Intense Singlet Research Articles

Synthesis, structure and some properties of 2-, 3-, 4-aminophenylacetic acids hexafluorosilicates

A method for the synthesis of new potential anti-caries agents, 2-, 3-, 4-aminophenylacetic acids hexafluorosilicates, whose ammonium cations contain a pharmacophore of anti-inflammatory activity, has been proposed. The composition and ionic structure of the synthesized compounds [2-, 3-, 4-HO(O)CCH2C6H4NH3]2SiF6 (I–III, respectively) were determined by the methods of elemental analysis, IR, 1H, 19F NMR, mass-spectrometry. In the IR spectra of I–III salts, the bands of valence and deformation vibrations of ammonium cations (NH3+), (NH3+) appear at 3179–2906 cm–1 and 1630–1619 cm–1; bands (SiF), (SiF2) of SiF62– anions are fixed at 774–703 cm–1, and 476–436 cm–1, respectively; and the doublet nature of (SiF2) vibrations in the I and II spectra may indicate a decrease in the anion geometry compared to the octahedral Oh. In the 19F NMR spectra of I–III aqueous solutions, intense singlet signals with characteristic values (19F) about –130 ppm and constants J(Si29–19F)=106.7 Hz, 107.3 Hz, and 107.9 Hz, respectively, correspond to SiF62– anions. The solubility of I–III in water, methanol, ethanol (96%) and dimethylsulfoxide was determined, the influence of the nature of the solvent and cation on the solubility characteristics of salts was characterized. For diluted (110–3, 110–4 mol/l) aqueous solutions of I–III, a decrease in the pH values to 3.38–3.70 was observed resulted from the hydrolysis process, a possible intermediate of which according to NMR 19F is an aqua-anion [SiF5(H2O)]–.

3, 3,5 and 2,6 Expanded Aza-BODIPYs Via Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions: Synthesis and Photophysical Properties.

Novel symmetrical aza-borondipyrromethene (aza-BODIPY) compounds bearing 4-methoxyphenyl, 4-methoxybiphenyl, 2,4-dimethoxybipheny, 4-bromophenyl and N,N-diphenyl-4-biphenylamine groups on the 3, 3,5 and 2,6 positions of aza-BODIPY core were synthesized via Suzuki-Miyaura coupling reactions while unsymmetrical analogues were obtained from the starting mono Br-substituted aza-BODIPY material which was obtained from nitrosolated pyrrole derivative. The characterizations were performed by means of 1H-NMR, 13C-NMR, FTIR and HRMS-TOF-ESI techniques. The spectral properties of the aza-BODIPY derivatives were investigated using absorption and fluorescence spectroscopy. The novel compounds with extended conjugation have broadband absorption in near infrared region and show significant shifts on their absorption and fluorescence spectra compared to unsubstituted analogues. The highest bathochromic shifts were observed π-extended and strong electron donating groups at 3,5 positions of the aza-BODIPY scaffold. Depend on substitution positions of attached groups to the indacene core, the fluorescence quantum yields of chromophores were determined to be drastic changes. The singlet oxygen generation capability of the compounds were evaluated and 2,6-bromine substituted compounds AA1 and CC1 showed high singlet oxygen quantum yields (71% and 74%, respectively). Enhanced photophysical properties such as intense absorption, extended conjugation and singlet oxygen production make the investigated aza-BODIPYs promising candidates for photodynamic therapy applications and organic photovoltaic cells in NIR region.

Synthesis and 19F NMR parameters of a perfluoro-tert-butoxy tagged L-DOPA analogue

The robust multistep synthesis of a perfluoro-tert-butoxy (PFTB) tagged analogue of the non-proteinogenic amino acid 3,4-dihydroxy-L-phenylalanine (L-DOPA) via diastereoselective benzylation of Oppolzer’s sultam glycinate was developed. The new compound is characterized by a flexible alkoxy linker connecting PFTB to the biochemically and pharmacologically relevant L-DOPA scaffold, which facilitates the free motion of the fluorinated moiety. Therefore, the nine chemically equivalent fluorine atoms give rise to an intense and sharp 19F NMR singlet signal that is easily detected in an aqueous environment. In addition, the kinetics of 19F NMR relaxation processes in blood solution fit the requirements for the potential use of the new compound as a probe in 19F magnetic resonance imaging applications in translational clinical field.

