Nitroxide Free Radicals Research Articles

When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical.

Joint refinement of X-ray and polarized neutron diffraction data has been carried out in order to determine charge and spin density distributions simultaneously in the nitronyl nitroxide (NN) free radical Nit(SMe)Ph. For comparison purposes, density functional theory (DFT) and complete active-space self-consistent field (CASSCF) theoretical calculations were also performed. Experimentally derived charge and spin densities show significant differences between the two NO groups of the NN function that are not observed from DFT theoretical calculations. On the contrary, CASSCF calculations exhibit the same fine details as observed in spin-resolved joint refinement and a clear asymmetry between the two NO groups.

Nitroxide stable radicals interacting as Lewis bases in hydrogen bonds: A search in the Cambridge structural data base for intermolecular contacts

1125 X-ray structures of nitroxide free radicals presenting intermolecular hydrogen bonds have been reported in the Cambridge Structural Database. We will report in this paper a qualitative and quantitative analysis of these bonds. The observation in some plots of an excluded region was statistically analyzed using convex hull and kernel smooting methodologies. A theoretical study at the MP2 level with different basis has been carried out indicating that the nitronyl nitroxide radicals (five electrons) lie just in between nitroso compounds (four electrons) and amine N-oxides (six electrons) as far as hydrogen-bond basicity is concerned.

Aqueously Released Graphene Oxide Embedded in Epoxy Resin Exhibits Different Characteristics and Phytotoxicity of Chlorella vulgaris from the Pristine Form

The environmental release of nanoparticles is attracting increasing attention. Graphene oxide (GO) embedded in epoxy resin (ER) is a popular composite that has been used in various fields, but the environmental release of GO-ER composites and the effects on organisms in the environment remain unknown. The present work found that GO-ER composites in water for 2-7 days resulted in the release of 0.3-2.1% GO-ER at nanoscale (2-3 nm thickness and approximately 70-130 nm lateral length). Interestingly, pristine GO quenched 30-45% hydroxyl and 12% nitroxide free radicals, whereas this capacity was not observed for the released particles from GO-ER. At environmentally relevant concentrations (μg/L), released GO-ER particles, but not GO or ER matrix, promoted algal reproduction by 34% and chlorophyll biosynthesis by 65-127% at 96 h. Released GO-ER entered algal cells and induced a slight increase in reactive oxygen species but did not elicit notable cell structure damage. The upregulated amino acids and phenylalanine metabolism, and the downregulated fatty acid biosynthesis contributed to algal growth promoted by released GO-ER. Previous studies of pristine nanoparticles were unable to reflect the environmental effects of released nanoparticles into the environment, and our research on the exposure-toxicological continuum adds important contributions to this field.

A comparison between nitroxide and hydrazyl free radicals in selective alcohols oxidation

Literature data are abundant in oxidations catalyzed by nitroxides free radicals, while hydrazyls free radicals are very seldom encountered. In this work we made a comparison between some nitroxides and hydrazyl free radicals towards the ability to selectively oxidize activated alcohols to the corresponding carbonyl derivatives. As nitroxides we used 2,2,6,6-tetramethylpirrolidin-N-oxide (TEMPO) and phtalimide-N-oxyl (PINO) free radicals, while as hydrazyls were used 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-p-nitrophenyl-1-picrylhydrazyl (DN-DPPH). The differences in the physico-chemical properties between nitroxides and hydrazyls were evaluated by UV–vis, EPR and cyclic voltammetry. For DN-DPPH the X-ray crystal structure was resolved. It has been shown that a nitroxide radical is a far better catalyst in such aerobic oxidations comparatively with a hydrazyl one. The explanation of these results consists firstly in a different mechanism involved in the oxidation procedures and secondly in the variation of the oxidation potentials of nitroxides comparatively with hydrazyls.

