Determination of low‐molecular‐weight amines and ammonium in saline waters by ion chromatography after their extraction by steam distillation

A new method was developed for the determination of ammonium ion, monomethylamine and monoethylamine in saline waters by ion chromatography. Steam distillation was used to eliminate matrix interferences. Variables such as distillation time, concentration of sodium hydroxide solution and analyte mass were optimized by using a full two‐level factorial (2³) design. The influence of steam distillation on the analytical curves prepared in different matrices was also investigated. Limits of detection of 0.03, 0.05 and 0.05 mg/L were obtained for ammoniumion, monomethylamine and monoethylamine, respectively. Saline water samples from the Brazilian oil industry, containing sodium and potassium concentrations between 2.0–5.2% w/v and 96–928 mg/L, respectively, were analyzed. Satisfactory recoveries (90–105%) of the analytes were obtained for all spiked samples, and the precision was ≤ 7% (n = 3). The proposed method is adequate for analyzing saline waters containing sodium to ammoniumion, monomethylamine and monoethylamine concentration ratios up to 28 000:1 and potassium to ammonium, monomethylamine and monoethylamine concentration ratios up to 12 000:1.     

Synthesis and structural characterization of novel pyranoluteolinidin dyes

The synthesis and structural characterization by LC–MS and NMR of novel pyranoluteolinidin derivatives are reported. The compounds result from the reactions between luteolinidin and three different carboxylic acids in wine model-like solutions. The three pigments possess different substituents attached to the D ring (methyl, catechol and dimethylaminophenyl groups) and the same catechol group in the B ring, yielding a wide spectrum of colors from yellow to pink-purple.     

The Influence of Network Properties on the Synchronization of Kuramoto Oscillators Quantified by a Bayesian Regression Analysis

The influence of the network structure on the emergence of collective dynamical behavior is an important topic of research that has not been fully understood yet. In the current work, it is shown how statistical regression analysis can be considered to address this issue. The regression model proposed suggests that the average shortest path length is the network property most influencing the degree of synchronization of Kuramoto oscillators. Moreover, this model revealed to be very accurate, being the predicted and measured values of synchronization highly correlated. Therefore, the regression modeling allows predicting the values of the dynamic variable in terms of network structure.     

Ward-Takahashi identity for the electromagnetic current of two-particle systems on the light front

The problem of nonconservation of the electromagnetic current for two-boson systems on the light front obtained by truncation of the quasi-potential expansion is studied. We found that current conservation can be restored by a subtle choice of the truncation of the expansion of the current operator, while the naive truncation of the expansion of both current and effective interaction violates covariance and current conservation. The framework allows to treat at the same level the current operator for bound and scattering states. The generalization to two-fermion systems is briefly discussed.     

Syntheses,crystal structures and electron paramagnetic resonance studies of Co- and Mn-coordination polymers with the twisted ligand di(4-pyridyl)disulfide in double bridge fashion

Four coordination polymers, {[Co₂(4-DPSS)₄(DMF)₄](ClO₄)₄}_n (1), {[Mn₂(4-DPSS)₄(DMF)₄](ClO₄)₄}_n (2), {[Co(4-DPSS)₂(H₂O)(NO₃)]NO₃·3H₂O}_n (3) and [Co(4-DPSS)₂(NCS)₂]_n (4) have been synthesized to study the reactivity of cobalt(II) and manganese(II) salts (perchlorate, thiocyanate and nitrate) with the flexible ligand di(4-pyridyl)disulfide (4-DPSS). These compounds have repeated rhomboidal structures in which the di(4-pyridyl)disulfide ligands coordinate the metal centers in a double bridged fashion. Each double chain and the metallocycle cavities are chiral and contain either the M- or the P-enantiomeric forms of 4-DPSS and are independent on recrystallization solvents or the metallic precursors. The crystal packing of these coordination polymers reveals that, in all cases, weak interactions such as classical and non-classical hydrogen bonds, as well as S?S interactions, connect the polymeric chains to increase the dimensionality of the network. Low temperature electron paramagnetic resonance (EPR) measurements on powdered samples show that the transition-metal ions, Co (II) and Mn (II) ions, are in the high spin states S = 3/2 and 5/2, respectively, and adopt octahedral geometry in case of compounds 1, 2 and 3, and rhombic environment in case of 4.     

Vanillin (1) As Starting Material for the Synthesis of Isomeric Phthalides

Phthalides have bcen employed as useful intcriucdiates in tic sqrnthcsis of my condcnscld aromatic carbocyclic and heterocyclic compounds, including several natural products In this paper we report two alternative synthetic pathways for the preparation of phthalides as shown for the synthesis of the isomeric pairs of compounds 5a-d and 7a-d.     

Application of Walphos Ligand in the Pd(0)-Catalyzed Asymmetric Allylic Alkylation Reaction

One relatively unexploited commercial ligand, Walphos 1, was tested in the Pd(0)-catalyzed asymmetric allylic alkylation using rac-1,3-diphenyl propenyl acetate and rac-1-acetoxycyclohexene as substrates, methyl malonate as nucleophile, and a variety of Pd precatalysts under standard conditions. The conversions and enantioselectivities were generally good, with the greatest substrate conversion of 99% and a greatest ee of 70%. With the latter cyclic substrate, an enantioselectivity of 98% was obtained, but the conversions were all poor (15–33%).     

Determination of Glycerol in Biodiesel Using a Nickel(II) Oxyhydroxide Chemically Modified Electrode by Cyclic Voltammetry

A glassy carbon electrode chemically modified with nickel oxyhydroxide from a nickel hexacyanoferrate (NiHCF) film was used to determine glycerol in biodiesel by cyclic voltammetry. The modified electrode exhibited a linear response to glycerol concentration in the range from 0.05 to 0.35 mmol L^?1, and a detection limit of 0.030 mmol L^?1. The glycerol concentration found in the biodiesel sample was 0.156 mmol L^?1. The method developed in this study showed a recovery of (100.3±5.0)%.     

Mass Spectrometry and X-ray Diffraction Analysis of Two Crystal Types of Dioclea virgata Lectin: An Antinociceptive Protein Candidate to Structure/Function Analysis

The lectin from seeds of Dioclea virgata (DvirL) was purified in a single step affinity chromatography, sequenced by tandem mass spectrometry and submitted to crystallization and biological experiments. DvirL has a molecular mass of 25,412?±?2 Da and the chains β and γ has 12,817 Da?±?2 and 12,612 Da?±?2, respectively. Primary sequence determination was assigned by tandem mass spectrometry and revealed a protein with 237 amino acids and 87% of identify with ConA. The protein crystals were obtained native and complexed with X-Man using vapor-diffusion method at a constant temperature of 293 K. A complete X-ray dataset was collected at 1.8 ? resolution. DvirL crystals were found to be orthorhombic, belonging to the space group I222, with a unit cell parameters a?=?647.5 ?, b?=?86.6 ?, c?=?90.2 ?. Molecular replacement search found a solution with a correlation coefficient of 77.1% and an R(factor) of 44.6%. The present study also demonstrated that D. virgata lectin presents edematogenic and antinociceptive activities in rodents electing this protein as a candidate to structure/function analysis.