Novel selenium-containing non-natural diamino acids

The general synthesis of a new class of non-natural diamino acids, 2-amino-3-[(2′-aminoalkyl)seleno]propanoic acids, or Se-(aminoalkyl)selenocysteines, is reported. Under the conditions devised, enantiopure N-Boc-protected β-l-iodoamines, which are readily generated from proteinogenic α-amino acids, were treated with the selenolate anion obtained from NaBH₄ splitting of the Se-Se bond in commercial l-selenocystine. The Se-alkylation products were enantiomerically pure and the reaction is high yielding (92-98%), without any detectable traces of accompanying by-products.     

Epidemic spreading in scale-free networks

The Internet has a very complex connectivity recently modeled by the class of scale-free networks. This feature, which appears to be very efficient for a communications network, favors at the same time the spreading of computer viruses. We analyze real data from computer virus infections and find the average lifetime and persistence of viral strains on the Internet. We define a dynamical model for the spreading of infections on scale-free networks, finding the absence of an epidemic threshold and its associated critical behavior. This new epidemiological framework rationalizes data of computer viruses and could help in the understanding of other spreading phenomena on communication and social networks.     

Universality class of absorbing phase transitions with a conserved field

We investigate the critical behavior of systems exhibiting a continuous absorbing phase transition in the presence of a conserved field coupled to the order parameter. The results obtained point out the existence of a new universality class of nonequilibrium phase transitions that characterizes a vast set of systems including conserved threshold transfer processes and stochastic sandpile models.     

Novel manganese (III) porphyrin containing peripheral “[RuCl(dppb)(X-bipy)]” cations [dppb = 1,4-bis(diphenylphosphino)butane and X = –CH3, –OMe, –Cl]. X-ray structure of the cis-[RuCl(dppb)(bipy)(4-Mepy)]PF6 complex

New tetraruthenated manganese (III) porphyrins were synthesized and characterized (³¹P NMR, cyclic voltammetry, UV–Vis). This new system presents four units of cationic “[RuCl(dppb)(X-bipy)]⁺”. The electrochemical and catalytic properties of the central manganese (III) show dependence on the characteristics of the peripheral ruthenium complexes as evidenced by the Mn^(III)/Mn^(II) reduction potential.     

A New Approach to The Synthesis of Enantiomerically Pure 4-Deoxy Sugars

In a recent paper² we have reported the design and synthesis of 3-C-lithiated 5,6-dihydro-1,4-dithiin-2-yl[(4-methoxybenzyl)oxy]methane (1) which can be utilized as an allylic alcohol anion equivalent and leads to three-carbon elongations of various electrophiles by introduction of a fully protected hydroxypropenyl moiety. The latter contains a double bond, which can be unravelled to the cis configuration by diastereoselective removal³ of the dimethylene-disulfur bridge, as well as a protected primary hydroxyl group that, depending on the deprotection conditions used (DDQ/NaBH₄ or DDQ), may either lead to the free allylic alcohol or to an α,β-unsaturated aldehyde.     

Mean-Field Analysis of the q-Voter Model on Networks

We present a detailed investigation of the behavior of the nonlinear q-voter model for opinion dynamics. At the mean-field level we derive analytically, for any value of the number q of agents involved in the elementary update, the phase diagram, the exit probability and the consensus time at the transition point. The mean-field formalism is extended to the case that the interaction pattern is given by generic heterogeneous networks. We finally discuss the case of random regular networks and compare analytical results with simulations.     

Reaction-diffusion system with self-organized critical behavior

We describe the construction of a conserved reaction-diffusion system that exhibits self-organized critical (avalanche-like) behavior under the action of a slow addition of particles. The model provides an illustration of the general mechanism to generate self-organized criticality in conserving systems. Extensive simulations in d = 2 and 3 reveal critical exponents compatible with the universality class of the stochastic Manna sandpile model. Received 16 November 2000     

Darstellung und Kristallstrukturen von Dicyanamido(triphenylphosphan)gold(I) und Nitrosodicyanmethanido(triphenylphosphan)gold(I)

Preparation and Crystal Structures of Dicyanamido(triphenylphosphane)gold(I) and Nitrosodicyanomethanido(triphenylphosphane)gold(I) The coordination compounds [(Ph₃P)Au{N(CN)₂}] ( 1 ) and [(Ph₃P)Au{ONC(CN)₂}] ( 2 ) are obtained by the reaction of [Au(PPh₃)]NO₃ with Na[N(CN)₂] or K[ONC(CN)₂] in CH₂Cl₂. The compounds are characterized by IR spectroscopy and by crystal structure determination. 1 crystallizes triclinic in the space group P 1 with a = 930.16(4), b = 1011.89(13), c = 1118.35(16) pm, α = 115.327(10), β = 90.899(8), γ = 103.394(8)°, Z = 2. 2 crystallizes monoclinic in the space group P2₁/n with a = 832.59(10), b = 1139.30(16), c = 2078.9(4) pm, β = 99.84(2)°, Z = 4. The crystal structures of both compounds are built up by pairs of antiparallel oriented molecules with linear coordinated gold atoms and weak intermolecular Au–N‐interactions.     

Velocity and hierarchical spread of epidemic outbreaks in scale-free networks

We study the effect of the connectivity pattern of complex networks on the propagation dynamics of epidemics. The growth time scale of outbreaks is inversely proportional to the network degree fluctuations, signaling that epidemics spread almost instantaneously in networks with scale-free degree distributions. This feature is associated with an epidemic propagation that follows a precise hierarchical dynamics. Once the highly connected hubs are reached, the infection pervades the network in a progressive cascade across smaller degree classes. The present results are relevant for the development of adaptive containment strategies.