Optically active poly[thio-1-(N,N-diethylaminomethyl) ethylene]

Poly[thio-1-(N,N-diethylaminomethyl) ethylene] [poly(TDAE)] of different optical purities were prepared by stereoelective polymerization of racemic N,N-diethyl-N-(thiirane-2-ylmethyl) amine (TDAE) using a (1:1) $\text{ZnEt}{}_2\text{R}$ (?) 3,3-dimethyl 1,2-butanediol (R(?)DMBD) chiral initiator system. Optically enriched TDAE samples were isolated as residual monomers. These monomers were thermally polymerized to give optically active poly(TDAE) with randomly distributed R and S repeat units in various proportions. The configuration of the enantiomer preferentially incorporated into growing chains during the stereoelective polymerization was determined as R on the basis of the presence of a positive Cotton effect at 260 nm in the c.d. spectrum of residual monomers. This configuration agrees well with the known homosteric character of the $\text{ZnEt}{}_2\text{(?)}\text{DMBD}$ initiator system. ¹³C n.m.r. spectra of the different optically active poly(TDAE) samples and those of more or less stereoregular racemic ones were compared. It was found that the carbon atom of the main chain methine group is the only one which is stereosensitive. Observed triad effects were used to determine the degree of isotacticity of optically active poly(TDAE)s prepared by thermal polymerization of partly enriched monomers. The stereoelectivity of the initiator system and the optical activity of optically pure TDAE and poly(TDAE) were deduced. Side-chain nitrogen atoms did not show any competitive effect with sulphur atoms in the coordination process to the chiral initiator system.     

Polymer translocation through a nanopore in mesoscopic simulations

Dissipative particle dynamics (DPD) simulations are carried out to study the translocation of a single polymer chain through a pore under fluid field. The influences of the field strength E, the chain length N, the solvent quality α_sp, and the pore size h on the translocation time are evaluated. The translocation time τ, which is defined as the time that the chain moves through the pore completely in the direction of the driving force, scales with the field strength E as τ ∼ E^{−0.48±0.01}. We find that the translocation time is proportional to the chain length, which is in agreement with the experimental results and theoretical predictions. Tracing the variation of the square radius of gyration, , and the polymer configuration during translocation, we observe that the chain is elongated when it is passing through the pore, which manifests that the chain is not in equilibrium during the translocation process. We also find that the worse the solvent quality is, the less time it will take to translocate, no matter what the size of the pore is. If the size of the pore is enlarged, the translocation time will be shorter. The information we gain from this study may benefit to the DNA sequencing.     

An application of Monte Carlo method to simulate disorders in polymer crystals

The Monte Carlo method is applied to polymer crystals of idealized linear chain molecules of 30 carbon atoms, and the unharmonic, large-amplitude, oscillations and the subsequent conformational disorders of the chains are investigated. A crystalline field that confines the chain is treated by the molecular field approximation, and assumed to be cylindrical in this work. A production type simulation is adopted taking into account rigorous statistical weights for each sample conformation. Both the rotational isomeric model and the continuous rotation model of chain conformation are considered. By averaging over 10⁴–8 × 10⁴ chains, mean-square end-to-end distance, fractions of gauche and trans states and a detailed distribution of internal rotation angle are obtained. The effects of temperature and pressure on the conformation of the chain in the crystals are also simulated.     

