Analysis of transient permeation fluxes into and out of membranes for adsorption measurements

A relationship between the integrated fluxes into and out of a membrane following a positive or negative step change in feed concentration was derived. This analysis allows adsorption isotherms in the transport pathways through membranes to be determined from transient permeation responses to step concentration changes in the feed without measuring the retentate response. For Fickian diffusion through a membrane with Langmuir adsorption and zero coverage at the permeate boundary, the difference between the time-integrated flux into and flux out of the membrane is shown to be three times the time-integrated difference between the steady-state flux and the flux out. For Maxwell-Stefan diffusion, this ratio of integrated flux differences is 3 at low coverages and decreases towards 2 at saturation coverage. Mass transfer resistance at the permeate boundary increases the Fickian ratio above 3, and the ratio increases with decreasing Sherwood number. The ratio of integrated flux differences is shown to be identical to the steady-state replenishment time divided by the time lag. Thus, the ratio can be calculated directly from the steady-state concentration profile and the concentration-dependent diffusion coefficient. Surface diffusion through zeolite membranes was analyzed to demonstrate the calculation of the flux relationship for specific adsorption and diffusion models, but the method developed can be applied to membrane permeation in general.     

Transient measurements of adsorption and diffusion in H-ZSM-5 membranes

A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H-ZSM-5 tubular membranes and modeled assuming Maxwell-Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N₂ and CO₂ were nearly identical to those measured by calorimetry on H-ZSM-5 powders. The CH₄ isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na-ZSM-5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients D_MS depended on concentration and were higher for higher feed partial pressures. Average D_MS values for the two membranes were 7.5, 5 and 1.5×10⁻¹⁰ m²/s for N₂, CH₄, and CO₂, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.     

Chemical Ecology of the host searching behavior in an Egg Parasitoid: are Common Chemical Cues exploited to locate hosts in Taxonomically Distant Plant Species?

Parasitoids are known to exploit volatile cues emitted by plants after herbivore attack to locate their hosts. Feeding and oviposition of a polyphagous herbivore can induce the emission of odor blends that differ among distant plant species, and parasitoids have evolved an incredible ability to discriminate them and locate their hosts relying on olfactive cues. We evaluated the host searching behavior of the egg parasitoid Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) in response to odors emitted by two taxonomically distant host plants, citrus and Johnson grass, after infestation by the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae), vector of Citrus Variegated Chlorosis. Olfactory response of female parasitoids toward plants with no herbivore damage and plants with feeding damage, oviposition damage, and parasitized eggs was tested in a Y-tube olfactometer. In addition, volatiles released by the two host plant species constitutively and under herbivore attack were characterized. Females of C. annulicornis were able to detect and significantly preferred plants with host eggs, irrespectively of plant species. However, wasps were unable to discriminate between plants with healthy eggs and those with eggs previously parasitized by conspecifics. Analysis of plant volatiles induced after sharpshooter attack showed only two common volatiles between the two plant species, indole and β-caryophyllene. Our results suggest that this parasitoid wasp uses common chemical cues released by many different plants after herbivory at long range and, once on the plant, other more specific chemical cues could trigger the final decision to oviposit.

     

Reversible H2 storage using a SAPO-34 zeolite layer

A SAPO-34 zeolite membrane was made essentially impermeable to high-pressure hydrogen at room temperature by adsorbing methanol in the SAPO-34 layer. Hydrogen permeance decreased three orders of magnitude when the methanol feed activity was 0.1, and it decreased more than six orders of magnitude when the methanol feed activity was higher than 0.85 at 293 K. The hydrogen permeance at 293 K was below 10⁻¹⁴ mol/m² s Pa for at least five days for a H₂ feed pressure of 6.6 MPa. At higher temperatures, methanol desorbed and the H₂ flux increased. The hydrogen permeance could be controlled by the activity of the methanol on the feed side. These results demonstrate that the SAPO-34 membrane had low fluxes through defects, and H₂ flow through these defects was blocked by capillary condensation of methanol at high methanol activities.     

