Synthetic small molecule, typical

Following the development of the technique and with the availability of commercial equipment, one of the first published real applications of HPLC-NMR was concerned with the identification of an impurity in a synthetic drug precursor [28], In this case, a 400 MHz HPLC-NMR system was tested with a small molecule typical of pharmaceuticals ... 

TABLE 2 Information Contained in a Typical Specification for a Synthetic Small Molecule... 

The chain nature of linear polymers not only causes special problems in crystallography but also permits structures which, as a rule, cannot exist in crystals of small molecules. Typical of these is a helical chain, which has been observed for a number of proteins and synthetic polymers. As the helix may also be prominent in some a-D-linked polysaccharides, and as its structure presents certain unique manifestations in x-ray diagrams, it will be briefly discussed. 

The idea of using membranes to filter molecules on the basis of size is not without precedent. Dialysis is used routinely to separate low molecular weight species from macromolecules [105]. In addition, nanofiltration membranes are known for certain small molecule separations (such as water purification), but such membranes typically combine both size and chemical transport selectivity and are particularly designed for the separation involved. Hence, in spite of the importance of the concept, synthetic membranes that contain a collection of monodisperse, molecule-sized pores that can be used as molecular filters to separate small molecules on the basis of size are currently not available. 

A by-product of the solvophobic collapse of the mPE backbone is the formation of a hydrophobic cavity. Similar cavities have been explored for use as hosts in molecular recognition however, these cavities are typically quite rigid and synthetically difficult to access [4, 6]. The formation of a hydrophobic cavity through supramolecular folding of the mPE backbone offers a modular platform for the study of small molecule binding with supramolecular hosts. 

A simple approach to understanding the factors which control the "conductivity of proteins towards electron tunneling is to develop "small molecule model systems to mimic intramolecular electron transfer in the protein systems. Appropriate models obviously require that the donor and acceptor be held at fixed distances and orientations which correspond to those in the protein-protein complexes. Models of this type have recently been obtained and investigated [103,104]. In these models the protein matrix is replaced by a simple synthetic spacer which separates two porphyrin molecules. By changing the chemical structure of the spacer, a series of molecules with different reaction distances and geometries has been synthesized. Typical examples of such molecules are presented in Fig. 21. 

The synthetic analogue or model approach (114) can provide insights into complex biomolecules through the design, synthesis, and study of small molecules that mimic a component, typically an active site or prosthetic group, of the biomolecule. The approach is particularly valid for metal active sites that have not been unambiguously characterized by other methods or where key chemical or spectroscopic information is required for the interpretation of the properties of the biomolecule. 

In many cases, the number of species occurring simultaneously in a synthetic polymer is so large, that it is not possible to separate them from one another. Hence the chromatogram obtained for a polymer by SEC seldom resembles the typical high efficiency separations obtained for small molecules by interactive chromatography (reversed-phase, etc.). However, the chromatogram of detector response versus retention volume, is a measure of the molecular size distribution, which can provide a vast amount of information on the polymer (Figure 9.5). 

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