Synthesis, reactivity, and ligand properties of a stable alkyl carbene

Stable tert-butyl diisopropylamino carbene is more nucleophilic but also more electrophilic than diamino carbenes; it undergoes cyclopropanation reactions and easily binds to metal fragments.     

A new route to aristocularine alkaloids: total synthesis of aristoyagonine

A short and efficient synthesis of aristocularines, involving the sequential construction of phosphorylated 4-alkoxyisoindolinones, Horner-type reaction, and ultimate cyclization by diaryl ether coupling, is disclosed. The success of this new conceptual approach is demonstrated by the total synthesis of the aristocularine alkaloid aristoyagonine.     

X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.     

Modeling of submicrometer aerosol penetration through sintered granular membrane filters

We present a deep-bed aerosol filtration model that can be used to estimate the efficiency of sintered granular membrane filters in the region of the most penetrating particle size. In this region the capture of submicrometer aerosols, much smaller than the filter pore size, takes place mainly via Brownian diffusion and direct interception acting in synergy. By modeling the disordered sintered grain packing of such filters as a simple cubic lattice, and mapping the corresponding 3D connected pore volume onto a discrete cylindrical pore network, the efficiency of a granular filter can be estimated, using new analytical results for the efficiency of cylindrical pores. This model for aerosol penetration in sintered granular filters includes flow slip and the kinetics of particle capture by the pore surface. With a unique choice for two parameters, namely the structural tortuosity and effective kinetic coefficient of particle adsorption, this semiempirical model can account for the experimental efficiency of a new class of "high-efficiency particulate air" ceramic membrane filters as a function of particle size over a wide range of filter thickness and texture (pore size and porosity) and operating conditions (face velocity).     

Comparison of fingerprint-based methods for virtual screening using multiple bioactive reference structures

Fingerprint-based similarity searching is widely used for virtual screening when only a single bioactive reference structure is available. This paper reviews three distinct ways of carrying out such searches when multiple bioactive reference structures are available: merging the individual fingerprints into a single combined fingerprint; applying data fusion to the similarity rankings resulting from individual similarity searches; and approximations to substructural analysis. Extended searches on the MDL Drug Data Report database suggest that fusing similarity scores is the most effective general approach, with the best individual results coming from the binary kernel discrimination technique.     

Synthesis and spectroscopic properties of monocyclic and bicyclic erbium phtalocyanines

Bimacrocyclic and monomacrocyclic erbium phtalocyanines have been synthesized and their luminescence spectra and lifetimes have been studied. The bi-planar structure of ErPc₂ complexes, although interesting at first sight, is non-luminescent because of a strong absorption band near 1.5 μm. However, the luminescence of the erbium ion can be recovered after oxidation or reduction of the macrocycle. Monomacrocyclic erbium phtalocyanines exhibit a strong luminescence of erbium as a result of the energy transfer between the excited phtalocyanine macrocycle and the erbium ion. With a perchlorinated phtalocyanine and a perdeuterated axial ligand in a deuterated solvent, the luminescence lifetime reaches 5 μs, which is the maximum lifetime found for conventional perdeutarated ligands. The large absorption cross-section of phtalocyanine in the red may counterbalance the fast luminescence lifetime, allowing the hope for a new all-organic integrated optical amplifier device.     

Time‐Dependent Density Functional Theory Molecular Dynamics Simulations of Liquid Water Radiolysis

The early stages of the Coulomb explosion of a doubly ionized water molecule immersed in liquid water are investigated with time‐dependent density functional theory molecular dynamics (TD–DFT MD) simulations. Our aim is to verify that the double ionization of one target water molecule leads to the formation of atomic oxygen as a direct consequence of the Coulomb explosion of the molecule. To that end, we used TD–DFT MD simulations in which effective molecular orbitals are propagated in time. These molecular orbitals are constructed as a unitary transformation of maximally localized Wannier orbitals, and the ionization process was obtained by removing two electrons from the molecular orbitals with symmetry 1B₁, 3A₁, 1B₂ and 2A₁ in turn. We show that the doubly charged H₂O²⁺ molecule explodes into its three atomic fragments in less than 4 fs, which leads to the formation of one isolated oxygen atom whatever the ionized molecular orbital. This process is followed by the ultrafast transfer of an electron to the ionized molecule in the first femtosecond. A faster dissociation pattern can be observed when the electrons are removed from the molecular orbitals of the innermost shell. A Bader analysis of the charges carried by the molecules during the dissociation trajectories is also reported.     

Transferable specific scaling factors for interpretation of infrared spectra of biomolecules from density functional theory

A set of transferable local scaling factors is established for assignment of infrared spectra of molecular systems of biological interest experimentally recorded under gas-phase conditions. Each scaling factor is specific for an experimentally observable vibrational mode chosen among those bringing significant structural information. Those factors are provided for harmonic calculations at the DFT B3LYP and DFT B3PW91 levels respectively with 7 and 2 different basis sets. The used training set of neutral molecules comprises nucleobases, aminoacids, peptides, sugars, and neurotransmitters. The proposed specific scaling factors usable for unambiguous conformer assignments lead to typical prediction errors ca. 10 cm(-1) for free and moderately hydrogen-bonded group frequencies with red-shifts up to 200 cm(-1).