Theoretical Investigation and Molecular Design: A Series of Tripod-Type Cu(I) Blue Light Thermally Activated Delayed Fluorescence Materials.

The photophysical properties and luminescent mechanism of a series of tripod-type Cu(I) complexes in solution and solids were comprehensively investigated through theoretical simulations. From a microscopic perspective, the experimental phenomenon is explained: (1) The intrinsic reason for the quenching of complex 1 in solution was attributed to the significant nonradiative transition caused by structural deformation; (2) In the solid, the reduced ΔEST for complex 2 effectively facilitate reverse intersystem crossing (RISC) and improves its luminescence efficiency; (3) The enhanced performance of complex 3 in solution is attributed to that its stronger steric hindrance is advantageous to decrease not only the ΔEST but also the reorganization energy through intramolecular weak interactions. Based on complex 3, the tert-butyl substituted isomeric complex 4 was designed. Complex 4 further amplifies the advantages of 3 to further promote the RISC to make full use of excitons. Meanwhile, it has an emission wavelength of 462.6 nm, which makes it an excellent candidate for high-efficiency deep-blue TADF materials. This study provides valuable information for obtaining efficient blue phosphorescence and TADF dual-channel luminescent materials.

Self-Consistent Quantum Mechanics/Embedded Charge Study on Aggregation-Enhanced Delayed Fluorescence of Cu(I) Complexes: Luminescence Mechanism and Molecular Design Strategy.

To elucidate the luminescence mechanism of highly efficient blue Cu(N^N)(POP)+-type thermally activated delayed fluorescence (TADF) materials, we have selected Cu(pytfmpz)(POP)+ (1) and Cu(pympz)(POP)+ (2) as targets to investigate the photophysical properties in both solution and solid phases. The self-consistent electrostatic potential (ESP) embedded charge within the quantum mechanics/molecular mechanics (QM/MM) method demonstrates a greater advantage over the charge equilibrium (QEQ) in accurately calculating atomic charges and reasonably describing the polarization effect, ultimately resulting in a favorable consistency between simulation and experimental measurements. After systematic and quantitative simulation, it has been found that complex 2, with an electron-donating group of -CH3, exhibits a much more blue-shifted spectrum and a significantly enhanced efficiency in comparison to complex 1 with -CF3. This is due to the widened HOMO-LUMO gap as well as the narrowed energy gap between the lowest singlet and triplet excited states (ΔEST), respectively. Then, the designed complex 3 is introduced with a stronger electron donor and larger tert-butyl group, which plays a key role in simultaneously suppressing the structural distortion and reducing the ΔEST. This leads to a faster reverse intersystem crossing process than that of the two experimental complexes in solution, turning out to be a new deep-blue-emitting material with excellent TADF performance.

Molecular Design of Highly Efficient Heavy-Atom-free NpImidazole Derivatives for Two-Photon Photodynamic Therapy and ClO- Detection.

Two-photon photodynamic therapy (TP-PDT), as a treatment technology with deep penetration and less damage, provides a broad prospect for cancer treatment. Nowadays, the development of TP-PDT suffers from the low two-photon absorption (TPA) intensity and short triplet state lifetime of photosensitizers (PSs) used in TP-PDT. Herein, we propose some novel modification strategies based on the thionated NpImidazole (the combination of naphthalimide and imidazole) derivatives to make efforts on those issues and obtain corresponding fluorescent probes for detecting ClO- and excellent PSs for TP-PDT. Density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to help us characterize the photophysical properties and TP-PDT process of the newly designed compounds. Our results show that the introduction of different electron-donating groups at the position 4 of NpImidazole can effectively improve their TPA and emission properties. Specifically, 3s with a N,N-dimethylamino group has a large triplet state lifetime (τ = 699 µs) and TPA cross section value (δTPA = 314 GM), which can effectively achieve TP-PDT; additionally, 4s (with electron-donating group 2-oxa-6-azaspiro[3.3]heptane in NpImidazole) effectively realizes the dual-function of a PS for TP-PDT (τ = 25,122 µs, δTPA = 351 GM) and a fluorescent probe for detecting ClO- (Φf = 29% of the product 4o). Moreover, an important problem is clarified from a microscopic perspective, that is, why the transition property of 3s and 4s (1π-π*) from S1 to S0 is different from that of 1s and 2s (1n-π*). It is hoped that our work can provides valuable theoretical clues for the design and synthesis of heavy-atom-free NpImidazole-based PSs and fluorescent probes for the detection of hypochlorite.

