Chemical space derived from structural

Clearly, the next step is the handling of a molecule as a real object with a spatial extension in 3D space. Quite often this is also a mandatory step, because in most cases the 3D structure of a molecule is closely related to a large variety of physical, chemical, and biological properties. In addition, the fundamental importance of an unambiguous definition of stereochemistry becomes obvious, if the 3D structure of a molecule needs to be derived from its chemical graph. The moleofles of stereoisomeric compounds differ in their spatial features and often exhibit quite different properties. Therefore, stereochemical information should always be taken into ac-count if chiral atom centers are present in a chemical structure. 

The first step to making the theory more closely mimic the experiment is to consider not just one structure for a given chemical formula, but all possible structures. That is, we fully characterize the potential energy surface (PES) for a given chemical formula (this requires invocation of the Born-Oppenheimer approximation, as discussed in more detail in Chapters 4 and 15). The PES is a hypersurface defined by the potential energy of a collection of atoms over all possible atomic arrangements the PES has 3N — 6 coordinate dimensions, where N is the number of atoms >3. This dimensionality derives from the three-dimensional nature of Cartesian space. Thus each structure, which is a point on the PES, can be defined by a vector X where... 

Good consistency of the parameters derived from various experimental data is observed for rigid materials with regular pore geometry and sharp boundary between solid surface and pore space. The contrast between empty pores and silica is large both for X-rays and positrons. However, in the case of chemically modified silica this interface boundary is characterized by the presence of transition layer for which the structure and density is not satisfactory established. Thus, pore dimensions determined by using different techniques exhibit some discrepancy. 

Nowadays nanocomposites are used in a broad variety of technical and scientific fields since they possess useful mechanical and chemical properties. Nanocomposite systems can be derived from different materials. Among these, clays are widely applied because their layered structure with high active surface area and cation exchange capacity has advantages for nanocomposite production. A possible way to improve and accelerate the incorporation of polymers (surfactants) into clay layers is the application of high-intensity ultrasonic treatment on to the suspension of a clay mineral in the presence of polymer (surfactants) molecules. Sonication promotes a drastic decrease of the incorporation time increasing the interlamellar space of clay minerals. 

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