Potential energy surfaces for all-trans P5H6(+) and P5Me6(+) may be less complicated than anticipated

Burford and co-workers recently (2007) investigated the synthesis, structure, and pseudorotation of a family of cyclotetraphosphinophosphonium ions comprehensively. We now report theoretical computations through the CCSD(T) level to study the conformations of the parent model rings, P5H6(+) and P5Me6(+). The all-trans conformations on the full pseudorotational cycle for the cyclotetraphosphinophosphonium cation (P5H6(+)) and for its methyl-substituted derivative (P5Me6(+)) were located systematically on their potential energy surfaces. The potential energy for the pseudorotational circuit of P5H6(+) is smooth and monotonic with only one minimum ((3)T4) and one maximum ((4)T3), but the analogous P5Me6(+) circuit has two minima. The P5H6(+) and P5Me6(+) potential surfaces appear to be qualitatively very different from that for the well investigated tetrahydrofuran. Since the (3)T4 form of P5H6(+)avoids unfavorable eclipsing PH-PH and lone pair-lone pair interactions, it is the global minimum among all possible P5H6(+) configurations and conformations.     

P5H6+和P5Me6+全反式构象的理论研究

用HF和MP2两种从头算方法结合cc-pVDZ和cc-pVTZ两种基组对P5H6 及其甲基取代物P5Me6 的反式构象进行理论计算,各限制优化出11个反式构象.进而分别得到其构象势能面曲线,P5H6 势能面曲线是单调平滑的,其上只有一个稳定点(3T4)和一个过渡态(4T3),说明3T4构象是势能面上的全局最小点.而P5Me6 势能面曲线与P5H6 大致相同,不同的是在势能面曲线中还存在另一个稳定点,在HF或MP2用cc-pVDZ基组时为2E(φ=216°),在HF/cc-pVTZ时为2T1(φ=198°),并且,3T4和2E的能量非常接近.最后将这两势能面与四氢呋喃进行了比较.     

Carbonyles tres decales par rapport a l'eclipse dans les aldehydes et les cetones aliphatiques satures: analyse conformationnelle theorique

The theoretical conformational analysis of two series of molecules HCOR, MeCOR is treated. Spectroscopic data [15] have indicated the existence of non-eclipsed conformations which become more important with increasing steric hindrance of the group R.All the methods used (semi-empirical quantum methods, P.C.I.L.O., I.N.D.O., C.N.D.O./2, and the Liquori empirical potential method) lead to the following stable conformations: with the carbonyl group exclusively eclipsed for slightly substituted R (R = Me, Et, tBu); with the carbonyl eclipsed and also staggered (? ? 60°) for moderately substituted compounds (MeCOPr, MeCOiBu, MeCOCiPr(Me)₂) (low rotational barriers permitting equilibria between eclipsed and staggered conformations); with the carbonyl exclusively staggered (? ? 60°) for more hindered compounds (MeCOCH₂tBu, MeCOCH(tBu)Me, MeCOC(Me),tBu, MeCOCH(tBu)₂).Contradictory results are obtained for certain compounds (iPrCOMe, tBuCH₂CHO for example) : the calculated changeover from eclipsed to staggered conformations differentiates the semi-empirical methods from the empirical potential method used.     

Polymer Chain Conformation on Deuterated Polystyrene Nanoparticles Investigated by SANS

We previously reported that grafted polystyrene (PS) chains on silica nanoparticles at a low grafting density show similar conformations to free PS chains in the same solvent, THF (diameter ?50 nm, Colloid.poly.Sci. (2013), 291, 9, 2087–2099). As an extension of our previous study we choose an organic nanoparticle (deuterated polystyrene, dPS) instead of inorganic nanoparticle to see the impact of the substrate material on chain conformation. Additionally, a wider range of molecular weights were prepared to investigate the conformation feature of grafted PS chains more in detail. Small angle neutron scattering (SANS) experiments were performed to characterize PS grafted dPS particles in good solvent condition, with deuterated toluene and deuterated THF as solvent. To get insight into the conformation of the grafted PS layer we apply a scaling law describing the dimension of free PS polymer in good solvent condition to the obtained thickness of the grafted PS layer. We find an overall agreement with the scaling law where the thickness of the grafted PS layer is slightly larger than 2R_g of the free polymer chains in the respective solvent giving hint for semi dilute polymer brush (SDPB) situation.     

