Photochemical Transformations Research Articles

α-aminonitriles synthesis and kinetic investigation via photooxidative cyanation of amines in a visible LED-based photomicroreactor

α-aminonitriles (AN) are valuable intermediates and building blocks with versatile applications in organic synthesis. Herein, we presented a visible LED-based photomicroreactor for the AN synthesis with three amine substrates, i.e., dibenzylamine (DBA), pyrrolidine (PYR) and piperidiene (PIP), using meso‑tetraphenylporphyrin (m-TPP) and trimethylsilyl cyanide (TMSCN) as photosensitizer and cyanide source, respectively. The results showed that the photooxidative cyanation is a chromoselective and wavelength-selective photochemical transformation with the optimum AN yield and selectivity of 98.2% and 99.5% at a residence time of 2.69 min. Computational studies indicated that a high energy gap between the molecular orbitals of PYP, PIR and their imine intermediates potentially led to their higher reactivity than DBA and formation of by-products with larger molecular weight. Kinetic investigation showed that the apparent rate constants of the DBA photooxidative cyantaion were improved by rising the LED input power, and the applied photosensitizer exhibited high photostability. The overall photonic efficiency of this photomicroreactor was found to be 54.3% within the wavelength range of 400–440 nm, which is higher than previously used photoreactors. Finally, linear correlations were developed between the input power of LED and apparent rate constants of DBA photooxidative cyanation, which would be beneficial for the design, optimization, and scale-up of this photochemical process.

Photochemical degradation mechanisms and ecotoxicity of propranolol in natural water under simulated and natural sunlight irradiation

The widespread use of propranolol (PRO) has led to its detection in all types of natural water bodies, and it is hazardous to both aquatic organisms and humans. In this study, the photochemical transformation of PRO in the natural environment was investigated using both simulated and outdoor light experiments. The photodegradation of PRO was found to be faster in Pearl river water and the dissolved organic matter (DOM) solutions than that in pure water under sunlight irradiation. Quenching experiments show that the excited triplet states DOM (3DOM*) played a major role while ·OH and 1O2 played minor roles in PRO degradation. The secondary reaction rate constants of 3DOM* with PRO were determined to be (4.32 ∼ 6.38) × 108 M−1 s−1. DOM with high steady-state concentrations of the generated reactive species has higher photochemical reactivity for PRO photodegradation. Total of seven products were identified in in pure water, Pearl River water and three DOM solutions. The degradation of PRO can be mainly through hydroxyl addition, dehydration, naphthalene removal and isopropyl removal reactions. The reaction sites predicted by frontier electronic density calculations can further infer degradation pathways. The ecotoxicity of degradation products was found to be decreased relative to PRO through Ecological Structure Activity Relationship (ECOSAR) program.

Synthesis of Boronates with a Protoilludane Skeleton

AbstractNaturally occurring sesquiterpenes with a protoilludane skeleton are frequently oxygenated at carbon atoms C4 and C8. Boronic acid pinacol esters (BPin) are potential precursors for hydroxy groups at these positions and synthetic methods have now been developed for their preparation. Introduction of a boronate in position C4 was achieved by Cu-catalyzed hydroboration of a photochemically generated cyclobutene precursor, which displayed the complete C15-carbon skeleton of protoilludanes. Introduction of BPin at carbon atom C8 was possible by starting with an alkenyl boronate as precursor in a photochemical transformation. A two-photon reaction cascade allowed for creation of the complete protoilludane skeleton with BPin selectively positioned at C8. Subsequent reactions were studied and the oxidative transformation of the boronates into the respective alcohols was shown.