Preparation of TEMPO-contained pyrrole copolymer by in situ electrochemical polymerization and its electrochemical performances as cathode of lithium ion batteries

Composite electrodes based on the nitroxide free radical-contained pyrrole copolymer (PPy-co-PPy-C-TEMPO) as active material were one-step synthesized by in situ electrochemical polymerization, which was then directly applied as the cathode of lithium ion batteries. The structure, morphology, electrochemical property, and charge-discharge performances of prepared copolymers were characterized by FTIR, SEM, cyclic voltammogram, electrochemical impedance spectroscopy, and galvanostatic charge-discharge testing, respectively. The results demonstrated that PPy-co-PPy-C-TEMPO-based composite cathodes have been successfully prepared by in situ electrochemical method, and the introduction of the nitroxide free radical (TEMPO) could obviously affect the morphology and electrochemical characteristics of the obtained electroactive polymers. And the charge/discharge tests showed that with the introduction of the TEMPO, PPy-co-PPy-C-TEMPO-based composite cathodes exhibited an improved specific capacity of 70.9 mAh g−1 for PPy-co-PPy-C-TEMPO (4:1) and 62.6 mAh g−1 for PPy-co-PPy-C-TEMPO (8:1) as measured at 20 mA g−1 between 2.5 and 4.2 V, which were remarkably higher than that of the pure PPy cathode of 41.0 mAh g−1 under the same experimental conditions. Also, the obtained PPy-co-PPy-C-TEMPO copolymers demonstrated an acceptable cycling stability during the charge-discharge process. These obtained cell performances for the composite cathodes were attributed to the application of the in situ electrochemical polymerization technology, which enhanced the intimate integration between conductive polymer film and electrode. Furthermore, the introduction of TEMPO-contained pyrrole (Py-C-TEMPO) improved the morphology of the composite cathode, which was in favor of the utilization of active materials and the improved electrochemical performances.

EPR Line Shifts and Line Shape Changes Due to Spin Exchange Between Nitroxide Free Radicals in Liquids 10. Spin-Exchange Frequencies of the Order of the Nitrogen Hyperfine Interaction: A Hypothesis.

The behavior of Electron paramagnetic resonance spectra due to 15N and 14N nitroxide free radicals undergoing spin exchange in liquids at high frequencies ωex , of the same order of magnitude as the nitrogen hyperfine coupling constant A0 is investigated. The well known features are reconfirmed: (1) at low values of ωex where the lines broaden, shift toward the center of the spectrum, and change shape due to the introduction of a resonance of the form of a dispersion component; (2) at values of ωex comparable to A0, the line merge into one; and (3) at values much larger than A0, the merged line narrows. It is found that each line of a spectrum may be decomposed into an admixture of a single absorption and a single dispersion component of Lorentzian shape. These two- or three-line absorption-dispersion admixtures, for 15N and 14N, respectively, retain their individual identities even after the spectrum has merged and has begun to narrow. For both isotopes, the average broadening and integrated intensities are equal to the predictions of perturbation theory although, in the case of 14N the outer lines broaden faster than the central line and intensity moves from the outer lines to the center line. In fact, the outer line intensity becomes zero and then negative at higher values of ωex which is compensated by the center line becoming more intense than the overall integrated intensity. For both isotopes, the dispersion components and the line shift depart from the perturbation prediction. The results are presented in terms of measurable quantities normalized to A0 so that they may be applied to any two- or three-line spectrum.

Nitroxide free radicals protect macular carotenoids against chemical destruction (bleaching) during lipid peroxidation

Macular xanthophylls (MXs) lutein and zeaxanthin are dietary carotenoids that are selectively concentrated in the human eye retina, where they are thought to protect against age-related macular degeneration (AMD) by multiple mechanisms, including filtration of phototoxic blue light and quenching of singlet oxygen and triplet states of photosensitizers. These physical protective mechanisms require that MXs be in their intact structure. Here, we investigated the protection of the intact structure of zeaxanthin incorporated into model membranes subjected to oxidative modification by water- and/or membrane-soluble small nitroxide free radicals. Model membranes were formed from saturated, monounsaturated, and polyunsaturated phosphatidylcholines (PCs). Oxidative modification involved autoxidation, iron-mediated, and singlet oxygen-mediated lipid peroxidation. The extent of chemical destruction (bleaching) of zeaxanthin was evaluated from its absorption spectra and compared with the extent of lipid peroxidation evaluated using the thiobarbituric acid assay. Nitroxide free radicals with different polarity (membrane/water partition coefficients) were used. The extent of zeaxanthin bleaching increased with membrane unsaturation and correlated with the rate of PC oxidation. Protection of the intact structure of zeaxanthin by membrane-soluble nitroxides was much stronger than that by water-soluble nitroxides. The combination of zeaxanthin and lipid-soluble nitroxides exerted strong synergistic protection against singlet oxygen-induced lipid peroxidation. The synergistic effect may be explained in terms of protection of the intact zeaxanthin structure by effective scavenging of free radicals by nitroxides, therefore allowing zeaxanthin to quench the primary oxidant, singlet oxygen, effectively by the physical protective mechanism. The redox state of nitroxides was monitored using electron paramagnetic resonance spectroscopy. Both nitroxide free radicals and their reduced form, hydroxylamines, were equally effective. Obtained data were compared with the protective effects of α-tocopherol, which is the natural antioxidant and protector of MXs within the retina. The new strategies employed here to maintain the intact structure of MXs may enhance their protective potential against AMD.

