Volume 45 Issue 5, May 2013

The morphology and the electronic conductive properties of self-assembled monolayers formed by helical oligopeptides suitably functionalized with electro- and photoactive units were investigated by electrochemical, spectroscopic and atomic force microscopy techniques. The versatility of peptide building blocks was also highlighted by the formation of bicomponent self-assembled monolayers exploiting interchain dipole–dipole interactions.

Theranostic agents based on nanovectors (liposomes, naposomes, micelles, polymeric micelles and micelles built around a solid core) able to carry, simultaneously, a drug and a contrast agent and externally modified with targeting peptides are described.

A detailed study of physical vapor deposition (PVD) technique applied to diphenylalanine (FF) peptides is described, following the self-assembly mechanism of deposited peptide nanostructures.Control of their chemical and physical properties have enabled us to develop a controllable deposition technology for fabricating peptide nanostructures. The PVD process of FF consists of elementary stages: first linear-FF (L-FF) molecules adhere to the substrate forming an amorphous layer, which grows into nanoclusters. Second, either PNT of L-FF or peptide nano fiber of cyclo-FF are formed, depending on the PVD environment.

Two and three times repeats of the self-assembling peptide RADA16 (RADARADARADARADA), namely RADA16x2 and RADA16x3, were genetically produced. The peptides were expressed as fusion proteins while retaining the activity of the fusion partner protein. The expressed peptides exhibited both fibril formation and cell adhesive activity. Moreover, the hydrogels formed by the peptides via addition of a medium provided a three-dimensional environment for cell proliferation.

Amphiphilic peptides herein also induce phase separation in peptide membranes, ‘peptide rafts’. Amphiphilic helical peptides self-assembled into nanotubes by themselves, but into vesicles with 1:1 mixture of their stereocomplex. Their mixtures also yielded a round-bottom flask morphology, an AB-type conjugate morphology of a nanotube and a vesicle, due to phase separation in peptide membrane. The open mouth of the round-bottom flask was further combined with other peptide vesicles to generate asymmetric dumbbell morphology, ABC-type conjugate morphology of a nanotube and two vesicles.

Aib/Ala-containing peptides, lacking any charge or polar group, dissolve in water by forming spherical aggregates with diameters up to 100 nm. These self-assembled nanostructures are able to incorporate molecules of relevant size, such as decorated Au nanoparticles. Such systems may widen the number of applications currently accessible to self-assembled aggregates in the fields of biomedicine and materials science.

The elastin-like peptide (ELP)–gold nanoparticle (AuNP) hybrid can be aligned selectively on the micro-patterned polystyrene ridges by directed assembly based on a thermo-triggered hydrophilic and hydrophobic phase transition of the ELP shell.

The binding behavior of guests (dyes and DNA) into peptide nanocapsules formed via self-assembly of a 24-mer β-annulus peptide fragment obtained from the capsid protein of the tomato bushy stunt virus is reported. Binding of sodium 8-anilinonaphthalene-1-sulfonate and uranine into the peptide nanocapsules minimally affected the size of the nanocapsules, whereas binding of other anionic dyes resulted in the formation of precipitates. Complexation of the β-annulus peptide with M13 phage DNA formed a core-shell nanosphere in which the DNA was encapsulated in the peptide assembly.

A novel peptide-array format system with a photo-cleavage linker for cellular toxicity analysis was constructed. In this system, a peptide was immobilized on a commercially available plate bottom via the photo-cleavable linker. UV light irradiation on the desired wells releases the peptide from the plate bottom, and then the cytotoxic behavior of the peptide can be monitored.

Platinum nanoparticles stabilized by linear polyethyleneimine (LPEI) were prepared by the liquid-phase reduction of chloroplatinic(IV) acid with sodium borohydride. The averaged radii of particles were 3.26 and 1.76 nm when the molecular weights of LPEI were 25 000 and 2150, respectively. These nanoparticles were well dispersed in water in the range of pH 1–6. Branched polyethyleneimine also provided nanoparticles that dispersed in water in the range of pH 0–8. Linear poly(ethyleneimine-co-N-methylethyleneimine) gave nanoparticles that dispersed in water in the range of pH −1 to 15.

The phase-transition point Tc from the low- to high-temperature phase of ethylene-tetrafluoroethylene copolymer is dependent on the type of the third monomeric unit having long (C4F9) or short (CF3) side groups. The existence of side chains affects more or less the unit cell dimension as well as the higher-order structure of stacked lamellae.

A new accepter unit, dimethyl-2H-benzimidazole, was prepared and utilized for the synthesis of the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics. Dimethyl-2H-benzimidazole unit was designed to substitute the benzothiadiazole (BT) unit of PCDTBT. The advantage of dimethyl-2H-benzimidazole compared with the BT moiety of PCDTBT is to improve the solubility of the polymer while keeping the 1,2-quinoid form to lead coplanarity of the backbone.

Novel amphiphilic graft copolymers composed of poly(γ-glutamic acid) (γ-PGA) as a hydrophilic backbone and enantiomeric PLA as hydrophobic side chains were successfully synthesized by using carbodiimide as the coupling agent. The enantiomeric γ-PGA-graft-PLLA (γ-PGA-g-PLLA) and γ-PGA-graft-PDLA (γ-PGA-g-PDLA) copolymers could form NPs, and stereocomplex crystallites were formed in the case of the mixture of γ-PGA-g-PLLA and γ-PGA-g-PDLA copolymers. These NPs with reactive functional groups would have great potential to be used as stable delivery vehicles for pharmaceutical and biomedical applications.

Noncovalent functionalization of multi-walled boron nitride nanotubes (BNNTs) was achieved through water-soluble synthetic polymers wrapping. This led to the excellent disentanglement and dispersion of BNNTs in an aqueous phase. Various spectroscopic techniques revealed that π-π stacking interactions played the key role for the polymer-functionalization of BNNT. To show a prospective application of polymer-functionalized BNNTs in surface engineering fields, the disentangled BNNTs were used as the raw/starting materials for the creation of superhydrophobic surfaces.

A series of two-dimensional conjugated polymers (P1–P4) based on benzo[1,2-b:4,5-b’]dithiophene donor unit and thiophene unit modified by pendant acceptor groups were synthesized. P1–P4 possess good solubility, thermal stability, tunable optical properties and low HOMO energy levels. Bulk heterojunction polymer solar cells based on P2 exhibit a power conversion efficiency of 1.89% and an impressively high V_oc of 0.93 V.

The May 2013 special issue of Polymer Journalon Peptide Materials features a collection of distinctive reviews and articles that discuss peptide materials and their applications. The accompanying web focus offers access to relevant articles selected from across Nature Publishing Group to provide further insights to readers of the special issue.