Search

We performed multiscale molecular dynamics (MD) simulations of bottlebrush polymers with fluorinated side chains to investigate the influence of the bottlebrush architecture on the spatial distribu...

Thermodynamic interaction and non-isothermal crystallization behavior in a series of protiated (H-) and deuterated (D-) poly(e-caprolactone) (PCL) blends have been systematically investigated. The blends were thermodynamically miscible in the melt. The Flory−Huggins interaction parameter (χ) between H- and D-PCL segments was estimated. The hydroxyl groups in the PCL chain-ends were found to contribute significantly to the negative χ values. Combined characterization of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) revealed that upon slow cooling, unique alternating H-rich and D-rich PCL lamellar structures are formed regardless of the blend ratio, which is attributed to the Tc difference between H- and D-PCLs. While upon rapid cooling, mixed crystals of H- and D-PCLs are predominantly formed. These results provide insightful information on the melt thermodynamics as well as detailed chain arrangements in lamellar crystals for semi-crystalline H/D polyester blends.

Using small angle neutron scattering, we conducted a detailed structural study of poly(3-alkylthiophenes) dispersed in deuterated dicholorbenzene. The focus was placed on addressing the influence of spatial arrangement of constituent atoms of side chain on backbone conformation. We demonstrate that by impeding the {\pi}- {\pi} interactions, the branch point in side chain promotes torsional motion between backbone units and results in greater chain flexibility. Our findings highlight the key role of topological isomerism in determining the molecular rigidity and are relevant to the current debate about the condition necessary for optimizing the electronic properties of conducting polymers via side chain engineering.

Selective deuteration is an important tool for many analytical techniques including neutron scattering and spectroscopies. However, the availability of deuterated materials is limited because of the challenges in their synthesis. Here, we report the synthesis of partially and fully deuterated e-caprolactone monomers and their corresponding polymers, poly(e-caprolactone)s (PCLs), and the investigation of isotope effects on their crystalline structures and physical properties. Deuteration of PCLs leads to smaller crystal lattices and volumes compared to protiated PCLs by the amount proportional to the deuteration levels. The linear trend suggests that the volume isotope effect in PCL is primarily governed by the vibrations of C–D and C–H bonds. The large intrachain contraction of deuterated PCLs compared to that of polyethylene reported in the literature can be ascribed to the presence of polar ester groups in PCLs. Deuterated PCLs also display lower melting temperatures than protiated PCLs proportional to ...

Polymer interfaces are key to a range of applications including membranes for chemical separations, hydrophobic coatings, and passivating layers for antifouling. While important, challenges remain in probing the interfacial monolayer where the molecular ordering and orientation can change depending on the chemical makeup or processing conditions. In this work, we leverage surface specific vibrational sum frequency generation (SFG) and the associated dependence on molecular symmetry to elucidate the ordering and orientations of key functional groups for poly(2,2,2-trifluoroethyl methacrylate) bottlebrush polymers and their linear polymer analogues. These measurements were framed by atomistic molecular dynamic simulations to provide a complementary physical picture of the gas-polymer interface. Simulations and SFG measurements show that methacrylate backbones are buried beneath a layer of trifluoroethyl containing side groups that result in structurally similar interfaces regardless of the polymer molecular weight or architecture. The average orientational angles of the trifluoroethyl containing side groups differ depending on polymer linear and bottlebrush architectures, suggesting that the surface groups can reorient via available rotational degrees of freedom. Results show that the surfaces of the bottlebrush and linear polymer samples do not strongly depend on molecular weight or architecture. As such, one cannot rely on increasing the molecular weight or altering the architecture to tune surface properties. This insight into the polymer interfacial structure is expected to advance the design of new material interfaces with tailored chemical/functional properties.

Bottlebrush polymers are important for a variety of applications ranging from drug delivery to electronics. The functional flexibility of the branched sidechains has unique assembly properties when compared to linear block polymer systems. However, reports of direct observation of molecular reorganization have been sparse. This information is necessary to enhance the understanding of the structure-property relationships in these systems and yield a rational design approach for novel polymeric materials. In this work, we report direct visualization of bottlebrush molecular organization and the formation of nematic-type ordering in an amorphous polymer bottlebrush system, captured with plasma etching and helium ion microscopy. By observing the unperturbed structure of this material at high resolution and quantifying image features, we were able to qualitatively link experimental results with structures predicted by coarse-grained molecular dynamics simulations. The direct visualization and computation workflow developed in this work can be applied to a broad variety of polymers with different architectures, linking imaging results with other, independent channels of information for better understanding and control of these classes of materials.

