Cationic Porphyrins With Large Side Arm Substituents As Resonance Light Scattering Ratiometric Probes For Specific Recognition Of Nucleic Acid G-quadruplexes

G-quadruplexes are noncanonical nucleic acid secondary structure formed by guanine(G)-rich DNAs or RNAs.Since genomic sequences with G-quadruplexforming potential are widely found in many important regions of human genome and increasing evidences reveal that G-quadruplex formation in these regions is closely related with some crucial biological functions,G-quadruplexes represent promising targets for development of new anticancer drugs.Specific G-quadruplex-probing is also crucial for both biological sciences and biosensing applications.Most reported probes are focused on fluorescent or colorimetric recognition of G-quadruplexes.Herein,for the first time,we reported a new specific G-quadruplex-probing technique——resonance light scattering(RLS)-based ratiometric recognition.Four water soluble cationic porphyrin derivatives,including an unreported octacationic porphyrin,with large side arm substituents were synthesized and developed as RLS probes.By testing these four water soluble cationic porphyrins,we demonstrated that these four RLS probes showed their individual best performance at different pH values,highlighting the important roles of side arm substituents.Combing these four RLS probes makes specific G-quadruplex recognition in the important physiological pH range of 7.4-6.0 become possible.These RLS probes were demonstrated to work well for ratiometric recognition of G-quadruplexes with high specificity against singleand double-stranded DNAs,including long double-stranded ones.RLS probe as an important member in G-quadruplex probe family,thus providing a useful tool for studies on G-quadruplex-related events concerning G-quadruplex formation,destruction and changes in size,shape and aggregation.Since the tested porphyrin derivatives can simultaneously provide three ways(UV-vis absorption,fluorescent and RLS)to specifically recoginize G-quadurplexes,we can apply a statistical method——linear discriminant analysis(LDA)to achieve a quantifiable discrimination of Gquadruplexes from ss DNAs and ds DNAs.The working mechanism was speculated to be based on the RLS signal changes caused by porphyrin protonation that was promoted by the end-stacking of porphyrins on G-quadruplexes.As a proof-of-concept example of applications,the RLS probes were demonstrated to work well for label-free and sequence-specific sensing of Micro RNA.This work adds an important member in G-quadruplex probe family,thus providing a useful tool for studies on G-quadruplex-related events.A new porphyrin derivative with eight positive charges was synthesized and characterized.Thus,this work also provides a simple and useful way for the preparation of cationic porphyrins with high charges.