Photodissociation dynamics of acetaldehyde at 267 nm: A computational study of the CO-forming channels

A recent experiment on the 267 nm photolysis of gaseous acetaldehyde reveals that the molecular products (CO + CH₄) present product state distributions with computation –experiment discrepancy. This work aims to provide solution to such issue. The direct dynamics simulation of classical trajectories and the generalized multi-center impulsive model (GMCIM) are both utilized to predict the product state distributions of CO and CH₄ from 267 nm photolysis of acetaldehyde. Comparison with the experimental observation provides an assessment of the conventional approach of minimum energy path within the framework of three-center transition state (TS) and CH₃-roaming pathways. The result shows that the high-speed products observed in experiment are likely formed via the three-center TS pathway. The reasons that lead to the discrepancy between computation and experiments in previous studies are also investigated. A better agreement between computational and state-resolved experimental results can be achieved by selecting specific internal states of CO product from the computational data.     

Electron-Transfer Protocol for the Hydroxyalkenylation of Alkenes Using 1,2-Bis(phenylsulfonyl)ethylene

We report a protocol for alkene hydroxyalkenylation. Using a persulfate anion as a one-electron-oxidation reagent and 1,2-bis(phenylsulfonyl)ethylene as a radical acceptor in the presence of water, alkenes were converted into the corresponding 1-phenylsulfonyl-4-hydroxyalkenes in good to high yields. The hydroxyalkenylation process involves the nucleophilic hydroxylation of alkene radical cations to give β-hydroxyalkyl radicals, which, after a radical addition/β-elimination sequence, provide the products. We also report a photocatalytic protocol for alkoxyalkenylation.     

A high-discernment microflow cytometer with microweir structure

Using a simple and reliable isotropic wet etching process, we fabricated a microflow cytometer in which cells/particles are concentrated in the center of the sample stream using a 2-D hydrodynamic focusing technique and an microweir structure. Having focused the cells/particles, they are detected and counted using a LIF method. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in squeezing the cells/particles into a narrow stream in the horizontal X-Y plane. Furthermore, it is shown numerically that the microweir structure results in the separation of the cells/particles in the vertical X-Z plane such that they pass through the detection region in a sequential fashion and can therefore be counted with a high degree of precision. The experimental results obtained using fluorescent polystyrene beads with diameters of 5 and 10 microm, respectively, confirm the suitability of the proposed device for microfluidic applications requiring the high-precision counting of particles or cells within a sample flow.     

Sorption and diffusion of HTO and cesium in crushed granite compacted to different lengths

In this study, batch and through-diffusion experiments have been performed in order to determine the distribution coefficients (K _d ), apparent diffusion coefficients (D _a ) and retardation factor (Rf), respectively. Both apparent and effective diffusion coefficient (D _a and D _e ) of Cs were obtained by accumulative concentration method developed by Crank (1975). In addition, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K _d ) obtained by batch tests in 14 days under aerobic and anaerobic systems were 2.06 and 3.52 ml/g. Moreover, it is found in through-diffusion test that Rf = 4.12 and 4.40 and K _d = 0.97 and 1.06 of Cs did not have an obvious discrepancy in a length/diameter/ (L/D) ratio of 0.44 and 1.78. However, Rf and K _d revealed a larger difference in an L/D ratio closing to 1 due to the geometric change of one-dimension diffusive hypothesis. Therefore, it demonstrates that Rf and K _d obtained by through-diffusion experiments only could be achieved at a lower or larger L/D ratio and would be reliable for long-term performance assessment.     

Formation of interstellar 2,4-pentadiynylidyne, HCCCCC(X 2Pi), via the neutral-neutral reaction of ground state carbon atom, C(3P), with diacetylene, HCCCCH(X 1Sigma(g)+)

The interstellar reaction of ground-state carbon atom with the simplest polyyne, diacetylene (HCCCCH), is investigated theoretically to explore probable routes to form hydrogen-deficient carbon clusters at ultralow temperature in cold molecular clouds. The isomerization and dissociation channels for each of the three collision complexes are characterized by utilizing the unrestricted B3LYP/6-311G(d,p) level of theory and the CCSD(T)/cc-pVTZ calculations. With facilitation of RRKM and variational RRKM rate constants at collision energies of 0-10 kcalmol, the most probable paths, thus reaction mechanism, are determined. Subsequently, the corresponding rate equations are solved that the evolutions of concentrations of collision complexes, intermediates, and products versus time are obtained. As a result, the final products and yields are identified. This study predicts that three collision complexes, c1, c2, and c3, would produce a single final product, 2,4-pentadiynylidyne, HCCCCC(X (2)Pi), C(5)H (p1)+H, via the most stable intermediate, carbon chain HC(5)H (i4). Our investigation indicates the title reaction is efficient to form astronomically observed 2,4-pentadiynylidyne in cold molecular clouds, where a typical translational temperature is 10 K, via a single bimolecular gas phase reaction.     

