Adamantane functionalized poly(2-oxazoline)s with broadly tunable LCST-behavior by molecular recognition

Smart or adaptive materials often utilize stimuli-responsive polymers, which undergo a phase transition in response to a given stimulus. So far, various stimuli have been used to enable the modulation of drug release profiles, cell-interactive behavior, and optical and mechanical properties. In this respect, molecular recognition is a powerful tool to fine-tune the stimuli-responsive behavior due to its high specificity. Within this contribution, a poly(2-oxazoline) copolymer bearing adamantane side chains was synthesized via triazabicyclodecene-catalyzed amidation of the ester side chains of a poly(2-ethyl-2-oxazoline-stat-2-methoxycarbonylpropyl-2-oxazoline) statistical copolymer. Subsequent complexation of the pendant adamantane groups with sub-stoichiometric amounts (0-1 equivalents) of hydroxypropyl beta-cyclodextrin or beta-cyclodextrin enabled accurate tuning of its lower critical solution temperature (LCST) over an exceptionally wide temperature range, spanning from 30 degrees C to 56 degrees C. Furthermore, the sharp thermal transitions display minimal hysteresis, suggesting a reversible phase transition of the complexed polymer chains (i.e., the beta-cyclodextrin host collapses together with the polymers) and a minimal influence by the temperature on the supramolecular association. Analysis of the association constant of the polymer with hydroxypropyl beta-cyclodextrin via H-1 NMR spectroscopy suggests that the selection of the macrocyclic host and rational polymer design can have a profound influence on the observed thermal transitions

Water-stable plasma-polymerized N,N-dimethylacrylamide coatings to control cellular adhesion

The plasma polymerization of amide-based precursors is a nearly unexplored research area, which is in contrast with the abundance of reports focusing on amide based surface modification using wet chemistry. Therefore, this study aims to profoundly investigate the near-atmospheric pressure plasma polymerization of N,N-dimethylacrylamide (DMAM) to obtain stable coatings. In contrast to the unstable coatings obtained at lower discharge powers, the stable coatings that were obtained at higher powers showed a lower hydrophilicity as assessed by water contact angle (WCA). This decrease in hydrophilicity with increasing plasma power was found to be related to a reduced preservation of the monomer structure, as observed by Fourier transform infrared (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and XPS C-60 depth profiling, a rarely used but effective combination of techniques. Furthermore, the chemical composition of the coating was found to be in good agreement with the plasma active species observed by optical emission spectroscopy. Additionally, XPS C-60 depth profiling indicated a difference between the top layer and bulk of the plasma polymer due to spontaneous oxidation and/or postplasma coating deposition. Finally, the stable coatings were also found to have cell-interactive behavior toward MC3T3 as studied by in vitro live/dead fluorescence imaging and (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (MTS) assays. With the latter technique, a cell viability of up to 89% as compared with tissue culture plates after 1 day of cell culture was observed, indicating the potential of these coatings for tissue engineering purposes

Bioresponsive polymers for nanomedicine: expectations and reality!

Bioresponsive polymers in nanomedicine have been widely perceived to selectively activate the therapeutic function of nanomedicine at diseased or pathological sites, while sparing their healthy counterparts. This idea can be described as an advanced version of Paul Ehrlich's magic bullet concept. From that perspective, the inherent anomalies or malfunction of the pathological sites are generally targeted to allow the selective activation or sensory function of nanomedicine. Nonetheless, while the primary goals and expectations in developing bioresponsive polymers are to elicit exclusive selectivity of therapeutic action at diseased sites, this remains difficult to achieve in practice. Numerous research efforts have been undertaken, and are ongoing, to tackle this fine-tuning. This review provides a brief introduction to key stimuli with biological relevance commonly featured in the design of bioresponsive polymers, which serves as a platform for critical discussion, and identifies the gap between expectations and current reality.Drug Delivery Technolog

The elusive seven-membered cyclic imino ether tetrahydrooxazepine

Cyclic imino ether heterocycles are used as ligands in transition metal catalysis, in various drugs and as reactive monomers in living cationic ring-opening polymerization (CROP). While five- and six-membered cyclic imino ethers, i.e. 2-oxazolines and 4,S-dihydro-1,3-oxazines, have extensively been studied in these areas, their seven-membered ring counterparts have remained unexplored. Herein, we report the synthesis of 2-phenyl-4,5,6,7-tetrahydro-1,3-oxazepine allowing reassignment of the earlier, incorrectly reported 4,5,6,7-tetrahydro-1,3-oxazepines as their N-acylated pyrrolidine isomers. Finally, we also report a comparison of the CROP reactivity of a homologous series of cyclic imino ethers with a 2-carbon, 3-carbon, and 4-carbon methylene bridge, revealing a remarkable ring size effect

