Ce Hao

Hormone Activity of Hydroxylated Polybrominated Diphenyl Ethers on Human Thyroid Receptor-β: In Vitro and In Silico Investigations

Background Hydroxylated polybrominated diphenyl ethers (HO-PBDEs) may disrupt thyroid hormone status because of their structural similarity to thyroid hormone. However, the molecular mechanisms of interactions with thyroid hormone receptors (TRs) are not fully understood. Objectives We investigated the interactions between HO-PBDEs and TRβ to identify critical structural features and physicochemical properties of HO-PBDEs related to their hormone activity, and to develop quantitative structure–activity relationship (QSAR) models for the thyroid hormone activity of HO-PBDEs. Methods We used the recombinant two-hybrid yeast assay to determine the hormone activities to TRβ and molecular docking to model the ligand–receptor interaction in the binding site. Based on the mechanism of action, molecular structural descriptors were computed, selected, and employed to characterize the interactions, and finally a QSAR model was constructed. The applicability domain (AD) of the model was assessed by Williams plot. Results The 18 HO-PBDEs tested exhibited significantly higher thyroid hormone activities than did PBDEs (p < 0.05). Hydrogen bonding was the characteristic interaction between HO-PBDE molecules and TRβ, and aromaticity had a negative effect on the thyroid hormone activity of HO-PBDEs. The developed QSAR model had good robustness, predictive ability, and mechanism interpretability. Conclusions Hydrogen bonding and electrostatic interactions between HO-PBDEs and TRβ are important factors governing thyroid hormone activities. The HO-PBDEs with higher ability to accept electrons tend to have weak hydrogen bonding with TRβ and lower thyroid hormone activities.

Important role of reaction field in photodegradation of deca-bromodiphenyl ether: theoretical and experimental investigations of solvent effects.

Photolysis of deca-bromodiphenyl ether (BDE-209) was investigated in tetrahydrofuran, dichloromethane, isopropanol, acetone, ethanol, methanol, acetonitrile and dimethylsulfoxide. Noticeable differences of the photolytic rates and quantum yields were found in the diverse solvents. Different to the previous deductions, hydrogen donating efficiency and electron donating efficiency of solvents were not the decisive factors for the photolytic rate in this study, which was proved by the fast photolysis of BDE-209 in CCl(4), a solvent without hydrogen and difficult to donate electrons. Besides hydrogen addition process, intermolecular polymerization might occur during the photolysis. Density functional theory (DFT) calculation was performed to understand the molecular properties of BDE-209 in different solvents. The lowest singlet vertical excitation energy (E(ex)) and the average formal charge on Br (q(Br)(+)) of BDE-209, reflecting the difficulty for the excitation of BDE-209 and for the departing of Br atom, respectively, were changed by the reaction fields formed by the different solvents. E(ex) and q(Br)(+) linearly correlated with the photolytic activity (logk). This study is helpful to better understand the photolytic behavior of BDE-209 in different media.

Time-dependent density functional theory study on the electronic excited-state hydrogen-bonding dynamics of 4-aminophthalimide (4AP) in aqueous solution: 4AP and 4AP–(H2O)1,2 clusters

The time‐dependent density functional theory (TDDFT) method has been carried out to investigate the excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in hydrogen‐donating water solvent. The infrared spectra of the hydrogen‐bonded solute−solvent complexes in electronically excited state have been calculated using the TDDFT method. We have demonstrated that the intermolecular hydrogen bond Cuf8fe O···Huf8ffO and Nuf8ffH···Ouf8ffH in the hydrogen‐bonded 4AP−(H2O)2 trimer are significantly strengthened in the electronically excited state by theoretically monitoring the changes of the bond lengths of hydrogen bonds and hydrogen‐bonding groups in different electronic states. The hydrogen bonds strengthening in the electronically excited state are confirmed because the calculated stretching vibrational modes of the hydrogen bonding Cuf8feO, amino Nuf8ffH, and Huf8ffO groups are markedly red‐shifted upon photoexcitation. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electroniclly excited state of chromophores in hydrogen‐donating solvents exists in many other systems in solution.