Modeling of Polymer Structure and Conformations in Polymer Nanocomposites from Atomistic to Mesoscale: A Review

Over the past two decades polymer nanocomposites have received tremendous interest from industry and academia due to their advanced properties comparative to polymer blends. Many computational studies have revealed that the macroscopic properties of polymer nanocomposites depend strongly on the microscopic polymer structure and conformations. In this article we review computer simulation studies of the fundamental problem of homopolymers structure and dimensions in nanocomposites containing bare or grafted spherical or rod nanoparticles. Experimentally, there is controversy over whether the addition of nanoparticles in a polymer matrix can perturb the polymer chains.     

Les deplacements chimiques carbone 13 des groupements methyles traites en termes d'interactions H/H,H/Me,Me/Me

The different conformations of the methyl groups for a series of saturated cyclic and linear hydrocarbons were analysed. From these results we were able to identify the different interactions H/H, H/Me, Me/Me and calculate the chemical shifts of the methyl group for a series of hydroxylated stereoisomers.     

Structural and spectroscopic properties of trans-dichlorobis(2,2-dimethyl-1,3-diaminopropane)chromium(III) chloride

The structure of trans-[CrCl(2)(Me(2)tn)(2)]Cl (Me(2)tn=2,2-dimethylpropane-1,3-diamine) has been determined by a single-crystal X-ray diffraction study at 150K. The analysis reveals that there are two independent Cr(III) complex cations in the structure, one with crystallographic inversion symmetry and the other with two-fold rotation symmetry, which are conformational isomers of each other. In both conformations, the chromium atom adopts a distorted octahedral structure with the four nitrogen atoms of two Me(2)tn ligands occupying the equatorial plane and two chlorine atoms occupying trans-axial positions. The six-membered chelate rings are in stable chair conformations with N-Cr-N angles of 87.03(8) degrees and 88.99(8) degrees . The two chelate rings in the centrosymmetric complex cation 1 are anti, while those in the rotation-symmetric complex cation 2 are in syn conformations. The mean Cr-N and Cr-Cl bond lengths are 2.0922 and 2.3253 A, respectively. The infrared and UV-visible absorption spectra of trans-[CrCl(2)(Me(2)tn)(2)]Cl have also been measured. The resolved band maxima of the electronic d-d spectrum are fitted with a secular determinant for a quartet energy state of the d(3) configuration in a tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the nitrogen atoms of the Me(2)tn ligand have a strong sigma-donor character, but the chloro ligand has weak sigma- and pi-donor properties toward the chromium(III) ion.     

Force-Extension Curve of an Entangled Polymer Chain:A Superspace Approach

The statistical mechanics of an ideal polymer chain entangled with static topological constraints is studied using a superspace approach, in which the probability distribution of the polymer is obtained as solutions of the Fokker-Planck equation in a superspace with an inner structure characterized by the n-generator free group. The theory predicts that the force-extension curve of the polymer under the topological constraints has the generic form F=kl+Z/l, where l is an effective extension. Asi...     

Elastic Behavior of Polymer Chains

The elastic behavior of the polymer chain was investigated in a three-dimensional off-lattice model. We sample more than 109 conformations of each kind of polymer chain by using a Monte Carlo algorithm, then analyze them with the non-Gaussian theory of rubberlike elasticity, and end with a statistical study. Through observing the effect of the chain flexibility and the stretching ratio on the mean-square end-to-end distance, the average energy, the average Helmholtz free energy, the elastic force, the contribution of energy to the elastic force, and the entropy contribution to elastic force of the polymer chain, we find that a rigid polymer chain is much easier to stretch than a flexible polymer chain. Also, a rigid polymer chain will become difficult to stretch only at a quite high stretching ratio because of the effect of the entropy contribution. These results of our simulation calculation may explain some of the macroscopic phenomena of polymer and biomacromolecular elasticity.     

