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The selectivity of the sodium channel has been the subject of numerous experimental and theoretical studies. In this work, this problem is approached from a theoretical point of view based on a model built from the Selective Filter (SF) of the open structure of the voltage-activated channel of the bacterium Magnetococcus marinus. This approach has allowed us to calculate the interaction energies of the system (cation-water-SF-fragment), both for the sodium cation and the potassium cation. The results have highlighted the importance of differential dehydration of cations, as well as the environment where it occurs. Semi-empirical and ab initio methods have been applied to analyze and quantify the interaction energies when the cations are in the SF of the sodium channel, with the DFT (ab initio) methods giving us the key to the distribution of the interaction energies and therefore how dehydration occurs. [ABSTRACT FROM AUTHOR]

Numerous theoretical and experimental studies have attempted to determine the mechanisms of bacterial potassium channel selectivity (KcsA). However, there are still different aspects that remain uncovered. In this paper, we have built a model based on a selective filter (SF) for the KcsA, taking into account its structure and calculating the system interaction energy (cation–water–SF-fragment), using both sodium and potassium as cations. The results tell us which aspects could be responsible for the higher selectivity of the channel. All this reveals that there are two most important aspects: the dehydration of potassium in relation to sodium, and the environment where such dehydration occurs, in the entrance of the SF. Both semi-empirical and ab initio methods are applied to analyse and quantify the change of the interactions that take place when the cation K+ or Na+ crosses the SF. [ABSTRACT FROM AUTHOR]

Recent interest in the absorption and photo-luminescence properties of a molecule with an envisioned optoelectronic use, such as TPD ( N, N $$^{\prime }$$ -diphenyl- N, N $$^{\prime }$$ -bis(3-methylphenyl)-(1,1 $$^{\prime }$$ -biphenyl)-4,4 $$^{\prime }$$ -diamine), prompted us to apply Density Functional Theory (DFT) and Time-Dependent DFT methods to obtain theoretical results in agreement with experimental findings. Based on these benchmark results, we tackled in a further step the study of a set of molecules derived from the triphenylamine moiety, trying thus to relate their structures with their expected behavior in optical devices . Therefore, we analyzed several key properties for it, like the Stokes shift (important for laser applications), or their absorption and emission spectra which, together with the energies of frontier molecular orbitals, help to determine their optical behavior. [ABSTRACT FROM AUTHOR]

The competition between Na + and K + with a protein for water was investigated by using Density Functional Theory (DFT) calculations. The optimized potential energy curves have been made in the DFT, together with balanced basis sets of split valence Def2-SV(P). Initially, calculations were done in order to know the organization of the hydration shell of the sodium and potassium ions, when up to sixteen molecules of water are added. The results indicate the structure and stability of these cations with water clusters. Then, this knowledge was used for the analysis of the hydrated protein when potassium or sodium cations approach them, showing that cation has a dehydration process more favorable energetically, and indicating for which cation, potassium or sodium is the competition with the protein for water more favorable. [ABSTRACT FROM AUTHOR]

The correlation factor of Colle and Salvetti is studied by comparing the behavior of three different correlation functionals. The normalization, sum rule, Coulomb hole, correlation energy integrand, and the Wigner exclusion hole have all been analyzed by applying the three approaches. The results indicate that the correlation factor proposed by Colle–Salvetti is a very good choice for modeling electron correlation in atoms. The flaws appearing in the development of the Colle–Salvetti equations seem mainly due to an inadequate use of the first mean value theorem of integral calculus. The Gaussian summation used for the two-body density matrix seems to be a good approximation to obtain the correlation factor equations. [ABSTRACT FROM AUTHOR]