o-Dihaloarenes as aryne precursors for nickel-catalyzed [2 + 2 + 2] cycloaddition with alkynes and nitriles

o-Dihaloarenes acting as aryne precursors react with acetylenes and nitriles catalyzed by the NiBr(2)(dppe)/dppe/Zn system to give substituted naphthalene, phenanthridine or triphenylene derivatives depending on the reaction conditions in moderate to excellent yields with good tolerance of functional groups.     

Vibrational-torsional excitation and direct overtone photodissociation of ethyl hydroperoxide at 5nuOH

We have observed OH radical products from the unimolecular dissociation of ethyl hydroperoxide (CH3-CH2OOH) excited to 5nuOH and have collected an action spectrum from 15,600 to 16,800 cm(-1) and an OH product state distribution at the maximum (16,119 cm(-1)). We use a vibrational-torsional model to simulate spectra in the 5nuOH region for the trans and gauche conformers. A combination of the two simulated spectra resembles the experimental action spectrum, provided that the trans conformer is assumed to dominate at room temperature. Energy disposal in the OH fragment yields an upper limit for the O-O bond dissociation energy at D0 < 44 kcal mol(-1).     

Single-step approach to beta-cyclodextrin-bonded silica as monolithic stationary phases for CEC

A novel single-step sol-gel approach for the preparation of beta-CD-bonded silica monolithic electrochromatographic columns is established. The porous silica networks were fabricated inside fused-silica capillaries using sol-gel processing of tetramethoxysilane and an organfunctional silicon alkoxide that contains beta-CD. Scanning electron micrographs and nitrogen adsorption-desorption data showed that these functional monolithic columns have double pores structures with micrometer-size co-continuous through-pores and silica skeletons with open mesopores. The beta-CD monolithic columns have successfully been applied to the separation of several neutral and negatively charged isomers by CEC. The column performance was evaluated by using positional isomers of naphthalenedisulfonic acid as model compounds. A plate height of less than 10 mum for the first eluted isomer of naphthalenedisulfonic acid was obtained at an optimal flow rate (0.47 mm/s) of the mobile phase. Moreover, the columns have been proved to be stable for more than 100 runs during 3 months period and show reasonable column reproducibility.     

Supercritical fluid chromatography-mass spectrometry for chemical analysis

Chromatography with a supercritical fluid as the mobile phase was suggested more than four decades ago (Klesper, E., Corwin, A. H., Turner, D. A., J. Org. Chem. 1962, 27, 700-701). Supercritical fluid chromatography (SFC) is basically a hybrid of GC and LC that eases the resolution of a mixture of compounds not conveniently resolved by either GC or LC. The mobile phases for SFC have low viscosities and high diffusion coefficients compared to those for HPLC and allow for high efficiency separations. SFC uses supercritical fluid as the mobile phase, polar organic solvents as the modifiers in conjunction with acidic/basic compounds as additives to run the chromatographic process like in HPLC. In many applications, SFC-based methods are advantageous over HPLC-based methods as a separation tool in terms of efficiency and economical impact perspectives. Today, the availability of commercial hardware and API interfaces with a mass spectrometer makes SFC even more widely applicable for chemical analysis in many research fields. This review summarizes a variety of novel SFC-MS methods for chemical analysis that have been reported in the peer-reviewed publications.     

