Towards Responsive Single-Molecule Device

Single-molecule devices,which are fabricated by the single molecule bridged through electrodes,provide a promising approach to investigate the intrinsic chemical or physical properties of individual molecules.Beyond the studies of single-molecule wires,a large number of responsive single-molecule junctions or devices with unique chemical or physical properties have been designed and fabricated by introducing the external field,which further offers the chance to explore conductive materials at the molecular level.Here,we summarized the latest studies on the behaviors of single-molecule devices based on the photon,thermal,electric,or magnetic responses,and discussed the development of responsive single-molecule devices in prospect.     

TRANSFER OF RADIATION-INDUCED SPINS FROM DEOXYRIBONUCLEIC AND TH

When calf thymus deoxyribonucleic acid (DNA), propyl gallate (PG) and their five mo-ecular mixtures (with PG content of 1, 2, 5, 10 and 20%) are irradiated with γ-rays indry state in vacuum at 296°K, the ESR spectra of all molecular mixtures differ strikinglyfrom those of DNA, but bear a close resemblance to those of PG. The spin yield in the PGcontained in these mixtures is two to three orders of magnitude higher than that in the caseof PG irradiated separately. Furthermore, on the basis of the relative saturation characteris-tics of ESR spectra, these molecular mixtures behave more like PG than like DNA. It maybe inferred that the radiation-induced spins could be transferred from DNA to PG. Withr representing the molar ratio of nucleotides to PG, we have found a good linear correlationbetween the transfer ratio (TR) and r~(1/2). One PG molecule could protect at least 68 nu-eleotides in the duplex DNA chain, and thereby the minimal range of spin transfer is estimat-ed at 115 ?. Results obtained from irradiation at 77°K show that PG exerts no protectiveeffect on DNA, so DNA sustains an irreversible damage. It is thought that the spin transferfrom DNA to PG is exclusively due to a hydrogen transfer mechanism. We have also demons-trated the transfer of radiation-induced spins from both thermally denatured DNA and TMPto PG. The former process can be ascribed primarily to the hydrogen transfer mechanism,Whereas the latter, as in the case of native DNA, exclusively to this mechanism.     

用于合成纯硅分子筛 AST 和 LTA 的动态有机结构导向剂(英文)

Pure-silica-zeolite(PSZ) AST and LTA are synthesized successfully by using the same structure-directing agent(SDA) molecule,but at different concentrations.A dynamic organic SDA is proposed to discuss the mechanism of phase discrimination between AST and LTA.Data suggest that the SDA molecules can self-assemble into dimer or trimer complexes at different concentrations by π-π interactions,and these differences can be taken advantage of to selectively synthesize either PSZ AST or LTA.These deviations from the Liebau's rules indicate that small changes in SDA chemistry,structure,and order in solution can have a great impact on the structure selectivity of the zeolite synthesis.     

Fragmentation Mechanism of Trans—α—Aryl—β—enamino Esters

Electron impact-induced fragmentation mechanism of Trans-α-Aryl-β-enamino esters were investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry and high resolution accurate mass data It was found that the main characteristic fragmentations of compounds studied were:an odd electron ion M^ -EtOH was formed by losing a neutral molecule of ethanol;and the skeletal rearrangements took place;and the ring opening reaction happened after losing a carbon monoxide;and the typical McLafferty rearrangement underwent in ester group.The cycliztion reation caused by losing neutral molecule of TsNH2 due to the ortho-effects of substituted group of gromatic ring was also observed.     

Investigation on the folding mode of a polymer chain in a spiral crystal by single molecule force spectroscopy

Investigation on the folding mode of a single polymer chain in its crystal is significant to the understanding of the mechanism of the fundamental crystallization as well as the engineering of new polymer crystal-based materials. Herein, we use the combined techniques of atomic force microscopy （AFM） imaging and force spectroscopy to pull a single polyethylene oxide （PEO） chain out of its spiral crystal in amyl acetate. From these data, the folding mode of polymer chains in the spiral crystal has been reconstructed. We find that the stems tilt in the typical flat area, leading to the decrease in the apparent lamellar height. While in the area of screw dislocation, the lamellar height gradually increases in the range of several nanometers. These results indicate that the combined techniques present a novel tool to directly unravel the chain folding mode of spiral crystals at single-molecule level.     

Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition： a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier (Four-member mechanism). Another mechanism involving a water molecule as catalyst to mediate the proton transfer (WCP mechanism), is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation (HOC6H4CH2+) which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.     