Theoretical study of the tuning role of ß-methylthio or ß-methylselenyl on the charge-transport properties of acenedithiophenes derivatives.

To date, the manipulation of intermolecular nonconjugation interactions in organic crystals is still a great challenge due to the complexity of weak intermolecular interactions. Here we designed molecules substituted by ß-methylselenyl on naphtho[1,2-b:5,6-b']dithiophene and anthra[2,3-b:6,7-b']dithiophene, respectively (anti-ß-MS-NDT, anti-ß-MS-ADT), which together with anti-ß-MS-BDT synthesized experimentally all exhibited 2D brickwork π-stacking. Moreover, their maximum molecular carrier mobilities reached 3.30 and 16.46 cm2 V-1 s-1. These results indicated that the substitution of ß-methylselenyl could be a strategy to directionally adjust the parent herringbone stacking into 2D brickwork π-stacking. Hirshfeld surface analysis and symmetry-adapted perturbation theory (SAPT) were used to investigate the nonconjugated interactions in the pitched π-stacking formed by the ß-methylthio-substituted acenedithiophene derivatives and the 2D brickwork π-stacking of the ß-methylselenyl-substituted ones; wherein, the steric hindrance caused by the introduction of the substituents promoted Csp2-Csp2⋯π interactions to replace Csp2-H⋯π to stabilize the face-to-face stacking. Moreover, by calculating the decomposition energy of the intermediate state model of the molecular stacking mode that may exist in the replacement conversion process, it was found that the energy of this intermediate state was larger than that of the actual ones, finally confirming the inevitability of the actual existence in this stacking. In addition, because of the reduction in intensity of the special vibration modes, it could be found that the ß-methylselenyl substitution showed better phonon assistance than ß-methylthio substitution in terms of dynamic disorder. This study is a further step toward fully understanding the relationship between intermolecular interactions and regulation of the molecular stacking.

Photophysical Exploration of Zn(II) Polypyridine Photosensitizers in Two-Photon Photodynamic Therapy: Insights from Theory.

The high incidence and difficulties of treatment of cancer have always been a challenge for mankind. Two-photon photodynamic therapy (TP-PDT) as a less invasive technique provides a new perspective for tumor treatment due to its low-energy near-infrared excitation, high targeting, and minor damage. At present, the emerging metal complexes used as the photosensitizers (PSs) in TP-PDT have aroused great interest. However, most metal complexes as PSs in TP-PDT still face some problems, such as slow clearance, unsatisfactory two-photon absorption (TPA) characteristics, high price, low reactivity, and poor solubility. In this work, density functional theory and time-dependent density functional theory were used to characterize the one/two-photon response, solvation free energy, and lipophilicity of a series of novel PSs applied in TP-PDT. The results suggest that based on complex 1, replacing Ru(II) center with Zn(II) (complex 2) can effectively prolong the triplet excited state lifetime while reducing the cost and environmental pollution, and the azetidine heterospirocycles were introduced into the ligand scaffold (complex 3), which effectively reduced the vibration relaxation of the ligand group and improved the water solubility; further, the addition of acetylenyl groups subtly enhanced the light absorption and significantly improved the two-photon response (complex 4). In addition, all complexes met the requirement of a PS and could be used as potential candidates for TP-PDT. In particular, complex 4 has the advantages of high solvation free energy, a large TPA cross-section (1413 GM), a long triplet state lifetime (671 µs), good chemical reactivity, and low cost, and it is easy to be scavenged by organisms. Overall, this contribution may provide an important clue to formulate clear design principles for type I/II PSs and rational design of PSs with high intersystem crossing rates, a long lifetime, and therapeutic excitation wavelengths.

Exogenous melatonin improves cadmium tolerance in Solanum nigrum L. without affecting its remediation potential.

Although Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium (Cd). Thus, the development of eco-friendly strategies to enhance its tolerance, maintaining remediation potential is of special interest. The present work aimed to evaluate the effects of exogenous application of melatonin (MT) in the physiological and biochemical responses of S. nigrum and remediation potential exposed to Cd. After 30 days of exposure, the results revealed that Cd-mediated inhibitory effects on biomass and photosynthetic pigment synthesis were efficiently mitigated upon application of melatonin, without affecting Cd accumulation. Higher levels of Cd were found in roots, regardless of the pretreatment with the melatonin. Foliar application of melatonin, however, induced distinctive effects, lowering malondialdehyde (MDA), relative electrical conductivity (REL), and proline levels in shoots. These changes contributed to improvements in the water status, photosynthetic pigment synthesis, and biomass production of S. nigrum under Cd stresses. Overall, our results indicate a protective effect of melatonin on S. nigrum response to excess Cd, contributing to a better tolerance and growth rate, without disturbing its phytoremediation potential.Novelty statementAlthough Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium. This study evaluated the potential of melatonin to boost S. nigrum defence against Cd toward a better growth rate and remediation potential.

