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PubMed Journal Database | Chemphyschem : a European journal of chemical physics and physical chemistry RSS

09:19 EDT 27th May 2019 | BioPortfolio

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Showing PubMed Articles 1–25 of 541 from Chemphyschem : a European journal of chemical physics and physical chemistry

Short-range structural correlations in amorphous 2D polymers.

Many 2D covalent polymers synthesized as single layers on surfaces show inherent disorder, expressed for example in their ring-size distribution. Systems which are expected to form the thermodynamically favored hexagonal lattice usually deviate from crystallinity and include high numbers of pentagons, heptagons, and rings of other sizes. Here we investigate the amorphous structure of two different covalent polymers in real space using scanning tunneling microscopy. Molecular dynamics simulations are employe...

Effect of Asymmetric Anchoring Groups on Electronic Transport in Hybrid Metal/Molecule/Graphene Single Molecule Junctions.

A combined experimental and theoretical study on molecular junctions with asymmetry in both the electrode type and asymmetry in the anchoring group type is presented here. A scanning tunnelling microscope is used to create the "anti-symmetricasymmetric" Au-S-(CH2)n-COOH-graphene molecular junctions and determine their conductance. These measurements are combined with electron transport calculations based on Density Functional Theory (DFT) to analyze the electrical conductance and its length attenuation fact...

Surface-confined self-assembly of asymmetric tetratopic molecular building blocks.

Surface-confined self-assembly of functional molecular building blocks has been recently widely used to create low-dimensional, also covalent, superstructures with tailorable geometry and physicochemical properties. In this contribution, using the lattice Monte Carlo simulation method, we demonstrate how the structure-property relation can be established for the 2D self-assembly of a model tetrapod molecule with reduced symmetry. To that purpose, a rigid functional unit comprising a few interconnected segme...

Influence of a perfluorohexane-enriched atmosphere on the viscoelasticity and structural order of self-assembled nanodomains of semifluorinated alkanes at the air/water interface.

Semifluorinated alkanes FnHm self-assemble into nanometer-sized surface micelles at the air/water interface. In this study, we investigated how an atmosphere enriched with perfluorohexane (PFH) influences the interfacial viscoelasticity and structural order of a monolayer of FnHm by the combination of dilational rheology and grazing-incidence small-angle X-ray scattering (GISAXS). The monolayers behaved predominantly elastic which can be attributed to the strong dipole repulsions of the surface domains. Enr...

On-surface Synthesis of One-dimensional Carbon-based Nanostructures via C-X and C-H Activation Reactions.

The past decades have witnessed the emergence of low-dimensional carbon-based nanostructures owing to their unique properties and various subsequent applications. It is of fundamental importance to explore the way to achieve atomically precise fabrication of these interesting structures. The newly developed on-surface synthesis method provides an efficient strategy for this challenging issue, which demonstrates the potential of atomically precise preparation of low-dimensional nanostructures. Up to now, the...

Short-lived radical intermediates in the photochemistry of glucose oxidase.

Glucose oxidase is a flavoprotein that is relatively well-studied as a physico-chemical model system. The flavin cofactor is surrounded by several aromatic acid residues that can act as direct and indirect electron donors to photoexcited flavin. Yet, the identity of the photochemical product states is not well established. We present a detailed full spectral reinvestigation of this issue using femtosecond fluorescence and absorption spectroscopy. Based on a recent characterization of the unstable tyrosine c...

Enhanced Hole Transport in Ternary Blend Polymer Solar Cells.

Recently, ternary blend polymer solar cells have attracted great attention to improve a short-circuit current density (Jsc) effectively because complementary absorption bands can harvest the solar light over a wide wavelength range from visible to near-IR region. Interestingly, some ternary blend solar cells have shown improvements not only in Jsc but also in a fill factor (FF). Previously, we also reported that a ternary blend solar cell based on a low-bandgap polymer PTB7-Th, a wide-bandgap polymer PDCBT,...

5 nm Ordered Structures Self-Assembled by C2-Symmetric Hybrids with Polyhedral Oligomeric Silsesquioxane and Hexa-peri-Hexabenzocoronene.

