Impacts of gold nanoparticle charge and ligand type on surface binding and toxicity to Gram-negative and Gram-positive bacteria

Although nanomaterials facilitate significant technological advancement in our society, their potential impacts on the environment are yet to be fully understood. In this study, two environmentally relevant bacteria, Shewanella oneidensis and Bacillus subtilis, have been used as model organisms to elucidate the molecular interactions between these bacterial classes and Au nanoparticles (AuNPs) with well-controlled and well-characterized surface chemistries: anionic 3-mercaptopropionic acid (MPA), cationic 3-mercaptopropylamine (MPNH₂), and the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). The data demonstrate that cationic, especially polyelectrolyte-wrapped AuNPs, were more toxic to both the Gram-negative and Gram-positive bacteria. The levels of toxicity observed were closely related to the percentage of cells with AuNPs associated with the cell surface as measured in situ using flow cytometry. The NP concentration-dependent binding profiles were drastically different for the two bacteria strains, suggesting the critical role of bacterial cell surface chemistry in determining nanoparticle association, and thereby, biological impact.     

Improving throughput in a wireless LAN with application to the Canadian army's situational awareness system

This paper employs optimization to improve the performance of the system the Canadian Army uses to give a Commander a picture of where his forces are. This system uses the Army's wireless battlefield communication network to send vehicle positions as data messages. The difficulty is that, when vehicles compete to send these reports, the messages sometimes collide and this wastes valuable network capacity. At the heart of the problem is the channel access control mechanism. We show how a simple change to this mechanism can improve the system's performance significantly.     

Atmospheric chemistry of perfluoroaldehydes (CxF2x+1CHO) and fluorotelomer aldehydes (CxF2x+1CH2CHO): quantification of the important role of photolysis

The UV absorption spectra of CF(3)CHO, C(2)F(5)CHO, C(3)F(7)CHO, C(4)F(9)CHO, CF(3)CH(2)CHO, and C(6)F(13)CH(2)CHO were recorded over the range 225-400 nm at 249-297 K. C(x)F(2)(x)(+1)CHO and C(x)F(2)(x)(+1)CH(2)CHO have broad absorption features centered at 300-310 and 290-300 nm, respectively. The strength of the absorption increases with the size of the C(x)F(2)(x)(+1) group. There was no discernible (<5%) effect of temperature on the UV spectra. Quantum yields for photolysis at 254 and 308 nm were measured. Quantum yields at 254 nm were 0.79 +/- 0.09 (CF(3)CHO), 0.81 +/- 0.09 (C(2)F(5)CHO), 0.63 +/- 0.09 (C(3)F(7)CHO), 0.60 +/- 0.09 (C(4)F(9)CHO), 0.74 +/- 0.08 (CF(3)CH(2)CHO), and 0.55 +/- 0.09 (C(6)F(13)CH(2)CHO). Quantum yields at 308 nm were 0.17 +/- 0.03 (CF(3)CHO), 0.08 +/- 0.02 (C(4)F(9)CHO), and 0.04 +/- 0.01 (CF(3)CH(2)CHO). The quantum yields decrease with increasing size of the C(x)F(2)(x)(+1) group and with increasing wavelength of the photolysis light. The photolysis quantum yield at 308 nm for CF(3)CHO measured here is a factor of at least 8 greater than that reported previously. Photolysis is probably the dominant atmospheric fate of C(x)F(2)(x)(+1)CHO (x = 1-4) and is an important fate of C(x)F(2)(x)(+1)CH(2)CHO (x = 1 and 6). These results have important ramifications concerning the yield of perfluorocarboxylic acids in the atmospheric oxidation of fluorotelomer alcohols.     

