Selective determination of uric acid in the presence of ascorbic acid using a penicillamine self-assembled gold electrode

The electrochemical behaviors of uric acid (UA) at the penicillamine (Pen) self-assembled monolayers modified gold electrode (Pen/Au) have been studied. The Pen/Au electrode is demonstrated to promote the electrochemical response of UA by cyclic voltammetry (CV). The diffusion coefficient D of UA is 6.97 × 10⁻⁶ cm² s⁻¹. In differential pulse voltammetric (DPV) measurements, the Pen/Au electrode can separate the UA and ascorbic acid (AA) oxidation potentials by about 120 mV and can be used for the selective determination of UA in the presence of AA. The detection limit was 1 × 10⁻⁶ mol L⁻¹. The modified electrode shows excellent sensitivity, good selectivity and antifouling properties.     

Two color up-conversion emissions of Er<Superscript>3+</Superscript>-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders prepared by non-aqueous sol-gel method

Er³⁺-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method using the aluminum isopropoxide as precursor, acetylacetone as a chelating agent, nitric acid as a catalyzer, and hydrated erbium nitrate as a dopant under isopropanol environment. The different phase structure, including three crystalline types of (Al, Er)₂O₃ phases, α, γ, θ, and an Er–Al–O stoichiometric compound phase, Al₁₀Er₆O₂₄, was observed for the 0.01–0.5 mol% Er³⁺-doped Al₂O₃ nanopowders at the sintering temperature of 1,000 °C. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978 nm semiconductor laser diodes excitation. With increasing Er³⁺ doping concentration from 0.01 to 0.1 mol%, the intensity of the green and red emissions increased with a decrease of the intensity ratio of the green to red emission. When the Er³⁺ doping concentration rose to 5 mol%, the intensity of the green and red emissions decreased with an increase of their intensity ratio. The maximum intensity of both the green and red emissions with the minimum of intensity ratio was obtained, respectively, for the 0.1 mol% Er³⁺-doped Al₂O₃ nanopowders composed of a single α-(Al,Er)₂O₃ phase. The intensity ratio of the green emission at 523 and 545 nm increased monotonously for all Er³⁺ doping concentrations. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er³⁺-doped Al₂O₃ nanopowders.     

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10⁻⁶ cm² s⁻¹. In 0.1 mol L⁻¹ phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10⁻⁵–2.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁷–1.0 × 10⁻⁶ mol L⁻¹. The detection limit is 5 × 10⁻⁸ mol L⁻¹. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.     

New 2D graphical representation of DNA sequences

We consider a 2D graphical representations of DNA sequences, which avoids loss of information associated with crossing and overlapping of the corresponding curve. We outline an approach, which is based on the construction of a three-component vector whose components are the normalized leading eigenvalues of the L/L matrices associated with DNA. The examination of similarities/dissimilarities among the coding sequences of the first exon of beta-globin gene of different species illustrates the utility of the approach.     

A cytotoxic compound from the leaves of Juglans mandshurica

From Juglans mandshurica leaves, a new quinone compound was isolated through bioassay-guided fractionation. The structure elucidation of the compound was established based on spectroscopic studies, notably of the 2D NMR spectra. The compound exhibited moderate cytotoxic activities against Hela, MCF-7, BGC823 and 3T3-Llcell lines with IC50 ranges from 7.5 to 26.8 μmol/L.     

Magnetic beads-based bioelectrochemical immunoassay of polycyclic aromatic hydrocarbons

A simple, rapid, and sensitive bioelectrochemical immunoassay method based on magnetic beads (MBs) has been developed to detect polycyclic aromatic hydrocarbons (PAHs). The principle of this bioassay is based on a direct competitive enzyme-linked immunosorbent assay using PAH-antibody-coated MBs and horseradish peroxidase (HRP)-labeled PAH (HRP-PAH). A magnetic process platform was used to mix and shake the samples during the immunoreactions and to separate free and unbound reagents after the liquid-phase competitive immunoreaction among PAH-antibody-coated MBs, PAH analyte, and HRP-PAH. After a complete immunoassay, the HRP tracers attached to MBs were transferred to a substrate solution containing 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂) for electrochemical detection. The voltammetric characteristics of the substrate were investigated, and the reduction peak current of TMB was used to quantify the concentration of PAH. The different parameters, including the amount of HRP-PAH conjugates, the enzyme catalytic reaction time, and the pH of the supporting electrolyte that governs the analytical performance of the immunoassay have been studied in detail and optimized. The detection limit of 50 pg mL⁻¹ was obtained under optimum experimental conditions. The performance of this bioelectrochemical magnetic immunoassay was successfully evaluated with tap water spiked with PAHs, indicating that this convenient and sensitive technique offers great promise for decentralized environmental applications.     

Characteristic sequences for DNA primary sequence

A DNA sequence can be identified with a word over an alphabet N = [A, C, G, T]. Characteristic sequences of a DNA sequence are given in term of classifications of bases of nucleic acids. Using the characteristic sequences, we construct a set of 2 x 2 matrices to represent DNA primary sequences, which are based on counting of the frequency of occurrence of all (0,1) triplets of characteristic sequences. Furthermore, the leading eigenvalues of these matrices are computed and considered as invariants for the DNA primary sequences. Similarity and dissimilarity analysis based on the characteristic sequences are given for eight exon-1 genes of beta-globin about eight species.     

Phase equilibrium calculations for carbon dioxide + n-alkanes binary mixtures with the Wong–Sandler mixing rules

Phase equilibrium for carbon dioxide + n-alkanes (from methane to n-decane) asymmetric binary systems was calculated using Peng–Robinson Stryjek–Vera equation of state coupled with Wong–Sandler mixing rules. NRTL model was utilized for predicting the excess Helmholtz free energy. The second virial coefficient binary interaction parameter k₁₂ and NRTL model parameters τ₁₂ and τ₂₁ for carbon dioxide + n-alkanes binary systems were optimized trough minimization of two different objective functions: one based on the calculation of the distribution coefficients, and the other one based on the determination of bubble point pressures. Generalized correlations for mixing rule parameters as a function of the n-alkane acentric factor and the equilibrium temperature were obtained from optimal parameters determined by the first objective function. Obtained results using both objective functions were satisfactory, but the estimation of the parameters calculated by the second objective function provided a better accuracy in vapor–liquid equilibrium prediction.     

Copper-catalyzed oxidative CH bond functionalization of N-allylbenzamide for CN and CC bond formation

CH bond functionalization for CN and CC bond formations via cross-dehydrogenative coupling (CDC) of N-allylbenzamides with indole as amine source has been developed under a copper-catalyzed condition. To the best of our knowledge, these are the first examples in which different classes of N-containing compounds were directly prepared from the readily available N-allylbenzamides using an inexpensive catalyst-oxidant (CuSO₄/TBHP) system. Further, it was applied for the synthesis of α-substituted N-allylbenzamides by using Grignard reagent as nucleophiles.