We report a very selective and sensitive spectroscopic detection of Z-DNA embedded in B-DNA in condensed as well as non-condensed DNA using anionic Ni(II) meso-tetrakis(4-sulphonatophenyl)porphyrin, NiTPPS. A combination of micromolar concentrations of Ni(II) and spermine(4+) allowed us to prepare left-handed Z-DNA in short oligonucleotides without DNA condensation. A strong induced circular dichroism (ICD) signal was observed in the visible absorption region when NiTPPS was added to BZ DNA (Z-DNA fragment located at the end of a B-DNA tract with one B/Z DNA junction) and BZB DNA (Z-DNA sequence embedded in B-DNA having two B/Z DNA junctions). Almost no ICD signal was detected when NiTPPS was added to B-DNA. NiTPPS showed different binding modes with condensed and non-condensed Z-DNAs and allowed the distinction between condensed Z-DNA (positive bisignate CD couplet) and non-condensed Z-DNA (negative bisignate CD couplet). (C) 2012 Elsevier Inc. All rights reserved.
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