Phase transitions in DNA

Experiments on light absorption in DNA solutions in the region of 260 nm demonstrate specific multiple sharp oscillations of $\frac{\mathrm{dA}}{\mathrm{dT}}$ vs temperature $T$, $A$ being the optical density. A one-dimensional Ising model with a long-range polyspin interaction in an inhomogeneous "magnetic field" is used to present a quantitative description of these oscillations. An explicit analytical formula, derived in the paper, provides a surprisingly good agreement between the theory and experiments. It also alows one to obtain from these experiments important information about the sequence of the "magnetic fields," which represents the DNA component sequence. This is demonstrated by an example of a particular DNA. The long-range interaction in the Ising model implies a phase transition. Its nature is shown to depend crucially on well-defined properties of the DNA sequence.