Enzyme‐Triggered Disassembly of Perylene Monoimide‐based Nanoclusters for Activatable and Deep Photodynamic Therapy

Photodynamic therapy (PDT) exhibits great potential for cancer therapy, but still suffers from nonspecific photosensitivity and poor penetration of photosensitizer. Herein, a smart perylene monoimide-based nanocluster capable of enzyme-triggered disassembly is reported as an activatable and deeply penetrable photosensitizer. A novel carboxylesterase (CE)-responsive tetrachloroperylene monoimide (P1) was synthesized and assembled with folate-decorated albumins into a nanocluster (FHP) with a diameter of circa 100 nm. Once P1 is hydrolyzed by the tumor-specific CE, FHP disassembles into ultrasmall nanoparticles (ca. 10 nm), facilitating the deep tumor penetration of FHP. Furthermore, such enzyme-triggered disassembly of FHP leads to enhanced fluorescence intensity (ca. 8-fold) and elevated singlet oxygen generation ability (ca. 4-fold), enabling in situ near-infrared fluorescence imaging and promoted PDT. FHP permits remarkable tumor inhibition in vivo with minimal side effects through imaging-guided, activatable, and deep PDT. This work confirms that this cascaded multifunctional control through enzyme-triggered molecular disassembly is an effective strategy for precise cancer theranostics.

Enzyme‐Triggered Disassembly of Perylene Monoimide‐based Nanoclusters for Activatable and Deep Photodynamic Therapy

AbstractPhotodynamic therapy (PDT) exhibits great potential for cancer therapy, but still suffers from nonspecific photosensitivity and poor penetration of photosensitizer. Herein, a smart perylene monoimide‐based nanocluster capable of enzyme‐triggered disassembly is reported as an activatable and deeply penetrable photosensitizer. A novel carboxylesterase (CE)‐responsive tetrachloroperylene monoimide (P1) was synthesized and assembled with folate‐decorated albumins into a nanocluster (FHP) with a diameter of circa 100 nm. Once P1 is hydrolyzed by the tumor‐specific CE, FHP disassembles into ultrasmall nanoparticles (ca. 10 nm), facilitating the deep tumor penetration of FHP. Furthermore, such enzyme‐triggered disassembly of FHP leads to enhanced fluorescence intensity (ca. 8‐fold) and elevated singlet oxygen generation ability (ca. 4‐fold), enabling in situ near‐infrared fluorescence imaging and promoted PDT. FHP permits remarkable tumor inhibition in vivo with minimal side effects through imaging‐guided, activatable, and deep PDT. This work confirms that this cascaded multifunctional control through enzyme‐triggered molecular disassembly is an effective strategy for precise cancer theranostics.

Amphiphilic Gemini Iridium(III) Complex as a Mitochondria-Targeted Theranostic Agent for Tumor Imaging and Photodynamic Therapy.

Clinical diagnostics and therapeutics of tumors are significantly benefitted by the development of multifunctional theranostic agents, which integrate tumor targeting, imaging, and therapeutics. However, the integration of imaging and therapy functionalities to a unimolecular framework remains a great challenge. Herein, a family of amphiphilic gemini iridium(III) complexes (GIC), Ir1-Ir6, are synthesized and characterized. The presence of quaternary ammonium (QA) groups endows GIC with adjustable water solubility and excellent self-assembly properties. Spectroscopic and computational results reveal that introducing QA groups into cyclometalating ligands (ĈN ligands) can overcome the drawback of aggregation-caused emission quenching and ensure Ir1-Ir3 with high emission intensity and excellent singlet oxygen (1O2) generation ability in aqueous media. Cell-based assays indicate that Ir3 shows higher cellular uptake efficiency and localizes specifically in the mitochondria, as well as exhibits outstanding photostability and an impressive phototoxicity index with satisfactory performance in mitochondria-targeted imaging and photodynamic therapy (PDT) of tumor cells. Furthermore, in vivo studies further prove that Ir3 possesses excellent antitumor activity and remarkably inhibits the growth of the HepG2 cells under PDT treatment. Consequently, this study presents a promising strategy for designing clinical application potential multifunctional iridium complex theranostic agents for mitochondria-targeted imaging and PDT in a single molecular framework.

DQF J-RES NMR: Suppressing the singlet signals for improving the J-RES spectra from complex mixtures.

