Assessment of the non-Gaussianity and non-linearity levels of simulated sEMG signals on stationary segments

The purpose of this paper was to evaluate the effects of the longitudinal single differential (LSD), the longitudinal double differential (LDD) and the normal double differential (NDD) spatial filters, the electrode shape, the inter-electrode distance (IED) on non-Gaussianity and non-linearity levels of simulated surface EMG (sEMG) signals when the maximum voluntary contraction (MVC) varied from 10% to 100% by a step of 10%. The effects of recruitment range thresholds (RR), the firing rate (FR) strategy and the peak firing rate (PFR) of motor units were also considered.A cylindrical multilayer model of the volume conductor and a model of motor unit (MU) recruitment and firing rate were used to simulate sEMG signals in a pool of 120 MUs for 5 s. Firstly, the stationarity of sEMG signals was tested by the runs, the reverse arrangements (RA) and the modified reverse arrangements (MRA) tests. Then the non-Gaussianity was characterised with bicoherence and kurtosis, and non-linearity levels was evaluated with linearity test.The kurtosis analysis showed that the sEMG signals detected by the LSD filter were the most Gaussian and those detected by the NDD filter were the least Gaussian. In addition, the sEMG signals detected by the LSD filter were the most linear. For a given filter, the sEMG signals detected by using rectangular electrodes were more Gaussian and more linear than that detected with circular electrodes. Moreover, the sEMG signals are less non-Gaussian and more linear with reverse onion-skin firing rate strategy than those with onion-skin strategy. The levels of sEMG signal Gaussianity and linearity increased with the increase of the IED, RR and PFR.     

High-density surface EMG study on the time course of central nervous and peripheral neuromuscular changes during 8 weeks of bed rest with or without resistive vibration exercise

The aim of the present study was to assess the time course and the origin of adaptations in neuromuscular function as a consequence of prolonged bed rest with or without countermeasure. Twenty healthy males volunteered to participate in the present study and were randomly assigned to either an inactive control group (Ctrl) or to a resistive vibration exercise (RVE) group. Prior to, and seven times during bed rest, we recorded high-density surface electromyogram (sEMG) signals from the vastus lateralis muscle during isometric knee extension exercise at a range of contraction intensities (5–100% of maximal voluntary isometric torque). The high-density sEMG signals were analyzed for amplitude (root mean square, RMS), frequency content (median frequency, F_med) and muscle fiber conduction velocity (MFCV) in an attempt to describe bed rest-induced changes in neural activation properties at the levels of the motor control and muscle fibers. Without countermeasures, bed rest resulted in a significant progressive decline in maximal isometric knee extension strength, whereas RMS remained unaltered throughout the bed rest period. In line with observed muscle atrophy, both F_med and MFCV declined during bed rest. RVE training during bed rest resulted in maintained maximal isometric knee extension strength, and a strong increase (～30%) in maximal EMG amplitude, from 10 days of bed rest on. Exclusion of other factors led to the conclusion that the RVE training increased motor unit firing rates as a consequence of an increased excitability of motor neurons. An increased firing rate might have been essential under training sessions, but it did not affect isometric voluntary torque capacity.     

EPR studies of the water oxidizing complex in the S1 and the higher S states: the manganese cluster and YZ radical

The parallel polarization electron paramagnetic resonance (EPR) method has been applied to investigate manganese EPR signals of native S₁ and S₃ states of the water oxidizing complex (WOC) in photosystem (PS) II. The EPR signals in both states were assigned to thermally excited states with S=1, from which zero-field interaction parameters D and E were derived. Three kinds of signals, the doublet signal, the singlet-like signal and g=11–15 signal, were detected in Ca²⁺-depleted PS II. The g=11–15 signal was observed by parallel and perpendicular modes and assigned to a higher oxidation state beyond S₂ in Ca²⁺-depleted PS II. The singlet-like signal was associated with the g=11–15 signal but not with the Y_Z (the tyrosine residue 161 of the D1 polypeptide in PS II) radical. The doublet signal was associated with the Y_Z radical as proved by pulsed electron nuclear double resonance (ENDOR) and ENDOR-induced EPR. The electron transfer mechanism relevant to the role of Y_Z radical was discussed.     