Monte Carlo Calculations of Polymer Adsorption at the Entrance of Cylindrical Pores in Flat Adsorbing Surfaces

The influence of surface interactions on the conformation of flexible polymers partially confined inside narrow cylindrical pores in a flat surface is studied above the critical adsorption energy in a good solvent. We use a static configurational bias computational sampling method to calculate the adsorption free energy and the radius of gyration components parallel and perpendicular to the pore axis as a function of the polymer center of mass position at different degrees of confinement. We find strong free‐energy minima just in front of the pore entry for all degrees of confinement studied. At the location of the free‐energy minimum, polymers are partially adsorbed inside the pore and on the outer solid surface and adopt “drawing pin”‐like conformations. A distinct maximum in the average loop length at the pore entry indicates that the polymer bridges the pore entry of small pores.     

Interaction of metal ions with polypyrrole on polyacrylic acid matrix

The oxidative matrix polymerization of pyrrole (Py) by Fe(III), Cu(II), Ni(II), Co(II), and Zn(II) in the presence of polyacrylic acid (PAA) was studied and water‐soluble products along with insoluble products were obtained. The metal (Me) content of the insoluble part was determined by using atomic absorption spectroscopy (AAS). The effects of the oxidation potential of Me ions and ligands on the aggregation of polypyrrole (PPy) on the matrix polymer were measured by ultraviolet (UV)‐visible spectra. These findings also were checked by cyclic voltammetry (CV) measurements on PAA–Cu and PAA–PPy–Cu interactions. The conductometric titration results of PAA–PPy–Me ternary solutions were explained in the light of the interaction of Me ions with Py to polymerize on the PAA matrix resulting in some free carboxyl groups with a possibility of having Me–polymer complexes and a ternary complex (PAA–Me–PPy). The insoluble products were characterized by Fourier transform infrared (FTIR), elemental analysis, scanning electron microscopy (SEM), and four point probe conductivity measurements. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1115–1123, 1999     

现场热引发聚丙烯酸酯类电解质的性能及应用

应用热引发现场聚合方法制备聚丙烯酸酯类电解质,并考察其电化学性能.实验表明:该聚合物电解质具有 4. 5V的电化学稳定窗口,较高的室温电导率及良好的低温性能.当前驱体电解液中液态电解质含量为 85%时,其室温电导率为 3. 2×10-3S·cm-1, -30℃下的电导率达到 5. 6×10-4 S·cm-1.采用现场聚合技术制备的聚合物电池,其电化学性能与液态锂离子电池基本一致,首次充放电效率为 92. 1%, 1. 0C率放电容量为 0. 2C率的 95%, -20℃下的放电容量为室温容量的 72%,以 0. 5C率循环 300周后,仍保持初始容量的 85%以上.     

高分子药物学的研究进展与期盼

自从20世纪70年代提出高分子前药的概念以来,伴随着纳米技术的发展,"高分子药物学"作为高分子科学和材料学、纳米科学、药物学、临床医学、分析科学的交叉学科,正在悄然形成.本文综述了近年高分子药物在药物化学、制剂学、药效学等方面所取得的进展,概述了高分子药物的药理学和药代动力学与小分子药物的区别与联系,指出了高分子药物药效学、药理学和药代动力学研究中的难题和瓶颈,特别是高分子药物可能存在的"三种状态"及从"纳米颗粒药"到"单个高分子药"再到"小分子药"的转变,分析了高分子药输送过程中存在的多重屏障如毛细血管壁、细胞外基质和细胞壁等,阐述了高分子药物的"生理靶向"和"EPR"效应的竞争,指出了高分子药在靶向输送和逆转耐药方面的优势,强调了发展相关分析方法的必要性,期盼高分子科学家与药物学家进行真诚有效的合作,大力促进我国高分子药物学和高分子药物产业的创新和发展.     

