Reorientation of the helix of the tryptophan-rich gp41W peptide from HIV-1 at interfaces

Ordering and Nonideality of Air-Ionic Liquid Interfaces in Surface Second Harmonic Generation

The air-ionic liquid interface for a series of ionic liquids involving imidazolium cations [C_nmim] with different alkyl chain lengths (n = 2, 4, 6, 8, 10, and 12) and the same [NTf₂] imide anion has been studied by polarization-resolved second harmonic generation (SHG). An increase as a function of the alkyl chain length of the orientational parameter reveals the increasing ordering of the air-pure ionic liquid interfaces although it is not possible to disentangle the change in mean tilt angle from a change in the tilt angle probability distribution width. Besides, the study of the air-mixed ([C₁₂mim])_x([C₂mim])_1-x[NTf₂] ionic liquid interface clearly demonstrates the interfacial nonideality of the mixed ionic liquids. The long alkyl chain cation perturbs the interface as seen from the orientational parameter and displaces the short alkyl chain one for bulk mixture contents as low as 10%. At higher long alkyl chain cation bulk mixture contents, the interface behaves close to a pure long alkyl chain ionic liquid.

Unique Vibrational Features as a Direct Probe of Specific Antigen-Antibody Recognition at the Surface of a Solid-Supported Hybrid Lipid Bilayer

Here, we demonstrate how sum frequency generation (SFG), a vibrational spectroscopy based on a nonlinear three-photon mixing process, may provide a direct and unique fingerprint of bio-recognition; This latter can be detected with an intrinsically discriminating unspecific adsorption, thanks to the high sensitivity of the second-order nonlinear optical (NLO) response to preferential molecular orientation and symmetry properties. As a proof of concept, we have detected the biological event at the solid/liquid interface of a model bio-active antigen platform, based on a solid-supported hybrid lipid bilayer (ss-HLB) of a 2,4-dinitrophenyl (DNP) lipid, towards a monoclonal mouse anti-DNP complementary antibody.