Graphene Quantum Dots Functionalized with 4-Amino-2, 2, 6, 6-Tetramethylpiperidine-N-Oxide as Fluorescence "Turn-ON" Nanosensors.

In this study, we report on the fabrication of simple and rapid graphene quantum dots (GQDs)-based fluorescence "turn-ON" nanoprobes for sensitive and selective detection of ascorbic acid (AA). Pristine GQDs and S and N co-doped-GQDs (SN-GQDs) were functionalized with 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4-amino-TEMPO, a nitroxide free radical). The nitroxide free radicals efficiently quenched the fluorescence of the GQDs and upon interaction of the nanoconjugates with ascorbic acid, the quenched fluorescence was restored. The linear ranges recorded were 0.5-5.7μM and 0.1-5.5μM for GQDs-4-amino-TEMPO and SN-GQDs-4amino-TEMPO nanoprobes, respectively. Limits of detection were found to be 60nM and 84nM for SN-GQDS-4-amino-TEMPO and GQDs-4-amino-TEMPO for AA detection, respectively. This novel fluorescence "turn-ON" technique showed to be highly rapid and selective towards AA detection.

Detailed Analysis of Manifestations of the Spin Coherence Transfer in EPR Spectra of 14N Nitroxide Free Radicals in Non-Viscous Liquids

Manifestations of the spin coherence transfer induced by the exchange and dipole–dipole interactions between spin probes in dilute solutions in the electron paramagnetic resonance (EPR) spectra have been studied. The perturbation theory of manifestations of the spin coherence transfer in the EPR spectra of nitroxide free radicals elaborated by one of the authors Salikhov (Applied Magnetic Resonance 38:237–256, 2010) has been generalized with allowance for the super hyperfine structure of the EPR spectra. For 14N nitroxide radicals, the total EPR spectrum was presented as a sum of three independent components in the case of slow and intermediate spin coherence transfer rates. The shapes of these components were found. The side components of the EPR spectrum contain the absorption and dispersion contributions and, as a result, have the asymmetric (mixed) shapes. These asymmetric components can be presented as J = Jabsorption ± pJdispersion. The p value is found for the arbitrary super hyperfine structure of the spectrum. In the slow and intermediate spin coherence transfer rate regime, the parameter p is independent of the super hyperfine interactions in the nitroxide radicals, but the shapes of Jabsorption and Jdispersion terms depend on the super hyperfine structure of the nitrogen components of the nitroxide EPR spectrum and on the spin coherence transfer rate. It is confirmed theoretically that a good strategy to evaluate the spin coherence transfer rate from the EPR spectra is using the dispersion contribution to the shape of the EPR spectra of nitroxide free radicals. An algorithm is suggested and tested for determining the spin coherence transfer and spin decoherence rates.

Covalently grafted TEMPO on graphene oxide: A composite material for selective oxidations of alcohols

4-Amino-TEMPO, a stable nitroxide free radical, was covalently grafted onto graphene oxides through an amide bond and the new composite solid materials thus obtained were characterized using scanning electron microscopy, thermal and elemental analysis, infrared, Raman and electron spin resonance spectroscopy. It was found that these materials can be successfully used as easily recoverable solid catalysts for selective oxidation of alcohols, using NOx as co-catalyst and oxygen as final oxidant, under very mild conditions.

DNP sensitivity of 19 F-NMR signals in hexafluorobenzene depending on polarizing agent type.

