High-temperature ultra-performance liquid chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry applied to ibuprofen metabolites in human urine

The application of sub-2 microm porous particle liquid chromatography (LC) operated at elevated temperatures, coupled with time-of-flight mass spectrometry (MS), to the separation and identification of metabolites of ibuprofen present in human urine following oral administrations is illustrated. The LC/MS system generated a high-resolution analytical separation that, with an analysis time of 20 min, provided a peak capacity in the order of ca. 350. Using this system a total of nine glucuronides of the drug and its metabolites were detected, including a number of isomeric acyl glucuronides of ibuprofen itself, a side-chain-oxidized carboxylic acid acyl glucuronide and a number of acyl glucuronides of various hydroxylated metabolites. The identities of the metabolites were confirmed by their accurate mass values and the presence of the common fragment ions from ibuprofen.     

Coarse-grained lattice kinetic Monte Carlo simulation of systems of strongly interacting particles

A general approach is presented for spatially coarse-graining lattice kinetic Monte Carlo (LKMC) simulations of systems containing strongly interacting particles. While previous work has relied on approximations that are valid in the limit of weak interactions, here we show that it is possible to compute coarse-grained transition rates for strongly interacting systems without a large computational burden. A two-dimensional square lattice is employed on which a collection of (supersaturated) strongly interacting particles is allowed to reversibly evolve into clusters. A detailed analysis is presented of the various approximations applied in LKMC coarse graining, and a number of numerical closure rules are contrasted and compared. In each case, the overall cluster size distribution and individual cluster structures are used to assess the accuracy of the coarse-graining approach. The resulting closure approach is shown to provide an excellent coarse-grained representation of the systems considered in this study.     

A velocity map ion imaging study of difluorobenzene-water complexes: binding energies and recoil distributions

The binding energies of the p-, m-, and o-difluorobenzene-H(2)O complexes have been measured by velocity map ion imaging to be 922+/-10, 945+/-10, and 891+/-4 cm(-1), respectively. The lack of variation provides circumstantial evidence for water binding to the three isomers via the same interaction, viz. an in-plane O-H...F hydrogen bond to one of the fluorine atoms on the ring, with a second, weaker interaction of the water O atom with an ortho hydrogen, as determined previously for the p-difluorobenzene-H(2)O complex [Kang et al., J. Phys. Chem. A 109, 767 (2005)]. The ground state binding energies for the difluorobenzene-H(2)O complexes are approximately 5%-11% larger than that for benzene-H(2)O, where binding occurs to the pi electrons out-of-plane. However, in the S(1) state the binding energies of the o- and p-difluorobenzene-H(2)O complexes are smaller than the benzene-H(2)O value, raising an interesting question about whether the geometry at the global energy minimum remains in-plane in the excited electronic states of these two complexes. Recoil energy distributions for dissociation of p-difluorobenzene-H(2)O have been measured from the 3(1), 5(2), and 3(1)5(1) levels of the excited electronic state. These levels are 490, 880, and 1304 cm(-1), respectively, above the dissociation threshold. Within the experimental uncertainty, the recoil energy distributions are the same for dissociation from these three states, with average recoil energies of approximately 100 cm(-1). These recoil energies are 60% larger than was observed for the dissociation of p-difluorobenzene-Ar, which is a substantially smaller increase than the 400% seen in a comparable study of dissociation within the triplet state for pyrazine-Ar, -H(2)O complexes. The majority of the available energy is partitioned into vibration and rotation of the fragments.     

Generation and spectroscopic characterization of ruthenacyclobutane and ruthenium olefin carbene intermediates relevant to ring closing metathesis catalysis

The reaction of phosphonium alkylidenes [(H2IMes)RuCl2=CHPR3]+[A]- (R = C6H11, A = OTf or B(C6F5)4, 1-Cy; R = i-C3H7, A = ClB(C6F5)3 or OTf, 1-iPr) with 1 equiv of ethylene at -78 degrees C, in the presence of 2-3 equiv of a trapping olefin substrate, yields intermediates relevant to olefin metathesis catalytic cycles. Dimethyl cyclopent-3-ene-1,1-dicarboxylate gives solutions of a substituted ruthenacyclobutane 3 of relevance to ring closing metathesis catalysis. 1H and 13C NMR data are fully consistent with its assignment as a ruthenacyclobutane, but 1JCC values of 23 Hz for the CalphaH2-Cbeta bond and 8.5 Hz for the CalphaH-Cbeta bond point to an unsymmetrical structure in which the latter bond is more activated than the former. In contrast, trapping with acenaphthylene leads to an olefin carbene complex (6) in which the putative ruthenacyclobutane has opened; this species was also fully characterized by NMR spectroscopy and compared to related species reported previously.     

