Heterofunctional Glycopolypeptides by Combination of Thiol-Ene Chemistry and NCA Polymerization.

Glycopolypeptides are prepared either by the polymerization of glycosylated amino acid N-carboxyanhydrides (NCAs) or by the post-polymerization functionalization of polypeptides with suitable functional groups. Here we present a method for the in-situ functionalization and (co-) polymerization of allylglycine N-carboxyanhydride in a facile one-pot procedure, combining radical thiol-ene photochemistry and nucleophilic ring-opening polymerization techniques, to yield well-defined heterofunctional glycopolypeptides.

Tuning Morphologies of Langmuir Polymer Films Through Controlled Relaxations of Non-Equilibrium States.

Langmuir polymers films (LPFs) frequently form nonequilibrium states which are manifested in a decay of the surface pressure with time when the system is allowed to relax. Monitoring and manipulating the temporal evolution of these relaxations experimentally helps to shed light on the associated molecular reorganization processes. We present a systematic study based on different compression protocols and show how these reorganization processes impact the morphology of LPFs of poly(γ-benzyl-L-glutamate)(PBLG), visualized by means of atomic force microscopy. Upon continuous compression, a fibrillar morphology was formed with a surface decorated by squeezed-out islands. By contrast, stepwise compression promoted the formation of a fibrillar network with a bimodal distribution of fibril diameters, caused by merging of fibrils. Finally, isobaric compression induced in-plane compaction of the monolayer. We correlate these morphological observations with the kinetics of the corresponding relaxations, described best by a sum of two exponential functions with different time scales representing two molecular processes. We discuss the observed kinetics and the resulting morphologies in the context of nucleation and growth, characteristic for first-order phase transitions. Our results demonstrate that the preparation conditions of LPFs have tremendous impact on ordering of the molecules and hence various macroscopic properties of such films.

Emerging bioinspired polymers: glycopolypeptides.

This article highlights the very recent advances in glycopolypeptide synthesis via NCA polymerization and first studies on stimuli-responsive solution behavior and self-assembling structures. Yet glycopolypeptides are almost exclusively considered as smart biofunctional materials for use in biomedical applications, for instance in targeted drug delivery, but also have high potential for usage as structural materials to fabricate bioinspired hierarchical structures.

Stimuli-responsivity of secondary structures of glycopolypeptides derived from poly(L-glutamate-co-allylglycine).

Copolypeptides containing L-glutamate and various amounts of either D-/DL-/L-allylglycine or D-/DL-/L-(3-(ß-D-glucopyranosyl)thio)propylglycine defect units were studied by circular dichroism (CD) and infrared (FT-IR) spectroscopy according to their secondary structures in dependence of pH and temperature. All samples adopt random coil conformation at high pH and α-helix at low pH without evidence for ß-sheet formation. Folding into the α-helix structure is strongly affected by the number and configuration of allylglycine defects (which intrinsically stabilize ß-sheets). Helix folding is facilitated upon the attachment of D-glucopyranose to the L- (but not the D-) allylglycine units, which is attributed to a different secondary structure preference of the L-(3-(ß-D-glucopyranosyl)thio)propylglycine (L: random coil; D: ß-sheet) and a majority rule effect.

pH-responsive bioactive glycopolypeptides with enhanced helicity and solubility in aqueous solution.

Copolypeptides of L-glutamate and glucosylated L-/DL-allyl- or DL-propargylglycine were synthesized by ring-opening polymerization and thiol-ene/yne photochemistry in aqueous solution, allowing the mild introduction of sugar units (here, glucose) in the final step. The glucosylated and non-glucosylated samples adopt a random-coil conformation in neutral and basic media and an α-helical conformation in acidic media, the helical content depending on the number and configuration of allyl-/propargylglycine units. The glucocopolypeptides unveil enhanced helical stability and solubility down to pH 3.5. Turbidity assays proved the selective binding of the polymers to the plant lectin concanavalin A.