Molecular-field

The little atomic magnets are of course quantum mechanical, but Weiss s original theory of paramagnetism and ferromagnetism (1907) [7] predated even the Boln atom. He assumed that in addition to the external magnetic field Bq, there was an additional internal molecular field B. proportional to the overall magnetization M of the sample. 

Continuum theory has also been applied to analyse tire dynamics of flow of nematics [77, 80, 81 and 82]. The equations provide tire time-dependent velocity, director and pressure fields. These can be detennined from equations for tire fluid acceleration (in tenns of tire total stress tensor split into reversible and viscous parts), tire rate of change of director in tenns of tire velocity gradients and tire molecular field and tire incompressibility condition [20]. 

Humphries R L, James P G and Luckhurst G R 1972 Molecular field treatment of nematic liquid crystals J. Chem. Soc. Faraday Trans. II 68 1031-44... 

Luckhurst G R, Zannoni C, Nordic P L and Segre U 1975 A molecular field theory for uniaxial nematic... 

Luckhurst G R 1985 Molecular field theories of nematics systems composed of uniaxial, biaxial or flexible molecules Nuclear Magnetic Resonance of Liquid Crystals ed J W Emsiey (Dordrecht Reidel)... 

Before the comparative molecular field analysis (CoMFA), BCUT descriptors, 4D-QSAR, and HYBOT descriptors arc discussed in more detail, some further descriptors are listed briefly. 

After an alignment of a set of molecules known to bind to the same receptor a comparative molecular field analysis CoMFA) makes it possible to determine and visuahze molecular interaction regions involved in hgand-receptor binding [51]. Further on, statistical methods such as partial least squares regression PLS) are applied to search for a correlation between CoMFA descriptors and biological activity. The CoMFA descriptors have been one of the most widely used set of descriptors. However, their apex has been reached. 

Partial Least Squares and Molecular Field Analysis... 

Cramer R D III, D E Patterson and J D Bunce 1988, Comparative Molecular Field Analysis (CoMFA). Effect of Shape on Binding of Steroids to Carrier Proteins. Journal of the American Chemical Societ 110 5959-5967. 

Poso A, R Juvonen and J Gynther 1995. Comparative Molecular Field Analysis of Compounds wii CYP2A5 Binding Affinity. Quantitative Structure-Activity Relationships 14 507-511. 

Once the molecules are aligned, a molecular field is computed on a grid of points in space around the molecule. This field must provide a description of how each molecule will tend to bind in the active site. Field descriptors typically consist of a sum of one or more spatial properties, such as steric factors, van der Waals parameters, or the electrostatic potential. The choice of grid points will also affect the quality of the final results. 

When a neutral molecule settles onto an electrode bearing a positive charge, the electrons in the molecule are attracted to the electrode surface and the nuclei are repelled (Figure 5.2), viz., the electric field in the molecule is distorted. If the electric field is sufficiently intense, this distortion in the molecular field reduces the energy barrier against an electron leaving the molecule (ionization). A process known... 

RD Cramer III, DE Patterson, JD Bunce. Comparative molecular field analysis (CoMFA). 1. Effect of shape on binding of steroids to carrier proteins. J Am Chem Soc 110 5959-5967, 1988. 

Bis(oxazohnes) figands have been so widely used for the Diels-Alder reaction between N-2-alkenoyl-l,3-oxazolidine-2-one and cyclopentadiene that Lipkowitz and Pradhan developed a QSAR (quantitative structure-activity relationship) using Comparative Molecular Field Analysis (CoMFA) for a set of 23 copper-catalysts containing mainly bis(oxazoline) figands. The generated... 

Schuffenhauer A, Gillet VJ, Willett P. Similarity searching in files of 3D chemical structures analysis of the BIOSTER database using 2D fingerprints and molecular field descriptors. J Chem Inf Comput Sci 2000 40 295-307. 

Cho SJ, Tropsha A. Cross-validated R2-Guided region selection for comparative molecular field analysis a simple method to achieve consistent results. I Med Chem 1995 38(7) 1060-6. 

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