Structure, Spectroscopy, and Reactivity Properties of Porphyrin Pincers: A Conceptual Density Functional Theory and Time-Dependent Density Functional Theory Study

Experimental and theoretical investigation on degradation of dimethyl trisulfide by ultraviolet/peroxymonosulfate: Reaction mechanism and influencing factors

With a large amount of domestic sewage and industrial wastewater discharged into the water bodies, sulfur-containing organic matter in wastewater produced volatile organic sulfide, such as dimethyl trisulfide (DMTS) through microorganisms, caused the potential danger of drinking water safety and human health. At present, there is still a lack of technology on the removal of DMTS. In this study, the ultraviolet/peroxymonosulfate (UV/PMS) advanced oxidation processes was used to explore the degradation of DMTS. More than 90% of DMTS (30 µg/L) was removed under the conditions of the concentration ratio of DMTS to PMS was 3:40, the temperature (T) was 25 ± 2℃, and 10 min of irradiation by a 200 W mercury lamp (365 nm). The kinetics rate constant k of DMTS reacting with hydroxyl radical (HO·) was determined to be 0.2477 min^-1. Mn²⁺, Cu²⁺ and NO₃^- promoted the degradation of DMTS, whereas humic acid and Cl^- in high concentrations inhibited the degradation process. Gas chromatography-mass spectrometry was used to analyze the degradation products and the degradation intermediates were dimethyl disulfide and methanethiol. Density functional theory was used to predict the possible degradation mechanism according to the frontier orbital theory and the bond breaking mechanism of organic compounds. The results showed that the SS, CS and CH bonds in DMTS molecular structure were prone to fracture in the presence of free radicals, resulting in the formation of alkyl radicals and sulfur-containing radicals, which randomly combined to generate a variety of degradation products.

Synthesis, structure and catalysis of organometallic porphyrin–pincer hybrids: a review

This review focuses on the comprehensive developments in the field of porphyrin–pincer hybrid organometallic chemistry.

Chelation technology: a promising green approach for resource management and waste minimization

Green chemical engineering recognises the concept of developing innovative environmentally benign technologies to protect human health and ecosystems. In order to explore this concept for minimizing industrial waste and for reducing the environmental impact of hazardous chemicals, new greener approaches need to be adopted for the extraction of heavy metals from industrial waste. In this review, a range of conventional processes and new green approaches employed for metal extraction are discussed in brief. Chelation technology, a modern research trend, has shown its potential to develop sustainable technology for metal extraction from various metal-contaminated sites. However, the interaction mechanism of ligands with metals and the ecotoxicological risk associated with the increased bioavailability of heavy metals due to the formation of metal-chelant complexes is still not sufficiently explicated in the literature. Therefore, a need was felt to provide a comprehensive state-of-the-art review of all aspects associated with chelation technology to promote this process as a green chemical engineering approach. This article elucidates the mechanism and thermodynamics associated with metal-ligand complexation in order to have a better understanding of the metal extraction process. The effects of various process parameters on the formation and stability of complexes have been elaborately discussed with respect to optimizing the chelation efficiency. The non-biodegradable attribute of ligands is another important aspect which is currently of concern. Therefore, biotechnological approaches and computational tools have been assessed in this review to illustrate the possibility of ligand degradation, which will help the readers to look for new environmentally safe mobilizing agents. In addition, emerging trends and opportunities in the field of chelation technology have been summarized and the diverse applicability of chelation technology in metal extraction from contaminated sites has also been reviewed.

