Radiationless Auger‐Like Electronic Transitions in Biomolecules: Bio‐Auger Process

AbstractNonradiative relaxation process caused by the interaction between electrons in biomolecules following radiative absorption is discussed herein. The process is akin to Auger transitions in atoms to fill K, L, or M shell vacancies. Such Auger transitions in light elements are much faster than the radiative transition rate, and half‐lives could be in femtoseconds, as observed in many recent biomolecules being exposed to laser beams. After a brief introduction, the basic theory of Auger and electromagnetic transitions in atomic systems and the calculations based on that indicating dominance of the Auger process over the radiative one are presented in Section 2.2. The similarity and differentiation between the Auger process in atomic systems and similar ones in biomolecules, termed asBio‐Auger processes, are presented in Section 2.3. The single orbital theory and the estimate of the timescale associated with Bio‐Auger processes are noted in Section 2.4, followed by a section on charge or electronic transfer associated with the Bio‐Auger process. In the last section, experimental evidence of the occurrence of the Bio‐Auger process after biomolecules are exposed to ultraviolet (UV) radiation is presented. In particular, calculations indicating the occurrence of electronic excited states in the energy range of UV radiation are noted. It is pointed out that (i) nonradiative transitions of Bio‐Auger type might be preventing cancer in biotissues exposed to the UV part of solar radiation; (ii) dark structures reported in exposing biomolecules to laser beam are electronic charge transfer; (iii) Bio‐Auger processes may lead to charge transfer of electrons from peridinin to chlorophyll‐ain peridinin‐chlorophyll‐a protein (PCP) complex; and (iv) Bio‐Auger processes lead to de‐dimerization of thymine duplex formed in UV activated thymine bases in DNA as it comes in contact with optically activated cofactor riboflavin.