Self-assembly of amphiphilic polymers in water is of fundamental and practical importance. Significant amounts of free unimers and associated micellar aggregates often coexist over a wide range of phase regions. The thermodynamic and kinetic properties of the microphase separation are closely related to the relative population density of unimers and micelles. Although the scattering technique has been employed to identify the structure of micellar aggregates as well as their time-evolution, the determination of the population ratio of micelles to unimers remains a challenging problem due to their difference in scattering power. Here, using small-angle neutron scattering (SANS), we present a comprehensive structural study of amphiphilic n-dodecyl-PNIPAm polymers, which shows a bimodal size distribution in water. By adjusting the deuterium/hydrogen ratio of water, the intra-micellar polymer and water distributions are obtained from the SANS spectra. The micellar size and number density are further determined, and the population densities of micelles and unimers are calculated to quantitatively address the degree of micellization at different temperatures. Our method can be used to provide an in-depth insight into the solution properties of microphase separation, which are present in many amphiphilic systems.

The microphase separation of a bioconjugate made of a globular protein and a zwitterionic polymer is studied in order to elucidate the role of charge in the polymer block on the self-assembly of protein–polymer bioconjugates. Zwitterionic polymer surfaces are resistant to nonspecific protein adsoprtion due to strong hydration; however, bioconjugates constructed from a red fluorescent protein, mCherry, and a zwitterionic polymer, PDMAPS, show a relatively narrow range of conditions for self-assembly in concentrated systems. The bioconjugates demonstrate weaker segregation strengths compared to previously studied mCherry–polymer conjugates with non-ionic polymers, as demonstrated by higher order-disorder transition concentrations (CODT) and a narrower range of ordered concentrations in the phase diagram. The results suggest that electrostatic segregation of mCherry is one of the main parameters governing the self-assembly of protein–nonionic polymer bioconjugates, and this driving force is perturbed by the zwitterionic polymer. Disruption of ordering upon addition of NaCl confirms that electrostatics play a critical role in the bioconjugate self-assembly. Order–disorder–order transitions are observed with increasing concentration of a kosmotropic salt, ammonium sulphate, due to the initial salt-in followed by salt-out effect, suggesting that stabilization of protein domains by enhancing attractive interactions between proteins can significantly improve long range ordering.

Protein–polymer conjugation can significantly affect many different aspects of protein behavior, ranging from their solution properties to their ability to form solution and bulk nanostructured materials. An underlying fundamental question is how the molecular design affects the shape of the conjugate and, consequently, its properties. This work measures the molecular configuration of model protein–polymer conjugates in dilute solution using small-angle neutron scattering (SANS) and uses quantitative model fitting to understand the shape of the molecules. Form factor measurements of four model bioconjugates of the red fluorescent protein mCherry and the polymers poly(N-isopropylacrylamide), poly(hydroxypropyl acrylate), poly(oligoethylene glycol acrylate), and poly(ethylene glycol) show that these protein–polymer conjugates are well described by a recently developed scattering function for colloid–polymer conjugates that explicitly incorporates excluded volume interactions in the polymer configuration. In the regime where the protein does not exhibit strong interactions with the polymer, modeling the protein–polymer interactions using a purely repulsive Weeks–Chandler–Andersen potential also leads to a coarse-grained depiction of the conjugate that agrees well with its scattering behavior. The coarse-grained model can additionally be used for systems with varying protein–polymer interactions, ranging from purely repulsive to strongly attractive, which may be useful for conjugates with strong electrostatic or hydrophobic attractive interactions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 292–302

Perfectly defined, monodisperse fusion protein block copolymers of a thermoresponsive coil-like protein, ELP, and a globular protein, mCherry, are demonstrated to act as fully biosynthetic analogues to protein-polymer conjugates that can self-assemble into biofunctional nanostructures such as hexagonal and lamellar phases in concentrated solutions. The phase behavior of two mCherry-ELP fusions, E10-mCherry-E10 and E20-mCherry, is investigated to compare linear and bola fusion self-assembly both in diluted and concentrated aqueous solution. In dilute solution, the molecular topology impacts the stability of micelles formed above the thermal transition temperature of the ELP block, with the diblock forming micelles and the bola forming unstable aggregates. Despite the chemical similarity of the two protein blocks, the materials order into block copolymer-like nanostructures across a wide range of concentrations at 30 wt% and above, with the bola fusion having a lower order-disorder transition concentration than the diblock fusion. The topology of the molecule has a large impact on the type of nanostructure formed, with the two fusions forming phases in the opposite order as a function of temperature and concentration. This new system provides a rich landscape to explore the capabilities of fusion architecture to control supramolecular assemblies for bioactive materials.

