RESUMO

The HF molecule is considered the main reservoir of fluorine in the interstellar medium (ISM). Also, the interactions of this molecule with the most common atoms and molecules in the ISM have attracted great interest from the astrochemical community. Collisions between HF and helium have recently caused controversy following a study using a two-dimensional SAPT potential energy surface (PES) that exhibited large discrepancies with previous scattering calculations based on more recent ab initio potentials. To address this issue, our current work aims to develop the most precise three-dimensional PES for the HF+He system. We employ the size-consistent CCSD(T) method in conjunction with the aug-cc-pV6Z basis set. The main features of the new PES as well as the bound states of the He-HF complex are compared to the existing data. The new PES is then utilised to conduct close coupling calculations that demonstrate He-HF as a good instance of vibration-rotation near resonant energy transfer. The novel rate coefficients will be accessible via the BASECOL database, and the use of the new PES is advised when describing HF in helium droplets.

RESUMO

The first six-dimensional potential energy surface (PES) for the SiCSi + H2 complex is presented in this work. This surface is developed from a large number of ab initio energies computed at the explicitly correlated coupled-cluster level of theory together with the augmented correlation-consistent polarized valence triple zeta basis set (CCSD(T)-F12/aug-cc-pVTZ). These energies are fitted to an analytical function through a procedure that combines spline, least-squares, and kernel-based methods. Two minimums of similar depths were found at the equilibrium geometry of the SiCSi molecule. The dependence of the PES on the bending angle is analyzed. Furthermore, a reduced four-dimensional PES averaged over the H2 orientation is presented. Finally, the six-dimensional PES is used for computing the second virial coefficient of the SiCSi + H2 pair using classical and semi-classical methods.

RESUMO

Reactions involving C and N play an essential role in the chemistry around the surface of a hypersonic spacecraft during its atmospheric re-entry. The collision of CN with other molecules and atoms has particular interest in aerothermodynamic modeling. This work focuses on the study of the CN + N → N2 + C reaction in the triplet manifold 3A″ of CN2. A high-level full-dimensional potential energy surface for this system is developed from ab initio calculations at the MRCI-F12 + Q level of theory. This surface is employed in quasiclassical trajectory calculations, and thermal rate coefficients from 100 to 20,000 K are computed. The rates for the formation of N2 are compared with the available experimental data, and good agreement is found. At low and intermediate temperatures, the N2 formation is more efficient than the N-exchange process, while at high temperatures, the rates for both processes are comparable. Finally, analytically modified Arrhenius expressions for the reaction rates of N2 formation and N-exchange are reported.

RESUMO

The HOC+ molecule has for long been detected in several regions of the interstellar medium (ISM). The collisional ro-vibrational rate coefficients of this molecule with the most common colliders in the ISM are then required for applying nonlocal thermal equilibrium models. However, this molecule has a low bending frequency (249 cm-1), and the use of the rigid rotor approximation is therefore limited to low collision energies. Also, the complete determination of the ro-vibrational rate coefficients of HOC+ in collision with He requires including the bending motion in the analytical model of the potential energy surface (PES) of the system. The first goal of this work is then to develop the first rigid bender four-dimensional PES for the interaction between HOC+ and He. To this aim, a large grid of ab initio energies are computed at the CCSD(T)-F12b/aug-cc-pVQZ level of theory and an analytical representation of the PES is obtained using a combination of least square and reproducing kernel Hilbert space procedures. The global minimum of this PES is found to be reached for a linear configuration of the complex. In the second part of this study, rigid rotor close-coupling calculations are performed at low collision energy, and the calculated rate coefficients are compared to those previously determined for the collisions of He with its HCO+ isomer.

RESUMO

The protein superoxide dismutase 1 (SOD1) is a copper and zinc-binding protein that has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). The Zn(II) binding to SOD1 is critical for the stability of the protein, and has been by itself implicated in ALS pathogenesis. Hence, the quantum mechanical (QM) study of the Zn(II)-site of SOD1 is relevant for understanding ALS. The hybrid QM-molecular mechanics (QM/MM) approach commonly employed for the QM study of proteins is highly dependent on the size of the sub-system treated quantum-mechanically. The size of the QM system also determines the computational feasibility of a given method. In the present work, we compare optimized geometries for the metal site and Zn(II) dissociation energies obtained with a QM/MM methodology employing different sizes for the QM sub-system. We find that geometries converge rapidly to RMSDs of around 0.3 Å, and fails to converge further, while a QM system of 480 atoms was required for converging the Zn(II) interaction energy of SOD1 to within 5 kcal*mol-1, and a 611-atoms QM system for a 1 kcal*mol-1 convergence with respect to our reference, 1280 QM-atoms system. Graphical Abstract The size of the QM system is critical for both the accuracy and the computational cost of a QM/MM calculation. We have identified a optimum balance for the study of the active site of the coppper, zinc superoxide dismutase.

Assuntos

RESUMO

Concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn) and lead (Pb) in dune sands from six urban and suburban Matanzas (Cuba) resorts and Varadero beach were estimated by X-ray fluorescence analysis. Ranges of metal contents in dune sands show a strong variation across the studied locations (in mg/kg(-1)): 20-2964 for Cr, 17-183 for Ni, 17-51 for Cu, 18-88 for Zn and 5-29 for Pb. The values of contamination factors and contamination degrees how that two of the studied Matanzas's resorts (Judio and Chirry) are strongly polluted. The comparison with Sediment Quality Guidelines shows that dune sands from Judio resort represent a serious risk for humans, due to polluted Cr and Ni levels, while sands from the rest of the studied resorts, including Varadero beach, do not represent any risk for public use.

Assuntos

RESUMO

Zinc content and Zn bioaccumulation in crops (rice and some vegetables and condiments) cultivated in 18 Cuban urban and suburban areas are reported. Zinc content in food and the corresponding farming soil samples was determined by X-Ray Fluorescence analysis and by Atomic Absorption spectrometry. The quality of the analysis was verified using the Certified Reference Materials IAEA 393 «Algae¼, MA-B-3/TM «Fish Tissue Lyophilised¼, IAEA V-10 «Hay¼ and IAEA Soil-7. The obtained results show rice, of the studied crops, as the major Zn bioaccumulator and important Zn source in Cuban human diet.

Se reportan los contenidos de zinc y su bioacumulación en cultivos (arroz, vegetales y condimentos) procedentes de 18 áreas de agricultura urbana y suburbana. El contenido de zinc en los alimentos, así como en sus correspondientes suelos de cultivo, fue determinado por Fluorescencia de Rayos X y por Espectrometría de Absorción Atómica. La calidad del estudio se verificó mediante el análisis de los Materiales de Referencia Certificados IAEA 393 «Algae¼, MA-B-3/TM «Fish Tissue Lyophilised¼, IAEA V-10 «Hay¼ e IAEA Soil-7. Los resultados mostraron al arroz, de los cultivos estudiados, como el cultivo de mayor bioacumulación de zinc y como fuente importante de Zn en la dieta de nuestra población.