Potentiometric studies on the complexes of tetracycline (TC) and oxytetracyclin (OTC) with some metal ions

Summary The interaction of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Pb(II), Al(III), and UO₂(II) ions with tetracycline (TC) were studied by potentiometricpH titrations. The formation constants of the different binary complexes formed in such systems have been determined at 25±0.1°C and =0.1 moll^–1 (NaNO₃). PotentiometricpH equilibrium measurements have been made under the same conditions for the interaction of oxytetracycline (OTC) and Cu(II), Cd(II), Pb(II), and UO₂(II). The formation of (1:1) binary complexes are inferred from the potentiometricpH tritration curves. The protonation constants ofTC andOTC were also determined under the same conditions and refined (ESAB2M computer program). The transition metal stability constants are consistent with the Irving-Williams series.

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Potentiometrische Untersuchungen der Komplexe von Tetracyclin (TC) and Oxytetracyclin (OTC) mit einigen Metall-Ionen

Zusammenfassung Die Wechselwirkungen von Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Zn(II), Cd(II), Hg(II), Pb(II), Al(III) und UO₂(II) Ionen mit Tetracyclin (TC) wurden mittels potentiometrischerpH-Titrationen untersucht. Die Komplexbildungskonstanten wurden bei 25±0.1°C und =0.1 mol/1(NaNO₃) bestimmt. Unter den gleichen Bedingungen wurden die Komplexierung von Cu(II), Cd(II), Pb(II) und UO₂(II) mit Oxytetracyclin (OTC) mittel potentiometrischerpH Gleichgewichtsmessungen untersucht. Aus den potentiometrischenpH-Titrationskurven ergab sich die Bildung von (1:1) binären Komplexen. Die Protonierungskonstanten vonTC undOTC wurden ebenfalls bestimmt und rechnerisch verfeinert (ESAB2M Computer Programm). Die Stabilitätskonstanten für die Übergangsmetalle stimmen mit der Irving-Williams Reihe überein.

     

Synthesis, X-ray characterization, NMR and ab initio molecular-orbital studies of some cadmium(II) macrocyclic Schiff-base complexes with two 2-aminoethyl pendant arms

Three new pendant arm Schiff-base macrocyclic complexes, [CdLⁿ]²⁺ (n = 5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexaamines in the presence of Cd(II). The ligands are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L⁵ = 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L⁶ = 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene and L⁷ = 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. All complexes were investigated by IR, ¹H and ¹³C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy and X-ray diffraction. In the solid state structure of each complex the Cd(II) ion is situated centrally within an approximately planar pentaaza macrocyclic ring, binding to the five nitrogen atoms, and also to the two pendant amines which are located on opposite sides of the macrocyclic plane. ab initio HF-MO calculations using a standard 3-21G* basis set have been used to verify that these similar basic structures correspond to energy minima in the gas phase.     

Regioselectivity in the reactions of diphenylnitrilimine with coumarin and chromone

The cycloaddition of diphenylnitrilimine with coumarin and chromone gave the cycloadducts 4 and 5 respectively. The structures of these products were based on elemental and spectral analyses and alternate synthesis. The orientations of the cycloaddition are interpreted in terms of FMO theory.     

DFT study of molecular structure and electronic properties of fluoromethylpyrrole oligomers including di-, tri- and tetramer

Structural and electronic properties of oligomers including dimer, trimer and tetramer of fluoromethylpyrroles (FMPs), NC₄H₄-CH_nF_3−n with n = 0, 1, 2, 3, and their radical cations have been studied using DFT-B3LYP method with 6-31G(d, p) basis set. FMPs are proposed in this research as candidate monomers for conducting polymers with modified characteristics compared to polypyrrole and polymethylpyrrole. A preliminary study using a set of ab initio computations (HF) with medium basis set was carried out on di-, tri- and tetramer in order to investigate the stability of configuration of polymer chains for FMPs. The B3LYP/6-31G** optimized geometry and stereochemistry show that the selectivity of branching of the propagating polymer chain is affected by the characteristics of the substitutions of monomer and, therefore, the growth pattern of the polymer chain can be predicted upon characterization of different centers of the monomers. Also, the results of this study, including quinoid coefficients, orbital energy spacing, charge- and spin-density distributions and electric dipole moment vectors show that conducting polymers consisted of trifluoromethyl pyrrole (Py-CF₃), compared with the other FMPs, are the most favorable to be used as monomers for conducting polymer structural and electronic properties.     

