Humin: No longer inactive natural organic matter

The discovery of the function of humin (HM), an insoluble fraction of humic substances (HSs), as an extracellular electron mediator (EEM) in 2012 has provided insight into the role of HM in nature and its potential for in situ bioremediation of pollutants. The EEM function is thought to enable the energy network of various microorganisms using HM. Recently, a number of studies on the application of HM as EEM in anaerobic microbial cultures have been conducted. Even so, there is a need for developing a holistic view of HM EEM function. In this paper, we summarize all the available information on the properties of HM EEM function, its applications, possible redox-active structures, and the interaction between HM and microbial cells. We also suggest scopes for future HM research.

Nature of S-N Bonding in Sulfonamides and Related Compounds: Insights into π-Bonding Contributions from Sulfur K-Edge X-ray Absorption Spectroscopy

Molecules containing sulfur-nitrogen bonds, like sulfonamides, have long been of interest because of their many uses and interesting chemical properties. Understanding the factors that cause sulfonamide reactivity is important, yet there continues to be controversy regarding the relevance of S-N π bonding in describing these species. In this paper, we use sulfur K-edge X-ray absorption spectroscopy (XAS) in conjunction with density functional theory (DFT) to investigate the role of S_3p contributions to π-bonding in sulfonamides, sulfinamides, and sulfenamides. We explore the nature of the electron distribution of the sulfur atom to its nearest neighbors and widen our scope to its effects on rotational barriers along the sulfur-nitrogen axis. The experimental XAS data together with time-dependent DFT calculations confirm that sulfonamides-and the other sulfinated amides in this series-have essentially no S-N π bonding involving S_3p contributions and that electron repulsion is the dominant force affecting rotational barriers along the S-N axis.

Using solution- and solid-state S K-edge X-ray absorption spectroscopy with density functional theory to evaluate M-S bonding for MS4(2-) (M = Cr, Mo, W) dianions

Herein, we have evaluated relative changes in M-S electronic structure and orbital mixing in Group 6 MS4(2-) dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as (1)A1 → (1)T2 transitions. For MoS4(2-), both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS4(2-), solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO4(2-) dianions, which allowed M-S and M-O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M-E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M-S bonds, but increased appreciably for M-O interactions. For the t orbitals (σ* + π*), mixing decreased slightly for M-S bonding and increased only slightly for the M-O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME4(2-) (E = O, S) dianions.

Decomposition of S-nitroso species

Not an ordinary day for Mario and Luigi; this work explores the decomposition pathways of RSNO⁺ species.