Theoretical Study of the Iodine-catalyzed Nucleophilic Addition by Halogen Bond

The iodine-catalyzed nucleophilic addition of pyrrole to acetone has been studied by density functional theory at the level of Lanl2DZ. It has been shown that the first iodine molecule appears to have a remarkable catalytic effect on this reaction by halogen bond between carbonyl oxygen and iodine molecule,but the second one does not improve the reaction largely. In general,the nucleophilic addition at the C(2) site of pyrrole is more favorable than that at the C(3) site; however,this trend is not prominent or even changed in acetronitrile solvent for the indole system,which is consistent with the experimental result by Bandgar.     

Synthesis of two mono-deoxy β-cyclodextrin derivatives as useful tools for confirming DIBAL-H promoted bis-de-O-methylation mechanism

Diisobutylaluminium hydride(DIBAL-H) promotes secondary rim regioselective bis-de-O-methylation of permethylatedβ-cyclodextrin (β-CD) to give diol 2.To gain an insight into the mechanism of this remarkable regioselective behavior,two corresponding permethylatedβ-CDs with an alcohol function at either 2- or 3-position were synthesized in our previous study.As a step further to this work,the two compounds were subjected to deoxygenation reaction with tributyltin hydride in the present of 2,2’- azobisisobutyronitrile affording the corresponding 2- and 3-deoxy permethylatedβ-CD derivatives(19 and 16).The structures of these two compounds were characterized by ID and 2D NMR and HRMS.Compounds 16 and 19 were unable to react with DIBALH which suggests that O-2~A and O-3~B are necessary for DIBAL-H promoted bis-de-O-methylation reaction of permethylatedβ-CD.     

Towards Understanding the Anticorrosive Mechanism of Novel Surfactant Based on Mentha pulegium Oil as Eco-friendly Bio-source of Mild Steel in Acid Medium:a Combined DFT and Molecular Dynamics Investigation

Today,due to the increasingly stringent European directives concerning the use of molecules with certain toxicities towards the environment or their users,the essential oils,extracts,and molecules derived from plants exhibiting the characteristic of being biodegradable can be considered as a source of green corrosion inhibitors instead of harmful synthetic chemicals.The present work was devoted to testing the essential oil extracted from Mentha pulegium leaves(M1) as a corrosion inhibitor for C-steel in 1mol/L HCl solution using both electrochemical techniques and gravimetric measurements for the evaluation of the inhibition efficiencies at different temperatures.The results obtained showed that the inhibition efficiency increased with an increase in Ml concentration to reach a maximum value of 92.21%.We sought to determine the molecule responsible for this high efficiency,starting with the analysis of oil chemical composition by gas chromatography coupled with mass spectrometry.This analysis revealed that menthol(M2)and isomenthol(M3)were the principal constituents.In order to identify the molecule responsible for the inhibition and explain the protection mechanism involved,quantum chemical calculations and Monte Carlo simulations were used to explain the interaction of menthol,the major constituent of M1 with the Fe-surface.To practically confirm these results,we studied the action of 1mol/L HCl on steel with and without the addition of M2 by both methods(gravimetric and electrochemical study).A very high efficiency was obtained,an efficiency of 94.90% at 10^-3 mol/L,which was retained for a long exposure time,and slightly decreased in function of temperature.Finally,a good correlation between the experimental data,theoretical calculations,and SEM studies was obtained,which denied that the Ml efficiency was only a result of a synergy effect and confirmed the high efficiency of Mentha oil and its main component(menthol)as a strong ecological inhibitor of corrosion.     

A mechanistic study of CO removal on a small H-saturated platinum cluster

CO poisoning to platinum catalysts has long been recognized as one of the major technical obstacles in heterogeneous catalysis and its successful removal represents a significant challenge to a wide variety of applications. Using density functional theory (DFT), we performed systematic theoretical calcula-tions to explore the CO removal mechanisms, in the presence of hydrogen, via oxidation by oxygen to form CO2 or reduction by hydrogen to form formaldehyde using a subnano Pt cluster as a model for catalyst nanoparticles. We show that CO oxidation is both thermochemically and kinetically difficult at low H coverage but becomes very exothermic with a moderate activation barrier at high H coverage, suggesting that the oxidation can be carried out readily at elevated temperatures. Doping the Pt cluster with Ru can significantly improve the oxidation thermochemical energy and moderately reduce the activation barrier. The results are consistent with experimental observations. We found that CO reduction by hydrogen to form formaldehyde is moderately endothermic. However, the reaction is predicted to be kinetically difficult due to the relatively high activation barriers associated with the sequential H attacks to the CO molecule.     

