Optimal conditions for tandem mass spectrometric sequencing of information-containing nitrogen-substituted polyurethanes.

RATIONALE: To prevent solubility issues faced with sequence-defined polyurethanes, a new family of digital polyurethanes was conceived with the alkyl coding chain held by the carbamate nitrogen (N) atom and CH3 instead of OH as the ϖ termination. This led to different dissociation mechanisms that were explored prior to optimizing tandem mass spectrometric (MS/MS) sequencing. METHODS: N-Substituted polyurethanes (N-R PUs) were dissolved in methanol and subjected to collision-induced dissociation (CID) as deprotonated chains in the negative ion mode, and as ammonium and sodium adducts in the positive ion mode, using electrospray ionization (ESI) as the ionization technique. Their dissociation behavior was thoroughly investigated using a quadrupole time-of-flight (QTOF) instrument in order to provide accurate mass measurements to support proposed fragmentation mechanisms. RESULTS: While O-(CO) bonds were broken in N-H PUs, the CH2 -O linkage between repeating units was cleaved upon CID of N-R PUs. This main process occurred either from deprotonated molecules or from cationized chains but was followed by different rearrangements, producing up to four product ion series. Yet, MS/MS spectra could be drastically simplified for precursor ions having their acidic α group methylated, as was found to spontaneously occur upon storage in methanol. CONCLUSIONS: Using experimental conditions aimed at avoiding any reactive proton in precursor ions (no acidic end-groups and alkali adduction), full coverage sequence of N-R PUs was successfully achieved with the single ion series observed in MS/MS, opening a promising perspective for reading large amounts of information stored in these dyad-encoded polymers.

Damage and Repair in Informational Poly(N-substituted urethane)s.

The degradation and repair of uniform sequence-defined poly(N-substituted urethane)s was studied. Polymers containing an ω-OH end-group and only ethyl carbamate main-chain repeat units rapidly degrade in NaOH solution through an ω→α depolymerization mechanism with no apparent sign of random chain cleavage. The degradation mechanism is not notably affected by the nature of the side-chain N-substituents and took place for all studied sequences. On the other hand, depolymerization is significantly influenced by the molecular structure of the main-chain repeat units. For instance, hexyl carbamate main-chain motifs block unzipping and can therefore be used to control the degradation of specific sequence sections. Interestingly, the partially degraded polymers can also be repaired; for example by using a combination of N,N'-disuccinimidyl carbonate with a secondary amine building-block. Overall, these findings open up interesting new avenues for chain-healing and sequence editing.

Fluorescent PEGulated Oligourethane Nanoparticles for Long-Term Cellular Tracing.

We have introduced a new ABA-type amphiphilic block copolymer consisting of functional oligourethane hydrophobic blocks and two polyethylene glycol (PEG) hydrophilic blocks. The polymer was synthesized in a single step by step-growth polymerization between two monomers, namely tetraphenylethylene (TPE)-diol and hexamehylene di-isocyanate in the presence of a monofunctional impurity PEG-2000. The polymer exhibits facile self-assembly in water by synergistic effects of H-bonding and π-π interaction among the oligourethane core, leading to the formation of robust nanoparticles with remarkable aggregation-induced emission (AIE). These nanoparticles show very low critical aggregation concentration, stability over a large pH window, and excellent biocompatibility as revealed by an MTT assay. Cellular imaging with cancer cells showed facile cellular uptake and, more importantly, retention of AIE in cellular milieu for long times, which was successfully utilized for long-term cancer cell tracking.

Hydrogen-bonding-induced chain folding and vesicular assembly of an amphiphilic polyurethane.

We have reported synthesis and vesicular assembly of a novel amphiphilic polyurethane with hydrophobic backbone and hydrophilic pendant carboxylic acid groups which were periodically grafted to the backbone via a tertiary amine group. In aqueous medium the polymer chain adopted a folded conformation which was stabilized by intrachain H-bonding among the urethane groups. Such a model was supported by concentration and solvent-dependent FT-IR, powder XRD, and urea-mediated "denaturation" experiments. Folded polymer chains further formed vesicular assembly which was probed by dynamic light scattering, TEM, AFM, SEM, and fluorescence microscopic studies, and dye encapsulation experiments. pH-dependent DLS and fluorescence microscopic studies revealed stable polymersome in entire tested pH window of 3.5-11.0. Zeta potential measurements showed a negatively charged surface in basic pH while a charge-neutral surface in neutral and acidic pH. MTT assay with CHO cell line indicated good cell viability.

Ferroelectricity in a hydrogen-bonded alternating donor-acceptor supramolecular copolymer.

