DNA as supramolecular scaffold for porphyrin arrays

Modified nucleotides are becoming increasingly attractive, e.g. to create supramolecular assemblies by using the Watson-Crick base pairing motif, or to incorporate various functionalities such as fluorophores or amino acid side chain mimics into the DNA itself. Here, we present a general synthetic route to porphyrinyl-nucleosides 31-38, where the substitution pattern and the metallation state of the porphyrin residue can be varied to introduce diversity. Based on the synthetic route, the corresponding phosphoramidites 39-42 were synthesized. First, diphenylporphyrin dimers were synthesised both in solution (46a, 46b) and on solid support 47. The building block was then successfully incorporated into trimer 57, tetranucleotides 54-56 and 21-mer oligo-deoxynucleotides 64-70 on solid support via an automated DNA synthesiser. The 21-mer DNA contains one central modification, two porphyrins separated by one thymidine, three consecutive and five consecutive porphyrins. These strands were purified by hybridisation of the complementary strand on support solid or by fluorous affinity chromatography. First results on the interaction of the dimer, the tetramer, and the 21-mer with the complementary strands are discussed. The UV-Visible and fluorescence spectroscopy show an electronic interaction between the different porphyrins in the hetero-tetranucleotide 55. Similarly, in the 21-mer porphyrin DNA strands, an electronic coupling between the chromatophore is evident from the broadened UV-Vis absorbances (porphyrin B-band)

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 spectroscop

Chiral and kryptoracemic Dy(III) complexes with field-induced single molecule magnet behavior

Two mononuclear Dy(III) compounds formulated as [Dy(PNO)6(H2O)2]Br3 (1) and [Dy(PNO)6(NO3)](ClO4)2 (2) have been synthesized and characterized. Single crystal X-ray diffraction studies show that chiral and kryptoracemic strcuctures are formed when different anions are introduced into the system. 1 crystallizes in the non-polar orthorhombic space group P212121, whereas 2 assembles as a kryptoracemate in the polar monoclinic space group P21. The optical activity of single crystals of these two compounds was confirmed by circular dichroism (CD) studies. Thermal gravimetric analyses (TGA) revealed that they are stable up to 376 K (1) and 428 K (2). Differential scanning calorimetry (DSC) measurements demonstrate the absence of structural phase transitions over the investigated temperature range. Magnetic studies show that both compounds are field-induced single molecule magnets (SMMs) with energy barriers of 36 (± 0.8) K for 1 and 32 (± 1.4) K for 2. Furthermore, the dielectric and ferroelectric properties of compound 2 were also investigated

Thieme chemistry journal awardees - Where are they now? Stabilisation of porphyrins in tetranucleotide-bisporphyrin arrays by duplex formation with peptide nucleic acid

UV irradiation of porphyrins in tetranucleotide-bisporphyrin arrays in organic solvents leads to selective bleaching of diphenyl porphyrins but not of tetraphenyl porphyrins. This was shown by absorbance and CD spectroscopy. The diphenyl porphyrin can be stabilised by duplex formation with a complementary PNA strand. These arrays are versatile building blocks for the synthesis of potential electronic arrays using a DNA scaffolding approach.<br/

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

Synthesis and Spectroscopic Properties of Porphyrin-Substituted Uridine and Deoxyuridine

A general synthetic route to porphyrin-substituted uridine and 2'-deoxyuridine using Sonogashira coupling with acetylene porphyrins is presented. Both diphenyl and tetraphenyl porphyrins, as free base or zinc metallated, can be attached to the nucleobase. Selective TBDMS protection of the deoxyribose does not affect the coupling reaction. The substituents on the porphyrins render the conjugates soluble either in organic solvents (carboxy esters) or in water (carboxylates). No electronic communication between the chromophore and the nucleobase occurs, as indicated by UV/Vis spectroscopy. In aqueous solution, the absorption of the porphyrins is substantially lower than in organic solvents

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

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

Syndrômes coronariens aigus et diabète

STRASBOURG-Medecine (674822101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF