The curious case of a sterically crowded Stenhouse salt

We report a peculiar Stenhouse salt. It does not evolve into cyclopentenones upon basification, due to the steric hindrance of its bulky stable carbene patterns. This allowed for the observation and characterization of the transient open-chain neutral derivative, which was isolated as its cyclized form. The latter features an unusually long reactive C–O bond (150 pm) and a rich electrochemistry, including oxidation into an air-persistent radical cation.

Bulky substituents of a Stenhouse salt prevent the usual formation of a cyclopentenone upon deprotonation. For the first time, a transient open-chain neutral derivative was observed; the cyclized form and an air-persistent radical were isolated.     

Organophosphorus chemistry 30 [1]. The behavior of 4-hydroxycoumarin toward methylenetriphenylphosphoranes (Wittig Reagents) and alkyl phosphites

4-Hydroxycoumarin (1) reacted with Wittig reagents (2) to give 4-benzoylmethylcoumarin(5A) or [3-(4-hydroxycoumarinyl)]carbonylmethyl-enetriphenylphosphorane (6) depending upon the nature of the phosphorus ylide used. Dialkyl phosphonates (3a,b) and trialkyl phosphites (4a,b) converted 1 into the respective O-alkyl ethers (11a,b). The ground-state structure of 1 is discussed in the light of experimental results. Compatible elementary and spectroscopic results were gained for the new products. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:427–431, 1998     

General approach for regioselective synthesis of fused phosphono substituted‐oxadiazines

A series of fused 1,3,4‐oxadiazines were regioselectively prepared in reasonable yields as major products from the reactions of the corresponding α‐carbonyl hydrazones with tetraethyl 1,3‐dithietane‐2,4‐diylidene‐bis(cyanomethylphosphonate) (1) . Side products were also observed wherein the dimeric products 8 or 17 and/or different types of N‐heterocycles such as pyrazole 24 or pyridazines 28 or 29 were isolated and identified. A comparative study on the chemistry of 1 toward α‐aminonitrile 30 is also described. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:196–204, 2000     

Asymptotic expansions of the binomial coefficients

A general formulae for the asymptotic expansion of not centered binomial coefficients are derived and some useful estimates of the binomial coefficients are presented. The sum of the binomial coefficients is also studied.     

On Some Integral and Tail Inequalities Motivated by Kesava Menon's Theorem

Kesava Menon's classical inequality is connected with the tails of Taylor's series. In this paper the original statements are improved, under the same or weaker conditions on functions involved.     

Sensitive routine liquid chromatography–tandem mass spectrometry method for serum estradiol and estrone without derivatization

The need for a routinely applicable assay to measure low estradiol levels in adult men, postmenopausal women, and young adolescents was recently discussed in an Endocrine Society position statement. Our aim was to develop a sensitive liquid chromatography–tandem mass spectrometry method for estradiol and estrone in human serum without the need for derivatization or extended extraction protocols. After protein precipitation of serum with a mixture of methanol/acetonitrile (85/15) (v/v) containing isotopic internal standards (17β-estradiol-16,16,17-d ₃ and estrone-2,3,4-¹³C), we quantified estradiol and estrone by two-dimensional liquid chromatography–tandem mass spectrometry with electrospray ionization in the negative mode monitoring 5?×?271.20→145.00 (17β-estradiol) and 269.20→145.00 (estrone). Sensitivity was increased by using fluoride and summation of 5 identical transitions for estradiol. Our method was analytically validated, compared against direct immunoassays using serum of 25 adult men, and clinically tested by measuring samples of 3 men at baseline and after chemical castration, 30 postmenopausal women and 15 patients receiving aromatase inhibitors. Total imprecision was below 20 % for the low quality controls. Limit of quantification was 1.3 ng/L (4.8 pmol/L) for estradiol and 1.2 ng/L (4.4 pmol/L) for estrone. Estradiol in Certified Reference Material BCR-576 was within specified uncertainty limits. No significant ion suppression or interference was observed. Our method showed modest correlation with direct immunoassay for estradiol (r ²?=?0.64) but no correlation for estrone (r ²?=?0.12). Patient sample results were within expected ranges. In conclusion, we developed a routinely applicable liquid chromatography–tandem mass spectrometry method for estradiol and estrone measurement which is sensitive enough for use in men, postmenopausal women, and young adolescents.

Invasive Plant Species Biomass—Evaluation of Functional Value

Invasive plant species (IAS), with their numerous negative ecological, health, and economic impacts, represent one of the greatest conservation challenges in the world. Reducing the negative impacts and potentially exploiting the biomass of these plant species can significantly contribute to sustainable management, protect biodiversity, and create a healthy environment. Therefore, the main objective of this study was to evaluate the nutritional potential, phytochemical status, and antioxidant capacity of nine alien invasive plant species: Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, Datura stramonium, Erigeron annuus, Galinsoga ciliata, Reynoutria japonica, Solidago gigantea, and Sorghum halepense. Multivariate statistical methods such as cluster and PCA were performed to determine possible connections and correlations among selected IAS depending on the phytochemical content. According to the obtained results, R. japonica was notable with the highest content of vitamin C (38.46 mg/100 g FW); while E. annuus (1365.92 mg GAE/100 g FW) showed the highest values of total polyphenolic compounds. A. retroflexus was characterized by the highest content of total chlorophylls (0.26 mg/g) and antioxidant capacity (2221.97 µmol TE/kg). Therefore, it can be concluded that the selected IAS represent nutrient-rich plant material with significant potential for the recovering of bioactive compounds.