A zwitterionic 1D/2D polymer co-crystal and its polymorphic sub-components: a highly selective sensing platform for HIV ds-DNA sequences

Abstract

Polymorphic compounds {[Cu(dcbb)₂(H₂O)₂]·10H₂O}_n (2, 1D chain), [Cu(dcbb)₂]_n (3, 2D layer) and their co-crystal {[Cu(dcbb)₂(H₂O)][Cu(dcbb)₂]₂}_n (4) have been prepared from the coordination reaction of a 2D polymer [Na(dcbb)(H₂O)]_n (1, H₂dcbbBr = 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium bromide) with Cu(NO₃)₂·3H₂O at different temperatures in water. Compounds 2–4 have an identical metal-to-ligand stoichiometric ratio of 1 : 2, but absolutely differ in structure. Compound 3 features a 2D layer structure with aromatic rings, positively charged pyridinium and free carboxylates on its surface, promoting electrostatic, π-stacking and/or hydrogen-bonding interactions with the carboxyfluorescein (FAM) labeled probe single-stranded DNA (probe ss-DNA, delineates as P-DNA). The resultant P-DNA@3 system facilitated fluorescence quenching of FAM via a photoinduced electron transfer process. The P-DNA@3 system functions as an efficient fluorescent sensor selective for HIV double-stranded DNA (HIV ds-DNA) due to the formation of a rigid triplex structure with the recovery of FAM fluorescence. The system reported herein also distinguishes complementary HIV ds-DNA from mismatched target DNA sequences with the detection limit of 1.42 nM.