Proton magnetic resonance study of the structure of two tutton's salts

Proton magnetic resonance spectra of single crystals of two Tutton's salts, K2Zn (SO4)2.6H22O and K2Mg (SO4)2.6H2O, have been studied and the orientations of the water molecules in the structure have been determined. Using the heavy-atom structure of (NH4) 2Mgt(SO4)2.6H2O as determined by x-ray diffraction, a system of hydrogen bonds between the water and sulfate oxygens in Tutton's salts has been proposed. It appears that the x-ray structure needs considerable refinement.

Studies in sesquiterpenes-XVIII. The proton magnetic resonance spectra of some sesquiterpenes and the structure of humulene

The nuclear magnetic resonance spectra of longifolene, zerumbone, humulene, and their hydroderivatives have been studied in order to gauge the potentialities of this new tool in the field of sesquiterpenes. On the basis of present study, it has been possible to unequivocally fix the positions of the ethylene linkages in humulene and thus provide a straightforward solution of this hitherto unsolved problem.

Classification of magnetic resonance brain images using wavelets as input to support vector machine and neural network

In this paper. we propose a novel method using wavelets as input to neural network self-organizing maps and support vector machine for classification of magnetic resonance (MR) images of the human brain. The proposed method classifies MR brain images as either normal or abnormal. We have tested the proposed approach using a dataset of 52 MR brain images. Good classification percentage of more than 94% was achieved using the neural network self-organizing maps (SOM) and 98% front support vector machine. We observed that the classification rate is high for a Support vector machine classifier compared to self-organizing map-based approach.

Contactless conductivity of nanoparticles from electron magnetic resonance lineshape analysis

A contactless method to determine the electrical conductivity of nanoparticles is presented. It is based on the lineshape analysis of electron magnetic resonance signals which are `Dysonian' for conducting samples of sizes larger than the skin depth. The method is validated bymeasurements on a bulk sample of La0.67Sr0.33MnO3 where it gives values close to those obtained from direct measurement of conductivity and is then used to determine the conductivity of nanoparticles of La0.67Sr0.33MnO3 dispersed in polyvinyl alcohol as a function of temperature. (C) 2010 Elsevier Ltd. All rights reserved.

Conformations of synthetic alamethicin fragments. Evidence for 310 helical folding from 270-MHz hydrogen-1 nuclear magnetic resonance and circular dichroism studies

IH NMR studies at 270 MHz on the synthetic alamethicin fragments Z-Aib-Pro-Aib-Ala-Aib-Ala-OMe (1-6), Boc-Gln-Aib-Val-Aib-Gly-Leu-Aib-OMe (7-1 3), Boc-Leu-Aib-Pro-Val-Aib-OMe (1 2-16), and Boc-Gly-Leu- Aib-Pro-Val-Aib-OMe (1 1-16) have been carried out in CDC13 and (CD3)2S0. The intramolecularly hydrogen bonded amide hydrogens in these peptides have been delineated by using solvent titration experiments and temperature coefficientsof NH chemical shifts in (CD3)+30. All the peptides adopt highly folded structures, characterized by intramolecular 4 - 1 hydrogen bonds. The 1-6 fragment adopts a 310 helical conformation with four hydrogen bonds, in agreement with earlier studies (Rao, Ch. P., Nagaraj, R., Rao, C. N. R., & Balaram, P. (1980) Biochemistry 19, 425-4311. The 7-13

Hyperfine effects in the nuclear magnetic resonance of paramagnetic molecules

Paramagnetic, or open-shell, systems are often encountered in the context of metalloproteins, and they are also an essential part of molecular magnets. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for chemical structure elucidation, but for paramagnetic molecules it is substantially more complicated than in the diamagnetic case. Before the present work, the theory of NMR of paramagnetic molecules was limited to spin-1/2 systems and it did not include relativistic corrections to the hyperfine effects. It also was not systematically expandable. --- The theory was first expanded by including hyperfine contributions up to the fourth power in the fine structure constant α. It was then reformulated and its scope widened to allow any spin state in any spatial symmetry. This involved including zero-field splitting effects. In both stages the theory was implemented into a separate analysis program. The different levels of theory were tested by demonstrative density functional calculations on molecules selected to showcase the relative strength of new NMR shielding terms. The theory was also tested in a joint experimental and computational effort to confirm assignment of 11 B signals. The new terms were found to be significant and comparable with the terms in the earlier levels of theory. The leading-order magnetic-field dependence of shielding in paramagnetic systems was formulated. The theory is now systematically expandable, allowing for higher-order field dependence and relativistic contributions. The prevailing experimental view of pseudocontact shift was found to be significantly incomplete, as it only includes specific geometric dependence, which is not present in most of the new terms introduced here. The computational uncertainty in density functional calculations of the Fermi contact hyperfine constant and zero-field splitting tensor sets a limit for quantitative prediction of paramagnetic shielding for now.

13 C nuclear magnetic resonance studies of the binding of alkali and alkaline earth metal salts to amides

13 C resonances of carbonyl and methyl groups in amides are shifted down-field on interaction with alkali and alkaline earth metal salts. The magnitude of the shift depends on the ionic potential of the cation. Ions like Li+ bind to the amide carbonyl group both in neat amide solutions as well as in concentrated salt solutions in water.

Proton Magnetic-Resonance Study of Cycloheximide-Ribosome Interactions

Cycloheximide-ribosome interactions from sensitive and resistant organisms were studied by proton magnetic resonance spectroscopic techniques. The two methyl resonances of cycloheximide upon interaction with ribosomes from Saccharomyces cerevisiae showed preferential broadening. Comparison of cycloheximide line broadening as effected by ribosomes from S. cerevisiae (sensitive) and Microsporum canis (resistant) revealed that less cycloheximide is bound to the M. canis ribosomes. From the decrease in line broadening observed with increasing temperature it may be concluded that cycloheximide-ribosome interaction is a fast exchange reaction. Tetracycline did not compete with cycloheximide for binding site(s) on the ribosomes of S. cerevisiae.

Circular dichroism and 13C nuclear magnetic resonance spectroscopy of pennisetin from pearl millet

The conformation and stability of pearl millet prolamin (pennisetin) were examined by using circular dichroism and C-13 nuclear magnetic resonance spectroscopy. The far UV spectrum of pennisetin in 70% (v/v) aqueous ethanol showed the presence of predominant alpha-helical structure and its occurrence in the alpha + beta class of protein. The far and near UV spectra of pennisetin in ethanol: trifluoroethanol also supported this observation. However pennisetin showed the presence of some helical structure in 8 M urea which is known to be a highly unordered structure forming solvent. A decrease in alpha helical content of native pennisetin was observed with rise in temperature from 5-75-degrees-C and this effect of temperature was found to be reversible. A C-13 NMR spectrum of pennisetin in 70% ethanol suggested a high degree of molecular mobility in ethanol. Comparison of the cross polarization spectrum with the single pulse excitation spectrum suggested pennisetin to be a heterogeneous protein.