Search results for " Spin"

Effects of nucleotide binding to LmrA: A combined MAS-NMR and solution NMR study

2015

ABC transporters are fascinating examples of fine-tuned molecular machines that use the energy from ATP hydrolysis to translocate a multitude of substrates across biological membranes. While structural details have emerged on many members of this large protein superfamily, a number of functional details are still under debate. High resolution structures yield valuable insights into protein function, but it is the combination of structural, functional and dynamic insights that facilitates a complete understanding of the workings of their complex molecular mechanisms. NMR is a technique well-suited to investigate proteins in atomic resolution while taking their dynamic properties into account…

The dynamic properties of the M121H azurin metal site as studied by NMR of the paramagnetic Cu(II) and Co(II) metalloderivatives

1998

The M121H azurin mutant in solution presents various species in equilibrium that can be detected and studied by 1H NMR of the Cu(II) and Co(II) paramagnetic metalloderivatives. In both cases up to three species are observed in slow exchange, the proportions of which are different for the two metalloderivatives. Above pH 5 the major species displays a tetrahedral coordination in which the His121 can be observed as a coordinated residue. Its metal site corresponds to a new type of site that is defined as a type 1.5 site. The second and third species resemble the wild type (type 1) azurin and, above pH 4.5, they are present only at a low concentration. At low pH a protonation process increases…

Non-negative blind source separation techniques for tumor tissue typing using HR-MAS signals.

2010

Given High Resolution Magic Angle Spinning (HR-MAS) signals from several glioblastoma tumor subjects, the goal is to differentiate between tumor tissue types by separating the different sources that contribute to the profile of each spectrum. Blind source separation techniques are applied for obtaining characteristic profiles for necrosis, high cellular tumor and border tumor tissue, and providing the contribution (abundance) of each tumor tissue to the profile of the spectra. The problem is formulated as a non-negative source separation problem. We illustrate the effectiveness of the proposed methods and we analyze to which extent the dimension of the input space could influence the perfor…

Precise measurement of 1H 90° pulse in solid-state NMR spectroscopy for complex and heterogeneous molecular systems

2007

The 90 degrees pulse calibration is essential in NMR spectroscopy to prevent artefacts in the liquid state or to enhance cross-polarization efficiency in the solid state. We verified pulse-angle (PA) errors due to circuit impedances in solid-state NMR and suggested a possible solution to prevent the inconvenience of PA errors. The classic pulse sequences used to calibrate (1)H 90 degrees pulse lengths by direct detection of protons or by cross-polarization were modified in order to replace single (1)H pulses with (1)H pulse trains. Pulse trains were found to decrease the effect of PA imperfections in the calibration of basic pulses (i.e. 90 degrees and 180 degrees ) for a number of organic …

Spin‐Labeled Heparins as Polarizing Agents for Dynamic Nuclear Polarization

2010

A potentially biocompatible class of spin-labeled macromolecules, spin-labeled (SL) heparins, and their use as nuclear magnetic resonance (NMR) signal enhancers are introduced. The signal enhancement is achieved through Overhauser-type dynamic nuclear polarization (DNP). All presented SL-heparins show high 1 H DNP enhancement factors up to E=-110, which validates that effectively more than one hyperfine line can be saturated even for spin-labeled polarizing agents. The parameters for the Overhauser-type DNP are determined and discussed. A striking result is that for spin-labeled heparins, the off-resonant electron paramagnetic resonance (EPR) hyperfine lines contribute a non-negligible part…

Quantification and classification of high-resolution magic angle spinning data for brain tumor diagnosis.

2007

The goal of this work is to propose a complete protocol (preprocessing, processing and classification) for classifying brain tumors with proton high-resolution magic-angle spinning ((1)H HR-MAS) data. The different steps of the procedure are detailed and discussed. Feature extraction techniques such as peak integration, including also the automated quantitation method AQSES, were combined with linear (LDA) and non-linear (least-squares support vector machine or LS-SVM) classifiers. Classification accuracy was assessed using a stratified random sampling scheme. The results suggest that LS-SVM performs better than LDA while AQSES performs better than the standard peak integration feature extr…

Metal complexes of phenobarbituric acid. Chelating behavior of the phenobarbiturate ring. Anticonvulsant properties of the K2[Cu(N-methylphenobarbitu…

1992

Abstract Na2Ni(phenobarbiturato)4·3H2O, Na2Ni3(phenobarbiturato)2(OH)6·4H2O, and NaZn(phenobarbiturato)2(OH)·H2O derivatives were prepared from Ni(II) and Zn(II) and phenobarbital. The Na2Ni(phenobarbiturato)4·3H2O complex is diamagnetic and isostructural with the complex previously reported, Na2Cu(phenobarbiturato)4, suggesting a square-planar environment around the Ni(II) ion. The DMF solutions of this complex show the existence of two species. The EPR spectra of the Cu(II) doped complex show the hyperfine and superhyperfine structures. The covalence parameters α2, β2, and δ2 show a strong bonding in the equatorial plane and suggests the formation of a [CuN4] chromophore. The anticonvulsa…

Cooperative onset of a different state of water in the presence of macromolecules.

1973

Magnetism and EPR spectra of the two‐sublattice manganese chain Mn2(EDTA)⋅9H2O

1990

We report on the magnetic behavior and single‐crystal EPR spectra of the chain complex Mn2(EDTA)⋅9H2O characterized by two different alternating sites for the manganese ions. Magnetic susceptibility data are indicative of weak antiferromagnetic exchange interactions between the manganese ions, showing a maximum of about 3 K. This behavior can be accurately described on the basis of a Heisenberg chain model that assumes classical spins, giving J/k=−0.72 K and g=2.0. The EPR spectra are typically low dimensional, with an angular dependence of the linewidth of the type (3 cos2 θ−1)n (n=4/3 or 2). Nevertheless, such a behavior cannot be reproduced from a one‐dimensional model with dipolar broad…

Presence of Genital Spines in a Male Corynosoma cetaceum Johnston and Best, 1942 (Acanthocephala)

2002

We collected 83 females and 80 males of Corynosoma cetaceum from 2 common dolphins, Delphinus delphis, collected in northern Patagonia (Argentina). Worms were most similar to specimens collected in other South American localities. However, 1 male had 2 spines adjacent to the genital pore and isolated from the rest of body spines. This finding confirms the recent reassignment of C. cetaceum to Corynosoma. Absence of genital spines is suggested to be avoided as the sole criterion to exclude specimens from Corynosoma or Andracantha. Aznar Avendaño, Francisco Javier, Francisco.Aznar@uv.es ; Raga Esteve, Juan Antonio, Toni.Raga@uv.es