Synthesis and optical properties of small Au nanorods using a seedless growth technique

Gold nanoparticles have shown potential in photothermal cancer therapy and optoelectronic technology. In both applications, a call for small size nanorods is warranted. In the present work, a one-pot seedless synthetic technique has been developed to prepare relatively small monodisperse gold nanorods with average dimensions (length × width) of 18 × 4.5 nm, 25 × 5 nm, 15 × 4.5 nm, and 10 × 2.5 nm. In this method, the pH was found to play a crucial role in the monodispersity of the nanorods when the NaBH(4) concentration of the growth solution was adjusted to control the reduction rate of the gold ions. At the optimized pH and NaBH(4) concentrations, smaller gold nanorods were produced by adjusting the CTAB concentration in the growth solution. In addition, the concentration of silver ions in the growth solution was found to be pivotal in controlling the aspect ratio of the nanorods. The extinction coefficient values for the small gold nanorods synthesized with three different aspect ratios were estimated using the absorption spectra, size distributions, and the atomic spectroscopic analysis data. The previously accepted relationships between the extinction coefficient or the longitudinal band wavelength values and the nanorods' aspect ratios found for the large nanorods do not extend to the small size domain reported in the present work. The failure of extending these relationships over larger sizes is a result of the interaction of light with the large rods giving an extinction band which results mostly from scattering processes while the extinction of the small nanorods results from absorption processes.     

pH-based cation exchange chromatography in the capture and elution of monoclonal antibodies

Cation exchange chromatography separates adsorbed proteins by controlling the salt concentration or the mobile phase pH. This study examines the pH‐based method for binding and elution of monoclonal antibodies (MAbs). Five different clones with isoelectric points from 6 to 9 were evaluated. We performed our studies using a new chromatography resin (Nuvia? S), which has high binding capacity. A three‐column process incorporating Nuvia S as a capture step was also demonstrated for the purification of MAb from tissue culture fluid. Chromatography performance of Nuvia S was demonstrated in a 50‐cycle study.     

Does activation of the anti proton, rather than concertedness, determine the stereochemistry of base-catalyzed 1,2-elimination reactions? Anti stereospecificity in E1cB eliminations of β-3-trifluoromethylphenoxy esters, thioesters, and ketones

As part of a comprehensive investigation on the stereochemical aspects of base-catalyzed 1,2-elimination reactions, we have studied a set of acyclic carbonyl substrates that react by an irreversible E1cB mechanism with largely anti stereospecificity. (2)H NMR data show that these reactions using KOH in EtOH/H(2)O under non-ion-pairing conditions produce a minimum of 85-89% anti elimination on stereospecifically labeled tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanoate, S-tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanethioate, and the related ketones, (4R*,5R*)- and (4R*,5S*)-5-(3-trifluoromethylphenoxy)-4,5-(2)H(2)-3-hexanone. With both diastereomers of each substrate available, the KIEs can be calculated and the innate stereoselectivities determined. The elimination reactions of the β-3-trifluoromethylphenoxy substrates occur by E1cB mechanisms with diffusionally equilibrated enolate-anion intermediates. Thus, it is clear that anti elimination does not depend solely upon concerted E2 mechanisms. Negative hyperconjugation provides a satisfactory explanation for the anti stereospecificity exhibited by our carbonyl substrates, where the leaving group activates the anti proton, leading to the enolate intermediate. The activation of the anti proton by negative hyperconjugation may also play a role in the concerted pathways of E2 mechanisms. We have also measured the rates of the hydroxide-catalyzed elimination reactions of butanoate, thiobutanoate, and ketone substrates in EtOH/H(2)O, with β-tosyloxy, acetoxy, and 3-trifluoromethylphenoxy nucleofuges.     

Synthesis,Crystal Structure and Properties of Li2Cu5(PO4)4

Li₂Cu^II₅(PO₄)₄ has been obtained by various reactions starting from copper or Cu₂O. Crystallization was achieved using I₂ as oxidant and mineralizer. The new orthophosphate crystallizes in space group P$\bar{1}$ , Z = 2, with a = 6.0502(3) Å, b = 9.2359(4) Å, c = 11.4317(5) Å, α = 75.584(2)°, β = 80.260(2)°, γ = 74.178(2)°, at 293 K. Its structure has been determined from X‐ray single‐crystal data and refined to R₁ = 0.022{wR₂ = 0.058 for 4633 unique reflections with F_o > 4σ (F_o)}. From magnetic measurements μ_eff = 1.51 μ_B/Cu and θ_P = –37.4 K have been determined. The Vis/NIR spectrum of aqua‐green Li₂Cu₅(PO₄)₄ shows a single broad band centered around $\bar{1}$ = 12000 cm^–1. Magnetic behavior and spectrum are discussed within the angular overlap model.     

