DIFFERENT CHROMATOGRAPHIC BEHAVIOR OF A THYMINE-CONTAINING NEW ULTRAVIOLET PHOTOPRODUCT AND SPORE PHOTOPRODUCT

Abstract— One- and two-dimensional cochromatography in five different solvents of a near UV photo-product induced by 365 nm irradiation of DNA in aqueous solution and the 'spore photoproduct', 5-thyminyl-5,6-dihydrothymine, produced by 254 nm irradiation of dry DNA, indicate that the two photoproducts seem to have related structures but are different.     

Early error detection: an action-research experience teaching vector calculus

This paper describes an action-research experience carried out with second year students at the School of Engineering of the National University of Entre Ríos, Argentina. Vector calculus students played an active role in their own learning process. They were required to present weekly reports, in both oral and written forms, on the topics studied, instead of merely sitting and watching as the teacher solved problems on the blackboard. The students were also asked to perform computer assignments, and their learning process was continuously monitored. Among many benefits, this methodology has allowed students and teachers to identify errors and misconceptions that might have gone unnoticed under a more passive approach.     

One-pot synthesis of orthogonally protected sugars through sequential base-promoted/acid-catalyzed steps: A solvent-free approach with self-generation of a catalytic species

A varied set of solvent-free, one-pot synthetic sequences were developed to carry out the orthogonal protection of saccharide polyols. These sequences are composed of an initial regioselective benzylation, silylation or iodination (under mildly basic conditions), followed by an acid catalyzed protection of two further hydroxyl sites via the generation of a cyclic acetal. These processes allow recycling of the ammonium or pyridinium side products generated in the former step as effective catalytic species for the latter step.     

Mechanochemically synthesized pyrite and its electrochemical behavior as cathode for lithium batteries

Journal of Solid State Electrochemistry - This study presents a simple and scalable synthesis of pyrite (FeS2) starting from S and Fe powders, which involves high-energy ball milling of precursor...     

Interconnected networks: structural and dynamic characterization of aqueous dispersions of dioctanoylphosphatidylcholine

Aqueous dispersions of the phospholipid dioctanoylphosphatidylcholine (diC 8PC) phase-separate below a cloud-point temperature, depending on lipid concentration. The lower phase is viscous and rich in lipid. The structure and dynamics of this system were explored via cryo-transmission electron microscopy (cryo-TEM), small-angle X-ray scattering (SAXS), and NMR. The lower phase comprises a highly interconnected tridimensional network of wormlike micelles. A molecular mechanism for the phase separation is suggested.     

Molecular field analysis and 3D-quantitative structure-activity relationship study (MFA 3D-QSAR) unveil novel features of bile acid recognition at TGR5

Bile acids regulate nongenomic actions through the activation of TGR5, a membrane receptor that is G protein-coupled to the induction of adenylate cyclase. In this work, a training set of 43 bile acid derivatives is used to develop a molecular interaction field analysis (MFA) and a 3D-quantitative structure-activity relationship study (3D-QSAR) of TGR5 agonists. The predictive ability of the resulting model is evaluated using an external set of compounds with known TGR5 activity, and six bile acid derivatives whose unknown TGR5 activity is herein assessed with in vitro luciferase assay of cAMP formation. The results show a good predictive model and indicate a statistically relevant degree of correlation between the TGR5 activity and the molecular interaction fields produced by discrete positions of the bile acid scaffold. This information is instrumental to extend on a quantitative basis the current structure-activity relationships of bile acids as TGR5 modulators and will be fruitful to design new potent and selective agonists of the receptor.     

Artarborol, a nor-caryophyllane sesquiterpene alcohol from Artemisia arborescens. stereostructure assignment through concurrence of NMR data and computational analysis

A nor-caryophyllane derivative, artarborol, has been isolated from wormwood (Artemisia arborescens) and its stereostructure established by using a combination of chemical derivatization, NMR data, molecular modeling, and quantum-mechanical calculations. In particular, comparison of experimental 13C NMR data with a Boltzmann-weighed average of 13C NMR chemical shifts, calculated by ab initio DFT method, supported the stereochemical assignment.     

Nearest-neighbor oxygen distances in liquid water and ice observed by x-ray Raman based extended x-ray absorption fine structure

We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 A for water and 2.76 A for ice) but a slightly shorter peak position (2.70 A for water and 2.71 A for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water.     

Methoxycarbonylation of olefins catalyzed by palladium complexes bearing P,N-donor ligands

The methoxycarbonylation of alkenes catalyzed by palladium(II) complexes with P,N-donor ligands, 2-(diphenylphosphinoamino)pyridine (Ph2PNHpy), 2-[(diphenylphosphino)methyl]pyridine (Ph2PCH2py), and 2-(diphenylphosphino)quinoline (Ph2Pqn) has been investigated. The results show that the complex [PdCl(PPh3)(Ph2PNHpy)]Cl or an equimolar mixture of [PdCl2(Ph2PNHpy)] and PPh3, in the presence of p-toluensulfonic acid (TsOH), is an efficient catalyst for this reaction. This catalytic system promotes the conversion of styrene into methyl 2-phenylpropanoate and methyl 3-phenylpropanoate with nearly complete chemoselectivity, 98% regioselectivity in the branched isomer, and high turnover frequency, even at alkene/Pd molar ratios of 1000. Best results were obtained in toluene-MeOH (3 : 1) solvent. The Pd/Ph2PNHpy catalyst is also efficient in the methoxycarbonylation of cyclohexene and 1-hexene, although with lower rates than with styrene. Related palladium complexes [PdCl(PPh3)L]Cl (L = Ph2PCH2py and Ph2Pqn) show lower activity in the methoxycarbonylation of styrene than that of the 2-(diphenylphosphinoamino)pyridine ligand. Replacement of the last ligand by (diphenylphosphino)phenylamine (Ph2PNHPh) or 2-(diphenylphosphinoaminomethyl)pyridine (Ph2PNMepy) also reduces significantly the activity of the catalyst, indicating that both the presence of the pyridine fragment as well as the NH group, are required to achieve a high performing catalyst. Isotopic labeling experiments using MeOD are consistent with a hydride mechanism for the [PdCl(PPh3)(Ph2PNHpy)]Cl catalyst.