Two-dimensional J-RESolved spectroscopy (J-RES) finds routine use in metabolomics for reducing signal overlap as it separates chemical shift and multiplet information along two frequency axes. However, only magnitude mode of the experiment is practical which prevents exploitation of its full resolving power. Tailing from high-intensity metabolite peaks often obscure nearby low-intensity metabolite peaks which leads to ambiguity in assignment of metabolites. Absorptive mode J-RES spectroscopy offers better-resolving power but comes at the cost of either sensitivity or complicated post-processing. Quite often for certain complex mixtures such as bio-fluids some components of the mixture display intense singlet signals which dominate the whole spectrum resulting in less reliable detection of weaker metabolite signals. Multi-frequency presaturation could suppress these intense singlets but will also remove the useful weaker multiplet peaks which are either totally eclipsed with the intense singlets or very close in frequency. We show that by using a double quantum filter (DQF) in magnitude mode J-RES technique, the intensity of the strong singlet metabolite peaks can be reduced relative to the intensity of the sparsely present multiplet metabolite signals. This approach leads to the identification of many weak intensity multiplet peaks which are otherwise undetected due to their overlap with intense singlet peaks in regular J-RES as well as 1D 1H spectra. Although the improved intensity of most of the weaker peaks relative to the strong singlet peaks is observed, some multiplets can disappear due to the delay-dependent modulation of the signals by the DQF. A few DQF J-RES spectra recorded with different DQF delays, therefore, produce better assignment when analyzed together. The technique is demonstrated on a mixture of eight compounds, human urine, and plant extract samples.

Stable, color-tunable 2D SCN-based perovskites: revealing the critical influence of an asymmetric pseudo-halide on constituent ions.

Two-dimensional (2D) layered perovskites (An+1BnX3n+1, n = 1, 2, …) have recently attracted significant research interest because of their enhanced ambient stability compared to their conventional 3D counterparts. In addition to the common A-site cation engineering, using an asymmetric pseudo-halide anion, SCN-, in the anion X-site has been recently proven to be another effective approach to constitute 2D perovskites. Among these, 2D (MA)2Pb(SCN)2I2 was the most widely investigated and was considered to be a promising material owing to its good optoelectronic properties; however, its poor stability has aroused concerns in recent researches. In this study, systematical composition engineering of A2Pb(SCN)2X2 (A = FA+, MA+, Cs+ and X = Br-, I-) was conducted. Our results revealed that the linear SCN- anion dictates critical restrictions on the constituent ions of its derived 2D framework (PbX4(SCN)2), which has not yet been extensively discussed. We demonstrated that using a smaller Cs+ cation can afford a more favorable 2D structure compared with the MA+ cation. Cs2Pb(SCN)2I2 was revealed to possess improved stability and photo-response compared to (MA)2Pb(SCN)2I2. Interestingly, Cs2Pb(SCN)2I2 and (MA)2Pb(SCN)2I2 appear to possess distinct electronic band structures. This is indicated by their discrepant photoluminescence spectra, in which the former exhibits a rather intense singlet emission at room temperature in contrast with the latter, which shows a dominant emission associated with triplet or defective states. Furthermore, using a smaller Cs+ cation enables facile replacement of a smaller halide anion. A series of mixed-halide 2D Cs2Pb(SCN)2(I1-xBrx)2 (x = 0, 1/3, 1/2, 2/3, 1) with varying vivid colors was explored by both calculation and experimental efforts to corroborate the enhanced stability when the x value increases. The results revealed in this study might represent a novel discovery of an inherent trait of the 2D SCN-based perovskites and also suggest that the all-inorganic 2D Cs2Pb(SCN)2X2 perovskite system is a promising class of materials with good stability and color-tunability that deserves further exploration.

