Search

In the search for efficient molecular dynamics simulation models both simplicity and acceptable accuracy matter. In the present study, a model of the graphene- $$\hbox {H}_2$$ physisorption system is used to explore its performance and limitations under canonical NVT and microcanonical NVE simulation conditions. The model implies several simplifications that can be summarized in (a) a single ideal planar frozen graphene-like layer of C atoms, (b) rigid rotor $$\hbox {H}_2$$ molecules and (c) interaction potentials written as C-H and $$\hbox {H}_2$$ - $$\hbox {H}_2$$ site-site Improved Lennard-Jones potentials parameterized to reproduce DFT calculations. This model can be used in a variety of molecular dynamics simulation conditions, both in NVT and NVE ensembles. Such simulations lead to the formation of a single layer of adsorbed $$\hbox {H}_2$$ molecules in dynamically stable equilibrium with a fluid-phase region. In addition, the incipient formation of secondary layers for high-density conditions is also observed. Some properties as average pressure, temperatures and fluid-phase densities are discussed as well as possible improvements of the model. [ABSTRACT FROM AUTHOR]

Introduction: The incidence of myotonic dystrophy type 1 (DM1), a disease with great phenotypic variety, in our region is unknown. This study aims to estimate the incidence of DM1 at our hospital (a reference centre in Aragon, Spain) and to identify the characteristics of our population (genotype-phenotype correlation)., Methods: Retrospective, descriptive study of 459 patients classified according to the number of CTG repeats, as follows: normal (5-35), premutation (36-50), protomutation (51-80), small expansions (81-150), intermediate expansions (151-1000), and large expansions (> 1000). Furthermore, according to clinical phenotype, patients were categorised as unaffected (5-50 CTG repeats), mild form or asymptomatic (51-150), classical form (151-1000), and severe form (> 1000)., Results: The incidence of DM1 was 20.61 cases per million person-years (95% CI, 19.59-21.63). An inverse correlation was observed between the number of CTG repeats and the age at genetic diagnosis (ρ = -0.547; 95% CI, -0.610 to -0.375; P < .001). CTG 5 was the most frequent polymorphic allele in healthy individuals. Of all patients with DM1, 28.3% presented the mild or asymptomatic form, 59.1% the classical form, and 12.6% the severe form. Inheritance was maternal in 35.1% of cases, paternal in 59.4%, and uncertain in 5.5%. In mild forms, frontal balding in men was the most prevalent phenotypic trait, as well as myotonia and cataracts, while in the classical form, ptosis, facial weakness, voice and pronunciation alterations, myotonia, and fatigue/sleepiness were most frequent., Conclusions: The incidence of DM1 in Aragon is significant. Multidisciplinary study of the phenotype of patients with DM1 is key to early diagnosis and personalised management., (Copyright © 2021 Sociedad Española de Neurología. Published by Elsevier España, S.L.U. All rights reserved.)

From coupled-cluster singles and doubles model including connected triples corrections [CCSD(T)] calculations on the water dimer and B97D/CC on the water-circumcoronene complex at a large number of randomly generated conformations, interaction potentials for the physisorption of water on graphene are built, accomplishing almost sub-chemical accuracy. The force fields were constructed by decomposing the interaction into electrostatic and van der Waals contributions, the latter represented through improved Lennard-Jones potentials. Besides, a Chemistry at Harvard Macromolecular Mechanics (CHARMM)-like term was included in the water-water potential to improve the description of hydrogen bonds, and an induction term was added to model the polarization effects in the interaction between water and polyaromatic hydrocarbons (PAHs) or graphene. Two schemes with three and six point charges were considered for the interactions water-water and water-PAH, as Coulomb contributions are zero in the water-graphene system. The proposed fitted potentials reproduce the ab initio data used to build them in the whole range of distances and conformations and provide results for selected points very close to CCSD(T) benchmarks. When applied to the water-graphene system, the obtained results are in excellent agreement with p-CCSD(T), revised symmetry-adapted perturbation theory based on density functional theory monomer properties (DFT-SAPT), and diffusion Monte Carlo reference values. Furthermore, the stability of the various conformers water-PAH and water-graphene, as well as the different trends observed between these systems are rationalized in terms of the modifications of the electrostatic contribution.

The adsorption-for separation, storage and transportation-of methane, hydrogen and their mixture is important for a sustainable energy consumption in present-day society. Graphene derivatives have proven to be very promising for such an application, yet for a good design a better understanding of the optimal pore size is needed. In this work, grand canonical Monte Carlo simulations, employing Improved Lennard-Jones potentials, are performed to determine the ideal interlayer distance for a slit-shaped graphene pore in a large pressure range. A detailed study of the adsorption behavior of methane, hydrogen and their equimolar mixture in different sizes of graphene pores is obtained through calculation of absolute and excess adsorption isotherms, isosteric heats and the selectivity. Moreover, a molecular picture is provided through z-density profiles at low and high pressure. It is found that an interlayer distance of about twice the van der Waals distance of the adsorbate is recommended to enhance the adsorbing ability. Furthermore, the graphene structures with slit-shaped pores were found to be very capable of adsorbing methane and separating methane from hydrogen in a mixture at reasonable working conditions (300 K and well below 15 atm).

