Influence of assembling pH on the stability of poly(L-glutamic acid) and poly(L-lysine) multilayers against urea treatment

Polyelectrolyte multilayers of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) were built up using the layer-by-layer (LbL) technique in low pH (3.6, PM3.6) and in neutral pH (7.4, PM7.4) solutions. The multilayers were then treated with a concentrated urea (one kind of denaturant for proteins and polypeptides) solution (8M) and rinsed with corresponding buffer. The buildup and treatment processes were investigated by ultraviolet visible spectroscopy and ellipsometry. The surface morphology was observed by scanning force microscopy (SFM). The inner structures were determined by X-ray reflectometry and circular dichroism spectroscopy (CD). An exponential growth of the optical mass and the layer thickness was observed for both PM3.6 and PM7.4. After urea treatment, a significant mass loss for PM3.6 was found, while no mass change was recorded for PM7.4. The dominant driving force for PM7.4 is electrostatic interaction, resulting in multilayers with an abundant beta-sheet structure, which has higher stability against urea treatment. By contrast, the dominant driving force for PM3.6 is hydrogen bonding and hydrophobic interaction, which are sensitive to the urea treatment. The mechanism is substantiated by molecular mechanics calculation. This has offered a convenient pathway to mediate the multilayer properties, which is of great importance for potential applications.     

Dynamic adsorption and characterization of phospholipid and mixed phospholipid/protein layers at liquid/liquid interfaces

Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, proteins and phospholipid/protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of pure protein solutions, i.e. human serum album (HSA), beta-lactoglobulin (beta-LG), beta-casein (beta-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a "skin-like" folded film of pure protein or phospholipid/protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of proteins.     

Reversibly permeable nanomembranes of polymeric microcapsules

Polymeric nanometer-thick membranes or nanomembranes possessing photocontrollable permeability are presented. Microcapsules are used as membrane model systems, while gold nanoparticle aggregates are used as active absorption centers. Upon laser light illumination the membranes change permeability reversibly because nanoparticles transiently affect the nearby polymeric network. Nanomembranes reseal to their impermeable state when the laser is switched off. This presents a novel and simple way of reversible permeability control of interest to intracellular signaling and membranes.     

Simple Peptide‐Tuned Self‐Assembly of Photosensitizers towards Anticancer Photodynamic Therapy

Peptide‐tuned self‐assembly of functional components offers a strategy towards improved properties and unique functions of materials, but the requirement of many different functions and a lack of understanding of complex structures present a high barrier for applications. Herein, we report a photosensitive drug delivery system for photodynamic therapy (PDT) by a simple dipeptide‐ or amphiphilic amino‐acid‐tuned self‐assembly of photosensitizers (PSs). The assembled nanodrugs exhibit multiple favorable therapeutic features, including tunable size, high loading efficiency, and on‐demand drug release responding to pH, surfactant, and enzyme stimuli, as well as preferable cellular uptake and biodistribution. These features result in greatly enhanced PDT efficacy in vitro and in vivo, leading to almost complete tumor eradication in mice receiving a single drug dose and a single exposure to light.     

Stepwise interfacial self-assembly of nanoparticles via specific DNA pairing

In the present work, we succeeded in alternatively depositing inorganic nanoparticles and functionalized DNA bases onto the water/oil interface from the water and oil bulk phases. The ligands used were functional thymines and adenines. Their thiol and phosphate groups were used to cap inorganic nanoparticles and their thymine and adenine groups to alter the surface functionality of the nanoparticles, thus enabling a layer-by-layer growth fashion of nanoparticles at the interface. The multiple particle ligation rendered the resulting nanoparticle films rather mechanically robust. As results, the freestanding asymmetric bilayer and trilayer films, composed of negatively-charged Au, positively-charged CdTe, and/or organic Ag nanoparticles were constructed; their areas were as large as over several centimetres, depending on the sizes of the containers used. Our work should bring up a novel methodology to generate asymmetric multilayer films of nanoparticles with a defined control of electron or charge across the films.     

Adsorption of the fusogenic peptide B18 onto solid surfaces: insights into the mechanism of peptide assembly

The adsorption and assembly of B18 peptide on various solid surfaces were studied by reflectometry techniques and atomic force microscopy. B18 is the minimal membrane binding and fusogenic motif of the sea urchin protein bindin, which mediates the fertilization process. Silicon substrates were modified to obtain hydrophilic charged surfaces (oxide layer and polyelectrolyte multilayers) and hydrophobic surfaces (octadecyltrichlorosilane). B18 does not adsorb on hydrophilic positively charged surfaces, which was attributed to electrostatic repulsion since the peptide is positively charged. In contrast, the peptide irreversibly adsorbs on negatively charged hydrophilic as well as on hydrophobic surfaces. B18 showed higher affinity for hydrophobic surfaces than for hydrophilic negatively charged surfaces, which must be due to the presence of hydrophobic side chains at both ends of the molecule. Atomic force microscopy provided the indication that lateral diffusion on the surface affects the adsorption process of B18 on hydrophobic surfaces. The adsorption of the peptide on negatively charged surfaces was characterized by the formation of globular clusters.     

Entrapment of α‐Chymotrypsin into Hollow Polyelectrolyte Microcapsules

Stable hollow polyelectrolyte capsules were produced by the layer‐by‐layer assembling of non‐biodegradable polyelectrolytes – poly(allylamine) and poly(styrenesulfonate) on melamine formaldehyde microcores followed by the core decomposition at low pH. A proteolytic enzyme, α‐chymotrypsin, was encapsulated into these microcapsules with high yields of up to 100%. The encapsulation procedure was based on the protein adsorption onto the capsule shells and on the pH‐dependent opening and closing of capsule wall pores. The protein in the capsules retained a high activity, and thermo‐ and storage stability. The nanostructured polyelectrolyte shell protected the proteinase from a high molecular weight inhibitor. Such enzyme‐loaded capsules can be used as microreactors for biocatalysis.     

Layer‐by‐Layer Assembled Nanotubes as Biomimetic Nanoreactors for Calcium Carbonate Deposition

Enzyme‐loaded magnetic polyelectrolyte multilayer nanotubes prepared by layer‐by‐layer assembly combined with the porous template could be used as biomimetic nanoreactors. It is demonstrated that calcium carbonate can be biomimetically synthesized inside the cavities of the polyelectrolyte nanotubes by the catalysis of urease, and the size of the calcium carbonate precipitates was controlled by the cavity dimensions. The metastable structure of the calcium carbonate precipitates inside the nanotubes was protected by the outer shell of the polyelectrolyte multilayers. These features may allow polyelectrolyte nanotubes to be applied in the fields of nanomaterials synthesis, controlled release, and drug delivery.