that (1) FECH siRNA improved the phototoxicity of ALA-PDT, (2) overexpression of HO-1 was associated with shorter (GT) _n repeat of the promoter region, and (3) siRNA-mediated knockdown of HO-1 could suppress the growth of bladder cancer cells overexpressing HO-1.