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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 retardation of polybutene-1 form II to form I transition in the late stage has been investigated by means of time-resolved wide-angle X-ray diffraction. Form II samples with different lamellar thickness and constituent in amorphous phase were generated via varying crystallization temperature and molecular weight and aged at room temperature for the form II to form I transition. The II to I polymorphic transition in polybutene-1 undergoes two stages, where slow nucleation and rapid growth proceed in the first stage and extremely slow secondary nucleation and growth take place in the late stage. The degree of transition reaches a plateau value in the late stage of transition, which depends highly on crystallization temperature and molecular weight that low molecular weight and high crystallization temperature always contribute to a greater degree of transition, but is less affected by the kinetics in the first stage. According to the crystal unit cell parameters of form II and form I, there should be an extension in the normal direction of lamellae and a shrinkage in the lateral direction during phase transition, which thus would induce an additional pressure in the normal direction and the tendency to expansion in the lateral direction on the residual from II crystallites. As a result, the nucleation and further growth of the II to I transition are retarded. Low molecular weight and high crystallization temperature lead to larger content of chain ends and higher chain mobility in the amorphous phase; hence, the samples are more likely to release the unfavorable factors restraining generation of form I nuclei to some extent. The transition degree in late stage is thus an intrinsic property of PB-1 samples determined by their microstructures and would not be influenced by the transition behavior in the first stage. [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]

As for the crystal structure of poly(3-hydroxybutyrate) (PHB) a-form, the methyl group was said to locate at an abnormally short distance from the oxygen atom of C-O unit, resulting in the formation of CH3···O-C hydrogen bond. This idea was proposed on the basis of infrared spectra detecting a band of antisymmetric methyl C-H stretching mode [Vas(CH3)] at anomalously high frequency position and the too short CH3···O-C interatomic distances calculated from the atomic coordinates derived from the previously reported X-ray structure analysis. However, the crystal structure analyzed by the X-ray method, even the C and O atomic positions, has not yet been established confirmatively because of the appreciably small number of the observed X-ray diffraction spots. We have reinvestigated the crystal structure of PHB a-form by collecting the observed X-ray diffraction spots of about twice larger total number than before, and confirmed the positions of the C, O and H atoms in the unit cell at enough high accuracy. The finally obtained crystal structure gave the reliability factor of 14.5% for the X-ray data at 23 °C (the total number of observed reflections 70) and 16.0% (94 at -140 °C). The thus-established crystal structure was found to exhibit the shortest H···O distance of 2.62 Å, which is shorter than the value expected from the normal van der Waals distance. In order to clarify the relation of this geometry with the observed higher-frequency shift of Vas(CH3) band from the viewpoint of space group symmetry, the factor-group analysis and the normal modes calculation were performed for the PHB a-crystal by referring to the presently analyzed crystal structure information. Among the plural possibilities to cause the high-frequency shift of originally doubly degenerated Vas(CH3) mode, the normal coordinates calculation has revealed that the vibrational coupling due to the intermolecular interactions between the adjacent molecular chains may be the most significant factor rather than the effect of lowering of C3v symmetry of regular CH3 groups coming from the site group symmetry. Once the crystal structure was established well, then the 3D anisotropic elastic constants matrix was calculated for the first time about the PHB a crystal. The ultimate Young's modulus along the chain axis was only 5 GPa, which was comparable to the moduli in the direction perpendicular to the chain axis. In other words, the mechanical property of this crystal is mostly isotropic as a whole. [ABSTRACT FROM AUTHOR]

This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1-xLax)2O2MnSe2 with x = 0-0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2]2+ and [MnSe2]2-. The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = αa*+ 0b*+0.5c* with α = 0.158(1), which can be described with a (3 + 1)D superspace structural model in super space group Cmme(α,0,1/2)0hs0 [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2]2- layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate case was obtained for (Ce0.78La0.22)2O2MnSe2 with α = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The super space model lets us unify the structural description of the five different ordering patterns reported to date for different Ln2O2MSe2 (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)2O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below ∼70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has σ = 9 × 10-6 Ω-1 cm-1 at room temperature and an activation energy for charge carrier mobility from RT to 170 °C of ∼0.4 eV. [ABSTRACT FROM AUTHOR]

The quaternary transition metal oxyselenide Ce2O²ZnSe2 has been shown to adopt a ZrCuSiAs-related structure with Zn2+ cations in a new ordered arrangement within [ZnSe2]2- layers. The color of the compound changes as a function of cell volume, which can vary by ~0.4% under different synthetic conditions. At the highest, intermediate, and lowest cell volumes, the color is yellow-ochre, brown, and black, respectively. The decreased volume is attributed to oxidation of Ce from 3+ to 4+, the extent of which can be controlled by synthetic conditions. Ce2O2ZnSe2 is a semiconductor at all cell volumes with experimental optical band gaps of 2.2, 1.4, and 1.3 eV for high, intermediate, and low cell volume samples, respectively. SQUID measurements show Ce2O2ZnSe2 to be paramagnetic from 2 to 300 K with a negative Weiss temperature of θ = -10 K, suggesting weak antiferromagnetic interactions. [ABSTRACT FROM AUTHOR]

