RESUMEN

CONTEXT: In this work, we did a theoretical exploration of C8F8 (Ib) and its anion radical analogue (IIb) in this work. By investigating the thermochemistry of electron capture, we find that the free energy associated with the conversion of C8H8 (Ia) into its anion radical analogue IIa is of the order of + 92.83 kcal.mol-1, while the conversion of Ib into IIb is - 6.42 kcal.mol-1. Therefore, species IIb is thermodynamically more stable than its neutral analogue. Natural bond orbitals (NBO) analyses revealed that compound Ib exhibits a relative electronic stability as a function of intramolecular delocalisations of the type [Formula: see text] of the order of 2.70 kcal.mol-1. Similar delocalizations for Ia are energetically lower (1.45 kcal.mol-1). Topological analyses of compounds Ib and IIb indicate that the addition of an electron to Ib enhances the covalency of the C-C bond, as can be seen by the reduction in the ellipticity of the C-C bond. The opposite is observed for Ia, whose addition of the electron (leading to IIa) reduces the covalency of the C-C bond. By comparing the free and packaged forms of the species, it is found that, in the crystalline form, the system will present greater relative stability due to the dispersive interactions involved, as evidenced by non-covalent interactions (NCI) analysis. Finally, it was possible to verify that the manifestation of the current density with a lower paratropic and less antiaromatic character in Ib and IIb point to C8F8 as a strong candidate for electron capture. METHODS: Geometry optimization calculations were carried out, for all monomer structures using the hybrid functional B3LYP-D3 and the 6-31+G(d,p) basis set. To determine the formation thermochemistry of the ions, electronic energy corrections was performed using the DLPNO-CCSD(T)/aug-cc-pVTZ/C method. Starting from the optimised forms, shielding, nuclear magnetic resonance (NMR) spectra employing gauge-independent atomic orbital (GIAO), and NBO calculations were performed for these monomers, using the PBE0 functional and the pCSseg-2 atomic basis set. The magnetochemical analysis of ring currents was performed using the GIMIC formalism. For the topological analysis, it was applied the combination DLPNO-CCSD(T)/aug-cc-pVTZ/C, previously used for correcting the electronic energy.

RESUMEN

Pyrazoloporphyrins (PzPs), which are porphyrin analogues incorporating a pyrazole subunit, are examples of carbaporphyrin-type structures with a carbon atom within the macrocyclic cavity. DFT calculations were used to assess a series of 17 PzP tautomers, nine monoprotonated species and four related diprotonated PzP dications. The geometries of the structures were optimized using M06-2X/6-311++G(d,p), and the relative stabilities computed with the cc-PVTZ functional. Nucleus independent chemical shifts, both NICS(0) and NICS(1)zz, were calculated, and the anisotropy of the induced current density (AICD) plots were generated for all of the species under investigation. The results for free base PzPs show that fully aromatic PzP tautomers are not significantly more stable than weakly aromatic cross-conjugated species. In addition, strongly aromatic structures with internal CH2's are much less stable, a feature that is also seen for protonated PzPs. The degree of planarity for the individual macrocycles does not significantly correlate with the stability of these structures. The results allow significant aromatic conjugation pathways to be identified in many cases, and provide insights into the aromatic properties of this poorly studied system. These investigations also complement experimental results for PzPs and emphasize the need for further studies in this area.

