R. H. González-Jonte

Journals that increase their impact factor at least fourfold in a few years: The role of journal self-citations

The aim of this study was to ascertain the possible effect of journal self-citations on the increase in the impact factors of journals in which this scientometric indicator rose by a factor of at least four in only a few years. Forty-three journals were selected from the Thomson—Reuters (formerly ISI) Journal Citation Reports as meeting the above criterion. Eight journals in which the absolute number of citations was lower than 20 in at least two years were excluded, so the final sample consisted of 35 journals. We found no proof of widespread manipulation of the impact factor through the massive use of journal self-citations.

A theoretical study of subphthalocyanine and its nitro- and tertbutyl-derivatives ☆

Abstract The unsubstitute subphthalocyanine (SubPc) and their tertbutyl- (tertbutyl-SubPc) and nitro-(nitro-SubPc) derivatives have been theoretically studied at Hartree–Fock (HF) and Density Functional Theory (DFT) levels using STO-3G and 6-31G basis sets. The geometric optimization of the molecules was carried out. The calculated geometry for SubPc agrees with experimental X-ray data. No significant geometrical changes with respect to SubPc were observed in the tertbutyl-SubPc and nitro-SubPc macrocycles. B–Cl distance systematically changes with the electron donor/acceptor properties of the peripheral substituents. The calculated dipole moments reproduce very well the experimental values, whereas the atomic charges reveal the polar character of the SubPc macrocycle. An extensive study of some frontier orbitals was performed. The present calculations reproduce the breakdown of Goutermans four-orbital model in SubPcs, this effect being less dramatic in the DFT description. The nodal patterns for the two highest occupied molecular orbitals and the two lowest unoccupied molecular orbitals obtained from different computational methods exhibit important differences, but in general an explanation for some of the most important aspects of the chemical reactivity of the SubPcs can be put forward.

Molecular electronic structure of subphthalocyanine macrocycles

Quantum chemical calculations at semiempirical (MNDO methods) and ab initio (6-31G and STO-3G basis ses) levels have been performed on boron(III) subphthalocyanines 1-10. Theoretical calculations predict a cone-shaped structure for these compounds independently of the kind of peripheral substitution and even of compositional changes in the central region of the macrocycle (for example, substitution of the boron atom by two hydrogens). The theoretical calculations are in excellent agreement with previous X-ray determinations.

Interaction of brassinolide with essential amino acid residues: A theoretical approach

The interaction of the most active natural brassinosteroid, brassinolide, with the twenty natural amino acids is studied applying the multiple minima hypersurface method to model the molecular interactions explicitly. The resulting thermodynamic data gives useful information about the amino acids with the greatest association for brassinolide and the stabilities of such complexes. Density functional theory (DFT) optimizations were further carried out to test the performance of semiempirical calculations. Additional calculations with a more accurate DFT method were performed to explore the formation of this type of molecular complexes. The semiempirical geometries and stability order of these complexes are in good agreement with the DFT calculations. Each group of amino acids possesses a preferential zone of interaction with brassinolide, forming the polar-charged amino acids the most stable complexes. This study could contribute to future investigations of the interaction of brassinosteroids with the receptor protein in plants.

Theoretical model of internal rotation in monosubstituted derivatives of furfural

The present work explores the effect of substitution in all free positions of furfural on conformational preferences of formyl group by using ab‐initio calculations at the MP2/6‐31G(p,d) level of theory. Theoretical modeling was made in vacuo. The selected substituents were CH3, NH2, NO2 and F groups in 3, 4, 5 and ipso carbonyl positions. Geometries of all derivatives were analyzed and it is ascertained that substitution has not important consequences on furan ring geometry. Differences of energy between OO‐cis and trans conformers and energy barriers between them are described and extreme cases are explained. Interesting features appear in the cases of NH2 and NO2 groups, and particularly when the 3 and ipso carbonyl positions are substituted. Variations in energy barriers are correlated with variations in C2‐C6 distances for the transition states and planar forms. Substitution effect on Mülliken charges are analyzed and related with internal rotation energy barriers and differences between conformers.

A theoretical approach to the influence of the macrocycle conformation on the molecular electronic structure in Mg-porphyrins

Nonplanar saddled (sad) ruffled (ruf) and domed (dom) conformations of the Mg-porphyrin (MgP) macrocycle in several degrees of deformation have been computed. These symmetrical distortion modes were induced in unsubstituted macrocycle using molecular definitions for calculations which permits us to achieve a systematical variation of the nonplanarity varying only a convenient geometrical parameter of the molecule. Series of nonplanar macrocycles like those synthesized in previous works employing peripheral substitutions are obtained. The procedure here used to induce deformations gives the possibility of investigating the modulator role of the out-of-plane distortions on the geometry and electronic properties of the porphyrin avoiding additional influences due to the substituents or the surrounding protein scaffolding.

Molecular Recognition of Aromatic Nitro Compounds at Cyclodextrin Dithiocarbamate-modified Electrodes

Silver electrodes were modified by the adsorption of α-, β-, and γ-cyclodextrin dithiocarbamates (2α–γ) and characterized by reductive desorption experiments. Their molecular recognition properties were studied by cyclic voltammetry using three families of positional isomers of aromatic nitro compounds. Electrodes modified with 2α and 2β were selective for meta and para isomers while 2γ showed little selectivity. These observations are explained in terms of cavity sizes and guest structure. Computational studies suggest that the main reason for the observed selectivity is the different position of the NO2 group in ortho and para isomers with respect to the CD cavity.