Broadband Dielectric Spectroscopy on Human Blood

Dielectric spectra of human blood reveal a rich variety of dynamic processes. Achieving a better characterization and understanding of these processes not only is of academic interest but also of high relevance for medical applications as, e.g., the determination of absorption rates of electromagnetic radiation by the human body. The dielectric properties of human blood are studied using broadband dielectric spectroscopy, systematically investigating the dependence on temperature and hematocrit value. By covering a frequency range from 1 Hz to 40 GHz, information on all the typical dispersion regions of biological matter is obtained. We find no evidence for a low-frequency relaxation (alpha-relaxation) caused, e.g., by counterion diffusion effects as reported for some types of biological matter. The analysis of a strong Maxwell-Wagner relaxation arising from the polarization of the cell membranes in the 1-100 MHz region (beta-relaxation) allows for the test of model predictions and the determination of various intrinsic cell properties. In the microwave region beyond 1 GHz, the reorientational motion of water molecules in the blood plasma leads to another relaxation feature (gamma-relaxation). Between beta- and gamma-relaxation, significant dispersion is observed, which, however, can be explained by a superposition of these relaxation processes and is not due to an additional delta-relaxation often found in biological matter. Our measurements provide dielectric data on human blood of so far unsurpassed precision for a broad parameter range. All data are provided in electronic form to serve as basis for the calculation of the absorption rate of electromagnetic radiation and other medical purposes. Moreover, by investigating an exceptionally broad frequency range, valuable new information on the dynamic processes in blood is obtained.Comment: 17 pages, 9 figure

Structural, volumetric, and thermodynamic characterization of a micellar sphere-to-rod transition

The thermotropic sphere-to-rod transition of nonionic surfactants was characterized in terms of a large set of parameters: the transition temp. and width, the partial vol., coeff. of thermal vol. expansion, enthalpy, isobaric heat capacity, and structural parameters, such as radius of gyration and hydrodynamic radius. Data were recorded as a function of concn. of surfactants in H2O and in D2O. To this end, pressure perturbation calorimetry (PPC), small angle neutron scattering (SANS), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and isothermal titrn. calorimetry (ITC) were applied in a study of aq. solns. contg. myristyl, tridecyl, and lauryl maltoside and heptaethyleneglycoltetradecyl ether (C14EO7). Small changes in the thermodn. and volumetric parameters (e.g., the partial vol. change is .apprx.+2.permill.) are discussed in detail as the result of three effects governing the transition. (i) Redn. of the water accessible hydrophobic surface area (ASAap) drives the transition. (ii) Shrinking in headgroup size by thermal dehydration triggers the transition. (iii) Hypothesized gradual ordering of the chains may control the effect of chain length on the transition. [on SciFinder (R)

Ultrafast Dynamics and Hydrogen-Bond Structure in Aqueous Solutions of Model Peptides

The dynamics of water molecules in the hydration layers of proteins are critical for biological function. Here the molecular dynamics in aqueous solutions of model hydrophilic and amphiphilic dipeptides are studied as a function of concentration using the ultrafast optical Kerr effect (OKE). The OKE is a direct time-domain method which yields both picosecond time scale molecular dynamics and low-frequency (Terahertz) Raman spectra, which contain information on the hydrogen-bonded structure of aqueous solutions. Two distinct concentration regimes are identified, above and below 0.4 M peptide concentration. In the low-concentration regime the tetrahedral water structure is largely preserved but the structural dynamics in water are slowed significantly by interaction with the peptide. The slow down is more marked for the hydrophilic than the amphiphilic peptide. Suppression of water structural dynamics observed is greater than that reported for retardation of the water reorientation in NMR, reflecting the different dynamics probed by these different methods. Above 0.4 M the tetrahedral water structure is more strongly perturbed, a contribution to the THz Raman spectrum from the solvated peptide is observed, and structural dynamics in the solution are markedly slowed. This is assigned to slow relaxation within an H-bonded network of peptide molecules. The strong concentration dependence observed goes some way toward explaining disagreements between different measurements of the dynamics of peptide solvation which have appeared in the literature