Ordered molecular assemblies of substituted bis(phthalocyaninato) rare earth complexes on Au(111): in situ scanning tunneling microscopy and electrochemical studies

Substituted bis(phthalocyaninato) rare earth complexes ML2 (M = Y and Ce; L = [Pc(OC8H17)8]2, where Pc = phthalocyaninato) were adsorbed onto single crystalline Au(111) electrodes from benzene saturated with either YL2 or CeL2 complex at room temperature. In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine the structures and the redox reactions of these admolecules on Au(111) electrodes in 0.1 mol dm(-3) HClO4. The CVs obtained with YL2- and CeL2-coated Au(111) electrodes respectively contained two and three pairs of redox peaks between 0 and 1.0 V (versus reversible hydrogen electrode). STM molecular resolution revealed that YL2 and CeL2 admolecules were imaged as spherical protrusions separated by 2.3 nm, which suggests that they were oriented with their molecular planes parallel to the unreconstructed Au(111)-(1 x 1). Both molecules when adsorbing from approximately micromolar benzene dosing solutions produced mainly ordered arrays characterized as (8 x 5 radical3)rect (theta = 0.0125). The redox reactions occurring between 0.2 and 1.0 V caused no change in the adlayer, but they were desorbed or oxidized at the negative and positive potential limits. The processes of adsorption and desorption at the negative potentials were reversible to the modulation of potential. Electrochemical impedance spectroscopy (EIS) and CV measurements showed that YL2 and CeL2 adlayers could block the adsorption of perchlorate anions and mediating electron transfer at the Au(111) electrode, leading to the enhancement of charge transfer for the ferro/ferricyanide redox couple.     

BF3-activated oxidation of alkanes by MnO4 -

The oxidation of alkanes and arylalkanes by KMnO(4) in CH(3)CN is greatly accelerated by the presence of just a few equivalents of BF(3), the reaction occurring readily at room temperature. Carbonyl compounds are the predominant products in the oxidation of secondary C-H bonds. Spectrophotometric and kinetics studies show that BF(3) forms an adduct with KMnO(4) in CH(3)CN, [BF(3).MnO(4)](-), which is the active species responsible for the oxidation of C-H bonds. The rate constant for the oxidation of toluene by [BF(3).MnO(4)](-) is over 7 orders of magnitude faster than by MnO(4)(-) alone. The kinetic isotope effects for the oxidation of cyclohexane, toluene, and ethylbenzene at 25.0 degrees C are as follows: k(C6H12)/k(C6D12) = 5.3 +/- 0.6, k(C7H8)/k(C7D8) = 6.8 +/- 0.5, k(C8H10)/k(C8D10) = 7.1 +/- 0.5. The rate-limiting step for all of these reactions is most likely hydrogen-atom transfer from the substrate to an oxo group of the adduct. A good linear correlation between log(rate constant) and C-H bond energies of the hydrocarbons is found. The accelerating effect of BF(3) on the oxidation of methane by MnO(4)(-) has been studied computationally by the Density Functional Theory (DFT) method. A significant decrease in the reaction barrier results from BF(3) coordination to MnO(4)(-). The BF(3) coordination increases the ability of the Mn metal center to achieve a d(1) Mn(VI) electron configuration in the transition state. Calculations also indicate that the species [2BF(3).MnO(4)](-) is more reactive than [BF(3).MnO(4)](-).     

Gross-Pitaevskii Equation as the Mean Field Limit of Weakly Coupled Bosons

We consider the dynamics of N boson systems interacting through a pair potential N ^?1 V _a (x _i ?x _j ) where V _a (x)=a ^?3 V(x/a). We denote the solution to the N-particle Schrödinger equation by Ψ _{N, t} . Recall that the Gross-Pitaevskii (GP) equation is a nonlinear Schrödinger equation and the GP hierarchy is an infinite BBGKY hierarchy of equations so that if u _t solves the GP equation, then the family of k-particle density matrices solves the GP hierarchy. Under the assumption that a=N ^?? for 0N→∞ the limit points of the k-particle density matrices of Ψ _{N, t} are solutions of the GP hierarchy with the coupling constant in the nonlinear term of the GP equation given by ∫V(x)dx. The uniqueness of the solutions of this hierarchy remains an open question.     

The diffeomorphic types of the complements of arrangements in ℂℙ3 II

For any arrangement of hyperplanes in ??³, we introduce the soul of this arrangement. The soul, which is a pseudo-complex, is determined by the combinatorics of the arrangement of hyperplanes. In this paper, we give a sufficient combinatoric condition for two arrangements of hyperplanes to be diffeomorphic to each other. In particular we have found sufficient conditions on combinatorics for the arrangement of hyperplanes whose moduli space is connected. This generalizes our previous result on hyperplane point arrangements in ??³.     

c = 2 Rational Toroidal Conformal Field Theories via the Gauss Product

We find a concise relation between the moduli , of a rational Narain lattice (,) and the corresponding momentum lattices of left and right chiral algebras via the Gauss product. As a byproduct, we find an identity which counts the cardinality of a certain double coset space defined for isometries between the discriminant forms of rank two lattices.     

