How Accessible Is Atomic Charge Information from Infrared Intensities? A QTAIM/CCFDF Interpretation

Infrared fundamental intensities calculated by the quantum theory of atoms in molecules/charge-charge flux-dipole flux (QTAIM/CCFDF) method have been partitioned into charge, charge flux, and dipole flux contributions as well as their charge-charge flux, charge-dipole flux, and charge flux-dipole flux interaction contributions. The interaction contributions can be positive or negative and do not depend on molecular orientations in coordinate systems or normal coordinate phase definitions, as do CCFDF dipole moment derivative contributions. If interactions are positive, their corresponding dipole moment derivative contributions have the same polarity reinforcing the total intensity estimates whereas negative contributions indicate opposite polarities and lower CCFDF intensities. Intensity partitioning is carried out for the normal coordinates of acetylene, ethylene, ethane, all the chlorofluoromethanes, the X(2)CY (X = F, Cl; Y = O, S) molecules, the difluoro- and dichloroethylenes and BF(3). QTAIM/CCFDF calculated intensities with optimized quantum levels agree within 11.3 km mol(-1) of the experimental values. The CH stretching and in-plane bending vibrations are characterized by significant charge flux, dipole flux, and charge flux-dipole flux interaction contributions with the negative interaction tending to cancel the individual contributions resulting in vary small intensity values. CF stretching and bending vibrations have large charge, charge-charge flux, and charge-dipole flux contributions for which the two interaction contributions tend to cancel one another. The experimental CF stretching intensities can be estimated to within 31.7 km mol(-1) or 16.3% by a sum of these three contributions. However, the charge contribution alone is not successful at quantitatively estimating these CF intensities. Although the CCl stretching vibrations have significant charge-charge flux and charge-dipole flux contributions, like those of the CF stretches, both of these interaction contributions have opposite signs for these two types of vibrations.     

Locally oriented potential field for controlling multi-robots

In this paper, we present an extension of the boundary value problem path planner (BVP PP) to control multiple robots in a robot soccer scenario. This extension is called Locally Oriented Potential Field (LOPF) and computes a potential field from the numerical solution of a BVP using local relaxations in different patches of the solution space. This permits that a single solution of the BVP endows distinct robots with different behaviors in a team. We present the steps to implement LOPF as well as several results obtained in simulation.     

Synthesis of α,β- and β-Unsaturated Acids and Hydroxy Acids by Tandem Oxidation,Epoxidation, and Hydrolysis/Hydrogenation of Bioethanol Derivatives

We report a reaction platform for the synthesis of three different high-value specialty chemical building blocks starting from bio-ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde-containing stream active for the production of C₄ aldehydes via base-catalyzed aldol-condensation. Then, the resulting C₄ adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β-hydroxy acid (3-hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β-dihydroxy acid (2,3-dihydroxybutanoic acid). Crotonic acid, 3-hydroxybutanoic acid, and 2,3-dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl-co-unsaturated acids resins, pharmaceutics, and bio-degradable/ -compatible polymers, respectively.     

Influence of Cu and Ni on the morphology and composition of the rust layer of steels exposed to industrial environment

Four samples of steels with alloying elements were exposed to an industrial environment during 1,955 days, aiming to elucidate the effect of the alloying elements Cu and Ni on the resistance of weathering steels to corrosion processes. The samples were characterized with optical microscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), saturation magnetization measurements and with energy dispersive (EDS), infrared, Mössbauer and Raman spectroscopies. All the steels originated orange and dark corrosion layers; their thicknesses were determined from the SEM images. EDS data of such rust layers showed that the alloying element content decreases from the steel core towards the outer part of the rust layer. Moreover, in the dark rust layer some light-gray regions were identified in the W and Cu-alloy steel, where relatively higher Cr and Cu contents were found. XRD patterns, infrared, Raman and Mössbauer spectra (298, 110 and 4 K) indicated that the corrosion products are qualitatively the same, containing lepidocrocite (γFeOOH; hereinafter, it may be referred to as simply L), goethite (αFeOOH; G), feroxyhite (δ′FeOOH; F), hematite (αFe₂O₃; H) and magnetite (Fe₃O₄; M) in all samples; this composition does not depend upon the steel type, but their relative concentrations is related to the alloying element. Mössbauer data reveal the presence of (super)paramagnetic iron oxides in the corrosion products. Saturation magnetization measurements suggest that feroxyhite may be an occurring ferrimagnetic phase in the rust layer.     

Quasisymmetric distortion and rigidity of expanding endomorphisms of

In this paper we examine a result of D. Sullivan according to which two expanding endomorphisms of the circle are conjugate as soon as they are symmetrically conjugate. We develop general a priori estimates on the local distortion of quasisymmetric mappings and combine them with the classical naive distortion lemma to present a complete proof of Sullivan's result. A new proof is offered at the end that renders unnecessary the use of Markov partitions or the control of eigenvalues at periodic points.

