An exploration of the reactivity of singlet oxygen with biomolecular constituents

The thermal reaction between biomolecules and singlet oxygen (1O2) is important for rendering the genetic material within toxic cells inactive. Here we present results obtained from state-of-the-art multi-reference computational methods that reveal the mechanistic details of the reaction between 1O2 and two exemplary biomolecular systems: guanine (Gua) and histidine (His). The results highlight the splitting of the doubly degenerate 1Δg state of O2 upon complexation and the essentially barrierless potential energy profile of the thermally allowed cycloaddition reaction when the O2 molecule is in its lower energy 1Δg state.</p

Mechanistic Insights into Excited State Intramolecular Proton Transfer in Isolated and Metal Chelated Supramolecular Chemosensors

Mechanistic studies of the excited state intramolecular proton transfer in a series of related and progressively more complex supramolecular chromophores.</p

Fragmentation dynamics of the ethyl bromide and ethyl iodide cations: a velocity-map imaging study

The photodissociation dynamics of ethyl bromide and ethyl iodide cations (C2H5Br+ and C2H5I+) have been studied. Ethyl halide cations were formed through vacuum ultraviolet (VUV) photoionization of the respective neutral parent molecules at 118.2 nm, and were photolysed at a number of ultraviolet (UV) photolysis wavelengths, including 355 nm and wavelengths in the range from 236 to 266 nm. Time-of-flight mass spectra and velocity-map images have been acquired for all fragment ions and for ground (Br) and spin–orbit excited (Br*) bromine atom products, allowing multiple fragmentation pathways to be investigated. The experimental studies are complemented by spin–orbit resolved ab initio calculations of cuts through the potential energy surfaces (along the RC–Br/I stretch coordinate) for the ground and first few excited states of the respective cations. Analysis of the velocity-map images indicates that photoexcited C2H5Br+ cations undergo prompt C–Br bond fission to form predominantly C2H5+ + Br* products with a near-limiting ‘parallel’ recoil velocity distribution. The observed C2H3+ + H2 + Br product channel is thought to arise via unimolecular decay of highly internally excited C2H5+ products formed following radiationless transfer from the initial excited state populated by photon absorption. Broadly similar behaviour is observed in the case of C2H5I+, along with an additional energetically accessible C–I bond fission channel to form C2H5 + I+ products. HX (X = Br, I) elimination from the highly internally excited C2H5X+ cation is deemed the most probable route to forming the C2H4+ fragment ions observed from both cations. Finally, both ethyl halide cations also show evidence of a minor C–C bond fission process to form CH2X+ + CH3 products