2D-LC/SEC-(MALDI-TOF)-MS Characterization of Symmetric and Nonsymmetric Biocompatible PEO_<i>m</i>–PIB–PEO_<i>n</i> Block Copolymers

Complex copolymer mixtures can be directly analyzed via multidimensional chromatographic techniques after successful synthesis. High-performance liquid chromatography coupled to size exclusion chromatography (LC/SEC) revealed detailed information on the chemical composition, polymeric structure, and molar mass distribution of copolymer mixtures, in particular of symmetric and nonsymmetric α-TEO-ω-PEO telechelic PIB copolymers. A series of azide/alkyne “click” reactions after living polymerization reactions were used to prepare the either symmetric or nonsymmetric PIB–PEO-based triblock copolymers of the general structure (PEO_<i>n</i>–PIB–PEO_<i>m</i> BCPs (with <i>n</i> = 3; <i>m</i> = 3, 12, or 17)). In order to demonstrate the efficiency of the “click” reaction and thus the purity of the final triblock copolymers, the critical conditions of the PIB-homopolymers (<i>M</i>_n = 3–30 kg mol^–1) in the isocratic elution mode (LCCC) were investigated. Thus, it was possible to separate the final polymers from their intermediates using a reversed-phase Atlantis-RP C18 column as stationary phase and a mixture of methyl-<i>tert</i>-butyl ether/methanol (85.34/14.66 (w/w)) as mobile phase. On the basis of the PEO segment length and overall hydrophobicity of the BCPs, we observed a complete separation of the stepwise “click” products. Finally, direct coupling of the 2D-LC/SEC to (MALDI-TOF) mass spectrometric techniques allowed a clear identification of all reaction steps proving the structure of the final symmetric and nonsymmetric triblock copolymers

Phase Changes in Mixed Lipid/Polymer Membranes by Multivalent Nanoparticle Recognition

Selective addressing of membrane components in complex membrane mixtures is important for many biological processes. The present paper investigates the recognition between multivalent surface functionalized nanoparticles (NPs) and amphiphilic block copolymers (BCPs), which are successfully incorporated into lipid membranes. The concept involves the supramolecular recognition between hybrid membranes (composed of a mixture of a lipid (DPPC or DOPC), an amphiphilic triazine-functionalized block copolymer TRI-PEO₁₃-<i>b</i>-PIB₈₃ (BCP <b>2</b>), and nonfunctionalized BCPs (PEO₁₇-<i>b</i>-PIB₈₇ BCP <b>1</b>)) with multivalent (water-soluble) nanoparticles able to recognize the triazine end group of the BCP <b>2</b> at the membrane surface via supramolecular hydrogen bonds. CdSe-NPs bearing long PEO₄₇-thymine (THY) polymer chains on their surface specifically interacted with the 2,4-diaminotriazine (TRI) moiety of BCP <b>2</b> embedded within hybrid lipid/BCP mono- or bilayers. Experiments with GUVs from a mixture of DPPC/BCP <b>2</b> confirm selective supramolecular recognition between the THY-functionalized NPs and the TRI-functionalized polymers, finally resulting in the selective removal of BCP <b>2</b> from the hybrid vesicle membrane as proven via facetation of the originally round and smooth vesicles. GUVs (composed of DOPC/BCP <b>2</b>) show that a selective removal of the polymer component from the fluid hybrid membrane results in destruction of hybrid vesicles via membrane rupture. Adsorption experiments with mixed monolayers from lipids with either BCP <b>2</b> or BCP <b>1</b> (nonfunctionalized) reveal that the THY-functionalized NPs specifically recognize BCP <b>2</b> at the air/water interface by inducing significantly higher changes in the surface pressure when compared to monolayers from nonspecifically interacting lipid/BCP <b>1</b> mixtures. Thus, recognition of multivalent NPs with specific membrane components of hybrid lipid/BCP mono- and bilayers proves the selective removal of BCPs from mixed membranes, in turn inducing membrane rupture. Such recognition events display high potential in controlling permeability and fluidity of membranes (e.g., in pharmaceutics)

