Load-collapse-release cascades of amphiphilic guest molecules in charged dendronized polymers through spatial separation of noncovalent forces.

The ability to pack guest molecules into charged dendronized polymers (denpols) and the possibility to release these guest molecules from subsequently densely aggregated denpols in a load-collapse-release cascade is described. Charged denpols, which constitute molecular objects with a persistent, well-defined envelope and interior, are capable of incorporating large amounts of amphiphilic guest molecules. Simultaneously, multivalent ions can coordinate to the surfaces of charged denpols, leading to counterion-induced aggregation of the already guest-loaded host structures. Thus, although the local guest concentration in denpol-based molecular transport might already be initially high due to the dense guest packing inside the dendritic denpol scaffolding, the "local" guest concentration can nonetheless be further increased by packing (through aggregation) of the host-guest complexes themselves. Subsequent release of guest compounds from densely aggregated dendronized polymers is then possible (e.g., through increasing the solution concentration of imidazolium-based ions). Augmented with this release possibility, the concept of twofold packing of guests, firstly through hosting itself and secondly through aggregation of the hosts, gives rise to a load-collapse-release cascade that strikingly displays the high potential of dendronized macromolecules for future molecular transport applications.

In-situ synthesis of Pt nanoparticles/reduced graphene oxide/cellulose nanohybrid for nonenzymatic glucose sensing.

In recent years, nanocellulose-based bioinorganic nanohybrids have been exploited in numerous applications due to their unique nanostructure, excellent catalytic properties, and good biocompatibility. To the best of our knowledge, this is the first report on the simple and effective synthesis of graphene/cellulose (RGO/CNC) matrix-supported platinum nanoparticles (Pt NPs) for nonenzymatic electrochemical glucose sensing. The Pt/RGO/CNC nanohybrid presented a porous network structure, in which Pt NPs, RGO, and CNCs were integrated well. Here, cellulose nanocrystals act as a biocompatible framework for wrapped RGO and monodispersed Pt nanoparticles, effectively preventing the restacking of graphene during reduction. The superior glucose sensing performance of Pt/RGO/CNC modified glass carbon electrode (GCE) was achieved with a linear concentration range from 0.005 to 8.5 mM and a low detection limit of 2.1 µM. Moreover, the Pt/RGO/CNC/GCE showed remarkable sensitivity, selectivity, durability, and reproducibility. The obtained results indicate that the CNCs-based bioinorganic nanohybrids could be a promising electrode material in electrochemical biosensors.

Cellulose nanocrystal driven microphase separated nanocomposites: Enhanced mechanical performance and nanostructured morphology.

The interest in the modification of cellulose nanocrystals (CNCs) lies in the potential to homogenously disperse CNCs in hydrophobic polymer matrices and to promote interfacial adhesion. In this work, poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PBA) were grafted onto CNCs, thereby imparting their hydrophobic traits. The successful grafting modification led to the increased thermal stability of modified CNCs (MCNCs), and the hydrophobic surface modification was integrated with crystalline structure and morphology of CNCs. The nanocomposites with 7 wt% MCNCs/PBA-co-PMMA had an increase in Young's modulus of >25-fold and in tensile strength at about 3 times compared to these of neat PBA-co-PMMA copolymer. In addition, a micro-phase separated morphology (PBA soft domains, and PMMA and CNC hard domains) of MCNCs/PBA-co-PMMA nanocomposites was observed. The large increase in the storage moduli (glass transition temperatures) and organized morphology of MCNCs/PBA-co-PMMA nanocomposites also elucidated the relationship between mechanical properties and micro-phase separated morphology. Therefore, the MCNCs are effective reinforcing agents for the PBA-co-PMMA thermoplastic elastomers, opening up opportunities for their wide-spread applications in polymer composites.

Stimuli-responsive zwitterionic block copolypeptides: poly(N-isopropylacrylamide)-block-poly(lysine-co-glutamic acid).