Plasmonic enhancement of cyanine dyes for near-infrared light-triggered photodynamic/photothermal therapy and fluorescent imaging

Near-infrared (NIR) triggered cyanine dyes have attracted considerable attention in multimodal tumor theranostics. However, NIR cyanine dyes used in tumor treatment often suffer from low fluorescence intensity and weak singlet oxygen generation efficiency, resulting in inadequate diagnostic and therapy efficacy for tumors. It is still a great challenge to improve both the photodynamic therapy (PDT) and fluorescent imaging (FLI) efficacy of cyanine dyes in tumor applications. Herein, a novel multifunctional nanoagent AuNRs@SiO2-IR795 was developed to realize the integrated photothermal/photodynamic therapy (PTT/PDT) and FLI at a very low dosage of IR795 (0.4 μM) based on metal-enhanced fluorescence (MEF) effects. In our design, both the fluorescence intensity and reactive oxygen species of AuNRs@SiO2-IR795 nanocomposites were significantly enhanced up to 51.7 and 6.3 folds compared with free IR795, owing to the localized surface plasmon resonance band of AuNRs overlapping with the absorption or fluorescence emission band of the IR795 dye. Under NIR laser irradiation, the cancer cell inhibition efficiency in vitro with synergetic PDT/PTT was up to 82.3%, compared with 10.3% for free IR795. Moreover, the enhanced fluorescence intensity of our designed nanocomposites was helpful to track their behavior in tumor cells. Therefore, our designed nanoagents highlight the applications of multimodal diagnostics and therapy in tumors based on MEF.

How Metals Can Help Multiphotochromism: An Ab Initio Study

Dimers of dithienylethenes containing a metallic center in their bridging unit often exhibit a full and stepwise photochromism, and their photoactivity typically surpasses the majority of their metal-free counterparts that are often plagued by the impossibility to switch all units. In this work, we investigate five different photochromic dimers with a relativistic spin–orbit time-dependent density functional theory (SO-TD-DFT) approach and explore the possible sources of this enhanced photoactivity. In particular the potential intersystem crossing (ISC) from an intense singlet state in the UV region to a triplet state presenting the necessary topology to trigger the ring closing of the switch is unravelled in several cases. The efficiency of this crossing is found to be dependent on both the nature of the metallic center and the structure of the dithienylethene ligand but, in general, improves the probability for the second ring closing starting from the partially switched dimer. This work provides the fi...

Exposing the Excited‐State Equilibrium in an IrIII Bichromophore: A Combined Time Resolved Spectroscopy and Computational Study

AbstractThe electronic structure and photophysical properties of a luminescent IrIII bis‐cyclometalated complex covalently attached to one 4‐piperidinyl‐1,8‐naphthalimide (PNI) chromophore through a coordinated 1,10‐phenanthroline, [Ir(ppy)2(phen‐PNI)](PF6), is presented. This bichromophore represents a new class of visible light‐harvesting IrIII complexes that exhibit markedly enhanced room‐temperature excited‐state lifetimes (τ = 8.8 ms) as a result of intervening ligand‐centered triplet states present on the pendant naphthalimide chromophore. In this IrIII complex, the intense singlet fluorescence of the pendant PNI chromophore is nearly quantitatively quenched and was found to sensitize the IrIII metal/ligand‐to‐ligand charge‐transfer (MLLCT) excited state. The excited state ultimately returns to the PNI chromophore as a long‐lived excited triplet that disposes of its energy by equilibrating with the photoluminescent IrIII MLLCT excited state. Evidence of the excited‐state equilibrium is provided through static and dynamic photoluminescence spectroscopy, transient absorption spectroscopy, and time‐dependent density functional theory calculations.

Detection and original dose assessment of egg powders subjected to gamma irradiation by using ESR technique

Abstract ESR (electron spin resonance) techniques were applied for detection and original dose estimation to radiation-processed egg powders. The un-irradiated (control) egg powders showed a single resonance line centered at g =2.0086±0.0005, 2.0081±0.0005, 2.0082±0.0005 (native signal) for yolk, white and whole egg, respectively. Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Responses of egg powders to different gamma radiation doses in the range 0–10 kGy were examined. The stability of the radiation-induced ESR signal of irradiated egg powders were investigated over a storage period of about 5 months. Additive reirradiation of the egg powders produces a reproducible dose response function, which can be used to assess the initial dose by back-extrapolation. The additive dose method gives an estimation of the original dose within ±12% at the end of the 720 h storage period.

