Phase Space Tunneling in Multistate Scattering

We prove exponentially small estimates on the off-diagonal terms of the scattering matrix associated to two-state semiclassical Schrödinger Hamiltonians. Our method is based on phase space tunneling estimates and a splitting of the operator by means of Toeplitz-type phase space cutoff operators.     

A contraction of the Lucas polygon

The celebrated Gauss-Lucas theorem states that all the roots of the derivative of a complex non-constant polynomial lie in the convex hull of the roots of , called the Lucas polygon of . We improve the Gauss-Lucas theorem by proving that all the nontrivial roots of lie in a smaller convex polygon which is obtained by a strict contraction of the Lucas polygon of .

     

Perturbations of Roots under Linear Transformations of Polynomials

Let be the complex vector space of all polynomials of degree at most n. We give several characterizations of the linear operators for which there exists a constant C > 0 such that for all nonconstant there exist a root u of f and a root v of Tf with . We prove that such perturbations leave the degree unchanged and, for a suitable pairing of the roots of f and Tf, the roots are never displaced by more than a uniform constant independent on f. We show that such "good" operators T are exactly the invertible elements of the commutative algebra generated by the differentiation operator. We provide upper bounds in terms of T for the relevant constants.     

Synthesis of the isonicotinoylnicotinamide scaffolds of the naturally occurring isoniazid-NAD(P) adducts

The first syntheses of the 1-hydroxy-1-(pyridin-4-yl)-1,2-dihydro-3H-pyrrolo[3,4-c]pyridin-3-one heterocycle and the 3-aminocarbonyl-4-isonicotinoyl-1,4-dihydropyridine framework present in the isoniazid-NAD(P) adducts are described.     

4,5-Bis(diphenylthiophosphinoyl)-1,2,3-triazolate interaction with gold nanoparticles and flat surfaces to form self-assembled monolayers

The interaction of the 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazolate (SPTz⁻) with different gold surfaces was investigated (nanoparticles, an electrode, and flat sheets). Studies on binding affinity of this dithiophosphin-triazolate on a gold electrode were performed by cyclic voltammetry (CV). Voltammograms exhibit two reductive desorption and only one oxidative readsorption, indicating that once reabsorbed, the molecule achieves a unique conformation. The morphology and average size of modified gold nanoparticles were studied by transmission electron microscopy (TEM) (av. diameter of 5.9 ± 1.8 nm). Further characterization was made by UV-visible (UV-vis) spectroscopy showing surface plasmon resonance (SPR) at about 580 nm. The bonding configurations of SPTz⁻ on gold have also been investigated by comparing the FT-IR and FT-Raman spectra. The ³¹P{¹H} NMR spectrum of capped nanoparticles exhibited two sharp signals at 30.3 and 29.6 ppm and a very broad signal at 72.7 ppm. X-ray photoelectron spectroscopy (XPS) showed SPTz⁻ can accomplish a strong interaction with gold nanoparticles through bonds involving a sulfur atom and a nitrogen from the triazole ring with a free terminal PS group, forming self-assembled monolayers (SAM). This may allow subsequent functionalization through free S/N atoms of the formed SAMs. The SPTz⁻ packing led to a reduction in packing density that permits large spaces between adsorbed headgroups and the inclusion of carbon and oxygen impurities from small molecules; nevertheless, oxidized sulfur or nitrogen species were not detected, indicating the chemical stability of the obtained SAMs.     

Validation of HPLC‐UV method for determination of minor glycosides contained in Stevia rebaudiana Bertoni leaves

Leaves of Stevia rebaudiana contain glycosides with sweetness and biological activity. However besides the major glycosides, there are other glycosides within extracts that may contribute to its activity, and therefore it is important to quantify them. In this work, an isocratic HPLC method was validated for determination of dulcoside A, steviolbioside, rebaudioside C and rebaudioside B. An HPLC method was performed using a C₁₈ column (250 × 4.6 mm, particle size 5 µm) and a UV detector set at 210 nm. The mobile phase consisted of a 32:68 (v/v) mixture of acetonitrile and sodium phosphate buffer (10 mmol/L, pH 2.6), set to a flow rate of 1.0 mL/min. The calculated parameters were: sensitivity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy and precision. The calibration curves were linear over the working range 25–150 µg/mL, with coefficient of correlation of ≥0.99 and coefficient of determination of ≥0.98. The LOD was 5.68–8.81 µg/mL, while the LOQ was 17.21–26.69 µg/mL. The percentage recoveries of fortified samples were 100 ± 10% and precision, relative standard deviation, was <10%. The method validation showed accuracy, linearity and precision; therefore this method can be applied for quantitative analysis of minor steviol glycosides in S. rebaudiana leaves. Copyright © 2014 John Wiley & Sons, Ltd.     

Xestosaprol D and E from the Indonesian marine sponge Xestospongia sp.

Chemical investigation of an extract of the marine sponge Xestospongia yielded a suite of pentacyclic compounds, including two new xestosaprol derivatives. Xestosaprol D (1) and E (2) are regioisomers, whose structures were defined through analysis of spectroscopic data.     

Serjanic Acid Glycosides from Chenopodium hybridum L. with Good Cytotoxicity and Selectivity Profile against Several Panels of Human Cancer Cell Lines

Two triterpene saponins, including a novel serjanic acid derivative, were isolated from Chenopodium hybridum L. (Amaranthaceae) aerial parts. Their structures were elucidated by a combination of spectroscopic methods (MS, 1D and 2D NMR). Both compounds were evaluated for cytotoxicity and selectivity on skin, prostate, gastrointestinal, thyroid and lung cancer cells. Their effect was dose and time-dependent with varied potency, the highest against prostate PC3 and melanoma WM793, where IC₅₀ was lower than the reference drug doxorubicin. Structure–activity relationship is briefly discussed.     

Larvicidal, antimycobacterial and antifungal compounds from the bark of the Peruvian plant Swartzia polyphylla DC

The 95% ethanol extract of the bark of Swartzia polyphylla DC (Fabaceae) possesses important larvicidal, antimycobacterial and antifungal activity in vitro. Bioassay-guided studies performed on the crude ethanol extract afforded T-cadinol as the larvicidal and anti-Mycobacterium tuberculosis principle, while the antifungal activity of the extract is due to the presence of the flavonoids biochanin A and dihydrobiochanin A.