Search query: Kieran michaeli electron

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abstract: Significance Charge transfer through organic molecules is extensively studied theoretically and experimentally owing to its importance in basic biological processes. Long distance electron transport through such molecules, which are typically insulating, is commonly attributed to thermally activated hopping. We introduce an additional mechanism that supports electron transfer across appreciable distances, even at zero temperature. It originates from the electric potential that is either internally created or externally applied before charge flows. The electronic wavefunctions are dramatically changed by this potential, allowing them to efficiently mediate current. This mechanism can explain recent experiments where electron transfer shows only a weak temperature dependence. Our result is an important contribution to the long standing challenge of developing a comprehensive theory for charge transfer through organic molecules. Biological structures rely on kinetically tuned charge transfer reactions for energy conversion, biocatalysis, and signaling as well as for oxidative damage repair. Unlike man made electrical circuitry, which uses metals and semiconductors to direct current flow, charge transfer in living systems proceeds via biomolecules that are nominally insulating. Long distance charge transport, which is observed routinely in nucleic acids, peptides, and proteins, is believed to arise from a sequence of thermally activated hopping steps. However, a growing number of experiments find limited temperature dependence for electron transfer over tens of nanometers. To account for these observations, we propose a temperature independent mechanism based on the electric potential difference that builds up along the molecule as a precursor of electron transfer. Specifically, the voltage changes the nature of the electronic states away from being sharply localized so that efficient resonant tunneling across long distances becomes possible without thermal assistance. This mechanism is general and is expected to be operative in molecules where the electronic states densely fill a wide energy window (on the scale of electronvolts) above or below the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) We show that this effect can explain the temperature independent charge transport through DNA and the strongly voltage dependent currents that are measured through organic semiconductors and peptides.
author_names: Karen Michaeli

David N Beratan

David H Waldeck

Ron Naaman
title: Voltage induced long range coherent electron transfer through organic molecules
venue: Proceedings of the National Academy of Sciences
year: 2019

abstract: The recently discovered chiral induced spin selectivity (CISS) effect gives rise to a spin selective electron transmission through biomolecules. Here we review the mechanism behind the CISS effect and its implication for processes in Biology. Specifically, three processes are discussed: long range electron transfer, spin effects on the oxidation of water, and enantioselectivity in bio recognition events. These phenomena imply that chirality and spin may play several important roles in biology, which have not been considered so far.
author_names: Karen Michaeli

Nirit Kantor-Uriel

Ron Naaman

David H Waldeck
title: The electron's spin and molecular chirality how are they related and how do they affect life processes?
venue: Chemical Society reviews
year: 2016

abstract: Laccase from Phoma sp. UHH 5 1 03 was cross linked to polyvinylidene fluoride membranes by electron beam irradiation. Immobilised laccase displayed a higher stability than the non immobilised enzyme with respect to typical wastewater temperatures, and pH at a range of 5 to 9. Batch tests addressed the removal of pharmaceutically active compounds (PhACs; applied as a mixture of acetaminophen, bezafibrate, indometacin, ketoprofen, mefenamic acid, and naproxen) by both immobilised and non immobilised laccase in municipal wastewater. High removal rates >85% of the most efficiently oxidised PhACs (acetaminophen and mefenamic acid) indicated a high efficiency of the immobilised laccase in wastewater. Continuous elimination of the aforementioned PhACs by the immobilised enzyme in a continuously operated diffusion basket reactor yielded a PhAC removal pattern qualitatively similar to those observed in batch tests. Clearly higher apparent Vmax values and catalytic efficiencies (in terms of both Vmax/S0.5 as well as Vmax/Km values obtained from data fitting according to the Hill and the Michaelis Menten model, respectively) observed for acetaminophen oxidation by the immobilised compared to the non immobilised enzyme are in support of a considerably higher functional stability of the immobilised laccase especially in wastewater. The potential influence of acetaminophen on the removal of comparatively less laccase oxidisable water pollutants such as the antimicrobial triclosan (TCS) was investigated. TCS was increasingly removed upon increasing the initial acetaminophen concentration in immobilised as well as non immobilised laccase reaction systems until saturation became evident. Acetaminophen was consumed and not recycled during laccase reactions, which was accompanied by the formation of various acetaminophen TCS cross coupling products. Nevertheless, the simultaneous presence of acetaminophen (and potentially even more pollutant removal enhancing laccase substrates) and more recalcitrant pollutants in wastewater represents an interesting option for the efficiency enhancement of enzyme based wastewater treatment approaches.
author_names: Elham Jahangiri

