We have recently introduced a novel paradigm for heterogeneous catalyst design by developing polymeric templates based on 9-allyl/9-(4-vinylbenzyl) nucleobase frameworks. These insoluble templates, when coordinated to metal ions, display significant rate enhancements for the hydrolysis of activated phosphate esters, conform to classical Michaelis-Menten kinetics with high turnover numbers. Interestingly, one copper-containing adenylated template displayed a remarkable enzyme-like activity of oxygen insertion between an aromatic C-H bond; an activity reminiscent of hydroxylase/oxidase protein enzymes that catalyze biosynthesis of tyrosine and catecholamines. We are currently applying the knowledge of nucleobase polymer catalysis to other interesting chemical and biochemical reactions. A representative example of the design of polymeric matrix is shown underneath.
(a) Chem. Commun. 2000, 515-516; (b) Chem. Eur. J. 2001, 7, 828-833; (c) Chem. Commun. 2003, 800-801; (d) Bioorg. Med. Chem. Lett. 2006, 16, 363-366.
Nucleic acids offer a versatile platform for metal ion coordination resulting in stabilization of higher order superstructures. The constituent heterocyclic nucleobases are bestowed with suitably predisposed metal ion binding sites, which are invoked for the generation of interesting supramolecular structural paradigms. The occurrence of nucleic acid/nucleobase architectures also holds great significance in the cellular milieu where motifs such as guanine(G)-quartets and adenosine platforms, are implicated for a variety of biological functions. We recently reported that 9-allyladenine afforded a 3N coordinated, silver tethered macrocyclic tetraplex, which exhibited aggregative ordering on graphite surface and luminescent properties. This unusual coordination mode, resemblance to biological purine quartets and the presence of silver-mediated helical motifs represents an interesting example of metal-nucleobase interaction, with possible application for the construction of architectures mimicking biological assemblies and metal-organic frameworks.
(a) Chem. Eur. J. 2002, 8, 5184-5191; (b) J. Am. Chem. Soc. 2006, 128, 400-401; (c) J. Am. Chem. Soc. 2007, 129, 3488-3489.
Ordered peptide aggregates:
We are currently involved in understanding structural aspects of ordered biological assemblies as observed during amyloidogenic protein aggregation. We have recently initiated investigations concerning potential role of conserved peptide motifs in biologically interesting proteins, such as prion protein (PrPc) and V3 loop of HIV-1, as “hot-spots” for aggregation. Aggregational behavior is studied using truncated peptide constructs which are aged for a given period of time followed by morphological evaluation of structures so formed by several microscopic techniques. In this context, we have been able to demonstrate aggregation in peptide segments derived from conserved octarepeat motif of prion protein and conserved hexapeptide motif in V3 loop of HIV-1. We have observed time-dependent aggregation leading to the formation of spherical pre-fibrillar structures, eventually culminating into persistent length fibrils. Such synthetic studies, coupled with morphological evaluation, offer an attractive design paradigm for enforcing aggregation in functional peptide segments and it may serve as a model to probe structural basis of protein agglomeration and related phenomenon.
(a) Chem. Commun. 2004, 638-639; (b) Chem. Commun. 2005, 2564-2566; (c) Angew. Chem. Int. Ed. 2007, 46, 2002-2004.