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Photosynthetic light-harvesting (LH) systems consist of photosynthetic pigments, which are non-covalently self-assembled with protein scaffolds in many phototrophs and attain highly efficient excitation energy transfer via ultrafast dynamics. In this study, we constructed a biohybrid LH system composed of an LH complex (LH2) from Rhodoblastus acidophilus strain 10050 and a hydrophobic fluorophore ATTO647N (ATTO) as an extrinsic antenna in the lipid bilayer. Through the addition of ATTOs into a solution of LH2-reconstituted lipid vesicles, ATTOs were incorporated into the hydrophobic interior of the lipid bilayer to configure the non-covalently self-assembled biohybrid LH. Steady-state fluorescence spectroscopy clearly showed efficient energy transfer from ATTO to B850 bacteriochlorophylls in LH2. Femtosecond transient absorption spectroscopy revealed that the energy transfer took place in the time range of 3–13 ps, comparable to that of the covalently linked LH2-ATTO that we previously reported. In addition, the biohybrid LH system exhibited a much higher antenna effect than the LH2-ATTO system because of the higher loading level of ATTO in the membrane. These findings suggest that the facile self-assembled biohybrid LH system is a promising system for constructing LH for solar-energy conversion. [ABSTRACT FROM AUTHOR]

Phenol blue (PhB) is a dye that exhibits positive solvatochromism which is also nonfluorescent due to its ultrashort excited state lifetime. We have conducted femtosecond time‐resolved transient absorption (TA) spectroscopic measurements of a PhB solution using two distinct excitation wavelengths, at shorter and longer wavelength sides of the visible absorption band. The results revealed that a long‐lived heterogeneity exists in protic solvents whereas, in aprotic solvents, the system rapidly returns to the original thermal equilibrium on the ultrafast timescale. Interestingly, the lifetime of the heterogeneity is longer for methanol (MeOH) compared to ethanol (EtOH) solution suggesting stronger interaction between PhB and MeOH. Additionally, since the excited state lifetime of PhB was still in the sub‐picosecond domain even in a polymer matrix, we suggest a nonradiative decay mechanism through high‐frequency vibrational modes without involving large structural reconfiguration such as twisting of the benzoquinone (BzQ) moiety. [ABSTRACT FROM AUTHOR]

Coherent wavepacket oscillation accompanying the ultrafast photoexcited intramolecular charge separation (CS) of 9,9′-bianthryl (BA) and 10-cyano-9,9′-bianthryl (CBA) in a room temperature ionic liquid, N,N-diethyl-N-methyl-N-(methoxyethyl)ammonium tetrafluoroborate (DemeBF4), was investigated by femtosecond time-resolved transient absorption spectroscopy. The frequency of the coherent oscillation observed for CBA in nonpolar n-hexane solution (Hex) was 377 cm−1, while this oscillation was undetectable in DemeBF4. For BA in DemeBF4, coherent oscillation with a frequency of 394 cm−1 was observed, which is similar to that for CBA in Hex. CS of CBA occurs in the ultrashort time range of ≤100 fs, while that of BA occurs in a few picosecond range [E. Takeuchi et al., J. Phys. Chem. C 120, 14502–14512 (2016)]. Hence, the oscillation of CBA in Hex and that of BA in DemeBF4 are assigned to the molecular vibration in the locally excited state, while this oscillation dephases instantaneously for CBA in DemeBF4 due to the ultrafast CS and no oscillation was generated in the CS state. This result suggests that the CS reaction is not mediated by a specific intramolecular vibration in the CS state but occurs incoherently through higher levels of multiple vibrational modes. [ABSTRACT FROM AUTHOR]

A light-harvesting strategy is crucial for the utilisation of solar energy. In this study, we addressed the expanding light-harvesting (LH) wavelength of photosynthetic LH complex 2 (LH2, from Rhodoblastus acidophilus strain 10050) through covalent conjugation with extrinsic chromophores. To further understand the conjugation architecture and mechanism of excitation energy transfer (EET), we examined the effects of the linker length and spectral overlap integral between the emission and absorption spectra of the energy donor and acceptor pigments. In the former case, contrary to the intuition based on the Förster resonance energy transfer (FRET) theory, the observed energy transfer rate was similar regardless of the linker length, and the energy transfer efficiency increased with longer linkers. In the latter case, despite the energy transfer rate increases at higher spectral overlaps, it was quantitatively inconsistent with the FRET theory. The mechanism of EET beyond the FRET theory was discussed in terms of the higher-lying exciton state of B850, which mediates efficient EET despite the small spectral overlap. This systematic investigation provides insights for the development of efficient artificial photosynthetic systems. [ABSTRACT FROM AUTHOR]

