Gold nanoparticles as dehydrogenase mimicking nanozymes for estradiol degradation

Small gold nanoparticles can mimic dehydrogenase activity to catalyze estradiol (E2) oxidation to estrone (E1), extending the range of nanozyme catalysis to environmentally and biologically important substrates.     

Time-resolved intraband electronic relaxation dynamics of Hg(n) (-) clusters (n=7-13,15,18) excited at 1.0 eV

Time-resolved photoelectron imaging has been used to study the relaxation dynamics of small Hg(n) (-) clusters (n=7-13,15,18) following intraband electronic excitation at 1250 nm (1.0 eV). This study furthers our previous investigation of single electron, intraband relaxation dynamics in Hg(n) (-) clusters at 790 nm by exploring the dynamics of smaller clusters (n=7-10), as well as those of larger clusters (n=11-13,15,18) at a lower excitation energy. We measure relaxation time scales of 2-9 ps, two to three times faster than seen previously after 790 nm excitation of Hg(n) (-), n=11-18. These results, along with size-dependent trends in the absorption cross-section and photoelectron angular distribution anisotropy, suggest significant evolution of the cluster anion electronic structure in the size range studied here. Furthermore, the smallest clusters studied here exhibit 35-45 cm(-1) oscillations in pump-probe signal at earliest temporal delays that are interpreted as early coherent nuclear motion on the excited potential energy surfaces of these clusters. Evidence for evaporation of one or two Hg atoms is seen on a time scale of tens of picoseconds.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

Evaluation of residual fuel oil standard reference materials as trace element standards

National Bureau of Standards residual fuel oil Standard Reference Materials, SRM 1619, 1620a, 1634a, and former SRM 1634 were analyzed for 20 trace elements by instrumental neutron activation analysis to determine whether these materials are suitable trace element standards for elements other than the 6 elements certified in SRM 1634a. The SRM 1634a is a suitable standard for Ni, V, Se, Na, Zn, As, Cr, Fe, Ce, Sm and La but Co, Ba, Nd, Cs, Eu, Sc, and Sb appear to be heterogeneously distributed and are probably present in mineral particulates. The SRM 1619 is a convenient standard for V and for low Ni content oils, but SRM 1620a does not appear to be a suitable standard for any trace element investigated.To whom correspondence should be addressed.     

Structure-enantioselectivity effects in 3,4-dihydropyrimido[2,1-b]benzothiazole-based isothioureas as enantioselective acylation catalysts

The catalytic activity and enantioselectivity in the kinetic resolution of (±)-1-naphthylethanol with a range of structurally related 3,4-dihydropyrimido[2,1-b]benzothiazole-based catalysts is examined. Of the isothiourea catalysts screened, (2S,3R)-2-phenyl-3-isopropyl substitution proved optimal, giving good levels of selectivity in the kinetic resolution of a number of secondary alcohols (S values up to >100 at ~50% conversion). Low catalyst loadings (0.10-0.25 mol%) of the optimal isothiourea can be used to generate enantiopure alcohols (>99% ee) in good yields.     

Determinant Forms for Extended Heat Functions and Expansions of Solutions of Associated Cauchy Problems

We briefly review series solutions of differential equations problems of the second order that lead to coefficients expressed in terms of determinants. Derivative type formulas involving a generating function with several parameters are developed for these determinant coefficients in first order problems. These permit constructing determinant forms for the heat polynomials and their Appell transforms. Hadamard's theorem for bounding determinants and conical regions are used to deduce simplified versions of expansion theorems involving these polynomials and associated Appell transforms. Extended versions of the heat equation are also considered.     

Time-resolved relaxation dynamics of Hgn- (11 <or = n <or = 16,n = 18) clusters following intraband excitation at 1.5 eV

Electron-nuclear relaxation dynamics are studied in Hg(n) (-) (11 相似文献