A theoretical investigation of internal conversion in 1,2-dithiane using non-adiabatic multiconfigurational molecular dynamics

Abstract

Non-adiabatic multiconfigurational molecular dynamics simulations have revealed a molecular "Newton's Cradle" that activates on absorption of light in the mid-UV and assists the S/S internal conversion process in 1,2-dithiane, protecting the disulfide bond from photodamage. This communication challenges contemporary understanding of the S/S internal conversion process in 1,2-dithiane and presents a classically-intuitive reinterpretation of experimental evidence.

Putting the Disulfide Bridge at Risk: How UV‐C Radiation Leads to Ultrafast Rupture of the S‐S Bond

“…The motion that leads to specific deactivation of an excited state via a specific degree of freedom in one case is hindered in another because the specific activation has taken place with too much vibrational energy. Our findings here are consistent with the results of Wan et al . who show that evolution of the wavepacket on the excited state surface can involve trajectories with S−S distances that are very long (up to 8.5 Å), whereby the disulfide moiety is destroyed.…”

UV-Photochemistry of the Disulfide Bond: Evolution of Early Photoproducts from Picosecond X-ray Absorption Spectroscopy at the Sulfur K-Edge

“…It will also be interesting to build upon our findings and devise small protein systems with disulfide bonds in well-defined configurations to study the sulfur photochemistry for ambient protein conditions and connect to work such as recent time-resolved mass spectrometry (TRMS) and nonadiabatic multiconfigurational molecular dynamics studies of model disulfide compounds. − These studies indicate that structural restrictions render disulfide bonds in proteins more stable because the photogenerated radicals remain in the vicinity of each other to geminately recombine. For instance, the restoration of the disulfide bond in the model system 1,2-dithiane takes place within picoseconds via an internal conversion process. , For comparison, this time scale is slower than excited state quenching in some DNA sequences − but comparable if not faster than that of intramolecular vibrational energy redistribution (IVR). The latter would allow the carbon backbone of the protein to move the two radicals away from each other resulting in an alteration of the tertiary structure.…”

“…The latter would allow the carbon backbone of the protein to move the two radicals away from each other resulting in an alteration of the tertiary structure. Comparison of these findings for the cyclic disulfide 1,2-dithiane with the linear diethyl disulfide (DEDS) further points toward the relative photostability of the disulfide bonds in proteins arising from a structural property that spatially confines the sulfur radical and permits efficient energy dissipation. , The disulfide bond may therefore act as radiation shield in proteins, protecting the integrity of the proteins tertiary structure by absorption of harmful radiation and benign dissipation of energy by ultrafast radical recombination and subsequent vibrational energy redistribution …”

“…For instance, the restoration of the disulfide bond in the model system 1,2-dithiane takes place within picoseconds via an internal conversion process. 54,55 For comparison, this time scale is slower than excited state quenching in some DNA sequences 56−58 but comparable if not faster than that of intramolecular vibrational energy redistribution (IVR). The latter would allow the carbon backbone of the protein to move the two radicals away from each other resulting in an alteration of the tertiary structure.…”

A molecular perspective on Tully models for nonadiabatic dynamics

“…1b). As examples of this category, one can mention molecules having coupled electronic states with different characters close in energy (4-N,N 0 -dimethylaminobenzonitrile, DMABN, see below), or molecules suffering photodissociation with electronic states getting close in energy, stimulating multiple crossings (see for example 1,2-dithiane 62 ). Another possible outcome of a nonadiabatic dynamics can be observed when a molecule hits a sloped conical intersection with a specific topography.…”