Alexander M. Spokoyny

Carborane-based metal–organic frameworks as highly selective sorbents for CO2 over methane

Separation of CO(2)/CH(4) mixtures was studied in carborane-based metal-organic framework materials with and without coordinatively unsaturated metal sites; high selectivities for CO(2) over CH(4) ( approximately 17) are obtained, especially in the material with open metal sites.

A Perfluoroaryl-Cysteine SNAr Chemistry Approach to Unprotected Peptide Stapling

We report the discovery of a facile transformation between perfluoroaromatic molecules and a cysteine thiolate, which is arylated at room temperature. This new approach enabled us to selectively modify cysteine residues in unprotected peptides, providing access to variants containing rigid perfluoroaromatic staples. This stapling modification performed on a peptide sequence designed to bind the C-terminal domain of an HIV-1 capsid assembly polyprotein (C-CA) showed enhancement in binding, cell permeability, and proteolytic stability properties, as compared to the unstapled analog. Importantly, chemical stability of the formed staples allowed us to use this motif in the native chemical ligation-mediated synthesis of a small protein affibody that is capable of binding the human epidermal growth factor 2 receptor.

Ni(III)/(IV) Bis(dicarbollide) as a fast, noncorrosive redox shuttle for dye-sensitized solar cells

Nickel bis(dicarbollide) is used as a fast, one-electron outer sphere redox couple in dye-sensitized solar cells. Device performances with this anionic shuttle are investigated with different electrolyte concentrations and additives, using only 0.030 M of the Ni(III) bis(dicarbollide) to efficiently regenerate the ruthenium dye. Atomic layer deposition of Al(2)O(3) on the nanoparticulate TiO(2) photoanodes is further used to improve device performances, increasing current densities almost 2-fold and attaining power conversion efficiencies approximately 10x greater than its metallocene analogue, ferrocene/ferrocenium. Open-circuit voltage decay is used to probe the kinetics of the Ni(III)/(IV) bis(dicarbollide) redox couple, and electron interception is found to be approximately 10(3)x slower than ferrocene/ferrocenium, explaining the large discrepancy in open-circuit voltage potentials between these two redox shuttles.

A coordination chemistry dichotomy for icosahedral carborane-based ligands

Although the majority of ligands in modern chemistry take advantage of carbon-based substituent effects to tune the sterics and electronics of coordinating moieties, we describe here how icosahedral carboranes-boron-rich clusters-can influence metal-ligand interactions. Using a series of phosphine-thioether chelating ligands featuring meta- or ortho-carboranes grafted on the sulfur atom, we were able to tune the lability of the platinum-sulfur interaction of platinum(II)-thioether complexes. Experimental observations, supported by computational work, show that icosahedral carboranes can act either as strong electron-withdrawing ligands or electron-donating moieties (similar to aryl- or alkyl-based groups, respectively), depending on which atom of the carborane cage is attached to the thioether moiety. These and similar results with carborane-selenol derivatives suggest that, in contrast to carbon-based ligands, icosahedral carboranes exhibit a significant dichotomy in their coordination chemistry, and can be used as a versatile class of electronically tunable building blocks for various ligand platforms.

Chemical reduction of a diimide based porous polymer for selective uptake of carbon dioxide versus methane

A diimide based porous organic polymer (POP) post-synthetically reduced with lithium metal demonstrates a drastic increase in selectivity for carbon dioxide over methane.

Separation of gas mixtures using Co(II) carborane-based porous coordination polymers

Separations of CO(2)/CH(4), CO(2)/N(2), and O(2)/N(2) mixtures were studied in three porous coordination polymers made of the same carborane ligand and Co(ii) nodes. High selectivities for CO(2) over CH(4) ( approximately 47) and CO(2) over N(2) ( approximately 95) were obtained, especially in the material with coordinated pyridine. Unusual selectivity for O(2) over N(2) (as high as 6.5) was demonstrated in the materials with open Co(ii) sites.

Electronic tuning of nickel-based bis(dicarbollide) redox shuttles in dye-sensitized solar cells

Rational design of a new series of boron-functionalized Ni{sup III}/Ni{sup IV}–bis(dicarbollide) clusters results in a family of robust and tunable redox shuttles (see diagram; EDG and EWG denote electron-donating and -withdrawing groups, respectively). This offers a means to rationally control the redox properties in dye-sensitized solar cells (DSCs), leading to exceptionally high open-circuit voltages.

Carborane-Based Pincers: Synthesis and Structure of SeBSe and SBS Pd(II) Complexes

We report the synthesis of several unique, boron-rich pincer complexes derived from m-carborane. The SeBSe and SBS pincer ligands can be synthesized via two independent synthetic routes and are metalated with Pd(II). These structures represent unique coordinating motifs, each with a Pd-B(2) bond chelated by two thio- or selenoether ligands. This class of structures serves as the first example of boron-metal pincer complexes and possesses several interesting electronic properties imposed by the m-carborane cage.

New ligand platforms featuring boron-rich clusters as organomimetic substituents* , **

200 years of research with carbon-rich molecules have shaped the development of modern chemistry. Research pertaining to the chemistry of boron-rich species has historically trailed behind its more distinguished neighbor (carbon) in the periodic table. Notably, a potentially rich and, in many cases, unmatched field of coordination chemistry using boron-rich clusters remains fundamentally underdeveloped. Our work has been devoted to examining several basic concepts related to the functionalization of icosahedral boron-rich clusters and their use as ligands, aimed at designing fundamentally new hybrid molecular motifs and materials. Particularly interesting are icosahedral carboranes, which can be regarded as 3D analogs of benzene. These species comprise a class of boron-rich clusters that were discovered in the 1950s during the “space race” while researchers were developing energetic materials for rocket fuels. Ultimately, the unique chemical and physical properties of carborane species, such as rigidity, indefinite stability to air and moisture, and 3D aromaticity, may allow one to access a set of properties not normally available in carbon-based chemistry. While technically these species are considered as inorganic clusters, the chemical properties they possess make these boron-rich species suitable for replacing and/or altering structural and functional features of the organic and organometallic molecules—a phenomenon best described as “organomimetic”. Aside from purely fundamental features associated with the organomimetic chemistry of icosahedral carboranes, their use can also provide new avenues in the development of systems relevant to solving current problems associated with energy production, storage, and conversion.

Atomically precise organomimetic cluster nanomolecules assembled via perfluoroaryl-thiol SNAr chemistry

The majority of biomolecules are intrinsically atomically precise, an important characteristic that enables rational engineering of their recognition and binding properties. However, imparting similar precision to hybrid nanoparticles has been challenging due to inherent limitations of the existing chemical methods and availability of properly designed functional building blocks. Here we report a new approach to form atomically precise and highly tunable hybrid nanomolecules with well-defined three-dimensionality. Perfunctionalization of atomically precise clusters with pentafluoroaryl-terminated linkers produces size-tunable rigid cluster nanomolecules. These species are amenable to facile modification with a variety of thiol-containing molecules and macromolecules. Assembly proceeds at room temperature within hours under mild conditions, and the resulting nanomolecules exhibit high stabilities due to their full covalency. We further demonstrate how these nanomolecules grafted with saccharides can exhibit dramatically improved binding affinity toward a protein. Ultimately, the developed strategy allows the rapid generation of precise molecular assemblies for investigating multivalent interactions.