Diffusion of water in the endosperm tissue of wheat grains as studied by pulsed field gradient nuclear magnetic resonance.

Pulsed field gradient nuclear magnetic resonance has been used to measure water self-diffusion coefficients in the endosperm tissue of wheat grains as a function of the tissue water content. A model that confines the water molecules to a randomly oriented array of capillaries with both transverse dimension less than 100 nm has been used to fit the data and give a unique diffusion coefficient at each water content. The diffusion rates vary from 1.8 x 10(-10) m2s-1 at the lowest to 1.2 x 10(-9) m2s-1 at the highest moisture content. This variation can be explained in terms of an increase in water film thickness from approximately 0.5 to approximately 2.5 nm over the moisture range investigated (200-360 mg g-1).     

Water permeability of plant cuticles: permeance,diffusion and partition coefficients

Summary Using isolated cuticular membranes from ten woody and herbaceous plant species, permeance and diffusion coefficients for water were measured, and partition coefficients were calculated. The cuticular membranes of fruit had much higher permeance and diffusion coefficients than leaf cuticular membranes from either trees or herbs. Both diffusion and partition coefficients increased with increasing membrane thickness. Thin cuticles, therefore, tend to be better and more efficient water barriers than thick cuticles. We compared the diffusion coefficients and the water content of cuticles as calculated from transport measurements with those obtained from water vapor sorption. There is good to fair agreement for cuticular membranes with a low water content, but large discrepancies appear for polymer matrix membranes with high permeance. This is probably due to the fact that diffusion coefficients obtained from transport measurements on membranes with high permeance and water content are underestimated. Water permeabilities of polyethylene and polypropylene membranes are similar to those of leaf cuticular membranes. However, leaf cuticles have much lower diffusion coefficients and a much greater water content than these synthetic polymers. This suggests that cuticles are primarily mobility barriers as far as water transport is concerned.     

温室茄子茎直径微变化与作物水分状况的关系

在温室条件下,采用盆栽土培和小区试验相结合的方法,以茄子(Solanummelongena,品种新乡糙青茄)为材料进行了植株茎直径微变化(膨胀或收缩)与作物体内水分状况的关系试验研究,旨在为利用茎直径微变化无损快速诊断作物水分状况提供理论依据。盆栽和小区试验均采用两因素(土壤水分梯度和作物不同生育阶段)随机区组设计,土壤水分控制下限分别取田间持水量的80%FC(Fieldwatercapacity),70%FC,60%FC和50%FC;生育阶段分别为苗期、花果期和采收期;共有4×3=12个处理组合,重复3次。结果表明:无论是在较高土壤含水量或在较低土壤含水量条件下,在晴好的天气里,茄子茎直径都是在白天收缩,傍晚、夜间复原或膨胀,而且这种微变化动态与植株体内的水分状况密切相关,不同土壤含水量条件下植株茎胀缩的幅度存在明显差异。高水分条件下,植株茎收缩幅度小,复原能力强;低水分条件下,植株茎收缩幅度大,恢复能力差。茎直径变化对环境因子水汽压差(VPD)的响应比较敏感,二者呈正相关关系,相关系数R2为0·8938。茎直径变化量(ΔSd)与叶水势(ψL)、叶片相对含水量(LRWC)呈极显著正相关关系,相关系数R2分别为0·867和0·965。这些结果显示,茎直径变化量能灵敏、实时、准确地反映植株体内的水分状况;与其它作物水分诊断方法(叶水势法,叶片相对含水量法,细胞液浓度法等)相比,茎直径微变化法可能具有简便、稳定、无损、连续监测和自动记录的优势。     

