Because different proteins compete for the proton gradient across the inner mitochondrial membrane, an efficient mechanism is required for allocation of associated chemical potential to the distinct demands, such as ATP production, thermogenesis, regulation of reactive oxygen species (ROS), etc. Here, we used the superresolution technique dSTORM (direct stochastic optical reconstruction microscopy) to visualize several mitochondrial proteins in primary mouse neurons and test the hypothesis that uncoupling protein 4 (UCP4) and F 0 F 1 -ATP synthase are spatially separated to eliminate competition for the proton motive force. We found that UCP4, F 0 F 1 -ATP synthase, and the mitochondrial marker voltage-dependent anion channel (VDAC) have various expression levels in different mitochondria, supporting the hypothesis of mitochondrial heterogeneity. Our experimental results further revealed that UCP4 is preferentially localized in close vicinity to VDAC, presumably at the inner boundary membrane, whereas F 0 F 1 -ATP synthase is more centrally located at the cristae membrane. The data suggest that UCP4 cannot compete for protons because of its spatial separation from both the proton pumps and the ATP synthase. Thus, mitochondrial morphology precludes UCP4 from acting as an uncoupler of oxidative phosphorylation but is consistent with the view that UCP4 may dissipate the excessive proton gradient, which is usually associated with ROS production. mitochondrial membrane proteins | proton diffusion | direct stochastic optical reconstruction microscopy | uncoupling | reactive oxygen species M itochondria are involved in a wide range of cell functions, including fatty acid oxidation, calcium homeostasis, apoptosis, reactive oxygen species (ROS) signaling, and above all, production of ATP (1, 2). In neurons, these organelles are transported along neuronal processes to provide energy for areas of high energy demand, such as synapses (3). To support their functions, mitochondria exhibit a complex morphology consisting of separate and functionally distinct outer mitochondrial membrane (OMM) and inner mitochondrial membrane (IMM). The latter is structurally organized into two domains: an inner boundary membrane (IBM) and a cristae membrane (CM) (4). The current hypotheses imply that the morphology/topology of the IMM is tightly related to biochemical function, the energy state, and the pathophysiological state of mitochondria (5). Whereas the OMM contains porins [e.g., voltage-dependent anion channel (VDAC)], which mediate its permeability to molecules up to 10 kDa, the IMM topology is highly complex. It is comprised of different transport proteins, the ATP synthase (complex V), and complexes I, III, and IV of the electron transport chain, which are responsible for generating the proton motive force (pmf); pmf represents the driving force for not only ATP synthesis, but also other protein-mediated transport activities (for example, phosphate, pyruvate, and glutamate transport). Uncoupling protein 1 (UCP1; thermogenin), a memb...

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In this work, the structural and mechanical properties of ternary Mo-Al-N alloys are investigated by combining thin film growth experiments and density functional theory (DFT) calculations. Mo 1−x Al x N y thin films (∼300 nm thick), with various Al fractions ranging from x = 0 to 0.5 and nitrogen-to-metal (Al + Mo) ratio ranging from y = 0.78 to 1.38, were deposited by direct-current reactive magnetron cosputtering technique from elemental Mo and Al targets under Ar + N 2 plasma discharges. The Al content was varied by changing the respective Mo and Al target powers, at a fixed N 2 (20 SCCM) and Ar (25 SCCM) flow rate, and using two different substrate temperatures T s = 350 and 500°C. The elemental composition, mass density, crystal structure, residual stress state, and intrinsic (growth) stress were examined by wavelength dispersive x-ray spectroscopy, x-ray reflectivity, x-ray diffraction, including pole figure and sin 2 ψ measurements, and real-time in situ wafer curvature. Nanoindentation tests were carried out to determine film hardness H and elastic modulus E IT , while the shear elastic constant C 44 was measured selectively by surface Brillouin light spectroscopy. All deposited Mo 1−x Al x N y films have a cubic rock-salt crystal structure and exhibit a fiber-texture with a [001] preferred orientation. The incorporation of Al is accompanied by a rise in nitrogen content from 44 to 58 at. %, resulting in a significant increase (2%) in the lattice parameter when x increases from 0 to 0.27. This trend is opposite to what DFT calculations predict for cubic defect-free stoichiometric Mo 1−x Al x N compounds and is attributed to variation in point defect concentration (nitrogen and metal vacancies) when Al substitutes for Mo. Increasing T s from 350 to 500°C has a minimal effect on the structural properties and phase composition of the ternary alloys but concurs to an appreciable reduction of the compressive stress from −5 to −4 GPa. A continuous increase and decrease in transverse sound velocity and mass density, respectively, lead to a moderate stiffening of the shear elastic constant from 130 to 144 GPa with increasing Al fraction up to x = 0.50, and a complex and nonmonotonous variation of H and E IT is observed. The maximum hardness of ∼33 GPa is found for the Mo 0.81 Al 0.19 N 1.13 film, with nitrogen content close to the stoichiometric composition. The experimental findings are explained based on structural and elastic constant values computed from DFT for defect-free and metal-or nitrogen-deficient rock-salt MoAlN compounds.

Herein we report on the synthesis of a metastable (Cr,Y)2AlC MAX phase solid solution by co‐sputtering from a composite Cr–Al–C and elemental Y target, at room temperature, followed by annealing. However, direct high‐temperature synthesis resulted in multiphase films, as evidenced by X‐ray diffraction analyses, room‐temperature depositions, followed by annealing to 760°C led to the formation of phase pure (Cr,Y)2AlC by diffusion. Higher annealing temperatures caused a decomposition of the metastable phase into Cr2AlC, Y5Al3, and Cr‐carbides. In contrast to pure Cr2AlC, the Y‐containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y‐content dependent and was increased by ∼200°C for 5 at.% Y compared to Cr2AlC. Calculations predicting the metastable phase formation of (Cr,Y)2AlC and its decomposition are in excellent agreement with the experimental findings.