Response Surface Methodology for Reduction of Pinking in Cooked Turkey Breast Mince by Various Dairy Protein Combinations

Nonfat dry milk (NFDM), sodium caseinate (SC), whey protein concentrate (WPC), and combinations of each were evaluated for abilities to reduce pink color development in cooked, ground, uncured turkey breast. Protein treatments were also evaluated in the presence of pink-color-generating ligands (nicotinamide, 1%, sodium nitrite, 10 ppm, and sodium nitrate, 50 ppm) with and without ethylenedinitrilo-tetraacetic acid disodium salt (200 ppm). NFDM and WPC at levels as low as 1.5% were effective in reducing CIE a* values (P < 0.05) regardless of ligand treatment; SC was not. EDTA reduced pink color within all protein and ligand treatments. Poultry producers can reduce pink color development in further-processed products by selective addition of dairy proteins.     

Origins of Systems Biology in William Harvey’s Masterpiece on the Movement of the Heart and the Blood in Animals

In this article we continue our exploration of the historical roots of systems biology by considering the work of William Harvey. Central arguments in his work on the movement of the heart and the circulation of the blood can be shown to presage the concepts and methods of integrative systems biology. These include: (a) the analysis of the level of biological organization at which a function (e.g. cardiac rhythm) can be said to occur; (b) the use of quantitative mathematical modelling to generate testable hypotheses and deduce a fundamental physiological principle (the circulation of the blood) and (c) the iterative submission of his predictions to an experimental test. This article is the result of a tri-lingual study: as Harvey’s masterpiece was published in Latin in 1628, we have checked the original edition and compared it with and between the English and French translations, some of which are given as notes to inform the reader of differences in interpretation.     

The positional distributions of fatty acids in the triacylglycerols and phosphatidylcholines of the intestinal and popliteal lymph and plasma of sheep

As part of a study of the contribution of the intestinal lymph lipoproteins and their lipid constituents to the plasma lipids in sheep, the positional distributions of the fatty acids in the triacyl-sn-glycerols and phosphatidylcholines in very low density/low density lipoprotein and high-density lipoprotein fractions were determined by stereospecific analysis procedures. The triacyl-sn-glycerols of these lipoprotein fractions in intestinal lymph did not differ appreciably in structure and resembled the plasma triacyl-sn-glycerols in the composition of positionsn-2 especially. However, there were appreciable amounts of the essential fatty acid, linoleic acid, in positionssn-1 andsn-3 of the triacylglycerols in lymph but not in plasma. This result is discussed in terms of the metabolism of the triacylglycerols of lymph after they enter the plasma as part of a mechanism for the conservation of essential fatty acids in ruminants. No differences of metabolic note were observed in the structures of the phosphatidylcholines between lipoprotein fractions and among tissues.     

Replacing the ({beta}{alpha})-unit 8 of E.coli TIM with its chicken homologue leads to a stable and active hybrid enzyme

In order to investigate how structural modifications interferewith protein stability, we modified a (ß)-unit inE.coli triosephosphate isomerase (TIM), a typical (ß)-barrelprotein, assuming that the pseudosymmetrical ß-barrelcan be divided into eight successive loop/ß-strand/loop/-helixmotifs. We replaced the eighth (ß)-unit of E.coliTIM with the corresponding chicken (ß)-unit. The substitution,involving the replacement of 10 of the 23 residues of this (ß)-unit, was evaluated first by modelling, then experimentally.Modelling by bomology suggests how the amino add replacementsmight be accommodated in the hybrid E.coli/chicken TIM (ETCM8CHI).Both natural and hybrid recombinant TIMs, overproduced in E.coli,were purified to homogeneity and characterized as to their stabilityand kinetics. Our kinetic studies show that the modificationperformed here leads to an active enzyme. The stability studiesindicate that the stability of ETIM8CHI is comparable to thatof the wild type TIM.