Influence of charge and structure on the coordination chemistry of copper aminoglycosides

Aminoglycosides are a family of molecules based on a 2-deoxystreptamine ring that is functionalized with a variety of sugar units that contain vicinal amine and hydroxyl functionality. These positively-charged amines promote selective high affinity binding to bacterial 16 s rRNA with resultant antibacterial activity. Aminoglycosides have also been shown to selectively target a variety of therapeutically relevant RNA motifs, and in combination with copper to promote irreversible degradation of the RNA target. The presence of multiple hydroxyl and amine groups on multiple rings creates many potential copper coordination sites. However, only a small subset of these sites actually bind copper, which have not been clearly defined experimentally, Herein we describe a more extensive structural characterization of the complexes of six aminoglycosides (kanamycin A, kanamycin B, neomycin B, neamine, tobramycin and paromomycin) that provide insights on the factors contributing to the coordination selectivity of aminoglycosides toward divalent copper. The presence of vicinal ligand donors capable of chelating the copper ion appears to be a prerequisite for stable metal binding, with charge density providing further tuning of the K(D). A possible role for metal coordination in antibacterial activity is also considered.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.     

Diffusion behavior of tungsten clusters on the tungsten (110) planes

Diffusion of tungsten diatomic clusters on the W (110) exhibits comparable prefactor (1.6×10^-4 cm²/sec) as single W atoms, but with slightly higher activation energy. Clusters with three atoms are unstable with respect to diffusion.     

Semi-metallic behaviour of HMTSF-TCNQ at low temperatures under pressure

Some results of electrical resistivity (?) and transverse magnetoresistance measurements on single crystals of the charge transfer compound HMTSF-TCNQ under pressure are reported. There is evidence that d?/dT remains positive over the whole temperature range under pressure, and that a T² law is obeyed from 0.19 to 2 K at 14 kbar. Together with a relatively large magnetoresistance this is an indication of semi-metallic behaviour.     

The preparation and cytotoxic properties of211at labelled concanavalin a bound to cell membranes

A method of labelling biologically active proteins with the alpha emmitting halogen²¹¹At is presented. The labelling procedure is discussed with reference to the chemistry of astatine. Proteins which have been labelled retain approximately 50% of their original biological activity. Using cell specific labelled proteins, dose response curves are given indicating that such reagents are extremely cytotoxic, D₃₇ human CML cells=5 atmos²¹¹At/cell. The research potential of²¹¹At labelled biologically active proteins is briefly discussed.     

Dynamics of peptidergic secretory granule transport are regulated by neuronal stimulation

Background  

Peptidergic neurons store and secrete the contents of large dense core vesicles (LDCVs) from axon terminals and from dendrites. Secretion of peptides requires a highly regulated exocytotic mechanism, plus coordinated synthesis and transport of LDCVs to their sites of release. Although these trafficking events are critical to function, little is known regarding the dynamic behavior of LDCVs and the mechanisms by which their transport is regulated. Sensory neurons also package opiate receptors in peptide-containing LDCVs, which is thought to be important in pain sensation. Since peptide granules cannot be refilled locally after their contents are secreted, it is particularly important to understand how neurons support regulated release of peptides.     

Traveling-wave Thomson scattering and optical undulators for high-yield EUV and X-ray sources

We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles >10°, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180°) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.     

Spinodal decomposition in solid isotopic helium mixtures

We report the first observations of spinodal decomposition in solid helium isotopic mixtures, using NMR measurements. The experiments were performed at a 3He concentration of 50% where the transition proceeds through the critical point. We used an initial pressure such that the system remained solid. Our observations indicate that the transition occurs by the mechanism of spinodal decomposition and we are able to study its evolution in real time.