Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene.

Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

Interplay between intrachain and interchain interactions in semiconducting polymer assemblies: the HJ-aggregate model.

A new model for analyzing the photophysics of polymer aggregates is introduced taking into account exciton motion along a polymer chain and across polymer chains. Excitonic coupling and vibronic coupling are treated on equal footing using a Holstein-based Hamiltonian represented in a multi-particle basis set. In the HJ-aggregate model the competition between intrachain (through-bond) coupling leading to Wannier-Mott excitons, and interchain (through-space) coupling leading to Frenkel excitons, is studied in detail for two model dimers: one composed of red-phase polydiacetylene (PDA) chains and the other composed of regioregular P3HT chains. The resulting photophysical properties are shown to depend critically on the relative magnitudes of the intrachain and interchain exciton bandwidths. Dominant intraband (interband) coupling favors a photophysical response resembling J-aggregates (H-aggregates). In PDA dimers, where intrachain coupling prevails, the absorption spectrum is dominated by the 0-0 peak, as is characteristic of J-aggregates. The photoluminescence (PL) spectrum displays hybrid character: the ratio of the main (0-0) band to the first vibronic sideband intensities is initially zero at T = 0 K due to the forbidden nature of the 0-0 transition, but then increases with temperature in a manner characteristic of H-aggregates, peaking when kT ≈ ΔE, where ΔE is the interchain splitting. Further increases in temperature result in a decline of the PL ratio, as in a J-aggregate. This remarkable H to J transition is also predicted for the temperature dependence of the radiative decay rate, k(rad). The maximum (peak) rate scales as, k(rad) (max)∼(W(intra)/W(inter))(1/2), where W(intra) (W(inter)) is the intrachain (interchain) exciton bandwidth. Hence, when W(intra) is sufficiently larger than W(inter) the dimer displays thermally activated superradiance. In P3HT the intrachain coupling is far weaker than in PDA making the intrachain and interchain couplings comparable in the crystalline phase. Although the absorption spectral line shape is still well-accounted for by the conventional H-aggregate model, the photoluminescence is more sensitive, with H or J behavior tunable by changes in morphology. Long range intrachain order which coincides with weaker interchain interactions induces J-aggregate behavior, while short range intrachain order and the resulting stronger interchain coupling induces H-aggregate behavior. Our predictions neatly account for the H-like dominance exhibited by the PL from spin-cast films and the J-like dominance exhibited by the PL from highly ordered P3HT nanofibers self-assembled in toluene.

Absorption, circular dichroism, and photoluminescence in perylene diimide bichromophores: polarization-dependent H- and J-aggregate behavior.

Using a single-mode Holstein Hamiltonian with through-space excitonic couplings evaluated quantum mechanically, the absorption, circular dichroism, and photoluminescence spectral line shapes of a chiral perylene diimide dimer complex were accurately reproduced. In general, a dimer consisting of two chromophores related through a C(2) rotation is neither a J- nor an H-aggregate because oscillator strength is divided between the top and bottom of the exciton band. The division gives rise to the two Davydov components per vibronic band in the absorption spectrum. Nevertheless, it is shown that the vibronic structure of the absorption component polarized in the same direction as the lower (upper) Davydov component is identical to what one would obtain from an ideal J- (H-) aggregate. Emission generally contains both polarization components, but the component polarized in the same direction as the lower (upper) Davydov component behaves similarly to the emission from an ideal J- (H-) aggregate. The basic photophysical behavior also applies to molecular crystals containing two molecules per unit cell in which the interactions between inequivalent molecules dominate over interactions between equivalent molecules.

Vibronic coupling in quantum wires: applications to polydiacetylene.

A theory describing vibronic coupling in direct band gap, one-dimensional semiconductors is developed to account for the photophysical properties of isolated, defect-free conjugated polymers. A Holstein-like Hamiltonian represented in a multi-particle basis set is used to evaluate absorption and emission due to Wannier-Mott excitons. The photophysical properties of such quantum wires are shown to strongly resemble those of Frenkel exciton J-aggregates. The 1(1)B(u) exciton coherence length and effective mass are readily determined from the ratio of the 0-0 and 0-1 line strengths, I(0 - 0)/I(0 - 1), in the photoluminescence spectrum. I(0 - 0)/I(0 - 1) is shown to follow a T(-1/2) dependence, in an excellent agreement with experiments on the red-phase of polydiacteylene.

The nature of singlet excitons in oligoacene molecular crystals.

