Synthesis and characterization of random and block copolypeptides derived from gamma-methylglutamate and leucine N-carboxyanhydrides

The synthesis of random and block copolypolyeptides derived from gamma-methylglutamate and leucine N-carboxyanhydrides using Al-Schiff's base complexes and allylamine as initiators is here reported. The copolymer structures were confirmed by (1)H and (13)C NMR. The calculation of the statistical average block lengths reveals the presence of longer methylglutamate units in the copolymer. The determination of the reactivity ratios indicated a slightly higher reactivity of gamma-methylglutamateNCA as compared to leucineNCA. Block copolypeptides containing glutamate and leucine units were obtained by sequential polymerization of the two NCAs using Al-Schiff's base complexes or allylamine in dioxane as solvent. Based on (13)C NMR spectra of copolymers exhibiting two signals corresponding to peptide linkages, we confirmed the block structure and concluded that the copolymerization proceeds by attack of an amino group present on a glutamate chain end onto a LeuNCA. The copolymerization with allylamine was also shown, from calculation of the average block lengths of sequences, to exhibit living behavior. Viscometry analysis further showed that molar masses of the copolypeptides obtained with Al-Schiff's base were quite close to those derived from allylamine, supporting the proposed mechanism of copolymerization.     

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.     

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).     

Architecturally induced multiresponsive vesicles from well-defined polypeptides: formation of gene vehicles

A series of novel, partially labeled amphiphilic triblock copolypeptides, PLL-b-PBLG-d7-b-PLL, has been synthesized, where PLL and PBLG-d7 are poly(L-lysine hydrochloride) and poly(gamma-benzyl-d7-L-glutamate), respectively. The synthetic approach involved the sequential ring-opening polymerization (ROP) of gamma-benzyl-L-glutamate and epsilon-Boc-L-lysine N-carboxy anhydrides by a diamino initiator using high-vacuum techniques, followed by the selective deprotection of the Boc groups. Combined characterization results showed that the copolypeptides exhibit high degrees of molecular and compositional homogeneity. The synthesized copolypeptides had similar molecular weights, while the composition of the middle block ranged between 19 and 74% with respect to the monomeric units. Due to the macromolecular architecture of the copolypeptide and the rigid nature of the middle block, the formation of monolayers was favored, and, surprisingly, vesicles were formed in water at neutral pH over the entire compositional range. The vesicular structures were extensively characterized by static and dynamic light scattering, small-angle neutron scattering, atomic force microscopy, cryo-transmission electron microscopy, scanning electron microscopy, UV and Fourier transform infrared spectroscopy, and circular dichroism. In contrast to other vesicular structures derived from conventional polymers, the formed polypeptidic vesicles possess the unique feature of being stimuli-responsive to pH and temperature. When the copolypeptides were mixed with plasmid DNA (pDNA), large vesicular structures were also formed. The molecular characterization of the vectors was performed with most of the methods mentioned above, and indicated that the pDNA is both partially condensed on the PLL phase and partially encapsulated inside the vesicle. Consequently, the synthesized vectors combine the advantages of the polylysine-DNA systems to condense large amounts of genes, as well as those of the liposome-DNA systems to better protect the encapsulated DNA. These vectors are expected to present better gene transfection efficiency to the cell nucleus.     

Selective enzymatic degradation of self-assembled particles from amphiphilic block copolymers obtained by the combination of N-carboxyanhydride and nitroxide-mediated polymerization

Combining controlled radical polymerizations and a controlled polypeptide synthetic technique, such as N-carboxyanhydride (NCA) ring-opening polymerization, enables the generation of well-defined block copolymers to be easily accessible. Here we combine NCA polymerization with the nitroxide-mediated radical polymerization of poly(n-butyl acrylate) (PBA) and polystyrene (PS), using a TIPNO and SG1-based bifunctional initiator to create a hybrid block copolymer. The polypeptide block consists of (block) copolymers of poly(L-glutamic acid) embedded with various quantities of L-alanine. The formed superstructures (vesicles and micelles) of the block copolymers possessed varying degrees of enzyme responsiveness when exposed to elastase and thermolysin, resulting in controlled enzymatic degradation dictated by the polypeptide composition. The PBA containing block copolymers possessing 50% L-alanine in the polypeptide block showed a high degradation response compared to polymers containing lower L-alanine quantities. The particles stabilized by copolypeptides with L-alanine near the hydrophobic block showed full degradation within 4 days. Particles containing polystyrene blocks revealed no appreciable degradation under the same conditions, highlighting the specificity of the system and the importance of synthetic polymer selection. However, when the degradation temperature was increased to 70 °C, degradation could be achieved due to the higher block copolymer exchange between the particle and the solution. A number of novel biohybrid structures are disclosed that show promise as enzyme-responsive materials with potential use as payload release vehicles, following their controlled degradation by specific, target, enzymes.     

