Construction of C-N Atropisomers by Aminocatalytic Enantioselective Addition of Indole-2-carboxaldehydes to o-Quinone Derivatives

The first atroposelective aminocatalytic methodology for the construction of C−N atropisomers is presented. The synthesis of this class of axially chiral molecules typically encompasses substrates in which the C−N bond is pre-formed. In contrast, this work presents the direct coupling of indole-2-carboxaldehydes to ortho-quinones, to form the stereogenic C−N axis in an atroposelective way. Application of typical secondary amine catalysts furnished the desired product, however, in low yields and as a complex mixture arising from poor regiocontrol among the C₃- and N₁-sites of the indole core. A new aminocatalyst was designed and synthesized with increased outer-sphere steric bulk to address these challenges thereby providing good levels of regio- and enantioselectivity. A novel library of functionalized and enantioenriched C−N atropisomers was obtained and their synthetic utility was demonstrated by various transformations.     

Investigation of the bioenergy potential of microalgae Scenedesmus acuminatus by physicochemical characterization and kinetic analysis of pyrolysis

In this work, the bioenergy potential of green microalgae Scenedesmus acuminatus was evaluated through the psychochemical characteristics and kinetic study of pyrolysis, where the results indicate a good candidate for application in the thermochemical process due to its low moisture and ash content and high calorific value. Its thermal behavior under a heating rate of 10 °C min^?1 and inert atmosphere shows that decomposition occurs in two stages. Stage I (125–309 °C) involves the pyrolysis of carbohydrates and protein and stage II (309–501 °C) the pyrolysis of lipids. The Starink isoconversional method showed a better application for simulation curves, compared with methods of FWO and KAS. The average values of activated energy were 107.1 and 132.6 kJ mol^?1 for stages I and II, respectively, which indicates that pyrolysis occurs more easily in stage I than in stage II. The conversion rate curves show that the calculated kinetic parameters are satisfactory for the evaluation of the thermochemical systems.

     

Functional desymmetrization of 1,3-dioximes for the obtention of 1,2,3-hetero trisubstituted carbocycles

Carbocylic 1,3-dioximes react with acyl chlorides giving systems that may, upon heating, suffer [3,3]-sigmatropic rearrangements in high yields in only one of the oximes esters, yielding 1,3-dinitrogen-2-oxygen trisubstituted carbocycles. Use of more reactive electrophiles, such as p-toluenesulfonyl chloride and diethyl chlorophosphate, introduces the halogen at position 2, while cleaving the N-O bond of just one of the oxime functions.     

Fluctuation conductivity along the c-axis and parallel to the ab-planes in melt-textured YBa2Cu3O7−δ samples doped with Y211 phase

We report measurements of in-plane and out-of-plane fluctuation conductivity under low applied magnetic fields up to 500 Oe in two melt-textured YBa₂Cu₃O_7−δ (YBCO) samples. 3D-Gaussian and genuine critical 3D-XY-E fluctuation regimes were identified in the conductivity parallel to the ab plane. In addition, a regime beyond 3D-XY was observed in the immediate vicinity of the superconducting transition of the in-plane fluctuation conductivity. The 3D-XY-E scaling was also identified in the fluctuation conductivity along the c-axis in the sample with smaller content of the Y₂BaCuO₅ (Y211) phase. This result indicates that the superconducting state in YBCO has a three-dimensional character, in contradiction to some studies suggesting that critical phenomenology is fundamentally distinct in orientations parallel or perpendicular to the Cu-O₂ planes of the high-temperature superconductors. However, the results suggests the presence of a sub-dominant order-parameter component in YBCO that has an appreciable projection along the c-axis.     

