Transient and Pulsed Electron Paramagnetic Resonance Spectroscopy on Type I Photosynthetic Reaction Centers

Two time-resolved EPR techniques, have been used to study the light induced electron transfer(ET) in Type I photosynthetic reaction centers(RCs). First, pulsed EPR was used to compare PsaA-M688H and PsaB-M668H mutants of Chlamydomonas reinhardtii and Synechosystis sp. PCC 6803.The out-of-phase echo modulation curves combined with other EPR and optical data show that the effect of the mutations is species dependent. Second, transient and pulsed EPR data are presented which show that PsaA-A660N and PsaB-A640N mutations in C. reinhardtii alter the relative quantum yield of ET in the A- and B-branches of PS I. Third, transient EPR studies on RCs from Heliobacillus mobilis that have been exposed to oxygen show partial inhibition of ET. In the RCs in which ET still occurs, the ET kinetics and EPR spectra show evidence of oxidation of some but not all of the, BChl g and BChl g' to Chl a.

Kinetics analysis and automated online screening of aminocarbonylation of aryl halides in flow

Temperature, pressure, gas stoichiometry, and residence time were varied to control the yield and product distribution of the palladium-catalyzed aminocarbonylation of aromatic bromides in both a silicon microreactor and a packed-bed tubular reactor. Automation of the system set points and product sampling enabled facile and repeatable reaction analysis with minimal operator supervision. It was observed that the reaction was divided into two temperature regimes. An automated system was used to screen steady-state conditions for offline analysis by gas chromatography to fit a reaction rate model. Additionally, a transient temperature ramp method utilizing online infrared analysis was used, leading to more rapid determination of the reaction activation energy of the lower temperature regimes. The entire reaction spanning both regimes was modeled in good agreement with the experimental data.

Pro-oxidative synergic bactericidal effect of NO: kinetics and inhibition by nitroxides

NO plays diverse roles in physiological and pathological processes, occasionally resulting in opposing effects, particularly in cells subjected to oxidative stress. NO mostly protects eukaryotes against oxidative injury, but was demonstrated to kill prokaryotes synergistically with H2O2. This could be a promising therapeutic avenue. However, recent conflicting findings were reported describing dramatic protective activity of NO. The previous studies of NO effects on prokaryotes applied a transient oxidative stress while arbitrarily checking the residual bacterial viability after 30 or 60min and ignoring the process kinetics. If NO-induced synergy and the oxidative stress are time-dependent, the elucidation of the cell killing kinetics is essential, particularly for survival curves exhibiting a "shoulder" sometimes reflecting sublethal damage as in the linear-quadratic survival models. We studied the kinetics of NO synergic effects on H2O2-induced killing of microbial pathogens. A synergic pro-oxidative activity toward gram-negative and gram-positive cells is demonstrated even at sub-μM/min flux of NO. For certain strains, the synergic effect progressively increased with the duration of cell exposure, and the linear-quadratic survival model best fit the observed survival data. In contrast to the failure of SOD to affect the bactericidal process, nitroxide SOD mimics abrogated the pro-oxidative synergy of NO/H2O2. These cell-permeative antioxidants, which hardly react with diamagnetic species and react neither with NO nor with H2O2, can detoxify redox-active transition metals and catalytically remove intracellular superoxide and nitrogen-derived reactive species such as (•)NO2 or peroxynitrite. The possible mechanism underlying the bactericidal NO synergy under oxidative stress and the potential therapeutic gain are discussed.