A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0-0) vibronic band of only -32 cm(-1), far smaller than the measured value of 631 cm(-1) and of the wrong sign-a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0-0 DS of 601 cm(-1) and a nearly quantitative reproduction of the relative spectral intensities of the 0-n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport.

Male death resulting from hybridization between subspecies of the gypsy moth, Lymantria dispar.

We explored the origin of all-female broods resulting from male death in a Hokkaido population of Lymantria dispar through genetic crosses based on the earlier experiments done by Goldschmidt and by testing for the presence of endosymbionts that are known to cause male killing in some insect species. The mitochondrial DNA haplotypes of the all-female broods in Hokkaido were different from those of normal Hokkaido females and were the same as those widely distributed in Asia, including Tokyo (TK). Goldschmidt obtained all-female broods through backcrossing, that is, F1 females obtained by a cross between TK females (L. dispar japonica) and Hokkaido males (L. dispar praeterea) mated with Hokkaido males. He also obtained all-male broods by mating Hokkaido females with TK males. Goldschmidt inferred that female- and male-determining factors were weakest in the Hokkaido subspecies and stronger in the Honshu (TK) subspecies. According to his theory, the females of all-female broods mated with Honshu males should produce normal sex-ratio broods, whereas weaker Hokkaido sexes would be expected to disappear in F1 or F2 generations after crossing with the Honshu subspecies. We confirmed both of Goldschmidt's results: in the case of all-female broods mated with Honshu males, normal sex-ratio broods were produced, but we obtained only all-female broods in the Goldschmidt backcross and obtained an all-male brood in the F1 generation of a Hokkaido female crossed with a TK male. We found no endosymbionts in all-female broods by 4,'6-diamidino-2-phenylindole (DAPI) staining. Therefore, the all-female broods observed in L. dispar are caused by some incompatibilities between Honshu and Hokkaido subspecies.

Requirement of voltage-dependent anion channel 2 for pro-apoptotic activity of Bax.

Mitochondrial membrane permeabilization is central to apoptotic signaling and is directly regulated by the Bcl-2 family of proteins, consisting of anti-apoptotic members and pro-apoptotic members, although the precise mechanisms involved remain elusive. When cells are deficient in both pro-apoptotic multidomain members of this family (Bax and Bak), mitochondrial membrane permeabilization does not occur in response to various apoptotic stimuli. We have previously reported that the voltage-dependent anion channel (VDAC or porin) plays a role in apoptotic mitochondrial membrane permeabilization by interacting with Bcl-2 family members. Here, we have provided additional evidence that VDAC2 is required for pro-apoptotic activity of Bax in the absence of Bak. In the absence of Bak, VDAC2-deficient cells showed strong resistance to various apoptotic stimuli, whereas re-introduction of the Vdac2 gene restored their apoptotic response. Consistently, silencing of VDAC2 in Bak-deficient cells, but not Bax-deficient cells, also conferred resistance to various apoptotic stimuli. In the absence of VDAC2 and Bak, the activation of Bax (assessed by mitochondrial membrane integration, conformational changes and oligomerization) was markedly impaired. Taken together, these findings indicate that VDAC2 is required for pro-apoptotic activity of Bax in the absence of Bak.

Heat island mitigation using water retentive pavement sprinkled with reclaimed wastewater.

In Japan, reclaimed wastewater has been recycled widely for non-potable urban applications and it is to be used for sprinkling roads to mitigate heat island in urban areas. To assess the heat island mitigation effects of the sprinkling reclaimed wastewater on water retentive pavement, we carried out a survey at Shiodome-District, Tokyo. The temperatures of air and roads, humidity, and WBGT (Wet-bulb globe temperature) were measured and heat flux was estimated to compare the condition of the areas with/without sprinkling. The following results were obtained. 1) Sprinkling reclaimed wastewater decreased the road surface temperature by 8 degrees during the daytime and by 3 degrees at night: temperatures equal to those on planting zones. Nevertheless sprinkling was done only in the daytime, the temperature decrease effect was not only obtained during the daytime: it continued through the night, due to the water retentive pavement. 2) Sprinkling reclaimed wastewater reduced the amount of sensible heat flux and increased that of latent heat flux. These results suggest that sprinkling reclaimed wastewater on water retentive pavement can effectively mitigate the heat island phenomenon.

Management of chemical substances in a water environment communicating among stakeholders.

