Reflectance spectroscopy of gold nanoshells: computational predictions and experimental measurements

Gold nanoshells are concentric spherical constructs that possess highly desirable optical responses in the near infrared. Gold nanoshells consist of a thin outer gold shell and a silica core and can be used for both diagnostic and therapeutic purposes by tuning the optical response through changing the core–shell ratio as well as the overall size. Although optical properties of gold nanoshells have already been well documented, the reflectance characteristics are not well understood and have not yet been elucidated by experimental measurements. Yet, in order to use gold nanoshells as an optical contrast agent for scattering-based optical methods such as reflectance spectroscopy, it is critical to characterize the reflectance behavior. With this in mind, we used a fiber-optic-based spectrometer to measure diffuse reflectance of gold nanoshell suspensions from 500 nm to 900 nm. Experimental results show that gold nanoshells cause a significant increase in the measured reflectance. Spectral features associated with scattering from large angles (~180°) were observed at low nanoshell concentrations. Monte Carlo modeling of gold nanoshells reflectance demonstrated the efficacy of using such methods to predict diffuse reflectance. Our studies suggest that gold nanoshells are an excellent candidate as optical contrast agents and that Monte Carlo methods are a useful tool for optimizing nanoshells best suited for scattering-based optical methods.     

Effect of hydrostatic pressure on the fluorescence of indole derivatives

Effects of hydrostatic pressure on the fluorescence emission of L-tryptophan, N-acetyl-L-trytophanamide and indole were investigated. An increase in pressure ranging from 1 bar to 2.4 kbar results in reversible red-shifts of the emission of the three fluorophores. The pressure-induced redshift amounts to about 170 cm^–1 at 2.4 kbar, and appears related to changes in Stokes shift of the fluorophores caused by pressure effects on the dielectric constant and/or refractive index of the medium. As the pressure range investigated here is the range commonly used in studies of protein subunit association and/or folding, these observations raise the need for caution in interpreting pressure-induced spectral shifts. The significance of these observations to pressure studies of proteins is illustrated by investigation of pressure effects on human Cu,Zn Superoxide dismutase (SOD) and azurin fromPseudomonas aeruginosa. A reversible 170 cm^–1 red-shift of the emission of SOD was observed upon pressurization to 2.4 kbar. This might be interpreted as pressure-induced conformational changes of the protein. However, further studies using SOD that had been fully unfolded by guanidine hydrochloride, and fluorescence anisotropy measurements indicated that the observed red-shift was likely due to a direct effect of pressure on the fluorescence of the single tryptophan residue of SOD. Similar pressure-induced red-shifts were also observed for the buried tryptophan residue of azurin or for azurin that had been previously denatured by guanidine hydrochloride. These observations further suggest that the effective dielectric constant of the protein matrix is affected by pressure similarly to water.     

Synthesis and Structures of Homoleptic Monomeric Potassium Aryloxolanthanoidate(III) Complexes

Reaction of lanthanoid tris(2, 6‐diphenylphenolates) [Ln(Odpp)₃] with KOdpp in 1, 2, 4, 5‐tetramethylbenzene (durene) at 200‐250 °C affords [K{Ln(OC₆H₃Ph₂‐2, 6)₄}], (Ln = La ( 1 ) or Nd ( 2 )) and 2 has also been obtained from the reaction of [Nd(Odpp)₃] with potassium hydride. In the solid state, 1 and 2 are monomeric bimetallics in which Ln is surrounded by a distorted tetrahedral array of oxygen atoms. Two Odpp ligands are oxygen bridged between K and Ln and also are η⁴‐Ph linked to potassium. One Odpp ligand bridges the metals in an O(Ln): η⁶‐Ph(K) manner that is new for lanthanoid complexes of this ligand, with no close K‐O contact, and the remaining Odpp is terminal on the Ln.     

Determination of the sulfur distribution in stone by electron microprobe analysis

An electron microprobe was used to determine the sulfur distribution in stone materials, especially sedimentary rocks. The investigations were performed to elucidate damage mechanisms in natural stones built in historical monuments. Quantitative results could be attained using one single calibration curve determined by synthetic standard samples. The applicability of the technique was proved by samples subjected to different exposure simulation experiments.     

A second-order implicit particle mover with adjustable damping

A new algorithm for the calculation of particle trajectories is introduced. The algorithm combines second-order accuracy in the real frequency with third-order user-adjustable attenuation. It requires little storage of data from previous time levels. The method was designed for use in implicit particle-in-cell plasma simulation codes, and this application is treated in detail. It may also prove useful in other applications where one seeks to preserve the accuracy of low-frequency oscillations while rapidly damping under-resolved high frequency motions, e.g., solution of the field equations in electromagnetic particle codes. An explicit variation, wherein future quantities are obtained by extrapolation, can provide attenuation but not large-timestep stability.     

cis-Bis(2-Phenylpyridine)platinum(II) (CBPPP). A simple molecular platinum compound preliminary communication

The deprotonated 2-phenylpyridine forms a 2:1 chelate with platinum(II) in cis-configuration, which exists as a dimer in a molecular solid.