Perchlorate and chlorate in dietary supplements and flavor enhancing ingredients

The oxyhalide anions perchlorate and chlorate were measured in a series of dietary (vitamin and mineral) supplements and flavor enhancing ingredients collected from various commercial vendors in two large US cities. Analyses were conducted using liquid chromatography with tandem mass spectrometry (LC-MS/MS). The limit of detection was based on the mass of supplements and ingredients extracted and ranged from 2 to 15 ng/g for perchlorate and 4 to 30 ng/g for chlorate. Perchlorate and chlorate were detected in 20 and 26, respectively, of the 31 dietary supplements tested, with concentrations ranging from non-detectable to as high as 2400 and 10,300 ng/g, respectively. Based upon the recommended dose provided by each manufacturer for different supplements, the daily oral dose of perchlorate and chlorate could be as high as 18 and 20 μg/day, respectively. The highest level of perchlorate was found in a supplement recommended for pregnant women as a prenatal nutritional supplement. Of the 31 dietary supplements investigated, 12 were specifically marketed for pregnant women and children. Perchlorate and chlorate were also detectable in four products marketed for the enhancement of food flavor. Perchlorate is found naturally in some parts of the world, is present in some natural fertilizers, is used as an oxidizer in solid fuel engines, and has been used at therapeutic doses in humans to treat overactive thyroid glands. Perchlorate has been detected in drinking water, dairy products, some produce and grains, and human breast milk. This is the first report of perchlorate measured in over-the-counter dietary supplements and flavor enhancing ingredients.     

Interfaces in bulk thermoelectric materials: A review for Current Opinion in Colloid and Interface Science

We review current progress in the understanding of interfaces in bulk thermoelectric materials. Following a brief discussion of the mechanisms by which embedded interfaces can enhance the electronic and thermal transport properties, we focus on emerging routes to engineer the nanoscale grain and interfacial structures in bulk thermoelectric materials. We address in particular (i) control of crystallographic texture, (ii) reduction of grain size to nanocrystalline dimensions, and (iii) formation of nanocomposite structures. While these approaches are beginning to yield promising improvements in performance, continued progress will require an improved fundamental understanding of the mechanisms governing the formation, stability, and properties of thermoelectric interfaces.     

Modeling of two-phase magnetic materials based on Jiles-Atherton theory of hysteresis

The Jiles-Atherton (JA) theory of hysteresis has been extended in the present paper to model hysteresis in two-phase magnetic materials. Two-phase materials are those that exhibit two magnetic phases in one hysteresis cycle: one at lower fields and the other at higher fields. In magnetic hysteresis, the transition from one phase to the other i.e. low field phase to high field phase depends mainly on the exchange field. Hence, the material-dependent microstructural parameters of JA theory: spontaneous magnetization, M_S, pinning factor, k, domain density, a, domain coupling, α, and reversibility factor, c, are represented as functions of the exchange field. Several cases based on this model have been discussed and compared with the measured data from existing literature. The shapes of the calculated and measured hysteresis loops are in excellent agreement.     

First observation of ground state dineutron decay: 16Be

We report on the first observation of dineutron emission in the decay of 16Be. A single-proton knockout reaction from a 53 MeV/u 17B beam was used to populate the ground state of 16Be. 16Be is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of 16Be was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.     

Subfactors of Index less than 5, Part 1: The Principal Graph Odometer

In this series of papers we show that there are exactly ten subfactors, other than A _∞ subfactors, of index between 4 and 5. Previously this classification was known up to index \({3+\sqrt{3}}\). In the first paper we give an analogue of Haagerup’s initial classification of subfactors of index less than \({3+\sqrt{3}}\), showing that any subfactor of index less than 5 must appear in one of a large list of families. These families will be considered separately in the three subsequent papers in this series.     

ChemInform Abstract: A Density Functional Theory Study of the Gas‐Phase Hydrolysis of Dinitrogen Pentoxide

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