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Bicarbonate and calcium set bounds on photosynthesis and degradation processes in calcareous freshwaters. Charophytic algae use bicarbonate in photosynthesis, and direct variable proportions to assimilate organic carbon and to precipitate calcium carbonate on their surfaces. To evaluate pools of organic carbon (Corg), carbonate carbon (Ccarbonate), and phosphorus (P) in dense charophyte vegetation, we studied apical and basal tissue and carbonate surface precipitates, as well as underlying sediments in ten calcareous ponds. We also quantified the release of calcium, bicarbonate and phosphate from charophyte shoots in dark experiments. We found that the Corg:Ccarbonate quotient in charophyte stands averaged 1.19 during spring and summer. The Corg:Ccarbonate quotient in the sediments formed by dead charophytes averaged 0.97 in accordance with some respiratory CO2 release without carbonate dissolution to bicarbonate. The molar quotient of carbon to calcium was close to 2.0 in sediment and pond water. In dark incubations, shoots subjected to calcium carbonate dissolution released bicarbonate and calcium with a molar quotient of 2:1; lowered pH (7.0–8.0) increased the release. Thus, the carbonate surface crust on living charophytes was not inert, as hitherto anticipated. Phosphate dark release occurred from basal shoots only, was unrelated to pH, and may have derived from organic decomposition, rather than from carbonate dissolution. Extensive phosphorus pools were associated with the charophyte stands (200–600 mg m−2) and had about 2/3 incorporated in alga tissue and 1/3 in carbonate crust. Overall, the biogeochemistry of carbon, calcium and phosphorus are closely linked in calcareous charophyte ponds. Carbonate dissolution from charophyte crusts at night and continuously from sediment might balance extensive carbonate precipitation during daytime photosynthesis. The substantial P-pool in charophyte stands may not derive from P-deprived water, but from P-rich sediment. Charophyte photosynthesis may still contribute to nutrient-poor conditions by forming carbonate-rich sediment of high P-binding capacity.

Naturally occurring antibodies are linked to inflammation, tissue injury and apoptosis, processes also linked to heart failure. Associations between antibodies, inflammation and myocardial damage, have not been elucidated in heart failure.We investigated if 25 antibodies to receptors expressed in the cardiovascular system were associated with troponin-T, biomarkers of inflammation and clinical measures of disease severity, in patients with heart failure.Antibodies in sera from patients (n=191) with ischemic (n=155) or non-ischemic (n=36) heart failure were measured with full-receptor sandwich enzyme-linked immunosorbent assays. All patients underwent coronary angiography with determination of left ventricular ejection fraction (LVEF) and left ventricular end-diastolic pressure (LVEDP). Measured biomarkers included troponin-T, C-reactive protein, erythrocyte sedimentation rate, fibrinogen and neopterin.Stabilin-1-antibodies correlated with troponin-T (β 0.23 p=0.008), soluble endoglin-antibodies with erythrocyte sedimentation rate (β 0.19, p=0.007) and fibrinogen (β 0.28, p0.001). Platelet-derived growth factor subunit β-antibodies were associated with neopterin (β 0.17, p=0.002). All antibodies were correlated (R 0.26 to 0.91) and formed 4 principal components (PCs). Patients with high CRP and high PC2 had higher NYHA class and patients with high troponin-T and high PC1 had lower LVEDP (interactions, all p0.05).Antibodies to receptors are correlated and are associated with biomarkers of inflammation and myocardial damage, which further modifies their association with disease severity in heart failure. Their functional activity and immunological function, remain undecided.

Dysregulation of the tryptophan (Trp)-NAD+ pathway has been related to several pathological conditions, and the metabolites in this pathway are known to influence mitochondrial respiration and redox status. The aim of this project was to investigate if stimulation of beta-oxidation and mitochondrial proliferation by the mitochondrial-targeted compound 2-(tridec-12-yn-1-ylthio)acetic acid (1-triple TTA) would influence metabolites of the Trp-Kyn-NAD+ pathway. We wished to investigate how carnitine depletion by meldonium-treatment influenced these metabolites. After dietary treatment of male Wistar rats with 1-triple TTA for three weeks, increased hepatic mitochondrial- and peroxisomal fatty acid oxidation resulted. The plasma content of total carnitines decreased compared to control animals, whereas hepatic genes involved in CoA biosynthesis were upregulated by 1-triple TTA treatment. The plasma Trp level and individual metabolites in the kynurenine pathway were increased by 1-triple TTA, associated with decreased hepatic gene expression of indoleamine2,3-dioxygenase. 1-triple TTA treatment increased conversion of Trp to nicotinamide (Nam) as the plasma content of quinolinic acid, Nam and N1-methylnicotinamide (mNam) increased, accompanied with suppression of hepatic gene expression of α-amino-α-carboxymuconate-e-semialdehyde decarboxylase. A positive correlation between mitochondrial fatty acid oxidation and Trp-derivatives was found. Almost identical results were obtained by 1-triple TTA in the presence of meldonium, which alone exerted minor effects. Moreover, the plasma Kyn:Trp ratio (KTR) correlated negatively to mitochondrial function. Whether increased flux through the Trp-NAD+ pathway increased redox status and lowered inflammation locally and systemically should be considered.

