Conductance study of the thermodynamics of ammonium ion complexes with several crown ethers in acetonitrile solution

A conductance study concerning the interaction between ammonium ion and several crown ethers in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 11 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The influence on the thermodynamic data of different parameters such as cavity size and dimensionality of crown ethers, nature of substituents in the polyether ring, conformations of the free and complexed ligands, solvent-ligand interaction and number of N–H bonds available for hydrogen bonding are discussed.     

Headspace solvent microextraction A new method applied to the preconcentration of 2-butoxyethanol from aqueous solutions into a single microdrop

A new procedure and experimental setup for the headspace solvent microextraction of volatile organic materials from aqueous sample solutions is described. The extraction occurs by suspending a 3-μl drop of the solvent from the tip of a microsyringe to the headspace of a stirred aqueous sample solution for a preset extraction time. The temperature of the microdrop and the bulk of sample solution should be kept constant at optimized values. The sample analyses were carried out by gas chromatography. The procedure was successfully applied to the extraction and determination of 2-butoxyethanol from content of some color samples used for painting the outer coverage of some machines such as coolers, refrigerator, cloths machine, etc. Parameters such as extraction time, nature of extraction solvent, size of microdrop, sample volume, stirring rate, ionic strength and pH of sample solution were studied and optimized, and the method performance was evaluated.     

Synthesis of N,N′-dimethyl-N,N′-dibutyl malonamide functionalized polymer and its sorption affinities towards U(VI) and Th(IV) ions

A novel chelating polymeric material was synthesized by chemical anchoring of N,N′-dimethyl-N,N′-dibutyl malonamide (DMDBMA) with chloromethylated polystyrene-divinyl benzene polymer. The polymeric material thus prepared was characterized by ¹³C NMR, FT-IR spectroscopy and CHN elemental analysis. The fabricated polymeric material exhibited superior binding for hexa-valent and tetra-valent metal ions such as U(VI) and Th(IV). Various physico-chemical properties of the functionalized polymer like phase adsorption kinetics, metal sorption mechanism and metal sorption capacity was studied in the static method. Adsorption kinetics studies show that <20 min was sufficient for >99.99% adsorption of Th(IV) and U(VI). The kinetics for adsorption of U(VI) and Th(IV) was found to follow the first order Lagergren rate kinetics. Adsorption of U(VI) on the malonamide functionalized polymer followed the Langmuir adsorption isotherm. The Langmuir monolayer adsorption phenomenon was also confirmed by the theoretical approach calculated based on the adsorption kinetics. The metal sorption capacities for uranium and thorium were found to be 18.78 ± 1.53 mg and 15.74 ± 1.59 mg/g of the chelating polymer at 3 M HNO₃, respectively.     

Diastereotopic effect in some N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones

1H NMR assignment of seven differently N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones (I) revealed that with the exception of allyl, N-methylene protons of the substituents exhibit diastereotopy due to presence of a chiral centre in the heterocyclic ring at C-3. The significant finding is that the methylenes at C-2' in the substituents n-propyl and n-butyl (Id, Ie) also show diastereotopy. However, the one closer to the chiral centre (at C-1') exhibits greater non-equivalence of its protons. The diastereotopic methylene groups reported in this study correspond to the simplest system AB on one hand and as complex as ABMM'X2 or ABMM'X3 on the other. Calculated spectra obtained from assigned set of data for most of the coupled protons were in good agreement with the observed ones.     

Ion pairing, H-bonding, and π–π interactions in copper(II) complex-organo-networks derived from a proton-transfer compound of the 1,10-phenanthroline-2,9-dicarboxylic acid

The one-pot reaction between the novel proton transfer compound (pydaH₂)²⁺(phendc)²⁻, LH₂, and Cu(II) afforded the compounds (pydaH)₂[Cu(phendc)₂]·10H₂O, 1, and (pydaH)₂[Cu(phendc)(phendcH)]₂·5H₂O, 2, where pyda=2,6-diaminopyridine, and phendcH₂=1,10-phenanthroline-2,9-dicarboxylic acid. The single crystal X-ray diffraction analysis of 1 and 2 revealed that these are two novel self-assembled 3D Cu(II) complex-organo-networks, in which (pydaH)⁺ ions and [Cu(phendc)₂]²⁻ or complex units are held together by ion pairing, H-bonding, and π–π interactions. Magnetic measurements over the temperature range 1.8–310 K revealed no significant magnetic coupling between Cu(II) centers in 1 or 2.     