Introduction: The incidence of myotonic dystrophy type1 (DM1), a disease with great phenotypic variety, in our region is unknown. This study aims to estimate the incidence of DM1 at our hospital (a reference centre in Aragon, Spain) and to identify the characteristics of our population (genotype-phenotype correlation)., Methods: Retrospective, descriptive study of 459 patients classified according to the number of CTG repeats, as follows: normal (5-35), premutation (36-50), protomutation (51-80), small expansions (81-150), intermediate expansions (151-1000), and large expansions (>1000). Furthermore, according to clinical phenotype, patients were categorised as unaffected (5-50 CTG repeats), mild form or asymptomatic (51-150), classical form (151-1000), and severe form (>1000)., Results: The incidence of DM1 was 20.61 cases per million person-years (95%CI: 19.59-21.63). An inverse correlation was observed between the number of CTG repeats and the age at genetic diagnosis (ρ=-0.547; 95%CI: -0.610 to -0.375; P<.001). CTG 5 was the most frequent polymorphic allele in healthy individuals. Of all patients with DM1, 28.3% presented the mild or asymptomatic form, 59.1% the classical form, and 12.6% the severe form. Inheritance was maternal in 35.1% of cases, paternal in 59.4%, and uncertain in 5.5%. In mild forms, frontal balding in men was the most prevalent phenotypic trait, as well as myotonia and cataracts, while in the classical form, ptosis, facial weakness, voice and pronunciation alterations, myotonia, and fatigue/sleepiness were most frequent., Conclusions: The incidence of DM1 in Aragon is significant. Multidisciplinary study of the phenotype of patients with DM1 is key to early diagnosis and personalised management., (Copyright © 2021 Sociedad Española de Neurología. Publicado por Elsevier España, S.L.U. All rights reserved.)

The interaction of CO with graphene was studied at different theoretical levels. Quantum-mechanical calculations on finite graphene models with the use of coronene for coupled cluster calculations and circumcoronene for B97D calculations showed that there was no preferential site for adsorption and that the most important factor was the orientation of CO relative to graphene. The parallel orientation was preferred, with binding energies around 9 kJ mol -1 at the CCSD(T) and B97D levels, which was in good agreement with experimental findings. From a large number of CO-circumcoronene and CO-CO interactions, computed at different distances and randomly generated orientations, parameters were fit to the improved Lennard-Jones potential. Such potentials, together with others describing the intramolecular dynamics of graphene, were subsequently employed in classical molecular-dynamics simulations of the adsorption of CO on graphene by using the canonical ensemble. The obtained results showed that the introduction of flexibility in graphene, which simulated the effects associated to curvature of the surface, diminished the adsorption level and that, as expected, adsorption also diminished with temperature., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Buckybowls have risen as appealing fullerene fragment derivatives. Their intrinsic curvature has been exploited in the generation of host-guest supramolecular assemblies, not only through concave-convex complementarity but also through less-known concave-concave staggered arrangements. Whereas the stabilization of bowl-in-bowl dispositions has been ascribed to efficient π-π forces together with favorable dipole-dipole interactions, a detailed analysis on the forces guiding the formation of the staggered arrangements is missing so far. Herein, we present a thorough theoretical characterization of bowl-in-bowl vs staggered hemifullerene-based homodimers and heterodimers with the electron-donor truxTTF molecule, as test cases, under the density functional theory and by means of chemical bonding techniques. Our results clearly reveal strong and localized noncovalent signatures, together with an enhanced orbital interaction, associated with CH-π and sulfur-mediated interactions governing the staggered formation. Bending the fullerene fragment is demonstrated to favor the stabilization in both homo- and heterodimers, in good accord with the depletion in the π-electron density calculated upon increasing the buckybowl curvature. The optimal buckybowl curvature for the highest interaction energy is, however, dependent on the type of supramolecular assembly (bowl-in-bowl vs staggered) and the concave region to which hemifullerene approaches truxTTF. Interestingly, two regimes are found as a function of buckybowl curvature for hemifullerene homodimers: bowl-in-bowl dispositions are calculated more stable at low curvatures whereas staggered dimers prevail for highly curved buckybowls. Our results highlight the potential of discrete CH-π and sulfur-mediated interactions to generate unconventional staggered supramolecular arrangements toward the development of a new and unexplored host-guest chemistry.