Impact of membrane immobilization on particle formation and trichloroethylene dechlorination for bimetallic Fe/Ni nanoparticles in cellulose acetate membranes

The use of membrane immobilization to carry out the batch dechlorination of trichloroethylene (TCE) using bimetallic Fe/Ni (4:1, Fe to Ni) nanoparticles in cellulose acetate membranes is examined using modeling of transport phenomenon based on experimental results. Membranes are synthesized using both gelation and solvent evaporation techniques for phase inversion. The reduction of metal ions within cellulose acetate phase-inversion membranes was accomplished using sodium borohydride reduction to obtain up to 2 wt % total metals. Characterization of the mixed-matrix structure reveals a bimodal particle distribution ranging between 18 and 80 nm within the membrane cross section. The distribution is the result of changes in the morphology of the cellulose acetate support. The diffusivity and linear partitioning coefficient for the chlorinated organic were measured and are 2.0 x 10(-8) cm2.s-1 and 3.5 x 10(-2) L.g-1, respectively. An unsteady-state model for diffusion through a membrane with reaction was developed to predict experimental results with an error of only 7.2%. The error can be attributed to the lack of the model to account for loss of reactivity through pH effects, alloy effects (bimetallic ratio), and oxidation of nanoparticles. Simulations were run to vary the major transport variables, partitioning and diffusivity, and determine their impact on reaction kinetics. Of the two, diffusivity was less significant because it really only influences the time required for maximum TCE partitioning to the membrane to be achieved and has no effect on the limiting capacity of the membrane for TCE. Therefore, selection of an appropriate support material is crucial for development of highly reactive mixed-matrix membrane systems.     

Binding of Organic Dyes with Human Serum Albumin: A Single‐Molecule Study

Kinetics of binding of dyes at different sites of human serum albumin (HSA) has been studied by single‐molecule spectroscopy. The protein was immobilized on a glass surface. To probe different binding sites (hydrophobic and hydrophilic) two dyes, coumarin 153 ( C153 , neutral) and rhodamine 6G ( R6G , cationic) were chosen. For both the dyes, a major (ca. 96‐98 %) and minor (ca. 3 %) binding site were detected. Rate constants of association and dissociation were simultaneously determined from directly measuring fluctuations in fluorescence intensity (τ_off and τ_on) and from this the equilibrium (binding) constants were calculated. Fluorescence lifetimes at individual sites were obtained from burst‐integrated lifetime analysis. Distributions of lifetime histograms for both the probes ( C153 and R6G ) exhibit two maxima, which indicates the presence of two binding domains in the protein. Unfolding of the protein has been studied by adding guanidinium hydrochloride (GdnHCl) to the solution. It is observed that addition of GdnHCl affects the dissociation and association kinetics and hence, binding equilibrium of the association of C153 . However, the effect of binding of R6G is not affected much. It is proposed that GdnHCl affects the hydrophobic binding sites more than the hydrophilic site.     

Metallic radionuclides in the development of diagnostic and therapeutic radiopharmaceuticals

Metallic radionuclides are the mainstay of both diagnostic and therapeutic radiopharmaceuticals. Therapeutic nuclear medicine is less advanced but has tremendous potential if the radionuclide is accurately targeted. Great interest exists in the field of inorganic chemistry for developing target specific radiopharmaceuticals based on radiometals for non-invasive disease detection and cancer radiotherapy. This perspective will focus on the nuclear properties of a few important radiometals and their recent applications to developing radiopharmaceuticals for imaging and therapy. Other topics for discussion will include imaging techniques, radiotherapy, analytical techniques, and radiation safety. The ultimate goal of this perspective is to introduce inorganic chemists to the field of nuclear medicine and radiopharmaceutical development, where many applications of fundamental inorganic chemistry can be found.     

The Influence of Science Summer Camp on African‐American High School Students' Career Choices

This study explored if a weeklong science camp changed Louisiana African‐American high school students' perception of science. A semi‐structured survey was used before and after the camp to determine the changes in science attitudes and career choices. Among the perceived benefits were parental involvement, increased science academic ability, and deepened scientific knowledge. These perceived benefits influenced the identities that students constructed for themselves in relation to science in their lives. Students who reported doing well in school science courses believed that science was more relevant to their lives. Female students who cited doing well in science reported less parental involvement in their schoolwork than males. This study draws attention to gender differences in science and to designing informal science learning experiences for African‐American high school students that can change attitudes toward career choices in science‐related fields.     

Femtosecond study of ultrafast fluorescence resonance energy transfer in a catanionic vesicle

Ultrafast fluorescence resonance energy transfer (FRET) in a catanionic [sodium dodecyl sulfate (SDS)-dodecyltrimethyl ammonium bromide (DTAB)] vesicle is studied by femtosecond up-conversion. The vesicles (diameter ～400 nm for SDS-rich and ～250 nm for DTAB-rich vesicles) are much larger than the SDS and DTAB micelles (diameter ～4 nm). In both micelle and vesicles, FRET occurs in multiple time scales and the time scales of FRET correspond to a donor-acceptor distance varying between 12 and 36 A?.     

