Centrifugation: an efficient technique for preconcentration in anodic stripping voltammetric analysis of mercury using a gold film electrode

The effect of centrifugation on the voltammetric behavior of mercury on a gold film electrode was investigated. Mercuric ion was reduced with borohydride to form metallic mercury droplets which were collected on a gold film electrode with the aid of centrifugal force without a carrier material. A special cell was constructed for this purpose. The effect of the amounts of reducing agent, stripping solution, time and speed of centrifugation on the anodic stripping peaks resulting from the re-oxidation of mercury were investigated. The calibration graph for mercury(II) has a regression coefficient of 0.9941; its linear range is from 3.0 pM to 10.0 nM. Due to the effect of accumulation, the detection limit of mercury(II) is as low as 3 pM.     

Mixed-mode oscillations and cluster patterns in an electrochemical relaxation oscillator under galvanostatic control

We studied the dynamics of a prototypical electrochemical model, the electro-oxidation of hydrogen in the presence of poisons, under galvanostatic conditions. The lumped system exhibits relaxation oscillations, which develop mixed-mode oscillations (MMOs) for low preset currents. A fast-slow analysis of the homogeneous dynamics reveals that the MMOs arise from a fast oscillating subsystem and a one-dimensional slow manifold. In the spatially extended system, the galvanostatic constraint imposes a synchronizing global coupling that drives the system into cluster patterns. The properties of the cluster patterns (CPs) result from an intricate interplay of the nature of the local oscillators, the global constraint, and a nonlocal coupling through the electrolyte. In particular, we find that the global constraint suppresses small-amplitude oscillations of MMOs and prevents domains oscillating out of phase from occupying equal regions in phase space. The nonlocal coupling causes each individual clustered region to oscillate on a different limit cycle. Typically multistability of CPs is found. Coexisting patterns possess different oscillation periods and a different total fraction in space that occupies the in-phase or out-of-phase state, respectively.     

Modulation of Metal Carbonyl Stretching Frequencies in the Second Coordination Sphere through the Internal Stark Effect

Spectroscopic and computational examination of a homologous series of rhodium(I) pybox carbonyl complexes has revealed a correlation between the conformation of the flanking aryl-substituted oxazoline donors and the carbonyl stretching frequency. This relationship is also observed experimentally for octahedral rhodium(III) and ruthenium(II) variants and cannot be explained through the classical, Dewar–Chatt–Duncanson, interpretation of metal-carbonyl bonding. Instead, these findings are reconciled by local changes in the magnitude of the electric field that is projected along the metal-carbonyl vector: the internal Stark effect.     

Crystal Structures of 2-Chloro-3-((3-(trifluoromethyl)phenyl)amino)naphthalene-1,4-dione and 2-Chloro-3-((4-(trifluoromethyl)phenyl)amino)naphthalene-1,4-dione

Crystallography Reports - 2-Chloro-3-((3-(trifluoromethyl)phenyl)amino)naphthalene-1,4-dione (1) and 2-chloro-3-((4-(trifluoromethyl)phenyl)amino)naphthalene-1,4-dione (2) were obtained according...     

The non-isothermal kinetics of mullite formation in mechanically activated kaolinite–alumina ceramic system

The non-isothermal kinetics of mullite formation from both non-activated and mechanically activated kaolinite?+?alumina ceramic system have been studied by differential thermal analysis (DTA). The mixture of kaolinite and alumina was activated mechanically in a planetary mill, while amorphization in the kaolinite and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for mullite formation have been calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15, and 20?°C?min^?1. The mechanical activation of the kaolinite and alumina mixture resulted in the decrease in activation energy values for mullite formation.     

Newly synthesized Cu(II) pyrazino[2,3‐f][1,10]phenanthroline complexes as potential anticancer candidates

New binary and ternary copper(II) complexes, [Cu(py‐phen)₂(NO₃)]NO₃ ( 1 ), [Cu₂(py‐phen)₂(gly)₂(NO₃)₂(H₂O)₂]?3H₂O ( 2 ) and [Cu₂(py‐phen)₂(tyr)₂(H₂O)₂](NO₃)₂?3H₂O ( 3 ) (py‐phen: pyrazino[2,3‐f][1,10]phenanthroline; gly: glycine; tyr: tyrosine), have been synthesized and characterized using CHN analysis, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy and single‐crystal X‐ray diffraction. Interaction of these complexes with calf thymus DNA has been investigated using absorption spectral titration, ethidium bromide and Hoechst 33258 displacement assay and thermal denaturation measurements. These complexes were found to be efficient cleaving agents and cleavage reactions were mediated by hydrolytic and oxidative pathways. The interaction between these complexes and bovine serum albumin (BSA) was investigated using electronic absorption and fluorescence spectroscopy. The experimental results show that the fluorescence quenching mechanism of these complexes and BSA is a static quenching process. Furthermore, in vitro cytotoxicities of these complexes against tumour cell lines (Caco‐2, MCF‐7 and A549) and healthy cell line (BEAS‐2B) showed that they exhibited anticancer activity with low IC₅₀ values. These complexes were markedly active against the cell lines and can be good drug candidates that are effective and safe for healthy tissue.     