With the implementation of Pollutant Discharge and Transfer Register (PRTR) in fiscal 2003, information on the quantity of chemical substances discharged annually from each business is released in Japan. Such information is expected to lead to heightened public concern about the presence of chemical substances in environment. This paper showed the effects of using PRTR data for managing chemical risk in a water environment communicating among stakeholders based on the results of the case study held in Japan. First, it was possible to identify the discharge sources using PRTR and related data for the chemicals such as Zn and NPs which were shown that they had relatively high risks based on the survey in a model area. Second, it was suggested that the chemical risk communication among the stakeholders including people using PRTR and related data would be a good way to encourage environmental activities of businesses, and to build a good relationship among stakeholders including people who have anxiety about chemical risk.

Identification of homozygous deletions of tumor suppressor gene FAT in oral cancer using CGH-array.

Homozygous deletions (HD) provide an important resource for identifying the location of candidate tumor suppressor genes. To identify the tumor suppressor gene in oral cancer, we employed high-resolution comparative genomic hybridization (CGH)-array analysis. We identified a homozygous loss of FAT (4q35), a new member of the human cadherin superfamily, from genome-wide screening of copy number alterations in one primary oral cancer. This result was evaluated by genomic polymerase chain reaction in 13 oral cancer cell lines and 20 primary oral cancers and Southern blot in the cell lines. We found frequent exonic HD of FAT in the cell lines (3/13, 23%) and in primary oral cancers (16/20, 80%). FAT expression was absent in these cell lines. Homozygous deletion hot spots were observed in exon 1 (9/20, 45%) and exon 4 (7/20, 35%). Moreover, loss of gene expression was identified in other types of squamous cell carcinoma. The methylation status of the FAT CpG island in squamous cell carcinomas correlated negatively with its expression. Our results identify mutations in FAT as an important factor in the development of oral cancer and indicate the importance of FATs function in some squamous cell carcinomas.

From critters to cancers: bridging comparative and clinical research on oxygen sensing, HIF signaling, and adaptations towards hypoxia.

The objective of this symposium at the First International Congress of Respiratory Biology (ICRB) was to enhance communication between comparative biologists and cancer researchers working on O(2) sensing via the HIF pathway. Representatives from both camps came together on August 13-16, 2006, in Bonn, Germany, to discuss molecular adaptations that occur after cells have been challenged by a reduced (hypoxia) or completely absent (anoxia) supply of oxygen. This brief "critters-to-cancer" survey discusses current projects and new directions aimed at improving understanding of hypoxic signaling and developing therapeutic interventions.

Risk evaluation for staphylococcal food poisoning in processed milk produced with skim milk powder.

The growth of S. aureus and the production of staphylococcal enterotoxin A (SEA) in skim milk concentrates stored at inappropriate temperatures in a recovery milk tank (tank for excess concentrated skim milk) used in the manufacture of skimmed milk powder were investigated. Also, it was estimated if a possible outbreak of food poisoning would occur if the contaminated skimmed milk powder was used in the manufacture of processed milk. Skim milk concentrates with milk solid content of 15, 25, and 35% were inoculated with S. aureus at 1-2 log CFU/ml and incubated at 15, 25, or 35 degrees C for 0 to 24 h with or without shaking. Bacterial growth and the level of SEA production were measured. At 35 degrees C with shaking, there was a significant difference (p<0.05) in one way layout analysis of variance, and it was demonstrated that the growth of S. aureus and SEA production could be milk solid content-dependent. Shaking accelerated the growth of S. aureus and SEA production at 35 degrees C. Generally, skim milk powder is produced by mixing a set percentage of skim milk concentrates (recovery milk) from the recovery milk tank into raw milk. If recovery milk contaminated with S. aureus at levels of 1-2 log CFU/ml is kept at 15 to 35 degrees C due to a power failure, it was estimated that processed milk consumption of 670-1200 ml, 420-1500 ml and 18-83 ml would trigger the onset of food poisoning symptoms when skim milk concentrates (recovery milk) are stored at 25 degrees C for 24 h, 35 degrees C for 10 h, and 35 degrees C for 24 h, respectively, during the production of the skim milk powder. Based on these consumption levels, it was concluded that, if recovery milk cannot be refrigerated and is stored at room temperature (25 to 35 degrees C), it must be used within 8 h and preferably within 6 h.

Comprehensive management of chemical substances in a water environment using PRTR data.