Chemical functionality of poly(methylenephosphine): phosphine-borane adducts and methylphosphonium ionomers

The chemical functionality of poly(methylenephosphine) n-Bu[MesP-CPh(2)](n)H () is examined in reactions with two isoelectronic species, namely BH(3) and CH(3)(+). The potential reactivity of polymer is modelled by examining the reactivity of molecular phosphines bearing similar substituents as the polymer. In particular, the phosphine-borane adducts Mes(Me)P(BH(3))-CPh(2)H () and Mes(Me)P(BH(3))-CPh(2)SiMe(2)H () are prepared from the reaction of BH(3).SMe(2) with Mes(Me)P-CPh(2)H () or Mes(Me)P-CPh(2)SiMe(2)H (), respectively. Treating with MeOTf affords the methylated model compound, [Mes(Me)(2)P-CPh(2)H]OTf (). X-Ray crystal structures are reported for each model compound. The reaction of n-Bu[MesP-CPh(2)](n)H (M(n) = 3.89 x 10(4), PDI = 1.34) with BH(3).SMe(2) affords the phosphine-borane polymer n-Bu[MesP(BH(3))-CPh(2)](n)H () (M(n) = 4.13 x 10(4), PDI = 1.26). In contrast, methylation of phosphine polymer gives n-Bu[MesP-CPh(2)](x)-/-[MesP(Me)-CPh(2)](y)H.(OTf)(y) () where approximately 50% of the phosphine moieties are methylated (from (31)P NMR).     

Collapse transitions of a supersized neutral chain due to irreversibly adsorbed small colloidal particles

 We performed Monte Carlo simulations to study the destabilization processes of large neutral and flexible polymer chains due to irreversibly adsorbed colloidal particles attached to the chains like beads on a necklace. The particles are modeled as charged spherical units which interact with each other via repulsive electrostatic and attractive van der Waals (vdW) potentials. The usual Monte Carlo search procedure is extended and carefully checked to completely sample the chain conformational space and achieve dense conformations in the limit of both strong attractive and repulsive interaction potentials. Configurational properties, such as the radius of gyration, the end-to-end length, and the Kuhn length, are calculated as a function of the intensity of the vdW interactions and ionic strength values. It is observed that chains exhibit a new range of possible conformations compared to the classical random walk and self avoiding walk chains or polyelectrolytes. In the limit of low salt concentration, by gradually increasing vdW interactions, chains undergo a cascade of transitions from extended structures to dumbbells, from dumbbells to pearl necklaces, and from pearl necklaces to collapsed coils. Because of strong competition between the vdW and electrostatic forces, the distance along the chain between the interacting particles, and the sampling limitations, these transitions are found to sample metastable domains and to depend on the initial conformations. To gain insight into the spatial organization of the collapsed conformations, the pair correlation functions of both monomers and particles are calculated. It is shown that collapsed conformations which are the result of strong particle–particle interactions exhibit two distinct parts: a hard core mainly composed of particles and a surrounding polymeric shell composed of loops and tails. Possible effects of such a collapsed transition on the kinetics of flocculation of a mixture containing large flexible chains and small adsorbing colloidal particles are discussed. Received: 26 July 1999 Accepted in revised form: 9 November 1999     

Rheologic Properties and Molecular Configuration of Polymers in Salt‐Alkali‐Surfactant Mixed Solutions

With the vacuum sublimation freezing‐drying and rheological techniques, the salt/alkali/surfactant effects on the solution properties and the aggregate conformations of the polymers, synthesized hydrophobically modified poly (acrylamide) (HMPAM), were investigated. The experimental methods included viscosity measurements, the photomicroscopy, scan electron microscopy, and the freeze fracture transmission electron microscopy. The variety of conformations of the ultramolecular aggregates, the hydrophobical region, and the spatial network structures resulted from the hydrophobical interaction were studied. Combined results confirmed that HMPAM could form several of interesting three‐dimensional network structures either in distilled water or NaCl solution. The results have revealed the mechanism of the salt/alkali/surfactant effects on the peculiar rheological properties of the solution.     

