Unambiguous Determination of the Absolute Configurations of Acetylene Alcohols by Combination of the <Emphasis Type="Italic">Sonogashira</Emphasis> Reaction and the CD Exciton Chirality Method – Exciton Coupling between Phenylacetylene and Benzoate Chromophores

Summary. The CD exciton chirality method was applied to various phenylacetylene alcohols to determine their absolute configurations; the long axis polarized –^* transition (_max=252nm) of the 4-methoxyphenylacetylene chromophore couples with the transition (_max=257nm) of the 4-methoxybenzoate group to generate intense exciton split CD Cotton effects, from the signs of which the absolute configurations of phenylacetylene alcohols were unambiguously determined. As an extension of the results, a new methodology for determining the absolute configurations of acetylene alcohols having the HCCCH(OH)-moiety by combination of the Sonogashira reaction and the CD exciton chirality method has been developed and applied. Since the –^* transition of acetylene triple bond is located below 180nm, it is difficult to observe ideal bisignate CD Cotton effects due to the exciton coupling between acetylene and benzoate chromophores. To observe the ideal exciton split Cotton effects necessary for the unambiguous determination of absolute configuration, the terminal acetylene group was converted, by the Sonogashira reaction, to the 4-methoxyphenylacetylene moiety, which exhibits an intense –^* absorption band polarized along the long axis of the chromophore at 252nm. As a partner of exciton coupling, 4-methoxybenzoate showing a –^* band at 257nm was introduced into the alcohol moiety, and the benzoates formed showed intense bisignate CD Cotton effects, from the signs of which the absolute configurations of original acetylene alcohols could be determined in an unambiguous manner.     

A biocompatible needle-type glucose sensor based on platinum-electroplated carbon electrode

A biocompatible needle-type glucose sensor with a 3-electrode configuration was constructed. A platinum-electroplated carbon stick was used as the working electrode, Ag/AgCl as the reference electrode, and a disposable hypodermic needle made of stainless steel as the counter electrode. A Nafion membrane, an immobilized glucose oxidase (GOD) membrane, and a biocompatible membrane with diffusion-limiting effect were coated successively onto the working electrode. The sensor showed a rapid response (< 120 s in batch operation), good reproducibility (RE < 3%), good stability (over 36 h in control serum), a wide dynamic range (5-600 mg/dL glucose), and superior biocompatibility. It was used to determine glucose in serum. The data obtained from the sensor showed good agreement with that from a clinical autoanalyzer (R > 0.95).     

Binding forces in complexation ofp-alkylphenols withβ-cyclodextrin and methylatedβ-cyclodextrins

Fluorescence spectroscopy has been used to determine the binding constants (K) for inclusion complexes of six kinds ofp-Akyphenols with-cyclodextrin (-CDx), heptakis(2,6-di-O-methyl)--CDx (DMe--CDxg), and heptakis(2,3,6-tri-O-methyl)--CDx (TMe--CDx). The stability of the inclusion complex of each cyclodextrin increases with increasing alkyl chain length of thep-alkylphenol. TheK values decrease in the order of DMe--CDx,-CDx, and TMe--CDx for each guest. In complexation of 3-(p-hydroxyphenyl)-1-propanol (3) with-CDx as well as with DMe--CDx, negative enthalpy (H) and positive entropy changes (S) have been obtained, suggesting both van der Waals and hydrophobic interactions as binding forces. The inclusion of 3 by TMe--CDx, however, is an enthalpically favorable but entropically unfavorable process. The van der Waals interactions may be the main binding forces for complexing3 with TMe--CDx.     

1-ethyl-3-methylimidazolium based ionic liquids containing cyano groups: synthesis, characterization, and crystal structure

New 1-ethyl-3-methylimidazolium (EMI) salts [EMI][C(CN)3] and [EMI][Ag(CN)2] were prepared and characterized. The C(CN)3 salt has a melting point at -11 degrees C and shows a low viscosity (18 cP) and a high ionic conductivity (1.8 x 10(-2) S cm(-1)) at room temperature. This conductivity is less than that of [EMI][N(CN)2] salt (2.7 x 10(-2) S cm(-1)), possibly due to the larger molecular weight of the anion. The first EMI salt containing Ag(I) complexes [EMI][Ag(CN)2] has a higher melting point of 73 degrees C. In the crystal, the C-H...pi interionic interactions between cations construct zigzag chains in the cationic two-dimensional layer. Close Ag..Ag interionic contacts of 3.226(1) A were observed in the one-dimensional anionic chain, and the relatively high melting point among the EMI salts with a monoanion appears to be governed essentially by these direct Ag...Ag interactions.     

