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In this study, the temperature-/frequency-dependent viscosity and tensile modulus of polymer nanocomposites were evaluated using the combination of developed Arrhenius's equation and percolation theory. To involve the drastic effects of the polymer/particles interphase region and the aggregation/agglomeration of nanoparticles in the model, the Nielsen-Lewis model was developed and used to interpret the related parameters from heat conduction test results. The value of different state-to-state conversion degrees was calculated using the developed percolation theory whose validity was evaluated via comparative studies with theoretical results obtained from developed Arrhenius's equations. The simultaneous effects of the nanoparticles content and temperature/frequency on the viscosity and tensile modulus were also studied, which defined the role of some important phenomena such as the breakdown of the nanoparticle clusters, the increased cluster stability by polar surface modifiers, the increased thermal conductivity of the nanocomposite due to the presence of nanoparticles, etc. Different PA nanocomposites samples, containing 1-4 vol% of spherical silica nanoparticles, were prepared and subject to dynamical mechanical analysis, by temperature ramps and frequency sweep, and the results were used to evaluate the accuracy of the model. The surface of the nanoparticles was chemically modified with (3-aminopropyl)triethoxysilane to ensure their perfect compatibility with PA phase. KEYWORDS glass transition, mechanical properties, nanocomposites, thermal properties, viscosity, 1 | INTRODUCTION The molecular structure of polymers as well as their perfect adaption with different macro, micro-, or nanofillers have made them a good choice for different industries. [1] [...]

The properties of knots are exploited in a range of applications, from shoelaces to the knots used for climbing, fishing and sailing.sup.1. Although knots are found in DNA and proteins.sup.2, and form randomly in other long polymer chains.sup.3,4, methods for tying.sup.5 different sorts of knots in a synthetic nanoscale strand are lacking. Molecular knots of high symmetry have previously been synthesized by using non-covalent interactions to assemble and entangle molecular chains.sup.6-15, but in such instances the template and/or strand structure intrinsically determines topology, which means that only one type of knot is usually possible. Here we show that interspersing coordination sites for different metal ions within an artificial molecular strand enables it to be tied into multiple knots. Three topoisomers--an unknot (0.sub.1) macrocycle, a trefoil (3.sub.1) knot.sup.6-15, and a three-twist (5.sub.2) knot--were each selectively prepared from the same molecular strand by using transition-metal and lanthanide ions to guide chain folding in a manner reminiscent of the action of protein chaperones.sup.16. We find that the metal-ion-induced folding can proceed with stereoinduction: in the case of one knot, a lanthanide(iii)-coordinated crossing pattern formed only with a copper(i)-coordinated crossing of particular handedness. In an unanticipated finding, metal-ion coordination was also found to translocate an entanglement from one region of a knotted molecular structure to another, resulting in an increase in writhe (topological strain) in the new knotted conformation. The knot topology affects the chemical properties of the strand: whereas the tighter 5.sub.2 knot can bind two different metal ions simultaneously, the looser 3.sub.1 isomer can bind only either one copper(i) ion or one lutetium(iii) ion. The ability to tie nanoscale chains into different knots offers opportunities to explore the modification of the structure and properties of synthetic oligomers, polymers and supramolecules. A molecular strand can be knotted and unknotted into three different topologies, depending on the complexing metal ion used (copper or lanthanide or none)., Author(s): David A. Leigh [sup.1] [sup.2] , Fredrik Schaufelberger [sup.2] , Lucian Pirvu [sup.2] , Joakim Halldin Stenlid [sup.3] , David P. August [sup.2] , Julien Segard [sup.2] Author Affiliations: [...]

Ontogeny describes the emergence of complex multicellular organisms from single totipotent cells. This field is particularly challenging in mammals, owing to the indeterminate relationship between self-renewal and differentiation, variation in progenitor field sizes, and internal gestation in these animals. Here we present a flexible, high-information, multi-channel molecular recorder with a single-cell readout and apply it as an evolving lineage tracer to assemble mouse cell-fate maps from fertilization through gastrulation. By combining lineage information with single-cell RNA sequencing profiles, we recapitulate canonical developmental relationships between different tissue types and reveal the nearly complete transcriptional convergence of endodermal cells of extra-embryonic and embryonic origins. Finally, we apply our cell-fate maps to estimate the number of embryonic progenitor cells and their degree of asymmetric partitioning during specification. Our approach enables massively parallel, high-resolution recording of lineage and other information in mammalian systems, which will facilitate the construction of a quantitative framework for understanding developmental processes. A multi-channel molecular recording technique is applied as a lineage tracer to assemble cell-fate maps from fertilization through gastrulation in the mouse, providing insights into ontogeny in a complex multicellular organism., Author(s): Michelle M. Chan [sup.1] [sup.2] , Zachary D. Smith [sup.3] [sup.4] [sup.5] , Stefanie Grosswendt [sup.6] , Helene Kretzmer [sup.6] , Thomas M. Norman [sup.1] [sup.2] , Britt Adamson [...]

