DYNAMICS OF TIN NUCLEI IN ALKYLTIN(IV) DEOXYRIBONUCLEIC-ACID CONDENSATES BY VARIABLE-TEMPERATURE SN-119 MOSSBAUER-SPECTROSCOPY

The dynamics of tin nuclei in the condensates SnR(2)(DNA monomer)(2) and SnR(3)(DNA monomer) (R = Me or Et). freeze-dried, has been investigated by variable-temperature Sn-119 Mossbauer spectroscopy. Linear functions In(A(t)/A(77.3))(T), in f(a)(ref,abs)(T) and [x(2)](T) (A(t) = total area under the resonant peaks, f(a) the relative and the absolute estimates of Lamb-Mossbauer factors, and [x(2)] the mean-square displacements of the Mossbauer nucleus extracted from f(a)(rel) and f(a)(abs) respectively) have been found at T greater than or equal to 77.3 K, which indicate harmonic motions and the lack of phase transitions. The latter is also suggested by the temperature-invariant hyperfine parameters, isomer shift, nuclear quadrupole splitting (Delta E) and peak widths. From the slopes of the functions in A(t)(T) and In f(a)(rel) (T), the dynamics of tin in alkyltin(IV)-DNA condensates is found to be analogous to that in organotin(IV) salts and complexes. on the assumption of effective vibrating masses, corresponding to molecular groups. The coincidence between f(a)(rel,abs), as well as the related [x(2)], data, indicates that the negative charge on the DNA backbone phosphodiester groups is fully neutralized by alkyltin(IV) cations in SnR(2)(DNA monomer)(2) (R = Me or Et) as well as in SnEt(3)(DNA monomer), while only partially in SnMe(3)(DNA monomer) and in SnMe(2)(DNA monomer)(2) obtained by standard procedures for DNA condensation. From the magnitude of the functions, as well as of the Debye temperatures, on fingerprint criteria. Sn(IV)R(2) moieties are assumed to bridge phosphodiester groups in toroidal condensates through interstrand bonding. while Sn(IV)R(3) would be appended to the double helix. Motions would involve SnR(2)(mononucleotide)(2) and SnR(3)(mononucleotide) units as the effective vibrating masses. Two tin co-ordination sites occur for Sn(IV)R(2) moieties at the DNA surface, both trans-octahedral, and a single trigonal-bipyramidal site for Sn(IV)R(3), the organometal moieties being co-ordinated by phosphodiester and water oxygen atoms. according to Delta E rationalization by point-charge model structure simulations, as well as to Mossbauer-Zeeman spectra of the Sn(IV)Et(2)- and Sn(IV)Et(3)-DNA condensates.