Complex macromolecular chimeras

By combining two living polymerizations, anionic and ring opening (ROP), the following novel multiblock multicomponent linear and miktoarm star (micro-star) polymer/polypeptide hybrids (macromolecular chimeras) were synthesized: Linear, PBLL-b-PBLG-b-PS-b-PBLG-b-PBLL; 3micro-stars, (PS)2(PBLG or PBLL), (PS)(PI)(PBLG or PBLL); 4micro-stars, (PS)2[P(alpha-MeS)](PBLG or PBLL), (PS)2(PBLG or PBLL)2 [PS, polystyrene; PI, polyisoprene; P(alpha-MeS), poly(alpha-methylstyrene); PBLG, poly(gamma-benzyl-L-glutamate); and PBLL, poly(-tert-butyloxycarbonyl-L-lysine)]. The procedure involves (a) the synthesis of end- or in-chain amino-functionalized polymers, by anionic polymerization high vacuum techniques and appropriate linking chemistry and (b) the use of the amino groups for the ROP of alpha-amino acid carboxyanhydrides (NCAs). Molecular characterization revealed the high molecular weight and compositional homogeneity of the macromolecular chimeras prepared. The success of the synthesis was based mainly on the high vacuum techniques used for the ROP of NCAs, ensuring the avoidance of unwanted polymerization mechanisms and termination reactions.     

New polymer syntheses. IV. Polypeptides of lysine and ornithine with pending pyrimidine bases

Starting with β-methoxy methacryloylisocyanate, β-methoxy methacrylisothiocyanate, and β-isocyanatopropionyl chloride, on the one hand, and N^α-Z-lysine or N^α-Z-ornithine, on the other hand, N^α-Z-amino acids with pyrimidine bases in the side chain were synthesized. These Z-protected nucleoamino acids were converted to the corresponding N-carboxyanhydrides (NCAs) via the silylester method. In the case of 2-thiothymine derivatives, the reaction intermediate of the NCA synthesis caused benzylation of the thioxo- group, so that a new class of 2-mercaptopyrimidine derivatives was isolated unexpectedly. The poly(nucleoamino acids) obtained by polymerization of the nucleoamino acid NCAs were characterized by elemental analyses, optical rotations ¹H-nmr and ¹³C-nmr spectra. Vapor pressure osmometry revealed that the DP s were in the range of 20–30. Their spectra suggest a helical secondary structure. While all homopolypeptides are insoluble in water, copolypeptides containing L -lysine N^ε-hydrobromide possess good solubility in water.     

General method for purification of α-amino acid-n-carboxyanhydrides using flash chromatography

We describe the application of flash column chromatography on silica gel as a rapid and general method to obtain pure α-amino acid-N-carboxyanhydride (NCA) monomers, the widely used precursors for the synthesis of polypeptides, without the need for recrystallization. This technique was effective at removing all common impurities from NCAs and was found to work for a variety of NCAs, including those synthesized using different routes, as well as those bearing either hydrophilic or hydrophobic side chains. All chromatographed NCAs required no further purification and could be used directly to form high molecular weight polypeptides. This procedure is especially useful for the preparation of highly functional and low melting NCAs that are difficult to crystallize and, consequently, to polymerize. This method solves many long-standing problems in NCA purification and provides rapid access to NCAs that were previously inaccessible in satisfactory quality for controlled polymerization. This method is also practical in that it requires less time than recrystallization and often gives NCAs in improved yields.     

Functionalized micellar assemblies prepared via block copolymers synthesized by living free radical polymerization upon peptide-loaded resins

Hybrid peptidic-synthetic amphiphilic block copolymers, synthesized by living free radical polymerization (LFRP) on solid support, have been utilized as precursors for nanoscale materials possessing bio-available peptides. LFRP initiators, coupled to the peptide terminus upon the resin, facilitated the growth of homo- and block copolymers via nitroxide mediated radical polymerization (NMRP) or atom transfer radical polymerization (ATRP). Herein, the versatile solid-support synthesis of the antimicrobial peptide tritrpticin, coupling of living free radical polymerization initiators to the peptide-loaded resin, and the controlled radical polymerization of various monomers to yield amphiphilic diblock copolymers are described. Assembly of the peptidic-synthetic block copolymers into micelles and a preliminary assessment of their in vitro biological properties are detailed.     