Carboxymethylation of cellulose using reactive extrusion

Carboxymethyl cellulose was prepared using a continuous, reduced solvent, reactive extrusion process with a short reaction time. The effects of the amounts of NaOH (30 g, 40 g and 50 g), water:ethanol ratio (100%, 70%, 50%, 30% and 10% H₂O) and their interactions on the physical, chemical and morphological properties of carboxymethyl cellulose were studied. Experiments were conducted using to a 5 × 3 blocked factorial design. X-ray diffraction analyses revealed higher degrees of crystallinity and fractions of cellulose-II crystalline structure when 100% H₂O was used as compared to that for 70%, 50%, 30% and 10% H₂O and a commercially available brand of carboxymethyl cellulose, AQUASORB A500. Statistical analysis revealed a significant interaction between the effects of NaOH and H₂O on the degrees of substitutions. The degrees of substitutions decreased with increasing amounts of NaOH and tended to increase with increasing alcohol concentrations. Liquid uptake measurements revealed that the extent of saline uptake, measured at intervals of 1 min, 5 min and 10 min, by carboxymethyl cellulose prepared with 100% H₂O, especially when 40 g and 50 g NaOH was used, was higher than that for 70%, 50%, 30% and 10% H₂O and AQUASORB A500. This may have been because of the higher crystallinity in carboxymethyl cellulose prepared with 100% H₂O. Carboxymethyl cellulose prepared with 70% H₂O and 30 g and 50 g NaOH had the highest saline absorption, using the soak method, before and after centrifugation, respectively. Scanning electron microscopy for carboxymethyl cellulose prepared with 100% and 10% H₂O, through images at 120X magnification, revealed fibers 100 μ to >800 μ in length and 0.8-3.3 μ in breadth. Some non fibrous particles, 0.8-6.7 μ in dimensions, also were observed for 100% H₂O. Images at 900× magnification revealed partially damaged fiber surfaces.     

Ion Diffusion Selectivity in Lecithin-Water Lamellar Phases

The diffusion coefficients of Na⁺, Rb⁺, and cl^- were determined in lecithin-water lamellar phases at 18°C as a function of phase hydration. Diffusion was measured within the phase with no transfer between phase and bulk aqueous medium. The relative diffusion coefficients of anion and cation depended strongly on phase hydration. At low water content, the diffusion coefficient of Cl^- was greater than that of Na⁺ or Rb⁺ whereas at high water content both cations diffused faster than the anion. The change in relative diffusion coefficient occurred at 0.24 g water/g phase (24% water). The possibility that a change in conformation of the lecithin polar head occurs at a phase water content of 24% is considered. The diffusion coefficients of all three ions decreased at the water content where the relative diffusion rates inverted. Freeze fracture and polarizing microscopy studies were carried out to obtain information on phase structure. The latter study indicated that a change in long-range organization of the phase occured at 24% water. This change accounts for the decrease in the ion diffusion coefficients at this water content. The change in conformation of the choline phosphate group proposed as an explanation for the change in ion selectivity could lead to changes in long-range organization of the phase as a second order-effect.     

A study of water diffusion into a high-amylose starch blend: the effect of moisture content and temperature

The effect of moisture content and temperature on water diffusion into a modified high amylose (< or = 90%) maize thermoplastic starch blend was investigated. Gravimetric and magnetic resonance imaging (MRI) studies were conducted to elucidate the diffusion mechanism and diffusion coefficients for this system. The diffusion coefficient data demonstrated that the rate of water diffusion into this blend was significantly dependent upon temperature and moisture content. Water diffusion was faster at higher temperatures and generally for samples stored at higher relative humidity environments. It was revealed from the gravimetric data that water diffusion into this starch blend was Fickian; however, further analysis of the MRI images found that the water diffusion mechanism was exponentially dependent on the concentration. This result was determined by comparing experimental water concentration profiles to a theoretical model calculated using the implicit Crank-Nicolson finite difference method.     

Physical and chemical characterization of lamb meat from different genotypes submitted to diet with different fibre contents

The objective of the study was to evaluate the effect of genotype and the dietary fibre concentration in the chemical composition and physical properties of lamb meat. Samples from 54 animals from Morada Nova and Santa Inês native breeds and Dorpper × Santa Inês half-breed were analyzed, which received two diets, one with 41.7% and another with 33.6% fibre content, until reaching the average slaughter weight of 30 kg. The design used was fully randomized 3 × 2 factorial, three genotypes and two diets with nine replicates. Colour and pH in Semimembranosus muscle were determined, together with the analyses of the water retention capacity, loss of weight due to cooking, shearing force, and chemical composition in Longissimus dorsi muscle. The factor genotype influenced the chemical composition of meat, with Santa Inês lamb and crossbreed showing the highest protein percentages. The diet with 33.6% fibre content provided meat with higher moisture percentage and lower protein value, and the loss of weight due to cooking and shearing force parameters did not interfere in other variables. In addition, lambs receiving higher fibre content diet produced meat with lower shear force values, having indicated to be more tenderness. Despite these variations, the meat of lambs from all genotypes and under the diets evaluated can be considered of good quality.     