Kinetics and mechanism of reaction between mercuric bromide and silver iodide in solid state

Kinetics and mechanism of the reaction between mercuric bromide and silver iodide were studied in the solid state. It has been established that HgBr₂ reacts via the gaseous state and that the reaction proceeds through counter diffusion of Ag⁺ and Hg²⁺. Thermal and conductivity measurements indicate that the reaction is multistep. X-ray and chemical analyses show that HgBr₂ and AgI mixed in different molar ratios give rise to different products. The data for the lateral diffusion fitted the equation X_iⁿ = kt, where X_i is the thickness of the product layer at time t, and n and k are constants. Evidence for the formation of solid solutions between reactant and product phases is reported.     

Development of a new fluorimetric bulk optode membrane based on 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) for nickel(II) ions

A highly sensitive and selective fluorimetric optode membrane for the determination of ultra trace amounts of Ni²⁺ ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) (TTBB), as a highly fluorescent chromoionophore, displays a calibration response for Ni²⁺ ions over a wide concentration range of 1.0×10⁻³ to 1.0×10⁻⁸ M. It has a relatively fast response of <40 s. In addition to high stability and reproducibility, and relatively long working lifetime, the sensor possesses good selectivity for nickel ions over several common diverse ions. The fluorescence signal of the optode membrane can be easily recovered by immersion in EDTA solution. The optode was applied successfully to the determination of traces of Ni²⁺ ion in edible oil and a wastewater sample from nickel electroplating industries.     

Conductance Study of Binding of Some Rb+ and Cs+ Ions by Macrocyclic Polyethers in Acetonitrile Solution

A conductance study of the interaction between Rb+ and Cs+ ions and18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6),dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) inacetonitrile solution has been carried out at various temperatures. The formationconstants of the resulting 1:1 complexes were determined from the molarconductance-mole ratio data and found to vary in the orderDC18C6 > 18C6 > DB30C10 > DB18C6 DB24C8for Rb+ ion andDC18C6 > 18C6 > DB30C10 DB24C8 > DB18C6for Cs+ ion. The enthalpy and entropy of complexation were determined fromthe temperature dependence of the formation constants. The complexes with the18-crowns are both enthalpy and entropy stabilized while, in the case of largecrown ethers, the corresponding complexes are enthalpy stabilized but entropydestabilized.     

Development,In-Vitro Characterization and Preclinical Evaluation of Esomeprazole-Encapsulated Proniosomal Formulation for the Enhancement of Anti-Ulcer Activity

Objective: The present study aimed to develop and optimize esomeprazole loaded proniosomes (EZL-PNs) to improve bioavailability and therapeutic efficacy. Method: EZL-PNs formulation was developed by slurry method and optimized by 33 box-Bhekhen statistical design software. Span 60 (surfactant), cholesterol, EZL concentration were taken as independent variables and their effects were evaluated on vesicle size (nm), entrapment efficiency (%, EE) and drug release (%, DR). Furthermore, optimized EZL-PNs (EZL-PNs-opt) formulation was evaluated for ex vivo permeation, pharmacokinetic and ulcer protection activity. Result: The EZL-PNs-opt formulation showed 616 ± 13.21 nm of vesicle size, and 81.21 ± 2.35% of EE. EZL-PNs-opt exhibited negative zeta potential and spherical confirmed scanning electron microscopy. EZL-PNs-opt showed sustained release of EZL (95.07 ± 2.10% in 12 h) than pure EZL dispersion. The ex-vivo gut permeation result exhibited a significantly (p < 0.05) enhanced flux than pure EZL. The in vivo results revealed 4.02-fold enhancement in bioavailability and 61.65% protection in ulcer than pure EZL dispersion (43.82%). Conclusion: Our findings revealed that EZL-PNs formulation could be an alternative delivery system of EZL to enhance oral bioavailability and antiulcer activity.