The annual quantity of discharge of 354 chemical substances from each business has been released based on PRTR law in Japan since 2003. MLIT and municipalities should be responsible for managing chemical risk in public water bodies through communication with stakeholders, such as the public and businesses. However, it is economically difficult to measure the discharge loads and behaviour of all chemical substances and reveal which substances should be particularly managed in each basin. NILIM has begun studies on survey methods to understand the discharge and behaviour of chemical substances in each basin based on PRTR information, and to conduct risk management of chemical substances in cooperation with stakeholders such as the public and businesses. We selected 30 chemical substances, such as those listed or nominated in environmental criteria and endocrine disrupters, collected the volume of discharge of chemical substances from public and industrial wastewater treatment plants using PRTR information, and surveyed their behaviour in the river in the model area. As a result, the discharge of 12 chemical substances were reported in PRTR, and 17 substances were detected in the river. Some inorganic compounds were detected intensively near discharge sites reported in the PRTR. But some organic compounds and endocrine disrupters, such as oestrone, were detected although their discharge was not reported in the model area in the PRTR. It suggested that PRTR information is useful to identify hot spots, but further study is needed to understand the discharge of chemical substances from small businesses, farmland and houses.

Incidence and prognosis of gastric cancer in a population-based cohort survey: the Hisayama study.

BACKGROUND: No population-based cohort studies have been undertaken to evaluate the incidence and prognosis of gastric cancer. The purpose of this investigation was to clarify the incidence and fatal prognosis of gastric cancer and to determine the factors that contribute to the prognosis in a general Japanese population in Hisayama using a prospective study design. METHODS: From 1988 to 1998 a total of 2605 subjects aged 40 years or older with no history of gastrectomy or gastric cancer were followed-up prospectively after a health examination. The diagnosis of gastric cancer was based on clinical records or autopsy findings. RESULTS: During the follow-up period, 76 subjects developed gastric cancer. The age-adjusted incidence of gastric cancer for men (4.9 per 1000 person-years) was 4-fold higher than that for women (1.2, P < 0.05). In men, the incidence of gastric cancer increased with advancing age, but this trend was not observed in women. The age- and sex-adjusted 5-year survival rate was significantly higher in cancers of the middle third of the stomach than in those of the upper third of the stomach. The survival rate was higher in cancers of well-differentiated adenocarcinoma than in those of the other histological types. There were no cases of cancer-related death among the early gastric cancers during the follow-up period. CONCLUSIONS: Our data suggest that men are at higher risk of gastric cancer than women in the general Japanese population. Clinical stage, histological type, and site of cancer in the stomach contribute to a fatal prognosis.

Comparison between ultrafiltration and trichloroacetic acid precipitation method for concentration of Staphylococcus aureus enterotoxin in dairy samples.

Staphylococcus aureus enterotoxin that may be contained at low concentrations in milk and dairy products can cause food poisoning. To detect this enterotoxin at low concentrations, samples should be concentrated. We evaluated the performance of centrifugal ultrafiltration method (UF) in comparison with trichloroacetic acid precipitation method (TCA) for the concentration of S. aureus enterotoxin in milk and dairy products. S. aureus enterotoxin A (SEA) were added at various concentrations to ultra high-temperature heating process (UHT) milk, UHT concentrated skim milk, UHT skim milk powder, low heat-treated (LH) skim milk powder, and raw milk. SEA was concentrated by TCA and UF once a day on a total of 3 days by different researchers to prepare test solutions. The fluorescence value (TV) of test solutions was determined using an immunofluorescence autoanalyzer (miniVIDAS), and the linearity and slope of the regression line, relative standard deviation (RSD(RW)) at each added concentration, detection limit (DL), quantification limit (QL), and the recovery rate by each concentration method were obtained according to the guidelines of the International Conference on Harmonization (ICH). The slope of the regression line obtained by UF was steeper than that by TCA for all dairy samples excluding LH (74 degrees C, 20 s) skim milk powder. RSDRW, DL, and QL obtained by UF were comparable to or more excellent than those obtained by TCA. The procedure of UF was simpler than that of TCA. The recovery rate and rapidity were similar between the two methods. The DL and QL of enterotoxins other than SEA in dairy products by UF or TCA were estimated based on the DL and QL of SEA. In this estimation, consideration was given to reactions between each enterotoxin and its antibody, and also to the immunoactivity maintenance rate of each enterotoxin after addition of trichloroacetic acid in TCA. The estimated values were similar to those obtained by experiments using enterotoxin C1 (SEC1). UF using a centrifugal ultrafiltration membrane can be more readily performed and similar to or more reliable than TCA. UF combined with a miniVIDAS can be used for quantitative routine analysis.

