Large Enhancement of the Single-Molecular Conductance of a Molecular Wire through a Radical Substituent

The single-molecular conductance between two π-conjugated wires with and without a radical substituent has been compared. Specifically, methyl- and iminonitroxide-substituted 4-(biphenyl-4-yl)pyridine wires bound onto a porphyrin template were subjected to scanning tunneling microscopy (STM) apparent-height measurement at the interface between highly oriented pyrolytic graphite (HOPG) and octan-1-oic acid. Statistical analysis of the STM images revealed that the radical-substituted wire has 3.2±1.7-fold higher conductance than the methyl-substituted reference. Although density functional theory (DFT) calculation suggests that only 17 % of the SOMO is distributed on the wire moiety, the effect was significant. This study presents the potential of radical substituents to achieve high conductivity in molecular wires.     

Synthesis and Characterization of a Two‐Dimensional Zinc Phosphite,Zn3(tren)(HPO3)3·xH2O (x ≈ 0.5; tren = tris(2‐aminoethyl)amine)

A new zinc phosphite with the formula Zn₃(tren)(HPO₃)₃·xH₂O (x≈0.5) has been synthesized under hydrothermal conditions and characterized by FTIR, elemental analysis, powder X‐ray diffraction, single‐crystal X‐ray diffraction, thermogravimetric analysis and its fluorescent spectrum. The compound crystallizes in the triclinic system, space group (No.2), a = 10.1188(9) Å, b = 10.4194(9) Å, c = 10.5176(9) Å, α = 60.763(2)°, β = 70.6150(10)°, γ = 80.725(2)°, V = 912.77(14) ų, Z = 2. The structure consists of double crankshaft chains, which are linked by Zn‐O‐P bonds to form 8‐ and 12‐membered channels along the [100] direction. The claw‐like Zn‐centered complexes of Zn(N₄C₆H₁₈) as the supported templates, hang into the 12‐MR channels through Zn‐O‐P linkages with framework.     

Triosmium clusters on a support: determination of structure by X-ray absorption spectroscopy and high-resolution microscopy

The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X‐ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration‐corrected STEM. The samples were synthesized from [Os₃(CO)₁₂] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high‐angle annular dark‐field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root‐mean‐square (rms) radii of 2.03±0.06 Å. The EXAFS Os? Os coordination number of 2.1±0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02±0.04 Å. The high‐resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining Os? Os distances of 2.80±0.14 Å, matching the EXAFS value of 2.89±0.06 Å. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters.     

Spinodal decomposition and phase separation kinetics in nanoclay–biopolymer solutions

Intensity of light, I(q,t), scattered from homogeneous aqueous solutions, of nanoclay (Laponite) and protein (gelatin‐A), was studied to monitor the temporal and spatial evolution of the solution into a phase‐separated nanoclay–protein‐rich dense phase, when the sample temperature was quenched below spinodal temperature, T_s (=311 ± 3 K). The zeta potential data revealed that the dense phase comprised charge‐neutralized intermolecular complexes of nanoclay and protein chains of low surface charge. The early stage, t < 500 s, of phase separation could be described adequately through Cahn‐Hilliard theory of spinodal decomposition where the intensity grows exponentially, I(q, t) = I₀ exp.(2R(q)t). The wave vector, q dependence of the growth parameter, R(q) exhibited a maxima independent of time. Corresponding correlation length, 1/q_c = ξ_c was found to be ≈75 ± 5 nm independent of quench depth. In the intermediate regime, anomalous growth described by I(q, t) ～ t^α with α = 0.1 ± 0.02 independent of q was observed. Rheological studies established that there was a propensity of network structures inside the dense phase. Isochronal temperature sweep studies of the dense phase determined the melting temperature, T_m = 312 ± 4 K, which was comparable with the spinodal temperature. The stress‐diffusion coupling prevailing in the dense phase when analyzed in the Doi‐Onuki model yielded a viscoelastic correlation length, ξ_v determined from low‐frequency storage modulus, G ′₀ ≈ k_B T/ξ, which was ξ_v ≈ 35 ± 3 nm indicating 2ξ_v ≈ ξ_c. It is concluded that the early stage of phase separation in this system was sufficiently described by linear Cahn‐Hilliard theory, but the same was not true in the intermediate stage. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 555–565, 2010     

