Excited-State Decay and Photolysis of O-Nitrophenol after Proton Transfer. II: A Theoretical Investigation in the Microsolvated Atmospheric Environment.

Changes in atmospheric humidity affect the number of water molecules surrounding o-nitrophenol (ONP), creating an anisotropic chemical environment. It, in turn, influences the photodynamic behaviors of ONP, differing from those observed in the gas phase and in solution. Recently, we explored the excited-state decay and the generation of the hydroxyl (OH) radical before proton transfer of ONP in the microsolvated environment using the MS-CASPT2//CASSCF approach. As is well known, ONP is capable of converting to its aci-nitro isomer (aciONP) via an excited-state intramolecular proton transfer (ESIPT) process. In the present work, the photoinduced dynamics of aciONP, which can lead to an OH radical and nitrous acid (HONO), was studied using the same computational model. Our calculations demonstrated that increasing the number of water molecules affects the molecular geometries, particularly the key bond lengths and dihedral angles of the HONO group, while also reducing the relative energies of minima and intersections. Moreover, we identified two distinct types of minimum structures: one that retains the intramolecular hydrogen bond and the other that breaks the hydrogen bond with the H atom flipping outward. The latter structure, compared with the former, has a different electronic-state character and facilitates intersystem crossing processes. Subsequently, two major excited-state decay paths were proposed: (PATH I) ESIPT → S1 → S1S0 → S0; (PATH II) ESIPT → S1 → S1-2 → S1T1 → T1 → S0T1 → S0. Furthermore, the T1 state has a relatively long lifetime, allowing for the formation of the OH radical and HONO, and the corresponding energy barriers decrease as the number of water molecules increases. These theoretical findings provide valuable insights into the photodynamics of aciONP in the microsolvated atmospheric environment.

Excited-State Decay and Photolysis of O-Nitrophenol before Proton Transfer. I: A Theoretical Investigation in the Microsolvated Atmospheric Environment.

As a potential source of the hydroxyl (OH) radical and nitrous acid (HONO), photolysis of o-nitrophenol (ONP) is of significant interest in both experimental and theoretical studies. In the atmospheric environment, the number of water molecules surrounding ONP changes with the humidity of the air, leading to an anisotropic chemical environment. This may have an impact on the photodynamics of ONP and provide a mechanism that differs from previously reported ones in the gas phase or in solution. Herein, the high-level MS-CASPT2//CASSCF method was performed to elucidate the excited-state decay and the generation of the OH radical for ONP before proton transfer in the microsolvated surrounding. We found that the varying number of water molecules affects the ground-state structures and alters the energy levels of nπ* and ππ* at the Franck-Condon (FC) region. Nevertheless, this is not the case for the excited-state minima, which exhibit very similar adiabatic excitation properties. In addition, the presence of water molecules also significantly influences the intersection structures since hydrogen bonds will hinder or alleviate the rotation or pyramidalization of the nitro (NO2) group. This will, in turn, change the excited-state relaxation mechanism of ONP. Finally, we speculated that the OH radical might be formed in the hot ground state of ONP in the microsolvated surrounding after exploring all possible electronic states.

Complete genome sequence of the 4-hydroxybenzoate-degrading bacterium Gymnodinialimonas sp. 57CJ19, a potential novel species from intertidal sediments.

A bacterium Gymnodinialimonas sp. 57CJ19, was isolated from the intertidal sediments of Aoshan Bay, and further assays showed that it has the ability to degrade the antibacterial preservative 4-hydroxybenzoate. The complete genome sequence was sequenced, and phylogenomic analyses indicated that strain 57CJ19 represents a potential novel species in the genus Gymnodinialimonas (family Rhodobacteraceae). Its genome contains a 3,861,607-bp circular chromosome with 61.25% G + C content. Gene prediction revealed 3716 protein-encoding genes, 41 tRNA genes, 3 rrn operons, and 3 non-coding RNA genes. Functional annotation revealed a complete metabolic pathway for 4-hydroxybenzoate. The genome sequence of strain 57CJ19 provides new insights into the potential and underlying genomic basis of aromatic compound pollutant degradation by marine bacteria.

Genomic and Metagenomic Insights into the Distribution of Nicotine-degrading Enzymes in Human Microbiota.