Molar absorption coefficient of the lowest excited state is an indispensable information for the quantitative investigation of photochemical reactions by means of transient absorption spectroscopy. In the present work, we quantitatively estimated the molar absorption coefficients of the S1 state of the solute in three solution systems, Rhodamine B in ethanol, ZnTPP in DMF and N,N'-bis(2,6-diisopropylphenyl)terrylene-3,4,11,12-tetracarboxydiimide (TDI) in chloroform, by perfectly bleaching the ground state molecules using the picosecond 532-nm laser pulse with a large number of photons. These solution systems were selected because no obvious photodegradation was detected in the present range of the excitation intensity. The molar absorption coefficient obtained by this method was verified by the numerical analysis of the excitation intensity dependence of the transient absorbance by taking into account the inner filter effect (absorption of the excitation light by the S1 state produced by the leading part of the pump pulse) and the decrease of the ground state molecules by the pump process (depletion). In addition, these molar absorption coefficients were confirmed by the comparison of relations between the excitation intensity and the transient absorbance of the S1 state under the condition where the fraction of the excited solute is ≪ 10% by the femtosecond pulsed laser excitation. From these results, the error of the molar absorption coefficients was estimated to be < 5%. These values can be used as reference ones for the estimation of molar absorption coefficients of other systems leading to the quantitative elucidation of the photochemical reactions detected by the transient absorption spectroscopy. [ABSTRACT FROM AUTHOR]

Enhancing the light-harvesting potential of antenna components in a system of solar energy conversion is an important topic in the field of artificial photosynthesis. We constructed a biohybrid light-harvesting complex 2 (LH2) engineered from Rhodobacter sphaeroides IL106 strain. An artificial fluorophore Alexa Fluor 647 maleimide (A647) was attached to the LH2 bearing cysteine residue at the N-terminal region (LH2-NC) near B800 bacteriochlorophyll a (BChl) assembly. The A647-attached LH2-NC conjugate (LH2-NC-A647) preserved the integrity of the intrinsic chromophores, B800- and B850-BChls, and carotenoids. Femtosecond transient absorption spectroscopy revealed that the sequential energy transfer A647 → B800 → B850 occurs at time scale of 9–10 ps with monoexponential dynamics in micellar and lipid bilayer systems. A B800-removed conjugate (LH2-NC[B800(−)]-A647) exhibited a significant decrease in energy transfer efficiency in the micellar system; however, surprisingly, direct energy transfer from A647 to B850 was observed at a rate comparable to that for LH2-NC-A647. This result implies that the energy transfer pathway is modified after B800 removal. The results obtained suggested that a LH2 complex is a potential platform for construction of biohybrid light-harvesting materials with simple energy transfer dynamics through the site-selective attachment of the external antennae and the modifiable energy-funnelling pathway. [ABSTRACT FROM AUTHOR]

For photosynthetic organisms that nourish the earth's biosphere, chlorophylls (Chls) are the major pigments utilized for light harvesting and primary charge separation. Although Chl molecules are effective photosensitizers, they are inevitably phototoxic to living organisms due to the facile generation of highly oxidative singlet oxygen (1O2) through triplet energy transfer from their photoexcited states to oxygen molecules. Such phototoxicity of Chls is a major problem for translucent microbes that feed on photosynthetic algae. Recently, it has been reported that the metabolic conversion of Chls-a/b to 132,173-cyclopheophorbide-a/b enols (cPPB-a/bEs) is the detoxification mechanism for algivorous protists. cPPB-a/bEs are colored π-conjugated cyclic tetrapyrroles but are nonfluorescent due to efficient nonradiative decay. In this study, femtosecond time-resolved transient absorption spectroscopy was applied to cPPB-aE with the aim of understanding its quenching mechanism. As a result, we have captured the ultrafast generation of an intermediate state (∼140 fs) that leads to the rapid internal conversion to the ground state (∼450 fs). [ABSTRACT FROM AUTHOR]

Studies the temperature dependence of the optical dephasing mechanism in an organic polymer glass, polymethylmethacrylate. Measurement of transient grating and three pulse photon echo; Recording of the three pulse photon echo peak shift as a function of the temperature; Time constants revealed by the peak shift data.

