Quantifying the conceptual problems associated with the isotropic NICS through analyses of its underlying density.

The isotropic Nucleus Independent Chemical Shift (NICSiso) is widely considered to be a suitable descriptor for aromaticity based on the correlations it exhibits with other aromaticity descriptors. To gain more insight into the origin of these correlations, we establish causal relations between the NICSiso and the underlying current density patterns by resolving the NICSiso into its underlying density. Our results indicate that the origin of the behavior of the NICSiso can be radically different from what is generally assumed.

Interpreting the behavior of the NICSzz by resolving in orbitals, sign, and positions.

The zz component of the nucleus independent chemical shift or the NICSzz is commonly used as a quantifier of the (anti)aromatic character of a (sub)system. One of the underlying assumptions is that a position can be found where the "aromatic" ring currents are adequately reflected in the corresponding NICSzz value. However, as the NICSzz is the result of an integration over the entire space, it no longer explicitly contains the information needed to quantify the separate contributions arising from underlying current density patterns.

Can the current density map topology be extracted from the nucleus independent chemical shifts?

Aromatic compounds are characterised by the presence of a ring current when in a magnetic field. As a consequence, current density maps are used to assess (the degree of) aromaticity of a compound. However, often a more discrete set of so-called Nucleus Independent Chemical Shift (NICS) values is used that is derived from the current density.

Bond Fukui indices: comparison of frozen molecular orbital and finite differences through Mulliken populations.

Bond Fukui functions and matrices are introduced for ab initio levels of theory using a Mulliken atoms in molecules model. It is shown how these indices may be obtained from first-order density matrix derivatives without need for going to second-order density matrices as in a previous work. The importance of taking into account the nonorthogonality of the basis in ab initio calculations is shown, contrasting the present results with previous work based on Hückel theory.

Theoretical studies on the transport mechanism of 5-fluorouracil through cyclic peptide based nanotubes.

Cyclic peptide nanotubes (CPNTs) formed by the self-assembly of cyclic peptides (CPs) with an even number of alternate l/d amino acids are typically used in the field of the transport of ions and drug molecules across the lipid bilayer. This study investigates the transport mechanism of the antitumor drug molecule, 5-fluorouracil (5FU), through the CPNT using classical and steered molecular dynamics simulations combined with umbrella sampling. During the transport of 5FU through the CPNT, 5FU is partially desolvated because the lumen of the CPNT is too small to allow for water molecules solvating it.

Structure and stability of cyclic peptide based nanotubes: a molecular dynamics study of the influence of amino acid composition.

The stability of self-assembling cyclic peptides (CPs) is attained by the intermolecular backbone-backbone hydrogen bonding (H-bonding) interactions. In addition to these H-bonding interactions, the self-assembled CPs are further stabilized by various intermolecular side chain-side chain interactions. This study investigates the role of amino acids on the structure and stability of self-assembled CPs using classical molecular dynamics (MD) simulations and molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) method.

Multidimensionality of delocalization indices and nucleus-independent chemical shifts in polycyclic aromatic hydrocarbons II: proof of further nonlocality.

In a recent contribution, we examined the effect of 10- and 14-center circuits on the nucleus-independent chemical shifts NICSs using multicenter bond indices (MCBIs) (Fias et al., J Comput Chem 2008, 29, 358). In this study, the nonlocal contributions to the NICS are further investigated for a larger set of polycyclic aromatic hydrocarbons (PAHs).

Electrostatic Potentials from Self-Consistent Hirshfeld Atomic Charges.

It is shown that molecular electrostatic potentials obtained from iterative or self-consistent Hirshfeld atomic point charges agree remarkably well with the ab initio computed electrostatic potentials. The iterative Hirshfeld scheme performs nearly as well as electrostatic potential derived atomic charges, having the advantage of allowing the definition of the atom in the molecule, rather than just yielding charges. The quality of the iterative Hirshfeld charges for computing electrostatic potentials is examined for a large set of molecules and compared to other commonly used techniques for population analysis.

Conceptual DFT properties-based 3D QSAR: analysis of inhibitors of the nicotine metabolizing CYP2A6 enzyme.

Structure-activity relationships of 46 P450 2A6 inhibitors were analyzed using the 3D-QSAR methodology. The analysis was carried out to confront the use of traditional steric and electrostatic fields with that of a number of fields reflecting conceptual DFT properties: electron density, HOMO, LUMO, and Fukui f- function as 3D fields. The most predictive models were obtained by combining the information of the electron density with the Fukui f- function (r2 = 0.

Prediction of blood-brain partitioning: a model based on ab initio calculated quantum chemical descriptors.

A new model for the prediction of log BB, a penetration measure through the blood-brain barrier, based on a molecular set of 82 diverse molecules is developed. The majority of the descriptors are derived from quantum chemical ab initio calculations, augmented with a number of classical descriptors. The quantum chemical information enables one to compute fundamental properties of the molecules.

Multidimensionality of delocalization indices and nucleus independent chemical shifts in polycyclic aromatic hydrocarbons.

The aromaticity and local-aromaticity of a large set of polycyclic aromatic hydrocarbons (PAHs) is studied using multicenter delocalization indices from generalized population analysis and the popular nucleus independent chemical shift (NICS) index. A method for the fast computation of the NICS values is introduced, using the so-called pseudo-pi-method. A detailed examination is made of the multidimensional nature of aromaticity.

A new computer program for QSAR-analysis: ARTE-QSAR.

A new computer program has been designed to build and analyze quantitative-structure activity relationship (QSAR) models through regression analysis. The user is provided with a range of regression and validation techniques. The emphasis of the program lies mainly in the validation of QSAR models in chemical applications.

Colonic arteriovenous malformation in a child misinterpreted as an idiopathic colonic varicosis on angiography: remarks on current classification of childhood intestinal vascular malformations.

A case of lower gastrointestinal hemorrhage in a child caused by an arteriovenous malformation (AVM) of the colon is presented. On diagnostic angiography, the lesion was misinterpretated as an idiopathic colonic varicosis because none of the characteristic features of an AVM were present. The role of angiography and shortcomings in nomenclature and classification of intestinal vascular anomalies in childhood are discussed.