Discovery and Its Applications

Closomers - New Motifs in Molecular Architecture

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The purpose of this research is to develop useful routes to a new class of structurally precise molecular collection platforms to which a variety of functional molecules may be attached to create a supramolecular structure or nanoscale device. The precise structure and functions of these nanostructures would be determined by specific needs and the nature of the complementary interactions between individual components. Our goal is to discover and develop the chemical methodologies required for the creation of the molecular collection platforms for general use and not the pursuit of devices specific to a predetermined goal. It is believed that the availability of a generic set of molecular platforms capable of supporting a wide range of molecular structure and function would stimulate a broad spectrum of successful applications.

closomer general

The unique chemical basis of this research is the discovery of the icosahedral closo-B12(OH)12-2 , its monocarba- and dicarbaborane counterparts and its successful twelve-fold derivatization to produce general structures, such as those shown above, and now known as closomers. The twelve-fold functionality of closo-B12(OH)12-2 is reflected in the closomer species derived from it by simple organic reactions characteristic of the hydroxyl group; carboxylate esters, aryl and alkyl ethers, carbamate esters and others.

closomer ester

The ability of the 26 cage-electron B12-2 closomer core of ether derivatives, closo-B12(OR)12-2, to be reversibly oxidized to the corresponding 25 cage-electron paramagnetic radical anion and diamagnetic 24 cage-electron D3d neutral species is unique and useful. The oxidized species are stabilized by nonbonded p-electron donation from the ether oxygen atoms to the electron deficient (less than 26 cage-electrons) B12 cages. Other attractive properties associated with the parent closo-B12H12-2 cage (as disodium salt) are the absence of strong absorption in the ultraviolet region above ca 210 nm and very low toxicity in animals and humans.

ether redox

Reversible oxidation of '12-ether Closomer' through two one-electron oxidation steps.

 

The twelve-fold functionality and the rigid, near-spherical icosahedral shape are unique to chemistry. Applications of these features may eventually involve the development of closomer clusters in which each of the twelve vertices become the anchoring site for a predetermined function, such as tumor cell targeting moieties, gadolinium chelators from MRI contrast agents, plasma membrane penetrators, radionuclide chelators for diagnosis or therapy, fluorophores, chemotherapeutics, targeting and therapeutic peptides, carbohydrates and glycobiologics, synthetic antigens, RNA and DNA segments, immunoproteins, etc.

Ideally, the resulting diagnostics, therapeutics, nanodevices, or a combination of these, would have the ability to carry multiple copies of selected payload species or a diverse multicomponent and specifically tailored payload to the targeted sites.

Selected Publications:

Toralf Peymann, Axel Herzog, Carolyn B. Knobler, and M. Frederick Hawthorne "Aromatic polyhedral hydroxyborates: bridging boron oxides and boron hydrides" Angewandte Chemie, International Edition in English 199938, 1062-1064.

Toralf Peymann, Carolyn B. Knobler, Saeed I. Khan, and M. Frederick Hawthorne "Dodecahydroxy-closo-dodecaborate(2)" Journal of the American Chemical Society 2001123, 2182-2185.

Andreas Maderna, Carolyn Knobler and M. Frederick Hawthorne "Twelvefold functionalization of an icosahedral surface by total esterification of [B12(OH)12]2- : 12(12)-closomers" Angewandte Chemie, International Edition in English 200140, 1662-1664.

Toralf Peymann, Carolyn Knobler, Saeed I. Khan and M. Frederick Hawthorne "Dodeca(benzyloxy)dodecaborane, B12(OCH2 Ph)12 : a stable derivative of hypercloso-B12H12 " Angewandte Chemie, International Edition in English 200140, 1664-1667.

Omar K. Farha, Richard L. Julius, Mark W. Lee, Ramon E. Huertas, Carolyn B. Knobler, and M. Frederick Hawthorne, "Synthesis of Stable Dodeca-(alkoxy) Derivatives of Hypercloso- B12H12 ", Journal of the AmericanChemical Society 2005127, 18243-18251.

Tiejun Li, Satish S. Jalisatgi, Michael J. Bayer, Andreas Maderna, Saeed I. Khan, and M. Frederick Hawthorne, "Organic Syntheses on an Icosahedral Borane Surface: Closomer Structures with Twelvefold Functionality",Journal of the American Chemical Society 2005127, 17832-17841.

Mark W. Lee, Omar K. Farha, M. Frederick Hawthorne, and Corwin H. Hansch "Alkoxy Derivatives of Dodecaborate: Discrete Nanomolecular Ions with Tunable Pseudometallic Properties" Angewandte Chemie, International Edition in English 200746, 3018-3022.