Study of three different families of water-soluble copolymers: synthesis, characterization and viscoelastic behavior of semidilute solutions of polymers prepared by solution polymerization

Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N,N-dialkylacrylamides (N,N-dihexylacrylamide (DHAM) and N,N-dioctylacrylamide (DOAM)) have been prepared via free radical solution polymerization, using two hydrophobic initiators derived from 4,4′-azobis(4-cyanopentanoic acid) (ACVA) containing long linear chains of 12 (C12) and 16 (C16) carbon atoms. This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. This class of polymers, termed ‘combined associative polymers’, has been studied and compared with the multisticker (with hydrophobic groups along the polymer chain) and telechelic (with hydrophobic groups at the chain ends) associative polymers, which were prepared with DHAM or DOAM and with the hydrophobic initiator (ACVA) modified with alkyl chains of two different lengths. The viscoelastic properties of these different families of associative polymers were investigated using steady-flow and oscillatory experiments. The effect of type, localization and concentration of the hydrophobic groups on the viscosity of the associative polymer solution was investigated. All viscosity curves clearly show two different regimes within the semidilute range: a first unentangled regime where the viscosity increases moderately; and a second entangled regime where the viscosity varies according to a power law, proportional to C⁴. The relaxation time, T_R, and the plateau modulus, G₀, showed relatively high values which increased with the number of carbon atoms in the hydrophobic groups. The combined associative polymer (PAM-co-DHAM/ACVA12) showed relaxation times that remained relatively constant along the concentrations studied, but very high values of G₀.     

Poly(4-diphenylaminostyrene) with a well-defined polymer chain structure: Controllable optical and electrical properties

The effect of polymer chain structure on the optical and electrical properties are reported for poly(4-diphenylaminostyrene) (PDAS), which was prepared by the living anionic polymerization of 4-diphenylaminostyrene (DAS) with the benzyllithium (BzLi)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) system. The optical properties of PDAS are strongly affected by the stereoregularity of the PDAS polymer chain; intramolecular excimer-forming fluorescence was observed from PDAS with a syndiotactic-rich configuration. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDAS were approximately −5.4 and −2.0 eV, respectively, regardless of the polymer chain structure. The hole and electron drift mobilities for PDAS were in the order of 10⁻⁴ to 10⁻⁵ (cm²/V s) and 10⁻⁵ (cm²/V s), respectively, with negative slopes. The distance of each triphenylamino (TPA) group in the polymer chain was a major factor influencing the drift mobility of PDAS. The current-voltage (I-V) characteristics of PDAS were controllable according to the polymer chain structure of PDAS.     

g-B3N3C: a novel two-dimensional graphite-like material

A novel crystalline structure of hybrid monolayer hexagonal boron nitride (BN) and graphene is predicted by means of the first-principles calculations. This material can be derived via boron or nitrogen atoms which are substituted by carbon atoms evenly in the graphitic BN with vacancies. The corresponding structure is constructed from a BN hexagonal ring linking an additional carbon atom. The unit cell is composed of seven atoms, three of which are boron atoms, three are nitrogen atoms, and one is a carbon atom. It shows a similar space structure as graphene, which is thus coined as g-B₃N₃C. Two stable topological types associated with the carbon bond formation, i.e., C-N or C-B bonds, are identified. Interestingly, distinct ground states of each type, depending on C-N or C-B bonds, and electronic bandgap as well as magnetic properties within this material have been studied systematically. Our work demonstrates a practical and efficient access to electronic properties of two-dimensional nanostructures, providing an approach to tackling open fundamental questions in bandgap-engineered devices and spintronics.     

Primary structure and chiroptical properties of polydiasteriomers obtained by steroelective polymerization of N-[(S)-sec-butyl] and N-[(R)-sec-butyl-N-methyl-N-(R,S)-thiirane-2-ylmethyl] amine isomers