Engineering soft nanostructured functional materials via orthogonal chemistry

Nanostructured amphiphilic block copolymers, graft copolymers, polymeric thermally responsive molecular brushes and polymer stars are only few examples of macromolecular architectures accessible either via controlled/living radical polymerization (CLRP) techniques or the combination of CLRP mechanisms with efficient post-polymerization routes including click chemistry. Precise control over the composition, molecular weight and functionalities is a prerequisite for soft polymeric materials to self-organize into ordered morphologies. This contribution describes novel orthogonal chemical routes for the synthesis of macromolecular architectures and self-assembly of functional soft polymeric materials. Emerging potential applications of well-defined block and graft copolymers are outlined as well.     

Stereoselective polymerization of gamma-benzyl glutamate NCA

The polymerization of γ-benzyl glutamate NCAs has been investigated. The results indicate that a coil-to-helix transformation is not responsible for the kinetic data. The results were rationalized by assuming formation of polymer aggregates coupled with the stereoselective adsorption of monomer onto growing polymer prior to reaction. From kinetic data a ratio of equilibrium constants for adsorption was determined. Independent data confirmed the assumption that adsorption of monomer onto polymer occurred. Equilibrium constants were evaluated, and their ratio was found to be comparable with that obtained from the kinetic data.     

Synthesis, swelling behavior, and biocompatibility of novel physically cross-linked polyurethane-block-poly(glycerol methacrylate) hydrogels

Physically cross-linked novel block copolymer hydrogels with tunable hydrophilic properties for biomedical applications were synthesized by controlled radical polymerization of polyurethane macroiniferter and (2,2-dimethyl-1,3-dioxolane) methyl methacrylate. The block copolymers were converted to hydrogels by the selective hydrolysis of poly[(2,2-dimethyl-1,3-dioxolane) methyl methacrylate] block to poly(glycerol methacrylate). The block copolymerization has been monitored by monomer conversion and molecular weight increase as a function of time. It was observed that the polymerization proceeded with a characteristic "living" behavior where both monomer conversion and molecular weight increased linearly, with increasing reaction time. The resulting hydrogels were investigated for their equilibrium water content (EWC), dynamic water contact angles, swelling kinetics, thermodynamic interaction parameters, plasma protein adsorption, and platelet adhesion. Similar to our previous mechanically responsive hydrogels (Mequanint, K.; Sheardown, H. J. Biomater. Sci. Polym. Ed. 2005, 10, 1303-1318), the present results indicated that block copolymer hydrogels have excellent hydrophilicity and swelling behavior with improved modulus of elasticity. The equilibrium swelling was affected by the hydrolysis time, block length of poly(glycerol methacrylate), temperature, and the presence of soluble salts. Fibrinogen adsorption and platelet adhesion were significantly lower for the hydrogels than for the control polyurethane, whereas albumin adsorption increased for the hydrogels in proportion to the contents of poly(glycerol methacrylate). These hydrogels have potential in a number of biomedical applications such as drug delivery and scaffolds for tissue engineering.     

Formins: processive cappers of growing actin filaments

Taking the advantage of single-molecule imaging, our recent study has revealed surprisingly long processive movement of a Formin protein, mDia1, surfing along with the growing end of actin filaments in living cells. This finding provides direct evidence for the ability of Formins to function as processive cappers that has been postulated from several lines of evidence in biochemical studies. With nucleating filaments from the profilin-actin pool, Formins may effectively generate long actin filaments, and contribute to the generation of the specific actin-based structures, that is, the contractile ring in cytokinesis, actin stress fibers in animal cells, and yeast actin cables. Furthermore, Formins have the potential to function as actin polymerization-driven molecular motors. Although much remains to be tested about the role of this novel molecular mobilization mechanism, cells might utilize actin polymerization energy for cell shape change and/or trafficking via Formin motors.     

