Open-loop and closed-loop control of dissociative ionization of ethanol in intense laser fields

The relative yield of the C-O bond breaking with respect to the C-C bond breaking in ethanol cation C2H5OH+ is maximized in intense laser fields (10(13)-10(15) Wcm2) by open-loop and closed-loop optimization procedures. In the open-loop optimization, a train of intense laser pulses are synthesized so that the temporal separation between the first and last pulses becomes 800 fs, and the number and width of the pulses within a train are systematically varied. When the duration of 800 fs is filled with laser fields by increasing the number of pulses or by stretching all pulses in a triple pulse train, the relative yield of the C-O bond breaking becomes significantly large. In the closed-loop optimization using a self-learning algorithm, the four dispersion coefficients or the phases of 128 frequency components of an intense laser pulse are adopted as optimized parameters. From these optimization experiments it is revealed that the yield ratio of the C-O bond breaking is maximized as far as the total duration of the intense laser field reaches as long as approximately 1 ps and that the intermittent disappearance of the laser field within a pulse does not affect the relative yields of the bond breaking pathways.     

Long-term observation of fluorescence of free single molecules to explore protein-folding energy landscapes

A method was developed to detect fluorescence intensity signals from single molecules diffusing freely in a capillary cell. A unique optical system based on a spherical mirror was designed to enable quantitative detection of the fluorescence intensity. Furthermore, "flow-and-stop" control of the sample can extend the observation time of single molecules to several seconds, which is more than 1000 times longer than the observation time available using a typical confocal method. We used this method to scrutinize the fluorescence time series of the labeled cytochrome c in the unfolded state. Time series analyses of the trajectories based on local equilibrium state analysis revealed dynamically differing substates on a millisecond time scale. This system presents a new avenue for experimental characterization of the protein-folding energy landscape.     

Glycine Substitution Effects on the Supramolecular Morphology and Rigidity of Cell-Adhesive Amphiphilic Peptides

Self-assembling peptides that are capable of adopting β-sheet structures can generate nanofibers that lead to hydrogel formation. Herein, to tune the supramolecular morphologies, mechanical properties, and stimuli responses of the hydrogels, we investigated glycine substitution in a β-sheet-forming amphiphilic peptide. Glycine substitution generally enhances conformational flexibility. Indeed, glycine substitution in an amphiphilic peptide weakened the hydrogels or even inhibited the gelation. However, unexpectedly, glycine substitution at the center of the peptide molecule significantly enhanced the hydrogel stiffness. The central glycine substitution affected the molecular packing and led to twisted β-sheet structures and to nanofiber bundling, which likely led to the stiffened hydrogel. Importantly, the supramolecular structures were accurately predicted by molecular dynamics simulations, demonstrating the helpfulness of these techniques for the identification of self-assembling peptides. The hydrogel formed by the amphiphilic peptide with the central glycine substitution had cell adhesive function, and showed a reversible thermal gel-to-sol transition. Thus, glycine substitution is effective in modulating self-assembling structures, rheological properties, and dynamics of biofunctional self-assembling peptides.     

Dual-Functional Mesoporous Copper(II) Metal-Organic Frameworks for the Remediation of Organic Dyes

By using tritopic and ditopic organic linkers derived from the same 2,4,6-triphenylpyridine core, copper(II) metal-organic frameworks with different three-dimensional structures have been successfully synthesized under ambient conditions. The crystalline framework, ^PTB MOF ([Cu₃(PTB)₂(H₂O)₃]_n, where H₃PTB=4,4′,4′′-(pyridine-2,4,6-triyl)tribenzoic acid, was observed to be mesoporous in nature and exhibited dual functionality in the removal of organic dyes. While cationic dyes such as methylene blue and malachite green, which are of different sizes, were adsorbed by ^PTB MOF ; anionic dyes such as tartrazine could be effectively degraded in a photo-Fenton-like reaction catalyzed by the MOFs under irradiation with visible light.     

