CHAPTER 12 • 119Sn Mossbauer Spectroscopy Studies: Organotin(lVj Salts and Complexes
235
model treatment of I1E parameters. The molecular dynamics parameters (e.g. the
slopes ofln(AT/ A77.3) vs. Treported in Table 12.3, NO.7 and 10) indicate the occurrence
of polymeric species in freeze-dried specimens analogous to the R2Sn(IV) crystalline
complexes of Alk2Sn(IV) with AMP and [P03(OPh)], No. 1-5, Table 12.3; consequently,
the occurrence of structure in Fig. 12.1b with trans-phospho diester groups could be
assumed, so that polymericity would originate from interstrand bonding in the
condensed, toroidal, DNA (vide supra). Slope of the function In(AT/ A77.3) vs. T for
gelled Et2Sn(DNA monomerh, NO.9 in Table 12.3, is instead in the border zone monomer/polymer for Alk2Sn(IV) derivatives, so that presence of H20 would influence
bonding to DNA: a structure like in Fig. 12.1b with cis-phosphodiester groups could
be assumed to occur, so that the Et2Sn(IV) moiety would be linked to two vicinal
phospho diester of a double helix of DNA. This behavior makes a consistent difference
with that of systems MeSn(IV)-DNA (vide supra), where the persistence also in gelled
phases of the assumed polymericity could be now attributed to the possible employment in bonding of a larger positive charge on MeSn(IV) with respect to Et 2 Sn(IV).
As far as systems Alk3Sn(IV)-DNA are concerned (Alk = Me, Et), hyperfine parameters in gelled condensates and frozen aqueous solutions, No. 9-13 in Table 12.2, are
invariant in freeze-dried specimens, which implies the persistence of a trigonal
bipyramidal structure such as in Fig. 12.1C, as extracted from point -charge model treatment of the nuclear quadrupole splitting LlE. From molecular dynamics studies, No.8
and 12 in Table 12.3, it appears that slopes dln(AT/ A77.3) / dT lie in the border zone between Alk3Sn(IV) monomers and polymers. As a consequence, structure in Fig. 12.1C
would indicate the occurrence of Alk3Sn(IV) moieties appended to the DNA double
helix in lyophilized specimens, showing the 1 : 1 composition Alk 3 Sn(DNA monomer).
In gelled systems Et3Sn(IV)-DNA, such as No. 11 in Table 12.3, slope increases, being
located in the monomers zone: then the presence of H 2 0 would provoke a further decrease in the interchain interactions by Alk 3 Sn(IV) bound to one phospho diester group,
the latter being perhaps due to interchain hydrogen bonds by the axial H 2 0 molecule
(Fig. 12.1C) (Barbieri et al. 1992, 1995; Posante 1996).
12.6
Interaction of Organotin(lV) Complexes with Deoxyribonucleic Acid,
and Ternary Systems RnSn(lV)-Amino Acid-Nucleic Acid
The field of bonding of metal ion complexes to nucleic acids is very widely investigated, as inferred from recent reviews (Yamauchi et al. 1996; Dubler 1996; Clarke and
Stubbs 1996; Kozelka 1996; Kimura and Shionoya 1996; Norden et al. 1996; Draganescu
and Tullius 1996; Sigman et a1.1996; Gravert and Griffin 1996; Burrows and Rokita 1996;
Petering et al. 1996); studies on the argument are continuing (Cusumano et al. 1998;
Navarro et al. 1998; Mandai et a1.1997; Wu et a1.1997; Tuite et a1.1997; Jacquet et a1.1997;
Bauer and Wang 1997; Jin and Yang 1997; Magda et al. 1997; Lippert 1997; Yam et a1.1997;
Kieft and Tinoco 1997; Cheatham and Kollman 1997). Cleavage of DNA by interaction
with Fe(III)-bleomycin and 57Fe Mossbauer irradiation (MIRAGE) has been investigated in relation to tumor therapy (Mac Donnell 1995).
