Anion bridges drive salting out of a simple amphiphile from aqueous solution

Neutron diffraction with isotope substitution has been used to determine the structural changes that occur on the addition of a simple salting-out agent to a dilute aqueous alcohol solution. The striking results obtained demonstrate a relatively simple process occurs in which interamphiphile anionic salt bridges are formed between the polar groups of the alcohol molecules. These ion bridges drive an increase in the exposure of the alcohol molecule nonpolar surface to the solvent water and hence point the way to their eventual salting out by the hydrophobic effect.     

Probing the mechanism of a fungal glycosyltransferase essential for cell wall biosynthesis. UDP-chitobiose is not a substrate for chitin synthase

Chitin synthase is responsible for the biosynthesis of chitin, an essential component of the fungal cell wall. There is a long-standing question as to whether "processive" transferases such as chitin synthase operate in the same manner as non-processive transferases. The question arises from analysis of the polysaccharide structure--in chitin, for instance, each sugar residue is rotated approximately 180 degrees relative to the preceding sugar in the chain. This requires that the enzyme account for the alternating "up/down" configuration during biosynthesis. An enzyme with a single active site, analogous to the non-processive transferases--would have to accommodate a distorted glycosidic linkage at every other synthetic step. An alternative proposal is that the enzyme might assemble the disaccharide donor, addressing the "up/down" conformational problem prior to polymer synthesis. We present compelling evidence that this latter hypothesis is incorrect.     

Direct determination of vibrational density of states change on ligand binding to a protein

The change in the vibrational density of states of a protein (dihydrofolate reductase) on binding a ligand (methotrexate) is determined using inelastic neutron scattering. The vibrations of the complex soften significantly relative to the unbound protein. The resulting free-energy change, which is directly determined by the density of states change, is found to contribute significantly to the binding equilibrium.     

Atomically Defined Monocarborane Copper(I) Acetylides with Structural and Luminescence Properties Tuned by Ligand Sterics

The weakly coordinating cluster [CB₁₁H₁₂]⁻ is used as a versatile building block for the preparation of luminescent copper(I) complexes. Treatment of [CB₁₁H₁₁-12-C≡CH]⁻ with CuI and ammonia affords {(CB₁₁H₁₁-12-C≡C)₂Cu₄(NH₃)₃}_n ( 2 ). Addition of selected phosphine and pyridine ligands transforms 2 to a range of homometallic products 3 – 13 . All compounds have been characterized by X-ray crystallography, which reveals a surprising variety of structural complexity featuring cores with two to ten Cu⁺ centers. In the solid state, products 3 – 13 exhibit room-temperature phosphorescence across the visible spectrum in colors from blue to deep red. Lifetimes at room temperature are in the microsecond regime, and quantum yields of up to Φ=0.99 are observed.     

Bernal’s road to random packing and the structure of liquids

Until the 1960s, liquids were generally regarded as either dense gases or disordered solids, and theoretical attempts at understanding their structures and properties were largely based on those concepts. Bernal, himself a crystallographer, was unhappy with either approach, preferring to regard simple liquids as ‘homogeneous, coherent and essentially irregular assemblages of molecules containing no crystalline regions’. He set about realizing this conceptual model through a detailed examination of the structures and properties of random packings of spheres. In order to test the relevance of the model to real liquids, ways had to be found to realize and characterize random packings. This was at a time when computing was slow and in its infancy, so he and his collaborators set about building models in the laboratory, and examining aspects of their structures in order to characterize them in ways which would enable comparison with the properties of real liquids. Some of the imaginative – often time consuming and frustrating – routes followed are described, as well the comparisons made with the properties of simple liquids. With the increase of the power of computers in the 1960s, computational approaches became increasingly exploited in random packing studies. This enabled the use of packing concepts, and the tools developed to characterize them, in understanding systems as diverse as metallic glasses, crystal–liquid interfaces, protein structures, enzyme–substrate interactions and the distribution of galaxies, as well as their exploitation in, for example, oil extraction, understanding chromatographic separation columns, and packed beds in industrial processes.     

Organocatalyzed anodic oxidation of aldehydes

A method for the catalytic formation of electroauxiliaries and subsequent anodic oxidation has been developed. The process interfaces N-heterocyclic carbene-based organocatalysis with electro-organic synthesis to achieve direct oxidation of catalytically generated electroactive intermediates. We demonstrate the applicability of this method as a one-pot conversion of aldehydes to esters for a broad range of aldehyde and alcohol substrates. Furthermore, the anodic oxidation reactions are very clean, producing only H(2) gas as a result of cathodic reduction.