A Cucurbit[8]uril 2:2 Complex with a Negative pKa Shift

A viologen derivative carrying a benzimidazole group ( V-P-I ²⁺; viologen–phenylene–imidazole V-P-I ) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pK_a, by more than 1 pH unit, contrasting with the positive pK_a shift usually observed for CB-based complexes. Whereas 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P- I ³⁺ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I ³⁺ ⋅ CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pK_a shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalyzing proton transfer or chemical reactions.     

Quantification of curium isotopes in environmental samples: drawbacks,speciation and specific tracer

Journal of Radioanalytical and Nuclear Chemistry - In this study, drawbacks of the use of 243Am as a tracer in order to quantify curium isotopes during a complex chemical procedure were...     

Nitroxydes 91 : β-Cétoénolates nitroxydes

β-Ketoaldehyde derivatives of simple piperidine and pyrrolidine nitroxides as spin labelled ligands give paramagnetic three-electron copper complexes.     

Nitroxydes-LXVIII : Synthese et etude cinetique de la decomposition du t-butyl isopropyl nitroxyde. Effet isotopique

Decomposition of t-butyl isopropyl nitroxide and its β²H-labelled homologue has been examined by UV and EPR. The bimolecular reaction does not show reversible formation of a dimer, but exhibits an isotope effect (k_H/k_d)_30°C?9 which shows that the rupture of the CH bond is involved in the slow step of the decomposition. The β proton coupling constant, determined by NMR, is +1.84 G.     

Impact of carbamylation on type I collagen conformational structure and its ability to activate human polymorphonuclear neutrophils

Carbamylation by urea-derived cyanate is a posttranslational modification of proteins increasing during chronic renal insufficiency, which alters structural and functional properties of proteins and modifies their interactions with cells. We report here the major structural alterations of type I collagen induced by carbamylation. Biophysical methods revealed that carbamylated collagen retained its triple-helical structure, but that slight changes destabilized some regions within the triple helix and decreased its ability to polymerize into normal fibrils. These changes were associated with the incapacity of carbamylated collagen to stimulate polymorphonuclear neutrophil oxidative functions. This process involved their interaction with LFA-1 integrin, but no subsequent p(125)FAK phosphorylation. Carbamylation of collagen might alter interactions between collagen and inflammatory cells in vivo and interfere with the normal remodeling of extracellular matrix, thus participating in the pathophysiological processes occurring during renal insufficiency.     

Hardware Implementation of Discrete Stochastic Arithmetic

In this paper we present a hardware implementation of the Discrete Stochastic Arithmetic (DSA) which is based on CESTAC (Controle et Estimation STochastique des Arrondis de Calculs), a method of controlling round-off errors in floating-point scientific computations. Real-time software implementation of this method suffers from computation bottlenecks. This paper gives a hardware alternative that would significantly accelerate the computation. The proposed architecture is based on a Stochastic Floating-Point Unit (SFPU) which performs discrete stochastic operations. This SFPU has been integrated in a coprocessor, used in a complete System on Chip (SoC).     

Facile synthesis of 1,3-diacetyl-2-methylcyclopentene a versatile synthetic intermediate.

Convenient access to 1,3-diacetyl-2-methylcyclopentene $\text{2}$ is reported by three routes: acetylation of methylcyclopentene ( or cyclohexane), condensation of acetylacetone with 1,2-dibromoethane, and the isomerisation of O-acrtylated dienolate of 1-actyl-2-methylcyclopentene. The process of isomerisation provides best results and its mechanism is discussed.     

Conjugate addition of allylsilanes to α,β-enones. Obtention of cyclobutyl derivatives

By conjugate addition of allylsilanes to α,β-enones, cyclobutyl derivatives are formed.     

A facile route to cyclopentenones by friedel-crafts acylation

Various cyclopentenones are obtained in fair to high yields when ethylenic acyl bromides are condensed with cyclohexene at low temperature. With less reactive reagents, condensation occurs at 0 °C, leading to β-chloro-ketones. A muscone precursor is obtained in two steps with excellent yields.