Diffusion monte carlo study of the hydrogen molecules adsorbed on C4H3Li

Diffusion Monte Carlo (DMC) simulations were used to calculate the binding energies for hydrogen molecules adsorbed on the lithium metal–organic complex C₄H₃Li. The calculations use all‐electron DMC techniques where every electron is explicitly included in the simulation. Also we have systematically studied it using density functional theory (DFT) methods, revealing that each C₄H₃Li can hold up to four H₂ molecules and the adsorption distance is about 2.2 Å. The DMC binding energies are in the range of 0.055–0.143 eV and are compared with those obtained with DFT using various exchange‐correlation functionals, with values ranging from 0.029 to 0.504 eV. These results indicate that caution is required applying DFT methods to weakly bound systems such as hydrogen storage materials based on lithium‐doped metal–organic frameworks. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Effect of the Linking Structure of Nonlinear Optical Side Groups on the Phase Behavior of an Aromatic Polyester Backbone

Summary: The phase behavior of poly(p‐phenylene terephthalate)s (PPT) with pendant side groups, N‐(4‐nitrophenyl)ethylaminoethanol (NPE) and N‐(4‐nitrophenyl)‐L ‐prolinol (NPP) has been studied by using differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), and second harmonic generation (SHG). PPT‐NPE showed a layered liquid crystalline morphology while PPT‐NPP showed a completely amorphous structure. Compressive or shear stress applied on the polymer melt surface at 210 °C induced a more prominent layered structure of PPT‐NPE whereas the amorphous structure of PPT‐NPP remained unchanged under the stress. In order to understand this phase difference in terms of the repeat structure, we attempted theoretical ab initio Hartree‐Fock, and DFT calculations for the monomers and molecular dynamics for the bulk state. The results indicated that molecular configurations are a good way of microscopically understanding the phases of rigid backbone polymers with functional side groups: The NPT (constant particle number, pressure, and temperature) simulation data at 210 °C agree qualitatively with the experimental data and the difference between PPT‐NPE and PPT‐NPP could be understood using rotational energy barrier, steric hindrance and inter‐chain interactions. X‐ray diffractometer (XRD) simulation patterns for the oligomers are also in qualitative agreement with the experimental WAXS data and the structural parameters of stacks of PPT‐NPE chains are estimated to be layer distance (4.6 Å), backbone distance (21.5 Å), and side distance (12 Å).

     

Surface and interface analysis of electrochemically synthesized ferromagnetic/semiconducting Ni/GaAs(001) thin film

Thin film of ferromagnetic (FM) metal (Ni) on a semiconducting substrate (GaAs), i.e. Ni/GaAs(001), has been synthesized using electrochemical method. The structural, chemical and magnetic properties at the surface and interface have been investigated using X‐ray diffraction (XRD)/grazing incidence X‐ray reflectivity (GIXRR), X‐ray photoelectron spectroscopy (XPS) and magneto‐optical Kerr effect (MOKE) techniques, respectively. A crystalline peak observed at 44.4º in the XRD pattern, corresponding to Ni(111) Bragg peak, confirms the monocrystalline nature of the film. The atomic force microscopy image shows small‐sized spherical crystallites uniformly deposited over the substrate. The fitted GIXRR pattern confirms a smooth Ni/GaAs(001) film surface with roughness of less than ~5 ± 0.4 Å. The micro‐structural parameters, such as film thickness, surface and interface roughness, and electron density, are found to be ~230 ± 5 Å, ~4.5 ± 1 Å, ~0.5 ± 0.02 Å and ~6.38 ± 0.5 (Å^?2), respectively. The chemical nature of the film at the surface and interface, investigated using a depth profile XPS technique, shows no diffusion of metallic Ga and As into Ni layer or vice versa, confirming a sharp FM/semiconducting Ni/GaAs(001) interface. The magnetization behavior investigated using MOKE technique at room temperature shows a soft FM nature of the film with coercivity of ~75 Oe at the film surface. However, coercivity was found to be ~35 Oe at the interface. In addition, the saturation magnetization is also found to decrease at the interface with decreasing Ni layer thickness. The observed magnetization behavior is correlated with structural and chemical changes that occur at the interface of Ni/GaAs(001) film. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,swelling properties,and network structure of new stimuli‐responsive poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels

