Host-Guest Chemistry

Lead pollution of shooting range soils has received tremendous attention in the past few years due to its adverse effects to the environment. High total Pb concentrations have been reported in shooting range soils. Soil physicochemical properties such as pH, organic matter, cation exchange capacity (CEC) and soil moisture have been found to have a strong influence on the transformation of Pb shots. Therefore, it is imperative that the soil physicochemical properties are well understood when investigating the environmental effects of Pb. Total Pb concentration gives a measure of the amount of Pb stored in soil but does not give a true picture of the environmental pollution risk. In their quest to control pollution of shooting range soils from Pb, scientists have applied soil remedial methods such as soil washing, chemical stabilisation and phytore-mediation. This review examines the pollution status of shooting range soils from Pb, the effect of soil properties on Pb mobility and bioavailability, the importance of Pb chemical speciation in understanding Pb mobility and shooting range management strategies applied in the control and management of Pb pollution of shooting range soils. This is a holistic review covering literature from 1983 to 2018, a period of 35 years.

This contribution emerged from an open, and continuing, discussion between a chemist and a philosopher, which resulted in a common awareness of the importance of trusting objects. The purpose of this biography of a molecular object - cyclodextrin - is both descriptive and normative. Descriptive: to understand how a thing can become an object of trust or/and distrust. The biography reveals three layers of valuation sustaining the process of generating trust: reputation, semiosis, and ontology. The first one acts at the level of actors' strategies and their interplay with regulations, the second operates with value-laden images conditioning the actors' expectations, and the last concerns the changing relationships between CD-technology and nature. As to the normative purpose, we aim at evaluating these valuations in order to allow critical trust generation. Finally, we try to appraise how nanotechnology reconfigures trust in objects by bringing visibility to the valuations.

The interplay of host−guest interactions and controlled modulation of spin-crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. In this work, we demonstrate the experimental approach of tuning the SCO behavior via controlled modulation of the spin-state cooperativity in a 2D Hofmann coordination polymer, [Fe II Pd-(CN) 4 (L) 2 ]•1.3MeOH (1•1.3MeOH; L = methyl isonicotinate). Removal of the solvent changes the four-step transition to a complete one-step spin transition with an enhanced hysteresis width (∼20 K). Structural analysis of solvated (1•1.3MeOH) and partially desolvated (1•0.3MeOH) compounds reveals that the crystal system changes from a monoclinic C2/c space group to an orthorhombic Imma space group, where the Fe II sites are present in a more symmetrically equivalent environment. Consequently, the axial ligand-field (LF) strength and face-to-face interactions of the ligands were increased by removing the guest, which is reflected in the highly cooperative SCO in 1 (desolvated compound). Also, the shift of the CN bond stretching frequencies and decrease of their relative intensities from the variable-temperature Raman spectroscopic measurements further corroborate the SCO behavior. Besides, theoretical calculations reveal that the singlet (1 Γ) LF terms decrease by removing guest molecules, enhancing the molecular population in the low-spin state at low temperature, as experimentally observed for 1. Notably, fine tuning of the SCO behavior via host−guests interactions provides a great opportunity to design potential chemosensors.

Multifunctional hybrid materials are obtained by modifying zeolite L (ZL) with stopcock molecules, consisting of a tail group that can enter the ZL nanochannels and a head group too large to pass the channel opening. However, to date no microscopic-level structural information on modified ZL materials has been reported. Herein we draw atomistic pictures of channel openings and stopcock-functionalized ZL based on first-principles calculations. We elucidate the interactions of the tail group with the inner surface of ZL channels and the space-filling properties of the stopcocks, revealing cork- or lid-sealing modes. Water is essential to obtain stable modifications. Al-OH groups are the preferred modification sites, bipodal modifications suffer from strain, and tripod binding is ruled out. Our results suggest the viability of recursive functionalization by cross-linking.