Donor-bases lead structures

Substitution of aqua ligands by nitrogen donors such as the nucleic acid bases leads to mono- and disubstituted complexes whose properties, of course, have been extensively studied (Chapter 4). Once inside the cell, however, only a small proportion of the platinum is complexed to the DNA. Metabolism of the platinum complexes therefore takes place with other biomolecules besides DNA. Amino acid reactions may take place which may sequester the complex. Further, in the case of substitution by nucleophiles with strong tram influence, especially those of sulfur, displacement of amine and deactivation may occur. Interestingly, amine labilization tram to a thioether in d5-[Pt(NH3)2(Me2S)2] has been observed [107]. In vivo, thioethers such as methionine could effect the same chemistry and the characterization of [Pt(methionine)2], assigned the structure as shown, as a metabolite of cisplatin [108] confirms this view ... 

Substituent effects on the are remarkable. Electron-withdrawing groups at the 5 -position, e.g., 5 -nitro-substitution (indoline component), and donor substituent at the 8-position (benzothiopyran component) in 44 leads to a longer wavelength shift. As the polarity of the solvent increases, the max of the colored form of spiroindolinobenzothiopyran results in hypsochromic shift. This can be interpreted as the existence of a polar structural component of the colored form in the ground state. Kinetic study has suggested that the zwitterionic structure largely contributes to the colored form of 6-nitrospiroindolinobenzothiopyran, as well as spiropy-rans.97 Based on H-NMR and X-ray analysis,98 99 the existence of an... 

Figure 5.38 displays the optimized structure and primary npt— ooh donor-acceptor interaction of the complex (5.70a) in which PtH2 serves as the Lewis-base donor. The qualitative similarity to the water dimer structure (Fig. 5.5(b)) is immediately apparent, including the short Pt H distance (2.47 A, more than 0.5 A inside van der Waals contact), the roughly linear Pt H—O angle (161°), and the characteristic elongation of the H-bonded versus free O—H bond of the water monomer (by 0.01 A). The leading nPt a0H donor-acceptor interaction in Fig. 5.38(b) is... 

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