Einar Sagstuen

• Jåstad, Eirik Ogner; Torheim, Turid K Gjerstad; Villeneuve, Kathleen; Kvaal, Knut; Hole, Eli Olaug; Sagstuen, Einar; Malinen, Eirik & Futsæther, Cecilia Marie (2017). In Quest of the Alanine R3 Radical: Multivariate EPR Spectral Analyses of X‑Irradiated Alanine in the Solid State. Journal of Physical Chemistry A.  ISSN 1089-5639.  121(38), s 7139- 7147 . doi: 10.1021/acs.jpca.7b06447 Fulltekst i vitenarkiv. Vis sammendrag

  The amino acid L-α-alanine is the most commonly used material for solidstate electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly stable radicals upon irradiation, with yields proportional to the radiation dose. Two major alanine radical components designated R1 and R2 have previously been uniquely characterized from EPR and electron−nuclear double resonance (ENDOR) studies as well as from quantum chemical calculations. There is also convincing experimental evidence of a third minor radical component R3, and a tentative radical structure has been suggested, even though no well-defined spectral signature has been observed experimentally. In the present study, temperature dependent EPR spectra of X-ray irradiated polycrystalline alanine were analyzed using five multivariate methods in further attempts to understand the composite nature of the alanine dosimeter EPR spectrum. Principal component analysis (PCA), maximum likelihood common factor analysis (MLCFA), independent component analysis (ICA), self-modeling mixture analysis (SMA), and multivariate curve resolution (MCR) were used to extract pure radical spectra and their fractional contributions from the experimental EPR spectra. All methods yielded spectral estimates resembling the established R1 spectrum. Furthermore, SMA and MCR consistently predicted both the established R2 spectrum and the shape of the R3 spectrum. The predicted shape of the R3 spectrum corresponded well with the proposed tentative spectrum derived from spectrum simulations. Thus, results from two independent multivariate data analysis techniques strongly support the previous evidence that three radicals are indeed present in irradiated alanine samples.

• Kusakovskij, Jevgenij; De Cooman, Hendrik; Sagstuen, Einar; Callens, Freddy J. & Vrielinck, Henk (2017). On the identity of the last known stable radical in X-irradiated sucrose. Chemical Physics Letters.  ISSN 0009-2614.  674, s 6- 10 . doi: 10.1016/j.cplett.2017.02.032 Fulltekst i vitenarkiv.
• Wiedmer, David; Sagstuen, Einar; Welch, Ken; Haugen, Håvard Jostein & Tiainen, Hanna (2016). Oxidative power of aqueous non-irradiated TiO2-H2O2 suspensions: Methylene blue degradation and the role of reactive oxygen species. Applied Catalysis B: Environmental.  ISSN 0926-3373.  198, s 9- 15 . doi: 10.1016/j.apcatb.2016.05.036 Vis sammendrag

  In the present study, the degradation of methylene blue in non-irradiated TiO2-H2O2 suspensions was investigated. Five commercially available catalysts were characterised (BET surface area, zeta potential, hydrodynamic diameter) and their oxidative power was assessed by means of the degradation of methylene blue. A subsequent EPR study was made to verify and identify potential oxidative radicals. The results showed that all suspensions could degrade methylene blue significantly stronger compared to hydrogen peroxide alone. A broad variation between the different catalysts in their capability to adsorb dye molecules was found which was essential for decomposition of methylene blue in darkness. The highest degradation rate of all samples was found for Degussa P25 at neutral pH. EPR studies of this sample verified the presence of oxygen centred radicals namely hydroxyl (radical dotOH) and superoxide radicals (O2−radical dot/radical dotOOH). Non-irradiated TiO2-H2O2 systems show great potential not only in dye removal applications but also in the field of disinfection where low concentrations of hydrogen peroxide are required and irradiation may not be feasible.

• Aalbergsjø, Siv Gundrosen & Sagstuen, Einar (2015). New Evidence for Hydroxyalkyl Radicals and Light- and Thermally Induced Trapped Electron Reactions in Rhamnose. Radiation Research.  ISSN 0033-7587.  184(2), s 161- 174 . doi: 10.1667/RR14081.1
• Knudtsen, Ingerid Skjei; Aalbergsjø, Siv Gundrosen; Hole, Eli Olaug & Sagstuen, Einar (2015). Radiation effects on crystalline l-asparagine, revisited: Radical formation by EMR and periodic DFT after X-irradiation at 275K. Radiation Physics and Chemistry.  ISSN 0969-806X.  106, s 151- 159 . doi: 10.1016/j.radphyschem.2014.07.008
• Krivokapic, Andre; Sanderud, Audun; Aalbergsjø, Siv Gundrosen; Hole, Eli Olaug & Sagstuen, Einar (2015). Lithium formate for EPR dosimetry (2): secondary radicals in X-irradiated crystals. Radiation Research.  ISSN 0033-7587.  183(6), s 675- 683 . doi: 10.1667/RR14046.1
• Øyen, Live Furnes; Aalbergsjø, Siv Gundrosen; Knudtsen, Ingerid Skjei; Hole, Eli Olaug & Sagstuen, Einar (2015). Direct Radiation Effects to the Amino Acid Side-Chain: EMR and Periodic DFT of X-Irradiated L-Asparagine at 6 K. Journal of Physical Chemistry B.  ISSN 1520-6106.  119(2), s 491- 502 . doi: 10.1021/jp5115866 Vis sammendrag

