Apparent Microporosity Research Articles

Spatial and temporal evolution of quantitative magnetic resonance imaging parameters of peach and apple fruit - relationship with biophysical and metabolic traits.

Fruits are complex organs that are spatially regulated during development. Limited phenotyping capacity at cell and tissue levels is one of the main obstacles to our understanding of the coordinated regulation of the processes involved in fruit growth and quality. In this study, the spatial evolution of biophysical and metabolic traits of peach and apple fruit was investigated during fruit development. In parallel, the multi-exponential relaxation times and apparent microporosity were assessed by quantitative magnetic resonance imaging (MRI). The aim was to identify the possible relationships between MRI parameters and variations in the structure and composition of fruit tissues during development so that transverse relaxation could be proposed as a biomarker for the assessment of the structural and functional evolution of fruit tissues during growth. The study provides species-specific data on developmental and spatial variations in density, cell number and size distribution, insoluble and soluble compound accumulation and osmotic and water potential in the fruit mesocarp. Magnetic resonance imaging was able to capture tissue evolution and the development of pericarp heterogeneity by accessing information on cell expansion, water status and distribution at cell level, and microporosity. Changes in vacuole-related transverse relaxation rates were mostly explained by cell/vacuole size. The impact of cell solute composition, microporosity and membrane permeability on relaxation times is also discussed. The results demonstrate the usefulness of MRI as a tool to phenotype fruits and to access important physiological data during development, including information on spatial variability.

Organic Molecules of Intrinsic Microporosity

Organic molecules of intrinsic microporosity (OMIMs) are rigid molecules with an awkward shape that are designed to pack space inefficiently in the solid state maximizing free volume and thereby generating apparent microporosity as determined by gas adsorption. In this perspective article, the origin of the OMIM concept is explained and the progress in its realization both by synthesis and packing simulation is reviewed.

Analysis of the dynamic mechanical properties of apple tissue and relationships with the intracellular water status, gas distribution, histological properties and chemical composition

Mechanical properties of fruit depend on many parameters, including microporosity, cell characteristics and cell wall composition/structure. Recent developments in quantitative MRI provide the possibility of studying fruit through local measurements of multi-exponential T2 reflecting water status and distribution at the subcellular level, and apparent microporosity. In the present study, dynamic mechanical analysis provided Young’s modulus and the damping factor, reflecting elastic and viscous properties of apple tissue, respectively. These measurements were compared to quantitative MRI measurements, biochemical analysis (water, free sugar and alcohol-insoluble solid contents, cell wall composition) and histological measurements, all performed on apple parenchyma tissue. The aim was to investigate the respective contributions of microporosity, intracellular water status and distribution, and chemical composition to mechanical properties characterizing fruit texture quality.Correlations between the measurements were studied for six apple cultivars with storage times varying from one to six months. A general behavior pattern independent of cultivar and storage time provided greater understanding of the parameters involved in mechanical properties. Cell wall arabinose composition and water status associated with the vacuole were correlated with Young’s modulus, the xylose and hemicellulose compositions were correlated with the damping factor and the relative amount of water attributed to the cytoplasm and the apparent microporosity of the samples were correlated with both the damping factor and Young’s modulus. Modification of the water pool attributed to the extracellular water/cell wall was shown to be involved in softening of the tissue. Comparison of the different measurements showed that variations in relaxation times were not explained by the water content, indicating that other phenomena such as membrane permeability, vacuole size and/or solute composition were predominant in the relaxation mechanism. A correlation between water pools attributed to the vacuole and cytoplasm evidenced water exchange occurring between the two compartments.

