Cores Of Block Copolymer Micelles Research Articles

Aggregation-Induced Ignition of Near-Infrared Phosphorescence of Non-Symmetric [Pt(C^N*N'^C')] Complex in Poly(caprolactone)-based Block Copolymer Micelles: Evaluating the Alternative Design of Near-Infrared Oxygen Biosensors.

In the present work, we described the preparation and characterization of the micelles based on amphiphilic poly(ε-caprolactone-block-ethylene glycol) block copolymer (PCL-b-PEG) loaded with non-symmetric [Pt(C^N*N’^C’)] complex (Pt1) (where C^N*N’^C’: 6-(phenyl(6-(thiophene-2-yl)pyridin-2-yl)amino)-2-(tyophene-2-yl)nicotinate). The obtained nanospecies displayed the ignition of near-infrared (NIR) phosphorescence upon an increase in the content of the platinum complexes in the micelles, which acted as the major emission component at 12 wt.% of Pt1. Emergence of the NIR band at 780 nm was also accompanied by a 3-fold growth of the quantum yield and an increase in the two-photon absorption cross-section that reached the value of 450 GM. Both effects are believed to be the result of progressive platinum complex aggregation inside hydrophobic poly(caprolactone) cores of block copolymer micelles, which has been ascribed to aggregation induced emission (AIE). The resulting phosphorescent (Pt1@PCL-b-PEG) micelles demonstrated pronounced sensitivity towards molecular oxygen, the key intracellular bioanalyte. The detailed photophysical analysis of the AIE phenomena revealed that the NIR emission most probably occurred due to the excimeric excited state of the 3MMLCT character. Evaluation of the Pt1@PCL-b-PEG efficacy as a lifetime intracellular oxygen biosensor carried out in CHO-K1 live cells demonstrated the linear response of the probe emission lifetime towards this analyte accompanied by a pronounced influence of serum albumin on the lifetime response. Nevertheless, Pt1@PCL-b-PEG can serve as a semi-quantitative lifetime oxygen nanosensor. The key result of this study consists of the demonstration of an alternative approach for the preparation of NIR biosensors by taking advantage of in situ generation of NIR emission due to the nanoconfined aggregation of Pt (II) complexes inside the micellar nanocarriers.

Synthesis, characterization, micellization and metal coordination polymerization of pentacyanoferrate-coordinated block copolymers for monodispersed soluble Prussian blue nanospheres

Monodispersed soluble prussian blue (PB) metal-coordination nanospheres are synthesized via a confined metal coordination polymerization within the cores of block copolymer micelles. Pentacyanoferrate-coordinated block copolymers of P(4VPFe-co-4VP)-b-PDMA (P4VPFe: pentacyanoferrate coordinated poly(4-vinylpyridine); PDMA: poly(dimethylacrylamide)) were synthesized through a ligand exchange reaction of [Fe(CN)5NH3]3− with pyridyl moieties in P4VP-b-PDMA. The polymers were isolated and characterized using UV-Vis, FT-IR, NMR and elemental analysis. In H2O/EtOH, selective solvents for PDMA, the polymers self-assembled into monodispersed nanospheres with P(4VPFe-co-4VP) forming cores and PDMA acting as the corona. Subsequent metal coordination polymerization of Fe3+ with ferrate confined within the cores of the micelles led to monodispersed PB nanospheres as confirmed by DLS, TEM, HRTEM and SEM. The particles are soluble both in water and organic solvents as a result of the robust solubility of PDMA corona chains. Several parameters, including the solvent used, the concentration of the block copolymers, the amount of FeCl3 added and the amount of water involved in the systems, have been found to be important in order to obtain well-defined monodispersed PB nanospheres.

Determination of the critical micelle concentration of surfactants and amphiphilic block copolymers using coumarin 153

We describe a method to determine the critical micelle concentration (CMC) of low molecular weight surfactants and amphiphilic diblock copolymers in water based on the use of the fluorescent dye coumarin 153 (C153). The method is based on the measurement of the fluorescence intensity, solvatochromic shift and fluorescence anisotropy of C153 and was tested with the low molecular weight surfactants SDS, CTAB and Triton X-405 in water, for which we obtained, within the experimental error, CMC values identical to those previously published. The method was further used to determine the CMC of a family of poly(N-decylacrylamide)-b-poly(N,N-diethylacrylamide) amphiphilic block copolymers synthesized by RAFT polymerization, with an equal poly(N-decylacrylamide) hydrophobic block length and increasing poly(N,N-diethylacrylamide) hydrophilic block lengths. By measuring the fluorescence anisotropy of C153 in block copolymer aqueous solutions, it is also possible to detect the formation of pre-micellar aggregates at concentrations below the CMC. The dye C153 is more appropriate than pyrene to study self-assembly in water, where pyrene forms ground and excited state aggregates at very low concentrations. Furthermore, C153 is an excellent anisotropy probe with a very high limiting anisotropy (0.375) that can be used to determine the CMC, detect the presence of pre-micellar aggregates, and evaluate the fluidity of the hydrophobic core of block copolymer micelles.

