Light-driven open-close motion of chiral molecular scissors

The first example of "light-driven chiral molecular scissors" (1), which consists of 1,1',3,3'-tetraarylferrocene as a pivot part and azobenzene as a driving part, was synthesized. Absorption, circular dichroism (CD), and 1H NMR spectral studies on the photoinduced isomerization process of an enantiomer of 1 agreed well with a prediction by a DFT calculation, where a motion of the handles via light-driven contraction/expansion of the connecting azobenzene strap was transformed, through a pivotal motion of the ferrocene unit, into an open-close motion of the blade parts.     

Spectrophotometric determination of uranium(vi) by the azide reaction

Azide has been investigated as a spectrophotometric reagent for uranium(VI). The system is more sensitive than the thiocyanate reaction. It obeys Beer's law in the range 2–180 p.p.m. of uranium. The colour is sensitive to hydrogen ion concentration ; maximum absorbance and stability are attained at pH 5–5.5. Iron(III) interferes seriously, but can be masked by EDTA. Fe⁺², Cr⁺³, Ni⁺², Th⁺⁴, Cr₂O₇^-2, WO₄^-2, VO₃^- and F^- interfere. The deep yellow colour cannot be extracted with organic solvents. A mono-azido-uranium(Vl) ion is present in dilute solutions; its dissociation constant is 2.3 ±20.27·10^-3.     

A polyamine coating for enhanced capillary electrophoresis-electrospray ionization-mass spectrometry of proteins and peptides

A procedure for enhanced capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) of proteins is presented. The use of a newly presented capillary coating, PolyE-323, provided fast separations of typically a few minutes with high efficiency, good deactivation, and no bleeding into the mass spectrometer. Capillaries coated with PolyE-323 showed high stability over a range of pH 2-10, and tolerance towards methanol and acetonitrile, two modifiers commonly used in CE-ESI-MS. Due to the speed and simplicity of the coating procedure, the polymeric surface could, if necessary, easily be regenerated. This capability is especially valuable when working with samples of complex matrix, where a capillary surface cleaning step might be desired in order to eliminate possible memory effects. The potential of PolyE-323-coated capillaries in bioanalysis using CE-ESI-MS was demonstrated by analyzing peptides and proteins up to 66 kDa using time of flight (TOF)-MS. Due to the stable, anodal electroosmotic flow generated by the coating, the use of a sheathless ESI interface was enabled, demonstrated in peptide analysis with attomole sensitivity. The fast on-line CE-ESI-TOF system using PolyE-323-coated capillaries provided efficient separation and detection of a large number of peaks in a short time, exemplified by the analysis of a tryptic digest of bovine serum albumin (BSA). The capability of the developed capillary surface coating was demonstrated by the separation of human plasma and cerebrospinal fluid (CSF).     

A novel supramolecular multicolor thermometer by self-assembly of a pi-extended zinc porphyrin complex

A zinc complex of (3-pyridyl)porphyrin with an alkynyl sidearm (1) preferentially formed a cyclic tetramer in toluene, which showed supramolecular thermochromism at ambient temperatures of 0-100 degrees C. Because of an appropriate extension of pi-electronic conjugation of the porphyrin chromophore, the thermal-induced self-assembling dynamics of 1 can be detected as a vivid color change from red to yellow to green. In sharp contrast, 2 without any alkynyl group, on heating, developed only a small color change from orange to pink, while 3 bearing two alkynyl groups stayed green and did not display any thermochromism.     

Syntheses and conformational analyses of the perhydrofuro[2,3-b]furan compounds by using lanthanide shift reagent and empirical force-field calculation

1-t-Butyl-7-hydroxyperhydrofuro[2,3-b]furan was synthesized via a furan-alcohol which was derived by a coupling reaction with an epoxide and a new reagent, Li di(3-furyl)cuprate. The configuration of the t-butyl substituent and the conformation of the furo[2,3-b]furan ring were decided by the combination of the LIS experiment and the empirical force-field calculation.     

Spin-crossover dendrimers: generation number-dependent cooperativity for thermal spin transition

Poly(benzyl ether) dendrons having a focal triazole unit (Gntrz: trz = triazole; n = generation number = 0-2) were found to react with (MeSO(3))(2)Fe to form dendritic coordination polymers ([Fe(Gntrz)(3)](MeSO(3))(2).2H(2)O) that undergo the thermal spin transition. When the generation number of the dendritic unit was larger (n = 0 --> 1 --> 2), the average degree of polymerization (D(p) = 20 --> 10 --> 3) and spin-crossover temperature (T(c) = 335 --> 315 --> 300 K) of the resulting polymer were lower. However, the abruptness of the spin transition was not monotonically dependent on the generation number; (G1trz)Fe exhibited an abrupt spin transition with a temperature width of only 10 K, while the smallest and largest members of the (Gntrz)Fe family both displayed a rather broad spin-transition temperature width (30 (n = 0) and 50 K (n = 2)). X-ray diffraction and calorimetric analyses indicated the presence of a discotic columnar core-shell assembly with a crystal lattice best occupied by a C(3)(v)() symmetric array of medium-sized (G1trz)Fe.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMST effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO-H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.