The multichannel i-propyl + O2 reaction system: A model of secondary alkyl radical oxidation.

The i-propyl + O2 reaction mechanism has been investigated by definitive quantum chemical methods to establish this system as a benchmark for the combustion of secondary alkyl radicals. Focal point analyses extrapolating to the ab initio limit were performed based on explicit computations with electron correlation treatments through coupled cluster single, double, triple, and quadruple excitations and basis sets up to cc-pV5Z. The rigorous coupled cluster single, double, and triple excitations/cc-pVTZ level of theory was used to fully optimize all reaction species and transition states, thus, removing some substantial flaws in reference geometries existing in the literature. The vital i-propylperoxy radical (MIN1) and its concerted elimination transition state (TS1) were found 34.8 and 4.4 kcal mol-1 below the reactants, respectively. Two ß-hydrogen transfer transition states (TS2, TS2') lie above the reactants by (1.4, 2.5) kcal mol-1 and display large Born-Oppenheimer diagonal corrections indicative of nearby surface crossings. An α-hydrogen transfer transition state (TS5) is discovered 5.7 kcal mol-1 above the reactants that bifurcates into equivalent α-peroxy radical hanging wells (MIN3) prior to a highly exothermic dissociation into acetone + OH. The reverse TS5 → MIN1 intrinsic reaction path also displays fascinating features, including another bifurcation and a conical intersection of potential energy surfaces. An exhaustive conformational search of two hydroperoxypropyl (QOOH) intermediates (MIN2 and MIN3) of the i-propyl + O2 system located nine rotamers within 0.9 kcal mol-1 of the corresponding lowest-energy minima.

Mechanism for the Reaction of White Phosphorus with Cp2Cr2(CO)6 Leading Ultimately to the Triple-Decker Sandwich Cp2Cr2(µ-η5,η5-P5): A Theoretical Study.

The experimentally known reaction of Cp2Cr2(CO)6 with white phosphorus (P4) to give CpCr(CO)2(η3-P3), Cp2Cr2(CO)4(µ-η,2η2-P2), and the triple-decker sandwich Cp2Cr2(µ-η,5η5-P5) is of interest since the P4 reactant having a tetrahedral cluster of four phosphorus atoms is converted to products having P2, P3, and P5 ligands. The mechanism of this obviously complicated reaction can be dissected into three stages using a coupled cluster theoretical method that has been benchmarked with the P2, Mn(CO)5, and CpCr(CO)3 dimerization processes. The first stage of the Cp2Cr2(CO)6/P4 reaction mechanism generates the unsaturated singlet intermediate Cp2Cr2(CO)5 that combines with the P4 reactant. Decarbonylation of the resulting Cp2Cr2(CO)5(P4) complex provides a singlet tetracarbonyl readily fragmenting into the stable triphosphacyclopropenyl complex CpCr(CO)2(η3-P3) and the chromium phosphide CpCr(CO)2(P). The isomeric triplet tetracarbonyl Cp2Cr2(CO)4(P4), readily fragments into CpCr(CO)2(η2-P2), which can generate the stable diphosphaacetylene complex Cp2Cr2(CO)4(η,2η2-P2) as well as the pentamer [CpCr(CO)2]5(P10). Combination of the coordinately unsaturated CpCr(CO)(η3-P3) with CpCr(CO)2(η2-P2) can lead to a ring expansion. This generates the P5 pentagonal ligand in a Cp2Cr2(CO)3(P5) precursor to the experimentally observed carbonyl-free triple-decker sandwich Cp2Cr2(µ-η,5η5-P5) after three successive decarbonylations.

Understanding the singlet-triplet energy splittings in transition metal-capped carbon chains.

The singlet-triplet energy splittings (STES) of dication carbon chains capped by three 16-electron and two 14-electron configuration transition metal termini have been investigated using density functional theory. All five transition metal-capped carbon chains (MCC) exhibit an odd-even STES alternation, suggesting that it is a general feature of the MCCs. Analysis of the frontier molecular orbitals indicates that the frontier and neighboring molecular orbitals (MOs) are π orbitals delocalized over the entire carbon chain, the transition metal termini, and the ancillary ligands. In even and odd metal-carbon chains the HOMOs and LUMOs are nearly degenerate and non-degenerate, respectively, resulting in the even-odd STES alternation. Further analysis of the MOs in the MCCs and the uncapped carbon chains indicate that the STES of the MCCs are determined substantially by the uncapped carbon chain. Other ancillary ligands also play important roles in tuning the energy splitting through their π donor and acceptor abilities. These observations are helpful for the design of cumulene materials exhibiting tunable electronic and optical properties.

