EPR spectroscopy was used to examine the magnetic properties of two enzymatically synthesized polyaniline (PANI) samples obtained in the presence of submicrometer-sized vesicles formed from sodium bis(2-ethylhexyl)sulfosuccinate (AOT) as templates. PANI-HRPC-AOT was synthesized with horseradish peroxidase isoenzyme C (HRPC) and hydrogen peroxide (H2O2) as oxidant while PANI-TvL-AOT was prepared with Trametes versicolor laccase (TvL) and dioxygen (O2) as oxidant. A commercial conductive sample of the emeraldine salt form of polyaniline (PANI-ES) was also used for comparison in order to correlate the experimental data obtained for PANI-HRPC-AOT and PANI-TvL-AOT with the properties of the well-characterized PANI-ES. It was shown that a model based on the concept of correlated polaronic bands could be applied for the interpretation of the EPR spectra of all three examined samples, although PANI-HRPC-AOT and PANI-TvL-AOT were significantly less conductive than PANI-ES. The magnetic properties of the PANI samples could be related to their conductivities, whereby a low conductivity was ascribed to decreased interchain spin interactions which were detectable from a splitting of the triplet spectrum at low temperatures (5-10 K). The obtained effective distance between the polyaniline chains is larger for enzymatically synthesized PANI than for PANI-ES, most likely mainly due to the presence of AOT which could not be removed completely during the work-up. AOT influences the chain conformation and the average chain-chain distance.

In this article, we present the novel application of the nuclear spin bath model and the cluster correlation expansion method on studying the matrix material structure via embedded electron spin decoherence. Profiles of embedded electron spin decoherence under the Carr-Purcell-Meiboom-Gill dynamical decoupling pulse series in a model system for organic solids (malonic acid) are calculated for different structures. Resulting decay profiles exhibit a strong correlation to the variations of an adjacent proton environment among them. In addition, the decoherence behavior of embedded spin in proton spin bath(s) of organic solids is found to be significantly different from bath models with other nuclei through the violation of the even-odd pulse parity, which characterizes the influence of large dipolar coupling between protons at the quantum level. Theoretical predictions of decoherence profiles in polycrystalline, the relative distribution of Hahn echo signal decay time scales among single crystal orientations, and the reduction in Hahn echo signal decay time scale by disorder are positively verified by experiments.

In photosynthesis, final electron transfer from ferredoxin to NADP+ is accomplished by the flavo enzyme ferredoxin:NADP+ oxidoreductase (FNR). FNR is recruited to thylakoid membranes via integral membrane thylakoid rhodanase-like protein TROL. We address the fate of electrons downstream of photosystem I when TROL is absent. We have employed electron paramagnetic resonance (EPR) spectroscopy to study free radical formation and electron partitioning in TROL-depleted chloroplasts. DMPO was used to detect superoxide anion (O2.−) formation, while the generation of other free radicals was monitored by Tiron. Chloroplasts from trol plants pre-acclimated to different light conditions consistently exhibited diminished O2.− accumulation. Generation of other radical forms was elevated in trol chloroplasts in all tested conditions, except for the plants pre-acclimated to high-light. Remarkably, dark- and growth light-acclimated trol chloroplasts were resilient to O2.− generation induced by methyl-viologen. We propose that the dynamic binding and release of FNR from TROL can control the flow of photosynthetic electrons prior to activation of the pseudo-cyclic electron transfer pathway.

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The study of double modulation continuous wave (CW) electron spin resonance (DM-EPR) is reported to detect narrow “spin-packet”-like lines within an inhomogeneous CW-EPR line of low concentration P1 (Ns0) centers ([Ns0] < 1 ppm) in diamond. These narrow lines appear as peaks at multiples of modulation frequency in the double modulation spectrum. It is shown that the respective line shape can be fitted assuming two Lorentzian line shapes. The linewidth of the narrower Lorentzian is comparable with the linewidth of the Lorentzian obtained from the T2 relaxation time δ1=1/πT2 estimated from the Hahn echo pulsed-EPR experiment. The broader component δ2 correlates with the T2* relaxation time obtained from the free induction decay measurement of the inhomogeneous spectral line shape of the P1 center. The ratio δ2/δ1∼18 derived from DM-EPR measurements approaches within the experimental error the value T2/T2*∼16 derived from pulsed-EPR. Sensitivity to the small shift of the magnetic field (∼0.6 μT) was shown to be detectable from the broadening behavior of the δ2 component. The results promote DM-EPR as a method complementary to pulsed-EPR for studying coherence times of low density paramagnetic centers in a diamond lattice like nitrogen-vacancy (NV−) center, since it exhibits similar properties to the here investigated P1 center in terms of long relaxation time at a monitored low concentration.