Photochemical Reactions Research Articles

Photoredox Radical Truce-Smiles Rearrangement of N-Sulfinyl Acrylamides with Bromodifluoroacetamides.

We herein report a photochemical Truce-Smiles rearrangement reaction of N-sulfinyl acrylamides with bromodifluoroacetamides resulting in the synthesis of a series of aryl difluoroglutaramides in moderate to good yields. The asymmetric synthesis using chiral sulfinamides produced quaternary carbon-centered glutaramide products with a modest enantioselectivity. This protocol effectively complements previous Truce-Smiles rearrangement methods involving N-sulfonyl acrylamides.

Assessing Nonadiabatic Dynamics Methods in Long Timescales.

Nonadiabatic dynamics simulations complement time-resolved experiments by revealing ultrafast excited-state mechanistic information in photochemical reactions. Understanding the relaxation mechanisms of photoexcited molecules finds application in energy, material, and medicinal research. However, with substantial computational costs, the nonadiabatic dynamics simulations have been restricted to ultrafast timescales, typically less than a few picoseconds, thus neglecting a wide range of photoactivated processes occurring in much longer timescales. Before developing new methodologies, we must ask: How well do the popular nonadiabatic dynamics methods perform in a long timescale simulation? In this study, we employ the multiconfiguration time-dependent Hartree (MCTDH) and its multilayer variants (ML-MCTDH), ab initio multiple spawning (AIMS), and fewest-switches surface hopping (FSSH) methodologies to simulate the excited-states dynamics of a weakly coupled multidimensional Spin-Boson model Hamiltonian designed for a long timescale decay behavior. Our study assures that despite having very different theoretical backgrounds, all the above methods deliver qualitatively similar results. While quantum dynamics would be very costly for long timescale simulations, the trajectory-based approaches are paving the way for future advancements.

Optically Controlled Drug Delivery Through Microscale Brain–Machine Interfaces Using Integrated Upconverting Nanoparticles

The aim of this work is to incorporate lanthanide-cored upconversion nanoparticles (UCNP) into the surface of microengineered biomedical implants to create a spatially controlled and optically releasable model drug delivery device in an integrated fashion. Our approach enables silicone-based microelectrocorticography (ECoG) implants holding platinum/iridium recording sites to serve as a stable host of UCNPs. Nanoparticles excitable in the near-infrared (lower energy) regime and emitting visible (higher energy) light are utilized in a study. With the upconverted higher energy photons, we demonstrate the induction of photochemical (cleaving) reactions that enable the local release of specific dyes as a model system near the implant. The modified ECoG electrodes can be implanted in brain tissue to act as an uncaging system that releases small amounts of substance while simultaneously measuring the evoked neural response upon light activation. In this paper, several technological challenges like the surface modification of UCNPs, the immobilization of particles on the implantable platform, and measuring the stability of integrated UCNPs in in vitro and in vivo conditions are addressed in detail. Besides the chemical, mechanical, and optical characterization of the ready-to-use devices, the effect of nanoparticles on the original electrophysiological function is also evaluated. The results confirm that silicone-based brain–machine interfaces can be efficiently complemented with UCNPs to facilitate local model drug release.

Vibronic Conical Intersection Trajectory Signatures in Wave Packet Coherences.

Conical intersections are ubiquitous in the energy landscape of chemical systems, drive photochemical reactivity, and are extremely challenging to observe spectroscopically. Using two-dimensional electronic spectroscopy, we observe the nonadiabatic dynamics in Wurster's Blue after excitation to the lowest two vibronic excited states. The excited populations relax ballistically through a conical intersection in 55 fs to the electronic ground state potential energy surface as the molecule undergoes an intramolecular electron transfer. While the kinetics are identical on both vibronic energy surfaces, we observe different patterns of coherent oscillations after traversing the conical intersection indicating distinct nonadiabatic relaxation pathways through the conical energetic funnel. These coherences are not created directly by the excitation pulses but are the result of the dynamical trajectories projecting differently on the conical intersection vibrational space. Our spectroscopic data offers a fresh perspective into the complex conical intersection topology and dynamics that emphasizes the critical involvement of the intersection space in dictating the dynamics.

Unraveling Photoinduced Desorption Dynamics of π-Conjugated Ligands in ZnS Nanocrystals via Pump-Push-Probe Spectroscopy.

