Ground-state interactions of spermine-substituted naphthalimides with mononucleotides

Cystine-derived bis-naphthalimides as stimuli-responsive fluorescent gelators

Stimuli-responsive fluorescence modulation of two cystine-derived bis-naphthalimide gelators was demonstrated using fluoride/tetrafluoroborate anions as the chemical inputs.

Unveiling the groove binding mechanism of a biocompatible naphthalimide-based organoselenocyanate with calf thymus DNA: an "ex vivo" fluorescence imaging application appended by biophysical experiments and molecular docking simulations

The present study embodies a detailed investigation of the binding modes of a potential anticancer and neuroprotective fluorescent drug, 2-(5-selenocyanato-pentyl)-6-chloro benzo[de]isoquinoline-1,3-dione (NPOS) with calf thymus DNA (ctDNA). Experimental results based on spectroscopy, isothermal calorimetry, electrochemistry aided with DNA-melting, and circular dichroism studies unambiguously established the formation of a groove binding network between the NPOS and ctDNA. Molecular docking analysis ascertained a hydrogen bonding mediated 'A-T rich region of B-DNA' as the preferential docking site for NPOS. The cellular uptake and binding of NPOS with DNA from "Ehrlich Ascites Carcinoma" cells confirmed its biocompatibility within tumor cells. Experimental and ex vivo cell imaging studies vividly signify the importance of NPOS as a potential prerequisite for its use in therapeutic purposes.

Synthesis and photophysical evaluation of a pyridinium 4-amino-1,8-naphthalimide derivative that upon intercalation displays preference for AT-rich double-stranded DNA

The synthesis, characterisation and solid state crystal structure of a cationic 4-amino-1,8-naphthalimide derivative (1) are described. The photophysical properties of 1 are shown to vary with the solvent polarity and H-bonding ability. The fluorescence of 1 is enhanced and blue-shifted in its 1:1 complex with 5'-adenosine-monophosphate while it is partially quenched and red-shifted in its complex with 5'-guanosine-monophosphate. Linear and circular dichroism measurements show that 1 binds to double-stranded DNA by intercalation. Comparative UV-visible and fluorescence studies with double stranded synthetic polynucleotides poly(dA-dT)(2) and poly(dG-dC)(2) show that 1 binds much more strongly to the AT polymer; 1 also has a strong preference for A-T rich sequences in natural DNA. Thermal denaturation measurements also reveal a much greater stabilisation of the double-stranded poly(dA-dT)(2) than of natural DNA.

Photophysical study of bis(naphthalimide)-amine conjugates: toward molecular design of excimer emission switching

The fluorescence properties of two bis(1,8-naphthalimides) with amino-containing spacers are investigated, giving special emphasis to the observation of excimer emission. It is found that a minor elongation of the spacer by two methylene units gives rise to a quantitative shut-down of the broad and red-shifted excimer emission. Furthermore, a switching of this emission is established through manipulation of a photoinduced electron transfer process, which involves the amino spacer. Protons as well as protic solvents lead to substantial excimer emission with lifetimes of 12 to 27 ns. The excimer quantum yield takes a maximum value of Φ(f) = 0.07 (acetonitrile with 1 equiv trifluoroacetic acid). The increased virtual Stokes shifts (ca. 150 nm) as compared to the fluorescence of monomeric 1,8-naphthalimides are an alternative approach to obtain colored, significant, and long-lived fluorescence from these chromophores. As an additional excited state pathway, the occurrence of homo-Förster resonance energy transfer (homo-FRET) is established by fluorescence polarization measurements and calculation of the corresponding critical Förster radius (R(0) ca. 13 Å). The average interchromophore distance between the naphthalimides is estimated as 7.5 Å and 9.5 Å for the dyad with the shorter and the longer spacer, respectively. These observations and the absence of a rise time component for excimer emission are in agreement with the formation of a "loose" ground state dimer, which upon excitation undergoes a fast geometrical adjustment to the excimer structure where the chromophores are at contact distance.

Sequence-dependent interactions of cationic naphthalimides and polynucleotides

The binding interactions of three naphthalimide derivatives with heteropoly nucleic acids have been evaluated using fluorescence, absorption and circular dichroism spectroscopies. Mono- and bifunctionalized naphthalimides exhibit sequence-dependent variations in their affinity toward DNA. The heteropoly nucleic acids, [Poly(dA-dT)]2 and [Poly(dG-dC)]2, as well as calf thymus (CT) DNA, were used to understand the factors that govern binding strength and selectivity. Sequence selectivity was addressed by determining the binding constants as a function of polynucleotide composition according to the noncooperative McGhee-von Hippel binding model. Binding affinities toward [poly(dA-dT)](2) were the largest for spermine-substituted naphthalimides (Kb = 2-6 x 10(6) M(-1)). The association constants for complex formation between the cationic naphthalimides and [poly(dG-dC)]2 or CT DNA (58% A-T content) were 2-500 times smaller, depending on the naphthalimide-polynucleotide pair. The binding modes were also assessed using a combination of induced circular dichroism and salt effects to determine whether the naphthalimides associate with DNA through intercalative, electrostatic or groove-binding. The results show that the monofunctionalized spermine and pyridinium-substituted naphthalimides associate with DNA through electrostatic interactions. In contrast, intercalative interactions are predominant in the complex formed between the bifunctionalized spermine compound and all of the polynucleotides.