Visfatin Level and The Risk of Hypertension and Cerebrovascular Accident: A Systematic Review and Meta-Analysis.

High blood pressure is related with increased cerebrovascular accident. High visfatin / NAMPT(nicotinamide phosphoribosyltransferase) plasma levels may promote vascular inflammation and atherosclerotic plaque destabilization and have been evaluated as a marker for identifying stages of essential hypertension. However, its role in the pathogenesis of hypertension and cerebrovascular accident (CVA) is still uncertain. In order to review and meta-analyze observational studies investigating visfatin concentration and the risk for hypertension or CVA, a systematic search of PubMed, ovid EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL) until December 07, 2016 was performed. After data extraction and quality assessment, a meta-analysis was performed using RevMan 5.3 and STATA 14.0. A total of 1693 adults from 8 studies for hypertension (974 with hypertension) and 1696 adults from 7 CVA studies (957 with CVA) were enrolled in the current meta-analysis. Cochran's Q-statistic and I2 test were applied to estimate the heterogeneity of the studies. The fixed-effects were used to compute the weighted mean difference in visfatin levels. Plasma visfatin concentration was much higher in hypertension and CVA patients than in healthy individuals. These evidences suggested the association of hypertension and CVA with higher plasma visfatin level.

Most favorable cumulenic structures in iron-capped linear carbon chains are short singlet odd-carbon dications: a theoretical view.

Iron-capped, linear-carbon-chain dications have been investigated at the M06L/DZP level of quantum chemistry in order to determine their structural and electronic properties, focusing on differences between chains containing odd and even numbers of carbon atoms. Such differences result from changes in the electronic states and the acetylenic or cumulenic nature of the carbon chain. Interestingly, the short even-carbon chains exhibit distinct properties, but upon chain lengthening undergo a transition to structures similar to those of odd-carbon chains, with a turning point around [FeC10Fe]2+. On the other hand, the less extensively investigated short odd-carbon chains, such as [FeC5Fe]2+, [FeC7Fe]2+ and [FeC9Fe]2+, due to synthetic difficulty, are predicted to exhibit more exceptional properties than the short even-carbon chains in every aspect, such as excellent back bonding as well as more cumulenic and more nearly linear structures. This theoretical study suggests that more experimental work should be considered on metal-capped, short linear odd-carbon chains as potential building blocks for novel electronic and optical materials.

Heavier Carbon Subchalcogenides as C3 Sources for Tungsten-Capped Cumulenes: A Theoretical Study.

Heavier carbon subchalcogenides C3E2 (E = S, Se) can bind to transition metals through either a C═C or a C═E double bond. These two binding modes on a reactive tungsten (PMe3)4WCl2 site have been explored by density functional theory methods (M06-L/DZP+Lanl2DZ). The important step controlling the reaction direction is the initial binding of the C3E2 ligand. Of particular significance is the M═C═C═C═E fragment resulting from the C═E coordination mode. This fragment can bind to additional C3E2 molecules or bridge to other metals. Ultimately C3E2 serves as a source of C3 units for building C3n carbon sp-hybridized allotropes.

Controlling the Reactivity of the Boronyl Group in Platinum Complexes toward Cyclodimerization: A Theoretical Survey.

A theoretical study of the cyclodimerization of (Cy3P)2Pt(BO)Br (1Br) and [(Cy3P)2Pt(BO)](+) (1) (Cy = cyclohexyl) suggests that the reactivity of the BO ligand is primarily controlled by M←BO σ donation. Therefore, increasing the electron density at the metal center through strong σ-donor and weak π-acceptor ancillary ligands and a low formal metal oxidation state are suggested to reduce the polarity of the boronyl ligand and thus lower its reactivity toward cyclodimerization. The stable 1Br has lower Pt←BO σ donation and thus a less electrophilic boron atom, leading to a less polarized BO ligand. However, 1 is unstable in dichloromethane, since the dicationic dimer and transition state are highly stabilized by strong electrostatic interactions.

Pathways to the polymerization of boron monoxide dimer to give low-density porous materials containing six-membered boroxine rings.