MRI investigation of subcellular water compartmentalization and gas distribution in apples

Water status and distribution at subcellular level in whole apple fruit were evaluated by Magnetic Resonance Imaging (MRI) measurement of the multi-exponential transverse (T2) relaxation of water protons. Apparent microporosity, also estimated by MRI, provided mapping of gas distribution in fruit tissues. Measuring for the first time the multi-exponential relaxation of water and apparent tissue microporosity in whole fruit and combining these with histological measurements provided a more reliable interpretation of the origins of variations in the transverse relaxation time (T2) and better characterization of the fruit tissue. Measurements were performed on 54 fruits from 3 different cultivars. Fruits of different sizes were selected for each cultivar to provide tissues with cells of different dimensions. Macrovision measurements were carried out on parenchymal tissue from all fruits to investigate the impact of cell size on T2 value.The results showed that the MRI transverse relaxation signal is well fitted by a tri-exponential decay curve that reflects cell compartmentalization. Variations in cell size partially explained the different T2 observed. This study highlighted the heterogeneity of apple tissues in terms of relaxation parameters, apparent microporosity and cell morphology and in relation to specific variations between fruit of different cultivars.

Quantification of microporosity in fruit by MRI at various magnetic fields: comparison with X-ray microtomography

Microstructure determines the mechanical and transport properties of fruit tissues. One important characteristic of the microstructure is the relative volume fraction of gas-filled intercellular spaces, i.e., the tissue microporosity. Quantification of this microporosity is fundamental for investigating the relationship between gas transfer and various disorders in fruit. We present a new method for quantifying the apparent microporosity using magnetic resonance imaging (MRI). The method is based on the differences in magnetic susceptibility between gas-filled intercellular spaces and their environment inside fruit tissues. It was tested at two different magnetic fields (1.5 and 0.2 T) on apple and tomato fruit. The method was validated by comparing the MRI results with estimation of local tissue porosity using X-ray microtomography experiments. MRI was shown to be effective in determining the distribution of apparent microporosity in fruit.

Geological controls on coalbed methane reservoir capacity and gas content

The influence of coal composition and rank on coalbed methane reservoir capacity, gas content and gas saturation have been investigated for a series of Australian, Canadian and United States coals. Globally there is no or little correlation between coal rank and methane adsorption capacity (as commonly assumed), although in particular basins there are general trends with rank and composition. Micropore 1 Micropores are less than 2 nm in diameter, mesopores 2 to 50 nm in diameter and macropores greater than 50 nm in diameter following current IUPAC classification [International Union of Pure and Applied Chemistry (IUPAC), 1994. Pure Applied Chemistry, 66, 1739]. 1 capacity and surface area, determined from low-pressure carbon dioxide adsorption isotherms (0°C) decrease and then increase with rank, passing through a minimum in the high volatile bituminous coal rank. There is no consistent variation in modal micropore size or size distribution with rank. For suites of isorank coals there is a poor (Permian Bulli and Wongawilli seams, Australia) to good positive correlation (Gates Formation coal seams, Lower Cretaceous, Canada) between vitrinite content and methane adsorption capacity (dry ash free and as received bases). For each isorank coal suite there is a good correlation between micropore capacity and abundance of vitrinite and high-pressure methane adsorption capacity. Comparison of coals of similar composition, but from different isorank suites, indicates however that the coals with the highest methane adsorption capacity do not necessarily have the highest micropore capacity. Such results are counterintuitive: most pore volume available for methane adsorption is generally assumed to be microporosity. It is suspected that moisture prevents methane from accessing (some?) microporosity or competes with methane for adsorption space. Carbon dioxide micropore capacity (which is performed on a dry basis) may thus not reflect the microporosity available for gas adsorption in moisture equilibrated coals. Alternatively because of differing physical and chemical properties of carbon dioxide and methane, apparent microporosity available to carbon dioxide (due to greater energy of adsorption) may not be available to methane. Total desorbed gas from canister analyses of Sydney Basin Australian coals suggests that most coals are under-saturated. For a small data set the degree of saturation is negatively correlated with permeability ( r=−0.78) suggesting preferential gas leakage from the higher permeability coals which are vitrite rich. Some degree of under-saturation is probably the result of increased reservoir capacity as a consequence of uplift of the coal seams and thus lower temperatures following gas generation. Rates of desorption are correlated with total gas content ( r=0.79) but do not correlate with rank or any compositional parameter.