Short Hydrophilic Chains Research Articles

Investigating AIE behaviors of amphiphilic AIEgen-based polymers through self-assembly architectures and hydrophobic core arrangements

This research found that star-like polymers display stronger AIE emission due to tighter TPEE aggregation, but short hydrophilic chains led to weaker emission, underscoring the role of the polymer structure in AIE emission behaviour.

Ultrahigh energy-density flexible dielectric films achieved by self-bundled polymer nanocluster in necklace-like arrangement

Flexible dielectric materials with ultrahigh energy density (Ue) is of critical importance to reduce the size of dielectric capacitors, which has recently drawn ever-increasing attention. Herein, different from the incorporation of traditional 1D/2D inorganic nanofiller into single/multi-layer polymer matrix, a multifunctional poly (p-phenylene terephthalamide) (PPTA)-based derivative fluxible polymer (f-PPTA) nanocluster is selected and introduced to typical ferroelectric poly (vinylidene fluoride) (PVDF) matrix. As a novel polymer-based nanofiller, the f-PPTA nanocluster consists of self-bundled parallel sulfonated PPTA skeleton and grafted with octadecylamine polyoxyethylene ether amphiphilic (PEGO) amine ligand through ionic interaction. In the multi-arm amphiphilic PEGO, one alkyl chain with the length of 15 carbon atoms provides similar hydrophobic nature to that of PVDF, which contributes to improving the interfacial compatibility between polymer nanocluster and matrix. Furthermore, the relatively short hydrophilic chain with the length of 8 carbon atoms induces a specific necklace-like arrangement of the f-PPTA nanoclusters in PVDF matrix during film fabrication spontaneously. Consequently, an ultrahigh Ue ~ 22.5 J•cm−3 of the dielectric film is acquired at 600 MV•m−1 electric field. This value is the highest reported so far among all the poly (vinylidene fluoride) (PVDF)-based dielectric nanocomposites to the best of our knowledge. In addition, the elongation at break of the film can be increased to 390%, which is over 9 times that of pure PVDF sample. This work provides a new route to PVDF-based polymer nanocomposites with ultrahigh Ue and highly stretchable performance.

Outstanding protein-repellent feature of soft nanoparticles based on poly(N-(2-hydroxypropyl) methacrylamide) outer shells

The influences of the hydrophilic chain length, morphology and chemical nature have been probed with regard to the adsorption of model proteins onto the surface of soft nanoparticles (crew-cut micelles and polymersomes). The investigations were based on assemblies manufactured from PEOm-b-PLAn (poly(ethylene oxide)-b-poly(lactic acid)), which is a well-established block copolymer platform towards the manufacturing of drug delivery vehicles, and PHPMAm-b-PDPAn (poly([N-(2-hydroxypropyl)]methacrylamide)-b-poly[2-(diisopropylamino)ethyl methacrylate]), which is pH-responsive and therefore potentially able to target damaged cells in slightly acid microenvironments. Besides, protein adsorption onto PHPMA-stabilized nanoparticles has been seldom explored up-to-date. The morphologies were produced using two different approaches (nanoprecipitation and thin-film hydration) and afterwards, the protein-repelling property of the assemblies in model protein environments (BSA - bovine serum albumin, lysozyme and IgG - immunoglobulin G) was evaluated. We report that, regardless the morphology, PHPMA35-b-PDPA42 block copolymer assemblies are highly stable with negligible protein binding. On the other hand, PEOm-b-PLAn nanostructures are susceptible to protein adsorption and the phenomenon is protein-dependent. The nanoparticles are more susceptible to adsorption of the model positively charged biomacromolecule (lysozyme). The adsorption phenomenon is thermodynamically complex with simultaneous endothermic and exothermic processes involved. Although the experimental data highlight that qualitatively the morphology plays negligible effects on the event, fluorescence spectroscopy measurements evidenced that the binding is stronger onto the surface of nanoparticles stabilized by shorter hydrophilic shells. Nevertheless, the adsorption does not affect the secondary structure of the model proteins as confirmed by circular dichroism spectroscopy. Overall, by comparing soft nanoparticles stabilized by PEO and PHPMA, the latter is herein proved to be a better choice towards the manufacturing of non-fouling structures (either core-shell or hollow spheres) where even a reasonably short hydrophilic chain confers outstanding protein-repelling feature.

Enhanced stability of crosslinked and charged unimolecular micelles from multigeometry triblock copolymers with short hydrophilic segments: dissipative particle dynamics simulation.

High micellar stability and well-performed drug loading and release are two conflicting factors for unimolecular micelles as an ideal drug delivery system. Achieving the formation of unimolecular micelles with short hydrophilic blocks is a challenging and promising approach to solve this bottleneck and limitation of current unimolecular micelle systems. In this work, dissipative particle dynamics (DPD) simulation is used to study the synergetic effect of crosslinking and electrostatic repulsion on stability of unimolecular micelles and to analyze the micro-mechanism and factors influencing this synergetic stabilization strategy. The strategy can generate unimolecular micelles with extremely high stability for various supramolecular polymers with short hydrophilic chains. Protonation of DEAEMA blocks leads to a large improvement in micellar hydrophilicity. The protonated middle layer further shrinks through crosslinking to produce the largest charge density, enlarging the electrostatic repulsion between colloidal particles. Additionally, the crosslinking and protonation treatment maximizes the extension degree of hydrophilic EO segments due to the increasing steric hindrance and poor compatibility between DEAHEMA and EO blocks. In this study, the relation between shrinkage degree of hydrophobic cores and stability of unimolecular micelles is first reported. The above-mentioned transition of micellar structures and properties results in the maximum degree of core shrinkage (Rg of MMA blocks) corresponding to the high stability of unimolecular micelles. Further study shows that the increasing cyclization degree, the mode of end cyclization, and the crosslinking and electrostatic repulsion of the middle layer all exert favorable effects on the stability of unimolecular micelles due to controlled shrinkage of hydrophobic cores.

