Equivariant Classification of <Emphasis Type="Italic">b</Emphasis><Superscript><Emphasis Type="Italic">m</Emphasis></Superscript>-symplectic Surfaces

Inspired by Arnold’s classification of local Poisson structures [1] in the plane using the hierarchy of singularities of smooth functions, we consider the problem of global classification of Poisson structures on surfaces. Among the wide class of Poisson structures, we consider the class of b^m-Poisson structures which can be also visualized using differential forms with singularities as b^m-symplectic structures. In this paper we extend the classification scheme in [24] for b^m-symplectic surfaces to the equivariant setting. When the compact group is the group of deck-transformations of an orientable covering, this yields the classification of these objects for nonorientable surfaces. The paper also includes recipes to construct b^m-symplectic structures on surfaces. The feasibility of such constructions depends on orientability and on the colorability of an associated graph. The desingularization technique in [10] is revisited for surfaces and the compatibility with this classification scheme is analyzed in detail.     

Fine-tuning ligand-receptor design for selective molecular recognition of dicarboxylic acids

The host-guest interaction between the hexaaza macrocyclic ligand 3,7,11,18,22,26-hexaazatricyclo[26.2.2.2]tetratriaconta-1(31),13(34),14,16(33),28(32),29-hexaene (P3) and three rigid dicarboxylic acids (isophthalic acid, H2is; phthtalic acid, H2ph; and terephthalic acid, H2te) has been investigated using potentiometric equilibrium methods and NMR spectroscopy including the measurement of intermolecular nuclear Overhauser effects (NOEs) and self-diffusion coefficients (D). Ternary complexes are formed in aqueous solution as a result of hydrogen bond formation and Coulombic interactions between the host and the guest. In the [(H6P3)(is)]4+ complex, those bonding interactions reach a maximum yielding a log K6R of 4.74. Competitive distribution diagrams and total species distribution diagrams are used to illustrate the main features of these systems. In particular, a selectivity of over 89% at p[H] = 5.0 is obtained for the complexation of the is versus the te substrates. The recognition capacity of P3 over dicarboxylic acids (da) is compared to the related hexaaza macrocycle Me2P3 (7,22-dimethyl-3,7,11,18,22,26-hexaazatricyclo[26.2.2.2]tetratriaconta-1(30),13,15,28,31,33-hexaene) that binds da with a lesser strength, and it is not selective. Theoretical calculations performed at molecular dynamics level have also been carried out and point out that the origin of selectivity is mainly due to the capacity of the P3 ligand receptor to adapt to the geometry of the dicarboxylic acid to form relatively strong hydrogen bonds.     

Simultaneous EEG-fMRI acquisition: how far is it from being a standardized technique?

Simultaneous EEG–fMRI is a powerful tool to study spontaneous and evoked brain activity because of the complementary advantages of the two techniques in terms of temporal and spatial resolution. In recent years, a significant number of scientific works have been published on this subject. However, many technical problems related to the intrinsic incompatibility of EEG and MRI methods are still not fully solved. Furthermore, simultaneous acquisition of EEG and event-related fMRI requires precise synchronization of all devices involved in the experimental setup. Thus, timing issue must be carefully considered in order to avoid significant methodological errors.

The aim of the present work is to highlight and discuss some of technical and methodological open issues associated with the combined use of EEG and fMRI. These issues are presented in the context of preliminary data regarding simultaneous acquisition of event-related evoked potentials and BOLD images during a visual odd-ball paradigm.     

Ultrathin Films of Porous Metal–Organic Polyhedra for Gas Separation

Ultrathin films of a robust Rh^II-based porous metal–organic polyhedra (MOP) have been obtained. Homogeneous and compact monolayer films (ca. 2.5 nm thick) were first formed at the air–water interface, deposited onto different substrates and characterized using spectroscopic methods, scanning transmission electron microscopy and atomic force microscopy. As a proof of concept, the gas separation performance of MOP-supported membranes has also been evaluated. Selective MOP ultrathin films (thickness ca. 60 nm) exhibit remarkable CO₂ permeance and CO₂/N₂ selectivity, demonstrating the great combined potential of MOP and Langmuir-based techniques in separation technologies.     

