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In recent years, the process of Rural Revitalization has been gradually promoted, and rural domestic sewage treatment has become the only way to promote rural revitalization. Anhui Province, as a major agricultural and rural province in China, its current situation of water resources and water pollution in rural areas is still severe. This paper selects the rural areas of 16 cities in Anhui Province as the research object, explores the existing problems at this stage, and puts forward suggestions from the government, enterprises and individuals, so as to play a role in the treatment and improvement of rural domestic sewage throughout the country and promote the experience of Anhui.

Native chemical ligation (NCL) and its modified versions (ligation-desulfurization chemistry) have revolutionized the way that large peptides and proteins are obtained by chemical synthesis. Ligation-desulfurization chemistry can generate thiol-derived peptide models, which can generate proteins through reductive desulfurization. The C-S bond cleavages are involved in the process. It is important for us to comprehend the strength of the C-S bond estimated by the homolytic bond dissociation enthalpies (BDEs). Therefore, 25 DFT methods were chosen to calculate the C-S BDEs of the 55 organic sulfides. It is reliable to predict C-S BDEs by M05-2X method with the corresponding root mean square error value of 6.2 kJ/mol. Then, the C-S BDEs of the thiol-derived peptide model and the structure-activity relationships were systematically researched by using this method. Besides, so as to comprehend the nature of the C-S BDE change mode, the analysis comprised of the natural bond orbit and the energies of frontier orbitals were studied.

The importance of selenium compounds in chemistry and biochemistry has become apparent. The pKa values are important for understanding the reactivity and applicability of selenium compounds. To this end, we calculated the the pKa values of 16 selenols in aqueous solution by using two kinds of DFT methods and PCM-Bondi, SMD and SMDsSAS models. It is observed that the highest precision with a lowest RMSE value of 0.38 pK units was provided by using the ωB97XD method with the SMD model. Therefore, this theoretical protocol was employed to calculate the pKa values of selenol compounds and selenoxo forms of selenocarboxylic acid compounds including R = alkyl, cycloalkyl, benzyl, allyl and aryl as well as the substituent effects. The results suggest that selenols can give higher pKa values than selenocarboxylic acids. Generally, for both substituted selenols and selenocarboxylic acids, EWGs can decrease the pKa values and EDGs can increase the pKa values, and the pKa of the EWG of –COOH is larger and the pKa values of the EDGs of –NH2 and –N(CH3)2 are smaller. In addition, linear relationships between the pKa values with the natural charges of Se atoms, EHOMO, etc. were obtained in different types of selenols and selenocarboxylic acids.

Thiol compounds have been shown to be important in many fields such as protein chemistry and carbohydrate chemistry. Their pKa's in aqueous solution are important for understanding the properties and reactivities of thiols in complex biochemical systems. To elucidate the structure–activity relationships and substituent effects on pKa's of thiols, pKa's of 58 thiols were calculated using different DFT methods with two types of solvation models including PCM-Bondi and SMDsSAS. It was found that the M06-2X method with the SMDsSAS model can give the optimal precision with the smallest RMSE value of 0.77 pK unit. Based on this model, the pKa's of thiols (R-SH in which R = alkyl, cycloalkyl, aryl, heterocyclyl and fluorinated hydrocarbyl) were systematically investigated. The substituent effects as well as the structure–activity relationships behind these data were also examined. Significant substituent effects were found in heterocyclyl, alkynyl and fluorinated hydrocarbyl thiols with a wide pKa range of over 10.0 pK units. In addition, analyses including the natural bond orbital (NBO) and the energies of frontier orbitals were performed in order to further understand the substituent effects on pKa's. Good linear relationships between the pKa's with substituent constants σp+ and natural charges on S atoms were observed in different types of thiols.

Rhodium transition-metal-organic cooperative catalysis, which has been intensively studied by many chemists, represents a great success in C–H bond activation because of high efficiencies and selectivities. Typically, in the reaction mechanism of aldehyde and alkene catalyzed by Rh(I) complex and 2-amino-3-picoline, two kinds of metala-cyclic transition-metal complexes of (iminoacyl)rhodium(III)hydride and (iminoacyl)rhodium(III) alkyl are generally formed. The two complexes play an important role in the overall reaction, in which the Rh–C bond formations are involved. So it is meaningful to understand the strength of Rh–C bond, which can be measured by the homolytic bond dissociation enthalpies (BDEs). To this end, we first calculated 16 relative Rh–C BDEs of Tp′Rh(CNneopentyl)RH (Tp′ = hydridotris-(3,5-dimethylpyrazolyl)borate) by 19 density functional theory (DFT) methods. Furthermore, the 5 absolute Rh–C BDEs of Rh transition-metal complexes were also calculated. The results show that the B97D3 is the most accurate method to predict the relative and absolute Rh–C BDEs and the corresponding RMSE values are the smallest of 2.8 and 3.3 kcal/mol respectively. Therefore, the Rh–C BDEs of (iminoacyl)rhodium(III)hydride and (iminoacyl)rhodium(III)alkyl as well as the substituent effects were investigated by using the B97D3 method. The results indicated that the different substituents exhibit different effects on different types of Rh–C BDEs. In addition, the analysis including the natural bond orbital (NBO) as well as the energies of frontier orbitals were performed in order to further understand the essence of the Rh–C BDE change patterns.

