Nanotube-grafted polyacrylamide hydrogels for electrophoretic protein separation

Multiwalled carbon nanotube-modified polyacrylamide gels have been employed for the electrophoretic separation of proteins. Two approaches are compared in this investigation, one using nanotubes only as fillers inside the gel matrix and the other using nanotubes as catalyst for polymerization of acrylamide. In both the cases, polymerization of acryl-amide/bisacrylamide has been carried out in situ in the presence of nanotubes dispersed in the gel buffer containing monomer and cross-linker. In the former case, initiator and catalyst have been added after ultrasonication of nanotubes in the gel buffer mixture where the nanotubes play the role of filler. On the other hand, the second approach precludes use of catalyst and involves addition of initiator alone during ultrasonication of nanotubes in the gel buffer containing monomer and cross-linker, which leads to the formation of nanotube-grafted gel after 25 min. When nanotubes are used as a catalyst instead of N,N,N',N'-tetramethylethylenediamine, pore size distribution of the gel matrix and linearity of molecular weight calibration plots are found to be improved. In addition, other issues associated with the use of an external catalyst like handling the moisture-sensitive and corrosive reagent and associated irreproducibility are addressed in this approach.     

Kinetics, mechanism, and thermochemistry of the gas phase reaction of atomic chlorine with dimethyl sulfoxide

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O)CH3; DMSO) as a function of temperature (270-571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P > or = 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k1a = 1.45 x 10(-11) cm3 molecule(-1) s(-1) and the following falloff parameters for the pressure-dependent addition channel in N2 bath gas: k(1b,0) = 2.53 x 10(-28) cm6 molecule(-2) s(-1); k(1b,infinity) = 1.17 x 10(-10) cm3 molecule(-1) s(-1), F(c) = 0.503. At the 95% confidence level, both k1a and k1b(P) have estimated accuracies of +/-30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k1a = (4.6 +/- 0.4) x 10(-11) exp[-(472 +/- 40)/T) cm3 molecule(-1) s(-1) (uncertainties are 2sigma, precision only). When our data at T > 430 K are combined with values for k1a at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k1a = 1.34 x 10(-15)T(1.40) exp(+383/T) cm3 molecule(-1) s(-1) (273 K < or = T < or = 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: delta(r)H(o)298 = -72.8 +/- 2.9 kJ mol(-1), deltaH(o)0 = -71.5 +/- 3.3 kJ mol(-1), and delta(r)S(o)298 = -110.6 +/- 4.0 J K(-1) mol(-1). In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for delta(r)H(o) lead to the following values for the standard enthalpy of formation of Cl-DMSO: delta(f)H(o)298 = -102.7 +/- 4.9 kJ mol(-1) and delta(r)H(o)0 = -84.4 +/- 5.8 kJ mol(-1). Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.     

Palladium-catalyzed multistep reactions involving ring closure of 2-iodophenoxyallenes and ring opening of bicyclic alkenes

[reaction: see text] An efficient ring closure of 2-iodophenoxy-, 2-iodobenzyloxy-, and 2-iodobenzylaminoallenes followed by ring opening of oxabenzonorbornadienes leading to the synthesis of 2-benzofuranyl, 1H-isochromenyl, or 1,2-dihydroisoquinoline methyl-1,2-dihydro-1-naphthalenol derivatives catalyzed by palladium complexes is described.     

Identification of radiative properties of reticulated ceramic porous inert media using ray tracing technique

The radiative properties of reticulated porous inert media are computationally identified using the real three-dimensional structural data of porous media. The computational grids data are reconstructed from three-dimensional computer tomography scans and magnetic resonance image scans of different reticulated porous media. A ray tracing algorithm is used to track the rays inside the grid structure. Statistically large numbers of rays are traced for their path length and incident angle, which are used to find the probability based equivalent extinction coefficient and scattering phase function. The equivalent extinction coefficients are found for porous media with different porosities and pore densities. The dependency of specular and diffuse scattering phase functions on the porous structure and surface reflectance are also studied.     

Nafion-multi-walled Carbon Nanotubes Supported Tris(bipyridyl)iron(II) for Nicotine Detection

This work reports an electrochemical sensing framework for nicotine determination based on glassy carbon electrode (GC) immobilized with Fe(bpy)₃²⁺ (where bpy is 2,2’-bipyridyl) supported by Nafion and multi-walled carbon nanotubes (Nf-MWCNTs). Fe(bpy)₃²⁺ immobilized Nf-MWCNTs modified GC (GC/Nf-MWCNTs/Fe(bpy)₃²⁺) manifests stable redox peaks, characteristics of Fe(bpy)₃²⁺. The GC/Nf-MWCNTs/Fe(bpy)₃²⁺ exhibits effective electrochemical oxidation of nicotine, diminishing the overpotential relative to GC/Nf-MWCNTs. The limit of detection is 0.1 μM (experimentally observed) with two different linear calibration ranges between 0.1 to 600 μM and 600 to 3000 μM. Electrocatalytic responses observed at GC/Nf-MWCNTs/Fe(bpy)₃²⁺ indicate superior performance for nicotine determination with acceptable selectivity, stability, and reproducibility. Additionally, the nicotine present in real samples such as beedi and tobacco are also analyzed with satisfactory recovery percentages.     

Leveraging Torsional and Steric Strains: A Pre-macrocyclization Strategy Enables Conformation-Specific Fullerene Binding in m-Cyclophanes

Though the chemistry of resorcinarenes is half a century old, the conformationally-locked resorcinarene crowns are generally constructed using hydrogen bonds or covalent tethers. Often, covalent tethering involves extra post-macrocyclization steps involving upper-rim functionalities. We have leveraged the torsional and steric strains through α-substituents of the lower-rim C-alkyl chains and accomplished conformationally-rigid fluorescent m-cyclophane deep-crowns in a predetermined way. The strategy offers a pre-macrocyclization route conserving upper-rim functionalities, an aspect overlooked in resorcinarene chemistry. X-ray structural and computational analyses unveil the cause for conformational rigidity in m-cyclophanes due to α-branching in C-alkyls (linear vs. α-/β-branched). The conformationally-locked fluorescent deep-crown with a preorganized cavity captures hydrophobic spherical guest C₆₀ in both solution and solid states specifically, when compared to conformationally-dynamic boats, enabling conformation-specific binding.