Isabell Thomas

Agnes Schulze

Bettina Seiwert

Hubert Cabana

Dietmar Schlosser
title: Characterisation of electron beam irradiation immobilised laccase for application in wastewater treatment.
venue: The Science of the total environment
year: 2018

abstract: Carbon nanotubes (CNTs) are excellent supports for electrocatalysts because of their large surface area, excellent electronic conductivity, and high chemical and structural stability. In the present study, the activity of CNTs on direct electron transfer (DET) and on immobilized glucose oxidase (GOX) is studied as a function of number of walls of CNTs. The results indicate that the GOX immobilized by the CNTs maintains its electrocatalytic activity toward glucose; however, the DET and electrocatalytic activity of GOX depend strongly on the number of inner tubes of CNTs. The GOX immobilized on triple walled CNTs (TWNTs) has the highest electron transfer rate constant, 1.22 s 1, for DET, the highest sensitivity toward glucose detection, 66.11 5.06 mA mM 1 cm 2, and the lowest apparent Michaelis Menten constant, 6.53 0.58 mM, as compared to GOX immobilized on single walled and multiwalled CNTs. The promotion effect of CNTs on the GOX electrocatalytic activity and DET is most likely due to the electron tunneling effect between the outer wall and inner tubes of TWNTs. The results of this study have general implications for the fundamental understanding of the role of CNT supports in DET processes and can be used for the better design of more effective electrocatalysts for biological processes including biofuel cells and biosensors.
author_names: Yuxiang Liu

Jin Zhang

Yi Cheng

San Ping Jiang
title: Effect of Carbon Nanotubes on Direct Electron Transfer and Electrocatalytic Activity of Immobilized Glucose Oxidase
venue: ACS omega
year: 2018

abstract: The DLR Institute of Planetary Exploration has proposed a novel design of a space instrument accommodated on a small satellite bus (SSB) that is dedicated to the detection of inner earth objects (IEOs) from a low earth orbit (LEO) The instrument design is based on a focal plane consisting of electron multiplied CCDs (EMCCD) operating at high frame rates for compensation of the spacecraft's pointing jitter at very low effective readout noise. The CCD detectors operate at a nominal operating temperature of 80degC and at a frame rate of 5fps. It is well known, that CCD detectors are prone to space radiation. However, EMCCD, designed to detect very low light levels of a few electrons, have not yet been used in space. Therefore, investigations have been initiated and performed by DLR for evaluation of the performance of EMCCDs before and after radiation. The main scope of the investigations was the characterization of the charge transfer efficiency (CTE) at low light levels because of its key impact on the detection performance. The non ionizing dose effects of space high energy particle radiation on the detector were simulated by 60MeV protons at two different fluence levels. The low light CTE was measured with point light sources without and with background light.
author_names: Harald Michaelis

Thomas Behnke

Stefano Mottola

Anja Krimlowski

Belinda Borgs

Andrew D Holland

Markus Schmid
title: Investigations on performance of Electron Multiplied CCD detectors (EMCCDs) after radiation for observation of low light star like objects in scientific space missions
venue: Remote Sensing
year: 2013

abstract: The response of low density polyethylene (LDPE) to high energy electron beam irradiation in air (10 MeV) between 25 and 400 kGy was examined and compared to non irradiated polyethylene in terms of the mechanical and structural properties. To quantify the degree of crosslinking, swelling studies were performed and from this it was observed that the crosslink density increased as the irradiation dose increased. Furthermore, a reduction was observed in the numerical data for molar mass between adjacent crosslinks and the number of monomeric units between adjacent crosslinks as the irradiation dose was conducted incrementally. Accelerated aging provided evidence that radicals became trapped in the polymer matrix of LDPE and this in turn initiated further reactions to transpire as time elapsed, leading to additional alteration in the structural properties. Fourier transform infrared spectroscopy (FTIR) was implemented to provide insight into this. This technique established that the aging process had increased the oxidative degradation products due to oxygen permeation into the polymer and double bonds within the material. Mechanical testing revealed an increase in the tensile strength and a decrease in the elongation at break. Accelerated aging caused additional modifications to occur in the mechanical properties which are further elucidated throughout this study. Dynamic frequency sweeps investigated the effects of irradiation on the structural properties of LDPE. The effect of varying the irradiation dose concentration was apparent as this controlled the level of crosslinking within the material. Maxwell and Kelvin or Voigt models were employed in this analytical technique to define the reaction procedure of the frequency sweep test with regards to non crosslinked and crosslinked LDPE.
author_names: Kieran A Murray

