Structural parameters of polyacrylamide hydrogels obtained by the Equilibrium Swelling Theory

In this paper, the synthesis and structural characterization of a series of polyacrylamide hydrogels with different degrees of reticulation are reported. Although the Equilibrium Swelling Theory was recognized as a simple and reliable tool for the determination of structural hydrogels network parameters like equilibrium degree of swelling, cross-link ratio and mesh size, this is the first application of this methodology for polyacrylamide hydrogels. By changing the total monomer content in the synthesis solution (%T) from 5 to 30%, at a fixed value of cross-linker content in the total monomer amount (%C) of 5%, the final parameter obtained, the mesh size, can be tuned from 2 to 0.3 nm. It was also possible to change the mesh size (0.19-0.35) by varying %C from 5 to 12% (at %T = 20%). Scanning Electron Microscopy images for the most different formulations are shown and corroborate data obtained from the theory.     

Interaction of Dimethyltin(IV) with DNA Constituents

Summary.  The interaction of dimethyltin(IV) (DMT) with some selected DNA constituents was investigated potentiometrically. The stepwise formation constants of the complexes were determined, and the concentration distribution of the various complex species was evaluated as a function of pH. The effect of dioxane on the protonation constants of the ligands and the formation constants of dimethyltin(IV) complexes are discussed. The thermodynamic parameters Δ H° and ΔS° were calculated from the temperature dependence of the equilibrium constants.     

“Charge transfer Complexes of Indolyldiene Aniline derivatives with p-benzoquinone derivatives”

Abstract

Charge transfer (CT) complexes of p-benzoquinone derivatives with Indolyldiene aniline derivatives have been prepared and investigated by Elemental analysis, IR, ¹H-NMR and electronic absorption spectroscopy. The spectral changes revealed that acidic acceptors form complexes with π - π? electronic interaction and proton transfer while non-acidic acceptors yield complexes having π - π transition only. The formation of 1:2 (D:A) complexes is also ascertained. The ionization potential and electron affinity are determined from the electronic absorption spectra for both the donors and acceptors respectivily.     

Equilibrium balking strategies in the observable single-server queue with breakdowns and repairs

We consider the Markovian single-server queue that alternates between on and off periods. Upon arriving, the customers observe the queue length and decide whether to join or balk. We derive equilibrium threshold balking strategies in two cases, according to the information for the server’s state.     

Investment and consumption without commitment

In this paper, we investigate the Merton portfolio management problem in the context of non-exponential discounting. This gives rise to time-inconsistency of the decision-maker. If the decision-maker at time t = 0 can commit her successors, she can choose the policy that is optimal from her point of view, and constrain the others to abide by it, although they do not see it as optimal for them. If there is no commitment mechanism, one must seek a subgame-perfect equilibrium policy between the successive decision-makers. In the line of the earlier work by Ekeland and Lazrak (Preprint, 2006) we give a precise definition of equilibrium policies in the context of the portfolio management problem, with finite horizon. We characterize them by a system of partial differential equations, and establish their existence in the case of CRRA utility. An explicit solution is provided for the case of logarithmic utility. We also investigate the infinite-horizon case and provide two different equilibrium policies for CRRA utility (in contrast with the case of exponential discounting, where there is only one optimal policy). Some of our results are proved under the assumption that the discount function h(t) is a linear combination of two exponentials, or is the product of an exponential by a linear function. I. Ekeland was supported by PIMS under NSERC grant 298427-04.     

Investigation of growth mechanism of nano-scaled cadmium sulfide within titanium dioxide nanotubes via solution deposition method

The growth mechanism of cadmium sulfide nanomaterials, including nanodots, nanotubes, and nanorods, within titanium dioxide nanotubes via solution deposition method was investigated. The materials obtained were characterized by field emission scanning electron microscopy, UV-visible spectroscopic and photoelectrochemical techniques. The results revealed that: (1) the concentration of ions introduced into the tubes influenced the morphology of the cadmium sulfide obtained: at low concentration, defects on the tube walls induce heterogeneous nucleation hence cadmium sulfide was observed attaching to the walls; at high concentration, particle aggregation occur due to negligible repulsion between the nuclei resulting in sedimentation of cadmium sulfide particles; (2) cadmium sulfide prefers to grow on seeds formed initially, so that nanodots or nanotubes and nanorods were formed at low and at high concentrations respectively; (3) the order of ions introduction also influences the morphology of cadmium sulfide formed within the tubes, (4) the photoresponse of the obtained nanomaterials was extended efficiently; and (5) the photoelectrochemical properties were strongly influenced by both the amount and the morphology of the deposited CdS sensitizer.     

