Counterion Distribution around Hydrophilic Molecular Macroanions: The Source of the Attractive Force in Self‐Assembly

Abstract

Growing blackberries: The association of counterions around {Mo72V30} polyoxometalate macroanions increases with increasing macroion concentration and decreasing solvent polarity. The counterion distribution extends about 2–9 Å from the macroion surface with the highest probability at 2–3 Å from the macroion surface. A close connection between counterion association and the self‐assembly of {Mo72V30} into “blackberry” structures is observed.

Determination of the Effective Charge Density of pH‐Responsive Keplerate Polyoxometalate Clusters by Means of Agarose Gel Electrophoresis

“…[23,24,26] Therefore, differences in mobility can be attributed mostly to the difference in their effective charge density. [6] A concentration of 1.0 mg mL -1 was chosen for this study to ensure that no self-assembled superstructures were formed. [26] Another strongelectrolyte-type POM is {Mo 72 V 30 }, which is stable in the form of discrete macroanions in dilute aqueous solution (theoretically, each cluster carries approximately 31 negative charges, balanced by 8 Na + , 14 K + , 2 VO 2 + , and 5 H + ions).…”

“…[4] This study was performed by using {Mo 72 Fe 30 } at 1.0 mg mL -1 , therefore a new measurement of R h at different pH values was performed. [6] The R h values of blackberries formed range from 46 nm at pH = 3.2 to 20 nm at pH = 5.5. [6] The R h values of blackberries formed range from 46 nm at pH = 3.2 to 20 nm at pH = 5.5.…”

“…[1][2][3][4][5][6][7] The formation of the blackberry structure is mainly due to counterion-mediated attractions and hydrogen bonding, but not due to van der Waals forces, hydrophobic interactions, or chemical reactions. The best polyoxometalate models are hydrophilic ones, such as the spherical Keplerate clusters, each of which are covered by a layer of coordinately attached water ligands.…”

“…It is known that such POM macroanions with a moderate amount of charges tend to spontaneously and reversibly assemble into stable, uniform, single-layered, shell-like blackberry structures instead of existing only as discrete ions in dilute solutions of polar solvents. [6] Therefore, the effective charge on the macroions is different from its structural charge obtained from its crystalline formula. [4][5][6] Recently, the self-assembly of some Keplerate POMs into large blackberries was found to demonstrate self-recognition behavior (i.e., two types of separate, individual blackberries, instead of mixed ones, were found in solutions that contained two types of structurally similar Keplerate POMs with slightly different charge densities and different water-ligand residence times).…”

Rational Design of Organically Functionalized Polyoxopalladates and Their Supramolecular Properties

“…[6d, 10] In previous reports, apart from the major driving forces, that is, counter cation-mediated attraction, [11] severalf actors including hydrophobic interaction, [12] hydrogen bonding, [13] solvent polarity, [14] and additional electrolytes [15] coulda lso contributet ot he size change tendency of POM-based single-layer hollow spherical blackberry structures. In addition, studying the solutionstate supramolecular "blackberry"-type self-assembly phenomenon of POPs might shed light on their homogeneous catalytic mechanism, whichi ss till rather elusive.…”