ESR studies of the spin-exchange interaction within parallel planar copper (II) dimers in frozen solutions

The temperature variations of the ESR spectral intensity of the triplet dimers over the range 1.6 to 4.2 K indicated that the spin-exchange interaction within the parallel planar dimers, which had been reported to be ferromagnetic in crystal, is antiferromagnetic (1.5–2.5 cm⁻¹) in frozen solutions.     

The extractive spectrophotometric determination of palladium(ii) as the mixed-ligand complex with picolinealdehyde-2-hydroxy-5-phenylanil and chloride ion

The extraction of palladium(II) with chloroform in the presence of PHPA and chloride ions is described. The extracted species has an absorption maximum at 627 nm, and Beer's law is obeyed over the range 10–200 μg of palladium. The molar absorptivity is 4.90·10³ l mol^?1 cm^?1 at 627 nm. The 1:1:1 Pd(PHPA)-Cl complex is extracted from aqueous solution. The effect of foreign ions on the determination of palladium(II) is examined.     

Syntheses and reactions of functional polymers. XLII. Preparation and use of polymers having N-hydroxy-succinimide unit in the chain

Styrene-maleic anhydride alternating copolymer was converted to N-hydroxymaleimide-styrene copolymer by reaction with hydroxylamine in pyridine at room temperature. The conversion was more than 90%. From this copolymer, N-acetoxy- or N-benzoyloxymaleimide-styrene copolymers were derived by action of acetic anhydride or benzoyl chloride in dimethylformamide at room temperature. Acylation of several primary amines was carried out effectively by use of these N-acyloxyimide-styrene copolymers. The reaction of the acetylated copolymer with diethylamine at room temperature afforded N-hydroxyimide copolymer.     

Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.     

A New Supramolecular Tetraruthenated Cobalt (II) Porphyrazine Displaying Outstanding Electrocatalytical Performance in Oxygen Evolution Reaction

A new supramolecular electrocatalyst for Oxygen Evolution Reaction (OER) was synthesized from a central multibridging cobalt tetrapyridylporphyrazine (CoTPyPz) species by attaching four [Ru(bpy)₂Cl]⁺ groups. Both CoTPyPz and the tetraruthenated cobalt porphyrazine species, TRuCoTPyPz, form very homogenous molecular films just by dropcasting their methanol solutions onto GCE electrodes. Such films exhibited low overpotentials for O₂ evolution, e.g., 560 e 340 mV, respectively, displaying high stability, typically exceeding 15 h. The kinetic parameters obtained from the Tafel plots showed that the peripheral complexes are very important for the electrocatalytic activity. Hyperspectral Raman images taken along the electrochemical process demonstrated that the cobalt center is the primary active catalyst site, but its performance is enhanced by the ruthenium complexes, which act as electron-donating groups, in the supramolecular system.     

Synthetic Studies on Sialoglycoconjugates 22: Total Synthesis of Tumor-Associated Ganglioside,Sialyl Lewis X1

ABSTRACT

The first total synthesis of tumor-associated glycolipid antigen, sialyl Lewis X is described. Glycosylation of 2-(trimethylsilyl)ethyl O-(2-acetamido-4,6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(1→3)-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside (1) with methyl 2,3,4-tri-O-benzyl-1-thio-β-L-fuco-pyranoside (4) gave the α-glycoside (5), which was converted by reductive ring-opening of the benzylidene acetal into the glycosyl acceptor (6). Dimethyl(methylthio)sulfonium triflate-promoted coupling of 6 with methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2,4,6-tri-O-benzoyl-1-thio-β-D-galactopyranoside (7) afforded the desired hexasaccharide 8 in good yield. Compound 8 was converted into the α-trichloroacetimidate 11, via reductive removal of the benzyl groups, O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octa-decene-1,3-diol (12), gave the β-glycoside 13. Finally, 13 was transformed, via selective reduction of the azide group, condensation with octadecanoic acid, O-deacylation, and hydrolysis of the methyl ester group, into the title compound 16.     

Communication: Synthetic Studies on Sialoglycoconjugates 110: Efficient Assembly of α-Linked Tetrameric Sialoglycosides Coupled with Galactose and Lactose

Polysialoglycoconjugates, such as polysialylated ganglio-series gangliosides and N-CAM (neural cell adhesion molecule), are of interest because of their important physiological functions in association with neural cell development, differentiation, neuron network formation, and so on.^2-4 Chemical synthesis of these glycoconjugates provides an effective method to elucidate their biological significance in nature at the molecular level, providing not only genuine original glycoconjugates but also their derivatives and analogs designed for biological investigation. We have established⁵ an efficient method to construct dimeric and trimeric sialoglycosides by using the lactonated sialic acid derivatives as building blocks, and succeeded in the systematic synthesis of various polysialogangliosides such as GD3, GQ1b, GQlbα and, very recently, GT3.⁶ In this paper, as a part of our continuous synthetic approach directed toward the polysialoglycoconjugates, we report the first synthesis of α-linked tetrameric sialoglycosides coupled with a galactose and lactose residue.     

On the internal stepsize of an extrapolation algorithm for IVP in ODE

We propose an extrapolation algorithm for initial value problems in ordinary differential equations. In the algorithm, an appropriately chosen stepsizeH is divided into smaller stepsizes by a sequence and a new stopping rule is proposed. The sequences applied to the algorithm are Romberg {2,4,8,16,32,...}, Bulirsch {2,4,6,8,16...} and Harmonic {2,4,6,8,10,12,...} types. The proposed algorithm is compared numerically with the algorithm introduced by Stoer. In view of the accuracy of numerical solutions, the relatively small number of calculations, the stability and reliability of the algorithm, we found that the algorithm with the Romberg sequence is the best.