In CD, α-helix has positive peak at:
Canonical α-helix CD displays characteristic negative minima at about 208 nanometers from exciton-split pi to pi-star parallel transition and at 222 nanometers from n to pi-star transition, accompanied by intense positive maximum near 190-193 nanometers. Positive peaks at 208 and 222 nanometers contradict established chiroptical signature; those wavelengths correspond to negative troughs whose mean residue ellipticity quantifies helical fraction in denaturation studies. Understanding correct sign and wavelength assignment allows monitoring helix-coil transitions, pH denaturation or ligand-induced stabilization during thermal or chemical unfolding experiments using circular dichroism.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.