Introduction: Nicotine degradation is a new strategy to block nicotine-induced pathology. The potential of human microbiota to degrade nicotine has not been explored. Aims: This study aimed to uncover the genomic potentials of human microbiota to degrade nicotine. Methods: To address this issue, we performed a systematic annotation of Nicotine-Degrading Enzymes (NDEs) from genomes and metagenomes of human microbiota. A total of 26,295 genomes and 1,596 metagenomes for human microbiota were downloaded from public databases and five types of NDEs were annotated with a custom pipeline. We found 959 NdhB, 785 NdhL, 987 NicX, three NicA1, and three NicA2 homologs. Results: Genomic classification revealed that six phylum-level taxa, including Proteobacteria, Firmicutes, Firmicutes_A, Bacteroidota, Actinobacteriota, and Chloroflexota, can produce NDEs, with Proteobacteria encoding all five types of NDEs studied. Analysis of NicX prevalence revealed differences among body sites. NicX homologs were found in gut and oral samples with a high prevalence but not found in lung samples. NicX was found in samples from both smokers and non-smokers, though the prevalence might be different. Conclusion: This study represents the first systematic investigation of NDEs from the human microbiota, providing new insights into the physiology and ecological functions of human microbiota and shedding new light on the development of nicotine-degrading probiotics for the treatment of smoking-related diseases.

Construction of Highly Accurate Machine Learning Potential Energy Surfaces for Excited-State Dynamics Simulations Based on Low-Level Data Sets.

Machine learning is capable of effectively predicting the potential energies of molecules in the presence of high-quality data sets. Its application in the construction of ground- and excited-state potential energy surfaces is attractive to accelerate nonadiabatic molecular dynamics simulations of photochemical reactions. Because of the huge computational cost of excited-state electronic structure calculations, the construction of a high-quality data set becomes a bottleneck. In the present work, we first built two data sets. One was obtained from surface hopping dynamics simulations at the semiempirical OM2/MRCI level. Another was extracted from the dynamics trajectories at the CASSCF level, which was reported previously. The ground- and excited-state potential energy surfaces of ethylene-bridged azobenzene at the CASSCF computational level were constructed based on the former low-level data set. Although non-neural network machine learning methods can achieve good or modest performance during the training process, only neural network models provide reliable predictions on the latter external test data set. The BPNN and SchNet combined with the Δ-ML scheme and the force term in the loss functions are recommended for dynamics simulations. Then, we performed excited-state dynamics simulations of the photoisomerization of ethylene-bridged azobenzene on machine learning potential energy surfaces. Compared with the lifetimes of the first excited state (S1) estimated at different computational levels, our results on the E isomer are in good agreement with the high-level estimation. However, the overestimation of the Z isomer is unimproved. It suggests that smaller errors during the training process do not necessarily translate to more accurate predictions on high-level potential energies or better performance on nonadiabatic dynamics simulations, at least in the present case.

[Spatio-temporal Evolution of Drought and Its Impact on Key Resources in the Important Ecological Functional Area: A Case Study in the Yellow River Basin].

This study explored the characteristics of spatial and temporal changes in drought in the Yellow River Basin from 2001 to 2020 based on TVPDI, surface runoff, vegetation net primary productivity, and grain yield data. Further, the effects of drought on water resources, grain resources, and vegetation resources were also analyzed using data spatialization methods, slope trend analysis, and Pearson correlation analysis. The results showed that:① The spatial distribution of drought in the Yellow River basin was stepped from southeast to northwest, and 60.6 % of the basin was in drought. The overall trend of drought in the basin was decreasing annually, and 94 % of the basin was gradually changing from drought to wet conditions, and the trend of drought from spring to winter decreased first and then increased. ② From the spatial and temporal changes in important resources in the basin, 53 % of the key surface runoff areas showed an increasing trend and were mainly located in the southwest of the basin; the net primary productivity (NPP) of vegetation and grain yield of food resources also showed an increasing trend. ③ Drought and the three types of resources showed significant spatial correlations, and the higher the degree of drought, the more significant the effects on surface runoff, vegetation productivity, and grain yield. However, the important resources in areas that had become wetter in recent years had not increased significantly, which indicated that the effects of drought on the three types of important resources had a time lag, and their lags had significant differences in spatial distribution and geographical differentiation patterns. This study has important theoretical implications for agricultural production, drought mitigation, and ecological conservation in the Yellow River Basin.

