The Self-Recognition and Self-Assembly of Folic Acid Salts in Isotropic Water Solution

The self-assembly of alkaline folates in isotropic water solutions, with or without added salts, has been investigated by small-angle neutron-scattering, circular-dichroism, and NMR techniques. The assembled species are chiral, cylindrical aggregates of finite length, composed of stacked tetramers; each tetramer is formed by Hoogsteen-bonded folate residues. The assembly process is more efficient in the presence of an excess of Na^I ions, leading to longer aggregates with stronger tetramer-tetramer-tetramer interaction. In pure water, the rods are shorter and the tetramer-tetramer interaction weaker. Association between folates can be detected by circular-dichroism spectroscopy starting from a concentration of 6· 10^?4 mol l^?1, well below the critical concentration for the formation of the cholesteric mesophase (ca. 0.5 mol l^?1).     

An algebraic version of Demailly's asymptotic Morse inequalities

We give an elementary algebraic proof of some asymptotic estimates (called by Demailly asymptotic Morse inequalities) for the dimensions of cohomology groups of the difference of two ample line bundles on a smooth complex projective variety of any dimension.

     

On the product of two tolerances

Summary In the present note we study the product (composition) of two tolerances; some known results concerning the product of two equivalence relations are generalized to that of two tolerances and new results are obtained via an analysis of possible interactions among them.

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Sunto Nella presente nota si studia il prodotto (composizione) di due tolleranze; alcuni noti risultati sul prodotto di due relazioni di equivalenza vengono generalizzati a quello di due tolleranze, e nuovi risultati sono ottenuti in base ad una analisi delle possibili interazioni tra di esse.

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Partially supported by a grant of italian M.P.I.     

Nucleation barriers in tetrahedral liquids spanning glassy and crystallizing regimes

Crystallization and vitrification of tetrahedral liquids are important both from a fundamental and a technological point of view. Here, we study via extensive umbrella sampling Monte Carlo computer simulations the nucleation barriers for a simple model for tetrahedral patchy particles in the regime where open tetrahedral crystal structures (namely, cubic and hexagonal diamond and their stacking hybrids) are thermodynamically stable. We show that by changing the angular bond width, it is possible to move from a glass-forming model to a readily crystallizing model. From the shape of the barrier we infer the role of surface tension in the formation of the crystalline clusters. Studying the trends of the nucleation barriers with the temperature and the patch width, we are able to identify an optimal value of the patch size that leads to easy nucleation. Finally, we find that the nucleation barrier is the same, within our numerical precision, for both diamond crystals and for their stacking forms.     

Behavioral multi-criteria decision analysis: the TODIM method with criteria interactions

In this paper a multi-criteria decision aiding model is developed through the use of the Choquet integral. The proposed model is an extension of the TODIM method, which is based on nonlinear Cumulative Prospect Theory. The paper starts by reviewing the first steps of behavioral decision theory. A presentation of the TODIM method follows. The basic concepts of the Choquet integral as related to multi-criteria decision aiding are reviewed. It is also shown how the measures of dominance of the TODIM method can be rewritten through the application of the Choquet integral. From the ordering of decision criteria the fuzzy measures of criteria interactions are computed, which leads to the ranking of alternatives. A case study on the forecasting of property values for rent in a Brazilian city illustrates the proposed model. Results obtained from the use of the Choquet integral are then compared against a previously made usage of the TODIM method. It is concluded that significant advantages exist derived from the use of the Choquet integral. The paper closes with recommendations for future research.     

Atomically Precise Metal Nanoclusters: Novel Building Blocks for Hierarchical Structures

Atomically precise ligand-protected nanoclusters (NCs) constitute an important class of compounds that exhibit well-defined structures and, when sufficiently small, evident molecular properties. NCs provide versatile building blocks to fabricate hierarchical superstructures. The assembly of NCs indeed offers opportunities to devise new materials with given structures and able to carry out specific functions. In this Concept article, we highlight the possibilities offered by NCs in which the physicochemical properties are controlled by the introduction of foreign metal atoms and/or modification of the composition of the capping monolayer with functional ligands. Different approaches to assemble NCs into dimers and higher hierarchy structures and the corresponding changes in physicochemical properties are also described.     

Study of anodizing process on aluminium foam to improve the corrosion behavior

Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm² for 60 seconds and 0.01 A/cm² for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H₂SO₄ at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy.     

The Importance of Detail: How Differences in Ligand Structures Determine Distinct Functional Responses in Integrin αvβ3

Ligand-based control of protein functional motions can provide novel opportunities in the study of fundamental biological mechanisms and in the development of novel therapeutics. In this work we addressed the ligand-based modulation of integrin functions. Inhibitors of integrin α_vβ₃ are interesting anticancer agents but their molecular mechanisms are still unclear: Peptides and peptidomimetics characterized by the Arg-Gly-Asp (RGD) or isoAsp-Gly-Arg (isoDGR) binding motifs have shown controversial agonist/antagonist effects. We have investigated the differential mechanisms of integrin activation/deactivation by three distinct ligands (cyclo-RGDf(NMe)V (Cilengitide), cyclo[DKP3-RGD], cyclo[DKP3-isoDGR]; DKP=diketopiperazine) through a comparative analysis of ligand-controlled protein internal dynamics: Although RGD facilitates the onset of dynamic states leading to activation, isoDGR induces a diffuse rigidification of the complex consistent with antagonist activities. Computational predictions have been experimentally probed by showing that the antibody AP5, which is capable of recognizing the active form of integrin, binds specifically to the RGD complexes and not to the isoDGR complex, which supports opposite functional roles of the two motifs targeting the same binding site.     

Contribution of the Purkinje network to wave propagation in the canine ventricle: insights from a combined electrophysiological-anatomical model

The heart includes a specialized conduction system that ensures the necessary activation sequence and timing of the ventricles to produce an effective contraction. The role of this system, called the Purkinje network, during ventricular tachyarrhythmias remains unclear. To understand how the Purkinje network interacts with ventricular muscle, we develop the first combined electrophysiology-structural model of the canine Purkinje network based on microelectrode recordings and a digitized reconstruction of the Purkinje system. For the Purkinje electrophysiology model, we construct a new model of canine Purkinje electrophysiology based on action potentials recorded from canine tissue and designed to reproduce the important phenomenon of alternans. In addition, we use digital photographs of canine ventricular endocardium stained with Lugol’s solution to develop a structural model of the Purkinje network. We combine these electrophysiological and anatomical models of the Purkinje system with a model of canine ventricular electrophysiology to study how the Purkinje network can interact with the ventricular muscle during arrhythmias. Using our combined model, we find that two different results can occur: The long-range connections provided by the Purkinje network can depolarize the tissue more quickly, thereby promoting arrhythmia termination, but if termination does not occur, the Purkinje system can increase the dispersion of refractoriness in the tissue, thereby sustaining the arrhythmia. The different behaviors result from the two competing effects contributed by the Purkinje network: effective reduction in tissue size and increased spatial heterogeneity.