STED nanoscopy : A novel way to image the pore space of geological materials

STED nanoscopy (Stimulated Emission Depletion). which can resolve details far below the diffraction barrier has been applied hitherto preferentially to life sciences. The method is however also ideal for the investigation of geological matrices containing transparent minerals, an application tested here, to our knowledge, for the first time. The measurements on altered granitic rock and sedimentary clay rock, both containing very fine-grained phases, were conducted successfully. The STED fluorophore was dissolved in C-14-labelled methylmethacrylate (C-14-MMA) monomer which was polymerised within the rock matrix, thereby labelling the pore space in the geomaterials. Double labelling provided by the C-14-labelled MMA enables autoradiography and scanning electron microscopy (SEM), providing necessary complementary information for characterisation and quantification of porosity distributions and mineral and structure identification. Promising perspectives for further investigations of geological matrices by using different fluorophores and the optimisation of measuring procedures or even higher resolution are discussed. The combination of these different methods enlarges the observation scale of porosity from nanometre to centimetre scale.Peer reviewe

On the connected porosity of mineral aggregates in crystalline rocks

International audienceThe 14C-PMMA impregnation of rock samples and mineral staining methods provide the connected porosity map and the spatial distribution of mineral aggregates, respectively. Combined image analysis of mineral and porosity maps allows quantification of the connected porosity distribution in rockforming mineral aggregates. After the two maps have been superimposed numerically, the 14C-PMMA method provides an indication of the extent of pore connectivity for each pixel in the analyzed area, which can be used to obtain the porosity distribution as a function of modal mineralogy.When applied to undeformed and deformed Kivetty granodiorite samples from Finland, the method allows for a detailed analysis of the rock porosity. Porosity distributions related to the undeformed rock are unimodal and approximately identical to each other. On the other hand, porosity distributions of the deformed granodiorite are multimodal and vary significantly. Constituent porosity sets of the deformed samples were albite crystals free of alkali feldspar patches and alkali feldspar phenocrysts (average porosity, Φ̅ = 0.21%), albite containing alkali feldspar patches (Φ̅ = 0.59%), rapakivi albitic mantles (Φ̅ = 1.15%), quartz (Φ̅ = 0.39%) and mafic minerals (Φ̅ = 5.8%). Moreover, the analysis indicates that the numerous micropores observed under SEM within alkali feldspar phenocrysts and albite crystals free of alkali feldspar patches are unconnected in 3D

The Effect of Rock Matrix Heterogeneities Near Fracture Walls on the Residence Time Distribution (RTD) of Solutes

International audienceFor interpreting solute transport experiments within rocks, the Residence Time Distributions (RTDs) of solutes in the rock matrix were either derived from the assumption of a homogeneous matrix, or were considered through analytical distributions of diffusion coefficients. A numerical approach based on a Lagrangian framework was developed in order to investigate the effect of spatial heterogeneities on RTDs. The matrix diffusion was simulated over two-dimensional computation grids, representing virtual or real digitized porosity maps. First, virtual porosity maps were used to mimic porous features linked to conductive fractures, such as (i) low-porosity coatings on fracture walls, and (ii) porosity gradients within the rock matrix. Furthermore, RTD was calculated for the real pore network of the Palmottu granite (Finland). It was shown that the arrangement of spatial heterogeneities located in the immediate vicinity of a conductive fracture modifies the RTD of solutes within the rock matrix. Porous zones located near fractures are of particular importance, because they generate anomalies on the RTD

Secretory production of an FAD cofactor-containing cytosolic enzyme (sorbitol-xylitol oxidase from Streptomyces coelicolor ) using the twin-arginine translocation (Tat) pathway of Corynebacterium glutamicum

Carbohydrate oxidases are biotechnologically interesting enzymes that require a tightly or covalently bound cofactor for activity. Using the industrial workhorse Corynebacterium glutamicum as the expression host, successful secretion of a normally cytosolic FAD cofactor-containing sorbitol–xylitol oxidase from Streptomyces coelicolor was achieved by using the twin-arginine translocation (Tat) protein export machinery for protein translocation across the cytoplasmic membrane. Our results demonstrate for the first time that, also for cofactor-containing proteins, a secretory production strategy is a feasible and promising alternative to conventional intracellular expression strategies

Radon emanation from fresh, altered and disturbed granitic rock characterized by 14 C-PMMA impregnation and autoradiography

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