The improving sequence effect on monetary sequences

Experimental studies reveal a preference for improving income sequences, challenging the axioms of the discounted utility model, such as the present value maximization principle. Through an experiment, we test the existence of this anomaly on short and long-term income sequences, by confirming previous experimental evidence. Although the participants are aware of the present value maximization, they select improving sequences of income mainly to cover their future spending needs, to feel motivation at work, and to receive a signal of success and status. In order to include this sequence effect in a mathematical valuation model, we propose an alternative model to value sequences which outperforms the traditional discounting model by fitting the present value with the preferences of the participants

Nanofibers with a tunable wettability by electrospinning and physical crosslinking of poly(2-n-propyl-2-oxazoline)

This work shows the design of highly porous membranes with tunable wettability based on poly(2-n-propyl-2-oxazoline) (PnPrOx) nanofibers. Wicking and advanced contact angle experiments demonstrate the high potential for applications requiring specific interactions with aqueous media. PnPrOx is a popular member among the biocompatible poly(2-oxazoline)s due to its thermoresponsiveness in aqueous solutions, enabling the production of ‘smart materials’. On material level, however, many interesting properties of this polymer remain undiscovered. Electrospinning is an ideal technique to transfer the properties observed in solutions to end-material properties, as the polymer is processed into highly porous, nanofibrous membranes. PnPrOx' electrospinnability is here investigated in environmentally friendly ethanol/water solvent systems, ensuring industrial scalability. The nanofibrous membranes show increased hydrophobicity exhibiting the rose-petal effect. Upon functionalization with tannic acid, the hydrophobic membranes are transformed into hydrophilic nanofibers showing water-stability in both fresh and salty water, even below the polymer cloud point temperature. By varying the tannic acid amount, the hydrophilicity can be fine-tuned as the contact area between water droplets and surface, the rate and manner of water uptake and the extent of the rose-petal effect can be manipulated easily. Hence an interesting material is designed for applications in which water caption and transport are important

Förster resonance energy transfer in fluorophore labeled poly(2-ethyl-2-oxazoline)s†

YesDye-functionalized polymers have been extensively studied to understand polymer chain dynamics, intra or inter-molecular association and conformational changes as well as in practical applications such as signal amplification in diagnostic tests and light-harvesting antennas. In this work, the Förster resonance energy transfer (FRET) of dye-functionalized poly(2-ethyl-2-oxazoline) (PEtOx) was studied to evaluate the effect of dye positioning and polymer chain length on the FRET efficiency. Therefore, both α (initiating terminus)- or ω (terminal chain end)-fluorophore single labeled and dual α,ω-fluorescent dye labeled PEtOx were prepared via cationic ring opening polymerization (CROP) using 1-(bromomethyl)pyrene as the initiator and/or 1-pyrenebutyric acid or coumarin 343 as the terminating agent, yielding well-defined PEtOx with high labeling efficiency (over 91%). Fluorescence studies revealed that intramolecular FRET is most efficient for heterotelechelic PEtOx containing both pyrene and coumarin 343 fluorophores as chain ends, as expected. A strong dependence of the energy transfer on the chain length was found for these dual labeled polymers. The polymers were tested in both dilute organic (chloroform) and aqueous media revealing a higher FRET efficiency in water due to the enhanced emissive properties of pyrene. The application of dual labeled polymers as fluorescent probes for temperature sensing was demonstrated based on the lower critical solution temperature behavior of the PEtOx. Furthermore, these polymers could be successfully processed into fibers and thin films. Importantly, the fluorescence properties were retained in the solid state without decreasing the FRET efficiency, thus opening future possibilities for application of these materials in solar cells and/or sensors

Consistency among elicitation techniques for intertemporal choice: a within-subjects investigation of anomalies

Three common anomalies of intertemporal choice (Gain/Loss Asymmetry, Short/Long Asymmetry, and the Absolute Magnitude Effect) are investigated using both sequences and matching in a within-subjects experiment. In both procedures, it appears that the participants in this study evaluate monetary outcomes over time differently than the traditional discounting model predicts. Patterns consistent with two of the anomalies (Gain/Loss and Absolute Magnitude Effect) surface and interact in both elicitation techniques. Finally, a systematic inconsistency exists between the two methods. We observe significantly more consistency between the two elicitation techniques when the outcome is a gain in the relatively far future than when it is an equitable future loss