  Radical formation in single crystals of L-asparagine monohydrate following X-irradiation at 6 K has been investigated at 6 K and at elevated temperatures using various Electron Magnetic Resonance (EMR) techniques like Electron Paramagnetic Resonance (EPR), Electron Nuclear DOuble Resonance (ENDOR) and ENDOR-Induced EPR (EIE) spectroscopy. Molecular structures of the three free radicals stable at 6K were assessed by detailed analysis of the experimental data and Density Functional Theory (DFT) calculations in a periodic approach. Radical LI is assumed to result from one-electron reduction at the amide functional group in the asparagine side chain followed by protonation at the amide carbonyl oxygen by proton transfer from a neighboring molecule across a hydrogen bond. Radical LII is assigned to an one-electron reduction of the carboxyl group in amino acid backbone, followed by proton transfer across a hydrogen bond between a carboxylic oxygen and a neighboring asparagine molecule. Radical LIII is suggested formed by a net CO2 abstraction from an initial one-electron oxidized amino acid backbone. For the DFT modeling of LIII at 6 K, it was chosen to include the CO2 group stably embedded in the crystalline lattice. The assignments made are discussed in relation to previous work on L-asparagine. The relevance of these results to possible charge transfer processes in protein-DNA complexes is discussed.

• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Van Yperen-De Deyne, Andy; Van Speybroeck, Veronique & Sagstuen, Einar (2014). Automated generation of radical species in crystalline carbohydrate using ab initio MD simulations. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  16(32), s 17196- 17205 . doi: 10.1039/c4cp02179g
• Krivokapic, Andre; Aalbergsjø, Siv Gundrosen; De Cooman, Hendrik; Hole, Eli Olaug; Nelson, William H. & Sagstuen, Einar (2014). Lithium formate for EPR dosimetry: Radiation-induced radical trapping at low temperatures. Radiation Research.  ISSN 0033-7587.  181(5), s 503- 511 . doi: 10.1667/RR13582.1
• Pauwels, Ewald; De Cooman, Hendrik; Waroquier, Michel; Hole, Eli Olaug & Sagstuen, Einar (2014). Solved? the reductive radiation chemistry of alanine. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  16(6), s 2475- 2482 . doi: 10.1039/c3cp54441a
• Vrielinck, Henk; De Cooman, Hendrik; Callens, Freddy J. & Sagstuen, Einar (2014). Radiation Chemistry of Solid-State Carbohydrates using EMR, In Anders Lund & Masaru Shiotani (ed.),  Applications of EPR in Radiation Research.  Springer.  ISBN 978-3-319-09215-7.  Chapter 6.  s 189 - 254 Vis sammendrag

  We review our research of the past decade towards identification of radiation- induced radicals in solid state sugars and sugar phosphates. Detailed models of the radical structures are obtained by combining EPR and ENDOR experiments with DFT calculations of g and proton HF tensors, with agreement in their anisotropy serving as most important criterion. Symmetry-related and Schonland ambiguities, which may hamper such identification, are reviewed. Thermally induced transformations of initial radiation damage into more stable radicals can also be monitored in the EPR (and ENDOR) experiments and in principle provide information on stable radical formation mechanisms. Thermal annealing experiments reveal, however, that radical recombination and/or diamagnetic radiation damage is also quite important. Analysis strategies are illustrated with research on sucrose. Results on dipotassium glucose-1-phosphate and trehalose dihydrate, fructose and sorbose are also briefly discussed. Our study demonstrates that radiation damage is strongly regio-selective and that certain general principles govern the stable radical formation.

• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; De Cooman, Hendrik; Hole, Eli Olaug & Sagstuen, Einar (2013). Structural specificity of alkoxy radical formation in crystalline carbohydrates. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  15(24), s 9615- 9619 . doi: 10.1039/c3cp50789k Vis sammendrag

  A DFT study of radiation induced alkoxy radical formation in crystalline a-L-rhamnose has been performed to better understand the processes leading to selective radical formation in carbohydrates upon exposure to ionizing radiation at low temperatures. The apparent specificity of radiation damage to carbohydrates is of great interest for understanding radiation damage processes in the ribose backbone of the DNA molecule. Alkoxy radicals are formed by deprotonation from hydroxyl groups in oxidized sugar molecules. In a-L-rhamnose only one alkoxy radical is observed experimentally even though there are four possible sites for alkoxy radical formation. In the present work, the origin of this apparently specific action of radiation damage is investigated by computationally examining all four possible deprotonation reactions from oxygen in the oxidized molecule. All calculations are performed in a periodic approach and include estimates of the energy barriers for the deprotonation reactions using the Nudged Elastic Band (NEB) method. One of the four possible radical sites is ruled out due to the lack of a suitable proton acceptor. For the other three possible sites, the reaction paths and energy profiles from primary cationic radicals to stable, neutral alkoxy radicals are compared. It is found that deprotonation from one site (corresponding to the experimentally observed radical) differs from the others in that the reaction path is less energy demanding. Hence, it is suggested that the alkoxy radical formation is not necessarily site specific, but that the observed radical is formed in much greater abundance than the others due to the different energetics of the processes and reaction products.

