R. Contreras

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The origin of catalysis and selectivity induced by room temperature ionic liquids in several organic reactions has putatively been associated with the concept of cation effect (hydrogen bond donor ability of the ionic liquids) or anion effect (hydrogen bond accepting ability of the ionic liquids). We show that there may be cases where this a priori(More)
Two complementary models of Lewis molecular acidity are introduced and tested in a wide series of 45 room temperature ionic liquids (RTIL). They are defined in the context of the conceptual density functional theory. The first one, which we tentatively call the excess electronic chemical potential, assesses the electron accepting power of the RTIL by(More)
The quantum mechanical SMD continuum universal solvation model can be applied to predict the free energy of solvation of any solute in any solvent following specification of various macroscopic solvent parameters. For three ionic liquids where these descriptors are readily available, the SMD solvation model exhibits a mean unsigned error of 0.48 kcal/mol(More)
The electronic properties of a chemical model that mimics the His-57...Asp-102 catalytic residues of alpha- chymotrypsine during the transition from normal hydrogen bond to short and strong hydrogen-bond regimes are presented. The results suggest that upon a global external stimulus induced by compression, the system response is the transfer of the(More)
The UV-vis absorption spectra of the photoreceptor chromophores biliverdin (BV) in the ZZZssa conformation and the phycocyanobilin (PCB) with conformations ZZZssa and ZZZasa have been investigated by means of time-dependent density functional theory (TD-DFT) with a polarized continuum model. The three systems are studied in different conditions to include(More)
The electron localization function (ELF) has been separated in its sigma and pi components. The topological analysis of the new ELFsigma and ELFpi functions has been used to quantify the concept of resonance. The highest bifurcation values of these functions describe in a correct way the aromaticity of classical ring molecules and some new aromatic(More)
This work deals with exploring some empirical scales of nucleophilicity. We have started evaluating the experimental indices of nucleophilicity proposed by Legon and Millen on the basis of the measure of the force constants derived from vibrational frequencies using a probe dipole H-X (X = F,CN). The correlation among some theoretical parameters with this(More)
Meroditerpenoids, 2-[2'(E)-3',7',11',15'-tetramethylhexadec-2-en-1'-yl]-6-methyl-1,4-benzohydroquinone diacetate and 4'-chlorostypotriol triacetate, along with eight known compounds isolated from the dichloromethane extract of the brown alga Stypopodium flabelliforme after peracetylation are reported. One of them,(More)
We have systematically studied NMOSFETs, MOSCAPs, and the interfacial chemistry on GaAs (100), (110), (111)A and (111)B-four different crystalline surfaces with direct ALD Al 2 O 3. We found that a much higher drain current on GaAs(111)A NMOSFET can be achieved compared to that obtained on the other 3 surfaces. Also, the results of MOS-CAPs and the(More)
The mechanism of the intramolecular Diels–Alder (IMDA) reaction of benzoquinone 1, in the absence and in the presence of three water molecules, 1w, has been studied by means of density functional theory (DFT) methods, using the M05-2X and B3LYP functionals for exploration of the potential energy surface (PES). The energy and geometrical results(More)