First example of the formation of a Si-C bond from an intramolecular Si-H?H-C diyhydrogen interaction in a metallacarborane: A theoretical study

The recently reported crystal structure of [NMe₄][1-SiMe₂H-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] shows short contacts between the Si-H proton acceptor group and the C_c-H proton donor moiety in the dicarbollide ligand. These short contacts were studied within the framework of the Quantum Theory of Atoms in Molecules (QTAIM) at different levels of DFT theory (B3LYP/6-311(d,p) and BP86/TZ2P(+)) that shows the existence of a bifurcated Si-H?H-C_c dihydrogen bond. This paper presents the study of an experimental uncommon Si-H group playing as proton acceptor bond in a dihydrogen bond where hydrides like M-H (M, as metal transition), B-H or Al-H usually perform this role. Furthermore, this paper accounts with a new simple method to estimate bonding energies for closed-shell intramolecular interactions in the scheme of Voronoi charge population analysis and Coulomb′s Law.     

Ab Initio Calculations on the Vinyl Fluoride Fragmentation Reactions

High level ab initio calculations for the fragmentation reactions of vinyl fluoride were performed. The relative energies calculated at the QCISD(T)/6-311G(2d,2p) level of theory, corrected with MP2/6-311G(2d,2p) zero-point energies (ZPEs), differ significantly from those obtained previously at a lower level of theory. The calculations suggest that both the threeand four-center HF elimination processes are likely to occur, with the three-center elimination favored over the four-center at high energies.     

An exact global optimization method for deriving weights from pairwise comparison matrices

Some multiple-criteria decision making methods rank actions by associating weights to the different criteria or actions, which are pairwise compared via a positive reciprocal matrix A. There is a vast literature on proposals of different mathematical-programming methods to infer weights from such matrix A. However, it is seldom observed that such optimization problems may be multimodal, thus the standard local-search resolution techniques suggested may be trapped in local optima, yielding a wrong ranking of alternatives. In this note we show that standard tools of global optimization based on interval analysis, lead to globally optimal weights in reasonable time.     

From Oligo(Phenyleneethynylene) Monomers to Supramolecular Helices: The Role of Intermolecular Interactions in Aggregation

Supramolecular helices that arise from the self-assembly of small organic molecules via non-covalent interactions play an important role in the structure and properties of the corresponding materials. Here we study the supramolecular helical aggregation of oligo(phenyleneethynylene) monomers from a theoretical point of view, always guiding the studies with experimentally available data. In this way, by systematically increasing the number of monomer units, optimized n-mer geometries are obtained along with the corresponding absorption and circular dichroism spectra. For the geometry optimizations we use density functional theory together with the B3LYP-D3 functional and the 6–31G** basis set. For obtaining the spectra we resort to time-dependent density functional theory using the CAM-B3LYP functional and the 3–21G basis set. These combinations of density functional and basis set were selected after systematic convergence studies. The theoretical results are analyzed and compared to the experimentally available spectra, observing a good agreement.     

Complex symmetric functions and generalized discrete Fourier transform

General systems of polynomials, satisfying prescribed symmetries and orthonormal on the unit circle with respect to weight functions belonging to a suitable symmetry class, are used in order to generalize the Discrete Fourier Transform (DFT) and the FFT algorithm.     

Non-ionic and cationic micelle nanostructures as drug solubilization vehicles: spectrofluorimetric and electrochemical studies

The use of colloidal organized media, such as micelles, to solubilize tetracaine hydrochloride (TC.HCl), a local anaesthetic drug, in aqueous solution has been studied by means of fluorescence spectroscopy at 298.15 K. Because tetracaine molecule is a fluorescent probe, changes in the fluorescence emission spectra of the drug when it is solubilized by the micelles enable the study of the micelles–drug association process through the calculation of the association constants. Two kinds of micelles have been selected to solubilize the drug: non-ionic micelles and cationic micelles. Complementary conductometric experiments were also done to determine the critical aggregation concentration of the surfactants in the presence of the drug. The micelle–drug association process has been also analyzed by deconvoluting the fluorescent of the drug into several Gaussian components, each of which assigned to the solubilization of the drug within different microenvironment inside and outside the cationic and/or non-ionic micelles.     

A binomial model for valuing equity-linked policies embedding surrender options

The computation of the fair periodical premiums for equity-linked policies in a Cox–Ross–Rubinstein (CRR) [Cox, J.C., et al., 1979. Option pricing: A simplified approach. J. Financial Economics 7, 229–263] evaluation framework is computationally complex. In fact, despite we assume that the equity value evolves according to a CRR lattice, the dynamics of the reference fund made up of equities of the same kind is described by a non-recombining tree since, at each contribution date, a constant contribution is added to the fund value. We propose to overcome this problem by selecting representative values among all the effective reference fund values. Then, the fair periodical premiums for equity-linked policies embedding a surrender option and a minimum guarantee are computed following the usual backward-induction scheme coupled with linear interpolation.     

Potential use of small basis set on the calculations of electronic properties of some four-membered heterocycles: a conformational study

The potential use of small basis sets upon a low level of theory was studied on the calculations of electronic properties (dipole moment, static polarisability and static hyperpolarisabilities) of a series of 16 four-membered heterocycles with an exocyclic double bond at the position 3 (1–16). First, the calculations were performed within the Hartree–Fock (HF) approximation using 6-31G, 6-31G(d,p) and 6-31+G(d,p) as basis sets for the different conformational states of each molecule, and the results obtained were compared with the MP2/6-31+G(d,p) results reported. In the second place, in order to know the real potential of HF calculations, these were compared with those calculated using larger approaches such as MP2/6-311+G(d,p), MP2/aug-cc-pVDZ, CCS/6-311+G(d,p), CCS/aug-cc-pVDZ, CCS/aug-cc-pVTZ, CCSD/6-31+G(d) and CCSD/cc-pVDZ, taken into account only the planar and equilibrium geometries of each molecules. The HF approaches permit us to obtain a good qualitative representation of the dipole moment as a function of puckering angle in comparison with MP2, CCS and CCSD levels for all tested molecules. However, only HF/6-31+G(d,p) provides quantitative values of dipole moment for the heterocycles 1, 5 and 13 in comparison with MP2, CCS and CCSD levels. On the other hand, the polarisability and hyperpolarisabilities were quite sensitive to the quality of level of theory and basis sets. In particular, HF/6-31+G(d,p) predicted a representative approximation of alpha for the molecule 16 in comparison with larger methods as MP2/aug-cc-pVDZ, CCS/aug-cc-pVDZ and CCS/aug-cc-pVTZ, while a detailed analysis showed that HF can be used in the calculation of alpha for the molecules 3, 7, 11 and 15, but it requires the use of extended basis sets. Also, HF/6-31+G(d,p) predicted values of beta very similar to those calculated at the MP2 and CCSD levels used, for the planar and equilibrium geometry of the molecules 10 and 14. Furthermore, HF/6-31+G(d,p) described a representative dependence of this property with the puckering angle for the heterocycles 9, 10 and 14, compared with the MP2 curves.