• Gustafsson, Håkan; Lund, Anders; Hole, Eli Olaug & Sagstuen, Einar (2013). SO3-- radicals for EPR dosimetry: X- and Q band EPR study and LET dependency of crystalline potassium dithionate. Radiation Measurements.  ISSN 1350-4487.  59, s 123- 128 . doi: 10.1016/j.radmeas.2013.05.001
• Sanchez, Luis; Taxt-Lamolle, Sebastien Francis Michel; Hole, Eli Olaug; Krivokapic, Andre; Sagstuen, Einar & Haugen, Håvard Jostein (2013). TiO2 suspension exposed to H2O2 in ambient light or darkness: Degradation of methylene blue and EPR evidence for radical oxygen species. Applied Catalysis B: Environmental.  ISSN 0926-3373.  142-143, s 662- 667 . doi: 10.1016/j.apcatb.2013.05.017
• Sagstuen, Einar; Hole, Eli Olaug & Lund, Anders (2012). Free Radical Products in X-Irradiated Rochelle Salt: Low Temperature ENDOR and DFT Studies. Radiation Physics and Chemistry.  ISSN 0969-806X.  81(2), s 168- 179 . doi: 10.1016/j.radphyschem.2011.10.001
• Tarpan, Mihaela Adeluta; De Cooman, Hendrik; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy J. (2011). Identification of primary free radicals in trehalose dihydrate single crystals X-irradiated at 10 K. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  13(23), s 11294- 11302 . doi: 10.1039/c0cp02616f
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Waroquier, Michel & Callens, F (2010). Oxidation and Reduction Products of X Irradiation at 10 K in Sucrose Single Crystals: Radical Identification by EPR, ENDOR, and DFT. Journal of Physical Chemistry B.  ISSN 1520-6106.  114(1), s 666- 674 . doi: 10.1021/jp909247z
• Krivokapic, Andre; Øhman, Kjell Tage; Munthe, Morten; Nelson, William H.; Hole, Eli Olaug & Sagstuen, Einar (2010). Radicals in 5-Methylcytosine by Ionizing Radiation. Electron Magnetic Resonance for Structural and Mechanistic Analyses. Radiation Research.  ISSN 0033-7587.  173(5), s 689- 702
• Pauwels, Ewald; De Cooman, Hendrik; Waroquier, Michel; Hole, Eli Olaug & Sagstuen, Einar (2010). On the identity of the radiation-induced stable alanine radical. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  12(31), s 8733- 8736 . doi: 10.1039/c004380j
• Waldeland, Einar; Hole, Eli Olaug; Sagstuen, Einar & Malinen, Eirik (2010). The energy dependence of lithium formate and alanine EPR dosimeters for medium energy x rays. Medical physics (Lancaster).  ISSN 0094-2405.  37(7), s 3569- 3575 . doi: 10.1118/1.3432567 Vis sammendrag

  Litium formate and alanine EPR dosemeters were exposed to 8 different X-ray beam qualities, with nominal potentials ranging from 50 kV to 200 kV. Following ionometry based on standards of absorbed dose to water, the dosemeters were given two different doses of approximately 3 and 6 Gy for each radiation quality, with three dosemeters for each dose. A reference series was also irradiated to three different dose levels at a 60Co unit. The dose to water energy response, that is, dosimeter reading per absorbed dose to water relative to that for 60Co gamma-rays, was estimated for each beam quality. In addition, the energy response was calculated by Monte Carlo simulations and compared to the experimental energy response. Experimental energy response estimates ranged from 0.89 - 0.94 and 0.68 - 0.90 for lithium formate and alanine, respectively. Uncertainties in the experimental energy response estimates were typically 3 %. The relative effectiveness, that is, the ratio of the experimental energy response to that following Monte Carlo simulations was on average 0.96 and 0.93 for lithium formate and alanine, respectively. This work shows that lithium formate dosimeters are less dependent on X-ray energy than alanine. Furthermore, as the relative effectiveness for both lithium formate and alanine were systematically less than unity, the yield of radiation-induced radicals is decreased following X-irradiation compared to irradiation with 60Co gamma-rays.

• Waldeland, Einar; Hole, Eli Olaug; Stenerlöv, Bo; Grusell, Erik; Sagstuen, Einar & Malinen, Eirik (2010). Radical Formation in Lithium Formate EPA Dosimeters after Irradiation with Protons and Nitrogen Ions. Radiation Research.  ISSN 0033-7587.  174(2), s 251- 257 . doi: 10.1667/RR2035.1 Vis sammendrag

  Radical formation in polycrystalline lithium formate monohydrate after irradiation with gamma rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.7–3.9 and 110–164 keV/mm for gamma rays, protons and nitrogen ions, respectively. Doses between 5 and 20 Gy were given. The EPR reading (the area under the EPR absorption resonance) increased linearly with dose for all types of radiation. As the LET increased, the relative effectiveness (the EPR reading per dose relative to that for gamma rays) decreased, while the EPR line width increased. Track structure theory and modeling of detector effectiveness predicted the dosimeter response observed after proton and nitrogen-ion irradiation. A semi-empirical line broadening model including dipolar spin-spin interactions was developed that explained the dependence of the line width on LET. The findings indicate that the local radical density in lithium formate is increased after high-LET irradiation.

