The kinetics and mechanism of the oxidation of DL ethionine and thiourea by potassium ferrate

The kinetics of the reaction between ethionine and thiourea were investigated under pseudo and non-pseudo-first-order conditions. Ethionine was oxidized to the sulfoxide within 500 s and thiourea was oxidized to urea within 10 s. Above a pH of ca. 8.5 the reaction was first-order in the concentration of the organosulfur compound, the hydrogen ions and the ferrate ions, whereas, below this pH, the kinetics were independent of the hydrogen ion concentration. A possible mechanism for both compounds is initial protonation of the ferrate ion followed by the two electron rate-determining step of addition of oxygen to the organosulfur compound. The kinetic parameters for ethionine compare favorably with those for similar compounds, whereas thiourea tends to be more active. The rate constant for the rate-determining step is 4.1 × 10² M^–1 s^–1 for ethionine and 4.1 × 10³ M^–1 s^–1 for thiourea.     

Exponential Stability for Discrete Time Linear Equations Defined by Positive Operators

In this paper the problem of exponential stability of the zero state equilibrium of a discrete-time time-varying linear equation described by a sequence of linear positive operators acting on an ordered finite dimensional Hilbert space is investigated. The class of linear equations considered in this paper contains as particular cases linear equations described by Lyapunov operators or symmetric Stein operators as well as nonsymmetric Stein operators. Such equations occur in connection with the problem of mean square exponential stability for a class of difference stochastic equations affected by independent random perturbations and Markovian jumping as well us in connection with some iterative procedures which allow us to compute global solutions of discrete time generalized symmetric or nonsymmetric Riccati equations. The exponential stability is characterized in terms of the existence of some globally defined and bounded solutions of some suitable backward affine equations (inequalities) or forward affine equations (inequalities).     

Kinetic analysis of isothermal decomposition of 2,4-dinitrophenylhydrazine using differential scanning calorimetry

Differential scanning calorimetry was used to study the thermal decomposition of 2,4-dinitrophenylhydrazine (DNPH) in isothermal regime. The DSC curves were carried out at several constant temperatures lower than the melting temperature. The standard isoconversional analysis of the obtained curves suggests an autocatalytic decomposition mechanism. This mechanism is also supported by the temperature dependence of the observed induction periods.     

Input-output admissibility and exponential trichotomy of difference equations

We propose a new method for the study of the asymptotic behavior of difference equations in infinite-dimensional spaces, providing characterizations for the property of uniform exponential trichotomy. We deduce the structure of the stable, unstable and bounded subspace and prove the uniqueness of the projection families. We introduce a new admissibility concept with respect to a discrete input-output system and prove that this is a necessary and sufficient condition for the existence of uniform exponential trichotomy. Throughout the paper, there is no assumption on the coefficients and the obtained results are applicable to any class of difference equations.     

Influence of the Substitution Degree on the Dilute Solution Properties of Cellulose Acetate

Modification of intrinsic viscosity, coil size, and preferential adsorption coefficients of cellulose acetate with various substitution degrees in single and mixed solvents was investigated at different temperatures. Miscibility is attained by specific competitive interactions between the solvent-solvent and solvent-polymer systems, which induce modification in the composition of solvent mixtures both inside and outside the polymer coil. The conformational properties in solutions were correlated with the preferential adsorption coefficients, known as depending on the interaction parameters of the polymer/solvent/solvent systems. The intermolecular interactions observed in the cellulose acetate solutions assure the main properties necessary for obtaining membranes with different applications.     

Effective Use of Empirical Data for Virtual Screening against APJR GPCR Receptor

Alzheimer’s disease is a neurodegenerative disorder incompatible with normal daily activity, affecting one in nine people. One of its potential targets is the apelin receptor (APJR), a G-protein coupled receptor, which presents considerably high expression levels in the central nervous system. In silico studies of APJR drug-like molecule binding are in small numbers while high throughput screenings (HTS) are already sufficiently many to devise efficient drug design strategies. This presents itself as an opportunity to optimize different steps in future large scale virtual screening endeavours. Here, we ran a first stage docking simulation against a library of 95 known binders and 3829 generated decoys in an effort to improve the rescoring stage. We then analyzed receptor binding site structure and ligands binding poses to describe their interactions. As a result, we devised a simple and straightforward virtual screening Stage II filtering score based on search space extension followed by a geometric estimation of the ligand—binding site fitness. Having this score, we used an ensemble of receptors generated by Hamiltonian Monte Carlo simulation and reported the results. The improvements shown herein prove that our ensemble docking protocol is suited for APJR and can be easily extrapolated to other GPCRs.     

Almost-periodic solutions for Riccati equations of stochastic control

We consider an average quadratic cost criteria for affine stochastic differential equations with almost-periodic coefficients. Under stabilizability and detectability conditions we show that the Riccati equation associated with the quadratic control problem has a unique almost-periodic solution. In the periodic case the corresponding result is proved in [4].     

On nonuniform exponential dichotomy of evolution operators in Banach spaces

The problem of nonuniform exponential dichotomy of evolution operators in Banach spaces is considered. Connections between this concept and admissibility of the pair (C ₀,C ₀) are established. Generalizations to the nonuniform case of some results of Van Min, Räbiger and Schnaubelt ([MRS]) are obtained. It is shown that an implication from the uniform case is not true for nonuniform exponential dichotomy. The results are applicable for general time-varying linear equations with unbounded coefficients in Banach spaces.