Polo-like kinase 4 promotes tumorigenesis and glucose metabolism in glioma by activating AKT1 signaling.

Glioblastoma (GBM) is an extremely aggressive tumor associated with a poor prognosis that impacts the central nervous system. Increasing evidence suggests an inherent association between glucose metabolism dysregulation and the aggression of GBM. Polo-like kinase 4 (PLK4), a highly conserved serine/threonine protein kinase, was found to relate to glioma progression and unfavorable prognosis. As revealed by the integration of proteomics and phosphoproteomics, PLK4 was found to be involved in governing metabolic processes and the PI3K/AKT/mTOR pathway. For the first time, this study supports evidence demonstrating that PLK4 activated PI3K/AKT/mTOR signaling through direct binding to AKT1 and subsequent phosphorylating AKT1 at S124, T308, and S473 to promote tumorigenesis and glucose metabolism in glioma. In addition, PLK4-mediated phosphorylation of AKT1 S124 significantly augmented the phosphorylation of AKT1 S473. Therefore, PLK4 exerted an influence on glucose metabolism by stimulating PI3K/AKT/mTOR signaling. Additionally, the expression of PLK4 protein exhibited a positive correlation with AKT1 phosphorylation in glioma patient tissues. These findings highlight the pivotal role of PLK4-mediated phosphorylation of AKT1 in glioma tumorigenesis and dysregulation of glucose metabolism.

Incorporation of a Boron-Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells.

An organoboron small-molecular acceptor (OSMA) MB←N containing a boron-nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on MB←N, OSMA MB-N, with the incorporation of a boron-nitrogen covalent bond (B-N), was designed. We have systematically investigated the charge-transport properties and interfacial charge-transfer characteristics of MB-N, along with MB←N, using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT). Theoretical calculations show that MB-N can simultaneously boost the open-circuit voltage (from 0.78 V to 0.85 V) and the short-circuit current due to its high-lying lowest unoccupied molecular orbital and the reduced energy gap. Moreover, its large dipole shortens stacking and greatly enhances electron mobility by up to 5.91 × 10-3 cm2·V-1·s-1. Notably, the excellent interfacial properties of PTB7-Th/MB-N, owing to more charge transfer states generated through the direct excitation process and the intermolecular electric field mechanism, are expected to improve OSCs performance. Together with the excellent properties of MB-N, we demonstrate a new OSMA and develop a new organoboron building block with B-N units. The computations also shed light on the structure-property relationships and provide in-depth theoretical guidance for the application of organoboron photovoltaic materials.

Atomistic Mechanism of Surface-Defect Passivation: Toward Stable and Efficient Perovskite Solar Cells.

Molecular engineering has been demonstrated to be a predominant strategy for augmenting the long-term stability and passivating adverse defects for perovskite solar cells (PSCs). Here, using density functional theory calculations combined with ab initio molecular dynamics (AIMD) simulations, the passivation effects of bidentate passivation molecules, 2-MP and 2-MDEP, on the iodine vacancy MAPbI3 were comprehensively investigated. We demonstrate that 2-MDEP engenders stronger adsorption and localized charges on Pb atoms because the separated binding sites match with the MAPbI3 lattice. Moreover, the activation barriers for ion migrations are improved by the passivation of 2-MP and 2-MDEP. Furthermore, AIMD simulations verify the improved structural stability and restrained nonradiative recombination after passivation. More importantly, the durable Pb-heteroatom interactions at the interface and stronger hydrophobicity endow 2-MDEP with more remarkable shielding effects against moisture compared to those of 2-MP. This work deepens our understanding of the passivation effects and paves the way for the design of passivation molecules toward the attainment of efficient and stable PSCs.

Theoretical insights into photo-induced isomerization mechanisms of phenylsulfinyl radical PhSO˙.

