Simulation of the optical properties of Tm:ZBLAN glass. II. Energy transfer between Tm ions under single- and dual-wavelength excitation

The energy transfer rate between Tm³⁺ ions in ZBLAN glass was estimated from the optical spectra and transition rates on the basis of a method proposed by Kushida. The optical spectra and radiative transition rates were obtained from the structural models prepared by molecular dynamic simulation and the crystal field theory. The lifetimes of ³H₄, ¹G₄ and ¹D₂ levels were estimated from the calculation and the results were experimentally confirmed. The numerical model was also used to predict emission intensities under dual-wavelength excitation and decay curves under CW excitation.     

Synthesis of biladienone and bilatrienone by coupled oxidation of tetraarylporphyrins

Tetraarylbiladien-ab-ones bearing various substituents (R) in the para position of the phenyl groups were preprared by coupled oxidation of tetraarylporphyrin iron complexes. The yields of 5,10,15-triaryl-19-aroyl-15-hydroxybiladien-ab-ones were 74% (R=H), 85% (R=OMe), 44% (R=COOMe), and 28% (R=CN). Kinetic studies of the iron porphyrin oxidation revealed that the reaction is accelerated by an electron-withdrawing substituent with the Hammett reaction constant rho=0.295. 5,10,15-Triaryl-19-aroyl-15-hydroxybiladien-ab-ones undergo the acid-catalyzed elimination reaction either by acetic acid or by mesoporous silica to afford 5,10,15-triaryl-19-aroylbilatrien-abc-one. The elimination reaction in acetic acid is accelerated by an electron-donating substituent with the Hammett reaction constant rho=-1.48.     

A pH-responsive carboxylic β-1,3-glucan polysaccharide for complexation with polymeric guests

The helix-forming nature of β-1,3-glucan polysaccharides is a characteristic that has potential for producing gene carriers, bio-nanomaterials and other chiral nanowires. Herein, carboxylic curdlan (CurCOOH) bearing the β-1,3-polyglucuronic acid structure was successfully prepared from β-1,3-glucan polysaccharide curdlan (Cur) by one-step oxidation using a 4-acetamido-TEMPO/NaClO/NaClO(2) system as the oxidant. The resulting high-molecular-weight CurCOOH was proved to bear the 6-COOH group in 100% purity. The optical rotatory dispersion (ORD) spectra indicated that the obtained CurCOOH behaves as a water-soluble single-strand in various pH aqueous media. This advantage has allowed us to use CurCOOH as a polymeric host to form various macromolecular complexes. For example, complexation of CurCOOH with single-walled carbon nanotubes (SWNTs) resulted in a water-soluble one-dimensional architecture, which formed a dispersion in aqueous solution that was stable for several months, and much more stable than SWNTs complexes of the similar negatively-charged polyacrylic acid (PAA) and polymethacrylic acid (PMAA). It was shown that in the complex, SWNTs are effectively wrapped by a small amount of CurCOOH, enabling them to avoid electrostatic repulsion. This pH-responsive CurCOOH formed a very stable complex with cationic water-soluble polythiophenes (PT-1), which was stabilized not only by the hydrophobic interaction but also by the electrostatic attraction between trimethylammonium cations in PT-1 and dissociated anionic COO(-) groups in CurCOOH. The included PT-1 became CD-active only in the neutral to basic pH region, and the positive Cotton effect suggested that the conjugated main chain is twisted in the right-handed direction. We also found that CurCOOH can interact with polycytidylic acid (poly(C)) only under high NaCl concentrations, the binding and release of which could be controlled by a change in the salt concentration. We believe, therefore, that CurCOOH bearing a dissociable COOH group can act as a new potential polymeric host to construct novel polymeric complexes applicable for gene carriers, biosensors, chiral polymer assemblies, etc.     

Synthesis of endohedral metallofullerene glycoconjugates by carbene addition

Endohedral metallofullerene glycoconjugates were synthesized under mild conditions by carbene addition using appropriate glycosylidene-derived diazirine with La(2)@I(h)-C(80). NMR spectroscopic studies revealed that the glycoconjugate consists of two diastereomers of [6,6]-open mono-adducts. The electronic properties were characterized using Vis/NIR absorption spectroscopy and electrochemical measurements. This study demonstrates that glycosylidene carbene is useful to incorporate carbohydrate moieties onto endohedral metallofullerene surfaces.     

