3,3′-Diethylthiatricarbocyanine Iodide: A Highly Sensitive Chiroptical Reporter of DNA Helicity and Sequence

Jung Kyu Choi,Murtaza Shabbir-Hussain,Mitch Trauernicht,Andrea E Holmes,Milan Balaz,Alessandro D’Urso

doi:10.3390/ijms12118052

Jung Kyu Choi, Murtaza Shabbir-Hussain + Show 4 more

Open Access

https://doi.org/10.3390/ijms12118052

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Abstract

Using UV-vis absorption and circular dichroism (CD) spectroscopies, we explored the binding interactions of 3,3′-diethylthiatricarbocyanine iodide (Cy7) with polynucleotides of different sequences and helicity. CD showed to be a very diagnostic tool giving different spectroscopic chiroptical signatures for all explored DNA sequences upon Cy7 binding. Cy7 was able to spectroscopically discriminate between the right handed B-DNA of poly(dG-dC)2 and its left handed Z-DNA counterpart induced by spermine or Co(III)hexamine via nearly opposite induced circular dichroic signal.

Highlights

Cyanine dyes represent an important class of chromophores due to their favorable optical properties, such as high extinction coefficients and fluorescence [1]
Binding of the achiral dyes to the chiral DNA helix can result in an induced circular dichroism (ICD) in the absorption spectrum of the dye (500–900 nm)
Titration of Cy7 into a solution of alternating adenine-thymine polynucleotide poly(dA-dT)2 resulted in a significant increase of intensity at 650 nm and 750 nm which was accompanied by the shift of the absorption maxima to a longer wavelength

Summary

Introduction

Cyanine dyes represent an important class of chromophores due to their favorable optical properties, such as high extinction coefficients and fluorescence [1]. Their highly conjugated structure results in a small HOMO-LUMO gap and red shifted absorbance and fluorescence [2,3]. Binding of the achiral dyes to the chiral DNA helix can result in an induced circular dichroism (ICD) in the absorption spectrum of the dye (500–900 nm). The absence of an ICD was explained by the ineffective, non-coupled orientation of Cy5 upon DNA binding [13]. Cy7, we have selected three polynucleotide sequences allowing us to access four DNA duplexes that differ in nucleobase sequence and helicity: (i) the B-form of poly(dA-dT); (ii) the B-form of poly(dC).poly(dG); (iii) and (iv) the B- and Z-forms of poly(dG-dC)

Results and Discussion

Experimental Section

Conclusions