Photoelectron spectroscopy of the molecular anions, Li3O- and Na3O-

The molecular anions, Li(3)O(-) and Na(3)O(-) were produced by laser vaporization and studied via anion photoelectron spectroscopy. Li(3)O(-) and Na(3)O(-) are the negative ions of the super-alkali neutral molecules, Li(3)O and Na(3)O. A two-photon process involving the photodetachment of electrons from the Li(3)O(-) and Na(3)O(-) anions and the photoionization of electrons from the resulting Li(3)O and Na(3)O neutral states was observed. The assignment of the Li(3)O(-) photoelectron spectrum was based on computational results provided by Zein and Ortiz [J. Chem. Phys. 135, 164307 (2011)].     

Gaussian fluctuations in tethered DNA chains

In a recent work [Gao et al., Appl. Phys. Lett. 134, 113902 (2007)], we reported a novel DNA separation method by tethering DNA chains to a solid surface and then stretching the DNA chains with an electric field. The anchor is such designed that the critical force to detach a DNA chain is independent of its length. Because the stretching force is proportional to the DNA net charge, a gradual increase of the electric field leads to size-based removal of the DNA strands from the surface and thus DNA separation. Originally proposed for separation of long double-stranded DNA chains (>10 000 bps), this method has been proven useful also for short single-stranded DNA fragments (<100 bases) for which the fluctuation force induced by the solvent becomes significant. Here we show that the fluctuation force can be approximately represented by a gaussian model for tethered DNA chains. Analytical expressions have been derived to account for the dependence of the fluctuation force on the surface confinement, the polymer chain length, and the DNA tethering potential. The theoretical predictions are found to coincide with experiment.     

Thermal Behavior of Sr(II) and Ba(II)‐Diclofenac Complexes in Solid State: Study of the Dehydration and Thermal Decomposition

Solid state compounds of general formula Sr(Diclof)₂·5.7H₂O and Ba(Diclof)₂·4.8H₂O were obtained. Thermogravimetry (TG), differential scanning calorimetry (DSC), X‐ray diffraction powder patterns and microscopy analysis were used to characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters have been described here. The kinetic behaviors of these stages were evaluated from several heating rates with samples masses of 2 and 5 mg in open crucibles under a nitrogen atmosphere. The results of the present study improve the knowledge on these compounds including their dehydration and thermal stability. The obtained data depend on the mass of the sample which results in two kinetic behavior patterns.     

PA66/PA12/clay based nanocomposites: morphology and physical properties

The structure and the physical properties of several polyamide 66 (PA66)/polyamide 12 (PA12) blends containing different amounts of the two polymers and obtained by melt‐blending have been investigated. A low amount of organically‐modified layered silicate (OMLS, 4 wt%) has also been introduced in order to further improve the physical properties and, in particular, to evaluate its effect on the blends' structure and components' miscibility. The microstructure and morphology of all the composites were analyzed by means of X‐Ray diffraction (WAXD), transmission electron microscopy (TEM), and high resolution scanning electron microscopy (SEM), while the macroscopic scale properties (mechanical behavior and water adsorption) were assessed in order to investigate and understand the materials' structure–properties relationships. The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed. The results also underlined the possibility to tailor the behavior of polymer blends in terms of mechanical water adsorption properties by varying the amount of PA12, added to PA66 with and without the addition of the OLMS. The effectiveness of the clay in modifying the components' miscibility as well as its tendency to segregate preferentially within separate PA66 domains have been assessed. WAXD results showed opposite effects of PA12 and clay on the crystallization behavior of PA66, an aspect that has also been deepened in another paper by the same authors discussing the results of the complete thermal characterization. Copyright © 2010 John Wiley & Sons, Ltd.     

