Novel 15-crown-5 ether or beta-diketone incorporated gadolinium complexes for the detection of potassium ions or magnesium and calcium ions

Novel gadolinium complexes (KMR-series: KMR-K and KMR-Mg), which have a bis-15-crown-5 ether or a charged beta-diketone structure as a recognition site, have been designed, synthesized and applied for the detection of K(+) or of Mg(2+) and Ca(2+) using MRI or NMR techniques. The measurements are based on the modulation of the longitudinal relaxation time (T(1)) of water protons in proximity of the gadolinium complexes. Relaxivity measurements of KMR-K1 in aqueous solution showed that the initial longitudinal relaxivity value (r(1)) of 5.05 mM(-1) s(-1) is monotonously decreasing with increasing K(+) concentrations, reaching a final value of 4.78 mM(-1) s(-1). This decrease is attributed to a change in the second sphere of hydration of the gadolinium (Gd(3+)) complex (KMR-K), resulting in a K(+) concentration-dependent contrast in MR images. From stoichiometric analysis using mass spectrometry and UV/VIS spectrometry, a 1 : 1 complex formation between KMR-K1 and K(+) in a sandwich-type manner with a log K of 3.20 was confirmed. In the case of KMR-Mg, the initial r(1) value of 4.98 mM(-1) s(-1) is monotonously decreasing with increasing Mg(2+) or Ca(2+) concentrations, reaching a final value of 3.95 or 4.16 mM(-1) s(-1), respectively, resulting in Mg(2+) and Ca(2+) concentration-dependent contrast in MR images. The formation of a 1:1 complex with a log K of 2.33 for Mg(2+) and 1.91 for Ca(2+) was confirmed. KMR-K1 and KMR-Mg are the first ion-selective or ion-sensitive gadolinium complexes for K(+) or Mg(2+) and Ca(2+), respectively.     

Manganese(III,IV) and manganese(III) oxide clusters trapped by copper(II) complexes

Reactions of quinquedentate Schiff base ligands with Mn and Cu ions afforded icosa- and hexadecanuclear mixed-metal clusters in which dinuclear CuII complexes trapped oxo-bridged [MnIII8MnIV4O12] and [MnIII6O6] cores, respectively. Maximum entropy method analysis for synchrotron X-ray diffraction data was used to determine the oxidation states of the Mn ions.     

Electron spin resonance study on H6+, H5D+, H4D2+, and H2D4+ in solid parahydrogen

We carried out an electron spin resonance (ESR) study on hydrogen ion radicals produced by radiolysis of solid para-H(2). In addition to quartet ESR lines proposed to be H(2) (+)-core H(6) (+) (D(2d)) ions in solid para-H(2) [T. Kumada et al., Phys. Chem. Chem. Phys. 7, 776 (2005)], we newly observed totally more than 50 resolved lines in gamma-ray irradiated solid para-H(2)-ortho-D(2) (1 mol %) and para-H(2)-HD (1 mol %) mixtures. We assigned these lines to be isotope substituents of H(2) (+)-core H(6) (+) ions such as H(5)D(+), H(4)D(2) (+), and H(2)D(4) (+) throughout the comparison of their ESR parameters with theoretical results. These results provide a conclusive evidence that H(2) (+)-core H(6) (+) ions are generated in irradiated solid hydrogens. Analysis of the EPR spectrum and ab initio calculations predicts D(2d) symmetry of the H(6) (+) ions, whereas a lowering symmetry (D(2d)-->C(2v)) induced by asymmetric nuclear wave function is observed in H(5)D(+) and H(4)D(2) (+). We also observed isotope-substitution reactions such as H(6) (+)+D(2)-->H(4)D(2) (+)+H(2) and H(6) (+)+HD-->H(5)D(+)+H(2), which are analogous to the well-known isotope-condensation reactions of H(3) (+) in dark nebula, H(3) (+)+HD-->HD(2) (+)+H(2) and HD(2) (+)+HD-->D(3) (+)+H(2).     

Interfacial tension studies of crown ethers at air/water and hexane/water interfaces

The adsorption of phase transfer catalysts, 18-crown-6 and dicyclohexano-18-crown-6, at the air/water and the hexane/water interfaces were investigated. Interfacial tension sigma decreased by increasing concentrations of these compounds and therefore both of these crown ethers are accumulated at interfaces. The variation of sigma with concentration for both compounds follows the Szyszkowski equation very well, from which the values of saturated surface densities and interaction parameters have been evaluated. On the basis of occupied surface area of each molecule, the orientation of each of molecules at the air/water and the hexane/water interfaces have been proposed. The present results show that dicyclohexano-18-crown-6 has the higher tendency not only to dissolve into the hexane phase but also to adsorb at the hexane/water interface than 18-crown-6 and that the Starks extraction mechanism was suggested for the present phase transfer catalysis systems.     

