A flow-injection biamperometric method for determination of pantoprazole in pharmaceutical tablets

A flow-injection biamperometric method for determination of pantoprazole (PTZ) in pharmaceutical tablets is reported for the first time. The reversible redox couples Fe3+/Fe2+, Fe(CN)6(3-)/Fe(CN)6(4-), Ce4+/Ce3+, VO3(-)NO2+, and I2/I- were tested as indicating redox systems for biamperometric determination of PTZ in a flow-injection assembly with optimized flow parameters. The best results were obtained using V03(-)NO2+, which showed to be a selective and sensitive biamperometric indicating system for PTZ even in the presence of excipients and antioxidants that typically are found in drugs. The analytical graph was linear (r = 0.99945) in the range from 10 to 100 mg/L using 25 mmol/L VO3(-) as the reagent and water as the carrier stream and applying 100 mV between the 2 platinum wire electrodes. The limits of detection and quantitation were 200 and 667 microg/L, respectively, with a sensibility of calibration of 22.6 mV/mg/L. The proposed method was successfully applied to determine PTZ in commercial pharmaceutical tablets with a mean relative error of 1.60% (n = 5) and mean relative standard deviation of 3.10%. Recoveries close to 100% showed good agreement between the expected amount of PTZ in tablets (40 mg) and the results found by the application of the proposed method and demonstrated that the formulations used in the tablet compositions do not interfere in the PTZ analysis. The system had good stability, with a relative standard deviation of 3.80% for 9 sequential injections of a 60 mg/L PTZ solution. A sampling rate of about 100 samples/h was obtained.     

Purification of glucose-6-phosphate dehydrogenase from baker’s yeast in aqueous two-phase systems with free triazine dyes as affinity ligands

To improve the selectivity of glucose-6-phosphate dehydrogenase (G6PDH) extraction by an aqueous two-phase system, a simple and inexpensive affinity aqueous two-phase system using unbound reactive triazine dyes as ligands was introduced. In a polyethylene glycol (PEG)/hydroxypropyl starch (PES) system, the unbound free triazine dyes, Cibacron Blue F3GA and Procion Red HE3B, partitioned unevenly in the top PEG-rich phase and thus showed an affinity effect on G6PDH, but no influence on hexokinase. The various parameters investigated were pH of the system, buffers, molecular weight of PEG, and ligand type and concentration. A two-step affinity extraction process was established for the purification of G6PDH from baker’s yeast. The total yield of G6PDH was 66.9% and purification factor was 2.35.     

Production of an antiproliferative furanoheliangolide by Lychnophora ericoides cell culture

This work reports for the first time the production a furanoheliangolide (goyazensolide) by plant cell culture. Monitoring of the goyazensolide metabolism revealed that the maximum production occurred during the lag phase of the Lychnophora ericoides callus culture. The antiproliferative activity of obtained goyazensolide was evaluated against seven cancer cell lines using MTT assay. The results revealed a potent cytotoxic activity for the furaheliangolide with IC50 values in the range of 0.06 microg/ml for CEM leukemia cells to 0.75 microg/ml for B16 melanome cells.     

Oxovanadium(IV) complexes of salicyl-L-aspartic acid and salicylglycyl-L-aspartic acid

The dipeptide and tripeptide analogues salicyl-L-aspartic acid (Sal-L-Asp) and salicylglycyl-L-aspartic acid (SalGly-L-Asp) were synthesized and their protonation and complex formation with V(IV)O2+ were studied in aqueous solution through the use of pH-potentiometry and spectroscopic (UV-Vis, CD and EPR) techniques. The phenolate terminus proved to be a good anchoring site to promote (i) the metal ion-induced deprotonation and subsequent coordination of the peptide amide group(s) in the pH range 4-5 for the dipeptide analogue, (ii) and in the pH range 5-6 in a very cooperative way for the tripeptide analogue. The results suggest that the presence of good anchoring donors on both sides of the amide groups is responsible for the cooperative deprotonation of the two amide-NH groups.     