The role of the atomic charges on the ligands and platinum(II) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation

One bond Pt-P coupling constants (1)J(PtP) of a series of cationic complexes [PtXL(PPh(3))(2)](+) (X = NO(3), Cl, Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a-k; or X = Cl, L = NH(3), PhCH(2)NH(2) and (i)PrNH(2), 5a-c) have been used to establish the trans and cis influence sequences of X and pyridines. The crystal structure of compound 4f(BF(4)) with Z = (t)Bu has been resolved. In the pyridine complexes 4a-d (Z = H, variable X), both the trans and cis influence series of the anionic ligands X decrease along the same sequence I > Br > Cl > NO(3), as previously found for [PtX(PPh(3))(3)](+) (X = NO(3), Cl, Br, I, 3a-d), however in 4a-d the cis influence turns out to be more important than the trans. On the contrary, in [PtCl(4-Z-py)(PPh(3))(2)](+) (4b,e-k) the sequence of the trans influence of the 4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me > (t)Bu > NH(2), i.e. the most basic pyridine gives rise to the lowest cis influence. This correlation was found to hold also for complexes 5a-c (L = amines). All the observed trends have been fully reproduced by B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader's Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans influences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon protonation and even more so when coordinated to the [PtCl(PPh(3))(2)](+) moiety. The least negatively charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis influencing pyridine derivative), which gives rise to the lowest positive charge on Pt, confirming the relationship between the lowering of the charge on the metal ion and a high cis influence. The trans influence can be described in terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour of pyridines, the positive charge on the phosphorous atom of free PPh(3) increases upon coordination to Pt(II), moreover the PPh(3) ligands acquire a substantial positive charge, thus efficiently delocalising the charge of the cationic complex.     

Phosphite-oxazole/imidazole ligands in asymmetric intermolecular Heck reaction

We describe the application of a new class of ligands--the phosphite-oxazole/imidazole (L1-L5a-g)--in asymmetric intermolecular Pd-catalyzed Heck reactions under thermal and microwave conditions. These ligands combine the advantages of the oxazole/imidazole moiety with those of the phosphite moiety: they are more stable than their oxazoline counterparts, less sensitive to air and other oxidizing agents than phosphines and phosphinites, and easy to synthesize from readily available alcohols. The results indicate that activities, regio- and enantioselectivities, are highly influenced by the type of nitrogen donor group (oxazole or imidazole), the oxazole and biaryl-phosphite substituents and the axial chirality of the biaryl moiety of the ligand. By carefully selecting the ligand components, we achieved high activities, regio- (up to 99%) and enantioselectivities (up to 99%) using several triflate sources. Under microwave-irradiation conditions, reaction times were considerably shorter (from 24 h to 30 min) and regio- and enantioselectivities were still excellent.     

Multi-component, regio-selective aldol addition of β-ketoesters to aldehydes: scope and applications

Simple and effective multi-component one-pot aldol addition/protection reactions of β-ketoesters to a series of aldehydes in the presence Me(3)SiCl and i-Pr(2)EtN have been described. The analysis of the scope of the reaction revealed a dramatic dependence of the reactivity on the substrates used. Thus the effect of a catalytic amount of DMF and different reaction conditions was widely investigated. Further transformations of the aldol adducts were particularly useful to give valuable diols and compounds with quaternary stereocenters, while X-ray structural analysis gave also important stereochemical information about this challenging reaction.     

Structure and cytotoxicity of phidianidines A and B: first finding of 1,2,4-oxadiazole system in a marine natural product

Two indole alkaloids, phidianidines A (1) and B (2), exhibiting an uncommon 1,2,4-oxadiazole ring linked to the indole system, have been isolated from the marine opisthobranch mollusk Phidiana militaris. The structures of the two metabolites have been elucidated by spectroscopic techniques. Phidianidines exhibit high cytotoxicity against tumor and nontumor mammalian cell lines in in vitro assays.     

A computational approach to design and evaluate enzymatic reaction pathways: application to 1-butanol production from pyruvate

We present a new computational strategy for the design and evaluation of novel enzymatic pathways for the biosynthesis of fuels and chemicals. The approach combines the use of the Biochemical Network Integrated Computational Explorer (BNICE) framework and a structure-based screening method for rapid generation and evaluation of novel enzymatic reactions and pathways. The strategy is applied to a case study of 1-butanol production from pyruvate, which yielded nine novel biosynthetic pathways. Using screening criteria based on pathway length, thermodynamic feasibility, and metabolic flux analysis, all nine novel pathways were deemed to be attractive candidates. To further assess their feasibility of implementation, we introduced a new screening criterion based on structural complementarity using molecular docking methods. We show that this approach correctly reproduces the native binding poses for a wide range of enzymes in key classes related to 1-butanol production and provides qualitative agreement with experimental measures of catalytic activity for different substrates. In addition, we show that the structure-based methods can be used to select specific proteins that may be promising candidates to catalyze novel reactions.