Effect of side chain and backbone length on lamellar spacing in polystyrene‐block‐poly(dimethyl siloxane) brush block copolymers
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99 GENERAL AND MISCELLANEOUS↗
SEARCH · Engineering Papers
Results for “CHAINS”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Initial Recognition of a Cellodextrin Chain in the Cellulose-Binding Tunnel May Affect Cellobiohydrolase Directional Specificity
Cellobiohydrolases processively hydrolyze glycosidic linkages in individual polymer chains of cellulose microfibrils, and typically exhibit specificity for either the reducing or nonreducing end of cellulose. Here in this article, we conduct molecular dynamics simulations and free energy calculations to examine the initial binding of a cellulose chain into the catalytic tunnel of the reducing-end-specific Family 7 cellobiohydrolase (Cel7A) from Hypocrea jecorina. In unrestrained simulations, the cellulose diffuses into the tunnel from the -7 to the -5 positions, and the associated free energy profiles exhibit no barriers for initial processivity. The comparison of the free energy profiles for different cellulose chain orientations show a thermodynamic preference for the reducing end, suggesting that the preferential initial binding may affect the directional specificity of the enzyme by impeding nonproductive (nonreducing end) binding. Finally, the Trp-40 at the tunnel entrance is shown with free energy calculations to have a significant effect on initial chain complexation in Cel7A.
60 APPLIED LIFE SCIENCES↗
Role of side-chain length on gas transport of CO 2 /CH 4 mixtures in polymers with side-chain porosity
Polymers of intrinsic microporosity (PIMs) are traditionally formed from ladder backbones, but recent synthetic advances have allowed for the formation of non-traditional PIMs using a poly(ladder) motif, whereby rigid PIM-like sidechains are appended onto more flexible backbones. The effect of side-chain length on free volume and gas transport properties was recently evaluated for a methoxy-functionalized poly(ladder) (OMe-ROMP). In this study, we elaborate on the role of side-chain length and its influence on mixed-gas performance and plasticization stability for OMe-ROMP. Pure-gas sorption results are also reported, including hysteresis effects from CO 2 conditioning. Taken together, this study reveals the role of side-chain length on gas sorption, diffusion, and plasticization for CO 2 /CH 4 separations. Finally, we conclude that the length of a rigid side chain in the poly(ladder) motif is a valuable structural parameter to control sorption, diffusion, and stability towards plasticization for gas separation membrane materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The Role of Chain-End Association Lifetime in Segmental and Chain Dynamics of Telechelic Polymers
Broadband dielectric spectroscopy, differential scanning calorimetry, and rheology were employed to study the impact of hydrogen (H)-bonding end-groups on segmental and chain dynamics of telechelic polypropylene glycol (PPG) and poly(dimethylsiloxane) (PDMS). Polymer chains with three types of H-bonding end-groups possessing different interaction strengths and a non-H-bonding end-group as reference were compared. The glass transition temperature (Tg) of H-bonding PPG systems with low molecular weight increases compared to the reference, and the Tg difference varies with chain-end interaction strength. In contrast, their shear viscosities (for Tg-scaled temperature, i.e., when the shift in Tg is accounted for) are similar to that one of the reference. This is in strong contrast to the behavior of telechelic PDMS with the same set of end-groups, where the Tg increase of all H-bonding systems is independent of H-bond strengths, while shear viscosity increases significantly only for the strongest H-bonding end-groups. These observations are explained by the difference in lifetime of the end-group associations relative to segmental and chain relaxation times.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mappings of open quantum systems onto chain representations and Markovian embeddings
We study systems coupled linearly to a bath of oscillators. In an iterative process, the bath is transformed into a chain of oscillators with nearest neighbour interactions. A systematic procedure is provided to obtain the spectral density of the residual bath in each step, and it is shown that under general conditions these data converge. That is, the asymptotic part of the chain is universal, translation invariant with semicircular spectral density. The methods are based on orthogonal polynomials, in which we also solve the outstanding so-called “sequence of secondary measures problem” and give them a physical interpretation.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Connecting Structural and Transport Properties of Ionic Liquids with Cationic Oligoether Chains
