Signed domination numbers of directed graphs

The concept of signed domination number of an undirected graph (introduced by J. E. Dunbar, S. T. Hedetniemi, M. A. Henning and P. J. Slater) is transferred to directed graphs. Exact values are found for particular types of tournaments. It is proved that for digraphs with a directed Hamiltonian cycle the signed domination number may be arbitrarily small.     

On the mechanism of rendering visible dislocations on the surface of iron crystals by anodic dissolving

The paper contains further results of studying dislocations rendered visible by anodic dissolving on the surface of single crystals of alpha-iron. The influence of the crystallographic orientation of the surface is investigated, the effect of carbon is confirmed and the anodic process is studied. The mechanism of dissolving of the crystal is given and a new more suitable method of rendering dislocations visible is derived.

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The author thanks F. Kroupa and J. Hejduk for critical remarks and discussion.     

The sub-structure of crystals of silicon-iron alloy

After electrolytic polishing and etching a network of boundaries between mosaic blocks was observed on the surface of single crystals of silicon-iron alloy prepared from the melt. Some of the boundaries are formed by a number of distinguishable pits, also found singly outside the boundary. An explanation is given on the basis of the conception that the pits are etched points of intersection of edge dislocations with the surface of the crystals.     

Bulky Barbiturates as Non-Toxic Ionic Dye Insulators for Enhanced Emission in Polymeric Nanoparticles

Bulky hydrophobic counterions (weakly coordinating anions) can insulate ionic dyes against aggregation-caused quenching (ACQ) and enable preparation of highly fluorescent dye-loaded nanoparticles (NPs) for bioimaging, biosensing and light harvesting. Here, we introduce a family of hydrophobic anions based on fluorinated C-acyl barbiturates with delocalized negative charge and bulky non-polar groups. Similarly to fluorinated tetraphenylborates, these barbiturates prevent ACQ of cationic dye alkyl rhodamine B inside polymer NPs made of biodegradable poly(lactic-co-glycolic acid) (PLGA). Their efficiency to prevent ACQ increases for analogues with higher acidity and bulkiness. Their structure controls dye-dye communication, yielding bright NPs with on/off switching or stable emission. They enhance dye encapsulation inside NPs, allowing intracellular imaging without dye leakage. Compared to fluorinated tetraphenylborates known as cytotoxic transmembrane ion transporters, the barbiturates display a significantly lower cytotoxicity. These chemically available and versatile barbiturate derivatives are promising counterion scaffolds for preparation of bright non-toxic fluorescent nanomaterials.     

Statistical description of the system electrons on the liquid helium surface

System of electrons on the liquid helium surface is considered. General methods for obtaining free energy functional for the systems in mean field approximation are developed. These methods applied for treating systems with particles arranged in a lattice. Thus obtained functional of free energy is analyzed. The localization distance for electron and conditions for existing square or triangular lattices as well as phase transition between them are obtained.     

Redox Properties of Novel Dinuclear Ni(II) Bis - Tetraazamacrocyclic Complex

Abstract

Dinuclear Ni(II) bis-tetraazamacrocyclic complex 1 with conjugated double bonds at deprotonated β-diimine linking group was characterized by ¹H NMR and cyclic voltammetry. Electrochemical studies indicated high stability of the mixed-valence (Ni^II- Ni^III) and (Ni^II- Ni^I) species, respectively. The main factor contributing to the stabilization of the mixed-valence states is the electronic delocalization through the system of the conjugated double bonds at the deprotonated β-diimine linking group. Complex 1 is the first example of dinuclear Ni(II) tetraazamacro-cyclic complex exhibiting two one-electron oxidation and two one electron reduction steps.     

Investigation of protein FTT1103 electroactivity using carbon and mercury electrodes. Surface-inhibition approach for disulfide oxidoreductases using silver amalgam powder

Recently, it was shown that electrochemical methods can be used for analysis of poorly water-soluble proteins and for study of their structural changes and intermolecular (protein–ligand) interactions. In this study, we focused on complex electrochemical investigation of recombinant protein FTT1103, a disulfide oxidoreductase with structural similarity to well described DsbA proteins. This thioredoxin-like periplasmic lipoprotein plays an important role in virulence of bacteria Francisella tularensis. For electrochemical analyses, adsorptive transfer (ex situ) square-wave voltammetry with pyrolytic graphite electrode, and alternating-current voltammetry and constant-current chronopotentiometric stripping analysis with mercury electrodes, including silver solid amalgam electrode (AgSAE) were used. AgSAE was used in poorly water-soluble protein analysis for the first time. In addition to basic redox, electrocatalytic and adsorption/desorption characterization of FTT1103, electrochemical methods were also used for sensitive determination of the protein at nanomolar level and study of its interaction with surface of AgSA microparticles. Proposed electrochemical protocol and AgSA surface-inhibition approach presented here could be used in future for biochemical studies focused on proteins associated with membranes as well as on those with disulfide oxidoreductase activity.