Two-stage formation of chloro (N-o-chlorobenzamido-meso-tetraphenylporphyrinato) zinc(II) methylene chloride solvate: Zn(N-NHCO(o-Cl)C6H4-tpp)Cl · CH2Cl2

The coordinating properties of N-o-chlorobenzamido-meso-tetraphenylporphyrin (N-NHCO(o-Cl)C₆H₄-Htpp; 11) have been investigated for the Zn²⁺ ion. Insertion of Zn results in the formation of the zinc complex Zn(N-NCO(o-Cl)C₆H₄-tpp)(MeOH) · MeOH (12 · MeOH). The diamagnetic 12 · MeOH can be transformed into the diamagnetic Zn(N-NHCO(o-Cl)C₆H₄-tpp)Cl · CH₂Cl₂ (13 · CH₂Cl₂) in a reaction with aqueous hydrogen chloride (2%). X-ray structures for 12 · MeOH and 13 · CH₂Cl₂ have been determined. The coordination sphere around the Zn²⁺ ion in 12 · MeOH is a distorted trigonal bipyramid with N(2), N(4) and O(2) lying in the equatorial plane, whereas for the Zn²⁺ ion in 13 · CH₂Cl₂, it is a square-based pyramid in which the apical site is occupied by the Cl(1) atom.     

Vaporization-condensation-recrystallization process-mediated synthesis of helical m-aminobenzoic acid nanobelts

One-dimensional (1D) helical organic nanostructures were synthesized by a modified vapor-solid (VS) process, called the vaporization-condensation-recrystallization (VCR) process. The conventional solution-phase synthetic methods generally mediate self-assemblies of repeating unit molecules. To provide enough intermolecular interaction forces among the unit molecules, such strategy requires specific designs and syntheses of complex unit molecules as they possess numerous functional groups including phenyl rings, hydroxyl groups, long aliphatic chains, etc. On the contrary, we found that small and simple organic molecules, for example, m-ABA, could be self-assembled by the VCR process, resulting in 1D helical organic nanostructures. When m-aminobenzoic acid (m-ABA) powders were vaporized and transported to be condensed on a cooler region, the condensates were recrystallized into 1D helical nanobelts. Each step of the VCR process was confirmed from control experiments performed by varying reaction times, substrate types, and reaction temperatures. Powder XRD data, SAED analysis, and theoretical calculations revealed that dimers of m-ABA molecules have repeating units, and the growth axis of m-ABA nanohelices is [100].     

Electrical behavior of droplet interface bilayer networks: experimental analysis and modeling

Aqueous droplets submerged in an oil-lipid mixture become enclosed by a lipid monolayer. The droplets can be connected to form robust networks of droplet interface bilayers (DIBs) with functions such as a biobattery and a light sensor. Such DIB networks might be used as model systems for the study of membrane-based biological phenomena. In this study, we develop and experimentally validate an electrical modeling approach for DIB networks by applying it to describe the current flow through a simple network containing protein pores and blocking molecules. We demonstrate the use of SPICE (Simulation Program with Integrated Circuit Emphasis) for simulating the electrical behavior of DIB networks. The modular and scalable nature of DIB networks should enable a straightforward extension of the analysis presented in this paper to large, complex networks.     

Poly(vinylpyrrolidone)-modified graphite carbon nanofibers as promising supports for PtRu catalysts in direct methanol fuel cells