We used X-ray diffraction and molecular dynamics simulations to probe the structures of two families of ionic liquids containing oligoether tails on the cations. Imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)amide ILs with side chains ranging from 4 to 10 atoms in length, including both linear alkyl and oligo-ethylene oxide tails, were prepared. Furthermore, their physical properties, such as viscosity, conductivity and thermal profile, were measured and compared for systematic trends. Consistent with earlier literature, a single ether substituent substantially decreases the viscosity of pyrrolidinium and imidazolium ILs compared to their alkyl congeners. Remarkably, as the number of ether units in the pyrrolidinium ILs increases there is hardly any increase in the viscosity, in contrast to alkylpyrrolidinium ILs where the viscosity increases steadily with chain length. Viscosities of imidazolium ether ILs increase with chain length but always remain well below their alkyl congeners. To complement the experimentally determined properties, molecular dynamics simulations were run on the two ILs with the longest ether chains. Our results point to specific aspects that could be useful for researchers designing ILs for specific applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Mixed Conduction in an N-Type Organic Semiconductor in the Absence of Hydrophilic Side-Chains
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Surgailis, Jokubas↗
Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO 2 -Elimination Channels
In this paper, Cl-initiated oxidation reactions of three small-chain methyl esters, methyl propanoate (CH 3 CH 2 COOCH 3 ; MP), methyl butanoate (CH 3 CH 2 CH 2 COOCH 3 ; MB), and methyl valerate (CH 3 CH 2 CH 2 CH 2 COOCH 3 ; MV), are studied at 1 or 8 Torr and 550 and 650 K. Products are monitored as a function of mass, time, and photoionization energy using multiplexed photoionization mass spectrometry coupled to tunable synchrotron photoionization radiation. Pulsed photolysis of molecular chlorine is the source of Cl radicals, which remove an H atom from the ester, forming a free radical. In each case, after addition of O 2 to the initial radicals, chain-terminating HO 2 -elimination reactions are observed to be important. Branching ratios among competing HO 2 -elimination channels are determined via absolute photoionization spectra of the unsaturated methyl ester coproducts. At 550 K, HO 2 -elimination is observed to be selective, resulting in nearly exclusive production of the conjugated methyl ester coproducts, methyl propenoate, methyl-2-butenoate, and methyl-2-pentenoate, respectively. However, in MV, upon raising the temperature to 650 K, other HO 2 -elimination pathways are observed that yield methyl-3-pentenoate and methyl-4-pentenoate. In each methyl ester oxidation reaction, a peak is observed at a mass consistent with cyclic ether formation, indicating chain-propagating OH loss/ring formation pathways via QOOH intermediates. Evidence is observed for the participation of resonance-stabilized QOOH in the most prominent cyclic ether pathways. Finally, stationary point energies for HO 2 -elimination pathways and select cyclic ether formation channels are calculated at the CBS-QB3 level of theory and assist in the assignment of reaction pathways and final products.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Confinement Effects on Host Chain Dynamics in Polymer Nanocomposite Thin Films
Incorporating nanoparticles (NPs) within a polymer host to create polymer nanocomposites (PNCs) while having the effect of increasing the functionality (e.g., sensing, energy conversion) of these materials influences other properties. One challenge is to understand the effects of nanoparticles on the viscosity of nanoscale thick polymer films. A new mechanism that contributes to an enhancement of the viscosity of nanoscale thick polymer/nanoparticle films is identified. We show that while the viscosities of neat homopolymer poly(2-vinylpyridine) (P2VP) films as thin as 50 nm remained the same as the bulk, polymer/nanoparticle films containing P2VP brush-coated gold NPs, spaced 50 nm apart, exhibited unprecedented increases in viscosities of over an order of magnitude. For thicker films or more widely separated NPs, the chain dynamics and viscosities were comparable to the bulk values. These results - NP proximities and suppression of their dynamics - suggest a new mechanism by which the viscosities of polymeric liquids could be controlled for nanoscale applications.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Enzymatic β-Oxidation of the Cholesterol Side Chain in Mycobacterium tuberculosis Bifurcates Stereospecifically at Hydration of 3-Oxo-cholest-4,22-dien-24-oyl-CoA
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99 GENERAL AND MISCELLANEOUS↗
Extended Electronic Structure Inhomogeneity Created by Double Chain Layer Defects Surrounding Columnar Tracks in Heavy-Ion Irradiated YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}.