Camptothecinoids from the seeds of Taiwanese Nothapodytes foetida

Two new alkaloids, 9-methoxy-18,19-dehydrocamptothecin (1) and 5- hydroxymappicine-20-O-beta-glucopyranoside (2a/2b as a racemic mixture), together with nine known compounds: camptothecin (3), 9-methoxy-camptothecin (4), 5-hydroxycamptothecin (5a/5b racemic mixture), 5-hydroxy-9-methoxycamptothecin (6a/6b racemic mixture), diosmetin (7), apigenin (8), apigenin-7-O-glucopyranoside (9), rosin (cinnamyl-O-beta-D-glucopyranoside) (10) and amarantholidoside IV (11) were isolated from the immature seeds of Nothapodytes foetida (Wight) Sleumer. The structures were elucidated by spectroscopic analyses. In the present research, compounds 1, 3, 4, 5a/5b and 6a/6b, also showed in vitro cytotoxicity against six cancer cell lines (HepG2, Hep3B, MDA-MB- 231, MCF-7, A549, and Ca9-22). Among them, compound 1 exhibited significant cytotoxicity against these cancer cell lines, with IC(50) of 0.24-6.57 microM. Furthermore, HPLC profiles were developed for qualitative and quantitative analysis of these active constituents in different parts of this plant, including mature and immature seeds, leaves, stems and roots. The results revealed that compounds 3 and 4 have the highest concentrations, which are found in the roots part of the plant.     

Excited‐State Double Proton Transfer in Model Base Pairs: The Stepwise Reaction on the Heterodimer of 7‐Azaindole Analogues

A four fused‐ring system 11‐propyl‐6H‐indolo[2,3‐b]quinoline ( 6 HIQ ) is strategically designed and synthesized; it possesses a central moiety of 7‐azaindole ( 7AI ) and undergoes excited‐state double proton transfer (ESDPT). Despite a barrierless type of ESDPT in the 6 HIQ dimer, femtosecond dynamics and a kinetic isotope effect provide indications for a stepwise ESDPT process in the 6 HIQ/7AI heterodimer, in which 6 HIQ (deuterated 6 HIQ ) delivers the pyrrolyl proton (deuteron) to 7AI (deuterated 7AI ) in less than 150 fs, forming an intermediate with a charge‐transfer‐like ion pair, followed by the transfer of a pyrrolyl proton (deuteron) from cation‐like 7AI (deuterated 7AI ) to the pyridinyl nitrogen of the anion‐like 6 HIQ (deuterated 6 HIQ ) in ～1.5±0.3 ps (3.5±0.3 ps). The barrier of second proton transfer is estimated to be 2.86 kcal mol^?1 for the 6 HIQ/7AI heterodimer.     

Bioisosteric replacement of the pyrazole 3-carboxamide moiety of rimonabant. A novel series of oxadiazoles as CB1 cannabinoid receptor antagonists

Based on the bioisosteric replacement of the pyrazole C3-carboxamide of rimonabant with a 5-alkyl oxadiazole ring, a novel class of oxadiazole derivatives with promising biological activity towards CB1 receptors was discovered. Among them, compounds with an alkyl linker containing a strong electron-withdrawing group (e.g., CF(3)) and a sterically favorable bulky group (e.g., t-butyl) exhibited excellent CB1 antagonism and selectivity, and thus might serve as potential candidates for further development as anti-obesity agents.     

Relaxation of stretched DNA in slitlike confinement

We experimentally observe two separate time scales governing the entropic recoil in the linear force-extension regime of single double-stranded DNA in slit confinement. We demonstrate the existence of two distinct relaxation regimes at different extensions during relaxation. Contrary to bulk measurements, the true longest relaxation time may only be probed very close to equilibrium. A simple model of the relaxation mechanism leads to a scaling analysis that correctly predicts the extension at the crossover between the two regimes.     

Magnetizing oxides by substituting nitrogen for oxygen

We describe a possible pathway to new magnetic materials with no conventional magnetic elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads to holes in N 2p states which form local magnetic moments. Because of the very large Hund's rule coupling of Nitrogen and O 2p electrons and the rather extended spatial extent of the wave functions these materials are predicted to be ferromagnetic metals or small band gap insulators. Experimental studies support the theoretical calculations with regard to the basic electronic structure and the formation of local magnetic moments. It remains to be seen if these materials are magnetically ordered and, if so, below what temperature.     

Guajadial: an unusual meroterpenoid from guava leaves Psidium guajava

Guajadial (1), a novel caryophyllene-based meroterpenoid, was isolated from the Leaves of Psidium guajava (guava). The structure and relative stereochemistry of guajadial (1) were elucidated by extensive spectroscopic analysis. A possible biosynthetic pathway for 1 was proposed.