Temperature dependence of intermolecular electron transfer (ET) between oxazine 1 (OX 1) in the excited state and electron donor solvents such as aniline (AN) and N,N-dimethylaniline (DMA) was studied by observing fluorescence dynamics of OX1. The fluorescence decay of OX1 in DMA showed a single exponential behavior with a time constant of ∼280 fs which was independent of temperature over the range of 280 to 353 K. In AN, the ET caused nonexponential fluorescence decay whose time constants range from a few hundred femtoseconds to a few picoseconds depending on temperature. The time constants of these ET were smaller than the solvation times obtained by dynamic fluorescence Stokes shift of coumarin 102. This indicates the importance of vibrational nuclear motion in ET. The extended Sumi–Marcus two-dimensional reaction coordinate model which concerns the effect of high frequency mode was applied to explain the experimental observations. Good agreements were obtained between the experiments and calculations in terms of necessary parameters such as electronic matrix element and solvent reorganization energy. The difference between the ET of OX1 in DMA and AN can be mainly explained by the free energy difference between the reactant and the product. [ABSTRACT FROM AUTHOR]

Molecular orbital calculations have shown that the structures of both trans and cis isomers of N,N’-disubstituted indigo dyes are considerably twisted about the central C=C bond. The twisting angle of the cis isomer is not always larger than that of the corresponding trans isomer, indicating that the large hypsochromic shift on the trans→cis isomerization of N,N’-disubstituted indigo dyes cannot be explained by the twisted structure of the cis isomer. It is shown that the hypsochromic shift can be ascribed to a larger contribution of the zwitterionic form to the resonance hybrid structure in the lowest excited singlet state S1 than in the ground state S0 .This makes the repulsion between the negative charges on the carbonyl oxygen atoms enhanced and the instability of the cis configuration compared to the trans configuration much larger in the S1 state than in the S0 state and leads to a larger vertical S1 ←S0 transition energy for the cis isomer than for the trans isomer. [ABSTRACT FROM AUTHOR]

Examines the influence of coupling strength and temperature on the solute-solvent interaction of chromophores in polymer glass. Use of three-pulse photon echo peak shift method; Description of different temperature sensitivities of the long-time peak shift; Presence of an ultrafast component in the transition frequency correlation function.

Discusses the use of the three pulse photon echo peak shift technique to study solvation dynamics in acetonitrile, methanol and ethylene glycol using the tricarbocyanine laser dye as a probe. Spectral density governing the solute-solvent interaction; Use of a simple dielectric continuum model and the dynamical mean spherical approximation.

Deuterium isotope effect on the solvation dynamics is observed in the system of aniline (AN) as a solvent for the first time by the dynamic Stokes shift method. Perdeuterated AN (AN–d7) or amino deuterated AN (AN–d2) shows slower solvation dynamics than normal AN. Deuterium effect on the solvation of N,N–dimethylaniline (DMA) is also studied and there is no isotope effect on the solvation process. The differences between AN and DMA are proposed to be related to the presence and absence of the intermolecular hydrogen bondings. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photoinduced intramolecular charge transfer (CT) dynamics of the asymmetric and symmetric molecules, 4-(9-anthryl)- N, N-dimethylaniline (ADMA) and 9,9′-bianthryl (BA), was investigated by means of time-resolved fluorescence (TRF) spectroscopy and compared with the solvation dynamics of coumarin 153 (C153) in several ionic liquids (ILs). The normalized dynamic Stokes shift (DSS) function for the CT state emission of ADMA in the sub-ns to ns time scale is almost the same as those of BA and C153 in most of the ILs studied, in spite of the much larger Stokes shift of ADMA compared to those of BA and C153. On the other hand, the contribution from ultrafast DSS within 30 ps, which was undetectable with the time resolution in the present study, was estimated to be smaller for BA than that for ADMA. Meanwhile, in phosphonium IL, the DSS in sub-ns to ns time range was solute dependent. This peculiarity in phosphonium IL is discussed from the viewpoint of the hierarchy of the solvation dynamics. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (ILs) are a new type of solvent with peculiar properties. ILs are usually composed of an anion and a bulky cation with one or more alkyl chains to decrease the melting point. These structural peculiarities lead to the high viscosity and the heterogeneity of ILs, which could affect chemical reactions. In the present perspective, we will first introduce the experimentally observed nature of the heterogeneous liquid structure and then introduce recent developments in the study on electron transfer (ET) and charge transfer (CT) reactions in relation with the solvation and the heterogeneity of ILs. Because of the high viscosity of ILs, diffusive solvation is expected to be slow which could be the rate-limiting factor for ET and CT processes. However, ILs could provide a unique reaction field depending on the location of the solute within the heterogeneous liquid structure and the reaction could be faster than that expected from the bulk viscosity due to the fast fluctuation of the local environment. [ABSTRACT FROM AUTHOR]

