Direct measurements of interactions between polypeptides and carbon nanotubes

The interactions of various polypeptides with individual carbon nanotubes (CNTs), both multiwall (MW) and single wall (SW), were investigated by atomic force microscopy (AFM). While adhesion forces arising from electrostatic attraction interactions between the protonated amine groups of polylysine and carboxylic groups on the acid-oxidized multi-wall carbon nanotubes (Ox-MWCNTs) dominate the interaction at a low pH, weaker adhesion forces via the hydrogen bonding between the neutral -NH2 groups of polylysine and -COO- groups of the Ox-MWCNTs were detected at a high pH. The adhesion force was further found to increase with the oxidation time for Ox-MWCNTs and to be negligible for oxidized single-wall carbon nanotubes (Ox-SWCNTs) because carboxylate groups were only attached onto the nanotube tips in the latter whereas onto both the nanotube tips and sidewall in the former. Furthermore, it was demonstrated that proteins containing aromatic moieties, such as polytryptophan, showed a stronger adhesion force with Ox-MWCNTs than that of polylysine because of the additional pi-pi stacking interaction between the polytryptophan chains and CNTs.     

The kinetics and mechanism of reaction between ethylenediaminetetraacetomanganate(III) and cyanide ion

Summary The title reaction has been followed spectrophotometrically at 325 nm (_max of [Mn(CN)₆]^3–) under pseudo-first order conditions with cyanide in a large excess at pH=10.0, I=0.1M (NaClO₄) and 25°C. The reaction follows first-order kinetics in [MnEDTA(OH)]^2– and exhibits variable-order dependence in [CN^–] one at high cyanide concentration, and two at low cyanide concentration. The product of above reaction has been identified as [Mn(CN)₆]^3–.The kinetics of the reverse reaction,i.e., the reaction of [Mn(CN)₆]^3- with EDTA^4– have also been followed spectrophotometrically. This reactions is first-order with respect to both [Mn(CN) ₆ ^3– ] and [EDTA^4–] and exhibits an inverse first-order dependence on [CN^–]. A six-step mechanism has been proposed in which the penultimate step is rate-determining. The activation parameters have been obtained and support the postulated mechanism.     

Spectral studies of Erbium doped heavy metal borophosphate glass systems

The ternary lead bismuth magnesium borophosphate glass system (LBMBPE) with molar concentrations of (50-x) PbO-xBi₂O₃-25MgHPO₄-24B₂O₃-1Er₂O₃ (x=10, 20, 30 and 40) was prepared using Melt quenching technique. The amorphous nature of these glass samples were confirmed with XRD studies, The spectral data from the optical absorption studies was employed to compute the spectroscopic parameters such as Racah coefficients (E¹, E² and E³), spin-orbit coupling (ξ_4f), configuration interaction factor (α) and Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6). The IR spectra exhibit the presence of vibrational modes of phosphates, borate radicals, bismuth, lead and magnesium ions. The Judd-Ofelt parameterization indicates the covalency and vibrationonic frequencies of the ligands with rare earth ions. The radiative parameters such as radiative transition probabilities (A), the total radiative transitional probabilities (A_T), radiative life times (τ_R), branching ratios (β) and absorption cross sections (∑) were computed for certain lasing levels. The effect of compositional changes on the optical band gap is also reported. The glass systems thus developed indicate their potential lasing candidature.     

Metal exchange kinetics: uncatalyzed replacement of Ni(II) from tetramethylenediaminetetraacetatonickel(II) complex by Cu(II)

The kinetics of metal exchange between copper(II) and tetramethylenediaminetetraacetatonickel(II), [Ni(TMDTA)] has been studied between pH 3.4 and 4.8 at an ionic strength of 1.25 M (NaClO₄) and a temperature of 25.0 ± 0.1 °C. The reaction is first order in [Ni(TMDTA)]. The reaction order in [Cu²⁺] varies from first to zero and then back to first as [Cu²⁺] is increased. At low copper concentration, the first-order rate constant is pH independent and represents the attack of copper on the nickel complex through a pathway in which TMDTA is partially uncoordinated before reaction with copper. Evidence is presented for a stepwise dechelation mechanism followed by attack of copper to give a dinuclear intermediate. The zero-order rate is pH dependent. At higher [Cu²⁺], the swing back to first order is due to the formation of a weak copper-tetramethylenediaminetetraacetatonickelate complex which then converts to products through a dinuclear intermediate. A plausible mechanism, consistent with all the kinetic data, is presented.     

Variation of magnetic properties in heat treated and ball milled Fe3Al alloy

The magnetic properties of three samples of Fe₃Al—as melted and annealed, high energy ball milled and milled sample followed by annealing—have been studied using a combination of X-ray diffraction, Transmission electron microscopy, room temperature ⁵⁷Fe M?ssbauer spectroscopy and DC magnetization. The different magnetic contributions in the M?ssbauer spectra have been explained in terms of the nearest neighbour Al configuration of Fe. These correlate well to the bulk magnetic properties determined by DC magnetization. High temperature DC magnetization studies show the presence of antiferromagnetic contributions from grain boundaries in the ball milled, nano sized sample.     

Models of information aggregation in financial markets: a review

This article reviews static and dynamic models of information aggregation in the literature. It highlights the key assumptions these models make, the results they obtain and the issues that still need to be explored to further our understanding of information aggregation in financial markets.