The membrane proximal external region (MPER) of HIV-1 envelope glycoprotein (gp) 41 is an attractive vaccine target for elicitation of broadly neutralizing antibodies (bNAbs) by vaccination. However, current details regarding the quaternary structural organization of the MPER within the native prefusion trimer [(gp120/41)3] are elusive and even contradictory, hindering rational MPER immunogen design. To better understand the structural topology of the MPER on the lipid bilayer, the adjacent transmembrane domain (TMD) was appended (MPER-TMD) and studied. Membrane insertion of the MPER-TMD was sensitive both to the TMD sequence and cytoplasmic residues. Antigen binding of MPER-specific bNAbs, in particular 10E8 and DH511.2_K3, was significantly impacted by the presence of the TMD. Furthermore, MPER-TMD assembly into 10-nm diameter nanodiscs revealed a heterogeneous membrane array comprised largely of monomers and dimers, as enumerated by bNAb Fab binding using single-particle electron microscopy analysis, arguing against preferential trimeric association of native MPER and TMD protein segments. Moreover, introduction of isoleucine mutations in the C-terminal heptad repeat to induce an extended MPER α-helical bundle structure yielded an antigenicity profile of cell surface-arrayed Env variants inconsistent with that found in the native prefusion state. In line with these observations, electron paramagnetic resonance analysis suggested that 10E8 inhibits viral membrane fusion by lifting the MPER N-terminal region out of the viral membrane, mandating the exposure of residues that would be occluded by MPER trimerization. Collectively, our data suggest that the MPER is not a stable trimer, but rather a dynamic segment adapted for structural changes accompanying fusion.

Decarbonized ammonia production through photocatalytic nitrogen fixation is appealing, as it may allow for farm-scale fertilizer production using earthabundant feedstocks, energy, and catalysts. Yet, the viability of decentralized ammonia production systems is largely dependent on the cost of a complete photocatalytic system reaching a Haber−Bosch parity point. Here, we demonstrate that an air separation unit for a farm-scale low-cost photocatalytic ammonia synthesis system can account for 70% of the total system cost. This high cost depends on the type of air separation unit and the purity of nitrogen. This promotes the need for a catalyst, which can tolerate trace oxygen or can even operate under aerobic conditions to attain Haber−Bosch cost parity. We further demonstrate the change in catalytic activity of prototypical undoped and metal-doped titania photocatalysts under aerobic and anaerobic conditions. Among various metal-doped titania photocatalyst, vanadium-and ruthenium-doped titania demonstrated no performance decline under aerobic conditions.

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Two-dimensional (2D) coordination polymer (CP) [Co III (CN) 6 ] 2 [Co II (TODA)] 3 •7H 2 O (TODA = 1,4,10-trioxa-7,13diazacyclopentadecane, Co-TODA) was reported earlier to show field-induced slow magnetic relaxation, displaying single-ion magnet (SIM) behaviors. Most SIMs are molecular compounds with fewer adopting coordination polymer (CP) or metal−organic framework (MOF) structures. In the current work, magnetic and phonon properties of Co-TODA have been studied by advanced spectroscopies and computations. The combined use of far-IR magneto-spectroscopy (FIRMS) and variable-temperature (VT) high-frequency and -field electron paramagnetic resonance (HFEPR) gives spin Hamiltonian (SH) parameters: Axial zerofield splitting (ZFS) parameter D as +38.0(1.0) ≤ D ≪ +40.2(1.0) cm −1 and rhombic ZFS parameter E as 0 ≪ |E| ≤ 7.3(1.0) cm −1 , showing that Co-TODA has the easy-plane magnetic anisotropy. Two Co II centers in the CP, as determined by synchrotron single-crystal X-ray diffraction at 15(2) K, show similar magnetic properties indistinguishable in FIRMS at 5.3(3) K or in HFEPR at 5−150 K. Ab initio calculations explore the origin of the magnetic anisotropy and magnetostructural correlations. VT inelastic neutron scattering (INS) spectra of Co-TODA have been obtained to show the phonon properties of the CP. Density functional theory (DFT) calculations, giving both a calculated INS spectrum and spin distributions in Co-TODA, demonstrate that, compared with other high-spin Co II complexes, the larger the spin density on a metal ion, the larger the ZFS in the complex. Pulsed X-band EPR studies probe relaxations of the Co II ions from the M S = +1/2 to −1/2 state in the ground Kramers doublet (KD), yielding spin−lattice (T 1 ) and spin−spin relaxation (T 2 ) times. The work reported here highlights the versatility and power of the spectroscopic techniques and computations in the characterization of magnetic and phonon properties of a CP and the understanding of its magnetic anisotropy.