Buildup of ultrathin multilayer films by a self-assembly process, 1 consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces

An anionic and a cationic bipolar amphiphile containing rigid biphenyl cores were synthesized. The compounds were dissolved in a mixture of dimethylsulfoxide (DMSO) and water and pure water, respectively. When a solid substrate with a positively charged planar surface is immersed in the solution containing the negatively charged bipolar amphiphile, a monolayer of the amphiphile is adsorbed and due to its bipolar structure the surface charge is reversed. After rinsing in pure water the substrate is immersed in the solution containing the positively charged bipolar amphiphile. Again a monolayer is adsorbed but now the original surface charge is restored. By repeating both steps in a cyclic fashion alternating multilayer assemblies of both compounds are obtained. It is demonstrated that multilayer films, composed of at least 35 consecutively alternating layers, which corresponds to a total film thickness of 170 nm can be assembled.     

Synthesis of Polyelectrolytes Bearing Phosphorylcholine Moieties

We report on the modification of the polyelectrolytes poly(L ‐glutamic acid) (PGA), poly(acrylic acid) (PAA), and poly(L ‐lysine) (PLL) with side groups bearing phosphorylcholine (PC) groups. Two different side chains were synthesized from monoamino tri‐ or tetraethylene glycol, both with PC group linked to the OH end: the tert‐butyloxycarbonyl protected compounds BOCNH(EO)_nPC (n = 2, 3) and the succinylated compound SucNH(EO)₃PC. BOCNH(EO)_nPC was deprotected and the resulting amine was condensed with PGA or PAA and SucNH(EO)₃PC was directly coupled to PLL. Degrees of substitution as high as 80% were obtained with the method described. These polyelectrolytes are potential candidates to fabricate multilayers with protein repellent properties.

     

AB initio calculation of the atomic and electronic structure for Sb adsorbed on GaAs(110)

We report results obtained by a systematic study of Sb adsorption on the relaxed GaAs(110) surface, using density-functional theory within the local-density approximation (LDA) and norm-conserving, fully separable, ab-initio pseudopotentials. The GaAs(110) surface is simulated by a slab geometry wherein the atomic structure of the Sb atoms at the preferred adsorption positions and the uppermost substrate layer is optimized by minimizing the total energy, in contrast to previously reported theoretical approaches obtaining the surface bandstructure for given geometrical equilibrium structures. Sb coverages of Q=1/2 and Θ=1 are considered. We give a detailed analysis of the total-energy surface of the Sb/GaAs(110) system and identify stable and metastable adsorption sites. The resulting equilibrium geometries are discussed: We interpret these results in terms of the Sb-Sb interaction within the chains parallel to the [1¯11] direction and of possible structural instabilities in such chains. The atomic positions are compared with results of LEED analysis, stating an overall agreement except the buckling of the chain atoms. The resulting electronic properties (surface bandstructure, photothreshold, Schottky barrier) are discussed within the context of experimental data available from STM, photoemission spectroscopy, etc.     

Rigorous derivation of nonlinear plate theory and geometric rigidityDérivation rigoureuse de la théorie non linéaire des plaques et rigidité géométrique

We show that nonlinear plate theory arises as a Γ-limit of three-dimensional nonlinear elasticity. A key ingredient in the proof is a sharp rigidity estimate for maps $\text{v:(0,1)}{}^3\text{→}\text{R}{}^3$. We show that the L² distance of ?v from a single rotation is bounded by a multiple of the L² distance from the set SO(3) of all rotations. To cite this article: G. Friesecke et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 173–178     

Synthese de cetoses a chaine ramifiee dans la serie du d-fructose et du d-psicose

Stereospecific synthesis of branched-chain 3-C-formyl, 3-C-hydroxymethyl and 3-C-methyl derivatives of d-psicose have been achieved via nucleophilic C-acylation by means of the 1,3-dithian carbanion of 1,2:4,5-di-O-isopropylidene-β-d-erythro-hexo-2,3-diulo-2,6-pyranose 1. Addition of nitromethane to 1 led to d-psicose and d-fructose derivatives 8 and 9.     

Ouverture régiospécifique d'un oxirane preparé á partir du d-xylose par des carbanions soufres: Synthèse de c-nucleosides branches

Two methods using the readily accessible D-xylose have been developed for the synthesis of epoxides 4 and 5. The oxirane 5 was considered as a good intermediate for the preparation of 3'-C-substituted nucleosides. The crucial step for the synthesis of 32 is the regiospecific opening of the epoxide 5 using two carbanions, derived from either dithiane or bis(phenylthio)methane, followed by desulphurisation leading to 17. The exclusive opening of the epoxide in 5 was unequivocally established by ¹³CNMR spectroscopy.     

Determination of the configurations of tertiary alcoholic centers in branched-chain carbohydrate derivatives : PMR spectroscopy with a lanthanide shift-reagent

Examination of the PMR spectral changes (expressed as shift gradients of individual protons) wrought by graduated addition of the paramagnetic lanthanide complex tris [1,1,1,2,2,3,3-heptafluoro- 7,7-dimethyloctane-4,6-dionato]europium(III) [Eu(fod)₃] permitted assignment of the configuration at tertiary alcoholic centers of certain sugar derivatives. The configurations of the tertiary position of 3- C-(1,3-dithian-2-yl)-1,2:5,6-di-O-isopropylidene-α-d-allofuranose (1), lethyl of 4,6-O-benzylidene-2- deoxy-3-C-(dithian-2-yl)-α-d-ribo-hexopyranoside (2) and the corresponding 3-C-butyl compound (2a), and methyl 2-C-(1,3-dithian-2-yl)-3,4-O-isopropylidene-δ-d-ribopyranoside (3) were assigned by comparison with reference spectra. The proton shift-gradients for 5-C-benzoyloxymethyl-2,3-O- cyclohexylidene-1-O-p-tolylsulfonyl-1(R),2(S),3(S),5(R)-cyclohexanetetrol (4), taken in conjunction with the spin-spin coupling values, permit direct assignment of relative stereochemistry in the latter compound.