Palladium(0)-catalyzed allylation of 4(5)-substituted imidazoles, 5(6)-substituted benzimidazoles,benzotriazole and 5(6)-methylbenzotriazole

Pd(0)-Catalyzed allylations of 4(5)-nitroimidazole, 1 , 2-methyl-4(5)-nitroimidazole, 2 , 4(5)-bromo-imidazole, 7 , 4(5)-methoxyimidazole, 10 , 5(6)-nitrobenzimidazole, 16a , 5(6)-methylbenzimidazole, 16b , benzotriazole, 19 , and 5(6)-methylbenzotriazole, 22 , were studied under several reaction conditions. Nitroimidazoles 1 and 2 were regioselectively allylated under thermodynamic control, leading to 1-allyl-4-nitro derivatives.     

α‐methylene‐γ‐butyrolactones: versatile skin bioactive natural products

Natural products containing an α‐methylene‐γ‐butyrolactone moiety, mainly of the sesquiterpene type, are widely observed in plants, which upon coming into contact with skin, will induce major skin toxicological side effects or phytodermatitis. Indeed two main dermatological pathologies have been associated with a skin exposure to molecules containing an α‐methylene‐γ‐butyrolactone moiety: allergic contact dermatitis (ACD) and chronic actinic dermatitis (CAD). ACD is an immunologically based disease resulting from modifications of epidermal proteins by sensitizers or haptens. Indeed, α‐methylene‐γ‐butyrolactones are highly electrophilic structures that can act as Michael acceptors towards nucleophilic residues of proteins. Cysteine and lysine are the most modified residues leading, in the case of enantiomerically pure lactones, to the formation of diastereomeric adducts. This chemical enantioselectivity induces an enantiospecificity of the allergic reaction, i.e., an individual sensitized to one enantiomer will not develop clinical symptoms when exposed to the other enantiomer and vice versa. Sesquiterpene lactones have been also associated with another pathology that involves UV irradiation and DNA modifications. Interestingly, it was found that α‐methylene‐γ‐butyrolactones, in addition to their electrophilic properties, were highly photoreactive molecules able to react with thymine/thymidine to form [2 + 2] photoadducts in very high yields. In all cases a syn regioselectivity was observed, probably associated with the polarization of the exomethylenic bond. This high photoreactivity of α‐methylene‐γ‐butyrolactones towards thymidine could be an explanation of the progressive evolution of allergic contact dermatitis towards chronic actinic dermatitis. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 000–000; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900013     

Three-dimensional opal-like silica foams

The synthesis of novel meso-/macroporous SiO2 monoliths by combining a nano-building-blocks-based approach with the confined geometry of a tailored air-liquid foam structure is described. The resulting macrostructure in which ordered close-packed colloidal silica nanoparticles constitute the monolith's scaffolds very closely resembles the tailored periodic air-liquid foam template. The void spaces between adjacent particles create textural mesoporosity; therefore, the as-prepared silica networks are characterized by hierarchical porosity at the macroscopic and mesoscopic length scales. The fine-tuning of both the liquid foam's fraction and the bubble size allows a rational design over the macroscopic cell morphologies (shape, Plateau border's length, and width). Striking results of this approach are the weak shrinkage of the as-synthesized opal-like scaffolds during the thermally induced sintering process and, in contrast with previous studies, the formation of closed-cell structures. Particle organization and the foam film surface roughness are investigated by atomic force microscopy (AFM), showing the influence of the liquid flow, within the foams' Plateau borders and films, on the final assemblies.     

Contrast reversal and shape changes of atomic adsorbates measured with scanning tunneling microscopy

Systematic, quantitative comparisons between scanning tunneling microscopy (STM) experiments and first principles simulations of O(2 x 2)/Ru(0001) have been performed. The shape of the atomic adsorbates in the images depends strongly on the tunneling resistance and changes reversibly from circular (high resistance) to triangular (low resistance). In addition, after adsorption of oxygen on the STM tip we observe a contrast reversal on the surface, confirmed by extensive numerical simulations.     

How similar is a molecule to another? An electron density measure of similarity between two molecular structures

A matching measure between two molecular structures based on density functions is described. Some examples related with an alarm pheromone activity are given; the results encourage the possible use of similarity density concepts in molecular engineering.     

Mathematical basis of approximate MO theories: Origin of mulliken's magic formula

The mathematical basis for the Ruedenberg's and Mulliken's approximations is given in a general framework.