Thermal stability of recombinant green fluorescent protein (GFPuv) at various pH values

The thermal stability of the recombinant green fluorescent protein (GFPuv) expressed by Escherichia coli cells and isolated by three-phase partitioning extraction with hydrophobic interaction chromatography was studied. The GFPuv (3.5–9.0 μg of GFPuv/mL) was exposed to various pH conditions (4.91–9.03) and temperatures (75–95°C) in the 10 mM buffers: acetate (pH 5.0–7.0), phosphate (pH 5.5–8.0), and Tris-HCl (pH 7.0–9.0). The extent of protein denaturation (loss of fluorescence intensity) was expressed in decimal reduction time (D-value), the time exposure required to reduce 90% of the initial fluorescence intensity of GFPuv. For pH 7.0 to 8.0, the thermostability of GFPuv was slightly greater in phosphate buffer than in Tris-HCl. At 85°C, the D-values (pH 7.1–7.5) ranged from 7.24 (Tris-HCl) to 13.88 min (phosphate) The stability of GFPuv in Tris-HCl (pH>8.0) was constant at 90 and 95°C, and the D-values were 7.93 (pH 8.38–8.92) and 6.0 min (pH 8.05–8.97), respectively. The thermostability of GFPuv provides the basis for its potential utility as a fluorescent biologic indicator to assay the efficacy of moist-heat treatments at temperatures lower than 100°C.     

On the centers of the weight-homogeneous polynomial vector fields on the plane

We classify all centers of a planar weight-homogeneous polynomial vector field of weight degree 1, 2, 3 and 4.     

Screening of variables in β-xylosidase recovery using cetyl trimethyl ammonium bromide reversed micelles

β-Xylosidase recovery by micelles using cetyl trimethyl ammonium bromide (CTAB) cationic surfactant was verified under different experimental conditions. A 2⁵⁻¹ fractional factorial design with center points was employed to verify the influence of the following factors on enzyme extraction: pH (x ₁), CTAB concentration (x ₂), electrical conductivity (x ₃), hexanol concentration (x ₄), and butanol concentration (x ₅). Statistical analysis of the results shows that of the fivevariables studied only hexanol and electrical conductivity did not have significant effects on the recovery of β-xylosidase. The other factors had significant effects in increasing order: (x ₁)>(x ₂)>(x ₅). The model predicts a recovery value of about 45%, which is similar to that obtained experimentally (43.5%).     

N-Salicylideneamino acidato complexes of oxovanadium(IV). The cysteine and penicillamine complexes

Oxovanadium(IV) complexes with ligands derived from the reaction of salicylaldehyde with L-cysteine and with D- and D,L-penicillamine are prepared. The compounds are characterised by elemental analysis, spectroscopy (UV-VIS, CD, EPR), TG, DSC and magnetic susceptibility measurements (9-295 K). We discuss several aspects related to the structure of these complexes in the solid state and in solution; in particular, the possibility of forming thiazolidine complexes, and their comparison with the characterised complexes is studied by molecular mechanics and density functional theory calculations. The solution structures depend on pH and solvent, and while with L-Cys the spectroscopic results show trends similar to those of the L-Ala and L-Ser systems up to ca. pH 8-9, where thiolate coordination starts being detected, the penicillamine system is quite distinct, namely thiolate coordination occurs for pH > 6.5. In the presence of salicylaldehyde and V(IV)O the desulfydration of cysteine proceeds rapidly, but no similar reaction occurs with penicillamine, although its decomposition is also activated. The DFT calculations do not indicate any energetic basis for this distinct reactivity, which possibly results from different complexes present in the Cys and Pen systems. In the cysteine system, the N-salicylidenedehydroalanine-V(IV)O complex V is believed to form in an intermediate stage of the desulfydration. Further, addition of several nucleophiles to the cysteine reaction mixtures produce amino acid derivatives by a Michael-type base-catalysed addition, a result compatible with the formation of V. The products of these reactions were analysed by TLC and HPLC, and in some cases isolated.     

Monitoring the removal of soluble salts from ancient tiles by ion chromatography

The application of ion chromatography, conductometry and total carbon analysis to the study of desalination of 18th century tiles and mortars is described. Ion chromatography is shown to be a simple and adequate technique for the identification and quantitative analysis of ions which are extracted during desalination. Chloride, nitrate, sulphate, carbonate, sodium, potassium, calcium and magnesium were always found in the immersion waters, and occasionally also nitrite and oxalate.     

Lipoic acid as an efficient and versatile redox catalyst for the electroanalysis of N-acetylcysteine: effects of the electrode nature and insights into the catalytic mechanism

Journal of Solid State Electrochemistry - In this work, the boron-doped diamond electrode (BDDE) was used for the electrocatalytic oxidation of N-acetylcysteine (NAC), in the presence of lipoic...