Electroreduction of oxygen on metal (Au, Cu)-ion exchanger nanocomposites in the diffusion mode

The kinetics of the electroreduction of oxygen in the diffusion mode on single granules of nanocomposites consisting of dispersed particles of the metal (Au, Cu) of the nanometer size and macroporous sulfonic cation-exchanger matrix KU-23 is studied. No noticeable effect of the factors of size of the metal component and ion exchange over the matrix on the external diffusion current of oxygen reduction is observed. The drop in current observed in a number of cases is due to a transition to the mixed external and internal kinetics as a result of the macroporous structure of the matrix and the chemical activity of nanoparticles of the metal component.     

De novo sequencing of peptides secreted by the skin glands of the Caucasian Green Frog Rana ridibunda

Amphibian skin glands are known to secrete various types of bioactive peptides. The array of these peptides is specific for every frog species. The present research deals with the identification of peptides isolated from the skin secretion of the Marsh frog R. ridibunda inhabiting the Kolkhida Canyon of the Caucasian region. The research is based on comprehensive high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) analysis of intact and chemically modified peptides. In particular, an oxidation procedure was applied directly to the crude skin secretion to open S--S loops whereas N-terminal acetylation was additionally carried out for one individual peptide. Sequences were determined by manual interpretation of electron capture dissociation (ECD) and collisionally induced dissociation (CID) tandem mass spectra. A total of 29 peptides were identified in the skin secretion of the Caucasian Marsh frog. The peptide profile is represented with disulfide-containing peptides belonging to the brevinin, esculentin and ranatuerin families, neuropeptides of the bradykinin and bombesin families. Two identified peptides belonging to the ranatuerins are the first peptides of this family discovered in the skin secretions of European frogs. Ten of the identified peptides coincide with those reported earlier for the European Edible frog. Another ten are identical to those found in R. ridubunda from the Moscow region. This fact verifies the described method as being an efficient analytical tool to compare intra- and interspecific variabilities.     

Limiting current of oxygen reduction on copper-ion exchanger nanocomposite

The kinetics of the reduction of oxygen on a granular copper-containing electron-ion exchanger, or a nanocomposite consisting of an ion-exchanging resin matrix and a nanodispersed copper bulk distributed in it, used for the deep removal of oxygen from water and gases, is investigated. It is established that reduction of oxygen with the cathodically polarized nanocomposite proceeds in two stages: external diffusion and internal diffusion. It is shown that the external diffusion transfer of oxygen is maintained by the electric current of the cathodic direction. Its contribution is prevalent under conditions of the localization of copper nanoparticles on a grain’s surface. It is established that the limiting current corresponds to the reduction rate of oxygen. It is noted that during the bulk distribution of copper nanoparticles in the grain pores, the contribution of the stage of the internal diffusion transfer of oxygen increases. It is shown that oxygen reduction rate exceeds the limiting external-diffusion current. The joint occurrence of both stages ensures a generally high oxygen reduction rate.     

Probing the mechanisms of ambient ionization by laser-induced fluorescence spectroscopy

The ionization mechanisms of several atmospheric pressure ion sources based on desorption and ionization of samples deposited on a surface were studied. Home-built desorption electrospray ionization (DESI), laserspray ionization (LSI), and atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) sources were characterized using low-molecular-weight compounds, in particular fluorescent dyes. Detection of the desorbed and ionized species was performed by laser-induced fluorescence and ion cyclotron resonance mass spectrometry. The dependences of the signal intensities on various experimental parameters were studied. The data obtained reveals common features, such as formation of solvated species and clusters in the ionization processes, in all of the techniques considered.     

Resistive Switching of Memristors Based on Stabilized Zirconia by Complex Signals

Physics of the Solid State - The specific features of resistive switching, which was initiated by triangular pulses with a high-frequency sine signal imposed on them, in experimental memristor...