A one-pot synthesis design on shape-controlledgrowth of Zn-basedisoreticular metal-organic framework (i.e., IRMOF-3) was carriedout in this work with the controllable crystal morphological evolution from simple cubes to several complex shapes. A new synthetic protocolwas devised where poly(vinylpyrrolidone) (PVP), noble metal source(AgNO3), mixed solvents (N,N-dimethylformamide (DMF)-ethanol mixture) and tetramethylammoniumbromide (TMAB) were mutually introduced to the reaction medium assurfactant, adjuvant, accelerator, and structure-directing agent (SDA),respectively. Meanwhile, the crystallization process was investigatedby a series of time-dependent experiments. Indeed, the added modulatorsand crystallization time were able to regulate the growth and thusthe morphology of the final products. The resulting homogeneous IRMOF-3-Ag-nmaterials with unique and novel crystal morphologieswere characterized via scanning electron microscopy (SEM), X-ray powderdiffraction (XRD), thermogravimetric and differential thermal analyses(TG-DTA), transmission electron microscopy (TEM), infrared spectrum(IR), and optical microscope characterizations. Various shapes ofIRMOF-3-Ag-ncrystals as sorbents forcapturing dibenzothiophene (DBT) were evaluated. Among all the morphology-controlledsamples, IRMOF-3-Ag-5with hollow sphere morphology wasdemonstrated to show the highest DBT capture capacity due to its uniquemorphology. [ABSTRACT FROM AUTHOR]

A novel oxonitridosilicate phosphor host Sr3Si2O4N2 was synthesized in N2/H2 (6%) atmosphere by solid state reaction at high temperature using SrCO3, SiO2 and Si3N4 as starting materials. The crystal structure was determined by a ltaetveld analysis on powder X-ray and neutron diffraction data. Sr3Si2O4N2 crystallizes in cubic symmetry with space group Pa3, Z = 24, and cell parameter a ≈ lS.6593(1) A. The structure of Sr3Si2O4N2 is constructed by isolated and highly corrugated 12 rings which are composed of 12 vertex-sharing [SiO2N2] tetrahedra with bridging N and terminal O to form threedimensional tunnels to accommodate the Sr2+ ions. The calculated band structure shows that Sr3Si2O4N2 is an indirect semiconductor with a band gap 2.84 eV, which is dose to the experimental value ≈ 2.71 eV from linear extrapolation of the diffuse reflection spectrum. Sr3Si2O4N2,xLi+ shows a typical emission band peaking at ∼600 nm under 460 nm excitation, which perfectly matches the emission of blue InGaN light-emitting diodes. For Ce3+/Li+-codoped Sr3Si2O4N2, one excitation band is in the UV range (280-350 nm) and the other in the liv blue range (380-420 nm), which matches emission of near-UV light-emitting diodes. Emission of Sr3-xSi2O4N2:xCe3+xLi+ shows a asymmetric broad band peaking at -S20 inn. The long-wavelength excitation and emission of Eu2+ and Ce3+/Lt-doped Sr3Si2O4N2 make them attractive ftr applications in phosphor-converted white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A solvent evaporation induced aggregating assembly (EIAA) method has been demonstrated for synthesis of highly ordered mesoporous silicas (OMS) in the acidic tetrahydrofuran (THF)/H2O mixture by using poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) as the template and tetraethylorthosilicate (TEOS) as the silica precursor. During the continuous evaporation of THF (a good solvent for PEO-b-PMMA) from the reaction solution, the template molecules, together with silicate oligomers, were driven to form composite micelles in the homogeneous solution and further assemble into large particles with ordered mesostructure. The obtained ordered mesoporous silicas possess a unique crystal-like morphology with a face centered cubic (fcc) mesostructure, large pore size up to 37.0 nm, large window size (8.7 nm), high BET surface area (508 m²/g), and large pore volume (1.46 cm³/g). Because of the large accessible mesopores, uniform gold nanoparticles (ca. 4.0 nm) can be introduced into mesopores of the OMS materials using the in situ reduction method. The obtained Au/OMS materials were successfully applied to fast catalytic reduction of 4-nitrophenol in the presence of NaHB4 as the reductant. The supported catalysts can be reused for catalytic reactions without significant decrease in catalysis performance even after 10 cycles. [ABSTRACT FROM AUTHOR]

Cationic surfactants modified clays exhibit high sorptive capability toward anionic radionuclides but retention of cationic radionuclides was concurrently reduced. In this study, organoclays were synthesized by intercalating a variety of primary/quaternary alkylammonium species (NH2R/(CH3)3N+RBr-, where R = benzyl, dodecyl, and octadecyl) into bentonite MX-80. The effect of surfactant's properties on enhancing or limiting cationic sorption capability was investigated by performing Cs sorption experiments. Experimental results were analyzed using the MINEQL+ software by considering Cs uptake by structural and edge sorption sites. Bentonites that were intercalated with primary alkylammonium surfactants had a higher sorptive capacity than those intercalated with quaternary alkylammonium surfactants. Samples intercalated with octadecyl-bearing surfactants had the lowest sorption rate. XRD and FTIR analyses revealed that each organoclay had a characteristic arrangement of alkyl chains. The cation retention of organoclays was dominated by the extent of hydrophobic interactions affected by the local distribution and arrangement of surfactants. The intercalated primary alkylammoniun surfactants tended to transform into local clusters with a high packing density, leaving more structural sites available for Cs uptake. In contrast, the NH3R+-surfactants tended to form a denser monolayer over clay surface, inhibiting the retention of Cs at structural sites. [ABSTRACT FROM AUTHOR]

