Search

We prepared planar hybrid Josephson junctions using Co-doped BaFeAs thin films and polished single crystals as base electrode, sputtered, and subsequently oxidized titanium layers as barrier and a counter electrode from evaporated lead. On all junctions, RCSJ-like current–voltage characteristics could be observed. The obtained products at 4.2 K range up to 95V for thin film junctions and up to 1.15 mV for junctions on single crystals. For most of the junctions, an excess current with variable contribution to the total current could be observed. Unusual temperature dependencies are discussed for the critical and the excess currents, respectively. Investigations of the junctions under microwave irradiation were performed, therein Shapiro steps up to high orders and very clear modulations of the steps could be observed. Additionally, the origin of the excess current is discussed with respect to the microwave dependence. Furthermore, instead of a single junction, a network-like modulation behavior of the critical current in magnetic fields was observed.

A new microextraction procedure termed agarose gel liquid phase microextraction (AG-LPME) combined with gas chromatography-mass spectrometry (GC-MS) was developed for the determination of selected polycyclic aromatic hydrocarbons (PAHs) in water. The technique utilized an agarose gel disc impregnated with the acceptor phase (1-octanol). The extraction procedure was performed by allowing the solvent-impregnated agarose gel disc to tumble freely in the stirred sample solution. After extraction, the agarose gel disc was removed and subjected to centrifugation to disrupt its framework and to release the impregnated solvent, which was subsequently withdrawn and injected into the GC-MS for analysis. Under optimized extraction conditions, the new method offered high enrichment factors (89-177), trace level LODs (9-14ngL(-1)) and efficient extraction with good relative recoveries in the range of 93.3-108.2% for spiked drinking water samples. AG-LPME did not exhibit any problems related to solvent dissolution, and it provided high extraction efficiencies that were comparable to those of hollow fiber liquid phase microextraction (HF-LPME) and significantly higher than those of agarose film liquid phase microextraction (AF-LPME). This technique employed a microextraction format and utilized an environmentally compatible solvent holder that supported the green chemistry concept.

A rapid estimation of octanol–water partition coefficient (log Pow) was developed for triazole fungicides by micellar electrokinetic chromatography (MEKC). Five standard compounds with known log Pow values from 2.9 to 4.3 (cyproconazole, bromuconazole, epoxiconazole, bitertanol and difenoconazole) were used for constructing the calibration curve of the log Pow against the MEKC retention factor, log k. A linear relationship was achieved between log Pow and log k, in the MEKC system containing 40 mM sodium deoxycholate (SDC) and 4 mM borate buffer at pH 9.3, with a correlation of determination, r2 = 0.9905. The log Pow values of four test compounds of triazole fungicides (triadimenol, myclobutanil, propiconazole and penconazole) were calculated based on the log k values measured by MEKC and the slope and intercept of the calibration curve. This MEKC method can give good estimation of the log Pow of the four test compounds of triazole fungicides with the differences between the literature log Pow values and estimated log Pow from the MEKC method were from 0.15 to 0.23 log units.

Food source could provide essential mineral elements necessary for preventing and remedying the cases of Mineral Deficiency Diseases (MDD). This source is cost effective, safe, affordable and accessible. In this study, essential elements: Ca, Mg, P, K, Na, Cu, Fe, Mn, Se and Zn were determined in 126 food samples eaten in Johor Bahru, Malaysia. The all-serving-units-inclusive food samples were oven-dried until constant weight, homogenized and wet digested serially with nitric acid and hydrogen peroxide mixture. The major and minor elements were respectively determined by FAAS and ICP-MS. The elements showed presence in all foods. The food element/RDA percentage ratios of (Ca: 50.0; P: 322.8) and (Mn: 10.5; P: 177.5) were obtained respectively relative to maximum and minimum Recommended Dietary Allowance (RDA). The study has proven that the foods could be viable source of the elements choosing appropriate foods. These essential elements containing foods can be exploited for health maintenance, remedy and even cure for MDD.

The increase in resistance to older drugs and the emergence of new types of infection have created an urgent need for discovery and development of new compounds with antimalarial activity. Quantitative-Structure Activity Relationship (QSAR) methodology has been performed to develop models that correlate antimalarial activity of artemisinin analogs and their molecular structures. In this study, the data set consisted of 197 compounds with their activities expressed as log RA (relative activity). These compounds were randomly divided into training set (n=157) and test set (n=40). The initial stage of the study was the generation of a series of descriptors from three-dimensional representations of the compounds in the data set. Several types of descriptors which include topological, connectivity indices, geometrical, physical properties and charge descriptors have been generated. The number of descriptors was then reduced to a set of relevant descriptors by performing a systematic variable selection procedure which includes zero test, pairwisecorrelation analysis and genetic algorithm (GA). Several models were developed using different combinations of modelling techniques such as multiple linear regression (MLR) and partial least square (PLS) regression. Statistical significance of the final model was characterized by correlation coefficient, r2 and root-mean-square error calibration, RMSEC. The results obtained were comparable to those from previous study on the same data set with r2 values greater than 0.8. Both internal and external validations were carried out to verify that the models have good stability, robustness and predictive ability. The cross-validated regression coefficient (r2cv) and prediction regression coefficient (r2 test) for the external test set were consistently greater than 0.7. The QSAR models developed in this study should facilitate the search for new compounds with antimalarial activity.