The structures of the free radicals formed by the irradiation of potassium dithionate (K2S2O6) with 60Co γ-rays and 14N7+ ions were investigated by EPR to further examine a recently proposed LET effect in this material. Two types of SO 3 − radical ions were identified in X-irradiated single crystals by measurements at X- and Q bands. One of these (S1) exhibited 33S hyperfine couplings A⊥ = 12.49, A|| = 15.60 mT, the other (S2) A⊥ = 11.29, A|| = 13.92 mT. The g-factors were nearly isotropic, g⊥ = 2.0010, g|| = 2.0003; and g⊥ = 2.0026, g|| = 2.0008, respectively. The 33S hyperfine coupling tensors and g-tensors were axially symmetric about the trigonal -axis, coinciding with the direction of the S–S bonds of the two non-equivalent S 2 O 6 2 − ions in the crystal. A model for the radiation damage was proposed in which the SO 3 − radical ions retain the orientation of the SO3 groups, aligned along the trigonal axis. The structure of a third main radical species (S3) with g⊥ = 2.0026, g|| = 2.0052 could not be unambiguously assigned, due to undetected 33S features. The relative integrated intensities of S1, S2 and S3 depended on the radiation quality and were approximately estimated as 0.18: 0.65:0.17 for 60Co γ-rays and 0.47: 0.38: 0.15 for 14N7+ ions. Additional weak lines on the low field side of the main signal were tentatively attributed to SO 2 − radical ions. An even weaker strongly anisotropic pair of lines was attributed to SO 3 − radical pairs separated by 0.93–0.95 nm along the trigonal axis.

A porous composite electrode of La0.8Sr0.2Cr0.97V0.03O3 − δ (LSCV) and yttria-stabilised zirconia (YSZ) was evaluated as a possible candidate for high-temperature potentiometric oxygen sensor measuring electrodes. The oxygen processes at the electrode were characterised by performing electrochemical impedance spectroscopy (EIS) measurements between 600 °C and 900 °C at oxygen partial pressures between 4.2×10 − 6 and 0.2 bar. The microstructure of the electrode was characterised by electron microscopy. The LSCV/YSZ electrode was porous and coherent with LSCV and YSZ grain sizes between 200 and 400 nm. At oxygen partial pressures around 0.2 bar at 700 °C, the oxygen reaction is dominated by solid-state diffusion of oxide ions and surface reaction kinetics. At oxygen partial pressures around 10 − 5 bar above 800 °C, gas phase mass transport processes dominate the impedance spectra. The relatively low response time at 700 °C at an oxygen partial pressure of around 5×10 − 6 bar and an inlet gas flow rate of 8 L h − 1 makes the LSCV/YSZ electrode suitable for use as an potentiometric oxygen sensor electrodes.

The electrochemical processes that limit the range of oxygen partial pressures in which potentiometric oxygen sensors can be used, were analysed using a theoretical and an experimental approach. Electrochemical impedance spectroscopy was performed on porous Pt/yttria stabilised zirconia (YSZ) electrodes between 10 −6 and 0.2 bar and at temperatures between 500 and 950 °C. The flow of oxide ions and electron holes through a sensor cell, with a YSZ electrolyte, were calculated under similar conditions. The oxygen permeation of the sensor cell was insignificant at an oxygen partial pressure of 10 −6 bar for an inlet flow rate higher than 2 L h −1 between 600 and 800 °C. The polarisation resistance measured between 10 −6 and 10 −4 bar was found to be inversely proportional to the oxygen partial pressure, nearly temperature independent and inversely proportional to the inlet gas flow rate, which shows that gas phase mass transport processes were dominating. The time constant of the gas phase mass transport processes was found to be inversely proportional to the oxygen partial pressure. The response time of these processes therefore limits the oxygen partial pressure range in which potentiometric oxygen sensors can be used.

With an increasing interest in using protons and light ions for radiation therapy there is a need for possibilities to simultaneously determine both absorbed dose (D) and linear energy transfer, LET, (LΔ). Potassium dithionate (K2S2O6) tablets were irradiated in a conventional 6 MV linear accelerator photon beam and a N7+ beam (E = 33.5 MeV/u) respectively. The EPR spectrum of irradiated potassium dithionate is a narrow doublet consisting of two signals, R1 and R2, with different microwave power saturation properties. On the basis of identification in related substances by EPR and ENDOR, these two signals are assigned to two non-equivalent SO3− – radicals. Our experiments showed that the ratios of these two lines (R1/R2) were clearly connected to beam LET. Irrespective of the mechanistic details this investigation suggests a new method for measurement of absorbed dose and beam LET by using potassium dithionate EPR dosimetry. Funding agencies|Swedish Cancer Society|4276-B05-07XBC

Patients respond differently to psychotropic drugs, and this is currently a controversial theme among psychiatrists. The effects of 16 psychotropics on cell membrane parameters have been reported. These drugs belong to three major groups used in therapeutic psychiatry: antipsychotics, antidepressants, and anxiolytic/hypnotics. Human platelets, lacking dopamine (D(2)) receptors (proposed targets of most psychotropics), have been used as a cell model. Here we discuss the effects of these drugs on three metabolic phenomena and also results from Langmuir experiments. Diazepam, in contrast to the remaining drugs, had negligible effects on metabolic phenomena and had no effects in Langmuir experiments. Psychotropic drugs may work through intercalation in membrane phospholipids. It is possible that the fluidity of membranes, rich in essential fatty acids, the content being influenced by diet, could be a contributing factor to the action of psychotropics. This might in turn explain the observed major differences in therapeutic response among patients.

