Zinc(II) oxide solubility and phase behavior in aqueous sodium phosphate solutions at elevated temperatures

A platinum-lined, flowing autoclave facility is used to investigate the solubility/phase behavior of zinc(II) oxide in aqueous sodium phosphate solutions at temperatures between 17 and 287°C. ZnO solubilities are observed to increase continuously with temperature and phosphate concentration. At higher phosphate concentrations, a solid phase transformation to NaZnPO₄ is observed. NaZnPO₄ solubilities are retrograde with temperature. The measured solubility behavior is examined via a Zn(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria are obtained from a least-squares analysis of the data. The existence of two new zinc(II) ion complexes, Zn(OH)₂(HPO₄)^2– and Zn(OH)₃(H₂PO₄)^2–, is reported for the first time. A summary of thermochemical properties for species in the systems ZnO–H₂O and ZnO–Na₂O–P₂O₅–H₂O is also provided.     

A novel Bicine running buffer system for doubled sodium dodecyl sulfate - polyacrylamide gel electrophoresis of membrane proteins

A novel, Bicine-based SDS-PAGE buffer system was developed for the analysis of membrane proteins. The method involves molecular weight-based separations of fully denatured and solubilized proteins in two dimensions. This doubled SDS-PAGE (dSDS-PAGE) approach produced a diagonal arrangement of protein spots and successfully circumvented problems associated with membrane proteome analysis involving traditional gel-based methods. Membrane proteins from the anaerobic bacterium Clostridium thermocellum were used for these investigations. Tricine-dSDS-PAGE and the newly developed Bicine-dSDS-PAGE were compared with the standard glycine-dSDS-PAGE (Laemmli protocol) in their suitability to separate C. thermocellum membrane proteins. Large-format gel experiments using optimized gel preparation and running buffer conditions revealed a 112% increase in protein spot count for Tricine-dSDS-PAGE and a 151% increase for Bicine-dSDS-PAGE, compared to glycine-dSDS-PAGE. The data clearly indicated that Bicine-dSDS-PAGE is a superior method for the analysis of membrane proteins, providing enhanced resolution and protein representation.     

Optimization techniques in energy calculations involving the Hartree-Fock density matrix

Three optimization procedures are examined for their utilization in determining the optimum density matrix for a single determinant wave function. The total energy of a molecular system is written as a function of the density matrix and then optimized subject to the constraints of idempotency and total electron population. This direct calculation of the density matrix (DCDM) method was studied in an attempt to have a formalism which would avoid convergence problems associated with the self-consistent field (SCF) cycle, and which would be applicable to large molecular systems. The optimization procedures studied were the Powell algorithm, Gauss-Jordan reduction, and dynamic programming. Computational factors studied include convergence criteria, stepsize, and weight factors for constraint equation penalty functions. The application considered is for HF. An ab-initio SCF method was used to obtain initial values for the density matrix, and its SCF results were compared to corresponding DCDM predictions. Approximations of the quadratic two-electron energy contributions will be necessary to apply dynamic programming, but this appears to be the method most applicable to large molecular systems if an acceptable approximation can be found. Gauss-Jordan reduction is an applicable technique, but probably not for large molecular systems. BOTM appears to be the method most applicable without introducing approximations, but weight factors for the penalty functions will have to be more efficiently determined as Lagrange multipliers, and this addition would result in a technique probably not applicable to large molecular systems.This paper is based in part on the PhD Thesis of C. A. Waggoner, Department of Chemistry, Mississippi State University. Partial support was furnished by the National Science Foundation, Grant No. Rii-89-02064, the State of Mississippi, and Mississippi State University. Other support was furnished by the Physical and Biological Sciences Institute of MSU and the Office of the Dean, College of Arts and Sciences, MSU. Computer time was furnished by the Thomas E. Tramel Computing Center.     

Measurement of the refractive index of highly turbid media: reply to comment

Peiponen et al. [Opt. Lett.35, 4108 (2010)] have expressed concern that a theoretical model we proposed in Calhoun et al. [Opt. Lett.35, 1224 (2010)] for total internal reflection from a turbid medium may be inconsistent with the experimental data, in the sense that the model fails to take into account unexplained oscillations in our data. We show that their concern arises from misinterpretation of our data and theory, and is, therefore, unfounded. NOTE: Optics Letters apologizes to the authors for the delay in the publication of this Reply.     

Aptamer‐Assisted Assembly of Gold Nanoframe Dimers

The assembly of nanoframe dimers assisted by aptamer‐functionalized smaller spherical gold nanoparticles as prospective surface‐enhanced Raman scattering (SERS) biotraps for riboflavin, an important molecule for biological electron transfer reactions, is reported. In this approach, the aptamer‐coated gold nanoparticles designed for selective binding of riboflavin also serve as the electrostatic driver for nanoframe dimerization in dilute solutions. The gold nanoframe dimers provide unique conditions for plasmonic coupling in a hot spot with sufficient space for the binding of bulky biomolecules. The use of an aptamer allows for highly selective binding of the targeted analyte as compared with conventional organic ligands with excellent low detection limit of one micromole of riboflavin.     

Silver Nanocube Aggregates in Cylindrical Pores for Higher Refractive Index Plasmonic Sensing

We report on silver nanocubes (AgNCs) infiltrated into cylindrical nanopores of porous alumina membranes (PAM) with an outstanding chemical sensitivity based on refractive index sensing (RIS) measurements. Numerical simulations performed using the finite‐difference time‐domain (FDTD) method suggested that the enhanced sensitivity is based mainly on the inter‐pore coupling plasmonic effect. This effect is related to plasmonic amplification based on localized surface plasmon resonance (LSPR) coupling between AgNCs located at the pore walls of neighboring cylindrical pores and separated by a nanoscale wall. Results are discussed for different aggregation scenarios ranging from individual nanocubes through pentamers on a flat glass surface, a flat alumina surface, and a concave local shape representing the experimental conditions. An experimental RIS sensitivity of about 770 nm per refractive index unit was found to be more than an order of magnitude higher for silver nanocube aggregates within cylindrical pores than that observed for ordinary planar substrates.     

On the mechanism of the 1,2-cycloaddition reaction of ketenimines and nitrosoarenes

The 1,2-cycloaddition of nitrosoarenes to ketenimines producing 3-iminosubstituted-1,2-oxazetidines has been found to proceed more rapidly if photosensitized conditions are employed. This data plus the specificity of the reaction allows for a reasonable postulation of the non-photochemical room temperature reaction.