Synthesis and investigation of the physicochemical properties of 2-(5-((theophylline-7'-yl)methyl)-4-phenyl-4H-1,2,4-triazole-3-ylthio)-acetic acid salts

Synthesis and investigation of the physicochemical properties of 2-(5-((theophylline-7'-yl)methyl)-4-phenyl-4H-1,2,4-triazole-3-ylthio)-acetic acid salts

Electronic and ionization spectra of 1,1-diamino-2,2-dinitroethylene, FOX-7

Singlet, triplet and ionized states of the energetic molecule 1,1-diamino-2,2-dinitroethylene, known as FOX-7 or DADNE, were investigated using the symmetry-adapted-cluster configuration interaction (SAC-CI) ab initio wave function. The 20 computed singlet transitions, with 2 exceptions, were bright. The most intense singlet transitions were of the n₀→π type-typical of molecules having nitro groups. Fast intersystem crossing (ISC) from the 1¹A, 2¹A and 8¹A bright singlet transitions is possible. Other feasible ISC processes are discussed. The computed singlet and ionization spectra have similar features when compared to nitramide and N,N-dimethylnitramine molecules, which have only a nitro group. The ionization energies of the first 20 states have differences in comparison with Koopmans' energy values that can reach 3 eV. Moreover, the character of the first ionized states, dominated by single ionizations, is not the same when compared with the character resulting from application of Koopmans' theorem.

The challenging combination of intense fluorescence and high singlet oxygen quantum yield in photostable chlorins — a contribution to theranostics

High fluorescence quantum yields, high singlet oxygen quantum yields and intense absorptions in the phototherapeutic window are fundamental properties for compounds intended for fluorescence diagnosis and photodynamic therapy. We report on photostable chlorins that combine these properties. The fluorinated tetraphenylchlorin FCMet has ΦF = 0.396 and ΦΔ = 0.58 ± 0.07, whereas F2CMet has ΦF = 0.360 and ΦΔ = 0.54 ± 0.05, and both have molar absorption coefficients larger than 30,000 M(-1) cm(-1) above 650 nm. These dual functional agents use nearly all the energy absorbed to perform the desired functions and are appropriate for theranostics applications.

Group independent component analysis of MR spectra

This study investigates the potential of independent component analysis (ICA) to provide a data-driven approach for group level analysis of magnetic resonance (MR) spectra. ICA collectively analyzes data to identify maximally independent components, each of which captures covarying resonances, including those from different metabolic sources. A comparative evaluation of the ICA approach with the more established LCModel method in analyzing two different noise-free, artifact-free, simulated data sets of known compositions is presented. The results from such ideal simulations demonstrate the ability of data-driven ICA to decompose data and accurately extract components resembling modeled basis spectra from both data sets, whereas the LCModel results suffer when the underlying model deviates from assumptions, thus highlighting the sensitivity of model-based approaches to modeling inaccuracies. Analyses with simulated data show that independent component weights are good estimates of concentrations, even of metabolites with low intensity singlet peaks, such as scyllo-inositol. ICA is also applied to single voxel spectra from 193 subjects, without correcting for baseline variations, line-width broadening or noise. The results provide evidence that, despite the presence of confounding artifacts, ICA can be used to analyze in vivo spectra and extract resonances of interest. ICA is a promising technique for decomposing MR spectral data into components resembling metabolite resonances, and therefore has the potential to provide a data-driven alternative to the use of metabolite concentrations derived from curve-fitting individual spectra in making group comparisons.

Detection of gamma irradiated fig seeds by analysing electron spin resonance

Seeds of fig produced in Turkey were studied by electron spin resonance (ESR) technique for detection purposes. Unirradiated fig seeds (control) exhibited a weak ESR singlet at g=2.0052±0.0003 (native signal). Irradiation induced at least one additional intense singlet overlapping to the control signal and caused a significant increase in signal intensity without any changes in spectral patterns. Variation of ESR signal intensity of irradiated samples at room temperature with time in a long-term showed that free radicals responsible from the ESR spectrum of fig seeds were not stable but detectable after 80days. Annealing studies at five different temperatures were used to determine the kinetic behaviour and activation energy of the radiation-induced radicals in fig seeds. A study on microwave saturation characteristics and thermal behaviour of the ESR singlet (g=2.0052) in irradiated and unirradiated fig seed samples was also carried out by using ESR technique. These preliminary results indicate that microwave saturation characteristics of the ESR signal at room and low temperatures may be useful method to distinguish irradiated fig seeds from unirradiated ones.

