α-Aminoisobutyric acid modified protected analogues of β-amyloid residue 17-20: a change from sheet to helix

The strong intermolecular interactions mediated by short hydrophobic sequences (e.g., 17-20, -l-Leu-l-Val-l-Phe-l-Phe-) in the middle of Aβ are known to play a crucial role in the neuropathology of Alzheimer's disease. FTIR, TEM and Congo red binding studies indicated that a series of l-Ala substituted terminally protected peptides related to the sequence 17-20 of the β-amyloid peptide, adopted β-sheet conformations. However, the Aib-modified analogues disrupt the β-sheet structure and switch over to a 3₁₀ helix with increasing number of Aib residues. X-ray crystallography shed some light on the change from sheet to helix at atomic resolution.     

Sorption of uranium on magnetite nanoparticles

Magnetite (Fe₃O₄) nanoparticle was synthesized using a solid state mechanochemical method and used for studying the sorption of uranium(VI) from aqueous solution onto the nanomaterial. The synthesized product is characterized using SEM, XRD and XPS. The particles were found to be largely agglomerated. XPS analysis showed that Fe(II)/Fe(III) ratio of the product is 0.58. Sorption of uranium on the synthesized nanomaterials was studied as a function of various operational parameters such as pH, initial metal ion concentration, ionic strength and contact time. pH studies showed that uranium sorption on magnetite is maximum in neutral solution. Uranium sorption onto magnetite showed two step kinetics, an initial fast sorption completing in 4–6 h followed by a slow uptake extending to several days. XPS analysis of the nanoparticle after sorption of uranium showed presence of the reduced species U(IV) on the nanoparticle surface. Fe(II)/Fe(III) ratio of the nanoparticle after uranium sorption was found to be 0.48, lower than the initial value indicating that some of the ferrous ion might be oxidized in the presence of uranium(VI). Uranium sorption studies were also conducted with effluent from ammonium diuranate precipitation process having a uranium concentration of about 4 ppm. 42% removal was observed during 6 h of equilibration.     

Synthesis and characterization of stable thiazolylazo anion radical complexes of ruthenium(II)

Two stable thiazolylazo anion radical complexes of ruthenium(II), [Ru(L1^•−)(Cl)(CO)(PPh₃)₂] (1) and [Ru(L2^•−)(Cl)(CO)(PPh₃)₂] (2) (where L1 = 2′-Thiazolylazo-2-imidazole and L2 = 4-(2′-Thiazolylazo)-1-n-hexadecyloxy-naphthalene), have been synthesized and characterized by spectroscopic and electrochemical techniques. The radical nature of the complexes has been confirmed from their room temperature magnetic moments and X-band ESR spectra. The radical complexes display a moderately intense (ε ~ 10⁴ M⁻¹ cm⁻¹) and relatively broad band in 430–460 nm region. In the microcrystalline state, complexes (1) and (2) display strong ESR signals at g = 1.951 and g = 1.988, respectively. In CH₂Cl₂ solution, complexes (1) and (2) show a quasireversible one-electron response near −0.64 and −0.59 V, respectively, versus Ag/AgCl due to the radical redox couple [Ru^II(L)(Cl)(CO)(PPh₃)₂]/[Ru^II (L^•−)(Cl)(CO)(PPh₃)₂].     

The development of phosphinoamine–Pd(II)–imidazole complexes: implications in room‐temperature Suzuki–Miyaura cross‐coupling reaction

The reaction of N‐methylimidazole (N‐MeIm) and N‐butylimidazole (N‐BuIm) with the complexes [PdCl₂(PPh₂py–P,N)] and [PdCl₂(PPh₂Etpy–P,N)] in the presence of NH₄PF₆ under N₂ at room temperature afforded four new cationic Pd(II) complexes [PdCl(PPh₂py–P,N)(N‐MeIm)](PF₆) ( 1 ), [PdCl(PPh₂py–P,N)(N‐BuIm)](PF₆) ( 2 ), [PdCl(PPh₂Etpy–P,N)(N‐MeIm)](PF₆) ( 4 ) and [PdCl(PPh₂Etpy‐P,N)(N‐BuIm)](PF₆) ( 5 ) in good yields, where PPh₂py is 2‐(diphenylphosphino)pyridine and PPh₂Etpy is 2‐{2‐(diphenylphosphino)ethyl}pyridine). The complexes were fully characterized. The catalytic activities of these complexes were investigated for Suzuki–Miyaura cross‐coupling reactions at room temperature. Complex 2 exhibited excellent activity compared to other analogs. Copyright © 2013 John Wiley & Sons, Ltd.     