A new microextraction procedure termed multi-walled carbon nanotube-impregnated agarose film microextraction (MWCNT-AFME) has been developed. The method utilized multi-walled carbon nanotubes (MWCNTs) immobilized in agarose film to serve as adsorbent in solid phase microextraction (SPME). The film was prepared by mixing the MWCNTs in agarose solution and drying the mixture in oven. Extraction of selected polycyclic aromatic hydrocarbons was performed by inserting a needle through circular MWCNT-impregnated agarose films (5 mm diameter) and the assembly was dipped into an agitated sample solution prior to micro high performance liquid chromatography-ultraviolet analysis. Back extraction was then performed using ultrasonication of the films in 100 μL of solvent. The film was discarded after single use, thus avoiding any analyte carry-over effect. Due to the mesoporous nature of the agarose film, the MWCNTs were immobilized easily within the film and thus allowing for close contact between adsorbent and analytes. Under the optimized extraction conditions, the technique achieved trace LODs in the range of 0.1 to 50 ng L(-1) for the targeted analytes, namely fluoranthene, phenanthrene and benzo[a]pyrene. The method was successfully applied to the analysis of spiked green tea beverage samples with good relative recoveries in the range of 91.1 to 107.2%. The results supported the feasibility of agarose to serve as adsorbent holder in SPME which then minimizes the consumption of chemicals and disposal cost of organic wastes.

Agarose film liquid phase microextraction (AF-LPME) procedure for the extraction and preconcentration of polycyclic aromatic hydrocarbons (PAHs) in water has been investigated. Agarose film was used for the first time as an interface between donor and acceptor phases in liquid phase microextraction which allowed for selective extraction of the analytes prior to gas chromatography–mass spectrometry. Using 1-octanol as acceptor phase, high enrichment factors in the range of 57–106 for the targeted analytes (fluorene, phenanthrene, fluoranthene and pyrene) were achieved. Under the optimum extraction conditions, the method showed good linearity in the range of 0.1–200 μg L−1, good correlation coefficients in the range of 0.9963–0.9999, acceptable reproducibility (RSD 6.1–9.2%, n = 3), low limits of detection (0.01–0.04 μg L−1) and satisfactory relative recoveries (92.9–104.7%). As the AF-LPME device was non-expensive, reuse or recycle of the film was not required, thus eliminating the possibility of analytes carry-over between runs. The AF-LPME technique is environment-friendly and compatible with the green chemistry concept as agarose is biodegradable polysaccharide extracted from seaweed and the procedure requires small volume of organic solvent and generates little waste. The validated method was successfully applied to the analysis of the four analytes in river water samples.

In this work, a two-phase hollow fiber liquid-phase microextraction (HF-LPME) method combined with gas chromatography-mass spectrometry (GC-MS) is developed to provide a rapid, selective and sensitive analytical method to determine polycyclic aromatic hydrocarbons (PAHs) in fresh milk. The standard addition method is used to construct calibration curves and to determine the residue levels for the target analytes, fluorene, phenanthrene, fluoranthene, pyrene and benzo[a]pyrene, thus eliminating sample pre-treatment steps such as pH adjustment. The HF-LPME method shows dynamic linearity from 5 to 500 µg/L for all target analytes with R(2) ranging from 0.9978 to 0.9999. Under optimized conditions, the established detection limits range from 0.07 to 1.4 µg/L based on a signal-to-noise ratio of 3:1. Average relative recoveries for the determination of PAHs studied at 100 µg/L spiking levels are in the range of 85 to 110%. The relative recoveries are slightly higher than those obtained by conventional solvent extraction, which requires saponification steps for fluorene and phenanthrene, which are more volatile and heat sensitive. The HF-LPME method proves to be simple and rapid, and requires minimal amounts of organic solvent that supports green analysis.

L'objectif de cette etude est de developper un modele de regression pour prevoir la retention chromatographique des biphenyles halogenes en utilisant des descripteurs emanant des structures moleculaires. L'etude comprend egalement le developpement d'un modele de regression pour la chromatographie utilisant la meme methodologie

Both quantitative and qualitative studies of the structure-activity relationships (SAR) of carcinogenic compounds are discussed. Using the ADAPT software system, examples are given of (1) predicting the gas and liquid chromatographic retention behavior of polycyclic aromatic compounds, (2) predicting the carcinogenicity of N-nitrosamines, and (3) predicting the mutagenic behavior of pesticides and other compounds in short-term test systems. It is concluded that the complexity and lack of understanding of the carcinogenic response should not prevent scientists from searching for useful empirical relationships between molecular structure and carcinogenicity. Computer generated molecular descriptors and statistical and pattern recognition techniques can be useful tools in this research.

The gas chromatographic retention times of polychlorinated biphenyls (PCBs) were predicted by using descriptors derived directly from the molecular structures. A five-variable regression equation with R/sup 2/ of 0.997 and relative standard deviation of 1.7% was developed. Descriptors that represent degree of chlorination, substitution pattern, and geometry of the molecules were among the variables included in the equation. At least 40 compounds are needed in order to accurately predict the retention times of all 209 PCB congeners.

Corrosion inhibition of mild steel in 0.5M H2SO4 at 30oC with thiophene-2- ethylamine (TEA) as inhibitor has been assess by quantitative structure activity relation (QSAR) model and quantum chemical calculations. The results were evaluated using weight loss and electrochemical methods such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results showed good performance of TEA in corrosion protection which behaves as mixed inhibitor from PDP. The micrograph from FESEM and EDX dot mapping showed that the inhibitor adsorbed onto the metal surface with different distribution for S, C and N atoms which indicate less damage on the metal surface in the presence of TEA.