A conformational model for poly(dichlorophosphazene) derived from molecular dynamics simulations

Cyclo- and Polyphosphazenes for Biomedical Applications

Cyclic and polyphosphazenes are extremely interesting and versatile substrates characterized by the presence of -P=N- repeating units. The chlorine atoms on the P atoms in the starting materials can be easily substituted with a variety of organic substituents, thus giving rise to a huge number of new materials for industrial applications. Their properties can be designed considering the number of repetitive units and the nature of the substituent groups, opening up to a number of peculiar properties, including the ability to give rise to supramolecular arrangements. We focused our attention on the extensive scientific literature concerning their biomedical applications: as antimicrobial agents in drug delivery, as immunoadjuvants in tissue engineering, in innovative anticancer therapies, and treatments for cardiovascular diseases. The promising perspectives for their biomedical use rise from the opportunity to combine the benefits of the inorganic backbone and the wide variety of organic side groups that can lead to the formation of nanoparticles, polymersomes, or scaffolds for cell proliferation. In this review, some aspects of the preparation of phosphazene-based systems and their characterization, together with some of the most relevant chemical strategies to obtain biomaterials, have been described.

A Computational Procedure for Atomistic Modelling of Polyphosphazenes towards Better Capturing Molecular-Level Structuring and Thermo-Mechanical Properties

Poly(phosphazenes)(PZ) are versatile polymers due to their tunable properties that can be tailored for specific applications. Despite extensive experimental research, not all properties are tested, and the list of PZs studied via molecular simulations is limited. Further, a general procedure to generate and test PZ systems is lacking. We present an in situ polymerization procedure developed to make, test, and tune the thermo-mechanical properties of four PZs—poly(dichlorophosphazene)(PZ-DC), poly[bis(2,2,2-trifluoroethoxy)]phosphazene (PZ-TFE), poly(2,2,2-trifluoroethoxy-5,6-diazidohexanoxy) phosphazene (PZ-Azido), and poly(2,2,2-trifluoroethoxy-5,6-dinitratohexanoxy)phosphazene (PZ-Nitrato) via molecular dynamics simulations. The predicted thermo-mechanical properties (i.e., density and glass transition temperature) agreed with experimental values when a direct comparison of PZ systems was possible. This demonstrates the reproducibility and reliability of our procedure which will help understand the behaviour of PZs at the molecular scale.

Structure and conformation of the medium-sized chlorophosphazene rings

Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization-mass spectroscopy (ESI-MS), their (31)P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3-5, 6, 8). The crystal structures of [P(OPh)2N]7 and [P(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.