Mechanism of the Deaquation of Aquopentaaminocobalt（Ⅲ）Bromide

There are two theories,SN1 and SN2, for the mechanism of the deaquation of aquopentaamincobalt(Ⅲ） bromide(AAC-B). Both of the theories are supported by some experimental and calculated data. But there are not any experiments to determine directly the structure of the intermediates at dififferent reaction time.In this paper the structures of the intermediates at different reaction time in deaquation-anation of AACB were determined by extended X-ray absorption fine structure (EXAFS) and the reaction process was studied by the combination of X-ray powder diffraction and EXAFS.It was demonstrated that the deaquation-anation of AACB obeys the SN2 theory.     

Conjugated polymer nanoparticles as fluorescence switch for selective cell imaging

Fluorescence switch plays a vital role in bioelectronics and bioimaging.Herein,we presented a new kind of facile electrostatic complex nanoparticles(ECNs)for fluorescence switching in cells and marking of individual cell.The ECNs were prepared by mixing positively charged poly(6-(2-(thiophen-3-yl)ethoxy)hexyl trimethylammonium bromide)(PT)and negatively charged diarylethene sodium salt(DAECOONa).DAE-COONa is a photoswitchable molecule which can be transformed between the ring-closed fo rm and ring-open form under the irradiation of UV or visible light.The closed-form of DAE-COONa can efficie ntly quench the fluorescence of PT through intermolecular energy transfer,while the open form of DAE-COONa does not influence the emission of PT.Thus,the fluorescence of ECNs can be modulated by light irradiation,and the ECNs with good fluorescence switching performance have been employed for fluorescence imaging and individual cell lighting up process successfully.We demonstrate that the electrostatic complex strategy provides a facile method to construct fluorescence switch fo r selective cell marking and imaging applications.     

A Kinetic Study on Dismutation of Superoxide Ion by Macrocyclic Dioxotetramine-Copper(Ⅱ) Complex by Using Pulse Radiolysis

We studied the reaction kinetics of dismutation for superoxide ion by copper (Ⅱ) complex of macrocycllc dioxotetramine ligand 12- ( 4' - nitro )- benzyl-1,4,7,10- tetraazacy-clotridecane-11,13-dionato copper (Ⅱ) by using pulse radiolysis. The rate constants of dismutation kcat's were measured to be 1. 78×106 mor-1 . L.s-1(at pH 7. 0) and 1. 06×106 mol-1. L. s-1(at pH 7. 8). The reaction mechanism is similar to that catalyzed by super-oxide dismutase.     

In-situ interaction of nano-PbS with gelatin

Water-soluble gelatin–PbS bionanocomposites(BNCs)were synthesized via a facile one-pot chemical reaction method at pH7.40.The samples were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),UV-vis absorption spectra(UV-vis),Fourier transform infrared spectra(FT-IR)and circular dichroism(CD).FT-IR data were used to envisage the binding of PbS particles with oxygen atoms of carbonyl groups of gelatin molecule.The possible integration mechanism between gelatin and PbS was discussed in detail.The effect of Pb2+and PbS on the conformations of gelatin has also been analyzed by means of UV-vis,CD and FT-IR spectra,resulting in less-helix content and more open structures(-sheet,β-turn,or expanded).A new formula to calculate the association constant was proposed according to the relationship between the absorbance of gelatin–PbS BNCs and the free concentration of PbS,and apparent association constants K(298/303/308 K:3.11/2.00/1.60×106mol/L)at three different temperatures were calculated based on this formula.Thermodynamic parameters such asΔGθ,ΔHθ andΔSθ were also determined.The results of the thermodynamic investigations indicated that the reaction was spontaneous(ΔGθ<0),and enthalpy-driven(ΔHθ<0).     

Synthesis and Gas-sensing Performance of Nanosized SnO2

Nanosized tin dioxide particles were prepared by sol-gel dialytic processes with tin(Ⅳ) chloride and alcohol as start materials. The nanoparticles of tin dioxide were charactered by thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET. The results show that the average diameter of tin dioxide particles dried at 353 K was about 2nm. Even if the tin dioxide particles were calcined at 873 K, the average diameter of particles was less than 10 nm. The removal of Cl^- was solved by using this kind of method. The mechanism of the formation of tin dioxide nanosized particles was proposed and analyzed in this paper. We also measured the sensitivity of the sensor based on the tin oxide powder calcined at 673K to NH3, alcohol, acetone, hexane and CO. The gas-sensing performance results indicate that this sensor has a higher sensitivity to alcohol and acetone, and selectivity for NH3, hexane and CO at an operating temperature of 343 K.     