     

Recent Strategies and Applications for l-Asparaginase Confinement

l-asparaginase (ASNase, EC 3.5.1.1) is an aminohydrolase enzyme with important uses in the therapeutic/pharmaceutical and food industries. Its main applications are as an anticancer drug, mostly for acute lymphoblastic leukaemia (ALL) treatment, and in acrylamide reduction when starch-rich foods are cooked at temperatures above 100 °C. Its use as a biosensor for asparagine in both industries has also been reported. However, there are certain challenges associated with ASNase applications. Depending on the ASNase source, the major challenges of its pharmaceutical application are the hypersensitivity reactions that it causes in ALL patients and its short half-life and fast plasma clearance in the blood system by native proteases. In addition, ASNase is generally unstable and it is a thermolabile enzyme, which also hinders its application in the food sector. These drawbacks have been overcome by the ASNase confinement in different (nano)materials through distinct techniques, such as physical adsorption, covalent attachment and entrapment. Overall, this review describes the most recent strategies reported for ASNase confinement in numerous (nano)materials, highlighting its improved properties, especially specificity, half-life enhancement and thermal and operational stability improvement, allowing its reuse, increased proteolysis resistance and immunogenicity elimination. The most recent applications of confined ASNase in nanomaterials are reviewed for the first time, simultaneously providing prospects in the described fields of application.     

Synthesis of indolizidines and pyrrolizidines through the [2 + 2]cycloaddition of five-membered endocyclic enecarbamates to alkyl ketenes. Unusual regioselectivity of Baeyer-Villiger ring expansions of alkyl aza-bicyclic cyclobutanones

The total syntheses of two indolizidine skeletons and of the necine base (+/-)-platynecine were accomplished in a concise manner with good overall yields starting from a common five-membered endocyclic enecarbamate. These syntheses feature a [2 + 2]cycloaddition of the five-membered endocyclic enecarbamate 5 to alkylketenes that proceeded in high yields and with high stereoselectivity to provide an endo alkyl cycloadduct as the major or only product. The minor exo alkyl cycloadducts, which can be observed in some [2 + 2]cycloadditions, seem to derive from the endo cycloadduct, the putative kinetic product, by epimerization. An unusual regioselectivity was observed for the Baeyer-Villiger oxidation of 7-alkyl-2-azabicyclic cyclobutanones. Endo-7-alkyl cycloadducts ring-expanded exclusively to a gamma-lactone in which oxygen is inserted into the C6-C7 bond in preference to the bridgehead C5-C6 bond. With the exo-7-alkyl cycloadduct the regioselectivity of the Baeyer-Villiger oxidation is drastically reduced, leading to mixtures of regioisomeric lactones in a ratio of approximately 1.5 to 1. It is hypothesized that the steric strain built into the Criegee cyclobutane intermediate is the regioselective controlling factor in these oxidations, overriding any stereoelectronic bias for ring expansion. A rationale for the mechanism of the [2 + 2]cycloaddition involving enecarbamates and ketenes is presented, which seems to involve the participation of an N-acyliminium-enolate intermediate.     

Formation of high concentrations of BrO(2) in acidic bromate solutions

A new procedure to produce the BrO(2) transient species allowed time-resolved UV-vis spectra that show a structured band (lambda(max) = 502 nm) in dichloromethane to be obtained. In water, because of the increase of the dielectric constant, the lambda(max) presents a blue shift to 474 nm and the species decomposes much faster. The time-resolved spectra show evidence for its equilibrium with a nonidentified colorless form. This route opens new possibilities to the study this species in solution.     

Mixtures with continuous diversity: general theory and application to polymer solutions

Received January 22, 2001 / Published online April 18, 2001     

Chemically‐reduced Graphene Oxide Sensor for Dipyrone Quantification in Pharmaceutical Samples Using Amperometric Detection

Dipyrone (metamizole sodium) is one of the most consumed drugs in the world. In this work a novel analytical method was developed for dipyrone sensing. This method involves the amperometric detection on a chemically‐reduced graphene‐oxide (CRGO)‐modified glassy carbon electrode. Raman spectroscopy and scanning electron microscopy revealed the presence of multilayer graphene layers that contributed to the electrocatalytic oxidation of dipyrone and increase in the electroactive area. Advantages of this sensor include elimination of previous separations, solvent extraction, or sample filtration, low detection limit (0.13 μmol L^?1) with a linear range from 48 to 246 μmol L^?1 and adequate recovery values (97–103 %). Applied to commercial pharmaceutical samples, this method showed results ranging from 451 to 541 mg of dipyrone per tablet, which agreed with the expected values. The results obtained by amperometry were compared statistically with the official method recommended by the Brazilian Pharmacopoeia (iodometric method), with no significant differences between them at 95 % confidence level. The proposed method is accurate for the monitoring of sodium dipyrone in pharmaceutical formulations, highlighting the lower reagent consumption and interferences in the analytical process.