Physical conditions of propagation media and their influence on the rooting of cuttings

Summary The air content in three types of propagation media, Jiffy-7 and Jiffy-9 which are Sphagnum peat and Grodan which is rockwool, were investigated when they were held at moisture tensions of 0,6 and 12 cm measured from the base of the media. At 0 cm tension the air content (vol. %) was highest in Jiffy-9 and lowest in Jiffy-7. At 12 cm tension the air content was higher in Grodan than in Jiffy-9 and Jiffy-7. Oxygen diffusion coefficients (ODC) and oxygen diffusion rates (ODR) were measured at the different air contents. At air contents below 20 vol. % ODC was about the same for Jiffy-9 and Grodan but at air contents above 20 vol.% it was larger for Jiffy-9 than for Grodan. The oxygen diffusion rate was measured at 0, 4 and 8 cm moisture tension. At all tensions it was approximately 20% higher in Jiffy-9 than in Grodan and Jiffy-7. The ODR in Jiffy-7 and Grodan were affected equally at the same tension, although Grodan contained more air. Report no 253     

Variations in the fibre repeat between samples of cellulose I from different sources

A powder X-ray diffractometer was used to measure the fibre repeat in cellulose I with sufficient precision to detect variations between samples from different sources. The variations were correlated with the lateral dimensions of the crystallites and were attributed to different minimum-energy fibre repeats for chains in the interiors and on the surfaces of crystallites. Results were interpreted in terms of a model for internal mechanical stress in which the interior chains were under compression and the surface chains under tension to ensure identical fibre repeats for all chains. The model was used to extrapolate the fibre repeat to a value of 1.043 nm for a hypothetical, infinitely large crystal, and to 1.029 nm for a crystallite so narrow that all chains were exposed on surfaces.     

High performance edible nanocomposite films containing bacterial cellulose nanocrystals

Bacterial cellulose obtained from Gluconacetobacter xylinus in the form of long fibers were acid hydrolyzed under controlled conditions to obtain cellulose nanocrystals. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed the formation of rod like cellulose nanocrystals having an average diameter and length of 20 ± 5 nm and 290 ± 130 nm respectively. These nanocrystals were used to prepare gelatin nanocomposite films and characterized for elucidating its performance. The formation of percolated networks of cellulose nanocrystals within gelatin matrix resulted in improving the mechanical properties of nanocomposites. The moisture sorption and water vapor permeability (WVP) studies revealed that the addition of cellulose nanocrystals reduced the moisture affinity of gelatin, which is very favorable for edible packaging applications. Results of this study demonstrated the use of bacterial cellulose nanocrystals (BCNCs) in the fabrication of edible, biodegradable and high-performance nanocomposite films for food packaging applications at relatively low cost.     

Size-Dependent Diffusion of Dextrans in Excised Porcine Corneal Stroma

Delivery of therapeutic agents to the eye requires efficient transport through cellular and extracellular barriers. We evaluated the rate of diffusive transport in excised porcine corneal stroma using fluorescently labeled dextran molecules with hydrodynamic radii ranging from 1.3 to 34 nm. Fluorescence correlation spectroscopy (FCS) was used to measure diffusion coefficients of dextran molecules in the excised porcine corneal stroma. The preferential sensitivity of FCS to diffusion along two dimensions was used to differentially probe diffusion along the directions parallel to and perpendicular to the collagen lamellae of the corneal stroma. In order to develop an understanding of how size affects diffusion in cornea, diffusion coefficients in cornea were compared to diffusion coefficients measured in a simple buffer solution. Dextran molecules diffuse more slowly in cornea as compared to buffer solution. The reduction in diffusion coefficient is modest however (67% smaller), and is uniform over the range of sizes that we measured. This indicates that, for dextrans in the 1.3 to 34 nm range, the diffusion landscape of corneal stroma can be represented as a simple liquid with a viscosity approximately 1.5 times that of water. Diffusion coefficients measured parallel vs. perpendicular to the collagen lamellae were indistinguishable. This indicates that diffusion in the corneal stroma is not highly anisotropic. Our results support the notion that the corneal stroma is highly permeable and isotropic to transport of hydrophilic molecules and particles with hydrodynamic radii up to at least 34 nm.     