Amphiphilic zinc bacteriochlorophyll a derivatives that function as artificial energy acceptors in photosynthetic antenna complexes chlorosomes of the green sulfur photosynthetic bacterium Chlorobaculum limnaeum

Abstract Green photosynthetic bacteria have extramembranous light-harvesting complexes called chlorosomes. Light-energy captured by bacteriochlorophyll (BChl) self-aggregates inside chlorosomes is transferred to BChl a -peptide complexes called baseplates on the chlorosome surface. We substitute the baseplate complex in chlorosomes from a green sulfur photosynthetic bacterium Chlorobaculum limnaeum with amphiphilic Zn BChl a derivatives. Zn BChl a derivatives 1 – 3 , which were esterified with polyethylene glycol (PEG) 600, PEG400, and diethylene glycol, respectively, were successfully hybridized with chlorosomes without baseplates. These derivatives in the hybridized chlorosomes emitted by predominant excitation of BChl e self-aggregates at 460 nm, indicating that they were able to accept the excitation energy from BChl e aggregates inside chlorosomes. Zn BChl a derivatives 1 and 2 emitted at 787 nm by the excitation energy transfer. In contrast, fluorescence from 3 esterified with a short hydrophilic chain, diethylene glycol, was broadened around 785 and 820 nm. The broad emission bands would consist of at least two bands, which were ascribable to the monomeric and aggregated forms. These results indicate that PEG600 and PEG400 provide appropriate amphiphilicity to Zn BChl a derivatives for dispersion in the membranous region of chlorosomes. The present study will be helpful for not only elucidation of the energy transfer mechanism in chlorosomes but also development of artificial photofunctional supramolecular complexes by hybridization of natural photosynthetic systems with synthetic molecules.

Temperature-Induced Intermicellization of “Hairy” and “Crew-Cut” Micelles in an Aqueous Solution of a Thermoresponsive Copolymer

Temperature-induced intermicellar structures in aqueous solutions of the thermoresponsive methoxypoly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEGn-b-NIPAAM71) copolymer that exhibit a lower critical solution temperature were studied by means of turbidimetry, dynamic light scattering (DLS), shear viscosity, and rheo small-angle light scattering (rheo-SALS) methods. The length of the hydrophilic chains (MPEG) of the copolymer varies from n=0 to n=114. It is shown that this change has a major impact on the temperature-induced association behavior of the polymer in solution. The turbidity results at quiescent conditions revealed a transition peak in the turbidity curve at intermediate temperatures, and this peak as well as the cloud point is shifted toward higher temperatures with increasing length of the hydrophilic chains of the copolymer. The DLS measurements disclosed a fast and a slow relaxation mode, which both are diffusive. From the fast and slow relaxation times the sizes of unimers/micelles and intermicellar clusters, respectively, can be determined. The temperature-induced aggregation is less pronounced in solutions of copolymers with long hydrophilic chains, and the intermicellar structures exhibit an interesting transition at intermediate temperatures. In the shear viscosity measurements large association complexes are formed at high temperatures and at low shear flow for the polymers with short hydrophilic chains, whereas at high shear rates breakup of interaggregate chains was observed. For the copolymer with the highest number of hydrophilic chains (n=114), a novel transition peak was found in the viscosity data. The rheo-SALS results divulged shear-induced structural changes of the association complexes at elevated temperatures. For copolymers with short hydrophilic chains, shear-induced disruption of association complexes was found at higher temperatures, whereas for hairy micelles augmented shear flow promoted the growth of complexes.

Interactions between Adsorbed Layers of αS1-Casein with Covalently Bound Side Chains: A Self-Consistent Field Study

The effect on the adsorbed layer properties of the modification of alpha S1-casein by covalent bonding with an uncharged polysaccharide side chain has been investigated using lattice-based self-consistent field (SCF) theory. Interactions between two hydrophobic planar surfaces coated by a layer of adsorbed modified alpha S1-casein have been studied as a function of pH and ionic strength. While the interactions of the unmodified alpha S1-casein layers become attractive at high ionic strength, it has been shown that the presence of polysaccharide attachment to the alpha S1-casein molecule can confer net repulsive interactions over a wide range of salt concentration. The disordered protein is represented as a linear flexible polyampholyte with a sequence of hydrophobic, polar, and charged units based on the known alpha S1-casein primary structure. The hydrophilic side chain is attached at various fixed positions along the casein backbone. Different lengths and locations of the attached polysaccharide side chain are examined. Interfacial structures and colloidal stability properties of the system are determined, including the surface-surface interaction potential, the extent of protein bridging, and the distribution of protein segments from the surface under different conditions of pH and ionic strength. It has been found that the covalent bonding of short hydrophilic chains may not only enhance but can also worsen the colloidal stabilizing properties of the modified protein, depending on the position of the attachment.