CpRu-catalyzed O-H insertion and condensation reactions of α-diazocarbonyl compounds

[CpRu(CH(3)CN)(3)][PF(6)] and diimine ligands catalyze together the decomposition of α-diazocarbonyl compounds leading to O-H insertion and condensation reactions. In comparison with Rh(II) and Cu(I) complexes, the CpRu catalysts produce rapid and often more selective reactions. Promising enantioselectivities are obtained in dioxole syntheses.     

Onset of hydrogen bonded collective network of water in 1,4-dioxane

We have studied the evolution of water hydrogen bonded collective network dynamics in mixtures of 1,4-dioxane (Dx) as the mole fraction of water (X(w)) increases from 0.005 to 0.54. The inter- and intramolecular vibrations of water have been observed using terahertz time domain spectroscopy (THz-TDS) in the frequency range 0.4-1.4 THz (13-47 cm(-1)) and Fourier transform infrared (FTIR) spectroscopy in the far-infrared (30-650 cm(-1)) and mid-infrared (3000-3700 cm(-1)) regions. These results have been correlated with the reactivity of water in these mixtures as determined by kinetic studies of the solvolysis reaction of benzoyl chloride (BzCl). Our studies show an onset of intermolecular hydrogen bonded water network dynamics beyond X(w) ≥ 0.1. At the same concentration, we observe a rapid increase of the rate constant of solvolysis of BzCl in water-Dx mixtures. Our results establish a correlation between the onset of collective hydrogen bonded network with the solvation dynamics and the activity of clustered water.     

Partition and composition matrices

This paper introduces two matrix analogues for set partitions. A composition matrix on a finite set X is an upper triangular matrix whose entries partition X, and for which there are no rows or columns containing only empty sets. A partition matrix is a composition matrix in which an order is placed on where entries may appear relative to one-another.We show that partition matrices are in one-to-one correspondence with inversion tables. Non-decreasing inversion tables are shown to correspond to partition matrices with a row ordering relation. Partition matrices which are s-diagonal are classified in terms of inversion tables. Bidiagonal partition matrices are enumerated using the transfer-matrix method and are equinumerous with permutations which are sortable by two pop-stacks in parallel.We show that composition matrices on X are in one-to-one correspondence with (2+2)-free posets on X. Also, composition matrices whose rows satisfy a column-ordering relation are shown to be in one-to-one correspondence with parking functions. Finally, we show that pairs of ascent sequences and permutations are in one-to-one correspondence with (2+2)-free posets whose elements are the cycles of a permutation, and use this relation to give an expression for the number of (2+2)-free posets on {1,…,n}.     

The usefulness of Bayesian optimal designs for discrete choice experiments

Recently, the use of Bayesian optimal designs for discrete choice experiments, also called stated choice experiments or conjoint choice experiments, has gained much attention, stimulating the development of Bayesian choice design algorithms. Characteristic for the Bayesian design strategy is that it incorporates the available information about people's preferences for various product attributes in the choice design. This is in contrast with the linear design methodology, which is also used in discrete choice design and which depends for any claims of optimality on the unrealistic assumption that people have no preference for any of the attribute levels. Although linear design principles have often been used to construct discrete choice experiments, we show using an extensive case study that the resulting utility‐neutral optimal designs are not competitive with Bayesian optimal designs for estimation purposes. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of steviol and its glycosides in Stevia rebaudiana leaves and commercial sweetener by ultra-high-performance liquid chromatography-mass spectrometry

Stevia rebaudiana leaves contain non-cariogenic and non-caloric sweeteners (steviol-glycosides) whose consumption could exert beneficial effects on human health. Steviol-glycosides are considered safe; nonetheless, studies on animals highlighted adverse effects attributed to the aglycone steviol. The aim of the present study was to develop and validate two different ultra-high-performance liquid chromatography methods with electrospray ionization mass spectrometry (UHPLC-MS) to evaluate steviol-glycosides or steviol in Stevia leaves and commercial sweetener (Truvia^®). Steviol-glycosides identity was preliminarily established by UV spectra comparison, molecular ion and product ions evaluation, while routine analyses were carried out in single ion reaction (SIR) monitoring their negative chloride adducts. Samples were sequentially extracted by methanol, cleaned-up by SPE cartridge and the analytes separated by UHPLC HSS C₁₈ column (150 mm × 2.1 mm I.D., 1.8 μm). The use of CH₂Cl₂ added to the mobile phase as source of Cl⁻ enhance sensitivity. The LLOD for stevioside, rebaudioside A, steviolbioside and steviol was 15, 50, 10 and 1 ng ml⁻¹, respectively. Assay validation demonstrated good performances in terms of accuracy (89–103%), precision (<4.3%), repeatability (<5.7%) and linearity (40–180 mg/g). Stevioside (5.8 ± 1.3%), rebaudioside A (1.8 ± 1.2%) and rebaudioside C (1.3 ± 1.4%) were the most abundant steviol-glycosides found in samples of Stevia (n = 10) from southern Italy. Rebaudioside A was the main steviol-glycosides found in Truvia^® (0.84 ± 0.03%). The amounts of steviol-glycosides obtained by the UHPLC-MS method matched those given by the traditional LC-NH₂-UV method. Steviol was found in all the leaves extract (2.7–13.2 mg kg⁻¹) but was not detected in Truvia^® (<1 μg kg⁻¹). The proposed UHPLC-MS methods can be applied for the routine quality control of Stevia leaves and their commercial preparations.     

