Solvent extraction studies using phosphonic acid monoesters

The extraction of radioactive^152–154Eu by ethyl hydrogen benzyl phosphonate (HEBP) and ethyl hydrogen benzoyl phosphonate (HEBOP) in n-hexane from an aqueous solution of ionic strength 0.1M (Na⁺, HClO₄) has been investigated at different temperatures and the thermodynamic functions evaluated. HEBOP was found to be more efficient than HEBP as extractant. In addition, the stability constant of the extracted complexes were determined.     

Commutativity of One Sided S- Unital Rings

In the present paper we extend some commutativity theorems for rings as follows: Let m > 1, n and k be fixed non- negative integers, and let R be a left or right s- unital ring satisfying the polynomial identity [xⁿ]y ? y^mx^k,x] = 0. Then R is commutative. Under appropriate conditions the commutativity of R has also been proved for the case m = 1.     

A utilization of properties of the discrete-time Riccati equation in stochastic realization theory

The problem of generating families of wide-sense, stochastic realizations of a discrete-time stationary stochastic process is considered. To do this, it is known that a Riccati equation has to be solved. In this paper, the non-Riccati algorithm of Lindquist and Kailath is used to generate families of realizations, the state covariances of which are totally ordered. Finally, the property of constant directions which the discrete-time Riccati equation enjoys is utilized to obtain families of realizations, the state covariances of which have the same value in certain directions.     

Activated nitriles in heterocyclic synthesis: Synthesis of 6-thiophen-2-yl and 6-furan-2-ylthiazolo[2,3—a]pyridine derivatives

A variety of new 6-thiophen-2-yl and 6-furan-2-ylthiazolo[2,3—a]pyridine derivatives could be prepared via the reaction of 2-functionally substituted methyl-2-thiazolin-4-one with cyanomethylenethiophen-2-yl and cyanomethylenefuran-2-yl derivatives. The structure of the reaction products was established based on spectral data.

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Aktivierte Nitrile in der Heterocyclen-Synthese: Die Synthese von 6-Thiophen-2-yl-und 6-Furan-2-yl-thiazolo[2,3—a]pyridin-Derivaten

Zusammenfassung Es konnte eine Reihe neuer 6-Thiophen-2-yl- und 6-Furan-2-yl-thiazolo-[2,3—a]pyridine über die Reaktion von 2-funktionell-substituierten Methyl-2-thiazolin-4-onen mit Cyanomethylenthiphen-2-yl bzw. Cyanomethylenfuran-2-yl-Derivaten hergestellt werden. Die Struktur der Reaktionsprodukte wurde mit spektroskopischen Methoden ermittelt.

     

Molecular dynamics simulation of cocaine binding with human butyrylcholinesterase and its mutants

Molecular dynamics (MD) simulations were carried out to study cocaine binding with wild-type human butyrylcholinesterase (BChE) and its mutants based on a recently reported X-ray crystal structure of human BChE. For each BChE-cocaine system, we simulated both the nonprereactive and prereactive complexes in water. Despite the significant difference found at the acyl binding pocket, the simulated structures confirm the fundamental structural and mechanistic insights obtained from earlier computational studies of wild-type BChE with cocaine based on a homology model, e.g. the rate-determining step for BChE-catalyzed hydrolysis of biologically active (-)-cocaine is the (-)-cocaine rotation in the active site from the nonprereactive BChE-(-)-cocaine complex to the prereactive complex. It has been demonstrated that the MD simulations on both the nonprereactive and prereactive BChE-cocaine complexes can clearly reveal whether specific mutations produce the desired BChE-(-)-cocaine binding structures in which the (-)-cocaine rotation is less hindered while the required prereactive BChE-(-)-cocaine binding is maintained. Based on the MD simulations, both A328W/Y332A and A328W/Y332G BChE's are expected to have catalytic activity for (-)-cocaine hydrolysis higher than that of wild-type BChE and the activity of A328W/Y332G BChE should be slightly higher than that of A328W/Y332A BChE due to the less-hindered (-)-cocaine rotation in the mutant BChE's. However, the less-hindered (-)-cocaine rotation is only a necessary condition for a higher activity mutant BChE. The (-)-cocaine rotation is also less hindered in A328W/Y332A/Y419S BChE, but (-)-cocaine binds with A328W/Y332A/Y419S BChE in a way that is not suitable for the catalysis. Thus, A328W/Y332A/Y419S BChE is expected to lose the catalytic activity. The computational predictions were confirmed by our experimental kinetic data, demonstrating that the MD simulation-based computational protocol used in this study is reliable in prediction of the catalytic activity of BChE mutants for (-)-cocaine hydrolysis.     

Thermal studies on some reactions in the solid-state

The solid-state thermal reactions of 2,6-diamino-4-chloropyrimidine, 3,3-dimethoxybenzidine and of thiosemicarbazide with each of 2-hydroxy-1-naphthaldehyde and 2,4-dihydroxybenzaldehyde in a mole ratio of 1∶1 produced (1+1) condensation products (‘half units’). These solid state reactions have been studied by means of differential thermal analysis (DTA). The products of the reactions were identified using elemental analysis and IR spectroscopy. Some kinetic parameters such as orders and activation energies of the reactions were evaluated form the DTA curves.     

Studies on the thermal behaviour of mono- and di-imines of some diaminonaphthalenes

The mono- and di-imines of some diaminonaphthalenes were prepared using a solid solid reaction technique. Their structures were studied using elemental analysis, infrared and electronic spectra. The thermal behaviour of the obtained compounds and their solid solid preparation reactions have also been studied. The energies of activation as well as the reaction orders of those reactions were determined.     

Equilibrium, kinetic and solvent effect studies on the reactions of [RuIII(Hedta)(H2O)] with thiols

The interaction of [Ru(III)(edta)(H(2)O)](-) with a series of selected thiols having extra functional groups was investigated potentiometrically and kinetically. The pK(a) values of the uncoordinated carboxylic acid group and coordinated water molecule are 3.12 and 7.41, respectively, in aqueous solution at 25 degrees C and 0.1 M ionic strength. The formation constants of the complexes were determined in the pH range 3-9, and the concentration distribution of the various complex species was evaluated as a function of pH. The effect of dioxane on the pK(a) values of [Ru(III)(Hedta)(H(2)O)] and the formation constants of the corresponding thiol complexes is presented. The study also provides mechanistic information on the reaction of [Ru(III)(edta)(H(2)O)](-) with the thiols. The low values of DeltaH(not equal) and negative values of DeltaS(not equal) and DeltaV(not equal) for the substitution reactions of [Ru(III)(edta)(H(2)O)](-) clearly support the associative character of the substitution process.     

An abstract Dirichlet problem in the Hilbert space

In the present paper, we consider an abstract partial differential equation of the form $\frac{{\partial ^2 u}}{{\partial t^2 }} - \frac{{\partial ^2 u}}{{\partial x^2 }} + A\left( {x,t} \right)u = f\left( {x,t} \right)$ , where $\left\{ {A\left( {x,t} \right):\left( {x,t} \right) \in \bar G} \right\}$ is a family of linear closed operators and $\bar G = G \cup \partial G,G$ is a suitable bounded region in the (x, t)-plane with boundary?G. It is assumed thatu is given on the boundary?G. The objective of this paper is to study the considered Dirichlet problem for a wide class of operatorsA(x, t). A Dirichlet problem for non-elliptic partial differential equations of higher orders is also considered.