J. Craig Bennett

Promoting DNA loading on magnetic nanoparticles using a DNA condensation strategy.

Maximizing DNA loading on magnetic nanoparticles (MNPs) is crucial for their successful utilization in gene transfer, DNA isolation, and bio-analytical applications. This enhancement is typically achieved by altering particle size and surfaces as well as charge density and ionic strength. We demonstrate a novel route for promoting DNA loading on amino-modified silica-coated magnetic nanoparticles (ASMNPs) by prior condensation of elongated DNA to a compact globule before adsorption. The enhanced DNA-loading capacity, as demonstrated by a reduction in the number of ASMNPs needed to achieve complexation, was presumably due to the elimination of DNA wrapping around nanoparticles and substantially reduced electrostatic interactions of DNA with nanoparticles because the compacted DNA globule conformation decreases its exposed surface charge. The maximum loading capacity of ASMNPs for condensed DNA was 4.4 times greater than that for elongated coiled DNA, achieving the highest ever reported value of 385 μg mg(-1). Practical applications for plasmid DNA isolation from cleared lysate confirmed the reliability of the proposed method.

Advances in the Crystallographic and Microstructural Analysis of Charge Density Wave Modulated Crystals

Preface. Alternative Approaches to the Crystallographic Description of Charge Density Wave Modulated System A. Prodan, A. Budkowski. X-Ray Crystallographic Analysis of the Charge Density Wave Modulated Phases in the NbTe4 -- TaTe4 System H. Bohm. Charge Density Wave Phase Transitions and Microstructures in the TaTe4 -- NbTe4 System J.C. Bennett, F.W. Boswell. Transmission Electron Microscopy of CDW-Modulated Transition Metal Chalcogenides J.M. Corbett. Influence of Defects and Impurities on Charge Density Wave Systems H. Mutka. Analysis of Scanning Tunneling and Atomic Force Microscopy Images M.-H. Whangbo et al. Elucidating Complex Charge Density Wave Structures in Low-Dimensional Materials by Scanning Tunneling Microscopy H. Dai et al. Index of Subjects.

Structural phase transition and related electronic properties in quasi‐one‐dimensional (NbSe4)10/3I

The real crystal structure of the (NbSe4)(10/3)I charge density wave (CDW) compound is studied by simulation of the X-ray diffuse scattering. The average structure of the low-temperature twinned phase is determined and the phase transition is attributed to the formation of a CDW. The diffuse streaking, present in X-ray diffraction patterns above and below the transition at T = 282 K, is shown to be a projection of diffuse concentric rings perpendicular to the c* direction. The simulated patterns, based on a mismatch model between infinite NbSe4 chains, correlated by I atoms, are in good accordance with the experimental patterns. In addition to the experiments, the electronic properties of the high- and the low-temperature phases are calculated with the extended Hückel tight-binding method. The Fermi surfaces of the average structures above and below the phase transition appear very similar. Their shapes support a nesting instability and a CDW formation. The weak incommensurate CDW satellites, present below the phase transition, are at 100 K properly described by a modulation wavevector q = [0.06 (1), 0, 0.55 (1)].

Light-activated Ullmann homocoupling of aryl halides catalyzed using gold nanoparticle-functionalized potassium niobium oxides

Lamellar, or layered, potassium niobium oxide perovskites are a class of underdeveloped semiconductors in organic photocatalysis that offer the inherent advantages of larger particle size and ease of recoverability as compared to traditional semiconductor materials. Using photochemical methodologies, gold nanoparticle-functionalized potassium niobium oxides are synthesized. Nanocomposite characterization using UV-visible spectroscopy, X-ray diffraction and TEM confirms nanoparticle deposition on the perovskite surface, with an average nanoparticle diameter of 17 nm. High resolution imaging and X-ray diffraction also confirmed the crystallinity of the niobium oxide support with an estimated interlayer spacing of 10 A. Given the importance of carbon–carbon bond formation in organic synthesis, the Ullmann homocoupling of aryl halides is examined as a probe reaction for the application of this new class of nanocomposites. The influence of nanoparticle dopant, semiconductor support, reaction solvent, reaction time and aryl substitution are examined and shows that UVA-activation of gold nanoparticle/potassium niobium oxides promotes carbon–carbon bond formation in as little as 1 hour with yields as high as 98%, with high recyclability of the catalyst. The experimental methodology shows good versatility for a series of substituted iodobenzenes. The suggested mechanism involves a single electron transfer from the nanoparticle to facilitate aryl-halide bond activation to drive adsorption of the aryl halide starting material onto the gold nanoparticle surface. The positive results obtained with this lamellar nanocomposite may prove useful as a more cost-effective alternative in future carbon–carbon couplings.

Environmentally relevant concentrations of amine-functionalized copper nanoparticles exhibit different mechanisms of bioactivity in Fundulus Heteroclitus in fresh and brackish water

Abstract The bioavailability of engineered nanomaterials should be limited in marine environments, but uptake and toxicity has been noted in marine fish and invertebrates, albeit at exposure doses far exceeding predicted environmental levels. We examined the bioactivity of amine functionalized copper nanoparticles (nCu; 5–10 nm core diameter) to the euryhaline killifish, Fundulus heteroclitus, in fresh (FW) and brackish water (BW). Free copper dissolution was undetectable in either water type and nCu remained relatively well dispersed in BW, despite the high ionic strength. Exposure to an environmentally relevant concentration of nCu (10 µg L−1) for 48 h significantly increased the maximum rate of oxygen consumption and aerobic scope in BW killifish. This effect was associated with gill remodeling which likely increased surface area and scope for oxygen uptake. In contrast, nCu exposure had no effect on oxygen consumption in FW killifish, but gill Na+/K+-ATPase activity was reduced by >40%, an effect not seen in BW. Osmotic and ionic homeostasis were protected and no indications of physiological or oxidative stress were observed in either FW and BW exposure groups. The results show that functionalized nCu formulations can exhibit bioactivity in both FW and BW and that the underlying mechanisms are different between water types.

Nanoparticulate-specific effects of silver on teleost cardiac contractility

Silver nanoparticles (nAg), due to their biocidal properties, are common in medical applications and are used in more consumer products than any other engineered nanomaterial. This growing abundance, combined with their ability to translocate across the epithelium and bioaccumulate, suggests that internalized nAg may present a risk of toxicity to many organisms in the future. However, little experimentation has been devoted to cardiac responses to acute nAg exposure, even though nAg is known to disrupt ion channels even when ionic Ag+ does not. In this study, we examined the cardiac response to nAg exposure relative to a sham and an ionic AgNO3 control across cardiomyocyte survival and homeostasis, ventricular contractility, and intrinsic pacing rates of whole hearts. Our results suggest that nAg, but not Ag+ alone, inhibits force production by the myocardium, that Ag in any form disrupts normal pacing of cardiac contractions, and that these responses are likely not due to cytotoxicity. This evidence of nanoparticle-specific effects on physiology should encourage further research into nAg cardiotoxicity and other potential sublethal effects.