Sulfinyl radicals (R-SO˙) play important roles in lots of reactions, while the isomer oxathiyl radicals (R-OS˙) and the isomerization between them are rarely observed due to the poor stability of R-OS˙. In this work, the complete active space self-consistent field (CASSCF) and its multi-state second order perturbation (MS-CASPT2) methods were employed to study the photo-induced reaction mechanisms of phenylsulfinyl radical PhSO˙ 1 and its isomer phenoxathiyl radical PhOS˙ 2. Our results show that 1 and 2 have similar singly occupied molecular orbitals in the ground state but different properties in the excited state, which determine their diverse behaviors after irradiation. Radical 1 can generate 2 by light irradiation, but 2 produces isomerization product 3 (2-hydroxyphenylthiyl radical) and ring-opening product 4 (acyclic thioketoketene radical) in two paths via S atom migration intermediate Int1 (2-carbonylcyclohexadienthiyl radical). The former path involves consequent hydrogen shift reactions with a strongly exothermic process while the latter path involves both ring-expansion and ring-opening processes with a high barrier, resulting in a structural and energetic preference for the former path. Moreover, we revealed several conical intersections that participate in the reactions and facilitate the photochemical processes. Our calculations not only remain consistent with and clarify the experimental observations (X. Zeng, et al., J. Am. Chem. Soc., 2018, 140(31), 9972-9978) but also enrich the knowledge of sulfinyl radicals and isomer oxathiyl radicals.

A π-extended triphenylamine based dopant-free hole-transporting material for perovskite solar cells via heteroatom substitution.

The triphenylamine (TPA) group is an important molecular fragment that has been widely used to design efficient hole-transporting materials (HTMs). However, the applicability of triphenylamine derived HTMs that exhibit low hole mobility and conductivity in commercial perovskite solar cells (PSCs) has been limited. To aid in the development of highly desirable TPA-based HTMs, we utilized a combination of density functional theory (DFT) and Marcus electron transfer theory to investigate the effect of heteroatoms, including boron, carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, germanium, arsenic, and selenium atoms, on the energy levels, optical properties, hole mobility, and interfacial charge transfer behaviors of a series of HTMs. Our computational results revealed that compared with the commonly referenced OMeTPA-TPA molecule, most heteroatoms lead to deeper energy levels. Furthermore, these heteroatom-based HTMs exhibit improved hole mobility due to their more rigid molecular structures. More significantly, these heteroatoms also enhance the interface interaction in perovskite/HTM systems, resulting in a larger internal electric field. Our work represents a new approach that aids in the understanding and designing of more efficient and better performing HTMs, which we hope can be used as a platform to propel the developmental commercialization of these highly desirable PSCs.

Theoretical Study of Non-Fullerene Acceptors Using End-Capped Groups with Different Electron-Withdrawing Abilities toward Efficient Organic Solar Cells.

Acceptors in organic solar cells (OSCs) are of paramount importance. On the basis of the well-known non-fullerene acceptor Y6, six acceptors (Y6-COH, Y6-COOH, Y6-CN, Y6-SO2H, Y6-CF3, and Y6-NO2) were designed by end-capped manipulation. The effects of end-capped engineering on electronic properties, optical properties, and interfacial charge-transfer states were systematically studied by density functional theory, time-dependent density functional theory, and molecular dynamics. The designed acceptors possess suitable energy levels and improved optical properties. More importantly, the electron mobility of the new acceptors was greatly enhanced, even more than 20 times that of the parent molecule. Among them, Y6-NO2 with the lowest-lying frontier molecular orbitals and the largest red-shifted absorption was selected to construct interfaces with the donor PM6. PM6/Y6-NO2 exhibits stronger interfacial interactions and enhanced charge-transfer characteristics compared with PM6/Y6. This work not only enhances the understanding of the structure-property relationship for acceptors but also offers a set of promising acceptors for high-performance OSCs.

Theoretical design of asymmetric A-D1A'D2-A type non-fullerene acceptors for organic solar cells.

The acceptor in organic solar cells (OSCs) is of paramount importance for achieving a high photovoltaic performance. Based on the well-known non-fullerene acceptor Y6, we designed a set of asymmetric A-D1A'D2-A type new acceptors Y6-C, Y6-N, Y6-O, Y6-Se, and Y6-Si by substituting the two S atoms of one thieno[3,2-b]thiophene unit with C, N, O, Se, and Si atoms, respectively. The electronic, optical, and crystal properties of Y6 and the designed acceptors, as well as the interfacial charge-transfer (CT) mechanisms between the donor PM6 and the investigated acceptors have been systematically studied. It is found that the newly designed asymmetric acceptors possess suitable energy levels and strong interactions with the donor PM6. Importantly, the newly designed acceptors exhibit enhanced light harvesting ability and more CT states with larger oscillator strengths in the 40 lowest excited states. Among the multiple CT mechanisms, the direct excitation of CT states is found to be more favored in the case of PM6/newly designed acceptors than that of PM6/Y6. This work not only offers a set of promising acceptors superior to Y6, but also demonstrates that designing acceptors with asymmetric structure could be an effective strategy to improve the performance of OSCs.

