Gel routes to environmental catalysts

Various methods for the preparation of metal oxide catalysts for environmental control purposes are described. These include coprecipitation, sol-gel, and impregnation, and are used to prepare mixed oxide catalysts of the types SnO₂-MO₂ (M=Ce or Zr), SnO₂-Ln₂O₃ (Ln = lanthanide), Ln-doped CeO₂, Cr (VI)-doped SnO₂, and Cu(II)-doped SnO₂. The aggregation in stable colloidal sols of SnO₂, CeO₂ and ZrO₂ is dependent on the concentration of the metal oxide. Techniques for the characterisation of these catalyst materials include gas adsorption, X-ray diffraction, and TEM/EDXA.     

Speciation of dissolved phosphorus in environmental samples by gel filtration and flow-injection analysis

A study of the factors affecting separation and detection of dissolved organic and inorganic phosphorus species found in waters sediments is reported. The system involved the use of gel filtration and flow injection analysis (FIA). Orthophosphate and myo-inositol hexakisphosphate, as model solutes representative of low molecular weight P (LMWP) and high molecular weight P (HMWP), were separated on a Sephadex G25 column incorporated into a flow-injection manifold which utilized photo-oxidation and spectrophotometry for detection of dissolved reactive phosphorus (DRP) and dissolved organic phosphorus (DOP). The influence of eluent pH and ionic strength on adsorption and anionic exclusion of the model solutes is described, and the optimum eluent composition and sample size are described. The method was used to determine LMWP and HMWP in natural and waste waters, and in sediment extracts. Potential limitations of this approach are discussed.     

Rotational and vibrational temperatures of naphthalene in a naphthalene-argon supersonic jet

In the $\text{A}$¹B_2u-$\text{X}$¹A_g system of naphthalene in a supersonic jet, rotational contour calculations show rotational temperatures of 2–60 K for argon carrier gas pressures of 1520-120 Torr. The b_1u vibration v₂₄ shows a high vibrational temperature which corresponds to the seeding temperature for pressures <400 Torr.     

An algorithm for semi-empirical design of nucleation rate surface

During the last half of century, Classical Nucleation Theory (CNT) has been developed and there have been advances in the molecular theory of nucleation. Most of these efforts have been directed towards small molecule system modeling using intermolecular potentials. Summarizing the nucleation theory, it can be concluded that the current theory is far from complete. Agreement is generally not obtained between experimental and theoretical results. In practical applications, parametric theories can be used for the systems of interest. However, experimental measurements are still the best source of information on nucleation. Experiments are labor intensive and costly, and thus, it is useful to extend the value of limited experimental measurements to a broader range of nucleation conditions. The available nucleation parameters represent only small regions of possible nucleation conditions over the range from the critical temperature to absolute zero. Thus, it is useful to develop better tools to use the data to estimate semi-empirical nucleation rate surfaces. Following our published approach, the nucleation rate surface for any system can be constructed over its phase diagram. This concept involves using the phase equilibrium diagram to establish lines of zero nucleation rates. Nucleation rate surfaces arise from equilibrium lines and their extensions that are representing unstable equilibria. Only limited experimental data is available for use in normalizing the slopes of the linearized nucleation rate surfaces. The nucleation rate surface is described in terms of steady-state nucleation rates. To design the surfaces of nucleation rates, several assumptions are presented. In the present study, an algorithm for the semi-empirical design of nucleation rate surfaces is introduced. The topology of the nucleation rate surface for a unary system using the example of water vapor nucleation is created semi-empirically. The nucleation of two concurrent (stable and unstable) phase states of critical embryos is considered in the context of multi-surface nucleation rates. Only one phase transition (melting) in the condensed state of water is considered for simplicity. The nucleation rate surface is constructed numerically using the available experimental results for vapor nucleation and phase diagram for water. The nucleation rate for water vapor is developed for the full temperature interval, i.e. from critical point to absolute zero. The results help to suggest a new direction for experimental nucleation research.     

A spirocyclic system comprising both phosphazane and phosphazene rings

The reaction of hexakis(cyclohexylamino) cyclotriphosphazene [NP(CyNH)(2)](3), 1, with phosphorus trichloride yields [NP(CyN)(2)PCl](3), 2, which contains three four-membered phosphazane rings fused in spirocyclic fashion to a central six-membered phosphazene ring and constitutes the first structurally characterized compound that comprises both phosphazene and phosphazane rings. The peripheral P atoms feature stereoactive lone pairs, and, thus, 2 exists in isomeric C(3h) and C(s) forms. The spirocyclic phosphazene-phosphazane derivative 2 carries three reactive PCl functions in peripheral positions, promising an interesting precursor molecule for the synthesis of extended phosphorus nitrogen structures of high rigidity. Extension of the PN moiety can be achieved by reaction of 2 with a primary amine yielding [NP(CyN)(2)PN(H)(t)Bu](3), 3, which features a central scaffold of 6 phosphorus and 12 nitrogen centers and aggregates via N-H...P hydrogen bonds in the solid state. On the contrary, the reaction of 1 with SbCl(3) undergoes incomplete proton abstraction, resulting in the formation of the tricyclic compound N(3)P(3)(CyNH)(4)(CyNSbCl(2))(2), 4, which contains two four-coordinate Sb centers chelated by N(exo)-N(ring) sites of the phosphazene.     

Synthesis of the Deuterium Labeled Isoflavone-<Emphasis Type="Italic">O</Emphasis>-glucoside 8,3′,5′-D<Subscript>3</Subscript>-Daidzin

The regio- and stereospecific glycosylation of 8,3′,5′-trideuterodaidzein 1 with α-acetobromoglucose to provide 8,3′,5′-trideuterodaidzein-7-O-β-glucopyranoside 2 is presented.     

Determination of internuclear distances in uniformly labeled molecules by rotational-resonance solid-state NMR

Rotational-resonance magic-angle spinning NMR experiments are frequently used to measure dipolar couplings and to determine internuclear distances. So far most measurements were performed on samples containing isolated spin pairs. Thus, extensive structure elucidation, for example in biomolecules, requires the preparation of a whole set of doubly labeled samples. Here, we describe the analysis of the rotational-resonance polarization-exchange curves obtained from a single, uniformly labeled sample. It is shown experimentally that, at a magnetic field of 14.09 T, the rotational-resonance conditions in uniformly (13)C-labeled threonine are sufficiently narrow to permit the measurement of five distances between the four carbon spins with an accuracy of better than 10%. The polarization-exchange curves are analyzed using a modified two-spin model consisting of the two active spins. The modified model includes an additional offset in the final polarization, which comes from the coupling to the additional, passive, spins. The validity of this approach is experimentally verified for uniformly (13)C-labeled threonine. The broader applicability of such a model is demonstrated by numerical simulations which quantify the errors as a function of the most relevant parameters in the spin system.     

The asymmetric synthesis of trans-substituted cyclopropanecarboxylic acid derivatives

The asymmetric synthesis of trans-substituted cyclopropanecarboxylic acid derivatives is achieved via stereoselective nucleophilic methylene transfer to E-,β-unsaturated acyl ligands bound to the iron chiral auxiliary [(η⁵-C₅H₅)Fe(CO)(PPh₃)].     

The structure of PR toxin,a mycotoxin from Penicillium roqueforti

An earlier report from our laboratories described the isolation, partial characterization, and biological activity of a new mycotoxin from cultures of Penicillium roqueforti, and the name “PR toxin” was tentatively assigned to the compound. On the basis of further chemical and spectral evidence we propose that PR toxin has the structure shown in formula 1.¹