Search

Over recent decades, electron paramagnetic resonance (EPR) spectroscopy has become an essential tool for exploring complex biological systems. Herein, we discuss the potential of pulsed EPR spectroscopy to shed light on the mechanisms of protein‐DNA interactions. To this end, we first provide an overview of pulsed EPR methodology (and specifically, double electron electron resonance; DEER), with a focus on the various spin‐labeling methods used today both for protein labeling and for DNA labeling. Next, after briefly discussing recent applications of DEER in protein‐DNA studies, we introduce a detailed case study, an example of how EPR spectroscopy has been used to resolve the transcription mechanism of the CueR copper regulator. [ABSTRACT FROM AUTHOR]

Double quantum coherence (DQC) ESR is a sensitive method to measure magnetic dipolar interactions between spin labels. However, the DQC experiment on Cu 2+ centers presents a challenge at X-band. The Cu 2+ centers are usually coordinated to histidine residues in proteins. The electron–nuclear interaction between the Cu 2+ ion and the remote nitrogen in the imidazole ring can interfere with the electron–electron dipolar interaction. Herein, we report on a modified DQC experiment that has the advantage of reduced contributions from electron–nuclear interactions, which enhances the resolution of the DQC signal to the electron–electron dipolar modulations. The modified pulse-sequence is verified on Cu 2+ –NO system in a polyalanine-based peptide and on a coupled Cu 2+ system in a polyproline-based peptide. The modified DQC data were compared with the DEER data and good agreement was found. [ABSTRACT FROM AUTHOR]

The use of pulsed electron spin resonance (ESR) to measure interspin distance distributions has advanced biophysical research. The three major techniques that use pulsed ESR are relaxation rate based distance measurements, double quantum coherence (DQC), and double electron electron resonance (DEER). Among these methods, the DEER technique has become particularly popular largely because it is easy to implement on commercial instruments and because programs are available to analyze experimental data. [ABSTRACT FROM AUTHOR]

The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM. A reaction mixture was sampled at different times after the addition of tetramethoxyorthosilane (TMOS) to an acidic solution of Pluronic P123 held at 50 °C. Solution microstructures were detected by direct imaging cryo-TEM in the time window of 6.5–40 min after the addition of the TMOS (t = 0). The micrographs revealed that the initial spheroidal micelles evolve into threadlike micelles, which become longer and straighter with time. Then bundles with the dimensions similar to those found in the final material appeared, although there was no sign of a hexagonal arrangement up to 40 min. Due to the appearance of a precipitate at 40 min the sample became too viscous, preventing clear observation of its content. To observe the structures present after 40 min, freeze-fracture replication was carried out as well. Such samples were collected also at 22 min and showed the presence of threadlike micelles in agreement with the direct imaging cryo-TEM micrographs. The 2 h samples showed some areas of hexagonal ordered structures, which become very clear at 2 h 50 min. The cryo-TEM measurements were carried out under the same reaction conditions used in earlier in situ EPR experiments, thus allowing us to correlate molecular level events with the microstructure shape evolutions. This showed that the elongation of the micelles is a consequence of a reduction of the polarity and the water content within the micelles due to silicate adsorption and polymerization. Similar experiments were carried out also on SBA-15 prepared with HCI and TMOS at 35 °C. The appearance of threadlike micelles, followed by clustering of the TLMs, was observed under these conditions as well, but the reaction rate was faster. This suggests that the observed mechanism for the formation of SBA-15 is general. [ABSTRACT FROM AUTHOR]

The essentiality and toxicity of copper in human, yeast, and bacteria cells requires precise mechanisms for acquisition, intimately linked to controlled distribution, which have yet to be fully understood. Herein, we utilise continuous wave and pulsed electron paramagnetic resonance (EPR) spectroscopy to explore one aspect in the controlled copper transportation mechanism. This was achieved by probing structural changes that occur in the c-terminal domain of the human copper transporter, CTR1, upon interacting with a methionine segment. The copper transporter CTR1 transports Cu(I) and Ag(I) ions to various intracellular pathways. Methionine motifs are methionine-rich metal binding segments found in many proteins involved in the transportation of copper ions to other cellular pathways. They are also found to bind Ag(I) with an affinity comparable to Cu(I). This study indicates that the methionine motif experiences conformational changes in the presence of the CTR1 c-terminal domain. These structural changes are dependent on the nature of the metal ion, Cu(I) vs. Ag(I). In addition, the data collected in this study emphasise how important the cysteine residue of the CTR1 c-terminal domain is to a correct conformational state of the target metal binding site. [ABSTRACT FROM PUBLISHER]

