EPR Interactions - Zero-Field Splittings

Telser, Joshua

doi:10.1002/9780470034590.emrstm1501

Cited by 53 publications

(64 citation statements)

References 100 publications

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“…For this reason, EPR spectra of these proteins can be simulated either as effective S = 1 / 2 systems, using a g eff tensor, where g x eff and g y eff are symmetrically split at ∼6 and g z eff is close to 2, or as real S = 5 / 2 systems, where the g tensor is almost isotropic with principal values close to 2, and the observed features depend essentially on the E / D ratio between the rhombic ( E ) and tetragonal ( D ) zero-field splitting parameters. 37 In this study, both simulation methods were used to obtain a complete picture of the systems under investigation. If a strong base is present at the sixth distal coordination position, the iron spin converts to the low-spin state ( S = 1 / 2 ).…”

Section: Resultsmentioning

confidence: 99%

Arresting the Catalytic Arginine in Chlorite Dismutases: Impact on Heme Coordination, Thermal Stability, and Catalysis

et al. 2021

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Chlorite dismutases (Clds) are heme b -containing oxidoreductases that can decompose chlorite to chloride and molecular oxygen. They are divided in two clades that differ in oligomerization, subunit architecture, and the hydrogen-bonding network of the distal catalytic arginine, which is proposed to switch between two conformations during turnover. To understand the impact of the conformational dynamics of this basic amino acid on heme coordination, structure, and catalysis, Cld from Cyanothece sp. PCC7425 was used as a model enzyme. As typical for a clade 2 Cld, its distal arginine 127 is hydrogen-bonded to glutamine 74. The latter has been exchanged with either glutamate (Q74E) to arrest R127 in a salt bridge or valine (Q74V) that mirrors the setting in clade 1 Clds. We present the X-ray crystal structures of Q74V and Q74E and demonstrate the pH-induced changes in the environment and coordination of the heme iron by ultraviolet–visible, circular dichroism, and electron paramagnetic resonance spectroscopies as well as differential scanning calorimetry. The conformational dynamics of R127 is shown to have a significant role in heme coordination during the alkaline transition and in the thermal stability of the heme cavity, whereas its impact on the catalytic efficiency of chlorite degradation is relatively small. The findings are discussed with respect to (i) the flexible loop connecting the N-terminal and C-terminal ferredoxin-like domains, which differs in clade 1 and clade 2 Clds and carries Q74 in clade 2 proteins, and (ii) the proposed role(s) of the arginine in catalysis.

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Section: Resultsmentioning

confidence: 99%

Arresting the Catalytic Arginine in Chlorite Dismutases: Impact on Heme Coordination, Thermal Stability, and Catalysis

et al. 2021

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“…In most cases, the latter represents short-lived triplet states and radical pairs generated by the laser pulse of the ultraviolet–visible (UV-Vis) range (targeted processes are related to photochemistry). At the same time, THz-radiation of NovoFEL has much less energy quanta and is used to excite either vibrational bands of studied compounds [22] or high-energy EPR transitions [3] in high-spin systems with large zero-field splitting (targeted processes are related to spin system excitation) [23]. Regardless of the type of targeted processes, the absorption of THz light by the sample leads to its heating.…”

Section: Resultsmentioning

confidence: 99%

Electronic Modulation of THz Radiation at NovoFEL: Technical Aspects and Possible Applications

et al. 2019

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The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm−1), far-infrared (~200 cm−1) and THz (~40 cm−1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.

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“…An unambiguous conclusion about the spin state of a complex cannot be made based solely on a single frequency cw-EPR experiment. 73 However, the interactions between the unpaired electrons in the high spin states usually result in a facilitated electron spin relaxation, and the consequent line broadening renders their EPR spectra often undetectable above liquid helium temperatures. The fact that we were able to record the spectrum of n Bu 4 N[ 1 ] at 94 K and a comparable linewidth was observed in the spectrum of Na[ 1 ] at 12 K, indicate the absence of such electron-electron interactions.…”

Section: Resultsmentioning

confidence: 99%

cis-Tetrachlorido-bis(indazole)osmium(iv) and its osmium(iii) analogues: paving the way towards the cis-isomer of the ruthenium anticancer drugs KP1019 and/or NKP1339

et al. 2017

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The relationship between cis-trans isomerism and anticancer activity has been mainly addressed for square-planar metal complexes, in particular, for platinum(II), e.g., cis- and trans-[PtCl2(NH3)2], and a number of related compounds, of which, however, only cis-counterparts are in clinical use today. For octahedral metal complexes, this effect of geometrical isomerism on anticancer activity has not been investigated systematically, mainly because the relevant isomers are still unavailable. An example of such an octahedral complex is trans-[RuCl4(Hind)2]−, which is in clinical trials now as its indazolium (KP1019) or sodium salt (NKP1339), but the corresponding cis-isomers remain inaccessible. We report the synthesis of Na[cis-OsIIICl4(κN2-1H-ind)2] (Na[1]) to show that cis-isomer of NKP1339 can in principle be prepared as well. The procedure involves heating (H2ind)[OsIVCl5(κN1-2H-ind)] in a high boiling point organic solvent resulting in an Anderson rearrangement with formation of cis-[OsIVCl4(κN2-1H-ind)2] ([1]) in high yield. The transformation is accompanied by an indazole coordination mode switch from κN1 to κN2 and stabilization of the 1H-indazole tautomer. Fully reversible spectroelectrochemical reduction of [1] in acetonitrile at 0.46 V vs NHE is accompanied by a change in electronic absorption bands indicating formation of cis-[OsIIICl4(κN2-1H-ind)2]− ([1]−). Chemical reduction of [1] in methanol with NaBH4 followed by addition of nBu4NCl afforded the osmium(III) complex nBu4N[cis-OsIIICl4(κN2-1H-ind)2] (nBu4N[1]). Metathesis reaction of nBu4N[1] with an ion exchange resin led to isolation of the water-soluble salt Na[1]. The X-ray diffraction crystal structure of [1]·Me2CO was determined and compared with that of trans-[OsIVCl4(κN2-1H-ind)]·2Me2SO (2·2Me2SO), also prepared in this work. EPR spectroscopy was performed on the OsIII complexes and the results analyzed by ligand-field and quantum chemical theories. We furthermore assayed effects of [1] and Na[1] on cell viability and proliferation in comparison to trans-[OsIVCl4(κN1-2H-ind)] [3] and cisplatin and found a strong reduction of cell viability at concentrations between 30 and 300 µM in different cancer cell lines (HT29, H446, 4T1 and HEK293). HT-29 cells are less sensitive to cisplatin than 4T1 cells, but more sensitive to [1] and Na[1], as shown by decreased proliferation and viability as well as an increased late apoptotic/necrotic cell population.

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EPR Interactions - Zero-Field Splittings

Cited by 53 publications

References 100 publications

Arresting the Catalytic Arginine in Chlorite Dismutases: Impact on Heme Coordination, Thermal Stability, and Catalysis

Arresting the Catalytic Arginine in Chlorite Dismutases: Impact on Heme Coordination, Thermal Stability, and Catalysis

Electronic Modulation of THz Radiation at NovoFEL: Technical Aspects and Possible Applications

cis-Tetrachlorido-bis(indazole)osmium(iv) and its osmium(iii) analogues: paving the way towards the cis-isomer of the ruthenium anticancer drugs KP1019 and/or NKP1339

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