The sedes BaBi1-xTaxO3 (0 ⩽ x ⩽ 0.5) has been synthesized by traditional solid-state reactions. Their structures are analyzed by the combinational use of X-ray, neutron, and converged-beam electron diffractions. They all crystallize in P1. FTIR and Raman data confirm that an inversion center is absent in the crystal structure of the series BaBi1-xja O3 (0 ⩽ x ⩽ 0.5). No obvious P-E (polarization-electrical field) loops are observed for them. [ABSTRACT FROM AUTHOR]

Low halogen content in tested Powder River Basin (PRB) coals and low loss of ignition content (LOl) in PRB-derived fly ash were likely responsible for higher elemental mercury content (averaging about 75%) in the flue gas and also lower mercury capture efficiency by electrostatic precipitator (ESP) and wet-FGD. To develop a cost-effective approach to mercury capture in a full-scale coal-fired utility boiler burning PRB coal, experiments were conducted adding hydrogen bromide (HBr) or simultaneously adding HBr and selected fly ashes in a slipstream reactor (0.152 × 0.152 m) under real flue gas conditions. The residence time of the flue gas inside the reactor was about 1.4s. The average temperature of the slipstream reactor was controlled at about 155 °C. Tests were organized into two phases. In Phase 1, only HBr was added to the slipstream reactor, and in Phase 2, HBr and selected fly ash were added simultaneously. HBr injection was effective (>90%) for mercury oxidation at a low temperature (155 °C) with an HBr addition concentration of about 4 ppm in the flue gas. Additionally, injected HBr enhanced mercury capture by PRB fly ash in the low-temperature range. The mercury capture efficiency, attesting conditions of the slipstream reactor, reached about 50% at an HBr injection concentration of 4 ppm in the flue gas. Compared to only the addition of HBr, simultaneously adding bituminous-derived fly ash in a minimum amount (30 lb/MMacf), together with HBr injection at 4 ppm, could increase mercury capture efficiency by 30%. Injection of lignite-derived fly ash at 30 lb/MMacf could achieve even higher mercury removal efficiency (an additional 35% mercury capture efficiency compared to HBr addition alone). [ABSTRACT FROM AUTHOR]

In an attempt to develop a biofriendly sol−gel route for the rapid formation of biofunctional silica gels, a biopolymer with good biocompatibility was used to assist the gelation of glycol-modified tetraethoxysilane (GMT) in aqueous system without the addition of any organic solvents. It was found that the biopolymer used could act as an effective accelerator for the sol−gel transition of GMT and an increase of its amount could shorten greatly the gelation time. For such a gelation reaction, its apparent activation energy was determined to be 64.9 kJ/mol according to the Arrhenius equation. In particular, the kinetic mechanism for the formation of the silica gel was investigated by using dynamic rheological data and a scaling fractal model. It was revealed that the biopolymer used could change the sol−gel transition mechanism from reaction-limited kinetics to diffusion-limited kinetics. Circular dichroism analyses confirmed the suitability of using the resultant silica gel for the in situ protein encapsulation. [ABSTRACT FROM AUTHOR]

Detailed studies of a new approach to the synthesis and encapsulation of silver and silver halide nanoparticles inside shell-cross-linked cylindrical block copolymer polyisoprene-block-polyferrocenyldimethylsilane (Pl-b-PFS) micelles (1) through in situ redox reactions are reported. The cylindrical nanostructures 1 were prepared by the solution self-assembly of the Pl-b-PFS diblock copolymer in the Pl-selective solvent hexane followed by Pt(O)-catalyzed Pl shell-cross-linking hydrosilylation reactions. The partial preoxidation of the swollen PFS core using tris(4-bromophenyl)aminium hexachloroantimonate [p-BrC6H4)3N][SbCl6] (2, Magic Blue) followed by redox reaction between the remaining Fe(II) centers in the PFS core and Ag+ cations led to the formation of silver nanoparticles. High-resolution scanning transmission electron microscopy images of the resulting peapod structures provided a clear indication that the nanoparticles were encapsulated inside the micelles. The composition of the nanoparticles was analyzed by energy-dispersive X-ray spectroscopy (EDX). By combining the evolution of the UV—vis spectra of the reaction mixture and EDX measurements, we surprisingly found that silver halide seed particles were formed through a precipitation reaction at an early stage of the encapsulation process. The size of the silver nanoparticles varied with different amounts of silver ions added to the micelle solution. When 12 was used as the preoxidant, Agl nanoparticles were formed and encapsulated inside the cylinders through the precipitation reaction between iodide anions and silver ions. The packing density of the resulting Agl nanoparticles was increased by an iterative addition method, which utilizes the reversible redox properties of PFS. The small encapsulated Agl nanoparticles were also shown to serve as seeds for the formation of larger Ag nanoparticles when a silver salt was subsequently added. [ABSTRACT FROM AUTHOR]

