A 119Sn Mössbauer spectroscopic study on the interaction of dimethyltin (IV) derivatives with rat hemoglobin, and of related model systems in aqueous solution

Intramolecular Chalcogen−Tin Interactions in (o-MeE-C6H4)CH2SnPh3-nCln (E = S, O; n = 0, 1, 2), Characterized by X-ray Diffraction and 119Sn Solution and Solid-State NMR

Organotin(IV) compounds of the type (o-MeE-C6H4)CH2SnPh3-nCln were synthesized, E = O, n = 0 (1), n = 1 (2), n = 2 (3) and E = S, n = 0 (4), n = 1 (5), n = 2 (6). The complexes exhibit significant trigonal bipyramidal pentacoordination at tin as a consequence of intramolecular Sn-O (1-3) and Sn-S (4-6) interactions upon substitution of the phenyl groups by chloro groups. The intramolecular Sn-O distances in 1, 2, and 3 are 83%, 75%, and 79% of the sum of the van der Waals radii. The equivalent Sn-S values for 4, 5, and 6 are 90%, 73%, and 71%, respectively. The geometry of compound 3 is complicated by intermolecular dimerization via bridging chlorines creating a distorted octahedral geometry at tin. The related dichloro sulfur compound 6 also exhibits an intermolecular association in the form of Sn-Cl-H hydrogen bonding leading to a polymeric structure in the solid state. CPMAS 119Sn NMR spectroscopy suggests that the intramolecular Sn-E interactions persist in solution and also facilitated the discovery of a new crystalline form of 4, 4', that contains a Sn-S distance which is 95% the sum of the van der Waals radii.

Effect of the fungicides tributyltin acetate and tributyltin chloride on multilamellar liposomes: fluorescence studies

The influence of tri-n-butyltin acetate (TBTA) and tri-n-butyltin chloride (TBTC) on the physico-chemical state of charged and neutral phospholipids was investigated using multilamellar liposomes. The thermal dependence of steady state fluorescence polarization of DPH and its charged derivative TMA-DPH was recorded. The two fungicides lowered DPPC phase transition temperature and broadened the temperature range of the transition in different ways. The effects were concentration-dependent. The results show that TBTC interacts more effectively with DPPC model membranes rather than TBTA. Moreover, TBTC broadens and shifts the main phase transition (Tm) more effectively in DPPC rather than in DMPC liposomes. Below Tm, TBTC decreases fluorescence polarization (P) in all phospholipids used. Above Tm P is almost constant in phospholipids with saturated acyl chains, except for DMPG. In fact, an increase of P is detectable in this lipid as in PLs with unsaturated acyl chains. It is suggested that the effects of TBT on liposomal membranes are dependent on the anion moiety and phospholipids characteristics.

The antitumor activity and the structure of bis(adeninato-N9) diphenyltin(IV)

Bis(adeninato-N9)diphenyltin(IV) has been selected as a tumor panel compound by the U.S. National Cancer Institute and tested against a number of tumors according to standard protocols. The activity criteria were not passed. The solid state structure of the environment of tin in the complex has been definitely established to be of the tetrahedral type by means of 119Sn Mössbauer-Zeeman spectroscopy; this configuration has been assumed to be maintained also in aqueous suspensions of the drug, in conditions corresponding to the administration to mice. The occurrence of strong Sn-N bonds, consistently resistant to hydrolytic processes, has been assumed, and correlated to the observed low toxicity of the drug. The extent of the antitumor action corresponds to the standard response to Ph2SnIV moieties.

The interaction of native DNA with dimethyltin(IV) species

The reaction of aqueous native DNA (calf thymus) with the solvated organotin(IV) species [(CH3)2SnCl2(C2H5OH)n], as well as with [(CH3)2Sn(OH)(H2O)n]+ and (CH3)2Sn(OH)2 (i.e., the hydrolysis products of aqueous (CH3)2SnCl2 at pH approximately 5 and pH approximately 7.4 respectively), was investigated by 119Sn Mössbauer spectroscopy. The addition of [(CH3)2SnCl2(C2H5OH)n] to DNA yielded a solid product, possibly (CH3)2Sn(DNA phosphodiester)2, where the environment of the tin atom is trans-octahedral with linear CSnC skeleton, and the equatorial atoms may consist of oxygen or nitrogen from water as well as from the nucleic acid constituents. No interaction with DNA apparently takes place due to hydrolyzed dimethyltin(IV) species, which occur in aqueous phases at approximate physiological pH values. The reaction pathway is then assumed to require weakly solvated, easily dissociable species such as [(CH3)2SnCl2(C2H5OH)n], which would imply in vivo reactivity of cellular DNA with organotins from hydrophobic sites.