Spectrophotometric Determination of the Stability Constants of Co(II) and DPKBH (DI-2-Pyridyl Ketone Benzoylhydrazone)

Abstract

In order to have more information about the thermodynamic properties of the complexes formed by Cobalt(II) and DPKBH (di-2-pyridyl ketone benzoylhydrazone) and for the development of speciation methods for cobalt, the respective stepwise formation constants were determined in ethanolic solution 50% (V/V), at pH 5.3 and 25.0°C. The spectrophotometric method of corresponding solutions was used and the following overall formation constants were obtained: β₁ = 5.305 × 10⁶ M^?1 and β₂ = 8.476 × 10¹⁰ M^?2. The molar absorptivities of the 1:1 (ε₁) and 1:2 (ε₂) complexes (Co(II):DPKBH) were determined to be 4.475 × 10 and 2.994 × 10 (M^?1cm^?1), respectively. The calculated distribution diagram shows the percentage of the species at equilibrium as a function of the free DPKBH concentration.     

Synthesis of New Cytosine and Thymine Derivatives of Potential Immunomodulatory Activity

The synthesis and the main chemical and physical properties of some N¹alkylated cytosines and thymines are described.     

Fractal Percolation,Porosity, and Dimension

We study the porosity properties of fractal percolation sets \(E\subset \mathbb {R}^d\). Among other things, for all \(0<\varepsilon <\tfrac{1}{2}\), we obtain dimension bounds for the set of exceptional points where the upper porosity of E is less than \(\tfrac{1}{2}-\varepsilon \), or the lower porosity is larger than \(\varepsilon \). Our method works also for inhomogeneous fractal percolation and more general random sets whose offspring distribution gives rise to a Galton–Watson process.     

Permethylated β-cyclodextrin/pesticide complexes: X-ray structures and thermogravimetric assessment of kinetic parameters for complex dissociation

The X-ray crystal structures of the inclusion complexes formed between three pesticides (two organophosphorus insecticides and one chloroacetanilide herbicide) and permethylated β-cyclodextrin (TRIMEB) are reported. The complexes TRIMEB–fenitrothion (1), TRIMEB–fenthion (2) and TRIMEB–acetochlor (3) are members of a commonly occurring isostructural series. The mode of inclusion of the two organophosphate insecticides is very similar, while the acetochlor molecule, which is structurally quite distinct from the two insecticide molecules, adopts a somewhat different position within the TRIMEB cavity. In addition to the structural elucidation of these complexes, their thermal behaviour was investigated using isothermal and non-isothermal thermogravimetry. The isothermal results showed that the dissociation of the guest molecules from the TRIMEB cavities can best be described by two mechanisms, namely a first-order reaction model and a three-dimensional diffusion model. Both the isothermal and non-isothermal methods allowed the determination of the activation energies of the guest loss process for each complex.     

Termite Trail Attractants: New Syntheses of Racemic (E)-α-, (Z)-α- and β-Bisabolenes

Racemic (E)-α-bisabolene (E)(1) was synthetized starting from 4-methyl-3-cyclohexenecarboxylic acid (3) by a reaction sequence involving the Pd(0)-catalyzed cross-coupling reaction between the (E)-2-methyl-1-alkenyltrimethylstannane 8 and 3-methyl-2-buten-1-yl acetate (9). Three different procedures, in which a common precursor was used as key intermediate, were tested for the synthesis of racemic (Z)-α-bisabolene (Z)(1). The best one, which involved the reaction between bromide 18 and lithium dialkenylcuprate 19, afforded a mixture of (Z)- and (E)-1 in a 93 : 7 molar ratio, respectively. Finally, racemic β-bisabolene (2) was synthetized by a simple reaction sequence involving the Zr-promoted methylenation of ketone 22 prepared from 3.     

InCl3-assisted one-pot synthesis of 1-aminocarbazoles

A novel InCl₃-mediated one-pot reaction leading to 1-aminocarbazoles is reported. Starting from easily available 2-acetyl-1H-indole, the reaction involves the alkylation of C-3 with a prop-2-yn-1-ol followed by a domino aminobenzannulation reaction in the presence of a secondary amine. The indium salt is most likely involved as catalyst in all three steps of the one-pot reaction. Starting from 2-acetyl-1H-indole and a series of prop-2-yn-1-ols and secondary amines a small library of products has been obtained.     

Interactions of Proteins with the Acidic Components of the Electrolyte Solution and Their Role in the Performance of Separations by CZE

This paper reports the results of a study performed to investigate the dependence of the performance of protein separation by capillary zone electrophoresis (CZE) on the anionic component of the electrolyte solutions consisting of 20 mM N,N,N′,N′-tetramethyl-1,3-butanediamine (TMBD) titrated to either pH 4.0 or pH 6.5 with either a monoprotic or a polyprotic acid. With the exception of hydrochloric acid, the acids were selected among those commonly used as the constituents of the solutions employed for protein analysis by either HPLC or CZE. TMBD was chosen for its effectiveness at preventing the interactions of proteins with the inner wall of bare fused-silica capillaries. The performance of separations was evaluated using four basic model proteins having pI value and molecular mass ranging from 9.5 to 11.0 and from 12,400 to 25,000 Da, respectively. It is shown that the different acids used as the components of the background electrolyte solutions, all containing the same concentration of TMBD, affect to different extents both migration time and peak shape of the tested proteins. The performance displayed by the BGE containing phosphate ions is enhanced using TMBD in combination with diethylenetriamine, an aliphatic vicinal triamine having effective buffering capacity at pH 4.0 and capability at minimizing protein–capillary wall interactions. The reported experimental evidences are discussed based on the possible interactions that the phosphate ions are known to establish with both the protein molecules and the surface of bare fused-silica capillaries.