2, ENS de Lyon, Lyon, , France
Studies of the interactions between dye molecules and nucleic acids and proteins are crucial for any applications of the dyes for imaging or manipulating biomolecules. The intercalation or groove binding lead to optical changes which can be used for monitoring the binding processes. Host-drugs complexation can be thus studied by numerous spectrophotometrical methods: UV-Vis absorption, fluorescence, circular dichroism and in some cases by nonlinear optical fluorescence response. Analysis of the induced spectral effects reveals considerable detail about the host-drug binding site size as well as thermodynamics of complex formation which is needed e.g. for efficient drug design.
A series of new photochromic aminoazobenzenes molecules was synthesized and their spectroscopic properties were determined. The kinetics of photoisomerisation in solvents of various polarity and viscosity was measured prior to the studies involving biomolecules. An important feature of the new aminoazobenzenes is high water solubility which is crucial for any biological applications. Moreover, the molecules showed fluorescent properties, unusual for this class of materials, and very interesting from the point of view of application as potential markers in biology . It has been found that the cis form of aminoazobenzene is thermally stable and the energy of activation (Ea) of the dark cis-trans reaction is 133 kJ/mol which is about 30% higher than that for unsubstituted azobenzene and results in 4 days of the thermal recovery of up to 50% of the trans form at room temperature.
A detailed description of the binding with salmon sperm DNA and Human Serum Albumin at physiological conditions (pH 7.25) was performed for a water soluble chromophore with star-shaped oligomeric arms, named Ant-PHEA and a similar molecule Ant-PIM. The results achieved by applying UV-vis absorption, fluorescence, Fourier transform infrared (FT-IR) and circular dichroism spectroscopy confirm that Ant-PHEA interacts mainly with the bases and the phosphate groups of DNA. The binding constants calculated at 298, 304 and 310K are 2.63x103, 2.70x103, and 4.67x103 L mol-1, respectively. The melting temperature (Tm) of the DNA and DNA-Ant-PHEA were determined . A significant increase of the two-photon induced fluorescence in the adducts was observed, especially with the detection of the non-canonical structures of DNA such as e.g. quadruplex DNA.
Fig.1 Ant-PHEA chemical structure
Funding from NCN HARMONIA grant UMO-2016/22/M/ST4/00275 is highly acknowledged.
 M. Deiana, Z. Pokladek, J. Olesiak-Bańska, P. Młynarz, M. Samoć, K. Matczyszyn, Scientific Reports 6 28605 (2016)
 M. Deiana, B. Mettra, K. Matczyszyn, D. Pitrat, J. Olesiak-Bańska, C. Monnereau, C. Andraud, M. Samoć, Biomacromolecules 17 (11), 3609-3618 (2016)