A sample of poly(ferrocenyldimethylsilane)- b-poly(2-vinylpyridine) (PFS 23- b-P2VP 230), with a short PFS block and a P2VP block 10-fold higher in degree of polymerization, forms spherical micelles when dissolved in ethanol. Over time (hours, days, and weeks), these solutions undergo a micelle sphere-to-cylinder transition eventually forming rather stiff, uniform fiber-like micelles with a core width of 10 nm, lengths between 20 and 50 µm, and approximately four polymer molecules per nm length. Here, we report the results of a combination of transmission electron microscopy, wide-angle X-ray scattering (WAXS), as well as static and dynamic laser light scattering measurements to follow the structural evolution. One key observation is the onset of partial aggregation of spherical micelles after an initial induction period (hours), so that the system as it ages consists of mixtures of free spherical micelles, micelle aggregates, and elongated structures with a high aspect ratio. Another important observation is the growth in intensity and sharpness of the WAXS peak characteristic of crystalline PFS domains as the number and uniformity of the cylindrical micelles increases. This formation of crystalline domains is the likely driving force for the structural transformation. [ABSTRACT FROM AUTHOR]

To develop biocompatible sol−gel silica matrix for the encapsulation of biomolecules or drugs, a novel water-soluble silica precursor, tetrakis(2-hydroxyethyl)orthosilicates (THEOS), was used in combination with a water-soluble polysaccharide derivative, hydroxypropyl guar gum (HPGG). We found that the introduction of HPGG could trigger and accelerate the sol−gel transition of THEOS in water and induce rapid formation of homogeneous gel matrix without the addition of any organic solvents or catalysts. Moreover, added HPGG macromolecules had a great influence on the network structure and particle dimension in the silica gel matrix, as confirmed by scanning electron microscope (SEM) observation. From the time sweep rheological measurements, it was found that a higher HPGG amount could lead to shorter gelation time for the sol−gel transition. From the strain and frequency sweep rheological experiments, it was found that the resultant silica matrix containing a higher amount of HPGG exhibited a narrower linear viscoelastic region, a higher dynamic muduli, and greater complex viscosity. In particular, the gel strength of the silica matrix could be modulated by the amount of HPGG. By investigating the controlled release of vitamin B12from the sol−gel silica matrixes, a strong dependence of the release profile on the amount of introduced HPGG was observed. In this case, a higher HPGG amount resulted in lower release rate. [ABSTRACT FROM AUTHOR]

The kinetics of the reaction CO HO2• → CO2•OH was studied using a combination of ab initio electronic structure theory, transition state theory, and master equation modeling. The potential energy surface was examined with the CCSD(T) and CASPT2 methods. The classical energy barriers were found to be about 18 and 19 kcal/mol for CO HO2• addition following the trans and cis paths, respectively. For the cis path, rate constant calculations were carried out with canonical transition state theory. For the trans path, master equation modeling was also employed to examine the pressure dependence. Special attention was paid to the hindered internal rotations of the HOOC•O adduct and transition states. The theoretical analysis shows that the overall rate coefficient is independent of pressure up to 500 atm for temperature ranging from 300 to 2500 K. On the basis of this analysis, we recommend the following rate expression for reaction R1 k(cm3/mol·s) 1.57 × 105T2.18e-9030Tfor 300 ≤ T≤ 2500 K with the uncertainty factor equal to 8, 2, and 1.7 at temperatures of 300, 1000, and 2000 K, respectively. [ABSTRACT FROM AUTHOR]

A new class of metal-containing diblock copolymers, PFS-b-P2VP (PFS poly(ferrocenyldimethylsilane), P2VP poly(2-vinylpyridine)), with a hydrophobic organometallic block and a highly polar hydrophilic organic block were synthesized via 1,1-dimethylsilacyclobutane (DMSB)-mediated sequential anionic polymerization. In the bulk state, PFS-b-P2VP copolymers with a volume fraction of PFS close to 0.20 give a morphology with cylindrical domains of PFS. A remarkable difference in the morphology of PFS-b-P2VP micelles was observed depending on the nature of selective solvent. Simply by using different alcoholic solvents either spherical or cylindrical micelles can be selectively formed from the same copolymer. WAXS experiments indicate that the crystallinity of the core-forming PFS block may be responsible for this difference. [ABSTRACT FROM AUTHOR]

Multifunctional diimidazole, 2,6-bis(imidazol-1-yl)methyl-4-methylphenol (BIP), was crystallized with different dicarboxylic acids, such as oxalic acid (OA), isophthalic acid (IPA), and terephthalic acid (TPA), affording crystals of (BIP2)·(OA2-) (1), (BIP)·(IPA) (2), (BIP)·(TPA) (3), and (BIP)·(TPA)0.5(4). X-ray single-crystal diffraction studies reveal that all four organic crystals contain strong classical hydrogen bonds (such as O−H···N, O−H···O, etc.), which are usually observed in organic cocrystals of carboxylic acids with heterocyclic bases. Besides, weak C−H···O hydrogen bonds and X··· (X , CH) interactions contribute to the formation of three-dimensional (3-D) networks for these crystals. Interesting annulus with internal dimensions of cavity (about 8.5 Å × 9.5 Å) are demonstrated in crystal 1, and these annuluses are connected through O−H···O hydrogen bonds to form a 2-D porous layer. Because of the coexistence of O−H···N and O−H···O hydrogen bonds between BIP and aromatic carboxylic acids, compounds 2and 3exhibit double-chain structures. Interestingly, while the molar ratio of BIP to TPA is 2:1 in crystal 4, an unusual single−double-chain structure is generated, which is obviously different from the double-chain structure of 3. [ABSTRACT FROM AUTHOR]

