supported on alumina. The appearance of all of the products and the disappearance of one of the reactants (OH-) can be simultaneously followed by FTIR.RhC13 has been shown to react with surface O H groups on alumina at 180 "C. The product of this reaction is believed to be Rh3+ bonded to a surface oxygen on alumina. This species is an intermediate in the room-temperature oxidation of CO listed above.Removal of the surface O H groups by reaction with RhC1, dramatically suppresses the reaction of COz with alumina.Acknowledgment. This work has been funded in part by the Office of Naval Research, and the University of Richmond Faculty Research Committee. We thank Dr. John Yates for his helpful comments and for his assistance in designing the experimental setup and Hampton Rexrode for his work on the apparatus construction. Previously a helical model was satisfactorily verified for sodium (NaDC) and rubidium (RbDC) deoxycholate micelles in aqueous solutions by means of SAXS, EXAFS, NMR, ESR, and CD measurements. Here we report the beginning of an analogous study carried out on sodium glycodeoxycholate (NaGDC) and taurodeoxycholate (NaTDC) following the strategy applied to NaDC and RbDC. The crystal structure of NaGDC sesquihydrate, solved by X-ray analysis, provides again a helical model that is compared with those of NaDC, RbDC, and NaTDC. Since it was previously observed that bilirubin-IXa (BR) exhibits a bisignate CD Cotton effect in NaDC aqueous solutions, and it was suggested that the chiral micelles of NaDC interact preferentially or exclusively with one of the two enantiomeric conformers of BR, we have recorded CD spectra of BR in aqueous micellar solutions of the bile salts in order to check the helical models. The spectra show in all cases two large and proximate bands of opposite sign between 400 and 500 nm, which support both our chiral models and the selection of the BR left-handed enantiomer. Moreover, we have accomplished van der Waals energy calculations for the system formed by a NaGDC helix and the left-or right-handed BR molecule to test if the interaction energy is lower for one of the two BR enantiomeric conformers. The results of the calculations seem to indicate that the NaGDC helix binds preferentially the BR molecule with left-handed chirality. Interaction models are proposed. IntroductionStudies carried out on sodium and rubidium deoxycholate (NaDC and RbDC, respectively) following a strategy previously reported' showed that a helical model, observed in the crystal structures of NaDC and RbDC,2v3 describes very satisfactorily the behavior of their micellar aggregates in aqueous solutions.'*e7 The helical structure of the NaDC and RbDC micelles was verified unambiguously by nuclear magnetic resonan~e,'.~ circular dichroism! electron spin resonance! small-angle X-ray scattering,6 and extended X-ray absorption fine structure7 measurements.Subsequently, the investigation of the structure of the sodium taurodeoxycholate (NaTDC) micellar aggregates was undert a k e~? +~ and other helical models were...

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The first interaction between lipoplexes and cells is charge-mediated and not specific. Endocytosis is considered to be the main pathway for lipoplex entry. Upon interaction between lipoplexes and the plasma membrane, intermixing between lipoplex and membrane lipids is necessary for efficient endocytosis. Here we study the mechanism of the different endocytic pathways in lipid-mediated gene delivery. We show that DC-Chol-DOPE/DNA lipoplexes preferentially use a raft-mediated endocytosis, while DOTAP-DOPC/DNA systems are mainly internalized by not specific fluid phase macropinocitosys. On the other hand, most efficient multicomponent lipoplexes, incorporating different lipid species in their lipid bilayer, can use multiple endocytic pathways to enter cells. Our data demonstrate that efficiency of endocytosis is regulated by shape coupling between lipoplex and membrane lipids. We suggest that such a shape-dependent coupling regulates efficient formation of endocytic vesicles thus determining the success of internalization. Our results suggest that tailoring the lipoplex lipid composition to the patchwork-like plasma membrane profile could be a successful machinery of coordinating the endocytic pathway activities and the subsequent intracellular processing.

Abstract. Mr= 1611.3, P2,, a= 19.834(13) (I). The molecules of rubidium deoxycholate form 21 helices mainly stabilized by hydrogen bonds and ion-ion and ion--dipole interactions. The interior of the helix is filled with Rb + ions surrounded by water molecules. The helices have non-polar outer surfaces and pack together through van der Waals interactions. The structure of the helix may be considered as a possible model of a micellar aggregate for some deoxycholic acid alkali-metal salts in aqueous solutions.,