We demonstrate the visualization of ultrafast hydrogen migration in deuterated acetylene dication (C2D2{2+}) by employing the pump-probe Coulomb explosion imaging with sub-10-fs intense laser pulses (9 fs, 0.13 PW/cm{2}, 800 nm). It is shown, from the temporal evolution of the momenta of the fragment ions produced by the three-body explosion, C2D2{3+}-->D{+} + C{+} + CD{+}, that the migration proceeds in a recurrent manner: the deuterium atom first shifts from one carbon site to the other in a short time scale (approximately 90 fs) and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation.

To assess the hepatic disposition of erlotinib, we performed positron emission tomography (PET) scans with [11C]erlotinib in healthy volunteers without and with oral pretreatment with a therapeutic erlotinib dose (300 mg). Erlotinib pretreatment significantly decreased the liver exposure to [11C]erlotinib with a concomitant increase in blood exposure, pointing to the involvement of a carrier‐mediated hepatic uptake mechanism. Using cell lines overexpressing human organic anion‐transporting polypeptides (OATPs) 1B1, 1B3, or 2B1, we show that [11C]erlotinib is selectively transported by OATP2B1. Our data suggest that at PET microdoses hepatic uptake of [11C]erlotinib is mediated by OATP2B1, whereas at therapeutic doses OATP2B1 transport is saturated and hepatic uptake occurs mainly by passive diffusion. We propose that [11C]erlotinib may be used as a hepatic OATP2B1 probe substrate and erlotinib as an OATP2B1 inhibitor in clinical drug–drug interaction studies, allowing the contribution of OATP2B1 to the hepatic uptake of drugs to be revealed.

The stereochemical control of free radical reaction is generally more difficult than that of the other types of reactions. 1 This is the case not only for the organic synthesis but also for macromolecular chemistry; only few examples are known as stereoregular free radical polymerization in solution. 2 -5 Further, the stereospecificity of free radical polymerization in solution relies mainly on the structure of starting monomer, which makes it difficult to obtain polymers with widely varying stereoregularity from a certain monomer.In the present study, we found remarkable effects of reaction temperature, monomer concentration in feed ([M] 0 ), and solvent on tacticity in the free radical polymerization of triphenylmethyl methacrylate (TrMA) and succeeded in the synthesis of the polymers having triad isotacticity (mm) ranging from 64% to 99%. 6 -8 This communication describes the stereochemistry of TrMA polymerization in comparison with that of the polymerizations of methyl methacrylate (MMA) and 1-phenyldibenzosuberyl methacrylate (PDBSMA), a TrMA analogue, which we have reported to give a highly isotactic polymer by radical polymerization. 3 TrMA is known to give an isotactic polymer by radical polymerization though the triad isotacticity has been reported to be only 64%. 2 The isospecificity in this polymerization can be ascribed to a helical conformation of the growing radical because TrMA leads to an optically active, almost perfectly isotactic, and purely single-handed helical polymer by asymmetric anionic polymerization 9 -11 as well as the other bulky methacrylates. 12 The conditions and results of polymerization ofTrMA, PDBSMA, and MMA in toluene are summarized in Table I. It can roughly be said that a lower temperature and a higher [M] 0 give a higher yield and a higher degree 556 of polymerization (DP) of the products in the polymerizations of the three monomers. A higher propagation rate at a higher [M] 0 and lower chances of depolymerization at a lower temperature may be responsible for these observations.The polymers having the wide range of tacticity were obtained by changing reaction temperature and [M] 0 in TrMA polymerization. At a higher polymerization temperature and at a lower [M] 0 , a higher isotacticity was achieved; the mm content of the polymer exceeded 98% under the conditions of runs 4 and 7 (Figure 1). In contrast to the TrMA polymerization, almost perfectly isotactic polymers were obtained regardless of [M] 0 and temperature in the polymerization of PDBSMA (runs 8-11) 13 and the stereochemistry of MMA polymerization was not affected by [M] 0 (runs 12-14). Reaction temperature is known to affect stereochemistry of MMA polymerization to a small extent; rr triad content decreases only by 5% with increasing reaction temperature from 30°C to 70oC. 14 We propose the following models of propagating species in order to understand the unusual results. ( 1) There are, at least, two types of helical propagating radicals having different possibilities of meso monomer addition. (2) The two m...

