Engineering peptides that present selective recognition and high affinity towards a material is a major challenge for assembly-driven elaboration of complex systems with wide applications in the field of biomaterials, hard-tissue regeneration and functional materials for therapeutics. Peptide–material interactions are of vital importance in natural processes, but less exploited for the design of novel systems for practical applications due to poor understanding of mechanisms underlying these interactions. Here, we present an approach based on the synthesis of several truncated peptides issued from a silicon-specific peptide recovered via phage display technology. We use the photonic response provided by porous silicon microcavities to evaluate the binding efficiency of fourteen different peptide derivatives. We identify and engineer a short peptide sequence (SLVSHMQT) revealing the highest affinity towards p+ -Si. The molecular recognition behavior of the obtained peptide fragment can be revealed through mutations enabling identification of the preferential affinity of certain amino acids towards silicon. These results constitute an advance in both the engineering of peptides that reveal recognition properties for silicon and the understanding of biomolecule-material interactions.

STRUCTURE OF VIRAL CAPSIDS AND LANDAU CRYSTALLIZATION THEORY

Viruses are organized biological nanosystems which display high levelof spatial organization. In the present work we focus on the group theory methods application to the problems of virus self-assembly and resulting viral structure formation. The approach is based on the successive application of methods of representation theory for continuous and discrete groups and invariant theory for the groups not-generated by reflections. It generalizes the Landau density wave theory of crystallization to the case of compact crystal-like manifold assembly. To compare the predictions of the theory with the available cryoelectronic microscopy data we use the calculated density distribution functions which generate the protein positions on a spherical surface of the cage protecting viral genome. We also discuss therelation between density distribution functions and viral infectivity.

In their letter, Chakrabarty et al. (1) point out that their data on the relaxation dynamics are inconsistent with the thermodynamic data presented in our paper (2). They argue that from their results and the predictions of the random first-order transition theory (3) one must conclude that our configurational entropy sc is “quantitatively not accurate.” In the following we will show that this conclusion is not necessarily valid.The main argument of Chakrabarty et al. (1) (figure 1, Left, of ref. 1) is that the self part of the intermediate scattering function Fs(k,t) decays to zero even in the glass phase (defined by sc=0) and that hence this phase …

Nanomaterials and solutions: examples and scattering methods for characterization

L’élasticité orientationelle des matrices cristal liquide nématique conduit à l’auto-organisation bidimensionnelle de dispersions colloïdales nématiques à l’échelle du micron [1]. Les mécanismes d’assemblages reposent sur l’existence de paires défauts/particules (dipôles élastiques). Ainsi, une microsphère à ancrage homéotrope, confinée dans une cellule de nématique aligné perturbe le champ du directeur et impose la création d’un défaut topologique. Dans une géométrie plane comme celle d’une cellule à ancrage planaire, le défaut topologique associé à une particule (même de forme quelconque [2]) est localisé à une distance comparable à sa taille. Ce n’est cependant pas le cas dans des géométries complexes comme la géométrie sphérique des coques minces de nématique, où le défaut peut se localiser à grande distance en raison de contraintes topologiques[3]. Nous avons mis en évidence une autre situation physique où les défauts se positionnent également à grande distance des particules en raison d’effets capillaires. Nous avons ainsi étudié des microparticules piégées dans un film nématique mince libre, étalé sur un fluide isotrope. Quand l’épaisseur du film nématique est de l’ordre de la taille des colloïdes, des dipôles élastiques géants sont observés. Pour des particules de 4µm, le défaut point peut ainsi se positionner à une distance supérieure à 100µm de la particule. La taille de ce dipôle élastique géant est contrôlée via l’épaisseur du film. Il existe une épaisseur critique pour laquelle on observe une transition du dipôle élastique classique vers le dipôle géant. Nous avons expliqué l’ensemble des phénomènes en tenant compte des déformations interfaciales du film. L’exploitation de la mesure du retard optique pixel par pixel, permet de mesurer la déformation capillaire autour du colloïde; celle-ci peut-être expliquée dans une approche scalaire simplifiée du problème. Dans un second temps, à profil d’épaisseur du film fixé, la minimisation numérique de l’énergie élastique permet de reproduire les champs directeurs observés. Ce couplage original élasto-capillaire pourrait être utilisé pour contrôler l’assemblage 2D de particules dans des films minces nématiques [4].

Agricultural spraying involves atomizing a liquid stream through a hydraulic nozzle forming a liquid sheet, which is subsequently destabilized into drops. Standard solution adjuvants as dilute oil-in-water emulsions are known to influence the spray drop size distribution. We will present model laboratory experiments that aim to elucidate the physical mechanisms causing the changes of drop size distribution. Model laboratory experiments based on the collision of a liquid drop on a small solid target are used to produce and visualize liquid sheets. With dilute oil-in-water emulsions, the liquid sheet is destabilized by the nucleation and growth of holes within the sheet that perforate it during its expansion. The physical-chemical parameters of the emulsion, such as the emulsion concentration, the chemical nature of the components and the emulsion drop size distribution, are varied to rationalize their influence on the perforation mechanisms. Thanks to an original technique that we recently developed to access the time and space-resolved thickness of the sheet, we measure that the formation of a hole within the sheet is preceded by a localized thinning of the liquid film. We show that this thinning results from the entry and spreading of emulsion oil droplets at the air/water interface. The oil droplet spreading, due to Marangoni driven surface tension gradient, drags subsurface fluid with it. This subsurface flow causes a local film thinning which can ultimately rupture the film. Quantitative analysis of the spreading dynamics unambiguous confirms the physical mechanism at the origin of our observations.