Design of Brønsted acid-assisted chiral Brønsted acid catalyst bearing a bis(triflyl)methyl group for a Mannich-type reaction

[Structure: see text] A new Br?nsted acid-assisted chiral Br?nsted (chiral BBA) acid catalyst (1) was developed by substituting a hydroxy group of optically active 1,1'-bi(2-naphthol) with a stronger Br?nsted acidic group such as a bis(trifluoromethanesulfonyl)methyl group. The enantioselective Mannich-type reaction of ketene silyl acetals with aldimines catalyzed by (R)-1 in the presence of stoichiometric achiral proton sources gave (S)-beta-amino esters in high yield with moderate to good enantiomeric excesses.     

Photochemical and thermal hydrogen production from water catalyzed by carboxylate-bridged dirhodium(II) complexes

A series of dinuclear Rh(II) complexes, [Rh(2)(μ-OAc)(4)(H(2)O)(2)] (HOAc = acetic acid) (1), [Rh(2)(μ-gly)(4)(H(2)O)(2)] (Hgly = glycolic acid) (2), [Rh(2)(μ-CF(3)CO(2))(4)(acetone)(2)] (3), and [Rh(2)(bpy)(2)(μ-OAc)(2)(OAc)(2)] (4), were found to serve as H(2)-evolving catalysts in a three-component system consisting of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)), methylviologen (MV(2+)), and ethylenediaminetetraacetic acid disodium salt (EDTA). It was also confirmed that thermal reduction of water into H(2) by MV(+)˙, in situ generated by the bulk electrolysis of MV(2+), is effectively promoted by 1 as a H(2)-evolving catalyst. The absorption spectra of the photolysis solution during the photocatalysis were monitored up to 6 h to reveal that the formation of photochemical or thermal byproducts of MV(+)˙ is dramatically retarded in the presence of the Rh(II)(2) catalysts, for the H(2) formation rather than the decomposition of MV(+)˙ becomes predominant in the presence of the Rh(II)(2) catalysts. The stability of the Rh(II)(2) dimers was confirmed by absorption spectroscopy, (1)H NMR, and ESI-TOF mass spectroscopy. The results indicated that neither elimination nor replacement of the equatorial ligands take place during the photolysis, revealing that one of the axial sites of the Rh(2) core is responsible for the hydrogenic activation. The quenching of Ru*(bpy)(3)(2+) by 1 was also investigated by luminescence spectroscopy. The rate of H(2) evolution was found to decrease upon increasing the concentration of 1, indicating that the quenching of Ru*(bpy)(3)(2+) by the Rh(ii)(2) species rather than by MV(2+) becomes predominant at the higher concentrations of 1. The DFT calculations were carried out for several possible reaction paths proposed (e.g., [Rh(II)(2)(μ-OAc)(4)(H(2)O)] + H(+) and [Rh(II)(2)(μ-OAc)(4)(H(2)O)] + H(+) + e(-)). It is suggested that the initial step is a proton-coupled electron transfer (PCET) to the Rh(II)(2) dimer leading to the formation of a Rh(II)Rh(III)-H intermediate. The H(2) evolution step is suggested to proceed either via the transfer of another set of H(+) and e(-) to the Rh(II)Rh(III)-H intermediate or via the homolytic radical coupling through the interaction of two Rh(II)Rh(III)-H intermediates.     

Tribo-Excited Chemical Reaction Using an EuIII Complex with a Stacked Anthracene Framework

A spin-selective tribo-chemical reaction using a dinuclear lanthanide complex is demonstrated for the first time. The dinuclear complex is composed of two Eu^III ions, hexafluoroacetylacetonato ligands, and anthracene-based phosphine oxide bridges. Single-crystal analysis revealed a face-to-face-type anthracene dimer structure in the dinuclear Eu^III complex. Mechanical stimulus on the dinuclear Eu^III complex induced selective formation of oxidized anthracene. The tribo-chemical reaction is based on a characteristic energy-transfer pathway for the selective formation of an excited triplet state.     

