On covering bridged plane triangulations with balls

We show that every plane graph of diameter 2r in which all inner faces are triangles and all inner vertices have degree larger than 5 can be covered with two balls of radius r. © 2003 Wiley Periodicals, Inc. J Graph Theory 44: 65–80, 2003     

Nombres de Liouville et nombres normauxLiouville numbers and normal numbers

We prove that there exist Liouville numbers which are normal, as well as Liouville numbers which are non-normal to any base. To cite this article: Y. Bugeaud, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 117–120.     

A convergent approach to huperzine A and analogues

We describe a concise and convergent synthesis of (rac)-5-methoxy-6-azatricyclco[7.3.1.0(2,7)]trideca-2(7),3,5,11-tetraen-13-ol, which has the basic ring system of huperzine A, a potent inhibitor of acetylcholinesterase. We also describe the synthesis of the novel system 5-methoxy-6-azatricyclo[7.2.2.0(2,7)]trideca-2(7),3,5-trien-10-one and a series of related systems.     

Total synthesis of anachelin H

[structure: see text] The first total synthesis of anachelin H is reported. Starting from L-Ser, a stereodivergent synthesis of the polyketide fragment resulting in all possible diastereoisomers is described. The alkaloid peptide fragment is prepared via a tellurium-mediated oxidative aza annulation as the key step. Coupling of the fragments gave synthetic anachelin H, which was found to be identical to a sample of the natural product, thus confirming the configuration by total synthesis.     

Aromatic foldamers as scaffolds for metal second coordination sphere design

As metalloproteins exemplify, the chemical and physical properties of metal centers depend not only on their first but also on their second coordination sphere. Installing arrays of functional groups around the first coordination sphere of synthetic metal complexes is thus highly desirable, but it remains a challenging objective. Here we introduce a novel approach to produce tailored second coordination spheres. We used bioinspired artificial architectures based on aromatic oligoamide foldamers to construct a rigid, modular and well-defined environment around a metal complex. Specifically, aza-aromatic monomers having a tethered [2Fe–2S] cluster have been synthesized and incorporated in conical helical foldamer sequences. Exploiting the modularity and predictability of aromatic oligoamide structures allowed for the straightforward design of a conical architecture able to sequester the metal complex in a confined environment. Even though no direct metal complex–foldamer interactions were purposely designed in this first generation model, crystallography, NMR and IR spectroscopy concurred to show that the aromatic oligoamide backbone alters the structure and fluxional processes of the metal cluster.

Wrapping a [2Fe–2S] metal complex in an aromatic foldamer helix is introduced as a new approach to tailor a second coordination sphere.     

Surface organometallic chemistry of main group elements: selective synthesis of silica supported [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+)

The reaction of the Lewis acid B(C(6)F(5))(3) with silanol groups of silica surfaces, dehydroxylated at different temperatures (300, 500, 700, and 800 degrees C), has been investigated in presence of the Br?nsted base NEt(2)Ph. The structure of the resulting modified silica supports [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) (1) has been carefully identified by IR and multinuclear solid-state NMR spectroscopies, isotopic (2)H and (18)O labeling, elemental analysis, molecular modeling, and comparison with synthesized molecular models. Highly dehydroxylated silica surfaces were required to transform selectively each silanol group into unique [triple bond Si-OB(C(6)F(5))(3)](-)[HNEt(2)Ph](+) fragments. For lower dehydroxylation temperatures, two sorts of surface sites were coexisting on silica: the free silanol groups [triple bond SiOH] and the ionic species 1.     

The Structure of Bis[N‐6‐aminopyridyl‐N‐(1S)‐(+)‐10‐camphorsulfonylamino]palladium in the Solid State and in Solution

The complex, bis[N‐6‐aminopyridyl‐N‐(1S)‐(+)‐10‐camphorsulfonylamino]palladium, Pd[(S)‐APCS]₂, 1 , was prepared by reaction of 2‐[(1S)‐(+)‐10‐camphorsulfonamino]‐6‐aminopyridine with PdCl₂ in THF. Complex 1 has been characterized by spectroscopic methods and its structure has been determined by X‐ray crystallography. Crystal data: space group C2, a= 16.082 (2), b = 17.104 (2), c = 13.051 (2)Å, β = 99.95 (1)°, V = 3535.9 (8) ų, Z = 2 with final residuals R1 = 0.0491 and wR2 = 0.0944. Two independent molecules, (S,S)‐Pd[(S)‐APCS]2, 1a , and (R,R)‐Pd[(S)‐APCS]2, 1b , were found in each asymmetric unit, which exchange to each other via a series of nitrogen inversion and C‐C bond rotation. The inversion energy (ΔGc₁^≠) and the energy barrier (δGc₂^≠) were 11.5 ± 0.1 Kcal mol^?1 at 246 K and 9.8 ± 0.1 Kcal mol^?1 at 199 K, respectively, calculated by dynamic NMR data.     

