Rhus laccase catalysis and product characterization of 1,2-dimethoxyphenol in organic solutions

Dimethoxyphenol was a widely used substrate in determination of laccases activity. It was surprised, however, that the products of it had not been completely determined until now. Studies were thus conducted on Rhus laccase （RL） and immobilized Rhus laccase （IRL）-catalyzed oxidation of 2,6-dimethoxyphenol （DMP） in water-organic solvent systems. Only one product, 3,3′,5,5′- tetramethoxy-1 ,1′-biphenyl-4,4′-diol （TMBP）, was produced by RL catalysis, and it was thoroughly characterized by FT-IR, NMR and GC-MS, etc.     

Fluorescence up-conversion study of excitation energy transport dynamics in oligothiophene-fullerene linked dyads

Photoinduced excitation energy transport dynamics in oligothiophene-fullerene linked dyads, nT-C60 (n = 4, 8, and 12), have been investigated by femtosecond fluorescence up-conversion. In 8T-C60 and 12T-C60, each time profile of the fluorescence due to the 1nT* moiety consists of two components. The sub-picosecond component and a few picosecond components were experimentally evaluated depending on the lengths of oligothiophenes (n =8 and 12) and on the analyzing wavelength of the fluorescence. However, the time trace of the fluorescence due to 14T*-C60 decayed with a single short component in approximately 300 fs due to direct excited energy transfer (EET) from the 14T* moiety to the C60 moiety. On the basis of the kinetic models considering the short and long locally pi-conjugative thiophene segments in 8T-C60 and 12T-C60, the rate parameters of the elemental processes were evaluated. Sub-picosecond time constants of nT-C60 were found to be EET from the thiophene segment vicinal to the C60 moiety and intrachain energy transfer. Slower picosecond dynamics mainly corresponds to EET from the thiophene segments apart from the C60 moiety.     

Spectral assignments and anisotropy data of cellulose I(alpha): 13C-NMR chemical shift data of cellulose I(alpha) determined by INADEQUATE and RAI techniques applied to uniformly 13C-labeled bacterial celluloses of different Gluconacetobacter xylinus strains

Solid-state (13)C-NMR spectroscopy was used to characterize native cellulose pellicles from two strains of Gluconacetobacter xylinus (ATCC 53582, ATCC 23769), which had been statically cultivated in Hestrin-Schramm (HS) medium containing fully (13)C-labeled beta-D-glucose-U-(13)C(6) as the sole source of carbon. For both samples, the (13)C-NMR chemical shifts were completely assigned for each (13)C-labeled site of cellulose I(alpha) with the aid of 2D refocused INADEQUATE NMR. To determine the principal chemical shift tensor components, a pulse sequence based on the recoupling of anisotropy information (RAI) was applied at 10 kHz MAS. The detailed (13)C tensors of cellulose I(alpha) from different bacterial celluloses are thus available now for the first time, and these results have been compared with previously published data of nonenriched material and with theoretical predictions.     

Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4'-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.     

Raman spectroscopy shows interchain through space charge delocalization in a mixed valence oligothiophene cation and in its pi-dimeric biradicaloid dication

The vibrational Raman spectra of a decathiophene are provided in three relevant oxidations states: for the radical cation, its class III mixed valence system and its "frozen, -170 degrees C" class II MV analogue; for the dication, its singlet biradical pi-dimer and its "hot, +70 degrees C" magnetically active triplet excited state. Everything is compatible with interpentathiophene charge delocalization occurring at distances of 4-5 A similar to those found in the crystals of pi-stacked oligothiophenes. This stresses the interest of this spectroscopic tool for the analyses of electronic processes in crystals or in thin films of conjugated organic molecules.     

Control of aqueous droplets using magnetic and electrostatic forces

Basic control operations were successfully performed on an aqueous droplet using both magnetic and electrostatic forces. In our droplet-based microfluidics, magnetic beads were incorporated in an aqueous droplet as a force mediator. This report describes droplet anchoring and separation of the beads from the droplet using a combination of magnetic and electrostatic forces. When an aqueous droplet is placed in an oil-filled reservoir, the droplet sinks to the bottom, under which an electrode had been placed. The droplet was adsorbed (or anchored) to the bottom surface on the electrode when a DC voltage was applied to the electrode. The magnetic beads were removed with magnetic force after the droplet had been anchored. Surfactant addition into droplet solution was very effective for the elimination of electric charge, which resulted in the stable adsorption of a droplet to hydrophobic substrate under an applied voltage of DC 0.5-3 kV. In a sequential process, small volume of aqueous liquid was successfully transferred using both magnetic and electrostatic forces.     

Existing condition and migration property of ions in lithium electrolytes with ionic liquid solvent

Ionization conditions of each ionic species in lithium ionic liquid electrolytes, LiTFSI/BMI-TFSI and LiTFSI/BDMI-TFSI, were confirmed based on the diffusion coefficients of the species measured by the pulsed gradient spin-echo (PGSE) NMR technique. We found that the diffusion coefficient ratios of the cation and anion species D(Li)(obs)/D(F)(obs) of the lithium salt and D(H)(obs)/D(F)(obs) of the ionic liquid solvent were effective guides to evaluate the ionization condition responsible for their mobility. Lithium ions were found to be stabilized, forming the solvated species as Li(TFSI)3(2-). TFSI- anion coordination could be relaxed by the dispersion of silica to form a gel electrolyte, LiTFSI/BDMI-TFSI/silica. It is expected that the oxygen sites on the silica directly attract Li+, releasing the TFSI- coordination. The lithium species, loosing TFSI- anions, kept a random walk feature in the gel without the diffusion restriction attributed from the strong chemical and morphological effect as that in the gel with the polymer. We can conclude that the silica dispersion is a significant approach to provide the appropriate lithium ion condition as a charge-transporting species in the ionic liquid electrolytes.     

Lamellar structure in poly(ala-gly) determined by solid-state NMR and statistical mechanical calculations

Lamellar structure of poly(Ala-Gly) or (AG)n in the solid was examined using 13C solid-state NMR and statistical mechanical approaches. Two doubly labeled versions, [1-13C]Gly14[1-13C]Ala15- and [1-13C]Gly18[1-13C]Ala19 of (AG)15 were examined by two-dimensional (2D) 13C spin diffusion NMR in the solid state. In addition five doubly labeled [15N,13C]-versions of the same peptide, (AG) 15 and 15 versions labeled [3-13C] in each of the successive Ala residues were utilized for REDOR and 13C CP/MAS NMR measurements, respectively. The observed spin diffusion NMR spectra were consistent with a structure containing a combination of distorted beta-turns with a large distribution of the torsion angles and antiparallel beta-sheets. The relative proportion of the distorted beta-turn form was evaluated by examination of 13C CP/MAS NMR spectra of [3-13C]Ala-(AG)15. In addition, REDOR determinations showed five kinds of atomic distances between doubly labeled 13C and 15N nuclei which were also interpreted in terms of a combination of beta-sheets and beta-turns. Our statistical mechanical analysis is in excellent agreement with our Ala Cbeta 13C CP/MAS NMR data strongly suggesting that (AG)15 has a lamellar structure.     

High-field 1H MAS and 15N CP-MAS NMR studies of alanine tripeptides and oligomers: distinction of antiparallel and parallel beta-sheet structures and two crystallographically independent molecules

beta-Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) beta-sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H...O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used.