Chitin as a Sorbent Superior to Other Biopolymers: Features and Applications in Environmental Research, Energy Conversion, and Understanding Evolution of Animals

Chitin is an effective sorbent which can be used in environmental monitoring, beyond obvious applications in withholding metal-containing pollutants from wastewater- or nuclear fuel reprocessing flows, since background levels in (purified) chitin are very low except for a few metals (Fe, Cu, Al, Ti, and Zn). Since retention of Mx+ and their complexes on chitin depend on an oxidation state, and to a lesser extent the presence of possible ligands or co-ligands, partition between chitin samples exposed to sediment and those exposed to water can be changed by environmental factors such as local biota producing or absorbing/metabolizing effective ligands such as citrate or oxalate and by changes of redox potential. Thermodynamics are studied via log P, using calibration functions log P vs. 1/r or log P vs. Σσ (sum of Hammett parameters of ligand donor groups) for di- and trivalent elements not involved in biochemical activity (not even indirectly) and thus measuring “deviations” from expected values. These “deviations” can be due to input as a pollutant, biochemical use of certain elements, precipitation or (bio-induced reduction of SO42− or CO2) dissolution of solids in sediment. Biochemical processes which occur deep in sediment can be detected due to this effect. Data from grafted chitin (saturation within ≤ 10 min) and from outer surfaces of arthropods caught at the same site do agree well. Log P is more telling than total amounts retrieved. Future applications of these features of chitin are outlined.

Hammett neural networks: prediction of frontier orbital energies of tungsten–benzylidyne photoredox complexes

The successful application of Hammett parameters as input features for regressive machine learning models is demonstrated and applied to predict energies of frontier orbitals of highly reducing tungsten–alkylidyne complexes of the form W(CArR)L4X.

Homogeneous benzoylation of cellulose in 1-allyl-3-methylimidazolium chloride: Hammett correlation, mechanism and regioselectivity

We revealed the mechanism of cellulose benzoylation in an ionic liquid by using Hammett parameters, and found that the benzoylation of cellulose exhibited a high C-6 regioselectivity.