Abstract
Electron Paramagnetic Resonance (EPR) was used to investigate the Tempyo spin label (3-carbamoyl-2,2,5,5-
tetramethyl-3-pyrrolin-1-yloxy) as a report group for the interactions and the conformational changes of lyophilized
bovine serum albumin (BSA) and bovine hemoglobin (BH), as function of pH values in the range 2.5–11. The EPR
spectra are similar with those of other non-covalently spin label porphyrins in frozen solution at very low temperatures.
This behavior indicated a possible spin–spin interaction between the hemic iron and the nitroxide group. The changes
in the EPR spectra as function of the pH are discussed in terms of conformational changes of the proteins. Spectral
simulations and magnetic EPR parameters reveal the following: (i) one single paramagnetic species, with Gaussian
line shape, was used for the best fits of experimental spectra in the case of serum albumin samples; and (ii) a
weighted sum of Lorentzian and Gaussian line shape in the case of hemoglobin samples. The representation of
correlation time vs. pH, reveals a dependence of degree of immobilization of spin label on the conformational changes
of proteins in acidic and basic environment.
SIMONA CAVALU_Rotational Correlation Times of proteinsSimona Cavalu
Noncovalent spin labeled proteins (ovalbumin, bovine serum albumin, hemoglobin, and cytochrome c) were
investigated in order to follow the different type of interactions between the nitroxide radical of 3-carbamoyl-
2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy spin label and functional groups of heme and nonheme proteins as
well as the pH influence on molecular motion of the label with respect to these proteins. EPR spectra were
recorded at room temperature and the computer simulation analysis of spectra was made in order to obtain
the magnetic parameters. Noncovalent labeling of proteins can give valuable information on the magnetic
interaction between the label molecule and the paramagnetic center of the proteins. The relevance of this
interaction can be obtained from line shape analysis: computer simulations for nonheme proteins assume
a Gaussian line shape, whereas for heme proteins, a weighted sum of Lorentzian and Gaussian components
is assumed. In the framework of the “moderate jump diffusion” model for rotational diffusion, the rotational
correlation time is strongly influenced by pH, because of the electrostatic interactions and hydrogen bonding.
SIMONA CAVALU_Raman and Surface Enhanced Raman Spectroscopy of 2,2,5,5-Tetram...Simona Cavalu
ABSTRACT: 2,2,5,5-Tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide (tempyo) labeled bovine
serum albumin and cytochrome c at different pH values were prepared and
investigated using Raman–resonance Raman (RR) spectroscopy and surface enhanced
Raman scattering (SERS) spectroscopy. The Raman spectra of tempyo labeled proteins
in the pH 6.7–11 range were compared to those of the corresponding free species. The
SERS spectra were interpreted in terms of the structural changes of the tempyo labeled
proteins adsorbed on the silver colloidal surface. The tempyo spin label was found to be
inactive in the Raman–RR and SERS spectra of the proteins. The a-helix conformation
was concluded to be more favorable as the SERS binding site of bovine serumalbumin.
In the cytochrome c the enhancement of the bands assigned to the porphyrin macrocycle
stretching mode allowed the supposition of the N-adsorption onto the colloidal surface.
Potentiometric Glucose Detection by Paper-based Electrochemical Sensor on CMO...TELKOMNIKA JOURNAL
This paper presents a low cost portable medical device for biochemical sensor using CMOS chip
and paper-based fluidic channel. We measured a potential produced by enzyme activity of glucose
between the working and reference electrode on CMOS chip. A liquid sample is transported by paperbased
fluidic channel, which is made of chromatography paper and silicone resin, and consists of the area
for filtering a sample (filter layer) and that for reacting enzyme (enyzme layer). The paper-based fluidic
channel is used by combining CMOS chip, and the solution with glucose is dropped from top of the paperbased
fluidic channel. The concentrations of glucose are detected by potentiometry (open circuit potential
time). The experimental results show that the glucose concentration is measured by CMOS chip and
paper-based fluidic channel.
The IOSR Journal of Pharmacy (IOSRPHR) is an open access online & offline peer reviewed international journal, which publishes innovative research papers, reviews, mini-reviews, short communications and notes dealing with Pharmaceutical Sciences( Pharmaceutical Technology, Pharmaceutics, Biopharmaceutics, Pharmacokinetics, Pharmaceutical/Medicinal Chemistry, Computational Chemistry and Molecular Drug Design, Pharmacognosy & Phytochemistry, Pharmacology, Pharmaceutical Analysis, Pharmacy Practice, Clinical and Hospital Pharmacy, Cell Biology, Genomics and Proteomics, Pharmacogenomics, Bioinformatics and Biotechnology of Pharmaceutical Interest........more details on Aim & Scope).
Vibrational Characterization and Antioxidant Activity of Newly Synthesized Ga...peertechzpublication
The gallium(III) complex of orotic acid (HOA) was synthesized and its structure was determined
by means of analytical and spectral analyses. Detailed vibrational analysis of HOA, sodium salt of HOA
(NaOA) and Ga(III)-OA systems based on both the calculated and experimental spectra confi rmed the
suggested metal-ligand binding mode. Signifi cant differences in the IR and Raman spectra of the complex
were observed as compared to the spectra of the ligand and confi rmed the suggested metal-ligand
binding mode.