Effects induced by axial ligands binding to tetrapyrrole-based aromatic metallomacrocycles

The axial positions of planar metallomacrocycles are unoccupied. The positively charged metal is thus a potential binding site for electron-donating groups. The binding strength is affected by the central metal, the ligand, and the macrocycle. One ligand leads to the out-of-plane displacement of the central metal, whereas two ligands from two sides structurally neutralize each other. The axial ligand donates charge to the central metal and the macrocycle when the lone pair orients along the interaction axis. The frontier orbital levels are elevated because of the charge donated to the macrocycle. Even though the singlet-triplet gap and the absorption maximum do not change significantly upon binding, the redox chemistry is considerably affected by the shifts of orbital levels. The macrocyclic M-N bonds are weakened by the binding, but their natures remain almost unchanged. Calcium phthalocyanine is a special case, as the central calcium is too large to fit the cavity. Accordingly, multiple ligands facilely bind to the calcium from one side. The aluminum phthalocyanine halogen is another special case, as it has a halogen ligand coordinating to the aluminum through a nondative bond. This leads to some effects different from those caused by dative binding. When there is no considerable steric demand, the lone pair points along the interaction axis to facilitate the donation. When in a stacked dimer, the electron-rich group is part of a large molecule, and the orientation of the lone pair is approximately perpendicular to the interaction axis. This induces the charge loss of the central metal. Because metallomacrocycles are widespread in the biological, medical, and material sciences, the results from this study are expected to bring useful insights to these fields.

Nanoassemblies of colloidal gold nanoparticles by oxygen-induced inorganic ligand replacement

This article reports a novel method of the fabrication of floating ultrathin nanoporous films and superlattice-like bottom sediment flakes of colloidal gold nanoparticles (Au NPs) by the oxygen-induced ligand replacement of inorganic species. The two nanoassemblies were realized in a weighing bottle simply by aging the Au colloid, which was synthesized and stabilized using more divalent tin Sn(II) than required for the reduction of HAuCl(4). In situ Raman spectroscopy was employed to trace the assembly process, and we found that the protective Sn(II) species (mostly SnCl(3)(-)) of the gold colloid could be gradually replaced by Cl(-) ions in the solution, while the strongly chemically adsorbed Sn(II) species on the Au NPs was oxidized by O(2) from the air contact. The destabilized colloidal Au NPs by the ligand replacement of SnCl(3)(-) with Cl(-) first assembled into an ultrathin nanoporous film at the air-water interface and then sedimentated to the bottom. Superlattice-like sediment flakes of Au NPs can be obtained at lower temperature (approximately 5 degrees C). Particularly, this method does not involve any organic substances, providing clean ultrathin nanoporous films and superlattice-like flakes of Au NPs. The ultrathin nanoporous films and superlattice-like flakes of Au NPs can serve as SERS substrates with strong and long activity.

Toward understanding the nature of internal rotation barriers with a new energy partition scheme: ethane and n-butane

On the basis of an alternative energy partition scheme where density-based quantification of the steric effect was proposed [Liu, S. B. J. Chem. Phys. 2007, 126, 244103], the origin of the internal rotation barrier between the eclipsed and staggered conformers of ethane and n-butane is systematically investigated in this work. Within the new scheme, the total electronic energy is decomposed into three independent components, steric, electrostatic, and fermionic quantum. The steric energy defined in this way is repulsive, exclusive, and extensive and intrinsically linked to Bader's atoms in molecules approach. Two kinds of differences, adiabatic (with optimal structure) and vertical (with fixed geometry), are considered for the molecules in this work. We find that in the adiabatic case the eclipsed conformer possesses a larger steric repulsion than the staggered conformer for both molecules, but in the vertical cases the staggered conformer retains a larger steric repulsion. For ethane, a linear relationship between the total energy difference and the fermionic quantum energy difference is discovered. This linear relationship, however, does not hold for n-butane, whose behaviors in energy component differences are found to be more complicated. The impact of basis set and density functional choices on energy components from the new energy partition scheme has been investigated, as has its comparison with another definition of the steric effect in the literature in terms of the natural bond orbital analysis through the Pauli Exclusion Principle. In addition, profiles of conceptual density functional theory reactivity indices as a function of dihedral angle changes have been examined. Put together, these results suggest that the new energy partition scheme provides insights from a different perspective of internal rotation barriers.