Resolution of complex mixtures of duplex and antiparallel triplex DNA structures by capillary electrophoresis and multivariate analysis.

Triplex DNA structures, which are formed by the addition of an extra strand to a target B-DNA duplex, have attracted increasing interest due to their analytical and therapeutic applications. These structures are classified into parallel and antiparallel, depending on the orientation of the Triplex-Forming Oligonucleotide (TFO) relative to the B-DNA duplex. Whereas the formation of parallel triplexes is easily detected by monitoring spectral changes in the UV region, the formation of antiparallel triplexes produces small or even no spectral variations, which makes their detection difficult and uncertain. In this study, we propose the use of capillary electrophoresis with ultraviolet absorption spectrophotometric (CE-UV) detection combined with the multivariate curve resolution-alternating least squares (MCR-ALS) chemometric method to analyse mixtures of DNA sequences capable of forming mixtures of B-DNA duplex and triplex antiparallel structures. Rapid and reproducible CE-UV analysis in hydroxypropylcellulose (HPC)-coated capillaries are done in a pH 7.4 buffer containing Mg(II) for the stabilization of the intermolecular species. Spectra measured from 220 to 300 nm along the CE-UV analysis of individual DNA strands and of their mixtures at different ratios are merged into an augmented data matrix. This is later analyzed with MCR-ALS to deconvolute characteristic pure spectra and electropherograms for each one of the CE-UV analysis considered. This procedure has allowed the resolution and detection of DNA species present in mixtures of DNA strands capable of forming duplexes, as well as antiparallel triplex structures.