Frontispiece: Photochemistry Driven by Excited‐State Aromaticity Gain or Antiaromaticity Relief

The reversal of aromaticity and antiaromaticity upon excitation to the lowest ππ* state impacts on the photophysics and photoreactivity of various annulenes. This unifying principle can guide the rationalization of a plethora of excited-state reactions and has a strong predictive power in the design of new photochemical transformations. For more details, see the Review by H. Ottosson et al. (DOI: 10.1002/chem.202203748)

Protective coatings for ceramic artefacts exposed to UV ageing

The commercial acrylic copolymer Paraloid B72 (PB72) and a synthesized nanostructured material (AMF) bearing silsesquioxane, methacrylate and fluorine units were analyzed to assess their performances as protective coatings for the conservation of Neolithic Cucuteni ceramic pottery when submitted to UV ageing. In the context of comparative evaluation of the protective efficiency, the present paper reports the use of a functional coating that operates via specific photochemical transformations at the coating-air interface as a UV resistant protection coating for cultural heritage artefacts. The main factors that influenced the photo-degradation behavior of the polymeric materials included their structure, the properties at the polymer/air interfaces, and the preferential orientation of functional groups at the surface of the polymeric coatings.

Photochemical transformation of anthracene (ANT) in surface soil: Chlorination and hydroxylation

To reveal the fate of anthracene (ANT) in soil, the photodegradation behavior of ANT was systematically studied using SiO2 to simulate a soil environment. Under xenon lamp irradiation, more than 90% of ANT loaded on SiO2 could be removed after 240 min. Moreover, the effects of water content, chloride ions (Cl-) and humic acid (HA) were examined. It was found that the presence of water and HA can significantly inhibit the photolysis of ANT on SiO2, while the addition of chloride alone has no obvious effect. However, when water is present, the inhibition effect of chloride became more obvious. According to radical quenching experiments and electron paramagnetic resonance (EPR) spectra, hydroxyl radicals (•OH) and chlorine radicals (Cl•) were formed in the system. Possible reaction pathways were speculated based on products identified by mass spectrometry. ANT was attacked by •OH to form hydroxylated products, which can be further hydroxylated and oxidized with the final formation of ring-opening products. ANT directly excited by light may also react with Cl• to produce chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). Finally, the experimental results were verified on real soil. This study provides important information for understanding the photochemical transformation mechanism of ANT at the soil/air interface.

Photochemical multicomponent transformation of acceptor-only diazoalkanes by merging their cycloaddition and carbene reactivities

Herein, we report an efficient photochemical method for the synthesis of poly-substituted pyrazoles through a multicomponent reaction of acceptor-only diazoalkanes, alkynes, and solvents (cyclic ethers or nitriles). The key to this success was driven by the photolysis of acceptor-only diazoalkanes to form free carbene species and the fast in situ [3 + 2]-cycloaddition formation of nucleophilic NH pyrazole derivatives. This work also serves as an entry to allow future reaction design on the combination of carbene reactivity of diazoalkanes with their other reaction modes.

Photochemical transformation and secondary aerosol formation potential of Euro6 gasoline and diesel passenger car exhaust emissions

Traffic remains a major source of urban air pollution although emission regulations have led to significant reductions in exhaust emissions of new vehicles. In this work the photochemical transformation of exhaust emissions from gasoline and diesel passenger vehicles compliant with the current European ‘Euro6’ emission standard and operated with traditional and alternative fuels was investigated using an environmental chamber. By assessing four different engine operation conditions, we show that vehicle operation notably affects the exhaust composition and secondary aerosol formation potential. For the gasoline vehicle, secondary aerosols dominate the total particulate emissions. In contrast, we observe no substantial secondary aerosol formation for exhaust emissions of a Euro6-level diesel vehicle. High engine load operation and cold start of the gasoline vehicle led to 11–470-fold particulate mass enhancement, while for moderate driving conditions the enhancement ratio was below 2. High aerosol enhancements also led to strong increases in particle light absorption. The results underline the necessity for future directives to include the emission components leading to secondary pollution, in addition to the freshly emitted pollutants. The link observed between secondary organic aerosol (SOA) formation and gaseous aromatic hydrocarbon emissions suggests that monitoring and limiting these gaseous species can provide an indirect regulation for SOA. Additionally, ammonia released as a byproduct of the gasoline vehicle is confirmed as an important precursor for secondary aerosols.

