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Chemistry (Weinheim An Der Bergstrasse,... Feb 2024Optical cavity/molecule strong coupling offers attractive opportunities to modulate photochemical or photophysical processes. When atoms or molecules are placed in an... (Review)
Review
Optical cavity/molecule strong coupling offers attractive opportunities to modulate photochemical or photophysical processes. When atoms or molecules are placed in an optical cavity, they can coherently exchange photonic energy with optical cavity vacuum fields, entering the strong coupling interaction regime. Recent work suggests that the thermodynamic and kinetic properties of molecules can be significantly changed by strong coupling, resulting in the emergence of intriguing photochemical and photophysical phenomena. As more and more physico-chemical systems are studied under strong coupling conditions, optical cavities have also advanced in their sophistication, responsiveness, and (multi)functionality. In this review, we highlight some of these recent developments, particularly focusing on Fabry-Perot microcavities.
PubMed: 37941155
DOI: 10.1002/chem.202303110 -
Selective and Functional-Group-Tolerant Photoalkylation of Imines by Energy-Transfer Photocatalysis.The Journal of Organic Chemistry Nov 2023Basic amines show broad bioactivity and remain a promising source of new medicines. The direct photoalkylation of imines offers a promising strategy for complex amines....
Basic amines show broad bioactivity and remain a promising source of new medicines. The direct photoalkylation of imines offers a promising strategy for complex amines. However, the lack of efficient imine photoreactivity hinders this reaction and remains a fundamental limitation in organic photochemistry. We report an efficient photoalkylation of imines that provides primary amines directly without protecting or leaving groups. The transformation effects C-H addition across -H imines under energy-transfer photocatalysis by a ketone. Our method is distinguished from organometallic, metal-catalyzed, and photoredox approaches to imine alkylation by its lack of protecting groups and its broad scope, which includes unactivated alkanes, protic substrates, basic amines, heterocycles, and ketone imines. We highlight this scope through the condensation and alkylation of two pharmaceutical ketones, providing complex amines succinctly. Our mechanistic analysis supports a three-step process, involving hydrogen-atom transfer to an imine triplet excited state, intersystem crossing, and radical recombination, with photocatalytic enhancement through energy transfer. We further show that -H imines are more photoreactive than -substituted imines, a distinction partially explained by sterics and side reactions. To fully explain this distinction, we introduce the thermodynamic parameter excited-state hydrogen-atom affinity, which is highly effective at predicting the photoreactivity of imines.
PubMed: 37875007
DOI: 10.1021/acs.joc.3c01722 -
Organic & Biomolecular Chemistry Jan 2024The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and... (Review)
Review
The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-NSOR) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, . aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).
PubMed: 38196324
DOI: 10.1039/d3ob01599h -
Water Research Aug 2023Concerns over human health risks associated with chemical contaminants (micropollutants) in drinking waters are rising due to the increased use of reclaimed water or... (Review)
Review
Concerns over human health risks associated with chemical contaminants (micropollutants) in drinking waters are rising due to the increased use of reclaimed water or water supplies impacted by upstream wastewater discharges. Ultraviolet (UV)-driven advanced oxidation processes (UV-AOPs) using radiation sources that emit at 254 nm have been developed as advanced treatments to degrade contaminants, while those UV-AOPs can be improved towards higher radical yields and lower byproduct formation. Several previous studies have suggested that Far-UVC radiation (200-230 nm) is a promising radiance source to drive UV-AOPs because the direct photolysis of micropollutants and production of reactive species from oxidant precursors can both be improved. In this study, we summarize from the literature the photodecay rate constants of five micropollutants by direct UV photolysis, which are higher at 222 than 254 nm. We experimentally determine the molar absorption coefficients at 222 and 254 nm of eight oxidants commonly used in water treatment and present the quantum yields of the oxidant photodecay. Our experimental results also show that the concentrations of HO, Cl, and ClO generated in the UV/chlorine AOP can be increased by 5.15-, 15.76-, and 2.86-fold, respectively, by switching the UV wavelength from 254 to 222 nm. We also point out the challenges of applying Far-UVC for micropollutant abatement in water treatment, including the strong light screening effect of matrix components (e.g., carbonate, nitrate, bromide, and dissolved organic matter), the formation of byproducts via new reaction pathways, and the needs to improve the energy efficiency of the Far-UVC radiation sources.
Topics: Humans; Water Pollutants, Chemical; Wastewater; Oxidation-Reduction; Chlorine; Oxidants; Water Purification; Ultraviolet Rays; Hydrogen Peroxide
PubMed: 37290191
DOI: 10.1016/j.watres.2023.120169 -
Chemistry (Weinheim An Der Bergstrasse,... Dec 2023Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing...
Medical treatment options for bones and teeth can be significantly enhanced by taking control over the crystallization of biomaterials like hydroxyapatite in the healing process. Light-induced techniques are particularly interesting for this approach as they offer tremendous accuracy in spatial resolution. However, in the field of calcium phosphates, light-induced crystallization has not been investigated so far. Here, proof of principle is established to successfully induce carbonate-hydroxyapatite precipitation by light irradiation. Phosphoric acid is released by a photolabile molecule exclusively after irradiation, combining with calcium ions to form a calcium phosphate in the crystallization medium. 4-Nitrophenylphosphate (4NPP) is established as the photolabile molecule and the system is optimized and fully characterized. A calcium phosphate is crystallized exclusively by irradiation in aqueous solution and identified as carbonate apatite. Control over the localization and stabilization of the carbonate apatite is achieved by a pulsed laser, triggering precipitation in calcium and 4NPP-containing gel matrices. The results of this communication open up a wide range of new opportunities, both in the field of chemistry for more sophisticated reaction control in localized crystallization processes and in the field of medicine for enhanced treatment of calcium phosphate containing biomaterials.
