Benzothiazole-substituted 1,3-diaza-2-oxophenoxazine as a luminescent nucleobase surrogate for silver(I)-mediated base pairing.

A benzothiazole-substituted derivative (X) of 1,3-diaza-2-oxophenoxazine was evaluated with respect to its ability to engage in Ag(I)-mediated homo base pair formation in two different DNA duplexes. The metal binding was determined by a combination of temperature-dependent UV spectroscopy, CD spectroscopy, and fluorescence spectroscopy, indicating the incorporation of two Ag(I) ions to generate a dinuclear X-Ag(I)2-X base pair. Interestingly, a luminescence increase was observed upon metal binding. Theoretical luminescence spectra were calculated using time-dependent density functional theory (TDDFT) for all possible Ag(I)-mediated X : X base pair geometries to identify the species responsible for the increase in luminescence. The study shows that even bulky non-planar artificial nucleobases can be applied to form stabilizing metal-mediated base pairs.

Silver(I)-mediated base pairing involving an S-glycosidic GNA nucleoside analogue.

The 4S-Ag(I)-C base pair (4S, 3-((2-(methylthio)pyrimidin-4-yl)thio)propane-1,2-diol; C, deoxycytidine) represents the first metal-mediated base pair comprising an S-glycosidic nucleoside analogue. We report here the synthesis of the phosphoramidite suitable for the automated solid-phase synthesis of DNA oligonucleotides containing 4S and its silver(I)-binding ability. The DNA duplexes comprising a 4S:C mispair exhibit a large thermal stabilization upon the addition of one equivalent of silver ions, giving rise to the formation of the above-mentioned silver(I)-mediated base pair. By formally replacing the sulfur atom in the glycosidic bond by an oxygen atom, i.e., by applying 3-((2-(methylthio)pyrimidin-4-yl)oxy)propane-1,2-diol (4 O) as the artificial nucleoside analogue, the participation of this atom as a donor atom in silver(I)-mediated base pairing is shown to be neglectable.Supplemental data for this article is available online at.

Silver(I)-mediated base pairing in DNA involving the artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine.

The artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine (X) was investigated with respect to its ability to engage in Ag(I)-mediated base pairing in DNA. Spectroscopic data indicate the formation of dinuclear X-Ag(I)2-X homo base pairs and mononuclear X-Ag(I)-C base pairs (C, cytosine). Density functional theory calculations and molecular dynamics simulations indicate that the nucleobase changes from its lactam tautomeric form prior to the formation of the Ag(I)-mediated base pair to the lactim form after the incorporation of the Ag(I) ions. Fluorescence spectroscopy indicates that the two Ag(I) ions of the homo base pair are incorporated sequentially. Isothermal titration calorimetry confirms that the affinity of one of the Ag(I) ions is about tenfold higher than that of the other Ag(I) ion. The computational analysis by means of density functional theory confirms a much larger reaction energy for the incorporation of the first Ag(I) ion. The thermal stabilization upon the formation of the dinuclear Ag(I)-mediated homo base pair exceeds the one previously observed for the closely related nucleobase 1,N6-ethenoadenine by far, despite very similar structures. This additional stabilization may stem from the presence of water molecules engaged in hydrogen bonding with the additional oxygen atom of the artificial nucleobase X. The highly stabilizing Ag(I)-mediated base pair is a valuable addition to established dinuclear metal-mediated base pairs.

Dynamic Structure and Stability of DNA Duplexes Bearing a Dinuclear Hg(II)-Mediated Base Pair.

Quantum mechanical (QM) and hybrid quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations of a recently reported dinuclear mercury(II)-mediated base pair were performed aiming to analyse its intramolecular bonding pattern, its stability, and to obtain clues on the mechanism of the incorporation of mercury(II) into the DNA. The dynamic distance constraint was employed to find initial structures, control the dissociation process in an unbiased fashion and to determine the free energy required. A strong influence of the exocyclic carbonyl or amino groups of neighbouring base pairs on both the bonding pattern and the mechanism of incorporation was observed. During the dissociation simulation, an amino group of an adenine moiety of the adjacent base pair acts as a turnstile to rotate the mercury(II) ion out of the DNA core region. The calculations provide an important insight into the mechanism of formation of this dinuclear metal-mediated base pair and indicate that the exact location of a transition metal ion in a metal-mediated base pair may be more ambiguous than derived from simple model building.

Silver(I)-mediated base pairing in parallel-stranded DNA involving the luminescent cytosine analog 1,3-diaza-2-oxophenoxazine.

1,3-Diaza-2-oxophenoxazine (X) has been introduced as a ligand in silver(I)-mediated base pairing in a parallel DNA duplex. This fluorescent cytosine analog is capable of forming stabilizing X-Ag(I)-X and X-Ag(I)-C base pairs in DNA duplexes, as confirmed by temperature-dependent UV spectroscopy and luminescence spectroscopy. DFT calculations of the silver(I)-mediated base pairs suggest the presence of a synergistic hydrogen bond. Molecular dynamics (MD) simulations of entire DNA duplexes nicely underline the geometrical flexibility of these base pairs, with the synergistic hydrogen bond facing either the major or the minor groove. Upon silver(I) binding to the X:X or X:C base pairs, the luminescence emission maximum experiences a red shift from 448 to 460 nm upon excitation at 370 nm. Importantly, the luminescence of the 1,3-diaza-2-oxophenoxazine ligand is not quenched significantly upon binding a silver(I) ion. In fact, the luminescence intensity even increases upon formation of a X-Ag(I)-C base pair, which is expected to be beneficial for the development of biosensors. As a consequence, the silver(I)-mediated phenoxazinone base pairs represent the first strongly fluorescent metal-mediated base pairs.