Optimal diffuse augmented atomic basis sets for extrapolation of the correlation energy

We seek correlation-consistent diffuse-augmented double-zeta and triple-zeta basis sets that perform optimally in extrapolating the correlation energy to the one-electron complete basis set limit, denoted oAVXZ and oAV(X + d)Z. The novel basis sets are method-dependent in that they are trained to perform optimally for the correlation energy at each specific level of theory. They are shown to yield accurate results in calculating both the energy and tensorial properties such as polarizabilities while not significantly altering the Hartree-Fock energy. Quantitatively, complete basis set limit (CBS)-/(oAVdZ,oAVtZ)-extrapolated correlation energies typically outperform, by 3- to 5-fold, the ones calculated with traditional ansatzes of similar flexibility. Attaining energies of CBS/(AVtZ,AVqZ) type or better accuracy, they frequently outperform expensive raw explicitly correlated ones. Promisingly, a limited test on CBS-extrapolated energies based on conventional basis sets has shown that they compare well even with extrapolated explicitly correlated ones. Calculated atomization and dissociation energies, molecular geometries, ionization potentials, and electron affinities also tend to outperform the ones obtained with traditional Dunning's ansatzes from which the new basis sets have been determined. The method for basis set generation is simple, and there is no reason of principle why the approach could not be adapted for handling other bases in the literature.     

Electron transfer in nonpolar solvents in fullerodendrimers with peripheral ferrocene units

Two new fullerodendrimers, with two and four ferrocene units on their periphery, have been synthesized by 1,3-dipolar cycloaddition reactions between the corresponding azomethine ylides and C(60). These new compounds have been studied by using cyclic voltammetry and UV/Vis spectroscopy. Weak intramolecular interactions between the fullerene cage and the ferrocene groups have been found. The photochemical events of both fullerene-ferrocene dendrimers have been probed by means of steady-state and time-resolved techniques. The steady-state emission intensities of the fulleropyrrolidine-ferrocene dendrimers 1 and 2 were found to be quenched relative to the N-methylfulleropyrrolidine without substituents that was used as a model. The nanosecond transient absorption spectral studies revealed efficient charge separation in both systems, even in toluene. The lifetimes of the (C(60))(*-)-(dendron)(*+) are higher for the second-generation fullerodendrimer (with four ferrocene units) and they are of the order of tens of nanoseconds in toluene and hundreds of nanoseconds in polar solvents.     

Unprecedented reactivity pattern of chromium fischer carbene complexes. Direct application to one-pot synthesis of 4-aryl-3,4-dihydrocoumarins on a multigram scale

[reaction: see text] Reaction of alkenyl carbene chromium(0) complexes and ketene acetals triggers the formation of 4-aryl-3,4-dihydrocoumarins. The reaction can be carried out as a simple one-pot protocol in air atmosphere. The huge interest of dihydrocoumarins has prompted us to optimize a multigram-scale process.     

New insights on the behavior of PRODAN in homogeneous media and in large unilamellar vesicles

The behavior of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) was studied in homogeneous media and in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC), using absorption, emission, depolarization, and time-resolved spectroscopies. In homogeneous media, the Kamlet and Taft solvatochromic comparison method quantified solute-solvent interactions from the absorption and emission PRODAN bands. These studies demonstrate that the absorption band is sensitive to the polarity-polarizability (pi) and the hydrogen bond donor ability (alpha) parameters of the media. PRODAN in the excited state is even more sensitive to these parameters and to the hydrogen bond acceptor ability (beta) of the media. The transition energy (expressed in kcal/mol) for both absorption and emission bands gives a linear correlation with the well-known polarity parameter E(T30). The results from the absorption and emission bands also reveal that PRODAN aggregates in water. The monomer has two fluorescence lifetimes, 2.27 and 0.65 ns, while the aggregate has a lifetime of 14.6 ns. Using steady-state anisotropy measurements, the calculated volumes of the aggregate and the monomer are 5590 and 222 mL mol(-1), respectively. In DOPC LUVs, PRODAN undergoes a partition process between the water bulk and the DOPC bilayer. We show that the partition constant (K(p)) value is large enough that only at [DOPC] below 0.15 mg/mL PRODAN in water can be detected. PRODAN dissolved in LUVs at [DOPC] > 1 mg/mL exists completely incorporated in its monomer form and senses two different microenvironments within the bilayer: a polar region in the interface near the water and a less polar and also less viscous environment, between the phospholipid tails. These environments were characterized by their fluorescence lifetimes (tau), showing that PRODAN in the polar microenvironment has a tau value of approximately 4 ns while in the less polar region gives a value of 1.2 ns. Moreover, this probe also senses the micropolarity of these two different regions of the bilayer and yields values similar to that of methanol and tetrahydrofuran.     

