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The effects of hydrogen absorption on the local lattice structure in palladium (Pd) were investigated by means of positron annihilation lifetime spectroscopy (PALS) and time-differential perturbed angular correlation (TDPAC) spectroscopy. The PALS measurements demonstrated that dislocations and vacancies formed in the preparation process of a pristine Pd plate can be clearly removed by vacuum annealing at 1073 K and the subsequent absorption of a large quantity of hydrogen, resulting in the production of the β-phase hydride PdH0.62, induces the formation of the open-volume defects again. It was also found that the absorbed hydrogen atoms remain in the Pd sample at 323 K but they are completely evacuated during 5 h heating at 383 K. In addition to the overall thermal behavior, an atomic scale observation of the hydrogen dynamics was carried out by means of TDPAC spectroscopy, indicating the nuclear quadrupole relaxation of the present (111m,111Pd → 111Ag→)111Cd probe, which evidently suggests that the hydrogen atoms show fast dynamic motion around the probe. From the temperature-dependent nuclear quadrupole relaxation rate, we obtained an activation energy of 41(4) meV for the motion. [ABSTRACT FROM AUTHOR]

Membrane binding is a crucial mechanism for many proteins, but understanding the specific interactions between proteins and membranes remains a challenging endeavor. Coagulation factor Va (FVa) is a large protein whose membrane interactions are complicated due to the presence of multiple anchoring domains that individually can bind to lipid membranes. Using molecular dynamics simulations, we investigate the membrane binding of FVa and identify the key mechanisms that govern its interaction with membranes. Our results reveal that FVa can either adopt an upright or a tilted molecular orientation upon membrane binding. We further find that the domain organization of FVa deviates (sometimes significantly) from its crystallographic reference structure, and that the molecular orientation of the protein matches with domain reorganization to align the C2 domain toward its favored membrane-normal orientation. We identify specific amino acid residues that exhibit contact preference with phosphatidylserine lipids over phosphatidylcholine lipids, and we observe that mostly electrostatic effects contribute to this preference. The observed lipid-binding process and characteristics, specific to FVa or common among other membrane proteins, in concert with domain reorganization and molecular tilt, elucidate the complex membrane binding dynamics of FVa and provide important insights into the molecular mechanisms of protein-membrane interactions. An updated version of the HMMM model, termed extHMMM, is successfully employed for efficiently observing membrane bindings of systems containing the whole FVa molecule. Author summary: Understanding the intricacies of protein-membrane interaction is essential for fleshing out the functional roles of membrane proteins. Substantial evidence indicates that the binding of some proteins, such as coagulation factor Va, proceeds in a multi-step manner requiring some form of rearrangements within the structure and dynamics of the protein, as well as in the protein's orientation relative to the membrane surface. In the case of factor Va, the intricate binding process can be attributed to the presence of multiple membrane-anchoring domains. In order to feasibly study the dynamics of these mechanisms, we employ an enhanced membrane-mimetic model, HMMM, capable of capturing such processes and rearrangements and making new discoveries possible using the molecular dynamics technique. The successful execution of these studies demanded several modifications to the original implementation of the HMMM. Our exploration not only improves our understanding of FVa's membrane binding dynamics but also contributes to the broader molecular mechanisms governing protein-membrane interactions. [ABSTRACT FROM AUTHOR]

