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  • In this contribution herein we


    In this contribution, herein we report our newly devised molecular probes with a triazole linked benzimidazole-indole-thiazolium mixed heterocyclic framework as depicted in Scheme 1. Their architecture was designed to achieve the advancement in selectivity and specificity toward DNA matrix over RNA through the incorporation of structural complexity into the molecular framework. The probes were synthesized by easy accessible synthetic protocols (see Scheme 1 and supplementary material). The optical behavior of the structurally characterized probes in the presence of DNA and other bioanalytes was examined by bmn and emission spectroscopy under physiological conditions. Moreover, a careful structure–interaction relationship study supported by the molecular simulation analysis revealed that the structurally engineered crescent geometry of the probes was the governing factor for their strong interaction with DNA matrix [18], [19], [20], [21], [22]. Furthermore, the set of cellular investigations established the potent standing of RD2 as a probe of choice for long-term cellular investigations as well as cell-proliferation mimicking and micronuclei detection. Click reaction has become the most preferred smart chemical tool in recent times for functionalization of biomolecules [23]. However, we have successfully shown here that click reaction can be used to introduce crescent geometry through rational design into molecular architecture for enhancing biomolecular selectivity of optical probes.
    Results and discussions
    Conclusions Summarily, a ‘turn-on’ molecular probe RD2 with advanced selectivity toward DNA was developed by the incorporation of semilunar geometry through molecular complexity. The influence of the complex molecular architecture was established through a well-planned structure–interaction relationship study by developing a series of compounds (RD1–RD8). The probe RD2 was found the owner of admirable quantum efficiency, optical brightness (brightness=7600M−1cm−1), strong binding affinity (Ka=1.2×105M−1) and high sensitivity (LOD≈0.45μM) in the presence of DNA. The commendable optical response of RD2 encouraged us to evaluate its applicability in biological medium. Amazingly, the probe RD2 permeated the cell membrane without the assistance of any permeabilization agent and stained the nuclei of cells with high contrast. Moreover, the probe displayed admirable photostability inside the live cells causing negligible photoinduced cellular deterioration under continuous exposure of laser. The negligible cytotoxicity of RD2 together with its high photobleaching resistance and insignificant phototoxicity shed light on its encouraging candidature. Furthermore, the specific chromosomal staining together with the successful fluorescence based detection of cell-proliferation and micronuclei enlightened its futuristic applicability for cytogenetically induced anomalies. In sum, we have been able to integrate through a rational design the key features such as high photostability, negligible cytotoxicity and phototoxicity, good brightness, large Stokes shift and high selectivity toward DNA over RNA into the newly developed probe RD2. The aforementioned outcomes of solution and cellular examinations revealed the profitable value of RD2 over commonly used stains as a probe of choice witch could find a wide scope in the field of biomedical application and long-term investigations of cellular dynamics.
    Author contributions
    Acknowledgements Financial support was received from the Department of Science and Technology, India (Grant No. SERB/F/2408/2012-13). PG and AK are grateful to DST and CSIR for their fellowship. We thankfully acknowledge the Director, IIT Mandi for research facilities. Sophisticated instrument facility of Advanced Materials Research Center (AMRC), IIT Mandi, is thankfully acknowledged. We acknowledge Dr. Sougata Sinha and Dr. Sunil Kumar for their help in manuscript preparation.