In this context, a study on the interaction of the complex Et 2 SnCIi o-phenanthroline)
with mononucleotides and DNA appears to be the only one insofar effected in the field
235
model treatment of I1E parameters. The molecular dynamics parameters (e.g. the
slopes ofln(AT/ A77.3) vs. Treported in Table 12.3, NO.7 and 10) indicate the occurrence
of polymeric species in freeze-dried specimens analogous to the R2Sn(IV) crystalline
complexes of Alk2Sn(IV) with AMP and [P03(OPh)], No. 1-5, Table 12.3; consequently,
the occurrence of structure in Fig. 12.1b with trans-phospho diester groups could be
assumed, so that polymericity would originate from interstrand bonding in the
condensed, toroidal, DNA (vide supra). Slope of the function In(AT/ A77.3) vs. T for
gelled Et2Sn(DNA monomerh, NO.9 in Table 12.3, is instead in the border zone monomer/polymer for Alk2Sn(IV) derivatives, so that presence of H20 would influence
bonding to DNA: a structure like in Fig. 12.1b with cis-phosphodiester groups could
be assumed to occur, so that the Et2Sn(IV) moiety would be linked to two vicinal
phospho diester of a double helix of DNA. This behavior makes a consistent difference
with that of systems MeSn(IV)-DNA (vide supra), where the persistence also in gelled
phases of the assumed polymericity could be now attributed to the possible employment in bonding of a larger positive charge on MeSn(IV) with respect to Et 2 Sn(IV).
As far as systems Alk3Sn(IV)-DNA are concerned (Alk = Me, Et), hyperfine parameters in gelled condensates and frozen aqueous solutions, No. 9-13 in Table 12.2, are
invariant in freeze-dried specimens, which implies the persistence of a trigonal
bipyramidal structure such as in Fig. 12.1C, as extracted from point -charge model treatment of the nuclear quadrupole splitting LlE. From molecular dynamics studies, No.8
and 12 in Table 12.3, it appears that slopes dln(AT/ A77.3) / dT lie in the border zone between Alk3Sn(IV) monomers and polymers. As a consequence, structure in Fig. 12.1C
would indicate the occurrence of Alk3Sn(IV) moieties appended to the DNA double
helix in lyophilized specimens, showing the 1 : 1 composition Alk 3 Sn(DNA monomer).
In gelled systems Et3Sn(IV)-DNA, such as No. 11 in Table 12.3, slope increases, being
located in the monomers zone: then the presence of H 2 0 would provoke a further decrease in the interchain interactions by Alk 3 Sn(IV) bound to one phospho diester group,
the latter being perhaps due to interchain hydrogen bonds by the axial H 2 0 molecule
(Fig. 12.1C) (Barbieri et al. 1992, 1995; Posante 1996).
12.6
Interaction of Organotin(lV) Complexes with Deoxyribonucleic Acid,
and Ternary Systems RnSn(lV)-Amino Acid-Nucleic Acid
The field of bonding of metal ion complexes to nucleic acids is very widely investigated, as inferred from recent reviews (Yamauchi et al. 1996; Dubler 1996; Clarke and
Stubbs 1996; Kozelka 1996; Kimura and Shionoya 1996; Norden et al. 1996; Draganescu
and Tullius 1996; Sigman et a1.1996; Gravert and Griffin 1996; Burrows and Rokita 1996;
Petering et al. 1996); studies on the argument are continuing (Cusumano et al. 1998;
Navarro et al. 1998; Mandai et a1.1997; Wu et a1.1997; Tuite et a1.1997; Jacquet et a1.1997;
Bauer and Wang 1997; Jin and Yang 1997; Magda et al. 1997; Lippert 1997; Yam et a1.1997;
Kieft and Tinoco 1997; Cheatham and Kollman 1997). Cleavage of DNA by interaction
with Fe(III)-bleomycin and 57Fe Mossbauer irradiation (MIRAGE) has been investigated in relation to tumor therapy (Mac Donnell 1995).
In this context, a study on the interaction of the complex Et 2 SnCIi o-phenanthroline)
with mononucleotides and DNA appears to be the only one insofar effected in the field