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Macromolecular Characteristics (macromolecular + characteristic)
Selected AbstractsSoil organic matter beyond molecular structure Part I: Macromolecular and supramolecular characteristicsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006Gabriele E. Schaumann Abstract This contribution reviews and discusses structural aspects of soil organic matter (SOM) and humic substances (HS) with special respect to the macromolecular and the supramolecular view. It can be concluded that (1) dissolved humic acids behave as supramolecular associations of relatively small molecules with an enormous flexibility of reaction of environmental conditions, (2) multivalent cations may increase the apparent molecular weight by the formation of coordinative crosslinks in dissolved and undissolved natural organic matter (NOM), (3) sorption nonlinearity in solid humic acids and SOM may be due to polymer properties of NOM, (4) sorbates affect sorbent characteristics of SOM, and (5) hysteresis and conditioning effects in SOM can up to now best be explained with the polymer analogy. A distinct polydispersivity of SOM over a wide range of molecular masses is to be assumed. The supramolecular and the macromolecular models were derived from humic acids with different composition and on the basis of different sample states. Although the supramolecular model has not explicitely been shown for unfractionated DOM, the combination of all discussed studies suggests supramolecular as well as macromolecular characteristics of NOM. Neither macromolecules nor small molecules can be fully excluded in solid and dissolved SOM. Microregions with different properties provide different types of sorption sites. SOM is suggested to be regarded as amorphous material. This point of view is not restricted to high molecular masses and may supplement our understanding of SOM by the model of physical aging. [source] New MRI method with contrast based on the macromolecular characteristics of tissuesMAGNETIC RESONANCE IN MEDICINE, Issue 2 2003Arnon Neufeld Abstract A new MRI method with a contrast that is derived from the macromolecular composition and spin dynamics in the tissue is described and demonstrated on excised mouse brain and rat spinal cord. In the method, magnetization is selectively excited in the macromolecules by using a double quantum filter and subsequently transferred to water. The new imaging method differs from previous methods that rely on magnetization transfer contrast (MTC) in that it enables a separate and independent control of the effect of the macromolecule characteristics, chemical exchange, and water-related parameters on the images. Magn Reson Med 50:229,234, 2003. © 2003 Wiley-Liss, Inc. [source] Migration of human and mouse primordial germ cells and colonization of the developing ovary: An ultrastructural and cytochemical study ,MICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2006Jaime Pereda Abstract This review is an account of the origin and migratory events of primordial germ cells until their settlement in the gonad before sexual differentiation in the human as well as mice. In this context, the morphodynamic characteristics of the migration of the primordial germ cells, the macromolecular characteristics of the extracellular matrix of the migratory pathway, and the factors involved in the germ cell guidance have been analyzed and discussed in the light of recent advances in this field, by means of immunocytochemical procedures. The events prior to gonadal morphogenesis and the origin of the somatic cell content of the human gonadal primordium have been also analyzed. In particular, evidences are presented showing that cells derived from the coelomic epithelium and mesenchyme are at the origin of the somatic components of the gonadal primordium, and that a mesonephric cell contribution to the generation of somatic cell components of the genital ridge in humans should be discarded due to the morphological stability of the different nephric structures during the period preceding the sexual differentiation of the gonad. Microsc. Res. Tech., 2006. © 2006 Wiley-Liss, Inc. [source] QSPR Analysis of Copolymers by Recursive Neural Networks: Prediction of the Glass Transition Temperature of (Meth)acrylic Random CopolymersMOLECULAR INFORMATICS, Issue 8-9 2010Carlo Giuseppe Bertinetto Abstract The glass transition temperature (Tg) of acrylic and methacrylic random copolymers was investigated by means of Quantitative Structure-Property Relationship (QSPR) methodology based on Recursive Neural Networks (RNN). This method can directly take molecular structures as input, in the form of labelled trees, without needing predefined descriptors. It was applied to three data sets containing up to 615 polymers (340 homopolymers and 275,copolymers). The adopted representation was able to account for the structure of the repeating unit as well as average macromolecular characteristics, such as stereoregularity and molar composition. The best result, obtained on a data set focused on copolymers, showed a Mean Average Residual (MAR) of 4.9,K, a standard error of prediction (S) of 6.1,K and a squared correlation coefficient (R2) of 0.98 for the test set, with an optimal rate with respect to the training error. Through the treatment of homopolymers and copolymers both as separated and merged data sets, we also showed that the proposed approach is particularly suited for generalizing prediction of polymer properties to various types of chemical structures in a uniform setting. [source] | ||||||||||