Stereoisomers of N-(sec-butyl)-N-methyl-N-((R,S)-thiirane 2-ylmethyl) amine ((S)-sec-butyl, optical purity O.P. ～94% and (R)-sec-butyl, O.P. ～26%) were polymerized using a chiral initiator system (1:1) $\text{ZnEt}{}_2\text{R}\text{(-)3,3-}\text{dimethyl}\text{-1,2-}\text{butanediol}$ (R(-)BMBD) (stereoelective polymerization). In agreement with the homosteric character of this initiator, the configuration of the asymmetric centre located in the heterocycle of the elected diastereoisomer is shown to be R from c.d. spectra of residual monomers, whatever the configuration of the asymmetric centre located in the pendant group. O.r.d. and c.d. spectra of stereoelected polydiastereoisomers are described and compared to those of corresponding polydiastereoisomers bearing racemic main-chain chiral centres. ¹³C n.m.r. spectra of different polydiastereoisomers are reported. The stereosensitivity to tacticity of the main-chain carbons is poor but some of the side-chain carbon atoms are very sensitive to the presence of two asymmetric centres per repeat unit. The optical purity of main-chain chiral centres is deduced from the split resonance of one of these carbons atoms. It is shown that chiroptical properties of polydiastereoisomers primarily depend on configurations of the two chiral sites without obvious contributions from macromolecular conformations. The 242 nm c.d. band assigned to the n → σ1 electronic transition of sulphur chromophores is sensitive only to the optical purity of main-chain chiral centres and can be used to evaluate the configurational enrichment due to the stereoelective polymerization.     

Design,Synthesis, Antifungal Activities and 3D-QSAR of New N,N′-Diacylhydrazines Containing 2,4-Dichlorophenoxy Moiety

A series of new N,N′-diacylhydrazine derivatives were designed and synthesized. Their structures were verified by ¹H-NMR, mass spectra (MS) and elemental analysis. The antifungal activities of these N,N′-diacylhydrazines were evaluated. The bioassay results showed that most of these N,N′-diacylhydrazines showed excellent antifungal activities against Cladosporium cucumerinum, Corynespora cassiicola, Sclerotinia sclerotiorum, Erysiphe cichoracearum, and Colletotrichum orbiculare in vivo. The half maximal effective concentration (EC₅₀) of one of the compounds was also determined, and found to be comparable with a commercial drug. To further investigate the structure–activity relationship, comparative molecular field analysis (CoMFA) was performed on the basis of antifungal activity data. Both the steric and electronic field distributions of CoMFA are in good agreement in this study.     

New fluorene-based alternating copolymers with pendent N,N-diethylaniline group: Highly sensitive and selective detection for Hg with “Turn-on” fluorescence response

Two fluorene-based alternating copolymers P1 and P2 with the N,N-diethylaniline pendent group in different contents on the polymer backbone were synthesized through Suzuki Coupling Reaction, and were fully characterized by ¹H NMR, elemental analysis, and gel-permeation chromatography (GPC). Photophysical studies show that changes of the contents of the N,N-diethylaniline groups have little effect on the ground state electronic structure, but take a significant effect on the excited state. The intensities of green emission band in these polymers changes with the different content of diethylaniline groups, and are supposed to be originated from an intramolecular charge transfer process. Both of the P1 and P2 show remarkable fluorescence emission “turn-on” responses exclusively to Hg²⁺. Moreover, fluorescent titration experiments indicate that the two copolymers have high sensitivity for Hg²⁺. The coordination between metal ions and N atoms could greatly weaken the electron-donating ability of N atoms, consequently inhibit the intramolecular charge transfer process, leading to fluorescence emission enhancement. As far as we know, this is the first report for detection of Hg²⁺ with “turn-on” output signals based on polyfluorenes.     

Thermal stability of idealized folded carbyne loops

Self-unfolding items provide a practical convenience, wherein ring-like frames are contorted into a state of equilibrium and subsequently  pop up’ or deploy when perturbed from a folded structure. Can the same process be exploited at the molecular scale? At the limiting scale is a closed chain of single atoms, used here to investigate the limits of stability of such folded ring structures via full atomistic molecular dynamics. Carbyne is a one-dimensional carbon allotrope composed of sp-hybridized carbon atoms. Here, we explore the stability of idealized carbyne loops as a function of chain length, curvature, and temperature, and delineate an effective phase diagram between folded and unfolded states. We find that while overall curvature is reduced, in addition to torsional and self-adhesive energy barriers, a local increase in curvature results in the largest impedance to unfolding.     