Magnetic Resonance Study of Detonation Nanodiamonds with Surface Chemically Modified by Transition Metal Ions

We report on electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) study of detonation nanodiamonds (DND) with the surface modified by copper and cobalt ions. The EMR spectrum of the pure DND sample shows an intense singlet originating from broken carbon bonds, while the spectra of copper- and cobalt-modified samples reveal additional signals with g > 2 and pronounced hyperfine structure (for copper). Increase in the Cu/Co concentration causes an increase of the corresponding EMR signals and broadening of the intense carbon-inherited singlet line. Subsequent annealing of the copper-modified samples in a hydrogen gas stream at 550 and 900°C causes narrowing of the singlet line and reduction of the Cu2+-related components. Applying the same annealing process to the cobalt-modified samples leads to broadening of the singlet line, reduction of Co2+ component and appearance of new intense low-field signals. NMR data correlate well with the EMR findings and yield information on interactions and locations of transition metal ions. 13C nuclear spin–lattice relaxation rate R 1 in pure DND is driven by the interaction of nuclear spins with unpaired electron spins of broken bonds. Chemical modification of the DND surface by Cu and Co causes an increase in the relaxation rate, revealing appearance of paramagnetic Cu2+ and Co2+ complexes at the DND surface and their interaction with the carbon nuclear spins, both directly and via a coupling of Cu2+ and Co2+ electrons with those of the broken bonds. The aforementioned annealing of the Cu- and Co-DND results in an inverse process, i.e., a reduction of the relaxation rate, indicating that these complexes are destroyed and metal ions presumably join each other forming copper and cobalt nanoclusters. In the case of Co the nanoclusters are ferromagnetic, which results in the noticeable broadening of the 13C NMR lines.

Identification of γ-ray irradiated medicinal herbs using pulsed photostimulated luminescence, thermoluminescence, and electron spin resonance spectroscopy

Dried herbal samples consisting of root, rhizome, cortex, fruit, peel, flower, spike, ramulus, folium, and whole plant of 20 different medicinal herbs were investigated using pulsed photostimulated luminescence (PPSL), thermoluminescence (TL), and electron spin resonance spectroscopy (ESR) to identify gamma-ray irradiation treatment. Samples were irradiated at 0-50 kGy using a 60Co irradiator. PPSL measurement was applied as a rapid screening method. Control samples of 19 different herbs had photon counts less than the lower threshold value (700 counts 60 s(-1)). The photon counts of non-irradiated clematidis radix and irradiated evodia and gardenia fruits were between the lower and upper threshold values (700-5,000 counts 60 s(-1)). TL ratios, i.e., integrated areas of the first glow (TL1)/the second glow (TL2), were found to be less than 0.1 in all non-irradiated samples and higher than 0.1 in irradiated ones providing definite proof of radiation treatment. ESR spectroscopy was applied as an alternative rapid method. In most of the irradiated samples, mainly radiation-induced cellulosic, sugar, and relatively complicated carbohydrate radical ESR signals were detected. No radiation-specific ESR signal, except one intense singlet, was observed for irradiated scrophularia and scutellaria root and artemisiae argyi folium.

EPR spectra induced by gamma-irradiation of some dry medical herbs

The radiation-induced EPR spectra in some medical herbs are reported. The samples studied are: (i) leaves of nettle, common balm, peppermint and thyme; (ii) stalks of common balm, thyme, milfoil, yarrow and marigold; (iii) blossoms of yarrow and marigold; (iv) blossoms and leaves of hawthorn and tutsan; and (v) roots of common valerian, nettle, elecampane (black and white), restharrows and carlina. Before irradiation all samples exhibit one weak anisotropic singlet EPR line with effective g-value of 2.0050±0.0002. The radiation-induced spectra fall into three groups. EPR spectra of irradiated blossoms of yarrow and marigold, stalks of common balm, thyme, tutsan and yarrow as well as roots of common valerian, nettle and elecampane (black and white) show “cellulose-like” EPR spectrum typical for irradiated plants. It is characterized by one intense central line with g=2.0050±0.0005 and two weak satellite lines situated ca. 30 G left and right to it. EPR spectra of gamma-irradiated restharrows and carlina are complex. They may be represented by one triplet corresponding to the “cellulose-like” EPR spectrum, one relatively intense singlet, situated in the center of the spectrum, and five weak additional satellite lines left and right to the center. The last spectrum was assigned as “carbohydrate-like” type. Only one intense EPR singlet with g=2.0048±0.0005 was recorded after irradiation of leaves of nettle and common balm. The lifetime of the radiation-induced EPR spectra was followed for a period of 3 months.