Power spectrum and blood flow velocity images obtained by dual-beam backscatter laser Doppler velocimetry

We developed a micro multipoint laser Doppler velocimeter (μ-MLDV) for noninvasive in-vivo measurements of blood flow and we presented the results of demonstrations performed on experimental animals. In this paper, we investigate the validity of power spectrum analysis for determining the flow velocity and the minimum power of the semiconductor laser in the μ-MLDV. Although average velocity is generally estimated from a peak position (f _peak) in the power spectrum, the power spectrum of blood flow included an additional component in the high-frequency region. The conventional method for determining the average velocity of flows of transparent artificial fluids, which involves determining the average velocity from f _peak, is unsuitable for in-vivo measurements of blood flow. The laser power was reduced from 140 to 30mW since 30mW was the minimum power at which images of blood flow velocity in microvessels could be obtained. About 30mW (power density of 15mW/mm²) is the maximum power which can be irradiated to humans. Further reduction in the laser power is necessary before this technique can be applied to humans.     

Syntheses of 4, 5-Di-O-bexzyl-2-deoxy-2-C-methyl L-lyxose and Methyl 4, 5-Di-O-bexzyl-2-deoxy-2-C-methyl-3-O-metkyl-L-lyxonate

The title compounds, which possess C-methyl groups at the α-position of carbonyl groups and vicinal hydroxyl groups with syn (three) relationship, were synthesized efficiently from known 3-decxy-1, 2-O-isopropylidene-3-C-methyl-α-D-allofuranose. The synthetic routes involve: 1) inversion of C-5 configuration of the starting sugar, 2) suitable protection of the 5, 6-diol, and 3) glycol cleavage of the 1, 2-diol to an aldehyde or direct oxidation of the diol to carboxylic acid.     

MECHANISM OF THE REACTION OF DIPHENYL N-BROMOSULFILIMINE WITH SULFIDES,PHOSPHINES AND TERTIARY AMINES

Abstract

The mechanism of the reactions of diphenyl N-bromosulfilimine (I) with such nucleophiles as sulfides, phosphines and tertiary amines was investigated. In the presence of water, (I) reacts with sulfides or phosphines to afford the corresponding sulfoxides or the phosphine oxides in moderate yields; however, the reaction with tertiary amine gave only the N-t-aminosulfilimine derivative. The effect of ring size in the reaction with cyclic sulfides suggests that the reaction proceeds via initial bromine transfer from the nitrogen atom to the sulfur atom of the cyclic sulfides followed by S_N2 type substitution of bromide on the sulfur atom of the cyclic sulfide with the sulfilimino group. The phosphine oxide obtained in the reaction of (I) with optically active methyl n-propyl phenyl phosphine was racemized but retained a small portion of the optical activity. In the case of tertiary amines, even 1,4-diazabicyclo-(2,2,2)-octane (DABCO), in which the back side of the nitrogen atom is blocked, reacted smoothly to afford the corresponding ammonium salts, suggesting the reaction to be of S_N2 type on the nitrogen atom of the sulfilimine.     

Fullerene-Derived Porous and Defective N-Doped Carbon Nanosheets as Advanced Trifunctional Metal-Free Electrocatalysts

Dopants and defects are crucial for multifunctional carbon-based metal-free electrocatalysts, but the rational design and facile production remain as a big challenge. Herein, we report a novel strategy using salt-assisted pyrolysis of derivatized fullerenes to fabricate defect-rich and N-doped carbon nanosheets. Molecular level modification of C₆₀ via amination and hydroxylation gives rise to well-defined fullerol molecules bearing N-containing groups (FNG). Subsequent calcination of FNG and NaCl at 750 °C generates porous carbon nanosheets (FNCNs-750) and turns the N-containing groups into high-level N dopants (12.43 at.%). Further pyrolysis of FNCNs-750 at 900 °C (FNCNs-900) leads to a reduced N content populated by graphitic-N. Meanwhile, abundant intrinsic defects (e. g., topological defects and edges) are created due to the breakdown of fullerene cages and partial removal of edged N atoms. These structural features endow FNCNs-900 with outstanding trifunctional catalytic performance, better than or close to the noble metal-based benchmark catalysts.