SIMONA CAVALU_Rotational Correlation Times of proteinsSimona Cavalu
Noncovalent spin labeled proteins (ovalbumin, bovine serum albumin, hemoglobin, and cytochrome c) were
investigated in order to follow the different type of interactions between the nitroxide radical of 3-carbamoyl-
2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy spin label and functional groups of heme and nonheme proteins as
well as the pH influence on molecular motion of the label with respect to these proteins. EPR spectra were
recorded at room temperature and the computer simulation analysis of spectra was made in order to obtain
the magnetic parameters. Noncovalent labeling of proteins can give valuable information on the magnetic
interaction between the label molecule and the paramagnetic center of the proteins. The relevance of this
interaction can be obtained from line shape analysis: computer simulations for nonheme proteins assume
a Gaussian line shape, whereas for heme proteins, a weighted sum of Lorentzian and Gaussian components
is assumed. In the framework of the “moderate jump diffusion” model for rotational diffusion, the rotational
correlation time is strongly influenced by pH, because of the electrostatic interactions and hydrogen bonding.
SIMONA CAVALU_Raman and Surface Enhanced Raman Spectroscopy of 2,2,5,5-Tetram...Simona Cavalu
ABSTRACT: 2,2,5,5-Tetramethyl-3-pyrrolin-1-yloxy-3-carboxamide (tempyo) labeled bovine
serum albumin and cytochrome c at different pH values were prepared and
investigated using Raman–resonance Raman (RR) spectroscopy and surface enhanced
Raman scattering (SERS) spectroscopy. The Raman spectra of tempyo labeled proteins
in the pH 6.7–11 range were compared to those of the corresponding free species. The
SERS spectra were interpreted in terms of the structural changes of the tempyo labeled
proteins adsorbed on the silver colloidal surface. The tempyo spin label was found to be
inactive in the Raman–RR and SERS spectra of the proteins. The a-helix conformation
was concluded to be more favorable as the SERS binding site of bovine serumalbumin.
In the cytochrome c the enhancement of the bands assigned to the porphyrin macrocycle
stretching mode allowed the supposition of the N-adsorption onto the colloidal surface.
Potentiometric Glucose Detection by Paper-based Electrochemical Sensor on CMO...TELKOMNIKA JOURNAL
This paper presents a low cost portable medical device for biochemical sensor using CMOS chip
and paper-based fluidic channel. We measured a potential produced by enzyme activity of glucose
between the working and reference electrode on CMOS chip. A liquid sample is transported by paperbased
fluidic channel, which is made of chromatography paper and silicone resin, and consists of the area
for filtering a sample (filter layer) and that for reacting enzyme (enyzme layer). The paper-based fluidic
channel is used by combining CMOS chip, and the solution with glucose is dropped from top of the paperbased
fluidic channel. The concentrations of glucose are detected by potentiometry (open circuit potential
time). The experimental results show that the glucose concentration is measured by CMOS chip and
paper-based fluidic channel.
The IOSR Journal of Pharmacy (IOSRPHR) is an open access online & offline peer reviewed international journal, which publishes innovative research papers, reviews, mini-reviews, short communications and notes dealing with Pharmaceutical Sciences( Pharmaceutical Technology, Pharmaceutics, Biopharmaceutics, Pharmacokinetics, Pharmaceutical/Medicinal Chemistry, Computational Chemistry and Molecular Drug Design, Pharmacognosy & Phytochemistry, Pharmacology, Pharmaceutical Analysis, Pharmacy Practice, Clinical and Hospital Pharmacy, Cell Biology, Genomics and Proteomics, Pharmacogenomics, Bioinformatics and Biotechnology of Pharmaceutical Interest........more details on Aim & Scope).
Vibrational Characterization and Antioxidant Activity of Newly Synthesized Ga...peertechzpublication
The gallium(III) complex of orotic acid (HOA) was synthesized and its structure was determined
by means of analytical and spectral analyses. Detailed vibrational analysis of HOA, sodium salt of HOA
(NaOA) and Ga(III)-OA systems based on both the calculated and experimental spectra confi rmed the
suggested metal-ligand binding mode. Signifi cant differences in the IR and Raman spectra of the complex
were observed as compared to the spectra of the ligand and confi rmed the suggested metal-ligand
binding mode.
Abstract
A small set of amphetamines has been analyzed by gas chromatography (GC) high-resolution time-of-flight mass spectrometry (TOFMS) using a microplasma photoionization (MPPI) soft-ionization source. This plasma-based, wavelength selectable ionization source enables ionization of the test compounds and their corresponding derivatives at ~8-12 eV that is a softer alternative to electron ionization at 70 eV. Three plasma gases were used in this study: Xe plasma that emits photons at resonance lines of 9.57 eV and 8.44 eV; Kr plasma at 10.63 eV and 10.02 eV, and Ar plasma at 11.82 eV and 11.61 eV. Derivatization of the test compounds with trifluoroacetic anhydride and α-methoxy-α-(trifluoromethyl)-phenylacetyl pyrazole was evaluated because the MPPI mass spectra of the underivatized amphetamines yield primarily iminium ions, which make the identification of the test compounds by GC-TOFMS inconclusive. The MPPI mass spectra of the TFA-derivatized amphetamines yield abundant molecular ions, when using Xe as plasma gas, and enough fragment ions with the Ar plasma that can help in formula generation. The structure elucidation of two "known unknowns" designer drugs using this "tunable" soft-ionization source and a high-resolution TOF mass spectrometer is presented in this study.
Simultaneous Electrochemical Measurement using Paper Fluidic Channel on CMOS ...TELKOMNIKA JOURNAL
This paper described the new system of biosensing using CMOS chip. The system was expected
to be used in various circumstances because it was suitable for miniaturization compared to the
conventional system. To conduct electrochemical measurements, the new system used paper fluidic
channel set on the CMOS chip to transport solution to the on-chip electrodes. The materials of paper fluidic
channel were only paper and silicone resin, and these were biocompatible. In experiment, we carried out
simultaneous detection of glucose and ethanol in liquid sample solutions on the 5mm square CMOS chip
and paper fluidic channel. Furthermore, this system can detect various target molecules in addition to
glucose and ethanol, and increase number of simultaneous measurement by adding some more process
to the paper and CMOS chip.
