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Cavaglià M, Deriu MA, Tuszynski JA. Toward a holographic brain paradigm: a lipid-centric model of brain functioning. Front Neurosci 2023; 17:1302519. [PMID: 38161798 PMCID: PMC10757614 DOI: 10.3389/fnins.2023.1302519] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 12/04/2023] [Indexed: 01/03/2024] Open
Abstract
Due to the stimulation of neuronal membrane dipoles by action potentials, under suitable conditions coherent dipole oscillations can be formed. We argue that these dipole oscillations satisfy the weak Bose-Einstein condensate criteria of the Froehlich model of biological coherence. They can subsequently generate electromagnetic fields (EMFs) propagating in the inter-neuronal space. When neighboring neurons fire synchronously, EMFs can create interference patterns and hence form holographic images containing analog information about the sensory inputs that trigger neuronal activity. The mirror pattern projected by EMFs inside the neuron can encode information in the neuronal cytoskeleton. We outline an experimental verification of our hypothesis and its consequences for anesthesia, neurodegenerative diseases, and psychiatric states.
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Affiliation(s)
| | | | - Jack A. Tuszynski
- DIMEAS, Politecnico di Torino, Turin, Italy
- Department of Data Science and Engineering, The Silesian University of Technology, Gliwice, Poland
- Department of Physics, University of Alberta, Edmonton, AB, Canada
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2
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Effects of solution conductivity on macropore size dynamics in electroporated lipid vesicle membranes. Bioelectrochemistry 2022; 147:108222. [PMID: 35944467 DOI: 10.1016/j.bioelechem.2022.108222] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/29/2022] [Accepted: 08/01/2022] [Indexed: 11/21/2022]
Abstract
Using fast imaging microscopy, we investigate in detail the expansion of micron-sized pores occurring in individual electroporated giant unilamellar vesicles composed of the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). To infer pore dynamics on the electrodeformed and electropermeabilized vesicles, we develop a computational approach and provide for the first time a direct evidence of quantitative agreement between experimental data and the well-established theoretical prediction of Smith, Neu and Krassowska (SNK). The analysis we describe also provides an extension to the current theoretical literature on how the conductivity ratio of the internal and the external vesicle solution plays a determinant role in the definition of the electrical force driving pore expansion kinetics.
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Yudovich S, Marzouqe A, Kantorovitsch J, Teblum E, Chen T, Enderlein J, Miller EW, Weiss S. Electrically Controlling and Optically Observing the Membrane Potential of Supported Lipid Bilayers. Biophys J 2022; 121:2624-2637. [PMID: 35619563 DOI: 10.1016/j.bpj.2022.05.037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2021] [Revised: 04/26/2022] [Accepted: 05/23/2022] [Indexed: 11/02/2022] Open
Abstract
Supported lipid bilayers are a well-developed model system for the study of membranes and their associated proteins, such as membrane channels, enzymes, and receptors. These versatile model membranes can be made from various components, ranging from simple synthetic phospholipids to complex mixtures of constituents, mimicking the cell membrane with its relevant physiochemical and molecular phenomena. In addition, the high stability of supported lipid bilayers allows for their study via a wide array of experimental probes. In this work, we describe a platform for supported lipid bilayers that is accessible both electrically and optically, and demonstrate direct optical observation of the transmembrane potential of supported lipid bilayers. We show that the polarization of the supported membrane can be electrically controlled and optically probed using voltage-sensitive dyes. Membrane polarization dynamics is understood through electrochemical impedance spectroscopy and the analysis of an equivalent electrical circuit model. In addition, we describe the effect of the conducting electrode layer on the fluorescence of the optical probe through metal-induced energy transfer, and show that while this energy transfer has an adverse effect on the voltage sensitivity of the fluorescent probe, its strong distance dependency allows for axial localization of fluorescent emitters with ultrahigh accuracy. We conclude with a discussion on possible applications of this platform for the study of voltage-dependent membrane proteins and other processes in membrane biology and surface science.
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Affiliation(s)
- Shimon Yudovich
- Department of Physics, Bar-Ilan University, Ramat-Gan, 52900, Israel; Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel.
| | - Adan Marzouqe
- Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel; Department of Chemistry, Bar-Ilan University, Ramat-Gan, 52900, Israel
| | - Joseph Kantorovitsch
- Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel
| | - Eti Teblum
- Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel
| | - Tao Chen
- Third Institute of Physics-Biophysics, Georg August University, 37077 Göttingen, Germany
| | - Jörg Enderlein
- Third Institute of Physics-Biophysics, Georg August University, 37077 Göttingen, Germany; Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), Georg August University, Germany
| | - Evan W Miller
- Departments of Chemistry, Molecular & Cell Biology, and Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, United States
| | - Shimon Weiss
- Department of Physics, Bar-Ilan University, Ramat-Gan, 52900, Israel; Institute for Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, 52900, Israel; Departments of Chemistry and Biochemistry, Physiology, and California NanoSystems Institute, University of California Los Angeles, Los Angeles, CA 90095.
