Novel Z-selective head-to-head dimerization of terminal alkynes catalyzed by lanthanide half-metallocene complexes

Various terminal alkynes have been cleanly dimerized into the corresponding head-to-head (Z)-enynes by use of the half-metallocene lutetium alkyl complexes Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) (Ar = Ph, C6H3Me2-2,6, C6H2Me3-2,4,6) as catalysts. Aromatic C-Cl, C-Br, and C-I bonds, which are known to be extremely susceptible to reductive cleavage by transition metals, survived in the present reactions. The corresponding dimeric alkynide species [Me2Si(C5Me4)(NAr)Lu(mu-CCR)]2 are thought to be the true catalysts, some of which have been isolated and structurally characterized. These alkynide species were thermally stable and soluble at the reaction temperatures (80-110 degrees C), but they precipitated upon cooling to room temperature after completion of the reaction. Therefore, this catalyst system works homogeneously but can be separated and reused, thus constituting the first example of a recyclable catalyst system for the dimerization of terminal alkynes and also the first example of (Z)-selective head-to-head dimerization of aromatic terminal alkynes.     

Drug-plasma protein binding assay by electrokinetic chromatography-frontal analysis

We developed a rapid, microscale and reliable analytical method for binding of drugs to plasma proteins using capillary electrophoresis (CE) with ionic cyclodextrins (CD) combined with frontal analysis. These CDs were used as pseudostationary phases of electrokinetic chromatography (EKC). The CD-modified EKC (CDEKC) approach allowed us to separate anionic drugs from plasma proteins, whereas CZE could not separate these drugs from plasma proteins because they had a similar mobility like plasma proteins. CDs uniquely interact with these drugs but not with plasma proteins. Therefore, CDEKC could be coupled with frontal analysis to measure the binding of anionic drugs to plasma proteins. The binding values obtained by CDEKC were highly consistent with those determined by the ultrafiltration method. Our CDEKC approach should expand the applicability of CE to protein binding analysis.     

Secondary hypervalent I(III)...O interactions: synthesis and structure of hypervalent complexes of diphenyl-lambda3-iodanes with 18-crown-6

Reported here for the first time are the synthesis and characterization of supramolecular complexes between diaryl-lambda(3)-iodanes and 18-crown-6 (18C6). Slow evaporation of solvents afforded 1:1 and 2:1 complexes between Ph(2)IBF(4) and 18C6 as stable crystals, depending on the conditions. X-ray crystal structures of these complexes indicated that each iodine atom contacts with the three adjacent oxygen atoms of 18C6 through two hypervalent secondary bonding and a weak interaction. (1)H NMR analyses and CSI-MS spectra showed that, in dichloromethane solution, Ph(2)IBF(4) exclusively forms the 1:1 complex with 18C6 (binding constant K(a), 1.02 x 10(3) M(-)(1)). The binding constants decrease with the increased solvent donor ability (Gutmann's DN). Changing the heteroatom ligand from BF(4) to the less nucleophilic PF(6) and AsF(6) increased the binding constant by about six times. Substitution of an electron-withdrawing group onto the para position of Ph(2)IBF(4) tends to increase in the complex stability. A linear Hammett relationship (rho = 0.59) between log K(a) and sigma(p)(+) values of substituents indicates that the diaryl-lambda(3)-iodanes with electropositive iodine(III) interact more efficiently with 18C6. Decreased binding magnitude was measured with 15C5, dibenzo-18C6, dibenzo-21C7, and dibenzo-30C10.     

13C nuclear magnetic resonance studies of cellulose acetate

¹³C-NMR spectra of ring carbons and O-acetyl carbonyl carbons of cellulose acetate (CA) in dimethyl sulfoxide-d₆ were analyzed. The CA samples with the degree of substitution (DS) ranging from 0.84 and 1.91 were prepared by homogeneous acetylation of cellulose with acetic anhydride in a 10% LiCl/dimethyl acetamide solvent. It was found that the use of these low DS samples permitted easier assignments not only of the ring carbon but also of the O-acetyl carbonyl carbon signals. The assignments were confirmed by comparing with the ¹H-NMR spectra of the samples obtained by complete acetylation of the corresponding CA samples with acetyl-d₃ chloride. Two methods for determining the distribution of O-acetyl groups of CA, i.e., the relative DS at the three different types of hydroxyl groups, were developed. One is based on the measurements of the relative intensities of the signals for the ring carbons and the other is based on the measurements of the relative intensities of the signals for the O-acetyl carbonyl carbons.     