Multi-fidelity machine learning for predicting bandgaps of nonlinear optical crystals.

Nonlinear optical (NLO) materials are of great importance in modern optics and industry because of their intrinsic capability of wavelength conversion. Bandgap is a key property of NLO crystals. In recent years, machine learning (ML) has become a powerful tool to predict the bandgaps of compounds before synthesis. However, the shortage of available experimental data of NLO crystals poses a significant challenge for the exploration of new NLO materials using ML. In this work, we proposed a new multi-fidelity ML approach based on the multilevel descriptors developed by us (Z.-Y. Zhang, X. Liu, L. Shen, L. Chen and W.-H. Fang, J. Phys. Chem. C, 2021, 125, 25175-25188) and the gradient boosting regression tree algorithm. The calculated and experimental bandgaps of NLO crystals were collected as the low- and high-fidelity labels, respectively. The experimental values were predicted based on chemical compositions of crystals without prior knowledge about crystal structures. The multi-fidelity ML model overcame the performance of single-fidelity predictor. Furthermore, it was observed that less accurate predictions on the low-fidelity label may result in more accurate prediction on the high-fidelity label, at least in the present case. Using the multi-fidelity ML model with the best performance in this work, the mean absolute error on the test set of experimental bandgaps was 0.293 eV, which is smaller than that using the single-fidelity model (0.355 eV). It is far from perfect but accurate enough as an effective computational tool in the first step to discover novel NLO materials.

Comparative molecular dynamics simulations provided insights into the mechanisms of cold-adaption of alginate lyases from the PL7 family.

Alginate is an important polysaccharide that is abundant in the marine environments, including the Polar Regions, and bacterial alginate lyases play key roles in its degradation. Many reported alginate lyases show characteristics of cold-adapted enzymes, including relatively low temperature optimum of activities (Topt) and low thermal stabilities. However, the cold-adaption mechanisms of alginate lyases remain unclear. Here, we studied the cold-adaptation mechanisms of alginate lyases by comparing four members of the PL7 family from different environments: AlyC3 from the Arctic ocean (Psychromonas sp. C-3), AlyA1 from the temperate ocean (Zobellia galactanivorans), PA1167 from the human pathogen (Pseudomonas aeruginosa PAO1), and AlyQ from the tropic ocean (Persicobacter sp. CCB-QB2). Sequence comparison and comparative molecular dynamics (MD) simulations revealed two main strategies of cold adaptation. First, the Arctic AlyC3 and temperate AlyA1 increased the flexibility of the loops close to the catalytic center by introducing insertions at these loops. Second, the Arctic AlyC3 increased the electrostatic attractions with the negatively charged substrate by introducing a high portion of positively charged lysine at three of the insertions mentioned above. Furthermore, our study also revealed that the root mean square fluctuation (RMSF) increased greatly when the temperature was increased to Topt or higher, suggesting the RMSF increase temperature as a potential indicator of the cold adaptation level of the PL7 family. This study provided new insights into the cold-adaptation mechanisms of bacterial alginate lyases and the marine carbon cycling at low temperatures.

Annotation of 2,507 Saccharomyces cerevisiae genomes.

Saccharomyces cerevisiae (baker's yeast, budding yeast) is one of the most important model organisms for biological research and is a crucial microorganism in industry. Currently, a huge number of Saccharomyces cerevisiae genome sequences are available at the public domain. However, these genomes are distributed at different websites and a large number of them are released without annotation information. To provide one complete annotated genome data resource, we collected 2,507 Saccharomyces cerevisiae genome assemblies and re-annotated 2,506 assemblies using a custom annotation pipeline, producing a total of 15,407,164 protein-coding gene models. With a custom pipeline, all these gene sequences were clustered into families. A total of 1,506 single-copy genes were selected as marker genes, which were then used to evaluate the genome completeness and base qualities of all assemblies. Pangenomic analyses were performed based on a selected subset of 847 medium-high-quality genomes. Statistical comparisons revealed a number of gene families showing copy number variations among different organism sources. To the authors' knowledge, this study represents the largest genome annotation project of S. cerevisiae so far, providing rich genomic resources for the future studies of the model organism S. cerevisiae and its relatives.IMPORTANCESaccharomyces cerevisiae (baker's yeast, budding yeast) is one of the most important model organisms for biological research and is a crucial microorganism in industry. Though a huge number of Saccharomyces cerevisiae genome sequences are available at the public domain, these genomes are distributed at different websites and most are released without annotation, hindering the efficient reuse of these genome resources. Here, we collected 2,507 genomes for Saccharomyces cerevisiae, performed genome annotation, and evaluated the genome qualities. All the obtained data have been deposited at public repositories and are freely accessible to the community. This study represents the largest genome annotation project of S. cerevisiae so far, providing one complete annotated genome data set for S. cerevisiae, an important workhorse for fundamental biology, biotechnology, and industry.

