No abstract

No abstract

19 F magnetic resonance imaging (MRI) is a powerful noninvasive imaging technique with demonstrated potential for the detection of important diseases. The major challenge in the design of 19 F MRI agents is signal attenuation caused by the reduced solubility and segmental mobility of probes with high numbers of fluorine atoms. Careful choice of the fluorinated moiety is required to maintain image quality at the fluorine contents required for high imaging sensitivity. Here we report the synthesis of perfluoropolyether (PFPE) end-functionalized homopolymers of oligo(ethylene glycol) methyl ether acrylate (poly(OEGA) m -PFPE) as highly sensitive 19 F MRI contrast agents (CAs). The structural characteristics, conformation and aggregation behavior, 19 F NMR relaxation properties, and 19 F MR imaging were studied in detail. Dynamic light scattering and molecular dynamics (MD) simulations were conducted and demonstrated that poly(OEGA) m -PFPE with the longest poly(OEGA) m segments (m = 20) undergoes single-chain folding in water while poly(OEGA) 10 -PFPE and poly(OEGA) 4 -PFPE with shorter OEGA segments experience multiple-chain aggregation. Long 19 F T 2 relaxation times were measured for all poly(OEGA) m -PFPE polymers in PBS and in the presence of serum (>80 ms), and no obvious decrease in 19 F T 2 was observed with increasing fluorine content up to ∼30 wt %. Moreover, the signal-to-noise ratio increased linearly with increasing concentration of fluorine, indicating that the PFPE-based polymers can be applied as quantitative tracers. Furthermore, we investigated the in vivo behavior, in particular their biodistribution, of the polymers with different aggregation properties. Control over the balance of hydrophobicity and hydrophilicity allows manipulation of the aggregation state, and this leads to different circulation behavior in a murine model. This first report of the synthesis of polymeric PFPE-based 19 F MRI CAs demonstrates that these polymers are an exciting new class of 19 F MRI CAs with extremely high fluorine content and outstanding imaging sensitivity.

High-resolution NMR measurements and molecular dynamics (MD) simulations have been applied to the study of thermo-responsive copolymers of poly(ethylene glycol) methyl ether methacrylate (OEGMA) and 2,2,2-trifluoroethyl acrylate (TFEA) (poly(OEGMA-co-TFEA)) synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization.The detailed chemical microstructure of poly(OEGMA-co-TFEA) was investigated by means of various high-resolution NMR techniques. The polymer in aqueous solution possesses a lower critical solution temperature (LCST) at which significant changes in conformation are apparent.1 H 2D NOESY spectra were collected at temperatures below and above the LCST and demonstrated closer association of the exterior segments of the OEGMA side chains with the TFEA units above the LCST. MD simulations provided additional information on the changes in conformation and were consistent with the experimental findings. The combination of MD simulations with a detailed experimental study of poly(OEGMA-co-TFEA) in water leads to a clearer understanding of conformation occurring at the phase transition.

In this work we show how different use of thermostating devices and modeling of walls influence the mechanical and dynamical properties of confined nanofluids. We consider a two dimensional fluid undergoing Couette flow using nonequilibrium molecular dynamics simulations. Because the system is highly inhomogeneous, the density shows strong fluctuations across the channel. We compare the dynamics produced by applying a thermostating device directly to the fluid with that obtained when the wall is thermostated, considering also the effects of using rigid walls. This comparison involves an analysis of the chaoticity of the fluid and evaluation of mechanical properties across the channel. We look at two thermostating devices with either rigid or vibrating atomic walls and compare them with a system only thermostated by conduction through vibrating atomic walls. Sensitive changes are observed in the xy component of the pressure tensor, streaming velocity, and density across the pore and the Lyapunov localization of the fluid. We also find that the fluid slip can be significantly reduced by rigid walls. Our results suggest caution in interpreting the results of systems in which fluid atoms are thermostated and/or wall atoms are constrained to be rigid, such as, for example, water inside carbon nanotubes.

Thermoresponsive dendronized polymers, displaying remarkable phase behavior, are currently being studied for their potential exploitation as polymeric sensors and biomaterials.Understanding the conformational transitions occurring at the LCST is essential for improved design and translation of these polymers. The combination of NMR and molecular dynamics simulations opens a unique window onto the thermal behavior, showing that the peripheries of the dendrons, while driving the thermal properties, largely retain mobility above the critical temperature. The cores of the dendrons and the polymeric main chain are highly rigid below the thermal transition and increasingly so above the LCST. Both the experimental and computational studies reveal stretching of the interior segments of the dendrons with associated changes in spatial arrangements of the structural units. Furthermore, diffusion-ordered NMR and DLS below and above the LCST show a further hierarchy of dynamics within different size aggregates. The combination of the detailed experimental study and molecular dynamics simulations provides a detailed understanding of thermoresponsive behavior of these dendronized polymers.

Stimuli-responsive contrast agents (CAs) show great promise for the early detection and understanding of cancer. In particular, CAs that respond to ion content may allow monitoring of both the development of cancer and the efficacy of novel therapies. Understanding the responsive behaviour of stimuli-responsive CAs in different ionic environments requires development of more advanced characterization methods. Here we report a high-resolution NMR and molecular dynamics (MD) study of conformational changes of ion-responsive 19 F co-polymers of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) and 2,2,2-trifluoroethyl acrylate (TFEA) (poly(OEGMA-co-TFEA)) in the presence of salt. 1 H 2D NOESY spectra were collected with and without the presence of NaCl and demonstrated that further separation of OEGMA and TFEA segments and closer association of OEGMA side chain were observed with the addition of NaCl. MD simulations provided additional information on the changes in conformation and were consistent with the experimental findings. Furthermore, we investigated the behaviour of polymer internalised by normal and cancer cells (MCF-12A and MCF-7) by monitoring the 19 F spin-spin relaxation time (T2) of poly(OEGMA-co-TFEA) copolymer in vitro. The 19 F NMR T2 values we obtained in MCF-7 cancer cells (82.3 ms) is much lower than that in MCF-12A normal cells (124.2 ms), and the difference is sufficient to obtain contrast using modern MRI methods in high field scanners. Our results encourage further attempts to develop even more potent CAs. This would also result in novel methods that allow monitoring of cancer at the cellular and molecular level.

Molecular dynamics simulations were employed to investigate diffusion and structural properties of water molecules confined in one-dimensional zeolites. Several water loadings and thermostatting methods were used, and insight into the effects of these was obtained by comparing diffusion and structural properties. Water diffusion was characterised via mean square displacements (self and collective diffusivities) and radial distribution functions enabled the structural ordering of water for different pore sizes and loadings to be compared. Interestingly at lower loadings, molecules tend to form clusters and move collectively, while at higher loadings, the self-diffusion coefficient in the pores is similar to that in bulk water. The length of the simulation cell was varied to determine the system size effects on the results, and narrow pores were also investigated in order to examine how this affected the effectiveness of water transport through the zeolite.