Heteropolyacid immobilized on polymer/magnetic zeolite nanocomposite as a new and recyclable catalyst for the selective oxidation of alcohols

A new magnetic oxidation catalyst was prepared using immobilization of tungstophosphoric acid on poly(N-vinylimidazole) entrapped magnetic nanozeolite and characterized by FTIR, TGA, XRD, SEM, TEM, EDX, VSM, and ICP-OES. The resulting heterogeneous catalyst displays high catalytic performance for selective oxidation of alcohols compared to the other catalysts. The catalyst could be reused eight times without any loss of catalytic activity.     

Direct Synthesis of a Covalent Triazine‐Based Framework from Aromatic Amides

There have been extensive efforts to synthesize crystalline covalent triazine‐based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide (P₂O₅)‐catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P₂O₅‐catalyzed condensation was applied on terephthalamide to construct a covalent triazine‐based framework (pCTF‐1). This approach yielded highly crystalline pCTF‐1 with high specific surface area (2034.1 m² g^?1). At low pressure, the pCTF‐1 showed high CO₂ (21.9 wt % at 273 K) and H₂ (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine‐based COF was also confirmed by model reactions, with the P₂O₅‐catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5‐triphenyl‐2,4,6‐triazine in high yield.     

High-Alkaline protease fromBacillus PB92 entrapped in calcium alginate gel

High-alkaline protease (HAP) has been entrapped in Manugel DMB (an alginate gel) and assayed with two sizes and types of substrates: neutral protein casein and synthetic chromogenic tripeptide substrate, Z-Gly-Pro-Cit-PNA. Increasing the concentration of calcium chloride used for capsule formation decreased the measured enzyme activity with both substrates. Capsules were found to be stable in water for long periods of time, but they dissolved in both phosphate and carbonate-bicarbonate buffers. The pH vs activity profiles of encapsulated enzyme showed pH optima between 10 and 11 with both substrates. The calcium alginate matrix surrounding the enzyme was quite effective in stabilizing the enzyme at 20–25 °C and even more so at 4°C. Enzyme stability at 50 °C was quite impressive, some enzyme activity being evident even after remaining for 1 wk at this temperature in water. Increasing concentrations of sodium dodecyl sulfate (SDS) were also found to inhibit the protease progressively, whereas a polyhexamethylene biguanidium chloride (PHMBH⁺Cl^-) and SDS:PHMBH⁺Cl^- combination showed the opposite effect. Optical microscopy, especially polarized light microscopy, provided a sensitive physical means of ascertaining some of the structural properties (sphericity, disorganization or organization, distinct layer enveloping the capsules, intensity of the maltese cross) of the capsules with and without enzyme before and after different chemical treatments and the presence or absense of the substrate.     

Estimation of the ground state correlation energy for isoelectronic series of 2 to 20 electrons

Correlation energies for all isoelectronic sequences of 2 to 20 electrons andZ=2 to 25 are obtained by taking differences between theoretical total energies of Dirac-Fock calculations and experimental total energies. These are pure relativistic correlation energies because relativistic and QED effects are already taken care of. The theoretical as well as the experimental values are analysed critically in order to get values as accurate as possible. The correlation energies obtained show an essentially consistent behaviour fromZ=2 to 17. ForZ>17 inconsistencies occur indicating errors in the experimental values which become very large forZ>25.     

Ethylenebis( N -methylimidazolium) Chlorochromate ( EBMICC ): An Efficient and Selective Reagent for the Oxidation of Thiols to Disulfides

Ethylenebis(N-methylimidazolium) chlorochromate was prepared by addition of N-methylimidazole to 1,2-dibromoethane to form the corresponding dibromide salt and subsequent treatment of this salt with CrO₃ in 6N HCl solution. It is a stable yellow-orange solid, which oxidized thiols to the corresponding disulfides at room temperature. Selective oxidation of thiols in the presence of sulfides and hydroxyl groups was also achieved with this reagent.     

Sulfate-selective PVC membrane electrode based on a strontium Schiff's base complex

A strontium Schiff's base complex (SS) can be used as a suitable ionophore to prepare a sulfate-selective PVC-based membrane electrode. The use of oleic acid (OA) and hexadecyltrimethylammonium bromide (HTAB), as additives, and nitrobenzen (NB), dibutyl phthalate (DBP) and benzyl acetate (BA) as solvent mediators, were investigated. The best performance was observed with a membrane composition PVC: NB: SS: HTAB of 30%: 62%: 5%: 3% ratio. The resulting sensor works well over a wide concentration range (1.0 x 10(-2)-1.0 x 10(-6) M) with a Nernstian slope of -29.2 mV per decade of sulfate activity over a pH range 4.0-7.0. The limit of detection of the electrode is 5 x 10(-7) M. The proposed sensor shows excellent discriminating ability toward SO4(2-) ions with regard to many anions. It has a fast response time of about 15 s. The membrane electrode was used to the determination of zinc in zinc sulfate tablets. The sensor was also used as an indicator electrode in the potentiometric titration of SO4(2-) against barium ion.     

Membrane extraction with sorbent interface-gas chromatography as an effective and fast means for continuous monitoring of thermal degradation products of polyacrylonitrile

A novel sample preparation technique, membrane extraction with a sorbent interface (MESI) has been optimized and used for continuous monitoring thermal degradation products in polyacrylonitrile (PAN) polymer headspace at different temperatures, followed by gas chromatography-mass spectrometry (GC-MS). MESI with a flat sheet poly(dimethyl siloxane)-polycarbonate (PDMS-PC) membrane and Tenax trap was used. The system is very simple, fast and reliable and allowed us to extract, enrich and continuously monitor major volatile compounds released from the polymer at different temperatures. The volatile and semi-volatile gaseous degradation products were identified. Sensitivity of the method depends on the length of time for trapping.     

[Pb2(AMP)2(μ‐X)2X2], X = Br− and I−, AMP = 2‐aminomethylpyridine,Two New Dimeric Lead(II) Complexes Extended in One‐dimensional Helical Chain Polymers by Noncovalent π–π‐stacking

The two lead(II) complexes [Pb₂(AMP)₂(μ‐X)₂X₂], X = Br^?, I^? and AMP = 2‐aminomethylpyridine, have been synthesized and characterized. Self‐assembly of these compounds in the solid state via π–π‐stacking interactions is discussed.     

Reductive Amination of Aldehydes and Ketones to Their Corresponding Amines with NaBH4 in Micellar Media

A variety of aliphatic and aromatic aldehydes and ketones were efficiently reduced to their corresponding amines when treated with primary and secondary amines and NaBH₄ in micellar media at room temperature under neutral conditions.