From luminescence quenching to high-efficiency phosphorescence: a theoretical study on the monomeric and dimeric forms of platinum(II) complexes with both 2-pyridylimidazol-2-ylidene and bipyrazolate chelates.

To develop solid-state light-emitting materials with high luminescence efficiency, determining the potential photophysics and luminescence mechanisms of the aggregation state remains a challenge and a priority. Here, we apply density functional theory to study the photophysical properties of a series of square planar Pt(ii) complexes in both monomeric and dimeric forms. We reveal that four monomeric Pt(ii) complexes are dominated by triplet ligand-to-ligand charge-transfer, and the lack of the triplet metal-to-ligand charge-transfer feature results in weak spin-orbit coupling (SOC), which leads to limited radiative rates; moreover, calculated nonradiative transition rates are one or two orders of magnitude higher than those radiative rates because a large amount of reorganization energy caused by the vibration of the bipyrazolate (bipz) ligand cannot be readily suppressed in the monomeric form. Therefore, four monomers exhibit photoluminescence quenching in CH2Cl2 solution in both theoretical calculations and experiments. However, in the solid state, the intense luminescence phenomenon indicates obviously distinct properties between the monomer and aggregation. We carried out a dimer model to interpret that the interaction of PtPt induces a metal-metal-to-ligand charge-transfer excimeric state, which leads more metal components to participate in the charge transfer and enhance the SOC effect. At the same time, the ligand vibration can be significantly reduced by the shortened distance, and there is a strong π-π packing interaction in the dimer; thus, an excellent quantum yield can be achieved in aggregation. In addition, we disclose that introducing bulky substituents bearing electron-donating groups at R' and R'' positions have little effect on the properties of the monomers; however, there is a benefit of restricting the internal reorganization energy through the intermolecular interaction when packing in the solid state. Therefore, substitutions can be tuned to improve the properties of monomers (such as emission energy and reorganization energy). We hope that our work will shine some light on Pt(ii) emitters in the fabrication of efficient OLEDs.

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy.

Investigation of the clear structure-property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6'-dimethyl-2,2'-bipyridine (1) or dmp = 2,9-dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure-TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S1 → S0, (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔEST) and plunged reorganization energy between the S1 and T1 states, the rate of RISC in complex 4 (1.05 × 108 s-1) increased 2 orders of magnitude relative to that of 2 (5.80 × 106 s-1), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.

Characterization of binding interaction of triclosan and bovine serum albumin.

Triclosan (TCS) is widely used in personal care products and acts as an antibacterial agent. Residues of TCS may have potential effects on the human health. In this article, the interaction between TCS and bovine serum albumin (BSA) has been characterized by using multi-spectroscopic approaches and molecular docking method under physiological conditions. Thermodynamic investigations revealed that TCS spontaneously bound to a binding site of BSA and hydrogen bonds played a dominant role in this process. The site marker competition experiments indicated that TCS bound at site II (subdomain IIIA) of BSA, which was well substantiated by molecular docking. The binding of TCS further led to changes of conformation and microenvironment of BSA. This work explored the interaction of TCS with BSA, which might be beneficial for evaluating the binding mechanism of other environmental pollutant at molecular level.

Theoretical Investigations into the Electron and Ambipolar Transport Properties of Anthracene-Based Derivatives.

To obtain anthracene-based derivatives with electron transport behavior, two series of anthracene-based derivatives modified by trifluoromethyl groups (-CF3) and cyano groups (-CN) at the 9,10-positions of the anthracene core were studied. Their electronic structures and crystal packings were also analyzed and compared. The charge-carrier mobilities were evaluated by quantum nuclear tunneling theory based on the incoherent charge-hopping model. Our results suggest that introducing -CN groups at 9,10-positions of the anthracene core is more favorable than introducing -CF3 to maintain great planar rigidity of the anthracene skeleton, decreasing more lowest unoccupied molecular orbital energy levels (0.45-0.55 eV), reducing reorganization energies, and especially forming a tight packing motif. Eventually, the excellent electron transport materials could be obtained. The molecule 1-B in Series 1 containing -CF3 groups is an ambipolar organic semiconductor (OSC) material with a 2D transport network, and its value of µh-max/µe-max is 1.75/0.47 cm2 V-1 s-1 along different directions; 2-A and 2-C in Series 2 with -CN groups are excellent n-type OSC candidates with the maximum intrinsic mobilities of 3.74 and 2.69 cm2 V-1 s-1 along the π-π stacking direction, respectively. Besides, the Hirshfeld surface and quantum theory of atoms in molecules analyses were applied to reveal the relationship between noncovalent interactions and crystal stacking.

