Synthesis and Circular Dichroism of Tetraarylporphyrin−Oligonucleotide Conjugates

Abstract

The preparation and circular dichroic (CD) studies of self-complimentary 8-mer DNA sequences with a porphyrin at the 3' end are presented. Electronic interaction between the two porphyrins (the interchromophoric distance is in the range of 28-40 A), attached to both ends of the double-stranded helix, gives rise to a long-range exciton-coupled CD in the visible region (400-450 nm). The porphyrin chromophores act as sensitive probes of geometrical changes in the DNA backbone and sensitively reflect the double-strand to single-strand transition. This study demonstrates the possibility of using exciton-coupled porphyrin CDs for conformational studies of DNA.

Significantly Enhanced DNA Thermal Stability Resulting from Porphyrin H‐Aggregate Formation in the Minor Groove of the Duplex

“…This negative CD exciton couplet (À/+ pattern) indicates the anticlockwise orientation of the transition dipoles of the porphyrins (Figure 4). [8,13,14] The flipping be- haviour was confirmed by the different CD profiles in the region of the Soret band for duplexes 11 and 12. Molecular modelling shows that in the nonflipped structures there is a clockwise orientation of the porphyrins' transition dipoles, which should provide a positive CD exciton couplet (+/À pattern).…”

“…[4] Covalent attachment of porphyrin moieties to DNA has been achieved by using a variety of methodologies, including: the modification of nucleobases, [5][6][7][8] ribofuranose residues, [9][10][11][12][13] phosphate backbone [14][15][16] and by using acyclic linkers. [17,18] This provides structures that have porphyrin residues as 3'-or 5'-molecular caps, [12,[18][19][20] thus introducing them instead of a nucleobase in the middle of the helix [17] or as a label in the minor [10,16] and major [6][7][8] grooves.…”

Vibrational and electronic circular dichroism study of the interactions of cationic porphyrins with (dG‐dC)10and (dA‐dT)10

“…with positive and negative bands of the same magnitude, are characteristic of the dipole-dipole through-space electronic interaction. 9,14,40 This bisignate pattern changed its sign in comparison with the signal for the 10/1 molar ratio. This change of the spectral pattern may indicate that the conformational change from right-handed to left-handed occurred.…”

“…9 Both UV and Soret regions were used in the ECD studies of bound porphyrin-oligonucleotide conjugates. [10][11][12][13][14] It has been shown that the CD signal of the porphyrin part of the conjugate can serve as a probe of the oligonucleotide conformation and its variation, e.g. the B-Z transitions.…”

A Cationic Zinc Porphyrin as a Chiroptical Probe for Z‐DNA

“…They have been covalently linked to specific chiral sequences, and their CD spectral properties have been used to resolve complicated stereochemical issues [12][13][14][15] as well as monitor polynucleotide dynamics. [16] Also, the noncovalent interactions of cationic or anionic water-soluble achiral porphyrins with chiral templates have been exploited to build supramolecular species to detect and/ or amplify the handedness of the matrix. [17,18] Achiral cationic porphyrins are indeed good candidates as noncovalent probes for right-and left-handed DNA.…”