2 research outputs found
Heterodimeric nitrate reductase (NapAB) from Cupriavidus necator H16: purification, crystallization and preliminary X-ray analysis
Acta Cryst. (2007). F63, 516â519The periplasmic nitrate reductase from Cupriavidus necator (also known as Ralstonia eutropha) is a heterodimer that is able to reduce nitrate to nitrite. It comprises a 91 kDa catalytic subunit (NapA) and a 17 kDa subunit (NapB) that is involved in electron transfer. The larger subunit contains a molybdenum active site with a bis-molybdopterin guanine dinucleotide cofactor as well as one [4Feâ4S] cluster, while the small subunit is a di-haem c-type cytochrome. Crystals of the oxidized form of this enzyme were obtained using polyethylene
glycol 3350 as precipitant. A single crystal grown at the High Throughput Crystallization Laboratory of the EMBL in Grenoble diffracted to beyond 1.5 A ° at the ESRF (ID14-1), which is the highest resolution reported to date for a nitrate reductase. The unit-cell parameters are a = 142.2, b = 82.4, c = 96.8 A ° , à = 100.7°, space group C2, and one heterodimer is present per asymmetric unit
Nanoscale-confined Terahertz Polaritons in a van der Waals Crystal
Electromagnetic field confinement is crucial for nanophotonic technologies,
since it allows for enhancing light-matter interactions, thus enabling light
manipulation in deep sub-wavelength scales. In the terahertz (THz) spectral
range, radiation confinement is conventionally achieved with specially designed
metallic structures - such as antennas or nanoslits - with large footprints due
to the rather long wavelengths of THz radiation. In this context, phonon
polaritons - light coupled to lattice vibrations - in van der Waals (vdW)
crystals have emerged as a promising solution for controlling light beyond the
diffraction limit, as they feature extreme field confinements and low optical
losses. However, experimental demonstration of nanoscale-confined phonon
polaritons at THz frequencies has so far remained elusive. Here, we provide it
by employing scattering-type scanning near-field optical microscopy (s-SNOM)
combined with a free-electron laser (FEL) to reveal a range of low-loss
polaritonic excitations at frequencies from 8 to 12 THz in the vdW
semiconductor . We visualize THz polaritons with i) in-plane
hyperbolic dispersion, ii) extreme nanoscale field confinement (below
) and iii) long polariton lifetimes, with a lower limit of > 2
ps