• Waldeland, Einar; Hörling, Magnus; Hole, Eli Olaug; Sagstuen, Einar & Malinen, Eirik (2010). Dosimetry of stereotactic radiosurgery using lithium formate EPR dosimeters. Physics in Medicine and Biology.  ISSN 0031-9155.  55(8), s 2307- 2316 . doi: 10.1088/0031-9155/55/8/012
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Van Doorslaer, Sabine; Waroquier, Michel & Callens, Freddy J. (2009). ENDOR and HYSCORE Analysis and DFT-Assisted Identification of the Third Major Stable Radical in Sucrose Single Crystals X Irradiated at Room Temperature. Physical Chemistry, Chemical Physics - PCCP.  ISSN 1463-9076.  11(7), s 1105- 1114 . doi: 10.1039/b816641b
• Krivokapic, Andre; Øhman, Kjell Tage; Nelson, William H.; Hole, Eli Olaug & Sagstuen, Einar (2009). Primary Oxidation Products of 5-Methylcytosine: Methyl Dynamics and Environmental Influences. Journal of Physical Chemistry A.  ISSN 1089-5639.  113(35), s 9633- 9640 . doi: 10.1021/jp904747j
• Lund, Anders; Sagstuen, Einar; Sanderud, Audun & Maruani, Jean (2009). Relaxation-Time Determination from Continuous-Microwave Saturation of EPR Spectra. Radiation Research.  ISSN 0033-7587.  172(6), s 753- 760 . doi: 10.1667/RR1890.1 Vis sammendrag

  Based on the theories of Portis and of Castner 50 years ago, different continuous-wave measurement procedures for analyzing the microwave saturation power dependence of inhomogeneously broadened EPR lines were developed. Although these procedures have been refined, they still use only a few selected points on the saturation curve. A non-linear least-squares procedure for analyzing the microwave-power dependence of inhomogeneously broadened lines using all data points on a saturation curve has been developed. This procedure provides a simple alternative method to obtain magnetic relaxation data when the more direct pulse-saturation techniques are not available or are less suitable. The latter includes applications of quantitative EPR such as dosimetry. Then microwave saturation data should be obtained under conditions similar to those used in the quantitative measurements, which are usually made on first derivative spectra recorded using continuous-wave spectrometers. Selected applications to benchmark literature data and within the field of EPR dosimetry are discussed. The results obtained illustrate that relaxation times comparable to those yielded by various pulse-saturation EPR techniques can be obtained. It appears as a systematic feature that, whenever the pulse EPR data are fitted using bi-exponential functions, the shortest relaxation times obtained are those that correspond best to those measured using the current continuous-wave saturation method.

• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Dimitrova, Anna; Sagstuen, Einar; Waroquier, Michel; Callens, Freddy & Callens, F (2008). Radiation-Induced Defects in Sucrose Single Crystals, Revisited: a Combined Electron Magnetic Resonance and Density Functional Theory Study. Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy.  ISSN 1386-1425.  69(5), s 1372- 1383 . doi: 10.1016/j.saa.2007.09.033
• De Cooman, Hendrik; Vanhaelewyn, Gauthier; Pauwels, Ewald; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy (2008). Radiation-Induced Radicals in Glucose-1-phosphate. I. Electron Paramagnetic Resonance and Electron Nuclear Double Resonance Analysis of in situ X-Irradiated Single Crystals at 77 K. Journal of Physical Chemistry B.  ISSN 1520-6106.  112(47), s 15045- 15053 . doi: 10.1021/jp804290e
• De Coomann, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Callens, F. & Waroquier, Michel (2008). Identification and Conformational Study of Stable Radiation-Induced Defects in Sucrose Single Crystals using Density Functional Theory Calculations of Electron Magnetic Resonance Parameters. Journal of Physical Chemistry B.  ISSN 1520-6106.  112, s 7298- 7307 . doi: 10.1021/jp712004g
• Gancheva, V.; Yordanov, N.D.; Callens, F.; Vanhaelewyn, Gauthier; Raffi, J.; Bortolin, E; Onori, S.; Malinen, Eirik; Sagstuen, Einar; Fabisiak, S. & Stuglik, Zofia (2008). An international intercomparison on "self-calibrated" alanine EPR dosimeters. Radiation Physics and Chemistry.  ISSN 0969-806X.  77, s 357- 364 . doi: 10.1016/j.radphyschem.2007.06.004
• Gorbitz, Carl Henrik & Sagstuen, Einar (2008). Potassium sodium (2R,3R)-tartrate tetrahydrate: the paraelectric phase of Rochelle salt at 105 K. Acta Crystallographica Section E: Structure Reports Online.  ISSN 1600-5368.  64, s m507- m508 . doi: 10.1107/S1600536808005266
• Krivokapic, Andre; Herak, Janko N. & Sagstuen, Einar (2008). Proton-Coupled Hole Transfer in X-Irradiated Doped Crystalline Cytosine.H2O. Journal of Physical Chemistry A.  ISSN 1089-5639.  112, s 3597- 3606 . doi: 10.1021/jp709855c
• Pauwels, Ewald; De Cooman, Hendrik; Vanhaelewyn, Gauthier; Sagstuen, Einar; Callens, Freddy & Waroquier, Michel (2008). Radiation-Induced Radicals in Glucose-1-phosphate. II. DFT Analysis of Structures and Possible Formation Mechanisms. Journal of Physical Chemistry B.  ISSN 1520-6106.  112(47), s 15054- 15063 . doi: 10.1021/jp804287c
• Tarpan, Michaela; Sagstuen, Einar; Pauwels, Ewald; Vrielinck, Henk; Waroquier, Michel & Callens, F. (2008). Combined Electron Magnetic Resonance and Density Functional Theory Study of 10 K X-Irradiated β-D-Fructose Single Crystals. Journal of Physical Chemistry A.  ISSN 1089-5639.  112, s 3898- 3905
• Vrielinck, Henk; De Cooman, Hendrik; Tarpan, Michaela Adeluta; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy (2008). Schonland ambiguity in the electron nuclear double resonance analysis of hyperfine interactions: Principles and practice. Journal of magnetic resonance (San Diego, Calif. 1997 : Print).  ISSN 1090-7807.  195(2), s 196- 205 . doi: 10.1016/j.jmr.2008.09.017
• Øhman, Kjell Tage & Sagstuen, Einar (2008). Free Radical Conformations and Conversions in X-Irradiated Single Crystals of L-Cysteic Acid by Electron Magnetic Resonance and Density Functional Theory Studies. Journal of Physical Chemistry A.  ISSN 1089-5639.  112, s 4284- 4293 . doi: 10.1021/jp711821c
• Malinen, Eirik; Waldeland, Einar; Hole, Eli Olaug & Sagstuen, Einar (2007). The energy dependence of lithium formate EPR dosimeters for clinical electron beams. Physics in Medicine and Biology.  ISSN 0031-9155.  52, s 4361- 4369 . doi: 10.1088/0031-9155/52/14/022
• Gancheva, V.; Sagstuen, Einar & Yordanov, N.D. (2006). Study on the EPR/dosimetric properties of some substituted alanines. Radiation Physics and Chemistry.  ISSN 0969-806X.  75, s 329- 335 Vis sammendrag

  Polycrystalline phenyl-alanine and perdeuterated L-a-alanine (L-a-alanine-d4) were studied as potential high-energy radiation sensitive materials (RSM) for solid state/EPR dosimetry. It was found that phenyl-alanine exhibits a linear dose response in the dose region 0.1 - 17 kGy. However, phenyl-alanine is about 10 times less sensitive to gamma-irradiation than standard L-a-alanine irradiated at the same doses. Moreover, the EPR response from phenyl-alanine is unstable and, independent of the absorbed dose, decreases by about 50 % within 20 days after irradiation upon storage at room temperature. Gamma-irradiated polycrystalline perdeuterated L-a-alanine (CD<SUB>3</SUB>CD(NH<SUB>2</SUB>)COOH) has not previously been studied at room temperature by EPR spectroscopy. The first part of the present analysis was with respect to the structure of the EPR spectrum. By spectrum simulations the presence of at least two radiation induced free radicals; R1 = CH<SUB>3</SUB>C<SUP>•</SUP>(H)COOH and R2 = H<SUB>3</SUB>N<SUP>+</SUP>-C<SUP>•</SUP> (CH<SUB>3</SUB>)COO- , was confirmed very clearly. Both these radicals were suggested previously from EPR and ENDOR studies of standard alanine crystals. The further investigations into the potential use of alanine-d4 as RSM, after choosing optimal EPR spectrometer settings parameters for this purpose, show that it is ca. two times more sensitive than standard L-a-alanine.

• Malinen, Eirik; Waldeland, Einar; Hole, Eli Olaug & Sagstuen, Einar (2006). LET effects following neutron irradiation of lithium formate EPR dosimeters. Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy.  ISSN 1386-1425.  63, s 861- 869
• Sagstuen, Einar; Close, David M.; Vågane, Randi; Hole, Eli Olaug & Nelson, William H. (2006). Electron Transfer in Amino Acid:Nucleic Acid Base Complexes:EPR, ENDOR and DFT Study of X-Irradiated N-Formylglycine:Cytosine Complex Crystals. Journal of Physical Chemistry A.  ISSN 1089-5639.  110(28), s 8653- 8662
• Vanhaelewyn, Gauthier; Pauwels, Ewald; Callens, F.; Waroquier, Michel; Sagstuen, Einar & Matthys, Paul (2006). Q-band EPR and ENDOR of low temperature X-irradiated beta-D-fructose single crystals. Journal of Physical Chemistry A.  ISSN 1089-5639.  110, s 2147- 2156
• Øhman, Kjell Tage; Sanderud, Audun; Hole, Eli Olaug & Sagstuen, Einar (2006). Single Crystals of L-O-Serine Phosphate X-Irradiated at Low Temperatures: EPR,ENDOR, EIE, and DFT Studies. Journal of Physical Chemistry A.  ISSN 1089-5639.  110, s 9585- 9596 . doi: 10.1021/jp061265o

Se alle arbeider i Cristin

• Sagstuen, Einar & Hole, Eli Olaug (2009). Radiation Induced Radicals. In: Electron Paramagnetic Resonance: A Practitioner’s Toolkit. John Wiley & Sons.  ISBN 978-0-470-25882-8.  57 s.