New insights into the structure and hydration of a stratum corneum lipid model membrane by neutron diffraction

The structure and hydration of a stratum corneum (SC) lipid model membrane composed of N-(-hydroxyoctadecanoyl)-phytosphingosine (CER6)/cholesterol (Ch)/palmitic acid (PA)/cholesterol sulfate (ChS) were characterized by neutron diffraction. The neutron scattering length density across the SC lipid model membrane was calculated from measured diffraction peak intensities. The internal membrane structure and water distribution function across the bilayer were determined. The low hydration of the intermembrane space is a major feature of the SC lipid model membrane. The thickness of the water layer in the SC lipid model membrane is about 1 Å at full hydration. For the composition 55% CER6/25% Ch/15% PA/5% ChS, in a partly dehydrated state (60% humidity) and at 32°C, the lamellar repeat distance and the membrane thickness have the same value of 45.6 Å . The hydrophobic region of the membrane has a thickness of 31.2 Å . A decrease of the Ch content increases the membrane thickness. The water diffusion through the SC lipid model multilamellar membrane is a considerably slow process relative to that through phospholipid membranes. In excess water, the membrane hydration follows an exponential law with two characteristic times of 93 and 44 min. At 81°C and 97% humidity, the membrane separates into two phases with repeat distances of 45.8 and 40.5 Å . Possible conformations of CER6 molecules in the dry and hydrated multilayers are discussed.     

Use of a composite Biomer-butyl rubber/Biomer material to prevent transdiaphragmatic water permeation during long-term, electrically-actuated left ventricular assist device (LVAD) pumping

The pumping diaphragm of the Texas Heart Institute (THI) E-Type ALVAD must perform the dual functions of providing a flexible blood interface and isolating the electrical actuator from adjacent fluids. Thus, protection is required against fluid leakage and moisture diffusion to prevent corrosion and damage to electrical actuator components. Average diffusion rates up to 1 ml per day through currently used elastomeric diaphragm materials have been measured during static in-vitro and in-vivo tests. To circumvent this problem, an improved pumping diaphragm has been recently developed for use with the electrically-actuated THI E-Type ALVAD. This trilaminar diaphragm consists of a composite Biomer and butyl rubber design. A.010 inch layer of butyl rubber (characterized by an extremely low diffusion rate for water, approximately 0 ml per day) is positioned between two Biomer layers (.020 and.010 inches in thickness). Initial invitro and in-vivo studies, in calves, indicate that this composite diaphragm provides an excellent barrier to water permeation, without sacrificing biocompatibility or structural integrity under conditions of chronic flexure.     

Determination of pollutant diffusion coefficients in naturally formed biofilms using a single tube extractive membrane bioreactor

A novel technique has been used to determine the effective diffusion coefficients for 1,1,2-trichloroethane (TCE), a nonreacting tracer, in biofilms growing on the external surface of a silicone rubber membrane tube during degradation of 1,2-dichloroethane (DCE) by Xanthobacter autotrophicus GJ10 and monochlorobenzene (MCB) by Pseudomonas JS150. Experiments were carried out in a single tube extractive membrane bioreactor (STEMB), whose configuration makes it possible to measure the transmembrane flux of substrates. A video imaging technique (VIT) was employed for in situ biofilm thickness measurement and recording. Diffusion coefficients of TCE in the biofilms and TCE mass transfer coefficients in the liquid films adjacent to the biofilms were determined simultaneously using a resistances-in-series diffusion model. It was found that the flux and overall mass transfer coefficient of TCE decrease with increasing biofilm thickness, showing the importance of biofilm diffusion on the mass transfer process. Similar fluxes were observed for the nonreacting tracer (TCE) and the reactive substrates (MCB or DCE), suggesting that membrane-attached biofilm systems can be rate controlled primarily by substrate diffusion. The TCE diffusion coefficient in the JS150 biofilm appeared to be dependent on biofilm thickness, decreasing markedly for biofilm thicknesses of >1 mm. The values of the TCE diffusion coefficients in the JS150 biofilms <1-mm thick are approximately twice those in water and fall to around 30% of the water value for biofilms >1-mm thick. The TCE diffusion coefficients in the GJ10 biofilms were apparently constant at about the water value. The change in the diffusion coefficient for the JS150 biofilms is attributed to the influence of eddy diffusion and convective flow on transport in the thinner (<1-mm thick) biofilms.     