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4
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Guo F, Qian K, Zhang L, Deng H, Li X, Zhou J, Wang J. Anisotropic conductivity for single-cell electroporation simulation with tangentially dispersive membrane. Electrochim Acta 2021. [DOI: 10.1016/j.electacta.2021.138426] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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5
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Zakhvataev VE. Dynamic structure factor of a lipid bilayer in the presence of a high electric field. J Chem Phys 2019; 151:234902. [PMID: 31864280 DOI: 10.1063/1.5123786] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The influence of a high average electric field (∼1 V/nm) in the hydrophobic interior of a bilayer lipid membrane on short-wavelength in-plane phononic motions of lipid chains is considered. The average electric field is assumed to be nearly constant on a picosecond time scale and a nanometer length scale. This field may be induced, for instance, by externally applied subnanosecond electric pulses or the membrane dipole potential. Using a generalized hydrodynamic approach, we derive a corresponding electrohydrodynamic model generalized to high wave numbers. In the considered approximation, all electric field effects are reduced only to a constant contribution to the generalized isothermal compressibility modulus. The corresponding dynamic structure factor for a lipid bilayer is derived. We show that due to polarization effects, the high field can critically impact the dynamics of longitudinal acousticlike modes at wave numbers near the major peak of the static structure factor. We estimate quantitatively that for typical lipid bilayers, transverse high electric fields can cause strong phonon energy softening, enhancement of phonon population, and formation of a gap in the dispersion of excitation frequency. The results obtained agree with simulations of the initiation of lipid bilayer electropores, suggesting that the proposed model reproduces the essential features of the field's impact on atomic density fluctuations. The proposed mechanism may have significant implications for the understanding of electroporation, passive molecular transport, and spontaneous pore formation in lipid bilayers.
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Affiliation(s)
- V E Zakhvataev
- Federal Research Center "Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences", Krasnoyarsk 660036 Russia and Siberian Federal University, Krasnoyarsk 660041 Russia
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6
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Alobeedallah H, Cornell B, Coster H. The Effect of Benzyl Alcohol on the Dielectric Structure of Lipid Bilayers. J Membr Biol 2016; 249:833-844. [PMID: 27803961 DOI: 10.1007/s00232-016-9934-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 10/22/2016] [Indexed: 11/25/2022]
Abstract
Molecularly tethered lipid bilayer membranes were constructed on a commercially available chemically modified gold substrate. This is a new and promising product that has allowed the construction of very robust lipid bilayers. Very high resolution electrical impedance spectroscopy (EIS) was used to determine the dielectric structure of the lipid bilayers and associated interfaces. The EIS data were modelled in terms of the dielectric substructure using purpose developed software. The hydrophobic region, where the lipid tails are located, was revealed by the EIS in the frequency range of (1-100) Hz and its thickness was calculated from the capacitance of this region and found to be approximately 3-4 nm. The hydrophilic region, where the polar heads are located, was revealed at higher frequencies and its thickness was estimated to be approximately 1-2 nm. The effect of the local anaesthetic benzyl alcohol (BZA) on the tethered lipid bilayers was investigated. The effect of BZA on the membrane capacitance and conductance allowed the changes in the thickness of the polar head and hydrophobic tails regions to be determined. It was found that the addition of BZA caused a significant increase in the capacitance (corresponding to a decrease in the thickness) of the hydrophobic region and an increase in the membrane electrical conductance. The EIS allowed a distinction between a hydrophobic region in the centre of the bilayer and an outer hydrophobic region. Benzyl alcohol was found to have the largest effect on the outer, hydrophobic region, although the inner hydrophobic region was also consistently affected.