Atmospheric chemistry of n-C(x)F(2)(x)(+1)CHO (x = 1, 2, 3, 4): fate of n-C(x)F(2)(x)(+1)C(O) radicals

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C(x)F(2)(x)(+1)C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O(2)/N(2) diluent at 298 +/- 3 K. A competition is observed between reaction with O(2) to form n-C(x)()F(2)(x)()(+1)C(O)O(2) radicals and decomposition to form n-C(x)F(2)(x)(+1) radicals and CO. In 700 Torr O(2)/N(2) diluent at 298 +/- 3 K, the rate constant ratio, k(n-C(x)F(2)(x)(+1)C(O) + O(2) --> n-C(x)F(2)(x)(+1)C(O)O(2))/k(n-C(x)F(2)(x)(+1)C(O) --> n-C(x)F(2)(x)(+1) + CO) = (1.30 +/- 0.05) x 10(-17), (1.90 +/- 0.17) x 10(-19), (5.04 +/- 0.40) x 10(-20), and (2.67 +/- 0.42) x 10(-20) cm(3) molecule(-1) for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O(2) accounts for 99%, 50%, 21%, and 12% of the loss of n-C(x)F(2)(x)(+1)C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C(x)F(2)(x)(+1)C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.     

Direct monitoring of toxic compounds in air using a portable mass spectrometer

A portable tandem mass spectrometer, capable of performing atmospheric pressure chemical ionization (APCI) using a direct atmospheric inlet, is applied to the real-time monitoring of toxic compounds in air. Analytes of interest include dimethyl methylphosphonate, arsine, benzene, toluene, pyridine and vinyl acetate. The detection, identification and quantification of organic and inorganic compounds in air is demonstrated using short analysis times (<5 seconds) with detection limits in the low ppb (v/v) levels and linear dynamic ranges of several orders of magnitude. Highly specific detection and identification is achieved, even when the analyte is a trace component in a complex mixture including such interferents as fuels, lubricants, and cleaners. The effects of environmental conditions, including temperature and humidity, are delineated. Receiver operating characteristic (ROC) curves are presented to show the trade-off between false positive and false negative detection rates. Tandem mass spectrometry based both on collision-induced dissociation and on selective atmospheric pressure ion/molecule reactions is also used to increase selectivity and sensitivity.     

Gradient estimates for the subelliptic heat kernel on H-type groups

We prove the following gradient inequality for the subelliptic heat kernel on nilpotent Lie groups G of H-type:

|∇Ptf|?KPt(|∇f|),     

Solution precursor synthesis and magnetic properties of Eu1−xCaxTiO3

Europium titanate, EuTiO₃, is a paraelectric/antiferromagnetic cubic perovskite with T_N=5.5 K. It is predicted that compressive strain could induce simultaneous ferroelectricity and ferromagnetism in this material, leading to multiferroic behavior. As an alternative to epitaxial strain, we explored lattice contraction via chemical substitution of Eu²⁺ with the smaller Ca²⁺ cation as a mechanism to tune the magnetic properties of EuTiO₃. A modified sol-gel process was used to form homogeneously mixed precursors containing Eu³⁺, Ca²⁺, and Ti⁴⁺, and reductive annealing was used to transform these precursors into crystalline powders of Eu_1−xCa_xTiO₃ with x=0.00, 0.05, 0.10, 0.15, 0.25, 0.35, 0.50, 0.55, 0.60, 0.65, 0.80, and 1.00. Powder XRD data indicated that a continuous Eu_1−xCa_xTiO₃ solid solution was readily accessible, and the lattice constants agreed well with those predicted by Vegard's law. SEM imaging and EDS element mapping indicated a homogeneous distribution of Eu, Ca, and Ti throughout the polycrystalline sample, and the actual Eu:Ca ratio agreed well with the nominal stoichiometry. Measurements of magnetic susceptibility vs. temperature indicated antiferromagnetic ordering in samples with x≤0.60, with T_N decreasing from 5.4 K in EuTiO₃ to 2.6 K in Eu_0.40Ca_0.60TiO₃. No antiferromagnetic ordering above 1.8 K was detected in samples with x>0.60.