Thermally activated association and dissociation behaviors of indium impurities in Zinc oxide (ZnO) were observed on an atomic scale by means of time-differential perturbed angular correlation spectroscopy with the radioactive 111In(→111Cd) probe. We found that In impurities associate in the process of thermal diffusion to form nanoscale clusters in the ZnO matrix under thermal treatment in air, and their structures depend on the concentration of In ions introduced. Heat treatment under vacuum, however, causes dissociation of part of the clusters, suggesting that In ions leave the clusters and migrate into the ZnO matrix. Positron annihilation lifetime spectroscopy performed for the In-doped ZnO also suggests that In ions as impurities migrate into the ZnO matrix by thermal diffusion to settle themselves in Zn vacancies. Dependences of thermal behavior of In impurities on their concentration, treatment temperature, and atmospheric condition are discussed based on the results observed by the nuclear spectroscopic techniques. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) was doped with radioactive 111mCd and 111In ions as impurities, and their residence sites and thermal stability were investigated by means of time-differential perturbed angular correlation (TDPAC) spectroscopy. Well-defined TDPAC spectra unequivocally show their sites: Cd ions are stably located only in the tetrahedral A site in all the temperature range of the present observation (77 K-873 K); In ions also specifically occupy the A site at low temperature, but at high temperature part of them select the B site in a reversible fashion. The energy difference between the A and B sites for the accommodation of In was experimentally determined to be 0.119 (9) eV by assuming a Boltzmann distribution for the populations of the 111In probe in the respective sites. The element-dependent thermal stabilities observed for Cd and In were well corroborated by density functional theory calculations. The successful observation of thermally activated site-tosite displacement of impurity In ions in Fe3O4 is reported. [ABSTRACT FROM AUTHOR]

Thermal behavior and interacting nature of 100-ppm Al and ~ 100-ppt In impurities doped in zinc oxide (ZnO) were investigated by means of the time-differential perturbed angular correlation method with the 111In(→ 111Cd) probe. Contrasting interactions between Al and In impurities were observed depending on different atmospheric conditions: (1) in air, Al and In impurities irreversibly associate with each other in the process of their thermal diffusion, but (2) in vacuum, their bound state formed in air dissociates by heat treatment at temperatures higher than 873 K, and this process is enhanced with increasing temperature. Detailed investigation of the thermal behavior of the impurities has revealed that the dissociation reaction is triggered by the formation of oxygen vacancies in the vicinity of the locally associated In-Al structure. A unique method to determine the activation energy of the oxygen-vacancy formation is presented with the estimated experimental value of Ea = 0.72(6) eV. [ABSTRACT FROM AUTHOR]

Local fields in normal spinel oxides, CdFe2O4 and CdIn2O4, were measured by means of time-differential perturbed angular correlation spectroscopy with the 111In(→111Cd) and 111mCd(→111Cd) probes. The spectra obtained with the different probes show contrastive patterns in spite of the same daughter nuclei: the former shows static perturbations with explicit oscillatory structures, whereas for the latter, the angular correlations become gradually isotropic. The exponential-like relaxation patterns of the spectra observed for the 111mCd(→111Cd) probe suggest that the probes occupying the Cd A site experience time-dependent perturbation causing nuclear spin relaxation. [ABSTRACT FROM AUTHOR]

Local fields in normal spinel oxides, CdFe2O4 and CdIn2O4, were measured by means of time-differential perturbed angular correlation spectroscopy with the 111In(→111Cd) and 111mCd(→111Cd) probes. The spectra obtained with the different probes show contrastive patterns in spite of the same daughter nuclei: the former shows static perturbations with explicit oscillatory structures, whereas for the latter, the angular correlations become gradually isotropic. The exponential-like relaxation patterns of the spectra observed for the 111mCd(→111Cd) probe suggest that the probes occupying the Cd A site experience time-dependent perturbation causing nuclear spin relaxation. [ABSTRACT FROM AUTHOR]

Magnetite (Fe3O4) was doped with radioactive 111mCd and 111In ions as impurities, and their residence sites and thermal stability were investigated by means of time-differential perturbed angular correlation (TDPAC) spectroscopy. Well-defined TDPAC spectra unequivocally show their sites: Cd ions are stably located only in the tetrahedral A site in all the temperature range of the present observation (77 K-873 K); In ions also specifically occupy the A site at low temperature, but at high temperature part of them select the B site in a reversible fashion. The energy difference between the A and B sites for the accommodation of In was experimentally determined to be 0.119 (9) eV by assuming a Boltzmann distribution for the populations of the 111In probe in the respective sites. The element-dependent thermal stabilities observed for Cd and In were well corroborated by density functional theory calculations. The successful observation of thermally activated site-tosite displacement of impurity In ions in Fe3O4 is reported. [ABSTRACT FROM AUTHOR]