Radiation-Induced Polymerization of Urea Canal Complex. Part 3. Radiation-Induced Polymerization of Acrylonitrile-Urea Canal Complex in the Frozen State

Radiation-induced polymerization of acrylonitrile-urea canal complexes formed in frozen ethylene glycol or tert-butyl alcohol media was investigated. Formation of canal complexes in the frozen state was prolonged. The initial rate of polymerization was enhanced in the frozen state. The degree of polymerization of polymers obtained is found to show no depression at high conversions and is higher in the frozen state, suggesting stabilization of canal complexes by the frozen medium.     

A Click-Chemistry Linked 2′3′-cGAMP Analogue

2′3′-cGAMP is an uncanonical cyclic dinucleotide where one A and one G base are connected via a 3′-5′ and a unique 2′-5′ linkage. The molecule is produced by the cyclase cGAS in response to cytosolic DNA binding. cGAMP activates STING and hence one of the most powerful pathways of innate immunity. cGAMP analogues with uncharged linkages that feature better cellular penetrability are currently highly desired. Here, the synthesis of a cGAMP analogue with one amide and one triazole linkage is reported. The molecule is best prepared via a first Cu^I-catalyzed click reaction, which establishes the triazole, while the cyclization is achieved by macrolactamization.     

Efficient preparation of an N-aryl β-amino acid via asymmetric hydrogenation and direct asymmetric reductive amination en route to Ezetimibe

Two routes for the preparation of an N-aryl β-amino acid, an important precursor for the cholesterol-lowering drug Ezetimibe, were investigated. The first pathway proceeds via an Rh- or Ir-catalyzed asymmetric hydrogenation of N-aryl enamine giving the desired product with up to 82% ee. The other pathway involves a direct asymmetric reductive amination (DARA) of the β-keto ester which yielded the β-amino ester in high yield and 97% ee. Subsequent copper-catalyzed N-arylation gave the target compound.     

Maxwell speed distribution and analogue Hawking–Unruh temperature in an ontological model of a Harmonic oscillator ground state

Within an ontological (hidden variable) model of quantum fluctuation, one can discuss the actual   properties of a system regardless (independent) of measurement. Here we apply an ontological model proposed earlier to investigate a Harmonic oscillator in the quantum mechanical ground state. We first show that the actual speed of the oscillator fluctuates randomly following the Maxwell–Boltzmann distribution. On the other hand, the actual energy obeys a broad Gamma distribution with an average 3?ω/2$3?\omega /2$, where ω$\omega$ is the classical angular frequency, so that one may conclude that the outcome of a single energy measurement reveals the average of the actual energy. The distribution of actual speed (energy) thus formally resembles the distribution of speed (energy) of an ideal gas in thermal equilibrium of temperature T_g=?ω/2$T_g=?\omega /2$. We shall then argue that T_g$T_g$ can be written in a form analogous to the Hawking temperature for a Schwarzschild black hole in which the average distance of the oscillator from the origin plays the analogous role of the radius of the black hole event horizon. It can also be written in a form analogous to the Unruh temperature experienced by a body moving with a uniform acceleration. In the analogy, the oscillator suffers an effective acceleration which balances the attractive force of the trapping Harmonic potential, thus keeps its average position away from the origin.     

Design of Mononuclear Ruthenium Catalysts for Low‐Overpotential Water Oxidation

Water oxidation is a key reaction in natural photosynthesis and in many schemes for artificial photosynthesis. Inspired by energy challenges and the emerging understanding of photosystem II, the development of artificial molecular catalysts for water oxidation has become a highly active area of research in recent years. In this Focus Review, we describe recent achievements in the development of single‐site ruthenium catalysts for water oxidation with a particular focus on the overpotential of water oxidation. First, we introduce the general scheme to access the high‐valent ruthenium–oxo species, the key species of the water‐oxidation reaction. Next, the mechanisms of the O? O bond formation from the active ruthenium–oxo species are described. We then discuss strategies to decrease the onset potentials of the water‐oxidation reaction. We hope this Focus Review will contribute to the further development of efficient catalysts toward sustainable energy‐conversion systems.     