The Origin of the Multiline and g = 4.1 Electron Paramagnetic Resonance Signals from the Oxygen-Evolving System of Photosystem II

Continuous illumination at 200 K of photosystem (PS) II-enriched membranes generates two electron paramagnetic resonance (EPR) signals that both are connected with the S₂ state: a multiline signal at g 2 and a single line at g = 4.1. From measurements at three different X-band frequencies and at 34 GHz, the g tensor of the multiline species was found to be isotropic with g = 1.982. It has an excited spin multiplet at ~30 cm^-1, inferred from the temperature-dependence of the linewidth. The intensity ratio of the g = 4.1 signal to the multiline signal was found to be almost constant from 5 to 23 K. Based on these findings and on spin quantitation of the two signals in samples with and without 4% ethanol, it is concluded that they arise from the ground doublets of paramagnetic species in different PS II centers. It is suggested that the two signals originate from separate PS II electron donors that are in a redox equilibrium with each other in the S₂ state and that the g = 4.1 signal arises from monomeric Mn(IV).     

The vastus lateralis neuromuscular activity during all-out cycling exercise

ObjectiveThe objective of this work was to study modifications in motor control through surface electromyographic (sEMG) activity during a very short all-out cycling exercise.MethodsTwelve male cyclists (age 23 ± 4 years) participated in this study. After a warm-up period, each subject performed three all-out cycling exercises of 6 s separated by 2 min of complete rest. This protocol was repeated three times with a minimum of 2 days between each session. The braking torque imposed on cycling motion was 19 N m. The sEMG of the vastus lateralis was recorded during the first seven contractions of the sprint. Time–frequency analysis of sEMG was performed using continuous wavelet transform. The mean power frequency (MPF, qualitative modifications in the recruitment of motor units) and signal energy (a quantitative indicator of modifications in the motor units recruitment) were computed for the frequency range 10–500 Hz.ResultssEMG energy increased (P ? 0.05) between contraction number 1 and 2, decreased (P ? 0.05) between contraction number 2 and 3 then stabilized between contraction number 3 and 7 during the all-out test. MPF increased (P ? 0.05) during the all-out test. This increase was more marked during the first two contractions.ConclusionsThe decrease in energy and the increase in the sEMG MPF suggest a large spatial recruitment of motor units (MUs) at the beginning of the sprint followed by a preferential recruitment of faster MUs at the end of the sprint, respectively.     

Biceps brachii myoelectric and oxygenation changes during static and sinusoidal isometric exercises

Surface myoelectric signal changes occurring during sustained isometric contractions have been extensively studied with quantitative surface electromyography (sEMG) and are described by means of some sEMG global variables in time and frequency domain (such as the median power spectral frequency). Recently, the possibility of studying local muscle O₂ saturation during exercise using non-invasive methods has been enhanced thanks to the use of near-infrared spectroscopy (NIRS). The purpose of this work was to combine NIRS and sEMG techniques to analyze the relationship between modifications of sEMG parameters and the underlying metabolic status of the exercising biceps brachii muscle. This relationship was tested under different isometric contraction modalities, namely static (ST) at 20, 40, 60 and 80%MVC and sinusoidal (SIN) at 40 ± 20 and 60 ± 20%MVC. Results clearly indicated the presence of an initial fast phase of muscle O₂ desaturation followed by a slow phase, regardless of the contraction modality. Moreover, the initial rate of muscle O₂ desaturation was related to the level of force output (R = 0.92), but it was independent on the contraction modality (p < 0.05). Similarly, changes in sEMG parameters were related to force level (Conduction Velocity-CV vs. Force: R = 0.87; sEMG Median Frequency-MDF vs. Force: R = 0.86). The high correlation found between CV-MDF and Tissue Oxygenation Index (TOI) slope (R = 0.73 and 0.72, respectively) suggests a strong relationship between NIRS and sEMG data. This study indicates that muscle O₂ demand during isometric contractions from low to high force levels is influenced by the type of active motor units and not from the type of isometric exercise modality.     

