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Selective hydrogenation over earth-abundant metal catalysts is challenging but particularly valuable for practical applications in heterogeneous catalysis. Herein, we demonstrate that the catalytic selectivity of the commercial Raney nickel catalyst can be greatly tuned by modulation of the nickel surface by silica. Using quinoline hydrogenation as a model, we show that the silica-modified Raney nickel catalysts exhibit good activity, excellent selectivity, and long stability, whereas the undesired overhydrogenation reactions are effectively hindered. In contrast, the pristine Raney nickel catalyst shows inferior selectivity for the targeted product. Mechanistic studies confirm a positive role of silica to facilitate the desorption of 1,2,3,4-tetrahydroquinoline from the catalyst surface, thus enhancing the product selectivity.

A combination of ab initio electronic structure theory, transition state theory and master equation modeling was used to study the kinetics of the reaction CO H[O.sub.2] -> C[O.sub.2] OH. The results have shown that the overall rate coefficient is independent of pressure up to 500 atm for temperature ranging from 300 to 2500 K.

A new type of hybrid gel matrix, which is prepared by the sol-gel process of tetrakis (2-hydroxyethyl) orthosilicates (THEOS), a completely water-soluble silica precursor, is developed and used for the construction of the amperometric hydrogen peroxide biosensor. The fabricated hydrogen peroxide biosensor has the characteristics of good analytical performance, reproducibility, and storage stability under the optimized experimental conditions.

The unimolecular decomposition of ethylene oxide and the oxiranyl radical is examined by molecular orbital calculations, Rice-Ramsperger-Kassel-Marcus (RRKM)/Master Equation analysis, and detailed kinetic modeling of ethylene oxide pyrolysis in a single pulse shock tube. It was found that the largest energy barrier to the decomposition of ethylene oxide lies in its initial isomerization to form acetaldehyde.

A study was conducted to investigate the thermal stability of anatase TiO2 nanoparticles produced by flame synthesis. Phase-pure anatase particles of ~4 nm in size could be reproducibly synthesized by using a tubular burner and rotating sampler.

The interactions of styrene and phenylacetylene and their isotope substitutions with a Si(111)-7x7 surface are studied to understand the chemical binding of conjugated pi-electron systems to di-radical-like silicon dangling bonds of the adjacent adatom-rest atom pair. The study shows that styrene mainly binds to the surface through a diradical reaction involving both the external C=C and is conjugated internal C=C of the phenyl ring with an adjacent adatom-rest atom pair, forming a 5-ethlidene-1, 3-cyclohexadiene-like skeleton.

The formation of fiberlike micelles in hexane with a very narrow weight-average distribution of lengths and the nature of their fragmentation following exposure to ultrasound are described. The results have shown that these fibers also rupture according to Gaussian fragmentation model and display a fracture rate that is very sensitive to fiber length.

A new approach is described for the synthesis and encapsulation of silver and silver halide nanoparticles inside shell-cross-linked cylindrical block copolymer polyisoprene-block-polyferrocenyldimethylsilane (PI-b-PFS) micelles by using in situ redox reactions. The small encapsulated AgI nanoparticles have served as seeds for the formation of larger Ag nanoparticles when a silver salt is added.

A biocompatible sol-gel silica matrix is developed for the encapsulation of biomolecules by using a novel water-soluble silica precursor, tetrakis(2-hydroxyethyl)orthosilicates (THEOS), along with a water-soluble polysaccharide derivative, hydroxypropyl guar gum (HPGG). The controlled release of vitamin [B.sub.12] from the sol-gel silica matrixes has shown a strong dependence of the release profile on the amount of introduced HPGG.

The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (Na[Cl.sub.aq]) are investigated using a novel experimental technique. The application of this novel method to the reaction of gaseous OH with deliquesced NaCl particles have given a lower limit to the reaction probability of [gamma.sub.net] > = 0.1 with an uncertainty of a factor of 2.

The synthesis of shell-cross-linked organometallic nanotubes of silver that contain a polyferrocenylsilane (PFS) inner wall covered by a cross-linked network of polymethylvinylsiloxane chains is reported. The result showed that pretreatment of PFS with organic oxidants such as dichloromethane is the key step to obtain silver particles within the tubes in high yields and the resulting soluble peapod-like hybrid nanostructures may ultimately be useful for the fabrication of nanodevices.