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Affiliation(s)
- Hadeel Alobeedallah
- School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW, 2006, Australia.
| | - Bruce Cornell
- SDx Tethered Membranes Pty Ltd., Roseville, Sydney, NSW, 2069, Australia
| | - Hans Coster
- School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW, 2006, Australia
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Stubbe M, Gimsa J. Maxwell's mixing equation revisited: characteristic impedance equations for ellipsoidal cells. Biophys J 2015; 109:194-208. [PMID: 26200856 PMCID: PMC4621811 DOI: 10.1016/j.bpj.2015.06.021] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 06/10/2015] [Accepted: 06/12/2015] [Indexed: 11/27/2022] Open
Abstract
We derived a series of, to our knowledge, new analytic expressions for the characteristic features of the impedance spectra of suspensions of homogeneous and single-shell spherical, spheroidal, and ellipsoidal objects, e.g., biological cells of the general ellipsoidal shape. In the derivation, we combined the Maxwell-Wagner mixing equation with our expression for the Clausius-Mossotti factor that had been originally derived to describe AC-electrokinetic effects such as dielectrophoresis, electrorotation, and electroorientation. The influential radius model was employed because it allows for a separation of the geometric and electric problems. For shelled objects, a special axial longitudinal element approach leads to a resistor-capacitor model, which can be used to simplify the mixing equation. Characteristic equations were derived for the plateau levels, peak heights, and characteristic frequencies of the impedance as well as the complex specific conductivities and permittivities of suspensions of axially and randomly oriented homogeneous and single-shell ellipsoidal objects. For membrane-covered spherical objects, most of the limiting cases are identical to-or improved with respect to-the known solutions given by researchers in the field. The characteristic equations were found to be quite precise (largest deviations typically <5% with respect to the full model) when tested with parameters relevant to biological cells. They can be used for the differentiation of orientation and the electric properties of cell suspensions or in the analysis of single cells in microfluidic systems.
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Affiliation(s)
- Marco Stubbe
- Chair of Biophysics, University of Rostock, Rostock, Germany
| | - Jan Gimsa
- Chair of Biophysics, University of Rostock, Rostock, Germany.
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8
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Denzi A, Merla C, Palego C, Paffi A, Ning Y, Multari CR, Cheng X, Apollonio F, Hwang JCM, Liberti M. Assessment of Cytoplasm Conductivity by Nanosecond Pulsed Electric Fields. IEEE Trans Biomed Eng 2015; 62:1595-603. [DOI: 10.1109/tbme.2015.2399250] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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9
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Gekle S, Netz RR. Nanometer-resolved radio-frequency absorption and heating in biomembrane hydration layers. J Phys Chem B 2014; 118:4963-9. [PMID: 24779642 DOI: 10.1021/jp501562p] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Radio-frequency (RF) electromagnetic fields are readily absorbed in biological matter and lead to dielectric heating. To understand how RF radiation interacts with macromolecular structures and possibly influences biological function, a quantitative description of dielectric absorption and heating at nanometer resolution beyond the usual effective medium approach is crucial. We report an exemplary multiscale theoretical study for biomembranes that combines (i) atomistic simulations for the spatially resolved absorption spectrum at a single planar DPPC lipid bilayer immersed in water, (ii) calculation of the electric field distribution in planar and spherical cell models, and (iii) prediction of the nanometer resolved temperature profiles under steady RF radiation. Our atomistic simulations show that the only 2 nm thick lipid hydration layer strongly absorbs in a wide RF range between 10 MHz and 100 GHz. The absorption strength, however, strongly depends on the direction of the incident wave. This requires modeling of the electric field distribution using tensorial dielectric spectral functions. For a spherical cell model, we find a strongly enhanced RF absorption on an equatorial ring, which gives rise to temperature gradients inside a single cell under radiation. Although absolute temperature elevation is small under conditions of typical telecommunication usage, our study points to hitherto neglected temperature gradient effects and allows thermal RF effects to be predicted on an atomistically resolved level. In addition to a refined physiological risk assessment of RF fields, technological applications for controlling temperature profiles in nanodevices are possible.
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Affiliation(s)
- Stephan Gekle
- Fachbereich Physik, Universität Bayreuth , Bayreuth, Germany
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10
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Saviz M, Faraji-Dana R. A THEORETICAL MODEL FOR THE FREQUENCY-DEPENDENT DIELECTRIC PROPERTIES OF CORNEAL TISSUE AT MICROWAVE FREQUENCIES. ACTA ACUST UNITED AC 2013. [DOI: 10.2528/pier12112510] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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11
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Merla C, Denzi A, Paffi A, Casciola M, d'Inzeo G, Apollonio F, Liberti M. Novel passive element circuits for microdosimetry of nanosecond pulsed electric fields. IEEE Trans Biomed Eng 2012; 59:2302-11. [PMID: 22692873 DOI: 10.1109/tbme.2012.2203133] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Microdosimetric models for biological cells have assumed increasing significance in the development of nanosecond pulsed electric field technology for medical applications. In this paper, novel passive element circuits, able to take into account the dielectric dispersion of the cell, are provided. The circuital analyses are performed on a set of input pulses classified in accordance with the current literature. Accurate data in terms of transmembrane potential are obtained in both time and frequency domains for different cell models. In addition, a sensitivity study of the transfer function for the cell geometrical and dielectric parameters has been carried out. This analysis offers a new, simple, and efficient tool to characterize the nsPEFs' action at the cellular level.