Substituted poly(silylenemethylene)s with short range interactions that induce a preference for the same local conformation in unperturbed atactic, isotactic, and syndiotactic chains

A rotational isomeric state model has been developed for the poly(silylenemethylenes) with repeating sequence [Si(CH₃)R-CH₂]_x, R=-O(CH₂)_NOC₆H₄C₆H₅. The model incorporates all first- and second-order interactions, as well as higher order interactions that are mandatory in some of the conformations. Chains with all possible stereochemical sequences prefer a local conformation that is a run of trans states at the C-Si bonds in the backbone. This preference arises from an attractive second-order interaction of the first methylene group in the side-chain bonded to chain atom i with the silicon atoms indexed i±2. Unperturbed chains have larger dimensions than the simpler chain in which R is merely a methyl group. The temperature coefficients of the unperturbed dimensions are large and negative. The preference of unperturbed atactic, isotactic, and syndiotactic chains for the same local conformation may contribute to the facile formation of smectic phases by the presumably atactic chain, as reported by Park et al. [Macromolecules 35 (2002) 2776].     

Amplified Spontaneous Emission Properties of Semiconducting Organic Materials

This paper aims to review the recent advances achieved in the field of organic solid-state lasers with respect to the usage of semiconducting organic molecules and oligomers in the form of thin films as active laser media. We mainly focus on the work performed in the last few years by our research group. The amplified spontaneous emission (ASE) properties, by optical pump, of various types of molecules doped into polystyrene films in waveguide configuration, are described. The various systems investigated include N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), several perilenediimide derivatives (PDIs), as well as two oligo-phenylenevinylene derivatives. The ASE characteristics, i.e., threshold, emission wavelength, linewidth, and photostability are compared with that of other molecular materials investigated in the literature.     

Translocation of compact polymer chains through a nanopore

We perform dynamical Monte Carlo simulation to study the forced translocation of compact polymer chains in three-dimensional lattices. The chains are driven through a nanopore connecting two infinite channels by an external field. The scaling properties of average translocation time τ and translocation time distribution (TTD) are studied. The effects of contact energy (?_C), electric field strength (E), and nanopore width (L) on the scaling exponent (α) of average translocation time τ ∼ N^α and the TTD are investigated. For the scaling behavior of τ ∼ N^α, we have found that there is no crossover behavior with weak field strength when the nanopore width is one lattice spacing, which is less than average bond length, while crossover behaviors are observed for larger nanopore widths. The scaling exponent α also depends on contact energy ?_C and electric field strength E. For the TTD, it shifts from the Gaussian to a right-skew distribution with the electric field E increasing for short chains; while for long chains, multi-peak distributions are observed. As a primary and simple model, compact polymer chains are extensively used to capture the structure and thermodynamic properties of proteins, therefore we can investigate the protein translocation by simulating compact chain translocation, and this study will be useful for exploring the complex translocation behaviors of proteins.     

Interface properties of SiOxNy layer on Si prepared by atmospheric-pressure plasma oxidation-nitridation

SiO_xN_y films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400°C by atmospheric-pressure plasma oxidation-nitridation process using O₂ and N₂ as gaseous precursors diluted in He. Interface properties of SiO_xN_y films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (D_it) and positive fixed charge density (Q_f). After forming gas anneal, D_it decreases largely with decreasing N₂/O₂ flow ratio from 1 to 0.01 while the change of Q_f is insignificant. These results suggest that low N₂/O₂ flow ratio is a key parameter to achieve a low D_it and relatively high Q_f, which is effective for field effect passivation of n-type Si surfaces.     

