Tannins analysis from different medicinal plants extracts using MALDI-TOF and MEKC

The matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF) and micellar electrokinetic chromatography (MEKC) methods were used to identify and quantify five tannins, (+)-catechin, (?)-epigallocatechin, (?)-epigallocatechin gallate, (?)-epicatechin gallate and (?)-epicatechin, from aqueous, ethanolic and acetonic extracts of Calendula officinalis, Hy-pericum, perforatum, Galium verum and Origanum vulgare. The MALDI-TOF technique was used for screening tannins monomers and oligomers in plant extracts. The sandwich method and matrix 2,5-dihydroxybenzoic acid with a concentration of 10 mg mL^?1 in acetonitrile/ultrapure water/trifluoroacetic acid (20: 80: 0.1, vol.) were used. The electrophoretic method developed for the separation and quantification of 5 catechins in 15 min exhibited good efficiency and precision, low limits of detection (0.0032–0.0153 μ.g mL-¹) and quantification (0.0096–0.0466 μ.g mL^?1). The correlation coefficients (R²) exceeded 0.9986 and the recovery values ranged between 94.25 % and 102.50 %. The present work provides new information on some of the less studied compounds present in plants frequently used in traditional medicine.     

Tunnel coupled dangling bond structures on hydrogen terminated silicon surfaces

We study both experimentally and theoretically the electronic behavior of dangling bonds (DBs) at a hydrogen terminated Si(100)-2×1 surface. Dangling bonds behave as quantum dots and, depending on their separation, can be tunnel coupled with each other or completely isolated. On n-type highly doped silicon, the latter have a net charge of -1e, while coupled DBs exhibit altered but predictable filling behavior derived from an interplay between interdot tunneling and Coulomb repulsion. We found good correlation between many scanning tunneling micrographs of dangling bond structures and our theoretical results of a corresponding extended Hubbard model. We also demonstrated chemical methods to prevent tunnel coupling and isolate charge on a single dangling bond.     

Synthesis of nanocrystalline nickel ferrite by thermal decomposition of organic precursors

Nickel ferrite powders were synthesized by thermal decomposition of the precursors obtained in the redox reaction between the mixture of Ni(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O with polyalcohol: 1,4-butanediol, polyvinyl alcohol and also with their mixture. During this reaction the primary C?COH groups were oxidized at ?CCOOH, while secondary C?COH groups at C=O groups. The carboxylic groups formed coordinate to the present Ni(II) and Fe(III) cations leading to carboxylate type compounds, further used as precursors for NiFe₂O₄. These precursors were characterized by thermal analysis and FT-IR spectrometry. All precursors thermally decomposed up to 350?°C leading to nickel ferrite weakly crystallized. By annealing at higher temperatures, nanocrystalline nickel ferrite powders were obtained, as resulted from XRD. SEM images have evidenced the formation of nanoparticulate powders; these powders present magnetic properties characteristic to the oxidic system formed by magnetic nanoparticles.     

Numerical schemes for multivalued backward stochastic differential systems

We define approximation schemes for generalized backward stochastic differential systems, considered in the Markovian framework. More precisely, we propose a mixed approximation scheme for the following backward stochastic variational inequality:

Organic nanostructures on hydrogen-terminated silicon report on electric field modulation of dangling bond charge state

We pursue dynamic charge and occupancy modulation of silicon dangling bond sites on H-Si(100)-2 × 1 with a biased scanning tunneling microscope tip and demonstrate that the reactivity and mechanism of product formation of cyclobutylmethylketone (CBMK) on the surface at the active sites may be thus spatially regulated. Reactivity is observed to be dependent on the polarity between tip and surface while the area over which reactivity modulation is established scales according to the dopant concentration in the sample. We account for these observations with examination of the competition kinetics applicable to the CBMK/H-Si reaction and determine how said kinetics are affected by the charge state of DB sites associated with reaction initiation and propagation. Our experiments demonstrate a new paradigm in lithographic control of a self-assembly process on H-Si and reveal a variant to the well-known radical mediated chain reaction chemistry applicable to the H-Si surface where self-assembly is initiated with dative bond formation between the molecule and a DB site.     

