Substitutional modulation

Different kinds of modulations can be considered the displacive modulation is related to the shift of the atom position from the average structure the occupational (or substitutional) modulation is related to the changes of the atomic occupation probability depending on the position. Generally, in alloys, displacive modulation is small but not negligible (Yamamoto 1996) whereas substitutional modulation often occurs. 

Bifunctional adamantyl, as a hydrophobic central core, can be used to construct peptidic scaffolding [151], as shown in Fig. 27. This is the reason why adamantane is considered one of the best MBBs. This may be considered an effective and practical strategy to substitute different amino acids or DNA segments on the adamantane core (Fig. 28). In other words, one may exploit nucleic acid (DNA or RNA) sequences as linkers and DNA hybridization (DNA probe) to attach to these modules with an adamantane core. Thus a DNA-adamantane-amino acid nanostructure may be produced. 

The consistency of the effects noted above and in Chap. 5 which modulate reproduction and involve the operation of the AOS, are unlikely to be wholly artifacts of captivity. Nevertheless, it needs to be shown which of the influences on male and female fertility have relevance to natural populations (Fig. 7.12). As mentioned, very few experiments on free-living social mammals have been reported, since the logistical problems of stimulus manipulation and control are formidable. A semi-feral population is an acceptable substitute, and provides some means of testing assumptions on the relevance of findings on caged laboratory-bred rodents. 

Liu, H. Liu, J. van Breemen, R. B. Thatcher, G. R. Bolton, J. L. Bioactivation of the selective estrogen receptor modulator desmethylated arzoxifene to quinoids 4 -fhioro substitution prevents quinoid formation. Chem. Res. Toxicol. 2005, 18, 162-173. 

When both the donor and the acceptor modules are bidentate, infinite chain (ID polymers) are formed. The simplest case is when the axes of the donor and acceptor sites are parallel and coaxial so that linear polymers are formed. This is the case in the homopolymers formed by bidentate and self-complementary tectons (e.g. 4-iodopyridine [157], 4-iodobenzonitrile [71, 72], halocyanoacetylenes [70]) and in the co-polymers formed when dihalo-carbons interact with dinitrogen, or dioxygen, substituted hydrocarbons (e.g. the systems formed when 1,4-DITFB, or 1,4-DIB, interact with 4,4/-BPY [50], when 1,4-dinitrobenzene interacts with 1,4-DIB [ 158-162]J, and when 1,4-DITFB interacts with DABCO [163]) (Fig. 7). 

Our studies showed that i) substitution of an exocyclic amino group of dG is effective in modulating the chemical properties of dG toward one-electron oxidation, and ii) decomposition of the guanine radical cation was effectively suppressed near dphG. These results indicate that dphG is a prototype of nucleosides functioning as an intrinsic antioxidant of duplex DNA toward one-electron oxidation. 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

Table 1 Modulation of the pKa and P-gp ratios of ORL1 antagonists through fluorine substitution ... 

The incorporation of fluorine into a molecule has been widely used to alter the pharmacokinetic properties and overall drug-like properties of compounds. This includes affecting the metabolism, oral absorption, and brain penetration of these molecules [18]. Metabolism can be affected by addition of fluorine directly at or adjacent to the site of metabolism. In addition, substitution with fluorine can increase the lipophilicity of compounds which has been shown to dramatically affect both oral absorption and brain penetration. Finally, the electron-withdrawing characteristic of fluorine has been exploited to lower the P-gp liability of compounds and modulate the pKa of adjacent groups which resulted in increased brain exposure. In the following section, representative examples will highlight the powerful nature of fluorine to modulate overall drug-like properties. 

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