The effects of a static electric field on the dynamics of lysozyme and its hydration water are investigated by means of incoherent quasi-elastic neutron scattering (QENS). Measurements were performed on lysozyme samples, hydrated respectively with heavy water (D 2 O) to capture the protein dynamics and with light water (H 2 O), to probe the dynamics of the hydration shell, in the temperature range from 210 < T < 260 K. The hydration fraction in both cases was about ∼ 0.38 gram of water per gram of dry protein.The field strengths investigated were respectively 0 kV/mm and 2 kV/mm (∼2 × 10 6 V/m) for the protein hydrated with D 2 O and 0 kV and 1 kV/mm for the H 2 O-hydrated counterpart. While the overall internal protons dynamics of the protein appears to be unaffected by the application of an electric field up to 2 kV/mm, likely due to the stronger intra-molecular interactions, there is also no appreciable quantitative enhancement of the diffusive dynamics of the hydration water, as would be anticipated based on our recent observations in water confined in silica pores under field values of 2.5 kV/mm. This may be due to the difference in surface interactions between water and the two adsorption hosts (silica and protein), or to the existence of a critical threshold field value E c ∼2-3 kV/mm for increased molecular diffusion, for which electrical breakdown is a limitation for our sample.

We present a pressure-dependence study of the dynamics of lysozyme protein powder immersed in deuterated α,α-trehalose environment via quasielastic neutron scattering (QENS). The goal is to assess the baroprotective benefits of trehalose on biomolecules by comparing the findings with those of a trehalose-free reference study. While the mean-square displacement of the trehalose-free protein (hydrated to dD2O≃40 w%) as a whole, is reduced by increasing pressure, the actual observable relaxation dynamics in the picoseconds to nanoseconds time range remains largely unaffected by pressure--up to the maximum investigated pressure of 2.78(2) Kbar. Our observation is independent of whether or not the protein is mixed with the deuterated sugar. This suggests that the hydrated protein's conformational states at atmospheric pressure remain unaltered by hydrostatic pressures, below 2.78 Kbar. We also found the QENS response to be totally recoverable after ambient pressure conditions are restored. Small-angle neutron diffraction measurements confirm that the protein-protein correlation remains undisturbed. We observe, however, a clear narrowing of the QENS response as the temperature is decreased from 290 to 230 K in both cases, which we parametrize using the Kohlrausch-Williams-Watts stretched exponential model. Only the fraction of protons that are immobile on the accessible time window of the instrument, referred to as the elastic incoherent structure factor, is observably sensitive to pressure, increasing only marginally but systematically with increasing pressure.

Recently frustrated magnetic materials have once again captured the condensed matter community's interests due to renewed evidence of being the best route to achieve quantum spin-liquid type physics. Generally, one has two strategies to achieve magnetic frustration: through geometric means or through interactions with different requirements and length scales. As the former leads to much simpler theoretical treatments it is generally favored and so magnetic sublattices with geometric frustration are sought after. One approach to finding such lattices is to design them chemically by using non-magnetic linker ligands. Here we report on the magnetic properties of one such family of materials, the transition metal (TM ) selenite hydrate compounds with chemical formula TM 3(SeO3)3H2O. These materials link highly distorted TM O6 octahedra via non-magnetic [SeO3] 2+ linkers. Using TM = Mn, Co and Ni we report on the structural effects of changing the TM site and how they may influence the magnetic structure. Using magnetic susceptibility and neutron powder diffraction we identify low temperature magnetic transitions for all three compounds characterized by the onset of long-range antiferromagnetic order with moderate frustration indexes. Consideration of the magnetic structures reveal that the magnetic order is sensitive to the TM site ion and is tunable as it is changed -especially from Mn to Co -with changes in both the moment direction and the ordering vector. Field dependent measurements of the susceptibility and heat capacity reveal metamagnetic transitions in both Mn3(SeO3)3H2O and Co3(SeO3)3H2O indicating nearby magnetic ground states accessible under relatively small applied fields. Density functional theory calculations broadly confirm these results, showing both a sensitivity of the magnetic structure to the TM and its local environment. Although no spin liquid behavior is achieved, these results suggest the fruitfulness of such synthesis philosophies and encourage future work to engender higher frustration in these materials via doping, field, pressure or larger linker ligands.

No abstract