Analysis of the NQR parameters in 2-nitro-5-methylimidazole derivatives by quantum chemical calculations

Latosińska, J.N.; Koput, Jacek

doi:10.1039/a906295e

Cited by 28 publications

(32 citation statements)

References 8 publications

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“…These methods are also able to provide quite accurately the electric field gradient at the site of the different nuclei [42,45,46]. Inspection of the crystal structure of the [NiFe] hydrogenase of D. gigas [2] shows that the closest nitrogen nucleus to the nickel atom is the N() of His72 of the large subunit.…”

Section: Dft Calculations Of Quadrupole Coupling Constantsmentioning

confidence: 96%

The H2 sensor of Ralstonia eutropha: biochemical and spectroscopic analysis of mutant proteins modified at a conserved glutamine residue close to the [NiFe] active site

et al. 2002

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[NiFe] hydrogenases contain a highly conserved histidine residue close to the [NiFe] active site which is altered by a glutamine residue in the H(2)-sensing [NiFe] hydrogenases. In this study, we exchanged the respective glutamine residue of the H(2) sensor (RH) of Ralstonia eutropha, Q67 of the RH large subunit HoxC, by histidine, asparagine and glutamate. The replacement by histidine and asparagine resulted in slightly unstable RH proteins which were hardly affected in their regulatory and enzymatic properties. The exchange to glutamate led to a completely unstable RH protein. The purified wild-type RH and the mutant protein with the Gln/His exchange were analysed by continuous-wave and pulsed electron paramagnetic resonance (EPR) techniques. We observed a coupling of a nitrogen nucleus with the [NiFe] active site for the mutant protein which was absent in the spectrum of the wild-type RH. A combination of theoretical calculations with the experimental data provided an explanation for the observed coupling. It is shown that the coupling is due to the formation of a weak hydrogen bond between the protonated N(epsilon) nucleus of the histidine with the sulfur of a conserved cysteine residue which coordinates the metal atoms of the [NiFe] active site as a bridging ligand. The effect of this hydrogen bond on the local structure of the [NiFe] active site is discussed.

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Section: Dft Calculations Of Quadrupole Coupling Constantsmentioning

confidence: 96%

The H2 sensor of Ralstonia eutropha: biochemical and spectroscopic analysis of mutant proteins modified at a conserved glutamine residue close to the [NiFe] active site

et al. 2002

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“…All calculations were performed within DFT with three-parameter hybrid functional of Becke B3, in which the local and nonlocal temas of the correlation functional are provided by the LYP expression [13][14][15] in the 6-31G* basis set. Our earlier studies [16][17][18][19] suggested that the calculations at the B3LYP level lead to results closer to the experimental data than those obtained at the levels HF or MP2. Since the crystallographic structure of HCTZ in solid phase is known [8], the calculations of the NQR parameters were carried out for the crystallographic as well as the optimized geometry.…”

Section: Calculation Detailsmentioning

confidence: 99%

Studies of molecular dynamics of thiazides by35Cl NQR spectroscopy and DFT calculation

2002

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Abstraet. Molecular dynamics of three derivatives of 1,2,4-benzothiadiazine-l,l-dioxide, hydrochlorothiazide (HCTZ), althiazide (ATZ) and chlorotbiazide (CTZ), was studied by 35C1 nuclear quadrupole resonance (NQR) spectroscopy. The temperature dependence of the resonance frequency was analyzed within the 6 known standard models. The activation energies estimated from the temperature dependence of the 3~C1 NQR frequency assuming the Bayer model were 1.07, 2.35 and 2.76 kJ/mot for HCTZ, ATZ and CTZ respectivety, wbich confirms that HCTZ is Iess rigid than CTZ and ATZ is much more rigid than HCTZ, and suggests that the mechanism of relaxation is based on small amplitude librations. The characteristic temperatures estimated from the Bayer model, with that for CTZ (332.5 K) being much higher than for HCTZ (132.1 K), mean that the intermolecular interactions in CTZ are much stronger than in HCTZ, as suggested by the melting point of CTZ being higher than that for HCTZ. For ATZ the characteristic temperature (288 K) takes an intermediate value, which suggests that the intermolecular interactions in this compound are stronger than in HCTZ and weaker than in CTZ. A significant narrowing of the resonance 3~C1 NQR line observed for all these compounds at room temperature, relative to that at the liquid nitrogen temperature, suggests an averaging of dipolar interactions asa result of fast rotation of nonquadrupole nuclei in the vicinity of the quadrupote nuclei, when 2nv~r~ 87 1 (a rotation of the -NH z group in the direct neighborhood of the chlorine nuclei) or a change in the gradient o¡ with its value preserved (which is equivalent to rotation of the quadrupole nucleus CI). The influence of the rotations of the -NH~ and -CH2SCH2CH=CH z groups (ATZ) or -CHCI z group (TCTZ) on the 3~C1 NQR frequency was modelled by the B3LYP/6-31G" method. The frequencies of the libration vibrations calculated from the temperature dependence of the NQR resonance frequency were compared with experimental ones and those implied by the density functional theory, infrared and Raman spectra. For HCTZ the anomalies in the temperature dependence of the 35C1 NQR frequency, the lack of hysteresis and small but notable changes in the slope and the jump in the frequency observed at 253 K which does not exceed 0.05 MHz suggest a second-order phase transition at 253 K.

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“…The calculated parameters of QCC asymmetry for thiazides cannot be compared with the experimental data, because the former are close to the values obtained for a compound of a similar structure-chlorobenzene. The quality of reproduction of the QCC anisotropy parameters is affected by the intermolecular interactions (hydrogen bond formation), as shown by the results obtained in [36][37][38].…”

Section: Reproduction Of Different Spectroscopic Parameters By Dftmentioning

confidence: 95%

“…2. Identification of tautomeric forms on the basis of 13 C-NMR is relatively well documented in literature [31][32][33][34][35], whereas there are only a few works on the application of NQR for that purpose [36][37][38].…”

Section: Polarisation and Delocalisation Effects In Thiazide Moleculesmentioning

confidence: 99%

Structure-activity study of thiazides by magnetic resonance methods (NQR, NMR, EPR) and DFT calculations

Latosińska

2005

Journal of Molecular Graphics and Modelling

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Analysis of the NQR parameters in 2-nitro-5-methylimidazole derivatives by quantum chemical calculations

Cited by 28 publications

References 8 publications

The H2 sensor of Ralstonia eutropha: biochemical and spectroscopic analysis of mutant proteins modified at a conserved glutamine residue close to the [NiFe] active site

The H2 sensor of Ralstonia eutropha: biochemical and spectroscopic analysis of mutant proteins modified at a conserved glutamine residue close to the [NiFe] active site

Studies of molecular dynamics of thiazides by35Cl NQR spectroscopy and DFT calculation

Structure-activity study of thiazides by magnetic resonance methods (NQR, NMR, EPR) and DFT calculations

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