The photoinduced ligand desorption from nanocrystal (NC) surfaces plays a critical role in the diverse functionalities of NCs. However, this reaction is inherently complex because photophysical and photochemical reactions are involved, and many aspects remain elusive. In this study, using ZnS NCs coordinated with perylenebisimide (PBI) ligands as a model system, we revealed that pump-push-probe spectroscopy provides detailed insights into the transient species following photoinduced ligand desorption reactions. This method successfully isolated the signal of the PBI radical anion, generated by photoinduced charge separation, which was difficult to identify by conventional pump-probe spectroscopy. Furthermore, pump-push-probe spectroscopy also revealed that the transiently formed aggregation of PBI after PBI desorption is the H-type aggregate. This research is expected to contribute to the analysis of complex photochemical reaction processes in composite nanomaterials and is important for the development of highly efficient NC photocatalysts and photodurable NCs.

Sulfur isotope anomalies in coal combustion: Applications to the present and early Earth environments

The observation of mass-independent sulfur isotope fractionations (S-MIF) in Archean-Paleoproterozoic rocks has been instrumental in constraining oxygen levels on early Earth. The S-MIF effect, experimentally demonstrated to result from photochemical reactions, has now been observed in coal combustion, expanding our understanding of this phenomenon. Our study reveals that the negative Δ33S anomalies produced by coal combustion are consistent with similar anomalies observed in present-day sulfate aerosols in Beijing, China, and the black crust sulfates formed on building stones, monument walls, and sculptures in Europe that contribute to carbonate stone deterioration and cultural heritage damage. This finding provides independent evidence for a critical role of atmospheric sulfate from coal combustion in maintaining isotopic balance and offers an effective method for tracing sulfate aerosol sources. These insights are vital for developing more effective regulatory policies to control air pollution and protect public health. Given that coal energy production remains a significant issue in climate science, accurately mapping the global distribution of its by-products is imperative.

Spectroscopic Signatures of Ultra-Thin Amorphous Carbon with the Tuned Disorder Directly Grown on a Dielectric Substrate.

The reduced structural complexity of atomically thin amorphous carbons makes it suitable for semiconductor technology. Inherent challenges arise from transfer processes subsequent to growth on metallic substrates, posing significant challenges to the accurate characterization of amorphous materials, thereby compromising the reliability of spectroscopic analysis. Here this work presents a novel approach: direct growth of ultra-thin amorphous carbon with tuned disorder on a dielectric substrate (SiO2/Si) using photochemical reaction and thermal annealing process with a solid precursor. This work characterizes the amorphous carbon films' disorder using spectroscopic techniques, such as X-ray photoelectron spectroscopy, Electron energy loss spectroscopy, and Raman spectroscopy, which offer greater convenience compared to microscopy-based studies. This method, rooted in comprehensive spectroscopic characterization, elucidates characteristic signatures inherent to the amorphous carbon films. These findings reveal that Raman spectroscopy is particularly effective in identifying the amorphous phase of atomically-thin carbon. Additionally, I-V characterization and high-frequency dielectric measurements showcase the potential application of directly grown amorphous carbon films in the semiconductor industry, where nanometer-level thin conductors and dielectrics are commonly utilized. This transfer-free characterization method provides a useful tool to find the correlation between atomic structure and electrical/optical properties, giving valuable insights into comprehensive crystallographic fundamental research.

Photochemical and Photocatalytic Deracemization Reactions

Under photochemical conditions and using an appropriate chiral catalyst, racemic mixtures of compounds can convert to enantioenriched mixtures through distinguished pathways which are called photochemical and photocatalytic deracemization reactions.

Synergistic Strategy toward Enhancing Photosynthesizing Reactive Oxygen Species of Covalent Organic Frameworks

AbstractPhotocatalytic reactive oxygen species (ROSs) plays an important role in photodynamic therapy and photochemical reactions. However, most reported photocatalysts suffer from insufficient utilization of visible light and low conversion of O2, which requires the development of higher performance catalysts toward practical applications. Herein, a series of porphyrin‐based COFs have been prepared. Comparative experimental and theoretical studies have revealed that the synergistic interaction between the two building blocks can significantly enhance the yields of ROSs by independently accomplishing photon harvesting and oxygen capture with smooth energy transfer between them. Particularly, the 1O2 yield of 3P‐Por‐COF is increased to 1.3 and 3.4 times that of the classical PCN‐224 and porphyrin molecular aggregates. Furthermore, the TOF of 3P‐Por‐COF is as high as 271 h−1 with ≈100% selectivity under red light irradiation in catalyzing thioanisole to methyl phenyl sulfoxide. The conversion and stability of degradation of toluene gas under natural light are also superior to the conventional Fenton catalytic system. The present results should contribute to the design of high‐performance frameworks‐based photocatalysts for ROSs production.