In YBa2Cu3O7-delta (YBCO), heavy-ion irradiation creates continuous amorphous tracks that are highly effective for vortex pinning. However, the electronic structure landscape of defects and consequently their vortex pinning roles are unclear. Here, we show double chain layer (DCL) defects which intersect the columnar tracks are additionally produced by high energy Pb ion irradiation in YBCO. The DCL defects are similar to 29 nm long, about three times the columnar defect diameter. The electronic structures of the DCL and columnar track defects were determined using atomic-resolution scanning transmission electron microscopy (STEM) and high resolution electron energy loss spectroscopy (EELS). Results show a decrease in the oxygen and copper content at the interface between the track and the YBCO matrix, resulting in interfacial strain. For the DCL defects, the STEM/EELS study revealed a localized electron doped CuO2 plane next to the DCL defect. The DCL defects thus further extend the electronic inhomogeneity into YBCO.
critical current↗
AAM Supply Chain Working Group: Aerospace Supply Chain and Manufacturing
This presentation provides an overview of the aerospace supply chain and how the AAM Supply Chain Working Group will help to make it more sustainable and resilient. The urgent needs are building a tiered system, a modeling and simulation platform, and an electronic exchange platform.
AAM↗
Branched Oligo(ether) Side Chains: A Path to Enhanced Processability and Elevated Conductivity for Polymeric Semiconductors
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99 GENERAL AND MISCELLANEOUS↗
A novel signal transduction protein: Combination of solute binding and tandem PAS-like sensor domains in one polypeptide chain: Periplasmic Ligand Binding Protein Dret_0059
We report the structural and biochemical characterization of a novel periplasmic ligand-binding protein, Dret_0059, from Desulfohalobium retbaense DSM 5692, an organism isolated from the Salt Lake Retba in Senegal. The structure of the protein consists of a unique combination of a periplasmic solute binding protein (SBP) domain at the N-terminal and a tandem PAS-like sensor domain at the C-terminal region. SBP domains are found ubiquitously and their best known function is in solute transport across membranes. PAS-like sensor domains are commonly found in signal transduction proteins. These domains are widely observed as parts of many protein architectures and complexes but have not been observed previously within the same polypeptide chain. In the structure of Dret_0059, a ketoleucine moiety is bound to the SBP, whereas a cytosine molecule is bound in the distal PAS-like domain of the tandem PAS-like domain. Differential scanning flourimetry support the binding of ligands observed in the crystal structure. There is significant interaction between the SBP and tandem PAS-like domains, and it is possible that the binding of one ligand could have an effect on the binding of the other. We uncovered three other proteins with this structural architecture in the non-redundant sequence data base, and predict that they too bind the same substrates. The genomic context of this protein did not offer any clues for its function. We did not find any biological process in which the two observed ligands are coupled. The protein Dret_0059 could be involved in either signal transduction or solute transport.