Role of higher excited electronic states on high harmonic generation in H2(+)--a time-independent Hermitian Floquet approach

We have theoretically studied the role of high-lying molecular electronic states on the high harmonic generation (HHG) in H(2)(+) within the framework of a time-independent Hermitian nonperturbative three-dimensional Floquet technique for continuous wave monochromatic lasers of intensities of 2.59 × 10(13), 4.0 × 10(13), and 5.6 × 10(13) W∕cm(2), and wavelengths of 1064, 532, and 355 nm. To evaluate the HHG spectra, the resonance Floquet quasienergy and the Fourier components of the Floquet state corresponding to the initial vibrational-rotational level v = 0, J = 0 have been computed by solving the time-independent close-coupled Schro?dinger equation following the Floquet method. The calculations include seven molecular electronic states in the basis set expansion of the Floquet state. The electronic states considered, apart from the two lowest 1sσ(g) and 2pσ(u) states, are 2pπ(u), 2sσ(g), 3pσ(u), 3dσ(g), and 4fσ(u). All the concerned higher excited molecular electronic states asymptotically degenerate into the atomic state H(2 l) with l = 0, 1. The computations reveal signature of significant oscillations in the HHG spectra due to the interference effect of the higher molecular electronic states for all the considered laser intensities and wavelengths. We have attempted to explain, without invoking any ionization, the dynamics of HHG in H(2)(+) within the framework of electronic transitions due to the electric dipole moments and the nuclear motions on the field coupled ground, the first and the higher excited electronic states of this one-electron molecular ion.     

Studies on the radiolytic stability of N,N,N′,N′-tetra-2-ethylhexyl diglycolamide in n-dodecane solution containing different phase modifiers

The radiolytic stability of a branched diglycolamide extractant, namely N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) dissolved in n-dodecane containing several phase modifiers, viz. N,N-dihexyloctanamide (DHOA), tri-n-butyl phosphate (TBP), 1-decanol and iso-decanol has been investigated. The distribution ratio of Am(III) decreased with increased radiation dose studied up to 1000 kGy. Nevertheless, all the composition of extractants showed satisfactory results up to 500 kGy, beyond which the extractants degraded drastically. The stripping behaviour of Am(III) with 0.2 M HNO₃ was found to be unaffected even with the ligand solution irradiated up to 1000 kGy. Extraction of fission product and structural elements was also investigated using the irradiated solvents and was found to be not significantly affected with increasing absorbed dose with the exception of Mo which showed sharp rise in the distribution coefficient values. Loading of Nd in the organic phase decreased with the irradiated solvent due to degradation of the carrier. The effect of the absorbed dose on physical parameters such as density, viscosity and interfacial tension of the solvents has also been investigated.     

Extraction chromatographic study on the separation of Am<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> using ethyl-BTP as the extractant

Ethyl-substituted bis-triazinylpyridine (Et-BTP), a nitrogen containing soft-donor extractant, was used in investigations pertaining to the separation of Am³⁺ and Eu³⁺ from dilute nitric acid feed solutions by extraction chromatography using XAD-4 as the inert support, chlorinated dicarbollide as the modifier and 2-nitrophenyloctylether (NPOE) as the diluent. After carrying out a series of experiments, the optimum composition of the extractant mixture for the resin was found out to be 0.1 M Et-BTP and 0.025 M CCD in NPOE. Separation factor values were encouraging to carry out subsequent batch uptake studies at varying nitrate ion concentration which indicated favourable separation behaviour up to NaNO₃ concentration of 2 M. Column studies have been carried out and conditions for elution and separation of Am³⁺ from Eu³⁺ have been found out. Long term stability of the resin was also investigated.     

Near‐exact supersymmetric partner potentials: Construction and exploitation

Precise supersymmetric (SUSY) partner potentials can be generated only for exactly solvable problems of the stationary Schrödinger equation. This is a severe restriction, as most problems are not amenable to exact solutions. We employ here a linear variational strategy to explicitly construct approximate SUSY partners of a few common, not exactly solvable potentials and subsequently examine their properties to explore the advantages in practical implementation. The efficacy of our proposed scheme is commendable. We demonstrate that, for symmetric potentials, the constructed partners may be so good that the overall recipe has the nicety of generating the whole eigenspectrum by employing only half of the full Hilbert space functions. A similar strategy is shown to work for the odd states too, with proper boundary conditions. Pilot calculations involve a number of low‐lying states of some mixed oscillator and double‐well potentials. Analysis of the results reveals a few interesting features of the problem of construction of approximate SUSY partners and their practical use. Particularly, we identify places where the operator‐level approximations are involved and how far they affect the bounding properties of energies that are obtained as eigenvalues of a matrix diagonalization problem associated with linear variations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electron distribution in partially reduced mixed metal oxide systems: infrared spectroscopy of CemVnOo(+) gas-phase clusters

Vibrational predissociation spectra of rare-gas-tagged [(CeO(2))(VO(2))(1-2)](+) and [(Ce(2)O(3))(VO(2))](+) clusters are measured in the 400-1200 cm(-1) region. Density functional theory (DFT) is used to determine the geometric and electronic structure of low-energy isomers of the partially reduced clusters. Comparison of experimental and simulated spectra provides evidence for the larger stability of Ce(+3)/V(+5) compared to that of Ce(+4)/V(+4), which confirms that the exceptionally high reducibility of Ce(+4) accounts for the promoting role of ceria in supported vanadium oxide catalysts.