Exploring the chemical profile of designer drugs by ESI(+) and PSI(+) mass spectrometry—An approach on the fragmentation mechanisms and chemometric analysis

The consumption of design drugs, frequently known as new psychoactive substances (NPS), has increased considerably worldwide, becoming a severe issue for the responsible governmental agencies. These illicit substances can be defined as synthetic compounds produced in clandestine laboratories in order to act as analogs of schedule drugs mimetizing its chemical structure and improving its pharmacological effects while hampering the control and making regulation more complicated. In this way, the development of new methodologies for chemical analysis of NPS drugs is indispensable to determine a novel class of drugs arising from the underground market. Therefore, this work shows the use of high‐resolution mass spectrometry Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) applying different ionization sources such as paper spray ionization (PSI) and electrospray ionization (ESI) in the evaluation of miscellaneous of seized drugs samples as blotter paper (n = 79) and tablet (n = 100). Also, an elucidative analysis was performed by ESI(+)MS/MS experiments, and fragmentation mechanisms were proposed to confirm the chemical structure of compounds identified. Besides, the results of ESI(+) and PSI(+)‐FT‐ICR MS were compared with those of GC–MS, revealing that ESI(+)MS showed greater detection efficiency among the methodologies employed in this study. Moreover, this study stands out as a guide for the chemical analysis of NPS drugs, highlighting the differences between the techniques of ESI(+)‐FT‐ICR MS, PSI(+)‐FT‐ICR MS, and GC–MS.     

The liquid water-benzene system

The 500 MHz NMR spectra of water-benzene solution near saturation at 303.15, 323.15, and 343.15 K indicate that there is a proton-proton exchange between the water and benzene molecules. In the solution water appears to be present as a dimer attached to the benzene pi cloud on one side of each of the two (initially degenerate) fundamental energy levels, as predicted by the Jahn-Teller effect. This view is reinforced by the fact that one of its hydrogen atoms hovers above one of the carbon atoms and the other three are spread upward around the C6 axis of the benzene molecule. It is also supported by the calculated NMR spectra. Both effects are responsible for the change in the NMR spectra of the water molecules from a single line into four AB signals.     

Analysis of a cycloheptenone derivative: an experimental and theoretical approach

A detailed analysis with total assignment of (1)H and (13)C NMR spectral data for a cycloheptenone derivative, a key intermediate for the synthesis of perhydroazulene terpenoids, is related. These assignments are based on 1D (1)H and (13)C NMR and on 2D NMR techniques including gCOSY, gHSQC, gHMBC, J-resolved and NOEDIF experiments. The unequivocal assignments were supported by theoretical chemical shifts and scalar coupling constant calculations at GIAO B3LYP/cc-pVDZ level from optimized structures at the same level of theory.     

High stereoselectivity on low temperature Diels-Alder reactions

We have found that some of the usually poor dienophiles (2-cycloenones) can undergo Diels-Alder reaction at -78 degrees C with unusually high stereoselectivity in the presence of niobium pentachloride as a Lewis acid catalyst. A remarkable difference in reaction rates for unsubstituted and alpha- or beta-methyl substituted 2-cycloenones was also observed.     

Long-range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long-range heteronuclear spin-spin coupling constants, especially 2, 3JCH spin-spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X-CPMG-HSQMBC and the 2D-coupled gHSQC {1H-13C} experiment     

Fast derivatives of likelihood functionals for ODE based models using adjoint-state method

We consider time series data modeled by ordinary differential equations (ODEs), widespread models in physics, chemistry, biology and science in general. The sensitivity analysis of such dynamical systems usually requires calculation of various derivatives with respect to the model parameters. We employ the adjoint state method (ASM) for efficient computation of the first and the second derivatives of likelihood functionals constrained by ODEs with respect to the parameters of the underlying ODE model. Essentially, the gradient can be computed with a cost (measured by model evaluations) that is independent of the number of the ODE model parameters and the Hessian with a linear cost in the number of the parameters instead of the quadratic one. The sensitivity analysis becomes feasible even if the parametric space is high-dimensional. The main contributions are derivation and rigorous analysis of the ASM in the statistical context, when the discrete data are coupled with the continuous ODE model. Further, we present a highly optimized implementation of the results and its benchmarks on a number of problems. The results are directly applicable in (e.g.) maximum-likelihood estimation or Bayesian sampling of ODE based statistical models, allowing for faster, more stable estimation of parameters of the underlying ODE model.