49 First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Pr...Cristian Randieri PhD
First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Proton near Threshold - July 2014
di P. Levi Sandri, G. Mandaglio, O. Bartalini, V. Bellini, J. P. Bocquet, M. Capogni, F. Curciarello, A. D’Angelo, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna and I. Zonta (2014)
Abstract
The Σ beam asymmetry in η' photoproduction off the proton was measured at the GRAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90°. The results are compared to the existing theories that fail to account for the data.
Bis-pyrene probes of foldamer conformation in solution and in phospholipid bi...madhu740653
Exploring the detailed structural features of synthetic molecules in the membrane phase requires sensitive
probes of conformation. Here we describe the design, synthesis and characterization of bis(pyrene) probes
that report conformational changes in membrane-active dynamic foldamers.
28 Measurement of η photoproduction on the proton from threshold to 1500-MeV ...Cristian Randieri PhD
Measurement of η photoproduction on the proton from threshold to 1500-MeV - The European Physical Journal A, Hadrons and Nuclei, August 2007, Vol. 33, N. 2, pp. 169-184, ISSN: 1434-6001, doi: 10.1140/epja/i2007-10439-9
di O. Bartalini, V. Bellini, J. P. Bocquet, P. Calvat, M. Capogni, L. Casano, M. Castoldi, A. D'Angelo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, M. Guidal, E. Hourany, R. Kunne, A. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, D. Moricciani, A. N. Mushkarenkov, V. Nedorezov, L. Nicoletti, C. Perrin, C. Randieri, D. Rebreyend, F. Renard, N. Rudnev, T. Russew, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2007).
Abstract
Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
Abstract
A small set of amphetamines has been analyzed by gas chromatography (GC) high-resolution time-of-flight mass spectrometry (TOFMS) using a microplasma photoionization (MPPI) soft-ionization source. This plasma-based, wavelength selectable ionization source enables ionization of the test compounds and their corresponding derivatives at ~8-12 eV that is a softer alternative to electron ionization at 70 eV. Three plasma gases were used in this study: Xe plasma that emits photons at resonance lines of 9.57 eV and 8.44 eV; Kr plasma at 10.63 eV and 10.02 eV, and Ar plasma at 11.82 eV and 11.61 eV. Derivatization of the test compounds with trifluoroacetic anhydride and α-methoxy-α-(trifluoromethyl)-phenylacetyl pyrazole was evaluated because the MPPI mass spectra of the underivatized amphetamines yield primarily iminium ions, which make the identification of the test compounds by GC-TOFMS inconclusive. The MPPI mass spectra of the TFA-derivatized amphetamines yield abundant molecular ions, when using Xe as plasma gas, and enough fragment ions with the Ar plasma that can help in formula generation. The structure elucidation of two "known unknowns" designer drugs using this "tunable" soft-ionization source and a high-resolution TOF mass spectrometer is presented in this study.
Simultaneous Electrochemical Measurement using Paper Fluidic Channel on CMOS ...TELKOMNIKA JOURNAL
This paper described the new system of biosensing using CMOS chip. The system was expected
to be used in various circumstances because it was suitable for miniaturization compared to the
conventional system. To conduct electrochemical measurements, the new system used paper fluidic
channel set on the CMOS chip to transport solution to the on-chip electrodes. The materials of paper fluidic
channel were only paper and silicone resin, and these were biocompatible. In experiment, we carried out
simultaneous detection of glucose and ethanol in liquid sample solutions on the 5mm square CMOS chip
and paper fluidic channel. Furthermore, this system can detect various target molecules in addition to
glucose and ethanol, and increase number of simultaneous measurement by adding some more process
to the paper and CMOS chip.
49 First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Pr...Cristian Randieri PhD
First Measurement of the Σ Beam Asymmetry in η' Photoproduction off the Proton near Threshold - July 2014
di P. Levi Sandri, G. Mandaglio, O. Bartalini, V. Bellini, J. P. Bocquet, M. Capogni, F. Curciarello, A. D’Angelo, V. De Leo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. Lapik, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. Mushkarenkov, V. Nedorezov, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna and I. Zonta (2014)
Abstract
The Σ beam asymmetry in η' photoproduction off the proton was measured at the GRAAL polarized photon beam with incoming photon energies of 1.461 and 1.480 GeV. For both energies the asymmetry as a function of the meson emission angle shows a clear structure, more pronounced at the lowest one, with a change of sign around 90°. The results are compared to the existing theories that fail to account for the data.
Bis-pyrene probes of foldamer conformation in solution and in phospholipid bi...madhu740653
Exploring the detailed structural features of synthetic molecules in the membrane phase requires sensitive
probes of conformation. Here we describe the design, synthesis and characterization of bis(pyrene) probes
that report conformational changes in membrane-active dynamic foldamers.
28 Measurement of η photoproduction on the proton from threshold to 1500-MeV ...Cristian Randieri PhD
Measurement of η photoproduction on the proton from threshold to 1500-MeV - The European Physical Journal A, Hadrons and Nuclei, August 2007, Vol. 33, N. 2, pp. 169-184, ISSN: 1434-6001, doi: 10.1140/epja/i2007-10439-9
di O. Bartalini, V. Bellini, J. P. Bocquet, P. Calvat, M. Capogni, L. Casano, M. Castoldi, A. D'Angelo, J. P. Didelez, R. Di Salvo, A. Fantini, D. Franco, C. Gaulard, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, M. Guidal, E. Hourany, R. Kunne, A. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, D. Moricciani, A. N. Mushkarenkov, V. Nedorezov, L. Nicoletti, C. Perrin, C. Randieri, D. Rebreyend, F. Renard, N. Rudnev, T. Russew, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2007).
