Arsenic(III) sorption on nanostructured cerium incorporated manganese oxide (NCMO): a physical insight into the mechanistic pathway

Arsenic(III) sorption was investigated with nanostructured cerium incorporated manganese oxide (NCMO). The pH between 6.0 and 8.0 was optimized for the arsenic(III) sorption. Kinetics and equilibrium data (pH=7.0±0.2, T=303±1.6 K, and I=0.01 M) of arsenic(III) sorption by NCMO described, respectively, the pseudo-second order and the Freundlich isotherm equations well. The sorption process was somewhat complicated in nature and divided into two different segments, initially very fast sorption followed by slow intraparticle diffusion process. Sorption reaction of arsenic(III) on NCMO was endothermic (ΔH°=+13.46 kJ mol(-1)) and spontaneous (ΔG°=-24.75 to -30.15 kJ mol(-1) at T=283-323 K), which took place with increasing entropy (ΔS°=+0.14 kJ mol(-1)K(-1)) at solid-liquid interface. Energy of arsenic(III) sorption estimated by analyzing the equilibrium data using the D-R isotherm model was 15.4 kJ mol(-1), indicating the ion-exchange type mechanism. Raman, FT-IR, pH effect, desorption, etc. studies indicated that arsenic(III) was oxidized to arsenic(V) during the sorption process.     

Acylimidazolides as Versatile Synthetic Intermediates for the Preparation of Sterically Congested Amides and Ketones: A Practical Synthesis of Proscar®

Acylimidazolides react with magnesium amides to produce car-boxamides in excellent yields, whereas Fe(III) catalyzed cross coupling between acylimidazolide and Grignard reagents produce ketones in high yields. These methods were utilized to prepare the α-reductase inhibitor Proscar® as well as various 17β-amide and ketone analogs of Δ¹-4-aza-5α-androsten-3-one.     

Syntheses, transfection efficacy and cell toxicity properties of novel cholesterol-based gemini lipids having hydroxyethyl head group

We have synthesized five new cholesterol based gemini cationic lipids possessing hydroxyethyl (-CH(2)CH(2)OH) function on each head group, which differ in the length of the polymethylene spacer chain. These gemini lipids are important for gene delivery processes as they possess pre-optimized molecular features, e.g., cholesterol backbone, ether linkage and a variable spacer chain between both the headgroups of the gemini lipids. Cationic liposomes were prepared from each of these lipids individually and as a mixture of individual cationic gemini lipid and 1,2-dioleoyl phosphatidylethanolamine (DOPE). Each gemini lipid based formulation induced better transfection activity than that of their monomeric counterpart. One such gemini lipid with a -(CH(2))(12)- spacer, HG-12, showed dramatic increase in the mean fluorescence intensity due to the expression of green-fluorescence protein (GFP) in the presence of 10% FBS compared to the conditions where there was no serum. Other gemini lipids retained their gene transfection efficiency without any marked decrease in the presence of serum. The only exception was seen with the gemini with a -(CH(2))(3)- spacer, HG-3, which on gene transfection in the presence of 10% FBS lost ~70% of its transfection efficiency. Overall the gemini lipid with a -(CH(2))(5)- spacer, HG-5, showed the highest transfection activity at N/P (lipid/DNA) ratio of 0.5 and lipid : DOPE molar ratio of 2. Upon comparison of the relevant parameters, e.g., %-transfected cells, the amount of DNA transfected to each cell and %-cell viability all together against Lipofectamine 2000, one of the best commercial transfecting agents, the optimized lipid formulation based on DOPE/HG-5 was found to be comparable. In terms of its ability to induce gene-transfer in the presence of serum and shelf-life DOPE/HG-5 liposome was found to be superior to its commercial counterpart. Confocal imaging analysis confirmed that in the presence of 10% serum using a Lipid : DOPE of 1 : 4 and N/P charge ratio of 0.75 with 1.2 μg DNA per well, HG-5 is better than Lipofectamine 2000.     

Electron transfer reactions of nickel(III) and nickel(IV) complexes

This review narrates the electron transfer reactions of various nickel(III) and nickel(IV) complexes reported during the period 1981 until today. The reactions have been categorized mainly with respect to the type of nickel complexes. The reactivity of nickel(III) complexes of macrocycles, 2,2′-bipyridyl and 1,10-phenanthroline, peptides and oxime–imine, and of nickel(IV) complexes derived from oxime–imine, oxime and miscellaneous ligands with various organic and inorganic electron donors have been included. Kinetic and mechanistic features associated with such interactions have been duly analyzed. The relevance of Marcus cross-relation equations in the delineation of the electron transfer paths has also been critically discussed.     

