Simultaneous spectrophotometric determination of phenanthridine, phenanthridinone and phenanthridine N-oxide using multivariate calibration methods

The multivariate calibration methods, partial least squares (PLS) and principle component regression (PCR) have been used to determine phenanthridine, phenanthridinone and phenanthridine N-oxide in spiked human plasma samples. Resolution of binary and ternary mixtures of analytes with minimum sample pre-treatment and without analyte separation has been successfully achieved analyzing the UV spectral data. The net analyte signal (NAS) concept was also used to calculate multivariate analytical figures of merit such as limit of detection, selectivity and sensitivity. The simultaneous determination of three analytes was possible by PLS and PCR processing of sample absorbance in the 210–355 nm region. Good recoveries were obtained for both synthetic mixtures and spiked human plasma samples.     

Trans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane/HBr System as New,Effective, Mild and Non‐toxic Reagent for Synthesis of 2‐Aryl‐1H‐benzothiazoles and 2‐Aryl‐1‐arylmethyl‐1H‐benzimidazoles

Ttrans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane has been used as new, effective, solid, inexpensive and nontoxic oxidant for in situ generation of Br⁺ from HBr. This system has been applied as catalyst for synthesis of 2‐aryl‐1H‐benzothiazoles and 2‐aryl‐1‐arylmethyl‐1H‐benzimidazoles at room temperature in excellent yields and high purity.     

Noncontact optogalvanic signal detection in DC discharge CO<Subscript>2</Subscript> lasers

A new noncontact method for detecting optogalvanic signals in DC discharge CO₂ lasers is reported. The presented technique is based on the detection of potential difference variations through a capacitor comprised of a discharge plasma column and a coaxial or parallel conductor. The obtained optogalvanic signals exhibit better responsivity and pulse shape in comparison with other conventional techniques; in addition, they are detectable as far as 3 m from a signal source.     

Development of a dispersive liquid–liquid microextraction method for determination of palladium in water samples using dicyclohexano-18- crown-6 as extracting agent

A new separation procedure for determination of palladium using dispersive liquid–liquid microextraction with dicyclohexano-18-crown-6 as complexing reagent was developed. In this method, potassium–dicyclohexano-18-crown-6 was used as a hydrophobic complex for the microextraction of palladium as PdCl₄ ^2? complex ion. The main factors affecting DLLME efficiency, such as type and volume of extractant and disperser solvent, concentration of chelating reagent, concentration of KCl and pH were optimized. Under the optimal conditions, the limit of detection for palladium was 16.0 ng mL^?1 with enrichment factor of 138. The present method was applied to the determination of palladium in water samples with satisfactory analytical results. The method was simple, rapid, cost efficient and sensitive for the extraction and preconcentration of palladium.     

Ambient analysis by thermal desorption atmospheric pressure photoionization

Ambient mass spectrometry has attracted substantial attention in recent years. Among ambient ionization methods, thermal desorption ionization stands out because of two attributes: (1) simplicity, rendering the technique suitable for in-field applications, and (2) ability to couple with a variety of gas-phase ionization methods thereby broadening the range of molecules that can be analyzed with this method. Here, we report on improving the performance of a direct analysis in real time (DART) source by implementing atmospheric pressure photoionization (APPI) downstream of the desorption region. At identical desorption and ion sampling conditions, APPI leads to detection of radical molecular ions from non-polar compounds that are absent from the spectra generated by DART alone. Moreover, a factor of 3–5 improvement in sensitivity is observed using APPI for positive ions commonly detected by DART and DART-APPI. Using helium and nitrogen as desorption gases, APPI shows identical performance regardless of desorption gas type. In contrast, a dramatic decrease in sensitivity is observed for DART operated with nitrogen compared to DART with helium. Comparable performance for DART and DART-APPI are observed in negative ion mode, although both show a drastic improvement in the absence of the Vapur interface. This interface creates a differentially pumped chamber prior to inlet of the mass spectrometer and reduces the mass spectrometer gas load when helium is used as desorption gas.     

Dynamic correlation function for the propagation of light in disordered medium

We have calculated the time autocorrelation function of the intensity of light multiply scattered in the medium with dynamical properties. A new asimptotic for larget is found.     

A highly sensitive RP-HPLC-fluorescence method to study aldehyde oxidase activity

Aldehyde oxidase is a widely distributed enzyme that is involved in the metabolism of an extensive range of aldehydes and N-heterocyclic compounds with physiological, pharmacological, and toxicological relevance. In the present study, a highly sensitive RP-HPLC-fluorescence method based on the oxidation of phenanthridine to phenanthridinone has been developed and validated to assay aldehyde oxidase activity in biological samples. Determination of phenanthridinone was achieved on a C18 column using 10 mmol/L phosphate buffer (pH 5.0) containing 0.1 mmol/L EDTA-acetonitrile (40 + 60, v/v) as the mobile phase. The fluorescence intensity of phenanthridinone was measured at 364 nm with excitation at 236 nm. The proposed method was precise, accurate, specific and rapid (analysis time, approximately 8 min) with a mean RSD of 2.54%. Peak responses were linear from 0.5 to 100 nmol/L, with an LOD of 0.125 nmol/L. The applicability of the method was demonstrated by measurement of aldehyde oxidase activity in rat liver, kidney, ovary, and heart fractions.     

A protein fold classifier formed by fusing different modes of pseudo amino acid composition via PSSM

Protein function is related to its chemical reaction to the surrounding environment including other proteins. On the other hand, this depends on the spatial shape and tertiary structure of protein and folding of its constituent components in space. The correct identification of protein domain fold solely using extracted information from protein sequence is a complicated and controversial task in the current computational biology. In this article a combined classifier based on the information content of extracted features from the primary structure of protein has been introduced to face this challenging problem. In the first stage of our proposed two-tier architecture, there are several classifiers each of which is trained with a different sequence based feature vector. Apart from the application of the predicted secondary structure, hydrophobicity, van der Waals volume, polarity, polarizability, and different dimensions of pseudo-amino acid composition vectors in similar studies, the position specific scoring matrix (PSSM) has also been used to improve the correct classification rate (CCR) in this study. Using K-fold cross validation on training dataset related to 27 famous folds of SCOP, the 28 dimensional probability output vector from each evidence theoretic K-NN classifier is used to determine the information content or expertness of corresponding feature for discrimination in each fold class. In the second stage, the outputs of classifiers for test dataset are fused using Sugeno fuzzy integral operator to make better decision for target fold class. The expertness factor of each classifier in each fold class has been used to calculate the fuzzy integral operator weights. Results make it possible to provide deeper interpretation about the effectiveness of each feature for discrimination in target classes for query proteins.