Coassembly of poly(ethylene glycol)-block-poly(glutamate sodium) and gemini surfactants with different spacer lengths

Properties and Applications of Quaternary Ammonium Gemini Surfactant 12-6-12: An Overview

Surfactants are amphiphilic molecules and one of the most versatile products of the chemical industry. They can be absorbed at the air-water interface and can align themselves so that the hydrophobic part is in the air while the hydrophilic part is in water. This alignment lowers the surface or interfacial tension. Gemini surfactants are a modern variety of surfactants with unique properties and a very wide range of potential applications. Hexamethylene-1,6-bis(N-dodecyl-N,N-dimethylammonium bromide) is one such representative compound that is a better alternative to a single analogue. It shows excellent surface, antimicrobial, and anticorrosion properties. With a highly efficient synthetic method and a good ecological profile, it is a potential candidate for numerous applications, including biomedical applications.

Turning double hydrophilic into amphiphilic: IR825-conjugated polymeric nanomicelles for near-infrared fluorescence imaging-guided photothermal cancer therapy

Developing biocompatible and photodegradable photothermal agents (PTAs) holds great promise for potential clinical applications in photothermal cancer therapy. Herein, a new PTA was innovatively constructed by conjugating the hydrophobic near-infrared (NIR) heptamethine cyanine molecule IR825-NH₂ with a double hydrophilic block copolymer methoxypoly(ethylene glycol)_5k-block-poly(l-aspartic acid sodium salt)₁₀ (abbreviated as PEG-PLD) via amine-carboxyl reaction. The as-designed PEG-PLD(IR825) was amphiphilic and could self-assemble into polymeric nanomicelles in aqueous solutions. Benefiting from the chemical conjugation strategy, PEG-PLD(IR825) nanomicelles realized a considerably high drug loading rate (∼21.0%) and substantially avoided the premature release of IR825 during systemic circulation. Confocal imaging revealed that the nanomicelles mainly located at mitochondria and endoplasmic reticulum after cellular internalization. In vitro photothermal therapy demonstrated the excellent cancer killing efficiency of PEG-PLD(IR825) nanomicelles due to their high light-to-heat conversion efficiency upon NIR laser irradiation. In addition, PEG-PLD(IR825) nanomicelles showed polarity-sensitive fluorescence at ∼610 nm (under 552 nm excitation) and 830 nm (under 780 nm excitation), which was especially useful for both in vitro visible fluorescence imaging and in vivo near-infrared fluorescence imaging-guided photothermal therapy (PTT). At the in vivo level, PEG-PLD(IR825) nanomicelles exhibited an excellent tumor-homing ability and a long retention time in tumor tissues as evidenced by the in vivo fluorescence imaging results. The desirable properties of PEG-PLD(IR825) nanomicelles ensured their effective tumor ablation during PTT treatment. More importantly, the PEG-PLD(IR825) nanomicelles underwent degradation after laser irradiation, which ensured their post-treatment biosafety. Therefore, the nanomicelles are promising to serve as an efficient and safe PTA for imaging-guided photothermal cancer therapy.

Surfactant-Mediated Crystallization-Driven Self-Assembly of Crystalline/Ionic Complexed Block Copolymers in Aqueous Solution

A series of crystalline/ionic complexed block copolymers (BCPs) with various compositions have been prepared by sequential reactions. The BCPs with different hydrophilic fractions can self-assemble into various morphologies, such as spindlelike, rodlike, and spherical micelles with different crystallinity of the core. Bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) is added as a surfactant to induce the morphological transition of BCPs in aqueous media. The introduced AOT can be tightly bound to the cationic units, and a water-insoluble unit in the corona forms, leading to a reduced tethering density. Consequently, morphological variety changing from rods to platelets to fibril to dendrite-like micelles can be observed.

Folding Behaviors of Protein (Lysozyme) Confined in Polyelectrolyte Complex Micelle

The folding/unfolding behavior of proteins (enzymes) in confined space is important for their properties and functions, but such a behavior remains largely unexplored. In this article, we reported our finding that lysozyme and a double hydrophilic block copolymer, methoxypoly(ethylene glycol)5K-block-poly(l-aspartic acid sodium salt)10 (mPEG(5K)-b-PLD10), can form a polyelectrolyte complex micelle with a particle size of ∼30 nm, as verified by dynamic light scattering and transmission electron microscopy. The unfolding and refolding behaviors of lysozyme molecules in the presence of the copolymer were studied by microcalorimetry and circular dichroism spectroscopy. Upon complex formation with mPEG(5K)-b-PLD10, lysozyme changed from its initial native state to a new partially unfolded state. Compared with its native state, this copolymer-complexed new folding state of lysozyme has different secondary and tertiary structures, a decreased thermostability, and significantly altered unfolding/refolding behaviors. It was found that the native lysozyme exhibited reversible unfolding and refolding upon heating and subsequent cooling, while lysozyme in the new folding state (complexed with the oppositely charged PLD segments of the polymer) could unfold upon heating but could not refold upon subsequent cooling. By employing the heating-cooling-reheating procedure, the prevention of complex formation between lysozyme and polymer due to the salt screening effect was observed, and the resulting uncomplexed lysozyme regained its proper unfolding and refolding abilities upon heating and subsequent cooling. Besides, we also pointed out the important role the length of the PLD segment played during the formation of micelles and the monodispersity of the formed micelles. Furthermore, the lysozyme-mPEG(5K)-b-PLD10 mixtures prepared in this work were all transparent, without the formation of large aggregates or precipitates in solution as frequently observed in other protein-polyelectrolyte systems. Hence, the present protein-PEGylated poly(amino acid) mixture provides an ideal water-soluble model system to study the important role of electrostatic interaction in the complexation between proteins and polymers, leading to important new knowledge on the protein-polymer interactions. Moreover, the polyelectrolyte complex micelle formed between protein and PEGylated polymer may provide a good drug delivery vehicle for therapeutic proteins.

Ultrasensitive ROS-Responsive Coassemblies of Tellurium-Containing Molecules and Phospholipids

Reactive oxygen species (ROS) play crucial roles in cell signaling and redox homeostasis and are strongly related to metabolic activities. The increase of the ROS concentration in organisms can result in several diseases, such as cardiovascular diseases and cancer. The concentration of ROS in biologically relevant conditions is typically as low as around tens of micromolars to 100 μM H2O2, which makes it necessary to develop ultrasensitive ROS-responsive systems. A general approach is reported here to fabricate an ultrasensitive ROS-responsive system via coassembly between tellurium-containing molecules and phospholipids, combining the ROS-responsiveness of tellurium and the biocompatibility of phospholipids. By using dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and NMR spectra, coassembly behaviors and the responsiveness of the coassemblies have been investigated. These coassemblies can respond to 100 μM H2O2, which is a biologically relevant ROS concentration, and demonstrate reversible redox properties.

Interactions between sodium polyacrylate and mixed surfactants of polyoxyethylene tert-octyl phenyl ether and dodecyltrimethylammonium bromide

Interactions between sodium polyacrylate and mixed surfactants of polyoxyethylene tert-octyl phenyl ether and dodecyltrimethylammonium bromide in 40 mM NaBr aqueous solutions were studied using isothermal titration calorimetry.