Ashutosh Kumar Mishra

The Many Facets of Adenine: Coordination, Crystal Patterns, and Catalysis

Canonical purine-pyrimidine base pairs, the key to the complementary hydrogen bonding in nucleic acids, are fundamental molecular recognition motifs crucial for the formation and stability of double-helical DNA. Consequently, focused study and modeling of nucleobase hydrogen-bonding schemes have spawned a vast array of chemical and biophysical investigations. The Watson-Crick, reverse Watson-Crick, Hoogsteen, and reverse Hoogsteen hydrogen-bonding schemes stabilize various nucleic acid structures. As a result, numerous modified bases have been designed to maximize such interactions, addressing specific problems related to base pairing and giving rise to supramolecular ensembles in solution or in the solid state. It is also important to realize that suitably predisposed imino nitrogens and other functional groups present in heterocyclic nucleobases present a versatile molecular framework for the construction of coordination architectures, which may be harnessed to mimic base polyads and higher order nucleic acid structures. Adenine, a purine nucleobase, is an important naturally occurring nitrogen heterocycle present in nucleic acids. It is notable that the adenine unit is also frequently encountered as an inextricable part of enzyme cofactors and second messenger systems, such as NAD(+), FADH(2), and cAMP, which are essential for certain catalytic reactions and biochemical processes. In addition, a crucial catalytic role of the adenine moiety is also observed in group II intron catalysis and at the ribosomal peptidyltransferase center. Such versatile functional roles of the adenine framework serve as an inspiration for addressing research problems, ranging from classical coordination chemistry to the development of new materials. In this Account, we begin by describing the emerging use of adenine nucleobase for the design of metal-nucleobase frameworks. The coordination of metal ions affords a variety of oligomeric and polymeric species; we focus on silver- and copper-based structures and also discuss ferrocenylated adenine tetrads. We then consider the use of supramolecular adenine coordination complexes for transferring molecular properties onto surfaces. This technique is particularly useful for transferring noncovalent interactions, such as van der Waals forces, electrostatic interactions, and hydrogen bonding, to designed architectures in nanoscale applications. Finally, we explore the issue of adenine-based catalytic entities. Here, adenine moieties are first fixed in a polymeric matrix, followed by metalation of the matrix. These metalated adenine-containing polymers are then assayed for catalytic assistance in various chemical and biochemical reactions. Taken together, the versatile coordination abilities and hydrogen-bonding capacity of adenine offer a novel entry point for a natural ligand into materials synthesis.

Silver-guided excimer emission in an adenine-pyrene conjugate: fluorescence lifetime and crystal studies

This Communication describes a novel adenine-pyrene conjugate (1) and its solid-state structure with silver and copper ions. Single-crystal studies of metal complexes of 1 offer insight into molecular interactions and provide a basis to rationalize possible interactions in the solution state, leading to excimer formation. The robust nature of this interaction was further confirmed by deposition of the silver complex on a graphite surface, which exhibited a remarkable resemblance to its solid-state structure. The structural basis of selective excimer formation in the presence of Ag(+) ions presents a viable approach for ratiometric detection of these ions.

Decanuclear Copper Framework Supported by a Tripodal Adenine Ligand

This Communication describes the synthesis, crystal structure, and magnetic properties of a unique decanuclear copper complex of a tripodal adenine ligand built around a phenyl ring core. This complex comprises two mu(4)-oxo tetranuclear copper(II) units of the type Cu(4)OCl(6)L(4), bridged together by two pentacoordinated copper centers. Variable-temperature magnetic susceptibility data reveal the possibility of interaction between copper sites.

Interconnected Trimeric, Pentameric, and Hexameric Metallacycles in a Singular Silver−Adenine Framework

This Article describes the synthesis and crystallographic investigation of a silver complex of a modified adenine derivative bearing a nitrile pendant at the N9 position. All three adenine ring nitrogen atoms coordinated to silver ions, while the fourth coordination was achieved at the nitrile functionality, thus resulting in the formation of silver-mediated interconnected trimeric, pentameric, and hexameric metallacyclic rings and helical signatures in two orthogonal directions.

Contrasting crystallographic signatures of Ag(I)- and Cu(II)-N6,N6′- bisadenine complexes: extended vs. foldback geometries

We report crystallographic studies with N6,N6′-crosslinked bisadenine derivative, where complexation with Ag(I) exhibits a pentacoordination mode affording a molecular box, while interaction with Cu(II) results in an intramolecular complex.

Preparation and structural properties of mononuclear and binuclear ruthenium(II) cyclopentadienyl complexes with 4-cyanopyridine and 4-cyanopyridine 1-oxide

Abstract Reactions of [Ru(η 5 -C 5 H 5 )L 2 Cl] (L = PPh 3 or AsPh 3 , L 2 = Ph 2 PCH 2 CH 2 PPh 2 or Ph 2 PCH 2 PPh 2 ) have been carried out with 4-cyanopyridine and 4-cyanopyridine 1-oxide in the presence of suitable anions (PF − 6 or BPh − 4 ). The reaction products were found to be cationic mono- and binuclear complexes which have been characterized by elemental analyses, spectroscopic (IR, UV-vis and NMR) and electrochemical studies. Conductivity measurements have also been carried out to confirm the charges on these cationic species.