Theoretical study on the photochemistry of furoylazides: Curtius rearrangement and subsequent reactions.

Organic azides are an efficient source of nitrenes, which serve as vigorous intermediates in many useful organic reactions. In this work, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods were employed to study the photochemistry of 2-furoylazide 1 and 3-furoylazide 5, including the Curtius rearrangement to two furylisocyanates (3 and 7) and subsequent reactions to the final product cyanoacrolein 9. Our calculations show that the photoinduced Curtius rearrangement of the two furoylazides takes place through similar stepwise mechanisms via two bistable furoylnitrenes 2 and 6. However, the decarbonylation and ring-opening process of 7 to 9 prefers a stepwise mechanism involving the 3-furoylnitrene intermediate 8, while 3 to 9 goes in a concerted asynchronous way without the corresponding 2-furoylnitrene intermediate 4. Importantly, we revealed that several conical intersections play key roles in the photochemistry of furoylazides. Our results are not only consistent and also make clear the experimental observations (X. Zeng, et al., J. Am. Chem. Soc., 2018, 140, 10-13), but additionally provide important information on the chemistry of furoylazides and nitrenes.

End-capped group manipulation of indacenodithienothiophene-based non-fullerene small molecule acceptors for efficient organic solar cells.

As the key component of organic solar cells (OSCs), the acceptor plays key roles in determining the power conversion efficiency (PCE). Based on the famous non-fullerene acceptor ITIC, a series of acceptors (A1-A5) were designed by introducing fused-ring units (phenanthrene, pyrene, benzopyrazine, dibenzo[a,c]phenazine, and phenanthro[4,5-abc]phenazine) as the end groups. Theoretical calculations showed that A1-A5 display improved solubility and redshifted absorption spectra compared with ITIC. More importantly, the newly designed acceptors exhibit much higher electron mobility, where the electron mobility of A5_h (similar to A5 but with the same hexyl side chain as ITIC) is about four orders of magnitude larger than that of ITIC. The computed binding energies of the donor PBDB-TF with the acceptor ITIC and A5_h are -2.52 eV and -3.75 eV, indicating much stronger interface interactions in PBDB-TF/A5_h. In terms of charge-transfer (CT) mechanism, we found that both PBDB-TF/ITIC and PBDB-TF/A5_h can generate CT states through direct excitation and hot excitons, meanwhile there exist more opportunities of producing CT states via the intermolecular electric field (IEF) mechanism in PBDB-TF/A5_h. Our results not only offer a set of promising ITIC-based acceptors, but also provide new insights into the donor/acceptor interface properties, which are closely related to the PCE of OSCs.

Molecular Engineering of Hexaazatriphenylene Derivatives toward More Efficient Electron-Transporting Materials for Inverted Perovskite Solar Cells.

The electron-transporting material (ETM) in inverted perovskite solar cells (PSCs) plays important role in reducing hysteresis and realizing simple processing procedures, while the improvement of power conversion efficiency is limited by low electron mobility and weak perovskite/ETM interface interaction. In this work, three new ETMs (HAT-1, HAT-2, and HAT-3) were designed by introducing methoxyphenyl, imide, and naphthalene groups into the hexaazatriphenylene (HAT) skeleton, based on the ETM HATNASOC7 synthesized experimentally [Jen; Angew. Chem., Int. Ed. 2016, 55, 8999]. Theoretical calculations showed that the electron mobilities of HAT-1, HAT-2, and HAT-3 are 2.98, 3.79, and 13.21 times that of HATNASOC7, which is attributed to the increased C···C and O···H interactions in the newly designed ETMs. More importantly, the evidently decreased perovskite/ETM interface distances and the significantly increased adsorption energies revealed that the interface interactions were markedly enhanced with the newly designed ETMs by forming additional Pb···O interactions, which promote the electron injection. The deep understanding of perovskite/ETM interface properties sheds new light on the complex factors determining the PSC function and paves the way for the rational design of highly efficient and stable components for PSCs.

Designing Hole Transport Materials with High Hole Mobility and Outstanding Interface Properties for Perovskite Solar Cells.

