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The field of lipidomics has been significantly advanced by mass spectrometric analysis. The distinction and quantitation of the unsaturated lipid isomers, however, remain a long-standing challenge. In this study, we have developed an analytical tool for both identification and quantitation of lipid C=C location isomers from complex mixtures using online Paternò–Büchi reaction coupled with tandem mass spectrometry (MS/MS). The potential of this method has been demonstrated with an implementation into shotgun lipid analysis of animal tissues. Among 96 of the unsaturated fatty acids and glycerophospholipids identified from rat brain tissue, 50% of them were found as mixtures of C=C location isomers; for the first time, to our knowledge, the quantitative information of lipid C=C isomers from a broad range of classes was obtained. This method also enabled facile cross-tissue examinations, which revealed significant changes in C=C location isomer compositions of a series of fatty acids and glycerophospholipid (GP) species between the normal and cancerous tissues.

NO[sub.2] primarily originates from natural and anthropogenic emissions. Given China’s vast territory and significant differences in topography and meteorological conditions, a detailed understanding of the impacts of weather and human emissions in different regions is essential. This study employs Kolmogorov–Zurbenko (KZ) filtering and stepwise multiple linear regression to isolate the effects of meteorological conditions on tropospheric NO[sub.2] vertical column densities. Long term trends indicate an overall decline, with anthropogenic contribution rates exceeding 90% in Shanghai, Changchun, Urumqi, Shijiazhuang, and Wuhan, where interannual variations are primarily driven by human emissions. In Guangzhou, the anthropogenic contribution rate exceeds 100%, highlighting the significant impact of human factors in this region, although meteorological conditions somewhat mitigate their effect on NO[sub.2]. In Chengdu, meteorological factors also play a role. Seasonal variations display a U-shaped trend, and there are significant differences in the impact of meteorological factors on seasonal variations among different regions. Meteorological contribution rates in Changchun and Chengdu are below 36.90% and anthropogenic contributions exceed 63.10%. This indicates that changes in NO[sub.2] are less influenced by meteorological factors than by human activities, with human emissions dominating. In other regions, meteorological contributions are greater than those from human activities.

In contrast to the wealth of catalytic systems that are available to control the stereochemistry of thermally promoted cycloadditions, few similarly effective methods exist for the stereocontrol of photochemical cycloadditions. A major unsolved challenge in the design of enantioselective catalytic photocycloaddition reactions has been the difficulty of controlling racemic background reactions that occur by direct photoexcitation of substrates while unbound to catalyst. Here, we describe a strategy for eliminating the racemic background reaction in asymmetric [2 + 2] photocycloadditions of α,β-unsaturated ketones to the corresponding cyclobutanes by using a dual-catalyst system consisting of a visible light–absorbing transition-metal photocatalyst and a stereocontrolling Lewis acid cocatalyst. The independence of these two catalysts enables broader scope, greater stereochemical flexibility, and better efficiency than previously reported methods for enantioselective photochemical cycloadditions.

Many applications of plasmonic nanoparticles require precise control of their optical properties that are governed by nanoparticle dimensions, shape, morphology and composition. Finding reaction conditions for the synthesis of nanoparticles with targeted characteristics is a time-consuming and resource-intensive trial-and-error process, however closed-loop nanoparticle synthesis enables the accelerated exploration of large chemical spaces without human intervention. Here, we introduce the Autonomous Fluidic Identification and Optimization Nanochemistry (AFION) self-driving lab that integrates a microfluidic reactor, in-flow spectroscopic nanoparticle characterization, and machine learning for the exploration and optimization of the multidimensional chemical space for the photochemical synthesis of plasmonic nanoparticles. By targeting spectroscopic nanoparticle properties, the AFION lab identifies reaction conditions for the synthesis of different types of nanoparticles with designated shapes, morphologies, and compositions. Data analysis provides insight into the role of reaction conditions for the synthesis of the targeted nanoparticle type. This work shows that the AFION lab is an effective exploration platform for on-demand synthesis of plasmonic nanoparticles. The automated synthesis of plasmonic nanoparticles with on-demand properties is a challenging task. Here the authors integrate a fluidic reactor, real-time characterization, and machine learning in a self-driven lab for the photochemical synthesis of nanoparticles with targeted properties.

The implementation of continuous flow technology is critical towards enhancing the application of photochemical reactions for industrial process development. However, there are significant time and resource constraints associated with translating discovery scale vial-based batch reactions to continuous flow scale-up conditions. Herein we report the development of a droplet microfluidic platform, which enables high-throughput reaction discovery in flow to generate pharmaceutically relevant compound libraries. This platform allows for enhanced material efficiency, as reactions can be performed on picomole scale. Furthermore, high-throughput data collection via on-line ESI mass spectrometry facilitates the rapid analysis of individual, nanoliter-sized reaction droplets at acquisition rates of 0.3 samples/s. We envision this high-throughput screening platform to expand upon the robust capabilities and impact of photochemical reactions in drug discovery and development. Translating discovery scale vial-based batch reactions to continuous flow scale-up conditions is limited by significant time and resource constraints. Here, the authors report a photochemical droplet microfluidic platform, which enables high throughput reaction discovery in flow to generate pharmaceutically relevant compound libraries.