Abstract
Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
We investigated the gas‐phase fragmentation reactions of a series of 2‐aroylbenzofuran derivatives
by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). The most intense fragment
ions were the acylium ions m/z 105 and [M+H–C6H6]+, which originated directly from the
precursor ion as a result of 2 competitive hydrogen rearrangements. Eliminations of CO and CO2
from [M+H–C6H6]+ were also common fragmentation processes to all the analyzed compounds.
In addition, eliminations of the radicals •Br and •Cl were diagnostic for halogen atoms at aromatic
ring A, whereas eliminations of •CH3 and CH2O were useful to identify the methoxyl group
attached to this same ring. We used thermochemical data, obtained at the B3LYP/6‐31+G(d) level
of theory, to rationalize the fragmentation pathways and to elucidate the formation of E, which
involved simultaneous elimination of 2 CO molecules from B.
Mechanism of the Reaction of Plasma Albumin with Formaldehyde in Ethanol - Wa...IOSR Journals
The Spectrophotometric determination of the acid dissociation/ionisation constant (pKa) of plasma albumin-formaldehyde adduct in both water solution and Ethanol solutions was carried out in this study. The pKa values obtained in both media were used to establish the Bronsted-linear type constants from plots of pKa against logarithm of second order rate constants obtained at varying pHs in the study. The result of the pKa values obtained in both water solution and ethanol-water mixtures were found to be in the range of 5.0 - 8.0. This pointed to the fact that only lysine residue with pKa value 8.3 that might have possibly reacted with formaldehyde in this reaction of all the known amino acid residues in plasma albumin. The corresponding Brønsted-type plots proportionality constants (β) for the reaction in water and ethanol-water mixtures were found to be β = 0.059 and 0.0057 respectively. The reaction mechanisms that have low values for proportionality constants α or β are considered to have a transition state closely resembling the reactant with little proton transfer (Cox et al, 1988). Thus, one would suggest that the cross-linking of formaldehyde with plasma albumin in water and ethanol-water mixtures proceeds through little proton transfer
SIMONA CAVALU_Raman and surface-enhanced Raman spectroscopy of tempyo spin la...Simona Cavalu
Tempyo labelled ovalbumin at different pH values was prepared and investigated using Raman and SERS spectroscopy.
Raman spectra of tempyo labelled ovalbumin in the pH range from 6.7 to 11 were compared to those of the corresponding free
ovalbumin. In the basic pH range from 6.7 to 11 the molecular conformation was found to be unaffected by the tempyo
presence. Adsorption versatility to the colloidal Ag particles of pure- and tempyo labelled ovalbumin was also found to be
unchanged in this basic pH range. As the SERS binding site of protein the a-helix conformation is favourable.
Novel composite electrodes:Preparation and application to the electroanalytic...Université de Dschang
M. Tchieno Melataguia Francis Merlin a soutenu une thèse de Doctorat/Phd en Chimie Inorganique ce 06 juin 2016 dans la salle des conférences de l'Université de Dschang. A l'issue de cette soutenance devant le jury présidé par le Prof. Emmanuel Ngameni lui a décerné la mention très honorable à l'unanimité de ses membres.
42 Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Jou...Cristian Randieri PhD
Beam Asymmetry Σ of the π- Photoproduction off Neutron - International Journal of Modern Physics E, June 2010, Vol. 19, N. 5-6, pp. 965-976, doi: 10.1142/S0218301310015412
di G. Mandaglio, V. Bellini, J. P. Bocquet, L. Casano, A. D'Angelo, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, A. S. Ignatov, A. M. Lapik, P. Levi Sandri, A. Lleres, F. Mammoliti, M. Manganaro, D. Moricciani, A. N. Mushkarenkov, V. G. Nedorezov, C. Randieri, D. Rebreyend, N. V. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2010)
Abstract
We present the analysis of data performed in order to identify the events of the γ + n → π- + p reaction obtained by bombarding a liquid Deuterium target with a polarised γ beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Σ of the π- fotoproduction off quasi-free neutron up to about θc.m., π- = 165° together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for Eγ =850-1740 MeV and θc.m., π- ≤105°.
41 Limits on Light-Speed Anisotropies from Compton Scattering of High-Energy ...Cristian Randieri PhD
Limits on Light-Speed Anisotropies from Compton Scattering of High-Energy Electrons -The American Physical Society, Physical Review Letters, June 2010, Vol. 104, N. 24, pp. 241601-1-241601-5, ISSN: 0031-9007, doi: 10.1103/PhysRevLett.104.241601
di J. P. Bocquet, D. Moricciani, V. Bellini, M. Beretta, L. Casano, A. D'Angelo, R. Di Salvo, A. Fantini, D. Franco, G. Gervino, F. Ghio, G. Giardina, B. Girolami, A. Giusa, V. G. Gurzadyan, A. Kashin, S. Knyazyan, A. Lapik, R. Lehnert, P. Levi Sandri, A. Lleres, F. Mammoliti, G. Mandaglio, M. Manganaro, A. Margarian, S. Mehrabyan, R. Messi, V. Nedorezov, C. Perrin, C. Randieri, D. Rebreyend, N. Rudnev, G. Russo, C. Schaerf, M. L. Sperduto, M. C. Sutera, A. Turinge, V. Vegna (2010)
Abstract
The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains such anisotropies representing the first non-threshold collision-kinematics study of Lorentz violation. When interpreted within the minimal Standard-Model Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients kappa_{o+} and c. This new constraint provides an improvement over previous bounds by one order of magnitude.