Two-domain hemoglobin gene of the water flea Moina macrocopa: duplication in the ancestral Cladocera, diversification, and loss of a bridge intron.

Two cDNAs encoding the two-domain hemoglobin (Hb) chains of a crustacean Cladocera, Moina macrocopa, were cloned and their nucleotide (nt) sequences were determined. The amino acid (aa) sequences of both the gene products deduced from the nt sequences consisted of 348 residues and showed 98% identity with each other. These sequences together with the NH(2)-terminal aa sequences of the Hb chains determined after separation by two-dimensional gel electrophoresis showed that the Hb chains are synthesized as a secretory precursor with a signal peptide of 17 aa residues. The aa sequences of M. macrocopa Hb chains shared the following features with those of Daphnia Hb chains. Firstly, the signal peptide is followed by an NH(2)-terminal extension containing a threonine-rich sequence that might play a role in the multimerization of subunit chains. Secondly, the identity between the aa sequences of the first and second domains is exceptionally low. These facts suggest that duplication of the cladoceran Hb gene occurred before the divergence of families Moinidae and Daphniidae. Analysis of genomic DNA showed that the M. macrocopa Hb genes consist of two large repeated regions, encoding the first and second domains of Hb chains, respectively. The intron-exon organization of the first region of the M. macrocopa Hb genes was similar to that found in the Daphnia Hb genes, having the three-exon, two-intron structure characteristic of animal Hb genes. However, the intron bridging the two regions and the most downstream intron in the second region were missing in the Moina genes, providing a new example of intron loss. The following elements in the 5' flanking region were conserved in the Moina and Daphnia genes: (1) TATAAA, a typical TATA box sequence accompanied by a downstream sequence, GAAXAGCATCAGTT (the fourth residue X was G or A in Daphnia and absent in Moina); (2) CCAAT boxes, located upstream of the TATA box; (3) the binding sites for HIF-1 and GATA-1, also located upstream of the TATA box, that may be responsible for up-regulation of the cladoceran Hb genes under hypoxia.

Characterization of the mutational specificity of DNA cross-linking mutagens by the Lac+ reversion assay with Escherichia coli.

The mutational specificities of DNA cross-linking compounds such as cisplatin, transplatin, carboplatin, mitomycin C, psoralen, and 8-methoxypsoralen were investigated in lacZ reversion assay systems of Escherichia coli. Tester strains were constructed by introducing the six kinds of F' plasmids (lacI-, lacZ461, and proAB+), each of which carries a different base-substitution mutation within the lacZ gene. Each of the six possible base-substitution mutations was assayed by Lac+ reversion. Cisplatin induced G.C-->A.T transitions and G.C-->T.A transversions, with the former predominating. Transplatin induced A.T-->G.C transitions in addition to G.C-->A.T transitions and G.C-->T.A. Carboplatin weakly induced G.C-->A.T transitions. On the other hand, mitomycin C induced only G.C-->T.A transversions, while psoralen and 8-methoxypsoralen reactivated with near-UV irradiation induced A.T-->G.C transitions preferentially. The Lac(+) reversion system was very convenient for rapidly determining mutational spectra.

Frequent loss of heterozygosity at 3p25-p26 is associated with invasive oral squamous cell carcinoma.

Recent molecular evidence suggests that allelic deletions of chromosomes are involved in the carcinogenesis of various neoplasms, including oral squamous cell carcinoma (OSCC). To determine the role of 3p deletions in Japanese OSCC and to define the localization of putative tumor suppressor genes, we initially examined loss of heterozygosity (LOH), using nine microsatellite markers in 36 OSCCs and 28 oral epithelial dysplastic lesions (OEDLs). LOH on chromosome 3p was observed at one or more loci in 72% of OSCCs and 18% of OEDLs. Fourteen (61%) of 23 OSCC patients informative at D3S2450 (3pter-p24.2) showed LOH most frequently, in contrast to OEDL, where LOH was never seen at this locus. Interestingly, we found a significant association between an allelic deletion at this locus and the histologic grade of mode of tumor invasion. Therefore, we also examined allelic deletion on chromosome 3p telomeric to where D3S2450 was located. A common deletion region was identified between D3S2450 and D3S3591. Our results provide evidence for the presence of a tumor suppressor gene in a 0.8-cM region bordered by D3S2450 and D3S3591 at 3p25-p26, which may play a role in carcinogenesis and invasion of OSCC.