Dielectric constants of acetonitrile, γ-butyrolactone,propylene carbonate,and 1,2-dimethoxyethane as a function of pressure and temperature

The dielectric constants of 1,2-dimethoxyethane, acetonitrile, -butyrolactone, and propylene carbonate were determined from capacitance measurements extrapolated to infinite frequency; ln are reported as a function of pressure up to 80 MPa at 15, 25, 35, 45°C and as a function of temperature in the range 10 to 50°C at 0.10133 MPa. The variation of ln with temperature or pressure can be expressed by a second order polynomial expression. The isothermal compressibilities of the solvents were determined at 25°C from sound velocities, densities, and heat capacities. A simple correlation can be established between ln /P and for most aprotic solvent.     

Protein matrix elasticity determined by fluorescence anisotropy of its tryptophan residues

Rotational motions of Trp residues embedded within human hemoglobin matrix have been measured by using their steady-state fluorescence anisotropy. The mean square angular displacement theta2 of Trp residues, depending on the temperature, can be expressed by W = 1/2Ctheta2 where W is the thermal energy acting on the Trp residues and C the resilient torque constant of the protein matrix. To study the external medium influencing the protein dynamics, comparative experiments were made with protein in aqueous buffer and in the presence of 32% glycerol. The data show that between 5 degrees C and 25 degrees C, external medium acts on the protein matrix elasticity.     

Dynamic combinatorial carbohydrate libraries: probing the binding site of the concanavalin A lectin

Dynamic combinatorial chemistry (DCC) has emerged as an efficient approach to receptor/ligand identification based on the generation of combinatorial libraries by reversible interconversion of the library constituents. In this study, the implementation of such libraries on carbohydrate-lectin interactions was examined with the plant lectin Concanavalin A as a target species. Dynamic carbohydrate libraries were generated from a pool of carbohydrate aldehydes and hydrazide linker/scaffold components through reversible acylhydrazone exchange, resulting in libraries containing up to 474 constituents. Dynamic deconvolution allowed the efficient identification of the structural features required for binding to Concanavalin A and the selection of a strong binder, a tritopic mannoside, showing an IC(50)-value of 22 microM.     

Crystal Structures of the Lithium Cryptates of Two Macrobicyclic Ligands Containing Pyridine,Bipyridine, and Biisoquinoline Units

The crystal structures of the LiBr complexes of two macrobicyclic ligands, [py.py.bpy] 1 and [py.biqi.biqi] 2 , have been determined. They confirm the cryptate nature of these species. In 3 , the Li⁺ cation is bound in the shallow cavity of a ligand of flattened shape, whereas in 4 , it is buried inside the macrobicycle and surrounded by its three bridges.     

Ruthenium(II) Complex of the Alkaloid 2-Bromoleptoclinidinone. Preparation and Interaction with Double-Stranded DNA

The fused pentacyclic alkaloid 2-bromoleptoclinidinone ( 1 ) isolated from an ascidian possesses a bidentate chelating site. Complexation of 1 with [cis-RuCl₂{(D₈)bpy}₂] · 2H₂O forms an octahedral complex which was isolated both as hexafluorophosphate 2 and chloride 3 salts. Intercalation of 3 in calf-thymus DNA was shown to occur as well as photoactivated cleavage of double-strand supercoiled DNA pBR322 under visible-light irradiation.     

Synthesis of phosphorylated calix[4]arene derivatives for the design of solid phases immobilising uranyl cations

With the aim of developing supports for uranyl cations immobilisation, new 1,3-alternate calix[4]arenes bearing both phosphonic acid functions as chelating sites and N-succinimide-4-oxabutyrate as the anchoring arm were synthesised in good yields. The coupling of such calixarenes to a gel was performed and a successful immobilisation of uranyl cations was obtained.     

Supramolecular Catalysis of Phosphoryl Transfer

Abstract

Reactivity and catalysis represent major features of the functional properties of supramolecular systems. Molecular receptors bearing appropriate functional groups may bind selectively to a substrate, react with it, and release the products. Supramolecular reactivity and catalysis thus involve two main steps: recognition of the substrate followed by transformation of the bound species into products. The design of efficient and selective molecular catalysts may give mechanistic insight into the elementary steps of catalysis, provide new types of chemical reagents, and produce models of reactions effected by enzymes that reveal factors contributing to enzymatic catalysis.     

Trifluoromethyl radical triggered radical cyclization of N-benzoyl ynamides leading to isoindolinones

Science China Chemistry - Under photocatalytic reductive conditions, trifluoromethyl radical addition onto an ynamide followed by cyclization on a benzoyl moiety produces diverse isoindolinone...