Polyanionic

Bausch J W, Prakash G K S, Olah G A, Tse D S, Lorents D C, Bae Y K and Malhotra R 1991 Considered novel aromatic systems. 11. Diamagnetic polyanions of the Cgg and C g fullerenes. preparation, 13-C and 7-Li NMR spectroscopic observation, and alkylation with methyliodide to polymethylated fullerenes J. Am. 

Selenium and tellurium react similarly, forming selenides and selenates(IV), and tellurides and tellurates(IV) respectively. Like the sulphide ion, S , the ions Se and Te form polyanions but to a much lesser extent. 

The polyions postulated in solution all have known structural analogues in crystalline borate salts. Investigations of the Raman (66) and B nmr (67) spectra of borate solutions have confirmed the presence of three of these species the triborate (3), B202(0H) 4, tetraborate (4), [B40 (0H) 4], and pentaborate (5) B O (OH) 4, polyanions. Skeletal stmctures were assigned based on coincidences between the solution spectra and those soHd borates for which definitive stmctural data are available (52). These same ions have been postulated to be present in alkah metal borate glasses as well. 

The crystal stmcture of colemanite has been shown to contain polyanion chains. The stmctural relationships between colemanite... 

CMC hydrates rapidly and forms clear solutions. Viscosity buUding is the single most important property of CMC. DUute solutions of CMC exhibit stable viscosity because each polymer chain is hydrated, extended, and independent. The sodium carboxylate groups are highly hydrated, and the ceUulose molecule itself is hydrated. The ceUulose molecule is linear, and conversion of it into a polyanion (polycarboxylate) tends to keep it in an extended form by reason of coulombic repulsion. This same coulombic repulsion between the carboxylate anions prevents aggregation of the polymer chains. Solutions of CMC are either pseudoplastic or thixotropic, depending on the type. 

The proteoglycan-hyaluronate aggregates are highly hydrated by virtue of strong interactions between water molecules and the polyanionic complex. 

Salts of several heavy main-group elements can be reduced to form polyanions such as Na4[Sn9], Na3[Sb3] and Na3[Sb7] (p. 588). 

The hydrated insular groups may polymerize in various ways by splitting out water this process may be accompanied by the breaking of boron-oxygen bonds within the polyanion framework. 

Complex borate polyanions may be modified by attachment of an individual side group, such as (but not limited to) an extra borate tetrahedron, an extra borate triangle, 2 linked triangles, an arsenate tetrahedron, and so on. 

M. T. Pope, Iso- and Hetero-polyanions, Chap. 38 in Comprehensive Coordination Chemistry, Vol. 3, pp. 1028-58, Pergamon Press, Oxford, 1987. 

The polymerization of acidified solutions of molybdenum(VI) or tungsten(VI) yields the most complicated of all the polyanion systems and, in spite of the fact that the tungsten system has been the most intensively studied, it is still probably the least well understood. This arises from the problem inevitably associated with studies of such equilibria, and which were noted (p. 983) in the discussion of the Group 5 isopolyanions. It must also be admitted that, whilst the observed structures of individual polyanions are reasonable, it is often difficult to explain why, under given circumstances, a particular degree of aggregation or a particular structure is preferred over other possibilities. 

Undoubtedly the first major polyanion formed when the pH of an aqueous molybdate solution is reduced below about 6 is the heptamolybdate [M07O24] , traditionally known as the paramolybdate ... 

Anions with 8, and probably 16-18, Mo atoms also appear to be formed, before increasing acidity suffices to precipitate the hydrous oxide. It is clear from the above equation that the condensation of M0O4 polyhedra to produce these large polyanions requires large quantities of strong acid as the supemumary oxygen atoms are removed in the form of water molecules. Careful... 

The nucleophilic behavior of polyanions can be anticipated by examining the shape of electron donor orbitals (typically the highest-occupied molecular orbital or HOMO). Examine the HOMO of the dianion. Which part of this orbital is best able to overlap with an electrophile ... 

S-Poly(L-malic acid) ionizes readily in water giving rise to a highly soluble polyanion. Thus, a 2% solution of the free acid of the polymer from Aureobasidium sp. A-91 showed a pH 2.0 [5]. The ionic constants have been determined to be pKa = 3.6 for the polymer from Aureo-basidumsp. A-9 [5] and pKa (25°C) = 3.45 for/3-poly(L-malic acid) of Mw 24 kDa from F. polycephalum (Valussi and Cesaro, unpublished results) Thus, the polymer is highly charged under physiological conditions (pH 7.0). 

Hydrophobization of Polyanionic Polymers to Achieve Higher Biological Activity... 

Since the pioneer work by Merigan in 1967 [1], many kinds of synthetic or natural polyanionic polymers have been examined for their biological activities [2-8], such as cytotoxicity, antiviral activity, antitumor activity, and immunomodulating activity. Although the biological results were interesting, the extent of activity for clinical application was still low. 

Several mechanisms between drug-encapsulated liposomes and cells was presented [9,10]. Sunamoto and coworkers [11] applied the liposomal technique for improving the biological activity of polyanionic polymers. 

We modified polyanionic polymers by use of a grafting reaction of hydrophobic groups onto the polymers. After an extensive evaluation for the affinity of the hy-drophobically modified (hydrophobized) polymers to cell membrane, the immuno-stimulating activity of polymers was investigated by in vitro or ex vivo experiments. Consequently, the increased biological activity was found in the hydrophobized polymer, indicating that... 

---