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Affiliation(s)
- C Merla
- Italian Inter-University Centre of Electromagnetic Fieldsand Bio-Systems, Italian National Agency for New Technologies, Energy,and Sustainable Economic Development, Rome, Italy.
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12
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Kaatze U. Bound water: Evidence from and implications for the dielectric properties of aqueous solutions. J Mol Liq 2011. [DOI: 10.1016/j.molliq.2011.06.012] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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Merla C, Paffi A, Apollonio F, Leveque P, d'Inzeo G, Liberti M. Microdosimetry for nanosecond pulsed electric field applications: a parametric study for a single cell. IEEE Trans Biomed Eng 2011; 58:1294-302. [PMID: 21216699 DOI: 10.1109/tbme.2010.2104150] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A microdosimetric study of nanosecond pulsed electric fields, including dielectric dispersivity of cell compartments, is proposed in our paper. A quasi-static solution based on the Laplace equation was adapted to wideband signals and used to address the problem of electric field estimation at cellular level. The electric solution was coupled with an asymptotic electroporation model able to predict membrane pore density. An initial result of our paper is the relevance of the dielectric dispersivity, providing evidence that both the transmembrane potential and the pore density are strongly influenced by the choice of modeling used. We note the crucial role played by the dielectric properties of the membrane that can greatly impact on the poration of the cell. This can partly explain the selective action reported on cancerous cells in mixed populations, if one considers that tumor cells may present different dielectric responses. Moreover, these kinds of studies can be useful to determine the appropriate setting of nsPEF generators as well as for the design and optimization of new-generation devices.
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Affiliation(s)
- Caterina Merla
- Italian Inter-University Center for the Study of Electromagnetic Fields and BioSystems (ICEmB) at ENEA, Italian Agency for New Technologies, Energy and Sustainable Economic Development, Rome 00123, Italy.
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14
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Sebastián JL, Muñoz S, Sancho M, Martínez G, Kaler KVIS. Polarizability of red blood cells with an anisotropic membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:022901. [PMID: 20365616 DOI: 10.1103/physreve.81.022901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Revised: 12/02/2009] [Indexed: 05/29/2023]
Abstract
We predict the complex polarizability of a realistic model of a red blood cell (RBC), with an inhomogeneous dispersive and anisotropic membrane. In this model, the frequency-dependent complex electrical parameters of the individual cell layers are described by the Debye equation while the dielectric anisotropy of the cell membrane is taken into account by the different permittivities along directions normal and tangential to the membrane surface. The realistic shape of the RBC is described in terms of the Jacobi elliptic functions. To calculate the polarizability, we evoke the effective dipole moment method to determine the cell internal electric field distribution, employing an adaptive finite-element numerical approach. We have furthermore investigated the influence of the anisotropic membrane and dispersive electrical parameters of each individual cell layer on the total complex polarizability. Our findings suggest that the individual layer contribution depends on two factors: the volume of the layer and the associated induced electric field, which in turn is influenced by other layers of the cell. These results further show that the average polarizability spectra of the cell are significantly impacted by the anisotropy and associated dispersion of the cellular compartments.