Organic-inorganic halide perovskite solar cells (PSCs) have attracted much attention due to their rapid increase in power conversion efficiencies (PCEs), and many efforts are devoted to further improving the PCEs. Designing highly efficient hole transport materials (HTMs) for PSCs may be one of the effective ways. Herein we theoretically designed three new HTMs (FDT-N, FDT-O, and FDT-S) by introducing a nitrogen-phenyl group, an oxygen atom, and a sulfur atom into the spiro core of an experimentally synthesized HTM (FDT), respectively. And then we performed quantum chemical calculation to study their application potential. The results show that the devices with FDT-O and FDT-S instead of FDT may have higher open circuit voltages owing to their lower highest occupied molecular orbital (HOMO) energy levels. Moreover, FDT-S exhibits the best hole transport performance among the studied HTMs, which may be due to the significant HOMO-HOMO overlap in the hole hopping path with the largest transfer integral. Furthermore, the results on interface properties indicate that introducing oxygen and sulfur atoms can enhance the MAPbI3 /HTM interface interaction. The present work not only offers two promising HTMs (FDT-O and FDT-S) for PSCs but also provides theoretical help for subsequent research on HTMs.

Understanding the effects of the co-sensitizing ratio on the surface potential, electron injection efficiency, and Förster resonance energy transfer.

Multiple absorbers that function in different absorption regions (near infra-red (NIR) and UV-Visible (UV-Vis)) have been widely used in solar cell applications to enhance the light-harvesting. Herein, two special co-sensitizing Models 1 and 2, which feature either saturated dye IQ21 or saturated co-sensitizer S2, have been added to a TiO2 surface to explore the effect of the altered sensitizing sequence, namely the co-sensitizing ratio of IQ21/S2 and S2/IQ21 on the electrostatic potential variation (ΔV), electron injection efficiency (ηinj'), and Förster resonance energy transfer (FRET), using density functional theory and first-principle molecular dynamics simulations. The ΔV related to the open-circuit voltage (Voc) is insensitive in both Models 1 and 2. However, the absorption (λabs) and ηinj' associated with the short-circuit density (Jsc) display a significant deviation (the λabs for 1 is red-shifted compared to that of 2, and the ηinj' for 1 is improved by 56%). Meanwhile, Model 1 manifests a suppressed FRET and potentially favors co-sensitizer S2 functioning as the electron-injector and not the energy-donor. Another two possible Models 3 and 4 that feature a reduced adsorption of IQ21 and S2 relative to 1 and 2 were considered further, and the result mirrors the main trend in 1 and 2, except for the ηinj'. Overall, it implies that sensitizing a larger absorber with NIR features to saturate it first, then introducing a smaller absorber with UV-Vis features, can potentially improve the electron injection and diminish electron-hole recombination considerably. Our results provide a comprehensive analysis of the active role of an optimized sensitizing sequence to improve the conversion efficiency.

Theoretical study on the regioselective photoisomerization of asymmetric N,C-chelate organoboron compounds.

Herein, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations were employed to investigate the isomerization reaction mechanisms of an asymmetric N,C-chelate organoboron compound, B(ppy)MesPh, in the ground (S0) state and the first singlet excited (S1) state. Our calculations show that isomerizations proceed via different pathways in the S0 and S1 states,; however, the energy barriers for mesityl isomerization are higher than those for phenyl isomerization in both states; this is in good agreement with the experimentally observed regioselectivity (S. Wang, et al. Angew. Chem., Int. Ed., 2017, 56, 6093-6097). Photoisomerization is motivated by charge transfer from two phenyl rings to the pyridyl moiety and initiated by the cleavage of the B-Cppy bond, followed by the formation of a boracyclopropane ring via an (S1/S0)X conical intersection and a biradical intermediate. Both steric and electronic features were found to be important for regioselective photoisomerization. Our results not only shed light on the experimental observations, but also provide valuable details on the excited state dynamics of organoboron compounds and can facilitate further syntheses and applications.

A peri-Xanthenoxanthene Centered Columnar-Stacking Organic Semiconductor for Efficient, Photothermally Stable Perovskite Solar Cells.