Low field dynamic nuclear polarization or low field magnetic double resonance technique enables enhanced nuclear magnetic resonance signals to be detected without increasing the strength of the polarizing field. The study reports that the dynamic nuclear polarization of 19 F nuclei in hexafluorobenzene solutions doped with nitroxide, BDPA, MC800 asphaltene and MC30 asphaltene free radicals at 15 G. The 19 F nuclei in all solutions gave positive DNP enhancements changing between 3.42 and 189.54, corresponding to predominantly scalar interactions with the unpaired electrons in the radicals. DNP sensitivity of 19 F nuclei in hexafluorobenzene was observed to be changed significantly depending on the radical type. Nitroxide was found to have the best DNP performance among the polarizing agents. Copyright © 2016 John Wiley & Sons, Ltd.

Photoluminescence Quenching of Colloidal CdSe and CdTe Quantum Dots by Nitroxide Free Radicals

Quantum dots (QDs) and other quantum confined semiconductor nanomaterials are emerging as an important class of materials for a variety of applications involving electronic processes. Here, we investigate QD–free radical interactions, focusing on II–VI semiconductor QDs (CdSe and CdTe) and TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and 4-amino-TEMPO (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl). Although these nitroxide free radicals have previously been shown to be efficient QD photoluminescence quenchers, we show here, using a combination of both steady-state and time-dependent photoluminescence studies, that some of these conclusions need to be revised. In particular, we show that TEMPO has no appreciable effect on the photoluminescence of II–VI QDs. Furthermore, we show that whereas 4-amino-TEMPO is indeed an efficient PL quencher for II–VI QDs (as previously reported) it is simultaneously limited by slow diffusion kinetics and low binding affinities to the nanocrystal surfaces. Our results highlig...

Melanin and humic acid-like polymer complex from olive mill waste waters. Part I. Isolation and characterization

A water soluble humic acid and melanin-like polymer complex (OMWW–ASP) was isolated from olive mill waste waters (OMWW) by ammonium sulfate fractionation to be used as natural additive in food preparations. The dark polymer complex was further characterized by a variety of biochemical, physicochemical and spectroscopic techniques. OMWW–ASP is composed mainly of proteins associated with polyphenols and carbohydrates and the distribution of its relative molecular size was determined between about 5 and 190kDa. SDS–PAGE shows the presence of a well separated protein band of 21.3kDa and a low molecular weight peptide. The OMWW–ASP complex exhibits a monotonically increasing UV–Vis absorption spectrum and it contains stable radicals. Antioxidant activity measurements reveal the ability of the OMWW protein fraction to scavenge both the cationic 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) radical, as well as the stable nitroxide free radical 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL).

An experimental NEXAFS and computational TDDFT and ΔDFT study of the gas-phase core excitation spectra of nitroxide free radical TEMPO and its analogues

Core-hole spectroscopy adds to the fundamental understanding of the electronic structure of stable nitroxide free radicals thus paving way for a sensible design of new analogues with desired functionalities. We study the gas-phase C 1s, N 1s and O 1s excitation spectra of three nitroxide free radicals - TEMPO and two of its amide-substituted analogues - using the experimental NEXAFS technique and the theoretical TDDFT and ΔDFT methods in the unrestricted setting. The short-range corrected SRC1-BLYP and SRC2-BLYP exchange-correlation functionals are used with TDDFT, and the standard B3LYP functional with ΔDFT. The TDDFT-based detailed spectral assignment includes the valence, mixed valence-Rydberg and Rydberg portions of the spectra from the onset of absorptions to the vicinity of the core-ionization thresholds. The relative overlaps between the experimental and TDDFT-modelled spectra are reasonably good, in the range of 0.7-0.8, 0.6-0.8, and 0.7-0.8 for the C 1s, N 1s, and O 1s spectra, respectively. The extent of spin contamination within the unrestricted framework and its effect on the accuracy of the calculated excitation energies and dipole intensities are discussed in detail. It is concluded that, despite the sizeable spin contamination, the presently used methods are capable of predicting the core-excitation spectra of comparatively large free radical species fairly reliably over a wide spectral range.

In vivo imaging of free radicals produced by multivitamin-mineral supplements.

