Promoting Effect Of Zn Research Articles

Supramolecular promotion of chemosensing effect in a new amino-acid-derivative macrocyclic ligand toward Fe(III) and Pb(II) by Zn(II) polymerization

A fluorescent synthetic amino acid appended with an N2O2-donor macrocyclic ligand L was prepared and characterized by single-crystal X-ray diffraction (SCXRD), elemental analysis, IR, 1H and 13C NMR, fluorescence (FL), and UV–vis spectroscopy. L exhibited an FL emission quenching in the presence of Fe(III) ion and showed a limit of detection (LOD) of 5.98 × 10−6 M while the periodic addition of EDTA to the Fe(III)/L solution in DMF reversibly enhanced the FL emission. Based on the bridging role of a water tetramer cluster (WTC) in the crystal structure of L for supporting the formation of the self-assembly of L, an aggregation-caused mechanism was proposed for the observed concentration-based quenching phenomena, confirmed by FL, and 1H NMR spectroscopy. Moreover, we synthesized a new one-dimensional Zn(II) coordination polymer (CP) [Zn(LH)(H2O)(NO3)(DMSO)]n (1) consisting of paddle-wheel Zn2(COO)4 subunits and four bridged L linkers, characterized by SCXRD method. 1 was assumed to be formed by replacing the WTC in the crystal structure of L. A parallel FL behavior for L and 1 was determined, attributable to a ligand-based electronic transition. 1 was found as a more sensitive chemosensor for Fe(III) than L, based on an improved LOD of 9.74 × 10−8 M for Fe(III). Meanwhile, the promotional effect of Zn(II) in CP of 1 has overcome the chemosensing incapability of L towards Pb(II), maybe due to the ease of trans-metalation of Pb(II) with Zn(II) in 1 instead of the direct coordination with L.

Dissecting the promotional effect of zinc on cadmium translocation from roots to shoots in rice.

It is often expected that Zn decreases Cd accumulation in plants due to competition for the same transporters. Here, we found that increasing Zn supply markedly increased the root-to-shoot translocation of Cd in rice. RNA sequencing showed that high Zn up-regulated expression of genes involved in glutathione biosynthesis and metabolism and the Zn/Cd transporter gene OsHMA2, but down-regulated expression of genes related to Zn uptake. Knockout of the iron or Zn transporter genes OsIRT1, OsIRT2, or OsZIP9 did not affect the Zn promotional effect on Cd translocation. Knockout of the manganese/Cd transporter gene OsNRAMP5 greatly reduced Cd uptake but did not affect the Zn promotional effect. Variation in the tonoplast transporter gene OsHMA3 affected Cd translocation but did not change the Zn promotional effect. Knockout of the Zn/Cd transporter gene OsHMA2 not only decreased Cd and Zn translocation, but also abolished the Zn promotional effect. Increased expression of OsHMA2 under high Zn conditions supports the hypothesis that this transporter participates in the promotional effect of Zn on Cd translocation. The results also show that OsIRT1, OsIRT2, and OsZIP9 made only small contributions to Cd uptake under low Zn conditions but not under high Zn conditions, whereas the dominant role of OsNRAMP5 in Cd uptake diminished under low Zn conditions.

Preparation of anisole in phenol by Zn/HZSM-5 catalyst from walnut shell catalyzed liquefaction

The promotional effect of Zn was investigated relative to the calcining activation of HZSM-5. It was found that the lignin separated from walnut shell could be liquefied into small molecular ethers such as anisole by the promotional effect of the modified catalyst. Experimental results showed that, after the loading of Zn, the HZSM-5 catalyst retained its original crystal structure, which exhibited good metal dispersion. Besides, due to the existence of two interactions respectively of Zn with Al and Zn with a Brønsted-Lowry acid on the Zn/HZSM-5 catalyst surface, the remaining catalyst intergranular distance increased, particularly for the 2% Zn/HZSM-5 catalyst. The inside of the catalyst was in a state of spherical particle aggregation with a narrow pore size distribution and uniform particle size. The peak intensity of the Si-O stretching vibration was affected by the content of Zn, which was least affected for the 2% Zn/HZSM-5 catalyst. The signal peak of this small molecule ether was not found in the absence of the metal ions, and the catalytic effect of 2% Zn/HZSM-5 was more distinct. Calculated by the mass difference method, the yield of the liquid via the 2% Zn/HZSM-5 catalyst was 59.8%, including phenol and small molecule ethers represented by anisole.

