Distance and Potential Dependence of Charge Transport Through the P700 Reaction Center of Photosystem I

Photoinduced charge separation and transport through photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. To investigate charge exchange processes mediated by the P700 reaction center of PSI, we have developed a strategy to functionalize gold electrodes with PSI complexes that orients and exposes their luminal side to the electrolyte. Bulk photoelectrochemical measurements demonstrate that PSI remains functional in a wide sample potential range around 0 mV/SSC. Electrochemical scanning tunneling microscopy (ECSTM) imaging of individual complexes shows lateral sizes in agreement with the dimensions of PSI and an apparent height that is gated by the probe potential of ECTSM as reported for smaller globular redox proteins. This experimental setup enables ECSTM current-distance spectroscopic measurements that unequivocally correspond to the P700 side of PSI. In these conditions, we observe that the spatial span of the current is enhanced (the distance-decay rate β is reduced) through the solution at sample potential 0 mV/SSC and probe potential 400 mV/SSC. This process corresponds to hole injection into an electronic state that is available in the absence of illumination. We propose that a pair of tryptophan residues located near P700 and known to integrate the hydrophobic recognition site for plastocyanin may have an additional role as hole exchange mediator involved in charge transport through PSI.<br>

Distance and Potential Dependence of Charge Transport Through the P700 Reaction Center of Photosystem I

Photoinduced charge separation and transport through photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. To investigate charge exchange processes mediated by the P700 reaction center of PSI, we have developed a strategy to functionalize gold electrodes with PSI complexes that orients and exposes their luminal side to the electrolyte. Bulk photoelectrochemical measurements demonstrate that PSI remains functional in a wide sample potential range around 0 mV/SSC. Electrochemical scanning tunneling microscopy (ECSTM) imaging of individual complexes shows lateral sizes in agreement with the dimensions of PSI and an apparent height that is gated by the probe potential of ECTSM as reported for smaller globular redox proteins. This experimental setup enables ECSTM current-distance spectroscopic measurements that unequivocally correspond to the P700 side of PSI. In these conditions, we observe that the spatial span of the current is enhanced (the distance-decay rate β is reduced) through the solution at sample potential 0 mV/SSC and probe potential 400 mV/SSC. This process corresponds to hole injection into an electronic state that is available in the absence of illumination. We propose that a pair of tryptophan residues located near P700 and known to integrate the hydrophobic recognition site for plastocyanin may have an additional role as hole exchange mediator involved in charge transport through PSI.<br>

Measurement of Floating Potential and Ion Concentration in Arc Plasma at Atmospheric Pressure

Arc plasma is generated using low voltage dc power supply for the measurement of plasma parameters such as floating potential and ion-concentration in the plasma seeded with molybdenum. Langmuir moving probe is used in order to measure the probe current at different values of the dc potential applied on the probe. A graph is plotted between the probe current and the probe potential, based on data at the atmospheric pressure, using the experimental set up in the gas discharge chamber for the single probe method. The floating potential is calculated to be 32V, and the average ion-concentration to be 1.43 - 10e16m3.

Amino acid inspired tunable superparamagnetic iron oxide (SPION) nanostructures with high magnetic hyperthermia potential for biofunctional applications

Amino acid inspired biocompatible and tunable magnetic SPION nanostructures with high saturation magnetization hyperthermia and biofunctional probe potential are shown.

It is about timing: Network prestige in asynchronous online discussions

Asynchronous online discussions are broadly used to support social learning. This paper reports on an undergraduate class’s online discussion activities over one semester. Applying Social Network Analysis, this study revealed a participation gap among students reflected by their varied levels of network prestige. The low-prestige group initiated equivalent volumes of interactions but were less reciprocated. In-depth analysis found the high-prestige group also advantageous in other network measures such as closeness centrality and eigenvector centrality, as well as the strength, persistence, and reciprocity of their ties. To probe potential explanations of the revealed gap, we further contrasted post content and posting behaviors between two groups. Results did not identify any significant differences in post content but found low-prestige students’ participation less timely and more temporally compressed. This paper calls for attention to the participation gap in online discussions, micro-level temporal patterns of student activities, and practical means to scaffold student participation in asynchronous onlinediscussions.

Experimental set up for the study of plasma parameters in seeded arc plasma using Langmuir Probes inside low-cost vacuum chamber

In this piece of study, the design and development of a low cost vacuum chamber with different ports are mentioned. I-V characteristic of Langmuir Probe is obtained using the primary data of the experimental set up for ‘single probe method’ in nitrogen seeded arc plasma at atmospheric pressure The floating potential was found to be 36V and the electron density to be 1.24 ´ 104 K. Variation in electron density of the arc plasma with probe potential is also studied at low pressure range from 10 Nm-2 (0.10 mbar) to 20 Nm-2.BIBECHANA 16 (2019) 1-6