Chemical Influence of Pore Pressure on Brine Flow in Clay-Rich Material

Hydromechanical properties of shales are complex due to the involved ma-terial structure, with the solid matrix being mainly formed by swelling clays and porosity dominated by nanometer scale tortuous voids with large aspect ratios. Intrinsic permeability of restructured Opalinus Clay (Swiss shale) brought to shallow geological storage conditions was measured with in situ brine. Under constant temperature, vertical stress, and downstream fluid pressure, steady-state flow experiments show a significant trend of permea-bility decrease with increasing differential (upstream minus downstream) fluid pressure, thus contradicting the conventional Darcy’s description. To interpret these experimental measurements, brine permeability is derived using a one-step self-consistent homogenization scheme based on the knowledge of material’s pore structure. While mechanical and thermal effects cannot ex-plain the permeability decrease, the trend is reproduced with the correct order of magnitude by considering a chemical effect: a pore size reduction in the sample due to water adsorption at mineral surface

Topography of tyrosine residues and their involvement in peroxidation of polyunsaturated cardiolipin in cytochrome c/cardiolipin peroxidase complexes

AbstractFormation of cytochrome c (cyt c)/cardiolipin (CL) peroxidase complex selective toward peroxidation of polyunsaturated CLs is a pre-requisite for mitochondrial membrane permeabilization. Tyrosine residues – via the generation of tyrosyl radicals (Tyr) – are likely reactive intermediates of the peroxidase cycle leading to CL peroxidation. We used mutants of horse heart cyt c in which each of the four Tyr residues was substituted for Phe and assessed their contribution to the peroxidase catalysis. Tyr67Phe mutation was associated with a partial loss of the oxygenase function of the cyt c/CL complex and the lowest concentration of H2O2-induced Tyr radicals in electron paramagnetic resonance (EPR) spectra. Our MS experiments directly demonstrated decreased production of CL-hydroperoxides (CL-OOH) by Tyr67Phe mutant. Similarly, oxidation of a phenolic substrate, Amplex Red, was affected to a greater extent in Tyr67Phe than in three other mutants. Tyr67Phe mutant exerted high resistance to H2O2-induced oligomerization. Measurements of Tyr fluorescence, hetero-nuclear magnetic resonance (NMR) and computer simulations position Tyr67 in close proximity to the porphyrin ring heme iron and one of the two axial heme-iron ligand residues, Met80. Thus, the highly conserved Tyr67 is a likely electron-donor (radical acceptor) in the oxygenase half-reaction of the cyt c/CL peroxidase complex