Polyion complexes formed by monolayers of quaternary ammonium amphiphiles containing the 4-nitro-4'-alkoxy azobenzene chromophore spread at the surface of aqueous solutions of a number of anionic polyelectrolytes were investigated. In general, pi-A isotherms were found to depend on the nature of the polyion present in the subphase, with monolayers of complexes involving polycarboxylates tending to exhibit larger limiting areas than those formed with polysulfonates or polysulfates. Monolayers of the polyion complexes can be transferred to hydrophilic solid substrates to yield Z-type LB films, although some peeling off for more than 10 layers is an impediment. X-ray reflectivity measurements indicate that relatively smooth and uniform films are obtained up to about 10 layers. Average layer thicknesses are, however, significantly smaller than extended molecular lengths, implying that the amphiphiles are strongly inclined from the surface normal. Polarized FT-IR measurements also indicate poor molecular orientation perpendicular to the surface. Preliminary SHG measurements for LB films of two systems, 12Q/CMC-Na and 12Q/PAA, confirm the presence of noncentrosymmetric out-of-plane chromophore ordering. Stable signals are observed for elevated temperatures up to 130 degrees C and for a period of 4 months at room temperature. To the best of our knowledge, this represents the first report of stable SHG in LB films of polyion complexes.

sciences et inge ´nie ´rie des macromole ´cules (CERSIM), De ´partement de chimie, Universite ´Laval, Que ´bec (QC), Canada G1K 7P4

This study is about (1) nanomanufacturing (focusing on microfluidic-assisted nanoprecipitation), (2) advanced colloid characterization (focusing on field flow fractionation), and (3) the possible restructuring of surface disulfides. Disulfides are dynamic and exchangeable groups, and here we specifically focus, first, on their use to introduce biofunctional groups and, second, on their re-organization, which may lead to variable surface chemistries and uncontrolled cell interactions. The particles were obtained via microfluidic-assisted (flowfocused) nanoprecipitation of poly(ethylene glycol)-b-poly(ε-caprolactone) bearing or not a 2-pyridyl disulfide (PDS) terminal group, which quantitatively exchanges with thiols in solution. In this study, we have paid specific attention to size characterization, thereby also demonstrating the limitations of dynamic light scattering (DLS) as a stand-alone technique. By using asymmetric flow field flow fractionation coupled with DLS, static light scattering (SLS), and refractive index detectors, we show that relatively small amounts of >100 nm aggregates (cryogenic transmission electron microscopy and SLS/DLS comparison suggesting them to be wormlike micelles) dominated the stand-alone DLS results, whereas the "real" size distributions picked <50 nm. Our key result is that the kinetics of the conjugation based on PDS−thiol exchange was controlled by the thiol pK a , and this also determined the rate of the exchange between the resulting disulfides and glutathione (GSH). In particular, more acidic thiols (e.g., peptides, where a cysteine is flanked by cationic residues) react faster with PDS, but their disulfides hardly exchange with GSH; the reverse applies to thiols with a higher pK a . Disulfides that resist against restructuring via thiol−disulfide exchange allow for a stable bioconjugation, although they may be bad news for payload release under reducing conditions. However, experiments of both thiol release and nanoparticles uptake in cells (HCT116) show that also the disulfides formed from less-acidic and, therefore, less-reactive, and more exchangeable thiols were stable for at least a few hours even in a GSH-rich (10 mM) environment; this suggests a sufficiently long stability of surface groups to achieve, for example, a cell-targeting effect.

Poly(2‐oxazoline) (POx) based materials have experienced renewed interest, due to their biocompatibility and broad functional diversity. Although research pertaining to cationic ring opening polymerization (CROP) of 2‐oxazoline derivatives spans upwards of 5 decades, modern characterization techniques, specifically Matrix Assisted Laser‐Desorption Ionization—Time of Flight Mass Spectrometry (MALDI‐TOF MS), were not available during early studies to aid in identifying polymer end‐groups. Through careful synthesis and analytical characterization, evidence supports an alternative mode of nucleophilic attack during ammonia termination, with nucleophilic attack occurring at a different site on the terminal oxazolinium than where polymer propagation occurs. Furthermore, investigations employing targeted end‐group modification, in conjunction with MALDI and NMR analysis, determined the structure of the resultant terminal group was a hydroxyethylamino end group. Based on the observed data, a mechanistic explanation for the observed 2‐oxazoline ring‐opening termination is proposed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1303–1312