Green synthesis of silver nanoparticles using seed extract of Jatropha curcas

An eco-friendly process for rapid synthesis of silver nanoparticles has been reported using aqueous seed extract of Jatropha curcas. Formation of stable silver nanoparticles at different concentration of AgNO₃ gives mostly spherical particles with diameter ranging from 15 to 50 nm. The resulting silver particles are characterized using HRTEM, XRD and UV–vis spectroscopic techniques. XRD study shows that the particles are crystalline in nature with face centered cubic geometry.     

Generation of pH-oscillations in closed chemical systems: method and applications

All pH-oscillators reported to date function only under open (flow reactor) conditions. We describe an approach to generating pH-oscillations in a closed system by starting from an open system pH-oscillator, finding semibatch conditions under which it oscillates with an inflow of a single reactant to an otherwise closed reactor containing the remaining components, and replacing this inflow with a layer of silica gel impregnated with the key reactant. We present data showing the successful application of this technique to the BrO(3)(-)-Mn(2+)-SO(3)(2-), IO(3)(-)-Fe(CN)(6)(4-)-SO(3)(2-), and BrO(3)(-)-Fe(CN)(6)(4-)-SO(3)(2-) systems. In all three cases, sulfite ion is the species that is replenished via dissolution from the gel layer.     

Communication: mode-specific photodissociation of vibrationally excited pyrrole

Laser-based spectroscopies coupled with molecular beam techniques facilitated the monitoring of H fragments released in ultraviolet photodissociation of pre-excited isoenergetic vibrational levels of pyrrole. Most noticeably, there was an order of magnitude larger reactivity for an eigenstate primarily consisting of two quanta of ring deformation than for another with one quantum of symmetric C-H stretch. The dynamics, the intramolecular interactions controlling the energy flow, and the mode-selectivity within a medium-sized, ten atom molecule, is discussed.     

On the Lifetime of the Transients (NP)?(CH3)n (NP=Ag0, Au0, TiO2 Nanoparticles) Formed in the Reactions Between Methyl Radicals and Nanoparticles Suspended in Aqueous Solutions

Methyl radicals react in fast reactions, with rate constants k>1×10⁸ M ^?1 s^?1, with Au⁰, Ag⁰ and TiO₂ nanoparticles (NPs) dispersed in aqueous solutions to form intermediates, (NP)? (CH₃)_n, in which the methyl groups are covalently bound to the NPs. These intermediates decompose to form ethane. As n≥2 is required for the formation of C₂H₆, the minimal lifetime (τ) of the methyls bound to the NPs, (NP)? CH₃, can be estimated from the rate of production of the CH₃^. radicals and the NPs concentration. The results obtained in this study, using a very low dose rate γ‐source for NP=Ag⁰, Au⁰, and TiO₂ point out that τ of these intermediates is surprisingly long, for example, ≥8 and ≥188 sec for silver and gold, respectively. These data point out that the NP? C bond dissociation energies are ≥70 kJ mol^?1. Under low rates of production of CH₃^., that is, when the rate of formation of ethane is very low, other reactions may occur, consequently the mechanism proposed is “broken”. This is observed in the present study only for TiO₂ NPs. These results have to be considered whenever alkyl radicals are formed near surfaces. Furthermore, the results point out that the rate of reaction of methyl radicals with (NP)? (CH₃)_n depends on n, that is, the number of methyl radicals bound to the NPs affect the properties of the NPs.     

Dechlorane Plus and related compounds in aquatic and terrestrial biota: a review

Dechlorane Plus, dechlorane 602, dechlorane 603 and dechlorane 604 are flame retardants that have been used for a long time as a substitute for mirex, but they have not been noticed as environmental contaminants until recently (2006). Regardless of their large molecular size and very high lipophilicity (log K _OW?>?9), Dechlorane Plus and related compounds have been detected in different aquatic and terrestrial species, supporting their bioaccumulation and biomagnification. Moreover, some studies showed different behaviour of the syn-Dechlorane Plus and anti-Dechlorane Plus isomers in the environment and different biomagnification factors in biota. This review describes the different analytical approaches applied to the determination of Dechlorane Plus and related compounds. Moreover, a summary of their levels in aquatic and terrestrial biota, as well as in humans, is presented, showing also current research results on their bioaccumulation and biomagnification potential. Finally, isomer-specific bioaccumulation of Dechlorane Plus is also discussed.     

