Chemometric approach in optimization of micellar liquid chromatographic separation of some halogenated phenols

Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content and pH of the mobile phase. The experiments were performed according to the face-centred cube central composite design and the inverse form of the experimental retention times for analytes were fitted to the polynomial models. The results of the analysis of variance showed that the models obtained explain greater than 99% of the variance observed in the chromatograms. Good predictive ability of the models was verified as high values of the statistics R² and F were obtained for the linear relationship between predicted cross-validated and experimental values of the dependent variable. The study showed that the use of Pareto-optimality method, an approach from multi-criteria decision-making, allows the selection of the best possible combinations of separation and analysis time in micellar liquid chromatography of chlorophenols.     

Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite

The adsorption of two dyes, namely, Acid Red 57 (AR57) and Acid Blue 294 (AB294), onto acid-activated bentonite in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. Acidic pH was favorable for the adsorption of these dyes. The surface characterization of acid-activated bentonite was performed using the FTIR technique. The pseudo-first-order and pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The dynamic data fitted the pseudo-second-order kinetic model well and also followed the intraparticle diffusion model up to 90 min, but diffusion is not the only rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The Freundlich model agrees very well with experimental data. The activation energies of adsorption were also evaluated for the adsorption of AR57 and AB294 onto activated bentonite.     

AN ACTION SPECTRUM FOR LETHAL PHOTOSENSITIZATION OF Candida albicans BY 8-MOP AFTER LOW-DOSE BROAD-BAND UV-A IRRADIATION; AN ACTION SPECTRUM FOR 8-MOP 4′,5′- MONOADDUCTS?

An action spectrum was obtained for lethal photosensitization of Candida albicans that had been pre-irradiated with a sub-lethal low dose of broad-band UV-A after incubation with 8-methoxypsoralen and then washed to remove any non-photobound 8-methoxypsoralen. The resultant spectrum with a peak in the 320-335 nm region was similar to that obtained by a conventional method (single irradiation only) and also to the absorption spectrum of the 4',5'-monoadduct. These data support the hypothesis that the chromophore for lethal photosensitization by 8-methoxypsoralen is the 8-methoxypsoralen/DNA 4',5'-monoadduct rather than 8-methoxypsoralen itself.     

Reaction of tris(trimethylsilyl)methylsilicon halides with methanolic sodium methoxide. Probability of sila-olefin intermediates

The compounds TsiSiR₂X [Tsi = Me₃Si)₃C; R = Me, X = Cl, Br, I, or R = Ph, X = F, Cl, Br, I)] react with boiling 2 M MeONa-MeOH to give products of the type (Me₃Si)₂CHSiR₂OMe. It is suggested that the reaction proceeds through an elimination, analogous to E2 eliminations of alkyl halides, involving synchronous attack of MeO^? at an Me₃Si group, liberation of X^?, and formation of (Me₃Si)₂CSiR₂. The compounds TsiSiPhMeF TsiSiPhCl₂ react analogously to give (Me₃Si)₂CHSiPhMe(OMe) and (Me₃Si)₂CHSiPh(OMe)₂ [tha latter presumably by solvolysis of the initially-formed (Me₃Si)₂CHSiPhCl(OMe)]. The compounds TsiSiMe₂OMe and TsiSiMe₃ do not react, while TsiSiMe₂H gives TsiH. The compound TsiSiCl₃ reacts with 0.1 M MeONa-MeOH to give the substitution and elmination products TsiSiCl₂(OMe) and (Me₃Si)₂CHSi(OMe)₃ in ca. $\text{1}\text{2}$ ratio.     

Structural characterization of dodecyltrimethylammonium (DTMA) bromide modified sepiolite and its adsorption isotherm studies

In this study, dodecyltrimethylammonium (DTMA) bromide was used to modify natural sepiolite via an ion exchange reaction to form DTMA-sepiolite. Sepiolite and DTMA-sepiolite were then characterized by using Brunauer–Emmett–Teller (BET), elemental analysis, XRD, FT-IR, thermogravimetric (TG) and zeta potential analysis techniques. The BET surface area of sepiolite significantly decreased from 152.14 m² g^–1 to 88.63 m² g^–1, after the modification, due to the coverage of the pores of sepiolite. DTMA was located onto sepiolite according to the differential thermogravimetric (dTG) peaks of DTMA-sepiolite. XRD results confirmed the interaction between DTMA⁺ cations and sepiolite. FT-IR spectra indicated the existence of DTMA functional groups on sepiolite surface. After the characterization was accomplished, adsorption isotherm studies of naphthalene, which is the first member of the polycyclic aromatic hydrocarbons (PAHs), were carried out. The maximum adsorption capacity of DTMA-sepiolite for naphthalene was determined from Langmuir isotherm equation at pH 6 and 20 °C as 1.88 × 10^–4 mol g^?1 or 24.09 mg g^?1.     