The RHIM of the Immune Adaptor Protein TRIF Forms Hybrid Amyloids with Other Necroptosis-Associated Proteins

TIR-domain-containing adapter-inducing interferon-β (TRIF) is an innate immune protein that serves as an adaptor for multiple cellular signalling outcomes in the context of infection. TRIF is activated via ligation of Toll-like receptors 3 and 4. One outcome of TRIF-directed signalling is the activation of the programmed cell death pathway necroptosis, which is governed by interactions between proteins that contain a RIP Homotypic Interaction Motif (RHIM). TRIF contains a RHIM sequence and can interact with receptor interacting protein kinases 1 (RIPK1) and 3 (RIPK3) to initiate necroptosis. Here, we demonstrate that the RHIM of TRIF is amyloidogenic and supports the formation of homomeric TRIF-containing fibrils. We show that the core tetrad sequence within the RHIM governs the supramolecular organisation of TRIF amyloid assemblies, although the stable amyloid core of TRIF amyloid fibrils comprises a much larger region than the conserved RHIM only. We provide evidence that RHIMs of TRIF, RIPK1 and RIPK3 interact directly to form heteromeric structures and that these TRIF-containing hetero-assemblies display altered and emergent properties that likely underlie necroptosis signalling in response to Toll-like receptor activation.     

The gastroprotective effect of oxycellulose pellets on gastric ulcers

Oxycellulose belongs to the wide range of pharmaceutically and medically used cellulose derivatives unique in its properties of biodegradability, non-toxicity, antioxidative activity, haemostasis supporting, tissue healing improvement, etc. Glycyrrhizin (Gly) represents the most prominent licorice triterpenoid glycoside, which is responsible for its pharmacological activity, and is closely linked to increasing levels of gastroprotective prostaglandins. In order to study the anti-ulcer activity of oxycellulose sodium and Gly, pellets containing only oxycellulose, or in combination with glycyrrhizin, were prepared using an extrusion/spheronization method. The physical properties and in vitro release rate of the prepared pellets were tested. Based on the obtained results, one sample prepared from oxycellulose only, and one containing glycyrrhizin were chosen for in vivo testing. The healing effect of the prepared pellet formulations was evaluated in the acetic acid induced gastric ulcers in rats. The improvement in gastric ulcer healing was documented for myeloperoxidase activity, alkaline phosphatase activity and gastric wall mucin levels using the Alcian blue binding capacity. The tested pellets significantly reduced myeloperoxidase and alkaline phosphatase activity, and increased gastric wall mucus levels compared to the non-treated group. The in vivo tests showed that oral administration of the prepared pellets accelerated the healing of gastric ulcers in rats.     

KINETICS AND MECHANISM OF THE REACTION BETWEEN OLIGOSILOXANES AND P-TRICHLORO-N-DICHLOROPHOSPHORYL MONOPHOSPHAZENE (Cl3P[dbnd]N-POCl2)

Abstract

³¹P NMR investigation has been made of the action of Cl₃P[dbnd]N-POCl₂(I) first on hexamethyldisiloxane (Me₃Si)₂O and then on oligosiloxanes Me₃Si-(OSiMe₂)_n-OSiMe₃ n = 2 and n=3. The reactions were carried out in bulk or in solution with molar ratios siloxane/(I) varying from I to 5. It was demonstrated that only the monosubstitution of a chlorine atom by the -(OSiMe₂)_n,-OSiMe₃ species n = 0, 2, 3 with elimination of trimethylchlorosilane occurred leading to the derivatives Cl₂OP-N[dbnd]PCl₂O(SiMe₂-O)_nSiMe₃ (II). For n=2, 3 the siloxane redistribution reactions were observed by ²⁹Si NMR analysis. A two steps mechanism is proposed. consisting in a nucleophilic substitution, involving a tricoordinate phosphazenium intermediate, followed by the formation of an active ionic centre probably an oxonium ion, arising from the solvatation by the siloxane of this phosphazeniurn ion and /or of (II) leading to the redistribution reactions. The influences of the solvent, of trimethylchlorosilane, of the temperature, and of the addition of a protonated species (MDH) were investigated.