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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 lowest-energy singlet ( S 1 ) and triplet ( T 1 ) excited states of organic conjugated chromophores are known to be accurately calculated by modern wavefunction and Time-Dependent Density Functional Theory (TD-DFT) methods, with the accuracy of the latter heavily relying on the exchange-correlation functional employed. However, there are challenging cases for which this cannot be the case, due to the fact that those excited states are not exclusively formed by single excitations and/or are affected by marked correlation effects, and thus TD-DFT might fall short. We will tackle here a set of molecules belonging to the azaphenalene family, for which research recently documented an inversion of the relative energy of S 1 and T 1 excited states giving rise to a negative energy difference ( Δ E S T ) between them and, thereby, contrary to most of the systems thus far treated by TD-DFT. Since methods going beyond standard TD-DFT are not extensively applied to excited-state calculations and considering how challenging this case is for the molecules investigated, we will prospectively employ here a set of non-standard methods (Multi-Configurational Pair Density Functional Theory or MC-PDFT) and correlation functionals (i.e., Lie–Clementi and Colle–Salvetti) relying not only on the electronic density but also on some modifications considering the intricate electronic structure of these systems. [ABSTRACT FROM AUTHOR]

The standard procedure to identify the hole- or electron-acceptor character of amorphous organic materials used in OLEDs is to look at the values of a pair of basic parameters, namely, the ionization potential (IP) and the electron affinity (EA). Recently, using published experimental data, the present authors showed that only IP matters, i.e., materials with IP > 5.7 (<5.7) showing electron (hole) acceptor character. Only three materials fail to obey this rule. This work reports ab initio calculations of IP and EA of those materials plus two materials that behave according to that rule, following a route which describes the organic material by means of a single molecule embedded in a polarizable continuum medium (PCM) characterized by a dielectric constant ε. PCM allows to approximately describe the extended character of the system. This "compound" system was treated within density functional theory (DFT) using several combinations of the functional/basis set. In the preset work ε was derived by assuming Koopmans' theorem to hold. Optimal ε values are in the range 4.4–5.0, close to what is expected for this material family. It was assumed that the optical gap corresponds to the excited state with a large oscillator strength among those with the lowest energies, calculated with time-dependent DFT. Calculated exciton energies were in the range 0.76–1.06 eV, and optical gaps varied from 3.37 up to 4.50 eV. The results are compared with experimental data. [ABSTRACT FROM AUTHOR]

• Efficient methodology for post-synthetic functionalization of polyaniline with phosphorus-containing compounds. • The electroactivity of modified polyaniline depends on the phosphorus precursor. • DFT results proved that the reaction occurs through the imine groups and the phosphorus atoms. P-postmodified polyaniline was obtained by reacting phosphorus trichloride (PCl 3) and chlorodiphenylphosphine (PPh 2 Cl) and polyaniline (PANI), under mild conditions. The reaction was found to be very selective, as only the imine groups were involved in the P-functionalization, and efficient as well, affording a P-loading of 3 at.% and 5 at.% for PPh 2 Cl and PCl 3 , respectively. All the polymers were characterized by different techniques and the results were endorsed by theoretical calculations. Experimental and Density Functional Theory results proved that the reaction occurs through the imine groups and the phosphorus atoms, generating N P bonds. The electrochemical properties of the N P modified materials were evaluated and the catalytic activity towards oxygen reduction reaction was measured. It was found that a high concentration of phenyl groups from PPh 2 Cl (about 3 at.%) affected negatively the activity of the catalyst since they prevented the access of the oxygen molecules to the catalytic active sites. However, a lower amount of PPh 2 groups (1 at.%) or the use of PCl 3 avoided this hindrance and resulted in an improved catalytic activity with respect to pristine PANI. [ABSTRACT FROM AUTHOR]