ABSTRACT:Asymmetric anionic polymerization of 1-phenyldibenzosuberyl methacrylate [5-phenyldibenzosuberan-5-yl methacrylate, 5-phenyl-10, 11-dihydrodibenzo[a,d] conformation of main chain. In contrast, 2 gave one-handed helical polymers only by the polymerization with the Sp and PMP complexes. The polymerization of 2 with the DDB complex was sluggish. Monomers 1 and 2 showed higher resistance against methanolysis compared with triphenylmethyl methacrylate and diphenyl-2-pyridylmethyl methacrylate, respectively. The obtained optically active polymers resolved several racemic compounds. KEY WORDSOptically active polymers having helical conformation are obtained by asymmetric polymerization of achiral monomers including methacrylates, isocyanates, isocyanides, and chloral. 2 The importance of the helical polymers lies in application for chiral recognition of racemic compounds in addition to unique structural characteristics. Purely one-handed helical poly(triphenylmethyl methacrylate) [poly(TrMA)] is the first vinyl polymer of its kind. 3 -6 Poly(TrMA) has an almost perfectly isotactic configuration and its helical conformation is maintained by steric repulsion between the bulky side groups. One-handed helical polymers have been obtained by anionic polymerization with the complexes of organolithiums and chiralligands. Poly(TrMA) can resolve many classes of racemates when used as chiral stationary phase for high performance liquid chromatography (HPLC). 7 However, the poly(TrMA) has a shortcoming that the ester linkage is readily solvolyzed by methanol which is often used as an HPLC eluent. In order to overcome this drawback, we synthesized several TrMA-analogues including those having electron-withdrawing substituent on the phenyl groups 8 or a pyridyl group 9 -11 in place of a phenyl group. In the present work, we synthesized and polymerized 1-phenyldibenzosuberyl methacrylate (PDBSMA) and 1-(2-pyridyl)dibenzosuberyl methacrylate (2PyDBSMA) having a dibenzosuberyl moiety in the ester group in order to obtain novel, solvolysis-resistant optically active polymethacrylates. Solvolysis of triaryl esters is considered to involve a triaryl cation as an intermediate. The triaryl cation can be stabilized by delocalization of the cation by the planar resonance structures. We assumed that PDBSMA and 2PyDBSMA are more resistant against methanolysis than TrMA 330 and diphenyl-2-pyridylmethyl methacrylate (D2PyMA), their parent monomers, respectively, since the planar structures are difficult to attain for a 1-

Photoelectron spectroscopy has been performed to study the multiphoton double ionization of Ar in an intense extreme ultraviolet laser field (hν ∼ 21  eV, ∼ 5  TW/cm²), by using a free electron laser (FEL). Three distinct peaks identified in the observed photoelectron spectra clearly show that the double ionization proceeds sequentially via the formation of Ar(+): Ar+hν→Ar (+) + e⁻ and Ar²(+) + 2hν→Ar(+) + e⁻. Shot-by-shot recording of the photoelectron spectra allows simultaneous monitoring of FEL spectrum and the multiphoton process for each FEL pulse, revealing that the two-photon ionization from Ar(+) is significantly enhanced by intermediate resonances in Ar(+).

The visualization of ultrafast isomerization of deuterated acetylene dication (C(2)D(2)(2+)) is demonstrated by time-resolved Coulomb explosion imaging with sub-10 fs intense laser pulses (9 fs, 0.13 PW cm(-2), 800 nm). The Coulomb explosion imaging monitoring the three-body explosion process, C(2)D(2)(3+)→ D(+) + C(+) + CD(+), as a function of the delay between the pump and probe pulses revealed that the migration of a deuterium atom proceeds in a recurrent manner; One of the deuterium atoms first shifts from one carbon site to the other in a short timescale (∼90 fs), and then migrates back to the original carbon site by 280 fs, in competition with the molecular dissociation. Correlated motion of the two deuterium atoms associated with the hydrogen migration and structural deformation to non-planar geometry are identified by the time-resolved four-body Coulomb explosion imaging, C(2)D(2)(4+)→ D(+) + C(+) + C(+) + D(+).

Nonlinear, three-photon double excitation of He in intense extreme ultraviolet free-electron laser fields (∼24.1  eV, ∼5  TW/cm2) is presented. Resonances to the doubly excited states converging to the He+ N=3 level are revealed by the shot-by-shot photoelectron spectroscopy and identified by theoretical calculations based on the time-dependent Schrödinger equation for the two-electron atom under a laser field. It is shown that the three-photon double excitation is enhanced by intermediate Rydberg states below the first ionization threshold, giving a greater contribution to the photoionization yields than the two-photon process by more than 1 order of magnitude.

The isomerization of acetylene via hydrogen migration in intense laser fields (8 x 10(14) W/cm2) has been investigated by coincidence momentum imaging of the three-body Coulomb explosion process, C2H2 (3+)-->H+ + C+ + CH+. When ultrashort (9 fs) laser pulses are used, the angle between the momenta of C+ and H+ fragments exhibits a sharp distribution peaked at a small angle ( approximately 20 degrees ), showing that the hydrogen atom remains near the original carbon site in the acetylene configuration. On the other hand, a significantly broad distribution extending to larger momentum angles ( approximately 120 degrees ) is observed when the pulse duration is increased to 35 fs, indicating that the ultrafast isomerization to vinylidene is induced in the longer laser pulse.