Identification of Al(III) species in a solution containing equimolar concentrations of Al(III) and citric acid using varying-temperature 27Al NMR spectrometry.

27Al NMR spectra of an equimolar (10 mM) Al(III)-citrate system were obtained at different temperatures. The linewidths of the signals decreased in the spectra recorded at elevated temperatures, which enabled us to unequivocally identify the resonance lines. From the spectrum recorded at 65 approximately C, a mononuclear Al(III)-citrate complex was identified at a solution pH of 3.0 in addition to trinuclear Al(III)-citrate complex, which dominated at pH 4.0.     

Inequivalent quantizations for non-linear σ model

We compute the homotopy groups ₀ and ₁ of the classical configuration space of anO(3) invariant field theory on ×, where is a compact two dimensional manifold for arbitrary genusg and- denotes the time coordinate. We also present the finite dimensional, unitary, irreducible, inequivalent representations of the appropriate fundamental groups and comment on some of their implications.     

Addition reactions of cyclooctatetraene with 1,3-diphenylisobenzofuran the benzene ring as dienophile in a [4+2] cycloaddition reaction

Addition reactions of cyclooctatetraene with 1,3-diphenylisobenzofuran resulted in the formation of three 1:1 cycloadducts, 1, 2, and 3, and a 1:2 cycloadduct, 4. Single crystal x-ray analysis established 3 to be a cage compound formed by an unprecedented [4+2] cycloaddition reaction of 1 in which the double bond of the benzene moiety acted as the dienophile.     

Studies of the polymerization of diallyl compounds. XXVII. Copolymerization of diallyl tartrate with several vinyl monomers

The radical copolymerization of diallyl tartrate (DATa) (M₁) with diallyl succinate (DASu), diallyl phthalate (DAP), allyl benzoate (ABz), vinyl acetate (VAc), or styrene (St) was investigated in order to disclose in more detail the characteristic hydroxyl group's effect observed in the homopolymerization of DATa. In the copolymerization with DASu or DAP as a typical diallyldicarboxylate, the dependence of the rate of copolymerization on monomer composition was different for different copolymerization systems and unusual values larger than unity for the product of monomer reactivity ratios, r₁r₂, were obtained. In the copolymerization with ABz or VAc (M₂), the r₁ and r₂ values were estimated to be 1.50 and 0.64 for the DATa/ABz system and 0.76 and 2.34 for the DATa/VAc system, respectively; the product r₁r₂ for the latter copolymerization system was found again to be larger than unity. In the copolymerization with St, the largest effect due to DATa monomer of high polarity was observed. Solvent effects were tentatively examined to improve the copolymerizability of DATa. These results are discussed in terms of hydrogen-bonding ability of DATa.     

Site-selective photocycloadditions of 2-pyrones with electron-poor olefins and the derivation from the cycloadducts

Photosensitized cycloaddition of 4,6-dimethyl-2-pyrone ( 1 ) with methacrylonitrile ( 3b ) afforded two types of [2 + 2]cycloadducts, 4b and 6b , across the C₅-C₆ and C₃-C₄ double bonds in 1 , respectively. Photosensitized reactions of 1 with dimethyl maleate and dimethyl cyclobutene-1,2-dicarboxylate gave [2 + 2]cycload-ducts 4d, 4e across the C₅-C₆ double bond, in addition to [4 + 2]cycloadduct 9d or bicyclo[4.2.0]octadiene 10e . The photoreactions of methyl 2-pyrone-5-carboxylate ( 2 ) with 3b and 2-chloroacrylonitrile ( 3c ) gave [4 + 2]cycloadducts 5b, 5c in addition to [2 + 2]cycloadducts 11b and 11c across the C₅-C₆ double bond in 2 . The photocycloaddition mechanism was explained from results calculated by means of PM3-CI method. Namely, the site- and/or regio-selective products, 4, 5, 8, 9 and 10 were thought to come from the same site-selective radical intermediates in the case of electron-poor olefins. Pyrolysis and/or hydrolysis of the cycload-ducts 4e, 5b, 5c gave 5,6-dihydro-2-pyrone 12 or benzene derivatives.     

Serially coupled capillary columns supercritical fluid chromatography with midpoint pressure control

Two capillary columns of different polarities were coupled in series by means of a coupling restrictor. The pressure of the first column and the midpoint pressure (between the coupling restrictor and the second column) were controlled independently of each other using two pumps. The selectivity of this separation system was highly dependent on the pressure difference and could be continuously changed between those of two columns. The pressure difference could be changed even in course of separation for fine tuning of the selectivity. Several examples were shown to demonstrate the utility of this method.     

Speciation of Arsenic Compounds in the Urine of Rats Orally Exposed to Dimethylarsinic Acid Ion Chromatography with ICP–MS as an Element-Selective Detector

A combined ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP—MS) system as an element-selective detector has been used for the determination of arsenic compounds. Seven arsenic compounds were separated by cation-exchange chromatography. Subsequently, the separated arsenic compounds were directly introduced into the ICP—MS and were detected at m/z =75. Detection limits for the seven arsenic compounds ranged from 0.8 to 3.8 μg As/l. The IC–ICP–MS system was applied to the determination of arsenic compounds in the urine of dimethylarsinic acid (DMAA)-exposed rats. DMAA was the most abundant arsenic compound detected. Arsenous acid, monomethylarsonic acid and trimethylarsine oxide were also detected.     

An investigation of FeCoCrO4 by Mossbauer spectroscopy

The spinel FeCoCrO₄ has been studied between 4.2 and 538°K. Characteristic Mossbauer spectra of paramagnetic, magnetic and electronic relaxation types have been observed. The Mossbauer parameters for Fe³⁺ ions situated at tetrahedral (A) and octahedral (B) sites have been calculated. The cation distribution in magnetic and paramagnetic phases is found to be approximately Fe_0.5³⁺Co_0.5²⁺[Co_0.5²⁺Fe_0.5³⁺Cr³⁺]O₄. The Neel temperature been determined by the temperature scanning method to be 310±5°K.