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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Analytical Chemistry".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 21173

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Dr. Yordanka Karakirova

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Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Interests: EPR spectroscopy; UV–Vis spectrometry; radiation dosimetry; free radicals; saccharides for EPR dosimetry; new materials for EPR dosimetry; application of EPR in catalysis; solid state chemistry

Special Issue Information

Dear Colleagues,

Electron paramagnetic resonance (EPR) spectroscopy has been widely used for more than 60 years. In recent years, EPR spectroscopy has expanded significantly in the field of practical applications. This is mainly due to its advantages, such as its high sensitivity (10¹²–10¹³ molecules, which means 10⁻¹¹ to 10⁻¹² M) and selectivity (only for paramagnetic species). Moreover, it is a quick, non-destructive method, and in some cases, samples may be kept as documents for future inspection. The design of portable EPR spectrometers with small dimensions greatly facilitates the use of the method in practice. The aim of the Special Issue “Applied EPR spectroscopy” is to highlight the current status, as well as the trends in the development and application of EPR spectroscopy. It covers EPR research in the field of biology and medicine, chemistry (metal complexes, polymers, catalysis), dosimetry, geology, mineralogy, archaeology, environmental control, food technology, quantitative EPR, etc.

It is our pleasure to invite you to contribute an original research paper, a short communication, or a review to this issue.

IN MEMORIAM

Prof. DSc Nicola Dragomirov Yordanov

text

Nicola Dragomirov Yordanov was born on May 25, 1936 in the city of Kazanlak. In 1965, he received a MSc degree at the Faculty of Physics at Sofia University. In 1971, he received the scientific degree "Doctor", and in 1987, "Doctor of Sciences". He was a professor since 1990.

Prof. Yordanov laid the foundations of EPR and ENDOR spectroscopy in Bulgaria and throughout his life worked on their further development and application. There is a number of achievements, among which stand out the theoretical development and experimental confirmation of the method "ENDOR crystallography of disordered systems" and the development of the so-called "self-calibrated" EPR dosimeters.

Prof. Yordanov delivered lectures at the Faculty of Chemistry of the University of St. Cl. Ohridski" and in a number of foreign universities. The results of his pedagogical activities are over 40 successfully defended diploma graduates, 10 doctoral students and the training of a large number of foreign colleagues from Germany, Austria, Hungary, Poland, Libya, Slovakia, etc.

Throughout his scientific career, Prof. Nicola Yordanov was a recipient of the Order of “St. St. Cyril and Methodius", honorary diploma of the Faculty of Chemistry of the Sofia University, gold badge of the BAS, academic award in chemistry of the Bulgarian Academy of Sciences, badge of honor of: the Faculty of Chemistry—SU, of the BAS—for "his significant scientific and scientific-applied contributions in the field of EPR spectroscopy found wide applications in our country" and "Marin Drinov" order of merit with a ribbon for "his significant merits to the BAS and his contributions to Bulgarian science and in particular in chemistry, physics, food science and bio-medical research" Prof. Yordanov is the founder and honorary chairman of the Association "Bulgarian EPR Society". The main activity of the Bulgarian EPR Society is the organizing of the International Symposium on "Electron Magnetic Resonance of Disordered Systems" (EMARDIS), which is internationally renowned.

I will remember Prof. Yordanov for his strong character, energy, willpower and consistency in following the set goals and bringing them to a successful fulfillment, and his willingness to help his colleagues with his vast knowledge and logical thinking.

A TRIBUTE TO HIS GLOWING MEMORY!