Enhancing electron transfer at a cytochrome c-immobilized microelectrode and macroelectrode

The redox reaction of cytochrome c immobilized on the bare surfaces of microelectrodes and macroscopic electrodes (macroelectrodes) composed of different planes of highly oriented pyrolytic graphite has been investigated using cyclic voltammetry. The protein-immobilized microelectrodes were fabricated using a simple masking method. For both macroelectrodes and microelectrodes, the redox reaction of immobilized cytochrome c needs to be activated by increasing the electrochemical potential maximum of cyclic voltammetry to a high positive value. The redox currents of this protein-electrode system can be enhanced using two approaches. The oxidation and reduction currents of cytochrome c adsorbed on microelectrodes that are composed of the edge plane show an anomalous enhancement compared to those for macroelectrodes composed of the basal plane. The difference in the surface chemical properties of the two kinds of electrodes results in the current anomaly. The oxidation current of the macroelectrode can be selectively enhanced by decreasing the potential minimum.     

Determination of ammonium and metal ions by capillary electrophoresis-potential gradient detection using ionic liquid as background electrolyte and covalent coating reagent

A capillary zone electrophoresis (CZE)-potential gradient detection (PGD) method coupled with field-amplified sample injection was developed to determine alkali metal, alkaline-earth metal, nickel, lead and ammonium ions. The capillary surface was coated with dialkylimidazolium-based ionic liquid and thus the electroosmotic flow (EOF) of the capillary was reversed. The buffer composed of 7.5 mM lactic acid, 0.6 mM 18-crown-6, 12 mM alpha-cyclodextrin (alpha-CD); it was adjusted to pH 4.0 by 1-hexyl-3-methylimidazolium hydroxide. The 11 cations were baseline separated within 14 min with 5.1-18.9 x 10(4) plates (for 40-cm-long capillary) in separation efficiency, and the detection limits were in the range of 0.27-7.3 ng/ml. The method showed good reproducibility in terms of migration time with RSD < or = 0.90% for run-to-run and < or = 1.65 for day-to-day assessment.     

Scanning tunneling microscopy of sulfur and benzenethiol chemisorbed on Ru(0001) in 0.1 M HClO4

In situ scanning tunneling microscopy (STM) combined with linear sweep voltammetry was used to examine spatial structures of sulfur adatoms (SA) and benzenethiol (BT) molecules adsorbed on an ordered Ru(0001) electrode in 0.1 M HClO4. The Ru(0001) surface, prepared by mechanical polishing and electrochemical reduction at -1.5 V (vs RHE) in 0.1 M HClO4, contained atomically flat terraces with an average width of 20 nm. Cyclic voltammograms obtained with an as-prepared Ru(0001) electrode in 0.1 M HClO4 showed characteristics nearly identical to those of Ru(0001) treated in high vacuum. High-quality STM images were obtained for SA and BT to determine their spatial structures as a function of potential. The structure of the SA adlayer changed from (2 x mean square root of 3)rect to domain walls to (mean square root of 7 x mean square root of 7)R19.1 degrees and then to disordered as the potential was scanned from 0.3 to 0.6 V. In contrast, molecules of BT were arranged in (2 x mean square root of 3)rect between 0.1 and 0.4 V, while they were disordered at all other potentials. Adsorption of BT molecules was predominantly through the sulfur headgroup. Sulfur adatoms and adsorbed BT molecules were stable against anodic polarization up to 1.0 V (vs RHE). These two species were adsorbed so strongly that their desorption did not occur even at the onset potential for the reduction of water in 0.1 M KOH.     

On the Tacticity of Polynorbornenes with 5,6‐endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6‐endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and ¹³C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the ¹³C NMR spectra when the substituents are electron‐withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ε_d, was linearly related to the Hammett constant σ. Polynorbornenes with electron‐withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.     

Metastability of Ginzburg-Landau model with a conservation law

The hydrodynamics of Ginzburg-Landau dynamics has previously been proved to be a nonlinear diffusion equation. The diffusion coefficient is given by the second derivative of the free energy and hence nonnegative. We consider in this paper the Ginzburg-Landau dynamics with long-range interactions. In this case the diffusion coefficient is nonnegative only in the metastable region. We prove that if the initial condition is in the metastable region, then the hydrodynamics is governed by a nonlinear diffusion equation with the diffusion coefficient given by the metastable curve. Furthermore, the lifetime of the metastable state is proved to be exponentially large.