Identification of secondary metabolites produced by cryptic gene in bacteria may be difficult, but in the case of nonribosomal peptide (NRP)-type secondary metabolites, this study can be facilitated by bioinformatic analysis of the biosynthetic gene cluster and tandem mass spectrometry analysis. To illustrate this concept, we used mass spectrometry-guided bioinformatic analysis of genomic sequences to identify an NRP-type secondary metabolite from Streptomyces peucetius ATCC 27952. Five putative NRPS biosynthetic gene clusters were identified in the S. peucetius genome by DNA sequence analysis. Of these, the sp970 gene cluster encoded a complete NRPS domain structure, viz., C-A-T-C-A-T-E-C-A-T-C-A-T-C domains. Tandem mass spectrometry revealed that the functional siderophore peptide produced by this cluster had a molecular weight of 644.4 Da. Further analysis demonstrated that the siderophore peptide has a cyclic structure and an amino acid composition of AchfOrn-Arg-hOrn-hfOrn. The discovery of functional cryptic genes by analysis of the secretome, especially of NRP-type secondary metabolites, using mass spectrometry together with genome mining may contribute significantly to the development of pharmaceuticals such as hybrid antibiotics.

The effects of protein surface potential on the self-assembly of protein-polymer block copolymers are investigated in globular proteins with controlled shape through two approaches: comparison of self-assembly of mCherry-poly(N-isopropylacrylamide) (PNIPAM) bioconjugates with structurally homologous enhanced green fluorescent protein (EGFP)-PNIPAM bioconjugates, and mutants of mCherry with altered electrostatic patchiness. Despite large changes in amino acid sequence, the temperature-concentration phase diagrams of EGFP-PNIPAM and mCherry-PNIPAM conjugates have similar phase transition concentrations. Both materials form identical phases at two different coil fractions below the PNIPAM thermal transition temperature and in the bulk. However, at temperatures above the thermoresponsive transition, mCherry conjugates form hexagonal phases at high concentrations while EGFP conjugates form a disordered micellar phase. At lower concentration, mCherry shows a two-phase region while EGFP forms homogeneous disordered micellar structures, reflecting the effect of changes in micellar stability. Conjugates of four mCherry variants with changes to their electrostatic surface patchiness also showed minimal change in phase behavior, suggesting that surface patchiness has only a small effect on the self-assembly process. Measurements of protein/polymer miscibility, second virial coefficients, and zeta potential show that these coarse-grained interactions are similar between mCherry and EGFP, indicating that coarse-grained interactions largely capture the relevant physics for soluble, monomeric globular protein-polymer conjugate self-assembly.

The self-assembly of nanostructured globular protein arrays in thin films is demonstrated using protein-polymer block copolymers based on a model protein mCherry and the polymer poly(oligoethylene glycol acrylate) (POEGA). Conjugates are flow coated into thin films on a poly(ethylene oxide) grafted Si surface, forming self-assembled cylindrical nanostructures with POEGA domains selectively segregating to the air-film interface. Long-range order and preferential arrangement of parallel cylinders templated by selective surfaces are demonstrated by controlling relative humidity. Long-range order increases with coating speed when the film thicknesses are kept constant, due to reduced nucleation per unit area of drying film. Fluorescence emission spectra of mCherry in films prepared at

Inspired by the simplicity and versatility of layer-by-layer (LbL) assembly, we applied multilayered polyelectrolyte assemblies on nanoparticles to create viable systemic delivery systems. Focusing on tumor-specific delivery, LbL nanoparticles that exhibit a pH-sensitive outer stealth layer are demonstrated to target and be retained in hypoxic tumor regions. The neutral layers shed in response to acidity to reveal a charged nanoparticle surface that is readily taken up by tumor cells. The first in vivo demonstration of this mechanism of targeting is presented, as well as an initial examination of the mechanism of uptake of the nanoparticles. We further demonstrate that this concept for tumor targeting is potentially valid for a broad range of cancers, with applicability for therapies that target hypoxic tumor tissue.