BackgroundRedox active minerals in dietary supplements can catalyze unwanted and potentially harmful oxidations.MethodsTo determine if this occurs in vivo we employed electron paramagnetic (EPR) imaging. We used 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CPH) as a reporter for one-electron oxidations, e.g. free radical-mediated oxidations; the one-electron oxidation product of CPH, 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (CP•), is a nitroxide free radical that is relatively persistent in vivo and detectable by EPR. As model systems, we used research formulations of vitamin mineral supplements (RVM) that are typical of commercial products.ResultsIn in vitro experiments, upon suspension of RVM in aqueous solution, we observed: (1) the uptake of oxygen in the solution, consistent with oxidation of the components in the RVM; (2) the ascorbate free radical, a real-time indicator of ongoing oxidations; and (3) when amino acid/oligosaccharide (AAOS; glycinate or aspartate with non-digestible oligofructose) served as the matrix in the RVM, the rate of oxidation was significantly slowed. In a murine model, EPR imaging showed that the ingestion of RVM along with CPH results in the one-electron oxidation of CPH by RVM in the digestive system. The resulting CP• distributes throughout the body. Inclusion of AAOS in the RVM formulation diminished the oxidation of CPH to CP• in vivo.ConclusionsThese data demonstrate that typical formulations of multivitamin/multimineral dietary supplements can initiate the oxidation of bystander substances and that AAOS-complexes of essential redox active metals, e.g. copper and iron, have reduced ability to catalyze free radical formation and associated detrimental oxidations when a part of a multivitamin/multimineral formulation.

Electron spin echo envelope modulation of molecular motions of deuterium nuclei

Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy is a powerful technique for the study of hyperfine interactions between an unpaired electron and nearby nuclei in solids, and is employed in quantitative structural studies. Here, we describe the use of ESEEM to study the slow motion of deuterium nuclei using their nuclear quadrupole resonance (NQR) line shapes. Two ESEEM techniques were employed: the conventional three-pulse ESEEM experiment, π/2 – τ – π/2 – T– π/2 – τ – echo, and the four-pulse ESEEM, π/2 – τ – π/2 – T/2 – π – T/2 – π/2 – τ – echo, with the time variable T scanned in both cases. The nitroxide free radical 4-tert-butyliminomethyl-2,2,5,5-tetramethyl(d12)-3-imidazoline-1-oxyl with four deuterated methyl groups was investigated in a glassy ortho-terphenyl matrix over a wide temperature range. It was shown that four-pulse ESEEM allowed measurement of the nearly pure 2H NQR line shape. Between 90K and 120K, the ESEEM spectra change drastically. At low temperatures, four-pulse ESEEM spectra show a Pake-like pattern, which evolves into a single line at higher temperatures, which is typical for NQR of rotating methyl CD3 groups. Comparison with literature data on NQR allows estimation of the reorientation rate, k. At ∼100K, where the spectral changes are most pronounced, k was found to be ∼105s−1. The spectral linewidths for the three-pulse ESEEM were found to decrease similarly with increasing temperature; so the three-pulse technique is also capable to detect motion of this type. The ESEEM approach, along with site-directed spin labeling, may be useful for detection of motional transitions near the spin labels in biological systems, when information on motion is required in a wide temperature range.

Kinetic analysis of nitroxide radical formation under oxygenated photolysis: toward quantitative singlet oxygen topology.

Reaction kinetics for two sterically hindered secondary amines with singlet oxygen have been studied in detail. A water soluble porphyrin sensitizer, 5,10,15,20-tetrakis-(4-sulfunatophenyl)-21,23H-porphyrin (TPPS), was irradiated in oxygenated aqueous solutions containing either 2,2,6,6-tetramethylpiperidin-4-one (TMPD) or 4-[N,N,N-trimethyl-ammonium]-2,2,6,6-tetramethylpiperidinyl chloride (N-TMPCl). The resulting sensitization reaction produced singlet oxygen in high yield, ultimately leading to the formation of the corresponding nitroxide free radicals (R2NO) which were detected using steady-state electron paramagnetic resonance (EPR) spectroscopy. Careful actinometry and EPR calibration curves, coupled with a detailed kinetic analysis, led to a simple and compact expression relating the nitroxide quantum yield ΦR2NO (from the doubly-integrated EPR signal intensity) to the initial amine concentration [R2NH]i. With all other parameters held constant, a plot of ΦR2NOvs. [R2NH]i gave a straight line with a slope proportional to the rate constant for nitroxide formation, kR2NO. This establishment of a rigorous quantitative relationship between the EPR signal and the rate constant provides a mechanism for quantifying singlet oxygen production as a function of its topology in heterogeneous media. Implications for in vivo assessment of singlet oxygen topology are briefly discussed.

