[Characteristics and Mechanism of Cd Release and Transport in Soil Contaminated with PE-Cd].

Microplastics （MPs） are a type of emerging contaminants that pose a potential threat to global terrestrial ecosystems. The accumulation of MPs in soil inevitably affects soil physical and chemical properties， both directly and indirectly. Additionally， owing to their small size and surface features， MPs have excellent sorption capacity for both organic and inorganic materials， thus affecting their fate in the environment. However， the influence of MPs on heavy metal sorption and transport in soil is still not fully understood. In this study， polyethylene （PE） and Cd were selected as research objects， and on the basis of clarifying the adsorption mechanism of Cd on PE MPs， the effects of PE concentration and particle size on Cd release and transport behavior in soil under different ionic strengths and types （Ca2+ and Na+） were studied using column leaching experiments. The results of the batch experiments showed that the adsorption capacity of PE MPs for Cd2+ decreased with the increase in particle size. Scanning electron microscopy （SEM）， Fourier transform infrared spectroscopy （FTIR）， and Zeta potential were used to analyze the properties of PE MPs and adsorption behavior of Cd2+ onto MPs. The adsorption was mainly a physical process and was controlled by intra-particle diffusion. The adsorption kinetics could be described well by the quasi-second-order kinetics and Webber-Morris model. The adsorption isotherm conformed to the Langmuir model， indicating monolayer adsorption. The results of leaching experiments showed that the effect of PE MPs on Cd release and transport in soil was related to the CaCl2 concentration. At high ionic strength （0.05 mol·L-1 and 0.1 mol·L-1）， PE promoted the transport of Cd. The effluent concentration of Cd2+ increased from 6.48 mg·L-1 and 16.79 mg·L-1 to 7.12 mg·L-1 and 23.45 mg·L-1， whereas at low ionic strength （0.01 mol·L-1）， Cd transport was inhibited by PE MPs， and the effluent concentration of Cd2+ decreased from 0.66 mg·L-1 to 0.57 mg·L-1. The larger the amount of PE added， the more significant the promoting or inhibiting effect. Additionally， the release and transport of Cd in soil were also affected by the MPs particle size and concentration. When the addition amount was small （1%， 4%）， the large-sized MPs were more conducive to the transport of Cd in soil. When the addition amount was large （7%， 20%）， MPs with small particle sizes promoted Cd2+ transport more significantly. When the leaching solution used was NaCl， soil permeability decreased significantly. PE MPs had no significant effect on Cd release and transport but changed the stability of soil aggregates. In conclusion， PE MPs could change the release and transport behavior of Cd in soil， and the impact results were not only related to the particle size and content of MPs but were also influenced by the chemical properties of the soil solution.

A new type of charge-transfer salts based on tetrathiafulvalene-tetracarboxylate coordination polymers and methyl viologen.

Although charge-transfer compounds based on tetrathiafulvalene (TTF) derivatives have been intensively studied, {[cation](n+)·[TTFs](n-)} ion pair charge-transfer (IPCT) salts have not been reported. The aim of this research is to introduce functional organic cations, such as photoactive methyl viologen (MV(2+)), into the negatively charged TTF-metal coordination framework to obtain this new type of IPCT complex. X-ray structural analysis of the four compounds (MV)2[Li4(L)2(H2O)6] (1), {(MV)(L)[Na2(H2O)8]·4H2O}n (2), {(MV)[Mn(L)(H2O)2]·2H2O}n (3), and {(MV)[Mn(L)(H2O)2]}n (4), reveals that the electron donor (D) TTF moiety and the electron acceptor (A) MV(2+) form a regular mixed-stack arrangement in alternating DADA fashion. The TTF moiety and the MV(2+) cation are essentially parallel stacked to form the column structures. The strong electrostatic interaction is a main force to shorten the distance between the cation and anion planes. Optical diffuse-reflection spectra indicate that charge transfer occurs in these complexes. The ESR and magnetic measurements confirm that there is strong charge-transfer-induced partial electron transfer. Compounds 2, 3, and 4 show an effective and repeatable photocurrent response. The current intensities of 3 and 4 are higher than that of 2, which reflects that the coordination center of the Mn(II) ion has a great effect on the increasing photocurrent response.

Metal centered oxidation or ligand centered oxidation of metal dithiolene? Spectral, electrochemical and structural studies on a nickel-4-pyridine-1,2-dithiolate system.

