Investigation of the interface in silica-encapsulated liposomes by combining solid state NMR and first principles calculations

In the context of nanomedicine, liposils (liposomes and silica) have a strong potential for drug storage and release schemes: such materials combine the intrinsic properties of liposome (encapsulation) and silica (increased rigidity, protective coating, pH degradability). In this work, an original approach combining solid state NMR, molecular dynamics, first principles geometry optimization, and NMR parameters calculation allows the building of a precise representation of the organic/inorganic interface in liposils. {(1)H-(29)Si}(1)H and {(1)H-(31)P}(1)H Double Cross-Polarization (CP) MAS NMR experiments were implemented in order to explore the proton chemical environments around the silica and the phospholipids, respectively. Using VASP (Vienna Ab Initio Simulation Package), DFT calculations including molecular dynamics, and geometry optimization lead to the determination of energetically favorable configurations of a DPPC (dipalmitoylphosphatidylcholine) headgroup adsorbed onto a hydroxylated silica surface that corresponds to a realistic model of an amorphous silica slab. These data combined with first principles NMR parameters calculations by GIPAW (Gauge Included Projected Augmented Wave) show that the phosphate moieties are not directly interacting with silanols. The stabilization of the interface is achieved through the presence of water molecules located in-between the head groups of the phospholipids and the silica surface forming an interfacial H-bonded water layer. A detailed study of the (31)P chemical shift anisotropy (CSA) parameters allows us to interpret the local dynamics of DPPC in liposils. Finally, the VASP/solid state NMR/GIPAW combined approach can be extended to a large variety of organic-inorganic hybrid interfaces.     

Access to antigens related to anthrose using pivotal cyclic sulfite/sulfate intermediates

Anthrose is the upstream terminal unit of the tetrasaccharide side chain from a major glycoprotein of Bacillus anthracis exosporium and is part of important antigenic determinants. A novel entry to anthrose-containing antigens and precursors is described. The synthetic route, starting from D(+)-fucose, makes use of intermediates featuring a cyclic sulfite or sulfate function which serves successively as a protecting and a leaving group.     

Carbamazepine on a carbamazepine monolayer forms unique 1D supramolecular assemblies

High-resolution STM imaging of the structures formed by carbamazepine molecules adsorbed onto a pseudo-ordered carbamazepine monolayer on Au(111) shows the formation of previously unreported 1-dimensional supramolecular assemblies.     

A new preparation of samarium dibromide and its use in stoichiometric and catalytic pinacol coupling reactions

A new convenient preparation of samarium dibromide in THF is reported. Pinacol coupling reactions using SmBr₂ in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonyl compounds.     

Response of circular plates to central pulse loading

An analysis is presented for the response of a clamped circular plate subjected to a rectangular pulse uniformly distributed over a central circular area. The plate is rigid-perfectly plastic with yielding according to the Johansen criterion and the associated flow rule. Bending is assumed to be the predominant response. Simple formulas are obtained for the permanent central deflection for all pressures and loaded areas.     

Spectrophotometric determination of calcium in soil extracts with calcichrome

A simple direct method is presented for the spectrophotometric determination of calcium in hydrochloric acid soil extracts. The chromugenic agent used is Calciehrome (self-coupled diazotized H-acid), and the method covers the range 4 to 175 μg of calcium. A comprehensive study of interferences has been carried out. and a cation-exchange procedure described for the preliminary separation of large amounts of phosphate.