Comparison of magnetic properties of DNA-cetyltrimethyl ammonium complex with those of natural DNA

Abstract

We prepared the DNA-cetyltrimethyl ammonium complex, as well as the same complex intercalated with stable organic free radicals, and studied their magnetic properties by electron magnetic resonance (EMR) spectroscopy and by measuring the magnetization on a superconducting quantum interference device (SQUID). The UV-vis and CD spectra of DNA-quaternary alkyl ammonium complex (DNA−-Q+) in organic solvent clearly demonstrated that it retained the double helical B-form conformation. The interhelical spacing of double strand DNA (dsDNA) increased when the counter ions (Na+) of phosphate groups of the natural DNA were replaced with the long alkyl quaternary ammonium groups. The inter-helical distance of DNA-cetyltrimethyl ammonium (CTMA) was 39.1 A as confirmed by X-ray diffractometry. In general, the magnetization of the DNA-CTMA complex solid was found to be significantly lower than that of natural DNA. Moreover, intercalation of the complex with stable organic free radicals did not improve magnetization, which again was in marked contrast to natural DNA. EMR spectroscopic behavior of the complex in the solid state also was quite different from that of natural DNA: The unique broad EMR signal of natural DNA in the low field region with g-value greater than 10 disappeared in the DNA-CTMA complex.