195Pt-NMR Spectroscopy

The reactions of the [Pt(H20)4]2+ ion with various anionic ( Am ) ligands have been studied by means of 195Pt NMR spectroscopy.295 The formation of complexes of the type... 

The advantage of these complexes is that each Pt complex is isolated in pure form, and the crystal structure is known. Based on 1H-and 195Pt-NMR spectroscopy, the antitumor active compounds were found to be disrupted as shown in Fig. 20, giving finally [Pt(NH3)2(H20)2]2+, which is the same hydrolysis product as ds-DDP and is responsible for the activity. Therefore, the subsequent reaction with DNA bases and the mechanism would be the same with those of cis-DDP. The antitumor inactive compounds are relatively stable and are disrupted only to dinuclear amidate-bridged compounds. No further decomposition to [Pt(NH3)2(H20)2]2+ occurs. 

The relative amounts of all these Pt species vary as a function of the pH and the chloride concentration. Only platinum species with a coordinated water molecule are regarded to be reactive, because, in contrast to coordinated chloride or hydroxide, this ligand can be easily substituted by other donor molecules. Hydroxo species are formed as indicated in Eqs. (3)-(7) (34, 35), with [ds-Pt(NH3)2(OH)2] as the stable end product in basic solution (36). It should be noted, however, that this species very easily dimerizes and trimerizes at higher concentrations, producing ions such as [cis-Pt(NH3)2]2(jU.-OH)2 and [cis-Pt(NH3)2]3(ju,-OH)3, as has been proved with, e.g., 195Pt NMR spectroscopy (36a, b). Very recently, accurate pAa values have been presented for the (de)hy-dronation equilibria (36b) the pKa values have been added to Eqs. (5)—(7). Miller and House (36c) have accurately determined the kinetic parameters for the several hydrolysis reactions. They concluded that acid hydrolysis of cis-Pt in vivo is unlikely to proceed beyond [cis-Pt(NH3)2Cl(H20)]+. 

In the absence of X-ray crystallographic data, 31P and 195Pt NMR spectroscopy is a useful method to investigate the nature of the products in the solution. In addition to earlier references to these topics, the Pople-Santry theory has been used to calculate the signs and relative magnitudes of the coupling constants for the type of phosphorus-bridged complexes covered in this section.1502... 

A number of Pt-ssDNA adducts platinated at d(G pG ) sites have been studied utilizing H, 31P, 15N, and 195Pt-NMR spectroscopy [31][32] [38][56—58] [61—63][67—70] [87][91—97]. Both C2- and non-C2-symmetrical A2 ligands have been used, but most of the results were similar, and both... 

With 195Pt-NMR spectroscopy, the kinetics and mechanism of binding of cisplatin and its inactive trans-isomer to fragments of chicken erythrocyte DNA (ca. 40 base pairs) have been investigated by Bancroft et al (Fig. 7) [22]. Both cisplatin and transplatin bind to DNA by two successive pseu-... 

Pt NMR spectra were employed to study the nature of Pt(bipy)22+ in aqueous alkaline solutions. The data were consistent with formation of a conformationally mobile pseudo-five-coordinate complex involving OH coordination.1079 The time dependence of Pt(II) complexation with poly(amid-oamine)dendrimers was established by 195Pt NMR spectroscopy.1080 The 2H and 13C NMR spectra for solutions of cA-[L2Pt 9-MeAd(-H) ]3(N03)3 show dissociation to a mononuclear species, e.g. cA-[L2Pt 9-MeAd(-H) ]+, where L... 

H-NMR spectroscopy is particularly useful for studying DNA because of the well-resolved base and H(l ) regions of the spectrum. Additional information can be gathered from studies with nuclei such as 31P, 13C, 15N, and 195Pt. Because DNA is conformationally fluxional, often the isolated crystallized form is A-form DNA, whereas a variety of physical methods show that DNA is normally B-form in aqueous solution. Thus, solution studies are particularly important for DNA. 

In phosphine complexes, the v MP modes (around 400 cm-1)36,64,20s are often obscured by aryl-group vibrations. Main efforts for the determination of stereochemistry are concentrated on 31P nmr spectroscopy, especially in the case of platinum(II) and platinum(IV) complexes36,371 (195Pt nucleus ... 

PtC=C and Pi C=C-C 13C chemical shifts were reported for (92) and related complexes.428 A typical 195Pt resonance was observed (—2180 ppm) for (93).429 A detailed analysis of and 13C resonances (from 2-D COSY and 13C, HMQC experiments) has been made for (94) and related systems.430 and 31P 1H NMR spectra for cz s-[PtCl L-K3C,P,P ], where L = sterically constrained diphosphonite ligands, gave characteristic Pt-P coupling constants.431 31P NMR spectroscopy was used to differentiate the isomers (95) and (96).432... 

Platinum ammine complexes have been a fertile area for studying transinfluence. Table 3.21 lists data for a range of ammines showing how /(195Pt-15N) depends upon the trans-atom [153]. (A further selection of data can be found in R.V. Parish, NMR, NQR, EPR and Mossbauer Spectroscopy in Inorganic Chemistry, Ellis-Horwood, Chichester, 1991, pp. 76, 87.) Possibly the most detailed study (of complexes of tribenzylphosphine) examined over a hundred neutral and cationic complexes [154] (Table 3.22). 

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