Unexpected multiple bond cleavage and rearrangement of organosulfide ligands in the presence of Cu(II) assisted by solvothermal and solvothermal-microwave conditions

An unprecedented in situ multiple bond cleavage of S-S, S-C(sp(2)) and C-N in the pyrimidinedisulfide (pym(2)S(2)) ligand is observed by the reaction of CuCl(2)·2H(2)O with this ligand under solvothermal and solvothermal-microwave conditions. In this process the formation of the compound [Cu(II)(μ-Cl)(Cl)L](2), where L represents the new ligand (L = 2-(pyrimidin-2-ylamino)-1,3-thiazole-4-carbaldehyde), is observed. This ligand has been further isolated and X-ray characterized. The similar reaction carried out under solvothermal-microwave conditions gives, in addition to the latter compound, the complex {9·[Cu(pym(2)S(3))(μ-Cl)(Cl)](2)·[Cu(pym(2)S(2))(μ-Cl)(Cl)](2)}. Coordination of a pyrimidinetrisulfide ligand (pym(2)S(3)) is reported for the first time. This work represents an illustrative example of the novel synthetic perspectives attainable via solvothermal-microwave procedures.     

The Structural Diversity Triggered by Intermolecular Interactions between AuIS2 Groups: Aurophilia and Beyond

The present study is aimed at elucidating the factors that direct the assembly of a specific family of Au^I species. The assembly of Au^I centers and dithiocarboxylato or xanthato ligands results in a surprising structural diversity observed by single‐crystal X‐ray diffraction. However, in solution, just evidences for discrete bimetallic [Au₂L₂] species have been observed. Interestingly, when dithiocarboxylato ligands have been used, a reversible supramolecular assembly has been observed forming the supramolecules of formulae [Au₂L₂]₂ and [Au₂L₂]₃. Initial studies on luminescent properties have been carried out at variable temperature. All the compounds show red emissions in the solid state at very similar energies, suggesting that the intramolecular interactions play a more relevant role in the luminescent properties than the intermolecular ones. The computational studies indicate that not only Au???Au interactions, but also Au???S and S???S ones play a role in the structure and energetic of the supramolecular species, as well as for the choice between supramolecular association or intramolecular oligomerization.     

Non-resonant boundary value problems with singular {\phi} -Laplacian operators

In this paper, using Leray–Schauder degree arguments, critical point theory for lower semicontinuous functionals and the method of lower and upper solutions, we give existence results for periodic problems involving the relativistic operator ${u \mapsto \left(\frac{u^\prime}{\sqrt{1-u^\prime 2}}\right)^\prime+r(t)u}$ with ${\int_0^Tr dt\neq 0}$ . In particular we show that in this case we have non-resonance, that is periodic problem $$\left(\frac{u^\prime}{\sqrt{1-u^\prime 2}}\right)^\prime+r(t)u=e(t),\quad u(0)-u(T)=0=u^\prime(0)-u^\prime(T),$$ has at least one solution for any continuous function ${e : [0, T] \to \mathbb {R}}$ . Then, we consider Brillouin and Mathieu-Duffing type equations for which ${r(t) \equiv b_1 + b_2 {\rm cos} t {\rm and} b_1, b_2 \in \mathbb{R}}$ .     

Hierarchical organization unveiled by functional connectivity in complex brain networks

How do diverse dynamical patterns arise from the topology of complex networks? We study synchronization dynamics in the cortical brain network of the cat, which displays a hierarchically clustered organization, by modeling each node (cortical area) with a subnetwork of interacting excitable neurons. We find that in the biologically plausible regime the dynamics exhibits a hierarchical modular organization, in particular, revealing functional clusters coinciding with the anatomical communities at different scales. Our results provide insights into the relationship between network topology and functional organization of complex brain networks.     

On the complexity of branch‐and‐bound search for random trees

Let T_n be a b‐ary tree of height n, which has independent, non‐negative, identically distributed random variables associated with each of its edges, a model previously considered by Karp, Pearl, McDiarmid, and Provan. The value of a node is the sum of all the edge values on its path to the root. Consider the problem of finding the minimum leaf value of T_n. Assume that the edge random variable X is nondegenerate, has E {X^θ}<∞ for some θ>2, and satisfies bP{X=c}<1 where c is the leftmost point of the support of X. We analyze the performance of the standard branch‐and‐bound algorithm for this problem and prove that the number of nodes visited is in probability (β+o(1))ⁿ, where β∈(1, b) is a constant depending only on the distribution of the edge random variables. Explicit expressions for β are derived. We also show that any search algorithm must visit (β+o(1))ⁿ nodes with probability tending to 1, so branch‐and‐bound is asymptotically optimal where first‐order asymptotics are concerned. ©1999 John Wiley & Sons, Inc. Random Struct. Alg., 14: 309–327, 1999     

Synthesis and characterization of optically active polyamides derived from carbohydrate-based monomers

The synthesis of three new stereoregular AB-type polyamides based on D -ribono-1,4-lactone, L -arabinose, and D -xylose has been carried out by the active ester polycondensation method. These polyamides were characterized by elemental analysis, IR and NMR spectroscopies, and powder X-ray diffraction. They displayed optical activity and had a pronounced affinity to water, although they were not soluble in this solvent. The polyamide obtained from D -ribono-1,4-lactone was highly crystalline and yielded films with spherulitic texture. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3645–3653, 1997     

Synthesis and properties of stereoregular poly(ester amides) derived from carbohydrates

Two poly(ester amides) containing three methoxy groups stereoregularly attached to the main chain have been prepared by using naturally occurring L -arabinose and D -xylose as the starting materials. The polymers were prepared by the active ester polycondensation method and characterized by elemental analysis, IR, and ¹H- and ¹³C-NMR spectroscopies. Both viscosimetry and GPC were used to estimate the molecular weights. The polymers are hydrophilic, one of them being water soluble, and exhibited moderate optical activity. Thermal and X-ray diffraction studies revealed that they are slightly crystalline and stable up to 250°C under nitrogen. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 67–77, 1998     

Toward Understanding the Molecular Recognition of Fungal Chitin and Activation of the Plant Defense Mechanism in Horticultural Crops

Large volumes of fruit and vegetable production are lost during postharvest handling due to attacks by necrotrophic fungi. One of the promising alternatives proposed for the control of postharvest diseases is the induction of natural defense responses, which can be activated by recognizing molecules present in pathogens, such as chitin. Chitin is one of the most important components of the fungal cell wall and is recognized through plant membrane receptors. These receptors belong to the receptor-like kinase (RLK) family, which possesses a transmembrane domain and/or receptor-like protein (RLP) that requires binding to another RLK receptor to recognize chitin. In addition, these receptors have extracellular LysM motifs that participate in the perception of chitin oligosaccharides. These receptors have been widely studied in Arabidopsis thaliana (A. thaliana) and Oryza sativa (O. sativa); however, it is not clear how the molecular recognition and plant defense mechanisms of chitin oligosaccharides occur in other plant species or fruits. This review includes recent findings on the molecular recognition of chitin oligosaccharides and how they activate defense mechanisms in plants. In addition, we highlight some of the current advances in chitin perception in horticultural crops.