Cover Feature: Photochemistry Driven by Excited‐State Aromaticity Gain or Antiaromaticity Relief (Chem. Eur. J. 19/2023)

A portfolio of photochemical transformations found in a variety of areas can be rationalized through consideration of either gain of 4nπ-electron aromaticity or relief of (4n+2) π-electron antiaromaticity in excited states of ππ* character. These back-of-an-envelope tools provided by Baird's rule serve as a compass for excursions in electronically excited states. More information can be found in the Review by H. Ottosson and co-workers (DOI: 10.1002/chem.202203748).

The impact of inorganic ions on the solar photolysis of chlorinated dissolved organic matter from different sources: Spectral characteristics, disinfection byproducts, and biotoxicities

Dissolved organic matter (DOM) from wastewater treatment plant (WWTP) effluent is chlorinated and then discharged into natural waters, where it is subject to solar irradiation. However, the impacts of inorganic ions in natural waters on the photochemical transformations of the chlorinated DOM (DOM-Cl) have not been studied comprehensively. In this study, variations in the spectral characteristics, disinfection byproducts (DBPs), and biotoxicities of DOM-Cl under solar irradiation at different pH values and in the presence of NO3- and HCO3- were revealed. Three sources of DOM, including DOM from a WWTP effluent, natural organic matter from the Suwannee River, and DOM from plant leaf leachate, were investigated. Solar irradiation resulted in the oxidation of the highly reactive aromatic structures and then reduced the amounts of chromophoric and fluorescent DOM, especially under alkaline conditions. Moreover, alkaline conditions significantly promoted the detected DBPs degradation and the biotoxicities attenuation, while NO3- and HCO3- generally impeded them (or did not work). Dehalogenation of the unknown halogenated DBPs and photolysis of the nonhalogenated organics were the main mechanisms for the DOM-Cl biotoxicity reductions. Hence, improving the ecological safety of WWTP effluents could be achieved through solar irradiation by removing the DBPs formed.

Bidirectional role of synthetic musk tonalide as photosensitizer and activator on amino acids: Formation of sensitizer imine at aqueous chemistry interface of skin

Personal care products (PCPs) inevitably come into contact with the skin in people’s daily life, potentially causing adverse effects on human health. The adverse effects can be exacerbated under UV irradiation but are rarely studied. In this study, to clearly understand the damage of representative PCPs to human skin and their photochemical transformation behaviors, fragrance tonalide (AHTN) was measured in the presence of amino acids as a basic building block of human tissue. The results showed that amino acids could decelerate the photochemical transformation rate of AHTN, increasing the likelihood of AHNT persisting on the skin surface and the health risk to the human being. Further, the interaction between amino acids and AHTN was investigated. AHTN could play bidirectional roles in damaging amino acids: the photosensitizer and reactive activator. As a photosensitizer, the 1O2 generated from the AHTN photosensitization was partly employed to oxidative damage amino acids. Furthermore, by combining experiments with quantum chemical computation, the carbonyl group of the activator AHTN was found to be the active site to activate the N-containing group of amino acids. The activation mechanism was the electron transfer between AHTN and amino acids. Imines formed during the photochemical transformation of AHTN with histidine/glycine were the molecular initiating event for potential skin sensitization. This study reported for the first time that skin photosensitizer formation threatens human health during the photochemical transformation of AHTN.