The ESR spectrum of the chain-end radical RCF2CF2* detected in Nafion perfluorinated membranes exposed to the photo-Fenton reagent was accurately simulated by an automatic fitting procedure, using as input the hyperfine coupling tensors of the two F alpha and two F beta nuclei as well as the corresponding directions of the principal values from density functional theory (DFT) calculations. An accurate fit was obtained only for different orientations of the hyperfine coupling tensors for the two F alpha nuclei, indicating a nonplanar structure about the C alpha radical center. The fitted isotropic hyperfine splittings for the two F beta nuclei in the Nafion radical, 24.9 and 27.5 G, are significantly larger than those for the chain-end radical in Teflon (15 G), implying different radical conformations in the two systems. The excellent fit indicated that the geometry and electronic structure of free radicals can be obtained not only from single-crystal ESR spectroscopy, but also, in certain cases, from powder spectra, by combination with data from DFT calculations. The optimized structures obtained by DFT calculations for the CF3CF2CF2CF2* or CF3OCF2CF2* radicals as models provided additional support for the pyramidal structure determined from the spectral fit. Comparison and analysis of calculated and fitted values for the hyperfine splittings of the two F beta nuclei suggested that the radical detected by ESR in Nafion is ROCF2CF2*, which originates from attack of oxygen radicals on the Nafion side chain. The combination of spectrum fitting and DFT is considered important in terms of understanding the hyperfine splittings from 19F nuclei and the different conformations of fluorinated chain-end-type radicals RCF2CF2* in different systems, and also for elucidating the mechanism of Nafion fragmentation when exposed to oxygen radicals in fuel cell conditions.

Electron paramagnetic resonance (EPR) studies of X-irradiated lithium dithionate, Li 2 S 2 O 6 ·2H 2 O, doped with Ni and Rh have shown that these impurities enhance the yield of radicals formed by X-irradiation at room temperature. The signal in the doped samples, measured peak-to-peak of the single EPR derivative line attributed to the SO 3 − anion was about 3–4 times that of the pure lithium dithionate and more than 10 times stronger than the alanine signal. These impurities also shortened the spin-lattice relaxation time, T 1 , which gives the possibility to measure the doped samples at a higher microwave power. This implies that sensitivity could be further enhanced in the already sensitive EPR dosimeter material lithium dithionate.

Copper (II) phthalocyanine (CuPc) molecules encapsulated into zeolite-Y with Si/Al ratios of 2.7 and 410 were prepared by an in situ synthesis and characterized by UV-Vis and electron paramagnetic resonance (EPR) spectroscopies. Resolved Cu-hyperfine and N-superhyperfine structures were observed in the EPR spectrum of CuPc encapsulated into zeolite-Y with a high Si/Al ratio. UV-Vis and EPR studies as well as theoretical calculations suggest that the encapsulated CuPc molecule was distorted in zeolite-Y with keeping of the square-planar symmetry around the center copper (II) ion. © 2005 Elsevier B.V. All rights reserved.

Polycrystalline, formates and dithionates are promising materials for EPR dosimetry, as large yields of radiation induced stable radicals are formed with a linear dose response. Rapid spin relaxation rates were detected in many of the substances, indicating that a high microwave power can be applied during EPR acquisition in order to improve sensitivity. Different techniques used to further improve the sensitivity, such as the replacement of Li-7 with Li-6 or exchange of protons with deuterons in the corresponding crystalline matrices and metal ion doping are discussed. It is concluded that formates and dithionates may be up to 10 times as sensitive as L-alpha-alanine. (C) 2004 Elsevier Ltd. All rights reserved.

The geometric and electronic structure of the diphenylamine radical cation Ph2(H)N+ obtained by X-irradiation of diphenylamine in CFCl3 at low temperature have been studied by the methods of EPR an ...

Alanine EPR dosimetry has been applied successfully when measuring intermediate and high radiation doses. Although the performance of alanine dosimetry is being improved, the sensitivity of the material is too low for a fast and simple low- dose determination. Here we present the results using ammonium formate as an EPR dosimeter material. Ammonium formate is seven times more sensitive than alanine, using spectrometer settings optimized for the latter. Deuterated ammonium formate is found to be more than eight times more sensitive than alanine. Analysis of signal stability with time shows that the ammonium formate signal is stable by 5 min after irradiation and that no change in signal intensity is found during 8 days. The atomic composition of ammonium formate is closer to that of tissue than alanine, and thus the energy dependence is smaller than that of alanine at photon energies below 200 keV. Power saturation studies indicate that the energy transfer between the spins and the lattice is fast in ammonium formate, which gives the possibility of using high microwave power without saturation to further increase the sensitivity. These results suggest that ammonium formate has some important properties required of an EPR dosimeter for applications in dosimetry in the dose range typical for radiation therapy.

