High-pressure synthesis and structural behavior of sodium orthonitrate Na3NO4

Sodium orthonitrate (Na₃NO₄) is an unusual phase containing the first example of isolated tetrahedrally bonded NO₄³⁻ groups. This compound was obtained originally by heating together mixtures of Na₂O and NaNO₃ for periods extending up to >14 days in evacuated chambers. Considering the negative volume change between reactants and products, it was inferred that a high-pressure synthesis route might favor the formation of the Na₃NO₄ compound. We found that the recovered sample is likely to be a high-pressure polymorph, containing NO₄³⁻ groups as evidenced by Raman spectroscopy. The high-pressure behavior of Na₃NO₄ was studied using Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell above 60 GPa. We found no evidence for major structural transformations, even following laser heating experiments carried out at high pressure, although broadening of the Raman peaks could indicate the onset of disordering at higher pressure.     

Nongenetic reprogramming of a fungal highly reducing polyketide synthase

The biosynthesis of the fungal metabolite tenellin from Beauveria bassiana CBS110.25 was investigated in the presence of the epigenetic modifiers 5-azacytidine and suberoyl bis-hydroxamic acid and under conditions where individual genes from the tenellin biosynthetic gene cluster were silenced. Numerous new compounds were synthesized, indicating that the normal predominant biosynthesis of tenellin is just one outcome out of a diverse array of possible products. The structures of the products reveal key clues about the programming selectivities of the tenellin polyketide synthase.     

Thin-film oxygen sensors using a luminescent polynuclear gold(I) complex

Robust thin-film oxygen sensors were fabricated by encapsulating a lipophilic, polynuclear gold(I) complex, bis{m-(bis(diphenylphosphino)octadecylamine-P,P′)}dichlorodigold(I), in oxygen permeable polystyrene and ormosil matrices. Strong phosphorescence, which was quenched by gaseous and dissolved oxygen, was observed from both matrices. The polystyrene encapsulated dye exhibited downward-turning Stern–Volmer plots which were well fitted by a two-site model. The ormosil trapped complex showed linear Stern–Volmer plots for dissolved oxygen quenching but was downward turning for gaseous oxygen. No leaching was observed when the ormosil based sensors were immersed in flowing water over an 8 h period. Both films exhibited fully reversible response and recovery to changing oxygen concentration with rapid response times.     

Factors that affect quantification of diode array data in comprehensive two-dimensional liquid chromatography using chemometric data analysis

There has been a tremendous increase in research on comprehensive two dimensional LC (LC×LC); however, to date, the central analytical issue, quantification, has received only minimal attention. It is vital to the further development of LC×LC that a greater understanding of the specific factors affecting peak quantification in LC×LC be attained. This work focuses on the following factors: data complexity, retention time shifting, dynamic range issues, chromatographic and spectral peak overlap and difficulties related to background signal removal. The above mentioned factors that affect peak quantification are investigated using fourteen replicate analyses of a urine sample, representing the effects of such factors when analyzing samples in complex matrices. We demonstrate that quantification of LC×LC data is improved following implementation of chemometric techniques that minimized the deleterious effects on quantification due to chromatographically overlapped peaks, retention time shifting and background signal interference. The chemometrically resolved data shows a 2.5-fold increase in precision of quantification over the quantification of the raw data. It is also demonstrated that the method quantifies sixteen peaks that were not visually evident prior to chemometric analysis. The purpose of this paper is to determine the impact of these issues on the effectiveness of LC×LC as a technique for the quantitative analysis of complex samples.     

New ternary and quaternary barium nitride halides; synthesis and crystal chemistry

New ternary and quaternary nitride halides, Ba(2)N(X,X') (X = F, Cl, Br; X' = Br, I), have been synthesized from the high temperature reactions of barium subnitride with the respective barium halides under an inert atmosphere. The former include the first fully characterized barium nitride halides for X other than F, and the latter are the first examples of barium nitride mixed halides. The variation in structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques. The heavier ternary and quaternary nitride halides (X, X' = Cl, Br, I) crystallize in the hexagonal space group R3m, with the anti-α-NaFeO(2) structure. Ba(2)NF forms with both an anti-α-NaFeO(2) structure, in which N(3-) and F(-) are ordered and an anion-disordered simple rock salt structure. The hexagonal polymorph of Ba(2)NF is the only example to date of a nitride fluoride adopting this layered structure. Both the ternary and the quaternary compounds display very weak, temperature independent paramagnetism.     

Generalized covering designs and clique coverings

Inspired by the “generalized t‐designs” defined by Cameron [P. J. Cameron, Discrete Math 309 (2009), 4835–4842], we define a new class of combinatorial designs which simultaneously provide a generalization of both covering designs and covering arrays. We then obtain a number of bounds on the minimum sizes of these designs, and describe some methods of constructing them, which in some cases we prove are optimal. Many of our results are obtained from an interpretation of these designs in terms of clique coverings of graphs. © 2011 Wiley Periodicals, Inc. J Combin Designs 19:378‐406, 2011     

Nonuniform Sampling and Recovery of?Multidimensional Bandlimited Functions by?Gaussian Radial-Basis Functions

Let S⊂ℝ ^d be a bounded subset with positive Lebesgue measure. The Paley-Wiener space associated to S, PW _S , is defined to be the set of all square-integrable functions on ℝ ^d whose Fourier transforms vanish outside S. A sequence (x _j :j∈ℕ) in ℝ ^d is said to be a Riesz-basis sequence for L ₂(S) (equivalently, a complete interpolating sequence for PW _S ) if the sequence (e^-iáx_j,·?:j ? \mathbb N)(e^{-i\langle x_{j},\cdot \rangle }:j\in \mathbb {N}) of exponential functions forms a Riesz basis for L ₂(S). Let (x _j :j∈ℕ) be a Riesz-basis sequence for L ₂(S). Given λ>0 and f∈PW _S , there is a unique sequence (a _j ) in ℓ ₂ such that the function

Rapid spectrofluorimetric determination of plasma salicylate with edta and terbium

A rapid single-reagent spectrofluorimetric assay for salicylate in human blood plasma is reported. The method is based on ternary complex formation with terbium and EDTA in alkaline solution; it requires only 10 μl of plasma, and protein precipitation is not necessary. Within-assay relative standard deviations were better than 2.5%, and correlation with the Trinder method was excellent. The procedure is particularly suited for emergency use in cases of suspected aspirin poisoning.