In-situ reaction monitoring and kinetics study of photochemical reactions by optical focusing inductive electrospray mass spectrometry

In-situ reaction monitoring and kinetics study of photochemical reactions by optical focusing inductive electrospray mass spectrometry

Temporal variability of ozone and its precursors at tropical megacity, Bengaluru, India: Effect of volatile organic compounds and meteorology

Routine observations of surface ozone (O3) and its precursors (NO, NO2, NOx) were taken over Bengaluru, a southern megacity, India, for 4 years period between January 2015 and December 2018. The seasonal variations of O3, NO, NO2, and NOx have been analysed to understand the short-term variability of the pollutants at this site. The magnitude of O3 varied significantly by season, with maximum concentration during winter (13.07 ppbv) and minimum concentration during monsoon (9.52 ppbv). The highest concentration was observed in the post-monsoon season (17.38 ppbv) for NO, while NO2 and NOx showed the highest (41.75, 50.42 ppbv) in the winter season. The lowest concentrations of NO (5.70 ppbv), NO2 (30.43 ppbv) and NOx(36.28 ppbv) were observed in summer. An estimate was performed to determine the site's VOC-NOx sensitivity, using the TNMHC/NOX ratio as a photochemical measure. This ratio indicates that the study region is NOX responsive in all seasons. Analysis was done on the effects of meteorological factors such as temperature, water vapour, and ventilation coefficient on pollutants. Higher correlation of O3 with temperature showed the role of photochemical reactions in the formation of ozone and water vapour content leads to the removal of ozone concentration. The influence of meteorological variables on NO2 and TNMHC did not appear to be very significant. An analysis of CAMS data with real-time measurements of ozone and oxides of nitrogen showed that ozone is significantly correlated, while nitrogen oxides are not significantly correlated with CAMS data.

Noncombustion Emissions of Organic Acids at a Site near Boise, Idaho.

Gas-phase organic acids are ubiquitous in the atmosphere with mixing ratios of several species, such as formic acid and acetic acid, often as high as several parts per billion by volume (ppbv). Organic acids are produced via photochemical reactions and are also directly emitted from various sources, including combustion, microbial activity, vegetation, soils, and ruminants. We present measurements of gas-phase formic, acetic, propionic, pyruvic, and pentanoic acids from a site near Boise, Idaho, in August 2019 made by iodide-adduct chemical ionization mass spectrometry (CIMS). The site is adjacent to a major interstate highway and beyond the urban/suburban core is surrounded by national forests to the north and northeast and by farmland to the west and south. Maximum mixing ratios of formic, acetic, propionic, and pentanoic acid were typically near 10, 3, 0.4, and 0.2 ppbv, respectively. Observed daytime concentrations of these acids were mostly consistent with other studies, but concentrations were persistently the highest at night between 20:00 to 8:00 (local standard time). Such elevated nighttime concentrations are unlike most other reported organic acid measurements. Although there were times when organic acid concentrations were enhanced by mobile source emissions, the organic acid concentrations appear to be mainly controlled by noncombustion surface primary emissions. Source apportionment by positive matrix factorization (PMF) supports the importance of significant noncombustion, nonphotochemical emissions. Two agricultural surface sources were identified and estimated to contribute to greater than half of total observed concentrations of formic and acetic acid. In contrast to the other measured organic acids, but in agreement with all other reported measurements in the literature, pyruvic acid concentrations peaked during the daytime and were largely controlled by photochemistry.