Stereochemical Heterogeneity Analysis of Polylactides by Multidimensional Liquid Chromatography

A new and robust high-performance liquid chromatography (HPLC) method that separates poly(lactic acid) (PLA) according to its stereochemical composition is presented. Using this method, poly(l-lactide) incorporating trace amounts of meso-lactide resulting from the racemization is separated from the pristine polymer. To prove this aspect in more detail, a representative poly(l-lactic acid) standard, assumed to be highly homogeneous, was separated using this method. The result showed that this was not the case as a fraction incorporating meso-lactide due to racemization occurring during the synthesis is separated. Employing two-dimensional liquid chromatography (2D-LC), the molar mass differences of the separated species were investigated, and fractions with similar molecular sizes were detected, confirming that the LC separation is solely based on stereochemical heterogeneity. The sample was further fractionated by preparative HPLC, followed by an in-depth analysis of the fractions using homonuclear decoupling in proton nuclear magnetic resonance (1H NMR). Convincing results that unveiled significant differences in the stereochemistry of the isolated PLA fractions were obtained. Subsequent analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) also confirmed oligomer series with different end group structures, indicating that the applied HPLC method is very sensitive to minor variations in stereochemistry and end groups. This integrated approach offers detailed insight into the structural characteristics of PLA polymers, contributing to a better understanding of their composition and potential applications

Controlling the Localization of Polymer-Functionalized Nanoparticles in Mixed Lipid/Polymer Membranes

Surface hydrophobicity plays a significant role in controlling the interactions between nanoparticles and lipid membranes. In principle, a nanoparticle can be encapsulated into a liposome, either being incorporated into the hydrophobic bilayer interior or trapped within the aqueous vesicle core. In this paper, we demonstrate the preparation and characterization of polymer-functionalized CdSe NPs, tuning their interaction with mixed lipid/polymer membranes from 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phophocholine and PIB₈₇-<i>b</i>-PEO₁₇ block copolymer by varying their surface hydrophobicity. It is observed that hydrophobic PIB-modified CdSe NPs can be selectively located within polymer domains in a mixed lipid/polymer monolayer at the air/water interface, changing their typical domain morphologies, while amphiphilic PIB-PEO-modified CdSe NPs showed no specific localization in phase-separated lipid/polymer films. In addition, hydrophilic water-soluble CdSe NPs can readily adsorb onto spread monolayers, showing a larger effect on the molecule packing at the air/water interface in the case of pure lipid films compared to mixed monolayers. Furthermore, the incorporation of PIB-modified CdSe NPs into hybrid lipid/polymer GUVs is demonstrated with respect to the prevailing phase state of the hybrid membrane. Monitoring fluorescent-labeled PIB-CdSe NPs embedded into phase-separated vesicles, it is demonstrated that they are enriched in one specific phase, thus probing their selective incorporation into the hydrophobic portion of PIB₈₇-<i>b</i>-PEO₁₇ BCP-rich domains. Thus, the formation of biocompatible hybrid GUVs with selectively incorporated nanoparticles opens a new perspective for subtle engineering of membranes together with their (nano-) phase structure serving as a model system in designing functional nanomaterials for effective nanomedicine or drug delivery

Spotlight on Excitonic Coupling in Polymorphic and Textured Anilino Squaraine Thin Films

Structural diffraction analysis of an anilino squaraine with <i>branched</i> isobutyl side chains shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing as Coulombic molecular H-(J)-aggregates supporting Davydov splitting. Pictures of projected Davydov components in oriented thin films fit well to polarization resolved spectro-microscopy and crossed-polarized light microscopy investigations. By comparison with literature on anilino squaraines with <i>linear</i> alkyl side chains, we point out a general trend for steering the thin film excitonic properties by simple side chain and/or processing condition variation. Combined with the ability to locally probe the direction of transition dipole moments, this adds value to the rational design of functional thin films for optoelectronic applications, especially envisioning ultrastrong light–matter interactions