Effects of excited-state structures and properties on photochemical degradation of polybrominated diphenyl ethers: A TDDFT study

This study presents new insight into the photochemical degradation of polybrominated diphenyl ethers (PBDEs), and it provides details about the structures and properties of 27 PBDE congeners in the electronically excited state using the time-dependent density functional theory method. Each PBDE congener exhibited remarkably different geometries in the ground state and the excited state. The significant lengthening of C-Br bond in each PBDE congener was observed in the excited state for the first time by theoretical calculation, which is directly involved in the photochemistry reductive debromination of n-BDE to (n-1)-BDE. Generally, the lengthening of C-Br bonds cannot occur at the para position. Furthermore, the calculated results demonstrated that the photoreactivity of PBDEs increased with an increase of bromination degree. It was also found that the pattern of Br substituents had an effect upon the photoreactivity of PBDEs. These findings suggest that the information obtained in the excited state is crucial to the mechanism explanation of the photochemical degradation of PBDEs.

Modeling photoinduced toxicity of PAHs based on DFT-calculated descriptors

Quantitative structure-activity relationships (QSARs) were established for photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) to two aquatic species. Partial least squares (PLS) regression and molecular structural parameters calculated by density functional theory (DFT) were employed for model development. Two QSAR models were established and their high R(2) and Q(CUM)(2) values indicated their good goodness-of-fit, robustness and internal predictive power. The descriptors that describe the partition behavior, light absorbance, and generation of reactive free radicals were found to be successful in modeling the photoinduced toxicity. The average molecular polarizability (alpha), energy gap (E(GAP)) between the energy of the lowest unoccupied molecular orbital and the highest occupied molecular orbital, lowest triplet excitation energy (E(T1)) and vertical electron affinity at the lowest excited triplet (VEA(T1)) were the main molecular structural factors. Polarizability which determines the partition of PAHs between water and lipid governs the photoinduced toxicity of selected PAHs. Moreover, the photoinduced toxicity increased with the decreasing of E(GAP) probably due to better spectral overlap. The parameter, VEA(T1) that characterizes the ability of PAH anion radical (PAH(*-)) generation from excited triplet state PAH ((3)PAH(*)), is also related with the photoinduced toxicity. This investigation will make us gain more insight into the photoinduced toxicity mechanism and assess the applicability of various DFT-based descriptors to toxicological QSARs.

Insight into the Mechanism of Selective Catalytic Reduction of NOx by Propene over the Cu/Ti0.7Zr0.3O2 Catalyst by Fourier Transform Infrared Spectroscopy and Density Functional Theory Calculations

The mechanism of selective catalytic reduction of NOx by propene (C3H6-SCR) over the Cu/Ti0.7Zr0.3O2 catalyst was studied by in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. Especially, the formation and transformation of cyanide (-CN species) during the reaction was discussed. According to FTIR results, the excellent performance of the Cu/Ti0.7Zr0.3O2 catalyst in C3H6-SCR was attributed to the coexistence of two parallel pathways to produce N2 by the isocyanate (-NCO species) and -CN species intermediates. Besides the hydrolysis of the -NCO species, the reaction between the -CN species and nitrates and/or NO2 was also a crucial pathway for the NO reduction. On the basis of the DFT calculations on the energy of possible intermediates and transition states at the B3LYP/6-311 G (d, p) level of theory, the reaction channel of -CN species in the SCR reaction was identified and the role of -CN species as a crucial intermediate to generate N2 was also confirmed from the thermodynamics view. In combination of the FTIR and DFT results, a modified mechanism with two parallel pathways to produce N2 by the reaction of -NCO and -CN species over the Cu/Ti0.7Zr0.3O2 catalyst was proposed.

Time-dependent density functional theory study on the coexistent intermolecular hydrogen-bonding and dihydrogen-bonding of the phenol-H2O-diethylmethylsilane complex in electronic excited states

An intermolecular coexistent hydrogen bond and a dihydrogen bond of a novel phenol-H(2)O-diethylmethylsilane (DEMS) complex in the electronically excited states were studied using the time-dependent density functional theory (TDDFT) method. Frontier molecular orbitals analysis revealed that the S(2) state of the dihydrogen-bonded phenol-H(2)O-DEMS complex is a locally excited state in which only the phenol site is electronically excited. Upon electronic excitation, the O-H and H-Si vibrational modes are red shifted compared with those calculated for the ground state. The O-H and H-Si bonds involved in the dihydrogen bond O-H...H-Si and hydrogen bond O-H...O are longer in the S(2) state than in the ground state. The H...H and H...O distances significantly shorten in the S(2) state. Thus, both the intermolecular dihydrogen bond and the hydrogen bond of the phenol-H(2)O-DEMS complex are stronger in the electronically excited state than in the ground state. In addition, the hydrogen bonding is favorable for the formation of the intermolecular dihydrogen bond in the ground state. However, they are competitive with each other in the electronically excited state.