Dr. Yordanka Karakirova
Guest Editor

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Keywords

electron paramagnetic resonance spectroscopy
free radicals
paramagnetic species
radiation dosimetry
food technology
archaeology
environmental control

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Published Papers (11 papers)

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Research

22 pages, 6268 KiB

Open AccessArticle

Heme Spin Distribution in the Substrate-Free and Inhibited Novel CYP116B5hd: A Multifrequency Hyperfine Sublevel Correlation (HYSCORE) Study

by Antonino Famulari, Danilo Correddu, Giovanna Di Nardo, Gianfranco Gilardi, George Mitrikas, Mario Chiesa and Inés García-Rubio

Molecules 2024, 29(2), 518; https://doi.org/10.3390/molecules29020518 - 20 Jan 2024

Viewed by 1597

Abstract

The cytochrome P450 family consists of ubiquitous monooxygenases with the potential to perform a wide variety of catalytic applications. Among the members of this family, CYP116B5hd shows a very prominent resistance to peracid damage, a property that makes it a promising tool for fine chemical synthesis using the peroxide shunt. In this meticulous study, we use hyperfine spectroscopy with a multifrequency approach (X- and Q-band) to characterize in detail the electronic structure of the heme iron of CYP116B5hd in the resting state, which provides structural details about its active site. The hyperfine dipole–dipole interaction between the electron and proton nuclear spins allows for the locating of two different protons from the coordinated water and a beta proton from the cysteine axial ligand of heme iron with respect to the magnetic axes centered on the iron. Additionally, since new anti-cancer therapies target the inhibition of P450s, here we use the CYP116B5hd system—imidazole as a model for studying cytochrome P450 inhibition by an azo compound. The effects of the inhibition of protein by imidazole in the active-site geometry and electron spin distribution are presented. The binding of imidazole to CYP116B5hd results in an imidazole–nitrogen axial coordination and a low-spin heme Fe^III. HYSCORE experiments were used to detect the hyperfine interactions. The combined interpretation of the gyromagnetic tensor and the hyperfine and quadrupole tensors of magnetic nuclei coupled to the iron electron spin allowed us to obtain a precise picture of the active-site geometry, including the orientation of the semi-occupied orbitals and magnetic axes, which coincide with the porphyrin N-Fe-N axes. The electronic structure of the iron does not seem to be affected by imidazole binding. Two different possible coordination geometries of the axial imidazole were observed. The angles between g_x (coinciding with one of the N-Fe-N axes) and the projection of the imidazole plane on the heme were determined to be −60° and −25° for each of the two possibilities via measurement of the hyperfine structure of the axially coordinated ¹⁴N. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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17 pages, 3050 KiB

Open AccessArticle

Spin-Label Electron Paramagnetic Resonance Spectroscopy Reveals Effects of Wastewater Filter Membrane Coated with Titanium Dioxide Nanoparticles on Bovine Serum Albumin

by Krisztina Sebők-Nagy, Zoltán Kóta, András Kincses, Ákos Ferenc Fazekas, András Dér, Zsuzsanna László and Tibor Páli

Molecules 2023, 28(19), 6750; https://doi.org/10.3390/molecules28196750 - 22 Sep 2023

Cited by 1 | Viewed by 1734

Abstract

The accumulation of proteins in filter membranes limits the efficiency of filtering technologies for cleaning wastewater. Efforts are ongoing to coat commercial filters with different materials (such as titanium dioxide, TiO₂) to reduce the fouling of the membrane. Beyond monitoring the desired effect of the retention of biomolecules, it is necessary to understand what the biophysical changes are in water-soluble proteins caused by their interaction with the new coated filter membranes, an aspect that has received little attention so far. Using spin-label electron paramagnetic resonance (EPR), aided with native fluorescence spectroscopy and dynamic light scattering (DLS), here, we report the changes in the structure and dynamics of bovine serum albumin (BSA) exposed to TiO₂ (P25) nanoparticles or passing through commercial polyvinylidene fluoride (PVDF) membranes coated with the same nanoparticles. We have found that the filtering process and prolonged exposure to TiO₂ nanoparticles had significant effects on different regions of BSA, and denaturation of the protein was not observed, neither with the TiO₂ nanoparticles nor when passing through the TiO₂-coated filter membranes. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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15 pages, 2932 KiB

Open AccessArticle

Long-Term Characterization of Oxidation Processes in Graphitic Carbon Nitride Photocatalyst Materials via Electron Paramagnetic Resonance Spectroscopy

by Elizaveta Kobeleva, Ekaterina Shabratova, Adi Azoulay, Rowan W. MacQueen, Neeta Karjule, Menny Shalom, Klaus Lips and Joseph E. McPeak

