Solvent effects on the motion of a crown ether/amino rotaxane.

Solvents have been recognized as a significant factor for modulating the shuttle of rotaxanes and regulating their functions regarding molecular machines by a lot of published studies. The mechanism of the effects of solvents on the motion of crown ether/amino rotaxanes, however, remains unclear. In this work, a rotaxane, formed by dibenzo-24-crown-8 (C[8]) and a dumbbell-shaped axle with two positively charged amino groups, was investigated at the atom level. Two-dimensional free-energy landscapes characterizing the conformational change of C[8] and the shuttling motions in chloroform and water were mapped. The results indicated that the barriers in water were evidently lower than those in chloroform. By analyzing the trajectories, there was no obvious steric effect during shuttling. Instead, the main driving force of shuttling was verified from electrostatic interactions, especially strong hydrogen bonding interactions between the axle and water, which resulted in the fast shuttling rate of the rotaxane. All in all, the polarity and hydrogen bond-forming ability of solvents are the main factors in affecting the shuttling rate of a crown ether/amino rotaxane. In addition, C[8] would adopt S-shaped conformations during shuttling except for situating in the amino sites with C-shaped ones adopted due to π-π stacking interactions. The results of this research improve the comprehension of the solvent modulation ability for shuttling in crown ether-based rotaxanes and illustrate the effects of structural modifications on motions. These new insights are expected to serve the efficient design and construction of molecular machines.

Distribution, Assessment, and Source of Heavy Metals in Sediments of the Qinjiang River, China.

Heavy metals are toxic, persistent, and non-degradable. After sedimentation and adsorption, they accumulate in water sediments. The aim of this study was to assess the extent of heavy metal pollution of Qinjiang River sediments and its effects on the ecological environment and apportioning sources. The mean total concentrations of Mn, Zn, Cr, Cu, and Pb are 3.14, 2.33, 1.39, 5.79, and 1.33 times higher than the background values, respectively. Co, Ni, and Cd concentrations are lower than the background values. Fe, Co, Ni, Cd, Cr, Cu, and Pb are all primarily in the residual state, while Mn and Zn are primarily in the acid-soluble and oxidizable states, respectively. Igeo, RI, SQGs, and RAC together indicate that the pollution status and ecological risk of heavy metals in Qinjiang River sediments are generally moderate; among them, Fe, Co, Ni, Cd, Cr, and Pb are not harmful to the ecological environment of the Qinjiang River. Cu is not readily released because of its higher residual composition, suggesting that Cu is less harmful to the ecological environment. Mn and Zn, as the primary pollution factors of the Qinjiang River, are harmful to the ecological environment. This heavy metal pollution in surface sediments of the Qinjiang River primarily comes from manganese and zinc ore mining. Manganese carbonate and its weathered secondary manganese oxide are frequently associated with a significant amount of residual copper and Cd, as a higher pH is suitable for the deposition and enrichment of these heavy metals. Lead-zinc ore and its weathering products form organic compounds with residual Fe, Co, Cr, and Ni, and their content is related to salinity. The risk assessment results of heavy metals in sediments provide an important theoretical basis for the prevention and control of heavy metal pollution in Qinjiang River.

Synthesis of cassava starch-g-acrylic acid/dimethylaminopropyl methacrylamide: A new hydrogel for brine solution.

A new hydrogel copolymer was synthesized via the graft copolymerization of acrylic acid (AA) and dimethylaminopropyl methacrylamide (DMAPMA) on cassava starch (CSt) in aqueous solution. FTIR, TGA-FTIR, solid-state 13C NMR, SEM analyses were used to characterize the polymer. The swelling behavior of the polymer was investigated in distilled water and in various brine solutions. The effects of CSt and the ratio of the two monomers on the water absorbency of the polymer was evaluated. CSt improved the polymer swelling properties. Both polyelectrolyte and anti-polyelectrolyte effects occurred and the polymer had good salt-resistance properties in brine solutions. Such polymers have potential applications in the absorption of ultra-high concentration brine solutions.

Synthesis and antiproliferative evaluation of novel steroid-benzisoselenazolone hybrids.

The two different types of steroidal benzisoselenazolone hybrids were synthesized by incorporating benzisoselenazolone scaffold into dehydroepiandrosterone and B-norcholesterol. The antiproliferative activity of the synthesized compounds against some carcinoma cell lines were investigated. The results showed that some of these compounds have better inhibitory activity than abiraterone on the proliferation of tumor cells associated with human growth hormone, and have less cytotoxicity on normal human cells. In particular, the IC50 values of the compound 8a and 8f are 5.4 and 6.5 µmol/L against human ovarian carcinoma (SKOV3) cell line, and possess SI values of 13.9 and 10.5, respectively. The information obtained from the studies may be useful for the design of novel chemotherapeutic drugs.

Synthesis of some steroidal derivatives with side chain of 20- and 22-hydrazone aromatic heterocycles and their antiproliferative acitivity.

BACKGROUND: The modification of steroidal structure is commonly used to change the biological activity of steroids in medicinal chemistry. Some steroids containing heterocycles exhibit distinct cytotoxicity against various cancer cell lines and have been gotten wide attention over the years by medicinal chemists for drug discovery. METHODS: Using pregnenolone and stigmasterol as starting materials, via different chemical reaction, two series of heterosteroids with side chain of 20- and 22-hydrazone aromatic cycles or heterocycles in their structures were synthesized and characterized by IR, NMR and HRMS. The antiproliferative activity of the compounds in vitro was evaluated against human HT-29, HeLa, Bel 7404 and SGC 7901 cancer cells by MTT assays. RESULTS: The steroidal compounds with side chain of 20-hydrazone aromatic cycles or heterocycles exhibited distinct cytotoxicity. However, analogues with the side chain of 22-hydrazone resulted in a dramatic decrease of the cytotoxicity. The result of Annexin V assay showed that the 20-hydrazone compounds were potent apoptotic inducers against these carcinoma cells. CONCLUSION: Steroidal compounds with the side-chain of 20-hydrazone aromatic heterocycles exhibit distinct antiproliferative activity in vitro. However, the compounds with the side-chain of 22-hydrazone aromatic heterocycle decreased the cytotoxicity of the compounds.