This communication reports synergistic H-bonding and charge-transfer (CT) interaction-promoted alternating supramolecular copolymerization of amide-functionalized pyrene (Py) and naphthalene-diimide (NDI) building blocks and the emergence of ferroelectricity with saturation polarization ∼3.2 µC cm-2, Curie temperature ∼304 K, and coercive field ∼8.5 kV cm-1 at 100 Hz. The Py or NDI molecules on their own do not exhibit any ferroelectric hysteresis, indicating an essential role of both CT-interaction and H-bonding in ferroelectricity. Computational studies provide insight into the origin of the polarization and the importance of the NDI/Py ratio. This study, showing room temperature ferroelectricity in purely organic systems, is of high relevance for flexible electronics and sensors. It opens up new opportunities for soft FE-materials with ample scope for further structural optimization.

Self-Assembled Polyurethane Capsules with Selective Antimicrobial Activity against Gram-Negative E. coli.

This article reports the antimicrobial activity of two segmented amphiphilic polyurethanes, PU-1 and PU-2, containing a primary or secondary amine group, respectively. In acidic water, intrachain H-bonding among the urethanes followed by hierarchical assembly resulted in the formation of capsules (Dh = 120 ± 20 and 100 ± 17 nm for PU-1 and PU-2, respectively) with a highly positive surface charge. They showed selective interactions with bacterial cell mimicking liposomes over mammalian cell mimicking liposomes with favorable enthalpy and entropy contributions, which was attributed to the electrostatic interaction and hydrophobic effect. Antimicrobial studies with Escherichia coli revealed very low minimum inhibitory concentration (MIC) values of 7.8 and 15.6 µg/mL for PU-1 and PU-2, respectively, indicating their ability to efficiently kill Gram-negative bacteria. Killing of Gram-positive Staphylococcus aureus was noticed only at C = 500 µg/mL, indicating unprecedented selectivity for E. coli, which was further confirmed by scanning electron microscopy (SEM) studies. Hemolysis assay revealed HC50 values of 453 and 847 µg/mL for PU-1 and PU-2, respectively, which were >50 times higher than their respective MIC values, thus making them attractive antimicrobial materials. Ortho-nitrophenyl-ß-galactoside (ONPG) assay and live-dead fluorescence assay confirmed that for both the polymers, a membrane disruption pathway was operative for wrapping of the bacterial membrane, similar to what was proposed for antimicrobial peptides. SEM images of polymer-treated E. coli bacteria helped in visualization of the pore formation and the disrupted membrane structure.

Synthesis and Self-assembly of a Helical Polymer Grafted from a Foldable Polyurethane Scaffold.

Herein a polyurethane graft poly-l-glutamate amphiphilic copolymer was synthesized from a polyurethane (PU)-based macro-initiator (containing pendant primary amine groups) through the ring opening polymerization of N-carboxy anhydride of γ-benzyl-l-glutamate (BLG-NCA). On average, twenty two l-glutamic acids were grafted from each amino group which was pendant on the polyurethane chain with 10 repeating units. The grafted polymer (PU-PP-1) exhibits self-assembly to produce a hydrogel in a wide pH window ranging from pH 5.0 to 8.0 with a critical gelation concentration (CGC) of 5.0 wt % (w/v) at pH 7.4. Furthermore, circular dichroism study revealed the transition of the α-helix to a random coil upon increasing the pH. Due to the protonation of side chains at pH 4.0, PU-PP-1 adopted an α-helical conformation whereas at pH >8.0 the side-chain carboxylic acid groups of the PLGAs were ionized, leading to the formation of an extended random coil conformation as a result of charge repulsion. Conformational switching was also supported by FTIR spectroscopy.

Efficient Protocol for the Synthesis of "N-Coded" Oligo- and Poly(N-Substituted Urethanes).

Sequence-defined poly(N-substituted urethanes) were synthesized via a solid-phase iterative protocol including two successive orthogonal coupling steps: the formation of an activated carbonate and its chemoselective reaction with the secondary amine group of amino alcohol building blocks. This simple method was used to write binary information on the formed polymers using four-coded molecules, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, and 2-(butylamino)ethanol, symbolizing binary dyads 00, 01, 10, and 11, respectively. The method is fast and allows synthesis of uniform oligomers and polymers with controlled lengths (4-mer to 28-mer) and digital information sequences. Furthermore, the coded poly(N-substituted urethanes) were easily characterized by electrospray mass spectrometry and decoded by tandem mass spectrometry. Overall, these digital macromolecules offer interesting advantages over conventional sequence-coded polyurethanes, i.e., synthesis of longer chains, reduced synthesis times, and better solubility and processing in common organic solvents.

Extended supramolecular organization of π-systems using yet unexplored simultaneous intra- and inter-molecular H-bonding motifs of 1,3-dihydroxy derivatives.

Unique H-bonding motifs of 1,3-dihydroxyl derivatives involving simultaneous intra- and inter-molecular H-bonding results in extended organization of pendant chromophores with a spatial distance suitable for π-π interaction. A preformed assembly with appended acceptor units exhibits host-guest interaction with specific donors by charge-transfer complex formation.