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Recent developments in lipid nanodisc technology have successfully overcome the major challenges in the structural and functional studies of membrane proteins and drug delivery. Among the different types of nanodiscs, the use of synthetic amphiphilic polymers created new directions including the applications of solution and solid-state NMR spectroscopy. The ability to magnetically align large-size (>20 nm diameter) polymer nanodiscs and flip them using paramagnetic lanthanide ions has enabled high-resolution studies on membrane proteins using solid-state NMR techniques. The use of polymer-based macro–nanodiscs (>20 nm diameter) as an alignment medium to measure residual dipolar couplings (RDCs) and residual quadrupole couplings by NMR experiments has also been demonstrated. In this study, we demonstrate the use of magnetically aligned and 90°-flipped polymer nanodiscs as alignment media for structural studies on proteins by solution NMR spectroscopy. These macro–nanodiscs, composed of negatively charged SMA-EA polymers and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids, were used to measure residual 1H–15N dipolar couplings (RDCs) from the water-soluble ∼21 kDa uniformly 15N-labeled flavin mononucleotide binding domain (FBD) of cytochrome-P450 reductase. The experimentally measured 1H–15N RDC values are compared with the values calculated from the crystal structures of cytochrome-P450 reductase that lacks the transmembrane domain. The N–H RDCs measured using aligned and 90°-flipped nanodiscs show a modulation by the function (3 cos2 θ – 1), where θ is the angle between the N–H bond vector and the applied magnetic field direction. This successful demonstration of the use of two orthogonally oriented alignment media should enable structural studies on a variety of systems including small molecules, DNA, and RNA.

Divalent cations, especially Ca2+and Mg2+, play a vital role in the function of biomolecules and making them important to be constituents in samples for in vitro biophysical and biochemical characterizations. Although lipid nanodiscs are becoming valuable tools for structural biology studies on membrane proteins and for drug delivery, most types of nanodiscs used in these studies are unstable in the presence of divalent metal ions. To avoid the interaction of divalent metal ions with the belt of the nanodiscs, synthetic polymers have been designed and demonstrated to form stable lipid nanodiscs under such unstable conditions. Such polymer-based nanodiscs have been shown to provide an ideal platform for structural studies using both solid-state and solution NMR spectroscopies because of the near-native cell-membrane environment they provide and the unique magnetic-alignment behavior of large-size nanodiscs. In this study, we report an investigation probing the effects of Ca2+and Mg2+ions on the formation of polymer-based lipid nanodiscs and the magnetic-alignment properties using a synthetic polymer, styrene maleimide quaternary ammonium (SMA-QA), and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids. Phosphorus-31 NMR experiments were used to evaluate the stability of the magnetic-alignment behavior of the nanodiscs for varying concentrations of Ca2+or Mg2+at different temperatures. It is remarkable that the interaction of divalent cations with lipid headgroups promotes the stacking up of nanodiscs that results in the enhanced magnetic alignment of nanodiscs. Interestingly, the reported results show that both the temperature and the concentration of divalent metal ions can be optimized to achieve the optimal alignment of nanodiscs in the presence of an applied magnetic field. We expect the reported results to be useful in the design of nanodisc-based nanoparticles for various applications in addition to atomic-resolution structural and dynamics studies using NMR and other biophysical techniques.

In an attempt to develop reversible sensors based on ionic liquid/porous silicon (IL/pSi) platforms, we introduce an approach using task-specific, alkene-terminal ILs (AT-ILs) for direct grafting to the hydrogen-passivated as prepared-pSi (ap-pSi) surface via UV-hydrosilylation to address previous shortcomings associated with IL pattern impermanence (i.e., spread). By employing photoluminescence emission (PLE) and Fourier-transform infrared (FT-IR) imaging measurements, we demonstrate that the covalent grafting of AT-ILs onto the ap-pSi surface via photochemical hydrosilylation not only mitigates such feature spreading but also greatly improves PLE pattern stability. Significantly, we have discovered that, upon hydrosilylation, the resulting contact pin printed IL features remain stable to repeated challenges by toluene vapors, demonstrating the utility of AT-IL hydrosilylation for producing high-fidelity microarray features on pSi toward robust optical sensory microarrays.

The ability of amphipathic polymers to self-assemble with lipids and form nanodiscs has been a boon for the field of functional reconstitution of membrane proteins. In a field dominated by detergent micelles, a unique feature of polymer nanodiscs is their much-desired ability to align in the presence of an external magnetic field. Magnetic alignment facilitates the application of solid-state nuclear magnetic resonance (NMR) spectroscopy and aids in the measurement of residual dipolar couplings via well-established solution NMR spectroscopy. In this study, we comprehensively investigate the magnetic alignment properties of styrene maleimide quaternary ammonium (SMA-QA) polymer-based nanodiscs by using 31P and 14N solid-state NMR experiments under static conditions. The results reported herein demonstrate the spontaneous magnetic alignment of large-sized (≥20 nm diameter) SMA-QA nanodiscs (also called as macro–nanodiscs) with the lipid bilayer normal perpendicular to the magnetic field direction. Consequently, the orientation of macro–nanodiscs is further shown to flip the alignment axis parallel to the magnetic field direction upon the addition of a paramagnetic lanthanide salt. These results demonstrate the use of SMA-QA polymer nanodiscs for solid-state NMR applications including structural studies on membrane proteins.