Biomedical subjects

M Blanchard-Desce

Publications and source records attributed to M Blanchard-Desce.

8 recordsLinked to original sources

PubMed2004

Organization and orientation of amphiphilic push-pull chromophores deposited in Langmuir-Blodgett monolayers studied by second harmonic generation and atomic force microscopy.

Orientation and organization of two amphiphilic push-pull chromophores mixed with two phospholipids (dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine) in Langmuir-Blodgett (LB) monolayers are investigated by second harmonic generation. The LB monolayers have also been characterized by atomic force microscopy and UV-vis spectroscopy. The effective molecular orientations and hyperpolarizabilities of the chromophores are studied as a function of the phospholipid concentrations. The experimental results are discussed within the frame of a model of orientational distribution of the chromophores which gives the orientational mean angle and bounds on the orientational disorder. The mean orientation of the chromophores is found to be within 45-55 degrees whereas their hyperpolarizability coefficients, measured with respect to quartz, are estimated to be in the range (0.3-0.7) x 10(-27) esu taking account of the maximal orientational disorder.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2003

Electro-optic response of second-harmonic generation membrane potential sensors.

We quantify and ascertain the nature of the second-harmonic generation (SHG) response of amphiphilic push-pull chromophores to a transmembrane electric field. Our technique is based on the application of an alternating field across labeled giant unilamelar vesicles. For chromophore responses that are purely electro-optic, our technique provides an estimate of photoinduced charge shifts based on the observed dispersion of the field response, in accord with a two-level perturbation theory. These results are applicable to the optimization of membrane potential sensors for SHG microscopy.

Cell Physiological Phenomena↗

PubMed2003

Time-resolved stimulated emission depletion in two-photon excited states.

A new approach to time-resolved fluorescence spectroscopy based on stimulated emission depletion (STED) of two-photon excited states is presented. Combined with time-resolved detection, STED can circumvent orientational averaging constraints and spontaneous emission selection rules inherent in all conventional techniques. Applications of STED to the study of molecular probe dynamics are presented, together with studies of STED dynamics in a new push-push two-photon chromophore.

Humans↗

PubMed2001

A hyperpolar, multichromophoric cyclodextrin derivative: synthesis, and linear and nonlinear optical properties.

A chiral, highly polar, multichromophoric supermolecule has been designed by gathering seven push-pull chromophores onto a beta-cyclodextrin assembling unit through covalent flexible linkers. The photophysical and nonlinear optical properties of this mutichromophoric conical bundle were investigated and compared with those of the monomeric chromophore. The strongly absorbing multichromophoric system combines interesting features: it has a high molecular first-order hyperpolarisability and a very large dipolar moment (u = 38 D) which reveal a self-arrangement of the dipolar chromophores within the supermolecule. The confinement of the push-pull chromophores within the nanoscopic bundle affects their optical properties and promotes interactions: the multichromophoric supermolecule is hypochromically and hypsochromically shifted with respect to its monomeric analogue. In addition, the close proximity promotes excitonic coupling, as well as excimer formation phenomena.

Circular Dichroism↗

PubMed2001

Coherent scattering in multi-harmonic light microscopy.

By focusing a pulsed laser beam into a sample, harmonic up-conversion can be generated as well as multi-photon excited fluorescence. Whereas multi-photon excited fluorescence microscopy is well established, the use of multi-harmonic generation for three-dimensional image contrast is very recent. Both techniques can provide similar resolution and, for adequate radiating source density, comparable signal levels, allowing them to be combined in a single versatile instrument. However, harmonic generation differs fundamentally from fluorescence generation in that it is coherent and produces radiation patterns that are highly sensitive to phase. As such, multi-harmonic generation microscopy provides a unique window into molecular spatial organization that is inaccessible to fluorescence.

Animals↗

PubMed2000

Intramolecular electron density redistribution upon hydrogen bond formation in the anion methyl orange at the water/1,2-dichloroethane interface probed by phase interference second harmonic generation

Surface second harmonic generation (SSHG) studies of the azobenzene derivative p-dimethylaminoazobenzene sulfonate, often referred as Methyl Orange (MO), at the neat water/1,2-dichloroethane (DCE) interface is reported. The two forms of the anionic MO dye, which are usually observed in bulk solution, with one form being hydrogen bonded to a water molecule through the azo nitrogens (MO/H2O) and the other form not being hydrogen bonded (MO) have also been observed at the water/DCE interface. Their equilibrium constant has been compared with the corresponding bulk solution and found to be identical. The adsorption equilibrium of the two forms has been determined and the Gibbs energy of adsorption measured to be -30 kJmol(-1) for both forms. From a light polarisation analysis of the SH signal, the angle of orientation of the MO transition dipole moment was found to be 34 +/- 2 degrees for MO and 43 +/- 2 degrees for MO/H2O under the assumption of a Dirac delta function for the angle distribution, a difference explained by the different solvation properties of the two forms. Furthermore, the wavelength dependence analysis of these data revealed an interference pattern resulting from the electronic density redistribution within the hydrated anionic form occurring upon the formation of the hydrogen bond with a water molecule. This interference pattern was clearly evidenced with the use of another dye at the interface in order to define a phase reference to both forms of Methyl Orange.

Journal Article↗

PubMed1997

Large molecular third-order optical nonlinearities in polarized carotenoids.

Garito and co-workers have suggested a mechanism to dramatically increase the second hyperpolarizability, gamma, in linear pi-electron-conjugated molecules. Polarization is introduced that leads to a difference between the dipole moments of the molecule's ground state and excited state. Here a series of carotenoids was examined that had increasing intramolecular charge transfer (ICT) from the polyenic chain to the acceptor moiety in the ground state, and gamma was measured for these compounds as a function of wavelength by third-harmonic generation. The compound with the greatest ICT exhibited a 35-fold enhancement of gammamax (the gamma measured at the peak of the three-photon resonance) relative to the symmetric molecule beta-carotene, which itself has one of the largest third-order nonlinearities known. Stark spectroscopic measurements revealed the existence of a large difference dipole moment, Delta mu, between the ground and excited state. Quantum-chemical calculations underline the importance of interactions involving states with large Delta mu.

Carotenoids↗

PubMed1986

Molecular devices: Caroviologens as an approach to molecular wires-synthesis and incorporation into vesicle membranes.

Molecular wires, which would allow electron flow to take place between different components, are important elements in the design of molecular devices. An approach to such species would be molecules possessing an electron-conducting conjugated chain, terminal electroactive polar groups, and a length sufficient to span a lipid membrane. To this end, bispyridinium polyenes of different lengths have been synthesized and their incorporation into the bilayer membrane of sodium dihexadecyl phosphate vesicles has been studied. Since they combine the features of carotenoids and of viologens, they may be termed caroviologens. Vesicles containing the caroviologen whose length approximately corresponds to the thickness of the sodium dihexadecyl phosphate bilayer display temperature-dependent changes of its absorption spectrum reflecting the gel --> liquid-crystal phase transition of the membrane. The data agree with a structural model in which the caroviologens of sufficient length span the bilayer membrane, the pyridinium sites being close to the negatively charged outer and inner surfaces of the sodium dihexadecyl phosphate vesicles and the polyene chain crossing the lipidic interior of the membrane. These membranes may now be tested in processes in which the caroviologen would function as a continuous, transmembrane electron channel-i.e., as a molecular wire. Various further developments may be envisaged along these lines.

Journal Article↗