Chemical determination topology

Quantitative structure-activity relationship (QSAR) dates back to the nineteenth century and is a computer-based tool that attempts to correlate variations in structural or molecular properties of compounds with their biological activities. These physicochemical descriptors, which include parameters to account for hydrophobicity, topology, electronic properties, and steric effects, are determined empirically or, more recently, by computational methods. The premise is that the structure of a chemical determines the physiochemical properties and reactivities that underlie its biological and toxicological properties. Being able to predict potential adverse effects not only aids in the designed development of new chemicals but also reduces the need for animal testing. It may ultimately or potentially lead to better... 

An attempt has been made to use the quantitative structure-property relationship (QSPR) method to correlate and predict the melting points of organic salts based on the quaternary ammonium cation [5], Moderate correlations were found for a set of 75 tetraalkylammonium bromides (see Figure 1), and for a set of 34 (n-hydroxyalkyl)trialkylammonium bromides. Descriptors used in the correlations were analyzed to determine which structural features led to lower melting points (e.g., asymmetry in the ions - see below). However, this technique cannot, as yet, extend to the prediction of melting points for salts that are either chemically or topologically dissimilar to those used in defining the QSPR. 

Further analysis of the computed energy parameters either requires some special symmetry such as that found in octahedral BeHe or icosahedral Bi2Hi2 or some further assumptions concerning the chemical bonding topology for less symmetrical systems in order to minimize the number of independent unknowns to be determined. In the cases of BeHe ... 

A substructure search algorithm is usually the first step in the implementation of other important topological procedures for the analysis of chemical structures such as identification of equivalent atoms, determination of maximal common substructure, ring detection, calculation of topological indices, etc. 

The chemical nature of the packing has the largest influence on the retention of molecules and a big impact on the efficiency of the separation itself. The chemical and physical properties of the sorbent are determined by the choice of the comonomers for the copolymerization. The type of the copolymerization process employed by the synthetic chemist introduces the macroporous structure into the sorbent and determines the surface topology (accessibility, resolution) and the surface chemistry of the packing (4). 

The chemical bonding and the possible existence of non-nuclear maxima (NNM) in the EDDs of simple metals has recently been much debated [13,27-31]. The question of NNM in simple metals is a diverse topic, and the research on the topic has basically addressed three issues. First, what are the topological features of simple metals This question is interesting from a purely mathematical point of view because the number and types of critical points in the EDD have to satisfy the constraints of the crystal symmetry [32], In the case of the hexagonal-close-packed (hep) structure, a critical point network has not yet been theoretically established [28]. The second topic of interest is that if NNM exist in metals what do they mean, and are they important for the physical properties of the material The third and most heavily debated issue is about numerical methods used in the experimental determination of EDDs from Bragg X-ray diffraction data. It is in this respect that the presence of NNM in metals has been intimately tied to the reliability of MEM densities. 

Chen, J. G., Liu-Chen, S., and Rudnick, G. (1998) Determination of external loop topology in the serotonin transporter by site-directed chemical labeling [In Process Citation], J. Biol. Chem. 273,12675-12681. 

Using the more advanced quantum chemical computational methods it is now possible to determine the fundamental electronic properties of zeolite structural units. The quantum chemical basis of Loewenstein s "aluminum avoidance" rule is explored, and the topological features of energy expectation value functionals within an abstract "nuclear charge space" model yield quick estimates for energy relations for zeolite structural units. 

Coarse-grained polymer models neglect the chemical detail of a specific polymer chain and include only excluded volume and topology (chain connectivity) as the properties determining universal behavior of polymers. They can be formulated for the continuum (off-lattice) as well as for a lattice. For all coarse-grained models, the repeat unit or monomer unit represents a section of a chemically realistic chain. MD techniques are employed to study dynamics with off-lattice models, whereas MC techniques are used for the lattice models and for efficient equilibration of the continuum models.36 2 A tutorial on coarse-grained modeling can be found in this book series.43... 

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