Compartmentalization in Hybrid Metallacarborane Nanoparticles Formed by Block Copolymers with Star-Like Architecture

One strategy to control the morphology of hybrid polymeric nanostructures is the proper selection of macromolecule architecture. We prepared metallacarborane-rich nanoparticles by interaction of double-hydrophilic block copolymers consisting of both poly­(2-alkyl oxazolines) and poly­(ethylene oxide) blocks with cobaltabisdicarbollide anion in physiological saline. The inner structure of the hybrid nanoparticles was studied by cryo-TEM, light scattering, SAXS, NMR, and ITC. Although the thermodynamics of diblock and star-like systems are almost identical, the macromolecular architecture has a great impact on the size and inner morphology of the nanoparticles. While hybrid nanoparticles formed by linear diblock copolymers are homogeneous, resembling gel-like nanospheres, the star-like shape of 4-arm block copolymers with PEO blocks in central parts of macromolecules leads to distinct compartmentalization. Because metallacarboranes are promising species in medicine, the studied nanoparticles are important for targeted drug delivery of boron cluster compounds

Hybrid Nanospheres Formed by Intermixed Double-Hydrophilic Block Copolymer Poly(ethylene oxide)-<i>block</i>-poly(2-ethyloxazoline) with High Content of Metallacarboranes

In search for biocompatible hydrophilic polymers suitable for preparation of delivery systems of boron cluster compounds with high loading capacity, we studied the interaction of metallacarborane sodium [3-cobalt­(III) bis­(1,2-dicarbollide)] with poly­(2-ethyloxazoline) (PEOX) and with a double-hydrophilic block copolymer poly­(ethylene oxide)-<i>block</i>-poly­(2-ethyloxazoline) (PEO–PEOX) in aqueous solutions by a combination of scattering, microscopy, spectroscopy, and thermochemistry techniques. The paper is a contribution to our long-time study of novel hybrid nanostructures based on hydrophilic polymer–metallacarborane complexes. PEOX homopolymer interacts with metallacarborane, resulting in a water-soluble, negatively charged complex. In the case of diblock copolymer PEO–PEOX, both blocks interact with metallacarborane via dihydrogen bonds and participate in the formation of hybrid gel-like nanostructures in 0.1 M NaCl aqueous solutions, which are unique as compared to other boron cluster-containing polymeric systems. The stable spherical nanoparticles with high metallacarborane content do not adopt core/shell structure, which has been observed for other PEO-containing double hydrophilic block copolymers [<i>Macromolecules</i> <b>2009</b>, <i>42</i>, 4829], but the nanospheres are homogeneous. They contain intermixed PEO and PEOX blocks, which are cross-linked by metallacarborane molecules. The size of the nanospheres depends on a preparation protocol, while their inner structure does not. Besides the detailed study on PEO–PEOX/metallacarborane system, a high application potential of PEO–PEOX complexes with several metallacarborane-based drugs is also shown. The study clearly demonstrates that PEOX is suitable polymer for designing novel hybrid nanostructures

Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters

This is the first experimental evidence that both self-assembly and surface activity are common features of all water-soluble boron cluster compounds. The solution behavior of anionic polyhedral boranes (sodium decaborate, sodium dodecaborate, and sodium mercaptododecaborate), carboranes (potassium 1-carba-dodecaborate), and metallacarboranes {sodium [cobalt bis­(1,2-dicarbollide)]} was extensively studied, and it is evident that all the anionic boron clusters form multimolecular aggregates in water. However, the mechanism of aggregation is dependent on size and polarity. The series of studied clusters spans from a small hydrophilic decaborate-resembling hydrotrope to a bulky hydrophobic cobalt bis­(dicarbollide) behaving like a classical surfactant. Despite their pristine structure resembling Platonic solids, the nature of anionic boron cluster compounds is inherently amphiphilicthey are stealth amphiphiles