Free Radical Generation by Selenium Compounds and Their Prooxidant Toxicity

Selemum (Se) and many of its compounds are among the most toxic of nutrients. Selenium toxicity was first described in range animals in the western United States in the 1930's which consumed' selenium accumulator' plants of the genus Astragalus, Xylorrhiza,Oonopsis, and Stanleya. Selenites and selenates from the soil accumulate in these plants primarily as methylated selenium compounds and plants evolve dimethyldiselenide and dimethyselenide.Dietary selenium, primarily as selenomethionine and selenocysteine for humans fulfill the dietary requirement for selenoenzymes and proteins. In humans and animals excessive dietary selenium may be toxic. In vitro, selenium compounds such as selenite, selenium dioxide and diselenides react with thiols, such as glutathione, producing superoxide and other reactive oxygen species. This catalytic reaction of selenium compounds with thiols likely accounts for selenium toxicity to cells ex vivo and in vivo where the major glutathione producing organ,the liver, is also the major target organ of selenium toxicity.Selenium enzymes and selenoethers that do not readily form a selenide (RSe-) anion and compounds such as Ebselen where selenium is sequestered, are not toxic. Methylation of selenium by both plants and animals serves to detoxify selenium by generating methylselenides. Alternatively, full reduction of Se to elemental selenium (Se0) as done by some bacteria and the formation of heavy metal selenides such as Ag2Se or Hg2Se, results in a non-catalytic nontoxic form of selenium.This catalytic prooxidant attribute of some selenium compounds appears to account for its toxicity when such activity exceeds plant and animal methylation reactions and antioxidant defenses. This prooxidant activity may also account for cellular apoptosis and may provide a useful pharmaceutical application for selenium compounds as antibacterial, antiviral, antifungal and anticancer agents

Structural Characterization and Acute Toxicity Simulation for Nitroaromatic Compounds

The three-dimensional holographic vector of atomic interaction field（3D-Ho VAIF） is used to characterize the molecular structures of 45 nitroaromatic compounds.Two quantitative structure-toxicity relationship（QSAR） models are built up by stepwise regression（SMR）,multiple linear regression（MLR） and partial least-squares regression（PLS）.The correlation coefficients（R） of the models are 0.960 and 0.961,respectively.Then the models are evaluated by performing the cross-validation with the leave-one-out（LOO） procedure and the correlation coefficients（RCV） are 0.949 and 0.941,respectively.The results show that the descriptors can successfully describe the structures of organic compounds.The stability and predictability of the model are satisfactory.

The use of yellow phosphorus to destroy toxic organic compounds

A new method for generating reactive species to destroy toxic organic chemicals has been developed. This method reacts yellow phosphorus with O_2, in moist air to produce species such as O,O_3, PO, and PO_2, which are capable of reacting with various types of organics. Toxic organic com-pounds are converted to small molecular wight organic acids, aldehydes, and/or alcohols, while yel-low phosphonis is oxidital into phosphoric acid, which may be recovered as a valuable byproduct.This technique has ben demonstrated to be effective for destroying many types of toxic organiccompounds. including PAH, aromatic chlorides, amines, alcohols, and acids, nitro-aromatics,heterocyclic hydrocarbons, PCB, aliphatic chlorides and sulfides, dyes, and pesticides.

Quantitative Structure-activity Relationship(QSAR) Study of Toxicity of Substituted Aromatic Compounds to Photobacterium Phosphoreum

