Features of selective kinase inhibitors

Small-molecule inhibitors of protein and lipid kinases have emerged as indispensable tools for studying signal transduction. Despite the widespread use of these reagents, there is little consensus about the biochemical criteria that define their potency and selectivity in cells. We discuss some of the features that determine the cellular activity of kinase inhibitors and propose a framework for interpreting inhibitor selectivity.     

Single molecule studies of quantum dot conjugates in a submicrometer fluidic channel

A microfluidic and optical system was created for the detection and analysis of single molecules in solution. Fluidic channels with submicrometer dimensions were used to isolate, detect and identify individual quantum dots conjugated with organic fluorophores. The channels were fabricated in fused silica with a 500 nm square cross section. The resulting focal volume of approximately 500 aL reduced fluorescent background and increased the signal to noise ratio of single molecule detection. The channels also enabled the rapid detection of 99% of quantum dots and organic fluorophores traversing the focal volume. Conjugates were driven through the channels electrokinetically at 2.3 kV cm(-1), excited with a single 476 nm wavelength laser and detected with a confocal microscope. Fluorescence emission was collected simultaneously from green (500-590 nm) and red (610-680 nm) regions of the spectrum. Signal rejection was minimized by the narrow and symmetric emission spectra of the quantum dots. To demonstrate efficient multicolor detection and characterization of single molecule binding, Qdot 655 Streptavidin Conjugates were bound to Alexa Fluor 488 molecules and individually detected. Photon counting histogram analysis was used to quantify coincident detection and degree of binding. Fluorescence correlation spectroscopy was used to measure the mobility of bound and unbound species. The union of fluidic channels with submicrometer dimensions and quantum dots as fluorescent labels resulted in efficient and rapid multiplexed single molecule detection and analysis.     

Electron spin-echo envelope modulation at S-band. 1: Analysis of hyperfine interaction effects

Electron spin-echo techniques have been successfully applied to the study of disordered systems mainly due to the nuclear modulation of the echo signal, the analysis of which gives information on the structural arrangement around the paramagnetic center. Most applications to date have been carried out at X-band (≈9 GHz). Here we report on the analysis of two and three pulse modulation patterns simulated at S-band (≈3 GHz) for which the modulation depth is about tenfold deeper and more quantitative analysis ofI=1/2 nuclei becomes possible. The investigation is applied to two different nuclei of experimental interest at different electron-nucleus distances, and comparison is done with the corresponding X-band patterns.¹³C and¹⁵N nuclei, both with nuclear spin quantum valueI=1/2, are chosen due to their different nuclearg-factors that produce quite different modulation periods. Modulation features due to isotropic hyperfine couplings are also analyzed. It is shown that in several cases complicated patterns arise, that are successfully interpreted by Fourier transform in the frequency domain. Some conclusions are drawn concerning the experimental conditions under which the use of S-band is really of significant advantage with respect to X-band.     

Four pulse electron spin echo modulation studies of Cu(II) complexes in MCM-41 silica tube materials

The coordination geometry of Cu(II) complexes with water and ammonia has been studied by four pulse electron spin echo modulation spectroscopy in siliceous (L)Cu-MCM-41 and in aluminum-containing (L)Cu-AlMCM-41 where (L) denotes Cu(II) incorporation by liquid phase ionexchange. An analysis of the proton sum peaks in the echo modulation pattern of the water and ammonia ligands reveals significant differences in the Cu(II) coordination between MCM-41 and AlMCM-41. In the aluminum-containing material (L)Cu-AlMCM-41, Cu(II) coordinates to two molecules of water or ammonia and three framework oxygens in a square-based pyramidal coordination geometry. The base of the pyramid is formed by two adsorbate molecules together with two framework oxygens. A third framework oxygen is located at the apex of the pyramid. The cupric ion site is slightly shifted from the plane of the pyramid base towards the apex resulting in an off-plane position. In the siliceous material (L)Cu-MCM-41, [Cu(H₂O)₆]²⁺ and [Cu(NH₃)₄]²⁺ complexes are observed. The results of four pulse electron spin echo modulation experiments support a distorted octahedral coordination geometry for the [Cu(H₂O)₆]²⁺ complex in (L)Cu-MCM-41.     

Further observations in atomic absorption spectroscopy

Three observations have been made pertinent to atomic absorption spectroscopy. With a flame atomizer, it is shown that (1) the absorption profile is controlled by metal oxide formation, (2) organo-metallic compounds give rise to greater absorption than metal salts, and (3) absorption by hydroxyl bands affects the apparent metal absorption in certain spectral regions.     

Electron spin-echo envelope modulation at S-band. 3: Analysis of nuclear quadrupole interaction effects

In the present paper the nuclear modulation of electron spin echo signals at S-band is investigated in the case of interacting nuclei with a quadrupole moment high enough to cause nuclear quadrupole couplings not negligible with respect to the nuclear Zeeman and dipolar hyperfine couplings. Both the two-pulse and three-pulse electron spin echo envelope modulation (ESEEM) due to²⁷Al and¹⁴N are simulated at different values of the nuclear quadrupole coupling by numerical diagonalization of the nuclear Hamiltonians. The behavior of their amplitude and periods is discussed on the basis of the ratios between the strengths of the nuclear quadrupole interaction and the nuclear Zeeman and the dipolar hyperfine interactions. The interpretation of their trends in terms of the eigenfunctions and eigenvectors of the nuclear Hamiltonians is carried out by using analytical equations obtained by perturbation approaches. First order perturbation treatments for integer and half-integer nuclear spin quantum numbers are developed when the nuclear quadrupole coupling is the main interaction. A discussion on the limits of the interpretation based on the perturbation approach is also given by comparing the magnitude Fourier transform of the patterns calculated by exact diagonalization and analytical equations.     

Low field microwave absorption and magnetic flux quantization in granular Rb3C60: Observation of nonperiodic sharp line microwave absorption

The low field microwave absorption (LFMA) of granular samples of superconducting Rb₃C₆₀ has been studied as a function of the microwave power, magnetic field modulation amplitude and temperature at dc magnetic fields less than 0.5 G. Nonperiodic sharp lines are observed for the first time in these new alkali-metal doped fullerenes. An interpretation is advanced based on a spin-glass model of a set of superconducting current loops with random orientations but uniform areas.     

On electron solvation in polar liquids

Experimental and theoretical evidence for the dominance of first solvation shell orientation on the spectral changes observed during electron solvation is evaluated.     

X-ray diffraction microscopy of magnetic structures

We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L3 edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.