Mechanistic insights into the SN2-type reactivity of aryl-Co(iii) masked-carbenes for C-C bond forming transformations.

Herein we describe the synthesis and characterization of a family of C-metalated aryl-Co(iii) enolates, which can be considered as masked-carbenes, using diazoacetates as coupling partners. These species have been proved to be necessary intermediates in the C(sp2)-C(sp3) bond forming event to obtain cyclic amides, taming the elusive Co(iii)-carbene species. The scope of diazoacetates has been exhaustively examined, varying the nature of the ester and the α-substitution, and a clear preference for electron-poor carbene precursors is observed. Exhaustive experimental and theoretical studies indicate that an unprecedented intramolecular SN2-type process governs the formation of the newly formed C-C bond. Furthermore, the key role of several Lewis acids as carboxylate-activating reagents is further explored by DFT calculations.

Rationalizing the relative abundances of trimetallic nitride template-based endohedral metallofullerenes from aromaticity measures.

The synthesis of endohedral metallofullerenes (EMFs) from a carbon soot sample of an arc discharge leads to a variety of EMFs that are obtained in different relative abundances. In the present work, we show that these abundances can be predicted from aromaticity calculations. In particular, we use the normalized Additive Local Aromaticity (ALAN) index. Our results show that the most abundant Sc3N-based and Y3N-based EMFs in fullerene soot are the most aromatic. This study reinforces the idea that aromaticity plays a key role in determining the stability of EMFs.

Electronic and vibrational linear and nonlinear polarizabilities of Li@C60 and [Li@C60]+.

Electronic and vibrational nuclear relaxation (NR) contributions to the dipole (hyper)polarizabilities of the endohedral fullerene Li@C(60) and its monovalent cation [Li@C(60)](+) are calculated at the (U)B3LYP level. Many results are new, while others differ significantly from those reported previously using more approximate methods. The properties are compared with those of the corresponding hypothetical noninteracting systems with a valence electron transferred from Li to the cage. Whereas the NR contribution to the static linear polarizabilities is small in comparison with the corresponding electronic property, the opposite is true for the static hyperpolarizabilities. A relatively small, but non-negligible, NR contribution to the dc-Pockels effect is obtained in the infinite frequency approximation.

Role of vibrational anharmonicity in atmospheric radical hydrogen-bonded complexes.

Harmonic and anharmonic vibrational frequency calculations are reported for the most stable hydrogen bonded complexes formed between the hydroperoxyl radical and formic, acetic, nitric, and sulfuric acids which are of atmospheric interest. A comparison between the calculated IR spectra of the hydrogen bonded complexes with the corresponding separate monomers is also reported with the aim to facilitate a possible experimental identification of these complexes. The calculations have been carried out using the second-order vibrational perturbative treatment implemented by Barone applied to the PES obtained with the B3LYP functional using the 6-31+G(d,p) and 6-311+G(2d,2p) basis sets. Our calculations for the separate monomers predict vibrational frequencies with quite a good agreement with the experimental values. The anharmonic contribution results in differences of around 40 cm(-1) with respect to the harmonic values; although in some cases involving highly anharmonic modes, these differences can rise up to 300 and 450 cm(-1).

Linear and nonlinear optical properties of [60]fullerene derivatives.

Using a wide variety of quantum-chemical methods we have analyzed in detail the linear and non-linear optical properties of [60]fullerene-chromophore dyads of different electron-donor character. The dyads are composed of [60]fullerene covalently linked with 2,1,3-benzothiadiazole and carbazole derivatives. Linear scaling calculations of molecular (hyper)polarizabilities were performed using wave function theory as well as density functional theory (DFT). Within the former approach, we used both semiempirical (PM3) and ab initio (Hartree-Fock and second-order Møller-Plesset perturbation theory) methods. Within the latter approach only the recently proposed long-range (LRC) schemes successfully avoid a large overshoot in the value obtained for the first hyperpolarizability (ß). Calculations on model fullerene derivatives establish a connection between this overshoot and the electron-donating capability of the substituent. Substitution of 2,1,3-benzothiadiazole by the triphenylamine group significantly increases the electronic first and second hyperpolarizabilities as well as the two-photon absorption cross section. For [60]fullerene-chromophore dyads we have, additionally, observed that the double harmonic vibrational contribution to the static beta is much larger than its electronic counterpart. The same is true for the dc-Pockels ß as compared to the static electronic value, although the vibrational term is reduced in magnitude; for the intensity-dependent refractive index the vibrational and electronic terms are comparable. A nuclear relaxation treatment of vibrational anharmonicity for a model fulleropyrrolidine molecule yields a first-order contribution that is substantially more important than the double harmonic term for the static ß.