RESUMEN

BACKGROUND: Molecular mechanisms of interaction between cells and extremely low frequency magnetic fields (ELF-MFs) still represent a matter of scientific debate. In this paper, to identify the possible primary source of oxidative stress induced by ELF-MF in SH-SY5Y human neuroblastoma cells, we estimated the induced electric field and current density at the cell level. METHODS: We followed a computational multiscale approach, estimating the local electric field and current density from the whole sample down to the single cell level. The procedure takes into account morphological modeling of SH-SY5Y cells, arranged in different topologies. Experimental validation has been carried out: neuroblastoma cells have been treated with Diphenyleneiodonium (DPI) -an inhibitor of the plasma membrane enzyme NADPH oxidase (Nox)- administered 24 h before exposure to 50 Hz (1 mT) MF. RESULTS: Macroscopic and microscopic dosimetric evaluations suggest that increased current densities are induced at the plasma membrane/extra-cellular medium interface; identifying the plasma membrane as the main site of the ELF-neuroblastoma cell interaction. The in vitro results provide an experimental proof that plasma membrane Nox exerts a key role in the redox imbalance elicited by ELF, as DPI treatment reverts the generation of reactive oxygen species induced by ELF exposure. GENERAL SIGNIFICANCE: Microscopic current densities induced at the plasma membrane are likely to play an active physical role in eliciting ELF effects related to redox imbalance. Multiscale computational dosimetry, supported by an in vitro approach for validation, is proposed as the innovative and rigorous paradigm to unveil mechanisms underlying the complex ELF-MF interactions.

Asunto(s)

RESUMEN

Magnetically induced current densities are different for different types of chemical bonds, and may help highlight some of their characteristics and stress their main differences. The present work considers magnetically induced current densities in the bonds of diatomic molecules bonded by covalent bonds as well as the gas phase molecules of 1:1 ionic compounds, comparing the current strength values and visualizing current density maps. The results show clear-cut differences for the different types of bonds (non-polar covalent, polar covalent, and ionic), and can also be related to the extent of the covalent or ionic character of a bond. For ionic compounds, the results also show relevant differences depending on the charges of the ions and on their electron configuration (including significant effects from the presence of d electrons in the outer shell of the ions). The article presents and analyses the results in detail. It is concluded that the magnetically induced current densities contribute to the description and interpretation of chemical bonding in diatomic molecules. © 2017 Wiley Periodicals, Inc.

RESUMEN

This paper describes measurements and computational modelling carried out in the MOBI-Kids case-control study to assess the extremely low frequency (ELF) exposure of the brain from use of mobile and cordless phones. Four different communication systems were investigated: Global System for Mobile (GSM), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT) and Wi-Fi Voice over Internet Protocol (VoIP). The magnetic fields produced by the phones during transmission were measured under controlled laboratory conditions, and an equivalent loop was fitted to the data to produce three-dimensional extrapolations of the field. Computational modelling was then used to calculate the induced current density and electric field strength in the brain resulting from exposure to these magnetic fields. Human voxel phantoms of four different ages were used: 8, 11, 14 and adult. The results indicate that the current densities induced in the brain during DECT calls are likely to be an order of magnitude lower than those generated during GSM calls but over twice that during UMTS calls. The average current density during Wi-Fi VoIP calls was found to be lower than for UMTS by 30%, but the variability across the samples investigated was high. Spectral contributions were important to consider in relation to current density, particularly for DECT phones. This study suggests that the spatial distribution of the ELF induced current densities in brain tissues is determined by the physical characteristics of the phone (in particular battery position) while the amplitude is mainly dependent on communication system, thus providing a feasible basis for assessing ELF exposure in the epidemiological study. The number of phantoms was not large enough to provide definitive evidence of an increase of induced current density with age, but the data that are available suggest that, if present, the effect is likely to be very small.

Asunto(s)

RESUMEN

The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Šabove the ring center correlates well (R (2)>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

RESUMEN

In this paper, the steady two-dimensional hydromagnetic free convective flow of an incompressible viscous and electrically conducting fluid between two parallel vertical porous plates has been considered. The effect of induced magnetic field arising due to the motion of an electrically conducting fluid is taken into account. The governing equations of the motion are a set of simultaneous ordinary differential equations and their analytical solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expression for the induced current density has been also obtained. The effects of various non-dimensional parameters on the velocity profile, the induced magnetic field profile, the temperature profile and the induced current density profile have been shown in the graphs. It is found that the effect of suction parameter is to decrease the velocity field and induced current density while it has increasing effect on the induced magnetic field.