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We computationally study the chiral transition process of the α-Ala molecule under confined different sizes of armchair SWBNNTs to explore the confinement effect. We find that the influence of a confinement environment (in armchair SWBNNTs) on the α-Ala molecule would lead to different reaction pathways. Meanwhile, the preferred reaction pathway is also different in various sizes of armchair SWBNNTs, and their energy barriers for the rate-limiting step decrease rapidly with the decreasing of the diameters of the nanotubes. It is obvious that significant decrease of the chiral transition energy barrier occurs compared with the isolated α-Ala molecule chirality conversion mechanism, by ∼15.6 kcal mol-1, highlighting the improvement in the activity the enantiomers of α-Ala molecule. We concluded that the confinement environment has a significant impact at the nanoscale on the enantiomer transformation process of the chiral molecule. [ABSTRACT FROM AUTHOR]

Hydroxyacetone (CH3C(O)CH2OH) is observed as a stable end product from reactions of the (CH3)2COO Criegee intermediate, acetone oxide, in a flow tube coupled with multiplexed photoionization mass spectrometer detection. In the experiment, the isomers at m/z = 74 are distinguished by their different photoionization spectra and reaction times. Hydroxyacetone is observed as a persistent signal at longer reaction times at a higher photoionization threshold of ca. 9.7 eV than Criegee intermediate and definitively identified by comparison with the known photoionization spectrum. Complementary electronic structure calculations reveal multiple possible reaction pathways for hydroxyacetone formation, including unimolecular isomerization via hydrogen atom transfer and -OH group migration as well as self-reaction of Criegee intermediates. Varying the concentration of Criegee intermediates suggests contributions from both unimolecular and self-reaction pathways to hydroxyacetone. The hydroxyacetone end product can provide an effective, stable marker for the production of transient Criegee intermediates in future studies of alkene ozonolysis. [ABSTRACT FROM AUTHOR]

Se--N dynamic covalent bond is a new dynamic covalent bond which has applications in the fabrication of stimuli responsive and self-healing functional materials. Although recent advances have been achieved in the experimental aspect, little is known about the formation mechanism of Se--N dynamic covalent bond. Here the structures and nature of Se--N dynamic covalent bond between three kinds of pyridine derivatives R-C5H4N, [pyridine (R = H), 4-methylpyridine (R = CH3), 4-dimethylamino-pyridine (R = N(CH3)2)] and phenylselenyl bromine (PhSeBr) have been analyzed using density functional theory. The interactions between Se atom in PhSeBr and N atom in pyridine or pyridine derivatives can be divided into three models: dissociation, nonbonding interaction and covalent bond interaction. Quantum chemical calculations on three series compounds show that these three models can convert mutually, which results in the generation of Se--N dynamic covalent bond. Solvent effects produced in polar solvents such as CH2Cl2 can make the conversion between Se--N covalent bond and Se...N nonbonding interactions easier. The kind of the substituents in pyridine ring can affect the conversion process: the stronger the electron-donating ability of the substituent, the easier the structure transformation. [ABSTRACT FROM AUTHOR]

To enhance the interfacial interaction between rubber and hybrid nanofiller (HS) consisting of halloysite nanotubes and silica, and simultaneously prevent migration and volatilization of rubber additives, commercial vulcanization accelerator N-cyclohexyl-2-benzothiazole sulfenamide (CZ) was chemically grafted onto HS to obtain a functionalized nanofiller (HS-s-CZ). It was found that the grafted CZ molecules within an inorganic host structure have better efficiency to accelerate cross-linking reaction than free CZ molecules. In addition, HS-s-CZ could be evenly dispersed into styrene butadiene rubber (SBR) with further improved filler-rubber interaction compared with that between HS and SBR. Consequently, SBR/HS-s-CZ composites exhibited greater mechanical strength than SBR/HS composites containing equivalent accelerator component, showing 45% increase in tensile strength when the filler content was 40 phr. Potentially, this work offers a new design strategy for the surface modification of nanofiller and preparation of high-efficiency rubber additives, which may represent a new path for preparing high-performance elastomer composites. [ABSTRACT FROM AUTHOR]

The effects of anchoring groups on electron injection from adsorbate to nanocrystalline thin films were investigated by comparing injection kinetics through carboxylate versus phosphonate groups to TiO2and SnO2. In the first pair of molecules, Re(LA)(CO)3Cl (ReC1A) and Re(Lp)(CO)3Cl (ReC1P), LA2,2‘-bipyridine-4,4‘-bis-CH2-COOH, Lp 2,2‘-bipyridine-4,4‘-bis-CH2-PO3H2, the anchoring groups were insulated from the bipyridine ligand by a CH2group. In the second pair of molecules, Ru(dcbpyH2)2(NCS)2(RuN3) and Ru(bpbpyH2)2(NCS)2(RuN3P), dcbpy 2,2‘-bipyridine-4,4‘-biscarboxylic acid, bpbpy 2,2‘-bipyridine-4,4‘-bisphosphonic acid, the anchoring groups were directly connected to the bipyridine ligands. The injection kinetics, as measured by subpicosecond IR absorption spectroscopy, showed that electron injection rates from ReC1P to both TiO2and SnO2were faster than those from ReC1A. The injection rates from RuN3 and RuN3P to SnO2films were similar. On TiO2, the injection kinetics from RuN3 and RuN3P were biphasic:  carboxylate group enhances the rate of the <100 fs component, but reduces the rate of the slower components. To provide insight into the effect of the anchoring groups, the electronic structures of Re−bipyridyl−Ti model clusters containing carboxylate and phosphonate anchoring groups and with and without a CH2spacer were computed using density functional theory. With the CH2spacer, the phosphonate group led to a stronger electronic coupling between bpy and Ti center than the carboxylate group, which accounted for the faster injection from ReC1P than ReC1A. When the anchoring groups were directly connected to the bpy ligand without the CH2spacer, such as in RuN3 and RuN3P, their effects were 2-fold:  the carboxylate group enhanced the electronic coupling of bpy with TiO2and lowered the energy of the bpy orbital. How these competing factors led to different effects on TiO2and SnO2and on different components of the biphasic injection kinetics were discussed. [ABSTRACT FROM AUTHOR]