Solid‐Phase Incorporation of an ATRP Initiator for Polymer–DNA Biohybrids

The combination of polymers with nucleic acids leads to materials with significantly advanced properties. To obviate the necessity and complexity of conjugating two macromolecules, a polymer initiator is described that can be directly covalently linked to DNA during solid‐phase synthesis. Polymer can then be grown from the DNA bound initiator, both in solution after the DNA‐initiator is released from the solid support as well as directly on the solid support, simplifying purification. The resulting polymer‐DNA hybrids were examined by chromatography and fluorescence methods that attested to the integrity of hybrids and the DNA. The ability to use DNA‐based supports expands the range of readily available molecules that can be used with the initiator, as exemplified by direct synthesis of a biotin polymer hybrid on solid‐support. This method expands the accessibility and range of advanced polymer biohybrid materials.     

Conductance of Some 1:1 Electrolytes in N,N-Dimethylacetamide at 25°C

Precise conductance measurements of solutions of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, tetrabutylammonium bromide, and tetrabutylammonium tetraphenylborate in N,N-dimethylacetamide are reported at 25°C in the concentration range 0.005–0.015 mol-dm^–3. The conductance data have been analyzed by the 1978 Fuoss conductance equation in terms of the limiting molar conductance (⁰), the association constant (K _a), and the association diameter (R). The limiting ionic conductances have been estimated from an appropriate division of the limiting molar conductivity of the reference electrolyte Bu₄NBPh₄. Slight ionic association was found for all these salts in this solvent medium. The results further indicate significant solvation of Li⁺ion, while the other ions are found to be unsolvated in N,N-dimethylacetamide.     

Adsorptive removal of Cr(III) from aqueous solution using tripolyphosphate cross-linked chitosan beads

Chitosan tripolyphosphate (CTPP) beads were prepared at two different cross-linking densities and adsorption of Cr(III) onto it were studied as a function of different operational parameters such as solution pH, equilibration time and initial Cr(III) ion concentration. Higher cross-linked beads were found to have more adsorption capacity at all the experimental pH employed (pH = 3–5), whereas adsorption capacity is found to increase with increase in pH. Adsorption data were analyzed using Langmuir and Freundlich isotherm models. Langmuir model is found be more suitable to explain the experimental results with a monolayer adsorption capacity of 469.5 mg/g. Among the kinetic models used, pseudo-second order kinetic model could best describe the adsorption process. Competition experiments done in presence of Na(I), Mg(II), Ca(II), Al(III) and Fe(III) revealed that, except in the case of Al(III), adsorption of Cr(III) is not significantly affected by the presence of foreign cations. NaCl is found to be a suitable leaching agent for the desorption of adsorbed Cr(III) from CTPP beads. FTIR spectroscopic investigations confirmed that phosphate groups are the principal binding site responsible for the sorption of Cr(III) onto CTPP beads.     

Aza-Michael Addition of Amines to α,β-Unsaturated Compounds Using Molecular Iodine as Catalyst

Aza-Michael adducts are obtained in very good yields by the conjugate addition of aliphatic amines to α,β-unsaturated compounds using molecular iodine as catalyst in dichloromethane at room temperature. Aromatic amines were found to be reactive under reflux in toluene.     

Green Synthesis of Tetraalkylammonium Tribromide using Cerium(IV) Ammonium Nitrate (CAN) as Oxidant

Cerium(IV) ammonium nitrate (CAN) mediates oxidation of tetraalkylammonium bromide to tetraalkylammonium tribromide in greener reaction conditions using water as solvent. The procedure is simple, convenient, and environmentally benign for the synthesis of tetraalkylammonium tribromide with great yields.     

Modeling and analytical simulation of rotating disk ultrafiltration module

An unsteady state mass transfer model has been developed for rotating disk ultrafiltration module. Starting from the basic physics of the system, analytical expression of back transport flux generated due to rotation-induced shear field is determined, which is subsequently incorporated in the fundamental material balance equation. In order to get an analytical solution of governing partial differential equation via Laplace transformation, pseudo steady state consideration is imposed both on permeate as well as back transport flux. Once the analytical form of concentration field is obtained using the expression permeate flux, membrane surface concentration are evaluated using polymer solution theory and irreversible thermodynamics. Finally an iterative scheme is designed to simulate the permeate flux and membrane surface concentration under specified set of operating parameters. The prediction from this model is found to be in good agreement with experimental data obtained from PEG-6000/water system using cellulose acetate membrane of 5000 Da molecular weight cut-off.