Hybrids consisting of polyhedral oligomeric silsesquioxane (POSS) and hexa-peri-hexabenzocoronene (HBC) with a dumbbell topology and C2 symmetry were designed and synthesized. They self-assemble into 5 nm ordered structures. In particular, the increased steric effect with increasing POSS units stabilizes a square columnar phase (Colsqu) which is important in nanotemplates. These hybrids containing the discotic liquid crystal HBC and POSS units have an excellent etching contrast and provide an approach to ob...

The effect of thermal treatment on the hydrogen storage properties of PIM-1.

There has been recent interest in polymers of intrinsic microporosity (PIMs) for solid-state hydrogen storage materials; however, the gas sorption properties and conditions for hydrogen uptake are relatively unexplored. PIM-1 has been synthesised using the condensation reaction between 3,3,3,3-tetramethyl-1,1-spirobisindane-5,5,6,6-tetraol and 2,3,5,6-tetrafluorophthalonitrile as precursors. The synthesized PIM-1 was annealed at different temperatures for varying times and then characterised for hydrogen up...

Uranyl-bound tetra-dentate non-innocent ligands: Prediction of structure and redox behaviour using density functional theory (DFT).

Computational methods have been applied to understand the reduction potentials of [UO2-salmnt-L] complexes (L=pyridine, DMSO, DMF and TPPO), and the redox behavior compared with a previous experiments in dichloromethane solution. Since the experimental results were inconclusive regarding the influence of the uranyl-bound tetra-dentate 'salmnt' ligand, here we will show that salmnt acts as a redox-active ligand and exhibits non-innocent behavior to interfere with the otherwise expected one-electron metal (U)...

Quantitative Assessment of B-B-B, B-Hb -B, and B-Ht Bonds: From BH3 to B12H122.

We report the thermodynamic stabilities and the intrinsic strengths of three- center-two-electron B - B - B and B - Hb - B bonds (Hb : bridging hydrogen), and two-center-two-electron B - Ht bonds (Ht : terminal hydrogen) which can be served as a new, effective tool to determine the decisive role of the intermediates of hydrogenation/dehydrogenation reactions of borohydride. The calculated heats of formation were obtained with the G4 composite method and the intrinsic strengths of B-B-B, B-Hb -B, and B-Ht bo...

Structural transformation of 2,7-dibromopyrene on Au(111) mediated by halogen-bonding motifs.

Fundamental understanding of the bonding motifs that elaborately mediate the formation of supramolecular nanostructures is essential for the rational design of stable artificial organic architectures. Herein, the structural transformation of the adsorption complex of 2, 7-dibromopyrene (Br2Py) on the Au(111) surface has been investigated by scanning tunnelling microscopy combined with X-ray photoemission spectroscopy and density function theory calculations. In the initial stage of self-assembly, well order...

Kinetically-controlled synthesis of four-member and six-member cyclic products via sequential aryl-aryl coupling on a Au(111) surface.

We synthesize four-member and six-member cyclic products via sequential multi-step aryl-aryl coupling reactions of 2,3,6,7,10,11-hexabromotriphenylene molecules on a Au(111) surface. The final products as well as the organo-gold intermediate structures are identified using scanning tunneling microscopy and density-functional theory simulation. By adjusting reaction temperature and post-annealing temperature, we enhance/suppress the yields of the four-member and six-member cyclic products. We propose an unde...

Cationic Gold(I) Diarylallenylidene Complexes: Bonding Features and Ligand Effects.

Using computational approaches, we qualitatively and quantitatively assess the bonding components of a series of experimentally characterized Au(I) diarylallenylidene complexes (N.Kim, R.A.Widenhoefer, Angew. Chem. Int. Ed. 2018, 57, 4722-4726). Our results clearly demonstrate that Au(I) engages only weakly in π-backbonding, which is, however, a tunable bonding component. Computationally identified trends in bonding are clearly correlated with the substitution patterns of the aryl substituents in the Au(I)...

Systematic experimental study on quantum sieving of hydrogen isotopes in metal-amide-imidazolate frameworks with narrow 1-D channels.

Quantum sieving of hydrogen isotopes is experimentally studied in isostructural hexagonal metal-organic frameworks having 1-D channels, named IFP-1, -3, -4 and -7. Inside the channels different molecules or atoms restrict the channel diameter periodically with apertures larger (4.2 Å for IFP-1, 3.1 Å for IFP-3) and smaller (2.1 Å for IFP-7, 1.7 Å for IFP-4) than the kinetic diameter of hydrogen isotopes. From a geometrical point of view, no gas should penetrate into IFP-7 and IFP-4, but due to the therm...

