Single-molecule magnets of ferrous cubes: structurally controlled magnetic anisotropy

Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe(II) centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4].2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4].2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4].MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1-6, the alkoxo groups of the Schiff base ligands bridge four Fe(II) ions in a mu3-mode forming [Fe4O4] cubic cores. The Fe(II) ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4-6 are shorter than those in 1-3. Dc magnetic susceptibility measurements for 1-6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, -0.64, -0.66, and -0.67 cm(-1) for 1-6, respectively. Ac magnetic susceptibility measurements for 4-6 showed both frequency dependent in- and out-of-phase signals, while 1-3 did not show out-of-phase signals down to 1.8 K, meaning 4-6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4-6. The bridging ligands R-sap2- in 1-3 and R-sae2- in 4-6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn-Teller distortions at Fe(II) centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry.     

The effect of angular momentum coupling on the angular distribution of fission fragments

We examine what information can be obtained from fission angular distributions through precise measurements and an analysis in terms of the simple statistical model of Ericson. We report on the systematics of the decoupling angle and present the role of the angular momentum coupling between the entrance and the exit channel. The results indicate that the directional coupling of the angular momentum in the entrance and the exit channel is always strong for heavy-ion induced fission, and the angular momentum coupling plays a decisive role on the angular distribution of fission fragments. The average channel spins of fission fragments 〈I_f〉 are deduced through the decoupling angles determined experimentally. They agree well with γ-multiplicity measurements.     

Energy damping feature in light heavy-ion reactions

The energy damped reaction products from³⁷Cl+¹²C,²⁷Al,⁴⁸Ti and¹⁶O+⁴⁸Ti were measured over a wide range of angles (typically 18°<θ _lab<70°), incident energies (160 <E _lab(³⁷Cl)<200 MeV,E _lab(¹⁶O)=118 MeV) and charges Z, including two systems (³⁷Cl+³⁷Al and¹⁶O+⁴⁸Ti) which lead to the same compound nucleus⁶⁴Zn with the same excitation energy and comparable angular momenta. The angular dependences of total kinetic energy (TKE) and dσ/dθ were decomposed into two components (forward peaked and nearly constant at backward angles), and the elemental TKE and cross sections were derived. The backward components of³⁷Cl+²⁷Al and¹⁶O+⁴⁸Ti exhibit very different Z-distributions, indicating that the fragments do not originate from compound nucleus decay. The results can be understood in terms of an energy damping process.     

The complete amino acid sequence of an abortifacient protein, karasurin

The complete amino acid sequence of a new abortifacient protein, karasurin, was determined. Karasurin, which was isolated from fresh root tubers of Trichosanthes kirilowii Maximowicz var, japonicum Kitamura (Cucurbitaceae), was a highly basic protein with pI 10.1 and molecular weight of 28,000. Intact karasurin was cleaved with cyanogen bromide, lysyl endopeptidase, formic acid and 2-(2'-nitrophenyl-sulfenyl)-3-methyl-3-bromoindolenine (BNPS-skatole), respectively. Cleavages with N-bromosuccinimide (NBS), trypsin and pepsin were performed for the fragments. The resultant peptide fragments were separated by gel filtration chromatography, reversed-phase high performance liquid chromatography (HPLC) or gel filtration HPLC following sequence analyses by automated Edman methods. Karasurin consists of 246 or 247 amino acid residues with a calculated molecular weight of 27,144 or 27,215 differing only at the C-terminus with the addition of alanyl residue. Two C-terminal sequences were identified as Asn-Asn-Met-OH and Asn-Asn-Met-Ala-OH by sequence analyses and hydrazinolysis, but there was no micro-heterogeneity in other peptides analysed. The sequence of karasurin revealed a considerable similarity to that of trichosanthin and alpha-trichosanthin, which are known as abortifacient, ribosome-inactivating and anti human immunodeficiency virus (HIV) (the virus causing acquired immunodeficiency syndrome (AIDS) proteins, with 93% and 98% identity, respectively.     

Corticosterone secretion-inducing activity of saikosaponin metabolites formed in the alimentary tract