The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (NaClaq) were investigated using a novel experimental approach. The technique utilizes the exposure of substrate-deposited aerosol particles to reactive gases followed by chemical analysis of the particles using computer-controlled scanning electron microscopy with energy-dispersive analysis of X-rays (CCSEM/EDX) capability. Experiments were performed at room temperature and atmospheric pressure with deliquesced NaCl particles in the micron size range at 70−80% RH and with OH concentrations in the range of 1 to 7 × 109cm-3. The apparent, pseudo first-order rate constant for the reaction was determined from measurements of changes in the chloride concentration of individual particles upon reaction with OH as a function of the particle loading on the substrate. Quantitative treatment of the data using a model that incorporates both diffusion and reaction kinetics yields a lower limit to the net reaction probability of net≥ 0.1, with an overall uncertainty of a factor of 2. [ABSTRACT FROM AUTHOR]

The interactions of styrene and phenylacetylene and their isotope substitutions with a Si(111)7×7 surface have been studied as model systems to mechanistically understand the chemical binding of conjugated π-electron systems to di-radical-like silicon dangling bonds of the adjacent adatom-rest atom pair. Vibrational studies show that styrene mainly binds to the surface through a di-radical reaction involving both the external C=C and its conjugated internal C=C of the phenyl ring with an adjacent adatom-rest atom pair, forming a 5-ethylidene-1,3-cyclohexadiene-like skeleton. On the other hand, phenylacetylene was shown to be covalently attached to Si(111)-7×7 through the external C≡C, forming a styrene-like conjugation system. These experimental results are consistent with density functional theory calculations. The different binding mechanisms for styrene and phenylacetylene clearly demonstrate that reaction channels for multifunctional organic molecules are strongly dependent on the chemical and physical properties of the functional groups. The resulting π-electron conjugation structures may possibly be employed as intermediates for further organic syntheses and fabrication of multilayer organic films on semiconductor surfaces. [ABSTRACT FROM AUTHOR]

Examines the synthesis of two ferrocene-containing phosphoramidites for electronic detection of nucleic acids. Thermal stability of ferrocene-modified DNA; Use of cyclic voltammetry; Impact of ferrocenyl group of the ribose ring on DNA stability.

The article reports on redox-induced synthesis and encapsulation of metal nanoparticles in shell-cross-linked organometallic nanotubes. The mechanism of the encapsulation generally relies on the diffusion of guest materials. Consequently, there is usually a lack of control in the quantity of entrapped materials and their spatial organization. The process of the encapsulation involves two steps: binding of metal ions through their interaction with the carboxylic groups lined in the cavity of the tubes, followed by an oxidation reaction for the formation of magnetic nanoparticles.

The crystal structure model of stereocomplex between poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) with the L/D ratio of 50/50 was proposed by several groups [the space group P1 model by Okihara et al. (1991) and R3c or R3c model by Cartier et al. (1997)], among which the model of the space group R3c (or R3c) had been currently recognized as the most preferable one. However, the thus apparently established model cannot explain such an important experimental fact that the stereocomplex is formed not only for the PLLA/PDLA blend of the L/D ratio 50/50 but also for the blends with the L/D ratio of 70/30-30/70. We have proposed here a new model with the space group P3, which can cover the SC structures of the L/D ratio in the range of 70/30-50/50-30/70. This model can show the more quantitative reproducibility of the observed X-ray diffraction data for both the hkl and 000l reflection profiles. In particular the experimental observation of the 0003 reflection is inconsistent with the previous model of the space group R3c, which requests the appearance of only the 000l with l = 6, 12, etc. In the newly proposed P3 model the molecular chains take the regular (3/1) helical conformation; however, the packing mode is not regular. The unit cell consists of the statistically disordered arrangement of the right-handed (R) and left-handed (L) chains of the upward (u) or downward (d) directionality. For example, in the case of the stereocomplex with L/D ratio 70/30, a pair of the left-handed downward (Ld) and right-handed upward (Ru) chains is located at one lattice site at the statistical occupancy of 70/30 ratio and another pair of the left-handed upward (Lu) and right-handed downward (Rd) chains is at the adjacent lattice site at the same 70/30 ratio. The unit cell contains the three sets of these two pairs, which are connected to each other by the symmetric relation of the 3-fold rotation axis. The proposed statistical packing model of the upward and downward chains can explain such various observations as the spherulite formation or the existence of the lamellae with the chain folding structure in the spherulite, the solvent-induced change from the stereocomplex to the a form, and so on. [ABSTRACT FROM AUTHOR]

