We
analyze how the photorelaxation dynamics of a molecule can be
controlled by modifying its electromagnetic environment using a nanocavity
mode. In particular, we consider the photorelaxation of the RNA nucleobase
uracil, which is the natural mechanism to prevent photodamage. In
our theoretical work, we identify the operative conditions in which
strong coupling with the cavity mode can open an efficient photoprotective
channel, resulting in a relaxation dynamics twice as fast as the natural
one. We rely on a state-of-the-art chemically detailed molecular model
and a non-Hermitian Hamiltonian propagation approach to perform full-quantum
simulations of the system dissipative dynamics. By focusing on the
photon decay, our analysis unveils the active role played by cavity-induced
dissipative processes in modifying chemical reaction rates, in the
context of molecular polaritonics. Remarkably, we find that the photorelaxation
efficiency is maximized when an optimal trade-off between light–matter
coupling strength and photon decay rate is satisfied. This result
is in contrast with the common intuition that increasing the quality
factor of nanocavities and plasmonic devices improves their performance.
Finally, we use a detailed model of a metal nanoparticle to show that
the speedup of the uracil relaxation could be observed via coupling
with a nanosphere pseudomode, without requiring the implementation
of complex nanophotonic structures.
We report a novel example of electro‐mediated photoredox catalysis (e‐PRC) in the reductive cleavage of C(sp3)−O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E‐selective and can be made Z‐selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation, and catalyst structural variations reveal that our new naphthalene monoimide‐type catalyst allows for an intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity‐determining C(sp3)−O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions tolerate aryl chlorides/bromides and do not give rise to Birch‐type reductions.
Electrocatalytic
hydrogen production via transition metal complexes
offers a promising approach for chemical energy storage. Optimal platforms
to effectively control the proton and electron transfer steps en route
to H2 evolution still need to be established, and redox-active
ligands could play an important role in this context. In this study,
we explore the role of the redox-active Mabiq (Mabiq = 2–4:6–8-bis(3,3,4,4-tetramethlyldihydropyrrolo)-10–15-(2,2-biquinazolino)-[15]-1,3,5,8,10,14-hexaene1,3,7,9,11,14-N6) ligand in the hydrogen evolution reaction (HER). Using spectro-electrochemical
studies in conjunction with quantum chemical calculations, we identified
two precatalytic intermediates formed upon the addition of two electrons
and one proton to [CoII(Mabiq)(THF)](PF6) (CoMbq
). We further examined the acid strength effect
on the generation of the intermediates. The generation of the first
intermediate, CoMbq-H1
, involves
proton addition to the bridging imine-nitrogen atom of the ligand
and requires strong proton activity. The second intermediate, CoMbq-H2
, acquires a proton at the diketiminate
carbon for which a weaker proton activity is sufficient. We propose
two decoupled H2 evolution pathways based on these two
intermediates, which operate at different overpotentials. Our results
show how the various protonation sites of the redox-active Mabiq ligand
affect the energies and activities of HER intermediates.
D-ribose was administered orally or intravenously over at least 5 h to eight healthy volunteers and five patients with myoadenylate deaminase deficiency. Intravenous administration rates were 83, 167, and 222 mg/kg/h, which were well tolerated but oral administration of more than 200 mg/kg/h caused diarrhea. The average steady state serum ribose level ranged between 4.8 mg/100 ml (83 mg/kg/h, oral administration) and 81.7 mg/100 ml (222 mg/kg/h, intravenous administration). Serum glucose level decreased during ribose administration. The intestinal absorption rate of orally administered ribose was 87.8%-99.8% of the intake at doses up to 200 mg/kg/h without first pass effect. Urinary losses were 23% of the intravenously administered dose at 222 mg/kg/h. Ribose appeared to be excreted by glomerular filtration without active reabsorption; a renal threshold could not be demonstrated. The amount of ribose transported back from the tubular lumen depended on the serum ribose level. There was no difference in ribose turnover in healthy subjects and patients with MAD deficiency.
UV light can induce chemical reactions in nucleic acids and thereby damage the genetic code. Like all of the five primary nucleobases, the isolated RNA base uracil exhibits ultrafast, nonradiative relaxation after photoexcitation, which helps to avoid photodamage most of the time. Nevertheless, within RNA and DNA strands, commonly occurring photolesions have been reported and are often ascribed to long-lived and delocalized excited states. Our quantum dynamical study now shows that excited-state longevity can also occur on a single nucleobase, without the need for delocalization. We include the effects of an atomistic RNA surrounding in wave packet simulations and explore the photorelaxation of uracil in its native biological environment. This reveals that steric hindrance through embedding in an RNA strand can inhibit the ultrafast relaxation mechanism of uracil, promoting excited-state longevity and potential photodamage. This process is nearly independent from the specific combination of neighboring bases.
A 55 years old patient suffering from exercise-induced muscle pain and stiffness due to primary myoadenylate deaminase deficiency has been successfully treated with D-ribose since 1984: single doses of 4 grams administered at the beginning of exercise prevented the symptoms completely; on continuation of exercise this dose had to be repeated all 10-30 min. Total doses of 50-60 g per day were tolerated without side-effects.
Low doses of rasburicase are effective and cost-saving for prophylaxis and treatment of TLS. Application of an initial dose of 3-4.5 mg of rasburicase and subsequently dosage as needed, depending on UA levels, is feasible.
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