The effects of acute and prolonged muscle vibration on the function of the muscle spindle’s reflex arc

Abstract

Purpose:?Localized mechanical vibration, applied directly to a muscle, is known to have powerful, duration-dependent effects on the muscle spindle’s reflex arc. Here, the conditioning of the function of the spindle reflex arc via vibration was examined with considerations for use as a non-invasive, sensorimotor research tool.

Methods:?Muscle spindle function was examined with patellar tendon taps prior to and following exposure to muscle vibration applied to the quadriceps femoris for acute (<5?s) and prolonged (20?min) durations. Surface electromyography (sEMG), torque, and accelerometry signals were obtained during the taps to quantify various measures of reflex magnitude and latency.

Results:?Our findings suggest that acute vibration had no effect on normalized reflex torque or sEMG amplitude (p?>?0.05), but increased total reflex latency (p?=?0.022). Alternatively, prolonged vibration reduced normalized reflex torque and sEMG amplitude (p?<?0.001), and increased reflex latency (p?<?0.001).

Conclusions:?Our findings support the use of prolonged vibration as a practical means to decrease the function of the muscle spindle’s reflex arc. Overall, this suppressive effect was evident in the majority of subjects, but the extent was variable. This approach could potentially be used to help delineate the muscle spindle’s role in various sensory or motor tasks in which more direct measures are not feasible. Acute vibration, however, did not potentiate muscle spindle function as hypothesized. Rather, our results suggest that acute vibration increased total reflex latency. Accordingly, potential mechanical and neurophysiological mechanisms are discussed.     

Ultrathin and Porous Ni3S2/CoNi2S4 3D‐Network Structure for Superhigh Energy Density Asymmetric Supercapacitors

3D‐networked, ultrathin, and porous Ni₃S₂/CoNi₂S₄ on Ni foam (NF) is successfully designed and synthesized by a simple sulfidation process from 3D Ni–Co precursors. Interestingly, the edge site‐enriched Ni₃S₂/CoNi₂S₄/NF 3D‐network is realized by the etching‐like effect of S^2? ions, which made the surfaces of Ni₃S₂/CoNi₂S₄/NF with a ridge‐like feature. The intriguing structural/compositional/componental advantages endow 3D‐networked‐free‐standing Ni₃S₂/CoNi₂S₄/NF electrodes better electrochemical performance with specific capacitance of 2435 F g^?1 at a current density of 2 A g^?1 and an excellent rate capability of 80% at 20 A g^?1. The corresponding asymmetric supercapacitor achieves a high energy density of 40.0 W h kg^?1 at an superhigh power density of 17.3 kW kg^?1, excellent specific capacitance (175 F g^?1 at 1A g^?1), and electrochemical cycling stability (92.8% retention after 6000 cycles) with Ni₃S₂/CoNi₂S₄/NF as the positive electrode and activated carbon/NF as the negative electrode. Moreover, the temperature dependences of cyclic voltammetry curve polarization and specific capacitances are carefully investigated, and become more obvious and higher, respectively, with the increase of test temperature. These can be attributed to the components' synergetic effect assuring rich redox reactions, high conductivity as well as highly porous but robust architectures. This work provides a general, low‐cost route to produce high performance electrode materials for portable supercapacitor applications on a large scale.     

