Part A: Coordination of pyridine and pyridine-type ligands to cobalt(II)- and cobalt(III)-substituted Keggin and Dawson-type heteropolyanions. Part B: Encapsulation of various heteropolyanions in artificial phospholipid vesicles: Effects of size, charge,

Cobalt derivatives of the lacunary heteropolytungstates ({dollar}alphasb1{dollar}-{dollar}rm Psb2Wsb{lcub}17{rcub}Osb{lcub}61{rcub}rbracksp{lcub}10-{rcub}{dollar} (I), ({dollar}alphasb2{dollar}-{dollar}rm Psb2Wsb{lcub}17{rcub}Osb{lcub}61{rcub}rbracksp{lcub}10-{rcub}{dollar} (II), ({dollar}alpha{dollar}-{dollar}rm SiWsb{lcub}11{rcub}Osb{lcub}39{rcub}rbracksp{lcub}8-{rcub}{dollar} (III), and ({dollar}alpha{dollar}-{dollar}rm PWsb{lcub}11{rcub}Osb{lcub}39{rcub}rbracksp{lcub}7-{rcub}{dollar} (IV), have been examined as possible precursors to surface-modified heteropolyanions stable at biological pH. Addition of excess pyridine to solutions of the Co(II) derivatives yields NMR signals for free and complexed pyridine from which the rates of ligand exchange can be determined. At 24{dollar}spcirc{dollar}C, these range from 9.2 s{dollar}sp{lcub}-1{rcub}{dollar} (III) to {dollar}rm1.6times10sp2 ssp{lcub}-1{rcub}{dollar} (IV).; Chemical or electrochemical oxidation of the aquacobalt(II) derivatives generates the corresponding Co(III) species which also undergo substitution by pyridine. The rates for this process at 30{dollar}spcirc{dollar}C are {dollar}rm3.0times10sp{lcub}-2{rcub} ssp{lcub}-1{rcub}{dollar} (I), {dollar}rm3.7times10sp{lcub}-4{rcub} ssp{lcub}-1{rcub}{dollar} (II), and {dollar}rm4.7times10sp{lcub}-4{rcub} ssp{lcub}-1{rcub}{dollar} (III). Complexes of the Co(III) derivative of (I) with pyridine, pyrazine, 4,4-bipyridyl (both 1:1 and 1:2 species), isonicotinic acid, and isonicotinoylglycylglycylethylester were isolated as cesium or guanidinium salts, and characterized by NMR, UV-vis and electrochemistry.; A procedure for the encapsulation of heteropolyanions in artificial phospholipid vesicles was developed. Vesicles with encapsulated heteropolyanions were found to be some 10-fold larger than "empty" vesicles. X-ray microprobe analysis and adsorption studies verified that the heteropolyanions were associated with the vesicles, and not with the liquid medium.; The relative fraction of dissolved heteropolyanion that was encapsulated (3-18% under standardized conditions) increased as the surface charge density (anion charge/anion volume) decreased, e.g. from {dollar}rmlbrack CoWsb{lcub}12{rcub}Osb{lcub}40{rcub}rbracksp{lcub}6-{rcub}{dollar} to {dollar}rmlbrack Psb2Wsb{lcub}18{rcub}Osb{lcub}62{rcub}rbracksp{lcub}6-{rcub}.{dollar} Further, heteropolyanions possessing distinct organic regions on their surfaces, such as {dollar}rmlbrack(BuSn)sb3(Psb2Wsb{lcub}15{rcub}Osb{lcub}59{rcub})rbracksp{lcub}9-{rcub},{dollar} had much higher encapsulation levels than expected from their charge to volume ratios.; Preliminary comparative experiments involving interactions of {dollar}rmlbrack(BuSn)sb3(Psb2Wsb{lcub}15{rcub}Osb{lcub}59{rcub})rbracksp{lcub}9-{rcub}{dollar} in solution and in phospholipid vesicles with wild-type breast cancer cells showed that the vesicle-encapsulated heteropolyanions were more effective at inhibiting cell growth than the aqueous solution of the same polyoxometalate. This difference demonstrated that encapsulation of heteropolyanions in phospholipid vesicles alters the interaction of heteropolyanions with cells.