Characteristics of Eucheuma cottonii waste from East Malaysia: physical,thermal and chemical composition

The aim of this paper was to examine the characteristics of Eucheuma cottonii waste in order to analyse its potential as renewable material. The morphology of Eucheuma cottonii (raw and wastes) was investigated through scanning electron microscopy (SEM), the thermal behaviour through thermogravimetric analysis (TGA) and the physical properties through FT-IR, XRD, gas pycnometer, particle size analyser, water absorption and moisture content analysis. The chemical compositions were determined by using acid detergent fibre (ADF), neutral detergent fibre (NDF) and acid detergent lignin (ADL) analysis. It was found that Eucheuma cottonii wastes have better thermal stability, higher crude fibre content, lower moisture content and similar density to the raw Eucheuma cottonii, which suggests that these biomass wastes have good potential as renewable filler material.     

Modulation of proton transfer in the water wire of dioxolane-linked gramicidin channels by lipid membranes

Proton conductance (g(H)) in single SS stereoisomers of dioxolane-linked gramicidin A (gA) channels were measured in different phospholipid bilayers at different HCl concentrations. In particular, measurements were obtained in bilayers made of 1,2-diphytanoyl 3-phosphocholine (DiPhPC) or its ethylated derivative 1,2-diphytanoyl 3-ethyl-phosphocholine (et-DiPhPC,). The difference between these phospholipids is that in et-DiPhPC one of the phosphate oxygens is covalently linked to an ethyl group and cannot be protonated. In relatively dilute acid solutions, g(H) in DiPhPC is significantly higher than in et-DiPhPC. At high acid concentrations, g(H) is the same in both diphytanoyl bilayers. Such differences in g(H) can be accounted for by surface charge effects at the membrane/solution interfaces. In the linear portion of the log g(H)-log [H] relationship, g(H) values in diphytanoyl bilayers were significantly larger (approximately 10-fold) than in neutral glyceryl monooleate (GMO) membranes. The slopes of the linear log-log relationships between g(H) and [H] in diphytanoyl and GMO bilayers are essentially the same (approximately 0.76). This slope is significantly lower than the slope of the log-log plot of proton conductivity versus proton concentration in aqueous solutions (approximately 1.00). Because the chemical composition of the membrane-channel/solution interface is strikingly different in GMO and diphytanoyl bilayers, the reduced slope in g(H)-[HCl] relationships may be a characteristic of proton transfer in the water wire inside the SS channel. Values of g(H) in diphytanoyl bilayers were also significantly larger than in membranes made of the more common biological phospholipids 1-palmitoyl 2-oleoyl phosphocholine (POPC) or 1-palmitoyl 2-oleoyl phosphoethanolamine (POPE). These differences, however, cannot be accounted for by different surface charge effects or by different internal dipole potentials. On the other hand, maximum g(H) measured in the SS channel does not depend on the composition of the bilayer and is determined essentially by the reduced mobility of protons in concentrated acid solutions. Finally, no experimental evidence was found in support of a lateral proton movement at the phospholipid/solution interface contributing to g(H) in single SS channels. Protein-lipid interactions are likely to modulate g(H) in the SS channel.     