Globules of microparacrystals in nascent isotactic polypropylene

SAXS and TEM measurements were used in studying the morphology of nascent isotactic polypropylene (PP) polymerized with a high-yield heterogeneous Ziegler-Natta MgCl₂ supported catalyst. In contrast to the melt- or solution- crystallized isotactic PP cases, the SAXS datam obtained here using Kratky-camera and TEM diagrams, show the characteristic scattering of globules (～ 1100Å in diameter) and a remarkably small polydispersity of 0.14. TEM observations also show sometimes the presence of smaller globular particles of about 300Åin diameter whose amount is below the resolving power of SAXS. Due to the lack of interparticle interference, lamellae do not exist and therefore no mention of an amorphous phase is required. WAXS can be analysed as a series of overlapping reflections with paracrystalline (liquid-like) distortions at g = 5%. These microparacrystals (mPC's) have in accordance with the α*-law, a mean size of (α*/g)²d¯=60Å and constitute the globules. From line profile analysis one finds that their polydispersity g_N is 0.4 and this agrees well with a relation between N and g_N which is deduced theoretically for microparacrystal-ensembles in the equilibrium state. A new relation between the polydispersity g^N of microparacrystals and the size of globules is derived from TEM observations. These observations sometimes show clearly separated spherical particles whose size distribution is in the range of the SAXS results, but varies from micrograph to micrograph. The morphology of the nascent PP is greatly influenced by the distribution of the active centres on the catalyst's carrier and this excludes the regular chain-folding in a crystalline phase and the existence of larger disordered chain segments in an amorphous phase. The whole volume is therefore filled with microparacrystals.     

Time-of-flight Rietveld neutron structure refinement and quantum chemistry study of Y-α-sialon

A Y-α-sialon was prepared using a specially designed temperature regime supporting formation of α-sialon and the amount of non-crystalline phase was remarkably reduced by a chemical treatment. Chemical composition of the sample was determined by EDX analysis. Crystal structure of Y-α-sialon was refined using high quality time-of-flight neutron powder diffraction data taken with the General Purpose Powder Diffractometer (GPPD) at the IPNS, Argonne National Laboratory. Unrestrained structure refinement was done in the P31c space group. The list of simultaneously refined parameters included profile parameters, atomic coordinates, individual isotropic temperature parameters and the occupancy parameter of Y. The contents of Y in the cell refined to 0.38(1) and calculated Si–N distances in tetrahedra varied from 1.716(3) to 1.773(3) Å, but their distributions in the respective tetrahedra differ as in the parent structure of α-Si₃N₄. Anisotropic temperature parameters refinement, as well as constrained refinements of the occupancy parameters of Si–Al and N–O pairs, were also attempted, but they all ended with unphysical values. Variation of the background was analyzed using RDF formalism. Three peaks centered around 1.7 Å (with a shoulder at 2.2 Å), 2.8 Å and 3.5 Å proved that the composition of amorphous phase was close to that of crystalline. Ab initio cluster calculations performed at the B3LYP/6-31G** level of theory excluded configuration with O atoms bonded to three Si atoms and proved that the most probable is the configuration where an O atom is shared by three Al atoms.     

Supercritical water oxidation of nitrogen compounds with multi-injection of oxygen

A supercritical water oxidation (SCWO) process with oxidant multi-injection was studied in a continuous flow system in which the same amount of oxidant feed is split between two points – a first injection at the reactor inlet and a second injection at one of the three different positions along the reactor. Under the same operating conditions, this multi-injection configuration showed advantages over the system with a single oxidant entry. Moreover, oxidant dosage in a SCWO reactor is a key aspect in energy management.In this work, experiments were performed to find the best oxidant dosage to obtain the maximum organic conversion. Experiments were carried out using N,N-dimethylformamide (DMF) as a model compound for nitrogen-containing hydrocarbons in wastewaters. All experiments were carried out at 250 bar with an oxygen coefficient n = 1 and a temperature of 400 °C. Each experiment was carried out at five different residence times (2, 4, 6, 8 and 10 s). Once the best configuration had been determined, the effect of temperature (400–550 °C), initial organic concentration (5–30 mM), oxygen coefficient (0.5–3) and residence time (2–10 s) was investigated in the SCWO process of DMF.     