Computationally tractable pairwise complexity profile

Quantifying the complexity of systems consisting of many interacting parts has been an important challenge in the field of complex systems in both abstract and applied contexts. One approach, the complexity profile, is a measure of the information to describe a system as a function of the scale at which it is observed. We present a new formulation of the complexity profile, which expands its possible application to high‐dimensional real‐world and mathematically defined systems. The new method is constructed from the pairwise dependencies between components of the system. The pairwise approach may serve as both a formulation in its own right and a computationally feasible approximation to the original complexity profile. We compare it to the original complexity profile by giving cases where they are equivalent, proving properties common to both methods, and demonstrating where they differ. Both formulations satisfy linear superposition for unrelated systems and conservation of total degrees of freedom (sum rule). The new pairwise formulation is also a monotonically nonincreasing function of scale. Furthermore, we show that the new formulation defines a class of related complexity profile functions for a given system, demonstrating the generality of the formalism. © 2013 Wiley Periodicals, Inc. Complexity 18:20–27, 2013     

Synthesis of asymmetrically substituted 1,4,7,10-tetraazacyclododecanes for the triggered near infrared emission from lanthanide complexes

A synthetic strategy to prepare asymmetrically substituted 1,4,7,10-tetrazadodecane derivatives was developed to prepare a novel series of photoactive donor-acceptor quencher triads based on Yb and Nd complexes; a nucleoside quencher is used to regulate the extent of energy transfer between the donor and the acceptor.     

Characterization of the flow of anisotropic colloidal particles using energy-dispersive X-ray diffraction

The technique of energy-dispersive X-ray diffraction to study the orientation of microscopic crystalline particles dispersed in a liquid has been described recently. This complements previous neutron diffraction studies by permitting measurements at higher spatial resolution. Work with synchrotron radiation and high-energy X-rays has allowed studies on liquid dispersions flowing in pipes with a thickness of about 1 cm and a spatial resolution of 100 mum. Kaolinite is often found as a dispersion of monocrystalline, microscopic plates. The crystallographic layer structure is commensurate with the particle shape: the 00l direction is normal to the plane of the plates. Measurements of diffraction of the flowing liquid dispersion in a pipe oriented in various directions to the incident beam can be used to deduce the average orientation and order parameters of the particles. The competing effects of alignment with walls and in flow fields were observed. Further work has measured the orientation near a bend in a pipe.     

Detection of polymorphism in the methlyenetetrahydrofolate reductase gene by Raman spectroscopy

A novel approach using micro‐Raman spectroscopy for the detection of alteration of global DNA methylation levels in human individuals with polymorphism in the methlyenetetrahydrofolate reductase (MTHFR) gene was tested. Comparison of measured Raman spectra from samples with wild type genotype to those with polymorphism (homozygous and heterozygous ) in the MTHFR gene revealed that the intensity of the ~ 2945 cm^–1 peak, representing C–H stretches in the DNA constituents and in the methyl group is sample dependent. The intensity ratios between the area of these peaks in the different samples and the peaks at 1667 cm^–1 were used to assess the extent of methylation, allowing classification of the DNA samples for the common MTHFR polymorphism, MTHFR 677 C > T. These results suggest that improvement of the identification capabilities of Raman spectroscopy for DNA methylation can contribute to disease diagnosis and to a better understanding of the physical and biomolecular processes related to epigenetic regulation of the genome. Copyright © 2012 John Wiley & Sons, Ltd.     

Signal-to-noise ratio and aberration statistics in ocular aberrometry

We define a signal-to-noise ratio (SNR) for eye aberrometry in terms of the sensor geometry, measurement noise, and population statistics. The overall estimation error is composed of three main contributions: the bias in the estimated modes, the truncation error, and the error due to the noise propagation. This last term can be easily parametrized by the proposed SNR. We compute the overall error as well as the magnitude of its three components for a typical sensor configuration, population statistics, and different SNR. We show that there are an optimum number of Zernike aberration modes to be retrieved in each case.