A number of LnOCuCh (Ln = La-Nd, Bi; Ch = S, Se, Te) compounds have been reported in the literature built from alternating layers of fluorite-like [Ln2O2]2+ sheets and antifluorite-like [M2Se2]2- sheets, where M is in the +1 oxidation state leading to full occupancy of available MSe4/2 tetrahedral sites. There is also a family of related LnOM0.5Se (Ln = La & Ce, M = Fe, Zn, Mn & Cd) compounds built from alternating layers of [Ln2O2]2+ sheets and [MSe2]2- sheets, where M is in the +2 oxidation state with half occupancy of available tetrahedral sites and complex ordering schemes in two dimensions. This paper reports a new family of compounds containing both +1 and +2 metal ions in the La2O2Cu2-4xCd2xSe2 family. We show how Cu1+ and Cd2+ ions segregate into distinct fully occupied and half occupied checkerboard-like layers respectively, leading to complex long-range superstructures in the third (stacking) dimension. To understand the structure and microstructure of these new materials we have developed and implemented a new methodology for studying low and high probability stacking faults using a Rietveld-compatible supercell approach capable of analyzing systems with thousands of layers. We believe this method will be widely applicable. [ABSTRACT FROM AUTHOR]

The new crystal structure models of forms I and II of isotactic polybutene-1 have been proposed by analyzing the 2-dimensional X-ray diffraction data measured for the highly oriented samples of almost pure crystal forms. The crystal form I was found to take the hexagonal packing structure of the (3/1) helices with the space group P3̅, different from the previously reported R3̅c or R3c models. The right- and left-handed chains are packed alternately with the random directionality along the chain axis. The crystal form II was concluded to take the tetragonal unit cell of the (11/3) helical chains, the space group of which is P4̅b2. The right-handed (left-handed) chains are positioned at one site with the statistical disorder of upward and downward directionality along the chain axis. The time-dependent electron diffraction measurement showed that the crystal lattices of forms I and II are related to each other with the common 110 plane boundary, as already reported by the other researchers. By referring to the crystal structures confirmed in this study, a new phase transition mechanism has been proposed for understanding this geometrical relation between these two crystal phases. The mechanism is based on a kind of soft mode concept; the mutually opposite translational movements of the right- and left-handed chains occur along the 110 plane of the tetragonal lattice of form II. The phase angle between the neighboring unit cells along the [110] direction is π. This translational lattice vibrational mode increases the amplitude and causes the softening of the original form II unit cell into a transient structure composed of the hexagonally packed pairs of right- and left-handed chains. Then, this transient structure is stabilized to the crystal form I, during which the chain conformation changes cooperatively from (11/3) to (3/1) form by a slight change in the trans and gauche torsional angles of the skeletal chains. This newly proposed transition mechanism can explain also the formation of twin structure of form I crystals. [ABSTRACT FROM AUTHOR]

The new crystal structure models of forms I and II of isotactic polybutene-1 have been proposed by analyzing the 2-dimensional X-ray diffraction data measured for the highly oriented samples of almost pure crystal forms. The crystal form I was found to take the hexagonal packing structure of the (3/1) helices with the space group P3, different from the previously reported R3c or R3c models. The right- and left-handed chains are packed alternately with the random directionality along the chain axis. The crystal form II was concluded to take the tetragonal unit cell of the (11/3) helical chains, the space group of which is P4b2. The right-handed (left-handed) chains are positioned at one site with the statistical disorder of upward and downward directionality along the chain axis. The time-dependent electron diffraction measurement showed that the crystal lattices of forms I and II are related to each other with the common 110 plane boundary, as already reported by the other researchers. By referring to the crystal structures confirmed in this study, a new phase transition mechanism has been proposed for understanding this geometrical relation between these two crystal phases. The mechanism is based on a kind of soft mode concept; the mutually opposite translational movements of the right- and left-handed chains occur along the 110 plane of the tetragonal lattice of form II. The phase angle between the neighboring unit cells along the [110] direction is p. This translational lattice vibrational mode increases the amplitude and causes the softening of the original form II unit cell into a transient structure composed of the hexagonally packed pairs of right- and left-handed chains. Then, this transient structure is stabilized to the crystal form I, during which the chain conformation changes cooperatively from (11/3) to (3/1) form by a slight change in the trans and gauche torsional angles of the skeletal chains. This newly proposed transition mechanism can explain also the formation of twin structure of form I crystals. [ABSTRACT FROM AUTHOR]

