Mónika Zsuzsanna Bokor

Publications (28) View all

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  Available from: Mónika Zsuzsanna Bokor

  Article: Quadrupole effects in63Cu NMR spectroscopy of copper nanocrystals

  K. Tompa, P. Bánki, M. Bokor, G. Lasanda, L. K. Varga, Y. Champion, L. Takács
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  ABSTRACT: Quadrupole effects in room-temperature continuous-wave (CW)63Cu nuclear magnetic resonance (NMR) spectra, “π/2” pulse length shortening and amplitudes of two-pulse generated echoes were investigated on nanocrystalline copper powders produced by cryogenic melting and by ball milling techniques. Systematic measurements on the parent polycrystalline copper and on copper-based copper-palladium dilute alloys on the basis of the same experimental techniques were also made and the results were compared to that of the nanophase samples. Fractions of Cu nuclei contributing to the specific NMR responses and average field gradients coming from noncubic neighborhoods were estimated in all the investigated cases. The satellite and/or central component origins of NMR spectra of the samples are not a priori trivial even in the simplest case. Comparative analysis of CW and pulsed experiments allowed a surprising technological conclusion to be drawn by finding a smaller chemical impurity content inside the nanograins than the value characteristic of the entire sample. The measured decrease of the impurity concentration in the inner region of the copper nanoparticles is the consequence of the applied technologies: cryogenic melting and ball milling. These preparation methods cause grain-boundary segregation and result in a cleaner inside of copper nanoparticles.
  Applied Magnetic Resonance 04/2012; 27(1):93-107. · 0.75 Impact Factor
• Article: Wide-line NMR and protein hydration.

  K Tompa, M Bokor, P Tompa
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  ABSTRACT: In this chapter, the reader is introduced to the basics of wide-line NMR, with particular focus on the following: (1) basic theoretical and experimental NMR elements, necessary before switching the spectrometer and designing the experiment, (2) models/theories for the interpretation of measured data, (3) definition of wide-line NMR spectrometry, the description of the measurement and evaluation variants, useful hints for the novice, (4) advice on selecting the solvent, which is not a trivial task, (5) a note of warning that not all data are acceptable in spite of the statistical confidence. Finally, we wrap up the chapter with the results on two proteins (a globular and an intrinsically disordered).
  Methods in molecular biology (Clifton, N.J.) 01/2012; 895:167-96.
• Article: Distinct hydration properties of wild-type and familial point mutant A53T of α-synuclein associated with Parkinson's disease.

  E Hazy, M Bokor, L Kalmar, A Gelencser, P Kamasa, K-H Han, K Tompa, P Tompa
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  ABSTRACT: The propensity of α-synuclein to form amyloid plays an important role in Parkinson's disease. Three familial mutations, A30P, E46K, and A53T, correlate with Parkinson's disease. Therefore, unraveling the structural effects of these mutations has basic implications in understanding the molecular basis of the disease. Here, we address this issue through comparing details of the hydration of wild-type α-synuclein and its A53T mutant by a combination of wide-line NMR, differential scanning calorimetry, and molecular dynamics simulations. All three approaches suggest a hydrate shell compatible with a largely disordered state of both proteins. Its fine details, however, are different, with the mutant displaying a somewhat higher level of hydration, suggesting a bias to more open structures, favorable for protein-protein interactions leading to amyloid formation. These differences disappear in the amyloid state, suggesting basically the same surface topology, irrespective of the initial monomeric state.
  Biophysical Journal 11/2011; 101(9):2260-6. · 3.65 Impact Factor
• Article: Hydration water/interfacial water in crystalline lens.

  K Tompa, P Bánki, M Bokor, P Kamasa, P Rácz, P Tompa
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  ABSTRACT: Wide-line (1)H NMR signal intensity, spin-lattice and spin-spin relaxation rates and differential scanning calorimetry (DSC) measurements were done on avian (chicken and turkey) crystalline lenses between -70 degrees C and +45 degrees C to provide quantitative measures of protein hydration characteristic of the protein-water interfacial region. These measures are of paramount importance in understanding both the physiology of crystalline lens and its transitions to the cataractous pathological state characterized by the formation of opaque protein aggregates. Water mobility shows a characteristic transition at about -60 degrees C, which is identified as the melting of the interfacial/hydrate water. The amount of water in the low-temperature mobile fraction is about h = 0.4 g water/g protein, which equals the hydration required for protein activity. The amount of mobile water is temperature-independent up to about -10 degrees C, with a significant increase at higher temperatures below 0 degrees C. Above 0 degrees C, the relaxation processes can be described by a single (for spin-lattice) and by a triple (for spin-spin relaxation) exponential function. The spin-spin relaxation rate component of R(2) = 10-20 s(-1) and its dynamical parameters characterize the interfacial water at ambient or physiological temperatures. When considered an independent phase, the specific heat of the hydrate water obtained by a combination of DSC and NMR data in the temperature range -43 degrees C to -28 degrees C is higher than that of pure/bulk water. This discrepancy can only be resolved by assuming that the hydrate water is in strong thermodynamic coupling with the protein matrix. The specific heat for the system composed of the protein molecule and its hydration water is 4.6 +/- 0.3 J g(-1) K(-1). Thus, in a thermodynamic sense, crystalline protein and its hydrate layer behave as a highly-interconnected single phase.
  Experimental Eye Research 07/2010; 91(1):76-84. · 3.26 Impact Factor
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  Available from: Mónika Zsuzsanna Bokor

  Article: Hydrogen spectroscopy of Pd0.9Ag0.1-H alloys on NMR scales

  K. Tompa, P. Bánki, M. Bokor, G. Lasanda
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  ABSTRACT: Simultaneous realisation of hydrogen charging or discharging process and in situ measurements of different NMR characteristic quantities give outstanding chances for the investigation and understanding of local physical properties of and hydrogen diffusion in disordered metal-hydrogen systems, including both equilibrium and non-equilibrium states. A few selected preliminary experimental results are presented in this letter for Pd0.9Ag0.1-H alloy on in situ hydrogen concentration, proton NMR line-shift and magnetic susceptibility, 1H NMR spectrum, spin-spin relaxation time and hydrogen diffusion activation energy and correlation time measurements. The motional averaged spectrum is asymmetric and the possible decompositions relate to the non-single-site residence of hydrogen in this alloy.
  EPL (Europhysics Letters) 01/2007; 53(1):79. · 2.17 Impact Factor