The complex Et(4)N[Ni(4-pedt)(2)] (1) (4-pedt = 1-(pyridine-4-yl) ethylene-1,2-dithiolate) was synthesized to investigate the behaviour of metal dithiolene compounds upon protonation and oxidation by absorption spectroscopy, electrochemistry and structural analyses and to further understand the electronic states of the dithiolene compounds. It is unexpected that the 915 nm NIR transition band is not shifted when H(+) is added, and it is only affected (blue-shifted) when the compound is oxidized. All the evidence of electronic spectra indicates that the NIR band is relevant to the central [Ni(edt)(2)] moiety (edt = ethylenedithiolate), not the behaviour of individual Ni ions or ligands. It is also not the band of intermolecular interaction of a dimer. The moderately intense band appearing at 655 nm upon protonation is assigned to the intramolecular charge-transfer band between the [Ni(edt)(2)] moiety and the pyridine. The redox potentials of the metal dithiolene are sensitive to the protonation of the pyridyl group. The structures of monocationic complex and the protonated compounds [Ni(4-Hpedt)(2)]·ClO(4)·H(2)O (2) and [Ni(4-Hpedt)(2)]·PhSO(3)·2DMF (3) were characterized by single crystal X-ray determination. The structural data demonstrate that the oxidation of the monoanionic dithiolene complex to neutral does not change the Ni-S bond distances obviously, which further indicates that the process is not only the metal centered oxidation.

A redox active proton transfer and hydrogen-bonding system of tetrathiafulvalene-dicarboxylic acid and pyridine bases.

Hydrogen bonds are important in supramolecular chemistry and responsible for proton transfer processes. This manuscript reports new hydrogen-bonding systems of redox-active acid-base assemblies consisting of dimethylthio-tetrathiafulvalene dicarboxylic acid (H(2)L) coupled with pyridine (py), 2,2'-bipyridine (2,2'-bpy), and 4,4'-bipyridine (4,4'-bpy). The (1)H NMR chemical shifts of the pyridines and the redox potential shifts of the tetrathiafulvalene moiety indicate that proton-transfer and strong hydrogen-bonding interactions exist between the acid and the bases in aprotic solvents. The results of cyclic voltammetry show a two-step square reaction with a redox and proton transfer coupled mechanism. The nature of the hydrogen bonds was characterized by X-ray single crystal analysis. In contrast to the mono-carboxyl-py system, in this ortho-substituted dicarboxyl-py system one proton of the H(2)L transfers completely from the carboxyl to the py group. The conjugated intramolecular and intermolecular hydrogen bonds are responsible for the proton transfer.

Supramolecular and redox chemistry of tetrathiafulvalene monocarboxylic acid with hydrogen-bonded pyridine and bipyridine molecules.

Although tetrathiafulvalene derivatives (TTFs) have been used as the redox-active unit in a lot of ion responsive receptors, only a few such examples of TTF carboxylic acids have been reported, especially about the responses to neutral organic molecules. In this work, electrochemical and spectral properties of dimethylthio-tetrathiafulvalene monocarboxylic acid (DMT-TTFCOOH) have been studied by both experimental methods and quantum chemical calculations. A square mechanism of proton transfer and electron transfer equilibriums was proposed. It is noteworthy that the process of oxidizing the TTF moiety of DMT-TTFCOOH could be controlled to obtain TTF(•+) radical cation or TTF(2+) dication by choosing suitable oxidizing reagents. Supramolecular responsive properties of DMT-TTFCOOH to py/bpy were investigated by cyclic voltammetry and (1)H NMR spectra. The results showed that the compound DMT-TTFCOOH is an electrochemically sensitive hydrogen bonding donor that can detect a tiny difference in the hydrogen bonding acceptor molecules. The theoretical calculations further confirm the results. The hydrogen-bonding structure of DMT-TTFCOOH-bpy in crystal was solved by X-ray diffraction analysis.

Bis(diamino-diamido)-tetrathiafulvalene, a redox active sensor for proton, anions, and cations.

A bis(diamino-diamido) tetrathiafulvalene (TTF) derivative H(4)L(2) has been designed and synthesized. Experiments of pH titration reveal that integrating the redox active TTF unit with the diamino-diamido moiety adds new properties to the traditional ligand. Oxidation of the TTF moiety increases the acidity of the amido group, and the coordination of metal ions is also sensitive to the oxidation state of the ligand. This compound is capable of acting as a leaving or accepting ligand for proton and metal ions. The electrochemistry of the protonated TTF derivative of H(4)L(2) was studied in the presence of a series of oxo anions and metal cations. The results indicate that the redox potentials selectively respond to HC(2)O(4)(-) and SO(4)(2-) anions, and Ni(II) and Cu(II) cations. Solid-state structures of a cation-anion salt H(8)L(2)·2SO(4)·8H(2)O and a nickel coordination compound [Ni(2)L(2)]·2DMF have been characterized by means of X-ray crystallography which are helpful in understanding the inter-ion interactions.