X-ray structural study of a zinc(II) inclusion complex of a phenolate-pendant cyclam

The molecular structure of phenol-pendant cyclam-zinc(II) complex,4a, has been determined by X-ray structure analysis. Crystals of4a · ClO₄ · CH₃OH (C₁₆H₂₇N₄OZn · ClO₄ · CH₃OH) are monoclinic, space groupP2₁/nn, with four molecules in the unit cell of dimensionsa=31.198(2) Å,b=8.426(1) Å,c=8.214(1) Å, and=93.96(1)°. The structure was solved by the heavy atom method and refined anisotropically toR=0.044,R _w=0.062 for 1551 independent reflections. The complex assumes a five-coordinate, square pyramidal geometry, where zinc(II) is surrounded by the cyclam moiety in a planar fashion with the pendant phenolate anion occupying an axial position. An extremely short Zn-O(phenolate) bond distance of 1.983(5) Å, in conjunction with the 0.288 Å displacement of Zn(II) above the cyclam N₄ plane toward the phenolate, accounts for the extremely low pK _a value of 5.8 for the pendant phenol. These facts about4a, in comparison with the previous findings for the Ni(II) (4b) and Cu(II) complexes (4c) with the same ligand, illustrate well the characteristics of zinc(II) ion coordination properties.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Regional distribution of manganese,iron, copper,and zinc in the rat brain during development

Manganese (Mn), iron (Fe), copper (Cu), and zinc (Zn) concentrations were determined in the brain regions of normal 1-, 3-, 5-, 7-, 14-, 21-, 42-, 77-, and 147-day-old Wistar rats using inductively coupled plasma mass spectrometry (ICP-MS), and their maps were illustrated in color to visually compare the distribution of the elements at various stages of the growth process. Sagittal slices (1-mm thickness) sectioned at the level of the substantia nigra were divided into 18 regions, and the small slice samples were digested in microwave-assisted closed vessels for ICP-MS measurement. Mn, Fe, Cu, and Zn concentrations increased region-specifically with age, and their distributional maps showed some characteristics. These findings are discussed in terms of needs for these trace elements in the normal brain. Among new findings about their brain distribution, it is especially noteworthy that higher concentrations of Mn, Fe, and Zn were observed in the substantia nigra compared with those in neighboring regions. The mapping method in this work is expected to open up possibilities for screening of the in vivo element–element interrelationships among these essential elements.     

Simultaneous determination of triterpene saponins in ginseng drugs by high-performance liquid chromatography

A HPLC method for the simultaneous determination of 11 triterpene saponins with four-type aglycones (protopanaxadiol, protopanaxatriol, ocotillol and oleanolic acid types) in Ginseng drugs was developed and validated. Using a gradient of acetonitrile and 10 mM K-phosphate buffer (pH 5.80) as the mobile phase and UV detection at 196 nm, more than 18 ginsenosides with different aglycones were separated satisfactorily within 60 min. The detection limits (signal/noise> or =3) were 0.1 microg for ginsenosides Rb1, Rc, Rd, Re and Rg1, chikusetsusaponin III, and notoginsenoside R2, 0.2 microg for gisenoside Ro and chikusetsusaponin IVa, 0.3 microg for chikusetsusaponin IV, and 3 microg for majonoside R2. The calibration curve of each saponin had a correlation coefficient close to 1. Intra- and interday precisions were less than 2.1% (n=5) and 3.3% (n=15), respectively. The recovery rates of extraction were in the range of 96.4-102.7% for all ginsenosides. By adopting this method, the determinations of 11 ginsenosides in three Ginseng drugs derived from Panax ginseng, Panax vietnamensis var. fuscidiscus and Panax japonicus (Japan) were achieved.     

Meso-tetrakis[o-(N-methyl)pyridinium]porphyrin ensembles with axially coordinated cyclodextrin-penetrating phenethylimidazole: reversible dioxygen-binding in aqueous DMF solution

alpha-Cyclodextrin (alpha CD)-penetrating 2-methyl-1-phenethylimidazole coordinates to the zinc(II) and iron(II) complexes of meso-tetrakis[o-(N-methyl)pyridinium] porphyrinate, giving non-covalently linked alpha CD-porphyrin ensembles; the iron(II) complex can reversibly bind and release dioxygen in aqueous DMF solution.     

Positive heterotropic cooperativity for selective guest binding via electronic communications through a fused zinc porphyrin array

Upon binding with C60 and diamines, such as 4,4'-bipyridine (bpy) and N,N,N',N'-tetramethylhexane-1,6-diamine (TMHDA), cyclic host 1 possessing two electronically coupled binding sites displays negative homotropic cooperativity and positive heterotropic cooperativity, and their ternary mixtures preferentially form inclusion complexes with hetero-guest pairs 1 supersetC60*bpy and 1 supersetC60*TMHDA under appropriate conditions. Spectroscopic titration profiles in toluene at 20 degrees C demonstrated that the association constants (Kassoc) of C60 with monodiamine complexes 1 supersetbpy (2.8 x 105 M-1) and 1 supersetTMHDA (1.5 x 105 M-1) are 8.5 and 4.5 times greater than that of C60 with guest-free 1 (3.3 x 104 M-1), respectively. On the other hand, mono-C60 complex 1 supersetC60 was 6.1 times more accessible than guest-free 1 toward TMHDA. Absorption spectroscopy in the absence of 1 indicated no direct interaction between C60 and diamines.     

Mechanism of plasma-initiated polymerization: Concerning the nature of solvent effects on the lifelike polymerization of water-soluble vinyl monomers

To provide a satisfactory basic understanding of the solvent effect of plasma-initiated polymerization, we have carried out several kinds of polymerizations of various water-soluble vinyl monomers. It has been shown that aqueous solution of such vinyl monomers underwent the polymerizations induced by methyl isobutyrate (MIB) plasma-exposed glass surface. The invisible ultrathin polymer film trapping an active radical species deposited on the plasma-exposed glass surface apparently induced the polymerizations. The efficiency, however, was largely dependent on the solvent used: the solvent can be considered to act as “an initiation-activator” for the lifelike postpolymerization. The nature of the solvent effect was ascribed to the physicomechanical property such as swelling ability and/or solubility toward the ultrathin film formed on the glass surface. Thus it has been suggested that the choice of good-balanced combination between the structural feature of the plasma-induced ultrathin polymer film and the solvent as an initiation-activator is important to achieve activity of a desired solution polymerization.