Ordered Nanoparticle Arrays Synthesized from Self-Assembled Diblock Copolymer Templates

AbstractWe present a comprehensive study of using diblock copolymer micelle templates to synthesize ordered nanoparticle arrays. Ionic and coordination bonds have been exploited to incorporate nanoparticle precursors into cores of block copolymer micelles. Polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) has been shown to be able to localize anions via electrostatic attraction with protonated pyridine cations while transitional metals can be sequestered through coordination bonds. Polystyrene-b-poly (acrylic acid) (PS-PAA) can localize a variety of cations via ionic bonds with acrylic anions. We have demonstrated that the size of nanoparticles can be tuned by controlling the solution concentration of an ionic precursor. By mixing these two distinct block copolymers which can selectively interact with different precursor species, complex nanoparticle architectures can be generated thus paving a path for new applications.

Conformation of Chains in Cores of Block Copolymer Micelles with Solubilized Homopolymer: a Monte Carlo Study

A system of compatible self-avoiding polymer chains solubilized in spherical cores of block copolymer micelles was studied by lattice Monte Carlo simultions. The core is modeled as a spherical cavity on a simple cubic lattice, filled in partially by tethered (core-forming) chains and partially by free (solubilized) chains. Molecular parameters (e.g., the ratio of the contour length of the model chains to the core radius) correspond to those in real micellar systems. The density (the fraction of lattice sites occupied) is 0.6 which corresponds to swollen micellar cores in real micellar systems. Simulations yield a constant segment density profile in the core. Both the tethered and solubilized chains acquire an ellipsoidal shape. The ellipsoids equivalent to both types of chains are more spherical than those in a melt and strongly oriented. The chains in the core show a Gaussian-like behavior. Minor deviations from Gaussian behavior for tethered chains are due to surface effects.

Conformation of Chains in Cores of Block Copolymer Micelles with Solubilized Homopolymer: a Monte Carlo Study

Conformation of Chains in Cores of Block Copolymer Micelles with Solubilized Homopolymer: a Monte Carlo Study

Laser Photolysis Formation of Gold Colloids in Block Copolymer Micelles

The laser photolysis of gold AuIII salts embedded in micelle cores of block copolymer micelles derived from polystyrene−poly-4-vinylpyridine was studied. Two types of polystyrene−poly-4-vinylpyridines having different block length have been employed, producing micelles with different properties. The influence of the type of gold salt, loading rate, presence of water, micelle characteristics, and some other parameters on the rate of reduction and gold colloid formation were investigated. The presence of water in the system containing HAuCl4·3H2O was found to accelerate the AuIII reduction, while the gold colloid size was not affected (about 3 nm). The substitution of HAuCl4·3H2O with AuCl3 results in much slower accumulation of AuI species with subsequent slower nucleation of gold colloids that results in bigger particles with mean diameter of 6.0 nm. Increasing the amount of metal compound was found to lead to an increase of the particle size.

Fluorescence Depolarization Due to Excitation Energy Migration in Polymeric Micelles: A Monte Carlo Study

Cores of block copolymer micelles have been studied by Monte Carlo simulation. Core-forming chains have been modeled as self-avoiding chains enclosed in a spherical cavity and tethered to its surface. A fraction of the untethered end segments of chains (18–53%) has been treated as fluorescent probes. The time-dependent solution of the Pauli master equation that describes excitation energy migration among probes has been averaged in an ensemble of 104 simulated cores. We have studied the dependence of the depolarization function GS(t), i.e., the probability that the originally excited probe is still excited at time t, on the chain length and on the energy migration critical radius of the probe. Cores with randomly solubilized probes and with clusters of probes have been also studied for comparison.

Release of Hydrophobic Substances from Polystyrene-Methacrylic Acid Block Copolymer Micelles into Aqueous Media

Abstract Block copolymer micelles are potential carriers for controlled-release drug delivery. In this study, the fundamental aspects of the release of a model compound from the micelles into the surrounding media were explored. A fluorescence-based technique was developed for following the release of the model compound from the cores of block copolymer micelles into aqueous media. The experimental release curves were compatible with theoretical dependences for diffusion controlled release from spherical particles. The diffusion coefficients found were of the order of 1018 cm2/s, which was expected for molecules with sizes of our probes and glassy polystyrene. The partition coefficients are also of the expected order of 105 magnitude. The fraction of the probe present outside of the cores at the start of the experiment may serve to characterize the efficiency of various procedures for the loading of various agents into the core.