Amine radical cations of the type R3N·+ and [R3NCH2]·+, R=CH3, C3H7, and nitric oxide, NO, have been used to probe the bonding to the surface and the dynamics of the radicals trapped in the confined space of cages or channels in the zeolite. Regular continuous-wave electron spin resonance (ESR) was employed to study the internal motion of the cation radicals formed by γ-irradiation of amines and related ammonium ions, introduced during the synthesis of the zeolites Al-offretite, SAPO-37, SAPO-42 and AlPO4-5. The ESR spectra of [(CH3)3NCH2]·+ radical cation in several studied systems changed reversibly with temperature, indicating dynamical effects. Free rotation about the >N−CH2 bond of the [(CH3)3NCH2]·+ species was found to occur in the temperature range of 110 to 300 K, while the rotation about the >N−CH3 bonds was hindered. The observations confirm the theoretical prediction on the basis of density functional theory calculations, which indicate that the corresponding barriers are of the order of 0.3 and 7 kJ/mol, respectively. The radical cations of the type R3N·+ with R=C2H5, C3H7 were found to undergo a different type of dynamics, involving a two-jump process of the methylene hydrogens next to the nitrogen. A cage or channel size effect on the stability and molecular dynamics was inferred in some cases. Pulsed ESR was employed to study the (NO)2 triplet-state dimers in Na-A type zeolite, with the purpose to resolve the interaction with surface groups, and to elucidate the role of the zeolite on stabilizing the triplet rather than the usual singlet state. Measurements performed at 5 K gave rise to Fourier transform spectra that were assigned to the dimer species interacting with one or more23Na nuclei, with approximative parameters A(23Na)=(4.6, 4.6, 8.2) MHz and Q(23Na)=(−0.3, −0.3, 0.6) MHz for the hyperfine and nuclear quadrupole coupling tensors, respectively. The values are of similar magnitude as those determined for the NO−Na+ complex. The stability of the triplet-state structure was attributed to unusual geometric structure imposed by the zeolite matrix, with the N−O bonds along a line as in [O−N−Na+−N−O], which according to UHF ab initio calculations has a triplet ground

When single crystals of the 5-membered heterocyclic ring structure 2-oxazolidinone (C3O2NH5) are irradiated at room temperature, the major radical formed (R1) decays during a period of a few hours, leaving a broad, unstructured EPR spectrum not amenable to analysis. Cooling the crystals to about 140 K immediately after irradiation at room temperature allows analysis of the R1 radical by EPR and ENDOR. The radical is formed by a net H-abstraction from one of the two methylene groups of the molecule. A full EPR and ENDOR analysis of four proton interactions (one α-coupling, and three β-couplings) together with ESR evidence for a small nitrogen hyperfine interaction allowed for a precise identification of R1. The results show that the carbon-centered radical R1 is puckered at the radical center. Using DFT calculations together with the experimental EPR and ENDOR results, the torsion angle of the C1–H bond with respect to the N–C1–C2 plane is estimated to be 13–15° (bending angle θ ≈ 7°). The DFT calculations reproduced the carbon-bonded proton hyperfine coupling constants satisfactorily but failed to reproduce the experimental results for the nitrogen and nitrogen-bonded proton hyperfine interactions.

New materials for electron spin resonance (ESR) dosimetry have been investigated with the aim to find systems more sensitive than L-alanine accepted as a standard for high dose determinations. Among the investigated systems ammonium tartrate, 2-methylalanine, salts of formic acids and dithionates have been found to be more sensitive than alanine by a factor 2-10. The lower limit applies to tissue equivalent materials, while much higher sensitivities were obtained with formates and dithionates containing heavier atoms. The increased sensitivity was mainly attributed to suitable ESR properties of the room temperature stable radicals as regards spectral shape (narrow lines, little or no hyperfine structure) and microwave saturation properties (short relaxation times). The radical structures have when necessary been clarified by ENDOR spectroscopy, while the saturation properties have been screened by pulsed ESR measurements.

Local structures and motions of radical reactants in highly selective tunneling abstraction reaction in neopentane-ethane mixture are investigated with CW-ESR, ENDOR, and ESEEM spectroscopy at diff ...

Photoinduced isomerization of secondary alkyl radicals to primary alkyl radicals in glassy solids was studied by ESR spectroscopy. The efficiencies for 2-, 3- and 4-heptyl radicals in 77 K perdeuterated methylcyclohexane decrease in this order. Molecular orbital calculations indicate that the isomerization occurs through a hydride ion transfer from the methyl groups to the radical site in the lowest Rydberg state of secondary alkyl radicals. The dependence of its efficiency on the position of the radical site can be explained by variation of the negative charge at the methyl groups with the position of the radical site.

An EPR study was carried out to investigate both the structure and molecular dynamics of triethylamine (Et3N) and tripropylamine (Pr3N) radical cations generated in γ-irradiated AlPO4-5 from neutral mother molecules incorporated as an organic template. Both Et3N+• and Pr3N+• radical cations were stable at 300 K and showed strongly temperature-dependent EPR spectral line-shapes in the temperature range from 77 to 300 K. The spectral change was successfully explained by assuming a two-site exchange model in which two inequivalent β-hydrogens interchange their positions with each other. The experimental spectra were quantitatively analyzed by a simulation method using the exchange rate as a variable parameter. From an Arrhenius plot of the rate constants, activation energies of 9.1 and 11.4 kJ mol−1 were evaluated for Et3N+• and Pr3N+• in AlPO4-5, respectively.

An EPR study was carried out to elucidate the zeolite cage effect on the stability and molecular dynamics of [(CH3)3N]•+ and [(CH3)3NCH2]•+ radical cations generated in γ-irradiated Al-offretite, SAPO-37 and SAPO-42, which contained (CH3)4N+ ions as organic template. The [(CH3)3N]•+ radical cation was stable at room temperature when it was generated in relatively small size cages such as the sodalite cages of SAPO-37 and the β-cages of SAPO-42. On the other hand, the [(CH3)3NCH2]•+ radical cation was stable not only in the sodalite cages of SAPO-37, but also in relatively large cages such as gmelinite cages or the main channels of Al-offretite and the α-cages of SAPO-42. Strongly temperature dependent EPR spectra were observed for the [(CH3)3NCH2]•+ radical cation stabilized in Al-offretite and SAPO-42. They were successfully analyzed by a spectral simulation method assuming a three-site exchange for the methyl protons. The evaluated exchange rates were in the order SAPO-37 (sodalite cages)

Triplet state NO dimers stabilized on the surface of sulfated zirconia (g ⊥ =1.993, g ∥ =1.942, D ⊥ =195 G, E≈0 ) have been observed by ESR. They are formed by adsorption of NO molecules on pair (acceptor) surface sites represented, most likely, by two adjacent ( d =5.2 A) low-coordinated Zr 4+ ions. A new single line (Lorentz line with g =1.993 and line width 18 G) of NO monomers adsorbed on active sites of sulfated zirconia has been observed. The sites where this form is stabilized seem to be very strong electron acceptors responsible for the formation of radical cations after adsorption of aromatic molecules.

