Action spectra of chiral secondary structure Mass spectra of DNA complexes photoreduced with polarized light reveal their handedness

Louis Pasteur has particular resonance in the midst of the coronavirus disease 2019 (COVID-19) pandemic, given his work on the germ theory of disease that led to the development of vaccines for rabies and anthrax. Some years before these better-known discoveries, Pasteur had already made a great contribution to science with his observation of molecular chirality in crystals (1). Chirality is a fundamental property of molecular asymmetry, which in turn dictates the secondary structure of proteins and gives rise to handedness in DNA helices. Some 170 years later, on page 1465 of this issue, Daly et al. (2) present a new method, mass-resolved electronic circular dichroism (CD) ion spectroscopy, that allows the chirality of secondary structures—in this case, isolated guanine-rich DNA quadruplexes—to be unambiguously defined.