Se alle arbeider i Cristin

• Hole, Eli Olaug; Edin, Nina Frederike J; Malinen, Eirik; Pettersen, Erik O & Sagstuen, Einar (2017). Biophysics and medical physics at UiO: Research and education. An incomplete overview..
• Papoutsis, iosif; Arnesen, Marius Røthe; Sande, Erlend P. S.; Sagstuen, Einar; Knudtsen, Ingerid Skjei & Malinen, Eirik (2017). From dose prescription to dose delivery - can dose painting by numbers be accurately delivered?.
• Sagstuen, Einar; Malinen, Eirik; Futsæther, Cecilia Marie & Hole, Eli Olaug (2017). Solid state dosimetry using the amino acid alanine: in quest for the third alanine radical using multivariate analysis..
• Henriksen, Thormod & Sagstuen, Einar (2016). Fysikk fra medisinsk diagnostikk til samfunnssikkerhet. Fra Fysikkens Verden.  ISSN 0015-9247.  (2), s 48- 54
• Sagstuen, Einar; Sanderud, Audun; Lund, Anders & Maruani, Jean (2016). Software for Relaxation-Time Determination from CW Microwave Saturated EPR Signals. Vis sammendrag

  Abstract: A non linear least-squares procedure for analyzing the microwave power dependence of inhomogeneously broadened lines using all data points on a saturation curve has been developed. The procedure provides a simple alternative method to obtain magnetic relaxation data when the more direct pulse saturation techniques are not available or are less suitable. A previously developed Fortran program has been updated and a Matlab version has been prepared. The performance of the software, available at http://www.liu.se/simarc/downloads/?l=en, has been examined by comparison with experimental data.