The existence of conducting islands in polyaniline
films has long been proposed in the literature, which
would be consistent with conducting mechanisms based on
hopping. Obtaining direct evidence of conducting islands,
however, is not straightforward. In this paper, conducting
islands were visualized in poly(o-ethoxyaniline) (POEA)
films prepared at low pH, using Transmission Electron Microscopy
(TEM) and atomic force spectroscopy (AFS). The
size of the islands varied between 67 and 470 Å for a
pH = 3.0, with a larger average being obtained with AFS,
probably due to the finite size effect of the atomic force microscopy
tip. In AFS, the conducting islands were denoted
by regions with repulsive forces due to the double-layer
forces. On the basis of X-ray diffraction (XRD) patterns for
POEA in the powder form, we infer that the conducting islands
are crystalline, and therefore a POEA film is believed
to consist of conducting islands dispersed in an insulating,
amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasione dimensional variable range hopping (VRH) mechanism.
Cavalu Simona_PMMA/Mg3Al2(SiO4)3 BONE CEMENTS: PRODUCTION, STRUCTURAL CHARACT...Simona Cavalu
In our approach, acrylic bone cements were prepared by reinforcing commercial PMMA-based bone cements with 5% Mg3Al2(SiO4)3. Structural investigation performed by ATR FTIR (Atenuated Total Reflectance Fourier Transform Infrared Spectroscopy) spectroscopy and XRD (X-Rays Difraction) demonstrated the inclusion of the crystalline phase in polymeric matrix. The SEM (Scanning Electron Microscopy) images (surface and fracture) revealed that the addition of 5% Mg3Al2(SiO4)3 create a porous structure in PMMA matrix, and facilitate the hydroxyapatite formation in vitro.
New evidences of key factors involved in “silent stones” ethiopathogenesis an...Simona Cavalu
The knowledge of the key factors involved in ethiopathogenesis of the gallstones disease requires chemical, structural and elemental composition analysis.
The knowledge of the key factors involved in ethiopathogenesis of the gallstones disease requires chemical, structural and elemental composition analysis
Simona cavalu_ Adherence Properties of Acrylic Bone Cement to AluminaSimona Cavalu
The aim of this study is to investigate the adherence properties of acrylic cement based on PMMA to alumina
ceramics. These ceramics are suitable for orthopedic and dental applications, as bioinert components in prosthetic
surgery. The surface of alumina specimens were subjected to a special treatment based on acid etched followed by
two dierent uoride treatments: SnF2 and NaBF4, respectively.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
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SIMONA CAVALU_EPR study of non covalent spin labeled serum albumin and haemoglobin 2002
1. Biophysical Chemistry 99 (2002) 181–188
0301-4622/02/$ - see front matter ᮊ 2002 Elsevier Science B.V. All rights reserved.
PII: S0301-4622Ž02.00182-5
EPR study of non-covalent spin labeled serum albumin and
hemoglobin
S. Cavalu *, G. Damian , M. Dansoreanua, b c
ˆ ¸
University of Oradea, Faculty of Medicine and Pharmacy, Department of Biophysics, RO-3700 Oradea, Romaniaa
‘‘Babes-Bolyai’’ University, Department of Physics, RO-3400 Cluj-Napoca, Romaniab
University of Medicine and Pharmacy ‘‘Iuliu Hatieganu’’, Department of Biophysics RO-3400 Cluj-Napoca, Romaniac
Received 5 February 2002; received in revised form 31 May 2002; accepted 5 June 2002
Abstract
Electron Paramagnetic Resonance (EPR) was used to investigate the Tempyo spin label (3-carbamoyl-2,2,5,5-
tetramethyl-3-pyrrolin-1-yloxy) as a report group for the interactions and the conformational changes of lyophilized
bovine serum albumin (BSA) and bovine hemoglobin (BH), as function of pH values in the range 2.5–11. The EPR
spectra are similar with those of other non-covalently spin label porphyrins in frozen solution at very low temperatures.
This behavior indicated a possible spin–spin interaction between the hemic iron and the nitroxide group. The changes
in the EPR spectra as function of the pH are discussed in terms of conformational changes of the proteins. Spectral
simulations and magnetic EPR parameters reveal the following: (i) one single paramagnetic species, with Gaussian
line shape, was used for the best fits of experimental spectra in the case of serum albumin samples; and (ii) a
weighted sum of Lorentzian and Gaussian line shape in the case of hemoglobin samples. The representation of
correlation time vs. pH, reveals a dependence of degree of immobilization of spin label on the conformational changes
of proteins in acidic and basic environment.
ᮊ 2002 Elsevier Science B.V. All rights reserved.
Keywords: EPR; Spin label; Serum albumin; Haemoglobin
1. Introduction
Proteins are polymeric chains that are built from
monomers called amino acids. All structural and
functional properties of proteins derive from the
chemical properties of the polypeptide side-chain.
The ionizable groups of the side-chains of charged
amino acids are often involved in biochemical
*Corresponding author. Fax: q40-59-41-8266.
E-mail address: scavalu@xnet.ro (S. Cavalu).
transactions (binding, catalysis). Therefore, pH
usually has rather dramatic effects on the function
of proteins. Polar residues are both buried as well
as on the surface of the protein. They either form
hydrogen bonds with other polar residues in the
protein or with water. Non-polar residues do not
interact favorably with water. However, a signifi-
cant number of non-polar residues are also found
on the surface of the protein. Therefore, it is
important to study the interactions of proteins with
well-defined molecules that will confer the total
2. 182 S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
Fig. 1. The chemical structure of Tempyo spin label.
molecules sufficient affinity for the binding site of
interest on protein w1,2x
The successful application of spin labeling to
protein structure investigations is limited by the
possibility to chemically change specific side
chains in proteins. However, useful information on
protein properties can be obtained by non-covalent
spin labeling if the affinity of the protein for the
label molecules is great enough to affect their
motional freedom w3–6x. The rate of rotation (or
tumbling) of the spin label influences the lineshape
of its EPR spectrum. Therefore, the EPR signal of
a spin label covalently or non-covalently bonded
to a biomolecule can yield a range of information
about its structural environment in conventional
ESR and allows for full spectral coverage w7,8x.
