Formation of H2\text{H}_{2} on polycyclic aromatic hydrocarbons under conditions of the ISM: an ab initio molecular dynamics study

Understanding how the $\mathrm{H}_2$ molecule is formed under the chemical conditions of the interstellar media (ISM) is critical to the whole chemistry of it. Formation of $\mathrm{H}_2$ in the ISM requires a third body acting as a reservoir of energy. Polycyclic aromatic hydrocarbons (PAH's) are excellent candidates to play that role. In this work we simulated the collisions of hydrogen atoms with coronene to form $\mathrm{H}_2$ via the Eley-Rideal mechanism. To do so, we used Born-Oppenheimer (ab initio) Molecular Dynamics simulations. Our results show that that adsorption of H atoms and subsequent release of $\mathrm{H}_2$ readily happen on coronene for H atoms with kinetic energy as large as 1 eV. Special attention is paid to dissipation and partition of the energy released in the reactions. The capacity of coronene to dissipate collision and reaction energies depends varies with the reaction site. Inner sites dissipate energy easier and faster than edge sites, thus evidencing an interplay between the potential energy surface around the reaction center and its ability to cool the projectile. As for the the recombination of H atoms and the subsequent formation of $\mathrm{H}_{2}$, it is observed that $\sim 15\%$ of the energy is dissipated by the coronene molecule as vibrational energy and the remaining energy is carried by $\mathrm{H}_{2}$. The $\mathrm{H}_{2}$ molecules desorb from coronene with an excited vibrational state ($\upsilon \geq 3$), a large amount of translational kinetic energy ($\geq$ 0.4 eV) and with a small activation of the rotational degree of freedom.Comment: Accepted in MNRA

Efectos de la disminución de temperatura sobre el desarrollo de la pared de la antera y el grano de polen en Oryza sativa L.

The effect of decreasing temperature from 30/20 ºC to 16 ºC during the reproductive stage on the development of the anther and pollen in rice ‘Diamante-INIA’, ‘Brillante-INIA’ and ‘Zafiro-INIA’, was studied. The objectives were to determine the relative tolerance of cultivars to low temperature and to describe cellular and ultrastructural damages caused by temperature stress. Plants were grown at 30/20 °C, day/night (optimum temperature), and at panicle initiation some of these were moved to 16 °C until anthesis. Spikelets were obtained at tetrad, free microspores and mature pollen stages, and sections were prepared for light and transmission electron microscopy. Normal development of the four layers of the anther wall (epidermis, endothecium, middle layer and tapetum) and of pollen grains were observed at 30/20 °C, while at 16 °C tapetal hypertrophy, atrophied locules, malformed grains, delayed anthesis and reduced pollen viability occurred. ‘Diamante-INIA’ was the less tolerant cultivar at 16 °C and ‘Zafiro-INIA’ the most tolerant to temperature stress.Se estudió el efecto de la disminución de temperatura de 30/20 ºC (temperatura óptima) a 16 ºC (temperatura baja) durante la etapa reproductiva en el desarrollo de la antera y el polen en los cultivares de arroz ‘Diamante-INIA’, ‘Brillante-INIA’ y ‘Zafiro-INIA’. Los objetivos fueron describir los daños causados por estrés térmico a nivel ultraestructural y determinar la tolerancia relativa de los cultivares a la baja temperatura. Se cultivaron plantas en macetas a 30/20 °C (día/noche) y al iniciarse la formación de la panícula parte de éstas se trasladaron a 16 ºC hasta antesis. Se recolectaron espiguillas en etapa de tétrada, micrósporas libres y polen maduro, y se realizaron cortes para microscopía óptica y electrónica de transmisión. A 30/20 °C se observó un desarrollo normal de los cuatro estratos de la pared de la antera (epidermis, endotecio, capa media y tapete) y de los granos de polen, mientras que a 16 ºC se observó hipertrofia del tapete, lóculos atrofiados, granos malformados, retraso de la antesis y disminución de la viabilidad. ‘Diamante-INIA’ se presentó como el cultivar menos tolerante a 16 ºC y ‘Zafiro-INIA’ como el más tolerante

