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Rotational and translational water diffusion in the hemoglobin hydration shell: dielectric and proton nuclear relaxation measurements.
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The dynamic properties of water in the hydration shell of hemoglobin have been studied by means of dielectric permittivity measurements and nuclear magnetic resonance spectroscopy. The temperature behavior of the complex permittivity of hemoglobin solutions has been measured at 3.02, 3.98, 8.59, and 10.80 GHz. At a temperature of 298 K the average rotational correlation time tau of water within a hydration shell of 0.5-nm thickness is determined from the activation parameters to be 68 +/- 10 ps, which is 8-fold the corresponding value of bulk water. Solvent proton magnetic relaxation induced by electron-nuclear dipole interaction between hemoglobin bound nitroxide spin labels and water protons is used to determine the translational diffusion coefficient D(T) of the hydration water. The temperature dependent relaxation behavior for Lamor frequencies between 3 and 90 MHz yields an average value D(298K) = (5 +/- 2) x 10(-10)m2 s-1, which is about one-fifth of the corresponding value of bulk water. The decrease of the water mobility in the hydration shell compared to the bulk is mainly due to an enhanced activation enthalpy. 相似文献
3.
In a continuing effort to understand the hydrogen bond through the study of dielectric and computational conformal studies of dilute solutions, succinic acid and maleic acid are studied in solutions of 1,4-dioxane solvent. Dielectric studies give an account of the net dipole moment of the system under study, which is then compared with the values obtained from conformal analysis. The dielectric measurements were made at 303 K at a frequency of 9.83 GHz using a X-band microwave test bench in order to determine the relaxation times and the dipole moments. The static dielectric permittivity and the high frequency dielectric permittivity were measured using a LCR meter and an Abbe's refractometer, respectively. The results are inspected in comparison with the dipole moment results of ab initio calculations of some of the conformers in gas phase and in liquid phase. Gaussian-03 software package with 6–31G(d) basis set optimisation was used for this purpose. Onsager's reaction field model is used to study the solvation of the dicarboxylic acids in 1,4-dioxane. The results are interpreted in terms of the intermolecular and intramolecular hydrogen bond interactions in the dilute systems. 相似文献
4.
In the present work, we provide a dielectric study on two differently concentrated aqueous lysozyme solutions in the frequency range from 1MHz to 40GHz and for temperatures from 275 to 330K. We analyze the three dispersion regions, commonly found in protein solutions, usually termed β-, γ-, and δ-relaxations. The β-relaxation, occurring in the frequency range around 10MHz and the γ-relaxation around 20GHz (at room temperature) can be attributed to the rotation of the polar protein molecules in their aqueous medium and the reorientational motion of the free water molecules, respectively. The nature of the δ-relaxation, which is often ascribed to the motion of bound water molecules, is not yet fully understood. Here we provide data on the temperature dependence of the relaxation times and relaxation strengths of all three detected processes and on the dc conductivity arising from ionic charge transport. The temperature dependences of the β- and γ-relaxations are closely correlated. We found a significant temperature dependence of the dipole moment of the protein, indicating conformational changes. Moreover we find a breakdown of the Debye-Stokes-Einstein relation in this protein solution, i.e., the dc conductivity is not completely governed by the mobility of the solvent molecules. Instead it seems that the dc conductivity is closely connected to the hydration shell dynamics. 相似文献
5.
The dielectric permittivity and conductivity of muscle fibers from the giant barnacle, Balanus nubilus, have been measured at 1, 25, and 37 degrees C, between 10 MHz and 17 GHz. The dominant microwave dielectric relaxation process in these fibers is due to dipolar relaxation of the tissue water, which shows a characteristic relaxation frequency equal to that of pure water, ranging from 9 GHz (1 degree C) to 25 GHz (37 degree C). The total permittivity decrease, epsilon 0 -- epsilon infinity, due to this process accounts for approximately 95% of the water content of the tissue; thus, the major fraction of tissue water is dielectrically identical to the pure fluid on a picosecond time scale. A second dielectric process contributes significantly to the tissue dielectric properties between 0.1 and 1--5 GHz, and arises in part form Maxwell-Wagner effects due to the electrolyte content of the tissue, and in part from dielectric relaxation of the tissue proteins themselves. 相似文献
6.