In the same time, EPR has been an invaluable
tool for probing microscopic molecular motions in
a variety of systems, including isotropic solvents
w9x, liquid crystals w10x, model membranes and
biomolecules w11–13x.
In the present work, non-covalent spin labeled
bovine serum albumin (BSA) and bovine hemo-
globin (BH) with Tempyo spin label (3-carba-
moyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy) were
investigated both in liquid and lyophilized sam-
ples, in the pH range 2.5–11, in order to obtain
useful information related to the interaction
between the nitroxide group and the functional site
of the proteins.
Interactions of spin label with hemic or non-
hemic proteins might affect the spin label spectra
and in the same time it is well known that the pH
strongly influences the conformation of proteins
leading to significant changes in the type and
degree of these interactions w14x. In this pH range,
we followed the effect of protein conformational
changes on the interactions between the nitroxide
and the functional groups of proteins and also the
pH influence on molecular motion emphasized by
the EPR spectra of the spin label.
2. Materials and methods
Powdered bovine serum albumin and hemoglo-
bin ()95% methemoglobin) from Sigma Chemi-
cals, were used without further purification.
Proteins were hydrated in phosphate buffer physi-
ological saline at a final concentration of 10 M.y3
Tempyo spin-label (3-carbamoyl-2,2,5,5-tetrame-
thyl-3-pyrrolin-1-yloxy), from Sigma Chemicals
(Fig. 1), was added to the liquid samples of each
protein in a final concentration of 10 M (pro-y3
teinyspin label molar ratio 1:1) and the pH values
were adjusted to the desired value in the range
2.5–11. An amount of 5 ml from each sample was
lyophilized for 30 h at y5 8C and used for the
EPR measurement, at room temperature.
EPR spectra for both liquid and lyophilized
samples, were recorded at room temperature with
a JEOL-JES-3B spectrometer, operating in X-band
(9.5 GHz), equipped with a computer acquisition
system. Samples were placed in quartz capillary
tubes. The spectrometer settings were: modulation
frequency 100 KHz, field modulation 1 G, micro-
wave power 20 mW. The computer simulation
analysis of spectra, for obtaining the magnetic
characteristic parameters, was made by using a
program that is available to the public through the
Internet (http:yyalfred.niehs.nihyLMB).
The lineshape of an EPR spectrum depends,
among other factors, on the orientation of the
paramagnetic center with respect to the applied
magnetic field. In a powder, or a frozen aqueous
solution, the paramagnetic centers will be fixed
with a random distribution of orientations, and in
the case of anisotropic g- and hyperfine interac-
tions this will lead to a broadened EPR spectrum,
since all orientations contribute equally. In the
liquid state, however, the paramagnetic centers are
not fixed but undergo rotational fluctuation. In the
case of fast rotation, the anisotropic interactions
are thereby averaged to zero, giving rise to sharp
EPR lines. If the velocity of the rotational motion
3. 183S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
decreases, the EPR spectrum will approach that of
the powder spectrum. Therefore, a rotational cor-
relation time for a paramagnetic molecule can also
be determined by EPR using semiempirical for-
mula w15x.
For isotropic motion in the rapid tumbling limit,
the spectra will be isotropic with the averages of
the principal components of the g-values and
hyperfine splitting factor, a . The rate of theN
isotropic motion determines the relative widths of
resonances and the width, DH , of an individualm
(hyperfine) line, in the first approximation can be
written as a function of the z component of the
nitrogen nuclear spin number (msy1, 0, 1)
w16,17x:
2
DH sAqBØmqCØm (1)m
where the A coefficient includes other contribu-
tions than motion. The terms B and C are functions
related to the rotational correlational time (t) and
can be defined as a function of peak-to-peak line
width of the central line, DH wGx, and the ampli-0
tudes of the mth line I w14x:m
B E
1 I I0 0
C FBs DH y0 y y2 I ID G1 y1
N
ws0.103v DgDae
w z3N 2 2 y1x |xŽ .Ž . Ž .q3 dg da t 1q 1qv t (2)B e B
y ~4
B E
1 I I0 0
C FCs DH q y20 y y2 I ID G1 y1
w 36 N N2 2 xŽ . Ž .s1.181Ø10 Da q3 da t 1yw x c
y 8
z12 2 2 2y1 y1|Ž . Ž .= 1qv t y 1qv t (3)c c e c
~8
in which
1 1N N N N N N N
Ž . Ž .Da sa y a qa , da a ya (4)zz xx yy xx yy
2 2
1 1
Ž . Ž .Dgsg y g yg , dgs g yg (5)zz xx yy xx yy
2 2
and v s8.8=10 Na M, a is the isotropicy6 N N
N
hyperfine splitting and v the ESR spectrometere
frequency in angular units.
In the range from 5=10 to 10 s (motiony11 y9
in the rapid tumbling limit) and magnetic field
above 3300 G, Dg and Da vanish, and theN
correlation times t and t are directly related toB C
the B and C coefficients by the following simple
relations w5x:
t st sK ØB (6)B z 1
t st sK ØC (7)C x,y 2
where K s1.27=10 and K s1.19=10 . They9 y9
1 2
average correlation times is:
1y2
Ž .ts t Øt (8)B c
The slow motion of spin probe, lead to a
broadening of the EPR lines. In this case, the
rotational correlation time, t, is larger than 10y9
s, and thus, the relation (8) is not applicable.
