Analytical theory of gamma-encoded double-quantum recoupling sequences in solid-state nuclear magnetic resonance

Many important double-quantum recoupling techniques in solid-state NMR are classified as being gamma-encoded. This means that the phase of the double-quantum effective Hamiltonian, but not its amplitude, depends on the third Euler angle defining the orientation of the molecular spin system in the frame of the magic-angle-spinning rotor. In this paper, we provide closed analytical solutions for the dependence of the powder-average double-quantum-filtered signal on the recoupling times, within the average Hamiltonian approximation for gamma-encoded pulse sequences. The validity of the analytical solutions is tested by numerical simulations. The internuclear distance in a (13)C(2)-labelled retinal is estimated by fitting the analytical curves to experimental double-quantum data.     

A Fluorescent Probe for Diacetyl Detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl.     

Low-loss coupling between two single-mode optical fibers with different mode-field diameters using a graded-index multimode optical fiber

We present a method for ultra-low-loss coupling between two single-mode optical fibers with different mode-field diameters using multimode interference in a graded-index multimode optical fiber. We perform a detailed analysis of the interference effects and show that the graded-index fiber can also be used as a beam expander or condenser. The results are important for devices in which optical fibers with different mode-field diameters are coupled in series, such as in ultra-short-pulse fiber ring lasers, or in optical fiber communication links.     

Theoretical analysis of a simple yet efficient portable magnetic separator design for separation of magnetic nano/micro-carriers from human blood flow

A technology that could physically remove substances from the blood such as biological, chemical, or radiological toxins could dramatically improve treatment of disease. One method in development proposes to use magnetic-polymer spheres to selectively bind toxins and remove them by magnetic filtration. Although magnetic filtration is a developed technology, the clinical boundary conditions described here require a new filter design. We investigated the removal of toxin-bound magnetic carriers from the blood stream using 2-D FEMLAB simulations. The magnetic separator consisted of a permanent magnet with parallel ferromagnetic prisms on the faces and in contact with a straight tube carrying the magnetic-polymer spheres in suspension. We varied the following parameters: blood flow velocity, the size, and number of ferromagnetic prisms, and the ferromagnetic material in both prisms and magnets. The capture efficiency reached maximum values when the depth of the prisms equaled the diameter of the tubing and the saturation magnetization of the prism material equaled twice that of the magnet. With this design a piece of 2 mm (diameter) tube carrying the fluid resulted in 95% capture of 2.0 μm magnetic-polymer spheres at 10 cm/s flow velocity.     

A diffuse-interface method for two-phase flows with soluble surfactants

A method is presented to solve two-phase problems involving soluble surfactants. The incompressible Navier-Stokes equations are solved along with equations for the bulk and interfacial surfactant concentrations. A non-linear equation of state is used to relate the surface tension to the interfacial surfactant concentration. The method is based on the use of a diffuse interface, which allows a simple implementation using standard finite difference or finite element techniques. Here, finite difference methods on a block-structured adaptive grid are used, and the resulting equations are solved using a non-linear multigrid method. Results are presented for a drop in shear flow in both 2D and 3D, and the effect of solubility is discussed.     

On the Photophysical Properties of New Luminol Derivatives and their Synthetic Phthalimide Precursors

The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity.     

(51)V solid-state NMR investigations and DFT studies of model compounds for vanadium haloperoxidases

Three cis-dioxovanadium(V) complexes with similar N-salicylidenehydrazide ligands modeling hydrogen bonding interactions of vanadate relevant for vanadium haloperoxidases are studied by (51)V solid-state NMR spectroscopy. Their parameters describing the quadrupolar and chemical shift anisotropy interactions (quadrupolar coupling constant C(Q), asymmetry of the quadrupolar tensor eta(Q), isotropic chemical shift delta(iso), chemical shift anisotropy delta(sigma), asymmetry of the chemical shift tensor eta(sigma) and the Euler angles alpha, beta and gamma) are determined both experimentally and theoretically using DFT methods. A comparative study of different methods to determine the NMR parameters by numerical simulation of the spectra is presented. Detailed theoretical investigations on the DFT level using various basis sets and structural models show that by useful choice of the methodology, the calculated parameters agree to the experimental ones in a very good manner.