Structure correlation, quantitative

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

Multilinear regressions Multipredictor nonlinear correlations Quantitative property-property relationships and quantitative structure-property relationships... 

Related research has been reported by Elder and Worley (39), in which MNDO was used to examine the structure of coniferyl alcohol, and its corresponding phenolate anion and free radical. This method represents an improvement over the PPP method, in that MNDO is an all-electron technique, and performs geometry optimizations. It was found that the calculated spin densities and charge values for the reactive sites did not correlate quantitatively with observed bond frequency, but it was observed that positions with partial negative charge and positive spin densities are the positions through which the polymerization has been found to occur. 

Much of the recent progress in drug design has been based on the fundamental understanding of drug-receptor interactions and the increased availability of high quality structural data. Quantitative correlations have been made between biological activity and... 

The attempt to correlate biological activity with chemical structure in quantitative terms assumes that a functional dependence exists between the observed biological response and certain physicochemical properties of molecules. Without a mechanistic model one obtains it by an empirical correlation. A rational way to define such empirical relationships is within the extrathermo-dynamic approach (1). Although extrathermodynamic relationships... 

Dietrich SW, Bolger MB, Kollman PA, Jorgensen EC. Thyroxine analogues 23. Quantitative structure-correlation studies of in vivo and in vitro thyromimetic activities. J Med Chem 1977 20 863-80. 

Katritzky, A.R., Maran, U., Lobanov, V.S. and Karelson, M. (2000) Structurally diverse quantitative structure-property relationship correlations of technologically relevant physical properties. J. Chem. Inf. Comput. Sci., 40, 1—18. 

After this rather sobering discussion of the limitations of interpreting structural correlations in a quantitative way, one may ask whether we can learn anything at all from scatterplots. We make three points here ... 

Is it possible to combine qualitative conclusions from structure correlation with specific, quantitative information on an actual reaction, and if yes, how ... 

Kubaschewski (1972) collected and compared the enthalpies of formation of complex oxides from binary oxides. He did not offer any systematic correlation of these enthalpies with structural properties. Hoppe (1966,1970a, b, 1975) developed the MAPLE concept (Madelung part of lattice energy) as a tool to guide the structural interpretation of bonding in complex oxides and halides. It requires as input parameters the unit cell of a compound and positions of all atoms, and it treats the crystal as an ionic array of point charges. If crystal structure determinations have been properly done, MAPLE calculations for a complex compound are within 2% (sometimes larger, sometimes smaller) of the MAPLE values of the binary (parent) compounds. Therefore, purely ionic-model calculations are not suflftciently sensitive to correlate quantitatively with the relatively small enthalpies of solid-state complexation. 

The examples presented in the preceeding sections have illustrated that the present FSGO-based Cl methods are very effective in providing a qualitative or semi-quantitative resolution of the electronic spectra of large molecules. Calculations on molecules containing 200 to 500 or more electrons may be performed with reasonable demands on computer resources. The methods are widely applicable, and the results provide for a useful interplay between theory and experiment in interpreting electronic spectra and understanding spectra-structure correlations. 

The ab initio molecular dynamics technique provides a powerful method in studying the properties of chemical systems under varying thermodynamic conditions without having to employ any empirical interaction potentials. In this chapter, a brief review has been made on our recent studies on water dynamics by using this method combined with a time series analysis. We have discussed the frequency-structure correlations of water molecules in both supercritical and normal water. Our calculations reveal that hydrogen bonds still persist to some extent in the supercritical state. However, the quantitative details of hydrogen bonding depend on the density. At... 

To what extent the schematic model systems A and B for a polymer melt show this typical relaxation behavior will be addressed in this subsection, by calculating various structural correlation functions that probe the dynamical changes of the melt on different length scales (Section 6.3.2.1). From these correlation functions it is possible to extract relaxation times the temperature dependence of which can be studied and compared to that of transport coefficients, such as the diffusion coefficient. This will be done in Section 6.3.2.2. The final paragraph of this subsection then deals with the calculation of the incoherent intermediate scattering function and its quantitative interpretation in the framework of the idealized mode coupling theory (MCT). " ... 

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