Electron magnetic resonance and SQUID measurement study of natural A-DNA in dry state

We present electron magnetic resonance study on the magnetization of fibrous salmon sperm A-DNA in dry state. Appearance of a unusually broad signal around 500 G overlapped with a narrower signal at about 3000 G persisted over the whole temperature range of 4.5-300 K. The results are explained by assuming coexistence of an applied magnetic field-induced mesoscopic orbital magnetism associated with a long-range coherent transport in well ordered regions and a Pauli paramagnetism arisen from an incoherent hopping transport in disordered regions. In the molecularly ordered regions, the partial interbase hybridization of pi(z) orbitals along the double helix axis is envisaged, whereas it is inhibited in the disordered regions due to structural defects and conformational irregularities along the backbone of the duplex. The spins located in the former regions exhibit the g value greater than 10, while those in the latter regions exhibid the g value of about 2.0. dc magnetic behavior of the natural A-DNA observed by the SQUID measurements also supports the explanation by a temperature-independent S-shaped magnetization accompanied with a linear Pauli susceptibility. We learn from the experimental results and the proposed model that the charge carriers are coherently transported giving rise to a strong orbital magnetic moment in the ordered regions.