N‐Linked Hydroxylamine Resin: Solid‐Phase Synthesis of Hydroxamic Acids

A novel hydroxylamine resin for solid‐phase synthesis of hydroxamic acids is described. Its facile application is illustrated by the solid‐phase synthesis of various hydroxamic acids. Cleavage is induced under acidic conditions by treatment with trifluoroacetic acid, providing hydroxamic acids in high purity and good yields.     

Supramolecular Diblock Copolymers Featuring Well‐defined Telechelic Building Blocks

We report supramolecular AB diblock copolymers comprised of well‐defined telechelic building blocks. Helical motifs, formed via reversible addition‐fragmentation chain‐transfer (RAFT) or anionic polymerization, are assembled with coil‐forming and sheet‐featuring blocks obtained via atom‐transfer radical polymerization (ATRP) or ring‐opening metathesis polymerization (ROMP). Interpolymer hydrogen bonding or metal‐coordination achieves dynamic diblock architectures featuring hybrid topologies of coils, helices, and/or π‐stacked sheets that, on a basic level, mimic protein structural motifs in fully synthetic systems. The intrinsic properties of each block (e.g., circular dichroism and fluorescence) remain unaffected in the wake of self‐assembly. This strategy to develop complex synthetic polymer scaffolds from functional building blocks is significant in a field striving to produce architectures reminiscent of biosynthesis, yet fully synthetic in nature. This is the first plug‐and‐play approach to fabricate hybrid π‐sheet/helix, π‐sheet/coil, and helix/coil architectures via directional self‐assembly.     

Skewness of generalized Petersen graphs and related graphs

The skewness of a graph G is the minimum number of edges in G whose removal results in a planar graph. In this paper, we determine the skewness of the generalized Petersen graph P(4k, k) and hence a lower bound for the crossing number of P(4k, k). In addition, an upper bound for the crossing number of P(4k, k) is also given.     

Ultracold atoms in a disordered crystal of light: towards a bose glass

We use a bichromatic optical lattice to experimentally realize a disordered system of ultracold strongly interacting 87Rb bosons. In the absence of disorder, the atoms are pinned by repulsive interactions in the sites of an ideal optical crystal, forming one-dimensional Mott-insulator states. We measure the excitation spectrum of the system as a function of disorder strength and characterize its phase-coherence properties with a time-of-flight technique. Increasing disorder, we observe a broadening of the Mott-insulator resonances and the transition to a state with vanishing long-range phase coherence and a flat density of excitations, which suggest the formation of a Bose-glass phase.     

Surface tension drawing of liquid from microplate capillary wells

Pressure differentials are routinely used to actuate flow in capillaries. We advance here an alternative means of flow generation that capitalizes on the extension of a liquid bridge achieved by the drawing of a rod through the action of surface tension. This meets the exigencies of creating controllable flow using simpler and more compact means. We found the ability to generate controllable flow to be strongly affected by the liquid bridge sustaining features, and that the use of rod diameters larger than the capillary was more conducive. The extensional flow resulting from the rupture of the liquid bridge was also found to have a strong circulation component which facilitated mixing. The approach here is highly amenable for use in capillary well microplates which have significant advantages over standard microplates. The features of this approach offer usage possibilities in biochemical applications in the field, such as in the leukocyte cell adhesion and hemagglutination tests of blood samples.     

Comparative stability constants for metal ions with tetraazamacrocycles of various ring sizes carrying a single amine or carboxylate pendant group

Acid dissociation constants for a series of tetraazamonocycloalkanes of {13}–{15} membered ring sizes, as well as for a related reinforced {15R} tetraazabicycloalkane, each with one primary amine or carboxylate C-pendant, are reported. Further, formation constants with the metal ions Zn^II, Cd^II, Pb^II, Hg^II, Mn^II and Co^II have been determined. The ligands differ in their selection of metal ions, reflected in the formation constants for 1:1 complexation (K _ML). Differences arise in part from the increasing ring size or rigidity and also from the availability of potential pendant O-donors versus N-donors in stepping from amine to carboxylate pendant ligands, implying a role for the pendants in binding the metal ions.     

