Simultaneous Binding ofmeso-Tetrakis(N-methylpyridinium-4-yl)porphyrin and 4‘,6-Diamidino-2-phenylindole at the Minor Grooves of Poly(dA)·poly(dT) and Poly[d(A−T)₂]:  Fluorescence Resonance Energy Transfer between DNA Bound Drugs

Abstract

The spectral properties of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) bound to poly(dA).poly(dT) and poly[d(A-T)(2)] in the presence and in the absence of 4',6-diamidino-2-phenylindole (DAPI) have been studied. DAPI fits deeply into the minor groove of both poly(dA).poly(dT) and poly[d(A-T)(2)], and TMPyP is also situated at the minor groove. The nature of the absorption, circular dichroism (CD), and flow linear dichroism (LD) spectra of the TMPyP-poly(dA).poly(dT) and -poly[d(A-T)(2)] complexes in the Soret band is essentially unaffected whether the minor groove is blocked by DAPI or not, although small variations been noticed in the presence of DAPI. Furthermore, a close analysis of the reduced LD spectrum in the Soret band results in angles of approximately 80 degrees and 55 degrees between transition moments of the TMPyP and DNA helix axes in the absence of DAPI. All these observations indicate that the side of TMPyP whose structure resembles that of classical minor groove binding drugs does not fit deeply into the minor groove. This suggests that TMPyP binds across the minor groove: two positively charged pyridiniumyl rings interact electrostatically with negatively charged phosphate groups of DNA. When DAPI and TMPyP are simultaneously bound to poly(dA).poly(dT) or poly[d(A-T)(2)], the fluorescence intensity of DAPI decreases as TMPyP concentration increases, indicating that the excited energy of DAPI is transferred to TMPyP.

DNA Mediated Energy Transfer from 4',6-Diamidino-2-phenylindole to tetra- and bis-cationic Porphyrins at Low Binding Densities

“…[20][21][22][23][24][25][26][27][28][29] Generally, the emission energy level of a donor molecule coincides with the absorption energy level of the acceptor, in the DNA mediated excited energy transfer, thus, is resonance energy transfer (RET) type in its nature. The excited energy of 4',6-diamidino-2-phenylindole (DAPI, Figure 1) has been reported to transfer to DNA intercalating [Ru (1,10-…”

“…The intercalating acceptor meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP, Figure 1) facilitates more efficient energy transfer from DAPI than that predicted by the "sphere of action model". 28,29 Important factors that affect the efficiency of RET include spectral overlap and the relative orientation of the donor and the acceptor molecules.…”

Energy Transfer from Ethidium to Cationic Porphyrins Mediated by DNA and Synthetic Polynucleotides at Low Binding Densities

“…The efficiency of the energy transfer from DAPI is far higher than predicted by the "sphere of action model" when meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (hereafter referred to as TMPyP, Figure 1) is used as an acceptor. 28,29 However, fluorescence quenching with cis-bis(N-methylpyridinium-4-yl)porphyrin (hereafter referred BMPyP, Figure 1), which stacks along DNA and poly[d(A-T) 2 ], 33,34 is less efficient than with TMPyP. For both TMPyP and BMPyP, the concentration of DAPI was high enough to saturate the minor groove of the DNA.…”

“…[20][21][22][23][24][25][26][27][28][29] In general, the emission energy level of the donor molecule coincides with the absorption energy level of the acceptor in the DNA mediated excited energy transfer. Therefore, its mechanism is believed to be mainly a Förster type resonance energy transfer.…”

“…Therefore, its mechanism is believed to be mainly a Förster type resonance energy transfer. [20][21][22][23][24][25][26][27][28][29] The excited energy of 4',6-diamidino-2-phenylindole (DAPI) has been reported to be transferred to DNA intercalating [Ru(1,10-phenanthroline) 2 dypyrido[3,2-a:2',3'-c]phenazine]…”