Carbon nanomaterials, including herringbone graphite carbon nanofibers (GNFH), multiwalled carbon nanotubes (MWCNT), and carbon black, were surface-modified by a new poly(vinylpyrrolidone) (PVP) grafting process as well as by the conventional acid-oxidation (AO) process, and characterized by FTIR, TGA, Raman, HRTEM, XRD, and XPS measurements. Pt nanoparticles of 1.8 nm were evenly deposited on all PVP-grafted carbon nanomaterials. The effects of the two surface modification processes on the dispersion, average Pt nanoparticle sizes, the electrocatalytic performance, and electrical conductivities of Pt-carbon nanocomposites in direct methanol oxidation were systematically studied and compared. It was found that the PVP-grafted carbon nanomaterials have much less loss in the electric conductivity and thus better electrocatalytic performance, 17-463% higher, than their corresponding acid oxidation-treated nanocomposites. The electrocatalytic performance of the Pt-carbon nanocomposites decreases in the following order: Pt-PVP-GNFH > Pt-PVP-MWCNTarc > Pt-AO-MWCNTarc > Pt-PVP-MWCNTCVD > Pt-AO-MWCNTCVD > Pt-XC-72R > Pt-AO-GNFH, with the Pt-PVP-GNFH nanocomposite having approximately 270% higher performance than that of the Pt-Vulcan XC-72R nanocomposite. In addition, PtRu-PVP-GNFH shows even better (50% higher) electrocatalytic activity than the Pt-PVP-GNFH nanocomposite at a 0.6 V applied voltage.     

ESR, zero-field splitting, and magnetic exchange of exchange-coupled copper(II)-copper(II) pairs in copper(II) tetraphenylporphyrin N-oxide

The crystal structures of the dimer form of copper(II) tetraphenylporphyrin N-oxide, [Cu(tpp-N-O)]2 (3-dimer), and zinc(II) tetraphenylporphyrin N-oxide, [Zn(tpp-N-O)]2 (4-dimer), were established. The geometry at the copper ion in 3-dimer is essentially square-pyramidal with one oxygen bridge [O(1A)] occupying the apical site, giving a much larger Cu-O bond distance compared to those at the basal plane. The respective Cu...Cu distance and Cu-O-Cu angle in the core of 3-dimer are 3.987(4) A and 148.1(3) degrees. The Zn(1) atom in 4-dimer has a distorted square-pyramidal [4 + 1] coordination geometry that gives a tau-value of 0.19. The respective Zn...Zn distance and Zn-O-Zn angle in the dimeric unit of 4-dimer are 4.025(3) A and 148.1(2) degrees. The 3-dimer displays axial X-band electron paramagnetic resonance spectral features (Es = 0) in the powder state at 4 K, giving g parallel = 2.51 (A(parallel,s) = (9.6 +/- 0.2) x 10-3 cm(-1)) and g(perpendicular) = 2.11 and in the same powder state at 293 K giving Ds = 0.0731 cm(-1) (as derived from DeltaMs = 1 lines) or 0.0743 cm(-1) (as derived from the DeltaMs = 2 lines). In addition, 3-dimer displays a DeltaMs = 2 transition at g = 4.17 indicating the presence of spin-exchange coupling. The anisotropic exchange interaction (Ds(ex)= 0.132 cm(-1)) gives the main contribution to Ds in 3-dimer. The theoretical fit of the susceptibility and effective magnetic moment data of 3-dimer in the temperature range of 5-300 K gives 2J = 68 cm(-1), g = 2.01, p = 0.06, and a temperature-independent paramagnetism of 10(-6) cm3 mol(-1). This magnetic susceptibility data indicates that the copper(II) ions in 3-dimer are coupled in a ferromagnetic manner with the ground-spin triplet stabilized by 68 cm(-1) with regard to the singlet.     

Dynamics of supercooled water in various mesopore sizes

Double-quantum-filtered NMR and T(1) inversion-recovery spectroscopy were employed to exploit the temperature-dependent dynamics of D(2)O confined in MCM-41. Samples with three pore sizes of 1.58, 2.03, and 2.34 nm and two D(2)O contents were investigated. The reorientation correlation times of confined D(2)O in variously sized pores exhibit different temperature dependencies. The results reveal that the D(2)O molecules at fast motion site remain mobile below approximately 225 K and a liquid-liquid phase transition occurs around this temperature for all samples studied. This temperature is thought to be unreachable for supercooled D(2)O. Particularly, in 20 wt % D(2)O loaded samples with pore diameters of 1.58 and 2.03 nm, the reorientational correlation times of D(2)O at fast motion site exhibit Arrhenius behavior between 225 and 290 K, while other samples show power law dependency. Thus, a liquid phase of the fragile type in bigger pores changes to the strong type in samples with smaller pores.     

