Reactivity of hydroxo palladium and platinum complexes towards N-substituted salicylaldimines and β-ketoimines

The binuclear hydroxo complexes [{M(C6F5)2(OH)}2]2–(M=PdandPt)reactwithN-substituted salicylaldimines (HSal=NR) or -ketoimines (RN=CMeCH2COR) to give the corresponding N-substituted salicylaldiminato or -ketoiminato mononuclear complexes, [M(C6F5)2(Sal=NR)]– (M=Pd or Pt; R= Me, Et, Ph, o-MeC6H4, p-MeC6H4 or p-ClC6H4) or [(C6F5)2M{N(R)C(CH3)CHC(O)R}]– (M=Pd or Pt; R=o-MeC6H4 or p-MeC6H4; R=Me or Ph), respectively. The complexes have been characterized by partial elemental analyses, conductance measurements and spectroscopic (i.r. and 1H and 19F- n.m.r.) methods.     

Determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with sepiolite

Summary A method is described for the determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with 10% (w/w) sepiolite. Preconcentration was carried out under open circuit conditions in 0.01 mol/l acetic acid/potassium acetate medium at pH 5.3 over 10 min, recording the voltammogram in 0.01 mol/l of KH₂PO₄/K₃PO₄ at pH 12. This led to the appearance of a peak at –1.32 V against SCE at 40 mVs^–1 and a pulse amplitude of 100 mV. Under these conditions determination limits of 45 ng ml^–1 were achieved. The method was applied to the determination of tetramethrin in soil and water samples.

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Bestimmung von Tetramethrin (Neo-Pynamin) durch Differential-Puls-Voltammetrie unter Verwendung einer mit Sepiolit modifizierten Kohlepaste-Elektrode

     

An azamacrocyclic receptor as efficient polytopic chiral solvating agent for carboxylic acids

The efficient use of a polyazamacrocycle as chiral solvating agent (CSA) for the determination of the enantiomeric excess of different carboxylic acids has been studied. All the data agree with the formation of multimolecular diastereomeric complexes in solution, which render good splitting of the NMR signals for the enantiomers of the acids (up to ΔΔδ = 0.20 ppm) using a small amount (even 0.125 equiv) of the receptor.     

Comparative use of solvent‐free KF‐A12O3 and K2CO3 in acetone in the synthesis of quinoxaline 1,4‐dioxide derivatives designed as antimalarial drug candidates

In this paper we describe two new basic conditions for the synthesis of quinoxaline 1,4‐dioxide derivatives in moderate to good yields. These conditions, exemplified by the use of K₂C0₃ in acetone or KF/A1₂0₃ in the absence of an organic solvent, were reproducible and applicable to the synthesis of 2‐(carboethoxy)‐3‐phenylquinoxaline 1,4‐dioxide derivatives substituted in position 4 with electron‐donating or electron‐withdrawing groups.     

Non-covalent allosteric regulation of capsule catalysis

Allosteric regulation is an essential biological process that allows enzymes to modulate their active site properties by binding a control molecule at the protein exterior. Here we show the first example of capsule catalysis in which activity is changed by exotopic binding. This study utilizes a simple Pd₂L₄ capsule that can partition substrates and external effectors with high fidelity. We also present a detailed, quantitative understanding of how effector interactions alter both substrate and transition state binding. Unlike other allosteric host systems, perturbations are not a consequence of large mechanical changes, rather subtle electronic effects resulting from weak, non-covalent binding to the exterior surface. This investigation paves the way to more sophisticated allosteric systems.

External effector binding allosterically regulates the catalytic properties of a simple Pd₂L₄ capsule.     

Liposomal benznidazole: a high-performance liquid chromatographic determination for biodistribution studies

In this work, an isocratic high-performance liquid chromatographic method for quantitation of liposomal benznidazole (BNZ) in biological tissues is presented. The method comprises protein precipitation together with an efficient extraction of bulk or liposomal BNZ with acetonitrile-dimethylsulfoxide (1:1, v/v) at a 2:1 (extraction solvent-tissue matrix, v/v or /vw) ratio; the process is completed by a final precipitation with trichloroacetic acid. The resultant supernatants are assayed chromatographically using a Kromasil C18 (25- x 0.4-cm i.d., 100 A, 5- microm particle size), with an isocratic mobil phase consisting of acetonitrile-water (40:60, v/v), a flow rate of 0.9 mL/min, and detected at 324 nm. Bulk BNZ is used as a reference standard for the analysis of samples containing liposomal BNZ. The assay is linear over a concentration range of 0.75 (the lowest quantity of analyte determined with precision and accuracy of >or= 20%) to 25 microg/mL-g in all liquid and solid matrices. Within-day precision is better than 6.4% in plasma and 8.6% in liver, the same for the two assayed concentrations. Between-day precision is 5.4% and 12.3% in plasma and 9% and 6.9% in liver for the two assayed concentrations, respectively. The absolute recoveries range between 70% and 97%. Therefore, the method is accurate and precise to be employed for detection of minor quantities of liposomal BNZ in biological tissues.     

New alternatives for high specific area γ-Al2O3 synthesis

-Al₂O₃ was synthesized from trisec-butoxide by the sol-gel method. pH was varied during reaction and solvents of different polarity were used. Solids with specific areas, greater than 200 m²/g, were obtained, which depend directly on the reaction parameters.

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-Al₂O₃ - -. . pH . , 200 ²/ .

     

4th order derivative spectrophotometric determination of quinine in soft drinks

A method is developed for the 4rd order derivative spectrophotometric determination of down to 1–6 g/ml of quinine. This method has been applied to its determination in soft drinks. Comparison are made between this method and a spectrofluorimetric method.     

Syntheses and X-ray characterization of metal complexes with the pentadentate thiosemicarbazone ligand bis(4-N-methylthiosemicarbazone)-2,6-diacetylpyridine. The first pentacoordinate lead(II) complex with a pentagonal geometry

In this paper we describe the electrochemical synthesis and characterization of new neutral manganese, iron, cobalt, nickel, copper, zinc, cadmium and lead complexes with the ligand bis(4-N-methylthiosemicarbazone)-2,6-diacetylpyridine, H4DAPTsz-Me. X-Ray structures of [Mn(H2DAPTsz-Me)(EtOH)2] 1, [Pb(H2DAPTsz-Me)] 3 and [Zn(H2DAPTsz-Me)]2.EtOH.2H2O 4, were also determined. In these complexes the ligand behaves as bis-deprotonated and SNNNS pentadentate. In the manganese complex the metal is heptacoordinated, in a distorted pentagonal-bipyramidal environment, with the N3S2 donor set of the ligand in the pentagonal girdle and two solvent molecules occupying the axial positions. In the lead complex 3 the metal is pentacoordinated, bound exclusively to the five donor atoms of the ligand, as a consequence of the existence of "inert pair effect". The bishelical zinc complex 4 shows each zinc atom with different coordination geometry, one octahedrally six-coordinate while the other is distorted tetrahedrally four-coordinate.