Nonuniform scaling applied to surface energies of transition metals

We construct a generalized gradient approximation of the exchange-correlation energy that satisfies the nonuniform scaling in one dimension and is accurate in the whole quasi-two-dimensional (Q2D) regime. Using spatial and energetic analyses of metal (111) surfaces, we show that the Q2D behavior is important at the surface of most transition metals, and that the here proposed Q2D-generalized gradient approximation functional predicts for these metals accurate surface energies as well as bulk properties.     

Measures not charging polar sets and Schrödinger equations in L p

We study the SchrSdinger equation （q -￡）u ＋μu = f, where ￡ is the generator of a Borel right process and μ is a signed measure on the state space. We prove the existence and uniqueness results in Lp, 1 ≤p 〈∞ . Since we consider measures μcharging no polar set, we have to use new tools： the Revuz formula with fine versions and the appropriate Revuz correspondence, the perturbation （subordination） operators （in the sense of G Mokobodzki） induced by the regular strongly supermedian kernels. We extend the results on the SchrSdinger equation to the case of a strongly continuous sub-Markovian resolvent of contractions on Lp. If the measure μ is positive then the perturbed process solves the martingale problem for ￡- μ and its transition semigroup is given by the Feynman-Kac formula associated with the left continuous additive functional having μ as Revuz measure.     

Anticanonical models of ruled surfaces

Summary One investigates the properties of the so-called anticanonical model of a ruled non-rational surfaceX with the anticanonical dimension 2 (see theorem 2 below). In such a way one gets a ?non-rational? analogue of a result of F. Sakai (see [12], and also theorem 1 below). As an application of these two theorems one characterizes the normal projective surfacesY overC with the property that there is a positive integerr such that—rK _Y is an ample Cartier divisor, whereK _y is a canonical (Weil) divisor ofY (see corollary 8 below).

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Riassunto Si studiano i modelli anticanonici delle superficie rigate non-razionali di dimensione anticanonica 2 (teorema 2). Si trova un risultato simile a quello di F. Sakai (teorema 1). Come applicazione si dà una caratterizzazione delle superficie proiettive normaliY sul campoC tali che un multiplo—rK _Y, conr>0, è un divisore di Cartier ampio, doveK _y è un divisore (di Weil) canonico (Corollario 8).

     

Kinetic method for acetylsalicylic acid determination based on its inhibitory effect upon the catalytic decomposition of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The catalytic reaction of catalase was investigated, by means of a Clark oxygen sensor, in the presence of various concentrations of acetylsalicylic acid. Michaelis-Menten kinetic parameters were determined from Lineweaver-Burk plots, obtained in the absence and in the presence of the inhibitor. The inhibition pattern, suggested by the Lineweave-Burk plots, corresponds to a fully mixed inhibition mechanism. A kinetic method, based on the indicator reaction: , was developed for the quantitative determination of acetylsalicylic acid. Calibration graphs of the reciprocal value of first-order rate constant versus acetylsalicylic concentration covered the concentration range (2.99–19.98)×10^–4 mol/L, while the detection limit was 4.12×10^–4 mol/L acetylsalicylic acid with a standard deviation of 2.1×10^–5 mol/L.     

Consequences of the nanoporosity of cellulosic fibers on their streaming potential and their interactions with cationic polyelectrolytes

Electrokinetic tests, based on the streaming potential method, were used to elucidate interactions between cationic polyelectrolytes and cellulosic fibers and to reveal aspects of fibers’ nanoporosity. The fibrillated and nanoporous nature of bleached kraft fibers gave rise to time-dependent changes in streaming potential, following treatment of the wetted fibers with poly-diallyldimethylammonium chloride. Electrokinetic test results were consistent with an expected longer time required for higher-mass polyelectrolytes to diffuse into pore spaces, compared to lower-mass polyelectrolytes. Further evidence of the relative inability of polyelectrolyte molecules to diffuse into the pores of cellulose was obtained by switching back and forth between high and low ionic strength conditions during repeated measurement of streaming potential, after the fibers had been treated with a moderate amount of cationic polymer. By changing the concentration of sodium sulfate it was possible to switch the sign of streaming potential repeatedly from positive to negative and back again. Such results imply that a continuous path for liquid flow exists either in a fibrillar layer or within the cell walls. The same concepts also helped to explain the dosages of high-charge cationic polymer needed to achieve maximum dewatering rates, as well as the results of retention experiments using positively and negatively charged microcrystalline cellulose particles.