Isolation of a fungus Pencicillium sp. with zinc tolerance and its mechanism of resistance.

A zinc (Zn)-tolerant fungus, designated BC109-2, was isolated from rhizosphere soil and was identified as Penicillium janthinellum BC109-2 based on ITS sequence analysis. To understand its Zn tolerance mechanisms, a series of studies was carried out addressing the subcellular distribution of Zn, its chemical forms, and the antioxidant system (superoxide dismutase, catalase, peroxidase, glutathione reductase, glutathione S-transferase, reduced glutathione, oxidized glutathione and malondialdehyde) of the fungus. The maximum level of resistance to Zn for strain BC109-2 is 2100 mg L-1. The Zn contents and percentages of cell wall and soluble fraction increased with increasing Zn concentration in the medium, which indicated extracellular accumulation/precipitation and vacuolar compartmentation mechanism might play significant role in the detoxificating process. The proportion of inactive forms of Zn was higher in the fungus, which indicated that BC109-2 mainly formed inactive Zn and stored it in the cell walls and vacuoles to decrease Zn toxicity. Furthermore, changes in antioxidant enzyme activities at various concentrations of Zn showed that the addition of Zn could cause oxidative stress in the fungal cells and that antioxidant enzymes in fungi played important roles in resistance to Zn toxicity. Moreover, the high level of lipid peroxidation showed that the protective effects of the antioxidant system were not sufficient at the high concentrations of Zn even though the antioxidant enzyme activity levels were very high. The purpose of this work is to figure out the heavy metal tolerance mechanisms of microorganisms in soil and the microbial isolate could be potentially used in bioremediation of Zn-contaminated environments.

Theoretical study of radiative and nonradiative decay rates for Cu(i) complexes with double heteroleptic ligands.

In this paper, we conducted DFT and TDDFT calculations on three double heteroleptic Cu(i) complexes to understand how different substituents on N^N ligands influence the phosphorescence quantum yield (PLQY). Both radiative and nonradiative decay processes were thoroughly investigated. Factors that determine the rate of radiative process (kr) were considered, including the lowest triplet excited state E(T1), the transition dipole moment MSm,j of the Sm → S0 transition, the spin-coupled matrix element SOC, and the singlet-triplet splitting energies ΔE(Sm-T1). The results indicate that E(T1), MSm,j and SOC increase and ΔE(Sm-T1) decreases upon introducing -Ph and -CH2- groups on the N^N ligands. The net results lead to a gradual increase of kr in the three Cu(i) complexes, from 1 (0.48 × 104 s-1) to 2 (0.64 × 104 s-1) and then to 3 (1.61 × 104 s-1). The rate of nonradiative decay process (knr) was computed by a convolution method. We explored how knr is determined by SOC between T1 and S0 states (T1|SOC|S02), effective energy gap ΔE' and the Huang-Rhys factor (S). We found that T1|SOC|S02 and ΔE' contribute significantly to knr, but S does not determine the order of knr. knr gradually decreases from complex 1 (2.51 × 106 s-1) to 2 (0.32 × 106 s-1) and then to 3 (0.14 × 106 s-1) after introducing -Ph and -CH2- groups on the N^N ligands. The computed PLQYs for the three complexes are 1: 0.0019, 2: 0.0198, and 3: 0.1011. These are quantitatively consistent with the experimental observation (1: 0.0028, 2: 0.0061, and 3: 0.1000).

Molecular interaction of triclosan with superoxide dismutase (SOD) reveals a potentially toxic mechanism of the antimicrobial agent.