A family of mixed-ligand oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands derived from acetylhydrazide and 2-hydroxybenzaldehyde/2-hydroxyacetophenone

In the title family the tridentate ONO donor ligands are the fully deprotonated forms of acetylhydrazones of 2-hydroxybenzaldehyde (H₂L¹) and 2-hydroxyacetophenone (H₂L²) (general abbreviation H₂L), while bidentate mononegative OO donor ligands are the deprotonated salicylaldehyde (Hsal), vanillin (Hvan) and monodeprotonated 1,2-ethanediol (H₂ed) (general abbreviation HB). The reaction of V^IVO(acac)₂ with H₂L and Hsal or Hvan in equimolar ratio in MeOH afforded the complexes of the type [V^VO(L)(B)], (1)–(4). The reaction of V^IVO(acac)₂ with H₂L¹ (in an equimolar ratio) and an excess of H₂ed in MeOH yielded the complex [V^VO(L¹)(Hed)], (5) but the similar reaction with H₂L² ligand failed to produce such a type of complex. Complexes have been characterized by elemental analyses and by i.r., n.m.r. and u.v.-vis. spectroscopies. All the complexes are diamagnetic and display only LMCT bands. ¹H-n.m.r. spectral data indicate that complexes (1)–(4) exist in two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios in CDCI₃ solution. Complexes (1)–(4) display a quasi-reversible one electron reduction peak in the −0.06 to +0.05 V versuss.c.e. region in CH₂CI₂ solution and (5) displays an irreversible reduction peak at −0.46 V versuss.c.e. in DMF solution. The trend in the redox potential values has been correlated with the basicity of both the primary and auxiliary ligands.     

Pervaporation from a dense membrane: roles of permeant-membrane interactions, Kelvin effect, and membrane swelling

Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation.     

Heteropoly acid catalyzed synthesis of 8-methyl-2-aryl/alkyl-3-oxabicyclo[3.3.1]non-7-ene derivatives through (3,5)-oxonium-ene reaction

A variety of aldehydes undergo a smooth coupling with (4-methylcyclohex-3-en-1-yl)methanol in the presence of 2 mol % of phosphomolybdic acid in dichloromethane to afford 3-oxabicyclo[3.3.1]non-7-ene in good yields through 3,5-oxonium-ene cyclization under mild conditions. The use of inexpensive, nontoxic, and readily available heteropoly acid catalyst makes this method simple, convenient, and environmental-friendly.     

Molecular-dynamics simulation of model polymer nanocomposite rheology and comparison with experiment

The shear-rate dependence of viscosity is studied for model polymer melts containing various concentrations of spherical filler particles by molecular-dynamics simulations, and the results are compared with the experimental results for calcium-carbonate-filled polypropylene. Although there are some significant differences in scale between the simulated model polymer composite and the system used in the experiments, some important qualitative similarities in shear behavior are observed. The trends in the steady-state shear viscosities of the simulated polymer-filler system agree with those seen in the experimental results; shear viscosities, zero-shear viscosities, and the rate of shear thinning are all seen to increase with filler content in both the experimental and simulated systems. We observe a significant difference between the filler volume fraction dependence of the zero-shear viscosity of the simulated system and that of the experimental system that can be attributed to a large difference in the ratio of the filler particle radius to the radius of gyration of the polymer molecules. In the simulated system, the filler particles are so small that they only have a weak effect on the viscosity of the composite at low filler volume fraction, but in the experimental system, the viscosity of the composite increases rapidly with increasing filler volume fraction. Our results indicate that there exists a value of the ratio of the filler particle radius to the polymer radius of gyration such that the zero-shear-rate viscosity of the composite becomes approximately independent of the filler particle volume fraction.     

Anion‐Directed Copper(II) Metallocages,Coordination Chain,and Complex Double Salt: Structures,Magnetic Properties,EPR Spectra,and Density Functional Study

A series of Cu^II metallo‐assemblies showing anion‐directed structural variations, including five metallocages [(G^n?)?{Cu₂(Hdpma)₄}]^(8?n)+(A^?)_8?n (G^n?=NO₃^?, ClO₄^?, SiF₆^2?, BF₄^?, SO₄^2?; A^?=NO₃^?, ClO₄^?, BF₄^?, CH₃SO₄^?; Hdpma=bis(3‐pyridylmethyl)ammonium cation), a complex double salt, namely, (H₃dpma)₄(CuCl₄)₅Cl₂, and a coordination chain, namely, [Cu₂(dpma)(OAc)₄], are reported. The influence of the anion can be explained by its coordinating ability, the affinity of which for the Cu^II center interferes significantly with metallocage formation, and its shape, which offers host–guest recognition ability to engage in weak metal–anion coordination and hydrogen bonding to the organic ligand, which are responsible for metallocage templation. EPR studies of these metallocages in the powder phase at room temperature and 77 K showed a trend of the g values (g_||>2.10>g_⊥>2.00) indicating a ‐based ground state with square‐pyramidal geometry for the Cu^II centers. The magnetism of these metallocages can be interpreted as the result of a combination of relatively small magnetic coupling integrals and a substantial contribution of temperature‐independent paramagnetism (TIP). The weak magnetic interaction is corroborated by the results of DFT calculations and the EPR spectra. Availability of the low‐lying state for spin population was confirmed by a magnetization study, which revealed a magnetic moment approaching 2Nβ, which would explain the presence of the larger TIP term.