The oxidation and reduction behavior of nitrite at carbon nanotube powder microelectrodes

Carbon nanotube electrodes were fabricated using powder microelectrode method, and the carbon nanotube powder microelectrodes (CNTPMEs) were characterized by the electro-oxidation and electro-reduction of nitrite. It was found that the kinetics of oxidation and reduction were greatly improved at CNTs compared with that at conventional graphite, indicating that CNTs could catalyze the electrochemical process of nitrite. The kinetic parameters of these process at CNTs were calculated, i.e. k was 0.593 cm s⁻¹, and (1-α)n_α was 0.501±0.018 for the nitrite oxidation. This CNTPME was also used as a nitrite carbon nanotube sensor, and the results showed that the detection limit was 8 μM.     

Adsorption of formaldehyde on Pt(111) and Pt(100) electrodes: cyclic voltammetry and scanning tunneling microscopy

The adsorption of formaldehyde (HCHO) on Pt(111) and Pt(100) electrodes was examined by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in 0.1 M HClO(4). The extent of HCHO adsorption at both Pt electrodes was evaluated by comparing the CVs, particularly for the hydrogen adsorption and desorption between 0.05 and 0.4 V, obtained in 0.1 M HClO(4) with and without HCHO. The adsorption of HCHO on these Pt electrodes was significant only when [HCHO] >/= 10 mM. Adsorbed organic intermediate species acted as poisons, blocking Pt surfaces and causing delays in the oxidation of HCHO. Compared to Pt(111), Pt(100) was more prone to poisoning, as indicated by a 200 mV positive shift of the onset of HCHO oxidation. However, Pt(100) exhibited an activity 3 times higher than that of Pt(111), as indicated by the difference in peak current density of HCHO oxidation. Molecular resolution STM revealed highly ordered structures of Pt(111)-( radical7 x radical7)R19.1 degrees and Pt(100)-( radical2 x radical2) in the potential region between 0.1 and 0.3 V. Voltammetric measurements further showed that the organic poisons produced by HCHO adsorption behaved differently from the intentionally dosed CO admolecules, which supports the assumption for the formation of HCO or COH adspecies, rather than CO, as the poison. On both Pt electrodes, HCHO oxidation commenced preferentially at step sites at the onset potential of this reaction, but it occurred uniformly at the peak potentials.     

Solid-state NMR yields structural constraints on the V3 loop from HIV-1 Gp120 bound to the 447-52D antibody Fv fragment

Solid-state NMR measurements were performed on the complex of an 18-residue peptide derived from the V3 loop sequence of the gp120 envelope glycoprotein of the HIV-1 MN strain with Fv fragments of the human anti-gp120 monoclonal antibody 447-52D in a frozen glycerol/water solution. The peptide was uniformly (15)N- and (13)C-labeled in a 7-residue segment containing the conserved GPGR motif in the epitope. (15)N and (13)C NMR chemical shift assignments for the labeled segment were obtained from two-dimensional (13)C-(13)C and (15)N-(13)C magic-angle spinning NMR spectra. Reductions in (13)C NMR line widths and changes in chemical shifts upon complex formation indicate the adoption of a well-defined, antibody-dependent structure. Intramolecular (13)C-(13)C distances in the complex, which constrain the peptide backbone and side chain conformations in the GPGR motif, were determined from an analysis of rotational resonance (RR) data. Structural constraints from chemical shifts and RR measurements are in good agreement with recent solution NMR and crystallographic studies of this system, although differences regarding structural ordering of certain peptide side chains are noted. These experiments explore and help delineate the utility of solid state NMR techniques as structural probes of peptide/protein complexes in general, potentially including membrane-associated hormone/receptor complexes.     

Thermal- and photo-induced transformations of N-aryl-N-nitrosohydroxylamine ammonium salts to azoxy compounds

Heating of an ethanolic solution containing N-aryl-N-nitrosohydroxylamine ammonium salts at 78 °C produced the desired azoxy compounds in 80–93% yields. Furthermore, irradiation with UV light (λ≥300 nm) of ethanolic solutions of those ammonium salts at room temperature also provided the desired azoxy compounds in 51–72% yields.     

On the Validity of the Definition of Angular Momentum in General Relativity

We exam the validity of the definition of the ADM angular momentum without the parity assumption. Explicit examples of asymptotically flat hypersurfaces in the Minkowski spacetime with zero ADM energy–momentum vector and finite non-zero angular momentum vector are presented. We also discuss the Beig–Ó Murchadha–Regge–Teitelboim center of mass and study analogous examples in the Schwarzschild spacetime.     

Fixed Energy Universality for Generalized Wigner Matrices

We prove the Wigner‐Dyson‐Mehta conjecture at fixed energy in the bulk of the spectrum for generalized symmetric and Hermitian Wigner matrices. Previous results concerning the universality of random matrices either require an averaging in the energy parameter or they hold only for Hermitian matrices if the energy parameter is fixed. We develop a homogenization theory of the Dyson Brownian motion and show that microscopic universality follows from mesoscopic statistics.© 2016 Wiley Periodicals, Inc.     

A Macrocyclic Ruthenium(III) Complex Inhibits Angiogenesis with Down‐Regulation of Vascular Endothelial Growth Factor Receptor‐2 and Suppresses Tumor Growth In Vivo

A macrocyclic ruthenium(III) complex [Ru^III(N₂O₂)Cl₂]Cl ( Ru‐1 ) is reported as an inhibitor of angiogenesis and an anti‐tumor compound. The complex is relatively non‐cytotoxic towards endothelial and cancer cell lines in vitro, but specifically inhibited the processes of angiogenic endothelial cell tube formation and cancer cell invasion. Moreover, compared with known anti‐cancer ruthenium complexes, Ru‐1 is distinct in that it suppressed the expression of vascular endothelial growth factor receptor‐2 (VEGFR2), and the associated downstream signaling that is crucial to tumor angiogenesis. In addition, in vivo studies showed that Ru‐1 inhibited angiogenesis in a zebrafish model and suppressed tumor growth in nude mice bearing cancer xenografts.     

From Riemann and Kodaira to Modern Developments on Complex Manifolds

We survey the theory of complex manifolds that are related to Riemann surface, Hodge theory, Chern class, Kodaira embedding and Hirzebruch–Riemann–Roch, and some modern development of uniformization theorems, Kähler–Einstein metric and the theory of Donaldson–Uhlenbeck–Yau on Hermitian Yang–Mills connections. We emphasize mathematical ideas related to physics. At the end, we identify possible future research directions and raise some important open questions.     

Molecular mechanisms of crystallization and defect formation

Using the atomic force microscope (AFM) in situ during the crystallization of the protein apoferritin, we show that for this system the kink density along the steps is an equilibrium property that, multiplied by the frequency of molecular attachment, fully determines the propagation of growth steps. The intermolecular bond energy is 3.2k(B)T. Point defects are nonequilibrial and are caused by incorporation of impurity molecules, and replicate in subsequent layers due to the strain they cause. Using single-molecule manipulation with the AFM tip, the defects can be healed to restore the regular lattice.     

Double phase conjugation with orthogonally polarized beams in a BaTiO(3) crystal

We have demonstrated experimentally the simultaneous self-conjugation of extraordinarily and ordinarily polarized light waves (lambda=514 nm), with the polarization state preserved, in a Ce:BaTiO(3) crystal. Conjugate o waves originate from coupling between o and e waves by means of a circular photogalvanic effect. The conjugator also takes advantage of the Ce:BaTiO(3) crystal, for which it is easy to generate an extraordinary conjugate beam by photorefractive backscattering. This beam of light is necessary for double phase conjugation.