Structure of methylene blue–DNA complexes studied by linear and circular dichroism spectroscopy

Abstract

SynopsisBradley et al. [(1972) Biopolyrners 11,645-6521 used electro-optical measurements to show that methylene blue (MB), like acridine orange, in its DNA complex is oriented more or less perpendicular to the helix axis as expected if intercalated. High-precision flow linear dichroism (LD) here confirms that MB is coplanar with the DNA bases at low dyeDNA binding ratios and low ionic strengths. CD shows two origins of induced optical activity for the transition of lowest energy (polarized parallel to the long-axis of the dye molecule): a t low binding ratios (r < 0.05), a weak monomeric CD with the same shape as the absorption curve is observed, while at higher binding ratios, a strong exciton CD dominates due to interaction between pairs of MB ligands. The monomeric CD spectrum shows a remarkable dependence on ionic strength: it is negative in the absence of extra salt, but changes sign (at ca 20 mM NaCl or 0.15 mM MgC12) and becomes essentially the positive mirror-image spectrum at high ionic strengths (>300 mM Na+ or >0.4 mM Mg2+). Nondegenerate coupled-oscillator theory can explain the CD in terms of interactions of transition moments of the dye and the nearest nucleotide bases and indicates a change between two intercalation geometries: a Lerman type of mode, denoted y-, and an orthogonal mode, denoted y+. This rotation of MB in the base-pair pocket is accomplished at Na+ and Mg2+ concentrations when the phosphates are effectively screened and the result suggests a more localized bonding of Mg2+ than is expected from simple polyelectrolyte models. The exciton effect at high binding ratios, observed both in CD and in LD, can be interpreted in terms of an interaction between an intercalated and a nonintercalated MB. The geometry of this "accidental" dimer is consistent with a location of the nonintercalated MB in the minor groove, bridging the strands by the positively charged amino groups directed towards phosphate groups. The dihedral angle of the MB pairs, corresponding to a left-handed helix, is opposite to that with acridine orange and proflavine on DNA, indicating that the latter ligands bind t o DNA in a different way.

Structures, spectra, and DNA-binding properties of mixed ligand copper(II) complexes of iminodiacetic acid: The novel role of diimine co-ligands on DNA conformation and hydrolytic and oxidative double strand DNA cleavage

“…7B) indicates that the complex exhibits a mode of DNA binding different from 1 and 3. It is possible that upon interaction with 2 the B-DNA transforms into an A-like conformation [64,65]. The shift in the positive ellipiticity band from 274 to 290 nm supports this type of transformation.…”

Study on the interaction between doxorubicin and Deoxyribonucleic acid with the use of methylene blue as a probe

“…[22][23][24][25][26] Most studies have indicated that at low ionic strength buffer and low concentration of DNA, the major binding mode of MB with DNA is through intercalation. 24,27 Moreover, MB has a low toxicity. Data from material safety data sheet of Vanderbilt Environmental Health & Safety (VEHS) show that MB is slightly hazardous in case of skin contact, eye contact, ingestion, inhalation and no evidence shows that MB is a carcinogenic compound.…”

Study on the interaction between morin-bi(III) complex and DNA with the use of methylene blue dye as a fluorophor probe

“…[26][27][28][29][30] Most studies indicated that (at low ionic strength buffer and low concentration of DNA) the major binding mode of MB with DNA was through intercalation. [28][29][30][31] Moreover, MB has a low toxicity; data from material Safety Data Sheet of Vanderbilt Environmental Health & Safety (VEHS) show that MB is slightly hazardous in case of skin contact, eye contact, ingestion, and inhalation but there is no evidence which shows that MB is a carcinogenic compound. 32 We were interested in understanding the correlation between different antitumour activities of morin and its complexes with the DNA binding mode and its affinity.…”