Chiral biscavitand propellers: synthesis, conformations and multiple guest binding

[structure: see text]. The synthesis and properties of molecules containing two cavitand bowls, with interbowl linkages comprising one carbon atom at various oxidation levels, are reported. A carbonyl-bridged biscavitand binds three CH2Cl2 molecules in the solid state through a helical conformation. Evidence for the same chiral conformation in the solution phase is presented.     

Definitive evidence for monoanionic binding of 2,3-dihydroxybiphenyl to 2,3-dihydroxybiphenyl 1,2-dioxygenase from UV resonance Raman spectroscopy, UV/Vis absorption spectroscopy, and crystallography

Ultraviolet resonance Raman spectroscopy (UVRRS), electronic absorption spectroscopy, and X-ray crystallography were used to probe the nature of the binding of 2,3-dihydroxybiphenyl (DHB) to the extradiol ring-cleavage enzyme, 2,3-dihydroxybiphenyl 1,2-dioxygenase (DHBD; EC 1.13.11.39). The lowest lying transitions in the electronic absorption spectrum of DHBD-bound DHB occurred at 299 nm, compared to 305 nm for the monoanionic DHB species in buffer. In contrast, the corresponding transitions in neutral and dianionic DHB occurred at 283 and 348 nm, respectively, indicating that DHBD-bound DHB is monoanionic. These binding-induced spectral changes, and the use of custom-designed optical fiber probes, facilitated UVRR experiments. The strongest feature of the UVRR spectrum of DHB was a Y8a-like mode around 1600 cm(-1), whose position depended strongly on the protonation state of the DHB. In the spectrum of the DHBD-bound species, this feature occurred at 1603 cm(-1), as observed in the spectrum of monoanionic DHB. Raman band shifts were observed in deuterated solvent, ruling out dianionic binding of the substrate. Thus, the electronic absorption and UVRRS data demonstrate that DHBD binds its catecholic substrate as a monoanion, definitively establishing this feature of the proposed mechanism of extradiol dioxygenases. This conclusion is supported by a crystal structure of the DHBD:DHB complex at 2.0 A resolution, which suggests that the substrate's 2-hydroxyl substituent, and not the 3-hydroxyl group, deprotonates upon binding. The structural data also show that the aromatic rings of the enzyme-bound DHB are essentially orthogonal to each other. Thus, the 6 nm blue shift of the transition for bound DHB relative to the monoanion in solution could indicate a conformational change upon binding. Catalytic roles of active site residues are proposed based on the structural data and previously proposed mechanistic schemes.     

The determination of trace metals in estuarine and coastal waters using a voltammetric in situ profiling system

This work presents the optimisation, validation and field deployment of a voltammetric in situ profiling (VIP) system for the simultaneous determinations of dynamic Cd(II), Cu(II) and Pb(II) in estuarine and coastal waters. Systematic studies in NaNO3 (as a supporting electrolyte) and seawater, indicated that variations in ionic strength, pH and dissolved oxygen did not affect the response of the instrument, whereas an Arrhenius type temperature response was observed. The VIP instrument allows the determination of 2-3 samples h(-1), and has a detection limit (defined as 3sigma) in seawater for Cd(II): 23 pM, Cu(II): 1.13 nM, and Pb(II): 23 pM. The VIP system accurately measured the total dissolved concentrations of Cd(II), Cu(II) and Pb(II) in two certified reference materials; SLRS-3, a river water, and SLEW-2, an estuarine water. Field evaluation of the instrumentation and analytical methods was achieved through a series of surveys in the Plym Estuary (Devon, UK), from which environmental data are presented.     

Elastic wave propagation and scattering in solids with uniaxially aligned cracks

In this article, elastic wave propagation and scattering in a solid medium permeated by uniaxially aligned penny-shaped microcracks are studied. The crack alignment refers to the case in which the unit normals of all cracks are randomly oriented within a plane of isotropy. The analysis is restricted to the limit of the noninteraction approximation among individual cracks. Explicit expressions for attenuations and wave speeds of the shear horizontal, quasilongitudinal, and quasishear vertical waves are obtained using stochastic wave theory in a generalized dyadic approach. The ensemble average elastic wave response is governed by the Dyson equation, which is solved in terms of the anisotropic elastic Green's dyadic. The analysis of expressions is limited to frequencies below the geometric optics limit. The resulting attenuations are investigated in terms of the directional, frequency, and damage dependence. In particular, the attenuations are simplified considerably within the low frequency Rayleigh regime. Finally, numerical results are presented and discussed in terms of the relevant dependent parameters.     

Observation of weak-limit quasiparticle scattering via broadband microwave spectroscopy of a d-wave superconductor

There has long been a discrepancy between microwave conductivity measurements in high temperature superconductors and the conductivity spectrum expected in the simplest models for impurity scattering in a d-wave superconductor. Here we present a new type of broadband measurement of microwave surface resistance that finally shows some of the spectral features expected for a d(x2-y2) pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency range in highly ordered crystals of YBa2Cu3O6.50 and YBa2Cu3O6.99.     

Twisted protein aggregates and disease: the stability of sickle hemoglobin fibers

We describe how twist could play an essential role in stabilizing 20 nm diameter sickle hemoglobin fibers. Our theory successfully reproduces the observed variation of helical pitch length with fiber diameter. With no remaining adjustable parameters it also yields a prediction for the torsional rigidity of sickle hemoglobin fibers that is in good agreement with experiment and hence retains the striking feature that such fibers can be highly mechanically anisotropic, even with a ratio of bending to torsional rigidity of about 50. We discuss how our study might be relevant to the development of treatment strategies.     

Folic acid-conjugated nanostructured materials designed for cancer cell targeting

Shell cross-linked nanoparticles (SCKs) constitute a unique class of materials with amphiphilic core-shell morphology; SCKs are characterised by their structural integrity and available functionality to attach receptor-recognising or receptor-specific ligands on the shell surface and, therefore, hold great potential in drug delivery applications; in an attempt to develop novel, cancer cell specific delivery vehicles, folate receptor targeted SCKs have been prepared.     

Crystal structures and properties of mutagenic N-acyloxy-N-alkoxyamides--"most pyramidal" acyclic amides

X-Ray data for two N-acyloxy-N-alkoxyamides, a class of direct-acting mutagens, indicate extreme pyramidalisation at the amide nitrogen in keeping with spectroscopic and theoretically determined properties of amides with bisoxosubstitution at nitrogen. The combined electronegativity of two oxygens leads to average angles at nitrogen of 107.8 and 108.1 degrees and [chiN] of 66 degrees and 65 degrees. The sp3 nature of nitrogen results in negligible amide resonance as evidenced by long N-C(O) bonds, high IR carbonyl stretch frequencies, carbonyl 13C NMR data and very low amide isomerisation barriers. In addition, conformations in the solid state support a strong n(O)-sigma*(NOAc), anomeric interaction as predicted by molecular orbital theory. HF/6-31G* calculations on formamide, N-methoxyformamide and N-formyloxy-N-methoxyformamide support these findings.