Determination of sultopride and tiapride in serum by gas chromatography using a surface ionisation detector

A sensitive and selective method has been developed for the determination of sultopride and tiapride in serum using gas chromatography with a surface ionisation detector. No interfering peaks from endogenous substances were observed. The method showed good reproducibility and accuracy, and the standard curve was linear up to 2 micrograms/ml with a correlation coefficient of 0.999. This method is applicable to pharmacokinetic studies and therapeutic drug monitoring of sultopride and tiapride.     

FLAVIN-PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMER IN THE PRESENCE OF MAGNESIUM PERCHLORATE

We have investigated the photosensitized monomerization of the cis,syn -cyclobutane dimer of 1,3-di-methylthymine using riboflavin tetraacetate and a 5-deazaflavin derivative as photosensitizer. Although little monomerization of the dimer is induced by photoexcitation of the flavins in the absence of any additives, the flavins can function as an efficient photosensitizer in the presence of magnesium perchlorate. Mechanistic studies involving spectroscopic, quantum-yield and flash-photolysis measurements demonstrated that the photosensitized monomerization exclusively proceeds through electron transfer from the dimer to the triplet flavins complexed with Mg²⁺. The effects of magnesium perchlorate are compared with those on the chloranil-photosensitized monomerization and also with the effects of HClO₄ on the flavin-photosensitized reaction.     

Capacitance-conductance detector for high-pressure liquid chromatography. Application to alkaloids and fatty acids

Summary A new type of detector for high-pressure liquid chromatography has been designed. This detector is equipped with a RC resonance circuit, and is similar to the capacitance detector previously reported. It is operated as a capacitance detector with nonpolar eluents; while with polar solvents, it behaves as a conductance detector. Electrolytes such as salts, acids and bases are sensitively detected. The detector was successfully used for the detection of fatty acids and alkaloids.

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Zusammenfassung Ein neuartiger Detektor für die Hochdruck-Flüssigchromatographie wurde entwickelt. Dieser ist mit einem Resonanzstromkreis ausgestattet und ähnelt dem kürzlich beschriebenen Kapazitanz-Detektor. Als solcher funktioniert er mit nichtpolaren Eluenten, während er sich mit polaren Lösungsmitteln wie ein Leitfähigkeitsdetektor verhält. Salze, Säuren und Basen werden empfindlich nachgewiesen. Das Gerät wurde zum Nachweis von Fettsäuren und Alkaloiden verwendet.

     

Complex formation of amphiphilic polymers with azo dyes and their photoviscosity behavior

The hydrophobic interaction of amphiphilic copolymers, which contain 2-hydroxyethyl methacrylate(HEMA) and 1vinyl-2-pyrrolidone (VPy), with Methyl Orange (MO) was compared with that of HEMA-acrylamide (AAm) copolymers to deduce the correlation between their complexation ability in a photochromic azo dye and the photoviscosity effect in aqueous copolymer/dye complex solution. On the basis of the dialysis data and fluorometric analysis it appeared that the complexation dependence on HEMA content in the copolymers was due to the hydrophobic interaction between the polymer and the dye. For a comparable HEMA content AAm copolymers bound less MO than VPy copolymers. It was confiied by photoviscosity measurements that the conformation of the complex composed of photochromic azo dye and HEMA copolymer changed reversibly in response to the photo- and thermal isomerization of the dye. In HEMA-AAm copolymer systems the photoviscosity effect was small compared with that of HEMA-VPy copolymer systems. From these results it was concluded that the complexation ability of polymers due to the hydrophobic interaction was an important factor in producing a large photoinduced conformational change in water.     

Preparation and lithium doping of gallium oxynitride by ammonia nitridation via a citrate precursor route

Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga_0.89□_0.11) (N_0.66O_0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750-850 °C. Approximately, 10 at% Li⁺ was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga³⁺ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li₂Ga₃NO₄, was also obtained with Li₂CN₂ impurity using similar preparations from a mixture of Li/Ga?1. The crystal structure was isostructural with h-GaN, and was refined as P6₃mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li₂CN₂ impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO₂. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm.     

Studies on palytoxins

The complete structure of palytoxin (1) was elucidated by us in 1982.¹ Our continuous interests in palytoxin led us to examine minor constituents of Okinawan Palythoa tuberculosa. In this paper, we describe successful isolation and structural elucidation of four minor toxins, which were named homopalytoxin (2), bishomopalytoxin (3), neopalytoxin (4) and deoxypalytoxin (5).