Phenolic glycosides and pyrrolidine alkaloids from Codonopsis tangshen

Chemical examination of the n-butanol extract of the root of Codonopsis tangshen led to the isolation of four new compounds named codonosides A (1) and B (2) and codonopyrrolidiums A (3) and B (4), with seven known compounds [(Z)-2-(beta-glucopyranosyloxy)-3-phenylpropenoic acid (5), lobetyolin (6), lobetyol (7), luteolin (8), friedelin (9), 5,6,9-trihydroxy-octadec-7-enoic acid (10), and adenosine (11)]. Based on spectroscopic evidence, the structures of codonosides A (1) and B (2) were established as phenolic glycosides, and those of codonopyrrolidiums A (3) and B (4) as pyrrolidines. The relative configuration of 3 was determined by X-ray crystallographic analysis.     

Synthesis and Evaluation of the Cytotoxicities of Neoflavenes

The synthesis of neoflavene and neoflavenes with methoxy substituents at different positions are described. As starting materials, various salicylaldehydes were run through sequential reactions such as O‐allylation, Grignard reaction, oxidation, Wittig reaction, and ring‐closing metathesis to yield the target neoflavenes in good yield. Among the prepared neoflavenes, 7‐methoxy‐4′‐methoxyneoflavene ( 6e ) and 8‐methoxy‐4′‐methoxyneoflavene ( 6f ) exhibiting potential cell toxicities against various cells were disclosed. In particular, 6f which exhibited an IC₅₀ value of 6.5 ± 2.0 and 5.1 ± 1.1 μM against gastric carcinoma and lung carcinoma cells in vitro was found, respectively. Meanwhile, the structure and activity relationship of our synthesized neoflavenes is further discussed briefly.     

Determination of Antioxidants and Preservatives in Cosmetics by SPME Combined with GC–MS

A rapid and simple procedure for the determination of antioxidants and preservatives in cosmetics has been developed utilizing solid-phase microextraction combined with GC–MS. A silica fiber coated with polyacrylate provided the highest extraction efficiency. Detection limits in the range from 0.4 to 8.5 ng mL⁻¹ were obtained. Linearity is over a wide range from 1 to 2,000 ng mL⁻¹ with a relative standard deviation under 16%. Cosmetic from a local supermarket were analysed for antioxidants and preservatives to demonstrate the effectiveness of the proposed method. The concentration of antioxidants and preservatives determined was 20–1,218 μg g⁻¹ for methylparaben and 5–3,779 μg g⁻¹ for propylparaben.     

Formations of mixed-valence oxovanadiumV,IV citrates and homocitrate with N-heterocycle chelated ligand

Dimeric mixed-valence oxovanadium citrate [V 2O 3(phen) 3(Hcit)].5H 2O ( 1) (H 4cit = citric acid, phen = 1,10-phenanthroline) was isolated from a weak acidic medium. It could be converted quantitatively into a tetrameric oxovanadium citrate adduct of 1,10-phenanthroline [V 2O 3(phen) 3(Hcit) 2(phen) 3O 3V 2].12H 2O ( 2). This was supported by the trace of infrared spectra and X-ray diffraction patterns. The two compounds feature a bidentate citrate group that chelates only to one vanadium center through their negatively charged alpha-alkoxy and alpha-carboxy oxygen atoms, while the other beta-carboxy and beta-carboxylic acid groups are free to participate in strong intramolecular and intermolecular hydrogen bonding [2.45(1) in 1 and 2.487(2) A in 2], respectively. This is also the case of homocitrato vanadate(V/IV) [V 2O 3(phen) 3( R, S-H 2homocit)]Cl.6H 2O ( 3) (H 4homocit = homocitric acid), which features a binding mode similar to that found in the R-homocitrato iron molybdenum cofactor of Mo-nitrogenase. Moreover, the homocitrato vanadate(V) [VO 2(phen) 2] 2[V 2O 4( R,S-H 2homocit) 2].4H 2O.2C 2H 5OH ( 4) is isolated as a molecular precursor for the formation of mixed-valence complex 3. The V-O alpha-alkoxy and V-O alpha-carboxy bond distances of homocitrate complexes 3 and 4 are 1.858(4) and 1.968(6) av and 2.085(4) and 1.937(5) A, respectively. They are shorter than those of homocitrate to FeVco (2.15 A). The gamma-carboxy groups of coordinated homocitrato complexes 3 and 4, and the free homocitrate salt Na 3(Hhomocit).H 2O ( 5), form strong hydrogen bonds with the chloride ion and the water molecule [2.982(5) in 3, 2.562(9) in 4, and 2.763(1) A in 5], respectively.