Simultaneous Densitometric Determination of Rifampicin and Isoniazid by High-Performance Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - High-performance thin-layer chromatography (HPTLC) on silica gel 60 F254 TLC plates, with ethyl acetate-methanol-acetone-acetic...     

Oxidative stability of lubricants measured by PDSC CEC L-85-T-99 test procedure

Summary The CEC L-85-T-99 pressure differential calorimetry (PDSC) test was developed in Europe for ACEA E5 specification for heavy duty diesel oils. This test differentiate between base oils, additives, indicates synergies between antioxidants and correlates with other oxidation tests. Occasionally, the PDSC test can have difficulties to provide a true value for the OIT, which can vary between samplings. This work gives evidence of such case and concludes that variability in results is caused by variability in the oil rather than in the test itself. It appeared possible that certain oils might not be fully homogenous and this could produce a problem for representative PDSC sampling.     

Mixing time of a non-Newtonian liquid in an unbaffled agitated vessel with an eccentric propeller

Experimental study of mixing time of non-Newtonian shear-thinning fluids within the transitional regime (3 × 10² < Re < 3 × 10³) of liquid flow is presented. The purpose of this study was to analyze the effect of eccentricity and pumping mode of the impeller as well as of position of the tracer dosage point into the agitated liquid on mixing time. The measurements were conducted in an unbaffled agitated vessel with inner diameter D = 0.7 m equipped with an up-or down-pumping propeller located centrically (e/R = 0) or eccentrically (e/R ≠ 0) in the vessel. Experiments were carried out by means of computer-aided unsteady-state thermal method for three positions of the tracer dosage point. The experimental data show that eccentric position of the propeller in an unbaffled vessel causes a decrease of the mixing time compared to that obtained in a vessel with a centrically located propeller. Mixing time depends also on the pumping mode of the propeller as well as on the position of the tracer dosage point. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

ZnFe2O4 as a new catalyst in theC-methylation of phenol

This paper reports the investigation ofC-alkylation of phenol with methanol over zinc ferrite as a catalyst. The reactions were carried out in gas phase at atmospheric pressure in dependence of increasing temperature. The total selectivity towardsortho-cresol and 2,6-xylenol over 300°C surpassed 90%. ZnFe₂O₄ was obtained by oxidative precipitation method from solution of iron (II) sulphate and zinc sulphate at 60°C. Based on the results, the best equation describing the oxidation reaction rate was found. The obtained products have been investigated using X-ray fluorescence spectrometry and X-ray diffraction analysis.     

Application and properties of butyl acrylate/pentaerythrite triacrylate copolymers and cellulose-based Granocel as carriers for trypsin immobilization

The main point was the search for a proper carrier and the kind of carrier activation for trypsin (EC 3.4.21.4) immobilization. The acrylic and cellulose-based carriers were specially prepared in that they possessed the most often used anchor groups: -OH, -NH(2), DEAE and/or -COOH. The immobilization procedures were selected to apply mainly to protein amine groups and appropriate anchor groups on the carrier. As activity tests low (N-benzoyl-dl-arginine-p-nitroanilide, BAPNA) and high (casein) molecular weight substrates were used. It was found, as a rule, that trypsin bound to -COOH groups with the help of carbodiimide was less active and that the amount of bound protein and measured activity (BAPNA) are considerably higher when protein is immobilized via divinyl sulfone. Both rules were observed irrespective of the nature of the polymer matrix. Both types of carriers were found suitable for trypsin immobilization and they were far better than the corresponding Eupergit C-bound enzyme preparations. Taking into account storage stability and activity for both substrates, the divinylsulfone linkage formed between unmodified Granocel and trypsin was the most effective method for the enzyme immobilization. For this preparation, BAPNA and casein conversion, thermal stability at 60 degrees C and estimated kinetic parameters were compared with those obtained for the native enzyme. It was shown that mass transport limitations could be effectively eliminated by suitable conditions and immobilized trypsin was considerably more stable. The values k(cat)/K(m) indicated that the immobilized enzyme was even better as amidase activity was regarded and its potential for protein hydrolysis was only less than twice.     

Interaction of serum albumin with vinyl sulfonate azo dye

The interaction between bovine serum albumin and the mono azo reactive dye Orange ZT has been investigated using absorption difference spectroscopy. The influence of pH and ionic strength of the solution on the stability of the dye-protein complex has been determined. At 25°C, the complex dissociation constants were equal to 24.0, 28.0, 7.0, 11.0, 17.6 and 46.0 μM at pH 7.0, 6.5, 6.0, 5.5, 5.0 and 4.3, respectively. In the presence of 0.1, 0.2, 0.3 M KCl, at pH 6.0 and 25°C, the complex dissociation constants were 8.8, 20.0, 18.0 μM, respectively. The protein-dye complex dissociation constants show that Orange ZT could be used as an affinity ligand for protein purification.      

