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Christian Girard

Publications and source records attributed to Christian Girard.

10 recordsLinked to original sources
PubMed2006

Theoretical near-field optical properties of branched plasmonic nanoparticle networks.

Extended branched networks of single-nanoparticle chains have recently been self-assembled from colloidal suspensions. In particular, gold nanoparticle linear chains and complex chain networks have revealed unique signatures of plasmon modes in their extinction spectra. In this Letter, we investigate theoretically their near-field optical properties and show that a real space mapping of these modes can be achieved with a photon scanning tunneling microscope setup. A distinct subwavelength patterning of the optical near-field gives rise to well-resolved photon scanning tunneling microscope images that can be used to identify the network segments able to efficiently carry optical energy.

Journal Article↗
PubMed2006

Reusable polymer-supported catalyst for the [3+2] Huisgen cycloaddition in automation protocols.

[reaction: see text] A polymer-supported catalyst for Huisgen's [3+2] cycloaddition reaction between azides and alkynes was prepared from copper(I) iodide and Amberlyst A-21. This catalyst was then used in an automated synthesis of 1,4-disubstituted 1,2,3-triazoles giving access to these products in good yields. The catalyst has shown good activity, stability, and recycling capabilities.

Journal Article↗
PubMed2005

Energy transfer in near-field optics.

When the probe tip of a near-field optical microscope illuminates nanoparticles with marked absorption bands, a large number of photons are absorbed before reaching the detector. These energy losses enhance the dark contrast usually observed in the vicinity of metallic nanoparticles. We demonstrate theoretically that this phenomenon can be exploited to image, in the optical frequency range, dissipative domains with a nanometer scale resolution. Simulations performed with noble-metal particles indicate that the detected signal significantly drops down when the excitation frequency is approaching the plasmon resonance of the particles.

Journal Article↗
PubMed2005

Sialyl Lewis(x) analogs based on a quinic acid scaffold as the fucose mimic.

(-)-Quinic acid was used as a starting material for the preparation of sialyl Lewis(x) mimetics in order to target E-selectin. Spatial orientation of the hydroxyl groups of quinic acid could mimic the l-fucose ones. Introduction of a side chain ending with a carboxylic acid was effected to replace the sialic acid interaction at the carbohydrate recognition domain. A first series of derivatives, incorporating amino acids linked to quinic acid, were tested for their affinity and found to interact with E-selectin with IC(50) within the millimolar range.

Cell Adhesion↗
PubMed2005

Three-dimensional reconstruction of basal cell carcinomas.

BACKGROUND: Basal cell carcinoma (BCC) is the most common type of skin cancer. One of the main problems with BCC is the risk of local recurrence of the tumor after treatment. This is mainly due to its irregular outgrowths, which cannot be detected clinically. OBJECTIVE: To better understand the tumor morphology and growth pattern of BCC, we tried to develop a method that provides a precise three-dimensional model of the tumor. METHODS: Because Mohs surgery provides the best overview of the tumor and the tumor margins (both lateral and in depth), the reconstruction was based on slides from Mohs surgery. After digitization and processing of the slides, the tumor was then surrounded by a Mohs surgeon on a computer screen. These selections (lines) were used for a three-dimensional reconstruction of the tumor using MedSurf3D software. RESULTS: This method allows three-dimensional reconstruction of any given BCC. The MedSurf3D software enables visualization of a three-dimensional model of the tissue, which is removed during the surgical procedure. CONCLUSIONS: Three-dimensional reconstruction is a fascinating tool that might improve our understanding of the behavior, growth pattern, and tumor morphology of BCCs. This technique might also be useful in other fields of cutaneous oncology, such as the calculation of the tumor volume of melanomas.

Basal Cell Carcinoma↗
PubMed2002

Synthesis of 3-C-(6-O-acetyl-2,3,4-tri-O-benzyl-alpha-D-mannopyranosyl)-1-propene: a caveat.

During the preparation of 3-C-(6-O-acetyl-2,3,4-tri-O-benzyl-alpha-D-mannopyranosyl)-1-propene, using a published Sakurai-type reaction on the parent methyl glycoside, some observations were made on the sensitivity to reaction conditions that were not previously reported. This Note presents the study of this allylation reaction followed by acetolysis, which ultimately led to the best conditions to obtain the C-glycoside, and on further transformations to yield the corresponding aldehydic and acidic derivatives.

Acetylation↗
PubMed2002

Polarization state of the optical near field.

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric-air interfaces reveals the intricate light-matter interaction that occurs in the near-field zone. From the experimental point of view, access to this information is not direct and can only be extracted from an analysis of the polarization state of the detected light. These polarization states can be calculated by different numerical methods, well suited to near-field optics. In this paper, we apply two different techniques (localized Green's function method and differential theory of gratings) to separate each polarization component associated with both electric and magnetic optical near fields produced by nanometer sized objects. A simple dipolar model is used to get an insight into the physical origin of the near-field polarization state. In a second stage, accurate numerical simulations of field maps complete data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.

Journal Article↗
PubMedDate not supplied

DNA complexing lipopolythiourea.

We present a neutral lipopolythiourea (DTTU) as a potential DNA-binding agent. Light scattering experiments showed that mixing a lipopolythiourea with dipalmitoylphosphatidylcholine (DPPC/DTTU) led to small particles with sizes ranging from 100 to 150 nm at optimum conditions. Setting a fixed DNA amount, an increasing amount of DTTU/DPPC or DPPC lipids was added. Particle size increased only with DTTU/DPPC, indicating that interaction occurred between the DTTU/DPPC particles and DNA. In the same way, only DTTU/DPPC limited the ethidium bromide accessibility to plasmid DNA. These data suggest that DTTU/DPPC liposomes associate to DNA, which was confirmed by agarose gel experiments. To prove the active part of the DTTU lipid itself in DNA compaction, pegoylated-lipid was used. Cholesterol-PEG(2000) alone was not able to condense DNA. In contrast, DTTU/PEG-cholesterol was able to retain plasmid DNA on an agarose gel. In vivo injection of DTTU/DPPC/complexes was studied. Circulation time increase for noncationic particles as compared to cationic. More obvious was the lack of nonspecific accumulation in the lung, where a gain of 3 to 40 fold was measured.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

Fast, easy, and efficient method for the purification of phenolic isomers using a selective solid-phase scavenging process.

The need for fast and efficient purification methods that can be easily handled and moreover automated is considerably increasing with the new techniques of high-throughput chemical synthesis. Following our previous work on the use of simple polymeric scavengers in fast reactions and purifications of organic substances, this article presents the results found during the development of a new method for the purification of phenolic substances. The purification method was found to be regulated by the interaction of acidic phenol groups with a basic polystyrene resin. Furthermore, the scavenging of phenolic isomers proved to be very selective for a given isomer. But the most interesting aspect of this method is that it is based on a simple contact in situ with the resin and that the adsorption/desorption process of the phenol was found to be solvent-dependent. The phenols can thus be freed from impurities, or other isomers, by a simple and fast contact with the resin in the first solvent, filtration, and washings, followed by liberation of the purified phenol by a last soaking in another solvent for desorption. The method was successfully applied to the purification of a crude reaction mixture issued from the Fries rearrangement of phenyl acetate, as well as to small libraries of phenolic derivatives.

Journal Article↗