Pulling apart protein unfolding: Elucidating the details of how complex proteins fold is a longstanding challenge. Key insights into the unfolding pathways of diverse proteins have come from single-molecule force spectroscopy (SMFS) experiments in which proteins are literally pulled apart. Yu et al. developed a SMFS technique that could unfold individual bacteriorhodopsin molecules in a native lipid bilayer with 1-µs temporal resolution (see the Perspective by Müller and Gaub). The technique delivered a 100-fold improvement over earlier studies of bacteriorhodopsin and revealed many intermediates not seen before. The authors also observed unfolding and refolding transitions between intermediate states. Science , this issue p. 945 ; see also p. 907

Advances in genetic manipulation of the biopolymers that compose plant cell walls will facilitate more efficient production of biofuels and chemicals from biomass and lead to specialized biomaterials with tailored properties. Here we investigate several genetic variants of Arabidopsis: the wild type, which makes a lignin polymer of primarily guaiacyl (G) and syringyl (S) monomeric units, the fah1 mutant, which makes lignin from almost exclusively G subunits, and a ferulate 5-hydroxylase (F5H) overexpressing line (C4H:F5H) that makes lignin from S subunits. We employ multiscale, multimodal imaging techniques that reveal the biomass of the C4H:F5H transgenic to be more susceptible to deconstruction by maleic acid treatment than the other variants. Enzymatic saccharification assays of the treated materials show that C4H:F5H transgenic tissue is significantly more digestible than the wild type, while the fah1 mutant is clearly the least digestible of these materials. Finally, we show by contact resonance force microscopy, an atomic force microscopy technique, that F5H overexpression in C4H:F5H transgenic plants significantly reduces the stiffness of the cell walls in the region of the compound middle lamella relative to wild type and fah1.

Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of gold nanorods unidirectionally aligned in a matrix that can be made of ordered cellulose nanocrystals or silica nanostructures obtained by using cellulose-based nanostructures as a replica. The ensuing long-range alignment of gold nanorods in both cellulose-based and nanoporous silica films results in a polarization-sensitive surface plasmon resonance. The demonstrated device-scale bulk nanoparticle alignment may enable engineering of new material properties arising from combining the orientational ordering of host nanostructures and properties of the anisotropic plasmonic metal nanoparticles. Our approach may also allow for scalable fabrication of plasmonic polarizers and nanoporous silica structures with orientationally ordered anisotropic plasmonic nanoinclusions.

We report novel metal-oxide-semiconductor field effect transistors (MOSFETs) based on individual gallium nitride (GaN) nanowires with fully conformal cylindrical gates. The W/Al₂O₃ gates were deposited by atomic layer deposition. Reverse-bias breakdown voltages exceeded the largest gate voltage tested (-35 V). The nanowire MOSFETs showed complete pinchoff, with threshold voltages between -4 and -12 V. Maximum transconductances exceeded 10 μS, and ON/OFF current ratios higher than 10 ⁸ were measured. Significant gating hysteresis and memory effects were also present, indicative of charge traps. Although further optimization is needed, these results represent a promising step forward in the development of efficient GaN nanowire-based FETs.

We explore the relationship between scattering-parameters (S-parameters), corrected for switch terms, and S-parameters calculated from wave-parameters measured with a two-port vector network analyzer. By deriving the equations for both representations using consistent notation, we clearly demonstrate their equivalence. This result proves that measuring wave-parameters enables us to obtain uniquely defined S-parameters for any changes of impedance behind the signal-separation hardware.