Mechanistic photophysics of tellurium-substituted cytosine: Electronic structure calculations and nonadiabatic dynamics simulations.

Previously, the MS-CASPT2 method was performed to study the static and qualitative photophysics of tellurium-substituted cytosine (TeC). To get quantitative information, we used our recently developed QTMF-FSSH dynamics method to simulate the excited-state decay of TeC. The CASSCF method was adopted to reduce the calculation costs, which was confirmed to provide reliable structures and energies as those of MS-CASPT2. A detailed structural analysis showed that only 5% trajectories will hop to the lower triplet or singlet state via the twisted (S2 /S1 /T2 )T intersection, while 67% trajectories will choose the planar intersections of (S2 /S1 /T3 /T2 /T1 )P and (S2 /S1 /T2 /T1 )P but subsequently become twisted in other electronic states. By contrast, ~28% trajectories will maintain in a plane throughout dynamics. Electronic population revealed that the S2 population will ultrafast transfer to the lower triplet or singlet state. Later, the TeC system will populate in the spin-mixed electronic states composed of S1 , T1 and T2 . At the end of 300 fs, most trajectories (~74%) will decay to the ground state and only 17.4% will survive in the triplet states. Our dynamics simulation verified that tellurium substitution will enhance the intersystem crossings, but the very short triplet lifetime (ca. 125 fs) will make TeC a less effective photosensitizer.

Insights into the composition and assembly mechanism of microbial communities on intertidal microsand grains.

Introduction: Marine microorganisms are essential in marine ecosystems and have always been of interest. Currently, most marine microbial communities are studied at the bulk scale (millimeters to centimeters), and the composition, function and underlying assembly mechanism of microbial communities at the microscale (sub-100 micrometers) are unclear. Methods: The microbial communities on microsand grains (40-100 µm, n = 150) from marine sediment were investigated and compared with those on macrosand grains (400-1000 µm, n = 60) and bulk sediments (n = 5) using amplicon sequencing technology. Results: The results revealed a significant difference between microsand grains and macrosand grains. Microsand grains had lower numbers of operational taxonomic units (OTUs(97%)) and predicted functional genes than macrosand grains and bulk-scale samples. Microsand grains also showed greater intersample differences in the community composition and predicted functional genes than macrosand grains, suggesting a high level of heterogeneity of microbial communities at the microscale. Analyses based on ecological models indicated that stochastic processes dominated the assembly of microbial communities on sand grains. Consistently, cooccurrence network analyses showed that most microbial cooccurrence associations on sand grains were highly unstable. Metagenomic sequencing and further genome-scale metabolic modeling revealed that only a small number (1.3%) of microbe pairs showed high cooperative potential. Discussion: This study explored the microbial community of marine sediments at the sub-100 µm scale, broadening the knowledge of the structure and assembly mechanism of marine microbial communities.

Enrichment Pretreatment Expands the Microbial Diversity Cultivated from Marine Sediments.

The majority of the microbial diversity in nature has not been recovered through cultivation. Enrichment is a classical technique widely used in the selective cultivation of specific taxa. Whether enrichment is suitable for cultivation studies that aim to recover large numbers of species remains little explored. To address this issue, we evaluated the potential of enrichment pretreatment in the cultivation of bacteria from marine sediments. Upon obtaining and classifying a total of 943 pure cultures from chitin and cellulose enrichment pretreatment systems and a control system, our results showed that species obtained using enrichment pretreatment differed greatly from those without enrichment. Multiple enrichment media and different enrichment times increased the number of cultivated species in a sample. Amplicon sequencing showed that the increased relative abundance during pretreatment contributed greatly to bacterial cultivation. The testing of degradation abilities against chitin and cellulose and the whole-genome sequencing of representative strains suggested that microorganism-microorganism interactions play roles in the expanded diversity of cultivated bacteria. This study provides new insights into the abilities of enrichment in exploring cultivable diversity and mining microbial resources.

