Direct versus resonances mediated F+OH collisions on a new 3A" potential energy surface

A theoretical study of the F(2P) + OH(2Pi) --> HF(1Sigma+) + O(3P) reactive collisions is carried out on a new global potential energy surface (PES) of the ground 3A" adiabatic electronic state. The ab initio calculations are based on multireference configuration interaction calculations, using the aug-cc-pVTZ extended basis sets of Dunning et al. A functional representation of the PES shows no nominal barrier to reaction, contrary to previous results by others. Wave packet and quasiclassical trajectory calculations have been performed for this PES to study the F + OH(v = 0,j) reactive collision. The comparison was performed at fixed and constant values of the total angular momentum from 0 to 110 and relative translational energy up to 0.8 eV. The reaction presents a dynamical barrier, essentially due to the zero-point energy for the bending vibration near the saddle point. This determines two different reaction mechanisms. At energies higher than approximately 0.125 eV the reaction is direct, while below that value it is indirect and mediated by heavy-light-heavy resonances. Such resonances, also found in the simulations of the photodetachment spectrum of the triatomic anion, manifest themselves in the quasiclassical simulations, too, where they are associated to periodic orbits.     

Analysis of conformational equilibria in aplidine using selective excitation 2D NMR spectroscopy and molecular mechanics/dynamics calculations

Aplidine (dehydrodidemnin B), a natural product with potent antitumor activity currently in multicenter phase II clinical trials, exists in DMSO as a mixture of four slowly interconverting conformations in a ratio of 47:33:13:7. NMR spectroscopy shows that these arise as a consequence of cis/trans isomerization about the NMe-Leu(7)-Pro(8) and Pro(8)-Pyr amide bonds of the molecule's side chain. Two major conformations account for 47% and 33% of the total population, a ratio of 60:40 between the two. They correspond to the cis- and trans-isomers, respectively, about the Pro(8)-Pyr amide bond. Two minor conformers arise as a consequence of similar isomerism about the Pro(8)-Pyr amide bond, but in structures in which the NMe-Leu(7)-Pro(8) amide bond is cis rather than trans. These account for approximately 13% and 7% of the total population, corresponding to a ratio of 65:35 cis/trans, respectively. Molecular dynamics simulations show that the three-dimensional structures of all four conformational isomers are similar in the macrocycle and that all are essentially unchanged with respect to the macrocycle of didemnin B. Significant differences in the conformation of the molecule's side chain are, however, observed between major and minor pairs. Analysis of hydrogen-bonding patterns shows that each major conformer exhibits a beta-turn like structure and is stabilized by hydrogen bonding between a different carbonyl group of the pyruvyl unit of the molecule's side chain and the NH of the Thr(6) residue. The minor isomers have a cis-amide bond between the NMe-Leu(7) and Pro(8) residues that obliges the side chain to adopt an extended disposition where hydrogen bonding to the macrocycle is absent. These results suggest that the ability of the molecule's side chain to adopt a beta-turn-like conformation may not be a prerequisite for biological activity in the didemnins and that conformations having an extended side-chain may play a role in the biological activity of aplidine.     

Evaluation of the Use of Elicitors for the Production of Antioxidant Compounds in Liquid Cultures of Ganoderma curtisii from Costa Rica

The use of substances or conditions as elicitors can significantly increase the production of secondary metabolites. In this research, the effects of different elicitors on the production of antioxidant secondary metabolites were evaluated in a strain of Ganoderma sp. The elicitors tested were pH changes in different growth phases of the fungus (pH 3, 5.5 and 8), different concentrations of peptone as a nitrogen source (1 g/L and 10 g/L), and the addition of chemical agents to the culture medium (ethanol, growth regulators, and salts). The alkaline pH during the stationary phase and the high availability of nitrogen were effective elicitors, producing cultures with higher antioxidant activity (37.87 g/L and 43.13 g/L dry biomass) although there were no significant differences with other treatments.     

Enantioselective 1,3-Dipolar Cycloaddition Using (Z)-α-Amidonitroalkenes as a Key Step to the Access to Chiral cis-3,4-Diaminopyrrolidines

The enantioselective 1,3-dipolar cycloaddition between imino esters and (Z)-nitroalkenes bearing a masked amino group in the β-position was studied using several chiral ligands and silver salts. The optimized reaction conditions were directly applied to the study of the scope of the reaction. The determination of the absolute configuration was evaluated using NMR experiments and electronic circular dichroism (ECD). The reduction and hydrolysis of both groups was performed to generate in an excellent enantiomeric ratio the corresponding cis-2,3-diaminoprolinate.     

PET Imaging of the Neuropeptide Y System: A Systematic Review

Neuropeptide Y (NPY) is a vastly studied biological peptide with numerous physiological functions that activate the NPY receptor family (Y₁, Y₂, Y₄ and Y₅). Moreover, these receptors are correlated with the pathophysiology of several diseases such as feeding disorders, anxiety, metabolic diseases, neurodegenerative diseases, some types of cancers and others. In order to deepen the knowledge of NPY receptors’ functions and molecular mechanisms, neuroimaging techniques such as positron emission tomography (PET) have been used. The development of new radiotracers for the different NPY receptors and their subsequent PET studies have led to significant insights into molecular mechanisms involving NPY receptors. This article provides a systematic review of the imaging biomarkers that have been developed as PET tracers in order to study the NPY receptor family.     

Directed ortho-lithiation of unprotected diphenylphosphinic acids

Directed ortho lithiation of diphenylphosphinic acid and subsequent electrophilic trapping provides mono ortho-functionalized derivatives including enantiopure γ-aminophosphinic acids in moderate yields. Copper catalyzed coupling of the ortho anion leads to biphenyl-2,2′-diylbis(phenylphosphinic acid), a phosphorus analogue of biphenyl-2,2′-dicarboxylic acid. Preliminary studies of the metal-binding abilities of this O,O-chelating ligand towards a series of metal cations are included.     

Synthesis of 1,3,6-triaryl-6-trifluoromethyl-5,6-dihydro-1,3,5-triazine-2,4(1H,3H)-diones by reaction of aryl trifluoromethyl ketone imines with aryl isocyanates

Russian Journal of Organic Chemistry -     

Mathematical modeling of flow in sound-absorbing structures of resonance type in the presence of a grazing flow

Sound-absorbing structures of resonance type are studied on the basis of integration of the unsteady Reynolds-averaged Navier-Stokes equations. The formation of the boundary layer over a sound-absorbing panel is compared with that on a flat plate in the presence of an incident wave. The dependence of the panel reflection coefficient on the presence of a grazing flow and the boundary layer thickness is investigated. The results of the numerical experiment are compared with the available experimental data.