Inhibitory Actions of Tropeines on the α3 Glycine Receptor Function

Glycine receptors (GlyRs) are chloride-permeable pentameric ligand-gated ion channels. The inhibitory activity of GlyRs is essential for many physiological processes, such as motor control and respiration. In addition, several pathological states, such as hyperekplexia, epilepsy, and chronic pain, are associated with abnormal glycinergic inhibition. Recent studies have pointed out that positive allosteric modulators targeting the GlyR α3 subunit (α3GlyR) displayed beneficial effects in chronic pain models. Interestingly, previous electrophysiological studies have shown that tropeines, which are a family of synthetic antagonists of the serotonin type 3 receptors (5-HT3Rs), potentiate the activity of GlyRs conformed by α1 subunits. However, despite its importance as a pharmacological target in chronic pain, it is currently unknown whether the α3GlyR function is modulated by tropeines. Using electrophysiological techniques and molecular docking simulations, here we show that tropeines are inhibitors of the α3GlyR function. Tropisetron, a prototypical tropeine, exerted concentration-dependent inhibitory effects on α3GlyRs at the low micromolar range. In addition, three other tropeines showed similar effects. Single-channel recordings show that tropisetron inhibition is associated with a decrease in the open probability of the ion channel. Molecular docking assays suggest that tropeines preferentially bind to an agonist-free, closed state of the ion channel. The tropeine binding occurs in a discrete pocket around the vicinity of the orthosteric site within the extracellular domain of α3GlyR. Thus, our results describe the pharmacological modulation of tropeines on α3GlyRs. These findings may contribute to the development of GlyR-selective tropeine derivatives for basic and/or clinical applications

Modulation of GABAA receptors and of GABAergic synapses by the natural alkaloid gelsemine

The Gelsemium elegans plant preparations have shown beneficial activity against common diseases, including chronic pain and anxiety. Nevertheless, their clinical uses are limited by their toxicity. Gelsemine, one of the most abundant alkaloids in the Gelsemium plants, have replicated these therapeutic and toxic actions in experimental behavioral models. However, the molecular targets underlying these biological effects remain unclear. The behavioral activity profile of gelsemine suggests the involvement of GABAA receptors (GABAARs), which are the main biological targets of benzodiazepines (BDZs), a group of drugs with anxiolytic, hypnotic, and analgesic properties. Here, we aim to define the modulation of GABAARs by gelsemine, with a special focus on the subtypes involved in the BDZ actions. The gelsemine actions were determined by electrophysiological recordings of recombinant GABAARs expressed in HEK293 cells, and of native receptors in cortical neurons. Gelsemine inhibited the agonist-evoked currents of recombinant and native receptors. The functional inhibition was not associated with the BDZ binding site. We determined in addition that gelsemine diminished the frequency of GABAergic synaptic events, likely through a presynaptic modulation. Our findings establish gelsemine as a negative modulator of GABAARs and of GABAergic synaptic function. These pharmacological features discard direct anxiolytic or analgesic actions of gelsemine through GABAARs but support a role of GABAARs on the alkaloid induced toxicity. On the other hand, the presynaptic effects of the alkaloid provide an additional mechanism to explain their beneficial effects. Collectively, our results contribute novel information to improve understanding of gelsemine actions in the mammalian nervous system

DFT exchange: sharing perspectives on the workhorse of quantum chemistry and materials science

In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners. The format of the paper is that of a roundtable discussion, in which the participants express and exchange views on DFT in the form of 302 individual contributions, formulated as responses to a preset list of 26 questions. Supported by a bibliography of 777 entries, the paper represents a broad snapshot of DFT, anno 2022

Independent Analysis of Decelerations and Resting Periods through CEEMDAN and Spectral-Based Feature Extraction Improves Cardiotocographic Assessment

Fetal monitoring is commonly based on the joint recording of the fetal heart rate (FHR) and uterine contraction signals obtained with a cardiotocograph (CTG). Unfortunately, CTG analysis is difficult, and the interpretation problems are mainly associated with the analysis of FHR decelerations. From that perspective, several approaches have been proposed to improve its analysis; however, the results obtained are not satisfactory enough for their implementation in clinical practice. Current clinical research indicates that a correct CTG assessment requires a good understanding of the fetal compensatory mechanisms. In previous works, we have shown that the complete ensemble empirical mode decomposition with adaptive noise, in combination with time-varying autoregressive modeling, may be useful for the analysis of those characteristics. In this work, based on this methodology, we propose to analyze the FHR deceleration episodes separately. The main hypothesis is that the proposed feature extraction strategy applied separately to the complete signal, deceleration episodes, and resting periods (between contractions), improves the CTG classification performance compared with the analysis of only the complete signal. Results reveal that by considering the complete signal, the classification performance achieved 81.7% quality. Then, including information extracted from resting periods, it improved to 83.2%

Exchange energy functional from a Pauli correlationfactor model

The spherical average of the Hartree-Fock second-order density matrix is approximated through an ansatz similar to that proposed by McWeeny for the exact second-order density matrix. This leads to the definition of a Pauli correlation factor which produces the exchange hole. In this work, the Pauli correlation factor is modeled in order to obtain an exchange energy density functional. The factor satisfies the normalization condition of the second-order density matrix. Numerical results are presented for the atoms He-Ar. © 1993

The static dipole polarizability of aluminium atom: discrepancy between theory and experiment

A serious discrepancy of almost 20% has been found between the experimentally measured static dipole polarizability of aluminium atom and very exhaustive theoretical calculations. This fact is important because in some experimental works the dipole polarizability of atomic clusters is measured with respect to the one of aluminium atom