Determination of flavonoids in citrus juices by micro-HPLC-ESI/MS

Flavonoids are a large class of naturally occurring aromatic secondary plant metabolites. They constitute one of the most characteristic classes found in nature and more than 4000 flavonoids have been identified and divided into several subclasses. Flavonoids have several effects on human health, mainly related to their antioxidant activity. As a result of the increased interest in the biologically active compounds in food, many research studies have investigated the detection and quantification of antioxidants. Citrus plants are of great interest since they accumulate large amounts of flavonoids and fruit and juices of these species are consumed in large quantities. Despite the extensive research performed on Citrus flavonoids, many compounds still remain unidentified. In this work, flavonoids of five citrus juices: lemon, grapefruit, bergamot, orange, and mandarin were analyzed by microHPLC coupled on-line with an MS detector equipped with an ESI source operating in negative mode. The use of microcolumn HPLC greatly enhanced detection performance. In total, 20 flavonoids of two different subclasses (flavanone and flavone glycosides) were identified with the help of retention data and MS spectral information.     

The synthesis and characterization of aliphatic sulfonic acid cation exchangers for HPLC

Summary Two oxidation procedures for the synthesis of silicabased aliphatic sulfonic acid cation-exchangers for HPLC are described. Several reaction conditions for oxidizing a terminal-bonded thiol with organic peroxides are provided along with their yields, capacities, reproducibility, and chromatographic behavior. Also, three methods for determining exchange capacity are discussed, and their relationship to the capacity factors of charged solutes is compared. The maximum capacity determined by the titration of the bonded silica was 0.34 meq/gram. The general problems of synthesizing cation-exchangers, measuring their efficiencies and exchange capacities, and evaluating their overall performances are outlined.     

Quantum heat switch with multiple qubits

We further elaborate on the device proposed by Karimi et al. [15], in which coupled superconducting qubits can play the role of a quantum heat switch. In the present paper we analyze the performances of the switch if the number of qubits increases considering in details the cases of three and four qubits. To this aim we study the effect of the number of qubits on the transmitted power between baths. As the number of qubits increases, the transmitted power between baths increases as well.     

Representing scientific activity: Affordances and constraints of central design and enactment features of a model‐based inquiry unit

This research explores how explaining an anchoring phenomena and engaging students in investigations, as central designs of a model‐based inquiry (MBI) unit, afforded or constrained the representation of scientific activity in the science classroom. This research is considered timely as recent standards documents and scholars in the field have highlighted the significance of identifying what features of scientific activity are important and how these can be represented for students in classrooms. Through taking advantage of qualitative research methods to closely examine the enactment of an MBI unit, both affordances and constraints were identified for each design. More specifically, explaining an anchoring phenomenon provided a context for more authentically framing the work of students, while investigations afforded students insight into the role these play in the refinement of models. Further, the teacher's attempts to support student reasoning and, at times, reasoning for students when they were found struggling were the most salient constraints identified connected to explaining an anchoring phenomenon and engaging students in investigations.     

Quasifission and difference in formation of evaporation residues in the O + W and F + Ta reactions

The role of the entrance channel has been studied to ascertain a cause of the observed difference between the evaporation residue cross sections normalized to the fusion cross sections in the ¹⁹F + ¹⁸¹Ta and ¹⁶O + ¹⁸⁴W reactions at high excitation energies. The theoretical analysis performed in the framework of the dinuclear system and advanced statistical models showed that the more intense yield of evaporation residues in the ¹⁶O + ¹⁸⁴W reaction in comparison with that in the ¹⁹F + ¹⁸¹Ta reaction was explained by the large capture and fusion cross sections in the former reaction, which is in agreement with the experimental data. The observed decrease in the evaporation residue cross section normalized to the fusion cross section in the ¹⁹F + ¹⁸¹Ta reaction, in comparison with one in the ¹⁶O + ¹⁸⁴W reaction at large excitation energies, is caused by the unintentional inclusion of the quasifission and fast fission contributions in the fissionlike fragment yields that were used in reconstructing the experimental fusion cross section in the normalizing procedure. The range of the angular momentum distribution for both systems was similar, but the partial cross sections are different, showing the presence of a difference in the hindrance to complete fusion in both reactions.     

Harnack inequality and regularity for degenerate quasilinear elliptic equations

We prove Harnack inequality and local regularity results for weak solutions of a quasilinear degenerate equation in divergence form under natural growth conditions. The degeneracy is given by a suitable power of a strong A _∞ weight. Regularity results are achieved under minimal assumptions on the coefficients and, as an application, we prove C ^1,α local estimates for solutions of a degenerate equation in non divergence form.     

Synthesis of sugar arrays in microtiter plate

1,3-Dipolar cycloadditions between azides and alkynes were exploited to attach oligosaccharides to a C(14) hydrocarbon chain that noncovalently binds to the microtiter well surface. Synthesis of sugar arrays was performed on a micromolar scale in situ in the microtiter plate. As a model study, the beta-galactosyllipid 5 was displayed on a 4-micromol scale. Formation of product was confirmed via ESI-MS, and the yield was determined via chemical and biological assays. Several complex carbohydrates (6-16) were also displayed in microtiter plates and successfully screened with various lectins. Moreover, sialyl Lewis x (17) was synthesized via the enzymatic fucosylation of a precursor displayed in the plate. Studies on inhibition of this biotransformation have been carried out, and the IC(50) value found for the known inhibitor 20 was consistent with previous studies in solution.     

Pd-catalyzed alkyl to aryl migration and cyclization: an efficient synthesis of fused polycycles via multiple C-H activation

A novel palladium migration methodology for the synthesis of complex fused polycycles has been developed. This process involves 1,4-palladium alkyl to aryl migrations via through-space C-H activation, followed by intramolecular arylation or an intermolecular Heck reaction providing a very efficient way to synthesize fused ring systems.     

Flux noise near the Berezinski\overset{\lower0.5em\hbox{-Kosterlitz-Thouless transition

The flux noise in Josephson junction arrays is studied in the critical regime above the Berezinskii-Kosterlitz-Thouless transition. In proximity-coupled arrays a local Ohmic damping for the phases is relevant, giving rise to anomalous vortex diffusion and a dynamic scaling of the flux noise in the critical region. The flux noise exhibits a crossover from white to 1/f noise at a frequency ω_ξ∝ξ^?z with a dynamic exponent z=2.