Vanadium-Containing Anionic Chelate for Spectrophotometric Determination of Hydroxyzine Hydrochloride in Pharmaceuticals.

Four azo dyes known to form anionic complexes with V(V) were investigated as potential liquid-liquid extraction-spectrophotometric reagents for the antihistamine medication hydroxyzine hydrochloride (HZH). A stable ion-association complex suitable for analytical purposes was obtained with 6-hexyl-4-(2-thiazolylazo)resorcinol (HTAR). The molar absorption coefficient, limit of detection, linear working range, and relative standard deviation in the analysis of real pharmaceutical samples (tablets and syrup) were 3.50 × 104 L mol-1 cm-1, 0.13 µg mL-1, 0.43-12.2 µg mL-1, and ≤2.7%, respectively. After elucidating the molar ratio in the extracted ion-association complex (HZH:V = 1:1), the ground-state equilibrium geometries of the two constituent ions-HZH+ and [VO2(HTAR)]--were optimized at the B3LYP level of theory using 6-311++G** basis functions. The cation and anion were then paired in four different ways to find the most likely structure of the extracted species. In the lowest-energy structure, the VO2 group interacts predominantly with the heterochain of the cation. A hydrogen bond is present (V-O···H-O; 1.714 Å) involving the terminal oxygen of this chain.

Immobilized microbial biosorbents for heavy metals removal.

Intensive industrial and urban growth has led to the release of increasing amounts of environmental pollutants. Contamination by metals, in particular, deserves special attention due to their toxicity and potential to bioaccumulate via the food chain. Conventional techniques for the removal of toxic metals, radionuclides and precious metals from wastewater all have a number of drawbacks, such as incomplete metal extraction, high cost and risk of generating hazardous by-products. Biosorption is a cost-effective and environment-friendly technology, an alternative to conventional wastewater treatment methods. Biosorption is a metabolically independent process, in which dead microbial biomass is capable of removal and concentrating metal ions from aqueous solutions. Free microbial biosorbents are of small size and low density, insufficient mechanical stability and low elasticity, which causes problems with metal ion desorption, separation of the sorbent from the medium and its regeneration. Hence, the possibilities for the implementation of continuous biosorbent processes for metal removal in flow-type reactor systems are reduced and the practical application of biosorption in industrial conditions is limited. By immobilizing microbial biomass on suitable carriers the disadvantages of free biosorbents are eliminated and more opportunities for practical use of biosorption become available. This review examines different immobilization techniques and carriers, certain basic features and possibilities of using immobilized microbial biosorbents for the removal and concentration of metals from aqueous solutions.

Electrochemical sensor based on Arthrobacter globiformis for cholinesterase activity determination.

The sensors applied recently for determination of cholinesterase activity are mostly enzymatic amperometric sensors, in spite of their disadvantages: short life-time at ambient temperature, instability of the response, interferences, as well as passivation of the electrode surface. In the present paper a new approach for determination of cholinesterase activity was proposed, overcoming the main drawbacks of the analysis performed with amperometric enzymatic sensors. Instead of the immobilization of enzymes on a conducting electrode surface, whole cells of Arthrobacter globiformis, containing choline oxidase were fixed on a Clark type oxygen probe. Current proportional to bacteria respiration is registered as a sensor response. The application of whole cells of bacteria as a sensing element permits to achieve high stability of the response and long life-time of the sensor at ambient temperature, due to the conservation of the enzyme in its natural micro-environment inside the immobilized cells. The proposed sensor keeps its functionality more than 7 weeks stored in deionized water at ambient temperature. For the first 2 weeks the amplitude of the response decreases with only 10% and at the end of the studied 7 weeks period the response was 50% of the initial. The other advantages of the proposed sensor are: the dissolved oxygen is used as a mediator which concentration can be reliably and interferences free measured by the aim of a Clark type oxygen probe applied as a transducer; reproducible bacterial membranes can be elaborated by filtration of resuspended bacterial culture after preliminary determination of its activity; application of membranes containing lyophilized bacteria capable to be conserved infinitely long time and activated just before their application; negligible cost compared with the sensors based on immobilized enzymes. The steady-state response of the proposed bacterial sensor to choline obtained in 200 s is linear in the investigated concentration range up to 2 x 10(-4) moldm(-3), with detection limit of 8 x 10(-8) moldm(-3) and sensitivity of 4 x 10(-1) microAcm(3)mol(-1), at pH 6, temperature of 25 degrees C and stirring rate of 300 rpm. Choline is formed as a result of the catalytic hydrolysis (depending on the cholinesterase activity) of the substrate acetylcholine. Linear calibration graph for cholinesterase activity determination was obtained in the range up to 11 mUcm(-3), with a slope of 1.97 x 10(-2) microAcm(3)mU(-1), at pH 6, temperature of 25 degrees C and stirring rate of 300 rpm. The tests with reconstituted lyophilized serum with known activity used as a control sample confirm the accuracy of the proposed method. The relative error of the determination was only 2.82%.