[en] electivity is a fundamental property of pervasive importance in chemistry and biology as reflected in phenomena as diverse as membrane transport, catalysis, sensing, adsorption, complexation, and crystallization. Although the key principles of complementarity and preorganization governing the binding interactions underlying such phenomena were delineated long ago, truly profound selectivity has proven elusive by design in part because synthetic molecular architectures are neither maximally complementary for binding target species nor sufficiently rigid. Even if a host molecule possesses a high degree of complementarity for a guest species, it all too often can distort its structure or even rearrange its conformation altogether to accommodate competing guests. One approach taken by researchers to overcome this challenge has been to devise extremely rigid molecules that bind species within complementary cavities. Although examples have been reported to demonstrate the principle, such cases are not generally of practical utility, because of inefficient synthesis and often poor kinetics. Alternatively, flexible building blocks can be employed, but then the challenge becomes one of locking them in place. Taking a cue from natural binding agents that derive their rigidity from a network of molecular interactions, especially hydrogen bonding, we present herein an example of a crystalline, self-assembled capsule that binds sulfate by a highly complementary array of rigidified hydrogen bonds (H-bonds). Although covalent or self-assembled capsules have been previously employed as anion hosts, they typically lack the strict combination of complementarity and rigidity required for high selectivity. Furthermore, the available structural data for these systems is either restricted to a limited number of anions of similar size and shape, or varies significantly from one anion to another, which hampers the rationalization of the observed selectivity. We have been employing crystalline host environments functionalized with anion-coordinating groups as a means to obtain maximal three-dimensional complementarity and rigidity. In the present study, we focused on the problem of sulfate recognition and separation, motivated by its high relevance to environmental remediation and nuclear waste cleanup

[en] The desire to improve and expand the scope of clinical magnetic resonance imaging (MRI) has prompted the search for contrast agents of higher efficiency. The development of better agents requires consideration of the fundamental coordination chemistry of the gadolinium(III) ion and the parameters that affect its efficacy as a proton relaxation agent. In optimizing each parameter, other practical issues such as solubility and in vivo toxicity must also be addressed, making the attainment of safe, high-relaxivity agents a challenging goal. Here we present recent advances in the field, with an emphasis on the hydroxypyridinone family of Gd^III chelates

[en] The dimeric bis(imido) uranium complex ({U(NtBu)2(I)(tBu2bpy)}2) (see picture; U green, N blue, I red) has cation-cation interactions between (U(NR)2)+ ions. This f1-f1 system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.

[en] We have shown here that "1"3C-start "1"3-C detected experiments do not suffer from fast hydrogen exchange between amide and solvent protons in IDP samples studied at close to physiological conditions, thus enabling us to recover information that would be difficult or even impossible to obtain through amide "1H-detected experiments. Furthermore, in favourable cases the fast hydrogen exchange rates can even be turned into a spectroscopic advantage. By combining longitudinal "1H relaxation optimized BEST-type techniques with "1"3C-direct detection pulse schemes, important sensitivity improvements can be achieved, and experimental times can be significantly reduced. This opens up new applications for monitoring chemical shift changes in IDPs upon interaction to a binding partner, chemical modification, or by changing the environment, under sample conditions that were inaccessible by conventional techniques. (authors)

[en] Knowledge of the supramolecular structure of the organic phase containing amphiphilic ligand molecules is mandatory for full comprehension of ionic separation during solvent extraction. Existing structural models are based on simple geometric aggregates, but no consensus exists on the interaction potentials. Herein, we show that molecular dynamics crossed with scattering techniques offers key insight into the complex fluid involving weak interactions without any long range ordering. Two systems containing mono- or diamide extractants in heptane and contacted with an aqueous phase were selected as examples to demonstrate the advantages of coupling the two approaches for furthering fundamental studies on solvent extraction. (authors)

[en] Coordination polymerization of pyridine-based ligands and zinc or silver ions was controlled by soft lithographic micromolding in capillaries. The polymer patterns that are produced are highly fluorescent and supramolecularly structured.

[en] The highly symmetric title compound contains a Ni atom that is tetrahedrally coordinated by four alkylindium(I) ligands InC(SiMe₃)₃. The ligand InR is isolobal with carbon monoxide, and the product is thus a remarkable addition to the class of [Ni(CO)₄] analogues. (orig.)

[en] Alternate stacking of single hexagonal perovskite (111) layers (La₂MnO₆) and 'Ca₂O' layers is present in the hexagonal perovskite intergrowth compound La₂Ca₂MnO₇. Comparison with the Ruddlesden-Popper phases (ABO₃)_nAO suggests that La₂Ca₂MnO₇ might be the first member (n=1) of a family of hexagonal perovskite intergrowth compounds of the formula (La_n+1Mn_nO_3n+3)(Ca₂O). (orig.)

[en] Catalytic CO₂ reduction to fuels and chemicals is a major pursuit in reducing greenhouse gas emissions. Here, one approach utilizes the reverse water–gas shift reaction, followed by Fischer–Tropsch synthesis, and iron is a well–known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resulted in limited success. Now, using ruthenium–iron oxide colloidal heterodimers, close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium–iron core–shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, a fourfold increase in hydrocarbon yield is achieved compared to the heterodimers. This work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO₂ conversion processes.

[en] CSI: Carbocation species identification: The nonhomogeneous distribution of the reaction products of styrene oligomerization on large ZSM-5 crystals was mapped with in situ IR microspectroscopy. Diffraction-limited spatial resolution was achieved with synchrotron light. IR spectra for possible reaction products were calculated with DFT/B3LYP; by comparison with experimental results carbocationic reaction species formed in zeolite channels could be singled out.