A Pb MAS-NMR study of Pb-containing glasses

²⁰⁷Pb magic angle spinning (MAS)-NMR spectra have been obtained for various Pb-containing crystalline compounds and high lead glasses. The isotropic chemical shifts were determined for the crystalline samples. The more ionic lead atoms with a coordination number larger than six had relatively small chemical shifts between 0 and 2382 ppm with respect to crystalline Pb(NO₃)₂. On the other hand, the covalent lead atoms with PbO₃ trigonal and PbO₄ square pyramidal configurations gave a multiplet line profile with shifts ranging from about 3000 to 6000 ppm. The lead atoms with different local environments in PbSiO₃ (alamosite) and H-Pb₂SiO₄, for instance, could be clearly distinguished from each other on the basis of the isotropic chemical shift. The NMR spectra for the high lead glasses of composition 67PbO·33SiO₂, 80PbO·20B₂O₃ and 70PbO· 30GaO_1.5 were found to exhibit an extremely broad peak with a shift ranging from about 3000 to 6000 ppm. This shift indicates that, in these glasses, neither such highly ionic lead atoms as found in symmetrical PbO₆ octahedra nor such highly covalent ones as found in PbO₄ square pyramids in the PbO crystal are predominant, but instead PbO₃ trigonal or PbO₄ square pyramids, with two or three other neighboring oxygens at larger distances as found in H-Pb₂SiO₄ or PbSiO₃, are the major lead-oxygen configuration.     

Convenient Preparation of Self-Assembled Monolayers Derived from Calix[4]resorcinarene Derivatives Exhibiting Resistance to Desorption

Crown conformers of O-carboxymethylated calix[4]resorcinarenes (CRA-CMs) bearing four perfluorooctyl- and octylazobenzene residues at the lower rim of the cyclic skeleton were synthesized to investigate the resistance to desorption of CRA-CMs forming self-assembled monolayers on aminosilylated silica substrates and the surface energy photocontrol based on E- to-Z photoisomerization of the azobenzene moiety. In comparison with CRA-CM monolayers on silica substrates, the desorption of CRA-CMs on the aminated substrate was remarkably suppressed even when CRA-CM monolayers were sonicated in polar solvents and even in water. The high desorption-resistance was attributable to multi-point adsorption of CRA-CMs through COOH/NH₂ interactions. UV-Vis spectral studies revealed that CRA-CM substituted with p-octylazobenzene exhibited high E- to-Z photoisomerizability up to 92% in self-assembled monolayers, while less photoisomerizability was observed for CRA-CM bearing p-perfluorooctylazobenzenes due to the steric hindrance of the larger perfluoroalkyl chains. Photoinduced changes of contact angles for water up to 8.3° were observed for a CRA-CM monolayer.     

E' centers in amorphous SiO(2) revisited: a new look at an old problem.

We present theoretical evidence that the paramagnetic E' defect centers in amorphous silicon dioxide (a-SiO(2)) do not have the same microscopic structures as those well-defined in the corresponding crystalline counterparts such as alpha-quartz. We then present alternative models of some paramagnetic defects that account for the underlying experimental features of the E'-center variants in a-SiO(2). We suggest that our new model should take the place of the conventional defect model of a-SiO(2).     

Needle-type ultra micro silver/silver chloride reference electrode for use in micro-electrochemistry.

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.     

Observing quantum correlation of photons in Laguerre-Gauss modes using the Gouy phase

The effect of the Gouy phase, which is one of the geometrical phases of photons, is observed through quantum correlation in Laguerre-Gaussian (LG) modes. In an experiment, the relative phase of two different LG modes of measurement basis states is manipulated via the Gouy phase, and the observed coincidence count rates agree well with theoretical predictions. This result suggests that the Gouy phase can be used as a new tool to manipulate multidimensional photonic quantum states.