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Determining the Serum Stability of Human Adenosine Deaminase 1 Enzyme
Published on: September 27, 2024
Deciphering low energy deactivation channels in adenine
Irene Conti1, Marco Garavelli, Giorgio Orlandi
1Dipartimento di Chimica G. Ciamician, Universita' di Bologna, Via F. Selmi, 2, 40126 Bologna, Italy.
Journal of the American Chemical Society
|October 23, 2009
Summary
The (1)L(a) state in 9H-adenine drives ultrafast decay, with other excited states not acting as intermediates. N(9)-H photocleavage is possible but rare, while N(10)-H bond breaking is hindered.
Area of Science:
- Photochemistry
- Quantum Chemistry
- Molecular Spectroscopy
Background:
- Adenine is a fundamental component of nucleic acids.
- Understanding excited-state dynamics is crucial for photobiology and photochemistry.
- Radiationless decay pathways govern the fate of excited molecules.
Purpose of the Study:
- To map the radiationless decay pathways of 9H-adenine in its lowest excited states.
- To elucidate the mechanisms behind the observed ultrafast biexponential decay.
- To investigate potential photocleavage pathways.
Main Methods:
- Computational chemistry using CASPT2//CASSCF level of theory.
- Mapping minimum energy paths (MEPs) for excited states.
- Analysis of conical intersections (CIs) and potential energy surfaces.
Main Results:
- The (1)L(a) state, responsible for strong absorption below 5 eV, decays monotonically along the puckering coordinate to a S(0)/(1)L(a) conical intersection.
- (1)npi* and (1)L(b) states relax to minima and require energy to reach CIs with the ground state (S(0)).
- The (1)L(a) state alone explains the observed biexponential decay, with other states not being significant intermediates.
Conclusions:
- The (1)L(a) state is the primary driver of 9H-adenine's ultrafast decay.
- N(9)-H photocleavage can occur following internal conversion from (1)L(a) to (1)pisigma(N9H)*, but with a low quantum yield.
- Photocleavage of the N(10)-H bond is energetically unfavorable due to a high barrier in the (1)pisigma(N10H)* state.
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