Molecules 2023, 28(18), 6475; https://doi.org/10.3390/molecules28186475 - 6 Sep 2023

Cited by 1 | Viewed by 1468

Abstract

Graphitic carbon nitride (gCN) materials have been shown to efficiently perform light-induced water splitting, carbon dioxide reduction, and environmental remediation in a cost-effective way. However, gCN suffers from rapid charge-carrier recombination, inefficient light absorption, and poor long-term stability which greatly hinders photocatalytic performance. To determine the underlying catalytic mechanisms and overall contributions that will improve performance, the electronic structure of gCN materials has been investigated using electron paramagnetic resonance (EPR) spectroscopy. Through lineshape analysis and relaxation behavior, evidence of two independent spin species were determined to be present in catalytically active gCN materials. These two contributions to the total lineshape respond independently to light exposure such that the previously established catalytically active spin system remains responsive while the newly observed, superimposed EPR signal is not increased during exposure to light. The time dependence of these two peaks present in gCN EPR spectra recorded sequentially in air over several months demonstrates a steady change in the electronic structure of the gCN framework over time. This light-independent, slowly evolving additional spin center is demonstrated to be the result of oxidative processes occurring as a result of exposure to the environment and is confirmed by forced oxidation experiments. This oxidized gCN exhibits lower H₂ production rates and indicates quenching of the overall gCN catalytic activity over longer reaction times. A general model for the newly generated spin centers is given and strategies for the alleviation of oxidative products within the gCN framework are discussed in the context of improving photocatalytic activity over extended durations as required for future functional photocatalytic device development. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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16 pages, 4487 KiB

Open AccessArticle

Conversion of a Single-Frequency X-Band EPR Spectrometer into a Broadband Multi-Frequency 0.1–18 GHz Instrument for Analysis of Complex Molecular Spin Hamiltonians

by Wilfred R. Hagen

Molecules 2023, 28(13), 5281; https://doi.org/10.3390/molecules28135281 - 7 Jul 2023

Cited by 2 | Viewed by 1869

Abstract

A broadband EPR spectrometer is an instrument that can be tuned to many microwave frequencies over several octaves. Its purpose is the collection of multi-frequency data, whose global analysis affords interpretation of complex spectra by means of deconvolution of frequency-dependent and frequency-independent interaction terms. Such spectra are commonly encountered, for example, from transition-metal complexes and metalloproteins. In a series of previous papers, I have described the development of broadband EPR spectrometers around a vector network analyzer. The present study reports on my endeavor to start from an existing X-band spectrometer and to reversibly re-build it into a broadband machine, in a quest to drastically reduce design effort, building costs, and operational complexity, thus bringing broadband EPR within easy reach of a wide range of researchers. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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13 pages, 3298 KiB

Open AccessArticle

Electron Paramagnetic Resonance Studies of Irradiated Grape Snails (Helix pomatia) and Investigation of Biophysical Parameters

by Aygun Nasibova, Rovshan Khalilov, Mahammad Bayramov, İslam Mustafayev, Aziz Eftekhari, Mirheydar Abbasov, Taras Kavetskyy, Gvozden Rosić and Dragica Selakovic

Molecules 2023, 28(4), 1872; https://doi.org/10.3390/molecules28041872 - 16 Feb 2023

Cited by 2 | Viewed by 2102

Abstract

A study of grape snails (Helix pomatia) using the electron paramagnetic resonance (EPR) spectroscopy method, where shells were exposed to ionizing gamma radiation, indicated that the effect of radiation up to certain doses results in the emergence of magnetic properties in the organism. The identification of the EPR spectra of the body and shell parts of the control and irradiated grape snails separately showed that more iron oxide magnetic nanoparticles are generated in the body part of the grape snail compared to the shells. A linear increase in free radical signals (g = 2.0023) in the body and shell parts of grape snails, and a non-monotonic change in the broad EPR signal (g = 2.32) characterizing iron oxide magnetic nanoparticles was determined depending on the dose of ionizing gamma radiation. Additionally, the obtained results showed that grape snails can be used as bioindicators for examining the ecological state of the environment. At the same time, the radionuclide composition of the body and shell parts of the grape snails and their specific activities were determined by CANBERRA gamma spectroscopy. The FTIR spectra of mucin, a liquid secreted by snails, were recorded. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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13 pages, 3537 KiB

