EPR studies of15N- and2H-substituted pH-sensitive spin probes of imidazoline and imidazolidine types

Glazachev, Yu. I.; Григорьев, И. А.; Reijerse, Eduard J.; Khramtsov, Valery V.

doi:10.1007/bf03162332

Cited by 11 publications

(18 citation statements)

References 12 publications

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“…The manifestation of exchange phenomena was first theoretically described in NMR 40 and explored for the measurements of the rates of proton exchange reactions 41, 42 . Similar studies of proton exchange in the EPR spectra include short-lived radicals 43–45 as well as stable nitroxyl radicals 30, 46, 47 . The proton exchange/transfer reactions are among the fastest in solution, and methods allowing direct measurements of the rate constants are valuable 31 .…”

Section: Discussionmentioning

confidence: 78%

Dual-Function pH and Oxygen Phosphonated Trityl Probe

et al. 2012

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Triarylmethyl radicals, TAMs, are used as persistent paramagnetic probes for EPR spectroscopic and imaging applications and as hyperpolarizing and contrast agents for MRI and proton-electron double-resonance imaging, PEDRI. Recently we proposed the concept of dual function pH and oxygen TAM probes based on the incorporation of ionizable groups into the TAM structure (J. Am. Chem. Soc. 2007, 129, 7240–7241). In this paper we report the synthesis of deuterated derivative of phosphonated trityl radical, pTAM. The presence of phosphono substitutes in the structure of TAM provides pH sensitivity of its EPR spectrum in the physiological range of pH from 6 to 8, the phosphorus hyperfine splitting being convenient and highly sensitive pH marker (spectral sensitivity, 3ΔaP/ΔpH≈0.5 G/pH unit; accuracy of pH measurements, ±0.05). In addition, substitution of 36 methyl protons with deuterons significantly decreased the individual linewidth of pTAM down to 40 mG and, as consequence, provided high sensitivity of the linewidth broadening to pO2 (ΔH/ΔpO2≈0.4 mG/mmHg; accuracy of pO2 measurements, ≈1 mmHg). The independent character of pH and [O2] effects on the EPR spectra of pTAM provides dual functionality to this probe allowing for an extraction of both parameters from a single EPR spectrum.

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Section: Discussionmentioning

confidence: 78%

Dual-Function pH and Oxygen Phosphonated Trityl Probe

et al. 2012

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“…It has been previously demonstrated by Khramtsov et al and others that the assumption of slow-exchange can be ensured by limiting concentrations of NR and accompanying buffer as well as by selecting 3 < pK a < 11 [32, 33, 19]. Generally, concentrations of 1 mM or less for NR and 10 mM or less for buffer are adequate to ensure slow-exchange [34, 35]. …”

Section: Discussionmentioning

confidence: 99%

Spectral modeling for accelerated pH spectroscopy using EPR

Ahmad

Potter

Khramtsov

2012

Journal of Magnetic Resonance

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A data modeling and processing method for electron paramagnetic resonance (EPR)-based pH spectroscopy is presented. The proposed method models the EPR spectrum of a pH-sensitive probe in both protonated and unprotonated forms. Under slow-exchange conditions, the EPR spectrum of a sample with an unknown pH value can be accurately represented by a weighted sum of the two models, with the pH value completely determined by their relative weights. Unlike traditional pH spectroscopy, which relies on locating resonance peaks, the proposed modeling-based approach utilizes the information from the entire scan and hence leads to more accurate estimation of pH for a given acquisition time. By employing the proposed methodology, we expect a reduction in the pH estimation error by more than a factor of three, which represents an order of magnitude reduction in acquisition time compared to the traditional method.

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“…The synthesis of the deuterated analogues of pH-sensitive nitroxides, e.g. deuterated R1 and R-GSH, would result in significant decrease of probe linewidth[35], therefore making in vivo pH mapping using VRF PEDRI feasible. Alternative strategy of the development of pH-sensitive probes with narrow EPR linewidths was proposed [36] and is based on the chemical modification of stable trityl radicals.…”

Section: Discussionmentioning

confidence: 99%

Variable radio frequency proton–electron double-resonance imaging: Application to pH mapping of aqueous samples

Efimova

Sun

Petryakov

et al. 2011

Journal of Magnetic Resonance

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Proton-Electron Double-Resonance Imaging (PEDRI) offers rapid image data collection and high resolution for spatial distribution of paramagnetic probes. Recently we developed the concept of Variable Field (VF) PEDRI which enables extracting a functional map from a limited number of images acquired at pre-selected EPR excitation fields using specific paramagnetic probes (Khramtsov et al. 2010, JMR, 202, 267-273). In this work, we propose and evaluate a new modality of PEDRI-based functional imaging with enhanced temporal resolution which we term Variable Radio Frequency (VRF) PEDRI. The approach allows for functional mapping (e.g., pH mapping) using specifically designed paramagnetic probes with high quality spatial resolution and short acquisition times. This approach uses a stationary magnetic field but different EPR RFs. The ratio of Overhauser enhancements measured at each pixel at two different excitation frequencies corresponding to the resonances of protonated and deprotonated forms of a pH-sensitive nitroxide is converted to a pH map using a corresponding calibration curve. Elimination of field cycling decreased the acquisition time by exclusion periods of ramping and stabilization of the magnetic field. Improved magnetic field homogeneity and stability allowed for the fast MRI acquisition modalities such as fast spin echo. In total, about 30-fold decrease in EPR irradiation time was achieved for VRF PEDRI (2.4 s) compared with VF PEDRI (70 s). This is particularly important for in vivo applications enabling one to overcome the limiting stability of paramagnetic probes and sample overheating by reducing RF power deposition.

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EPR studies of15N- and2H-substituted pH-sensitive spin probes of imidazoline and imidazolidine types

Cited by 11 publications

References 12 publications

Dual-Function pH and Oxygen Phosphonated Trityl Probe

Dual-Function pH and Oxygen Phosphonated Trityl Probe

Spectral modeling for accelerated pH spectroscopy using EPR

Variable radio frequency proton–electron double-resonance imaging: Application to pH mapping of aqueous samples

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