Low-temperature specific heat of the heavy-fermion superconductor PrOs4Sb12

We report the magnetic field dependence of the specific-heat C of single crystals of the first Pr-based heavy-fermion superconductor Pr(Os4Sb12. The variation of C at low temperature and the magnetic phase diagram inferred from C, the resistivity and magnetization provide compelling evidence of a doublet ground state. Two distinct superconducting anomalies in C indicate an unconventional superconducting state, where the splitting may arise from a weak lifting of the ground state degeneracy. In combination this identifies Pr(Os4Sb12 as a strong contender for quadrupolar pairing, i.e., superconductivity that is neither electron-phonon nor magnetically mediated.     

Studies of the kinetics and thermochemistry of the forward and reverse reaction Cl + C6H6 = HCl + C6H5

The laser flash photolysis resonance fluorescence technique was used to monitor atomic Cl kinetics. Loss of Cl following photolysis of CCl4 and NaCl was used to determine k(Cl + C6H6) = 6.4 x 10(-12) exp(-18.1 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 578-922 K and k(Cl + C6D6) = 6.2 x 10(-12) exp(-22.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 635-922 K. Inclusion of literature data at room temperature leads to a recommendation of k(Cl + C6H6) = 6.1 x 10(-11) exp(-31.6 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) for 296-922 K. Monitoring growth of Cl during the reaction of phenyl with HCl led to k(C6H5 + HCl) = 1.14 x 10(-12) exp(+5.2 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 294-748 K, k(C6H5 + DCl) = 7.7 x 10(-13) exp(+4.9 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 292-546 K, an approximate k(C6H5 + C6H5I) = 2 x 10(-11) cm(3) molecule(-1) s(-1) over 300-750 K, and an upper limit k(Cl + C6H5I) < or = 5.3 x 10(-12) exp(+2.8 kJ mol(-1)/RT) cm(3) molecule(-1) s(-1) over 300-750 K. Confidence limits are discussed in the text. Third-law analysis of the equilibrium constant yields the bond dissociation enthalpy D(298)(C6H5-H) = 472.1 +/- 2.5 kJ mol(-1) and thus the enthalpy of formation Delta(f)H(298)(C6H5) = 337.0 +/- 2.5 kJ mol(-1).     

Friedländer synthesis of poly‐substituted quinolines in the presence of triethylammonium hydrogen sulfate [Et3NH][HSO4] as a highly efficient,and cost effective acidic ionic liquid catalyst

A rapid and an efficient method for the preparation of a variety of substituted quinolines has been developed through the reactions of o‐aminoarylketones with carbonyl compounds containing a reactive α‐methylene moiety in the presence of molten [Et₃NH][HSO₄] under solvent‐free conditions in high yields. J. Heterocyclic Chem., (2011).     

A surfactant–heme–sulfonyl imidazole system as a nano-artificial enzyme

The heme–imidazole–sodium dodecyl sulfate (SDS) ternary complex has been designed as a peroxidase-like nano-artificial enzyme, in which the imidazole moiety functions like the histidine ligand in the native horseradish peroxidase (HRP) and increases the reactivity and catalytic efficiency of the designed artificial enzyme by promoting the heterolytic cleavage of hydrogen peroxide. In the present study, three different ligands were used as the imidazole-based ligands in the heme–ligand–SDS ternary system: (1) 1-methylsulfonyl-1H-imidazole, (2) 1-(benzensulfonyl)-1H-imidazole, and (3) 1-tosyl-1H-imidazole (TsIm). The three different ligands gave variable reactivity in the system studied, and the enzymatic activation parameters, using spectrophotometric measurements, showed that the TsIm ligand had a higher catalytic efficiency at 26.38 % of the native HRP efficiency. To investigate the increase in catalytic activity, its mechanism was explored based on the original mechanism of HRP and the structure of its first catalytic intermediate (compound I). Based on the mechanism of HRP and the structure of compound I, a suggested mechanism for Tslm is as follows: the TsIm cation radical makes up part of the compound I structure, which is stabilized in the enzymatic process by charge distribution that is induced via phenyl and methyl groups. Suicide inactivation of heme–TsIm–SDS and heme–imidazole–SDS models was also compared to each other. Suicide inactivation was less exhibited in the presence of TsIm than imidazole in this system unless high concentrations of hydrogen peroxide were used.     

Gas-phase protonation and deprotonation of acrylonitrile derivatives N[triple chemical bond]C--CH==CH--X (X=CH(3), NH(2), PH(2), SiH(3))

A combined experimental and theoretical study on the gas-phase basicity and acidity of a series of cyanovinyl derivatives is presented. The gas-phase basicities and acidities of (N[triple chemical bond]C--CH==CH--X, X=CH(3), NH(2)) were obtained by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry techniques. The corresponding calculated values were obtained at the G3B3 level of theory. The effects of exchanging CH(3) for SiH(3), and NH(2) for PH(2), were analyzed at the same level of theory. For the neutral molecules, the Z isomer is always the dominant species under standard gas-phase conditions at 298 K. The loss of the proton from the substituent X was found systematically to be much more favorable than deprotonation of the HC==CH linking group. The corresponding isomeric E ion is much more stable than the Z ion, so that only the former should be found in the gas phase. The most significant structural changes upon deprotonation occur for the methyl and amino derivatives because, in both cases, deprotonation of X leads to a significant charge delocalization in the corresponding anion. Protonation takes place systematically at the cyano group, whereby the isomeric E ion is again more stable than the Z ion. Push-pull effects explain the preference of aminoacrylonitrile to be protonated at the cyano group, which also explains the high basicity of this derivative relative to other members of the analyzed series that present rather similar gas-phase basicities, GB approximately 780 kJ mol(-1), indicating that the different nature of the substituents has only a weak effect on the intrinsic basicity of the cyano group. The cyanovinyl derivatives have a significantly stronger gas-phase acidity than that of the corresponding vinyl compounds CH(2)==CH--X. This acidity-strengthening effect of the cyano group is attributed to the greater stabilization of the anion with respect to the corresponding neutral compound.