Direct spectroscopic quantification of small molecules using low cost, low field (< 0.1 T) large bore portable magnets is not possible using conventional techniques due the presence of strong... Show moreDirect spectroscopic quantification of small molecules using low cost, low field (< 0.1 T) large bore portable magnets is not possible using conventional techniques due the presence of strong homonuclear coupling which results in complicated spectral patterns with resonances separated by much less than the achievable spectral linewidth. In contrast, a method using the signals from a Carr-Purcell-Meiboom-Gill (CPMG) train, in which the data are Fourier transformed in this indirect dimension, can produce so-called J-spectra in which several distinct spectral features can be distinguished. In this work, we evaluate this technique to quantify the amount of alcohol (ethanol) in intact bottles of wines or spirits. Show less
Zurlo, E.; Passerini, L.; Kumar, P.; Huber, M. 2021
Self-aggregation of amyloid proteins is a crucial step in neurodegenerative disease. The protein alpha-synuclein (alpha S) is implicated in Parkinson's disease. In an extension of the demonstration... Show moreSelf-aggregation of amyloid proteins is a crucial step in neurodegenerative disease. The protein alpha-synuclein (alpha S) is implicated in Parkinson's disease. In an extension of the demonstration of in situ observation of intermediates in alpha S-aggregation by continuous wave (cw) EPR at room temperature (Zurlo et al. PLoS One 16: e0245548, 2021) by spin-label EPR, here the spin label is attached to position 90 (R1 alpha S90), rather than at position 56. The aim is to determine, if the spin-label position affects the kinetics of aggregation and if local information on the intermediates is accessible. Probed by the MTSL ((1-Oxyl-2,2,5,5-tetramethylpyrroline-3-methyl) methanethiosulfonate) spin label at position 90, using diamagnetic dilution of 9:1 wild type alpha S to R1 alpha S90, similar aggregation kinetics are found. Rotation correlation times for the spin label in the oligomer cannot be determined with sufficient accuracy to obtain local information on the oligomer under the conditions used. At the present stage, higher resolution EPR approaches, such as high-field EPR are more promising. Show less
Matysik, J.; Ding, Y.H.; Kim, Y.; Kurle, P.; Yurkovskaya, A.; Ivanov, K.; Alia, A. 2021
Photo-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarization created by the spin-chemical evolution of spin-correlated radical pairs (SCRPs). This phenomenon... Show morePhoto-CIDNP (photo-chemically induced dynamic nuclear polarization) refers to nuclear polarization created by the spin-chemical evolution of spin-correlated radical pairs (SCRPs). This phenomenon occurs in gases, liquids and solids. Based on the solid-state photo-CIDNP effect observed under magic-angle spinning (MAS), photo-CIDNP MAS NMR has been developed as analytical method. Here we report the origin, the theory and the state of the art of this method. Show less
A high-field (D-band, 130 GHz) electron spin echo-detected spectrum of the primary electron donor triplet state, P-3, in quinone-depleted photosynthetic reaction centers from the bacterium... Show moreA high-field (D-band, 130 GHz) electron spin echo-detected spectrum of the primary electron donor triplet state, P-3, in quinone-depleted photosynthetic reaction centers from the bacterium Rhodobacter sphaeroides R26 is obtained. It shows a significant g-anisotropy, which is larger than that of the primary donor oxidized state, P+. Simulation gives the triplet g-tensor principal values of 2.0037, 2.0028, and 2.0022 (precision +/-0.0001), assuming that the g-tensor is coaxial to a zerofield splitting tensor. The P-3 spectral lineshape reveals an orientational anisotropy of the triplet quantum yield. We explain this anisotropy as arising from the difference in the main values and relative orientations between the g-tensors of P+ and I-A(-.) in the primary radical pair (the triplet state's precursor). Show less
The electron spin polarization (ESP) of the triplet of the primary donor (P-3) in, reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis shows an anisotropic temperature... Show moreThe electron spin polarization (ESP) of the triplet of the primary donor (P-3) in, reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis shows an anisotropic temperature dependence (Van Wijk, F.G.H. and Schaafsma, T.J. (1988) Biochim. Biophys. Acta 936, 236). The reported inversion of the initial electron spin polarization (IESP) for the canonical Y-direction of P-3 at 100 K has been explained by means of coherent S-T-z mixing in the radical pair, due to a fast relaxing electron spin on the iron-quinone acceptor complex X (Here, P.J., Hunter, D.A., Van Wijk, F.G.H., Schaafsma, T.J. and Hoff, AJ. (1988) Biochim. Biophys. Acta 936, 249). Using direct-detection EPR, we show that at 100 K the IESP in randomly oriented samples is not inverted for the canonical Y-direction of P-3. Furthermore, in single crystals the IESP at 100 K is shown to be almost zero for the complete YZ-plane of P-3. Since X(.-) shows a strong g-anisotropy, the model of Here et al., in wg-anisotropy, the model of Here et al., in which polarization-inversion only occurs when the effective g-value of X(.-) is around g = 2.00, is inadequate to explain the temperature-dependent changes of the IESP. Therefore, we conclude that anisotropic fast spin-lattice relaxation in the radical pair triplet state is the origin of the temperature dependence of the ESP. The inversion for the canonical Y-direction under continuous illumination is the result of the interplay of spin-lattice relaxation in P-3 and its triplet decay rates, in combination with changes in the IESP. Show less
Brink, J.S. van den; Gast, P.; Hoff, A.J.; Manikowski, H. 1994
The electron spin polarization (ESP) of triplet of the primary donor (P-3) of Rhodopseudomonas viridis reaction centers (RCs) is anomalous at temperatures above 25 K, i.e. the steady-state ESP... Show moreThe electron spin polarization (ESP) of triplet of the primary donor (P-3) of Rhodopseudomonas viridis reaction centers (RCs) is anomalous at temperatures above 25 K, i.e. the steady-state ESP changes from AEEAAE to AEAEAE. Fast, time-resolved EPR measurements in solid solution and single crystals of RCs show that this phenomenon results most probably from fast anisotropic spin-lattice relaxation in the radical pair triplet state (k(r) almost-equal-to 5 . 10(9) s-1 at 25 K). Show less