The role of quantum tunneling in hydrogen shift in linear heptyl radicals is explored using multidimensional, small-curvature tunneling method for the transmission coefficients and a potential energy surface computed at the CBS-QB3 level of theory. Several one-dimensional approximations (Wigner, Skodje and Truhlar, and Eckart methods) were compared to the multidimensional results. The Eckart method was found to be sufficiently accurate in comparison to the small-curvature tunneling results for a wide range of temperature, but this agreement is in fact fortuitous and caused by error cancellations. High-pressure limit rate constants were calculated using the transition state theory with treatment of hindered rotations and Eckart transmission coefficients for all hydrogen-transfer isomerizations in n-pentyl to n-octyl radicals. Rate constants are found in good agreement with experimental kinetic data available for n-pentyl and n-hexyl radicals. In the case of n-heptyl and n-octyl, our calculated rates agree well with limited experimentally derived data. Several conclusions made in the experimental studies of Tsang et al. (Tsang, W.; McGivern, W. S.; Manion, J. A. Proc. Combust. Inst. 2009, 32, 131-138) are confirmed theoretically: older low-temperature experimental data, characterized by small pre-exponential factors and activation energies, can be reconciled with high-temperature data by taking into account tunneling; at low temperatures, transmission coefficients are substantially larger for H-atom transfers through a five-membered ring transition state than those with six-membered rings; channels with transition ring structures involving greater than 8 atoms can be neglected because of entropic effects that inhibit such transitions. The set of computational kinetic rates were used to derive a general rate rule that explicitly accounts for tunneling. The rate rule is shown to reproduce closely the theoretical rate constants. [ABSTRACT FROM AUTHOR]

A class of acenaphthene derivatives is shown to contain weak central carbon−carbon bonds that may be easily cleaved at high temperatures or even at ambient conditions to yield persistent free diradicals. To demonstrate the weak C−C bond strength, density functional theory calculations were carried out at several levels of theory for both the parent molecules and the diradicals resulting from the C−C bond cleavage. To assess the accuracy of the calculations, hexaphenylethane was chosen as a model compound due to its similarity with the molecules studied here, its great resonance stabilization, and long-standing history within the chemistry community. The C−C bond dissociation energy of hexaphenylethane was determined to be 11.3 ± 1.4 kcal/mol using a combination of isodesmic reactions and calculations at the M06-2X/6-31+G(d,p) level of theory. The types of molecules presented here are proposed as strong possibilities for the natural existence of free radicals in young and mature soot formed in hydrocarbon combustion. [ABSTRACT FROM AUTHOR]

Sustained oscillations in pH and redox potential are found in the chlorite−sulfide reaction in a continuous-flow stirred tank reactor (CSTR). Autocatalytic oxidation of HSO3−by ClO2−is the major source of positive feedback of hydrogen ions. The reaction between H2S and ClO2−to form S8, which consumes H+, is an important source of negative feedback. A model consisting of five protonation−deprotonation equilibria and nine redox reactions is proposed for the oscillatory reaction between S2-and ClO2−. The 10 species included are HS−, H2S, S2O32−, SO32−, HSO3−, OCl−, HOCl, ClO2−, H+, and OH−. In contrast to the H2O2−S2-oscillatory reaction, S2O32−is shown here by capillary electrophoresis to be an important intermediate. Simulations give qualitative agreement with the pH oscillatory behavior observed in the CSTR. [ABSTRACT FROM AUTHOR]

Investigates the formation of cumulative double bonds in the attachment of multifunctional molecules on silicon (Si). Mechanism of binding of acrylonitrile on the Si unit cells; Band structures of the adlayers; Process of acrylonitrile adsorption on Si.

Presents information relating to the use of the connection of two carbon band electrodes with an anodically grown film of poly(aniline) in making an enzyme switch, or microelectrochemical enzyme transistor, responsive to hydrogen peroxide. Chemical properties of horseradish peroxidase; How hydrogen peroxide was produced; Consistency of electrochemical work stations.

Poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically polymerized to in situ modify stainless steel (SS) plate electrode to improve its microbial bioelectrocatalytic activity as high-performance anode in microbial fuel cells. After modification, the surface of the electrode became rougher and showed better wettability. The electrochemical characteristics of PEDOT modified SS (PEDOT/SS) and bare SS electrodes were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel corrosion polarization curves, respectively. It has been demonstrated that PEDOT modification could increase electrode capacitance and reduce electron transfer resistances. Compared with untreated SS, PEDOT/SS electrode showed better anticorrosion property as well. The modified anode produced a maximum power density of 608.6 mW/m2, which was about 6 times higher than bare SS anode. These results indicate that PEDOT treatment is an efficient method for SS to improve its performance as anode in MFCs. [ABSTRACT FROM AUTHOR]

Controllable integration of metal nanoparticles (NPs) and metal-organic frameworks (MOFs) is of significant importance in many applications owing to their unique properties. In situ efficient synthesis of metal NPs with different structures into MOFs is a great challenge. Herein, we report the nanostructures of octahedron and flower Pt-Cu frame@HKUST-1, which is successfully synthesized under a microwave irradiation method in only 30 min. In this study, Pt-Cu alloys, serving as the self-template, are synthesized first, followed by the HKUST-1 shell growing in situ via the consumption of Cu0. As multifunctional catalysts, the core-shell structures exhibit excellent performance for the hydrogenation of 1-hexene. Notably, octahedron Pt-Cu frame@HKUST-1 displays high turnover number (TON) and turnover frequency (TOF) of 1004 and 2008 h-1, respectively. Thanks to the protective effect of HKUST-1, the octahedron Pt-Cu frame@HKUST-1 can be recycled for at least four runs without serious loss of activity and obvious aggregation of Pt-Cu alloys. Furthermore, the size-selective catalysis is also well-demonstrated by choosing 1-hexene, cis-cyclooctene, and styrene as substrates. [ABSTRACT FROM AUTHOR]