Luminescent, redox-active diphenothiazine dumbbells expanded by conjugated arenes and heteroarenes

Dumbbell-shaped diphenothiazines bridged by conjugatively linked (hetero)aromatic moieties were synthesized in a modular fashion by Suzuki-Miyaura coupling in good yields. The electronic structure was studied by DFT computations, determining the geometry optimized lowest energy conformers and scrutinizing the Kohn-Sham FMOs. The torsional deviation from coplanarity is predominantly influencing the electronic structure, i.e., by deviation from ideal overlap and maximal electron transmission. The reversible oxidation potentials assigned to the phenothiazinyl electrophores in most cases can thereby be qualitatively rationalized. All dumbbell-shaped diphenothiazines are strongly luminescent, which can be attributed to extended π-electron conjugation with considerable excited state electronic coupling as a consequence of large structural and electronic distributional changes upon photoexcitation.     

Removal of an olefin metathesis catalyst using 4-nitrophenyl acrylate based polymer supports

A polymer-supported 1,4-butanediolvinyl ether derivative was used for removal of an olefin metathesis catalyst (PCy₃)₂(Cl)₂Ru(3-phenyl-indenylid-1-ene) (M1, PCy₃ = tricyclohexylphosphine) from the reaction solution. Poly(styrene-co-4-nitrophenyl acrylate), cross-linked with either ethylene glycol dimethacrylate or divinylbenzene was prepared via suspension polymerisation and modified chemically to yield a supported acid chloride and subsequently a 1,4-butanediolvinyl ether derivative. A batch reaction of supported vinyl ether with M1 resulted in binding of the catalyst onto the polymer. A high accessibility of up to 43% of reactive sites in the polymer matrix could be achieved.     

Large-Volume Sample Stacking with Polarity Switching in CE for Determination of Natural Polyphenols in Plant Extracts

A simple on-column preconcentration method for capillary electrophoretic determination of eight polyphenolic compounds (carnosic acid, cinnamic acid, caffeic acid and rosmarinic acid, quercetin, apigenin, luteolin and rutin) was devised. The method was applied for the assay of polyphenols in methanolic extract of the medicinal plant Orthosiphon Stamineus Benth. The analysis was carried out in fused silica capillaries (I.D. 50 μm, effective length 50 cm, total length 60 cm) with UV detection at 200 nm. The background electrolyte was 50 mM sodium tetraborate of pH 9.0 (adjusted with phosphoric acid). Large volume sample stacking with polarity switching was used for sensitivity enhancement. With sample injection representing 50% of capillary volume and polarity switching at 1.6 min, an average 90-fold enhancement of absorbance signal of the analytes was achieved. The calibration curves were linear (r = 0.9956–0.9994) in the range 0.2 to 1.8 μg mL^?1 of an analyte. The repeatability of migration times and peak areas was characterized by RSD values 0.11–0.57 and 1.63–5.66%, respectively. The proposed method offers favourable limits of detection (9–16 ng mL^?1) that compare well with those of LC.     

Expedient Synthesis of C‐Aryl Carbohydrates by Consecutive Biocatalytic Benzoin and Aldol Reactions

The introduction of aromatic residues connected by a C?C bond into the non‐reducing end of carbohydrates is highly significant for the development of innovative structures with improved binding affinity and selectivity (e.g., C?aril‐sLex). In this work, an expedient asymmetric “de novo” synthetic route to new aryl carbohydrate derivatives based on two sequential stereoselectively biocatalytic carboligation reactions is presented. First, the benzoin reaction of aromatic aldehydes to dimethoxyacetaldehyde is conducted, catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I. Then, the α‐hydroxyketones formed are reduced by using NaBH₄ yielding the anti diol. After acetal hydrolysis, the aldol addition of dihydroxyacetone, hydroxyacetone, or glycolaldehyde catalyzed by the stereocomplementary D ‐fructose‐6‐phosphate aldolase and L ‐rhamnulose‐1‐phosphate aldolase is performed. Both aldolases accept unphosphorylated donor substrates, avoiding the need of handling the phosphate group that the dihydroxyacetone phosphate‐dependent aldolases require. In this way, 6‐C‐aryl‐L ‐sorbose, 6‐C‐aryl–L ‐fructose, 6‐C‐aryl–L ‐tagatose, and 5‐C‐aryl‐L ‐xylose derivatives are prepared by using this methodology.