Recent Advances in Electro- or Photochemical Driven Transformations via Cleavage of the C–N Bond of Quaternary Ammonium Salts

AbstractSelective functionalization via cleavage of the C–N bond of amines has proven to be challenging partly because of its relatively high bond dissociation energy, even though amines are abundant and readily available. To meet this challenge, many new transformations based on the pre-activation of the C–N bond before the cleavage have been developed. Among them, the conversion of amines into quaternary ammonium salts has certain advantages, such as easy preparation from primary, secondary, or tertiary amines, as well as stable storage and usage. Although transition metal catalysis has been frequently applied for developing new transformations via oxidative addition of the C–N bond of quaternary ammonium salts, recent studies have shown a new dimension by using green electro- or photochemical tools. In this short review, recent advances in electro-, photo-, or photoelectrochemical driven synthetic applications of quaternary ammonium salts have been summarized and discussed.1 Introduction2 Electrochemical Driven Transformations3 Photochemical Driven Transformations4 Photoelectrochemical Driven Transformations5 Conclusion and Outlook

Evolvement of carbamazepine under solar irradiation in the presence of chlorine: Efficiency, influences, degradation pathways and ecotoxicity

Carbamazepine (CBZ) and residual chlorine coexist in wastewater discharged from wastewater treatment plants (WWTPs), while the mechanism of their photochemical transformation in the natural aquatic environment is still unclear. In this study, an approach combining experiment and quantum chemical calculation was used to explore the degradation mechanism of CBZ under chlorine/solar irradiation. The degradation of CBZ was not evident during disinfection alone or sunlight irradiation. However, CBZ was rapidly degraded under chlorine/solar irradiation (kobs = 0.463 min−1 at pH = 8.0). Quenching and probe experiments showed that the efficient removal of CBZ under chlorine/solar irradiation was credited with the production of ·Cl, ·OH, and O3, in which ·Cl (61.95%) and ·OH (33.14%) contributed significantly. The reaction mechanism of CBZ degradation was postulated, in conjunction with the identification of degradation products by HPLC/MS analysis and density functional theory. Among them, the primary degradation way was acridine production under the action of ·Cl and ·OH, and the decarboxylation process was the rate-limiting step. In addition, bioassay results indicated that the luminescent bacteria toxicity and genotoxicity of CBZ after chlorine/solar irradiation increased. Based on the identified transformation products and the quantitative structure-activity relationship, the elevated ecotoxicity was attributed to the TP209 and TP179 generated by pathway 1, and then controlling the decarboxylation process by adjusting pH and temperature to reduce the high toxic degradation products were proposed for ecological safety.

Relationship between photolysis mechanism and photo-enhanced toxicity to Vibrio Fischeri for neonicotinoids with cyano-amidine and nitroguanidine structures

Neonicotinoids are widely used pesticides that contaminate aquatic environments. Although these chemicals can be photolyzed under sunlight radiation, it is unclear for the relationship between photolysis mechanism and toxicity change in aquatic organisms. This study aims to determine the photo-enhanced toxicity of four neonicotinoids with different main structures (acetamiprid, and thiacloprid for cyano-amidine structure, imidacloprid and imidaclothiz for nitroguanidine). To Achieve the goal, photolysis kinetics, effect of dissolved organic matter (DOM) and reactive oxygen species (ROSs) scavengers on photolysis rates, photoproducts, and photo-enhanced toxicity to Vibrio fischeri were investigated for four neonicotinoids. The results showed direct photolysis plays a key role in the photo-degradation of imidacloprid and imidaclothiz (photolysis rate constants are 7.85 × 10−3 and 6.48 × 10−3 min−1, respectively), while the photosensitization process of acetamiprid and thiacloprid was dominated by ·OH reactions and transformation (photolysis rate constants are 1.16 × 10−4 and 1.21 × 10−4 min−1, respectively). All four neonicotinoid insecticides exerted photo-enhanced toxicity to Vibrio fischeri, indicating photolytic product(s) posed greater toxicity than their parent compounds. The addition of DOM and ROS scavengers influenced photo-chemical transformation rates of parent compounds and their intermediates, leading to diverse effects on photolysis rates and photo-enhanced toxicity for the four insecticides as a result of different photo-chemical transformation processes. Based upon the detection of chemical structures of intermediates and Gaussian calculations, we observed different photo-enhanced toxicity mechanisms for the four neonicotinoid insecticides. Molecular docking was used to analyze the toxicity mechanism of parent compounds and photolytic products. A theoretical model was subsequently employed to describe the variability of toxicity response to each of the four neonicotinoids.