1,3-Migration of Trimethylsilyl Group from Carbon to Oxygen in Highly Sterically Hindered Silanol of the Type (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH and Reaction of the Related Iodide with Iodine Monochloride and Iodine Monobromide

The silanol (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH has been shown to isomerize to (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) when it was kept at room temperature for 10 h in 0.2 M NaOMe/MeOH. Corresponding isomerizations of the above silanol (to give (Me 3 Si) 2 CHSi(C 6 H 4 Me- p ) (Me)(OSiMe 3 )) are complete after 26 h under reflux in pyridine. The reaction involve 1,3-migration from carbon to oxygen within a silanolate ion to give a carbanion, which rapidly acquires a proton from the solvent. Treatment of (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH with MeLi in Et 2 O/THF give, by the same rearrangement, the organolithium reagent (Me 3 Si) 2 CLiSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) which on treatment with Me 2 SiHCl gives (Me 3 Si) 2 C(SiMe 2 H)Si(C 6 H 4 Me- p )(Me)(OSiMe 3 ) and (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). When the experiment was repeated, but with Me 3 SiCl in place of Me 2 SiHCl, it gives exclusively (Me 3 Si) 2 CHSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). Treatment of the organolithium reagent (Me 3 Si) 2 CLiSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ) with Mel gives exclusively (Me 3 Si) 2 CMeSi(C 6 H 4 Me- p )(Me)(OSiMe 3 ). The related iodide (Me 3 Si) 3 CSi(C 6 H 4 Me- p )Mel reacts with ICI and IBr to give rearranged (Me 3 Si) 2 C(SiMe 2 X)Si(C 6 H 4 Me- p )Me 2 and unrearranged products (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeX, (X = Cl, Br) respectively. The rearranged bromide (Me 3 Si) 2 C(SiMe 2 Br)Si(C 6 H 4 Me- p )Me 2 reacts with a range of silver [I] salts AgY (Y = OOCCH 3 , SO 4 2 m ) and Mercury [II] salt HgY 2 (Y = OOCCH 3 , SO 4 2 m ) in glacial CH 3 COOH to give the corresponding species (Me 3 Si) 2 C(SiMe 2 OOCCH 3 )Si(C 6 H 4 Me- p )Me 2 . The reaction of the bromide with AgBF 4 in MeOH or i -PrOH give the corresponding rearranged products (Me 3 Si) 2 C(SiMe 2 Y)Si(C 6 H 4 Me- p )Me 2 (Y = --OMe, --OPr i ).     

Synthesis of Novel Organosilicon Compounds Possessing Fully Substituted Imidazole Nucleus Sonocatalyzed by Fe-Cu/ZSM-5 Bimetallic Oxides

An efficient four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles is described by one-step condensation of an aldehyde, benzil, ammonium acetate, and primary aromatic amine with nanostructure Fe-Cu/ZSM-5 bimetallic oxides in water under ultrasonic irradiation. The short reaction time, good yields, environmental friendly procedure, mild reaction conditions, and convenient operation are important advantage of this protocol. The products generated during the study have been utilized as substrates for synthesis of organosilicon-containing imidazoles. Synthesis of tris(triorganosilyl)methylimidazole derivatives were carried out using organolithium reagent (Me₃Si)₃CLi, prepared via metalation of (Me₃Si)₃CH with methyllithium in tetrahydrofuran, in excellent yields.     

Strong Bragg gratings photoinduced by 633-nm illumination in evaporated As2Se3 thin films

Bragg gratings are used in several photonic devices to reflect, and thus to isolate, specific wavelengths of light. Gratings can be photoinduced in chalcogenide glasses by illumination of bandgap light in an interference pattern. We used holographic interferometry to create Bragg gratings in amorphous As2Se3 thin films with a period of 0.56 microm by illumination with 633-nm light. The quality of the gratings was tested in real time, and refractive-index modulations as high as 0.037 were measured. These gratings were found to be stable over a period of several months if they were kept in the dark.     

Comparison of Two Stability-Indicating Chromatographic Methods for the Determination of Mirabegron in Presence of Its Degradation Product

Mirabegron is a novel β₃-adrenoceptor agonist containing an amide group. It was subjected to stress conditions of acidic and alkaline hydrolyses. The hydrolytic degradation product was isolated and its structure was confirmed using mass and IR spectrometry. Two stability-indicating chromatographic methods have been proposed for the determination of mirabegron. TLC method was applied using silica gel as stationary phase and chloroform–methanol–ammonia (9.0:1.0:0.1 by volume) as the mobile phase, and chromatograms were scanned at 250 nm. Accurate determination of the drug was achieved over the concentration range of 2–12 μg per band. In addition, an isocratic HPLC method was developed on Agilent C18 column (150 mm × 4.5 mm I.D., particle size 5 µm) using ethanol-phosphate buffer pH 2.5 (30:70, by volume) as a mobile phase with flow rate of 1 mL min^?1.The intact drug was detected at 250 nm with running time less than 5 min. Mirabegron was determined accurately in a concentration range of 1–25 µg mL^?1. The proposed chromatographic methods were applied successfully for the assay of mirabegron in pharmaceutical dosage form and both methods were validated as per the International Conference on Harmonization guidelines and statistically compared with a reported gradient HPLC method.     

Theoretical study of indirect excitons’ lifetime in coupled AlGaN/GaN quantum wells in the presence of an electrostatic trap

The lifetime of electrostatically trapped indirect excitons in a field-effect structure based on coupled AlGaN/GaN quantum wells has been theoretically studied. Within the plane of a double quantum well, indirect excitons are trapped between the surfaces of the AlGaN/GaN heterostructures and a semitransparent metallic top gate. The trapping mechanism has been assumed to be a combination of the quantum confined Stark effect and local field enhancement. In order to study the trapped exciton lifetime, the binding energy of indirect excitons in coupled quantum wells is calculated by finite difference method in the presence of an electric field. Thus, the lifetime of trapped excitons is computed as a function of well width, AlGaN barrier width, the position of double quantum well in the device and applied voltage.