In the early 2000s, the first articles regarding the calculation of NMR parameters for natural products appeared in the literature. Since then, modelling 1H and 13C chemical shifts and spin–spin ...coupling constants for this class of compounds has experienced a remarkable increase in precision, accessibility, and application, leading to considerable advances in the field. More recently, significant contributions from several authors have led to continuous growth in this research field, updating and broadening the simulation of NMR parameters, in particular with the application of new techniques for data treatment. Nowadays, such studies are routinely found in the high impact literature. In this review, we intend to cover the general guidelines and the main advances in NMR calculations of natural products published since 2012. We intend to address the bottlenecks of quantum chemical calculations of NMR parameters, including mathematical definitions, updates, and a discussion of relevant examples, and to highlight novel tools, for example DU8+, CP3, DP4, DP4+ and J-DP4. We will cover all aspects of NMR simulation focusing on natural products, from the fundamentals to the new computational toolboxes available, combining advanced quantum chemical calculations with complex upstream data processing and machine learning.
The possibility of finding the fragmentation routes by theoretical methods led us to compare the molecular ions between neutral molecules of benzene, aniline, and o-, m-, and p-nitroaniline, using ...the density functional theory (DFT), under an aug-cc-pVDZ base set and a B3LYP exchange-correlation functional. After determining the structure and electronic energy of neutral and doubly ionized species, we used a new protocol based on analyzing Wiberg’s binding indexes and the quantum theory of atoms in Bader molecules (QTAIM). The charge transfer and electronic distribution in aromatic monomers indicate the possibility of fragment formation in at least two pairs of carbon-carbon (CC) atoms. They show the possible loss of the -
CNH
2
and -
NO
2
groups in the aniline and nitroaniline molecules doubly ionized.
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The Amazon rainforest is considered a megadiverse biome, where several species of its rich flora are still unknown. The anatomy of their leaves usually identifies species. In this paper, we present a ...complete characterization of the leaf surface of Amazon Carapa guianensis Aubl. (Andiroba), using microscopy and fractal theory to be considered a possible tool for investigating different leaves spatial patterns, especially in species with similar leaf architecture. The SEM results revealed the cellular structures and other non-cellular structures that make up the leaf architecture, both for the abaxial and adaxial sides. The cells responsible for the plant photosynthesis process were observed in the internal structure of the leaf. The wettability analysis showed that the abaxial side is more hydrophobic, while the adaxial side is more hydrophilic. AFM images exposed the relevant details of the microstructure of the leaf abaxial side, such as stomata, pores, furrows, contour, particles, and rough profiles generated by topographic irregularities. The statistical parameters revealed that the scale size influences the topographic roughness, surface asymmetry, and shape of the height distribution, also observed by advanced parameters obtained according to the standard of the international organization for standardization (ISO). The fractal and advanced fractal parameters confirmed changes in spatial patterns as a function of scale size. The largest area exhibited greater spatial complexity, low dominant spatial frequencies, more excellent surface percolation, intermediate topographic homogeneity, and high uniformity of spatial patterns.
The increase of operational lifetime for Organic Light-Emitting Diodes has stimulated many studies focused on the mechanisms responsible for their degradation. Degradation studies of the ...N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine thin films have been performed using synchrotron radiation in order to elucidate the modification of the electronic structure in such organic compound, when non-monochromatized light was used to simulate the degradation caused by intense sunlight. Core level photoabsorption at the N 1s-edge and valence level photoemission measurements suggest stronger structural stability and a minor loss in the hole transporting properties. The degradation leads to the decrease of the injection and charge mobility, associated with the loss of nitrogen and benzene rings, which causes an increase of the impedance in the electroluminescent device.
Photon stimulated ion desorption (PSID) from condensed carbon dioxide has been studied for photon excitation energies ranging from 93 to 193 eV. PSID studies have been performed at the Brazilian ...synchrotron light source (LNLS), Campinas, during a multi-bunch operation mode of the storage ring. The results showed that after photon excitation several ions desorbed from the CO2 films: C+ , O+ , CO+ and O2+. PSID experiments showed that ion desorption was enhanced only at the Si resonance excitations. When the thickness of the CO2 was ~ 500 L or higher, almost no desorption yield was observed. The study of the dependence of the relative partial ion yield on the photon excitation showed that the X-ray induced Electron Stimulated Desorption (XESD) mechanism has to be invoked to explain the origin of the desorbed ions in the energy region studied.
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