• The paper discusses the significant challenge in analytical chemistry of determining chirality in solid materials using electron paramagnetic resonance (EPR) spectroscopy. • The paper introduces a novel approach using electron paramagnetic resonance (EPR) spectroscopy on chiral crystals doped with Cu2+ ions to determine chirality of crystals. • The method is demonstrated using l - and DL-Histidine crystals doped with Cu2+, showing promising results in accurately determining chirality and enantiomeric composition. • This work provides an initial example of this technique and envisions its potential application to various other chiral organic crystal systems in the future. One of the most challenging tasks in analytical chemistry is the determination of the chirality (identification of an enantiomeric composition) in solids mainly because of the strict requirements of the pharmaceutical industry for enantiomerically pure drugs. Although there are a few methods available to accomplish enantio‑differentiation in solids, for example: X-ray diffraction (XRD), Thermogravimetric analysis (TGA), CD spectroscopy, and low-frequency (LF) Raman spectroscopy, this is still very challenging. In this work, we have developed a new method to measure the chirality of crystals, based on electron paramagnetic resonance (EPR) spectroscopy of chiral crystals doped with Cu2+ as the EPR active ion. Here, we demonstrate our approach using a model system of l - and DL-Histidine crystals doped with Cu2+. We show that EPR measurements of the Cu2+-doped Histidine crystals can accurately determine the chirality and enantiomeric composition of the crystals. We present a very preliminary example of this technique, and we hope that in the future it will be possible to refine and develop this method for many other chiral organic crystal systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Paramagnetic centers in diamonds are affected by nitrogen atom contamination in the lattice. This study aimed to better understand the nitrogen concentration and anisotropy impact on the EPR (electron paramagnetic resonance) spectrum of natural diamonds (i.e. appropriate for color enhancement treatments). All the diamonds used were natural either colorless or faintly colored (D–M color range), which were selected according to the targeted final color post-treatment: green, blue, pink, orange, and yellow. Their paramagnetic centers were studied using EPR spectroscopy at various microwave power levels and evaluated for nitrogen concentration via FTIR spectroscopy. The results show a correlation between nitrogen concentrations and spin concentrations in all the pretreated diamonds, whereas the most abundant fast-relaxing paramagnetic center is similar to the C-centered radical. In addition, the hyperfine interaction anisotropy of the paramagnetic centers of nearby nitrogen atoms was found to be valid for pretreated green, pink, and orange diamonds. By clarifying the final structure of the treated fancy diamonds, which are visibly affected by adjacent nitrogen atoms, this study contributes to the refinement of colorless natural diamond selection for color enhancement. [ABSTRACT FROM AUTHOR]

Many inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ‐Zn(OH)2 (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ‐Zn(OH)2 were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l‐ or d‐arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ‐Zn(OH)2. In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ‐Zn(OH)2 crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications. [ABSTRACT FROM AUTHOR]

Many inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ‐Zn(OH)2 (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ‐Zn(OH)2 were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l‐ or d‐arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ‐Zn(OH)2. In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ‐Zn(OH)2 crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications. [ABSTRACT FROM AUTHOR]

Metallo-corroles have shown to have unique catalytic properties for oxygen reduction when adsorbed on a high surface area carbon such as BP2000. The nature of the interaction between carbon surfaces and metallo-corroles has yet to be identified. This work suggests that the catalytic activity lays not in a bond between the carbon surface and the corrole molecule, but rather in the arrangement of corrole molecules within the porous structure of the carbon surface. This hypothesis was studied here using Electron Paramagnetic Resonance (EPR), X-ray diffraction (XRD), UV-VIS spectroscopy, elemental analysis, N 2 adsorption and several electrochemical methods. BP2000 carbon was compared to four other carbons with different properties (oxygen surface groups, surface area, porous structure and crystallinity). All of these show that the Fe-corrole that was incorporated in BP2000 tends to adsorb in pores of 20–25 nm in diameter, which allow synergistic effects to take place, and enhance the electrocatalysis of oxygen reduction reaction. Image 1 [ABSTRACT FROM AUTHOR]

Abstract We propose herein a bio-mimetic catalytic structure as a new approach to increase the oxygen reduction catalytic selectivity of transition metal complexes. As in biological systems, where there is a series of mediators between the active site and the surface, that lowers the activation energy of the overall reaction and increases its selectivity, we use here a structure where a molecular catalyst Fe(III)tetrakis(1-methyl-4-pyridyl) porphyrin is bonded to a surface via a benzimidazole mediator. Using electron paramagnetic resonance (EPR), UV–vis spectroscopy and electrochemical measurements, we compared the ORR activity of the molecular catalyst with and without benzimidazole and show that this ligand strongly influences the selectivity of the reaction and shifts it from the 2 to the 2+2-electron reduction. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Diamonds contain carbon paramagnetic centers (stable carbon radicals) in small concentrations (at the level of ~1 × 1012 spins/mg) that can help in elucidating the structure of the nitrogen atoms' contaminants in the diamond crystal. All diamonds that undergo polishing are exposed to high temperatures, owing to the friction force during the polishing process, which may affect the carbon-centered radicals' concentration and structure. The temperature is increased appreciably; consequently, the black body radiation in the visible range turns orange. During polishing, diamonds emit an orange light (at a wavelength of about 600 nm) that is typical of a black body temperature of 900 °C or higher. Other processes in which color-enhanced diamonds are exposed to high temperatures are thermal treatments or the high-pressure, high-temperature (HPHT) process in which the brown color (resulting from plastic deformation) is bleached. The aim of the study was to examine how thermal treatment and polishing influence the paramagnetic centers in the diamond. For this purpose, four rough diamonds were studied: two underwent a polishing process, and the other two were thermally treated at 650 °C and 1000 °C. The diamonds were analyzed pre- and post-treatment by EPR (Electron Paramagnetic resonance), FTIR (Fourier transform infrared, fluorescence, and their visual appearance. The results indicate that the polishing process results in much more than just thermal heating the paramagnetic centers. [ABSTRACT FROM AUTHOR]

Copper's essentiality and toxicity mean it requires a sophisticated regulation system for its acquisition, cellular distribution and excretion, which until now has remained elusive. Herein, we applied continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) spectroscopy in solution to resolve the copper trafficking mechanism in humans, by considering the route travelled by Cu(I) from the metallochaperone Atox1 to the metal binding domains of ATP7B. Our study revealed that Cu(I) is most likely mediated by the binding of the Atox1 monomer to metal binding domain 1 (MBD1) and MBD4 of ATP7B in the final part of its extraction pathway, while the other MBDs mediate this interaction and participate in copper transfer between the various MBDs to the ATP7B membrane domain. This research also proposes that MBD1-3 and MBD4-6 act as two independent units. [ABSTRACT FROM AUTHOR]