Search

Block copolypeptides with their inherent nanometer length scale of phase separation, provide means of manipulating the type (alpha-helices, beta-strands) and persistence of peptide secondary structures. Two such examples are employed based on the alpha-helical poly(gamma-benzyl-L-glutamate) (PBLG) polypeptide as one block and poly(L-leucine) (alpha-helical) or poly(O-benzyl-L-tyrosine) (POBT) (beta-strands) as the second block. Although both secondary structures are present in the copolypeptides the effect of nano-scale confinement is to induce folding in the POBT beta-sheets and to maintain the defected alpha-helices of PBLG and PLEU with a limited lateral coherence. (C) 2010 Elsevier Ltd. All rights reserved. European Polymer Journal more...

The hierarchical self-assembly at the submicrometer, nanometer and alpha-helilcal length scales has been Studied in a miktoarm star rod-coil chimera composed of poly(gamma-benzyl-L-glutamate) (PBLG), polystyrene, and polyisoprene blocks by X-ray scattering, solid state NMR, and transmission electron microscopy. The propensity of the rod block toward alpha-helices that are further hexagonally packed gives rise to pure PBLG domains and induces the partial mixing of the two amorphous blocks. These structural results were confirmed by independent dynamic probes at the segmental and alpha-helical level by NMR and dielectric spectroscopy, respectively. Macromolecules more...

A fluorous biphasic hexa(3,5-substituted-phenyl)benzene (HPB), analogous to semifluorinated alkanes, was synthesized such that precise chemical and orthogonally directed, supramolecular placement of amphiphilic side chains at their bulk density was achieved. The grafting or tethering of incommensurate hydrocarbon and fluorocarbon chains to the rotationally flexible HPB core inextricably links intermolecular phase separation with intramolecular conformational behavior and results in rich self-assembly. The self-assembled structure was studied with polarized optical microscopy, differential scanning calorimetry, X-ray scattering, and (19)F magic-angle spinning solid-state NMR and found to be kinetically trapped with mixed fluorocarbon and hydrocarbon side chains, despite packing into a lattice defined by the HPB scaffold. The addition of 1% of the parent biphasic diphenylacetylene unlocks the frustrated conformation in the HPB, resulting in the formation of a thermodynamically favorable bilayer structure. J Am Chem Soc more...

The stability, persistence and dynamics of the peptide secondary motifs are investigated in a series of poly(gamma-benZyl-L-glutainate)-b-polyalanine (PBLG-b-PAla) polypeptides through a combination of structural (X-rays, NMR) and dynamic (Dielectric Spectroscopy, NMR) probes. The unfavorable enthalpic interactions between the unlike blocks give rise to nanophase separation that results in the destabilization of PAla beta-sheets. Contrary to. this, the overall helicity of PBLG alpha-helices is enhanced. The dynamics of the "defected" amorphous segments and of the more ordered segments are studied by DS and C-13 NMR, respectively. These probes provide information on the time scale and the mechanism of molecular and supramolecular motion. Macromolecules more...

The self-assembly, the molecular dynamics, and the kinetics of structure formation are studied in dipole-functionalized hexabenzocoronene (HBC) derivatives. Dipole substitution destabilizes the columnar crystalline phase except for the dimethoxy- and monoethynyl-substituted HBCs that undergo a reversible transformation to the crystalline phase. The disk dynamics are studied by dielectric spectroscopy and site-specific NMR techniques that provide both the time-scale and geometry of motion. Application of pressure results in the thermodynamic phase diagram that shows increasing stability of the crystalline phase at elevated pressures. Long-lived metastability was found during the transformation between the two phases. These results suggest new thermodynamic and kinetic pathways that favor the phase with the highest charge carrier mobility. J Am Chem Soc more...

We report on the self-assembly and molecular dynamics in a series of poly(gamma-methyl-L-glutamate-co-gamma-stearyl-L-glutamate) [poly(MLG-co-SLG)] using thermodynamic (differential scanning calorimetry), structural (wide-angle X-ray scattering and (13)C solid-state NMR), as well as dynamic (dielectric spectroscopy and site-specific solid-state NMR) techniques. Stearyl crystallization takes place in the copolymers with W(PSLG) >= 18% which reflects changes of the hydrocarbon side chains conformation. Extruded fibers of the copolymers are composed of both alpha-helical and beta-sheet secondary structures oriented along the fiber axis with a bottleneck structure with MLG/SLG sequences forming the neck and more distant SLG sequences forming the bottle. This supramolecular organization has direct consequences on the dynamics. Two dielectrically active processes with strong temperature dependences were found. Site-specific NMR allowed the identification of the geometry of motions. One is associated with small-amplitude motions of amorphous segments along the polypeptide backbone and at the chain ends that freeze at the liquid-to-glass transition. The slower process is associated with the relaxation of the alpha-helical peptide secondary structure. The analysis of the dielectric strength associated with the slower process revealed that helices are objects of low persistence. Macromolecules more...