Analysis and calculation of the 31P and 19F NMR spectra of hexafluorocyclotriphosphazene

The higher order high-resolution (31)P and (19)F NMR spectra of hexafluorocyclotriphosphazene (F(2)PN)(3) were measured at 183 K and interpreted using subspectral analysis and iterative fitting computation. (F(2)PN)(3) forms a rigid nine-spin system [A[X](2)](3) with D(3h) symmetry. Two complete and very similar sets of six experimental spin-spin coupling constants, (1)J(P,F), (2)J(P,P), (2)J(F,F), (3)J(P,F), (4)J(F,F)(cis) and (4)J(F,F)(trans), were determined for the first time. Theoretical DFT calculations of chemical shifts and coupling constants were performed to assess their predictive value. The PP/aug-cc-pVDZ treatment rendered the best agreement with experimental data.     

A new fluorogenic transformation: development of an optical probe for coenzyme Q

[reaction: see text] A new fluorogenic transformation based on a quinone reduction/lactonization sequence has been developed and evaluated as a tool for probing redox phenomena in a biochemical context. The probe presented herein is an irreversible redox probe and is reduced selectively by biologically relevant quinols such as ubiquinol but is inert to reduced nicotinamides (e.g., NADH). The ensuing cyclization is fast and quantitative and provides a measurable optical response.     

Quantitative trace analysis of fullerenes in river sediment from Spain and soils from Saudi Arabia

A quantitative method based on ultrasound-assisted toluene extraction followed by liquid chromatography–electrospray ionization–tandem mass spectrometry for the analysis of C₆₀ and C₇₀ fullerenes, N-methylfulleropyrrolidine, [6, 6]-phenyl C₆₁ butyric acid methyl ester and [6, 6]-thienyl C₆₁ butyric acid methyl ester has been developed. The method was validated using fortified blank river sediments according to the criteria of Commission Decision 2002/657/EC. The method limits of detection ranged from 14 to 290 pg/g, making it suitable for its application in environmental analysis. The method has been applied to investigate fullerene content in 58 soil samples collected from different urban and industrial areas in Saudi Arabia and in river sediment from six different sites in the Llobregat River Basin. In addition, in the case of the Llobregat River, superficial water samples from the same sites of the sediments were collected and analysed using a previous method. In soils from Saudi Arabia, C₆₀-fullerene was the only compound that was detected and quantified in 19 % of samples. In the sediments of the Llobregat River, C₆₀-fullerene was also the only one detected (33 % of the samples), while in river water, C₇₀-fullerene was the most frequent compound, and it was quantified in 67 % of the samples. However, C₆₀-fullerene was present in two of the six samples, but at higher concentrations than C₇₀-fullerene, ranging from 0.9 to 7.8 ng/L.     

Diversity synthesis via C-H bond functionalization: concept-guided development of new C-arylation methods for imidazoles

Herein, we have formulated the concept of systematic derivatization of a structural motif via C-H bond functionalization. This concept may not only serve as a blueprint for new strategies in diversity synthesis but also provide systematic guidance for the identification of unsolved and important synthetic challenges. To illustrate this point, 2-phenylimidazole was selected as the core motif for this study, a choice inspired by numerous azole-based synthetics, including pharmaceuticals (compound SB 202190), and also fluorescent and chemiluminescent probes. We were able to show that systematic and comprehensive arylation of the 2-phenylimidazole core was feasible, and in the context of this study new arylation methods were developed. The direct 4-arylation of free 2-phenylimidazole was achieved with iodoarenes as the aryl donors in the presence of palladium catalyst (Pd/Ph(3)P) and magnesium oxide as the base. A complete switch from C-4 to C-2' arylation was accomplished using a ruthenium catalyst [CpRu(Ph(3)P)(2)Cl] and Cs(2)CO(3). The corresponding transformations for (N,2)-diphenylimidazole (C-5 and C-2' arylation) were accomplished via the palladium-based method [Pd(OAc)(2)/Ph(3)P/Cs(2)CO(3)] and a rhodium-catalyzed procedure [Rh(acac)(CO)(2)/Cs(2)CO(3)], respectively. All of the arylation methods described herein demonstrated broad synthetic scope, high efficiency, and exclusive selectivity. Furthermore, these new methods proved to be orthogonal to one another and applicable to sequential arylation schemes. With these methods in hand, arrays of arylated imidazoles may now be accessed in a direct manner from 2-phenylimidazole. This strategy stands in sharp contrast to a traditional approach, wherein a distinct and multistep synthesis would be required for each analogue.     

On Solution to an Optimal Shape Design Problem in 3-Dimensional Linear Magnetostatics

In this paper we present theoretical, computational, and practical aspects concerning 3-dimensional shape optimization governed by linear magnetostatics. The state solution is approximated by the finite element method using Nédélec elements on tetrahedra. Concerning optimization, the shape controls the interface between the air and the ferromagnetic parts while the whole domain is fixed. We prove the existence of an optimal shape. Then we state a finite element approximation to the optimization problem and prove the convergence of the approximated solutions. In the end, we solve the problem for the optimal shape of an electromagnet that arises in the research on magnetooptic effects and that was manufactured afterwards.     

An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles

An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe₃O₄@Au NPs) is presented. ADH was immobilized on Fe₃O₄@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO₂. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD⁺); working electrode: carbon paste with magnetically attached Fe₃O₄@Au NPs (0.012 mg ? cm^?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm² of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r²=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM^?1 ? cm^?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %.     

Photopolymerized silver-containing conducting polymer films. Part II. Physico-chemical characterization and mechanism of photopolymerization process

Physico-chemical and mechanical characterizations of nanophase silver-containing polypyrrole films prepared using a new photopolymerization process were performed. In general, the recorded physical, chemical, and mechanical data characteristic of these films was similar to corresponding literature data obtained from electropolymerized or chemically polymerized polypyrrole. However, photopolymerized polypyrrole films possessed an unusually high anion-to-monomer ratio of 0.8:1. Also, the photopolymerized material contained silver nanoparticles, having diameters of 2 μm or less, uniformally distributed throughout the polymer matrix. While the photopolymerization mechanism is complex, it is suggested that a pyrrole–silver cation complex is most likely the key component involved in the photopolymerization initiation step. Paper submitted for inclusion in the special issue of the Journal of Solid State Electrochemistry honoring the 85th birthday of Professor John O’M. Bockris.     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Synthesis of luminescent heterometallic bis-lanthanide complexes via selective, sequential metallation

A modular synthetic method for the differential incorporation of two lanthanide ions into a single molecular scaffold is reported; the mixed bimetallic Tb/Eu complex displays an interesting solvent polarity-dependent ratiometric luminescence.