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Affiliation(s)
- José Luis Sebastián
- Departamento de Física Aplicada III, Facultad de Ciencias Físicas, Universidad Complutense, 28040 Madrid, Spain
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15
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Krahn A, Lottmann P, Marquardsen T, Tavernier A, Türke MT, Reese M, Leonov A, Bennati M, Hoefer P, Engelke F, Griesinger C. Shuttle DNP spectrometer with a two-center magnet. Phys Chem Chem Phys 2010; 12:5830-40. [DOI: 10.1039/c003381b] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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16
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Merla C, Liberti M, Apollonio F, d'Inzeo G. Quantitative assessment of dielectric parameters for membrane lipid bi-layers from RF permittivity measurements. Bioelectromagnetics 2009; 30:286-98. [DOI: 10.1002/bem.20476] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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17
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Sheppard AR, Swicord ML, Balzano Q. Quantitative evaluations of mechanisms of radiofrequency interactions with biological molecules and processes. HEALTH PHYSICS 2008; 95:365-396. [PMID: 18784511 DOI: 10.1097/01.hp.0000319903.20660.37] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The complexity of interactions of electromagnetic fields up to 10(12) Hz with the ions, atoms, and molecules of biological systems has given rise to a large number of established and proposed biophysical mechanisms applicable over a wide range of time and distance scales, field amplitudes, frequencies, and waveforms. This review focuses on the physical principles that guide quantitative assessment of mechanisms applicable for exposures at or below the level of endogenous electric fields associated with development, wound healing, and excitation of muscles and the nervous system (generally, 1 to 10(2) V m(-1)), with emphasis on conditions where temperature increases are insignificant (<<1 K). Experiment and theory demonstrate possible demodulation at membrane barriers for frequencies < or =10 MHz, but not at higher frequencies. Although signal levels somewhat below system noise can be detected, signal-to-noise ratios substantially less than 0.1 cannot be overcome by cooperativity, signal averaging, coherent detection, or by nonlinear dynamical systems. Sensory systems and possible effects on biological magnetite suggest paradigms for extreme sensitivity at lower frequencies, but there are no known radiofrequency (RF) analogues. At the molecular level, vibrational modes are so overdamped by water molecules that excitation of molecular modes below the far infrared cannot occur. Two RF mechanisms plausibly may affect biological matter under common exposure conditions. For frequencies below approximately 150 MHz, shifts in the rate of chemical reactions can be mediated by radical pairs and, at all frequencies, dielectric and resistive heating can raise temperature and increase the entropy of the affected biological system.
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Krahn A, Priller U, Emsley L, Engelke F. Resonator with reduced sample heating and increased homogeneity for solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2008; 191:78-92. [PMID: 18187352 DOI: 10.1016/j.jmr.2007.12.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2007] [Revised: 11/29/2007] [Accepted: 12/11/2007] [Indexed: 05/25/2023]
Abstract
In the application of solid-state NMR to many systems, the presence of radiofrequency (rf) electric fields inside classical solenoidal coils causes heating of lossy samples. In particular, this is critical for proteins in ionic buffers. Rf sample heating increases proportional to frequency which may result in the need to reduce the rf pulse power to prevent partial or total sample deterioration. In the present paper, we propose a multifrequency-tunable NMR resonator where the sample is electrically shielded from the NMR coil by a conductive sheet that increases the magneto-electric ratio. Expressions for the B1 efficiency as function of magnetic and electric filling factors are derived that allow a direct comparison of different resonators. Rf efficiency, homogeneity, signal-to-noise, and rf sample heating are compared. NMR spectra at 700MHz on ethylene glycol, glycine, and a model protein were acquired to compare the resonators under realistic experimental conditions.
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Affiliation(s)
- Alexander Krahn
- Bruker Biospin GmbH, Silberstreifen, D-76287 Rheinstetten, Germany
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19
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Sebastián JL, Muñoz S, Sancho M, Álvarez G, Miranda JM. Electric field distribution and energy absorption in anisotropic and dispersive red blood cells. Phys Med Biol 2007; 52:6831-47. [DOI: 10.1088/0031-9155/52/23/004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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20
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Dillmann B, Elbayed K, Zeiger H, Weingertner MC, Piotto M, Engelke F. A novel low-E field coil to minimize heating of biological samples in solid-state multinuclear NMR experiments. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2007; 187:10-8. [PMID: 17448715 DOI: 10.1016/j.jmr.2007.02.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Revised: 02/20/2007] [Accepted: 02/26/2007] [Indexed: 05/15/2023]
Abstract
A novel coil, called Z coil, is presented. Its function is to reduce the strong thermal effects produced by rf heating at high frequencies. The results obtained at 500MHz in a 50 microl sample prove that the Z coil can cope with salt concentrations that are one order of magnitude higher than in traditional solenoidal coils. The evaluation of the rf field is performed by numerical analysis based on first principles and by carrying out rf field measurements. Reduction of rf heating is probed with a DMPC/DHPC membrane prepared in buffers of increasing salt concentrations. The intricate correlation that exists between the magnetic and electric field is presented. It is demonstrated that, in a multiply tuned traditional MAS coil, the rf electric field E(1) cannot be reduced without altering the rf magnetic field. Since the detailed distribution differs when changing the coil geometry, a comparison involving the following three distinct designs is discussed: (1) a regular coil of 5.5 turns, (2) a variable pitch coil with the same number of turns, (3) the new Z coil structure. For each of these coils loaded with samples of different salt concentrations, the nutation fields obtained at a certain power level provide a basis to discuss the impact of the dielectric and conductive losses on the rf efficiency.
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