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Results for “structural complexity”
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Solution Structure of the Atg1 Complex: Implications for the Architecture of the Phagophore Assembly Site
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Spectroscopic Signatures of MQ-Resins in Silicone Elastomers
Polysiloxane elastomers have a large application space due to their versatile cross-linking chemistry and highly tunable physical and mechanical properties. One approach for improving the mechanical integrity of commercial polysiloxane “silicone” elastomers while maintaining their optical transparency is the addition of small, silicone-resin molecules to the network. However, both the poly(dimethylsiloxane) (PDMS) network and the silicone-resin particles have an amorphous structure and complex chemistry, which makes the characterization of their structural properties and segmental network dynamics difficult. Here, we report the synthesis and characterization of a series of model silicone networks modified with a specific class of silicone-resin known as MQ-resin using Raman and advanced nuclear magnetic resonance (NMR) spectroscopy methods. Raman spectroscopy was successfully used to quantify the contribution of the MQ-resin to the network, to determine the type of MQ-resin present in the network, and to investigate the completeness of the network cross-linking reaction. Furthermore, solid-state and 1H double-quantum (DQ) NMR spectroscopies were used not only as a detection method for the MQ-resins but also to quantify changes in the segmental dynamics of the network as a function of MQ-resin concentration. The combination of Raman and NMR spectroscopies describes a series of samples where the MQ-resin particles and PDMS chains maintain their independent segmental dynamics up to high concentrations of MQ-resins (40–50% MQ), where the physical properties of the resin dominate the physical properties of the overall network. The results from our spectroscopic analyses are consistent with the results from macroscopic characterization techniques such as solvent uptake and mechanical testing. The spectroscopic insights into the structure–property relationships of PDMS-MQ composites presented in this study are a valuable tool not only for the synthesis and reverse engineering of future generations of commercial silicone elastomers but also for understanding the mechanisms of aging and degradation over the material lifetime.
Thermodynamic and Structural Factors That Influence the Redox Potentials of Tungsten–Alkylidyne Complexes
The thermodynamic and structural factors that influence the redox properties of an extensive set of tungsten–alkylidyne complexes (W(CR)L 4 X) are assessed by combining synthesis, electrochemistry, and computational modeling based on free energy calculations of oxidation potentials at the density functional theory level. The observed linear correlations among oxidation potentials, HOMO energies, and gas-phase ionization energies are found to be consistent with the approximately constant solvation free energy differences between reduced and oxidized species over the complete set. The W–X bond length, trans to the alkylidyne ligand, is discovered to be a good descriptor of the positioning of the key frontier orbitals that regulate the redox properties of the complexes.
Crystal Structure of FOXC2 in Complex with DNA Target
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Structural Diversity in the Complexes of Trimeric Perfluoro- o -phenylene Mercury with Tetrathia- and Tetramethyltetraselenafulvalene
Five potential charge transfer complexes of trimeric perfluoro-o-phenylene mercury (I) with tetrathiafulvalene (TTF) and tetramethyltetraselenefulvalene (TMTSF) were grown from different solvent mixtures. The adducts (I)2·TTF (1) and I·TTF (2) were grown by slow evaporation from the 1:1 mixture of dichloromethane (CH 2 Cl 2 , DCM) and carbon disulfide (CS 2 ). Use of the different 1:1 solvent mixtures of dichloromethane (CH 2 Cl 2 , DCM) and dichloroethane (C 2 H 4 Cl 2 , DCE) has led to the crystalline adducts I·TTF (3) and I·TTF·DCE (4). Adduct I.TMTSF (5) was grown by the interface crystallization on the border of two immiscible layers, ethyl acetate, and carbon disulfide. The cocrystals differ by the donor–acceptor ratio, molecular packing, and the solvent inclusion. The components in 1–5 form mixed donor–acceptor stacks. The stacks are stabilized by Hg···S and Hg···C short contacts, while the lateral interactions between stacks include F···F, CH···F, and S/Se···F short contacts.
Synthesis of Carba-NAD and the Structures of Its Ternary Complexes with SIRT3 and SIRT5
Abstract not provided
Role of backbone strain in de novo design of complex α/β protein structures
Abstract We previously elucidated principles for designing ideal proteins with completely consistent local and non-local interactions which have enabled the design of a wide range of new αβ-proteins with four or fewer β-strands. The principles relate local backbone structures to supersecondary-structure packing arrangements of α-helices and β-strands. Here, we test the generality of the principles by employing them to design larger proteins with five- and six- stranded β-sheets flanked by α-helices. The initial designs were monomeric in solution with high thermal stability, and the nuclear magnetic resonance (NMR) structure of one was close to the design model, but for two others the order of strands in the β-sheet was swapped. Investigation into the origins of this strand swapping suggested that the global structures of the design models were more strained than the NMR structures. We incorporated explicit consideration of global backbone strain into the design methodology, and succeeded in designing proteins with the intended unswapped strand arrangements. These results illustrate the value of experimental structure determination in guiding improvement of de novo design, and the importance of consistency between local, supersecondary, and global tertiary interactions in determining protein topology. The augmented set of principles should inform the design of larger functional proteins.
