We report results of our study on the mechanism of spin-dependent O 2 binding to hemoglobin, which we represent as FePIm (Fe = iron, P = porphyrin, Im = imidazole). This involves the transition between two states, viz., the oxyhemoglobin state and the deoxyhemoglobin state. The deoxyhemoglobin state pertains to FePIm and a free O 2 molecule, while the oxyhemoglobin state pertains to an O 2 bound to FePIm. The deoxyhemoglobin and oxyhemoglobin systems have triplet and singlet total magnetizations, respectively. We found that a spin transition from triplet to quintet to singlet mediates the O 2 binding process, and this accelerates the reaction. We also found that the position of the Fe atom out of the porphyrin plane is an important indicator of O 2 affinity.
The Rochow process is the most common technology used to prepare organosilicon compounds on an industrial scale, and yet the mechanism is still not well understood. It involves the reaction of methyl chloride (CH3Cl) with silicon, catalyzed by copper. To understand the elementary steps of the reaction involved, we studied the molecular adsorption of CH3Cl/Cu(410) at 100 K and its complete desorption at higher temperatures, 100 K < T D < 200 K. Temperature-programmed desorption (TPD) spectra show two CH3Cl desorption peaks. We attribute the low temperature TPD peak (T D ≈ 120 K) to CH3Cl desorbing from both step-edges and terraces and the high temperature TPD peak (T D ≈ 160 K) to CH3Cl desorbing from the step-edges. Infrared reflection–absorption spectra (IRAS) indicate that at low CH3Cl coverage (Θ = 0.06 ML), CH3Cl adsorbs with its molecular axis (Cl–C bond) aligned either parallel or perpendicular to [001]. At high CH3Cl coverage (Θ ≥ 0.09 ML), CH3Cl adsorbs with its molecular axis aligned perpendicular to [001].
The fabrication of a hydrogen isotope enrichment system is essential for the development of industrial, medical, life science, and nuclear fusion fields, and therefore, efficient enrichment techniques with a high separation factor and economic feasibility are still being explored. Herein, we report a hydrogen/deuterium (H/D) separation ability with polymer electrolyte membrane electrochemical hydrogen pumping (PEM-ECHP) using a heterogeneous electrode consisting of palladium and graphene layers (PdGr). By mass spectroscopic analysis, we demonstrate significant bias voltage dependence of the H/D separation factor with a maximum of ∼25 at 0.15 V and room temperature, which is superior to those of conventional separation methods. Theoretical analysis demonstrated that the observed high H/D factor stems from tunneling of hydrogen isotopes through atomically thick graphene during the electrochemical reaction and that the bias dependence of H/D results from a transition from the quantum tunneling regime to the classical overbarrier regime for hydrogen isotopes transfer through the graphene. These findings will help us understand the origin of the isotope separation ability of graphene discussed so far and contribute to developing an economical hydrogen isotope enrichment system using two-dimensional materials.
Some fluctuations in composition are commonly observed in epitaxial-grown III-V multinary alloys. These fluctuations are attributed to compositional pulling effects, and an insight into their atomistic origin is necessary to improve current epitaxial growth techniques. In addition, the crystallinity of III-V multinary alloys varies widely depending on the constituent atoms. Using first-principles calculations, we then investigated different geometric configurations of gallium nitride (GaN)-based ternary alloy, X 0.125 Ga 0.875 N where X is the minority atom which is boron (B), aluminum (Al), or indium (In). The minority atoms are presented as two atoms in the simulation cell, and the energetics of five geometric configurations are analyzed to estimate the most stable configuration. For the B 0.125 Ga 0.875 N alloy, the most stable configuration is the one where the minority atoms occupy gallium (Ga) sites in a collinear orientation along the c-axis. On the contrary, the configurations along the in-plane direction result in a higher energy state. In 0.125 Ga 0.875 N and Al 0.125 Ga 0.875 N also show the same trend with a small relative energy difference. These preferential sites of minority atoms are consistent with composition pulling effects in wurtzite nitride phases. Moreover, the degree of crystallinity for wurtzite nitride alloys can be well described by the order of calculated relative energy.
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