Poly(N‐acryloyl‐N′‐ethyl piperazine‐co‐N‐isopropylacrylamide) hydrogels were prepared by thermal free‐radical copolymerization of N‐acryloyl‐N′‐ethyl piperazine (AcrNEP) and N‐isopropylacrylamide (NIPAM) in solution using N, N′‐methylene bisacrylamide as the crosslinking agent. The gels were responsive to changes in external stimuli such as pH and temperature. The pH and temperature responsive character of the gels was greatly dependent on the monomer content, namely AcrNEP and NIPAM, respectively. The gels swelled in acidic (pH 2) and de‐swelled in basic (pH 10) solutions with a response time of 60 min. With increase in temperature from 23 to 80 °C the swelling of the gels decreased continuously and this effect was different in acidic and basic solutions. The temperature dependence of equilibrium water content of the gels was evaluated by the Gibbs–Helmholtz equation. Detailed analysis of the swelling properties of these new gels in relation to molecular heterogeneity in acidic (pH 2) and basic (pH 10) solutions were performed. Water transport property of the gels was studied gravimetrically. In acidic solution, the diffusion process was non‐Fickian (anomalous) while in basic solution, the diffusion was quasi‐Fickian. The effect was more evident in solution of pH 2 than in pH 10. Various structural parameters of the gels such as number‐average molar mass between crosslink (M_c), the crosslink density (ρ_c), and the mesh size (ξ) were evaluated. The mesh sizes of the hydrogels were between 64 and 783 Å in the swollen state in acidic solution and 20 and 195 Å in the collapsed state in basic solution. The mesh size increased between three to four times during the pH‐dependent swelling process. The amount of unbound water (free water) and bound water of the gels was also evaluated using differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Electrochemical Investigation of Cytochrome c Immobilized onto Self‐Assembled Monolayer of Captopril

The electrochemical behavior of cytochrome c (cyt‐c) that was electrostatically immobilized onto a self‐assembled monolayer (SAM) of captopril (capt) on a gold electrode has been investigated. Cyclic voltammetry, scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy were employed to evaluate the blocking property of the capt SAM. SECM was used to measure the bimolecular electron transfer (ET) kinetics (k_BI) between a solution‐based redox probe and the immobilized protein. In addition, the tunneling ET between the immobilized protein and the underlying gold electrode was calculated. A k_BI value of (5.0±0.6)×10⁸ mol^?1 cm³ s^?1 for the bimolecular ET and a standard tunneling rate constant (k⁰) of 46.4±0.2 s^?1 for the tunneling ET have been obtained.     

Novel Conjugated Polymers Based on Dithieno[3,2‐b:6,7‐b]carbazole for Solution Processed Thin‐Film Transistors

Two conjugated polymers (CPs) P‐tCzC12 and P‐tCzC16 comprising alternating dithieno[3,2‐b:6,7‐b]carbazole and 4,4′‐dihexadecyl‐2,2′‐bithiophene units have been designed and synthesized. Upon thermal annealing, they can form ordered thin films in which the polymer backbones dominantly adopted an edge‐on orientation respective to the substrate with a lamellar spacing of ≈24 Å and a π‐stacking distance of ≈3.7 Å. Organic thin‐film transistors (OTFTs) were fabricated by solution casting. A hole mobility of 0.39 cm² V⁻¹s⁻¹ has been demonstrated with P‐tCzC16. This value is the highest among the CPs containing heteroacenes larger than 4 rings.     

Synthesis and structure of complexes of phosphorus pentachloride with 4‐dimethylaminopyridine and n‐methylimidazole

Complexes of phosphorus pentachloride with 4‐dimethylaminopyridine and N‐methylimidazole were synthesized. The molecular structure of the phosphorus pentachloride complex with N‐methylimidazole was determined by single‐crystal X‐ray diffraction. In the cationic part of the complex, the phosphorus atom possesses four P Cl bonds within the range 2.109–2.148 Å and two cis‐P–N bonds (1.811 and 1.832 Å) with N‐methylimidazole and exhibits slightly distorted octahedral coordination with angles at phosphorus atom in the range 87.57°–91.50°. The relative stability of the cis and trans conformations of the complex was studied by DFT calculations. The chemical properties and reactivity of the compounds obtained are determined; their utility as condensing agents in the synthesis of amides from acids and amines was shown. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:171–177, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20392     

DFT plus PCM calculation for pairing specificity of Watson–Crick‐type bases in aqueous solutions

This study is aimed at explaining the preference for AT and CG pairings and the possible insertion of other tautomeric DNA base pairs such as G_enolT, that respect energetic and steric requirements including at least two hydrogen bonds and 11 ± 0.5Å distance between the 9‐CH₃ of purine and 5‐CH₃ of pyrimidine. The calculated free energy of formation ΔΔG at the DFT B3LYP/6‐31G*‐PCM/BEM level pointed out the CG and AT pairs as the most favored, followed closely by G_enolT, in good agreement with Michaelis–Menten first order kinetics (CG ≈ AT > G_enolT). Unusual DNA base pairs complexes such as AG (BEM) and CT (PCM) resulted to be stable, but it is very difficult to assume that they are likely to be included in the double strand DNA. The calculated enthalpy and dipole moments of isolated DNA bases agree well with experiment. The free energy of hydration, ΔG_hyd, was found to depend on the electrostatic term, while cavitation‐dispersion components are almost constant. The stability of DNA complexes in water resulted from PCM calculations is markedly influenced by the free energy of hydration. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

