Imenne Bouamaied

Supramolecular helical porphyrin arrays using DNA as a scaffold

A diphenyl porphyrin substituted nucleotide was incorporated site specifically into DNA, leading to helical stacked porphyrin arrays in the major groove of the duplexes. The porphyrins show an electronic interaction which is significantly enhanced compared to the analogous tetraphenyl porphyrin (TPP) as shown in the large exciton coupling of the porphyrin B-band absorbance. Analogous to the TPP-DNA, an induced helical secondary structure is observed in the single strand porphyrin-DNA. The modified DNA can be hybridised to an immobilised complementary strand leading to fluorescent beads.

Axial Coordination to Metalloporphyrins Leading to Multinuclear Assemblies

The use of axial coordination to metalloporphyrins is discussed on the basis of constructing multinuclear complexes. Starting with single metalloporphyrin-ligand complexes where the ligand is designed to bring a functional moiety close to the porphyrin, the discussion further expands to the design, synthesis, and detailed analysis of multiporphyrin assemblies. The porphyrin-as-ligand concept combined with orthogonal binding modes is presented, and selected examples show that in this way a large diversity in multiporphyrin assemblies can be achieved. New emerging concepts such as dynamic combinatorial chemistry, porphyrin-fullerene complexes and porphyrins assembled around gold nanoclusters or on surfaces are presented as well, because these systems are expected to play a leading role in the design of new materials in near future.I. Bouamaied, T. Coskun, E. Stulz: Axial Coordination to Metalloporphyrins Leading to Multinuclear Assemblies.- Y. Kobuke: Porphyrin Supramolecules by Self-Complementary Coordination.- E. Iengo, F. Scandola, E. Alessio: Metal-Mediated Multi-Porphyrin Discrete Assemblies and Their Photoinduced Properties.- J.T. Hupp: Rhenium-Linked Multiporphyrin Assemblies: Synthesis and Properties.- G. Ercolani: Thermodynamics of Metal-Mediated Assemblies of Porphyrins.- L. Flamigni, V. Heitz, J.-P. Sauvage: Porphyrin Rotaxanes and Catenanes: Copper(I)-Templated Synthesis and Photoinduced Processes.- M.J. Gunter: Multiporphyrin Arrays Assembled Through Hydrogen-Bonding

CG base pair recognition within DNA triple helices by modified N-methylpyrrolo-dC nucleosides

3-Aminophenyl-modified analogues of the bicyclic nucleoside N-methyl-3H-pyrrolo[2,3-d]pyrimidin-2(7H)-one were synthesised and incorporated directly into triplex-forming oligonucleotides in order to utilise their extended hydrogen bonding motif for recognition of the CG base pair. All analogues demonstrated strong binding affinity and very good selectivity for CG from pH 6.2 to 7.0; a marked improvement on previous modifications.

Discrimination against the Cytosine Analog tC by Escherichia coli DNA Polymerase IV DinB

The cytosine analog 1,3-diaza-2-oxophenothiazine (tC) is a fluorescent nucleotide that forms Watson-Crick base pairs with dG. The Klenow fragment of DNA polymerase I (an A-family polymerase) can efficiently bypass tC on the template strand and incorporate deoxyribose-triphosphate-tC into the growing primer terminus. Y-family DNA polymerases are known for their ability to accommodate bulky lesions and modified bases and to replicate beyond such nonstandard DNA structures in a process known as translesion synthesis. We probed the ability of the Escherichia coli Y-family DNA polymerase DinB (Pol IV) to copy DNA containing tC and to incorporate tC into a growing DNA strand. DinB selectively adds dGTP across from tC in template DNA but cannot extend beyond the newly formed G:tC base pair. However, we find that DinB incorporates the tC deoxyribonucleotide triphosphate opposite template G and extends from tC. Therefore, DinB displays asymmetry in terms of its ability to discriminate against the modification of the DNA template compared to the incoming nucleotide. In addition, our finding that DinB (a lesion-bypass DNA polymerase) specifically discriminates against tC in the template strand may suggest that DinB discriminates against template modifications in the major groove of DNA.

Porphyrin-substituted dinucleotides : Synthesis and spectroscopy

Deoxyuridine, which is substituted with either 5,15-diphenyl porphyrin (DPP) or 5,10,15,20-tetraphenyl porphyrin (TPP) at the 5-position via an alkynyl linker, was dimerised to the homo- and hetero-porphyrin dinucleotide. The synthesis was performed either in solution or on solid phase in order to compare the reactivity of the phosphoramidite building blocks under both conditions. The absorbance properties reveal electronic interactions in the dimers that are strongly dependent on the nature of the porphyrin. The DPP-containing dimers show significant differences between the calculated and the measured UV-Vis spectra, whereas in the TPP dimer hardly any difference is observed. Formation of the duplex with the corresponding diadenosine changes the electronic interactions between the chromophores in the heteroporphyrin dimer, as shown by a blue shift of the absorbance. The low solubility of the DPP dimer in pure chloroform prevented formation of the duplex due to the necessity to add about 10% of methanol. The dimerisation is detectable using MALDI-TOF mass spectrometry for all dinucleotides.

Porphyrin-DNA: A Supramolecular Scaffold for Functional Molecules on the Nanometre Scale

We are pursuing the aim to use DNA as a supramolecular scaffold for the creation of electronically functional molecules on the nanometre scale. Here, we give a review on our results on porphyrin modified nucleotides used for this purpose. A general synthetic route to porphyrin-nucleotides has been devised, and the building blocks can be incorporated into oligonucleotides using standard solid phase synthesis methods. Up to 11 porphyrins were incorporated into DNA, reaching a length of approximately 4 nm in the array. The spectroscopic data are consistent with a porphyrin induced secondary structure stabilisation in the single strands.

Tetranucleotides as a scaffold for diporphyrin arrays

The incorporation of porphyrin-substituted nucleosides into tetranucleotides using phosphoramidite chemistry on solid support is reported. Both diphenyl and tetraphenyl porphyrin nucleosides were used as building blocks. This method allows the synthesis of chiral homo- and heteroporphyrinic arrays, where the composition and thus the physical properties of the array can be modulated simply by reprogramming the DNA synthesizer. The porphyrin arrays are initially isolated in the free-base form. Remetallation to give the zinc-porphyrins can be achieved using standard procedures in solution. The UV-vis spectra of the arrays are reproducible by a superposition of the absorbance spectra of the individual porphyrins, indicating an undisturbed electronic ground state of the porphyrins in the arrays. The same is true for the steady-state emission spectra of the homoporphyrinic arrays, which are not influenced by the presence of the nucleotide strand. In the mixed porphyrin arrays, large differences in the excited-state properties compared to an equimolar mixture of the building blocks are observed by means that the emission of the diphenyl porphyrin moiety is quenched to a large extent, and the overall emission is dominated by the tetraphenyl porphyrin. The covalent connection of the porphyrins via the DNA-derived backbone therefore substantially alters the excited-state and energy-transfer properties of mixed porphyrin systems. The circular dichroism (CD) spectra show induced negative cotton effects in the region of the porphyrin B-band absorption, which is due to the attachment of the chromophores to the chiral oligonucleotide backbone. Addition of a complementary tetra-adenosine did not alter any of the spectroscopic properties, neither in chloroform nor in acetonitrile solutions. Therefore, it can be concluded that no duplex is formed, which is corroborated by 1H NMR spectroscopy.