Magnetic–fluorescent Langmuir–Blodgett films of fluorophore-labeled ferritin nanoparticles

We have covalently coupled fluorophore 4-(2-hydroxyethoxy)-7-nitro-2,1,3-benzoxadiazole (NBD) to the external ferritin shell through lysine residues. An increase in the luminescence quantum yield of the fluorescent ferritin particles and a blue shift in its emission peak compared to individual fluorophore were observed. The study of the particles by transmission electron microscopy showed that the native iron core ferritin is intact and that no degradation occurs during chemical functionalization of the protein shell. The NBD-labeled ferritin particles are water soluble, which allowed their controlled deposition by the Langmuir–Blodgett (LB) technique. Superparamagnetic and fluorescent properties of the particles are preserved within the LB film.     

Struggle for space: viral extinction through competition for cells

The design of protocols to suppress the propagation of viral infections is an enduring enterprise, especially hindered by limited knowledge of the mechanisms leading to viral extinction. Here we report on infection extinction due to intraspecific competition to infect susceptible hosts. Beneficial mutations increase the production of viral progeny, while the host cell may develop defenses against infection. For an unlimited number of host cells, a feedback runaway coevolution between host resistance and progeny production occurs. However, physical space limits the advantage that the virus obtains from increasing offspring numbers; thus, infection clearance may result from an increase in host defenses beyond a finite threshold. Our results might be relevant to devise improved control strategies in environments with mobility constraints or different geometrical properties.     

The importance of selection rate in the evolution of cooperation

How cooperation emerges in human societies is still a puzzle. Evolutionary game theory has been the standard framework to address this issue. In most models, every individual plays with all others, and then reproduces and dies according to what she earns. This amounts to assuming that selection takes place at a slow pace with respect to the interaction time scale. We show that, quite generally, if selection speeds up, the evolution outcome changes dramatically. Thus, in games such as Harmony, where cooperation is the only equilibrium and the only rational outcome, rapid selection leads to dominance of defectors. Similar non trivial phenomena arise in other binary games and even in more complicated settings such as the Ultimatum game. We conclude that the rate of selection is a key element to understand and model the emergence of cooperation, and one that has so far been overlooked.     

Synthesis of 2-substituted 4-oxo-5-nitropyrimidines from methyl 3-ethoxy-2-nitroacrylate and other reactions

Methyl 3-ethoxy-2-nitroacrylate (MENA) ( 1 ) has been the subject of study for the development of new syntheses leading to nitro-substituted heterocycles.     

Existence, uniqueness, and convergence of the regularized primal-dual central path

In a recent work [J. Castro, J. Cuesta, Quadratic regularizations in an interior-point method for primal block-angular problems, Mathematical Programming, in press (doi:10.1007/s10107-010-0341-2)] the authors improved one of the most efficient interior-point approaches for some classes of block-angular problems. This was achieved by adding a quadratic regularization to the logarithmic barrier. This regularized barrier was shown to be self-concordant, thus fitting the general structural optimization interior-point framework. In practice, however, most codes implement primal-dual path-following algorithms. This short paper shows that the primal-dual regularized central path is well defined, i.e., it exists, it is unique, and it converges to a strictly complementary primal-dual solution.     

The pattern of distribution of amino groups modulates the structure and dynamics of natural aminoglycosides: implications for RNA recognition

Aminoglycosides are clinically relevant antibiotics that participate in a large variety of molecular recognition processes involving different RNA and protein receptors. The 3-D structures of these policationic oligosaccharides play a key role in RNA binding and therefore determine their biological activity. Herein, we show that the particular NH2/NH3(+)/OH distribution within the antibiotic scaffold modulates the oligosaccharide conformation and flexibility. In particular, those polar groups flanking the glycosidic linkages have a significant influence on the antibiotic structure. A careful NMR/theoretical analysis of different natural aminoglycosides, their fragments, and synthetic derivatives proves that both hydrogen bonding and charge-charge repulsive interactions are at the origin of this effect. Current strategies to obtain new aminoglycoside derivatives are mainly focused on the optimization of the direct ligand/receptor contacts. Our results strongly suggest that the particular location of the NH2/NH3(+)/OH groups within the antibiotics can also modulate their RNA binding properties by affecting the conformational preferences and inherent flexibility of these drugs. This fact should also be carefully considered in the design of new antibiotics with improved activity.     

Synthesis, structure, and reactivity of mononuclear RE(I) oximato complexes

Complexes [Re(ONCMe2)(CO)3(bipy)] (1) and [Re(ONCMe2)(CO)3(phen)] (2), synthesized by reaction of the respective triflato precursors [Re(OTf)(CO)3(N-N)] (N-N = bipy, phen) with KONCMe2, feature O-bonded monodentate oximato ligands. Compound [Re(CO)3(phen)(HONCMe2)]BAr'4 (3), with a monodentate N-bonded oxime ligand, was prepared by reaction of [Re(OTf)(CO)3(phen)], HONCMe2, and NaBAr'4. Deprotonation of 3 afforded 2. The oximato complexes reacted with p-tolylisocyanate, p-tolylisothiocyanate, maleic anhydride, and tetracyanoethylene, affording the products of the insertion of the electrophile into the Re-O bond, compounds 4-7. One representative of each type of compound was fully characterized, including single-crystal X-ray diffraction. The reactions of 1 and 2 with dimethylacetylenedicarboxylate were found to involve first an insertion as the ones mentioned above but followed by incorporation of water, loss of acetone, and formation of the charge-separated neutral amido complexes 9 and 10. The structure of 9 and 10 was determined by X-ray diffraction, and key features of their electronic distribution were studied using a topological analysis of the electron density as obtained from the Fourier map.