Molecular weight segregation on surfaces of polyethylene blended films as estimated from nanoscratch tests using scanning probe microscopy

Nanoscratch tests using scanning probe microscopy (SPM) were performed on films prepared from two polyethylene (PE) materials polymerized by using a metallocene catalyst system with different molecular weights (MWs). Blended samples were prepared by dissolving both PE materials at various ratios in hot p-xylene. The pure and blended samples were compression molded into films at 180 degrees C for different holding times in the molten state. The results of SPM nanoscratch tests with an applied load of 30 nN indicated that the lower-MW surface could be easily plowed with wear debris but the higher-MW surface was less deformed. However, the deformation pattern of the blended film surface was similar to that of the lower-MW surface. These results suggest that MW segregation occurs during holding in the molten state as lower-MW components rise to the film surface.     

Azobenzene derivatives carrying a nitroxide radical

Several trans-azobenzene derivatives carrying a nitroxide (aminoxyl) radical (2a, 6a-12a) were prepared, and their photoisomerization reactions to the corresponding cis-isomers were investigated. Although no fruitful results could be obtained for the photoisomerizations of the derivatives with para-subsituents (9a-12a), the unsubstututed derivatives at the para-position (2a, 6a, 7a, 8a) were found to show photoisomerizations by irradiation to give the corresponding cis-isomers (2b, 6b, 7b, 8b), being isolated as relatively stable solid materials, and the change of the intermolecular magnetic interactions was apparently observed by the structural change for each photochromic couple.     

La2XB3 (X = Cl,Br): A Novel Layered Structure with Planar Boron Nets of B3, B6 and B8 Rings

Two new layered rare earth boride halides, La₂XB₃ (X = Cl, Br) have been synthesized. They crystallize in the space group (No. 174) with a = 7.872(1) Å, c = 8.219(2) Å, V = 441.1(1) ų for the chloride, and with a = 7.834(1) Å, c = 8.440(1) Å, V = 448.6(1) ų for the bromide compound, respectively. The crystals of La₂ClB₃ are twinned resulting in an apparent symmetry P6/mmm (No. 191). In the crystal structure of La₂XB₃, trigonal La₆ prisms are condensed into sheets in the a‐b plane, and the halogen atoms X sandwich the La double layers. The connection of B atoms which center the prisms and rectangular prism faces leads to B nets of B₃, B₆ and B₈ rings embedded between the La atom double layers. The chemical bonding is analyzed for the well ordered bromide, and the characteristic disorder in the chloride is discussed.     

Color‐Discriminating Retinal Configurations of Sensory Rhodopsin I by Photo‐Irradiation Solid‐State NMR Spectroscopy

SRI (sensory rhodopsin I) can discriminate multiple colors for the attractant and repellent phototaxis. Studies aimed at revealing the color‐dependent mechanism show that SRI is a challenging system not only in photobiology but also in photochemistry. During the photoreaction of SRI, an M‐intermediate (attractant) transforms into a P‐intermediate (repellent) by absorbing blue light. Consequently, SRI then cycles back to the G‐state. The photoreactions were monitored with the ¹³C NMR signals of [20‐¹³C]retnal‐SrSRI using in situ photo‐irradiation solid‐state NMR spectroscopy. The M‐intermediate was trapped at ?40 °C by illumination at 520 nm. It was transformed into the P‐intermediate by subsequent illumination at 365 nm. These results reveal that the G‐state could be directly transformed to the P‐intermediate by illumination at 365 nm. Thus, the stationary trapped M‐ and P‐intermediates are responsible for positive and negative phototaxis, respectively.     

Highly Efficient Chiral Resolution of dl‐Arginine by Cocrystal Formation Followed by Recrystallization under Preferential‐Enrichment Conditions

An excellent chiral symmetry‐breaking spontaneous enantiomeric resolution phenomenon, denoted preferential enrichment, was observed on recrystallization of the 1:1 cocrystal of dl ‐arginine and fumaric acid, which is classified as a racemic compound crystal with a high eutectic ee value (>95 %), under non‐equilibrium crystallization conditions. On the basis of temperature‐controlled video microscopy and in situ time‐resolved solid‐state ¹³C NMR spectroscopic studies on the crystallization process, a new mechanism of phase transition that can induce preferential enrichment is proposed.