In the dual catalytic Suzuki–Miyaura reactions, the cross-coupling of Csp3-hybridized center organotrifluoroborate salts has been implemented successfully by single-electron transfer (SET), where the redox potentials are important for understanding the reactivities of organotrifluoroborate salts. To this end, the ΔGgas values of 27 organotrifluoroborate anions were calculated by using different composite high-level ab initio and DFT methods. Among different DFT methods, the M05-2X method gave the highest precision with a smallest RMSE of 1.58 kcal mol−1. Then, the 24 E° values of organotrifluoroborate anions were calculated by using the M05-2X method with two types of solvation models including PCM and SMD. It was found that the M05-2X method with a PCM–UAHF model can provide the most accurate results with the lowest RMSE value of 0.16 V. Therefore, the E° values of Csp3-hybridized center organotrifluoroborate anions (R–CH2–BF3−) including R = alkenyl, alkynyl, aryl and heterocyclyl and the Csp2-hybridized center vinyltrifluoroborate anions were systematically investigated with this theoretical protocol. The results indicated that for the Csp3-hybridized center organotrifluoroborate anions, the E° values range from 0.36 V to 1.57 V, and the electron-donating groups (EDG) of –N(CH3)2, –NHCH3etc. can significantly lower the E° values of organotrifluoroborate anions, which are favorable for reactions, whereas the electron-withdrawing groups (EWG) of –NO2, –CN etc. make the organotrifluoroborate anions unfavorable for reactions. For the Csp2-hybridized center organotrifluoroborate anions, the E° values range from 1.38 V to 2.43 V. In addition, the analysis of the natural bond orbital (NBO), the ground-state effect (GE), the radical-state effect (RE) and the energies of frontier orbitals was performed in order to further disclose the essence of the E° value change patterns. The linear relationships between the E° values with substituent constants σ+p and the natural charges of the corresponding C atoms of radicals, etc. were found in different types of organotrifluoroborate anions.

The study presents copper (Cu) isotope data of mineral separates of chalcopyrite from four drill core samples in the Miocene Dabu porphyry Cu-Mo deposit formed in a post-collisional setting in the Gangdese porphyry copper belt, southern Tibet. Copper isotope values in hypogene chalcopyrite range from –1.48‰ to +1.12‰, displaying a large variation of up to 2.60‰, which demonstrates Cu isotope fractionation at high-temperature during hydrothermal evolution. The majority of measured chalcopyrite isotopic compositions show a gradual increasing trend from –1.48‰ to +1.12‰ with the increase of drilling depth from 130m to 483m, as the alteration assemblages change from potassic to phyllic. Similarly, the other δ 65 Cu values (δ 65 Cu = (( 65 Cu/ 63 Cu) sample /( 65 Cu/ 63 Cu) standard − 1) × 1000) of the chalcopyrite show a gradual increasing trend from −1.48‰ to +0.59‰ with the decrease of drilling depth from 130 m to 57 m, as the alteration assemblages change from potassic, phyllic, through argillic to relatively fresh. These observations suggest a genetic link between Cu isotope variation and silicate alteration assemblages formed at different temperatures, indicative of a Rayleigh precipitation process resulting in the large variation of δ 65 Cu values at Dabu. In general, samples closest to the center of hydrothermal system dominated by high-temperature potassic alteration are isotopically lighter, whereas samples dominated by low-temperature phyllic alteration peripheral to the center are isotopically heavier. The predicted flow pathways of hydrothermal fluids are from No. 0 to No. 3 exploration line, and the lightest δ 65 Cu values are the most proximal to the hydrothermal source. Finally, we propose that the northwest side of the No. 0 exploration line has high potential for hosting undiscovered orebodies. The pattern of Cu isotope variation in conjunction with the features of silicate alteration in porphyry system can be used to trace the hydrothermal flow direction and to guide mineral exploration.