The alpha-proton hyperfine coupling observed by electron paramagnetic resonance (EPR) spectroscopy on the radical (CH)-C-.(COOH)(2) in irradiated crystals of malonic acid, CH2(COOH)(2), has served ...

In single crystals of malonic acid grown from heavy water, the methylene protons have been partially exchanged with deuterons. Upon X irradiation at room temperature, the (CD)-C-.(COOD)(2) radical is formed in an amount comparable to the (CH)-C-.(COOD): radical species. In the present work, EPR and ENDOR analyses of the a-deuteron hyperfine coupling (hfc) and nuclear quadrupolar coupling (nqc) tensors at room temperature have been performed. The hyperfine coupling tensor is, when scaled with the differences in the nuclear g-factor, almost identical to the a-proton coupling of the (CH)-C-.(COOH)(2) radical at room temperature. The quadrupolar coupling tensor was found to be virtually coaxial with the hyperfine coupling tensor. The quadrupolar coupling constant is 149.8 +/- 1 kHz, and the asymmetry factor eta = 0.092 +/- 0.020. It is known that, at room temperature, the malonic acid radical exhibits thermal motion between two potential energy minima separated by about +/-12 degrees. Assuming that the observed hfe and nqc tensors are the result of thermal avenging between these two conformations of the radical, a simple two-site jump model was used to estimate the rigid-limit tensors. The most significant result obtained was for the nyc tensor, for which the calculations resulted in a quadrupolar coupling constant of 160 kHz and an asymmetry factor eta = 0.026. These values are fairly close to the nqc parameters for the methylene deuterons in malonic acid at low temperature. The quadrupolar coupling tensor has been theoretically modeled using Slater orbitals and formal electronic populations, as well as electron populations obtained from RHF/CI INDO-type calculations. The simple model to compute the electric field gradient at the alpha-deuteron caused by the charge distribution at the sp(2)-hybridized alpha-carbon was found to be as successful as more advanced methods. Furthermore, density functional theoretical (DFT) calculations for both the malonic acid radical and the native malonic acid molecule have been performed. Field gradients calculated by the DFT method significantly overestimate the quadrupolar tensors for both the alpha-deuteron of the radical and the methylene deuterons of the malonic acid molecule. Calculations using electron populations from the RHF/CI INDO calculations show that contributions to the quadrupolar coupling tensor from electrons and nuclei beyond the nearest-neighbor atom of the Jeuteron are significant.

An EPR study was carried out to investigate the structure and motional dynamics of the [(CH3)3N–CH2]+• radical formed in a γ-irradiated Al-offretite. Strongly temperature-dependent EPR spectra were observed in the temperature range between 4 and 300 K. The observed 1H hyperfine (hf) splitting was a1=0.46 mT for three magnetically equivalent hydrogens, one of each methyl group at 110 K and a1′=0.15 mT for three of each methyl group at 300 K; the hf splittings due to two equivalent CH2 hydrogens and the central 14N were a2=2.24 and a3=0.35 mT, respectively, independent of the temperature. This result suggests that rotation of the methyl group around the N–CH3 bond is responsible for the temperature dependent line shapes. Assuming a three-site jump model in which three methyl protons interchange their positions with each other, the EPR line shapes were successfully analyzed by a simulation method using the jump rate as a variable parameter in the temperature range from 140 to 270 K. The rate was found to increase from 7.0×106 s−1 (140 K) to 4.1×108 s−1 (270 K) with temperature. From an Arrhenius plot of the rate constants, an activation energy of 8.1 kJ mol−1 was evaluated for the methyl group rotation of [(CH3)3N–CH2]+• in Al-offretite.

The structure and dynamics of the radical cations produced from benzene, monodeuterated benzene and toluene in various low-temperature matrices were characterized by EPR and ENDOR spectroscopy. It was found that the nature of the matrix had a dramatic effect on the EPR spectra of benzene cation. Rigid structures corresponding to the 2B1g and 2B2g states are revealed in solid argon and halocarbon (CFCl3) matrices, respectively, whereas only dynamically averaged patterns are observed in other hosts used (krypton, xenon, sulfur hexafluoride). Deuterium monosubstitution has no appreciable effect on the cation structure observed in argon and halocarbon matrices, which implies matrix control of the preferred electronic state. In contrast, the toluene radical cation exhibits only a 2B2g-like structure both in argon and in CFCl3 matrices, that is, the internal structural effect strongly predominates over environment effects in this case. The results are discussed in qualitative terms taking into consideration the matrix and substituent effects on the charge distribution in benzene cation.