Translocation dynamics of a semiflexible chain under a bias: Comparison with tension propagation theory

We study translocation dynamics of a semi-flexible polymer through a nanoscopic pore in two dimensions (2D) using Langevin dynamics simulation in presence of an external force inside the pore. We observe that for a given chain length N the mean first passage time (MFPT)〈τ〉 increases for a stiffer chain. By repeating the calculation for various chain lengths N and bending rigidity parameter κ _b we calculate the translocation exponent α (〈τ〉 ～ N ^α). For chain lengths N and bending rigidity κ _b considered in this paper we find that the translocation exponent satisfies the inequality α < 1 + ν, where is the equilibrium Flory exponent for a given chain stiffness, as previously observed in various simulation studies for fully flexible chains. We observe that the peak position of the residence time W(s) as a function of the monomer index s shifts at a lower s-value with increasing chain stiffness κ _b . We also monitor segmental gyration 〈R _g (s)〉 both at the cis and trans side during the translocation process and find that for κ _b ≠ 0 the late time cis conformations are nearly identical to the early time trans conformations, and this overlap continues to increase for stiffer chains. Finally, we try to rationalize dependence of various quantities on chain stiffness κ _b using Sakaue’s tension propagation (TP) theory [Phys. Rev. E 76, 021803 (2007)] and Brownian Dynamics Tension Propagation (BDTP) theory due to Ikonen et al. [Phys. Rev. E 85 051803 (2012); J. Chem. Phys. 137 085101 (2012)] originally developed for a fully flexible chain to a semi-flexible chain.     

The phase behaviors of adsorbed polymethylene chains

The phase behaviors of a single adsorbed polymethylene chain are investigated by using molecular dynamics simulations. In the free space, it is confirmed in our calculation that the isolated polymer chain exhibits a disordered coil state at high temperatures, and collapses into a condensed state at low temperatures, i.e., the coil-to-globule transition, and finite chain length effects are considered since the critical region may depend on the chain length. When the chain is adsorbed on an attractive surface, however, the equilibrium properties may not only depend on chain length but also depend on the adsorption energy. For short chain of N = 40 monomers, a coil-to-globule transition is found for weak adsorption energy of w = 2.5 kcal/mol, but the critical temperature is lower than the free chain, and for strong adsorptions of w = 3.5 and 4.5 kcal/mol, the structures at low temperatures are adsorbed hairpin like, so we may call the transition process coil-to-hairpin transition. For long chains of N = 80 monomers and N = 120 monomers, the critical regions are the same for the free chains both at T = 265 K, and for the adsorption energies of w = 2.5, 3.5, and 4.5 kcal/mol, the curves of the heat capacities are smooth when T > 200 K, and while T < 200 K, the values of the heat capacities decrease as the temperatures decreasing, so the transition may be from loose globular structures to compact globular structures, and for more stronger adsorption energy of w = 6.5 and 8.5 kcal/mol, the critical regions are obvious and they are coil-to-crystal like transitions.     

N,N′-alkylated Imidazolium-Derivatives Act as Quorum-Sensing Inhibitors Targeting the Pectobacterium atrosepticum-Induced Symptoms on Potato Tubers

Bacteria belonging to the Pectobacterium genus are the causative agents of the blackleg and soft-rot diseases that affect potato plants and tubers worldwide. In Pectobacterium, the expression of the virulence genes is controlled by quorum-sensing (QS) and N-acylhomoserine lactones (AHLs). In this work, we screened a chemical library of QS-inhibitors (QSIs) and AHL-analogs to find novel QSIs targeting the virulence of Pectobacterium. Four N,N′-bisalkylated imidazolium salts were identified as QSIs; they were active at the μM range. In potato tuber assays, two of them were able to decrease the severity of the symptoms provoked by P. atrosepticum. This work extends the range of the QSIs acting on the Pectobacterium-induced soft-rot disease.