Circularly Polarized Absorption and Luminescence of Semiconductor Eu-OCN Nanocrystals in the Blue Region of the Electromagnetic Spectrum

Semiconductor nanomaterials with efficient polarized-light control in the blue region of the visible spectrum are promising candidates for modern and future photo-information technology, display devices, and optical sensing applications. New-type semiconductor Eu(OCN)₂ nanocrystals with circularly polarized absorption (CD: circular dichroism) and emission (CPL: circularly polarized luminescence) under an applied magnetic field are demonstrated here for the first time. The effective CD signal at 1.6 T was observed at approximately 440 nm. The dissymmetry factor of CPL under 100 K, g_M-CPL, was estimated to be 0.01. These characteristic circularly polarized absorption and emission phenomena of Eu(OCN)₂ nanocrystals should be caused by combination between the “Faraday A and C terms” of the magnetic moment in the excited state. Polarized-light control using Eu(OCN)₂ nanocrystals in the blue-light region of the electromagnetic spectrum is a large first step into a new world of photo-functional semiconductor nanomaterials.     

Distinctive Properties of Dark Reversion Kinetics between Two Red/Green‐Type Cyanobacteriochromes and their Application in the Photoregulation of cAMP Synthesis

Cyanobacteriochromes (CBCRs) are photoreceptors that bind to a linear tetrapyrrole within a conserved cGMP‐phosphodiesterase/adenylate cyclase/FhlA (GAF) domain and exhibit reversible photoconversion. Red/green‐type CBCR GAF domains that photoconvert between red‐ (Pr) and green‐absorbing (Pg) forms occur widely in various cyanobacteria. A putative phototaxis regulator, AnPixJ, contains multiple red/green‐type CBCR GAF domains. We previously reported that AnPixJ's second domain (AnPixJg2) but not its fourth domain (AnPixJg4) shows red/green reversible photoconversion. Herein, we found that AnPixJg4 showed Pr‐to‐Pg photoconversion and rapid Pg‐to‐Pr dark reversion, whereas AnPixJg2 showed a barely detectable dark reversion. Site‐directed mutagenesis revealed the involvement of six residues in Pg stability. Replacement at the Leu294/Ile660 positions of AnPixJg2/AnPixJg4 showed the highest influence on dark reversion kinetics. AnPixJg2_DR6, wherein the six residues of AnPixJg2 were entirely replaced with those of AnPixJg4, showed a 300‐fold faster dark reversion than that of the wild type. We constructed chimeric proteins by fusing the GAF domains with adenylate cyclase catalytic regions, such as AnPixJg2‐AC, AnPixJg4‐AC and AnPixJg2_DR6‐AC. We detected successful enzymatic activation under red light for both AnPixJg2‐AC and AnPixJg2_DR6‐AC, and repression under green light for AnPixJg2‐AC and under dark incubation for AnPixJg2_DR6‐AC. These results provide platforms to develop cAMP synthetic optogenetic tools.     

Synthesis of new CO2-soluble ruthenium(II) and cobalt(II) polypyridine complexes bearing fluorinated alkyl chains and their application to photoreduction of liq. CO2

Eight types of new CO₂-soluble or CO₂-philic ruthenium(II) and cobalt(II) polypyridine complexes, namely, [M(F84OPh)₃](BArF)₂, [M(F44OPh)₃](BArF)₂, [M(F62Ph)₃](BArF)₂, and [M(F62O)₃](BArF)₂ (M = Ru or Co, BArF: tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), were prepared from bipyridine derivatives bearing highly fluorinated alkyl chains and applied to the photoreduction of liq. CO₂ under a high pressure of 6.8 MPa at 35 °C. All these complexes have higher philicity toward liq. CO₂ than the corresponding complexes with PF⁶⁻ as the counteranion. Using the Ru(II)-Co(II) systems of [M(F44OPh)₃](BArF)₂ and [M(F62O)₃](BArF)₂, direct photoreduction of CO₂ was achieved without the use of any organic solvent.     