Palladium-Catalyzed C–H Arylation of Benzofurans with Triarylantimony Difluorides for the Synthesis of 2-Arylbenzofurans

Pd-catalyzed regioselective C–H arylation is a useful tool for the chemical modification of aromatic heterocycles and 2-arylbenzofuran derivatives are of interest as biologically active substances. Herein, the reaction of triarylantimony difluorides with benzofurans under aerobic conditions in 1,2-DCE, using 5 mol% Pd (OAc)₂ and 2 eq. of CuCl₂ at 80 °C, produced a variety of 2-arylbenzofurans in moderate-to-high yields. The reaction is sensitive to the electronic nature of the substituents on the benzene ring of the triarylantimony difluorides: an electron-donating group showed higher reactivity than an electron-withdrawing group. Single crystal X-ray analysis of tri(p-methylphenyl) antimony difluoride revealed that the central antimony atom exhibits trigonal bipyramidal geometry.     

Constituents of regenerated plants of Ophiorrhiza pumila; formation of a new glycocamptothecin and predominant formation of (3R)-deoxypumiloside over (3S)-congener

The regeneration of plantlets was successful from Ophiorrhiza pumila callus cultures, from which a new glucosyloxy camptothecin, 9-β-glucosyloxycamptothecin, together with 15 metabolites including six camptothecin-related alkaloids was isolated. (3S)-Deoxypumiloside, one of the plausible biogenetic precursors of camptothecin, could not be found, whereas the (3R) epimer was isolated from the regenerated plants.     

An optical rotatory detector for high-performance liquid chromatography using polarization modulation.

A sensitive and variable-wavelength optical rotatory (OR) detector for high-performance liquid chromatography is presented. This design is entirely different from that of conventional OR detectors consisting of a crossed polarizer pair. By placing a polarizing prism and a retardation plate into a commercial circular dichroism (CD) detector, the OR signal was obtained. The Mueller matrix approach was used to prove the principle of the OR signal appearance. Sugars and 4-androstene-3,17-dione were chosen as test compounds. The limit of detection was below 0.5 microg of injected sucrose at 260 nm, which was superior to that obtained with a conventional OR detector. For 4-androstene-3,17-dione, which is CD active, and shows a large anomalous OR dispersion curve, our detector gave a large OR signal with approximately half the intensity of the CD signal at 340 nm.     

Demonstration of a recombined Fabry-Perot-Michelson interferometer with suspended mirrors

We describe preliminary experimental results concerning the operation of a 3 m arm-length Michelson interferometer with two Fabry-Perot cavities whose mirrors and beam splitter are suspended independently by wires. The reflected light beams from the two Fabry-Perot cavities are recombined to obtain interference at a photo-detector; this scheme is necessary for future power-recycled laser interferometers used to detect gravitational waves. The fundamental properties of the interferometer are presented, including the power spectral density of the displacement noise.     

Acyclic stereocontrol by heteroconjugate addition — 3 : Diastereoselective synthesis of either syn or anti diastereoisomer

A stereoselective synthesis of both syn- and anti-diastereoisomers (3 and 4) was established by a method involving heteroconjugate addition, as the key step, with various nucleophiles such as alkoxyvinyllithiums which can be functionalized after the addition. Two examples with aliphatic and carboxylic groups are demonstrated in high specificity.     

Synthesis and structural characterization of centrosymmetric multinuclear nickel(II) complexes with neutral tetradentate N6-ligand

A neutral tetradentate ligand L1 [L1?=?3,6-bis(pyrazol-1-yl)-pyridazine] reacts with Ni(ClO₄)₂·6H₂O and undergoes counterion exchange with PF ^?₆ to give di- and tetranuclear complexes [Ni₂(L1)₂(CH₃CN)₄](PF₆)₄·4H₂O (1) and [Ni₄(L1)₄(µ-OH)₄](ClO₄)₄·2H₂O (2), respectively. The presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base controls the nuclearity of the complex formation. Both complexes were structurally characterized by physicochemical and spectroscopic techniques. Their crystal structures revealed that both complexes are centrosymmetric and adopt slightly distorted octahedral geometry. Complex 1 crystallizes in monoclinic space group C2/c as the Ni(II) center is octahedrally bound to L1 in a trans-isomer arrangement. Complex 2 crystallizes in tetragonal space group I4₁/amd with four L1 and four hydroxy bridging ligands linked to Ni(II) center in cis-isomer arrangement. Cyclic voltammograms of complexes 1 and 2 were measured under Ar and CO₂. Under CO₂, the quasireversible peaks of both complexes become irreversible and a current enhancement occurs under reduction.