Quantum mechanics/molecular mechanics studies on the excited-state decay mechanisms of cytidine aza-analogues: 5-azacytidine and 2'-deoxy-5-azacytidine in aqueous solution.

The excited state properties and deactivation pathways of two DNA methylation inhibitors, i.e., 5-azacytidine (5ACyd) and 2'-deoxy-5-azacytidine (5AdCyd) in aqueous solution, are comprehensively explored with the QM(CASPT2//CASSCF)/MM protocol. We systematically map the feasible decay mechanisms based on the obtained excited-state decay paths involving all the identified minimum-energy structures, conical intersections, and crossing points driving the different internal conversion (IC) and intersystem crossing (ISC) routes in and between the 1ππ*, 1nπ*, 3ππ*, 3nπ*, and S0 states. Unlike the 1nπ* state below the 1ππ* state in 5ACyd, deoxyribose group substitution at the N1 position leads to the 1ππ* state becoming the S1 state in 5AdCyd. In 5ACyd and 5AdCyd, the initially populated 1ππ* state mainly deactivates to the S0 state through the direct 1ππ* → S0 IC or mediated by the 1nπ* state. The former nearly barrierless IC channel of 1ππ* → S0 occurs ultrafast via the nearby low-lying 1ππ*/S0 conical intersection. In the latter IC channel of 1ππ* → 1nπ* → S0, the initially photoexcited 1ππ* state first approaches the nearby S2/S1 conical section 1ππ*/1nπ* and then undergoes efficient IC to the 1nπ* state, followed by the further IC to the initial S0 state via the S1/S0 conical intersection 1nπ*/S0. The 1nπ*/S0 conical intersection is estimated to be located 6.0 and 4.9 kcal mol-1 above the 1nπ* state minimum in 5ACyd and 5AdCyd, respectively, at the QM(CASPT2)/MM level. In addition to the efficient singlet-mediated IC channels, the minor ISC routes would populate 1ππ* to T1(ππ*) through 1ππ* → T1 or 1ππ* → 1nπ* → T1. Relatively, the 1ππ* → 1nπ* → T1 route benefits from the spin-orbit coupling (SOC) of 1nπ*/3ππ* of 8.7 cm-1 in 5ACyd and 10.2 cm-1 in 5AdCyd, respectively. Subsequently, the T1 system will approach the nearby T1/S0 crossing point 3ππ*/S0 driving it back to the S0 state. Given the 3ππ*/S0 crossing point located above the T1 minimum and the small T1/S0 SOC, i.e., 8.4 kcal mol-1 and 2.1 cm-1 in 5ACyd and 6.8 kcal mol-1 and 1.9 cm-1 in 5AdCyd, respectively, the slow T1 → S0 would trap the system in the T1 state for a while. The present work could contribute to understanding the mechanistic photophysics and photochemistry of similar aza-nucleosides and their derivatives.

Improved Interfacial Ion Migration and Deposition through the Chain-Liquid Synergistic Effect by a Carboxylated Hydrogel Electrolyte for Stable Zinc Metal Anodes.

The large-scale applicability of Zn-metal anodes is severely impeded by the issues such as the dendrite growth, complicated hydrogen evolution, and uncontrollable passivation reaction. Herein, a negatively charged carboxylated double-network hydrogel electrolyte (Gelatin/Sodium alginate-acetate, denoted as Gel/SA-acetate) has been developed to stabilize the interfacial electrochemistry, which restructures a type of Zn2+ ion solvent sheath optimized via a chain-liquid synergistic effect. New hydrogen bonds are reconstructed with water molecules by the zincophilic functional groups, and directional migration of hydrated Zn2+ ions is therefore induced. Concomitantly, the robust chemical bonding of such hydrogel layers to the Zn slab exhibits a desirable anti-catalytic effect, thereby greatly diminishing the water activity and eliminating side reactions. Subsequently, a symmetric cell using the Gel/SA-acetate electrolyte demonstrates a reversible plating/stripping performance for 1580 h, and an asymmetric cell reaches a state-of-the-art runtime of 5600 h with a high average Coulombic efficiency of 99.9 %. The resultant zinc ion hybrid capacitors deliver exceptional properties including the capacity retention of 98.5 % over 15000 cycles, energy density of 236.8 Wh kg-1 , and high mechanical adaptability. This work is expected to pave a new avenue for the development of novel hydrogel electrolytes towards safe and stable Zn anodes.