In this article, the interaction mechanism between the superoxide dismutase (SOD) and the triclosan (TCS), a kind of antimicrobial agent which is of widely application with potential effects both on environment and human health, was explored through a series of spectroscopic methods, animal experiment and the molecular docking simulation. The negative free energy change ∆G, enthalpy change (∆H = 162.21 kJmol-1) and entropy change (∆S = 615 Jmol-1K-1) demonstrated that TCS could combine with SOD spontaneously through hydrophobic interaction to form a complex. The binding constants of Ka293 and Ka313 were 1.706 × 103 and 1.2 × 105 Lmol-1, respectively. Furthermore, the interaction could also influence the skeleton structure and secondary contents of SOD. The molecular docking analysis revealed the TCS located between two subunits of SOD, and there was a hydrogen bond between TCS and the residue Asn51 of SOD, which influenced the structure of protein and resulted in a decrease of enzyme activity. This work could help understand the interaction mechanism between SOD and TCS. Moreover, it could also be used to consult for toxicity assessment of TCS at molecular level.

Characterization of the binding of 2-mercaptobenzimidazole to bovine serum albumin.

2-Mercaptobenzimidazole (MBI) is widely utilized as a corrosion inhibitor, copper-plating brightener and rubber accelerator. The residue of MBI in the environment is potentially harmful to human health. In this article, the interaction of MBI with bovine serum albumin (BSA) was explored using spectroscopic and molecular docking methods under physiological conditions. The positively charged MBI can spontaneously bind with the negatively charged BSA through electrostatic forces with one binding site. The site marker competition experiments and the molecular docking study revealed that MBI bound into site II (subdomain IIIA) of BSA, which further led to some secondary structure and microenvironmental changes of BSA. This work provides useful information on understanding the toxicological actions of MBI at the molecular level.

Are triphenylamine-functionalized or carbazole-functionalized iridium complexes the more effective phosphorescent materials? A theoretical perspective.

The ground and excited states, charge injection/transport, and phosphorescence properties of eleven carbazole- and triphenylamine-functionalized Ir(III) complexes were investigated by using the DFT method. By analyzing the spin-orbit coupling (SOC) matrix elements, radiative decay rate constants k(r), and the electronic structures and energies at the S0(opt) and T1(opt) states, it was possible to rationalize the order of the experimental phosphorescence quantum yields of a series of Ir(III) complexes and to predict that [Ir(Nph-2-Cz-tz)3] has a higher phosphorescence quantum yield than [Ir(TPA-tz)3] (TPA=triphenylamine, tz=thiazolyl, Cz=carbazole, Nph=N-phenyl). Carbazole-functionalized Ir(III) complexes were shown to be efficient phosphorescent materials that have not only fast but also balanced electron/hole-transport performance as well as high phosphorescence quantum yields. The phosphorescence emission spectra can be modulated by modifying or replacing a pyridyl substituent.

Design, synthesis, and optoelectronic properties of dendrimeric Pt(II) complexes and their ability to inhibit intermolecular interaction.

Dendrimeric Pt(II) complexes [(C(∧)N)Pt(dpm)] and [Pt(C(∧)N)2] (Hdpm = dipivaloylmethane, HC(∧)N = 1,2-diphenylbenzoimidazole and its derivatives containing the carbazole dendrons) have been synthesized and characterized systematically. All of the complexes display green emission in the range of 495-535 nm that originated from the 360-440 nm absorption bands, which are assigned to dπ(Pt)→π*(L) metal-to-ligand charge transfer (MLCT) mixed with intraligand π(L)→π*(L) transition. Solution photoluminescence quantum yield (φp 0.26-0.31) of the heteroleptic complexes [(C(∧)N)Pt(dpm)] obviously increases when compared with that of complex [(C(∧)N)Pt(acac)]. Organic light-emitting diode devices based on these Pt(II) complexes with a multilayer configuration were fabricated and gave desirable electroluminescent (EL) performances, such as non- or less red-shifted EL spectra, in comparison with the photoluminescence spectra and slow efficiency roll-off with increasing brightness or current density. Complex [(t-BuCzCzPBI)Pt(dpm)] (where t-BuCzCzPBI = 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))carbazol-9-yl)phenyl-2-phenylbenzoimidazole) showed the best performance, with a maximum current efficiency of 29.31 cd/A and a maximum external quantum efficiency (EQE) of 9.04% among the fabricated devices. Likewise, for homoleptic [Pt(t-BuCzCzPBI)2] dendrimer, the powder φp (0.14) and maximum EQE (0.74%) improve by 7 and 7.4 times, respectively, as high as they do for nondendrimeric [Pt(1,2-diphenylbenzoimidazole)2] (0.02, 0.10%), although its efficiency is still lower than that of the heteroleptic counterpart due to the severely distorted square-planar geometry of the emitting core. These results reveal that large steric hindrance from ancillary ligand (dpm) or the homoleptic conformation can effectively inhibit intermolecular interaction for these dendrimeric Pt(II) complexes.

