PDEs structural information

For quite some time now it has likewise been recognized that these key enzymes also present an important opportunity for pharmacological intervention, and efforts in this area have begun to pay off. There is now a considerable body of information available on a multitude of PDE inhibitors. The purpose of this chapter is to take a unifying view of this complex field and try to extract the now apparent general structural features useful in PDE inhibitor design [2],... 

Above r, PDMS is in the amorphous state, and there are no indications in the literature concerning the possible appearance of a mesophase in it. The first information on phase transitions in polydiethylsiloxane (PDES) and polydipropylsiloxane (PDFS) was published in [17], in which low-temperature solid-phase transitions were detected in these polymCTS, but the existence of a mesophase was not found. A mesophase which appears after melting (>270°K) and persists up to =3(X)°K was found in a more detailed study of PDES [18] above 300 K, the sample turned into an amorphous melt. Beatty et al. called the observed mesophase a viscocrystalline state and attempted to characterize it by several physical methods (calorimetry, NMR, dielectric relaxation, optical observations). However, neither the structure nor the physical properties of this mesomorphic state have been studied completely enough. The mesomorphic state in PDFS was first detected and studied in our research [19, 20]. There is no information on the following representatives of linear polysiloxanes in the literature at present. 

In addition to the use of H, C, and N NMR chemical shifts, it has been shown that observation of solid-state chemical shifts and quadrupolar couplings adds important information on the higher-ordered and hydrogen-bonded structures of polypeptides and peptides in the solid state [62-65], Solid-state NMR has been shown to be useful, moreover, for determining the local structures of alkali silicates [66-70]. Therefore, it is expected that solid-state NMR may reveal further dimensions of the structural and dynamic behavior of PDES in the crystalline, biphasic, and isotropic phases, in addition to the H, C, and Si NMR results reported previously. Due to the low natural abundance of nuclei (0.037%), the NMR analysis requires labeling. The structure and dynamics of 0-enriched... 

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