N‐Alkylation of imides using phase transfer catalysts under solvent‐free conditions

N‐Alkylation of imides in the reaction of imides and alkylhalides, catalyzed by PT catalysts under solvent‐free conditions, has been developed. The reaction occurs in the presence of K₂CO₃, and in many cases it takes place spontaneously. In the N‐benzylation reaction, it has been recognized that TBAB (tetrabutylammonium bromide) and TBATFB (tetrabutylammonium tetrafluoroborate) show highest catalytic effect. Versatility and synthetic capacity of the solvent‐free alkylation has been confirmed by N‐benzylation and N‐ethylation of various imides. The developed procedure gives easy access to N‐(ω‐bromoalkyl)imides.     

Synthesis of deuterium-labelled halogen derivatives of L-tryptophan catalysed by tryptophanase

The isotopomers of halogen derivatives of l-tryptophan (l-Trp) (4′-F-, 7′-F-, 5′-Cl- and 7′-Br-l-Trp), specifically labelled with deuterium in α-position of the side chain, were obtained by enzymatic coupling of the corresponding halogenated derivatives of indole with S-methyl-l-cysteine in ²H₂O, catalysed by enzyme tryptophanase (EC 4.1.99.1). The positional deuterium enrichment of the resulting tryptophan derivatives was controlled using ¹H NMR. In accordance with the mechanism of the lyase reaction, a 100% deuterium labelling was observed in the α-position; the chemical yields were between 23 and 51%. Furthermore, β-F-l-alanine, synthesized from β-F-pyruvic acid by the l-alanine dehydrogenase reaction, has been tested as a coupling agent to obtain the halogenated deuterium-labelled derivatives of l-Trp. The chemical yield (～30%) corresponded to that as observed with S-methyl-l-cysteine but the deuterium label was only 63%, probably due to the use of a not completely deuterated incubation medium.     

Transport of chloride and carboxyfluorescein through phospholipid vesicle membranes by heptapeptide amphiphiles

Seven synthetic anion transporters (SAT) of the general form R(2)N-COCH(2)OCH(2)CO-(Gly)(3)-Pro-(Gly)(3)-OR' were prepared. Three pairs of compounds each contained twin n-hexyl, n-decyl, and n-octadecyl (R) groups at the N-terminus and one contained twin n-tetradecyl groups. Three of the compounds were C-terminated by benzyl and three by heptyl (R') residues. The ability of these compounds to mediate ion release from phospholipid vesicles was assessed. Chloride release was measured by ion selective electrode measurements and by chloride quenching of the fluorescent dye lucigenin. Transport of the anion carboxyfluorescein (CF) was measured by fluorescence dequenching. Differences in both the C- (R') and N-terminal (R) residues within the ionophores affected anion transport. The chloride release data acquired by ion selective electrode and fluorescence methods were similar but not identical. A possible carrier mechanism for Cl(-) transport was discredited. Both Cl(-) and CF anions were released from vesicles by these compounds. The results of CF and Cl(-) transport showed good consistency when the ionophore's N-terminal chains were either decyl or octadecyl but not when they were hexyl. The transport of CF and Cl(-) appears to be fundamentally different when R is C(6) compared to C(10) or C(18). Differences between the behavior of SATs with Cl(-) and CF were also reflected in negative ion mass spectrometric studies.     

The Interaction between Polycationic Poly-Lysine Dendrimers and Charged and Neutral Fluorescent Probes

The interactions between polycationic poly-lysine dendrimers and hydrophobic fluorescent probes (anionic ANS and neutral Prodan) were studied. R121 and R131 dendrimers were not able to interact with anionic and neutral hydrophobic groups. R124 was able to interact with neutral and anionic hydrophobic fluorescent probes, however mainly through hydrophobic forces. Dendrimers R155 and R169 showed the maximal effects. The strongest interactions observed for R169 can be explained by intramolecular folding (stacking) of its two L-proline residues. Using double fluorescence titration technique for ANS probe allowed to receive such constant of binding and the number of binding centers: for R121, 1.8·10³ (mol/l)⁻¹ and 1.07; for R124, 12.1·10³ (mol/l)⁻¹ and 0.48; for R131, 4.7·10³ (mol/l)⁻¹ and 0.48; for R155, 9.2·10³ (mol/l)⁻¹ and 1.36; for R169, 39.6·10³ (mol/l)⁻¹ and 0.97. Thus, neutral and anionic hydrophobic probes can be used for the fast preliminary screening of binding properties of newly synthesized polycationic dendrimers.