On the affinity regulation of the metal-ion-dependent adhesion sites in integrins

Density functional theory and a polarizable continuum model are used to (i) understand the affinity modulating mechanisms of the interaction between the metal-ion-dependent adhesion site (MIDAS) of a selected integrin, lymphocyte function-associated antigen-1 (LFA-1) and a ligand mimetic acetate molecule and to (ii) propose a new, promising family of inhibitors to block the interaction of the integrin with intercellular adhesion molecule-1 (ICAM-1). We quantify the effect of isolated factors, such as the metal coordination, the nature of the ligand or the cation present on the MIDAS, and the effect of the permittivity of the media. We show that the affinity for ligand decreases when metal coordination changes from the open conformation to the closed conformation. In addition, Mn2+ and Zn2+ showed to be good competitors for the octahedrically coordinated Mg2+ and yielded excellent affinity values, whereas Ca2+ in an octahedric environment would decrease the affinity for the ligand. Our affinity studies of the open MIDAS showed that nitronate-derived or carboxylic acid-containing ligands may represent new promising scaffolds of future inhibitors. Finally, we show that affinities are always highly favored by low-dielectric environments, which explains the propensity of MIDAS motifs to be surrounded by hydrophobic residues in integrins and highlights the importance of including hydrophobic groups in the inhibitors.     

IB-01212, a new cytotoxic cyclodepsipeptide isolated from the marine fungus Clonostachys sp. ESNA-A009

IB-01212, a new cytotoxic cyclodepsipeptide featuring C2 symmetry, was isolated from the mycelium extract of Clonostachys sp. ESNA-A009. The amino acid sequence of the compound was determined by spectroscopy techniques. The absolute configuration of the amino acids was determined by a combination of the Marfey and menthol methods. The structure, which was confirmed by comparison of the analytical data for the natural product with a sample obtained by solid-phase peptide synthesis, was revealed to be a cyclic dimer formed by two chains of L-N,N-Me2Leu-L-Ser-L-N-MeLeu-L-N-MePhe bound by the two esters formed between the carboxylic acid of the L-N-MePhe and the hydroxyl function of the L-Ser. IB-01212 is highly cytotoxic to different tumor cell lines.     

Methane activation at low temperature in an acidic electrolyte using PdAu/C,PdCu/C,and PdTiO2/C electrocatalysts for PEMFC

Pd/C, PdAu/C, PdCu/C, and PdTiO₂/C electrocatalysts were prepared by a sodium borohydride reduction process for methane activation at low temperatures in a PEMFC reactor. These electrocatalysts were characterized by XRD, TEM, XPS, ICP-MS, ATR-FTIR, and cyclic voltammetry. The diffractograms of Pd/C, PdAu(50:50)/C, PdCu(50:50)/C, and PdTiO₂(50:50)/C electrocatalysts showed peaks associated with Pd face-centered cubic structure. PdAu(50:50)/C showed a small shift in the peak center when it was compared to Pd/C, while PdCu(50:50)/C showed a shift to higher angles when it was also compared to Pd/C. This effect can be due to the formation of an alloy between Pd and Au, and Pd and Cu. By TEM experiments, a mean nanoparticle size was observed between 6.9 and 8.9 nm for all electrocatalysts. Cyclic voltammograms of Pd/C, PdAu/C, PdCu/C and PdTiO₂/C electrocatalysts showed an increase in current density values after the adsorption of methane The ATR-FTIR experiments showed for all electrocatalysts the formation of methanol and formic acidic. Polarization curves at 80 °C acquired in a PEMFC reactor showed that PdAu(50:50)/C and PdTiO₂(50:50)/C had superior performance when compared to Pd/C, indicating the beneficial effect of adding the co-catalyst; this behavior has been attributed to the bifunctional mechanism or electronic effect.

     

Cacaoidin,First Member of the New Lanthidin RiPP Family

Lantibiotics are ribosomally synthesized and post-translationally modified peptides (RiPPs) characterized by the presence of lanthionine or methyllanthionine rings and their antimicrobial activity. Cacaoidin, a novel glycosylated lantibiotic, was isolated from a Streptomyces cacaoi strain and fully characterized by NMR, mass spectrometry, chemical derivatization approaches and genome analysis. The new molecule combines outstanding structural features, such as a high number of d -amino acids, an uncommon glycosylated tyrosine residue and an unprecedented N,N-dimethyl lanthionine. This latter feature places cacaoidin within a new RiPP family located between lanthipeptides and linaridins, here termed lanthidins. Cacaoidin displayed potent antibacterial activity against Gram-positive pathogens including Clostridium difficile. The biosynthetic gene cluster showed low homology with those of other known lanthipeptides or linaridins, suggesting a new RiPP biosynthetic pathway.     

P-derived organic cations as structure-directing agents: synthesis of a high-silica zeolite (ITQ-27) with a two-dimensional 12-ring channel system

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite, ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on synchrotron powder diffraction data (lambda = 0.8702 A) after the unit cell and space group were determined from tilt electron diffraction experiments on individual microcrystals. The material crystallizes in space group Fmmm, where a = 27.7508(5) A, b = 25.2969(7) A, and c = 13.7923(4) A. The final model, refined by Rietveld methods, comprises seven unique T-sites forming a framework with straight 12-MR channels that are connected by 14-MR openings between them. (Corresponding 12-ring pore dimension is 6.94 A x 6.20 A.) Since access from one 14-MR opening to the next is through the 12-MR channel, the structure is best described as a two-dimensional, 12-MR framework.     

Quantum-sized carbon dots for bright and colorful photoluminescence

We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.