Phosphorus-Mediated Local Charge Distribution of N-Configuration Adsorption Sites with Enhanced Zincophilicity and Hydrophilicity for High-Energy-Density Zn-Ion Hybrid Supercapacitors.

Tailor-made carbonaceous-based cathodes with zincophilicity and hydrophilicity are highly desirable for Zn-ion storage applications, but it remains a great challenge to achieve both advantages in the synthesis. In this work, a template electrospinning strategy is developed to synthesize nitrogen and phosphorous co-doped hollow porous carbon nanofibers (N, P-HPCNFs), which deliver a high capacity of 230.7 mAh g-1 at 0.2 A g-1 , superior rate capability of 131.0 mAh g-1 at 20 A g-1 , and a maximum energy density of 196.10 Wh kg-1 at the power density of 155.53 W kg-1 . Density functional theory calculations (DFT) reveal that the introduced P dopants regulate the distribution of local charge density of carbon materials and therefore facilitate the adsorption of Zn ions due to the increased electronegativity of pyridinic-N. Ab initio molecular dynamics (AIMD) simulations indicate that the doped P species induce a series of polar sites and create a hydrophilic microenvironment, which decreases the impedance between the electrode and the electrolyte and therefore accelerates the reaction kinetics. The marriage of ex situ/in situ experimental analyses and theoretical simulations uncovers the origin of the enhanced zincophilicity and hydrophilicity of N, P-HPCNFs for energy storage, which accounts for the faster ion migration and electrochemical processes.

Understanding the Excited-State Relaxation Mechanisms of Xanthophyll Lutein by Multi-configurational Electronic Structure Calculations.

The contradictory behaviors in light harvesting and non-photochemical quenching make xanthophyll lutein the most attractive functional molecule in photosynthesis. Despite several theoretical simulations on the spectral properties and excited-state dynamics, the atomic-level photophysical mechanisms need to be further studied and established, especially for an accurate description of geometric and electronic structures of conical intersections for the lowest several electronic states of lutein. In the present work, semiempirical OM2/MRCI and multi-configurational restricted active space self-consistent field methods were performed to optimize the minima and conical intersections in and between the 1Ag-, 2Ag-, 1Bu+, and 1Bu- states. Meanwhile, the relative energies were refined by MS-CASPT2(10,8)/6-31G*, which can reproduce correct electronic state properties as those in the spectroscopic experiments. Based on the above calculation results, we proposed a possible excited-state relaxation mechanism for lutein from its initially populated 1Bu+ state. Once excited to the optically bright 1Bu+ state, the system will propagate along the key reaction coordinate, i.e., the stretching vibration of the conjugated carbon chain. During this period of time, the 1Bu- state will participate in and forms a resonance state between the 1Bu- and 1Bu+ states. Later, the system will rapidly hop to the 2Ag- state via the 1Bu+/2Ag- conical intersection. Finally, the lutein molecule will survive in the 2Ag- state for a relatively long time before it internally converts to the ground state directly or via a twisted S1/S0 conical intersection. Notably, though the photophysical picture may be very different in solvents and proteins, the current theoretical study proposed a promising calculation protocol and also provided many valuable mechanistic insights for lutein and similar carotenoids.

Quantum mechanics/molecular mechanics studies on mechanistic photophysics of cytosine aza-analogues: 2,4-diamino-1,3,5-triazine and 2-amino-1,3,5-triazine in aqueous solution.