Open AccessArticle

Application of Amino Acids for High-Dosage Measurements with Electron Paramagnetic Resonance Spectroscopy

by Yordanka Karakirova

Molecules 2023, 28(4), 1745; https://doi.org/10.3390/molecules28041745 - 12 Feb 2023

Viewed by 1692

Abstract

A comparative investigation of amino acids (proline, cysteine, and alanine) as dosimetric materials using electron paramagnetic resonance (EPR) spectroscopy in the absorbed dosage range of 1–25 kGy is presented. There were no signals in the EPR spectra of the samples before irradiation. After irradiation, the complex spectra were recorded. These results showed that the investigated amino acids were sensitive to radiation. In the EPR spectrum of cysteine after irradiation, RS• radicals dominated. The effects of the microwave power on the saturation of the EPR signals showed the presence of at least three different types of free radicals in proline. It was also found out that the DL-proline and cysteine had stable free radicals after irradiation and represented a linear dosage response up to 10 kGy. On the other hand, the amino acid alanine has been accepted by the International Atomic Energy Agency as a transfer standard dosimetry system. In view of this, the obtained results of the proline and cysteine studies have been compared with those of the alanine studies. The results showed that the amino acids proline and cysteine could be used as alternative dosimetric materials in lieu of alanine in a dosage range of 1–10 kGy of an absorbed dose of γ-rays using EPR spectroscopy. Regarding the radiation sensitivity, the following order of decreased dosage responses was determined: alanine > DL-proline > cysteine > L-proline. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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11 pages, 4899 KiB

Open AccessArticle

Zinc–Cobalt Oxide Thin Films: High Curie Temperature Studied by Electron Magnetic Resonance

by Bogumił Cieniek, Ireneusz Stefaniuk, Ihor Virt, Roman V. Gamernyk and Iwona Rogalska

Molecules 2022, 27(23), 8500; https://doi.org/10.3390/molecules27238500 - 2 Dec 2022

Cited by 3 | Viewed by 1835

Abstract

The material with a high Curie temperature of cobalt-doped zinc oxide embedded with silver-nanoparticle thin films was studied by electron magnetic resonance. The nanoparticles were synthesized by the homogeneous nucleation technique. Thin films were produced with the pulsed laser deposition method. The main aim of this work was to investigate the effect of Ag nanoparticles on the magnetic properties of the films. Simultaneously, the coexisting Ag⁰ and Ag²⁺ centers in zinc oxide structures are shown. A discussion of the signal seen in the low field was conducted. To analyze the temperature dependence of the line parameters, the theory described by Becker was used. The implementation of silver nanoparticles causes a significant shift of the line, and the ferromagnetic properties occur in a wide temperature range with an estimated Curie temperature above 500 K. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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9 pages, 1981 KiB

Open AccessArticle

Electron Spin Resonance Dosimetry Studies of Irradiated Sulfite Salts

by Amanda Burg Rech, Angela Kinoshita, Paulo Marcos Donate, Otaciro Rangel Nascimento and Oswaldo Baffa

Molecules 2022, 27(20), 7047; https://doi.org/10.3390/molecules27207047 - 19 Oct 2022

Cited by 1 | Viewed by 1471

Abstract

The study of new materials for radiation dosimetry is important to improve the present state of the art and to help in cases of accidents for retrospective dosimetry. Sulfites are compounds that contain a sulfur ion, widely used in the food industry. Due to the significant application of these compounds, sulfites are interesting candidates for accidental dosimetry, as fortuitous radiation detectors. The presence of the SO₃⁻ anion enables its detection by electron spin resonance (ESR) spectroscopy. The Dose–Response behavior, signal stability and other spectral features were investigated for sodium sulfite, sodium bisulfite, sodium metabisulfite and potassium metabisulfite, all in crystalline forms. The ESR spectrum of salts presented stability and proportional response with dose, presenting potential for dosimetry applications. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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13 pages, 3055 KiB

