G-quartets

A unique aspect of the G-quartets 34 and 16 is that their assembly involves only metal-ligand bond formation. Since the sites on the nucleobase involved in coordination are either N7 or [N7 + N3] this... 

Fig. 10.13 The guanine-silylated conjugate 5 self-associates in the presence of alkali-metal cations to form hexagonal nanorod hybrids, presumably formed by G-quartet-based interactions.

Davis, J.F. (2004) G-quartets 40 years later, from 5 GMP to molecular biology and supramolecular chemistry. Angewandte Chemie-Intemational Edition, 43, 668-698. 

Figure 7.8 Schematized structure of four-stranded helix of G-wire only G-quartet core is shown.

Metal ions are required for the activity of anti-HIV G-quartet oligonucleotides (antisense oligonucleotides) such as T30177, a potent inhibitor of the enzyme HIV-1 integrase. 

Figure 9.10 The structure of a G-quartet. (From Wozki and Schmidt, 2002. Reproduced with permission from John Wiley Sons., Inc.)...

Selection-coupled analysis/phase segregation. One strategy for simplifying the analytical challenge is to use phase segregation. Three subclasses are possible. In the first of these, a phase transition is part of the selection process. This includes not only the familiar crystallization-induced enantiomeric enrichment discussed above but also the experiments (primarily employed in experiments directed toward the production of novel materials) such as those described by Lehn and coworkers in 2005. In this study, an acylhydrazone library was created from guanosine hydrazide and a mixture of aldehydes (Fig. 1.22) in the presence of metal ions, formation of G-quartet structures led to the production of a gel. 

Polythiophene binding to a sequence of DNA capable of forming a G-quartet was demonstrated (Ho and Leclerc 2004). Addition of polythiophene 12 to the single-stranded DNA resulted in a chromatic transition from yellow to pink/red. 

Figure 12.17 Detection of potassium mediated G-quartet formation. Reprinted from Ho and Leclerc (2004). Copyright 2004 American Chemical Society.

Fig. 7 View down the long axis of the top G quartet taken from coordinates given in [64]. The N7 atoms of the two lower quartets are shown as gray spheres. Reprinted with permission from [35], Copyright (2000) American Chemical Society...

Hoogsteen pairs were first observed in nature in transfer RNA molecules (Fig. 5-31). These molecules contain mostly Watson-Crick base pairs but there are also two reversed Hoogsteen pairs. One of them, between U8 and A14, is invariant in all tRNAs studied. Hoogsteen pairing also occurs in four-stranded DNA, which has important biological functions. A G quartet from a DNA tetraplex held together by Hoogsteen base pairs is shown in Fig. 5-8. 

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