title: Spectroscopic and structural investigation of the confinement of D and L dimethyl tartrate in lecithin reverse micelles.
abstract: The confinement of D and L dimethyl tartrate in lecithin reverse micelles dispersed in cyclohexane has been investigated by FT-IR, polarimetry, electronic and vibrational circular dichroism (ECD and VCD), 1H NMR, and small-angle X-ray scattering (SAXS). Measurements have been performed at room temperature as a function of the solubilizate-to-surfactant molar ratio (R) at fixed lecithin concentration. The analysis of experimental data indicates that the dimethyl tartrate molecules are solubilized within reverse micelles in proximity to the surfactant head groups in the same way for the D and L forms. The encapsulation of dimethyl tatrate within lecithin reverse micelles involves changes in its H-bonds, from what is observed in the pure solid or in CCl4 solutions; this is a consequence of the establishment of specific solute-surfactant headgroup interactions and of confinement effects. In the 0 < or = R < or = 1.7 range, SAXS profiles of dimethyl tartrate/lecithin/ cyclohexane micellar solutions are well-described by a model of interacting polydisperse spherical micellar cores whose mean radius does not change appreciably with R (i.e., it changes from about 18 to 20 angstroms). 1H NMR diffusion measurements of both dimethyl tartrates and lecithin were rationalized in terms of collective translational motions of the entire micellar aggregate and of their molecular diffusion among clusters of reverse micelles. The association of optically active lecithin with D and L dimethyl tartrate leads to the formation of self-organized supramolecular aggregates whose interesting chiroptical features are evidenced by polarimetry and CD.
authors.affiliation: Dipartimento di Scienze Biomediche e Biotecnologie, Università di Brescia, Viale Europa 11, 25123 Brescia, Italy. abbate@.unibs.it
authors.forename: Sergio
authors.initials: S
authors.lastname: Abbate
authors.forename: Franca
authors.initials: F
authors.lastname: Castiglione
authors.forename: France
authors.initials: F
authors.lastname: Lebon
authors.forename: Giovanna
authors.initials: G
authors.lastname: Longhi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Longo
authors.forename: Andrea
authors.initials: A
authors.lastname: Mele
authors.forename: Walter
authors.initials: W
authors.lastname: Panzeri
authors.forename: Angela
authors.initials: A
authors.lastname: Ruggirello
authors.forename: Vincenzo Turco
authors.initials: VT
authors.lastname: Liveri
mesh_terms: D002627:Chemistry, Physical / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004548:Elasticity; D054709:Lecithins / Q000737:chemistry*; D008823:Micelles; D008956:Models, Chemical; D015233:Models, Statistical; D010713:Phosphatidylcholines / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D012212:Rheology / Q000379:methods; D013053:Spectrophotometry / Q000379:methods; D013644:Tartrates / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity
chemical_list: D054709:Lecithins; D008823:Micelles; D010713:Phosphatidylcholines; D013644:Tartrates; D011092:Polyethylene Glycols