• Krivokapic, Andre; Aalbergsjø, Siv Gundrosen; Sanderud, Audun; Hole, Eli Olaug & Sagstuen, Einar (2015). Radiation chemistry of the EPR dosimeter lithium formate monohydrate.
• Wiedmer, David; Tiainen, Hanna; Sagstuen, Einar & Haugen, Håvard Jostein (2015). TiO2 nanoparticles as antibacterial debridement strategy for permanent infected dental implants.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Van Yperen-De Deyne, Andy; Van Speybroeck, Veronique & Sagstuen, Einar (2014). A method for investigating radiation damage.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Van Yperen-De Deyne, Andy; Van Speybroeck, Veronique & Sagstuen, Einar (2014). Radiation induced damage in biomolecules. An ab initio molecular dynamics study on crystalline α-L-rhamnose.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Van Yperen-De Deyne, Andy; Van Speybroeck, Veronique & Sagstuen, Einar (2014). ab initio molecular dynamics simulations of radiation induced radical formation.
• Krivokapic, Andre; Aalbergsjø, Siv Gundrosen; Hole, Eli Olaug; Nelson, William H. & Sagstuen, Einar (2014). Radiation physics of the EPR dosimeter lithium formate.
• Øyen, Live Furnes; Aalbergsjø, Siv Gundrosen; Knudtsen, Ingerid Skjei; Hole, Eli Olaug & Sagstuen, Einar (2014). Primary radiation-induced radicals in l-asparagine monohydrate at 6 K: EMR and DFT-PBC studies.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; De Cooman, Hendrik; Hole, Eli Olaug & Sagstuen, Einar (2013). Understanding selective radical formation in biomolecules after irradiation.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; De Cooman, Hendrik; Hole, Eli Olaug & Sagstuen, Einar (2013). Why are only certain radicals formed in sugars after irradiation?.
• Sagstuen, Einar (2013). EPR spectroscopy at the University of Oslo.
• Sagstuen, Einar; Gustafsson, Håkan; Waldeland, Einar; Lund, Anders; Hole, Eli Olaug & Malinen, Eirik (2013). Photon and hadron dosimetry by EPR methods: LET dependence of EPR response function.
• Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Hole, Eli Olaug & Sagstuen, Einar (2012). "Seeing" the molecules - using DFT calculations and periodiv boundary conditions.
• Krivokapic, Andre; Aalbergsjø, Siv Gundrosen; Malinen, Eirik; De Cooman, Hendrik; Hole, Eli Olaug & Sagstuen, Einar (2012). Lithium formate - a challenging low-dose radiation dosimeter.
• Sagstuen, Einar (2011). Developing Physics. Public Service Review: European Science & Technology.  (10), s 111- 112
• Aalbergsjø, Siv Gundrosen; De Cooman, Hendrik; Hole, Eli Olaug; Sagstuen, Einar & Pauwels, Ewald (2010). DFT and TD-DFT studies of deprotonation from oxygen in rhamnose cations.
• Aalbergsjø, Siv Gundrosen; De Cooman, Hendrik; Hole, Eli Olaug; Sagstuen, Einar & Pauwels, Ewald (2010). Deprotonering fra oksygen i rhamnose kationer studert ved DFT og TD-DFT metoder.
• De Cooman, Hendrik; Aalbergsjø, Siv Gundrosen; Pauwels, Ewald; Sagstuen, Einar; Hole, Eli Olaug; Callens, Freddy J. & Waroquier, Michel (2010). Which role do excited states play in radiation damage to organic solid-state compounds?.
• De Cooman, Hendrik; Tarpan, Michaela; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy J. (2010). Exploring the direct-effect radiation chemistry of solid-state carbohydrates using EMR and DFT.
• Gjøvik, Marie; Malinen, Eirik; Sagstuen, Einar & Hole, Eli Olaug (2010). Lithium formate in EPR dosimetry: The story continues.
• Waldeland, Einar; Hole, Eli Olaug; Sagstuen, Einar & Malinen, Eirik (2010). Energy dependence of alanine and lithium formate EPR dosimeters and LiF TL-dosimeters.
• Waldeland, Einar; Hole, Eli Olaug; Sagstuen, Einar & Malinen, Eirik (2010). Energy response to medium-energy X-rays for alanine and lithium formate EPR dosimeters.
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Callens, Freddy J. & Waroquier, Michel (2009). Modelling radiation-damage processes in organic solids via DFT calculations of EMR parameters.
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy J. (2009). Radiation-induced radical formation in solid state sugars: a review of recent EMR and DFT results.
• De Cooman, Hendrik; Vrielinck, Henk; Pauwels, Ewald; Sagstuen, Einar; Waroquier, Michel & Callens, Freddy J. (2009). Thermally activated reactions of radiation-induced radicals in sugar single crystals: an electron magnetic resonance and DFT study.
• Krivokapic, Andre; Øhman, Kjell Tage; Hole, Eli Olaug; Nelson, William H. & Sagstuen, Einar (2009). Primary Oxidation Radical in X-irradiated 5-Methylcytosine; Hindered rotation of Methyl group.
• Pauwels, Ewald; Hole, Eli Olaug; Sagstuen, Einar & Waroquier, M (2009). Elucidation of radiation-induced processes using DFT calculations.
• Sagstuen, Einar (2009, 08. oktober). Vinnere og tapere i norsk forskning.  Morgenbladet.
• Stølen, Svein & Sagstuen, Einar (2009). Budsjettkutt truer klimadrøm. Dagens næringsliv.  ISSN 0803-9372.
• Stølen, Svein & Sagstuen, Einar (2009). Finansieringsordning truer miljøforskningen. Uniforum.  ISSN 1891-5825.
• Tarpan, Michaela; De Cooman, Hendrik; Vrielinck, Henk; Pauwels, Ewald; Waroquier, Michel; Sagstuen, Einar & Callens, Freddy J. (2009). Combined electron magnetic resonance study and density functional theory study of thermally induced. free radical reactions in fructose and trehalose single crystals.
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Waroquier, Michel & Callens, F. (2008). Radicals in sucrose single crystals induced by X-rays at different temperatures: a combined EPR and DFT study. Radioprotection - Revue de la Societé Francaise de Radioprotection.  ISSN 0033-8451.  43(5), s 223
• De Coomann, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Sagstuen, Einar; Waroquier, Michel & Callens, F. (2008). Radicals induced in sucrose single crystals by X-irradiation: unravelling radical formation mechanisms using EMR experiments and DFT calculations.
• Hole, Eli Olaug; Gjøvik, Marie E.; Grøvik, Endre; Paulsen, Kristin; Fetene, Deneke & Sagstuen, Einar (2008). Stabilisering av radikaler i litiumformat for lav-dose EPR spektroskopi.
• Knudtsen, Ingerid Skjei; Hole, Eli Olaug & Sagstuen, Einar (2008). Strålingsindusert radikaldannelse i enkrystaller av l-asparagin monohydrat ved 295 K.
• Krivokapic, Andre & Sagstuen, Einar (2008). Methyl group tunneling rotation in the primary electron loss product in X-irradiated 5-methylcytosine.
• Krivokapic, Andre; Øhman, Kjell Tage; Hole, Eli Olaug; Nelson, William H. & Sagstuen, Einar (2008). Primary oxidation radical in X-irradiated 5-methylcytosine, a mutational hotspot in DNA. Radioprotection - Revue de la Societé Francaise de Radioprotection.  ISSN 0033-8451.  43(5), s 133
• Olsen, Bård; Sagstuen, Einar & Hole, Eli Olaug (2008). Strålingsinduserte radikaler i enkrystaller av L-arginine monofosfat monohydrat ved 295 K og 77 K.
• Pauwels, Ewald; Sagstuen, Einar; Hole, Eli Olaug & Waroquier, Michel (2008). Elucidation of radiation induced processes in alanine using DFT calculations.
• Øhman, Kjell Tage & Sagstuen, Einar (2008). A cluster DFT study of the decarboxylation radical in single crystals of l-cysteic acid monohydrate.
• De Cooman, Hendrik; Pauwels, Ewald; Vrielinck, Henk; Dimitrova, Anna; Yordanov, N.D.; Sagstuen, Einar; Waroquier, Michel & Callens, F. (2007). Radiation-Induced Defects in Sucrose Single Crystals, Revisited: a Combined Electron Magnetic Resonance and Density Functional Theory Study.
• Krivokapic, Andre; Herak, Janko N. & Sagstuen, Einar (2007). Long-range Proton-Coupled Electron- and Hole Transfer between DNA Components in the solid State.
• Sagstuen, Einar & Hole, Eli Olaug (2007). Radiation Physics and Chemistry in Oslo.
• Øhman, Kjell Tage & Sagstuen, Einar (2007). Calculation of Carboxylic Anion Hyperfine Couplings and Determination of Molecular Conformation by Computational Chemistry.
• Eldevik, Kristine; Sagstuen, Einar & Hole, Eli Olaug (2006). Radikaldanning i røntgenbestrålte einkrystaller av N-acetyl-L-tyrosin. EPR, ENDOR, EIE of DFT studiar.
• Hole, Eli Olaug; Malinen, Eirik; Vestad, Tor Arne; Waldeland, Einar & Sagstuen, Einar (2006). Is Lithium Formate an Alternative to Alanine at Low Doses?.
• Krivokapic, Andre & Sagstuen, Einar (2006). Proton-coupled Hole Transfer between DNA Components in the Solid State.
• Sagstuen, Einar; Hole, Eli Olaug; Close, David M.; Vågane, Randi & Nelson, William H. (2006). Stråleskader i DNA:proteinkomplekser.
• Sagstuen, Einar; Hole, Eli Olaug; Vågane, Randi & Nelson, William H. (2006). Radiation induced spin transfer in model DNA:protein complexes.
• Sagstuen, Einar; Malinen, Eirik; Vestad, Tor Arne; Waldeland, Einar & Hole, Eli Olaug (2006). Development of a solid state EPR dosimeter for low radiation doses.
• Sagstuen, Einar; Malinen, Eirik; Vestad, Tor Arne; Waldeland, Einar & Hole, Eli Olaug (2006). Lithium Formate as a Low-Dose EPR Radiation Dosimeter.
• Vanhaelewyn, Gauthier; Sagstuen, Einar & Callens, F. (2006). Electron magnetic resonance of radiation-induced radicals in sugar compounds relevant for radiation-induced damages in DNA.
• Øhman, Kjell Tage; Sanderud, Audun; Hole, Eli Olaug & Sagstuen, Einar (2006). Single crystals of l-o-Serine Phosphate X-irradiated at low temperatures: EOR, ENDOR, EIE and DFT studies.
• Sanderud, Audun; Vestad, Tor Arne & Sagstuen, Einar (2006). Strålingsinduserte radikaler i litium formate monohydrat. Vis sammendrag