Open AccessArticle

A Review of the Dawn of Benchtop EPR Spectrometers—Innovation That Shaped the Future of This Technology

by Vasily V. Ptushenko and Vladimir N. Linev

Molecules 2022, 27(18), 5996; https://doi.org/10.3390/molecules27185996 - 14 Sep 2022

Viewed by 1827

Abstract

By the early 1980s, unique devices appeared in the USSR: a series of benchtop specialized EPR spectrometers. This equipment was quickly accepted not only in science but also in medicine and in many technical and economic areas including chemical industries and geologic exploration. The appearance of these devices was perceived as a salvation for the Soviet magnetic resonance (MR) scientific instrumentation by those who worked in the field of EPR spectroscopy in the USSR. (However, the program of MR scientific instrumentation ceased to exist along with the USSR a few years later). The Belarusian State University in Minsk was the center of these developments. At that moment and for many years afterwards, these devices were unique with no analogues in the worldwide EPR industry. They remained the only mass-produced MR spectrometers on the territory of the former USSR after its collapse. For the first time, based on archival materials, patents, and our personal memoirs, we describe the development of these EPR spectrometers and discuss the most original technical solutions and the scientific tasks solved with this equipment We also remember the participants of the work, showing the historical context of these events. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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12 pages, 2885 KiB

Open AccessArticle

Electron Paramagnetic Resonance Study of PbSe, PbTe, and PbTe:In Semiconductors Obtained by the Pulsed Laser Deposition Method

by Aleksandra Wędrychowicz, Bogumił Cieniek, Ireneusz Stefaniuk, Ihor Virt and Romana Śliwa

Molecules 2022, 27(14), 4381; https://doi.org/10.3390/molecules27144381 - 8 Jul 2022

Cited by 1 | Viewed by 1952

Abstract

The magnetic properties of lead selenide (PbSe) and indium-doped lead telluride (PbTe:In) composites have been studied by using the electron paramagnetic resonance (EPR) technique. The samples were obtained by using the pulsed laser deposition method (PLD). Temperature dependences of the EPR spectra were obtained. The analysis of the temperature dependencies of the integral intensity of the EPR spectra was performed using the Curie–Weiss law. In these materials, the paramagnetic centers of Pb¹⁺ and Pb³⁺ ions were identified. The results are discussed. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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18 pages, 4436 KiB

Open AccessArticle

Dating Sediments by EPR Using Al-h Centre: A Comparison between the Properties of Fine (4–11 µm) and Coarse (>63 µm) Quartz Grains

by Zuzanna Kabacińska and Alida Timar-Gabor

Molecules 2022, 27(9), 2683; https://doi.org/10.3390/molecules27092683 - 21 Apr 2022

Cited by 4 | Viewed by 2043

Abstract

The possibility of EPR dating for sediments using Al-h signals of fine (4–11 μm) grains of quartz has not been previously discussed. Here, the Al-h and peroxy EPR spectra of fine (4–11 μm) and coarse (63–90, 125–180 μm) sedimentary quartz from thoroughly investigated loess sites in Eastern Europe were examined. By comparing experimental spectra with a simulated signal, we evaluated the overestimation observed when using the standard approach established by Toyoda and Falguères to measure Al-h intensity for different doses of radiation, up to 40,000 Gy. This overestimation, caused by the presence of peroxy signals, was much more pronounced for fine grains. Fine grains exhibited some additional dose-dependent signals, which, for some samples, caused a complete distortion of the Al-h spectra at high doses, making it impossible to measure the standard amplitude. We propose a new approach to measuring Al-h signal intensity, focusing on the peak-to-baseline amplitude of the part of the signal at g ≈ 2.0603, which is not affected by the peroxy signals and therefore has the potential of providing more accurate results. The shapes of dose response curves constructed for coarse and fine grains using the new approach show considerable similarity, suggesting that Al-h centre formation in fine and coarse grains upon artificial radiation at room temperature follows the same pattern. Full article

(This article belongs to the Special Issue Applied EPR Spectroscopy)

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