Basic properties stereochemistry

Thus, it is quite difficult to derive a relationship between substitution stereochemistry and any physical property of the leaving group (basicity, electronegativity, or polarizability). This failure prompted us to consider an empirical relationship between the observed stereochemistry (inversion or retention) and the ability of the leaving group to be displaced (23. 33). 

Another important feature of InChl is its layered structure. Unlike in SMILES, where all data related to one atom are stored in one place, in InChl different properties of the structure are encoded in different parts of the identifier. This organization of the data has one very important advantage molecules with the same basic structure that differ only in some minor property, such as in stereochemistry or isotopic composition, have the same InChl, with only the exception of the corresponding layer. This makes it possible not only to compare two InChls to find if they represent exactly the same structure, but to use a more intelligent comparison of two InChl strings to reveal molecules with the same basic structure that differ only in some detail. It is then up to the user to decide which deviations in the InChl are significant for his or her purpose and which are not. 

Many molecular parameters, such as ionization, molecular and electronic structure, size, and stereochemistry, will influence the basic interaction between a solute and a solvent. The addition of any substance to water results in altered properties for this substance and for water itself. Solutes cause a change in water properties because the hydrate envelopes that are formed around dissolved molecules are more organized and therefore more stable than the flickering clusters of free water. The properties of solutions that depend on solute and its concentration are different from those of pure water. The differences can be seen in such phenomena as the freezing point depression, boiling point elevation, and increased osmotic pressure of solutions. 

Extensive studies by NMR methods have shown that the conformations of PAH diol epoxide-N2-dG and - N6-dA adducts in double-stranded DNA depend markedly on the stereochemistry, PAH topology, and base sequence context Earlier work has been summarized by us [53]. Since then, we have published the NMR solution structures of a number of other DNA adducts [79, 88, 89, 92]. The structural properties of various DNA adducts have been reviewed more recently by Lukin and de los Santos [93]. The basic structural motifs, based on our work and that of others [94—98] that are relevant to the NER studies described in this chapter, are summarized in Figure 12.3. Computational analyses have provided insights into the origins and stereochemistry dependence of these remarkably different adduct conformations [26, 42, 47, 54, 99]. In the following, we summarize the main features of these different conformations. 

Enantiomers also are referred to as chiral compounds, antipodes, or enantiomorphs. When introduced into an asymmetric, or chiral, environment, such as the human body, enantiomers will display different physicochemical properties, producing significant differences in their pharmacokinetic and pharmacodynamic behavior. Such differences can result in adverse side effects or toxicity, because one or more of the isomers may exhibit significant differences in absorption (especially active transport), serum protein binding, and metabolism. With the latter, one isomer may be converted into a toxic substance or may influence the metabolism of another drug. To discuss further the influence of stereochemistry on drug action, some of the basic concepts of stereochemistry need to be reviewed. 

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