Density functional theory has been used to examine the key mechanistic details of the polymerization of boron monoxide (BO) via its O≡B-B≡O dimer to give ultimately low-density porous polymeric (BO)n materials. The structures of such materials consist of planar layers of six-membered boroxine (B3O3) rings linked by boron-boron bonds. Initial cyclooligomerization of B2O2 leads to a B4O4 dimer with a four-membered B2O2 ring, a B6O6 trimer containing a six-membered B3O3 (boroxine) ring, a B8O8 tetramer containing an eight-membered B4O4 ring, and even a B10O10 pentamer containing a ten-membered B5O5 ring. However, an isomeric B10O10 structure containing two boroxine rings linked by a B-B bond is a much lower energy structure by ∼31 kcal/mol owing to the special stability of the aromatic boroxine rings. Rotation of the boroxine rings around the central B-B bond in this B10O10 structure has a low rotation barrier suggesting that further oligomerization to give products containing either perpendicular or planar orientations of the B3O3 rings is possible. However, the planar oligomers are energetically more favorable since they have fewer high-energy external BO groups bonded to the network of boroxine rings. The pendant boronyl groups are reactive sites that can be used for further polymerization. Mechanistic aspects of the further oligomerization of (BO)x systems to give a B24O24 oligomer with a naphthalene-like arrangement of boroxine rings and a B84O84 structure with a coronene-like arrangement of boroxine rings have been examined. Further polymerization of these intermediates by similar processes is predicted to lead ultimately to polymers consisting of planar networks of boroxine rings. The holes between the boroxine rings in such polymers suggests that they will be porous low-density materials. Applications of such materials as absorbents for small molecules are anticipated.

A hyaluronic acid modified cuprous metal-organic complex for reversing multidrug resistance via redox dyshomeostasis.

Multidrug resistance (MDR) which is often related to the overexpression of P-glycoprotein (P-gp) in drug-resistant cancer cells has been a major problem faced by current cancer chemotherapy. Reversing P-gp-related MDR by disrupting tumor redox homeostasis that regulates the expression of P-gp is a promising strategy. In this work, a hyaluronic acid (HA) modified nanoscale cuprous metal-organic complex (HA-CuTT) was developed to reverse P-gp-related MDR via two-way regulated redox dyshomeostasis, which was achieved by both Cu+-catalyzed generation of •OH and disulfide bonds-mediated depletion of glutathione (GSH). In vitro studies reveal that the DOX-loaded complex (HA-CuTT@DOX) has excellent targeting ability to HepG2-ADR cells due to the modification of HA and effectively induces redox dyshomeostasis in HepG2-ADR cells. Moreover, HA-CuTT@DOX can cause mitochondrial damage, decrease ATP level, and downregulate the P-gp expression, thereby leading to the reversal of MDR and the increased drug accumulation in HepG2-ADR cells. Importantly, in vivo experimental results show that it can achieve effective inhibition (89.6 %) of tumor growth in nude mice bearing HepG2-ADR cells. This is the first work to reverse P-gp-related MDR via two-way regulated redox dyshomeostasis based on a HA modified nanoscale cuprous metal-organic complex, providing a new therapeutic paradigm for effective treatment of MDR-related cancer.

Chiral phosphoric acid-catalyzed dual-ring formation for enantioselective construction of N-N axially chiral 3,3'-bisquinazolinones.

In contrast with the well-developed C-C and C-N axial chirality, research focusing on the catalytically asymmetric synthesis of N-N axially chiral compounds is still limited. As a privileged subunit of many antibiotics, the synthesis of N-N axially chiral 3,3'-bisquinazolinones has not been updated with atroposelective construction. Herein, we firstly report a chiral phosphoric acid-catalyzed dual-ring formation strategy leading to the aforementioned compounds with good chemical yields and enantioselectivities. Notably, metal-free reaction conditions are another advantage of this procedure.

A GLUTs/GSH cascade targeting-responsive bioprobe for the detection of circulating tumor cells.

A GLUTs/GSH cascade targeting-responsive bioprobe, GluCC, was rationally designed and synthesized for the first time via the coordination of copper ions with a glucose-modified coumarin derivative ligand (GluC). GluCC can specifically detect circulating tumor cells (CTCs) in lung metastatic mice models by targeting the Warburg effect and responding to overexpressed glutathione in the tumor microenvironment. This bioprobe with a simple detection procedure has significant advantages for CTC detection.

Hydrogen bonding in hydrates with one acetic acid molecule.

