Competitive binding exchange between alkali metal ions (K+, Rb+, and Cs+) and Na+ ions bound to the dimeric quadruplex [d(G4T4G4)]2: a 23Na and 1H NMR study

A comparative study of the competitive cation exchange between the alkali metal ions K⁺, Rb⁺, and Cs⁺ and the Na⁺ ions bound to the dimeric quadruplex [d(G₄T₄G₄)]₂ was performed in aqueous solution by a combined use of the ²³Na and ¹H NMR spectroscopy. The titration data confirm the different binding affinities of these ions for the G‐quadruplex and, in particular, major differences in the behavior of Cs⁺ as compared to the other ions were found. Accordingly, Cs⁺ competes with Na⁺ only for the binding sites at the quadruplex surface (primarily phosphate groups), while K⁺ and Rb⁺ are also able to replace sodium ions located inside the quadruplex. Furthermore, the ¹H NMR results relative to the CsCl titration evidence a close approach of Cs⁺ ions to the phosphate groups in the narrow groove of [d(G₄T₄G₄)]₂. Based on a three‐site exchange model, the ²³Na NMR relaxation data lead to an estimate of the relative binding affinity of Cs⁺ versus Na⁺ for the quadruplex surface of 0.5 at 298 K. Comparing this value to those reported in the literature for the surface of the G‐quadruplex formed by 5′‐guanosinemonophosphate and for the surface of double‐helical DNA suggests that topology factors may have an important influence on the cation affinity for the phosphate groups on DNA. Copyright © 2009 John Wiley & Sons, Ltd.     

Computer-aided evaluation of liquid-chromatographic profiles for anthocyanins in vaccinium myrtillus fruits

The anthocyanin constituents of thirty samples of Vaccinium myrtillus fruits of various origin were examined by high-performance liquid chromatography. The data, characterized by 15 peaks for each chromatogram, were subjected to principal component analysis in order to reveal differences in the chromatograms. The vector space generated by eigenvector projection produced a clear separation between a group composed of Norwegian and Swedish berries and a group of berries of Italian or Romanian origin. Cyanidin glycosides are highly better represented in all the samples of the first group, while delphinidin glycosides are better represented in the latter.     

Scatter Search for Network Design Problem

A fixed charge capacitated multicommodity network design problem on undirected networks is addressed. At the present time, there exists no algorithm that can solve large instances, common in several applications, in a reasonable period of time. This paper presents an efficient procedure using a scatter search framework. Computational experiments on a large set of randomly generated problems show that this procedure is capable of finding good solutions to large-scale problems within a reasonable amount of time.     

Clinical analysis of human urine by means of potentiometric Electronic tongue

The Electronic tongue (ET) composed of different kind of potentiometric chemical sensors has been applied for the detection of urinary system dysfunctions and creatinine levels. The creatinine contents evaluated by ET were compared with those obtained by automated Jaffe’s method and GC-MS, obtaining a satisfying agreement for both methods. Partial least square regression discriminate analysis (PLS-DA) and feed forward back-propagation neural network (FFBP NN) classified 51 urine specimens from healthy volunteers in four classes, according to the creatinine content, showing that both techniques can satisfactorily differentiate urines according to this parameter. The best accuracy result of 92.2% correct classification of unknown samples was achieved with FFBP NN. Moreover, the possibility of ET system to distinguish between urine samples of healthy patients, and those with malignant and non-malignant tumor diagnosis of bladder has been shown.     

Indirect determination of pepsin activity in human seric protein samples by polyphenol oxidase electrodes

We present a new chronoamperometric methodology for the indirect determination of pepsin activity in proteic solutions. The high-sensitive polyphenol oxidase (PPO) carbon paste bioelectrodes, prepared with 150–200 U of PPO adsorbed on the carbon paste surface and trapped behind a dialysis membrane were able to detect free -tyrosine ( -Tyr) as well as -Tyr-containing peptides, the product of pepsin hydrolysis on haemoglobin samples. The electroactive enzymatic products were determined by their reduction current at −0.050 V, a working potential low enough for preventing electrochemical interferences. The external diffusional barrier posed by the dialysis membrane and the high PPO-superficial concentrations allowed us to prevent electrode surface fouling and to reach stationary diffusional currents after 3 min. The electrochemical -Tyr concentrations measured with proper internal standards, were correlated to those determined by the spectrophotometric reference method (Folin–Ciocalteu), reaching a linear relationship with a slope of 1.05±0.04 and a linear regression coefficient of 0.9951. These results as well as a recovery assay of 98% and the detection limit lower than that of the spectrophotometric method indicate that the proposed methodology is very satisfactory and potentially useful for indirect determination of pepsin in biological samples. The technique was also applied for the determination of pepsin activity in hydrolysed immuno globulin solutions of different composition.     

Grasp Embedded Scatter Search for the Multicommodity Capacitated Network Design Problem

A GRASP embedded Scatter Search is developed for the multicommodity capacitated network design problem. Difficulty for this problem arises from the fact that selection of the optimal network design is an NP-complete combinatorial problem. There exist no polynomial exact algorithms which can solve this problem in a reasonable period of time for realistically sized instances. In such cases, heuristic procedures are commonly used. Two strategies were designed for GRASP: a traditional approach and a memory based technique. As for Scatter Search, 5 different strategies were used to update the reference set. Computational results on a large set of randomly generated instances show the convenience of the proposed procedures.     

Core excitons in solid rare gases: Kr-3d and Xe-4d transitions

Core excitons from 3d levels of Kr and 4d levels of Xe are examined within the integral equation formalism both in the isolated atoms and in the crystals. Earlier interpretation that resonances at the interband edge Kr-3d and Xe-4d are due to 1s, 2p, 3p excitons is well supported by the present calculation.     

Determination of tellurium in geochemical materials by flameless atomic-absorption spectroscopy

A method is described for the determination of tellurium at nanogram levels in rocks and in other complex materials by the use of flameless atomic-absorption spectroscopy. A very selective organic extraction procedure is applied to avoid matrix interference effects during extraction of Te and the atomization stage in the graphite furnace. Prior separation of iron and other interfering elements is achieved by a combined cupferron-ethyl acetate extraction. Tellerium is extracted from 6M hydrochloric acid with MIBK and stripped into aqueous medium. Pipetting of the aqueous extract into the graphite furnace gives fairly good instrumental reproducibility (2-3% error). Detection limits of about 10 ppM Te for a 0.5-g sample have been achieved with the medium-performance apparatus used. Results for Te in some geochemical reference materials are reported. Indications are given for the determination of Sb and Mo in the same solutions.