High performance liquid chromatographic analysis of dehydroepiandrosterone and its pharmaceutical tablet formulation

A rapid, sensitive and stability indicating high performance liquid chromatographic method was developed and validated for the analysis of dehydroepiandrosterone (DHEA) in pharmaceutical tablet formulation. The analysis was done on a Supelcosil C(18) column (25 cm x 4.6 mm i.d., 5 microm). The mobile phase consisted of methanol:sodium acetate buffer solution (5 g/L):acetic acid (500 mL/L), 57:42:1, v/v/v, adjusted to pH 5 at a flow rate of 1 mL/min. Detection was carried out at a wavelength of 258 nm. The polynomial regression data for the calibration curve showed good linear relationship in the concentration range of 0.2-1 mg/mL with r = 0.9996. The method was validated for precision, accuracy and recovery. The limit of detection was found to be 50 ng/ microL. The method was applied for the analysis of DHEA in its pharmaceutical tablet formulation. The effects of different buffers and alcohols on the retention of DHEA were studied and the role of acetic acid as an organic phase modifier was also investigated.     

Enantioanalysis of l-2-hydroxyglutaric acid in urine samples using enantioselective, potentiometric membrane electrodes based on maltodextrins

Quantitative assay of l-2-hydroxyglutaric acid (l-2-HGA) is important for the diagnosis of l-2-hydroxyglutaric aciduria. Three enantioselective, potentiometric membrane electrodes (EPMEs) based on maltodextrins with different dextrose equivalent (DE) (DE: 4.0-7.0 (I), 13.0-17.0 (II), 16.5-19.5 (III)), were designed for the enantioanalysis of l-2-HGA. The enantioselective, potentiometric membrane electrodes can be used reliably for enantiopurity assay of l-2-HGA using the direct potentiometric method in the ranges of 10⁻⁹-10⁻⁵, 10⁻⁶-10⁻³ and 10⁻⁸-10⁻⁵ mol L⁻¹ for the enantioselective, potentiometric membrane electrodes based on maltodextrins I, II and III, respectively, with very low detection limits. A high reliability was obtained when the electrodes were used for the assay of l-2-HGA in urine samples.     

Ion-selective electrodes in organic functional group analysis: Microdetermination of hydrazines with the copper electrode

Summary A simple micromethod is described for the determination of hydrazines using the copper ion-selective electrode. The method is based on direct potentiometric titration of the sample in ammoniacal solution of pH 9.5±0.2 with copper(II) ions at room temperature. N-Shaped curves with well-defined inflections at 11 and 12 molar ratios are obtained. This is probably due to the formation of copper monohydrazinate and copper dihydrazinate complexes. Various alkyl and aryl hydrazines and hydrazine salts have been satisfactorily analyzed with an average recovery of 99.4% and a relative standard deviation of ±0.4%. The reaction of hydrazines with Fehling's solution followed by measuring the copper(I) oxide formed using the copper ion-selective electrode also has been investigated.

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Zusammenfassung Eine einfache Mikromethode zur Bestimmung von Hydrazinen mit einer kupferionen-selektiven Elektrode wurde beschrieben. Sie beruht auf der direkten potentiometrischen Titration in ammoniakalischer Lösung mit Cu(II)ionen bei pH 9,5±0,2 bei Zimmertemperatur. N-förmige Kurven mit gut ausgebildeten Spitzen bei Molverhältnissen 11 und 12 wurden erhalten, wahrscheinlich auf Grund der Bildung von Mono- bzw. Dihydrazinatkomplexen des Kupfers. Verschiedene Alkyl- und Arylhydrazine und deren Salze wurden zu 99,4% mit einer Standardabweichung von ±0,4% wiedergefunden. Die Reaktion der Hydrazine mit Fehlingscher Lösung wurde ebenfalls durch Messung des entstandenen Cu(I) mit der erwähnten Elektrode untersucht.