  Formater (maursyre) har de siste årene blitt undersøkt med henblikk på å finne et EPR-dosimeter egnet for klinisk bruk (doser i cGy området). Polykrystallinske pellets av litium format monohydrat (LiHCO2·H2O) blitt sett på som den mest lovende kandidat, med mulighet for å måle doser under 0.1 Gy og med effektivt atomnummer på 7.31, nært det for vann. En EPR og ENDOR-studie av bestrålte enkrystaller Li-format har fastslått at EPR-spektret til bestrålt Li-format hovedsaklig skyldes •CO2¯-radikalet, Radikal I, men at spektret også må inneholde ett eller flere minoritets-radikaler. For bedre å forstå Li-format sine egenskaper som EPR-dosimeter har det blitt utført nye undersøkelser for å fastslå minoritets-radikalenes struktur og opphav. Enkrystaller av Li-format har blitt bestrålt ved romtemperatur og undersøkt med EPR og ENDOR spektroskopi ved 200 K kort tid (noen dager) etter bestråling. Krystallene har deretter blitt lagret ved romtemperatur og i dagslys i 8 måneder for deretter igjen å bli undersøkt med EPR ved romtemperatur. I tillegg har det blitt gjennomført en lav-temperatur ENDOR-studie der krystaller har blitt bestrålt og undersøkt ved 80K for deretter å ha blitt varmet opp og undersøkt ved romtemperatur. I de nye enkrystall-studiene har det ved romtemperatur blitt observert to minoritetsradikaler, Radikal II og III, i tillegg til hoved-radikalet. Hovedradikalet, Radikal I, observeres allerede ved 80K sammen med minst tre andre ukjente radikaler som forsvinner ved oppvarming. Radikal II og III dannes først ved oppvarming til romtemperatur. Etter lagring har Radikal I forsvunnet og EPR-spektret består hovedsakelig av spektrene fra Radikal II og III. Assosiert til Radikal II er en Li-hyperfin-kobling. I tillegg ga de lagrede krystallene mulighet for å bestemme g-tensoren til dette radikalet. Selv med disse parameterne er det ikke fastslått noen radikalstruktur for Radikal II. For Radikal III er en proton hyperfinkobling av α-type bestemt. Denne koblingen stemmer god overens med tensoren assosiert med O(•CH)-OCOO2-2-radikalet observert i bestrålt Na-format.

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