EPR studies of the oxygen-evolving enzyme of Photosystem II

The light-induced EPR multiline signal is studied in O₂-evolving PS II membranes. The following results are reported: (1) Its amplitude is shown to oscillate with a period of 4, with respect to the number of flashes given at room temperature (maxima on the first and fifth flashes). (2) Glycerol enhances the signal intensity. This effect is shown to come from changes in relaxation properties rather than an increase in spin concentration. (3) Deactivation experiments clearly indicate an association with the S₂ state of the water-oxidizing enzyme. A signal at g = 4.1 with a linewidth of 360 G is also reported and it is suggested that this arises from an intermediate donor between the S states and the reaction centre. This suggestion is based on the following observations: (1) The g = 4.1 signal is formed by illumination at 200 K and not by flash excitation at room temperature, suggesting that it arises from an intermediate unstable under physiological conditions. (2) The formation of the g = 4.1 signal at 200 K does not occur in the presence of DCMU, indicating that more than one turnover is required for its maximum formation. (3) The g = 4.1 signal decreases in the dark at 220 K probably by recombination with Q^?_AFe. This recombination occurs before the multiline signal decreases, indicating that the g = 4.1 species is less stable than S₂. (4) At short times, the decay of the g = 4.1 signal corresponds with a slight increase in the multiline S₂ signal, suggesting that the loss of the g = 4.1 signal results in the disappearance of a magnetic interaction which diminishes the multiline signal intensity. (5) Tris-washed PS II membranes illuminated at 200 K do not exhibit the signal.     

A new EPR signal attributed to the primary plastosemiquinone acceptor in Photosystem II

A study of signals, light-induced at 77 K in O₂-evolving Photosystem II (PS II) membranes showed that the EPR signal that has been attributed to the semiquinone-iron form of the primary quinone acceptor, Q^?_AFe, at g = 1.82 was usually accompanied by a broad signal at g = 1.90. In some preparations, the usual g = 1.82 signal was almost completely absent, while the intensity of the g = 1.90 signal was significantly increased. The g = 1.90 signal is attributed to a second EPR form of the primary semiquinone-iron acceptor of PS II on the basis of the following evidence. (1) The signal is chemically and photochemically induced under the same conditions as the usual g = 1.82 signal. (2) The extent of the signal induced by the addition of chemical reducing agents is the same as that photochemically induced by illumination at 77 K. (3) When the g = 1.82 signal is absent and instead the g = 1.90 signal is present, illumination at 200 K of a sample containing a reducing agent results in formation of the characteristic split pheophytin^? signal, which is thought to arise from an interaction between the photoreduced pheophytin acceptor and the semiquinone-iron complex. (4) Both the g = 1.82 and g = 1.90 signals disappear when illumination is given at room temperature in the presence of a reducing agent. This is thought to be due to a reduction of the semiquinone to the nonparamagnetic quinol form. (5) Both the g = 1.90 and g = 1.82 signals are affected by herbicides which block electron transfer between the primary and secondary quinone acceptors. It was found that increasing the pH results in an increase of the g = 1.90 form, while lowering the pH favours the g = 1.82 form. The change from the g = 1.82 form to the g = 1.90 form is accompanied by a splitting change in the split pheophytin^? signal from approx. 42 to approx. 50 G. Results using chloroplasts suggest that the g = 1.90 signal could represent the form present in vivo.     