The isotropic nitrogen hyperfine splitting chang-
es to a powder like spectrum, with the peak-to-
peak distance between the external peaks of the
spectrum w2Øa9 (N)x depending on the magnitudezz
of the rotational correlation time, t w18,19x. Anoth-
er lineshape theory for slow isotropic Brownian
rotational diffusion of spin-labeled proteins has
been developed by Freed w9x. Thus, the correlation
time can be evaluated from the ratio of the
observed splitting between the derivate extreme
a9 and principal value a , determined from rigidzz zz
matrix spectrum w5,7x:
bB E
a9zz
C Ftsa 1y (9)
aD Gzz
The a and b parameters depend on the kind of
the diffusion process, where a and b are empirical
constants, which are tabulated in e.g. Poole and
Farach (1987) w15x. For small spin probe, the
intermediate jump diffusion is preferable w15x.
3. Results and discussion
In the low concentration liquid state BSA and
BH solution, the Tempyo spin label which is a
relatively small molecule, gives rise to a spectrum
with narrow lines and constant hyperfine splitting,
typical for fast isotropic rotational motion (Fig. 2)
with a very low rate of migration between protein
molecule and water. For this kind of rotation, the
4. 184 S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
Fig. 2. EPR spectrum of the Tempyo spin label at low pH.
Fig. 3. Experimental (——) and simulated (««) EPR spectra
of Tempyo spin label in lyophilized bovine serum albumin at
various pH values.
Table 1
Magnetic parameters values of Tempyo spin label in lyophili-
zed bovine serum albumin at various pH values
pH gxx gyy gzz A (G)xx A (G)yy A (G)zz
11 2.01028 2.00841 2.00441 4.72 8.53 35.48
9.5 2.00113 2.00762 2.00484 6.16 5.91 33.96
8.1 2.01128 2.00781 2.00461 6.41 5.69 32.98
6.7 2.00113 2.00742 2.00500 6.15 6.55 32.20
5.5 2.01147 2.00809 2.00505 6.03 7.83 35.45
4.5 2.01259 2.00672 2.00588 7.79 6.98 35.52
3.5 2.01243 2.00660 2.00538 8.28 5.34 35.46
2.5 2.01269 2.00662 2.00459 6.38 5.66 35.91
rotational correlation time can be estimated from
the intensity ratio of the low-field and high-field
N-lines using a semi-empirical formula (8). For
the Tempyo spin label in BSA and BH aqueous
solution, the calculated rotational correlation times
was 2=10 s and 2.5=10 , respectively,y10 y10
which is consistent with fast rotation as expected
for a small molecule.
No detectable changes were observed in EPR
spectra of aqueous solution of Tempyo spin label
without proteins, at different pH values.
The characteristic EPR spectra of a Tempyo spin
label in lyophilized BSA is due primarily to
anisotropy in the nitrogen hyperfine coupling
which is typical for slow rotation. For slow rota-
tions, the EPR spectrum of spin labels depends, in
a much more complicated fashion, on the com-
bined influences of molecular motion and magnetic
interactions. Fig. 3 displays the experimental and
simulated spectra for Tempyo spin label in lyo-
philized BSA at different pH values. In order to
find the magnetic parameters, the experimental
EPR spectra were simulated. The best fit of exper-
imental EPR spectra of Tempyo spin label in
lyophilized BSA, was obtained assuming a single
paramagnetic species with magnetic parameters
listed in Table 1, and a Gaussian lineshape corre-
sponding to static dipolar interactions.
The main feature of the EPR spectra of Tempyo
spin label in lyophilized haemoglobin (Fig. 4),
like the Tempyo spin label in lyophilized BSA,
exhibit the characteristics to slow motion of spin
label but with more broadening of the lineshape.
The best fit of the simulated experimental EPR
spectra can be obtained by assuming the presence
of two functional groups in hemoglobin associated
with two non-equivalent paramagnetic species.
Computer simulations indicate a weighted sum of
mixed Gaussian lineshapes (static dipolar interac-
tions) and Lorentzian lineshapes (spin–spin inter-
actions). Generally, the broadening of the Gaussian
lineshape are due to static dipolar interactions of
5. 185S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
Fig. 4. Experimental (——) and simulated (««) EPR spectra
of Tempyo spin label in lyophilized bovine hemoglobin at var-
ious pH values.
Fig. 5. The experimental EPR spectrum and its subspectra of
Tempyo spin label in lyophilized hemoglobin at pH 2.5
the spin label molecules whereas the broadening
of the Lorentzian lineshape is due to to spin–spin
interactions w20x. Figs. 5 and 6 present the EPR
spectra of Tempyo spin label in the lyophilized
BH at low and high pH, in which the contribution
of each species is displayed. At low pH (pH 2.5),
the main contributions are due to species with
Gaussian line shape (;80%). This contribution
decreases to ;50% at high pH (pH 11). The first
species with Gaussian lineshape and poor resolved
hyperfine splitting is not influenced by the pres-
ence of the hemic iron and, therefore, we assume
to be located far from the hemic group. The second
species with Lorentzian lineshape and a well
resolved hyperfine structure is located, probably,
near the hem group, giving rise to a spin–spin
interaction between the nitroxide radical and the
paramagnetic iron of the hem group. Our results
are in accordance with covalently labeled methe-
moglobin and other porphyrins in frozen samples
under 50 K w21,22x. In these previous studies,
spectra of covalently labeled methemoglobin were
analyzed by using perturbation calculations in
order to estimate the iron to nitroxyl distances and
it was suggested that plausible distances are in the
range of 14.5–17.5 A. The g tensor and A tensor˚
components used in the simulation for the best fit
values of the simulation of the effective powder
spectrum, are presented in Table 2.