The photoinduced electron transfer properties of two photo-hydrogen-evolving molecular devices (PHEMDs) [(bpy)2Ru(ii)(phen-NHCO-bpy-R)Pt(ii)Cl2]2+ (i.e., condensation products of [Ru(bpy)2(5-amino-phen)]2+ and (4-carboxy-4′-R-bpy)PtCl2; bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline; RuPt-COOH for R = COOH and RuPt-CN for R = CN) were investigated. RuPt-CN demonstrates higher photocatalytic performance relative to RuPt-COOH arising from a larger driving force for the intramolecular photoinduced electron transfer (PET) associated with a stronger electron-withdrawing effect of R (ΔGPET = −0.43 eV for RuPt-CN and −0.16 eV for RuPt-COOH). This is the first study on PET events using ultrafast spectroscopy. Dramatic enhancement is achieved in the rate of PET in RuPt-CN (1.78 × 1010 s−1) relative to RuPt-COOH (3.1 × 109 s−1). For each system, the presence of three different conformers giving rise to three different PET rates is evidenced, which are also discussed with the DFT results. Formation of a charge-separated (CS) state [(bpy)2Ru(iii)(phen-NHCO-bpy−Ṗ-R)Pt(ii)Cl2]2+ in the sub-picosecond time regime and recombination in the picosecond time regime are characterized spectrophotometrically. The CS-state formation was found to compete with reductive quenching of the triplet excited state by EDTA whose dianionic form ion-pairs with dicationic RuPt-COOH. Thus, a key intermediate [(bpy)2Ru(ii)(phen-NHCO-bpy−Ṗ-R)Pt(ii)Cl2]+ (i.e., the one-electron-reduced species) prior to the H2 formation was found to be formed either via reduction of the CS state by EDTA or via formation of [(bpy)2Ru(ii)(phen−Ṗ-NHCO-bpy-R)Pt(ii)Cl2]+ by reductive quenching of the triplet excited state. More importantly, it is also shown that some of the conformers in solution possess a CS lifetime sufficiently long to drive hydrogen evolution from water. [ABSTRACT FROM AUTHOR]

Photoinduced charge separation processes of linear phenyleneethynylene derivatives (PEN) with different sequences of electron-withdrawing perfluorophenyl groups (A) and electron-donating phenyl groups (D) were investigated in an ionic liquid (IL), BmimTFSI, by picosecond time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopies. Very rapid photoinduced charge separation within 10 ps in AADD was followed by the stabilization of the charge-transfer (CT) state by the solvation, while the excited states in ADAD and ADDA were ascribable to the locally excited (LE) state. Equilibrium between the LE and CT states was established for DAAD with time constants of forward and backward processes much faster than the solvation time. The relative population of the CT state increases with time owing to the dynamic stabilization of the CT state by the solvation. The elementary charge separation process, the increase in the CT population, and their relation to the solvation time were discussed. [ABSTRACT FROM AUTHOR]

Ultrafast pump-probe measurement was applied to investigate the excited state deactivation dynamics of bisimidazolyl radical, 1,4-bis-(4,5-diphenylimidazol-2-ylidene)cyclohexa-2,5-diene (BDPI-2Y). BDPI-2Y is non-fluorescent and the recovery of the ground state took place in the time scale of femtoseconds to picoseconds, indicating a direct ultrafast nonradiative decay from the excited state. Coherent intermolecular vibrations were also observed and the low-frequency mode at 150 cm -1 and 128 cm -1 had a phase shift of ~ p compared to the mode at 290 cm -1 . [ABSTRACT FROM AUTHOR]