Dioxotungsten 1,2-benzenedithiolate complex stabilized by NH...S hydrogen bonds

Novel dioxo-tungsten(VI) bis(1,2-benzenedithiolate) complexes with neighboring amide groups, as models for tungsten enzymes, (NEt4)2[W(VI)O2{1,2-S(2)-3,6-(RCONH)2C6H2}2] (R = CH3, t-Bu), were designed and synthesized. The presence of the NH...S hydrogen bond was confirmed through IR spectrometry and X-ray crystallographic analysis. In the W(VI)O2 complexes, the NH...S hydrogen bond trans to the oxo ligand is stronger than that cis to oxo. On the basis of comparisons with [W(VI)O2(1,2-S2C6H4)2](2-), the NH...S hydrogen bond positively shifted the W(VI)/W(V) redox potentials and depressed the reduction by benzoin or triphenylphosphine. These results suggest that the NH...S hydrogen bond stabilizes the oxo ligand through trans influence and regulates O-atom transfer in tungsten and molybdenum enzymes.     

O-atom-transfer oxidation of [molybdenum(IV) oxo{3,6-(acylamino)2- 1,2-benzenedithiolato}2]2- promoted by intramolecular NH...S hydrogen bonds

Novel molybdenum dithiolene compounds having neighboring amide groups as models for molybdoenzymes, (NEt(4))(2)[Mo(IV)O{1,2-S(2)-3,6-(RCONH)(2)C(6)H(2)}(2)] (R = CH(3), CF(3), t-Bu, Ph(3)C), were designed and synthesized. The contributions of the NH...S hydrogen bond to the electrochemical properties of the metal ion and the reactivity of the O-atom-transfer reaction were investigated by a comparison with [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-). The MoOS(4) core of [Mo(IV)O{1,2-S(2)-3,6-(CH(3)CONH)(2)C(6)H(2)}(2)](2)(-) shows no significant geometrical difference from that of [Mo(IV)O(1,2-S(2)C(6)H(4))(2)](2)(-) in the crystal. The hydrogen bonds positively shifted the Mo(IV/V) redox potential and accelerated the reduction of Me(3)NO.     

Zinc(II) Complexes with 1H‐Imidazol‐4‐yl‐Containing Polyamine Ligand

The protonation and Zn^II/Cu^II complexation constants of tripodal polyamine ligand N¹‐(2‐aminoethyl)‐N¹‐(1H‐imidazol‐4‐ylmethyl)‐ethane‐1,2‐diamine (HL) were determined by potentiometric titration. Three new compounds, i.e. [H₃(HL)](ClO₄)₃ ( 5 ), [Zn(HL)Cl](ClO₄) ( 6 ) and {[Zn(L)](ClO₄)}_n ( 7 ) were obtained by reactions of HL · 4HCl with Zn(ClO₄)₂ · 6H₂O under different reaction pH, and they were compared with the corresponding Cu^II complexes reported previously. The results indicate that the reaction pH and metal ions have remarkable influence on the formation and structure of the complexes.     

Withdrawn: Analysis of thermal parameters and factors acting on thermal conduction of low‐k films

This paper appeared in the October issue, occupying pp. 1362‐1366. It was a duplicate of SIA.2880, which appears on pp. 1328‐1332 of the same issue. It has therefore been withdrawn from Wiley InterScience. The publisher apologises to the authors for the error. Copyright © 2008 John Wiley & Sons, Ltd.     

Energy-scale dependence of the lepton flavor-mixing matrix

We study an energy-scale dependence of the lepton flavor-mixing matrix in the minimal supersymmetric standard model with the effective dimension-five operators, which give Majorana masses of neutrinos. We analyze the renormalization group equations of the coefficients () of these effective operators under an approximation that neglects terms of order . We find that only (where is the generation number) real independent parameters in the lepton flavor-mixing matrix depend on the energy scale. In particular, all the phases in are scale-independent. Received: 10 April 1999 / Revised version: 23 May 1999 / Published online: 28 September 1999