Improving chemical recycling rate by reclaiming polyurethane elastomer from polyurethane foam

Flexible polyurethane foam was decomposed into a polyol mixture by an extruder with diethanolamine (DEA) as a decomposing agent. The resulting decomposed product could be used as an alternative virgin polyol in reclaiming polyurethane. In the case of reclaiming elastomer by using the decomposed product without any purification, virgin polyol could be alternated by the decomposed product up to 80%. It is a great improvement compared with the reclamation to foam, whose percentage was maximum 5%. Furthermore, the percentage could be improved up to 100% by purifying the decomposed product. We have found that physical properties of reclaimed polyurethane elastomer, such as tensile strength, hardness, and elongation, can be regulated by the ratio of unrefined/refined polyol. Whereas the tensile strength and the hardness increased as the content increased, the elongation decreased.     

Evaluation of a radioimmunoassay of alpha 1-microglobulin (alpha 1-m) with simplified procedures

A newly established double antibody radioimmunoassay (RIA) was fundamentally and clinically evaluated. Original procedures were partially modified as follows: Sample volume for serum and urine was changed to 25 microliters, and thus 200 mg/l of alpha 1-m standard was prepared using 50 microliters of original standard solution (100 mg/l). The results were satisfactory in sensitivity (0.3 mg/l obtained from -2SD method), intra-assay precision with its coefficient variation (CV) ranging from 3.0 to 7.4%, interassay precision with its CV ranging from 3.0 to 10.7%, and recovery with the mean value of 102.4% in serum and 108.2% in urine respectively. There were no changes about alpha 1-m value between diluted (2 times) and undiluted with high concentration samples. Normal levels of alpha 1-m were less than 25 mg/l in serum and less than 10 mg/l in urine. The present results indicate that the determination of alpha 1-m could be very simple and useful for the most sensitive screening test for the evaluation of renal function.     

Synthetic Studies on Sialoglycoconjugates 52: Synthesis of Sialyl Lewis X Analogs Containing Azidoalkyl Groups at the Reducing End

Abstract

Stereocontrolled synthesis of sialyl Le^x epitope analogs in which the terminal N-acetylglucosamine residue of sialyl Le^x determinant is replaced by a D-glucopyranose residue containing β-glycosidically linked azidoalkyl groups is described. Glycosylation of 2-(trimethylsilyl)ethyl O-(2,6-di-O-benzoyl-3,4-O-isopropylidene-β-D-galactopyra-nosyl)-(1→4)-2,6-di-O-benzoyl-β-D-glucopyranoside (2), prepared from 2-(trimethylsi-lyl)ethyl β-lactoside (1) by 3,4-O-isopropylidenation and selective-O-benzoylation, with methyl 2,3,4-tri-O-benzyl-l-thio-β-L-fucopyranoside (3) gave the desired a-glycoside 4, which was converted by O-deisopropylidenation into 7, and via O-debenzoylation, selective 2,6,6′-tri-O-benzoylation and O-deisopropylidenation into 8, respectively. N-Iodosuccinimide (NIS)-TfOH-promoted glycosylation of 7 or 8 with methyl (phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto-2-nonulopyra-nosid)onate (9) afforded the desired tetrasaccharides 10 and 11.

Compound 11 was converted into the α-trichloroacetimidate 14 via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group and treatment with trichloroacetonitrile. Coupling of 14 with 2-azidoethanol, 8-azidooc-tanol, and 2-[2-(2-azidoethoxy)ethoxy]ethanol, gave the desired β-glycosides 15-17, respectively. O-Deacylation of 12, 15-17 and subsequent hydrolysis of the methyl ester group yielded the tide compounds.