Characterisation of hybrid xerogels synthesised in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as precursors

The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials. Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors. The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm⁻¹, which was attributed to vibrational modes of methyl group. The band around 1092 cm⁻¹ associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The ²⁹Si spectra only showed the Q ⁿ (n=2, 3, 4) signal in xerogels with 0% MTEOS and the T ⁿ (n=2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH₃–SiO_3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy.     

Phytochemical study and anti-inflammatory, antidiabetic and free radical scavenger evaluations of Krameria pauciflora methanol extract

The plant Krameria pauciflora MOC et. Sessé ex DC. is used as an anti-inflammatory and antidiabetic in traditional medicine. The aim of this study was to evaluate the in vivo anti-inflammatory and antidiabetic effects of a methanol extract from the roots of K. pauciflora. Dichloromethane and ethyl acetate extracts obtained by partitioning the methanol extract were also evaluated. Complete methanol and dichloromethane extracts showed anti-inflammatory effects at 3 mg/kg. An anti-inflammatory effect similar to indomethacin (10 mg/kg) was observed when the methanol and dichloromethane extracts, which contain a cycloartane-type triterpene and an sterol, were administered orally at several doses (3, 10, 30 and 100 mg/kg), whereas no anti-inflammatory effect was observed at any dose for the ethyl acetate extract, which contains catechin-type flavonoids. The antidiabetic effect of each extract was also determined. An antihyperglycaemic effect was observed in diabetic rats, but no effect in normoglycaemic animals was observed when the methanol extract was administrated at 30 mg/kg. All of the extracts exhibited radical scavenger activity. Additionally, constituents from all of the extracts were identified by NMR. This article supports the use of K. pauciflora as an anti-inflammatory because it exhibits a similar effect to indomethacin. However, its antidiabetic effect is not completely clear, although it could be useful for preventing diabetic complications.     

Coibanoles, a new class of meroterpenoids produced by Pycnoporus sanguineus

Three new terpenoids of mixed biosynthetic origin were isolated from the culture filtrate of the endophytic fungus Pycnoporus sanguineus. Their structures were determined by extensive spectroscopic analyses. We have named these tricyclic and tetracyclic metabolites ‘coibanoles A-C’ in reference to Coiba Island and Coiba National Park, Panamá, from which the plant and endophyte were collected. The extract was inactive to the human parasites Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum at a test concentration of 10 μg/mL.     

Organocatalytic enantioselective pyrazol-3-one addition to maleimides: reactivity and stereochemical course

The enantioselective synthesis of pyrazol-3-ones has not been extensively studied in organic synthesis. Here in we report the first asymmetric addition of pyrazolones to maleimides catalyzed by bifunctional thiourea catalysts.     

Self-consistent Green's function calculation of the nucleon mean free path

The extension of Green's functions techniques to the complex energy plane provides access to fully dressed quasiparticle properties from a microscopic perspective. Using self-consistent ladder self-energies, we find both spectra and lifetimes of such quasiparticles in nuclear matter. With a consistent choice of the group velocity, the nucleon mean-free path can be computed. Our results indicate that, for energies above 50?MeV at densities close to saturation, a nucleon has a mean-free path of 4 to 5?fm.     

Highly Enantio‐ and Diastereoselective Organocatalytic Desymmetrization of Prochiral Cyclohexanones by Simple Direct Aldol Reaction Catalyzed by Proline

Panacea for aldol desymmetrizations : We describe an easy entry for the desymmetrization of 4‐substituted‐cyclohexanones catalyzed by proline, using as cocatalysts different hydrogen‐bonding donors (see scheme), which dramatically improves the catalytic efficiency of proline in desymmetrization reactions.

     

Vibrational entropy and the structural organization of proteins

In this paper we analyze the vibrational spectra of a large ensemble of non-homologous protein structures by means of a novel tool, that we coin Hierarchical Network Model (HNM). Our coarse-grained scheme accounts for the intrinsic heterogeneity of force constants displayed by protein arrangements and also incorporates side chain degrees of freedom. Our analysis shows that vibrational entropy per unit residue correlates with the content of secondary structure. Furthermore, we assess the individual contribution to vibrational entropy of the novel features of our scheme as compared with the predictions of state-of-the-art network models. This analysis highlights the importance of properly accounting for the intrinsic hierarchy in force strengths typical of the different atomic bonds that build up and stabilize protein scaffolds. Finally, we discuss possible implications of our findings in the context of protein aggregation phenomena.     

Coarse grained variables and deterministic chaos in an excitable system

Temporal coarse graining was applied to the dynamical variables of a semiconductor laser with optical feedback. The chaotic low frequency fluctuations obtained in numerical and experimental data are shown to have properties of a self-excitable deterministic system. External exciting noise is replaced by the ultrafast chaotic oscillations of the system. A low dimensional coarse-grained phase space is defined and time constants are introduced and measured for the exponential drop and recovery of the randomly excited equally shaped spikes.     

Acetaldehyde: A Small Organic Molecule with Big Impact on Organocatalytic Reactions

Stereocontrolled formation of carbon?carbon and carbon?heteroatom bonds through asymmetric organocatalysis is a formidable challenge for modern synthetic chemistry. Among the most significant contributions to this field are the transformations involving the use of acetaldehyde or α‐heteroatom‐substituted acetaldehydes for constructing valuable synthons (e.g., amino acid derivatives and hydroxycarbonyl). In this Minireview, versatile (enantioselective) organocatalytic transformations are discussed.