Catalytic activity and electrochemical properties of Cu(II)-Schiff base complex encapsulated in the nanocavities of zeolite-Y for oxidation of olefins and sulfides

Copper(II) complex of a Schiff base ligand (H₂L) was synthesized, characterized, and encapsulated in the cavities of zeolite-Y by a fixed ligand method. The zeolite encapsulated metal complex (CuL-Y) was characterized using FT-IR, UV–Vis and atomic absorption spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), scanning electron microscopy images (SEM), energy-dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET). The catalytic activity and electrochemical behavior of the encapsulated complex has been studied in the oxidation of a wide range of sulfides and olefins using H₂O₂ in ethanol. This heterogeneous catalytic system shows a dramatic increase in total turnover number (46,500) for oxidation of styrene. It could be readily reused for at least eight successive times without discernible activity and selectivity deterioration, which displays potential for practical applications.     

Synthesis,X-ray structural and DFT studies of n-membered ring P,C-chelated complexes of Pd(II) and Pt(II) derived from unsymmetrical phosphorus ylides and application of Pd(II) complexes as catalyst in Suzuki reaction

The phosphonium salts [Ph₂P(CH₂)_nPPh₂CH₂C(O)C₆H₄-m-OMe]Br (n = 1 (S₁) and n = 2 (S₂)) were synthesized in the reaction of bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)ethane (dppe) with 2-bromo-3?-methoxy acetophenone, respectively. Further treatment with NEt₃ gave the phosphorus ylides Ph₂P(CH₂)_nPPh₂C(H)C(O)C₆H₄-m-OMe (n = 1 (Y₁) and n = 2 (Y₂)). These ligands were treated with [MCl₂(cod)] (M = Pd or Pt; cod = 1,5-cyclooctadiene) to give the P, C-chelated complexes, [MCl₂(Ph₂P(CH₂)_nPPh₂C(H)C(O)C₆H₄-m-OMe)] (n = 1, M = Pd (3), Pt (4), and n = 2, M = Pd (5), Pt (6)). These compounds were characterized by elemental analysis, spectroscopic methods, UV–visible, and fluorescence emission spectra. Further, the structures of complexes 3 and 6 were characterized crystallographically. The palladium complexes 3 and 5 proved to be excellent catalysts for the Suzuki reactions of various aryl chlorides. Also, a theoretical study on the structure of complexes 3–6 has been investigated at the BP86/def2-SVP level of theory. The strength and nature of donor?acceptor bonds between the phosphorus ylides (L) and MCl₂ fragment in the [LMCl₂] (M = Pd, Pt, L = Y₁, Y₂) were studied by NBO and energy decomposition analysis (EDA), as well as their natural orbitals for chemical valence variation (EDA-NOCV).     

Structural diversity in pseudohalide complexes of cadmium(II) with N-methylthiourea (Metu): Polymeric [Cd(Metu)2(NCS)2]n versus monomeric [Cd(Metu)2(CN)2]

Cadmium(II) complexes, catena-poly[bis(thiocyanato-κN)bis(N-methylthiourea)cadmium(II)], [Cd(Metu)₂(NCS)₂]_n (1) and dicyanidobis(N-methylthiourea)cadmium(II), [Cd(Metu)₂(CN)₂] (2) were prepared and their structures were determined by single crystal X-ray analysis. In 1, the cadmium(II) ion is bound to four sulfur atoms of bridging Metu ligands and two nitrogen atoms of thiocyanate adopting a distorted octahedral environment. In 2, the geometry around cadmium is distorted tetrahedral attained by two cyanide ions and two methylthiourea molecules bound through the sulfur atoms. The crystal structures of both complexes show intra and intermolecular hydrogen bonding interactions. The complexes were also characterized by IR and NMR spectroscopy and the spectroscopic data were discussed in terms of the nature of bonding.     

Defining the characteristics of spherical Janus particles by investigating the behavior of their corresponding particles at the oil/water interface in a Pickering emulsion

In this study, a new analytical/experimental method is proposed in order to investigate the adsorption of different-sized spherical silica particles at the oil/water interface in a Pickering emulsion system as a well-known method to produce Janus particles. Accordingly, the characteristic of the produced silica Janus particles was defined based on their penetration depth into dispersed oil droplets. To ensure the accuracy of the method, the penetration depth of silica particles was also measured using field emission scanning electron microscopy images of solidified oil droplets covered with particles. The results revealed that the penetration depth increases with the size of the particles.     

A novel method of measuring electrophoretic mobility of gas bubbles

Accurate measurement of electrophoretic mobility for gas bubbles is a challenging task as it requires the creation of a desired number of very small air bubbles to ensure negligible rise velocities during the course of the measurement. Here, we report a simple and reliable method for generating stable dispersions of "nano-bubbles." Preparation of such dispersions relies on the nucleation of nano-bubbles in solutions supersaturated with gas. Electrophoretic mobility of these nano-bubbles is determined by the ZetaPALS technique (Brookhaven Instruments) using Uzgiris electrodes coated with palladium. The Smoluchowski limit is assumed in the calculation of zeta potentials. In regard to reproducibility and reliability, this novel method shows a clear advantage over other existing techniques of zeta potential measurement for bubbles.     