Three types of polyethylene (PE), with different molecular structure, were selected and used in the production of films using a semi-industrial blown film extrusion line. Carbon nuclear magnetic resonance and crystallization analysis fractionation tests were performed on the PE polymers to assess their molecular structure. Sealability properties of the films, as well as crystallization kinetics, were evaluated and the results are discussed according to the molecular structures of the polymers. It was found that distribution of short chain branching (average comonomer sequence nH or nO) on the backbone of the PE chains are the main factor controlling the beginning of sealability. The completely random placement of the comononer on the polymer backbone (monomer dispersity 100%) generated crystals with smaller size and a lower melting temperature. Sealing was controlled by crystal distribution, chain diffusion, and entanglement formation at the interface. PE with lower melting point and linear molecular structure showed greater hot tack strength. PE with long chain branching showed a delay on seal process leading to lower sealing speed., INTRODUCTION Polyethylene is one of the most interesting polymers available in the marketplace. The variety of commercial grades is huge because of the vast number of variables like catalysts systems, [...]

ABSTRACT Background: Traditionally, molecular docking is primarily employed to screen pure compounds; the top-ranking chemicals are subsequently selected for experimental validation. Unlike synthetic chemicals, most natural products are commercially unavailable. [...]

During post-implantation development of the mouse embryo, descendants of the inner cell mass in the early epiblast transit from the naive to primed pluripotent state.sup.1. Concurrently, germ layers are formed and cell lineages are specified, leading to the establishment of the blueprint for embryogenesis. Fate-mapping and lineage-analysis studies have revealed that cells in different regions of the germ layers acquire location-specific cell fates during gastrulation.sup.2-5. The regionalization of cell fates preceding the formation of the basic body plan--the mechanisms of which are instrumental for understanding embryonic programming and stem-cell-based translational study--is conserved in vertebrate embryos.sup.6-8. However, a genome-wide molecular annotation of lineage segregation and tissue architecture of the post-implantation embryo has yet to be undertaken. Here we report a spatially resolved transcriptome of cell populations at defined positions in the germ layers during development from pre- to late-gastrulation stages. This spatiotemporal transcriptome provides high-resolution digitized in situ gene-expression profiles, reveals the molecular genealogy of tissue lineages and defines the continuum of pluripotency states in time and space. The transcriptome further identifies the networks of molecular determinants that drive lineage specification and tissue patterning, supports a role of Hippo-Yap signalling in germ-layer development and reveals the contribution of visceral endoderm to the endoderm in the early mouse embryo. Spatially resolved transcriptomes of cell populations at defined positions in the early mouse embryo reveal molecular bases of lineage specification and tissue patterning., Author(s): Guangdun Peng [sup.1] [sup.2] [sup.3] [sup.4] , Shengbao Suo [sup.5] [sup.10] , Guizhong Cui [sup.1] , Fang Yu [sup.1] , Ran Wang [sup.1] , Jun Chen [sup.1] , Shirui [...]

Environmental stress cracking (ESC) is considered a leading cause of plastic part failure. It is the premature embrittlement and subsequent cracking of a plastic due to the simultaneous and synergistic [...]

Homologous recombination is a mechanism for DNA repair that enables the exchange of genetic information between DNA molecules. Structural analysis reveals how the protein RecA orchestrates this process. Structural data reveal how RecA protein orchestrates recombination., Author(s): Upasana Roy, Eric C. Greene Author Affiliations: Demystifying the D-loop during DNA recombination Our chromosomes are subjected to a constant barrage of DNA-damaging agents that can lead to the [...]

A theoretical study of the molecular structure of the triethylsilanol molecule and a thorough conformational analysis of the species following the Boltzman's distribution law is reported. The role of hydrogen bonding in the shifting of the vibrational bands of the silanol group in the spectra of the liquid phase is discussed using a model of triethylsilanol dimer.

Monte Carlo structure simulations are used to study water-dioxane interactions in aqueous solutions with increasing dioxane concentrations. The structure analysis shows that in aqueous solution the dioxane molecules arrange at a distance of 4-8 [Angstrom] for the ring symmetry and each dioxane oxygen forms one hydrogen bond to a water molecule, indicating dioxanes unique hydrogen-bond acceptor character.