Study of adsorption and preconcentration by using a new silica organomodified with [3‐(2,2′‐dipyridylamine)propyl] groups

In this work, a silica surface chemically modified with [3‐(2,2′‐dipyridylamine)propyl] groups, named [3‐(2,2′‐dipyridylamine)propyl]silica (Si‐Pr‐DPA) was prepared, characterized, and evaluated for its heavy metal adsorption characteristics from aqueous solution. To our knowledge, we are the first authors who have reported the present modification. The material was characterized using infrared spectroscopy, SEM, and NMR ²⁹Si and ¹³C solid state. Batch and column experiments were conducted to investigate for heavy metal removal from dilute aqueous solution by sorption onto Si‐Pr‐DPA. From a number of studies the affinity of various metal ions for the Si‐Pr‐DPA sorbent was determined to follow the order Fe(III) > Cr(III) >> Cu(II) > Cd(II) > Pb(II) > Ni(II). Two standard reference materials were used for checking the accuracy and precision of the method. The proposed method was successfully applied to the analysis of environmental samples. This ligand material has great advantage for adsorption of transition‐metal ions from aqueous medium due to its high degree of organofunctionalization associated with the large adsorption capacity, reutilization possibility, and rapidity in reaching the equilibrium.     

Topical emulgel formulation containing inclusion complex of calcipotriol with cyclodextrin

Psoriasis is a relatively common, chronic, inflammatory disease that affects the skin, scalp, and joints. Calcipotriol is one of the most commonly used topical agents for the treatment of psoriasis. However, it is a water-insoluble active substance and frequently leads to skin irritation in patients. Cyclodextrins (CDs) are cyclic oligosaccharides consisting of (α-1,4-)-linked d-glucopyranose units. CD molecules have a hydrophilic outer surface and a lipophilic central cavity, and they are able to form inclusion complexes in aqueous solutions with many drugs. They can increase bioavailability, aqueous solubility, and stability and also reduce the side effects of the drugs. The aim of this study was to develop a new topical drug delivery system of calcipotriol in order to improve the solubility and dissolution characteristics of the drug and reduce the undesirable side effects. For this purpose, an inclusion complex of calcipotriol with Captisol^® was prepared, and complex formation was confirmed. The inclusion complex and pure drug were formulated separately in an emulgel base. Dissolution profiles of calcipotriol from emulgel formulations were compared with a commercial product of the drug. The drug release was significantly increased with the emulgel formulations compared to the commercial cream product.     

Effect of polymerization methods on the residual monomer level of acrylic resin denture base polymers

Wearing dental acrylic prosthesis causes adverse reactions to oral tissues due to bioactive leachables from resins such as residual methyl methacrylate (MMA). The aim of this study is to apply the high performance liquid chromatography (HPLC) method to quantify and compare the amount of MMA monomers released from denture base resin polymers processed by the conventional compression molding method (Paladent), microwave polymerization (Acron MC), and injection molding technique (PalaXpress). Six specimens of 10 ± 0.2 mm in diameter and 2.0 ± 0.2 mm in thickness of each material were prepared according to manufacturer's instructions. Specimens were stored in nanopure water at room temperature (23 ± 2°C) for 4 hr, 48 hr, 8 days, and 15 days separately. Residual MMA released into water was determined with HPLC for all time intervals. Data for all time intervals were analyzed among each group using the Friedman test and differences were found to be statistically significant for all time intervals for Acron MC, Paladent, and PalaXpress (p > 0.05). Kruskal–Wallis test was used to compare changes of residual MMA within time intervals among denture base resin groups and statistically significant differences were found between all time intervals (p > 0.05). Acron MC exhibited significantly lower residual MMA leach compared both to Paladent and PalaXpress, and Paladent showed more residual MMA leach compared to PalaXpress. Residual MMA leach for Acron MC, PalaXpress, and Paladent showed statistically significant leach in the first 48 hr of immersion in water followed by gradual longer‐lasting moderate increase until the 15 day interval which was not statistically significant (p < 0.05). Copyright © 2007 John Wiley & Sons, Ltd.