Terbium(III) and yttrium(III) complexes with pyridine-substituted nitronyl nitroxide radical and different β-diketonate ligands. Crystal structures and magnetic and luminescence properties.

A terbium(III) complex of nitronyl nitroxide free radical 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro1H-imidazolyl-1-oxy-3-oxide (NIT2Py), [Tb(acac)3NIT2Py]·0.5H2O (3) (acac = acetylacetonate), was synthesized for comparison with the previously reported [Tb(hfac)3NIT2Py]·0.5C7H16 (1) (hfac = hexafluoroacetylacetonate), together with their yttrium analogues [Y(hfac)3NIT2Py]·0.5C7H16 (2) and [Y(acac)3NIT2Py]·0.5H2O (4). The crystal structures show that in all complexes the nitronyl nitroxide radical acts as a chelating ligand. Magnetic studies show that 3 like 1 exhibits slow relaxation of magnetization at low temperature, suggesting single-molecule magnet behavior. The luminescence spectra show resolved vibronic structure with the main interval decreasing from 1600 cm(-1) to 1400 cm(-1) between 80 and 300 K. This effect is analyzed quantitatively using experimental Raman frequencies.

EPR line shifts and line shape changes due to Heisenberg spin exchange and dipole-dipole interactions of nitroxide free radicals in liquids: 9. An alternative method to separate the effects of the two interactions employing ¹⁵N and ¹⁴N.

A method to separate the effects of Heisenberg spin exchange (HSE) and dipole–dipole (DD) interactions on EPR spectra of nitroxide spin probes in solution by employing 15N and 14N nitroxide spin probes in parallel experiments is developed theoretically and tested experimentally. Comprehensive EPR measurements are reported of 4-oxo-2,2,6,6-tetramethylpiperidine-d16;1-15N-1-oxyl (perdeuterated 15N Tempone; 15pDT), in 70 wt % aqueous glycerol as functions of concentration and temperature. The method, termed the relative broadening constant method (RBCM), is demonstrated by using the present results together with those in the literature that employed perdeuterated 14N Tempone (14pDT) under identical conditions. In principle, the separation of DD and HSE is dependent on the model of diffusion and molecular-kinetic parameters; however, within present day experimental uncertainties, the RBCM method turns out to be insensitive to the model. The earlier methods to separate DD and HSE by measuring the dispersion component introduced by the two interactions shows general agreement with the RBCM; however, there are discrepancies larger than estimated uncertainties due to random errors. Thus, further support is found for Salikhov’s recent theory of the effects of DD and HSE on EPR spectra (Appl. Magn. Reson.2010, 38, 237); however, detailed confirmation is still lacking. The RBCM affords a possible approach to separate HSE and DD in spectra complicated by slow motion and/or overlap with other resonance lines, allowing the method to be used in situations more complicated than low-viscosity simple liquids.

Reliability of Density Functional and Perturbation Theories for Calculating Core-Ionization Spectra of Free Radicals

The C 1s, N 1s, and O 1s ionization energies were calculated for the three stable nitroxide free radicals, viz., tempo and its two analogues, and compared to their most recent high-resolution core photoelectron spectra. We compare the performance of unrestricted and restricted open shell based ΔHF, ΔMP2, and ΔB3LYP methods. A mixed basis set is employed in all cases, which consists of the core-valence correlation-consistent triple-ζ basis set (cc-pCVTZ or cc-pwCVTZ) on the atom whose core-electron binding energy is calculated, model core potentials on the remaining first row atoms, and the cc-pVDZ basis set on the hydrogen atoms. The best overall performance for the three free radicals is offered by the restricted open shell based ΔB3LYP method. Surprisingly, both the restricted open and unrestricted second-order perturbation theories perform relatively poorly and typically do not warrant additional computational effort over the reference ΔHF methods. This is particularly true of the ΔZAPT method, which exhibits a number of grave failures that render it unsuitable for calculating the core-ionization spectra.