[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] 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] 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] 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] 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] 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.

[en] In this report we demonstrate that RDCs for a given residue are essentially determined by the identity of the amino acid in question and its two neighbors, and sequence dependent corrections defining local alignment and the polymeric nature of the protein. Combining these effects, we propose a simplified, automatic, and highly accurate method for directly predicting RDCs from the primary sequence of unfolded proteins. Analysis of local and long-range effects, corresponding to the conformational sampling of the region of interest and the chain-like nature of the unfolded protein, respectively, reveals that theoretical RDCs can be determined by consideration of these factors alone. Using insights gained from these studies, we find that RDC prediction can in general be de-convoluted to four components: the sampling of the amino acid of interest, nearest-neighbor-dependent effects, sequence-dependent scaling factors to correct the local alignment tensor, and a length-dependent baseline to incorporate the polymeric nature of the unfolded protein. We demonstrate that a database of combinations of triplets of amino acids, combined with corrections for the presence of the triplet in a chain of known composition, defines to a very good approximation expected random coil values of RDCs in unfolded states. This obviates the need to calculate explicit and extensive ensembles of atomic resolution structures, resulting in a significant improvement in the efficiency of calculating RDCs from unfolded sequences