D W Urry R Henze P Redington M M Long K U Prasad 《Biochemical and biophysical research communications》1985,128(2):1000-1006
The dielectric permittivity of alpha-elastin coacervate is reported over the frequency range of 1 MHz to 1000 MHz and the temperature dependence from 6.8 degrees C to 70 degrees C is also reported. A temperature-dependent simple Debye-type relaxation is observed with a correlation time of 8 nsec (40 degrees C) which is similar to that of the polypentapeptide of elastin (i.e. 7 nsec at 40 degrees C) where the band has been assigned to a peptide librational mode. By analogy this allows for the first assignment of a peptide librational mode in a naturally occurring polypeptide or protein. The strong spectrally localized band indicates a regularity of structure. The low temperature dependence of the correlation time, giving a 1.7 kcal/mole enthalpy of activation, is consistent with torsional motions associated with a peptide librational mode. 相似文献
7.
The electric permittivity of aqueous solutions of different synthetic polyelectrolytes have been measured as a function of frequency in the range 5 kHz up to 100 MHz in the absence of added salt. Solutions of polymethacrylic acid and polyacrylic acid of different degrees of polymerization, both partially neutralized with NaOH, were investigated as well as solutions of Na-polystyrenesulphonate at different concentrations.For all systems a dispersion profile with two separated dispersion regions was obtained with a molecular weight dependent value of the static electric permittivity. The low frequency dispersion region was found to be characterized by a molecular weight dependent mean relaxation time while for the high frequency dispersion region both the mean relaxation time and the dielectric increment are molecular weight independent. It is shown that the reciprocal values of the specific increments and of the relaxation times depend linearly on the macromolecular concentration. Extrapolation of the corresponding quantities to infinite dilution was found to be possible. A comparison of these extrapolated values with calculated ones according to the previously derived theory also applicable to flexible macromolecules establishes that this theory describes satisfactorily the dielectric behaviour of the systems investigated.The conclusion is reached that the high frequency dispersion and relaxation can be attributed to fluctuations in the distribution of bound counterions along limited parts of the macromolecule. The relaxation time of the low frequency dispersion region seems to be essentially determined by the rotation of the complete molecule and the static electric permittivity can he explained in terms of fluctuations in the counterion density extending over the whole macromolecule. 相似文献
8.
Ten experiments on pigs were performed to investigate possible postmortem changes of the dielectric properties of brain gray matter in the frequency range of 800-1900 MHz. After keeping the animals in stable anaesthesia for at least 45 min, they were euthanatised by an intravenous injection of hypertonic potassium chloride (KCl), causing cardiac arrest within 3 min. Measurements of the dielectric properties were performed repeatedly from at least 45 min prior to death to 18 h after euthanasia. The anaesthesia regimen was chosen to minimize influence on brain tissue characteristics such as brain water content, intracranial blood volume, and cerebral blood flow. The data showed a decline of mean gray matter equivalent conductivity of about 15% at 900 MHz and about 11% at 1800 MHz within the first hour after death. The decline in permittivity was less pronounced (about 3-4%) and almost frequency independent. The results indicate that in vitro measurements of dielectric properties of brain tissue underestimate equivalent conductivity as well as permittivity of living tissue. These changes may affect the generally accepted data of dielectric properties of brain tissue widely used in RF dosimetry. 相似文献
9.
The electric permittivity of poly-L-glutamic acid (PGA) in salt-free aqueous solutions was measured in the frequency range 2.5 kHz – 100 MHz at different concentrations and degrees of ionization. Two samples of different molecular weight were investigated. The experimental results could under most circumstances be described by a superposition of two dispersion curves of the Cole-Cole type. The low-frequency dielectric parameters were strongly molecular weight dependent, the high-frequency ones not. Strong concentration effects were observed resulting in increasing specific dielectric increments and relaxation times with decreasing concentration. Using the theory proposed by Van der Touw and Mandel to interpret the experimental results these concentration effects could be ascribed to the influence of the polyion interactions on the average dimensions and the rigidity of the polyelectrolyte chains. The change in the total dielectric increment and low-frequency relaxation time with degree of ionization correctly reflects the helix-coil transition of PGA occurring in ths region α = 0.3–0.5. The effect of counterion size and charge on the dielectric behaviour was also found to be consistent with the theoretical model. 相似文献
10.
Walter Scheider 《Biophysical journal》1965,5(5):617-628
When a dissolved macromolecule is in chemical equilibrium with a free ionic species, the charge configuration, and hence the dipole vector, of the macromolecule is fluctuating. Expressions for the static dielectric constant and the relaxation spectrum of such a mixture are here derived in terms of the components of the mean moment and the root mean square fluctuation moment, the molecular relaxation time constants, and the chemical rate constants of the ionic binding reaction. Contrary to a previous treatment of this problem by Kirkwood and Shumaker (1), it is shown that fluctuations introduce no independent components into the relaxation spectrum. 相似文献
11.