Metal–Adsorbate Interactions Modulate Plasmonic Reactivity of Chemisorbed Nitrophenyl Derivatives

Energetic hot electrons generated upon nonradiative decay of localized plasmons in metallic nanostructures can be effectively harnessed to catalyze photochemical transformations of molecular adsorbates through unique reaction pathways. When designing metal–adsorbate hybrid systems for hot electron-driven photocatalysis, both the intrinsic plasmonic properties of metallic photocatalysts and the chemical nature of metal–adsorbate interactions should be taken into careful considerations. In this work, we show that the reactivity of nitrophenyl derivative adsorbates on Ag nanoparticle surfaces toward plasmon-driven reductive coupling reactions is intimately tied to the bonding nature of molecular chemisorption. We focus on the comparative studies of three representative nitrophenyl derivatives, specifically para-nitrothiophenol, para-nitrophenylacetylene, and para-nitrophenylisocyanide, which covalently interact with the Ag photocatalysts using chemically distinct surface-anchoring groups. Taking full advantage of the unique time-resolving and molecular fingerprinting capabilities offered by surface-enhanced Raman spectroscopy, we have been able to precisely correlate the chemical nature of metal–adsorbate interactions to the kinetic characteristics of molecular transformations under a broad range of reaction conditions. Although the kinetic features of the coupling reactions change substantially upon variation of the excitation wavelength, the light illumination power, and the pH of the reaction medium, we have consistently observed that the plasmonic reactivity of the nitrophenyl derivative adsorbates drops drastically, as reflected by significant decrease in both reaction rates and yields, when the bonding modes dominating the metal–adsorbate interactions are switched from σ-donation to π-back-donation.

Global Corrections to Reference Irradiance Spectra for Non-Clear-Sky Conditions.

Photochemical reactions in surface waters play important roles in element cycling and in the removal of organic contaminants, among other processes. A central environmental variable affecting photochemical processes in surface waters is the incoming solar irradiance, as this initiates these processes. However, clear-sky incident irradiance spectra are often used when evaluating the fate of aquatic contaminants, leading to an overestimation of contaminant decay rates due to photochemical transformation. In this work, incident irradiance satellite data were used to develop global-scale non-clear-sky correction factors for commonly used reference irradiance spectra. Non-clear-sky conditions can decrease incident irradiance by over 90% depending on the geographic location and time of the year, with latitudes above 40°N being most heavily affected by seasons. The impact of non-clear-sky conditions on contaminant half-lives was illustrated in a case study of triclosan in lake Greifensee, which showed a 39% increase in the triclosan half-life over the course of a year under non-clear-sky conditions. A global annual average correction factor of 0.76 was determined as an approximate way to account for non-clear-sky conditions. The correction factors are developed at monthly and seasonal resolutions for every location on the globe between 70°N and 60°S at a 4 km spatial resolution and can be used by researchers, practitioners, and regulators who need improved estimates of incident irradiance.