The [V.sup.}([H.sub.2]O) and Ar[V.sup.}([H.sub.2]O) complexes were studied by coupled-cluster methods including single and double excitations (CCSD). The ground state was predicted to be [5.sup.A.sub.1] for [V.sup.}([H.sub.2]O) but argon tagging was found to change the lowest lying state to [5.sup.B.sub.1] for [V.sup.}([H.sub.2]O) and zero-point vibration averaging increases the effective bond angle.

Fluorescence antibunching is a well-known technique for determining the number of independent emitters per molecule or molecular complex. It was rarely applied to autofluorescent proteins due to the necessity of collecting large numbers of fluorescence photons from a single molecule, which is usually impossible to achieve with rather photolabile autofluorescent proteins. Here, we measure fluorescence antibunching on molecules in solution, allowing us to accumulate data over a large number of molecules. We use that method for determining an average stoichiometry of molecular complexes. The proposed method is absolute in the sense that it does not need any calibration or referencing. We develop the necessary theoretical background and check the method on pure dye solutions and on molecular complexes with known stoichiometry.

The average cross-link density, number of the network bonds per unit volume, average stretching force constant, atomic ring size and the ratio [K.sub.bc]/[K.sub.e] have been calculated and discussed according to bond compression model for borotellurite glass. The result showed that the connectivity and rigidity of the borotellurite glasses increases with Te[O.sub.2] content due to the transformation of [BO.sub.3] units to [BO.sub.4] and [TeO.sub.3] units to Te[O.sub.4]. Comparison between theoretical calculated and experimental elastic moduli and Poisson's ratio has been carried out. The results showed good agreement between experimental and theoretical calculated elastic moduli. Key words: Borotellurite glass, bond compression model, INTRODUCTION Tellurite glasses with the unique physical properties and applications were reported by El- Mallawany[1]. Elastic properties are very informative about the structure of solids and are directly related to [...]

The equilibrium structure of the more stable conformer of [H.sub.2]S[O.sub.4] of [C.sub.2] symmetry is calculated by using the connected triple excitations (CCSD(T)) method and taking into account the core correlation correction. The accuracy of this structure is checked by comparing it to the similar molecules and by estimating the effects of basis set enlargement and of diffuse functions.

Two alkyl-substituted dual oligothiophenes, quarterthiophene (4T)-trimethylene (tm)-octithiophene (8T) and 4T-tm-4T, were used to fabricate molecular structures on highly oriented pyrolytic graphite and Au(111) surfaces. The resulted structures were investigated by scanning tunneling microscopy. The 4T-tm-8T and 4Ttm-4T molecules self-organize into long-range ordered structures with linear and/or quasi-hexagonal patterns on highly oriented pyrolytic graphite at ambient temperature. Thermal annealing induced a phase transformation from quasi-hexagonal to linear in 4T-tm-8T adlayer. The molecules adsorbed on Au(111) surface in randomly folded and linear conformation. Based on scanning tunneling microscopy results, the structural models for different self-organizations were proposed. Scanning tunneling spectroscopy measurement showed the electronic property of individual molecules in the patterns. These results are significant in understanding the chemistry of molecular structure, including its formation, transformation, and electronic properties. They also help to fabricate oligothiophene assemblies with desired structures for future molecular devices. phase transition | self-assembly | molecular structure

The self-consistent field theory (SCFT) simulations are used to investigate the self-assembled morphologies of the amphiphilic ABC star triblock polymers and the blends with their counterpart linear AB diblock copolymers. The results demonstrate that the addition of the linear AB diblock copolymers highly affect the aggregate morphology of the triblock polymer, as it leads to the shortening of the long segmented worms to form hamburger micelles.

Ab initio and density functional methods are used to study the molecular structures and thermochemical properties of the five-membered nitrogen-containing heterocycles and their anions and radicals corresponding to respective heterolytic and homolytic loss of a hydrogen atom from either a nitrogen or carbon site. Electron affinities are calculated for all anions and the results have supported the hypothesis, explaining the effect of adjacent N atoms on N-H bond energies, where there is an unfavorable dipole-dipole interaction in the nitrogen-centered radical species.

Steady-state and time-resolved fluorescence techniques were used to investigate the strong solvatochromism observed for two fluorene-dibenzothiophene-S, S-dioxide oligomers in polar solvents. The solvatochromism and thermochromism of both compounds demonstrate that the molecules, in their excited states, undergo an intramolecular charge-transfer reaction stabilized by the solvent polarity and accompanied/followed by molecular structural changes.

The gas-phase structure of 6,9-CS[B.sub.8][H.sub.12] and 6,9-CN[B.sub.8][H.sub.13] were configured by electron diffraction and ab initio calculations. Results show that the position of the sulfur atom is very close to that of the boron atom occupying the equivalent position in the parent molecule [[B.sub.10][H.sub.14].sup.2-]], reflecting the similarity of sizes of sulfur and boron atoms.