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii.

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

In-depth theoretical analysis of the influence of an external electric field on charge transport parameters.

It is important to develop materials with environmental stability and long device shelf life for use in organic field-effect transistors (OFETs). The microscopic, molecular-level nature of the organic layer in OFETs is not yet well understood. The stability of geometric and electronic structures and the regulation of the external electric field (EEF) on the charge transport properties of four typical homogeneous organic semiconductors (OSCs) were investigated by density functional theory (DFT). The results showed that under the EEF, the structural changes in single-bond linked oligomers were more sensitive and complex than those of condensed molecules, and there were non-monotonic changes in their reorganization energy (λ) during charge transport under an EEF consisting of decreases and then increases (Series D). The change in λ under an EEF can be preliminarily and qualitatively determined by the change in the frontier molecular orbitals (FMOs) - the number of C-atoms with nonbonding characteristics. For single-bonded molecules, the transfer integral is basically unchanged under a low EEF, but it will greatly change at a high EEF. Because the structure and properties of the molecule will greatly change under different EEFs, the effect of an EEF should be fully considered when determining the intrinsic mobility of OSCs, which could cause a deviation 0.3-20 times in mobility. According to detailed calculations, one heterogeneous oligomer, TH-BTz, was designed. Its λ can be greatly reduced under an EEF, and the change in the energy level of FMOs can be adjusted to different degrees. This study provides a reasonable idea for verification of the experimental mobility value and also provides guidance for the directional design of stable high-mobility OSCs.

Computational design of two-photon fluorescent probes for a zinc ion based on a Salen ligand.

A two-photon fluorescent probe has become a critical tool in biology and medicine owing to its capability of imaging intact tissue for a long period of time, such as in two-photon fluorescence microscopy (TPM). In this context, a series of Salen-based zinc-ion bioimaging reagents that were designed based on an intramolecular charge-transfer mechanism were studied through the quantum-chemical method. The increase of one-photon absorption and fluorescence emission wavelength and the reduction of the oscillator strength upon coordination with a zinc ion reveal that they are fluorescent bioimaging reagents used for ratiometric detection. When the Salen ligand is incorporated with Zn(2+), the value of the two-photon absorption (TPA) cross-section (δmax) will decrease, and most of the ligands and complexes exhibit a TPA peak in the near-infrared spectral region. That is, a substituent at the end of the ligand can influence the luminescence property, besides increasing solubility. In addition, the effect of an end-substituted position on the TPA property was considered, such as ortho and meta substitution. The detailed investigations will provide a theoretical basis to synthesize zinc-ion-responsive two-photon fluorescent bioimaging reagents as powerful tools for TPM and biological detection in vivo.

Soil organic carbon stability and exogenous nitrogen fertilizer influence the priming effect of paddy soil under long-term exposure to elevated atmospheric CO2.

Soil organic carbon (SOC) stability and dynamics are greatly influenced by long-term elevated atmospheric CO2 [CO2]. The priming effect (PE) is vital in SOC stability and dynamics, but its role in paddy soil under long-term elevated [CO2] remains unclear. To examine how SOC stability changed in paddy soil after long-term elevated atmospheric CO2 enrichment, the PE was quantified through a 13C-glucose-induced experiment with different N levels for topsoil (0-20 cm) from paddy free-air CO2 enrichment (FACE) platform. Compared with the ambient CO2 concentration ([CO2]), 10 years of elevated [CO2] (500 µmol·mol-1) significantly increased SOC and TN content by 18.4% and 19.0%, respectively, while the C/N ratio was not changed. The labile C fractions including dissolved organic carbon (DOC) and readily oxidizable organic carbon (ROC), but excluding microbial biomass C (MBC), accumulated faster than SOC in paddy soil, which implied the reduced SOC stability for long-term elevated [CO2] enrichment. With the decline of SOC stability, the exogenously induced cumulative specific PE (PE per gram of SOC) remarkably increased by 41.1-72.7% for elevated [CO2] fumigation. The cumulative PE, especially the cumulative specific PE, was found significantly linearly correlated with the ROC content or ROC/SOC ratio (labile SOC pool). Furthermore, the application of nitrogen fertilizer slowed down the PE under elevated [CO2] condition. Our results showed that long-term elevated [CO2] enrichment reduced SOC stability and, together with exogenous nitrogen fertilizer, regulated the PE in paddy soil.