Structural effects of high laser power densities on an early bacteriorhodopsin photocycle intermediate

Time-resolved serial crystallography at X-ray Free Electron Lasers offers the opportunity to observe ultrafast photochemical reactions at the atomic level. The technique has yielded exciting molecular insights into various biological processes including light sensing and photochemical energy conversion. However, to achieve sufficient levels of activation within an optically dense crystal, high laser power densities are often used, which has led to an ongoing debate to which extent photodamage may compromise interpretation of the results. Here we compare time-resolved serial crystallographic data of the bacteriorhodopsin K-intermediate collected at laser power densities ranging from 0.04 to 2493 GW/cm2 and follow energy dissipation of the absorbed photons logarithmically from picoseconds to milliseconds. Although the effects of high laser power densities on the overall structure are small, in the upper excitation range we observe significant changes in retinal conformation and increased heating of the functionally critical counterion cluster. We compare light-activation within crystals to that in solution and discuss the impact of the observed changes on bacteriorhodopsin biology.

Antioxidant properties of the soluble carotenoprotein AstaP and its feasibility for retinal protection against oxidative stress.

Photodamage to the outer segments of photoreceptor cells and their impaired utilization by retinal pigment epithelium (RPE) cells contribute to the development of age-related macular degeneration (AMD) leading to blindness. Degeneration of photoreceptor cells and RPE cells is triggered by reactive oxygen species (ROS) produced by photochemical reactions involving bisretinoids, by-products of the visual cycle, which accumulate in photoreceptor discs and lipofuscin granules of RPE. Carotenoids, natural antioxidants with high potential efficacy against a wide range of ROS, may protect against the cytotoxic properties of lipofuscin. To solve the problem of high hydrophobicity of carotenoids and increase their bioaccessibility, specialized proteins can ensure their targeted delivery to the affected tissues. In this study, we present new capabilities of the recombinant water-soluble protein AstaP from Coelastrella astaxanthina Ki-4 (Scenedesmaceae) for protein-mediated carotenoid delivery and demonstrate how zeaxanthin delivery suppresses oxidative stress in a lipofuscin-enriched model of photoreceptor and pigment epithelium cells. AstaP in complex with zeaxanthin can effectively scavenge various ROS (singlet oxygen, free radical cations, hydrogen peroxide) previously reported to be generated in AMD. In addition, we explore the potential of optimizing the structure of AstaP to enhance its thermal stability and resistance to proteolytic activity in the ocular media. This optimization aims to maximize the prevention of retinal degenerative changes in AMD.

Computational Study on the Photo‐Induced Antibiotic Activity of an Azoquinolone with Promising Applications in Photopharmacology

Azocompounds are among the most important group of molecular photoswitches due to their multiple applications in various scientific areas. We studied the thermal and photochemical reactions of an azocompound with photo‐induced antibiotic properties using ab‐initio calculations based on Kohn‐Shan, Spin‐Flip and time‐dependent Density Functional Theory. Our primary goal is to understand the absorption spectra and isomerization pathways governing the molecule’s light‐controlled antibiotic activity. The nuclear ensemble approach was used for the most stable trans and cis isomers, and the absorption spectra were calculated and fitted to predict the cis/trans isomer ratios in the carboxylate form, using experimental measurements as a reference. We stablished that rotation is involved in the most favorable cis⇄cis and trans⇄trans thermal isomerization pathways, while the inversion mechanism is the most likely for cis⇄trans isomerizations. We found that the photochemical trans→cis isomerization follows a consistent mechanism across all trans isomers, involving excitation to S2(ππ*), an in‐plane ultrafast internal conversion to S1(nπ*), followed by rotation of the azo bond up to a twisted S1(nπ*)/S0 conical intersection. We used a custom approach to evaluate the most favorable decay pathway from the S1(nπ*)/S0 conical intersections to trans and cis photoproducts using static calculations.

Recent Developments in the Photochemical Reactions of N‐Heterocyclic Compounds

The adoption of clean and renewable light sources is becoming increasingly prevalent in organic synthesis due to their welfare, workability and economic benefits. In recent times, photo‐redox catalysis has emerged as a valuable tool in organic transformations owing to its environmentally friendly nature and utilization of abundant resources. Since harmful or polluting reagents are not needed for the organic photochemical reactions, these reactions provide insights into sustainable processes and green chemistry. N‐Heterocyclic compounds (NHC’s) constitute fundamental structural motifs in numerous organic compounds and are widely encountered in natural products and pharmaceuticals with diverse biological activities. Consequently, investigations into the synthesis and modification of these NHC’s such as indole, carbazole, benzimidazole, quinoline, isoquinoline and pyridine hold particular significance for chemists and pharmacologists. This review provides an overview of the impact of photocatalysis on synthesis of NHC’s and their modification from 2019 to 2024. These transformations are achieved through the utilization of both metal photocatalysts (e.g., Ir, Pd, Co, Gd etc.) and non‐metallic photocatalysts (e.g., Eosin‐Y, 4CzIPN, Mes‐Acr+ClO4‐ etc.), or even without the necessity of photocatalysts. It is anticipated that this review will serve as a valuable resource for researchers delving into the promising realm of photocatalyzed transformations.