Characterization of the pore-surface gel phase in functionalized macroporous polymeric materials

Covalently immobilized pore-surface gel phases were prepared in a functionalized macroporous ultra-high-molecular-weight polyethylene by covalent coupling of lightly cross-linked polymer colloid particles [50% styrene, 49.8% (chloromethyl)stryrene, 0.2% divinylbenzene] to the interstitial pore surfaces. Swelling the covalently coupled colloid particles in a good solvent followed by chemical derivitization resulted in an immobilized pore-surface gel phase rich in primary amine groups. The macromolecular reactivity and molecular size-exclusion characteristics of the aminated pore-surface gel phase were then determined using monofunctional, amine-reactive, poly (ethylene glycol)s (PEG). Pegylated pore-surface gel phases that ranged from 71% (10,000 molecular weight PEG) to 56% (40,000 molecular weight PEG) PEG by weight resulted from reaction of the aminated gel phase with the PEG probe molecules. The number of PEG molecules reacting with the aminated pore-surface gel phase depends only on the Flory radius (or radius of gyration) of the PEG molecule to the negative 2.49th power i.e., 1/R _f ^2.49, corresponding to a M^−1.48 dependence. The immobilized and pegylated polymer colloid particles swell by a factor of 16–25 times the diameter of the original polymer colloid particles in water, thereby demonstrating that pegylation occurred though a substantial fraction of the volume of the immobilized colloid particles. Received: 18 January 1999 Accepted in revised form: 8 June 1999     

On the release of strain in overcrowded substituted ethylenes

Minimum energy conformations of all possible Me, i-Pr, and t-Bu substituted ethylenes as well as some mixed methyl-t-butyl substituted ethylenes have been calculated using a consistent force field derived by least-squares fitting of a large set of observed conformational, vibrational, and thermochemical olefin properties. Large angle deformations and nonplanar double bond distortions were obtained for t-Bu containing systems. Nonbonded interactions appeared to decrease Me torsional frequencies of cis-dimethyl substituted ethylenes and to increase Me CH stretching frequencies of cis-di-t-Bu substituted ethylenes.     

Conformations and energetics of sulfur and selenium diimides

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR)(2) (E = S, Se; R = H, Me, (t)Bu, C(6)H(3)Me(2)-2,6, SiMe(3)) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH)(2), but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH)(2) the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6-31G proved to be the most suitable method for predicting the geometries of chalcogen diimides. The optimized geometrical parameters are in a good agreement with all available experimental data. While qualitative energy ordering of the different conformations is independent of the level of theory, the quantitative energy differences are dependent on the method used. The performance and reliability of higher level ab initio calculations and DFT methods using large basis sets were tested and compared with experimental information where available. All of the higher level ab inito methods give very similar results, but the use of large basis sets with the B3PW91 method does not increase the reliability of the results. The combination of CCSD(T)/cc-pVDZ with the B3PW91/6-31G-optimized geometries is found to be the method of choice to study energetic properties of chalcogen diimides.     

MODELING THE CHAIN CONFORMATION OF POLYMER MELTS IN CONTRACTION FLOW

A constitutive model of quasi-Newtonian fluid based on the type of flow is used in abrupt planar contraction now.The numerical results from finite element analysis are consistent with experimental data for stress patterns and velocityprofiles in the flow field. The chain conformations of polymer melts are then investigated in such a planar contraction byusing the phenomenological model with internal parameters proposed by the author. That is, the shape and orientation ofpolymer chain coils are predicted and discussed in different flow regions of the contraction flow field that possess simpleshear flow, extensional flow, vortical flow, and mixed flow respectively.