Nanosize effect of ZrO2 in Au/ZrO2 catalyst was studied by deposition-precipitation of Au nanoparticles in similar sizes (4-5 nm) on ZrO2 nanoparticles of varying sizes. The findings indicate that nanocomposite Au/ZrO2 consisting of comparably sized Au-metal (4-5 nm) and ZrO2 (5-15nm) nanoparticles are found advantageous over those containing similar sized Au-metal but larger ZrO2 (40-200nm) particles for CO oxidations.

The reaction of C2 with water and the possible subsequent reactions were investigated using ab initio methods. The most feasible reaction following the formation of association intermediate (CCOH2) is the intramolecular hydrogen migration leading to hydroxythyne (HCCOH).

The attachment chemistry of pyridine on Si(100) was studied using thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS) and DFT theoretical calculations. Experimental results and DFT calculations show that pyridine molecules interact with Si (100) through both Si: N dative bonding and the [4+2] - like cycloaddition between the N1 and C4 atoms of the pyridine molecules with a Si=Si dimer, forming pyridine like and 1, 4- dihydropyridine like adducts respectively.

The cumulative double bond (C=C=N), an important intermediate in synthetic organic chemistry, was successfully prepared through the selective attachment of acrylonitrile to Si(111)-7 x 7. The observation of the characteristic vibrational modes and electronic structures of the C=C=N group in the surface species demonstrates the [4 + 2]-like cycloaddition occurring between the terminal C and N atoms of acrylonitrile and the neighboring adatom-rest atom pair, consistent with the prediction of DFT calculations.

The investigation on the covalent binding and structure of acetonitrile on Si(111)-7 * 7 is done to provide information on the interaction of pi-electrons of the C triple bond N group with the dangling bonds of Si(111)-7 * 7. The density functional theory (DFT) calculation results and all the experimental evidence revealed that functional organic monolayer of acetonitrile on Si(111)-7 * 7 are formed through a di-sigma binding mechanism involving the coupling of one pi(sub CN) bond with an adatom-rest atom pair at the interface.

A new approach to the synthesis of 2-phosphinoylindoles through photoredox catalysis without external oxidants has been developed. Promoted by a ruthenium photoredox catalyst, a broad scope of 2-phosphinoylindoles can be synthesized through phosphinoylation/cyclization of diphenylphosphine oxide at room temperature under irradiation without external oxidants. The estrone skeleton isocyan is also an amenable substrate for this cyclization, yielding a molecule that has potential medicinal applications. [ABSTRACT FROM AUTHOR]

The syndiotactic polystyrene (sPS) γ-to-α/β phase transition was investigated using temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurement. The sPS γ form samples, which were obtained from acetone solvent induced crystallization followed by annealing at various temperatures (Ta), exhibited a regular manner on the selection of the α or β crystal modification during the phase transition process. As the Ta was increased from 25 to 150 °C, the weight fraction of β form in bulk sPS decreased from 55% to 0%, but that of the α form increased from 45% to 100%. In other words, the α form became the dominating crystalline modification at higher Ta. The lamellar thickness (dc) of the γ form at the initial state (before heating) ranged from 4.4 to 5.8 nm, and the weight crystallinity (Xc) was between 0.52 and 0.64. However, the dc values of the γ form at the final state (before γ-to-α/β phase transition) were very close for the samples pretreated at different Tas, which were in the range 7.0-7.4 nm. Therefore, the most plausible interpretation for the crystal modification selection during the γ-to-α/β phase transition was that the nucleation of β form was suppressed totally in the γ form with higher initial dc value (>5.8 nm). With the elevated Ta and increase of initial dc, the promoted nucleation of α form in the γ form resulted in the enhanced growth of the α crystalline phase during the γ-to-α/β phase transition. As a result, after the phase transition the crystalline phase in bulk sPS had a gradually increased weight fraction of the α form and turned out to be pure α form when Ta was increased from 25 to 150 °C. [ABSTRACT FROM AUTHOR]