James E Kennedy

Brian McEvoy

Olivier Vrain

Damien Ryan

Richard Cowman

Clement L Higginbotham
title: The effects of high energy electron beam irradiation in air on accelerated aging and on the structure property relationships of low density polyethylene
year: 2013

abstract: Thick GEM like (THGEM) gaseous electron multipliers are made of standard printed circuit board perforated with sub millimeter diameter holes, etched at their rims. Effective gas multiplication factors of 10 5 and 10 7 and fast pulses in the few nanosecond rise time scale were reached in single and cascaded double THGEM elements, in atmospheric pressure standard gas mixtures with single photoelectrons. High single electron detection efficiency is obtained in photon detectors combining THGEMs and semitransparent UVsensitive CsI photocathodes or reflective ones deposited on the top THGEM face; the latter benefits of a reduced sensitivity to ionizing background radiation. Stable operation was recorded with photoelectron fluxes exceeding MHz/mm 2 The properties and some potential applications of these simple and robust multipliers are discussed.
author_names: C Shalem

Rachel Chechik

Amos Breskin

Karen Michaeli
title: Advances in Thick GEM like gaseous electron multipliers Part I: atmospheric pressure operation
year: 2006

abstract: Abstract Radiation is currently being exploited to modify polyethylene in order to improve properties for various applications such as hip replacements. This paper thoroughly examines the effects of high energy electron beam irradiation (10 MeV) on low density polyethylene (LDPE) material. ASTM (American Society for Testing and Materials) testing specimens were manufactured from LDPE and subjected to a broad range of doses ranging between 25 and 400 kGy at room temperature in an air atmosphere. Extensive characterisation techniques such as modulated differential scanning calorimetry (MDSC) and the Fourier transform infrared spectroscopy (FTIR) were conducted on the non irradiated and irradiated samples. While considering the semicrystalline nature of LDPE during the MDSC experiment, the melting temperature T m and the temperature crystallinity T c were calculated. This revealed that the T m and the T c decreased in temperature as the irradiation dose increased. The FTIR analysis was implemented to evaluate the presence of polar species such as carbonyl groups and trans vinylene double bond groups. The IR spectra illustrated that the concentration of characteristic bands for trans vinylene bonds increased with increasing radiation dose indicating the formation of carbonyl bond groups. Furthermore, the results demonstrated an occurrence of oxidative degradation due to the formation of carbonyl groups at 1718 cm 1
author_names: Kieran A Murray

James E Kennedy

Brian McEvoy

Olivier Vrain

Damien Ryan

Clement L Higginbotham
title: The effects of high energy electron beam irradiation on the thermal and structural properties of low density polyethylene
year: 2012

abstract: It is well known that polyurethane (PU) provides good irradiation resistance; however, extremely high irradiation doses can alter the structure and/or function of macromolecules, resulting in oxidation, chain scission and crosslinking. In this present study, modifications to the material characteristics resulting from irradiation were extensively examined through a broad array of analytical techniques. Fourier transform infrared spectroscopy (FTIR) revealed that there were a number of changes to the chemical structure after electron beam irradiation while dynamic frequency sweeps identified an occurrence of crosslinking particularly in the higher irradiation doses. The degree of crosslinking was further analysed by implementing the crosslink density experiment, which illustrated a high level of crosslinking at 200 kGy only. X ray diffraction (XRD) and differential scanning calorimetry (DSC) identified an increase in phase segregation and as a consequence it could lead to soft segment mobility. This increase in mobility could be responsible for an increase in the degree of chain orientation. Surface morphology of the electron beam irradiated material was determined using scanning electron microscope (SEM) imagery and this provided evidence that the surface of the material had clearly transformed with the development of additional ridges. The influence of such modifications initiated a significant reduction in the contact angle at the upper irradiation dose regime. Overall, this study demonstrated that the medical grade PU was highly affected by radiation exposure, particularly at high irradiation doses.
author_names: Kieran A Murray

James E Kennedy

Brian McEvoy

Olivier Vrain

Damien Ryan

Richard Cowman

Clement L Higginbotham
title: The influence of electron beam irradiation conducted in air on the thermal, chemical, structural and surface properties of medical grade polyurethane
year: 2013

abstract: The spin transfer mechanisms of three B site ordered double perovskites, Ba2YMO6 (M Mo, Re, and Ru) were determined using variable temperature 89Y and 137Ba magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. On the basis of symmetry compatible overlap and trends observed in the MAS NMR, spin polarization was determined to be the dominant mechanism at the Y sites and spin delocalization to be the operative mechanism at the Ba sites. The MAS NMR spectra display 89Y and 137Ba chemical shifts that far exceed those of other paramagnetic solids, appearing at up to 6402 and +12 200 ppm, respectively. Detection of additional resonances in 89Y MAS NMR indicates a small degree of cation site mixing in two cases.
author_names: Vladimir K Michaelis

Brandon J Greer

Tomoko Aharen

John E Greedan

Scott Kroeker
title: Determining Electron Spin Transfer Mechanisms in Paramagnetic Ba2YMO6 (M Mo, Re, Ru) Double Perovskites by 89Y and 137Ba MAS NMR Spectroscopy
year: 2012