The effect of restricted hydration on the rate of reaction of glucose 6-phosphate dehydrogenase, phosphoglucose isomerase, hexokinase and fumarase. Relevance for metabolism in xeric (near-dry) conditions

A method is described for the measurement of enzyme activity under xeric conditions. The reaction mixtures had water contents ranging between 0.1 and 0.6g/g of reaction mixture. For glucose 6-phosphate dehydrogenase, hexokinase and fumarase, enzyme activity became detectable (about 0.05% of the fully hydrated rate) when the water content was about 0.2g/g of reaction mixture, and for phosphoglucose isomerase, around 0.15g/g of reaction mixture. With the water content raised to 0.3g/g of reaction mixture the reaction rates were only increased to 0.1-3% of the fully hydrated rate. When the combined rates for phosphoglucose isomerase and glucose 6-phosphate dehydrogenase were measured, reasonable agreement was found between the experimental data and those calculated from the individual experimentally determined rates on the assumption that diffusion was not further limiting. A method was devised for measuring the diffusion coefficients of low-molecular-weight substances in solutions having low water contents. The diffusion coefficients of riboflavin in sorbitol solution decreased by about 100-fold when the water content of the latter was reduced from 3 to 0.25g/g of sorbitol. It is concluded that to detect enzyme activity a certain minimal amount of water is required and that above this minimum the rate is still restricted by diffusion limitation. The relevance of the results to the physical state of water in reaction mixtures and to metabolism in seeds and spores in xeric conditions is discussed.     

Theoretical basis of protocols for seed storage

The protocols presently established for optimum seed storage do not account for the chemical composition of different seed species, the physiological status of the seed, and the physical status of water within the seed. The physiological status of seeds from five species with varying chemical compositions was determined by measurements of rates of oxygen uptake and seed deterioration. The physical status of water was determined by water sorption characteristics. For each species studied, there was a specific moisture content for the onset of respiration, chemical reactions, and accelerated aging rates. The moisture contents at which these physiological levels were observed varied among the species and correlated with the lipid content of the seed. However, the changes in physiological activities and the physical status of water occurred at specific relative humidities: 91% for the onset of respiration, 27% for the increased rates of thermal-chemical reactions, and 19% for optimum longevity. Based on these observations, we propose that equilibrating seeds between 19 and 27% relative humidity provides the optimum moisture level for maintaining seed longevity during longterm storage.     

Self-diffusion of water into silk fibers from magnetic field pulse gradient data

Self-diffusion of water was studied in fibers of natural silk (Bombyx mori) with a water content of 0.18 g H2O/g dried material. Self-diffusion measurements were conducted by pulsed gradient of magnetic field (stimulated echo) at diffusion times from 10 to 200 mc. The dependence of experimental diffusion coefficients Dexp = f(delta) (observed decrease when delta increased) was determined to be responsible for the restricted diffusion. A model of planar and regularly spaced permeable barriers to diffusion of water molecules was applied to estimate the barrier spacing a and the permeability constant p. The maximal value of Dexp (at short diffusion time) in B. mori silk fibres was about 0.06 of the value of Dexp in bulk free water. The results obtained are compared to literature data on self-diffusion of water in hydrated biopolymer fibers and are discussed in connection with molecular mobility in natural macromolecular systems with low water content.     

Developmental changes in mesophyll diffusion conductance and photosynthetic capacity under different light and water availabilities in Populus tremula: how structure constrains function

Finite mesophyll diffusion conductance (g(m) ) significantly constrains net assimilation rate (A(n) ), but g(m) variations and variation sources in response to environmental stresses during leaf development are imperfectly known. The combined effects of light and water limitations on g(m) and diffusion limitations of photosynthesis were studied in saplings of Populus tremula L. An one-dimensional diffusion model was used to gain insight into the importance of key anatomical traits in determining g(m) . Leaf development was associated with increases in dry mass per unit area, thickness, density, exposed mesophyll (S(mes) /S) and chloroplast (S(c) /S) to leaf area ratio, internal air space (f(ias) ), cell wall thickness and chloroplast dimensions. Development of S(mes) /S and S(c) /S was delayed under low light. Reduction in light availability was associated with lower S(c) /S, but with larger f(ias) and chloroplast thickness. Water stress reduced S(c) /S and increased cell wall thickness under high light. In all treatments, g(m) and A(n) increased and CO(2) drawdown because of g(m) , C(i) -C(c) , decreased with increasing leaf age. Low light and drought resulted in reduced g(m) and A(n) and increased C(i) -C(c) . These results emphasize the importance of g(m) and its components in determining A(n) variations during leaf development and in response to stress.