Nachweis und Bestimmung des Bleis

Ohne Zusammenfassung     

T lymphocyte migration to lymph nodes is maintained during homeostatic proliferation.

The immune system maintains appropriate cell numbers through regulation of cell proliferation and death. Normal tissue distribution of lymphocytes is maintained through expression of specific adhesion molecules and chemokine receptors such as L-selectin and CCR7, respectively. Lymphocyte insufficiency or lymphopenia induces homeostatic proliferation of existing lymphocytes to increase cell numbers. Interestingly, homeostatic proliferation of T lymphocytes induces a phenotypic change from na?ve- to memory-type cell. Na?ve T cells recirculate between blood and lymphoid tissues whereas memory T cells migrate to nonlymphoid sites such as skin and gut. To assess effects of homeostatic proliferation on migratory ability of T cells, a murine model of lymphopenia-induced homeostatic proliferation was used. Carboxyfluorescein diacetate, succinimidyl ester-labeled wild-type splenocytes were adoptively transferred into recombination activation gene-1-deficient mice and analyzed by flow cytometry, in vitro chemotactic and in vivo migration assays, and immunofluorescence microscopy. Homeostatically proliferated T cells acquired a mixed memory-type CD44high L-selectinhigh CCR7low phenotype. Consistent with this, chemotaxis to secondary lymphoid tissue chemokine in vitro was reduced by 22%-34%. By contrast, no differences were found for migration or entry into lymph nodes during in vivo migration assays. Therefore, T lymphocytes that have undergone homeostatic proliferation recirculate using mechanisms similar to na?ve T cells.     

Assigned and unassigned distance geometry: applications to biological molecules and nanostructures

Considering geometry based on the concept of distance, the results found by Menger and Blumenthal originated a body of knowledge called distance geometry. This survey covers some recent developments for assigned and unassigned distance geometry and focuses on two main applications: determination of three-dimensional conformations of biological molecules and nanostructures.     

Dynamic Models of Simple Judgments: II. Properties of a Self-Organizing PAGAN (Parallel, Adaptive, Generalized Accumulator Network) Model for Multi-Choice Tasks

This is the second of two papers comparing connectionist and traditional stochastic latency mechanisms with respect to their ability to account for simple judgments. In the first, we reviewed evidence for a self-regulating accumulator module for two- and three-category discrimination. In this paper, we examine established neural network models that have been applied to predicting response time measures, and discuss their representational and adaptational limitations. We go on to describe and evaluate the network implementation of a Parallel Adaptive Generalized Accumulator Network (PAGAN), based on the interconnection of a number of self-regulating, generalized accumulator modules. The enhancement of PAGAN through the incorporation of distributed connectionist representation is briefly discussed.     

Silver Trifluoromethanesulfonate(Triflate) Activation of Trichloroacetimidates in Glycosylation Reactions

Abstract

Chemical syntheses of biologically active oligosaccharides, glycolipids and glycopeptides requires efficient stereospecific glycosylation reactions.² One of the most effective glycosylation methods involves activation of anomeric imidates, particularly mchloroacetimidates, by Lewis acids such as boron trifluoride etherate (BF₃·OEt₂), mmethylsilyl mfluoromethanesulfonate (TMSOTF)³ and mfluoromethanesulfonic anhydride.⁴ In a recent example from this laboratory, BF₃·OEt₂, has been used to promote the glycosylation of methyl 2,3,6-tri-O-benzoyl-B-D-galactopyranoside (I)⁵ with 2-deoxy-2-phthalimido-3,4,6-tri-O-acetyl-B-D-galactopyranosyl mchloroacetimidate (I): see Scheme 1. The expected β1-4-linked disaccharide III was obtained in 40% yield. The yield was so low since both the α-anomer and a 1-3-linked disaccharide were formed as by products, the latter in particularly large quantities (cf. Ref.⁷). The 1-3 disaccharide could be formed from a product of acid-catalyzed 3,4-migration of the benzoyl group which is not surprising, considering the cis relationship of the 3,4-hydroxyl groups in galactose.⁸ In fact, when the glycosylation reaction was quenched before all unreacted alcohol was consumed, the chromatographic fraction corresponding to the starting alcohol II contained at least three different tribenzoates (as shown by NMR analysis).⁹ Other promoters, ZnBr₂ ¹⁰ and TMSOTF, led to lower yields and more complicated mixtures than BF₃·OEt₂.