Mössbauer study of the magnetic axis in RbFeF3 in the interval T2<T<TN

The antiferromagnetic axis in RbFeF₃ in the interval T₂<T<T_N has been expected to be along [111] from powder Mössbauer studies and along [001] from an X-ray diffraction study. We report our direct observation of the magnetic axis by Mössbauer spectroscopy using stressed single crystal samples. The results show that the magnetic axis is along [111].     

A matrix partition problem

In the set of positive definite semi-integral symmetric matrices we propose a partition problem. Then by introducing the notion of “additively prime” we obtain the generating function for this problem. Finally we establish the analyticity of the generating function.     

The reaction of aqua-(ethylenediaminetetra-acetato)ruthenium(III) with o-phenylenediamine under aerobic conditions

An electron-transfer reaction between [Ru(III)(Hedta)(H₂O)] and o-phenylenediamine in the presence of O₂ takes place to give a Ru(II)-edta complex with coordinated (bidentate) o-benzoquinone diimine. The complex obtained has been characterized by analysis, magnetic measurements, electronic, IR, ¹H and ¹³C NMR spectral data.     

Chain conformations of block copolymers

An analytical theory of block copolymer conformations is developed for systematically studying the effects of the chain length, chain architecture, and segment interactions. The main results obtained for AB diblock and ABA triblock chains are as follows: (i) In the absence of AA and BB interactions, both diblock and triblock chains collapse to a dense form if the AB interaction is attractive. In the collapsed coil form, the mean-square end-to-end distance 〈R²〉 is proportional to the square root of the number of segments n^1/2. (ii) The diblock chain has a dumbbell form if AA and BB interactions are attractive and AB interaction repulsive, but the triblock chain collapses. In the dumbbell form, 〈R²〉 is proportional to n.     

Correlation of57Fe hyperfine interactions with Fe-Fe distance in Laves phase compounds RFe2 (R=rare earth)

The⁵⁷Fe Mössbauer isomer shifts and magnetic hyperfine fields in Laves phase compounds RFe₂ (R=Pr, Nd and Sm) are studied with particular reference to the effect of the Fe–Fe interatomic distance on the hyperfine interactions. It is shown that the charge density at the Fe nuclei scales linearly with fractional volume change up to 20%. The⁵⁷Fe hyperfine field corrected for the influence of rare-earth moment shows a systematic variation with the distance, which can be understood in terms of the Bethe-Slater curve arguments. The similarity of the atomic volume dependence of the⁵⁷Fe hyperfine interactions in Lves phase compounds to those in iron with close-packed structure is emphasized.This paper is based on a paper presented at the 5th Int. Conf. on hyperfine interactions, Berlin, July 21–25, 1980.     

Heat capacity of a five-coordinated iron(III) complex,chlorobis(N,N-dimethyldithiocarbamato) iron(III), between 0.4 and 300 k: New finding of a magnetic phase transition

The heat capacity of the title complex, Fe[S₂CN(CH₃)₂]₂Cl, has been measured between 0.4 and 300 K. A λ -type phase transition with a small shoulder arising from magnetic ordering was found at (0.609 ± 0.005) K. The character of the ordered phase has been suggested to be ferromagnetic on the basis of comparison between the methyl- and ethyl-homologues. The magnetic hyperfine structure of the Mössbauer spectra and the line broadening due to electronic relaxation effects at 1.2 K hitherto reported are concluded to result from a critical slowing-down when the magnetic transition temperature is approached from the high-temperature side. A Schottky-type anomaly arising from the zero-field splitting of a single ferric ion was observed around 2 K. The excess entropy beyond the lattice contribution at low temperatures amounts to (14.05 ±0.27) J K^?1mol^?1, which cannot be accounted for solely by the magnetic entropy of Rln 4 (= 11.53 JK^?1mol^?1) for the intermediate spin of $\text{S =}\text{3}\text{2}$. Two possibilities concerning additional conntribution have been discussed; one is a mixing of spin species of $\text{S =}\text{5}\text{2}$ and the other is a tunnel-splitting of the rotational levels of four methyl-constituents. The present study cannot give a definite conclusion as to the existence of dimeric units suggested from Mössbauer spectroscopy.     