The electric permittivity of alfalfa virus particles in buffer solutions of three different concentrations at pH 7 was studied between 10 kHz and 100 MHz. The experimental results could be described with one single dispersion curve of the Cole-Cole type characterized by a concentration independent specific dielectric increment and mean relaxation time. The results were interpreted semi-quantitatively in terms of counterions–atmosphere polarizability, neglecting counterion repulsion. 相似文献
12.
Planar bilayer lipid membranes formed from egg phosphatidylcholine in aqueous media containing the lipophilic anion, dipicrylamine (DPA), were studied by dielectric spectroscopy over a frequency range of 10 Hz–10 MHz. The membranes showed dielectric relaxation due to the translocation of DPA between the membrane interfaces. Incorporating either cholesterol or 6-ketocholestanol into the membranes increased the characteristic frequency of the relaxation, which is proportional to the translocation rate constant of DPA. The results suggested that the sterol dipoles induced positive potential changes within the membrane interior. The changes of the dipole potential were 70 mV for cholesterol and 150 mV for 6-ketocholestanol when the sterol mole fraction was 0.67. The opposite effect was caused by phloretin added to the aqueous media, and the maximum dipole potential change was ?90 mV at 100 μM. 相似文献
13.
The interaction of the nonionic detergent Triton X-100 with phospholipid bilayers of liposomes made of egg yolk phosphatidylcholine was studied through the behavior of several physical properties. The dielectric permittivity spectra between 30 kHz and 13 MHz, the viscosity, the density, and the d.c. conductivity (1 kHz) of aqueous liposomes suspensions at various mole ratios were measured at 22 degrees C. For detergent-to-phospholipid ratios lower than 3, a dielectric relaxation process of characteristic frequency of about 50 kHz was recorded. This process does not appear for the liposomes in water, and becomes smaller and smaller for detergent-to-phospholipid ratios higher than 3. The viscosity of these suspensions showed a biphasic behavior, being remarkably increased by the detergent for concentration ratios lower than 3. The measured d.c. conductivity of these samples showed no relation with this process, being slightly increased when the detergent content is increased. As a conclusion of these results a well defined concentration range appears where the phospholipid organization changes forming highly asymmetrical structures. 相似文献
14.
As a continuation of previous papers [Biopolymers (1976) 15 , 879; (1978) 17 , 1508], the low-frequency dielectric relaxation of DNA solutions was studied with a four-electrode cell and the simultaneous two-frequency measurement. Below a critical concentration, the dielectric relaxation time agrees with the rotational relaxation time estimated from the reduced viscosity and is almost independent of DNA concentration Cp, and the dielectric increment is proportional to Cp. The critical concentration is approximately 0.02% of DNA for molecular weight Mr 2 × 106 and 0.2% for Mr 4.5 × 105 in 1 mM NaCl. Dielectric relaxations are compared for samples before and after deproteinization, and the protein contamination is found to have a minor effect on the dipole moment of DNA. The effect of a mixed solvent of water and ethanol on the dielectric relaxation of DNA is well interpreted in terms of changes in viscosity and the dielectric constant of the solvent, assuming that the relaxation arises from rotation of the molecule with a quasi-permanent dipole due to counterion fluctuation. 相似文献
15.
Dielectric dispersion of DNA was studied in the frequency range 100 Hz–100 kHz at four different temperatures (6–30°C). The dielectric increment ε0–ε∞ increased with the rise of temperature. The relaxation time, on the other hand, decreased. Both the increase in dielectric increment and the decrease in relaxation time could not be explained on the basis of the counterion polarization theory. Dipole moment was estimated from Kirkwood theory. It was found to decrease systematically with temperature. Even at 0°C there was a dipole moment of 104D. 相似文献
16.
《International journal of biological macromolecules》1987,9(2):95-97
The permittivity ϵ′ and dielectric loss ϵ′' of low-molecular weight mannan triacetate in chloroform in the frequency range 1 kHz to 10 MHz at 20°C are reported. Deviations from a rod-like configuration are suggested to account for the observed behaviour of the dielectric relaxation time as a function of the degree of polymerization. 相似文献
17.