Hydrogen bonding (H-bond) interaction significantly influences the separation of acetic acid (HAc) from the HAc/H(2)O mixtures, especially the dilute solution, in distillation processes. It has been examined from the HAc mono-, di-, tri-, and tetrahydrates by analyzing the structures, binding energies, and infrared vibrational frequencies from quantum chemical calculations. For the first coordinate shell the 6-membered head-on ring is surely the most favorable structure because it has (1) the most favorable H-bonding parameters, (2) almost the largest binding energy per H-bond, (3) the biggest wavenumber shifts, and (4) the highest ring distribution (the AIMD simulations). Moreover, the comparison of the calculations with the experiments (the X-ray scattering data and IR frequencies) suggests that the possible structures in dilute aqueous solution are those involving two or more coordinate shells. The H-bonding in these water-surrounded HAc hydrates are the origin of the low-efficiency problem of isolating HAc from the dilute HAc/H(2)O mixtures. It is apparently a tougher work to break the H-bonds among HAc and the surrounded H(2)O molecules with respect to the case of more concentrated solutions, where the dominant structures are HAc or H(2)O aggregates.

Tumor microenvironment responsive supramolecular glyco-nanovesicles based on diselenium-bridged pillar[5]arene dimer for targeted chemotherapy.

Supramolecular glyco-nanovesicles (SeSe-(P5)2⊃Man-NH3+) based on the host-guest complex of a diselenium-bridged pillar[5]arene dimer and a mannose derivative have been successfully developed for the first time, which possessed tumor microenvironment-responsiveness and specific targetability due to their diselenium bonds and mannose units, respectively.

Hydrogen bonding of hydrates of double acetic acid molecules.

In the chemical industry, the separation of the acetic acid from the HAc/H(2)O system is always influenced by the hydrogen bonding. In the present work, an investigation on the hydrogen bonding of various hydrates of double acetic acid (HAc) molecules is carried out with two first-principle methods including ab initio molecular dynamics (AIMD) simulation and quantum chemical calculations (QCC). From the AIMD simulation, the distribution of the head-on rings of acetic acid is revealed and shows that the favorable structures tend to be the acetic acid hydrates rather than the HAc cyclic dimer. The 6- and 10-membered head-on rings involving single and double HAc molecules, respectively, appear to be the dominant structures. According to the QCC, the most stable structure is found to be the conformer with the biggest head-on ring in each group. The energetics of the rings indicates that the stability of the ring increases with increased ring size (with the exception of the 9-membered ring), and the 10-membered ring is the most stable. The relative stability of the ring structures implied by the static QCC result is in good agreement with the statistical ring distribution of the AIMD simulation.

Tricolor Luminescence Switching by Thermal and Mechanical Stimuli in the Crystal Polymorphs of Pyridyl-substituted Fluorene.

Stimuli-responsive organic luminescence-switching materials have attracted much attention for a decade. Most of the reported examples display a reversible two-color luminescence switching, and multicolor-switching materials remain extremely rare. Herein, we report a simple organic molecule, 4,4'-(9,9-dimethyl-9H-fluorene-2,7-diyl)dipyridine (MFDP), which exhibits three different crystal polymorphs (V-MFDP, B-MFDP and G-MFDP) with different luminescent colors. Furthermore, the three crystal polymorphs show a reversible tricolor fluorescent switching from violet to blue and to green upon physical stimuli. The single-crystal structures of the three polymorphs were obtained, and the results indicate that the stimuli-responsive properties of the three polymorphs come from the different stacking modes induced by intermolecular interactions. The competition between weak π-π stacking and weak hydrogen bonding is the main reason for the the phase transformations among the three crystal polymorphs.

Multimodal Transformer for Unaligned Multimodal Language Sequences.

Human language is often multimodal, which comprehends a mixture of natural language, facial gestures, and acoustic behaviors. However, two major challenges in modeling such multimodal human language time-series data exist: 1) inherent data non-alignment due to variable sampling rates for the sequences from each modality; and 2) long-range dependencies between elements across modalities. In this paper, we introduce the Multimodal Transformer (MulT) to generically address the above issues in an end-to-end manner without explicitly aligning the data. At the heart of our model is the directional pairwise cross-modal attention, which attends to interactions between multimodal sequences across distinct time steps and latently adapt streams from one modality to another. Comprehensive experiments on both aligned and non-aligned multimodal time-series show that our model outperforms state-of-the-art methods by a large margin. In addition, empirical analysis suggests that correlated crossmodal signals are able to be captured by the proposed crossmodal attention mechanism in MulT.

Anhydrides-Cured Bimodal Rubber-Like Epoxy Asphalt Composites: From Thermosetting to Quasi-Thermosetting.