Modulating the structure and property of hole-transporting organic semiconductors is of paramount importance for high-efficiency and stable perovskite solar cells (PSCs). This work reports a low-cost peri-xanthenoxanthene based small-molecule P1, which is prepared at a total yield of 82 % using a three-step synthetic route from the low-cost starting material 2-naphthol. P1 molecules stack in one-dimensional columnar arrangement characteristic of strong intermolecular π-π interactions, contributing to the formation of a solution-processed, semicrystalline thin-film exhibiting one order of magnitude higher hole mobility than the amorphous one based on the state-of-the art hole-transporter, 2,2-7,7-tetrakis(N,N'-di-paramethoxy-phenylamine 9,9'-spirobifluorene (spiro-OMeTAD). PSCs employing P1 as the hole-transporting layer attain a high efficiency of 19.8 % at the standard AM 1.5 G conditions, and good long-term stability under continuous full sunlight exposure at 40 °C.

Nitrogen substitution improves the mobility and stability of electron transport materials for inverted perovskite solar cells.

A suitable electron transport material (ETM) plays key roles in efficient perovskite solar cells (PSCs), because it is beneficial for exciton dissociation and charge transport at the interface thus increasing the short circuit current density. Based on the experimentally reported efficient electron transport molecule 10,14-bis(5-(2-ethylhexyl)thiophen-2-yl)-dipyrido[3,2-a:2',3'-c][1,2,5]thiadiazolo[3,4-i]phenazine (TDTP), we theoretically design a set of new ETMs (TDTP-1, TDTP-2a, TDTP-2b, TDTP-3a, and TDTP-3b) by introducing a nitrogen atom into the thiophene ring or replacing a hydrogen atom on the methyl with an amino group. Quantum-chemical calculations reveal that the designed molecules behave much better than TDTP in terms of electron mobility, air stability, and solubility, where the electron mobility of TDTP-3b is two orders of magnitude higher than that of TDTP owing to the extra SN interactions in TDTP-3b that lead to the quasi two-dimensional π packing motif which facilitates electron transport evidently. Moreover, we find that the substitution effect of the nitrogen atom strongly depends on the position, where the nitrogen atom at the ß-position of the thiophene ring (TDTP-2b and TDTP-3b) is more conducive to electron transport. Importantly, our calculations show that the ETM/perovskite interface interaction is enhanced after the introduction of the nitrogen atom and amino group thanks to the added NPb interaction, which favors electron transport with the newly designed ETMs. Our results not only report a set of novel promising ETMs, but also provide a useful design strategy for efficient ETMs.

Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit. A combination of quantum chemistry and Marcus theory approaches is employed to investigate the effect of different π-bridge units on the optical, electronic, and charge transport properties of P1-P6. The calculation results show that the designed molecules P2 and P5 can become potential acceptor replacements of P1 due to their red-shifted absorption bands, appropriate energy levels, low exciton binding energy, and high electron affinity and electron mobility. Additionally, compared with P3HT/P1, P3HT/P2 and P3HT/P5 exhibit stronger and wider absorption peaks, larger electron transfer distances (DCT), greater transferred charge amounts (Δq), and smaller overlaps (Λ), which shows that P2 and P5 have more significant electron transfer characteristics and favorable exciton dissociation capabilities for enhancing the short-circuit current density (JSC) and thus, they are potential acceptors in OSCs.

Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines.

Arylchlorodiazirines (ACDA) are thermal and photochemical precursors of carbenes that form these molecules via nitrogen elimination. We have studied this reaction with multireference quantum chemical methods (CASSCF and CASPT2) for a series of ACDA derivatives with different substitution at the aromatic ring. The calculations explain the different reactivity trends found in the ground and excited state, with good correlation between the calculated barriers and the experimental reaction rates. The ground state mechanism can be described as a reverse cycloaddition with small charge transfer from the aromatic ring to the diazirine moiety. This is consistent with the lack of correlation between the Hammett σ descriptors and the experimental rates. In contrast, the excited state reaction is the cleavage of a single C-N bond mediated by small barriers of 4-6 kcal mol-1. The reaction path goes through a conical intersection with the ground state, which facilitates radiationless decay and explains the disappearance of the transient absorption signal measured experimentally. This leads to a diazomethane intermediate that ultimately yields the carbene. Electronically, excitation to S1 is characterized initially by significant charge transfer from the phenyl ring to the diazirine. The charge transfer is reversed during the C-N cleavage reaction, and this explains the preferential stabilization of the excited-state minimum by polar solvents and electron-donating substituents. Therefore, our calculations reproduce and explain the relationship found experimentally between the Hammett σ+ parameters and the life time of S1 (Y. L. Zhang, et al. J. Am. Chem. Soc., 2009, 131, 16652-16653).