The radical cations of methyl-substituted benzene toluene, p-xylene, o-xylene, m-xylene, and their deuterated analogues generated in CFCl3 and CF3CCl3 matrices by X-ray irradiation at 77 K were investigated by ESR and high-resolution ENDOR spectroscopy. The ESR and ENDOR spectra in these radical cations are dominated by large axially symmetric hyperfine splitting due to methyl-group protons. The anisotropic hyperfine coupling constants (hfcc) of methyl protons and ring protons in radical cations of toluene and p-xylene were measured accurately by ENDOR spectroscopy. In the case of deuterated p-xylene and o-xylene radical cations in CF3CCl3 matrix, the hyperfine coupling constants are scaled by their magnetogyric ratio (γH/γD = 6.51). Theoretical calculations of the isotropic and dipolar hyperfine coupling constants in these radical cations are found to be in good agreement with experimental results. The experimental and theoretical calculations supported the stabilization of the 2B2g type of state for the...

ENDOR investigations of the benzene radical cation in a CFCl3 matrix at 30 K gave evidence for a static Jahn–Teller distortion with the unpaired electron density predominantly in the 2 b 2g orbital. In this distortion the equivalence of the six protons is lost, with the major spin densities on H1 and H4. From ENDOR measurements the isotropic and dipolar couplings were accurately measured (aiso=−25.31 MHz (H1 and H4) and aiso=−5.43 MHz (H2, H3, H5 and H6)) which agree with those reported earlier from EPR measurements and theoretical calculations. (C6H6)2+., formed by warming in CFCl3 at 140 K and initially present in CF3CCl3, was characterised with ENDOR and assigned to a π-electron complex. The intermolecular distance was estimated from the measured dipolar hyperfine coupling to be in the range 2–3 A.

Single crystals of the amino acid analogue hippuric acid, PhCONHCH2COOH, have been X-irradiated at 295 K and studied using X-band EPR, ENDOR, and ENDOR-induced EPR (EIE) spectroscopy at 295 and 130 K. Two different radical species were observed and characterized. The dominant species is radical R1, PhCONH-•CH2, supposedly formed by net decarboxylation from a pristine oxidation product. The nitrogen hyperfine and quadrupolar interactions yield information on the electronic structure in the nitrogen valence orbitals. The second radical species, radical R2, is formed by a net hydrogen addition to the phenyl entity of hippuric acid. As a reduction product, it may be formed by protonation of the negatively charged anion of the phenyl group, but the alternative mechanism of direct hydrogen addition to the phenyl ring cannot be ruled out. Spectral simulations indicate that radical R1 contributes about 85% of the total EPR spectrum, while the remaining 15% is contributed by radical R2.

The naphthalene radical cation generated from the corresponding neutral compound by UV- or X-irradiation on H−ZSM-5 zeolite and in frozen CFCl3 solution has been studied by EPR, ENDOR, and ESEEM sp...

The electronic structure of trimethylenemethane (TMM) radical cation has been investigated by ESR spectroscopy and ab initio MO calculations. The 4.2 K ESR spectrum of TMM+ consists of a septet with isotropic 1H hf splittings of 0.93 mT (6 H) in a CF2ClCF2Cl matrix. The ESR lineshape did not change appreciably between 4 and 125 K. Ab initio MO calculations predict that TMM+ is a 2A2 state in a distorted C2v structure, in which the unpaired electron mainly resides in the pz orbitals of the two equivalent terminal carbons. The spectra were explained by intramolecular dynamics between the three energetically equivalent C2v structures to average the structural distortion giving an apparent D3h structure even at a low temperature of 4.2 K.

Two simultaneous dynamical processes are studied in solutions of varying viscosity by using the EPR linewidth data of a Cu(I) o-semiquinone complex with two triphenylphosphine ligands (PPh 3 ), i.e. the overall reorientation (tumbling) of the complex and intramolecular exchange of the PPh 3 ligands in the coordination sphere of the complex. It is shown that for fast motion the line broadening of the hyperfine components is due to both modulation of the anisotropic magnetic parameters by rotational diffusion and to modulation of the isotropic part of the 31 P hyperfine interaction by intramolecular exchange. The intramolecular dynamics of the coordination sphere appears to be dependent on the solvent dynamics.

For the title reaction, the pressure dependent rate coefficients were studied at 298 K using two complementary experimental techniques. Pulse radiolysis combined with UV absorption was employed at pressures between 500 and 1000 mbar, while a fast-flow system with a quadrupole mass spectrometer (at low ionization energies) was applied at pressures in the range of 0.7–5.1 mbar. The fall-off curve was constructed in terms of Troe's analysis, and the following high- and low-pressure limiting rate coefficients were derived: k rec,∞ = (1.3 ± 0.3) × 10 −10 × ( T /300) 0.42 cm 3 molecule −1 s −1 and k rec,0 /[ He ] = (1.8 ± 0.5) × 10 −25 × ( T /300) −3.85 cm 6 molecule −2 s −1 .

The biphenyl radical cation absorbed on H-ZSM-5 zeolite and silica gel and isolated in frozen CFCl3 has been studied by EPR and ENDOR spectroscopy. The recorded spectra can be explained by anisotropy of proton hyperfine interactions in para and ortho position and of the g-tensor. The experimental results indicate that the cation has a nearly planar structure, with a twist angle of less than 10°. The ENDOR spectra are analysed by computer simulations. A simple theory to calculate ENDOR transition moments to first order in disordered systems is presented. The simulations show that the observed ENDOR line positions correspond to principal hyperfine tensor values of the para and ortho ring protons.