The synthesis of methanol and the reverse water-gas shift reaction over Zn-deposited Cu(100) and Cu(110) surfaces: comparison with Zn/Cu(111)

The catalytic activity of Zn vapor-deposited Cu(100) and Cu(110) surfaces for methanol synthesis by the hydrogenation of CO 2 and the reverse water-gas shift reaction were studied using an XPS apparatus combined with a high-pressure flow reactor (18 atm). At a reaction temperature of 523 K, no promotional effect of Zn was observed for the methanol synthesis on both Zn/Cu(100) and Zn/Cu(110). The results were quite different from those for Zn/Cu(111), on which a significant promotion of methanol synthesis activity appeared to be due to the deposition of Zn, indicating that the promotional effect of Zn was sensitive to the surface structure of Cu. However, hysteresis was observed in the catalytic activity for methanol synthesis over the Zn/Cu(110) surface upon heating above 543 K in the reaction mixture. The activity became twice that measured before heating, which was close to the methanol synthesis activity of Zn/Cu(111) at the same Zn coverage. On the other hand, no such hysteresis was observed for the reverse water-gas shift reaction on Zn/Cu(110), indicating that the active site for methanol synthesis was not identical to that for the reverse water-gas shift reaction. In the post-reaction surface analysis, formate species was detected on both Zn/Cu(100) and Zn/Cu(110), whose coverage increased with increasing Zn coverage at 0< Θ Zn<0.2. No correlation between the formate coverage and the methanol synthesis activity was obtained, which was in contrast to the results for Zn/Cu(111). Thus, the structure sensitivity observed in the catalytic activity of methanol synthesis over Zn-deposited Cu surfaces is ascribed to the significant difference in the reactivity of the formate intermediate.

The kinetics and mechanism of methanol synthesis by hydrogenation of CO 2 over a Zn-deposited Cu(111) surface

The hydrogenation of CO 2 over a Zn-deposited Cu(111) surface has been studied using an X-ray photoelectron spectroscopy (XPS) apparatus combined with a high-pressure flow reactor. It was shown that the turnover frequency (TOF) for methanol formation linearly increased with Zn coverage below ϑ Zn=0.19 and decreased above ϑ Zn=0.20. The optimum TOF obtained at ϑ Zn=0.19 was thirteen-fold larger than that of the Zn-free Cu(111) surface. On the other hand, the TOF for CO formation started to decrease at ϑ Zn=0.10 and approached zero at ϑ Zn=0.5. No promotional effect of Zn was thus observed for the reverse water-gas shift (RWGS) reaction on Cu(111). Post-reaction surface analysis by XPS showed the formation of formate species (HCOO a) on the Cu(111) surfaces. The formate coverage linearly increased with the Zn coverage below ϑ Zn=0.15, suggesting that the formation of the formate species was stabilized by the Zn species. The relation between ϑ HCOO and ϑ Zn is similar to that between TOF and ϑ Zn; thus, the formate species is considered to be the reaction intermediates during methanol formation, and the amount of the formate species should determine the rate of the reaction. It was found that the surface chemistry of the Zn-deposited Cu surface drastically changed at ϑ Zn=0.15. At higher Zn coverages ( ϑ Zn>0.15), Zn on Cu(111) was readily oxidized to ZnO during the CO 2 hydrogenation reaction. On the other hand, at low Zn coverages below ϑ Zn=0.15, Zn was partially oxidized in the absence of oxygen in ZnO or O a on the Cu surface under the reaction conditions. It was suggested that the Zn on Cu(111) was directly bound to the oxygen in the surface formate species as the role of the active sites.