With the artificial neural network（ANN） method combined with the multiple linear regression（MLR）,based on a series of quantum chemical descriptors and molecular connectivity indexes,quantitative structure-activity relationship（QSAR） models to predict the acute toxicity（-lgEC50） of substituted aromatic compounds to Photobacterium phosphoreum were established.Four molecular descriptors that appear in the MLR model,namely,the second order valence molecular connectivity index（2XV）,the energy of the highest occupied molecular orbital（EHOMO）,the logarithm of n-octyl alcohol/water partition coefficient（logKow） and the Connolly molecular area（MA）,were inputs of the ANN model.The root-mean-square error（RMSE） of the training and validation sets of the ANN model are 0.1359 and 0.2523,and the correlation coefficient（R） is 0.9810 and 0.8681,respectively.The leave-one-out（LOO） cross validated correlation coefficient（Q L2OO） of the MLR and ANN models is 0.6954 and 0.6708,respectively.The result showed that the two methods are complementary in the calculations.The regression method gave support to the neural network with physical explanation,and the neural network method gave a more accurate model for QSAR.In addition,some insights into the structural factors affecting the acute toxicity and toxicity mechanism of substituted aromatic compounds were discussed.

Insight into fluorescence properties of 14 selected toxic single-ring aromatic compounds in water:Experimental and DFT study

Various single-ring aromatic compounds in water sources are of great concern due to its hazardous impact on the environment and human health.The fluorescence excitation-emission matrix(EEMs)spectrophotometry is a useftil method to identify organic pollutants in water.This study provides a detailed insight into the fluorescence properties of the 14 selected toxic single-ring aromatic compounds by experimental and theoretical analysis.The theoretical analysis were done with Time-Dependent Density Functional Theory(TD-DFT)and B3LYP/6-31G(d,p)basis set,whereas,Polarizable Continuum Model(PCM)was used to consider water as solvent.The selected compounds displayed their own specific excitation-emission(Ex/Em)wavelengths region,at Ex<280 nm and Em<340 nm,respectively.Whereas the theoretical Ex/Em was observed as.Ex at 240 nm-260 nm and Em at 255 nm-300 nm.Aniline as a strong aromatic base has longer Em(340 nm)than alkyl,carbonyl,and halogens substituted benzenes.The lone pair of electrons at amide substituent serves as a 7r-electron contributor into the aromatic ring,hence increasing the stability and transition energy,which results in longer emission and low quantum yield for the aniline.The fluorescence of halogenated benzenes illustrates an increase in the HOMO-LUMO energy gap and a decrease in quantum yield associated with atomic size(F>Cl>Br>I).In this study the theoretical results are in line with experimental ones.The understanding of fluorescence and photophysical properties are of great importance in the identification of these compounds in the water.

Changing Gly311 to an acidic amino acid in the MATE family protein DTX6 enhances Arabidopsis resistance to the dihydropyridine herbicides

In modern agriculture,frequent application of herbicides may induce the evolution of resistance in plants,but the mechanisms underlying herbicide resistance remain largely unexplored.Here,we report the char-acterization of rtp 1(resistant to paraquat 1),an Arabidopsis mutant showing strong resistance to the widely used herbicides paraquat and diquat.The rtp1 mutant is semi-dominant and carries a point mutation in the gene encoding the multidrug and toxic compound extrusion family protein DTX6,leading to the change of glycine to glutamic acid at residue 311(G311E).The wild-type DTX6 with glycine 311 conferred weak para-quat and diquat resistance when overexpressed,while mutation of glycine 311 to a negatively charged amino acid(G311E or G311D)markedly increased the paraquat and diquat resistance of plants,whereas mutation to a positively charged amino acid(G311R or G311K)compromised the resistance,suggesting that the charge property of residue 311 of DTX6 is critical for the paraquat and diquat resistance of Arabi-dopsis plants.DTX6 is localized in the endomembrane trafficking system and may undergo the endosomal sorting to localize to the vacuole and plasma membrane.Treatment with the V-ATPase inhibitor ConA reduced the paraquat resistance of the rtp1 mutant.Paraquat release and uptake assays demonstrated that DTX6 is involved in both exocytosis and vacuolar sequestration of paraquat.DTX6 and DTX5 show functional redundancy as the dtx5 dtx6 double mutant but not the dtx6 single mutant plants were more sen-sitive to paraquat and diquat than the wild-type plants.Collectively,our work reveals a potential mecha-nism for the evolution of herbicide resistance in weeds and provides a promising gene for the manipulation of plant herbicide resistance.