DFT‐D Studies of Single Porphyrin Molecule on Doped Boron Silicon Surfaces

We present a theoretical study in the framework of density functional calculations, taking into account the van der Waals interactions (DFT‐D) of isolated Cu‐5,10,15,20‐tetrakis(3,5‐di‐tert‐butyl‐phenyl) porphyrin (Cu‐TBPP) molecules in a C2v conformation adsorbed on a Si(111)√3x√3R30°‐boron surface [denoted Si(111)‐B]. With this approach, we investigate interactions between perfect or boron‐defect Si(111)‐B substrates and the Cu‐TBPP molecule as well as the consequences of demetallation of Cu‐TBPP. For each model, we determine the structural equilibrium, the spatial charge‐density distribution and the electronic properties of the ground state. We conclude that there is potential for Si adatom capture by a porphyrin without strong modification of the porphyrin response, as seen from simulated scanning tunneling microscopy (STM) images.     

Optical Resolution and Structure Determination of New Indolizidine Alkaloids from Elaeocarpus sphaericus

Two new indolizidine alkaloids, (±)‐3‐oxoisoelaeocarpine ( 1 ) and (±)‐elaeocarpine N‐oxide ( 2 ), along with three known alkaloids, (±)‐isoelaeocarpine ( 3 ), (±)‐elaeocarpine ( 4 ), and (?)‐isoelaeocarpiline ( 5 ), were isolated from an EtOH extract of the branches and leaves of Elaeocarpus sphaericus. The structures of these compounds were determined by spectroscopic and chemical methods. Furthermore, enantiomers of compounds 1 and 3 were separated on a chiral CD‐Ph column, and their absolute configurations were determined by TD‐DFT (=time‐dependent density‐functional theory) quantum‐chemical calculations of their electronic circular dichroism (ECD) spectra.     

Replacing AgTSSCH2‐R with AgTSO2C‐R in EGaIn‐Based Tunneling Junctions Does Not Significantly Change Rates of Charge Transport

This paper compares rates of charge transport by tunneling across junctions with the structures Ag^TSX(CH₂)_2nCH₃ //Ga₂O₃ /EGaIn (n=1–8 and X= ? SCH₂? and ? O₂C? ); here Ag^TS is template‐stripped silver, and EGaIn is the eutectic alloy of gallium and indium. Its objective was to compare the tunneling decay coefficient (β, Å^?1) and the injection current (J₀, A cm^?2) of the junctions comprising SAMs of n‐alkanethiolates and n‐alkanoates. Replacing Ag^TSSCH₂‐R with Ag^TSO₂C‐R (R=alkyl chains) had no significant influence on J₀ (ca. 3×10³ A cm^?2) or β (0.75–0.79 Å^?1)—an indication that such changes (both structural and electronic) in the Ag^TSXR interface do not influence the rate of charge transport. A comparison of junctions comprising oligo(phenylene)carboxylates and n‐alkanoates showed, as expected, that β for aliphatic (0.79 Å^?1) and aromatic (0.60 Å^?1) SAMs differed significantly.     

New clostebol metabolites in human urine by liquid chromatography time‐of‐flight tandem mass spectrometry and their application for doping control

In this study, clostebol metabolic profiles were investigated carefully. Clostebol was administered to one healthy male volunteer. Urinary extracts were analyzed by liquid chromatography quadrupole time‐of‐flight mass spectrometry (MS) using full scan and targeted MS/MS techniques with accurate mass measurement for the first time. Liquid–liquid extraction and direct injection were applied to processing urine samples. Chromatographic peaks for potential metabolites were found by using the theoretical [M–H]^? as target ion in full scan experiment, and their actual deprotonated ions were analyzed in targeted MS/MS mode. Fourteen metabolites were found for clostebol, and nine unreported metabolites (two free ones and seven sulfate conjugates) were identified by MS, and their potential structures were proposed based on fragmentation and metabolism pathways. Four glucuronide conjugates were also first reported. All the metabolites were evaluated in terms of how long they could be detected and S1 (4ξ‐chloro‐5ξ‐androst‐3ξ‐ol‐17‐one‐3ξ‐sulfate) was considered to be the long‐term metabolite for clostebol misuse detected up to 25 days by liquid–liquid extraction and 14 days by direct injection analysis after oral administration. Five conjugated metabolites (M2, M5, S2, S6 and S7) could also be the alternative biomarkers for clostebol misuse. Copyright © 2015 John Wiley & Sons, Ltd.     