Incorporation of inhomogeneous ion diffusion coefficients into kinetic lattice grand canonical monte carlo simulations and application to ion current calculations in a simple model ion channel

To deal with inhomogeneous diffusion coefficients of ions without altering the lattice spacing in the kinetic lattice grand canonical Monte Carlo (KLGCMC) simulation, an algorithm that incorporates diffusion coefficient variation into move probabilities is proposed and implemented into KLGCMC calculations. Using this algorithm, the KLGCMC simulation method is applied to the calculation of ion currents in a simple model ion channel system. Comparisons of ion currents and ion concentrations from these simulations with Poisson-Nernst-Planck (PNP) results show good agreement between the two methods for parameters where the latter method is expected to be accurate.     

Organophosphonate self-assembled monolayers for gate dielectric surface modification of pentacene-based organic thin-film transistors: a comparative study

Organic thin-film transistors using pentacene as the semiconductor were fabricated on silicon. A series of phosphonate-based self-assembled monolayers (SAMs) was used as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region. Octadecylphosphonate, (quarterthiophene)phosphonate, and (9-anthracene)phosphonate SAMs were examined. Significant improvements in the sub-threshold slope and threshold voltage were observed for each SAM treatment as compared to control devices fabricated without the buffer. These improvements were related to structural motif relationships between the pentacene semiconductor and the SAM constituents. Measured transistor properties were consistent with a reduction in density of charge trapping states at the semiconductor-dielectric interface that was effected by introduction of the self-assembled monolayer.     

Influence of Electronic Environment on the Radiative Efficiency of 9-Phenyl-9H-carbazole-Based ortho-Carboranyl Luminophores

The photophysical properties of closo-ortho-carboranyl-based donor–acceptor dyads are known to be affected by the electronic environment of the carborane cage but the influence of the electronic environment of the donor moiety remains unclear. Herein, four 9-phenyl-9H-carbazole-based closo-ortho-carboranyl compounds (1F, 2P, 3M, and 4T), in which an o-carborane cage was appended at the C3-position of a 9-phenyl-9H-carbazole moiety bearing various functional groups, were synthesized and fully characterized using multinuclear nuclear magnetic resonance spectroscopy and elemental analysis. Furthermore, the solid-state molecular structures of 1F and 4T were determined by X-ray diffraction crystallography. For all the compounds, the lowest-energy absorption band exhibited a tail extending to 350 nm, attributable to the spin-allowed π–π* transition of the 9-phenyl-9H-carbazole moiety and weak intramolecular charge transfer (ICT) between the o-carborane and the carbazole group. These compounds showed intense yellowish emission (λ_em = ~540 nm) in rigid states (in tetrahydrofuran (THF) at 77 K and in films), whereas considerably weak emission was observed in THF at 298 K. Theoretical calculations on the first excited states (S₁) of the compounds suggested that the strong emission bands can be assigned to the ICT transition involving the o-carborane. Furthermore, photoluminescence experiments in THF‒water mixtures demonstrated that aggregation-induced emission was responsible for the emission in rigid states. Intriguingly, the quantum yields and radiative decay constants in the film state were gradually enhanced with the increasing electron-donating ability of the substituent on the 9-phenyl group (‒F for 1F < ‒H for 2P < ‒CH₃ for 3M < ‒C(CH₃)₃ for 4T). These features indicate that the ICT-based radiative decay process in rigid states is affected by the electronic environment of the 9-phenyl-9H-carbazole group. Consequently, the efficient ICT-based radiative decay of o-carboranyl compounds can be achieved by appending the o-carborane cage with electron-rich aromatic systems.