PubMed: 37665635
DOI: 10.1002/chem.202302327 -
Angewandte Chemie (International Ed. in... Jul 2023The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet... (Review)
Review
The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In Cr and Mn complexes with the d valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In Fe and Co complexes with the low-spin d electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d ) isocyanide complexes of Cr and Mn , the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals.
PubMed: 37057372
DOI: 10.1002/anie.202303864 -
Nature Communications Oct 2023Efficiently balancing photochemistry and photoprotection is crucial for survival and productivity of photosynthetic organisms in the rapidly fluctuating light levels...
Efficiently balancing photochemistry and photoprotection is crucial for survival and productivity of photosynthetic organisms in the rapidly fluctuating light levels found in natural environments. The ability to respond quickly to sudden changes in light level is clearly advantageous. In the alga Nannochloropsis oceanica we observed an ability to respond rapidly to sudden increases in light level which occur soon after a previous high-light exposure. This ability implies a kind of memory. In this work, we explore the xanthophyll cycle in N. oceanica as a short-term photoprotective memory system. By combining snapshot fluorescence lifetime measurements with a biochemistry-based quantitative model, we show that short-term memory arises from the xanthophyll cycle. In addition, the model enables us to characterize the relative quenching abilities of the three xanthophyll cycle components. Given the ubiquity of the xanthophyll cycle in photosynthetic organisms the model described here will be of utility in improving our understanding of vascular plant and algal photoprotection with important implications for crop productivity.
Topics: Xanthophylls; Photosynthesis; Photochemistry; Plants; Stramenopiles; Light
PubMed: 37857617
DOI: 10.1038/s41467-023-42281-8 -
ChemPlusChem May 2024Organic electrochemistry is currently experiencing an era of renaissance, which is closely related to the possibility of carrying out organic transformations under mild...
Organic electrochemistry is currently experiencing an era of renaissance, which is closely related to the possibility of carrying out organic transformations under mild conditions, with high selectivity, high yields, and without the use of toxic solvents. Combination of organic electrochemistry with alternative approaches, such as photo-chemistry was found to have great potential due to induced synergy effects. In this work, we propose for the first time utilization of plasmon triggering of enhanced and regio-controlled organic chemical transformation performed in photoelectrochemical regime. The advantages of the proposed route is demonstrated in the model amination reaction with formation of C-N bond between pyrazole and substituted benzene derivatives. Amination was performed in photo-electrochemical mode on the surface of plasmon active Au@Pt electrode with attention focused on the impact of plasmon triggering on the reaction efficiency and regio-selectivity. The ability to enhance the reaction rate significantly and to tune products regio-selectivity is demonstrated. We also performed density functional theory calculations to inquire about the reaction mechanism and potentially explain the plasmon contribution to electrochemical reaction rate and regioselectivity.
PubMed: 38747893
DOI: 10.1002/cplu.202400020 -
IScience Sep 2023We establish a general kinetic scheme for energy transfer and trapping in the photosystem I (PSI) of cyanobacteria grown under white light (WL) or far-red light (FRL)...
We establish a general kinetic scheme for energy transfer and trapping in the photosystem I (PSI) of cyanobacteria grown under white light (WL) or far-red light (FRL) conditions. With the help of simultaneous target analysis of all emission and transient absorption datasets measured in five cyanobacterial strains, we resolved the spectral and kinetic properties of the different species present in PSI. WL-PSI can be described by Bulk Chl , two Red Chl , and a reaction center compartment (WL-RC). The FRL-PSI contains two additional Chl compartments. The lowest excited state of the FRL-RC is downshifted by ≈ 29 nm. The rate of charge separation drops from ≈900 ns in WL-RC to ≈300 ns in FRL-RC. The delayed trapping in the FRL-PSI (≈130 ps) is explained by uphill energy transfer from the Chl compartments with Gibbs free energies of ≈kT below that of the FRL-RC.
PubMed: 37680463
DOI: 10.1016/j.isci.2023.107650 -
Environmental Science & Technology Oct 2023One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly...
One strategy for mitigating the indoor transmission of airborne pathogens, including the SARS-CoV-2 virus, is irradiation by germicidal UV light (GUV). A particularly promising approach is 222 nm light from KrCl excimer lamps (GUV); this inactivates airborne pathogens and is thought to be relatively safe for human skin and eye exposure. However, the impact of GUV on the composition of indoor air has received little experimental study. Here, we conduct laboratory experiments in a 150 L Teflon chamber to examine the formation of secondary species by GUV. We show that GUV generates ozone (O) and hydroxyl radicals (OH), both of which can react with volatile organic compounds to form oxidized volatile organic compounds and secondary organic aerosol particles. Results are consistent with a box model based on the known photochemistry. We use this model to simulate GUV irradiation under more realistic indoor air scenarios and demonstrate that under some conditions, GUV irradiation can lead to levels of O, OH, and secondary organic products that are substantially elevated relative to normal indoor conditions. The results suggest that GUV should be used at low intensities and in concert with ventilation, decreasing levels of airborne pathogens while mitigating the formation of air pollutants.
Topics: Humans; Air Pollution, Indoor; Volatile Organic Compounds; Respiratory Aerosols and Droplets; Ozone; Air Pollutants
PubMed: 37827494
DOI: 10.1021/acs.est.3c05680