Precise ultramicro determination of steroid hormones by combined TLC and GLC analysis

The migration of steroid hormones on TLC plates is predictable on the basis of the number of double bonds and carbonyl and hydroxyl groups they contain. Developed plates can therefore be divided into zones or bands corresponding to well-defined classes of steroids. Steroids can be eluted from the adsorbent quantitatively and without contamination. The eluate from each zone contains a mixture which is much simpler than the original one. The conversion of OH-containing steroids to trimethylsilyl ether (TMS) derivatives is quantitative; it is complete after 3 hr by the described technic. All TMS derivatives are very stable in CS₂ solution. Whether or not they contain OH groups, steroids other than corticosteroids are stable under the present GLC conditions after treatment with TMS reagents. With amts of injected sample increasing from 0 to 0.2 μg, a small apparent increase in specific response is observed with some steroids. This effect is reproducible. The use of calibration curves obtained with an internal standard (5α-pregnane) leads to accurate analyses of mixtures with injections containing 25 nanograms (0.025 μg) of individual steroid. Values obtained from single trials fall 95% of the time within 2% of the mean. Peak elution time of each compound is accurately predictable on the basis of number, position, and stereoconfiguration of functional groups. An integrated TLC-GLC method of analysis based on these findings is outlined. Contribution number 187 of Animal Research Institute.     

Effects of initial cell concentration,growth phase,and process parameters on the viability of Lactobacillus rhamnosus GG after spray drying

Abstract

During spray drying, probiotics encounter several stresses which can reduce their viability. To obtain powder with a sufficient amount of viable probiotics, we evaluated the effects of different process parameters, such as initial cell concentration and the bacterial growth phase, on the viability of the model probiotic Lactobacillus rhamnosus GG. Increasing the initial biomass did not positively impact bacterial viability after spray drying. For growth, we found that stationary grown bacterial cells were more resistant to the spray-drying process than mid-log grown cells, probably owing to an initiated stress response. Furthermore, a full factorial 3³ design was used to assess the influence of three different conditions of inlet temperature, feed rate, and atomizing air flow on the outlet temperature and bacterial viability after spray drying. As expected, inlet temperature had the largest influence on both outlet temperature and log-reduction in bacterial viability. An interaction effect was also observed between feed rate and inlet temperature. Considering the viability of L. rhamnosus GG, the optimal outlet temperature ranged between 50 and 60?°C for obtaining powders with the lowest log-reductions in viability.     

Mapping and interpreting soil textural layers to assess agri-chemical movement at several scales along the eastern seaboard (USA)

Despite numerous cases of groundwater contamination with agricultural chemicals on layered sandy soils, monitoring and prediction of the fate of these chemicals in the vadose zone has eluded researchers and bureaucrats alike so far. To aid in a better understanding of this phenomena, the movement and fate of agricultural chemicals were assessed at different scales for the (sandy and layered) floodplain soil occurring along the Eastern Seaboard. At the point and field scale ground penetrating radar was used to locate the coarse sand lenses and tracer experiments were initiated to study the flow pattern of the chemicals. Results show that water and solutes moved over the coarse layers and were funneled into fingers bypassing most of the soil matrix and reaching the groundwater much faster than when the solute would move evenly through the vadose zone. At field scale a computer simulation indicated that the exact location of the layers does not have to be known for calculating travel times, indicating that pedo-transfer functions could be developed for calculating groundwater pollution potential for different combinations of soil and chemicals. In the future, groundwater pollution on a regional scale can be predicted by using these pedo-transfer functions in a Geographic Information System.     

Lipid-protein interactions and cohesional forces in the lipoproteins systems of membranes

The lipid-protein positional relationship deseribed by the simple Danielli model leads to a concept of the basic structure which is consistent sistent with recent findings. The stability of membranes is insured by internal cohesion forces and by the potential barrier of surrounding water molecules. The properties of cohesional forces are reviewed with reference to membrane stability and order. The existence of a higher degree of organization is discussed in the light of recent electron microscopic data. A “particulate” concept which is compatible with the simple model is discussed with regard to transport phenomena and component turnover in membranes. Contribution No. 219 from Animal Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Canada.     

Separation of steroids by gas chromatography

Journal of the American Oil Chemists' Society -     

Study of biological structure at the molecular level with stereomodel projections I. The lipids in the myelin sheath of nerve

Considerable uncertainty still exists regarding the detailed arrangement in protein-lipid molecular associations found in serum lipoproteins, plasma-membranes of cell organelles, the myelin sheath of nerve, and many other structures of paramount importance to biological mechanisms both in health and disease. Working hypotheses concerning such structures must eventually be tested by comparing known properties with those suggested by exact stereomodels. In this type of study, orthogonal projections of the molecules offer several advantages over the tri-dimensional stereomodels from which they can be derived by a described photographic process. The rules governing the configuration to be given the molecular models used for this purpose are discussed, and the possible applications of the resulting diagrams are described and illustrated by numerous examples taken in the lipid field. These rules are then applied to the lipids in the myelin sheath of nerve. Striking similarities in the configurational features of the two main classes of myelin lipids, the phosphatidyl (dal) and the sphingolipids, immediately suggest very similar models for them. On the other hand, numerous independent observations have indicated the highly probable occurrence of bimolecular complexes involving members of either class with cholesterol. Such complexes are exemplified by proposed models of cholesterol-lecithin and cholesterol-sphingomyelin units. It is demonstrated that the cohesional forces at play should indeed promote stable complexes of this kind. All configurational features of the lipids in myelin fit these basic models. Dimensional variations induced by a broad spectrum of component fatty acids, affect only the length of the resulting complex units. Moreover, the tail-to-tail arrangement of these units provides paired elements of the same length. The latter corresponds exactly to the fundamental dimension predicted for the bimolecular leaflet by low angle X-ray diffraction studies on fresh, unfixed myelin. A model of the bimolecular lipid leaflet produced by parallel grouping of the paired elements is discussed.