A new non-covalent electron transfer model system, based on the use of cytidine–guanosine hydrogen bonding interactions, is described that incorporates a phthalocyanine photodonor and a C60 fullerene acceptor.
Hydrogen-bonding interactions in DNA/RNA systems are a defining feature of double helical systems. They also play a critical role in stabilizing other higher-order structures, such as hairpin loops, and thus in the broadest sense can be considered as key requisites to the successful translation and replication of genetic information. This importance, coupled with the aesthetic appeal of nucleic acid base (nucleobase) hydrogen-bond interactions, has inspired the use of such motifs to stabilize a range of synthetic structures. This, in turn, has led to the formation of a number of novel ensembles. This tutorial review will discuss these structures, both from a synthetic perspective and in terms of their potential application in areas that include, but are not limited to, self-assembled macrocyclic and high-order ensemble synthesis, supramolecular polymer preparation, molecular cage construction, and energy and electron transfer modeling.
All four one: The covalent attachment (A) of a porphyrin head group onto a guanine-rich oligonucleotide strand can enhance the self-assembly of DNA quadruplexes through porphyrin-based π–π interactions (B). Modulation of these allosteric interactions, by addition of a porphyrin-complexing cyclodextrin derivative, allows for a high degree of control over the formation and disassembly of the guanine quadruplexes (C and D).
Electronic absorption and emission properties of a new cytidine tethered zinc phthalocyanine 2 were used to probe the aggregation and guanosine/C60 derived de-aggregation of this nucleobase linked phthalocyanine. These experiments revealed that 2 aggregates even at low concentrations in a competitive solvent system (1.1×10−6 M in 20% DCM/toluene). Nucleobase–metal coordination and slipped co-facial π-stacking interactions are both important in aggregate formation. Guanosine 5, C60 6, and a guanosine-C60 chimera 4 were employed as potential aggregate disruptors. These experiments revealed that both guanosine and fullerene subunits are effective in disrupting the aggregate formed by 2. Such findings support the conclusion that base-pairing, π-stacking, as well as nucleobase–metal coordination interactions play important roles in the de-aggregation of 2.
Electronic absorption and fluorescence spectroscopies were used to study the aggregation and de-aggregation behavior of a novel cytidine tethered zinc phthalocyanine shown schematically above. De-aggregation of this conjugate, can be effected using guanosine, C60, as well as via the addition of a synthetic guanosine-C60 hybrid.
*picked as 'hot-paper' by the editors
A novel porphyrin–fullerene dyad assembled through Watson–Crick hydrogen bonds is described; this system undergoes photoinduced electron transfer upon irradiation with visible light to produce a charge separated state that is substantially longer lived than that of previous dyads of this type.
This article discusses the development of synthetic supramolecular systems derived from hydrogen bond driven base-pairing, with a focus on the self-assembly of individual nucleobase analogues.
A pyrrole-appended purine nucleoside 1 is described that can form an “extended” three-point Hoogsteen-type interaction due to the stabilization of the donor−acceptor−acceptor (DAA) motif. Nucleoside 1 is shown to bind guanosine 10 (a classic ADD motif) to form ensemble I. This interaction competes effectively with guanosine self-assembly and, as such, is capable of disrupting guanosine quadruplex formation.
Synthesis and assembly studies of a guanosine−cytidine dinucleoside 1 that self-assembles into a trimeric supramolecule (I) are presented. Dinucleoside 1 was obtained by utilizing two consecutive palladium-catalyzed cross-coupling reactions. Ensemble I was analyzed by ESI-MS, NMR spectroscopies, size exclusion chromatography (SEC), and vapor pressure osmometry (VPO).