Wu, R.↗
Lignocellulosic crop supply chains (eg, Miscanthus, switchgrass, reed canary grass, rye, giant reed, etc.) Chapter 12 of "Biomass Supply Chains for Bioenergy and Biorefining"
This chapter provides an overview of lignocellulosic crop supply chains such as Miscanthus, switch grass, reed canary grass, rye, and giant reed by outlining typical logistic operations in support of a liquid biofuel market. We present two strategies for managing feedstocks within the biomass supply system: (1) the conventional bale feedstock supply system and (2) the advanced supply system concept. Finally, we discuss feedstock blending and integrated landscape management as innovative improvements to the lignocellulosic crop supply chain.
09 BIOMASS FUELS↗
Beyond the universal Dyson singularity for 1-D chains with hopping disorder
We study a simple non-interacting nearest neighbor tight-binding model in one dimension with disorder, where the hopping terms are chosen randomly. This model exhibits a well-known singularity at the band center both in the density of states and localization length. If the probability distribution of the hopping terms is well-behaved, then the singularities exhibit universal behavior, the functional form of which was first discovered by Freeman Dyson in the context of a chain of classical harmonic oscillators. We show here that this universal form can be violated in a tunable manner if the hopping elements are chosen from a divergent probability distribution. We also demonstrate a connection between a breakdown of universality in this quantum problem and an analogous scenario in the classical domain — that of random walks and diffusion with anomalous exponents.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Supermolecular structures of recrystallized starches with amylopectin side chains modified by amylosucrase to different chain lengths
Understanding the supermolecular structures of recrystallized starches is imperative to manufacture novel starches with controllable physicochemical properties enabling novel applications. In this study, native amylopectin (AP) from maize was modified to different chain lengths using amylosucrase from Neisseria polysaccharea. Native AP granules showed well-organized lamellar structures with a periodicity of ca. 9.0 nm whereas modified starches formed heterogeneous structures with the average crystallite size ranging from 19.77 to 29.88 nm. Acidic treatments eroded amorphous domains in both native AP granules and modified starch particles, producing nanocrystals composed of double helices. A-type nanocrystals (~40 nm) from native AP granules showed quadrangular shape with an acute angle of ca. 60°, while irregular B-type nanocrystals were observed for the modified starches. Molecular characterizations suggested that the nanocrystals had relatively uniform chain lengths (DP 16.5–25.2), and the helix length (the thickness of nanocrystals) was positively correlated to the thermal stability of starches.
60 APPLIED LIFE SCIENCES↗
New hybrid lead iodides: From one-dimensional chain to two-dimensional layered perovskite structure
Two new hybrid lead halides (H{sub 2}BDA)[PbI{sub 4}] (1) (H{sub 2}BDA=1,4-butanediammonium dication) and (HNPEIM)[PbI{sub 3}] (2) (HNPEIM=N-phenyl-ethanimidamidine cation) have been synthesized and structurally characterized. X-ray diffraction analyses reveal that compound 1 features a two-dimensional corner-sharing perovskite layer whereas compound 2 contains one-dimensional edge-sharing double chains. The N-phenyl-ethanimidamidine cation within compound 2 was generated in-situ under solvothermal conditions. The optical absorption spectra collected at room temperature suggest that both compounds are semiconductors having direct band gaps, with estimated values of 2.64 and 2.73 eV for 1 and 2, respectively. Results from the density functional theory (DFT) calculations are consistent with the experimental data. Density of states (DOS) analysis reveals that in both compounds 1 and 2, the energy states in the valence band maximum region are iodine 5p atomic orbitals with a small contribution from lead 6s, while in the region of conduction band minimum, the major contributions are from the inorganic (Pb 6p atomic orbitals) and organic components (C and N 2p atomic orbitals) in compound 1 and 2, respectively. - Graphical abstract: Two new hybrid lead halides built on one-dimensional edge-sharing double chains and two-dimensional corner-sharing perovskite layers are synthesized and their structural and electronic properties are analyzed. - Highlights: • Two new hybrid lead iodides are designed, synthesized, and characterized. • They are closely related to, but different from, perovskite structures. • The electronic properties of both compounds are analyzed by DFT calculations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