Dynamic structures of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers induced in oriented lipid membranes, which are interacting with membrane-acting antimicrobial peptides (AMPs), magainin-2 and aurein-3.3, were explored by 31P and 2H solid-state NMR (ssNMR) spectroscopy. Various types of phospholipid systems, such as POPC-d31, POPC-d31/POPG, and POPC-d31/cholesterol, were investigated to understand the membrane disruption mechanisms of magainin-2 and aurein-3.3 peptides at various peptide-to-lipid (P:L) ratios. The experimental lineshapes of anisotropic 31P and 2H ssNMR spectra measured on these peptide-lipid systems were simulated reasonably well by assuming the presence of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers, in membranes. Furthermore, the observed decrease in the anisotropic frequency span of either 31P or 2H ssNMR spectra of oriented lipid bilayers, particularly when anionic POPG lipids are interacting with AMPs at high P:L ratios, can directly be explained by a thinned membrane surface model with fast lateral diffusive motions of lipids. The spectral analysis protocol we developed enables extraction of the lateral diffusion coefficients of lipids distributed on the curved surfaces of pores and thinned bilayers on a few nanometers scale.

Here we present fundamental studies of a new blending strategy for enhancing water permeability in ionomeric reverse osmosis membrane materials. A random disulfonated poly(arylene ether sulfone) copolymer containing 20 mol percent hydrophilic units (BPS-20) in the potassium salt (-SO 3 K) form was blended with hydroxyl-terminated poly(ethylene glycol) oligomers (PEG, M n = 600-2 000) to increase the water permeability of BPS-20. Blending PEG with the copolymer resulted in pseudoimmobilization of the BPS-20 polymer chains because PEG complexes with cations in the sulfonated polymer matrix. Strong ion-dipole interactions between the potassium ions of the BPS-20 sulfonate groups (-SO 3 K) and the PEG oxyethylene (-CH 2 CH 2 O-) groups were observed via NMR spectroscopy. These interactions are similar to those reported between crown ethers and free alkali metal systems. The PEG oligomers were compatible with the copolymer at 30 °C in an aqueous environment. Transparent and ductile BPS-20_PEG blend films exhibited a Fox-Flory-like glass transition temperature depression as the PEG volume fraction increased. This depression depended on both PEG chain length and concentration. Both ion-dipole interactions and high coordination of -CH 2 CH 2 O-with -SO 3 K yielded a defined and interconnected hydrophilic channel structure. The water permeability and free volume of BPS-20_PEG blend films containing 5 or 10 wt % PEG increased relative to BPS-20. The blend films, however, exhibited reduced sodium chloride (NaCl) rejection compared to BPS-20. Addition of PEG did not significantly alter the material's dry-and hydrated-state mechanical properties. Unlike commercial state-of-the-art polyamide RO membranes, the blend materials do not degrade when exposed to aqueous chlorine (hypochlorite) at pH 4. This comprehensive suite of measurements provides understanding of the molecular and morphological features needed for rational design of next-generation, chlorine-tolerant water purification materials.

We have investigated the dynamics-transport correlations of a chlorine-resistant polymeric system designed as a next-generation reverse osmosis (RO) membrane material by solid-state NMR spectroscopy. A random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt (-SO(3)(-)K(+)) form (BPS-20K) was blended with poly(ethylene glycol)s (PEGs) for improving water permeability. Blended BPS-20K/PEG membranes maintained the intrinsic chlorine-resistant property of BPS-20K, with a somewhat reduced salt rejection. The dynamic characteristics of BPS-20K/PEG blends studied by the spin-lattice relaxation time (T(1)) and rotating frame spin-lattice relaxation time (T(1)ρ) indicated correlations with the observed water uptake and permeability. (1)H T(1) measured on the polymer's aromatic phenylene rings and (1)H T(1)ρ measured on the oxyethylene (-CH(2)CH(2)O-) units of PEG were sensitive to the morphological changes, due to the blending of PEGs, induced in the mixed matrices. Membranes made of BPS-20K/PEG blends, with a lower molecular weight and higher amount of PEGs, that exhibited higher water permeability also provided shorter (1)H T(1) and T(1)ρ relaxation times. PEGs behaved as a plasticizer in the BPS-20K matrix, providing shorter (1)H T(1) times and therefore shorter motional correlation times in the nanosecond regime. (1)H T(1)ρ data have indicated the formation of networks among different polymeric chains via K(+)-oxyethylene ion-dipole interactions. Other properties that exhibit ad hoc correlations with the observed T(1) and T(1)ρ times include density, glass transition temperature, and salt rejection. Additionally, the ring flip motions measured on the hydrophobic phenylene rings did not reveal any correlations to the molecular weight and amount of PEGs blended, suggesting that the blending of PEG molecules modifies only the ionic domains of the BPS-20K polymer matrix.

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Cross-polarization (CP) nuclear magnetic resonance experiments show that water within about 1 nm of C 60 molecules is anisotropic and undergoes rotational motion that is greatly hindered compared with motion in bulk. The experimental observation of a Hartmann-Hahn CP contact shows that the motion of water is slow enough for intermolecular 1 H (water)-13 C (C 60 ) dipolar coupling to occur, suggesting that the time scale of the rotational (tumbling) motion of the water adjacent to the C 60 is slower than the microsecond range. This is much slower than the picosecond range previously observed for bulk water. The dipolar coupling decreases with temperature in the range of 3-22 °C. This work provides molecular-scale evidence that a small hydrophobic particle can order surrounding liquid water molecules.