Isolation, identification and antimicrobial activity of ombuoside from Stevia triflora.

From aerial parts of Stevia triflora DC the flavonol glycoside ombuoside (7,4'-di-O-methylquercetin-3-O-beta-rutinoside) has been isolated and identified on the basis of spectral data. Ombuoside and the synthetic derivatives octa-acetylombuoside, ombuine and retusine were tested for antimicrobial activity against several strains of Gram-positive and Gram-negative bacteria and the yeast Candida albicans, using the agar diffusion method. The flavonol glycoside ombuoside and the respective aglycone ombuine, both exhibited moderated activity against Corynebacterium diphtheria, Staphylococcus aureus, Escherichia coli and Candida albicans. To a lesser degree, octaacetylombuoside and retusine showed activity against the Gram-positive bacteria C. diphtheria and S. aureus, but proved to be inactive against Gram-negative bacteria and Candida albicans. These results indicate that the presence of free hydroxyl groups, either alcoholic or phenolic, is an important chemical feature for the expression of flavonol antimicrobial activity. It is worth noting that this is the first study reported on the antibacterial and antifungal activity of these substances.

[A substitute treatment for dialysis?]. / Tratamiento sustitutivo de la diálisis?

One of the major problems regarding the administration of amino acids by intravenous feeding is the use of racemic mixtures that are forbidden by the pharmacological regulations; other current problems is the high cost of obtaining pure amino acids. Because of this, our group has been working in the obtention of L-amino acids (assimilables by living organisms) and ketoacids (used by the body as precursors of racemic amino acid mixtures) in a less expensive and simpler way, with the aim of using these products for different pathologies.

[Clinical characteristics of gastric infection caused by Helicobacter pylori]. / Características clínicas de la afección gástrica por Helicobacter pylori.

In a series of 150 patients submitted for diagnostic gastroscopy, a prospective study of nine anamnesis variables and four exploratory ones was done. Endoscopic and histopathologic diagnoses, as well as the clinical data, were obtained by blinded observers. Helicobacter pylory (Hp) presence in antral mucosa was determined by culture. A clear relationship between Hp presence and peptic ulcer disease, bulboduodenitis and histologic gastritis was found, as expected, but no clinical variable correlated positively with it. We conclude, therefore, that Hp presence in antral mucosa cannot be predicted clinically, a fact probably related to the unspecificity of symptoms in gastroduodenal disease and not to a lack of pathogenicity of this organism.

[Histopathologic changes associated with the presence of Helicobacter pylori in antral mucosa]. / Alteraciones histopatológicas asociadas a la presencia de Helicobacter pylori en mucosa antral.

Helicobacter pylori is a gram negative bacteria which has recently been associated to tissular changes of the upper digestive tract, however, the causal role has not yet been determined. Of 150 patients studied, 63 had tissular changes associated to Helicobacter pylori (Hp), 8 had Hp without tissular related changes (of whom 3 suffered bulbar ulcus and 1 gastric ulcus); the rest of the patients had hiatus hernia associated to distal esophagitis or pyloric stenosis; and only one patient was found to have normal tissue. A clear associated to distal esophagitis or pyloric stenosis; and only one patient was found to have normal tissue. A clear association between Hp and chronic or atrophic gastritis was determined, but no association was found between Hp and gastric cancer.

New Coumarins from Pilocarpus goudotianus.

The leaves of PILOCARPUS GOUDOTIANUS afforded in addition to eight known coumarins three new ones, donatin, alloxanthoxyletol, and (+)-elisin. The structures were elucidated on the basis of spectroscopic evidence and chemical derivatives.