Due to increased spatial restrictions of protein
structure in the vicinity of the label, by lyophili-
zation, the mobility of spin label is slow on the
EPR time scale (;5=10 s ), leading to a6 y1
broadening of the EPR lines, with the peak-to-
peak distance between the external peaks of the
spectrum w2Øa9 (N)x depending on the magnitudezz
of the rotational correlation time, t. Generally,
broadening of the peaks in an EPR spectrum is
6. 186 S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
Fig. 6. The experimental EPR spectrum and its subspectra of
Tempyo spin label in lyophilized hemoglobin at pH 11.
Table 2
Magnetic parameters values of Tempyo spin label in lyophili-
zed bovine hemoglobin at various pH values
pH gxx gyy gzz A (G)xx A (G)yy A (G)zz
11 2.01242 2.00771 2.00372 4.81 8.70 34.01 L( )
2.01117 2.00497 2.00610 6.42 7.76 33.16 G( )
9.5 2.00935 2.00839 2.00478 6.19 13.89 34.82 L( )
2.01079 2.00695 2.00465 6.11 7.29 33.06 G( )
8.1 2.01133 2.00702 2.00464 8.38 6.68 33.87 L( )
2.01500 2.00428 2.00592 8.64 6.50 32.60 G( )
6.7 2.00115 2.00773 2.00425 3.27 8.20 33.73 L( )
2.01213 2.00476 2.00556 7.43 8.88 35.84 G( )
5.5 2.012442 2.00821 2.00471 9.52 7.32 34.62 L( )
2.001050 2.00592 2.00541 5.86 6.12 35.45 G( )
4.5 2.01609 2.00768 2.00522 9.20 7.66 36.03 L( )
2.01198 2.00416 2.00523 7.43 8.88 35.15 G( )
3.5 2.01265 2.00816 2.00413 4.14 5.39 36.59 L( )
2.01169 2.00287 2.00506 7.06 9.36 35.46 G( )
2.5 2.01344 2.00844 2.00506 9.83 10.38 36.26 L( )
2.01270 2.00471 2.00548 4.67 5.80 35.78 G( )
(L), Lorentzian lineshape; (G), Gaussian lineshape.
Fig. 7. Correlation times (t) as a function of pH for Tempyo
spin label in lyophilized bovine serum albumin (j) and bovine
hemoglobin (m).
indicative of immobilization of the spin label,
whereas sharpening of the peaks is indicative of
an increase in label mobility. By comparing the
apparent nitrogen hyperfine splitting wtermed a9zz
(N)x with the nitrogen hyperfine splitting obtained
from their rigid limit values wa (N)x, the rotation-zz
al correlation times can be calculated using for-
mula 9. The values of a and b coefficients depend
on the motional model. The study of the influence
of different diffusional models on the spectral line
shape in the regime of slow motional spin label
by high EPR fields has shown that jump diffusion
mainly affects the line widths at the same motional
rates w23x. In our calculations, the intermediate
jump diffusion model was considerate, with coef-
ficients values of as5.4=10 s and bsy1.36y10
w15x. The average correlation time for different
values of pH are plotted in Fig. 7. As shown in
figure, the pH influences the rotational correlation
time. In the acidic pH range the NH groups of2
the label molecule as well as those of the amino
acids residues are protonated. The fact that t shows
greater values in this range followed by a signifi-
cant decrease in the basic pH range, indicate a
low mobility of spin label in acidic environment
while an increasing of mobility can be noticed in
the basic pH range. A minimum mobility can be
observed around the isoelectric point of both pro-
teins (for BSA pH s4.8, and for BH, pH s6.8).i i
From the pH dependence of correlation time
(involving the mobility of the label as well), we
assume that in an acidic environment the mobility
of spin label molecules are reduced due to the
7. 187S. Cavalu et al. / Biophysical Chemistry 99 (2002) 181–188
formation of hydrogen bonds between the NH2
group of spin label and side chains of neighboring
amino acids. One can correlate this observation
with the fact that serum albumin undergoes revers-
ible isomerization in the pH range 2.7–7 from the
expanded form characterized by 35% a-helix con-
tent, to normal form characterized by 55% a-helix
content accompanied by a decrease in b-sheet
w24,25x. It is well known that b-sheet conformation
favors the formation of hydrogen bonding.
By comparing with the BSA case, we notice
that the mobility of Tempyo is greater with respect
to hemoglobin, which is not surprising if we take
into account that hydrogen bonding opportunities
depends on the b-sheet content: in hemoglobin the
b-sheets represent 50% while in BSA the percent-
age varies from 70 to 45%, depending on the pH.
As shown in Fig. 7 the mobility of this species
increases in an acidic environment, reaching a
maximum value corresponding to pH 6.8 followedi
by a slow decrease. We suggest that in basic pH
range, where the label is not subject to strong
electrostatic interactions, dipolar and spin–spin
interactions are manifested almost with the same
contribution in the broadening of the spectrum.
4. Conclusions
EPR spectroscopy is very useful to study the
mobility of nitroxide radicals with respect to hemic
or non-hemic proteins in different environmental
conditions. Non-covalent labeling of proteins can
give valuable information on the magnetic inter-
actions between the label molecule and the para-
magnetic center of the proteins. The relevance of
this interaction can be obtained from lineshape
analysis: computer simulations for non-hemic pro-
tein assume a Gaussian lineshape, while for hemic
protein a weighted sum of Lorentzian and Gaussian
components is assumed. The contribution of the
each line shape to experimental spectrum depends
on the pH.
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