Biomedical subjects

Nathalie Katsonis

Publications and source records attributed to Nathalie Katsonis.

6 recordsLinked to original sources

PubMed2006

Self-organized monolayer of meso-tetradodecylporphyrin coordinated to Au(111).

The structure of molecular monolayers formed at the interface between atomically flat surfaces and a solution of free-base meso-tetradodecylporphyrins (H2Ps) was examined by scanning tunneling microscopy (STM) at the liquid/solid interface. On the surface of graphite (HOPG), H2Ps form a well-ordered monolayer characterized by an oblique unit cell. On Au(111), H2Ps form a self-organized monolayer comprised of two distinct domain types. In both types of domains, the density of the porphyrin cores is increased in comparison to the arrangement observed on HOPG. Also, high-resolution STM images reveal that, in contrast to what is observed on HOPG, physisorption on Au(111) induces a distortion of the porphyrin macrocycle out of planarity. By using X-ray photoelectron spectroscopy, we demonstrate that this is likely to be due to the coordination of the lone pairs of the iminic (-C=N-) nitrogen atoms of the porphyrin macrocycle to Au(111).

Gold↗

PubMed2006

Rotational reorganization of doped cholesteric liquid crystalline films.

In this paper an unprecedented rotational reorganization of cholesteric liquid crystalline films is described. This rotational reorganization results from the conversion of a chiral molecular motor dopant to an isomer with a different helical twisting power, leading to a change in the cholesteric pitch. The direction of this reorganization is correlated to the sign of the change in helical twisting power of the dopant. The rotational reorganization of the liquid crystalline film was used to rotate microscopic objects 4 orders of magnitude larger than the bistable dopants in the film, which shows that molecular motors and switches can perform work. The surface of the doped cholesteric liquid crystalline films was found to possess a regular surface relief, whose periodicity coincides with typical cholesteric polygonal line textures. These surface features originate from the cholesteric superstructure in the liquid crystalline film, which in turn is the result of the presence of the chiral dopant. As such, the presence of the dopant is expressed in these distinct surface structures. A possible mechanism at the origin of the rotational reorganization of liquid crystalline films and the cholesteric surface relief is discussed.

Crystallization↗

PubMed2006

Molecular machines: nanomotor rotates microscale objects.

Nanomachines of the future will require molecular-scale motors that can perform work and collectively induce controlled motion of much larger objects. We have designed a synthetic, light-driven molecular motor that is embedded in a liquid-crystal film and can rotate objects placed on the film that exceed the size of the motor molecule by a factor of 10,000. The changes in shape of the motor during the rotary steps cause a remarkable rotational reorganization of the liquid-crystal film and its surface relief, which ultimately causes the rotation of submillimetre-sized particles on the film.

Journal Article↗

PubMed2003

Substrate-induced pairing in 2,3,6,7,10,11-hexakis-undecalkoxy-triphenylene self-assembled monolayers on Au111.

We present an STM study of self-assembled monolayers of 2,3,6,7,10,11-undecalkoxy-substituted triphenylene (T11) at the n-tetradecane/Au(111) interface under ambient conditions. T11 molecules self-organize as paired rows with molecules lying flat on the surface in an antiparallel position. Three alkyl chains of each T11 molecule align along the 110 direction of the underlying Au(111) substrate. The association of T11 in molecular pairs appears to result from a substrate-induced mechanism governed by the strong anisotropic interaction between T11 alkyl chains and Au(111).

Journal Article↗

PubMed2003

A molecular approach to self-assembly of trimethylsilylacetylene derivatives on gold.

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long-range and highly stable self-assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self-assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n-tetradecane interface. The four TMSA-terminated linear silanes that we synthesized self-assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self-assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self-assembly. Removing the C triple bond C triple bond of TMSA or substituting the Si atom by a C atom also hinders self-assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self-assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi-epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self-assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the <112> direction, and 2) the C triple bond C triple bond of TMSA activates the Si atom and induces the creation of a surface Si-Au chemical bond. The highly stable TMSA-based SAMs appear then as promising materials for applications in surface modification.

Journal Article↗

PubMed2002

Long-range self-assembly of a polyunsaturated linear organosilane at the n-tetradecane/Au(111) interface studied by STM.

We report on the formation of self-assembled monolayers of 13-(trimethylsilyl)-1-tridecene-6,12-diyne [C13H17-Si(CH3)3], an organosilane derivative with a linear polyunsaturated chain, on Au(111) substrates. Molecular resolution STM images recorded at the liquid-solid interface between gold and tetradecane reveal a long-range and densely packed hexagonal lattice with a ( radical3 x radical3)R30 degrees -like structure commensurate against gold adlattice.

Journal Article↗