Dechlorination of chloroacetanilide herbicides by plant growth regulator sodium bisulfite

Chloroacetanilide herbicides are frequently detected in groundwater and surface waters, and pose high risks to aquatic biota. In this study, sodium bisulfite (NaHSO(3)), a plant growth regulator used in China, was used to remove three chloroacetanilide herbicides including alachlor, acetochlor and S-metolachlor. These herbicides were rapidly dechlorinated by NaHSO(3) in neutral conditions. The dechlorination was accelerated with increasing pH, temperature and NaHSO(3) concentrations. Kinetic analysis and mass spectrum identification revealed that the reaction followed S(N)2 nucleophilic substitution, in which the chlorine was replaced by the reactive specie sulfite. Alachlor and its isomer acetochlor had similar reaction rates, whereas they were more readily transformed than S-metolachlor that had larger steric hindrance and weaker electrophilicity. The transformation products were chloroacetanilide ethane sulfonic acids (ESAs), which were also encountered as major metabolites of these herbicides in natural environment via common metabolic pathways and were less toxic to green algae compared to the parent herbicides. These results indicate that NaHSO(3) can accelerate transformation of chloroacetanilide herbicides to the less toxic transformation products by nucleophilic substitution and dechlorination in aquatic environment. NaHSO(3) can be potentially used for the removal of chloroacetanilide herbicides from wastewater effluent, spill sites and accidental discharge.

Time‐dependent density functional theory study on excited‐state dihydrogen bonding OH···HGe of the dihydrogen‐bonded phenol‐triethylgermanium complex

Intermolecular dihydrogen bond Ouf8ffH···Huf8ffGe in the electronically excited state of the dihydrogen‐bonded phenol–triethylgermanium (TEGH) complex was studied theoretically using time‐dependent density functional theory. Analysis of the frontier molecular orbitals revealed a locally excited S1 state in which only the phenol moiety is electronically excited. In the predicted infrared spectrum of the dihydrogen‐bonded phenol–TEGH complex, the Ouf8ffH stretching vibrational mode shifts to a lower frequency in the S1 state in comparison with that in ground state. The Geuf8ffH stretching vibrational mode demonstrates a relatively smaller redshift than the Ouf8ffH stretching vibrational mode. Upon electronic excitation to the S1 state, the Ouf8ffH and Geuf8ffH bonds involved in the dihydrogen bond both get lengthened, whereas the Cuf8ffO bond is shortened. With an increased binding energy, the calculated H···H distance significantly decreases in the S1 state. Thus, the intermolecular dihydrogen bond Ouf8ffH···Huf8ffGe of the dihydrogen‐bonded phenol–TEGH complex becomes stronger in the electronically excited state than that in the ground state.

Combined experimental and theoretical study on photoinduced toxicity of an anthraquinone dye intermediate to Daphnia magna

The toxicity of chemicals can be enhanced by light through two photochemical pathways: Photomodification to more toxic substances and photosensitization. In the present study, the reactive oxygen species (ROS) mechanism for photoinduced acute toxicity of 1-amino-2,4-dibromoanthraquinone (ADBAQ) to Daphnia magna was clarified by experiment and theoretical calculation. The results of the present study show that ADBAQ exhibited high toxicity to D. magna under simulated solar radiation (SSR), with a median effective concentration of 1.23 +/- 0.19 nM (mean +/- standard deviation). The photomodified ADBAQ (mixtures of ADBAQ and its photoproducts) was less phototoxic than the intact ADBAQ. The SSR-only or ADBAQ-only treatments did not affect the ROS level in D. magna, whereas increased ROS levels were observed in the presence of SSR and ADBAQ. The ROS in vivo were determined by measuring the fluorescence of 2,7-dichlorofluorescein, which is a useful technique to assess toxicity of chemicals to aquatic organisms. The antioxidants, including vitamin C, vitamin E, and beta-carotene, decreased the photoinduced oxidative damage to D. magna, probably by scavenging ROS. These experimental results demonstrate that photosensitization is the potential mechanism of photoinduced toxicity of ADBAQ to D. magna. Proposed phototoxic pathways of ADBAQ were elucidated by means of time-dependent density functional theory. The theoretical calculation indicates that superoxide anion and singlet oxygen are able to be generated through electron transfer or energy transfer in the photosensitization reactions.