     

Enantioselective high-performance liquid chromatographic method for the determination of baclofen in human plasma

A new analytical method for the separation and determination of R-(−)- and S-(+)- baclofen enantiomers in human plasma by high-performance liquid chromatography (HPLC) with UV detection was developed. Enantioselective resolution of the baclofen enantiomers was achieved by using teicoplanin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic T with a polar ionic mobile phase (PIM) consisting of methanol: glacial acetic acid: triethylamine, 100:0.1:0.1, (v/v/v) at a flow rate of 0.5 ml min⁻¹ and UV detection set at 220 nm. The analytes of interest with S-(+)-sulpiride as the internal standard were extracted from human plasma using liquid-liquid extraction procedure with ethyl ether under alkaline condition prior to HPLC analysis. Recoveries for R-(−)- and S-(+)-baclofen enantiomers were in the ranges of 96-103% at 60-2500 ng ml⁻¹ level. Intra-day and inter-day precision calculated as %RSD was in the ranges of 1.2-5.2 and 1.3-4.3% for both enantiomers, respectively. Intra-day and inter-day accuracy calculated as percentage error were in the ranges of 1.2-3.9 and 1.1-3.9% for both enantiomers, respectively. Linear calibration curves in the concentration ranges of 20-3000 ng ml⁻¹ for each enantiomer showed correlation coefficient (r) of 0.9997. The limit of quantitation (LOQ) and limit of detection (LOD) for each enantiomer in human plasma were 20 and 10 ng ml⁻¹ (S/N=3) respectively.     

Design and enhanced gene silencing activity of spherical 2′-fluoroarabinose nucleic acids (FANA-SNAs)

Drug delivery vectors for nucleic acid therapeutics (NATs) face significant barriers for translation into the clinic. Spherical nucleic acids (SNAs) – nanoparticles with an exterior shell made up of DNA strands and a hydrophobic interior – have recently shown great potential as vehicles to improve the biodistribution and efficacy of NATs. To date, SNA design has not taken advantage of the powerful chemical modifications available to NATs. Here, we modify SNAs with 2′-deoxy-2′-fluoro-d-arabinonucleic acid (FANA-SNA), and show increased stability, enhanced gene silencing potency and unaided uptake (gymnosis) as compared to free FANA. By varying the spacer region between the nucleic acid strand and the attached hydrophobic polymer, we show that a cleavable DNA based spacer is essential for maximum activity. This design feature will be important when implementing functionalized nucleic acids into nanostructures for gene silencing. The modularity of the FANA-SNA was demonstrated by silencing two different targets. Transfection-free delivery was superior for the modified SNA compared to the free FANA oligonucleotide.

Optimizing FANA modified spherical nucleic acids (FANA-SNAs) for highly efficient delivery of nucleic acid therapeutics.     

Polarographic behaviour and determination of selenite and tellurite in simple solutions or in a binary mixture

Summary The polarographic behaviour of simple solutions of selenite and tellurite in 1M ammonium salts of formate, acetate, tartrate, oxalate, and benzoate solutions in absence and in presence of Triton X-100 as a maximum suppressor and a temperature of 25°C has been investigated. Schemes for the mechanism of reductions occurring at the DME have been deduced. A method for analytical determination of selenite and tellurite in simple solutions as well as in a binary mixture in the presence of 4–14·10^–3% Triton X-100 is reported.

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Polarigraphisches Verhalten und die Bestimmung von Selenit und Tellurit in einfachen Lösungen oder in binären Mischungen

Zusammenfassung Es wurde das polarographische Verhalten von einfachen Lösungen von Selenit und Tellurit in 1M Ammonsalzlösungen von Formiat, Acetat, Tartrat, Oxalat und Benzoat-Lösungen mit und ohne Triton X-100 als Suppressor bei einer Temperatur von 25°C untersucht. Es wurde ein Reaktionsschema für den Mechanismus der Reduktion an der DME abgeleitet. Eine Methode zur analytischen Bestimmung von Selenit und Tellurit in einfachen Lösungen und in binären Mischungen in Gegenwart von 4–14·10^–3% Triton X-100 wird berichtet.