Photophysical properties of N-alkylated azahelicene derivatives as DNA intercalators: counterion effects

Abstract

In this work, three compounds having the same organic moiety (N-methyl-5-azahelicenium salts) but different counterions (I-, NO3- and COOCF3-) have been investigated in buffered aqueous solutions and in the presence of DNA to give information on the counterion effects on the binding. In particular, the absorption spectra, fluorescence quantum yields and fluorescence lifetimes in aqueous solution for free organic molecules have been determined by steady-state and time-resolved spectrofluorimetric measurements. The obtained values are compared with those of the chromophores in the presence of increasing concentrations of DNA. The results allow determination of the association constants (K(a)) and the number of base couples per chromophore molecule (n) by means of the McGhee Von Hippel model. The binding parameters are strongly affected by the nature of counterions since the highest K(a) value was determined for the compound having COOCF3-; on the other hand the NO3- derivative is able to interact with the highest number of binding sites. The morphology and structural properties of the DNA-chromophore complexes were investigated by circular dichroism (CD) and atomic force microscopy (AFM). The data revealed that I- and COOCF3- derivatives preferentially form intercalation complexes, while the NO3- salt is able to form intercalation and grove binding complexes at the same time.

Functionalization of nanostructured gold substrates with chiral chromophores for SERS applications: The case of 5‐Aza[5]helicene

“…In addition to SERS, we have also investigated the fluorescence behavior of the helicene‐functionalized plasmonic substrates, motivated by the appealing photophysical properties reported for these systems . As shown in Figure , by adopting a second experimental setup, with exciting laser radiation within the visible range (458 nm), we can collect the fluorescence originating from the helicene layer anchored on the gold surface, while no SERS peaks are observed.…”

“…In addition to SERS, we have also investigated the fluorescence behavior of the helicene-functionalized plasmonic substrates, motivated by the appealing photophysical properties reported for these systems. 22,23 As shown in Figure 6, by adopting a second experimental setup, with exciting laser radiation within the visible range (458 nm), we can collect the fluorescence originating from the helicene layer anchored on the gold surface, while no SERS peaks are observed. This happens because the 458-nm excitation lies far away from the plasmon resonance of the gold substrates, which have been optimized for SERS action with 785-nm excitation, 43,44 while being able to excite the 5-aza [5]helicene moiety, enabling the fluorescence peak observed at 517 nm ( Figure 6).…”

“…They may find useful applications in the biotechnological field as enantioselective fluorescent sensors because water‐soluble quaternary N ‐methyl[5]helicenium salts have been extensively tested for DNA binding, showing the ability to chromatically distinguish different subcellular compartments and to follow the cell uptake process . Interestingly, N ‐methyl[5]helicenium iodide, despite its fluorescence, displays a strong SERS activity in ordinary Lee‐Meisel silver colloids, as illustrated in Figure . Actually, N ‐methyl‐5‐aza[5]helicenium iodide shows a fluorescence emission peak at 503 nm, with 270‐nm excitation line, but the presence of the colloids enables fluorescence quenching, thus allowing the measurement of an intense SERS signal.…”

Dutch Resolution of a configurationally stable [5]helquat

“…14,15 Comparatively less studied are cationic helicenoids ( Figure 1). [16][17][18][19][20][21][22][23][24][25][26][27][28] Representative examples are heterohelicenium systems studied by Lacour group 20 or helical dications called helquats developed by our group. 23 These and similar cationic systems promise attractive range of properties and applications [29][30][31][32][33][34][35][36][37][38] that may be complementary to non-ionic helicenes.…”

Chiral Selectivity in the Binding of [4]Helicene Derivatives to Double‐Stranded DNA

“…Other molecules that belong to the helicene family have also been used to examine chiral selectivity. [9] For example, the P enantio-A C H T U N G T R E N N U N G mer of helicene, bearing a protonated amino group, displays structural selectivity for binding to DNA as it discriminates between B-and Z-DNA. [10] In the latter case, the binding mode was not determined.…”