N-Annulated Perylene-Based Hole Transporters for Perovskite Solar Cells: The Significant Influence of Lateral Substituents.

Perylene derivatives are a family of well-known organic electron-transporting materials with excellent photochemical and thermal stabilities, and have been widely used in various optoelectronic devices. In this work, two diphenylamine functionalized N-annulated perylenes are reported as hole-transporting materials (HTMs) for perovskite solar cells. Through joint theoretical and experimental studies, the HTM employing a methoxyphenyl lateral substituent is found to feature a closer stacking distance and better aggregate connectivity in the solid film than its analogue with the bulky 2-hexyldecyl lateral substituent, contributing to a higher hole mobility and a remarkably enhanced device performance of perovskite solar cells. This work demonstrates the significant influence of lateral substituents of HTMs on the intermolecular packing and solid microstructure, giving a clear insight on the molecular design of high-performance organic semiconductors.

Coconut-based activated carbon fibers for efficient adsorption of various organic dyes.

In this study, using coconut fibers as raw material, activated carbon fibers were prepared via carbonization and KOH activation processes. The morphology, composition, specific surface area, pore structure and thermal stability of the resulting activated carbon fibers were systematically characterized. It was found that the activation process increases the specific surface area of carbon fibers to a greater extent via formation of a large number of micropores (0.7-1.8 nm) and a certain amount of slit-shaped mesopores (2-9 nm). The specific surface area and the pore volume of the activated carbon fibers reach 1556 m2 g-1 and 0.72 cm3 g-1, respectively. The activation process can also decompose the tar deposits formed after the carbonization process by pyrolysis, making the surface of the activated carbon fibers smoother. To study the adsorption properties of the as-prepared activated carbon fibers, the adsorption capacities and adsorption kinetics of various organic dyes including methylene blue, Congo red and neutral red were investigated. The adsorption capacities of the dyes increased with the increasing initial dye concentrations, and varied greatly with the pH value of the system. In methylene blue and neutral red systems, the adsorption capacities reach the maximum at pH 9, and in the Congo red system, it reaches the maximum at pH 3. The adsorption capacities of the activated carbon fibers in methylene blue, Congo red and neutral red systems reached equilibrium at 150, 120, and 120 min, and the maximum adsorption capacities were 21.3, 22.1, and 20.7 mg g-1, respectively. The kinetics of the adsorption process was investigated using three models including pseudo-first-order, pseudo-second-order and intraparticle diffusion models. The results indicated that the dynamic adsorption processes of coconut-based activated carbon fibers to methylene blue, Congo red and neutral red were all in accordance with the second-order kinetic model, and the equations are as follows: t/Q t = 0.1028 + t/21.3220, t/Q t = 0.1128 + t/21.5982 and t/Q t = 0.0210 + t/20.6612.

Effect of Water on the Structure and Stability of Hydrogen-Bonded Oxalic Acid Dimer.

As the simplest and most abundant dicarboxylic acid in the atmosphere, oxalic acid (OA) not only plays a key role in aerosol nucleation, but also acts as a prototypical compound for the investigation of intra- and intermolecular hydrogen-bonding interactions. A systematic theoretical study on the hydrated OA dimers performed by using DFT at the M06-2X/6-311++G(3df, 2p) level is discussed herein. The properties of hydrogen bonds in clusters are inspected through topological analysis by using atoms in molecules (AIM) theory. The most stable OA dimer involves a cyclic structure with two intermolecular hydrogen bonds. Calculations show that one H2 O has a slight effect on the hydrogen bonds, whereas two water molecules weaken and three water molecules break the two intermolecular hydrogen bonds between OAs. Furthermore, there are no hydrogen-bond interactions between OAs in almost all stable clusters as the number of H2 O molecules increases to four and five. Additionally, ionization and isomerization of OA through water-assisted proton-transfer phenomena are observed in tetra- and pentahydrates. This work provides new insights into the conversion of anhydrous OA into hydrated clusters that are helpful for further understanding the atmospheric nucleation process and nature of hydrogen bond.