Crystal-Packing-Driven Enrichment of Atropoisomers

Crystal-packing forces can have a significant impact on the relative stabilities of different molecules and their conformations. The magnitude of such effects is, however, not yet well understood. Herein we show, that crystal packing can completely overrule the relative stabilities of different stereoisomers in solution. Heating of atropoisomers (i.e. “frozen-out” conformational isomers) in solution leads to complex mixtures. In contrast, solid-state heating selectively amplifies minor (<25 mole %) components of these solution-phase mixtures. We show that this heating strategy is successful for compounds with up to four rotationally hindered σ bonds, for which a single stereoisomer out of seven can be amplified selectively. Our results demonstrate that common supramolecular interactions—for example, [methyl⋅⋅⋅π] coordination and [C−H⋅⋅⋅O] hydrogen bonding—can readily invert the relative thermodynamic stabilities of different molecular conformations. These findings open up potential new avenues to control the folding of macromolecules.     

The effects of conductivity and electrochemical doping on the reduction of methemoglobin immobilized in nanoparticulate TiO2 films

Methemoglobin (bovine) is immobilized from aqueous phosphate buffer (pH 5.5) solution into thin porous TiO(2) (anatase) films at ITO electrode surfaces. Films of TiO(2) are produced in a deposition process employing 40 nm diameter TiO(2) nanoparticles suspended in dry methanol followed by calcination. The pore size in these films is sufficient for methemoglobin (ca. 6 nm diameter) to diffuse into the porous structure (over several hours) and to remain immobilized in electrochemically active form. The electrochemical reduction of methemoglobin immobilized in TiO(2) and immersed in aqueous phosphate buffer at pH 5.5 is observed in two steps with (i) a small quasi-reversible voltammetric response at -0.16 V vs. SCE (Process 1) and (ii) an irreversible reduction peak at ca. -0.5 V vs. SCE (Process 2). The irreversible response is recovered only after slow chemical re-oxidation of hemoglobin to methemoglobin. At sufficiently negative applied potential "electrochemical doping" of the TiO(2) host is observed to lead to a considerably enhanced reduction Process 1. TiO(2) can be temporarily switched from a non-conducting (irreversible electron transfer) into a conducting (reversible electron transfer) state.     

The Hausdorff dimension of visible sets of planar continua

For a compact set and a point , we define the visible part of from to be the set

(Here denotes the closed line segment joining to .)

In this paper, we use energies to show that if is a compact connected set of Hausdorff dimension greater than one, then for (Lebesgue) almost every point , the Hausdorff dimension of is strictly less than the Hausdorff dimension of . In fact, for almost every ,

We also give an estimate of the Hausdorff dimension of those points where the visible set has dimension greater than for some .

     

The path relation for directed planar graphs in rectangles, and its relation to the free diad

In this paper, we define the path relation of a directed graph to be the relation which relates two vertices if there is a path from the first to the second. We study the restriction of this relation to paths from sources to sinks, and consider the question of when two finite graphs embedded in a rectangle give the same relation. We find a set of local changes to these graphs which can be used to get between any two graphs for which this relation is the same. Furthermore, we classify the relations which can arise as this relation for a finite directed graph embedded in a rectangle as the triconvex relations between finite ordinals (defined in this paper).This work originated from some of the author’s work on category theory. It turns out that the category of finite ordinals and relations that can be the path relation of a directed graph embedded in a rectangle, is relevant to the study of diads—introduced by the author as a common generalisation of monads and comonads (note that the terms diad and dyad have been used to mean different things by other authors). More specifically, the referee of one of the author’s papers suggested that it would be useful to identify the category which plays the role for diads that the category of finite ordinals and order-preserving functions plays for monads. It turns out that the category of finite ordinals and relations that can be path relations of graphs embedded in a rectangle, is exactly the category that plays this role.     

Decarboxylative biaryl synthesis in a continuous flow reactor

A practical protocol was developed that allows performing decarboxylative cross-coupling reactions in continuous flow reactors. Various biaryls were thus synthesized from aromatic carboxylic acids and aryl triflates using a Cu/Pd-catalyst system.     

Chemically targeting the emergent properties of a chaperone complex

In this issue, Chang et?al. (2011) report a small molecule screen against the reconstituted DnaK-DnaJ-GrpE chaperone cycle. Through this approach, they identified myricetin as an inhibitor of DnaJ-stimulated DnaK ATPase activity, indicating the potential for their screening approach to identify modulators of emergent properties of protein complexes.     

Antimicrobial surface grafted thermally responsive PNIPAM-co-ALA nano-gels

Thermally responsive Poly(N-isopropylacrylamide) co-allylamine (PNIPAM-co-ALA) nano-gels were synthesised and grafted onto non-woven polypropylene. Silver nitrate was incorporated into the nano-gels in their expanded state and their antimicrobial properties tested. Bacterial growth was measured before and after the Lower Critical Solution Temperature. Below the LCST, bacteria grew, above the LCST bacterial growth was prevented or retarded.     

New rhodamine nitroxide based fluorescent probes for intracellular hydroxyl radical identification in living cells

The synthesis, characteristics, and biological applications of a series of new rhodamine nitroxide fluorescent probes that enable imaging of hydroxyl radicals (?OH) in living cells are described. These probes are highly selective for ?OH in aqueous solution, avoiding interference from other reactive oxygen species (ROS), and they facilitate ?OH imaging in biologically active samples. The robust nature of these probes (high specificity and selectivity, and facile synthesis) offer distinct advantages over previous methods for ?OH detection.