Dielectric relaxation data covering a temperature range from above room temperature to below the glass transition for 40% (w/w) and 75% (w/w) glucose/water solutions in the frequency range between 5 and 13 MHz are presented. These data are used to obtain correlation times for the dielectric relaxation in the viscous liquid and the glass and are compared with correlation times determined from deuterium nuclear spin relaxation times [J. Chem. Phys., 110 (1999) 3472-3483]. The two sets of results have the same temperature dependence, but differ in magnitude by a factor of 3, implying that the relaxation is a small-step rotational diffusion. Both the structural relaxation (alpha process) and the slow beta process are present. In the 40% glucose/water sample, there is a dielectric relaxation attributable to the ice that forms at low temperature. It is shown that the reciprocal of the viscosity, the correlation time derived from the dielectric relaxation, and the dc conductivity have a similar dependence on temperature. 相似文献
18.
The complex permittivities of L-alpha-lysolecithin in the absence and presence of the gramicidin A ion channel were measured over the temperature range 0-60 degrees C and over the frequency range 1-1000 MHz. One dielectric relaxation/loss has been observed. It is located at 103.3 MHz (1.54 ns) for a micellar 0.4 M L-alpha-lysolecithin solution at 20 degrees C, whereas it is shifted to 71.7 MHz (2.22 ns) for a lamellar L-alpha-lysolecithin-gramicidin A aqueous solution (0.4 M L-alpha-lysolecithin, 0.0308 M gramicidin A) at 20 degrees C. The dielectric relaxation decreases and the relaxation time increases when gramicidin A is incorporated into L-alpha-lysolecithin. These dielectric changes are related, in part, to the micellar-to-lamellar lipid phase transition induced by the incorporation of gramicidin A into lysolecithin. We suggest that the diffuse rotational motion of the polar head group of L-alpha-lysolecithin contributes to the dielectric relaxation/loss at around 100 MHz. 相似文献
19.
The apparently symmetrical hexagonal bilayer hemoglobin from Lumbricus terrestris has a large dipole moment 总被引:1,自引:0,他引:1
The giant approximately 3.6 MDa hexagonal bilayer hemoglobin (HBL Hb) from Lumbricus terrestris consists of 12 213-kDa dodecamers of four globin chains ([b + a + c]3[d]3) tethered to a central scaffold of approximately 36 non-globin, linker subunits L1-L4 (24-32 kDa). Three-dimensional reconstructions obtained by electron cryomicroscopy showed it to have a D6 point-group symmetry, with the two layers rotated approximately 16 degrees relative to each other. Measurement of the dielectric constants of the Hb and the dodecamer over the frequency range 5-100 kHz indicated relaxation frequencies occurring at 20-40 and 300 kHz, respectively, substantially lower than the 700-800 kHz in HbA. The dipole moments calculated using Oncley's equation were 17,300 +/- 2300 D and 1400 D for the Hb and dodecamer, respectively. The approximately threefold higher dipole moment of the dodecamer relative to HbA is consistent with an asymmetric shape in solution suggested by small-angle X-ray scattering. Although a two-term Debye equation and a prolate ellipsoid of revolution model provided a good fit to the experimental dielectric dispersion of the dodecamer, a three-term Debye equation based on an oblate ellipsoid of revolution model was required to fit the asymmetric dielectric dispersion curve of the Hb: the required additional term may represent either an induced dipole moment or a substructure which rotates independently of the main permanent dipole component of the Hb. The D6 point-group symmetry implies that the dipole moments of the dodecamers cancel out. Thus, in addition to a possible contribution from fluctuations of the proton distribution, the large dipole moment of the Hb may be due to an asymmetric distribution of the heterogeneous linker subunits. 相似文献
20.
Soham Roy Ranko Richert 《Biochimica et Biophysica Acta - Proteins and Proteomics》2014,1844(2):323-329
Due to the interest in protein dynamics, there are numerous dielectric relaxation studies of proteins in water and in glass-forming aqueous solvents such as glycerol-water mixtures. In the regime of low frequencies, the inevitable dc-conductivity of such systems limits the resolution of dynamics that are slow compared with the solvent relaxation. Solutions of myoglobin in glycerol/water mixtures of various compositions are measured by dielectric spectroscopy in the frequency range from 10 mHz to 10 MHz. The resolution of low frequency modes is improved by two approaches: electrical ‘cleaning’ and the analysis of the derivative of the real component of permittivity, which shows no direct signature of dc-conductivity. Effects of internal interfacial polarization are also addressed by measuring the same solvents in confinement as well as mixed with glass beads. We find two processes, the structural relaxation of the solvent and the slower rotational mode of the protein, with no indication at even lower frequencies of a dielectric signature of fluctuations associated with protein dynamics. 相似文献