Combined experimental and computational modeling studies on 3,5‐dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester

The title compound, 3,5‐Dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester, has been synthesized and structurally characterized by X‐ray single crystal diffraction, elemental analysis, IR spectra, and UV‐Vis spectrum. The crystal belongs to orthorhombic, space group P212121, with a = 5.3829(15), b = 11.193(3), c = 21.824(6) Å, V = 1315.0(6) ų, and Z = 4. The molecules are connected via intermolecular C–H···N hydrogen bonds into 1D infinite chains. The crystal structure is consolidated by the intramolecular C–H···S hydrogen bonds. Furthermore, Density functional theory (DFT) calculations of the structure, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the title compound were performed by means of Gaussian 03W package and taking B3LYP/6‐31G(d) basis set. The time‐dependent DFT (TD‐DFT) calculations have been employed to calculate the electronic spectrum of the title compound, and the UV‐Vis spectra has been discussed on this basis. The results show that DFT method at B3LYP/6‐31G(d) level can well reproduce the structure of the title compound. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Electronic Structure of a Semiconducting Imine‐Covalent Organic Framework

Imine COF (covalent organic framework) based on the Schiff base reaction between p‐phenylenediamine (PDA) and benzene‐1,3,5‐tricarboxaldehyde (TCA) was prepared on the HOPG‐air (air=humid N₂) interface and characterized using different probe microscopies. The role of the molar ratio of TCA and PDA has been explored, and smooth domains of imine COF up to a few μm are formed for a high TCA ratio (>2) compared to PDA. It is also observed that the microscopic roughness of imine COF is strongly influenced by the presence of water (in the reaction chamber) during the Schiff base reaction. The electronic property of imine COF obtained by tunneling spectroscopy and dispersion corrected density functional theory (DFT) calculation are comparable and show semiconducting nature with a band gap of ≈1.8 eV. Further, we show that the frontier orbitals are delocalized entirely over the framework of imine COF. The calculated cohesive energy shows that the stability of imine COF is comparable to that of graphene.     

Tungsten Biscorroles: New Chiral Sandwich Compounds

The oxidative metalation method, involving the interaction of free‐base meso‐triarylcorroles and W(CO)₆ in refluxing decalin, led to a set of three tungsten(VI) biscorroles, the first homoleptic sandwich compounds involving corroles. Single‐crystal X‐ray structures of two of the complexes revealed square‐antiprismatic coordination and strongly domed corroles with long W?N distances of 2.15–2.22 Å and a substantial displacement of ～1.17 Å of the metal relative to the mean N₄ planes of the ligands. The structures correspond to approximate C₂ symmetry and are thus chiral. DFT calculations strongly indicate that the enantiomers are configurationally stable and hence amenable to chiral resolution. Their other notable properties include a strongly blueshifted Soret band at (357±2) nm, a relatively intense π→W(d ) near‐IR feature at (781±3) nm, and a low electrochemical HOMO–LUMO gap of approximately 1.3 V. The results obtained herein suggest that metallobiscorroles may emerge as a new class of inherently chiral chromophores with novel optical and electrochemical properties.     

Surface Charge Changes upon Formation of the Signaling State in Visual Rhodopsin†

The cytoplasmic surface of G protein‐coupled receptors plays a central role for activation and deactivation of the receptor. To understand the molecular mechanisms which underlie these processes, we determined the surface charge density and its changes upon activation directly at the cytoplasmic surface of bovine rhodopsin and correlated these changes with key events in receptor activation. The surface charge density was calculated from the ionic strength dependence of the apparent pK_a of the surface‐bound pH‐indicator dye fluorescein according to the Gouy‐Chapman theory. The surface charge density at pH 6.5 changes by 0.8 ± 0.2 elementary charge/1000 Ų in rod outer segment disk membranes and by 0.4 ± 0.2 elementary charge/1000 Ų in rhodopsin/dodecylmaltoside micelles upon formation of the active metarhodopsin‐II state. By comparison of these surface charge density values determined with and without the native lipid environment, we calculated the charge change to about 1 elementary charge/cytoplasmic rhodopsin surface. The more positive surface charge density in metarhodopsin‐II decreases back to the dark state level of σ = ?2.0 ± 0.2 elementary charges/1000 Ų in the opsin state, providing further evidence that the cytoplasmic surface properties after metarhodopsin‐II decay resemble almost those of the dark state.