Synthesis and properties of new biotin compounds containing hexyltriethylene glycol chain

The synthesis of a new halogenide containing hexyltriethylene glycol chain functionalized with biotin is reported. The general possibility of this linker to use as the building block for biotinylated compounds syntheses is demonstrated. Two biotinylated esters with different properties for useful surface modification and as fluorescence probes for proteins marking were synthesized. The properties of mentioned compounds were investigated by using surface plazmon resonance ellypsometry and fluorescence spectroscopy.     

Algebraic approach for the exploration of the onset of chaos in discrete nonlinear dynamical systems

An algebraic approach based on the rank of a sequence is proposed for the exploration of the onset of chaos in discrete nonlinear dynamical systems. The rank of the partial solution is identified and a special technique based on Hankel matrices is used to decompose the solution into algebraic primitives comprising roots of the modified characteristic equation. The distribution of roots describes the dynamical complexity of a solution and is used to explore properties of the nonlinear system and the onset of chaos.     

Spontaneous Bi-modification of polycrystalline Pt electrode: fabrication, characterization, and performance in formic acid electrooxidation

Spontaneous modification of polycrystalline Pt by irreversibly adsorbed bismuth was performed in BiCl₃ solution in concentrated hydrochloric acid under open-circuit conditions. After spontaneous modification, followed by extensive rinsing with water and drying, the surface was characterized using X-ray photoelectron spectroscopy and electrochemistry. Bi-oxy(chloride), oxide species, and metallic Bi were found at a submonolayer coverage on the Pt surface after spontaneous modification. The electrochemical response of Bi-modified polycrystalline Pt electrode in sulfuric acid solution exhibits a complex multi-peak feature, which is resulting in about constant redox charge (Bi species coverage) in the potential region from 0 to 0.9 V (vs. a standard hydrogen electrode). The spontaneously Bi-modified Pt catalyst in model studies exhibits a superior activity towards formic acid oxidation at fuel cell anode relevant potentials. The catalytic effect of bismuth oxy-species is explained in terms of both inhibition of CO_ad formation and oxidation of CO_ad in reaction with Bi-oxy-species.     

Probing of lipase activity at air/water interface by sum-frequency generation spectroscopy

The infrared-visible sum-frequency generation (SFG) vibrational spectroscopy was used to probe enzymatic activity of Thermomyces lanuginosus lipase (TLL) at air/water interface. A monolayer of amphiphilic O-palmitoyl-2,3-dicyanohydroquinone (PDCHQ), containing target ester group and two CN groups serving as vibrational markers, was utilized as an enzyme substrate. SFG data revealed the detailed molecular scale structure and properties of the PDCHQ layer at the interface. In particular, we demonstrate that hydrophilic headgroup of PDCHQ is mainly in the form of an oxyanion, and the enzyme-induced cleavage of the ester bond could be spectroscopically monitored by the disappearance of the intense C tripple bond N resonance at 2224 cm(-1). The enzymatic nature of the ester bond cleavage was confirmed by the control experiments with deactivated S146A mutant variant of TLL. By comparing action of wild type (WT) TLL and its inactive S146A mutant, it was shown that two effects take place at the interface: disordering of the lipid monolayer due to the adsorption of enzyme and enzymatic cleavage of the ester bond. The concentration of enzyme as low as 10 nM could be easily sensed by the SFG spectroscopy. We present spectroscopic evidence that upon hydrolysis one of the products, 2,3-dicyanohydroquinone, leaves the surface, while the other, palmitic acid, remains at air/water interface in predominantly undissociated form with the mono-hydrogen-bonded carbonyl group. Strong amide I (1662 cm(-1)) and amide A (3320 cm(-1)) SFG signals from TLL suggest that enzyme molecules position themselves at air/water interface in an orderly fashion. Presented work demonstrates the potential of SFG spectroscopy for in situ real-time monitoring of enzymatic processes at air/water interface.     

The Effect of Anions and pH on the Activity and Selectivity of an Annealed Polycrystalline Au Film Electrode in the Oxygen Reduction Reaction-Revisited

Aiming at a better understanding of correlations between the activity and selectivity of Au electrodes in the oxygen reduction reaction (ORR) under controlled transport conditions, we have investigated this reaction by combined electrochemical and in situ FTIR measurements, performed in a flow cell set-up in an attenuated total reflection (ATR) configuration in acid and alkaline electrolytes. The formation of incomplete reduction products (hydrogen peroxyde/peroxyls) was detected by a collector electrode, the onset of OH_ad formation was probed by bulk CO oxidation. Using an electroless-deposited, annealed Au film on a Si prism as working electrode and three different electrolytes for comparison (sulfuric acid, perchloric acid, sodium hydroxide solution), we could derive detailed information on the anion adsorption behavior, and could correlate this with the ORR characteristics. The data reveal pronounced effects of the anions and the pH on the ORR characteristics, indicated e. g., by a grossly different activity and selectivity for the 4-electron pathway to water/hydroxyls, with the onset ranging from ca. 1.0 V in alkaline electrolyte to 0.6 V in sulfuric acid electrolyte, and the selectivity for the 4-electron pathway ranging from 100 % (alkaline electrolyte, low overpotentials) to 40 % (acidic electrolytes, alkaline electrolyte at high overpotentials). In contrast, the effect of the ORR on the anion adsorption characteristics is small. Anion effects as well as correlations between anion adsorption and ORR are discussed.     

Algebraic operator method for the construction of solitary solutions to nonlinear differential equations

Solutions of the KdV equation are derived by the algebraic operator method based on generalized operators of differentiation. The algebraic operator method based on the generalized operator of differentiation is exploited for the derivation of analytic solutions to the KdV equation. The structure of solitary solutions and explicit conditions of existence of these solutions in the subspace of initial conditions are derived. It is shown that special solitary solutions exist only on a line in the parameter plane of initial and boundary conditions. This new theoretical result may lead to important findings in a variety of practical applications.     

Room Temperature COad Desorption/Exchange Kinetics on Pt Electrodes—A Combined In Situ IR and Mass Spectrometry Study

The room temperature desorption and exchange of CO in a saturated CO adlayer on a Pt electrode, at potentials far below the onset of oxidation, was investigated by isotope labeling experiments, using a novel spectroelectrochemical setup, which allows the simultaneous detection of adsorbed species by in situ IR spectroscopy and of volatile (side) products and reactants by online mass spectrometry under controlled electrolyte flow conditions. Time‐resolved IR spectra show a rapid, statistical exchange of pre‐adsorbed ¹³CO_ad by ¹²CO_ad in ¹²CO containing electrolyte; mass spectrometric data reveal first‐order exchange kinetics, with the rate increasing with CO partial pressure. The increasing CO_ad desorption rate in equilibrium with a CO containing electrolyte is explained by a combination of an increasing CO_ad coverage upon increasing the CO pressure, and a decrease of the CO adsorption energy with coverage, due to repulsive CO_ad–CO_ad interactions.     

The explosive divergence in iterative maps of matrices

The effect of explosive divergence in generalized iterative maps of matrices is defined and described using formal algebraic techniques. It is shown that the effect of explosive divergence can be observed in an iterative map of square matrices of order 2 if and only if the matrix of initial conditions is a nilpotent matrix and the Lyapunov exponent of the corresponding scalar iterative map is greater than zero. Computational experiments with the logistic map and the circle map are used to illustrate the effect of explosive divergence occurring in iterative maps of matrices.