Heat capacity of [Ni(OCH3)(acac)(CH3OH)]4 from 0.4 to 285 K: Spin interaction and tunnel-splitting of internal rotation of methyl group

The heat capacity of the tetranuclear nickel cluster complex, tetrakis [μ₃-methoxo-2,4-pentanedionato (methanol) nickel (2)], has been measured from 0.4 to 285 K. Contrary to the previous prediction by Bertrand et al.[6], that this complex exhibits an intercluster ferromagnetic spin coupling, the present heat capacity measurement shows no indication of the spin-ordering effect caused by the intercluster interaction at least down to 0.4 K. Instead, a heat capacity anomaly centered around 1.5 K with a shoulder at 0.5 K has been observed. This anomaly is well accounted for in terms of both a level splitting of the ground S = 4 state due to a uni-axial crystalline anisotropy and a tunnel-splitting of the rotational levels of methyl groups. The intracluster spin exchange constant J and the single-ion zero-field splitting parameter D are determined to be $\text{J}\text{hc}\text{= 7.0 cm}{}^{\mathrm{?1}}$ and $\text{D}\text{hc}\text{= 3.65 cm}{}^{\mathrm{?1}}$ (h being the Planck constant and c the speed of light in a vacuum). The temperature dependence of the effective Bohr magneton [6] is also satisfactorily accounted for on the basis of this model. The tunnel-splitting δ of the lowest rotational level of the four methyl groups belonging to methoxides is estimated to be $\text{δ}\text{hc}\text{= 0.4–0.7 cm}{}^{\mathrm{?1}}$ and the corresponding potential barrier V_o is found to be V_o = 1.9–1.5 kJmol^?1.     

Characterization and online detection of aromatic alkaloids in the ascidian Lissoclinum cf. badium by liquid chromatography/UV detection mass spectrometry

A detection method based on high-performance liquid chromatography coupled with ultraviolet diode-array detection and electrospray ionization ion trap tandem mass spectrometry (HPLC-UV-ESI-MS/MS) was developed to investigate the total alkaloids prepared from the ascidian Lissoclinum cf. badium. The aromatic alkaloids possessing polysulfide structures are the major bioactive constituents isolated from ascidians of the genera Lissoclinum, Eudistoma, and Polycitor. These compounds presented various important biological activities. The ESI-MS fragmentation behavior of this kind of alkaloids was studied, and the fragmentation was characterized by elimination of the NH(CH(3))(2) moiety. The use of reversed-phase HPLC/UV-ESI-MS allowed the online separation and detection of 25 aromatic alkaloids. This approach provided data that can be used for detection of biologically active aromatic alkaloids from marine organisms.     

A study of the calcium complex of a glucosylceramide, soya-cerebroside II

In order to study calcium ion complex of soya-cerebroside II (1), an ionophoretic glucosylceramide isolated from soybean, C8-cerebroside (3) and 3,3',6'-trideoxy-C8-cerebroside (4) are designed and synthesized. On the basis of extensive 1H-NMR studies in the presence of Ca2+ and a continuous variation method via (1)H-NMR, soya-cerebroside II is suggested to form a calcium complex with 1/Ca2+ ratio of 1 : 1. Soya-cerebroside II serves as a tridentate chelating ligand for Ca2+; the amide carbonyl, C2'-hydroxy, and C2'-hydroxy oxygens are responsible for the Ca2+ binding. Soya-cerebroside II is structurally analogous to a neural glucosylceramide. Thus, the accumulated neural glucosylceramide inside of endoplasmic reticulum (ER) membrane may serve as an endogenous Ca2+-binding and -transport molecule (ionophore) that result in mobilization of Ca2+ from intracellular calcium stores.     

Miscibility and interaction between 1-alkanol and short-chain phosphocholine in the adsorbed film and micelles

The miscibility and interaction of 1-hexanol (C6OH) and 1-heptanol (C7OH) with 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) in the adsorbed films and micelles were investigated by measuring the surface tension of aqueous C6OH-DHPC and aqueous C7OH-DHPC solutions. The surface density, the mean molecular area, the composition of the adsorbed film, and the excess Gibbs energy of adsorption g(H,E), were estimated. Further, the critical micelle concentration of the mixtures was determined from the surface tension versus molality curves; the micellar composition was calculated. The miscibility of the 1-alkanols and DHPC molecules in the adsorbed film and micelles was examined using the phase diagram of adsorption (PDA) and that of micellization (PDM). The PDA and the composition dependence of g(H,E) indicated the non-ideal mixing of the 1-alkanols and DHPC molecules due to the attractive interaction between the molecules in the adsorbed film, while the PDM indicated that the 1-alkanol molecules were not incorporated in the micelles within DHPC rich region. The dependence of the mean molecular area of the mixtures on the surface composition suggested that the packing property of the adsorbed film depends on the chain length of 1-alkanol: C6OH expands the DHPC adsorbed film more than C7OH.