The kinetics of the self-reaction and the reaction with OH of the amidogen radical were studied at 298 K by pulse radiolysis combined with UV detection of NH 2 and OH radicals at 597.7 and 309.0 nm. The rate constant for the association reaction of NH 2 radicals was found to be pressure dependent in the range 200–1000 mbar of SF 6 , and by Troe's analysis the following high- and low-pressure limiting rate constants were obtained: κ rec, ∞ (7.1 ± .8) × 10 10 ( T /300) 0.27 M −1 s −1 and κ rec, 0 /[SF 6 ]=(7.1 ± 1.5) × 10 12 ( T /300) −3.9 M −2 s −1 in the temperature range 200–400 K. For the reaction between NH 2 and OH radicals no pressure dependence was observed in the range 500–1000 mbar SF 6 , and the following high-pressure limiting rate constant was derived: (5.6 ± 1.0) × 10 10 ( T /300) 0.20 M −1 s −1 in the temperature range 200–400 K.

Single crystals of Rochelle salt, [(-)OOC-CHOH-CHOH-COO(-), Na(+) K(+)]center dot 4H(2)O, X-irradiated at 10 K, have been examined using EPR, ENDOR and EIE spectroscopic techniques to characterize the radiation induced radicals stable at that temperature and their reactions upon warming. The one-electron gain product was observed and from the hyperfine interaction with a beta-proton it was unambiguously centered at the C(4) position of the tartrate moiety. An additional nearly isotropic hyperfine structure of about 21 MHz was tentatively assigned to interaction with a sodium ion exhibiting a close contact to O(3) in the crystal. Evidence was obtained that the one-electron reduced radical had become protonated at one of the C(4) bonded carboxyl oxygens, most probably O(4). No evidence for the corresponding C(1)-centered reduction product was found. Two resonance lines (R2, A1) were shown by EIE to belong to a species formed by decarboxylation at C(3), a secondary oxidation product. Two other resonance lines (K1, K2) were assigned to two varieties of another decarboxylation radical, centered at C(2), distinguished by differences in the potassium ion coordination. Furthermore, one other resonance line (A2) was tentatively ascribed to a third decarboxylation radical, centered at the opposite end of the tartrate moiety. The precursor of these products, that is, the one-electron loss product, was not observed after X-irradiation at 10 K. Thermally induced free radical reactions followed by EPR in the temperature range of 12-119K indicate that a water molecule or a hydroxyl ion is eliminated from the one-electron reduction product radical and that a C(3)-centered radical is formed. The reduction and oxidation reaction pathways of hydroxy acid derivatives are discussed.

The catalytic activity of detonation nanodiamond and its modifications obtained through treatment with hydrogen or air at elevated temperatures is studied in the conversion of C(2)-C(3) alcohols. The catalysts were characterized by means of electron microscopy, optical (FTIR) spectroscopy, elemental analysis and pulse microcatalytic method. It has been established that nanodiamond exhibits high catalytic activity in the conversion of alcohols. The oxidizing and reducing treatment of nanodiamond changes its activity and selectivity, and the activity of oxidized nanodiamond is considerably higher than that of reduced nanodiamond. Funding Agencies|Swedish Institutes Visby program|00996/2008

The kinetics of the reaction CH 3 + OH (+M)→CH 3 OH(+M) was studied in the temperature range 283–373 K and in the pressure range 85–1000 mbar SF 6 by pulse radiolysis combined with UV absorption spectroscopy. The methyl and hydroxyl radical decays were followed by monitoring the transient UV absorption signals at 216.4 nm and 309.0 nm respectively. The reaction was studied in the fall-off region and by Troe's analysis the following high- and low-pressure limiting rate constants were obtained: k rec,∞ =(8.7±0.7)×10 10 ( T /300) 0.1 M −1 s −1 and k rec,0 /[SF 6 ]=(9.0±2.4)×10 14 ( T /300) −3.8 M −2 s −1 . The low-pressure limiting rate constant for the OH radical self-reaction was also derived: k OH+OH,0 /[SF 6 ]=(4.0±0.7)×10 11 ( T /300) −1.4 M −2 s −1 using the value of k OH+OH,∞ =1.8×10 10 ( T /300) −0.37 M −1 s −1 for the high-pressure limit.

A nonperturbative simulation of the temperature-dependent ESR lineshape of the anisotropic ⋅ CD 2 -COO − radical in the presence of exchange of the two deuterons has been performed in the diffusional region for this radical, e.g. 170–300 K. Both anisotropic hyperfine (hfi) tensors and considerable nuclear quadrupolar interactions (nqi) were necessary in the simulation of the rigid limit lineshape and the dynamics. By comparison with the earlier reported protonated case and for temperatures higher than 170 K no isotope effect was observed in the Arrhenius barrier of the hindered rotation, being 7.1 kcal/mol in both cases.

Trans-azobenzene dissolved in different liquid hydrocarbons absorbs fluorescence arising from all acceptors previously used in Fluorescence Detected Magnetic Resonance (FDMR) and Optically Detected ESR (OD ESR) spectroscopy making optical detection impossible. In this report a new acceptor,rubrene, having sufficient quantum yield of fluorescence in the red band 550–620 nm, has been proven successful. OD ESR spectra of the radical-ion pairtrans-azobenzene+/rubrene− were detected in liquid squalane (2,6,10,15,19,23-hexamethyl-tetracosane) solution in the temperature range 294–243 K. The experimental isotropic hyperfine splittings of the radical cation oftrans-azobenzene (a N=1.4 mT) have been compared with those from MNDO/INDO calculations and with those of earlier work using freon matrix studies.

Electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and electron spin echo, (ESE) spectroscopy have been used to characterise radical cations of benzene (benzene-d6 and benzene-d1), generated by ionising radiation, and stabilised on silica gel and HY molecular sieve surfaces. The electronic structure and dynamic features of the benzene cation were found to be different from those in the case of stabilisation in a Freon matrix (CFCl3). The monomeric cation was found to undergo pseudorotation at 3.5 K with hyperfine structure (h.f.s.) constants due to six averaged hydrogen nuclei. Simulations of the time-domain deuterium electron spin echo envelope modulation (ESEM) (C6D+6 cation) gave the following h.f.s. constants: the perpendicular component of the axially symmetric tensor T⊥ = −0.8 MHz, and the isotropic component a = 2.17 MHz, consistent with ENDOR results at 105 K. It was concluded that the monodeuterated benzene cation ‘slowed down’ the rotation at 3.5 K, although not enough to allow an analysis in the rigid limit. ENDOR spectra of the protonated and deuterated monomeric and dimeric benzene radical cations on silica gel and HY molecular sieve surfaces are presented. On HY molecular sieve the ENDOR results revealed two types of dimer, one stabilised at low temperature (below 110 K) characterised by h.f.s. constants of 4.8 and 8.9 MHz, and the other stabilised at higher temperatures with an h.f.s. constant of 6.5 MHz. Only the latter type of dimer could be detected on silica gel. In addition to hyperfine splittings from ring protons, a smaller hyperfine splitting attributed to hydroxyl protons situated on the surface was determined from the ENDOR results.

The geometric and electronic structure of the cyclopentane radical cation has been investigated, employing semiempirical (MNDO and INDO) calculations, as well as ab initio unrestricted Hartree—Fock (UHF), Moller—Plesset perturbation theory (MP2 to MP4) and configuration interaction (SDCI) methods. The intramolecular motion of C 5 H + 10 is discussed in terms of isodynamic groups. The present analysis shows that previous interpretations of the electron spin resonance (ESR) spectra of C 5 H + 10 must be reconsidered. Rather than an antisymmetric (A″) state in C s symmetry, as previously assumed, the calculations unequivocally show the ground state to be totally symmetric ( 2 A′ in C s or 2 A in C 2 symmetry), with the latter assignment being favoured by dynamical considerations especially in the fast-motion limit.

The electronic ground states of the 1- and 2-pentene radical cations have been studied by ab initio calculations at the UHF, MP2, and SDCI levels, as well as experimentally, using low-temperature matrix isolation electron spin resonance (ESR). The ESR spectra, recorded in halocarbon matrices at temperatures between 77 and 145 K, are reported together with calculated structural parameters, total energies, and isotropic hyperfine (hf) coupling constants. For the 1-pentene radical cation, the ESR spectrum is explained by a rigid, nonplanar structure where the two terminal aliphatic carbon atoms are rotated out of the plane of the allylic fragment by approximately 25 o

CW-ESR spectroscopy combined with matrix isolation method and ionizing radiation is applied to investigate structure and reactions of intermediate radicals in low temperature solid matrices. ESR parameters are predicted with considerable precision by computations, affording a valuable bridge between experiment and theory. Cyclic-CnF2n – radicals (n = 3–5) have a planar structure with an entirely delocalized singly occupied MO. Unsaturated CnF2n-2 – radicals have a distorted pyramidal structure occurring by mixing the π* and σ* orbitals. The acetylene anion has a trans-bent structure. Structural distortion occurs in methane cation from original T d to C 2v symmetry due to the Jahn-Teller effect. A similar symmetry lowering from D 3 h to C 2v is discussed for the trimethylenemethane cation. High-resolution ESR spectra of D-labelled methyl radicals in solid Ar are discussed in terms of nuclear spin-rotation couplings. The formation of “H—CH3” radical pairs and of a “H—H2” complex” in solid Ar is presented. The structure of [H2(H2)H2]+ formed in para-H2 is discussed based on the ESR spectra of D-substituted samples and on computations.

The electronic ground states of the 1- and 2-pentene radical cations have been studied by ab initio calculations at the UHF, MP2, and SDCI levels, as well as experimentally, using low-temperature matrix isolation electron spin resonance (ESR). The ESR spectra, recorded in halocarbon matrices at temperatures between 77 and 145 K, are reported together with calculated structural parameters, total energies, and isotropic hyperfine (hf) coupling constants. For the 1-pentene radical cation, the ESR spectrum is explained by a rigid, nonplanar structure where the two terminal aliphatic carbon atoms are rotated out of the plane of the allylic fragment by approximately 25 o

The CH 3 COOD − and CD 3 COOD − radical anions have been studied by ESR in irradiated crystal acetic acid in the temperature region 77–170 K. The line-shape variations which are due to methyl rotation are simulated with a program based on the Liouville direct method. The activation energy to the motion is evaluated and is found not to be appreciably affected by susbtitution of the methyl protons by deuterons. The activation energies are determined to be 2.2 and 2.5 kcal/mol respectively. Indications of hydrogen bond effects on the activation barrier are also found.

The effects of intrathecal administration of substance P and N-methyl-D-aspartate (NMDA) were studied in the formalin test in mice. Both substances were administered 5 min before injection of formalin into the hind paw. Co-administration of substance P and NMDA intensified the response in both the 1st (0-10 min) and the 2nd phase (20-30 min) of the formalin test, and increased the duration of the response. The increase in the response to formalin depended on the formalin concentration and was significant with 1% and 5% concentrations of formalin but not with a 0.05% concentration. No increase in the response was observed when NMDA or substance P was given alone. These findings indicate that concurrent activation of spinal NMDA and substance P receptors induces an enhancement of spinal transmission of nociception, and that this enhancement is dependent on the intensity or the quality of the peripheral stimulus.