Benzodithiophene-fused Perylene Bisimides as Electron Acceptors for Non-fullerene Organic Solar Cells with High Open-Circuit Voltage.

Tandem-junction organic solar cells require solar cells with visible light photo-response as front cells, in which an open-circuit voltage (Voc) above 1.0 V is highly demanded. In this work, we are able to develop electron acceptors to fabricate non-fullerene organic solar cells (NFOSCs) with a very high Voc of 1.14 V. This was realized by designing perylene bisimide (PBI)-based conjugated materials fused with benzodithiophene, in which Cl and S atom were introduced into the molecules in order to lower the ...

Substituent Effect Transmission Power of Alkyl, Alkenyl, Alkynyl, Phenyl, Thiophenyl and Polyacene Spacers.

The transmission of substituent effect through a variety of spacers viz. alkyl, alkenyl, alkynyl, phenyl, thiophenyl, and polyacene has been studied by modeling Y-G-X type molecular systems (Y- reaction center, G - spacer moiety and X - substituent) using B3LYP/6-31G(d,p) density functional theory. The reaction center is always kept as a CC double bond and the molecular electrostatic potential (MESP) minimum (Vmin) observed for this bond showed subtle variation with respect to the changes in the spacer unit...

Molecular Dynamics of Excited State Intramolecular Charge Transfer in Solution by Coherent Nuclear Wave Packets.

Revealing a proper reaction coordinate in a chemical reaction is the key step towards elucidation of the molecular reaction dynamics. In this report, we investigated dynamics of intramolecular charge transfer (ICT) of 8-aminopyrene-1,3,6-trisulfonic acid (APTS) occurring in the excited state by time-resolved fluorescence (TF) and TF spectra. Accurate reaction rates and rate-dependent nuclear wave packets in the product state allow detailed investigation of the molecular reaction dynamics. The ICT rate is so...

Understanding regium bonds and their competition with hydrogen bonds in Au2:HX complexes.

A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au2:HX complexes have been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between -24 and -180 kJ·mol-1 while those HB complexes are between -6 and -19 kJ·mol-1. DFT-SAPT also indicated that while HB complexes are governed by electrostatics, RB complexes p...

The Driving Force for the Acylation of β-Lactam Antibiotics by L,D-Transpeptidase 2: Quantum Mechanics/Molecular Mechanics (QM/MM) Study.

β-lactam antibiotics, which are used to treat infectious diseases, are currently the most widely used class of antibiotics. This study focused on the chemical reactivity of five- and six-membered ring systems attached to the β-lactam ring. The ring strain energy (RSE), force constant (FC) of amide (C-N), acylation transition states and second-order perturbation stabilization energies of 13 basic structural units of β-lactam derivatives were computed using the M06-2X and G3/B3LYP multistep method. In the ...

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY-Fullerene C Dyad as Potential Antimicrobial Agent.

A covalently linked BODIPY-fullerene C dyad (BDP-C ) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C to inactivate bacteria. The absorption spectrum of BDP-C was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C . S...

Release of Formic Acid from Copper Formate: Hydride, Proton Coupled Electron and Hydrogen Atom Transfer All Play their Role.

While the mechanism of transforming carbon dioxide to formate with copper hydride is well understood, it is not clear how formic acid is ultimately released. Here, we show how formic acid is formed in the decomposition of the copper formate clusters Cu(II)(HCOO)3- and Cu(II)2(HCOO)5-. Infrared irradiation resonant with the antisymmetric C-O stretching mode activates the cluster, resulting in the release of formic acid and carbon dioxide. For the binary cluster, electronic structure calculations indicate tha...

Corrigendum: Effects of Electric Fields on Multiple Exciton Generation.

Corrigendum: Time-Resolved Diffusion NMR Measurements for Transient Processes.

Examining the structure sensitivity of the Oxygen Evolution Reaction on Pt single crystal electrodes: a combined experimental and theoretical study.

In the present work we investigate the structure sensitivity of the oxygen evolution reaction (OER) combining electrochemistry, in-situ spectroscopy and density functional theory calculations. The intrinsic difficulty of such studies is the fact that at electrode potentials where the OER is observed the electrode material is highly oxidized. As a consequence, the surface structure during the reaction is in general ill-defined and only scarce knowledge exists concerning the structure-activity relationship of...


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