Abstract Background and Aim: Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the human gut. They frequently have gain-of-function mutations of the c-kit gene, which encodes a receptor, tyrosine kinase. The mutations were found at exon 11 in most cases, and either at exon 9 or at exon 13 in rare cases. Recently, we found a family with multiple GIST and a gain-of-function mutation at exon 17. The family was the first reported GIST case with c-kit gene mutation at exon 17 including sporadic GIST. Although we previously reported that the c-kit gene mutation at exon 17 was not detected in 124 sporadic GIST by single-strand conformation polymorphism (SSCP) analysis, the mutation at exon 17 observed in the familial GIST was detectable by the use of direct sequencing but not by our SSCP method. In the present study, we examined the mutations at exon 17 and exon 13 by using direct sequencing. Methods: Genomic DNA was extracted from formalin-fixed, paraffin-embedded GIST tissues. We could obtain 143 sporadic GIST cases appropriate for DNA analysis at exon 17 and 141 at exon 13. Exons 17 and 13 were amplified by using polymerase chain reaction and direct sequencing was conducted. Results: No mutation was found at exon 17, and only one case with the mutation at exon 13 was observed. The GIST with the mutation at exon 13 was large and showed frequent mitosis, and the patient died of the recurrent GIST 3 years after the first operation. Conclusion: The mutation at exons 17 or 13 was considered to be very rare in sporadic GIST. [ABSTRACT FROM AUTHOR]

The genetic mechanisms of carcinomas of the small intestine are not well understood. We report the results of analysis of genetic alterations in a case of small intestinal carcinoma. A tumor in the terminal ileum was resected in a 59-yr-old woman. Histologically, the tumor was classified as well-differentiated adenocarcinoma. We screened for genetic alterations in adenomatous polyposis coli (APC), β-catenin, K-ras, and p53 genes, as well as microsatellite instability, which are known to be involved in colorectal tumorigenesis. The tumor exhibited somatic interstitial deletion of 425-bp, which included the entire exon 3 in β-catenin gene. Immunohistochemical staining confirmed accumulation of aberrant β-catenin protein in the cytoplasm and nuclei of the malignant tissue. Furthermore, a frameshift mutation in the transforming growth factor β receptor type II gene with replication error phenotype was detected in the tumor DNA. In contrast, no genetic alterations were found in the APC, K-ras, and p53 genes. Our results suggested that both β-catenin gene mutation and replication error phenotype might contribute to carcinogenesis of the small intestinal tumor in our case. This is the first report that activation of β-catenin gene by somatic gene mutation is involved in the development of carcinoma of the small intestine. [ABSTRACT FROM AUTHOR]

Abstract We have isolated a human cDNA encoding a protein of 1288 amino acids that shows 77% identity in amino acid sequence to XCAP-C, Xenopus chromosome-associated polypeptide-C, belonging to the family of structural maintenance of chromosomes (SMC), which is known to play a crucial role in the proper condensation and segregation of mitotic chromosomes. In particular, an almost 200-amino-acid domain in the N-terminal, including an NTP-binding motif and that in the C-terminal domain, including a DA-box, were well conserved and showed 95% identity between human and frog, indicating that these two domains are functionally very important. The transcript of this gene was expressed ubiquitously in various human tissues, but thymus, testis, and colon seemed to express this gene more abundantly. We also determined its chromosomal location at 3q26.1 by fluorescence in situ hybridization. [ABSTRACT FROM AUTHOR]

Natural chlorophylls have a D-ring reduced chlorin π-system; however, no naturally occurring photosynthetically active B-ring reduced chlorins have been reported. Here we report a B-ring reduced chlorin, 17,18-didehydro-bacteriochlorophyll (BChl) a, produced by in situ oxidation of B800 bacteriochlorophyll (BChl) a in a light-harvesting protein LH2 from a purple photosynthetic bacterium Phaeospirillum molischianum. The regioselective oxidation of the B-ring of B800 BChl a is rationalized by its molecular orientation in the protein matrix. The formation of 17,18-didehydro-BChl a produced no change in the local structures and circular arrangement of the LH2 protein. The B-ring reduced 17,18-didehydro-BChl a functions as an energy donor in the LH2 protein. The photoactive B-ring reduced Chl isomer in LH2 will be helpful for understanding the photofunction and evolution of photosynthetic cyclic tetrapyrrole pigments. [ABSTRACT FROM AUTHOR]