Structural and co-conformational effects of alkyne-derived subunits in charged donor-acceptor [2]catenanes

Four donor-acceptor [2]catenanes with cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-electron-accepting cyclophane and 1,5-dioxynaphthalene (DNP)-containing macrocyclic polyethers as pi-electron donor rings have been synthesized under mild conditions, employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu2+-mediated Eglinton coupling in the final steps of their syntheses. Oligoether chains carrying terminal alkynes or azides were used as the key structural features in template-directed cyclizations of [2]pseudorotaxanes to give the [2]catenanes. Both reactions proceed well with precursors of appropriate oligoether chain lengths but fail when there are only three oxygen atoms in the oligoether chains between the DNP units and the reactive functional groups. The solid-state structures of the donor-acceptor [2]catenanes confirm their mechanically interlocked nature, stabilized by [pi...pi], [C-H...pi], and [C-H...Omicron] interactions, and point to secondary noncovalent contacts between 1,3-butadiyne and 1,2,3-triazole subunits and one of the bipyridinum units of the CBPQT4+ ring. These contacts are characterized by the roughly parallel orientation of the inner bipyridinium ring system and the 1,2,3-triazole and 1,3-butadiyne units, as well as by the short [pi...pi] distances of 3.50 and 3.60 A, respectively. Variable-temperature 1H NMR spectroscopy has been used to identify and quantify the barriers to the conformationally and co-conformationally dynamic processes. The former include the rotations of the phenylene and the bipyridinium ring systems around their substituent axes, whereas the latter are confined to the circumrotation of the CBPQT4+ ring around the DNP binding site. The barriers for the three processes were found to be successively 14.4, 14.5-17.5, and 13.1-15.8 kcal mol-1. Within the limitations of the small dataset investigated, emergent trends in the barrier heights can be recognized: the values decrease with the increasing size of the pi-electron-donating macrocycle and tend to be lower in the sterically less encumbered series of [2]catenanes containing the 1,3-butadiyne moiety.     

A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3 mm × 5 mm) is immobilized on a wafer polyimide microchip (size 13.5 mm × 3.5 mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1 ± 0.1 mV decade⁻¹ over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, the lower detection limit is 0.05 μg mL⁻¹, the working pH is 2-9,and the output is 70-90 samples h⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.     

A novel wire-type lead-selective electrode based on bis (1'-hydroxy-2'-acetonaphthone)-2,2'-diiminodiethylamine

The preparation of a lead-selective electrode based on bis(1'-hydroxy-2'-acetonaphthone)-2,2'-diiminodiethylamine (L) as sensing material is reported. The plasticized PVC membrane containing 30% PVC, 67% ortho-nitrophenyloctylether (NPOE) and 3% ionophore L was directly coated on a graphite rod. This electrode exhibits a nearly Nernstian slope of 27.8+/-0.2 mV decade(-1) over a concentration range 10(-6)-10(-2) M with a detection limit of 4.0 x 10(-7) M. The response time of the electrode was found to be <20 s. The potential of the sensor was independent on pH variations in the range 5-7. The selectivity of the electrode towards lead ions over Na+, K+, Ag+, Ca2+, Sr2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, La3+, Sm3+ and Er3+ ions was investigated. The prepared electrode was successfully used as an indicator for titration of a lead solution with a standard solution of EDTA. The applicability of the sensor for Pb2+ measurement in various synthetic and real samples has been also demonstrated.     

Synthesis and antibacterial activity of new N-[2-(thiophen-3-yl)ethyl] piperazinyl quinolones

As a part of continuing search for potential antibacterial agents in the quinolones field, we have synthesized novel quinolone agents bearing N-[2-(thiophen-3-yl)ethyl] piperazinyl moiety in the 7-position of the quinolone ring. In vitro antibacterial evaluation of the target compounds showed that N-[2-(thiophen-3-yl)ethyl] group attached to piperazine ring served as promising C-7 substituent for piperazinyl quinolone antibacterials. Among these derivatives, ciprofloxacin analogues, containing N-[2-(thiophen-3-yl)-2-hydroxyiminoethyl] or N-[2-(thiophen-3-yl)-2-methoxyiminoethyl] residue provided a high inhibition against all the tested Gram-positive organisms including methicillin-resistant Staphylococcus aureus comparable or superior with respect to the reference drugs norfloxacin and ciprofloxacin.     

An environmentally friendly electrochemical method for synthesis of benzofuranoquinone derivatives

Electrochemical oxidation of catechols (1a-c) has been studied in the presence of 2-hydroxy-1,4-naphtoquinone (3b) in aqueous solutions, using cyclic voltammetry and controlled-potential coulometry. The results indicated that the electrochemically generated o-benzoquinones (2a-c) participate in Michael addition reaction with 3b to the corresponding benzofuranoquinones (8a-c, 10a-c). The electrochemical synthesis of these compounds has been successfully preformed at a carbon rod electrode with good yields using an environmentally friendly method.