The excited-state properties and photophysics of cytosine aza-analogues, i.e., 2,4-diamino-1,3,5-triazine (2,4-DT) and 2-amino-1,3,5-triazine (2-AT) in solution have been systematically explored using the QM(MS-CASPT2//CASSCF)/MM approach. The excited-state nonradiative relaxation mechanisms for the initially photoexcited S1(ππ*) state decay back to the S0 state are proposed in terms of the present computed minima, surface crossings (conical intersections and singlet-triplet crossings), and excited-state decay paths in the S1, S2, T1, T2, and S0 states. Upon photoexcitation to the bright S1(ππ*) state, 2,4-DT quickly relaxes to its S1 minimum and then overcomes a small energy barrier of 5.1 kcal mol-1 to approach a S1/S0 conical intersection, where the S1 system hops to the S0 state through S1 → S0 internal conversion (IC). In addition, at the S1 minimum, the system could partially undergo intersystem crossing (ISC) to the T1 state, followed by further ISC to the S0 state via the T1/S0 crossing point. In the T1 state, an energy barrier of 7.9 kcal mol-1 will trap 2,4-DT for a while. In parallel, for 2-AT, the system first relaxes to the S1 minimum and then S1 → S0 IC or S1 → T1 → S0 ISCs take place to the S0 state by surmounting a large barrier of 15.3 kcal mol-1 or 11.9 kcal mol-1, respectively, which heavily suppress electronic transition to the S0 state. Different from 2,4-DT, upon photoexcitation in the Franck-Condon region, 2-AT can quickly evolve in an essentially barrierless manner to nearby S2/S1 conical intersection, where the S2 and T1 states can be populated. Once it hops to the S2 state, the system will overcome a relatively small barrier (6.6 kcal mol-1vs. 15.3 kcal mol-1) through IC to the S0 state. Similarly, an energy barrier of 11.9 kcal mol-1 heavily suppresses the T1 state transformation to the S0 state. The present work manifests that the amination/deamination of the triazine rings can affect some degree of different vertical and adiabatic excitation energies and nonradiative decay pathways in solution. It not only rationalizes excited-state decay dynamics of 2,4-DT and 2-AT in aqueous solution but could also provide insights into the understanding of the photophysics of aza-nucleobases.

Photoinduced boron atom insertion of benzocyclobutene forming an unprecedented fused boron heterocyclic radical.

Two novel boron heterocyclic radicals, an addition bicyclo[4.2.1]octa-1,3,5-trien-1-yl-borane radical (A) and an insertion 7-1H-borolo[1,2-a]borinine radical (B), were synthesized, and characterized in the reaction of atomic boron with benzocyclobutene. Species B involving a fused boron heterocyclic was spectroscopically characterized for the first time. This work is a new approach for boron-mediated molecular editing and the synthesis of fused boron heterocyclic compounds.

Modulating Cation Migration and Deposition with Xylitol Additive and Oriented Reconstruction of Hydrogen Bonds for Stable Zinc Anodes.

Highly reversible plating/stripping in aqueous electrolytes is one of the critical processes determining the performance of Zn-ion batteries, but it is severely impeded by the parasitic side reaction and dendrite growth. Herein, a novel electrolyte engineering strategy is first proposed based on the usage of 100 mM xylitol additive, which inhibits hydrogen evolution reaction and accelerates cations migration by expelling active H2 O molecules and weakening electrostatic interaction through oriented reconstruction of hydrogen bonds. Concomitantly, xylitol molecules are preferentially adsorbed by Zn surface, which provides a shielding buffer layer to retard the sedimentation and suppress the planar diffusion of Zn2+ ions. Zn2+ transference number and cycling lifespan of Zn∥Zn cells have been significantly elevated, overwhelmingly larger than bare ZnSO4 . The cell coupled with a NaV3 O8 cathode still behaves much better than the additive-free device in terms of capacity retention.

Combined QM (MS-CASPT2)/MM studies on photocyclization and photoisomerization of a fulgide derivative in toluene solution.

Photocyclization and photoisomerization of fulgides have been extensively studied experimentally and computationally due to their significant potential applications for example as photoswitches in memory devices. However, the reported excited-state decay mechanisms of fulgides do not include the effects of solvation explicitly to date. Herein, calculations using the high-level MS-CASPT2//CASSCF method were conducted to explore the photoinduced excited-state decay processes of the Eα conformer of a fulgide derivative in toluene with solvent effects treated by implicit PCM and explicit QM/MM models, respectively. Several minima and conical intersections were optimized successfully in and between the S0 and S1 states; then, two nonadiabatic excited-state decay channels that could efficiently drive the system to the ground state were proposed based on the excited-state ring-closure and isomerization paths. In addition, we also found that in the ring-closure path, the potential energy surface is essentially barrierless before approaching the conical intersection, while it needs to overcome a small energy barrier along the E → Z photoisomerization path for the nonadiabatic S1 → S0 internal conversion process. The present computational results could provide useful mechanistic insights into the photoinduced cyclization and isomerization reactions of fulgide and its derivatives.