Several Au, Sb, Sb–Au, Pb–Zn, and Sb–Pb–Zn–Ag deposits are present throughout the North Himalaya in southern Tibet, China. The largest Sb–Pb–Zn–Ag deposit is Zhaxikang (18 Mt at 0.6 wt% Sb, 2.0 wt% Pb, 3.5 wt% Zn, and 78 g/t Ag). Zhaxikang veins are hosted within N–S trending faults, which crosscut the Early–Middle Jurassic Ridang Formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin. Ore paragenesis indicates that Zhaxikang mineralization occurred in two main phases composed of six total stages. The initial phase was characterized by assemblages of fine-grained Mn–Fe carbonate + arsenopyrite + pyrite + sphalerite (stage 1), followed by relatively coarse-grained Mn–Fe carbonate + Fe-rich sphalerite + galena + pyrite (stage 2). The second phase was marked by assemblages of quartz + pyrite + Fe-poor sphalerite and Ag-rich galena + tetrahedrite + sericite (stage 3), quartz + Sb–Pb sulfosalt minerals mainly composed of boulangerite and jamesonite (stage 4), quartz + stibnite ± cinnabar (stage 5), and quartz ± calcite (stage 6). Sulfides of stage 2 have δ34SV–CDT of 8.4–12.0‰, 206Pb/204Pb ratios of 19.648 to 19.659, 207Pb/204Pb ratios of 15.788 to 15.812, and 208Pb/204Pb ratios of 40.035 to 40.153. Sulfides of stage 3 have similar δ34SV–CDT of 6.1–11.2‰ and relatively more radiogenic lead isotopes (206Pb/204Pb = 19.683–19.792). Stage 4 Sb–Pb sulfosalt minerals have δ34SV–CDT of 5.0–7.2‰ and even more radiogenic lead (206Pb/204Pb = 19.811–19.981). By contrast, stibnite of stage 5 has δ34SV–CDT of 4.5–7.8‰ and less radiogenic lead (206Pb/204Pb = 18.880–18.974). Taken together with the geological observations that the Pb–Zn-bearing Mn–Fe carbonate veins were crosscut by various types of quartz veins, sphalerite and galena of stage 2 underwent dissolution and remobilization, and that Sb–Pb(−Fe) sulfosalts formed at the expense of Pb from stage 2 galena and of Fe from stage 2 sphalerite, we argue that the early Pb–Zn veins were overprinted by later Sb-rich fluids. Stage 2 fluids were likely acidic and oxidized and leached lead from high-grade metamorphic rocks of the Greater Himalayan crystalline complex (GHC) and sulfur from reduced rocks, such as slate of the Ridang Formation, along N–S trending faults, leading to precipitation of Pb–Zn sulfides and Mn–Fe carbonate and formation of solution collapse breccias. Later Sb-rich fluids leached Pb from the GHC and the pre-existing sulfides and deposited Fe-poor sphalerite, Ag-rich galena, tetrahedrite, Sb–Pb sulfosalts, and stibnite in quartz veins that cut pre-existing Pb–Zn-bearing Mn–Fe carbonate veins. The Sb-rich fluids also likely leached Pb from Early Cretaceous gabbro and formed stibnite at shallow levels where early Pb-Zn-bearing Mn-Fe carbonate veins are absent. A sericite 40Ar–39Ar plateau age of 17.9 ± 0.5 Ma from stage 3 veins represents the timing of the onset of stage 3 mineralization.

Zhaxikang is one large Sb–Pb–Zn–Ag deposit located in the North Himalaya of southern Tibet. To date, the genesis of this deposit still remains controversial. Here, we present new pyrite Fe and sphalerite Zn isotopic data for the first three stages of mineralization, Fe–Zn isotopic data for Mn–Fe carbonate that formed during the first two stages of mineralization, and Zn isotopic data for the slate wall rocks of the Jurassic Ridang Formation to discuss the genesis of the Zhaxikang deposit. The overall δ 56 Fe and δ 66 Zn values range from −0.80‰ to 0.43‰ and from −0.03‰ to 0.38‰, respectively. The δ 56 Fe values of Mn–Fe carbonates are lighter than those of associated pyrite in six mineral pairs, indicating that the iron carbonates are preferentially enriched in light Fe isotopes relative to pyrite. The sphalerite has lighter δ 66 Zn values than associated Mn–Fe carbonates in three mineral pairs. The δ 56 Fe values of pyrite that formed during the first three stages of mineralization gradually increase from stage 1 (−0.33‰ to −0.09‰) through stage 2 (−0.30‰ to 0.19‰) to stage 3 (0.16‰–0.43‰). In comparison, the sphalerite that formed during these stages has δ 66 Zn values that gradually decrease from stage 1 (0.16‰–0.35‰) through stage 2 (0.09‰–0.23‰) to stage 3 (−0.03‰ to 0.22‰). These data, in conjunction with the observations of hand specimens and thin sections, suggest that the deposit was overprinted by a second pulse of mineralization. This overprint would account for these Fe–Zn isotopic variations as well as the kinetic Rayleigh fractionation that occurred during mineralization. The temporally increasing δ 56 Fe and decreasing δ 66 Zn values recorded in the deposit are also coincident with an increase in alteration, again supporting the existence of two pulses of mineralization. The δ 56 Fe values of the first pulse of ore-forming fluid were calculated using theoretical equations, yielding values of −0.54‰ to −0.34‰ that overlap with those of submarine hydrothermal solutions (−1‰ to 0‰). However, the δ 56 Fe values of the stage 3 pyrite are heavier than those of typical submarine hydrothermal solutions, which suggests that the second pulse of mineralization was probably derived from a magmatic hydrothermal fluid. In addition, the second pulse of ore-forming fluid has brought some Fe and taken away parts of Zn, which results the lighter δ 66 Zn values of sphalerite and heavier δ 56 Fe values of pyrite from the second pulse of mineralization. Overall, the Zhaxikang deposit records two pulses of mineralization, and the overprint by the second pulse of mineralization causes the lighter δ 66 Zn values and heavier δ 56 Fe values of modified samples.