Quadriceps EMG frequency content following isometric lumbar extension exercise

A relationship exists between muscles of the lumbar spine and those of the lower extremity where the quadriceps become more inhibited after lumbar paraspinal. The purpose of this experiment was to compare surface electromyography (sEMG) total frequency content after lumbar paraspinal fatiguing exercise. Scope: 50 subjects performed fatiguing lumbar extension exercise indexed by downward shifts in median frequency calculated from lumbar paraspinal sEMG signal. Before and after each exercise set we recorded maximal, isometric knee extension torque and quadriceps central activation ratio (QI) using the superimposed burst technique while recording vastus lateralis sEMG. We calculated total frequency content of the sEMG signal (fEMG_TOTAL) as the area of the quadriceps sEMG frequency spectrum. Quadriceps fEMG_TOTAL decreased from baseline following the first and second exercise sets. There was no significant change in quadriceps sEMG median frequency among baseline and post-exercise measures. The change in fEMG_TOTAL was correlated with the change in QI following the first (r = ?0.41, P = 0.003) and second (r = ?0.32, P = 0.02) exercise sets. Conclusion: Quadriceps fEMG_TOTAL decreased following fatiguing lumbar extension exercise, in the absence of a significant change in quadriceps median frequency.     

Detection of surface electromyography recording time interval without muscle fatigue effect for biceps brachii muscle during maximum voluntary contraction

The effects of fatigue on maximum voluntary contraction (MVC) parameters were examined by using force and surface electromyography (sEMG) signals of the biceps brachii muscles (BBM) of 12 subjects. The purpose of the study was to find the sEMG time interval of the MVC recordings which is not affected by the muscle fatigue. At least 10 s of force and sEMG signals of BBM were recorded simultaneously during MVC. The subjects reached the maximum force level within 2 s by slightly increasing the force, and then contracted the BBM maximally. The time index of each sEMG and force signal were labeled with respect to the time index of the maximum force (i.e. after the time normalization, each sEMG or force signal’s 0 s time index corresponds to maximum force point). Then, the first 8 s of sEMG and force signals were divided into 0.5 s intervals. Mean force, median frequency (MF) and integrated EMG (iEMG) values were calculated for each interval. Amplitude normalization was performed by dividing the force signals to their mean values of 0 s time intervals (i.e. ?0.25 to 0.25 s). A similar amplitude normalization procedure was repeated for the iEMG and MF signals. Statistical analysis (Friedman test with Dunn’s post hoc test) was performed on the time and amplitude normalized signals (MF, iEMG). Although the ANOVA results did not give statistically significant information about the onset of the muscle fatigue, linear regression (mean force vs. time) showed a decreasing slope (Pearson-r = 0.9462, p < 0.0001) starting from the 0 s time interval. Thus, it might be assumed that the muscle fatigue starts after the 0 s time interval as the muscles cannot attain their peak force levels. This implies that the most reliable interval for MVC calculation which is not affected by the muscle fatigue is from the onset of the EMG activity to the peak force time. Mean, SD, and range of this interval (excluding 2 s gradual increase time) for 12 subjects were 2353, 1258 ms and 536–4186 ms, respectively. Exceeding this interval introduces estimation errors in the maximum amplitude calculations of MVC–sEMG studies for BBM. It was shown that, simultaneous recording of force and sEMG signals was required to calculate the maximum amplitude of the MVC–sEMG more accurately.     

Evaluation of Respiratory Muscle Activation Using Respiratory Motor Control Assessment (RMCA) in Individuals with Chronic Spinal Cord Injury

During breathing, activation of respiratory muscles is coordinated by integrated input from the brain, brainstem, and spinal cord. When this coordination is disrupted by spinal cord injury (SCI), control of respiratory muscles innervated below the injury level is compromised^1,2 leading to respiratory muscle dysfunction and pulmonary complications. These conditions are among the leading causes of death in patients with SCI³. Standard pulmonary function tests that assess respiratory motor function include spirometrical and maximum airway pressure outcomes: Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV₁), Maximal Inspiratory Pressure (PI_max) and Maximal Expiratory Pressure (PE_max)^4,5. These values provide indirect measurements of respiratory muscle performance⁶. In clinical practice and research, a surface electromyography (sEMG) recorded from respiratory muscles can be used to assess respiratory motor function and help to diagnose neuromuscular pathology. However, variability in the sEMG amplitude inhibits efforts to develop objective and direct measures of respiratory motor function⁶. Based on a multi-muscle sEMG approach to characterize motor control of limb muscles⁷, known as the voluntary response index (VRI)⁸, we developed an analytical tool to characterize respiratory motor control directly from sEMG data recorded from multiple respiratory muscles during the voluntary respiratory tasks. We have termed this the Respiratory Motor Control Assessment (RMCA)⁹. This vector analysis method quantifies the amount and distribution of activity across muscles and presents it in the form of an index that relates the degree to which sEMG output within a test-subject resembles that from a group of healthy (non-injured) controls. The resulting index value has been shown to have high face validity, sensitivity and specificity^9-11. We showed previously⁹ that the RMCA outcomes significantly correlate with levels of SCI and pulmonary function measures. We are presenting here the method to quantitatively compare post-spinal cord injury respiratory multi-muscle activation patterns to those of healthy individuals.     

Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during prolonged dynamic exercises at low force levels

In surface electromyography (sEMG), the distribution of motor unit potential (MUP) velocities has been shown to reflect the proportion of faster and slower propagating MUPs. This study investigated whether the distribution of MUP velocities could distinguish between sprinters (n = 11) and endurance athletes (n = 12) in not-specifically trained muscle (biceps brachii) during prolonged dynamic exercises at low forces. sEMG was acquired during 4 min’ exercises: unloaded, 5%, 10% and 20% of maximal voluntary contraction (MVC). The features extracted from the sEMG were: the mean muscle conduction velocity – estimated using the inter-peak latency and cross-correlation methods, the within-subject skewness (expressing the proportions of faster and slower propagating MUPs) and the within-subject standard deviation of MUP velocities (SD-mup). Sprinters showed a greater proportion of faster propagating MUPs than endurance athletes. During fatigue, the SD-mup of sprinters broadened progressively, whereas that of endurance athletes did not. The findings suggest that sprinters conveyed a greater proportion of faster motor units than endurance athletes and that motor unit behavior during fatigue differed between groups. Thus, the distribution of MUP velocities enables distinction between a muscle of sprinters and endurance athletes during prolonged dynamic exercises at low forces.     

Conversion of the g = 4.1 EPR signal to the multiline conformation during the S2 to S3 transition of the oxygen evolving complex of Photosystem II

The oxygen evolving complex of Photosystem II undergoes four light-induced oxidation transitions, S₀-S₁,…,S₃-(S₄)S₀ during its catalytic cycle. The oxidizing equivalents are stored at a (Mn)₄Ca cluster, the site of water oxidation. EPR spectroscopy has yielded valuable information on the S states. S₂ shows a notable heterogeneity with two spectral forms; a g = 2 (S = 1/2) multiline, and a g = 4.1 (S = 5/2) signal. These oscillate in parallel during the period-four cycle. Cyanobacteria show only the multiline signal, but upon advancement to S₃ they exhibit the same characteristic g = 10 (S = 3) absorption with plant preparations, implying that this latter signal results from the multiline configuration. The fate of the g = 4.1 conformation during advancement to S₃ is accordingly unknown. We searched for light-induced transient changes in the EPR spectra at temperatures below and above the half-inhibition temperature for the S₂ to S₃ transition (ca 230 K). We observed that, above about 220 K the g = 4.1 signal converts to a multiline form prior to advancement to S₃. We cannot exclude that the conversion results from visible-light excitation of the Mn cluster itself. The fact however, that the conversion coincides with the onset of the S₂ to S₃ transition, suggests that it is triggered by the charge-separation process, possibly the oxidation of tyr Z and the accompanying proton relocations. It therefore appears that a configuration of (Mn)₄Ca with a low-spin ground state advances to S₃.     