A model for sequential threading of alpha-cyclodextrin onto a guest: a complete thermodynamic and kinetic study in water

The first variable-temperature and variable-pressure stopped-flow spectrophotometric study of the sequential threading of alpha-cyclodextrin (alpha-CD) onto the guest dye Mordant Orange 10, S, is reported. Complementary (1)H one-dimensional (1D) variable-temperature kinetic studies and two-dimensional (2D) rotating-frame nuclear Overhauser effect spectroscopy (ROESY) and EXSY NMR studies are also reported. In aqueous solution at 298.2 K, the first alpha-CD threads onto S to form a 1:1 complex S.alpha-CD with a forward rate constant k(1,f) = 15 200 +/- 200 M(-1) s(-1) and dethreads with a reverse rate constant k(1,r) = 4.4 +/- 0.3 s(-1). Subsequently, S.alpha-CD isomerizes to S.alpha-CD (k(3,f) = 0.158 +/- 0.006 s(-1), k(3,f) = 0.148 +/- 0.006 s(-1)). This process can be viewed as a thermodynamically controlled molecular shuttle. A second alpha-CD threads onto S.alpha-CD to form a 1:2 complex, S.(alpha-CD)(2), with k(2,f) = 98 +/- 2 M(-1) s(-1) and k(2,r) = 0.032 +/- 0.002 s(-1). A second alpha-CD also threads onto S.alpha-CD to form another 1:2 complex, S.(alpha-CD)(2), characterized by k(4,f) = 9640 +/- 1800 M(-1) s(-1) and k(4,r) = 61 +/- 6 s(-1). Direct interconvertion between S.(alpha-CD)(2) and S.(alpha-CD)(2) was not detected; instead, they interconvert by dethreading the second alpha-CD and through the isomerization equilibrium between S.alpha-CD and S.alpha-CD. The reaction volumes, DeltaV(0), were found to be negative for the first three equilibria and positive for the fourth equilibrium. For the first three forward and reverse reactions, the volumes of activation are substantially more negative, indicating a compression of the transition state in comparison with the ground states. These data were used in conjunction with DeltaH, DeltaH degrees, DeltaS, and DeltaS degrees data to deduce the dominant mechanistic threading processes, which appear to be largely controlled by changes in hydration and van der Waals interactions, and possibly by conformational changes in both S and alpha-CD. The structure of the four complexes were deduced from (1)H 2D ROESY NMR studies.     

Preclinical radiotherapy at the Australian Synchrotron's Imaging and Medical Beamline: instrumentation,dosimetry and a small‐animal feasibility study

Therapeutic applications of synchrotron X‐rays such as microbeam (MRT) and minibeam (MBRT) radiation therapy promise significant advantages over conventional clinical techniques for some diseases if successfully transferred to clinical practice. Preclinical studies show clear evidence that a number of normal tissues in animal models display a tolerance to much higher doses from MRT compared with conventional radiotherapy. However, a wide spread in the parameters studied makes it difficult to make any conclusions about the associated tumour control or normal tissue complication probabilities. To facilitate more systematic and reproducible preclinical synchrotron radiotherapy studies, a dedicated preclinical station including small‐animal irradiation stage was designed and installed at the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron. The stage was characterized in terms of the accuracy and reliability of the vertical scanning speed, as this is the key variable in dose delivery. The measured speed was found to be within 1% of the nominal speed for the range of speeds measured by an interferometer. Furthermore, dose measurements confirm the expected relationship between speed and dose and show that the measured dose is independent of the scan direction. Important dosimetric parameters such as peak dose, valley dose, the collimator output factor and peak‐to‐valley dose ratio are presented for 5 mm × 5 mm, 10 mm × 10 mm and 20 mm × 20 mm field sizes. Finally, a feasibility study on three glioma‐bearing rats was performed. MRT and MBRT doses were prescribed to achieve an average dose of 65 Gy in the target, and magnetic resonance imaging follow‐up was performed at various time points after irradiation to follow the tumour volume. Although it is impossible to draw conclusions on the different treatments with such a small number of animals, the feasibility of end‐to‐end preclinical synchrotron radiotherapy studies using the IMBL preclinical stage is demonstrated.