Binary diffusion coefficients were measured for n-pentane, n-hexane, and n-octane in helium and of n-pentane in nitrogen over the temperature range of 300 to 600 K, using reversed-flow gas chromatography. A generalized, analytical theory is proposed for the binary diffusion coefficients of long-chain molecules in simple diluent gases, taking advantage of a recently developed gas-kinetic theory of the transport properties of nanoslender bodies in dilute free-molecular flows. The theory addresses the long-standing question about the applicability of the Chapman-Enskog theory in describing the transport properties of nonspherical molecular structures, or equivalently, the use of isotropic potentials of interaction for a roughly cylindrical molecular structure such as large normal alkanes. An approximate potential energy function is proposed for the intermolecular interaction of long-chain n-alkane with typical bath gases. Using this potential and the analytical theory for nanoslender bodies, we show that the diffusion coefficients of n-alkanes in typical bath gases can be treated by the resulting analytical model accurately, especially for compounds larger than n-butane. [ABSTRACT FROM AUTHOR]

At present, quantum-dot-sensitized solar cells (QDSCs) still exhibit moderate power conversion efficiency (with record efficiency of 6-7%), limited primarily by charge recombination. Therefore, suppressing recombination processes is a mandatory requirement to boost the performance of QDSCs. Herein, we demonstrate the ability of a novel sequential inorganic ZnS/SiO2 double layer treatment onto the QD-sensitized photoanode for strongly inhibiting interfacial recombination processes in QDSCs while providing improved cell stability. Theoretical modeling and impedance spectroscopy reveal that the combined ZnS/SiO2 treatment reduces interfacial recombination and increases charge collection efficiency when compared with conventional ZnS treatment alone. In line with those results, subpicosecond THz spectroscopy demonstrates that while QD to TiO2 electron-transfer rates and yields are insensitive to inorganic photoanode overcoating, back recombination at the oxide surface is strongly suppressed by subsequent inorganic treatments. By exploiting this approach, CdSexTe1-x QDSCs exhibit a certified record efficiency of 8.21% (8.55% for a champion cell), an improvement of 20% over the previous record high efficiency of 6.8%, together with an additional beneficial effect of improved cell stability. [ABSTRACT FROM AUTHOR]

Single crystals of YbOs2Al10 and LuOs2Al10 were grown for the first time using an aluminum self-flux method. The compounds crystallized into a cagelike structure in space group Cmcm, similar to the prototype compound YbFe2Al10. YbOs2All0 exhibited a mixed-valent nature, as determined by magnetic susceptibility measurements over a wide temperature range from 2 to 900 K, in which the inter-configuration--fluctuation model revealed a broad peak around 400 K. In contrast, LuOs2Al10 displayed Pauli-like paramagnetic behavior over the same temperature range. Both compounds were metallic in nature between 2 and 300 K. The electronic specific heat coefficient of 21.3(2) mJ mol-l K-2 for YbOs2Al10 was determined to be larger than that for LuOs2Al10 [8.9(1) mJ mol-1 K-2], reflecting the mixed-valent nature of the former. First-principles calculations predicted the presence of a mixed-valent state in YbOs2Al10, in agreement with the experimental observations. The novel compound YbOs2Al10 elucidates the evolution of the mixed-valent nature of the Yb-based ternary transition metal aluminides from the 3d to 5d elements. [ABSTRACT FROM AUTHOR]

HIV-1 integrase (IN) is one of three enzymes encoded by the HIV genome and is essential for viral replication. Recently, HIV-1 IN inhibitors have emerged as a new promising class of therapeutics. Herein, we report the discovery of azaindole carboxylic acids and azaindole hydroxamic acids as potent inhibitors of the HIV-1 IN enzyme and their structure−activity relationships. Several 4-fluorobenzyl substituted azaindole hydroxamic acids showed potent antiviral activities in cell-based assays and offered a structurally simple scaffold for the development of novel HIV-1 IN inhibitors. [ABSTRACT FROM AUTHOR]

The application of microscopic Fourier transform infrared (micro-FT-IR) spectroscopy combined with complementary methods of particle analysis is demonstrated here for investigations of phase transitions and hygroscopic growth of micron-sized particles. The approach utilizes the ex- posure of substrate-deposited, isolated particles to hu- midified nitrogen inside a sample cell followed by micro- FT-IR spectroscopy over a selected sample area. Phase transitions of NaCI, sea salt, NaNO3, and (NH4)2SO4 particles are monitored with this technique to evaluate its utility and applicability for particle hydration studies. The results are found in excellent agreement with literature data in terms of (a) reliable and reproducible detection of deliquescence and efflorescence phase transitions, (b) quantitative measurements of water-to-solute ratios in particles as a function of relative humidity, and (c) changes in the IR spectra resulting from phase transitions and changing relative humidity. Additional methods of particle analysis are employed to complement and assist in the interpretation of particle hygroscopicity data obtained from micro-FT-IR measurements. The analytical approach and the experimental setup presented here are relatively simple, inexpensive, readily available and therefore may be practical for hydration studies of environmental particles collected in both laboratory and field studies. [ABSTRACT FROM AUTHOR]