A Stability-Indicating LC Method for Assay of Topotecan Hydrochloride

This paper describes the development of a stability-indicating high-performance liquid chromatographic (HPLC) method for quantitative determination of topotecan hydrochloride, a semi-synthetic derivative of camptothecin and anti-tumor drug with topoisomerase I-inhibitory activity. Chromatographic separation was achieved on a C₁₈ column with a mixture of phosphate buffer and acetonitrile as mobile phase. The method was validated for linearity, accuracy, precision, and robustness. Forced degradation studies were performed by treating bulk samples of topotecan hydrochloride with acid (0.5 M hydrochloric acid), base (0.5 M sodium hydroxide), oxidizing agent (10% v/v hydrogen peroxide), heat (60 °C), and UV light (254 nm).     

The structure,stability, and reactivity of oxalato-monoperoxovanadium(V) in solution

In order to understand the solution chemistry of an oxalato-monoperoxovanadium(V) complex (K₃[VO(O₂)(C₂O₄)₂] · ½H₂O, mpVox), the solid and solution-state NMR characteristics, transformation behavior, and exchange phenomena in the solution are described in this article. NMR experimental and theoretical results indicated that the vanadium of mpVox in solid and solution state are seven coordinate. However, some geometric parameters tend to change upon dissolution. The dynamic transformation of mpVox in solution was investigated using NMR, IR, and UV-Vis. The reduction product is oxalato-bisoxovanadate. Concentration, pH, and temperature affect this transformation. ⁵¹V NMR investigation on the system of mpVox with picolinc acid showed that two oxalates are substituted to produce [VO(O₂)(ox)(pic)]^2? and [VO(O₂)(pic)₂]^?.     

A comparison of solution and solid state coordination environments for calcium(II), zirconium(IV), cadmium(II) and mercury(II) complexes with dipicolinic acid and methylimidazole derivatives

Four new supramolecular compounds, (2-mimH)[Ca(pydcH)₃][Ca(pydcH₂)(pydc)(H₂O)₂]·4H₂O (1), (1-mimH)₂[Zr(pydc)₃] (2), (2-mimH)₂[Cd(pydc)₂]·8H₂O (3), and (2-mimH)₂[Hg(pydc)₂]·8H₂O (4) [where pydcH₂ = pyridine-2,6-dicarboxylic acid (dipicolinic acid), 1-mim = 1-methylimidazole, and 2-mim = 2-methylimidazole], have been synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–vis, ¹H NMR, and ¹³C NMR), thermal (TG/DTG/DTA) analysis as well as single-crystal X-ray diffraction. All four compounds are proton-transfer salts of the methylimidazolium cations and metal complex anions that crystallized from a solution of pyridine-2,6-dicarboxylic acid, methylimidazole, metal nitrates or chlorides as starting materials. The coordinating dicarboxylic acid is deprotonated at the carboxyl group and methylimidazole is protonated to balance the charge. In the crystal structures of 1–4, hydrogen bonding and π–π stacking play important roles. Water clusters are formed in 1, 3, and 4. The equilibrium constants of dipicolinic acid (pydc) and methylimidazole derivatives (1-mim and 2-mim), pydc-2-mim, pydc-1-mim proton-transfer systems as well as those of their complexes were investigated by a potentiometric pH titration method. The stoichiometries of most of the complex species in solution were very similar to the cited crystalline metal ion complexes.     

SYNTHESIS AND SOLUTION NMR-STUDIES OF THE TRIS(3,5-DIMETHYLPYRAZOL-1-YL) HYDROBORATOPALLADIUM(II) COMPLEX,Pd{(pz*)3BH}(PPh3)CI

Abstract

The sterically hindered tris(3, 5-dimethylpyrazol-l-yl)hydroborate complex of palladium, Pd{(pz*)₃BH}(PPh₃)Cl (1) has been prepared by the stepwise reaction of (CH₃CN)₂PdCl₂ with K{(pz*)₃BH}, and then PPh₃. The complex 1 has been fully characterized by microanalysis and various spectroscopic methods. A solution NMR study of 1 revealed that two pz* groups of the {(pz*)₃BH} ligand coordinate to palladium in cis positions, while the remaining group is not coordinated. VT NMR experiments have been performed to determine that signal broadening of the phenyl proton resonances in the ¹H-NMR spectrum is likely attributed to restricted rotation of the coordinated PPh₃ within the congested complex on the NMR time scale. Complex 1 was metastable in solution towards reaction with water to decompose into several uncharacterized species, in which a facile hydrolytic cleavage of the B-H bond proceeded as judged by IR and ¹H-NMR spectra of the products. Reaction of 1 with PPh₃ in CDCl₃ exclusively yielded cis-PdCl₂(PPh₃)₂, implicating a chlorine abstraction from the solvent.