In living cells the mechanical properties of the actin cytoskeleton are defined by the local activation of different actin cross-linking proteins. These proteins consist of actin-binding domains that are separated and geometrically organized by different numbers of rod domains. The detailed molecular structure of the cross-linking molecules determines the structural and mechanical properties of actin networks in vivo. In this study, we systematically investigate the impact of the length of the spacing unit between two actin-binding domains on in vitro actin networks. Such synthetic cross-linkers reveal that the shorter the constructs are, the greater the elastic modulus changes in the linear response regime. Because the same binding domains are used in all constructs, only the differences in the number of rod domains determine their mechanical effectiveness. Structural rearrangements of the networks show that bundling propensity is highest for the shortest construct. The nonlinear mechanical response is affected by the molecular structure of the cross-linker molecules, and the observed critical strains and fracture stress increase proportional to the length of the spacing unit. actin cytoskeleton | cross-linking molecules | mechanical properties

The molecular structures of the three heterodecaboranes arachno-6,9-[C.sub.2][B.sub.8][H.sub.14], arachno-6,9-[N.sub.2][B.sub.8][H.sub.12] and arachno-6,9-[Se.sub.2][B.sub.8][H.sub.10] were determined by ab inito theory and structure of 6,9-[C.sub.2][B.sub.8][H.sub.14] was determined by gas-phase electron diffraction (GED). The additional comparison of the GIAO-HF and GIAO-MP2 method shows that for these heteroborane clusters, electron correlation effects on the computed [delta](11B) values are significant.

New compound containing [[[O.sub.3]PC[H.sub.2]P[O.sub.3]].sup.4-] ligands {[Mo.sub.2.sup.V][O.sub.4]} units were obtained. A hexanuclear rectangular anion and octanuclaer wheels encapsulating S[O.sub.3.sup.2-] or C[O.sub.3.sup.2-] templating agents were isolated. Their structural characterization allowed a discussion on the influence of the counterions on the structure of the anions and their stability while DFT calculations confirmed the observed equilibrium between syn and anti isomers.

The results from quantum chemical calculations are used to determine the structures of benzoic acid and 2-hydroxybenzoic acid in gas phase by electron diffraction. The comparison of pertinent structural parameters between the two compounds showed the effect of internal hydrogen bonding in 2-hydroxybenzoic acid.

The synthesis of 'designer' dendrimers and dendrons with sulfonlmide units at every branching point is reported. Two models branched oligosulfonimides are characterized in the solid state by single-crystal X-ray analysis and the reaction selectivities and conformation of sulfonimide branching points are rationalized by DFT calculations.

The electronic gases are used in manufacturing by the electronics (semiconductor) industry. The chemistry of these electronic gases can be used in the classroom in order to provide interesting and relevant examples of molecular structures, chemical equations, and reaction mechanisms.

A series of four multinuclear Zn-Nd Schiff-base complexes are prepared and their structures determined and photophysical properties are examined. The stoichiometry and structures of these complexes are dependent on the Zn:Nd ratio employed in their syntheses as well as the nature of the anion present ([CI.sup.-] vs N[O.sub.3.sup.-]).

Mono- and multilayers of nitroazobenzene (NAB), azobenzene (AB), nitrobiphenyl (NBP), biphenyl (BP), and fluorene (FL) were covalently bonded to flat pyrolyzed photoresist films (PPF) by electrochemical reduction of their diazonium derivatives. The structure and orientation of the molecular layers were probed with ATR-FLIR and Raman spectroscopy. A hemispherical germanium ATR element used with p-polarized light at 65[degrees] incidence angle yielded high signal/noise IR spectra for monolayer coverage of molecules on PPF. The IR spectra are dominated by in-plane vibrational modes in the 1000-2000-[cm.sup.-1] spectral range but also exhibit weaker out-of-plane deformations in the 650-1000-[cm.sup.-1] region. The average tilt angle with respect to the surface normal for the various molecules varied from 31.0 [+ or -] 4.5[degrees] for NAB to 44.2 [+ or -] 5.4[degrees] for FL with AB, NBP, and BP exhibiting intermediate adsorption geometries. Raman intensity ratios of NAB and AB for p- and s-polarized incident light support the conclusion that the chemisorbed molecules are in a predominantly upright orientation. The results unequivocally indicate that molecules electroreduced from their diazonium precursors are not chemisorbed flat on the PPF surface, but rather at an angle, similar to the behavior of Au/thiol self-assembled monolayers, Langmuir-Blodgett films, and porphyrin molecules chemisorbed thermally on silicon and PPF from alkyne and alkene precursors.