55Mn NMR in Mn12 acetate: Hyperfine interaction and magnetic relaxation of cluster

The 55Mn NMR in oriented powder Mn12Ac has been investigated at 1.4-2.0 K in zero field and with external fields along the c-axis. Three kinds of 55Mn NMR composed of five-fold quadrupole-split lines for I=5/2 nuclei have been interpreted to arise from Mn4+ ion, and two crystallographically-inequivalent Mn3+ ions, respectively. It is found that the isotropic hyperfine field in the Mn4+ ion with 3d3 configuration indicates a large amount of reduction (26%) as compared with the theoretical evaluation. In the analysis for the hyperfine field of Mn3+ ions with 3d4 configuration, we have taken into account of the anisotropic dipolar contribution in addition to the Fermi-contact term in order to explain two kinds of 55Mn NMR frequencies in Mn3+ ions in inequivalent sites. By using the hyperfine coupling constants of twelve manganese ions in Mn12Ac, the total hyperfine interaction of the ferrimagnetic ground state of S=10 has been determined to amount to 0.3 cm-1 in magnitude at most, the magnitude of which corresponds to the nuclear hyperfine field he(0.32 kG seen by Mn12 cluster spin. The relaxation of the cluster magnetization was investigated by observing the recovery of the 55Mn spin-echo intensity in the fields of 0.20-1.90 T along the c-axis at 2.0 K. It was found that the magnetization of the cluster exhibits the (t-recovery in the short time regime. The relaxation time decreases with increasing external field following significant dips at every 0.45 T. This is interpreted to be due to the effects of thermally-assisted quantum tunneling between the spin states at magnetic level crossings.Comment: Text 25 pages, five figures and two table

A Spectroscopic Behavior of Zeaxanthin Molecular Aggregate and Its From

Lutein, one of the xanthophylls, can be dispersed in various aqueous solutions, for example, protein solution, dilute acetone solution, dilute sodium dodecyl sulfate (SDS) solution, dodecyl trimethylammonium bromide solution, hen egg yolk phosphatidyl-choline (PC) liposome, or digalactosyldiglyceride liposome, to from chiral helical aggregates which acquire an optical activity in the visible region, and have a left handed helical structure. In this report, zeaxanthin, a structural isomer of lutein, was subjected to investigation as to whether zeaxanthin formed the chiral helical aggregate. When zeaxanthin was dispersed in SDS solution, some differences from lutein were obserbed. (1) CD spectrum of positive Cotten effect was shown, which was the reverse of lutein. (2) SDS concentration giving the reversion of the CD spectrum pattern was higher (3.5mM) than that of lutein (0.6mM). IN spite of these differences, however, the results showed that zeaxanthin molecules also associated to from molecular aggregate in such a manner performing π*-π*interaction at conjjugated polyene sites. zeaxanthin dispersed in PC liposome gave both left and right-handed helical structure under presence of Ca2+ at alkaline condition in comparison with lutein's left-handed structure. This result may depend on the fact that synthesized racemic zeaxanthin is subjected to this experiment. Those results gave the general conclusion that xanthophylls had the same basic types of behavior for making molecular aggregate in aqueous dispersion.我々はxanthophyllの一つであるluteinが種々の水溶液例えばたんぱく質溶液、うすいアセトン溶液、うすい界面活性剤水溶液、卵黄レシチン製リポソーム、あるいはホウレンソウdigalactosyl diglyceride製リポソームに分散溶解してキラルならせん状集合体を形成し、可視領域に光学活性を示すと同時に左巻きのらせん構造体を作ることを既に明らかにしている。本報告ではluteinの構造異性体であるzeaxanthinを用いて同様に分子集合体を形成するかどうかを検討した。zeaxanthinをsodiumdodecylsulfate (SDS)に分散させると、円2色性(CD)スペクトルが逆のCotton効果を与え、またそのスペクトルパターンが逆転するSDS濃度がluteinのとき0.6mMであったのに対して約3.51mMと高く、またそのときのSDS結合量も多いという相異はあるが水系においてπ*-π*相互作用行わせるような分子集合体を形成するという基本的挙動を示した。PCリポソームに分散させたときアルカリ性でCa2+存在下らせん構造を与える点もluteinと同じであった。しかし、用いたzeaxanthinが合成された光学異性体混合物であったためか左巻きと右巻きらせんの両方とも観察されたホウレンソウlutein Aの左巻きらせんだけの結果と異なった。以上の結果からzeaxanthinもluteinと同じく水系で分子集合体を形成するという基本的分子挙動をとることが明らかとなった

Synthesis and Magnetic Properties of Fergusonite Structured La(NbVMn)O4

The authors have synthesized fergusonite-structured La(Nb0·71V0·04Mn0·25)O4 samples. The samples, consisting of La3+, Nb5+, V5+, Mn4+ and oxygen ions, demonstrated temperature-dependent magnetization that increased with lowering the temperature below ≈200 K, and almost saturated below ≈100 K. At 75 K, the field-dependent magnetization demonstrated sigmoidal curve and reached 3 μB/Mn at 1 T. Such a magnetic behavior can be ascribed to exchange interaction between Mn4+Nb2O11 nanoclusters. The Mn4+ substitution for the V5+ sites of the crystal resulted also in the occupied state above the valence band maximum

Inhibitory Effect of 1α-Hydroxyvitamin D3 on N-nitrosobis (2-oxopropyl)Amine-induced Cholangiocarcinogenesis in Syrian Hamsters

Sixty-three male 5-week-old Syrian hamsters received the carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) s.c. in 5 weekly injections (the first, 70mg/kg body, and the remaining, 20mg/kg each). The hamsters that received BOP were given intragastric administration of 0.2ml of medium chain triglyceride (MCT) with or without 0.04μg of 1α-hydroxyvitamin D3 [1α(OH)D3] through a feeding tube for 12 weeks. Thus, 3 groups were assigned:Group 1;BOP alone (n＝20), Group 2;BOP＋MCT (n＝18) and Group 3;BOP＋1α(OH)D3 (n＝25). The mean body weight of Group 3 was lower than those of Groups 1 and 2 at the end of the experiment (p＜0.001,Tukey-Kramer HSD test). At the end of week 12, all surviving hamsters were put to sleep. The incidences of liver tumors were 80%, 72% and 32% in Groups 1, 2 and 3, respectively. The incidence of tumors in Group 3 was significantly lower than in Group 1 and Group 2 (p＜0.05, χ2-test). All tumors were cholangiocarcinoma. These results indicated that BOP-induced cholangiocarcinogenesis was suppressed by the supplemental administration of 1α(OH)D3

A Substellar Companion to the Intermediate-Mass Giant 11 Com

We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong station and Okayama Astrophysical Observatory (OAO) revealed Keplerian velocity variations with an orbital period of 326.03 +/- 0.32 days, a semiamplitude of 302.8 +/- 2.6 m/s, and an eccentricity of 0.231 +/- 0.005. Adopting a stellar mass of 2.7 +/- 0.3 M_solar, the minimum mass of the companion is 19.4 +/- 1.5 M_Jup, well above the deuterium burning limit, and the semimajor axis is 1.29 +/- 0.05 AU. This is the first result from the joint planet search program between China and Japan aiming at revealing statistics of substellar companions around intermediate-mass giants. 11 Com b emerged from 300 targets of the planet search program at OAO. The current detection rate of a brown dwarf candidate seems to be comparable to that around solar-type stars within orbital separations of $\sim$3 AU.Comment: 19 pages, 4 figures, accepted by Ap