In the previous report we proposed, on the basis of the detailed X-ray diffraction data analysis, the crystal structure of PLLA/PDLA stereocomplex (SC) with the space group P3, which is different from the R3c or R3c models proposed in the literature. The most important point of the change of the structure model is to explain the experimental data that the SC can be formed in the region of the L/D ratio of 70/30-30/70, not only for the L/D = 50/50 ratio. In our P3 structural model, one crystal site is occupied by the Ru and Ld (or Rd and Lu) (3/1) helices at the statistical probability determined by the L/D ratio, where R and L indicate the right-handed and left-handed helical chains and u and d show the upward and downward directionality along the chain axis, respectively. In other words, the D and L chain stems can coexist in a heterogeneous way in the SC crystalline lattice. This structural model has been supported experimentally from the totally different point of view on the basis of the vibrational circular dichroism IR spectral measurement. When the right-handed (r) and left-handed (l) circularly polarized IR beams are incident to the optically active chemical species, the ratio between the r and l band intensity changes depending on the relative content of the R and L species (IR circular dichroism). The IR circular dichroism of PLLA/PDLA blend sample was found to change its dichroic ratio depending on the L/D content in the sample. The most important finding is that the dichroic ratio change was detected not only for the amorphous IR bands but also for the crystalline bands, indicating definitely that the D and L chain stems can coexist in the crystalline region at the various L/D ratios as proposed by the X-ray structure analysis. [ABSTRACT FROM AUTHOR]

Bufadienolides are the major pharmacologic constituents of traditional Chinese medicine Chan'su, which is frequently used clinically for cancer treatment in China. Motivated by reducing or avoiding the cardiac toxicity of bufadienolides, we have designed, synthesized, and evaluated the fibroblast activation protein α (FAPα) activated tripeptide arenobufagin prodrugs with the purpose of improving the safety of arenobufagin (a representative bufadienolide). Among these FAPα-activated prodrugs, 3f exhibited the best hydrolytic efficiency by recombinant human FAPα (rhFAPα) and was activated in tumors. The LD50 of 3f was 6.5-fold higher than that of arenobufagin. We also observed that there are nonapparent changes in echocardiography, pathological section of cardiac muscle, and the lactate dehydrogenase activities (LDH) in 3f-treatment tumor-bearing mice, even when the dose reached 3 times the amount of parent drug arenobufagin that was used. Compound 3f also exhibits significant antitumor activity in vitro and in vivo. The improved safety profile and favorable anticancer properties of 3f warrant further studies of the potential clinical implications. Our study suggests that FAPα prodrug strategy is an effective approach for successful increasing the therapeutic window of bufadienolides. [ABSTRACT FROM AUTHOR]

The crystal structure of poly(l-lactic acid) β form has been reinvestigated on the basis of the 2-dimensional X-ray diffraction diagram measured for the sample obtained by stretching the highly crystalline α form at a high temperature. The six helical chains of (3/1) conformation are packed in a rectangular unit cell of the space group P1 with the complicated but systematic packing mode of the upward and downward chains. This structural model is different from the previously reported trigonal model [Puiggali; Polymer 2000, 41, 8921]. The structural phase transition mechanism from the α form to the β form via the δ form has been proposed by assuming the cooperative displacements of the upward and downward helical chains as well as the conformational change. To support this mechanism, the two types of experiments were performed: (i) The highly oriented regular α form was stretched at about 165 °C to the various drawing ratios and cooled to the room temperature with the sample length fixed constantly. The X-ray diffraction data of these samples revealed the transition from the α to the mechanically deformd α (αd), to the δ form, and then to the β form depending on the drawing ratio. (ii) The α sample was suspended vertically with a constant load in the heating process, and the X-ray diffraction pattern was measured as a function of time (temperature). The original α form was found to melt at about 200 °C via the transition to the αd form and then to the δ form, followed by the recrystallization into the highly oriented β form. From these two experiments, the tension-induced structural transition from the α to the β form was found to occur via the disordering of the α form to the αd and to δ form under tension. The structural change process was derived on the basis of all of the knowledge collected from the X-ray structure analysis and the ex-situ and in-situ X-ray diffraction measurements: the molecular chains experience the cooperative translational slippage along the diagonal directions in the ab-plane to give the complicatedly mixed packing of the upward and downward chains to give the characteristic structure of the β form. At the same time, the chain conformational changes from the regular (10/3) to the disordered (10/3) and then to the (3/1) form during the disordering in the chain packing mode. [ABSTRACT FROM AUTHOR]