Sustainability of Visible Light-Driven Organic Transformations - A Review

:The literature survey reveals the applications of visible light as a sustainable energy source in the various constructive organic transformations by using homogeneous and heterogeneous photocatalysts, catalysts under suitable solvents, or under solvent-free conditions to attain green and sustainable chemistry. Recently, the crises of energy sources demand a sustainable and renewable energy source worldwide. In these circumstances, visible lightdriven organic transformations attracted much attention as a good alternative energy source.:Due to the visible-light-driven organic synthesis offers several advantages such as natural abundance in the solar spectrum, friendly to the equipment, fewer side reactions, costfriendly, selective product formation, higher isolated yields of products, environmental friendliness and sustainability. On the other hand, the developments in chemistry are adopting the green culture, in this state of affairs, visible light will be a great substitute for non-renewable energy sources for chemical transformations and synthesis. It will reduce the consumption of fossil fuels which will lead the world toward achieving the goals of sustainable development.:A number of different organic molecules are synthesized using different homogeneous and heterogeneous photocatalysts under visible light via different methods such as one-pot multi-component protocol, multi-step method, coupling and condensation method, etc.:In this review paper, we have highlighted the basics and history of photochemical organic transformations using suitable photo-catalysts and dye-sensitized photochemical reactions. We have presented details of organic transformations under visible light using MOF, nano-material, COF, metal, graphitic carbon, organocatalyst as photocatalysts. We have also highlighted organic transformations using visible light in the absence of any metal or other catalysts. Thus, this review covers wide range of organic reactions under visible light and will benefit the synthetic organic chemist community.

Understanding α-lipoic acid photochemistry helps to control the synthesis of plasmonic gold nanostructures.

We propose the photopolymerization of lipoic acid (LA) as an novel approach to produce a cross-linked polymeric matrix of lipoic acid monomers (PALA) which helps to control the size of plasmonic gold nanostructures when using 3,3,6,8-tetramethyl-1-tetralone as the photo-initiator for the reduction of Au(III) to Au0. A complete characterization of the polymer is included, and the dual behaviour of LA as an in situ stabilizer and reducing agent is investigated. These findings are relevant to the understanding of the photochemical transformation of this biologically relevant compound and would benefit the increasing use of LA and PALA for the synthesis of various nanomaterials.

Recent developments in the investigation of driving forces for transforming coinage metal nanoclusters.

Metal nanoclusters serve as an emerging class of modular nanomaterials. The transformation of metal nanoclusters has been fully reflected in their studies from every aspect, including the structural evolution analysis, physicochemical property regulation, and practical application promotion. In this review, we highlight the driving forces for transforming atomically precise metal nanoclusters and summarize the related transforming principles and fundamentals. Several driving forces for transforming nanoclusters are meticulously reviewed herein: ligand-exchange-induced transformations, metal-exchange-induced transformations, intercluster reactions, photochemical transformations, oxidation/reduction-induced transformations, and other factors (intrinsic instability, pH, temperature, and metal salts) triggering transformations. The exploitation of transforming principles to customize the preparations, structures, physicochemical properties, and practical applications of metal nanoclusters is also disclosed. At the end of this review, we provide our perspectives and highlight the challenges remaining for future research on the transformation of metal nanoclusters. Our intended audience is the broader scientific community interested in metal nanoclusters, and we believe that this review will provide researchers with a comprehensive synthetic toolbox and insights on the research fundamentals needed to realize more cluster-based nanomaterials with customized compositions, structures, and properties.

N,N-Dimethylaniline and Zno nanoparticles mediated photochemical transformation of metronidazole

The present study evaluates the photochemical behavior of a nitroimidazole derivative drug metronidazole in presence of N,N dimethylaniline and ZnO nanoparticles. The photochemical behavior was examined in a photochemical reactor by irradiating with a light of 254 and 310 nm. After completion of reaction one photoproduct was obtained. The photoproduct was isolated by using column chromatography and the structure of the isolated photoproduct was established by different spectroscopic techniques. This study provides the probable mechanism of the photochemical transformation of metronidazole in presence of an electron donor and in presence of ZnO NPs. During the photochemical transformation the nitro group of metronidazole was reduced in the amine group by a series of electron transfer processes. The ZnO nanoparticles are very efficient catalysts, and they degrade almost 90% metronidazole in the 60 min of UV irradiation. The photocatalytic mechanism of the ZnO nanoparticles is also discussed.