Resolving structures of transition metal complex reaction intermediates with femtosecond EXAFS
Femtosecond EXAFS is implemented at an XFEL and can be used to observe short-lived intermediate states of photoexcited transition metal complexes in solution.
Influences of the propyl group on the van der Waals structures of 4-propylaniline complexes with one and two argon atoms studied by electronic and cationic spectroscopy
4-propylaniline complexes with one and two argon atoms formed in the molecular beam were studied in the first excited electronic state, S{sub 1}, using resonance enhanced two-photon ionization spectroscopy and in the cation ground state, D{sub 0}, using mass analyzed threshold ionization spectroscopy. The combination of electronic and cationic spectra of the clusters allows two conformations to be identified in both aniline-Ar{sub 1} and aniline-Ar{sub 2}, which are assigned to either the gauche configuration or anti-configuration of 4-propylaniline. The gauche isomer exhibits complex bands shifted 29 cm{sup −1} and 89 cm{sup −1} from the S{sub 1} origin bands and 83 cm{sup −1} and 148 cm{sup −1} from the ionization potential assigned to the Ar{sub 1} and Ar{sub 2} complexes, respectively. For the anti-rotamer, the corresponding shifts actually become nearly additive, 53 cm{sup −1} and 109 cm{sup −1} for the S{sub 1} origin bands, and 61 cm{sup −1} and 125 cm{sup −1} for the ionization potentials. Ab initio calculations provide insights into the influences of the propyl and amino groups on the positions of the argon atoms within the clusters. In addition, the binding energy of one argon with the gauche isomer of 4-propylaniline has been measured to be 550 ± 5 cm{sup −1} in the D{sub 0} state, 496 ± 5 cm{sup −1} in the S{sub 1} state, and 467 ± 5 cm{sup −1} in the neutral ground state, S{sub 0}.
Crystal structure of PhnZ in complex with substrate reveals a di-iron oxygenase mechanism for catabolism of organophosphonates
Abstract not provided
X-RAY HIGH-RESOLUTION SPECTROSCOPY REVEALS FEEDBACK IN A SEYFERT GALAXY FROM AN ULTRA-FAST WIND WITH COMPLEX IONIZATION AND VELOCITY STRUCTURE
Winds outflowing from active galactic nuclei (AGNs) may carry significant amounts of mass and energy out to their host galaxies. In this paper we report the detection of a sub-relativistic outflow observed in the narrow line Seyfert 1 galaxy IRAS 17020+4544 as a series of absorption lines corresponding to at least five absorption components with an unprecedented wide range of associated column densities and ionization levels and velocities in the range of 23,000–33,000 km s{sup −1}, detected at X-ray high spectral resolution (E/ΔE ∼ 1000) with the ESA's observatory XMM-Newton. The charge states of the material constituting the wind clearly indicate a range of low to moderate ionization states in the outflowing gas and column densities that are significantly lower than observed in highly ionized ultra-fast outflows. We estimate that at least one of the outflow components may carry sufficient energy to substantially suppress star formation and heat the gas in the host galaxy. IRAS 17020+4544 therefore provides an interesting example of feedback by a moderately luminous AGN that is hosted in a spiral galaxy, a case barely envisaged in most evolution models, which often predict that feedback processes take place in massive elliptical galaxies hosting luminous quasars in a post-merger phase.
Structural mechanisms of DREAM complex assembly and regulation
Abstract not provided
Complex pressure-temperature structural phase diagram of the honeycomb iridate Cu 2 IrO 3
Cu 2 IrO 3 is among the newest layered honeycomb iridates and a promising candidate to harbor a Kitaev quantum spin liquid state. Here, we investigate the pressure and temperature dependence of its structure through a combination of powder x-ray diffraction and x-ray absorption fine structure measurements, as well as ab initio evolutionary structure search. At ambient pressure, we revise the previously proposed C2/c solution with a related but notably more stable P2 1 /c structure. Pressures below 8 GPa drive the formation of Ir-Ir dimers at both ambient and low temperatures, similar to the case of Li 2 IrO 3 . At higher pressures, the structural evolution dramatically depends on temperature. Furthermore, a large discontinuous reduction of the Ir honeycomb interplanar distance is observed around 15 GPa at room temperature, likely driven by a collapse of the O-Cu-O dumbbell bonds. At 15 K, pressures beyond 20 GPa first lead to an intermediate phase featuring a continuous reduction of the interplanar distance, which then collapses at 30 GPa across yet another phase transition. However, the resulting structure around 40 GPa is not the same at room and low temperatures. Remarkably, the reduction in interplanar distance leads to an apparent healing of the stacking faults at room temperature, but not at 15 K. Possible implications on the evolution of electronic structure of Cu 2 IrO 3 with pressure are discussed.