A DFT Investigation on the Co-adsorption of H_2 and Ions inside the Carbon Nanotube

We studied the co-adsorption of hydrogen molecule and ions (Li,K,Mg,Ca) inside the single-walled carbon nanotubes (SWNTs) by using density-functional theory (DFT).The band structures (BS),density of states (DOS),charge transfer and difference charge density are presented.We discussed the interaction between the ions (Li,K,Mg,Ca) and H 2.Meanwhile,the binding energy indicates that ionization can increase the adsorption energy of H 2 in CNT.     

Saucer-and Rod-like WO_3 3-D Microstructures:Synthesis,Characterization,and Optical Properties

Three-dimensional(3-D)saucer-and rod-like WO3 microstructures have been synthesized by a simple hydrothermal route using tartaric acid as the assistant agent.X-ray powder diffraction(XRD)patterns indicate that the as-prepared samples are the pure hexagonal phase WO3.The morphologies are characterized by scanning electron microscope(SEM)and are found to be highly sensitized to the reaction temperature.A probable formation mechanism of the WO3 microstructures from saucer-like at low temperatures to rod-like at high temperatures is proposed.The optical properties of the novel WO3 microstructures are studied by UV-vis diffuse reflectance spectroscopy(DRS).The mechanism of strong absorption at visible region and red shift of calcined sample is also discussed.     

A β-sheet-targeted theranostic agent for diagnosing and preventing aggregation of pathogenic peptides in Alzheimer's disease

Amyloid-β peptide(Aβ) aggregates, particularly Aβ oligomers, are established biomarker and toxic species in Alzheimer's disease(AD). Early detection and disaggregation of Aβ aggregates are of great importance for the treatment of AD due to the unavailability of therapy at the advanced stages of the disease. A multitalented agent, 2-{2-[(1 H-benzoimidazol-2-yl)methoxy]phenyl}benzothiazole(BPB), is designed by merging two β-sheet targeting groups into one molecule to detect and inhibit the Aβaggregation. BPB can quantitatively measure the β-sheet level of soluble Aβ oligomers and specifically distinguish the aggregates of Aβ40 and Aβ42 by unique luminescence spectrum. Animal tests demonstrate that BPB can efficiently penetrate the blood brain barrier and precisely stain Aβ plaques in the brain; more importantly, it can differentiate the blood of APP transgenic mice from that of normal ones. In addition to the diagnostic potential, BPB also suppresses the generation of ROS, protects the neurons from neurotoxicity, and disaggregates the Aβ aggregates in brain homogenates of APP transgenic mice induced by metal ions or self-assembly. In view of its detective ability toward Aβ oligomers and inhibition to Aβ-related neurotoxicity, BPB may be developed into a sensitive probe for screening blood samples in the early diagnosis of AD as well as an effective inhibitor for diminishing Aβ aggregates in the treatment of the disease.     

Effect of Annealing Temperature on Low-temperature Toughness of β-Nucleated Polypropylene Random Copolymer/Ethylene-Propylene-Diene Terpolymer Blends

In this study, the effect of annealing temperature on the impact toughness of β-nucleated polypropylene random copolymer(PPR) and ethylene-propylene-diene terpolymer(EPDM) blends was investigated by differential scanning calorimetry(DSC), wide-angle X-ray diffraction(WAXD), dynamic mechanical analysis(DMA) and scanning electron microscopy(SEM). Interestingly, the impact strength of β-PPR/20 EPDM blend annealed at 120 ℃ is 1.8 times as high as that of unannealed samples. In addition, the crystalline structure, the relaxation of chain segments and fracture morphology of β-PPR/EPDM blends were also investigated to explore the toughening mechanism related to annealing. The results show that annealing at moderate temperatures results in the improvement of integrity of the crystal structure and the relative content of β-phase. The work provides a possible method to toughen the semicrystalline polymer at low temperatures by annealing.     

Study of Oxidation of Carbon Monoxide on the Surface of Sn-doped Carbon Nanotube

In recent years, the discovery of suitable catalyst to the oxidation of carbon monoxide(CO) is a major concern in industry. In present study, in the first step the carbon nanotube(CNT) with Sn was doped and the surface of Sn-CNT via O_2 molecule was activated. In the second step the CO oxidation on the surface of Sn-CNT via Langmuir Hinshelwood(LH) and Eley Rideal(ER) mechanisms was investigated. Results show that O_2-Sn-CNT can oxidize the CO molecule via Sn-CNT-O-O* + CO → Sn-CNT-O-O*-CO → Sn-CNT-O* + CO_2 and Sn-CNT-O* + CO → Sn-CNT + CO_2 reactions. Results show that CO oxidation on activated Sn-CNT surface via the ER mechanism has lower energy barrier than LH mechanism. Finally, calculated parameters reveal that activated Sn-CNT is an acceptable catalyst with high potential to the oxidation of CO molecule.