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Séminaires MSC
"Matière et Systèmes Complexes"

                      
Lundi 10 mai 2010 à 11h30
Bâtiment Condorcet, 4ème étage, salle 454 A.

Paolo Peixoto
(LCMC, Université Paris 6)

Collagen I – Liquid crystal phases

Collagen I is a lyotropic semi-flexible polymer composed of three polypeptide chains (about 1000 aminoacids each) structured in a right handed super helix. It is the major structural protein of the body, where it is found as fibrils elements. Those fibrils are found organized in a hierarchical manner in the extra-cellular matrix of several tissues (bone, tendon, cornea and sclera, etc.). It is already known that collagen I is capable of forming cholesteric liquid crystalline phases that once stabilized by a pH increase, mimic the organization of the organic extracellulaire matrix in bone.

In the present work, we have analysed physicochemical ways to modulate the organizations obtained in this liquid state. Using SHG (second harmonic generation) coupled to multi-photon excited fluorescence, we have studied the effect of different physico-chemical parameters over a large concentration range. We have shown strong dependence of acetic acid concentration over cholesteric pitch and phase transition. We have studied the dependence of the cholesteric pitch upon ionic force and discussed cholesteric pitch origin based on the lastest theories. The most exciting result is the evidence of phase transition from cholesteric to smectic with twist grain boundaries.