I am using circular dichroic spectrum to analysis the changes in the ctDNA structure. The only obvious phenomenon was the change of a positive peak at 185-195nm. However, this wavelength range seems to have not been paid much attention in most studies. I only found this comment: "The intense positive CD band between 180 and 190 nm is characteristic of right-handed helicity" in a classic paper Determination of the Conformation of Nucleic Acids by Electronic CD. The redshift and reducing of the peak at this range mean what to DNA? Especially when the other DNA characteristic peaks (like ~275 nm) were stable.