The present engineering practices show the potential that epoxy asphalt composites (EACs) would be a better choice to obtain long life for busy roads. To understand the service performance⁻related thermorheological properties of prepared bimodal anhydrides-cured rubber-like EACs (REACs), a direct tensile tester, dynamic shear rheometer and mathematical model were used. Tensile tests demonstrate that all the REACs reported here are more flexible than previously reported anhydrides-cured REACs at both 20 and 0 °C. The better flexibility is attributed to the change of bimodal networks, in which cross-linked short chains decreased and cross-linked long chains increased, relatively. Strain sweeps show that all the REACs have linear viscoelastic (LVE) properties when their strains are smaller than 1.0% from -35 to 120 °C. Temperature sweeps illustrate that the thermorheological properties of REACs evolve from thermosetting to quasi-thermosetting with asphalt content, and all the REACs retain solid state and show elastic properties in the experimental temperature range. A Cole⁻Cole plot and Black diagram indicate that all the REACs are thermorheologically simple materials, and the master curves were constructed and well-fitted by the Generalized Logistic Sigmoidal models. This research provides a facile approach to tune the thermorheological properties of the REACs, and the cheaper quasi-thermosetting REAC facilitates their advanced applications.

Coupling of chalcocarbonyl ligands (CE: E = S, Se, Te) on an iron carbonyl site: effect of the chalcogen.

B3LYP/DZP(Lanl2dz) study of Fe(CO)n(CE)2 (E = S, Se, Te; n = 4, 3) suggests that the Fe(η(2)-E-C) structures are energetically preferred for singlet Fe(CO)4(C2E2) and triplet Fe(CO)3(C2E2). The tendency for coupling reactions of CE ligands to form C2E2 ligands by carbon-carbon bond formation increases in the sequence S < Se < Te.

Expression and purification of the chimeric virus-like particles displaying enterovirus 71 epitopes / 中华实验和临床病毒学杂志

Objective@#To study the expression and purification of the chimeric virus-like particles displaying epitopes of EV71 as a candidate of enterovirus 71 gene recombined vaccinet.@*Methods@#The fusion protein hepatitis B core (HBc)-SP70 was constructed by inserting SP70 into the main immunogenic region of truncated hepatitis B core antigen (HBcAg) sequence, expressed in E. Coli, and purified through sonication, ion exchange chromatography, CsCl cushion centrifugation and density gradient centrifugation. Then its antigenicity was detected by ELISA and Western blot assay.@*Results@#Recombinant plasmid pHBc-SP70 was successfully constructed. And the soluble fusion protein was efficiently expressed induced by IPTG. The purity of the chimeric virus-like particles (VLPs) was up to 90% after the purification process described in method . The purified fusion protein HBc-SP70 could be spontaneously folded and assembled into empty virus-like particles and react with the monoclonal antibodies against HBc and SP70.@*Conclusions@#The chimeric VLPs displaying epitopes of EV71 were efficiently expressed and purified in E. Coli. with excellent antigenicity, which laid a foundation for evaluation of the immune effect evoked by this EV71 gene recombined vaccine.

Efficient Humoral and Cellular Immune Responses Induced by a Chimeric Virus-like Particle Displaying the Epitope of EV71 without Adjuvant / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To eliminate the side effects of aluminum adjuvant and His-tag, we constructed chimeric VLPs displaying the epitope of EV71 (SP70) without His-tagged. Then evaluating whether the VLPs could efficiently evoke not only humoral but also cellular immune responses against EV71 without adjuvant.</p><p><b>METHODS</b>The fusion protein was constructed by inserting SP70 into the MIR of truncated HBcAg sequence, expressed in E. Coli, and purified through ion exchange chromatography and density gradient centrifugation. Mice were immunized with the VLPs and sera were collected afterwards. The specific antibody titers, IgG subtypes and neutralizing efficacy were detected by ELISA, neutralization assay, and EV71 lethal challenge. IFN-γ and IL-4 secreted by splenocytes were tested by ELISPOT assay.</p><p><b>RESULTS</b>HBc-SP70 proteins can self-assemble into empty VLPs. After immunization with HBc-SP70 VLPs, the detectable anti-EV71 antibodies were effective in neutralizing EV71 and protected newborn mice from EV71 lethal challenge. There was no significant difference for the immune efficacy whether the aluminum adjuvant was added or not. The specific IgG subtypes were mainly IgG1 and IgG2b and splenocytes from the mice immunized produced high levels of IFN-γ and IL-4.</p><p><b>CONCLUSION</b>The fusion proteins without His-tagged was expressed and purified as soluble chimeric HBc-SP70 VLPs without renaturation. In the absence of adjuvant, they were efficient to elicit high levels of Th1/Th2 mixed immune response as well as assisted by aluminum adjuvant. Furthermore, the chimeric VLPs have potential to prevent HBV and EV71 infection simultaneously.</p>