Electroactive bacteria-established long-distance electron transfer to oxygen facilitates bio-transformation of dissolved organic matter for sediment remediation

Electroactive bacteria (EAB) in sediment commonly establish long-distance electron transfer (LDET) to access O2, facilitating the degradation of organic contaminants, which we hypothesize is mediated by the bio-transformation of dissolved organic matter (DOM). This study confirmed that EAB-established LDET to O2 via a microbial electrochemical snorkel raised the electric potential of sediment by increasing HCl-extracted Fe(III) and NO3− concentrations while reducing DOM concentrations, which further modified microbial diversity and composition, notably reduced the relative abundance of fermentative bacteria. As a result, DOM showed the highest SUVA254 value (3.88) and SUVA280 value (1.61), preliminarily suggesting their enhanced aromaticity, humification and average molecular weight. Additionally, these DOM exhibited the highest electron transfer capacity (174.14±3.62 μmol e− /g C) and redox current. Based on these findings, we propose four possible avenues through which EAB-established LDET to O2 facilitates sediment remediation, mainly including DOM involved affinity, direct and indirect electron transfer, and induced photochemical reaction in degradation or humification process of organic contaminants. Although these proposed avenues require further verification, this work sheds light on deciphering the mechanisms underlying the augmented degradation of organic contaminants facilitated by EAB-established LDET to O2, offering fresh insights into sediment remediation.

Unveiling photochemical CO2 reduction processes on PbBiO2I/GO surfaces: Insights from in-situ Raman spectroscopy

Bismuth-based materials are increasingly valued for their dual capability in catalyzing the photochemical CO2 reduction reaction (CO2RR) and enhancing the selectivity towards multi-carbon (C2+) products. This study introduces a novel PbBiO2I/graphene oxide (PbBiO2I/GO) composite, synthesized to leverage the unique properties of both components for improving catalytic performance. The physical and chemical properties of these composites were characterized to delineate their functionality and interaction mechanisms. The heterojunction structure in the composites significantly facilitated the CO2RR, with a noted CH4 conversion rate of 0.8376 µmolg−1h−1. This rate is significantly higher ∼1.78 times that of standalone PbBiO2I under similar conditions. Advanced X-ray photoelectron spectroscopy (XPS) analysis indicated that the incorporation of graphene oxide enhances the electronic environment around Pb2+ and Bi3+ ions, reducing their charge states and increasing oxygen vacancies. This modification likely contributes to the observed catalytic enhancement. Furthermore, in-situ Raman spectroscopy provided insights into the dynamic formation of key intermediates during the CO2RR. Under targeted light irradiation, distinct intermediates such as *COO−, *CO, H*CO/H*COH, OC*C*O, O*CCHO, and C–H were detected, facilitating a deeper understanding of the mechanistic pathways involved in C1 and C2 product formation. This comprehensive analysis not only elucidates the enhanced catalytic pathways facilitated by the composite structure but also sets a foundation for future optimizations in bismuth-based photocatalytic systems.

REACTIVE DYNAMICS OF THE DENTAL TISSUES STATE IN RESPONSE TO THE ACTION OF PHOTOPOLYMERIZERS (EXPERIMENTAL STUDY)

Thepurpose of the study: to study the effect of radiation from dental photopolymerizers on tooth tissueMaterials and methods.50 rats (4 groups): No. 1 control (5), No. 2-4 main (15 animals each)Results.Negative photochemical reactions in the tooth pulp Conclusion. The changes in the pulp were reversible

Formation of Multiple Naturally Occurring Meroterpenoid Scaffolds by the Norrish-Yang Reaction of a p-Benzoquinone.

The Norrish-Yang reaction, as a typical example, demonstrates the inherent ability of photochemical reaction to facilitate formation of sterically congested C-C bonds, efficiently crafting intricate ring structure in complex organic molecules. Herein we report for the first time a unified synthesis using quinone-based acid-promoted Norrish-Yang photocyclization for the stereoselective construction of multiple avarane-type meroterpenoid natural products.