Photoprocesses of Naphthalene Imide and Diimide Derivatives in Aqueous Solutions of DNA

Abstract

Despite the growing number of redox-active chromophores utilized to photoinduce oligonucleotide cleavage, detailed correlations between the degree of ground-state complexation and product yields have not been developed. To elucidate the specific role of singlet and triplet excited states in nucleotide photooxidation, the photochemical reactivities of N-(2-(N-pyridinium)ethyl)-1,8-naphthalene imide (NI) and N,N‘-bis-[2-(N-pyridinium)ethyl]-1,4,5,8-naphthalene diimide (NDI) with calf-thymus DNA have been explored as a function of ground-state complexation with the DNA polymer. Upon addition of calf-thymus DNA to a phosphate buffered solution of the naphthalene imide derivatives, distinct changes in the UV absorption spectrum of the chromophores, along with single isosbestic points, are observed. Analysis of these changes using the noncooperative model of McGhee and von Hippel yield association constants of (2.46 ± 0.42) × 104 M-1 and (7.78 ± 0.11) × 105 M-1 for NI and NDI, respectively. Pulsed 355 nm excitation of either NI or NDI in the presence of calf-thymus DNA produced the reduced NI•- and NDI•- species that absorbed maximally at 400 and 480 nm, respectively, from the triplet excited states. For both compounds, the yield of radical anion from self-quenching processes was substantial (φI •- = 0.11 ± 0.01 and 0.25 ± 0.01 for NI and NDI, respectively). However, pulsed excitation of NI in the presence of DNA resulted in the production of radical species that were not attributed to self-quenching processes. For both compounds, the fraction of associated imide was systematically varied between 0 and 1. The intersystem crossing yield was found to decrease linearly with the fraction bound to DNA from 0.71 to 0.08 for NI and 0.35 to 0.004 for NDI.

Unexpected DNA binding properties with correlated downstream biological applications in mono vs. bis-1,8-naphthalimide Ru(ii)-polypyridyl conjugates

“…40 However, in the absence of electron transfer from a suitable nucleotide the decrease in intensity may also arise due to disruption of energy transfer from the naphthalimide to the metal centre due to the presence of the DNA environment as observed in the excitation spectrum ( Fig. S13 ESI †).…”

“…[30][31][32][33][34][35][36][37][38] Such structures have tuneable electronic properties, and have been shown to exhibit good DNA binding affinity through either intercalation or groove binding. [39][40][41][42][43][44] In addition to being effective DNA intercalators or groove binders, the 1,8-naphthalimides can also act as sensitising antenna for the Ru(II)-based metal-to-ligand charge transfer (MLCT) emission, allowing for the population of the excited state using two excitation channels. 45 Herein, we present two new DNA targeting Ru(II) com- DNA in a cooperative manner, 38 and potentially enhance cellular uptake.…”

Direct observation of hole transfer through double-helical DNA over 100 Å

“…Photophysical and redox properties for NI, PTZ, and nucleobases have been established (39)(40)(41)(42). From the reduction potential of Ϫ1.0 V (vs. normal hydrogen electrode) for NI and the excitation energy of 3.4 eV for NI in the singlet excited state ( 1 NI*), reduction potential of 1 NI* is calculated to be 2.4 eV.…”

Photosensitized one-electron oxidation of DNA

“…In contrast, no transient absorption spectrum was observed for the hairpin ODN possessing only NDI, suggesting that the PTZ worked as a hole trap to inhibit the charge recombination process between NDI ؒ-and A ؒ+ , and that A-hopping occurs very fast within the pulse duration of 5 ns. Unfortunately, we could not distinguish the transient absorption of PTZ ؒ+ from that of NDI ؒ-because the molar extinction coefficient of the PTZ ؒ+ (1 × 10 4 M -1 cm -1 at 520 nm) [20] is much smaller than that of NDI ؒ-(1 × 10 5 M -1 cm -1 at 495 nm) [19]. Thus, NDI ؒ-in the charge-separated state was mainly observed in the transient absorption measurement.…”

“…3a). This transient absorption spectrum was assigned to NDI ؒ-of NDI ؒ--A 5 -PTZ ؒ+ [19], demonstrating the charge separation process via the A-hopping. In contrast, no transient absorption spectrum was observed for the hairpin ODN possessing only NDI, suggesting that the PTZ worked as a hole trap to inhibit the charge recombination process between NDI ؒ-and A ؒ+ , and that A-hopping occurs very fast within the pulse duration of 5 ns.…”