Real-time monitoring of actin polymerization in living cells using split luciferase

Real-time monitoring of actin polymerization in living cells is beneficial for characterizing cellular activities such as migration, proliferation, and death. We developed new bioluminescence-based probe proteins that enable the monitoring of actin polymerization in living cells. Unlike other ordinary split luciferase probes, our probes were incorporated in endogenous actin filament that enabled it to measure the actin polymerization quantitatively. The probe proteins exhibited a dose-responsive decrease in photon emission intensity in response to the filamentous (F)-actin-disrupting agent latrunculin A. This technique has a high sensitivity with a high signal-to-noise ratio and is nontoxic compared with other methods of monitoring actin polymerization in living cells. Using this technique, we succeeded in monitoring the F-actin level in living cells during apoptosis progression induced by UV irradiation continuously for 12 h. F-actin was transiently upregulated after UV irradiation. Since UV-induced cell death was enhanced by treatment with latrunculin A during the period which F-actin is increased, transient upregulation of F-actin after UV is likely a protective reaction against UV-induced cell death. Our novel technique is an effective tool for investigating actin polymerization in living cells.     

Highly efficient antibacterial diblock copolypeptides based on lysine and phenylalanine

A series of amphiphilic diblock copolypeptides (K₃₀‐b ‐F₁₅, K₃₀‐b ‐F₃₀, and K₃₀‐b ‐F₄₅) were synthesized via N ‐carboxy‐α‐amino‐anhydride ring‐opening polymerization. The copolypeptides had excellent antibacterial efficacy to both Gram positive (S. aureus ) and Gram negative (E. coli ) bacteria. The minimum inhibitory concentrations (MICs) against E. coli and S. aureus are 8 μg mL^?1 and 2 μg mL^?1, respectively, lower than most natural and artificial antimicrobial peptides (AMPs). The morphological changes of the bacteria treated with diblock copolypeptides were investigated by transmission electron microscopy; the results proved that the diblock copolypeptides had a similar antibacterial pore‐forming mechanism to natural cationic peptides. This was confirmed by laser scanning confocal microscope images. CCK‐8 results and the MICs showed that the diblock copolypeptides have high selectivity to bacteria, which suggested that the diblock copolypeptides could be excellent candidates to replace traditional antibiotics in future.     

Synthesis and gelation of copolypept(o)ides with random and block structure

Copolypept(o)ides of polysarcosine (PSar) and poly(N‐isopropyl‐L‐glutamine) (PIGA) with random and block sequence structures were synthesized by ring‐opening polymerization (ROP) of sarcosine N‐carboxyanhydrides (Sar‐NCA) and γ‐benzyl‐l ‐glutamate N‐carboxyanhydrides (BLG‐NCA) and post modification. With different distribution of Sar along the main chain, H‐bonding pattern and secondary structure of polypeptides were turned, as well as aggregation and gelation behavior. Both copolypept(o)ides formed hydrogels above their critical gelation concentrations (CGCs) without thermo‐sensitivity, which was normally reserved for PEG copolypeptides (eg, PEG‐b‐PIGA). In particular, a different mechanism from previously reported micellar percolation or fibrillar entanglement was suggested for gelation of the random copolypept(o)ide. Therefore, hydrogels from copolymers of PSar and PIGA represented a new approach to construct easy‐handling, biocompatible, biodegradable and thermo‐stable gels that could potentially be applied in biomedical fields.     

Buoyant and potentiometric titrations of synthetic polpeptides. II. Five copolypeptides and two nonionizable homopolypeptides in CsCl solutions.

The buoyant density titrations of five ionizable copolypeptides in concentrated CsCl solutions have been determined. The results are used to formulate models for predicting the buoyant density titration behavior of copolypeptides and proteins using the previously reported homopolypeptide buoyant density titration curves. It was determined for these copolypeptides that the best predictive model must include not only the buoyant densities of the constituent amino acid residues and the relative composition, but also hydration and salt binding. Hydrations determined for the homopolypeptides are used in the copolypeptide predictive model. The hydrations of the neutral homopolypeptides were readily calculable since their buoyant densities are thermodynamically defined in terms of their partial specific volumes and hydrations. For the case of a charged macromolecule, an expression for the buoyant density as a function of the number and nature of the bound ions, its partial specific volume, and its relative hydration has also been available for some time. This heretofore intuitive relationship is now derived from thermodynamic principles and allows calculations of hydrations to charged macromolecules which bind either cations, anions, or both. The potentiometric titrations of three of the five copolypeptides in concentrated CsCl solutions were determined in order to study the effect of residue interaction and solvation effects on their ionization behavior. The potentiometric results are also combined directly with the buoyant density titration results to determine the correlation of the buoyant density with the degree of ionization. As in the cases of poly(Glu) and poly(His), the buoyant density of the copolypeptides changed linearily with the degree of ionization. The buoyant density titrations of two nonionizable homopolypeptides, poly(Gly) and poly(Ala), were determined in concentrated CsCl solutions. The buoyant density was found to increase with increasing pH, despite the fact that side chains do not contain ionizable groups. This is the first evidence from homopolypeptide or copolypeptide data that buoyant density changes can be observed from effects other than side-chain ionizations.     