EPR detection of a cryogenically photogenerated intermediate in photosynthetic oxygen evolution

In Photosystem II preparations at low temperature we were able to generate and trap an intermediate state between the S₁ and S₂ states of the Kok scheme for photosynthetic oxygen evolution. Illumination of dark-adapted, oxygen-evolving Photosystem II preparations at 140 K produces a 320-G-wide EPR signal centered near g = 4.1 when observed at 10 K. This signal is superimposed on a 5-fold larger and somewhat narrower background signal; hence, it is best observed in difference spectra. Warming of illuminated samples to 190 K in the dark results in the disappearance of the light-induced g = 4.1 feature and the appearance of the multiline EPR signal associated with the S₂ state. Low-temperature illumination of samples prepared in the S₂ state does not produce the g = 4.1 signal. Inhibition of oxygen evolution by incubation of PS II preparations in 0.8 M NaCl buffer or by the addition of 400 μM NH₂OH prevents the formation of the g = 4.1 signal. Samples in which oxygen evolution is inhibited by replacement of Cl^? with F^? exhibit the g = 4.1 signal when illuminated at 140 K, but subsequent warming to 190 K neither depletes the amplitude of this signal nor produces the multiline signal. The broad signal at g = 4.1 is typical for a $\text{S =}\text{5}\text{2}$ spin system in a rhombic environment, suggesting the involvement of non-heme Fe in photosynthetic oxygen evolution.     

Electron paramagnetic resonance and Mössbauer spectroscopy of intact mitochondria from respiring <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Mitochondria from respiring cells were isolated under anaerobic conditions. Microscopic images were largely devoid of contaminants, and samples consumed O₂ in an NADH-dependent manner. Protein and metal concentrations of packed mitochondria were determined, as was the percentage of external void volume. Samples were similarly packed into electron paramagnetic resonance tubes, either in the as-isolated state or after exposure to various reagents. Analyses revealed two signals originating from species that could be removed by chelation, including rhombic Fe³⁺ (g = 4.3) and aqueous Mn²⁺ ions (g = 2.00 with Mn-based hyperfine). Three S = 5/2 signals from Fe³⁺ hemes were observed, probably arising from cytochrome c peroxidase and the a₃:Cu_b site of cytochrome c oxidase. Three Fe/S-based signals were observed, with averaged g values of 1.94, 1.90 and 2.01. These probably arise, respectively, from the [Fe₂S₂]⁺ cluster of succinate dehydrogenase, the [Fe₂S₂]⁺ cluster of the Rieske protein of cytochrome bc ₁, and the [Fe₃S₄]⁺ cluster of aconitase, homoaconitase or succinate dehydrogenase. Also observed was a low-intensity isotropic g = 2.00 signal arising from organic-based radicals, and a broad signal with g _ave = 2.02. Mössbauer spectra of intact mitochondria were dominated by signals from Fe₄S₄ clusters (60–85% of Fe). The major feature in as-isolated samples, and in samples treated with ethylenebis(oxyethylenenitrilo)tetraacetic acid, dithionite or O₂, was a quadrupole doublet with ΔE _Q = 1.15 mm/s and δ = 0.45 mm/s, assigned to [Fe₄S₄]²⁺ clusters. Substantial high-spin non-heme Fe²⁺ (up to 20%) and Fe³⁺ (up to 15%) species were observed. The distribution of Fe was qualitatively similar to that suggested by the mitochondrial proteome.     

The influence of pH on the EPR and redox properties of cytochrome c oxidase in detergent solution and in phospholipid vesicles