Electrocatalytic performance of fuel oxidation by Pt3Ti nanoparticles

A Pt-based electrocatalyst for direct fuel cells, Pt3Ti, has been prepared in the form of nanoparticles. Pt(1,5-cyclooctadiene)Cl2 and Ti(tetrahydrofuran)2Cl4 are reduced by sodium naphthalide in tetrahydrofuran to form atomically disordered Pt3Ti nanoparticles (FCC-type structure: Fm3m; a = 0.39 nm; particle size = 3 +/- 0.4 nm). These atomically disordered Pt3Ti nanoparticles are transformed to larger atomically ordered Pt3Ti nanoparticles (Cu3Au-type structure: Pm3m; a = 0.3898 nm; particle size = 37 +/- 23 nm) by annealing above 400 degrees C. Both atomically disordered and ordered Pt3Ti nanoparticles show lower onset potentials for the oxidation of formic acid and methanol than either pure Pt or Pt-Ru nanoparticles. Both atomically disordered and ordered Pt3Ti nanoparticles show a much lower affinity for CO adsorption than either pure Pt or Pt-Ru nanoparticles. Atomically ordered Pt3Ti nanoparticles show higher oxidation current densities for both formic acid and methanol than pure Pt, Pt-Ru, or atomically disordered Pt3Ti nanoparticles. Pt3Ti nanoparticles, in particular the atomically ordered materials, have promise as anode catalysts for direct fuel cells.     

Prompt determination of evacuee radiation dose from a nuclear event

In anticipation of a nuclear detonation, techniques to quickly assess the radiation exposure of evacuees should be developed. Based on experience relating neutron radiation exposures to activation products, measurement of activation products can be performed in a few minutes. Personal items exposed to significant levels of radiation allows neutron dose assessment via the activation products. This approach allows prompt collection of important data on human exposure following a nuclear attack. Data collected will facilitate triage decisions for emergency medical treatment to ameliorate the radiation effects on exposed individuals. Activation experiments with everyday items exposed to a neutron source are presented.     

Crystal structures,Hirshfeld analysis,and energy framework analysis of two differently 3′-substituted 4-methylchalcones: 3′-(N=CHC6H4-p-CH3)-4-methylchalcone and 3′-(NHCOCH3)-4-methylchalcone

Two crystal structures of chalcones, or 1,3-diarylprop-2-en-1-ones, are presented; both contain a p-methyl substitution on the 3-Ring, but differ with respect to the m-substitution on the 1-Ring. Their systematic names are (2E)-3-(4-methylphenyl)-1-(3-{[(4-methylphenyl)methylidene]amino}phenyl)prop-2-en-1-one (C₂₄H₂₁NO) and N-{3-[(2E)-3-(4-methylphenyl)prop-2-enoyl]phenyl}acetamide (C₁₈H₁₇NO₂), which are abbreviated as 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone and 3′-(NHCOCH₃)-4-methylchalcone, respectively. Both chalcones represent the first reported acetamide-substituted and imino-substituted chalcone crystal structures, adding to the robust library of chalcone structures within the Cambridge Structural Database. The crystal structure of 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone exhibits close contacts between the enone O atom and the substituent arene ring, in addition to C…C interactions between the substituent arene rings. The structure of 3′-(NHCOCH₃)-4-methylchalcone exhibits a unique interaction between the enone O atom and the 1-Ring substituent, contributing to its antiparallel crystal packing. In addition, both structures exhibit π-stacking, which occurs between the 1-Ring and R-Ring for 3′-(N=CHC₆H₄-p-CH₃)-4-methylchalcone, and between the 1-Ring and 3-Ring for 3′-(NHCOCH₃)-4-methylchalcone.     

Elusive Terminal Copper Arylnitrene Intermediates

We report herein three new modes of reactivity between arylazides N₃Ar with a bulky copper(I) β-diketiminate. Addition of N₃Ar^X3 (Ar^X3=2,4,6-X₃C₆H₂; X=Cl or Me) to [ⁱPr₂NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [ⁱPr₂NN]Cu(NCMe) with bulkier azides N₃Ar leads to terminal nitrenes [ⁱPr₂NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-ⁱPr₂C₆H₃) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr₂C₆H₂). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [ⁱPr₂NN]Cu=NAr that undergo nitrene group transfer to PMe₃, ^tBuNC, and even into a benzylic sp³ C−H bond of ethylbenzene.