Development of nanobiocomposite fibers by controlled assembly of rod-like tobacco mosaic virus

One-dimensional composite nanofibers were generated via in-situ polymerization of polyaniline on the surface of tobacco mosaic virus (TMV) and the head-to-tail assembly of TMV. These composite nanofibers have very high aspect ratio and good processibility. Two factors contribute to the formation of such TMV-composite fibers: (1) the accumulation and polymerization of monomers on the surface of TMV; and (2) the possibility of prolongation and stabilization of TMV helices. This strategy has been used in the synthesis of other polymeric bionanofibers with a variety of starting materials. In addition, the morphology of the final composite materials can be modulated by the covalent modification of TMV. When sulfonic acid groups are tailored to the exterior surface of TMV, polymerization of aniline can induce TMV to form branched structures with knot-like connections. On the other hand, modification of TMV with noncharged groups like acetylenes can block the assembly process completely. TEM and AFM are used to analyze the morphology and structure of composite fibers. This novel strategy to assemble TMV into 1D supramolecular assembly could be utilized in the fabrication of advanced materials for potential applications including electronics, optics, sensing, and biomedical engineering. M.A. Bruckman and Z. Niu contributed equally to this work.     

Synthesis, characterization, properties, and drug release of poly(alkyl methacrylate-b-isobutylene-b-alkyl methacrylate)

Polyisobutylene (PIB)-based block copolymers have attracted significant interest as biomaterials. Poly(styrene-b-isobutylene-b-styrene) (SIBS) has been shown to be vascularly compatible and, when loaded with paclitaxel (PTx) and coated on a coronary stent, has the ability to deliver the drug directly to arterial walls. Modulation of drug release from this polymer has been achieved by varying the drug/polymer ratio, by blending SIBS with other polymers, and by derivatizing the styrene end blocks to vary the hydrophilicity of the copolymer. In this paper, results are reported on the synthesis, physical properties, and drug elution profile of PIB-based block copolymers containing methacrylate end blocks. The preparation of PIB-poly(alkyl methacrylate) block copolymers has been accomplished by a new synthetic methodology using living cationic and anionic polymerization techniques. 1,1-Diphenylethylene end-functionalized PIB was prepared from the reaction of living PIB and 1,4-bis(1-phenylethenyl)benzene, followed by the methylation of the resulting diphenyl carbenium ion with dimethylzinc (Zn(CH(3))(2)). PIB-DPE was quantitatively metalated with n-butyllithium in tetrahydrofuran, and the resulting macroinitiator could initiate the polymerization of methacrylate monomers, yielding block copolymers with high blocking efficiency. Poly(methyl methacrylate-b-isobutylene-b-methyl methacrylate) (PMMA-b-PIB-b-PMMA) and poly(hydroxyethyl methacrylate-b-isobutylene-b-hydroxyethyl methacrylate) (PHEMA-b-PIB-b-PHEMA) triblock copolymers were synthesized and used as drug delivery matrixes for coatings on coronary stents. The PMMA-b-PIB-b-PMMA/PTx system displayed zero-order drug release, while stents coated with PHEMA-b-PIB-b-PHEMA/PTx formulations exhibited a significant initial burst release of PTx. Physical characterization using atomic force microscopy and differential scanning calorimetry of the formulated PMMA-b-PIB-b-PMMA coating matrix indicated the partial miscibility of PTx with the PMMA microphase of the matrix.     

Effect of chain topology on the self-organization and dynamics of block copolypeptides: from diblock copolymers to stars

The effect of chain topology on (i) the peptide secondary structure, (ii) the nanophase self-assembly, and (iii) the local segmental and global peptide relaxations has been studied in a series of model diblock and 3-arm star copolypeptides of poly(epsilon-carbobenzyloxy-L-lysine) (PZLL) and poly(gamma-benzyl-L-glutamate) (PBLG) with PZLL forming the core. Diblock copolypeptides are nanophase separated with PBLG and PZLL domains comprising alpha-helices packed in a hexagonal lattice. Star copolypeptides are only weakly phase separated, comprising PBLG and PZLL alpha-helices in a pseudohexagonal lattice. Phase mixing has profound consequences on the local and global dynamics. The relaxation of the peptide secondary structure speeds up, and the helix persistence length is further reduced in the stars, signifying an increased concentration of helical defects.