The EPR signals of oxidized and partially reduced cytochrome oxidase have been studied at pH 6.4, 7.4, and 8.4. Isolated cytochrome oxidase in both non-ionic detergent solution and in phospholipid vesicles has been used in reductive titrations with ferrocytochrome c.The g values of the low- and high-field parts of the low-spin heme signal in oxidized cytochrome oxidase are shown to be pH dependent. In reductive titrations, low-spin heme signals at g 2.6 as well as rhombic and nearly axial high-spin heme signals are found at pH 8.4, while the only heme signals appearing at pH 6.4 are two nearly axial g 6 signals. This pH dependence is shifted in the vesicles.The g 2.6 signals formed in titrations with ferrocytochrome c at pH 8.4 correspond maximally to 0.25–0.35 heme per functional unit (aa₃) of cytochrome oxidase in detergent solution and to 0.22 heme in vesicle oxidase. The total amount of high-spin heme signals at g 6 found in partially reduced enzyme is 0.45–0.6 at pH 6.4 and 0.1–0.2 at pH 8.4. In titrations of cytochrome oxidase in detergent solution the g 1.45 and g 2 signals disappear with fewer equivalents of ferrocytochrome c added at pH 8.4 compared to pH 6.4.The results indicate that the environment of the hemes varies with the pH. One change is interpreted as cytochrome a₃ being converted from a high-spin to a low-spin form when the pH is increased. Possibly this transition is related to a change of a liganded H₂O to OH^? with a concomitant decrease of the redox potential. Oxidase in phosphatidylcholine vesicles is found to behave as if it experiences a pH, one unit lower than that of the medium.     

Boosting the Stable Na Storage Performance in 1D Oxysulfide

Exploring new structure prototypes and phases by material design, especially anode materials, is essential to develop high‐performance Na‐ion batteries. This study proposes a new anode, Na₂Cu_2.09O_0.50S₂, with a 1D crystal structure and outstanding Na storage performance. In view of the crystal structure of Na₂Cu_2.09O_0.50S₂, [Cu₄S₄] chains act as electrically conducting units enabling conductivity as high as 0.5 S cm^?1. The residual Na₄[CuO] chains act as ionically conducting units forming rich channels for the fast conduction of Na ions as well as maintaining the structural stability even after Na ion extraction. Additional ball milling on the as‐prepared Na₂Cu_2.09O_0.50S₂ significantly decreases its grain size, achieving a capacity of 588 mA h g^?1 with a high initial Coulombic efficiency of 93% at 0.2 A g^?1. Moreover, the Na₂Cu_2.09O_0.50S₂ anode demonstrates outstanding rate capability (408 mA h g^?1 at 2 A g^?1) and extending cyclic performance (82% of capacity retention after 400 cycles). The general structural design idea based on functional units may offer a new avenue to new electrode materials.     

Kinetics study of pyridine biodegradation by a novel bacterial strain,Rhizobium sp. NJUST18

Biodegradation of pyridine by a novel bacterial strain, Rhizobium sp. NJUST18, was studied in batch experiments over a wide concentration range (from 100 to 1,000 mg l^?1). Pyridine inhibited both growth of Rhizobium sp. NJUST18 and biodegradation of pyridine. The Haldane model could be fitted to the growth kinetics data well with the kinetic constants μ* = 0.1473 h^?1, K _s = 793.97 mg l^?1, K _i = 268.60 mg l^?1 and S _m = 461.80 mg l^?1. The true μ _max, calculated from μ*, was found to be 0.0332 h^?1. Yield coefficient Y _X/S depended on S _i and reached a maximum of 0.51 g g^?1 at S _i of 600 mg l^?1. V _max was calculated by fitting the pyridine consumption data with the Gompertz model. V _max increased with initial pyridine concentration up to 14.809 mg l^?1 h^?1. The q _S values, calculated from $V_{ \hbox{max} }$ , were fitted with the Haldane equation, yielding q _Smax = 0.1212 g g^?1 h^?1 and q* = 0.3874 g g^?1 h^?1 at S _m′ = 507.83 mg l^?1, K _s′ = 558.03 mg l^?1, and K _i′ = 462.15 mg l^?1. Inhibition constants for growth and degradation rate value were in the same range. Compared with other pyridine degraders, μ _max and S _m obtained for Rhizobium sp. NJUST18 were relatively high. High K _i and K _i′ values and extremely high K _s and K _s′ values indicated that NJUST18 was able to grow on pyridine within a wide concentration range, especially at relatively high concentrations.