A novel g-C 3 N 4 nanoparticle@porous g-C 3 N 4 (CNNP@PCN) composite has been successfully fabricated by loading g-C 3 N 4 nanoparticles on the porous g-C 3 N 4 matrix via a simply electrostatic self-assembly method. The composition, morphological structure, optical property, and photocatalytic performance of the composite were evaluated by various measurements, including XRD, SEM, TEM, Zeta potential, DRS, PL, FTIR, and XPS. The results prove that the nanolization of g-C 3 N 4 leads to an apparent blueshift of the absorption edge, and the energy band gap is increased from 2.84 eV of porous g-C 3 N 4 to 3.40 eV of g-C 3 N 4 nanoparticle (Fig. 6). Moreover, the valence band position of the g-C 3 N 4 nanoparticle is about 0.7 eV lower than that of porous g-C 3 N 4 . Therefore, the photo-generated holes and electrons in porous g-C 3 N 4 can transfer to the conduction band of g-C 3 N 4 nanoparticle, thereby obtaining higher separation efficiency of photo-generated carriers as well as longer carrier lifetime. Under visible-light irradiation, 6CNNP@PCN exhibits the highest photocatalytic performance (Fig. 8) on MB, which is approximately 3.4 times as that of bulk g-C 3 N 4 .

Mercury (Hg), a global contaminant, is emitted mainly in its elemental form Hg⁰ to the atmosphere where it is oxidized to reactive HgII compounds, which efficiently deposit to surface ecosystems. Therefore, the chemical cycling between the elemental and oxidized Hg forms in the atmosphere determines the scale and geographical pattern of global Hg deposition. Recent advances in the photochemistry of gas-phase oxidized HgI and HgII species postulate their photodissociation back to Hg⁰ as a crucial step in the atmospheric Hg redox cycle. However, the significance of these photodissociation mechanisms on atmospheric Hg chemistry, lifetime, and surface deposition remains uncertain. Here we implement a comprehensive and quantitative mechanism of the photochemical and thermal atmospheric reactions between Hg⁰, HgI, and HgII species in a global model and evaluate the results against atmospheric Hg observations. We find that the photochemistry of HgI and HgII leads to insufficient Hg oxidation globally. The combined efficient photoreduction of HgI and HgII to Hg⁰ competes with thermal oxidation of Hg⁰, resulting in a large model overestimation of 99% of measured Hg⁰ and underestimation of 51% of oxidized Hg and ∼66% of HgII wet deposition. This in turn leads to a significant increase in the calculated global atmospheric Hg lifetime of 20 mo, which is unrealistically longer than the 3–6-mo range based on observed atmospheric Hg variability. These results show that the HgI and HgII photoreduction processes largely offset the efficiency of bromine-initiated Hg⁰ oxidation and reveal missing Hg oxidation processes in the troposphere.

Heterojunction creation is demonstrated as an effective strategy to enhance the transfer and separation of charge carriers, which is beneficial for subsequent photocatalytic reactions. In this study, “sea urchin-like” W[sub.18]O[sub.49] was in situ-grown on the surface of Bi[sub.12]GeO[sub.20] through a hydrothermal process, and the released Cl[sup.−] anions tended to produce BiOCl simultaneously. Systematical characterizations confirmed the construction of ternary composites Bi[sub.12]GeO[sub.20]/BiOCl/W[sub.18]O[sub.49] (GBW), in which Type I and Z-scheme models were integrated to promote charge carrier migration and separation by combining the structural merits of both models. Under UV–visible light, the catalytic performance of the as-synthesized samples was tested in terms of NO oxidation removal. Compared to pure Bi[sub.12]GeO[sub.20], the composite GBW5 showed the highest NO photocatalytic removal efficiency of 42%, which was nearly four times that of pure Bi[sub.12]GeO[sub.20]. These improvements were mainly due to enhanced light absorption, suitable morphological features, effective separation of charge carriers, and the boosted generation of reactive species in the GBW series. This study paves the way for the construction of Bi[sub.12]GeO[sub.20]-based ternary composites using a comprehensive utilization of waste method and the employment of the composites for the photocatalytic removal of low concentrations of NO at the ppb level.

Organisms from bacteria to humans sense and react to light. Proteins that contain the light-sensitive molecule retinal couple absorption of light to conformational changes that produce a signal or move ions across a membrane. Nogly et al. used an x-ray laser to probe the earliest structural changes to the retinal chromophore within microcrystals of the ion pump bacteriorhodopsin (see the Perspective by Moffat). The excited-state retinal wiggles but is held in place so that only one double bond of retinal is capable of isomerizing. A water molecule adjacent to the proton-pumping Schiff base responds to changes in charge distribution in the chromophore even before the movement of atoms begins. Science , this issue p. eaat0094 ; see also p. 127 Ultrafast crystallography captures the response of the pigment of bacteriorhodopsin to absorption of light. Ultrafast isomerization of retinal is the primary step in photoresponsive biological functions including vision in humans and ion transport across bacterial membranes. We used an x-ray laser to study the subpicosecond structural dynamics of retinal isomerization in the light-driven proton pump bacteriorhodopsin. A series of structural snapshots with near-atomic spatial resolution and temporal resolution in the femtosecond regime show how the excited all-trans retinal samples conformational states within the protein binding pocket before passing through a twisted geometry and emerging in the 13-cis conformation. Our findings suggest ultrafast collective motions of aspartic acid residues and functional water molecules in the proximity of the retinal Schiff base as a key facet of this stereoselective and efficient photochemical reaction.