The corticosterone secretion-inducing activities of saikosaponin a, saikosaponin c and saikosaponin d, isolated from the root of Bupleurum falcatum L., and 27 metabolites formed in the murine alimentary tract were studied in mice. Serum corticosterone was determined by high-performance liquid chromatography (HPLC). Intraperitoneal administration of saikosaponin a and its intestinal metabolite, prosaikogenin F, showed corticosterone secretion-inducing activity at a dose of 0.1 mmol/kg, and maximally increased it at a dose of 0.4 mmol/kg. On the other hand, the genuine sapogenin, saikogenin F, was inactive. Saikosaponin b1 and saikosaponin g, gastric metabolites of saikosaponin a, and their intestinal metabolites, prosaikogenin A, prosaikogenin H, saikogenin A and saikogenin H, were also inactive. Serum corticosterone was increased by the administration of saikosaponin d and its intestinal metabolite, prosaikogenin G, at a dose of 0.04 mmol/kg, and it reached the maximal level at the dose of 0.1 mmol/kg. Saikogenin G also showed a slight activity. A gastric metabolite of saikosaponin d, saikosaponin b2, and its intestinal metabolites, prosaikogenin D and saikogenin D, were inactive. In the experiments on saikosaponin c and its metabolites, saikosaponin c was inactive but its intestinal metabolites, especially prosaikogenin E-2, showed activity almost equal to that of saikosaponin a. Saikosaponin h and saikosaponin i, gastric metabolites of saikosaponin c, were also inactive, but their prosaikogenins showed slight activities. When these compounds were orally administered, their corticosterone secretion-inducing activities were similar to those obtained in the intraperitoneal experiment. These results suggest that a proper polar balance between the sugar moiety and the aglycone is important for the corticosterone secretion-inducing activity of saikosaponins and their metabolites.     

Novel biphenyl ether lignans from the rhizomes of Curcuma chuanyujin

Three new biphenyl ether lignans, 1, 2 and 3, were isolated from the rhizomes of Curcuma chuanyujin along with curcuminoid compounds 4, 5 and 6 and their chemical structures were determined to be 1-feruloyloxy-2-methoxycinnamic acid, 1-feruloyloxy cinnamic acid and (1-p-hydroxycinnamoyl) cinnamic acid by means of spectral evidence. The latter three known substances showed antioxidant activity.     

Photodissociation of CO from [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] in acetonitrile, where L = pyridine, 4-cyanopyridine and methanol

Photodissociation of CO from oxo-centered trinuclear ruthenium clusters [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] (L = pyridine (py): 1; 4-cyanopyridine (cpy): 2; methanol: 3) dissolved in organic solvents has been examined. Upon photolysis (> or = 290 nm, a 450-W Xe lamp), an absorption peak at 585 nm observed for 1 in CH3CN decreases its intensity and a new absorption band appears and grows at 896 nm. This spectral change, presenting isosbestic points, corresponds to photosubstitution of CO in 1 to form [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(py)2] 4. Photoexcitation of carbonyl complexes 2 and 3 in CH3CN also affords the corresponding CH3CN-coordinated complexes [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(cpy)2] 6 and [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)3] 7, respectively. The photosubstitution reactions (excitation wavelength, > or = 290 nm) are well described by the first-order kinetics: k = 7.3 x 10(-4) s(-1) for 1, 4.9 x 10(-4) s(-1) for 2 and 5.1 x 10(-4) s(-1) for 3 (298 K). In the presence of a 100-fold excess of py, photolysis of 1 yields a tris(py) complex [Ru3(mu3-O)(mu-OOCCH3)6(py)3] 5 via photochemical loss of CO followed by coordination of py. The overall reaction (photochemical and thermal) is also confirmed by 1H NMR spectroscopy. The dissociative character of the photosubstitution is supported by negligible effects of the concentration of the entering pyridine molecule, the nature of solvents and the type of terminal monodentate ligands (other than CO) attached to the cluster. Quantum yield measurements with varied excitation wavelengths have shown that absorption bands located in the UV region (< 400 nm) play a principal role in photosubstitution, whereas an absorption band in the visible region (centered at approximately 580 nm), ascribed to an "intracluster" charge transfer, is not at all responsible for photosubstitution.     

The structure of nephritogenoside

Nephritogenoside is a minor component of the basement membrane of normal animals (including humans). It is a glycopeptide with the ability to induce chronic progressive glomerulonephritis (end stage kidney) when administered as a single footpad injection, and contains a novel carbohydrate-peptide linkage. The total chemical structure was investigated. It was revealed that nephritogenoside is a simple glycopeptide composed of three glucose residues [alpha-Glc-(1----6)-beta-Glc-(1----6)-Glc] and twenty-one amino acids [1Asn-Pro-Leu-Phe-5Gly-Ile-Ala-Gly-Glu-10Asp-Gly-Pro -Thr-Gly-15Pro-Ser-Gly-Ile-Val-20Gly-21Gln], and that the glucose residues are linked alpha-N-glycosidically to the N-terminal amino acid.     

Iridoid glucosides from Veronica hederifolia

A new iridoid glucoside, urphoside A, and six known iridoid glucosides, pikuroside, aucubin, veronicoside, catalposide, amphicoside, and verminoside, were isolated from Veronica hederifolia together with a known megastigmane glucoside, 3-hydroxy-5,6-epoxy-beta-ionol-9-O-beta-D-glucopyranoside, and a hexitol, dulcitol. The structures of the isolated compounds were established by the extensive 1D- and 2D-NMR spectroscopy.