Search results for "RESONANCE"
showing 10 items of 6625 documents
Biological Activity of Flavonoids Copper Complexes
2005
Three flavonoid copper(II) complexes Cu2(quercetin)(CH3COO)3(CH3OH) (1), Cu(anthrarufin)(CH3COO)·1/2H2O (2) and Cu(naringin)(OCH3)(CH3OH)2 (3) have been synthesized and characterized by elemental analysis, IR, electronic absorption and EPR (X-band) spectroscopy. The complexes have a strong protective action over the Δsod1 mutant of S. cerevisiae against reactive oxygen radicals generated by an external source of free radicals (H2O2 or the superoxide-generating, menadione). On the other hand, the complexes cleave DNA efficiently even in the absence of reducing agents. The main reactive oxygen species responsible for the DNA strand cleavage have been determined using radical scavengers. A pro…
Zero- to Ultralow-Field NMR Spectroscopy of Small Biomolecules.
2021
Nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique used to study chemicals and their transformations. However, high-field NMR spectroscopy necessitates advanced infrastructure, and even cryogen-free benchtop NMR spectrometers cannot be readily assembled from commercially available components. We demonstrate construction of a portable zero-field NMR spectrometer employing a commercially available magnetometer and investigate its applications in analytical chemistry. In particular, J-spectra of small representative biomolecules [13C]-formic acid, [1-13C]-glycine, [2,3-13C]-fumarate, and [1-13C]-d-glucose were acquired, and an approach relying on the prese…
A novel Cu(II) dimer containing oxime-hydrazone Schiff base ligands with an unusual mode of coordination: Study of magnetic, autoreduction and soluti…
2013
Abstract Synthesis of a new hydrazone based Schiff base ligand, 3-methylpyrazole-5-carbohydrazone of 2,3-butanedione monoxime (HL) is reported. The reaction of Cu(ClO4)2·6H2O with HL in any ratio in ethanol affords the dinuclear complex [CuL(EtOH)]2(ClO4)2·2H2O (1). An unusual coordination mode of the ligand was observed, in which the ligand forms stable six and five membered chelate rings around the metal centres without enolization of the carbonyl group of the hydrazone moiety. The same coordination behavior of the ligand was observed in its cobalt(III) complex. The reaction of CoCl2·6H2O in methanol with the ligand HL affords the mononuclear complex [CoL2]Cl (2). Both 1 and 2 were charac…
NMR Matrix Technique for Detecting Self Diffusion in Polymers
1979
A technique is discussed where monodisperse small spheres or cylindrical fibers of a polymer are embedded in a matrix of the corresponding fully deuterated polymer. On annealing the sample at a temperature above the glass transition the protonated macromolecules diffuse into the deuterated matrix and vice versa. Since the NMR spectrum depends upon the intermolecular proton proton dipolar coupling, the decrease of this coupling can be used to monitor the diffusion process. For particle diameters d ∼ 10−4 cm and annealing times t ∼ 105 s, extremely small diffusion constants D < d2/t are attainable. The NMR analysis of prospective diffusion experiments with polystyrene is discussed in some det…
Effect of ramp size and sample spinning speed on CPMAS 13C NMR spectra of soil organic matter
2011
Abstract Cross polarization (CP) magic angle spinning (MAS) 13C NMR spectroscopy is a solid state NMR technique widely applied to study the chemical composition of natural organic matter. In high magnetic fields (>7 T), fast sample spinning is required in order to reduce the influence of spinning sidebands underlying other chemical shift regions. As the spinning speed increases, the Hartmann–Hahn matching profiles break down into a series of narrow matching bands. In order to account for this instability variable amplitude cross polarization techniques (e.g. VACP, ramp-CP) have been developed. In the present study, we experimentally verified the stability of the Hartmann–Hahn condition unde…
Cu2+ Coordination Properties of a 2-Pyridine Heptaamine Tripod: Characterization and Binding Mechanism
2009
The synthesis, protonation, and Cu(2+) coordination chemistry of a tripodal heptaamine ligand (L(1)) functionalized with 2-pyridine fragments at the ends of its three branches are reported. L(1) presents six relatively high protonation constants followed by much more reduced constant that as indicated by the UV-vis and NMR data, occur on the pyridine fragments. p[H]-metric, ESI/MS(+), EPR and UV-vis data show that L(1) is able to form mono-, di-, and trinuclear Cu(2+) complexes. Slippage movements and molecular reorganizations have been observed to occur as a function of p[H] in the 1:1 Cu(2+) complexes. The kinetic studies showed that the complex formation is fast and proceeds through a di…
Direct monitoring of spin state in dinuclear iron(II) coordination compounds
2001
So far there has been no direct method to determine the spin state of molecules in dinuclear iron(II) compounds. The molecular fractions of high-spin (HS) and low-spin (LS) species have been deduced from magnetic susceptibility and zero-field Mossbauer spectroscopy data irrespective of whether they belong to LS–LS, LS–HS and HS–HS pairs. However, the distinction of pairs becomes possible if Mossbauer measurements are carried out in an external magnetic field. The proposed method opens new possibilities in the study of spin crossover phenomena in dinuclear compounds.
HACANCOi : a new Hα-detected experiment for backbone resonance assignment of intrinsically disordered proteins
2020
AbstractUnidirectional coherence transfer is highly efficient in intrinsically disordered proteins (IDPs). Their elevated ps-ns timescale dynamics ensures long transverse (T2) relaxation times allowing sophisticated coherence transfer pathway selection in comparison to folded proteins. 1Hα-detection ensures non-susceptibility to chemical exchange with the solvent and enables chemical shift assignment of consecutive proline residues, typically abundant in IDPs. However, many IDPs undergo a disorder-to-order transition upon interaction with their target protein, which leads to the loss of the favorable relaxation properties. Long coherence transfer routes now result in prohibitively large dec…
13C NMR study of aromatic ring-substituted (E)-3-phenylpropenals and (2E,4E)-5-phenylpenta-2,4-dienals
1990
13C and 1H chemical shifts together with C,H and H,H coupling constants are presented for (E)-3-phenylpropenal, (2E,4E)-5-phenylpenta-2,4-dienal and their o-OCH3- and o-, m- and p-NO2-substituted derivatives. The SCSs calculated for the aldehyde chains show similar effects on the ring carbons, except in the para position where the shorter chain causes a 3.3 ppm deshielding and the longer chain a 1.0 ppm shielding effect. This shift difference is reflected in all the ring-substituted derivatives of the two series of aldehydes, but not in the one-bond C,H coupling constants. The effect of aromatic ring substitution on 2J(C,CHO) seems to be mainly inductive in origin. The importance of the str…
Über tetraaryl-methan-analoga in der gruppe 14
1994
Abstract The title compounds have been synthesized by Grignard reactions or pyrolysis of diplumbanes respectively. The crystal structures of m -Tol 4 Pb and Ph 4 Pb (redetermination) have been determined. All eight compounds (Ph/Tol) 4 (Sn/Pb) are S 4 symmetric and contracted along this unique axis. The 13 C-NMR chemical shifts and the couplings 1 J ( 119 Sn/ 207 Pb 13 C) as well depend additively upon the methyl substituents. The ratios 1 K ( 207 Pb 13 C): 1 K ( 119 Sn 13 C) of the reduced coupling constants are all near to 1.61; a comparison with values from the literature for alkyl, alkenyl and alkinyl substituents is given. The ratio δ( 207 Pb):δ( 119 Sn) results in 2.28. IR (700 dow…