H2O2-mediated oxidation of zero-valent silver and resultant interactions among silver nanoparticles, silver ions, and reactive oxygen species

The H(2)O(2)-mediated oxidation of silver nanoparticles (AgNPs) over a range of pH (3.0-14.0) is investigated here, and an electron charging-discharging model capable of describing the experimental results obtained is developed. AgNPs initially react with H(2)O(2) to form Ag(+) and superoxide, with these products subsequently reacting to reform AgNPs (in-situ-formed AgNPs) via an electron charging-discharging mechanism. Our experimental results show that the AgNP reactivity toward H(2)O(2) varies significantly with pH, with the variation at high pH (>10) due particularly to the differences in the reactivity of H(2)O(2) and its conjugate base HO(2)(-) with AgNPs whereas at lower pH (3-10) the pH dependence of H(2)O(2) decay is accounted for, at least in part, by the pH dependence of the rate of superoxide disproportionation. Our results further demonstrate that the in-situ-formed AgNPs resulting from the superoxide-mediated reduction of Ag(+) have a different size and reactivity compared to those of the citrate-stabilized particles initially present. The turnover frequency for AgNPs varies significantly with pH and is as high as 1776.0 min(-1) at pH 11.0, reducing to 144.2 min(-1) at pH 10.0 and 3.2 min(-1) at pH 3.0.     

Liquid–liquid–solid microextraction and detection of nerve agent simulants by on-membrane Fourier transform infrared spectroscopy

A coupling of novel liquid–liquid–solid microextraction (LLSME) technique based on porous hydrophobic membrane and Fourier-transform infrared spectroscopy has been presented for the detection, identification and quantification of markers and simulants of nerve agents. Two isomers O,O′-dihexyl methylphosphonate (DHMP) and O,O′-dipentyl isopropylphosphonate (DPIPP) were chosen as model analytes for the study. In the present technique, organic phase was immobilised within the pores of membrane after fixing it in an assembly, which was then immersed into aqueous sample of target analytes for extraction. The analytes were directly determined on the surface of membrane by FTIR spectroscopy without elution. On comparison with solid phase microextraction (SPME), LLSME was found to be much more efficient. The method was optimised and quantitative analyses were performed using calibration curves obtained via Beer's law and employing processing of spectra obtained, via a multivariate calibration technique partial least square (PLS). Relative standard deviations (RSDs) for intraday repeatability and interday reproducibility were found to be in the range of 0.20–0.50% and 0.20–0.60%, respectively. Limit of detection (LOD) was achieved up to 15 ng mL⁻¹. Applicability of the method was tested with an unknown real sample obtained in an international official proficiency test (OPT).     

Energy and photoinduced electron transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex

Functional mimics of a photosynthetic antenna-reaction center complex comprising five bis(phenylethynyl)anthracene antenna moieties and a porphyrin-fullerene dyad organized by a central hexaphenylbenzene core have been prepared and studied spectroscopically. The molecules successfully integrate singlet-singlet energy transfer and photoinduced electron transfer. Energy transfer from the five antennas to the porphyrin occurs on the picosecond time scale with a quantum yield of 1.0. Comparisons with model compounds and theory suggest that the F?rster mechanism plays a major role in the extremely rapid energy transfer, which occurs at rates comparable to those seen in some photosynthetic antenna systems. A through-bond, electron exchange mechanism also contributes. The porphyrin first excited singlet state donates an electron to the attached fullerene to yield a P(*+)-C(60)(*-) charge-separated state, which has a lifetime of several nanoseconds. The quantum yield of charge separation based on light absorbed by the antenna chromophores is 80% for the free base molecule and 96% for the zinc analogue.     

Use of prior information in the consistent estimation of regression coefficients in measurement error models

A multivariate ultrastructural measurement error model is considered and it is assumed that some prior information is available in the form of exact linear restrictions on regression coefficients. Using the prior information along with the additional knowledge of covariance matrix of measurement errors associated with explanatory vector and reliability matrix, we have proposed three methodologies to construct the consistent estimators which also satisfy the given linear restrictions. Asymptotic distribution of these estimators is derived when measurement errors and random error component are not necessarily normally distributed. Dominance conditions for the superiority of one estimator over the other under the criterion of Löwner ordering are obtained for each case of the additional information. Some conditions are also proposed under which the use of a particular type of information will give a more efficient estimator.     

Contention reduction and service differentiation in OBS networks

Optical burst switching (OBS) has been proposed to be a competitive switching technology for wavelength division networks (WDM) networks. In this switching technique, single burst loss due to contention influences loss of multiple data. Thus, burst loss ratio (BLR) is the main deciding factor for determining the performance of an OBS network. Also, inefficient data channel scheduling algorithm causes burst loss in OBS. In addition to this, the same service to all model of the current Internet is inadequate for the diverse quality of service expectations of Internet applications and users. In this paper, an efficient technique is proposed in which data burst is assembled from several Internet protocol (IP) packets in such a manner that the number of IP packets is changed according to the traffic load. In the proposed scheme, the burst is segmented because the segment located at the end of the contended burst has a greater chance of surviving contention (as the dropped segments are those at the beginning of the contending burst). Thus, the most important (or higher priority) information is enveloped in the last segmented. Further to prevent resource wastage due to over admitting of bursts, the proposed scheme is extended by admission control test for an output link without a fiber delay line (FDL) buffer. Also, modified latest available unscheduled channel with void filling (LAUC-VF) scheduling algorithm utilizing MPLS has been used to provide a scalable and manageable architecture for service differentiation (DiffServ) in IP networks. Simulation results demonstrate that the proposed technique has reduced burst loss rate and better quality of service (QoS) performance in comparison to existing techniques.     

Intense two-cycle laser pulses induce time-dependent bond hardening in a polyatomic molecule

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules such as TMS do not exhibit a prominent molecular ion (TMS(+)) as unimolecular dissociation into [Si(CH(3))(3)](+) proceeds very fast. Under a strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond hardening: a field-induced potential well is created in the TMS(+) potential energy curve that effectively traps a wave packet. The time dependence of this bond-hardening process is verified using longer-duration (≥100 fs) pulses; the relatively slower falloff of optical field in such pulses allows the initially trapped wave packet to leak out, thereby rendering TMS(+) unstable once again.     

Moisture uptake in nanocellulose: the effects of relative humidity,temperature and degree of crystallinity

Cellulose - Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of...     

ChemInform Abstract: High Pressure Phase Transitions in Scheelite Structured Fluoride: ErLiF4.

ErLiF₄ is prepared by solid state reaction of stoichiometric amounts of LiF and ErF₃ (1.     

Ligand-Promoted [Pd]-Catalyzed α-Alkylation of Ketones through a Borrowing-Hydrogen Approach

A new class of palladium complexes bearing bidentate 2-hydroxypyridine based ligands have been prepared and fully characterized. The applications of these new complexes towards ketone alkylation reactions with alcohols through a metal-ligand cooperative borrowing-hydrogen (BH) process were demonstrated.