Synthesis of novel zwitterionic block copolypeptides, poly(N-isopropylacrylamide)-block-poly(L-glutamic acid-co-L-lysine) [PNiPAM(n)(PLG(x)-co-PLLys(y))m , where n is the number-average degree of polymerization (DP(n)) of PNiPAM block, x and y are the mole fraction of glutamic acid and lysine residues, respectively, and m is the total DP(n) of the peptide block], and their stimuli-responsiveness to temperature and pH variation in aqueous solutions are described. Initiated with the amino-terminated poly(N-isopropylacrylamide) (PNiPAM(n)-NH2), ring-opening polymerization (ROP) of a mixture of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA), and Boc-L-lysine N-carboxyanhydride (BLLys-NCA) afforded the block copolypeptides PNiPAM(n)(PBLG(x)-co-PBLLys(y))m, with a poly(N-isopropylacrylamide) block together with a random copolypeptide block, which was then deprotected with HBr/trifluoroacetic acid into the double hydrophilic block copolypeptides, PNiPAM(n)(PLG(x)-co-PLLys(y))m. Their block ratios and lengths, as well as the amino acid residue ratios in the random copolypeptide block are varied (n = 360, x = 0.4-0.5, y = 0.4-0.6, and m = 220-252). The secondary structures of the copolypeptides in aqueous solution at different pH conditions were examined. Phase transitions in aqueous solutions induced by both pH and temperature variation were investigated by (1)H NMR spectroscopy. The transitions induced by temperature were also explored by turbidity measurements using UV/vis spectroscopy for their lower critical aggregation temperature (LCAT) determination. Furthermore, these aggregation processes were followed by dynamic light scattering measurements.

Remarkable structure effects on chiroptical properties of polyisocyanides carrying proline pendants.

Chiral polymers with simple chemical structures and high helical conformation stabilities are important for their applications as chiral supports and asymmetrical catalysts. We report herein the synthesis of a series of aliphatic polyisocyanides carrying proline pendants of different chiralities, and an investigation of the effects of the chemical structures of these pendants on the chiroptical properties of the polymers. The configuration of the chiral center at the 4-position of the proline pendants was changed from S to R to check its effect on the handedness of the helical conformation. To examine the effects of steric hindrance on the stabilities of the helical conformation for these aliphatic representatives, proline pendants with various substituents at both the carboxyl and amine terminals were designed. To further examine the steric effects of the proline pendants, aromatic counterparts were also prepared. In the latter case, the effects of hydrogen bonds between pendant units on the enhancement and stabilities of the helical conformation were investigated by switching from the ester to an amide linkage. The Cotton effects and signal intensities of both aliphatic and aromatic polyisocyanides from circular dichroism spectroscopy were compared based on the bulkiness of the pendant groups, solvent polarities, and solution temperatures. It was found that highly stable helical conformations of polyisocyanides could be imposed by small bulky monoproline pendants.

Synthesis and characterization of thermo- and pH-responsive double-hydrophilic diblock copolypeptides.

Synthesis of novel double-hydrophilic diblock copolypeptides (BCPs), poly(l-glutamic acid)-block-poly(N-isopropylacrylamide) (PLGnPNm), and their thermoresponsive properties in aqueous solutions at different pH values are described. The diblock copolypeptides were synthesized by a combination of ring-opening polymerization (ROP) of gamma-benzyl-l-glutamate N-carboxyanhydrides (BLG-NCA) and reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NiPAM). A new class of RAFT agents (CTA-2 and CTA-3) with amino-functional groups was designed for this purpose. Two different strategies, i.e., macrochain transfer agent (CTA) and macroinitiator routes, were utilized and compared on the control of the chemical structures of the resulting BCPs. Their block ratios and lengths are broadly varied (n = 21-600 and m =180-442). Their thermally switchable aggregation behaviors in aqueous solutions were investigated at the microscopic level by 1H NMR spectroscopy and at the macroscopic level by turbidity measurements using UV/vis spectroscopy. The latter was also utilized for their lower critical aggregation temperature (LCAT) determination. The effects of block lengths and ratios as well as solution pH values on the collapse of NiPAM chain and aggregation process of BCPs were examined. This aggregation process was also followed by dynamic light scattering (DLS) measurements, and the thermally induced aggregate structures were investigated by transmission electron microscopy (TEM).