Power Transient Analysis of Experimental Devices for Jules Horowitz Material Testing Reactor (JHR)

The objective of this thesis is the power transient analysis concerning experimental devices placed within the reflector of Jules Horowitz Reactor (JHR). Since JHR material testing facility is designed to achieve 100 MW core thermal power, a large reflector hosts fissile material samples that are irradiated up to total relevant power of 3 MW. MADISON devices are expected to attain 130 kW, conversely ADELINE nominal power is of some 60 kW. In addition, MOLFI test samples are envisaged to reach 360 kW for what concerns LEU configuration and up to 650 kW according to HEU frame. Safety issues concern shutdown transients and need particular verifications about thermal power decreasing of these fissile samples with respect to core kinetics, as far as single device reactivity determination is concerned. Calculation model is conceived and applied in order to properly account for different nuclear heating processes and relative time-dependent features of device transients. An innovative methodology is carried out since flux shape modification during control rod insertions is investigated regarding the impact on device power through core-reflector coupling coefficients. In fact, previous methods considering only nominal core-reflector parameters are then improved. Moreover, delayed emissions effect is evaluated about spatial impact on devices of a diffuse in-core delayed neutron source. Delayed gammas transport related to fission products concentration is taken into account through evolution calculations of different fuel compositions in equilibrium cycle. Provided accurate device reactivity control, power transients are then computed for every sample according to envisaged shutdown procedures. Results obtained in this study are aimed at design feedback and reactor management optimization by JHR project team. Moreover, Safety Report is intended to utilize present analysis for improved device characterization.

Laser-induced transient grating analysis of dynamics of interaction between sensory rhodopsin II D75N and the HtrII transducer.

The interaction between sensory rhodopsin II (SRII) and its transducer HtrII was studied by the time-resolved laser-induced transient grating method using the D75N mutant of SRII, which exhibits minimal visible light absorption changes during its photocycle, but mediates normal phototaxis responses. Flash-induced transient absorption spectra of transducer-free D75N and D75N joined to 120 amino-acid residues of the N-terminal part of the SRII transducer protein HtrII (DeltaHtrII) showed only one spectrally distinct K-like intermediate in their photocycles, but the transient grating method resolved four intermediates (K(1)-K(4)) distinct in their volumes. D75N bound to HtrII exhibited one additional slower kinetic species, which persists after complete recovery of the initial state as assessed by absorption changes in the UV-visible region. The kinetics indicate a conformationally changed form of the transducer portion (designated Tr*), which persists after the photoreceptor returns to the unphotolyzed state. The largest conformational change in the DeltaHtrII portion was found to cause a DeltaHtrII-dependent increase in volume rising in 8 micros in the K(4) state and a drastic decrease in the diffusion coefficient (D) of K(4) relatively to those of the unphotolyzed state and Tr*. The magnitude of the decrease in D indicates a large structural change, presumably in the solvent-exposed HAMP domain of DeltaHtrII, where rearrangement of interacting molecules in the solvent would substantially change friction between the protein and the solvent.

Effects of cross sections tables generation and optimization on rod ejection transient analyses

Best estimate analysis of rod ejection transients requires 3D kinetics core simulators. If they use cross sections libraries compiled in multidimensional tables,interpolation errors – originated when the core simulator computes the cross sections from the table values – are a source of uncertainty in k-effective calculations that should be accounted for. Those errors depend on the grid covering the domain of state variables and can be easily reduced, in contrast with other sources of uncertainties such as the ones due to nuclear data, by choosing an optimized grid distribution. The present paper assesses the impact of the grid structure on a PWR rod ejection transient analysis using the coupled neutron-kinetics/thermal-hydraulicsCOBAYA3/COBRA-TF system. Forthispurpose, the OECD/NEA PWR MOX/UO2 core transient benchmark has been chosen, as material compositions and geometries are available, allowing the use of lattice codes to generate libraries with different grid structures. Since a complete nodal cross-section library is also provided as part of the benchmark specifications, the effects of the library generation on transient behavior are also analyzed.Results showed large discrepancies when using the benchmark library and own-generated libraries when compared with benchmark participants’ solutions. The origin of the discrepancies was found to lie in the nodal cross sections provided in the benchmark.

A transient expansion of the native state precedes aggregation of recombinant human interferon-γ

Aggregation of proteins, even under conditions favoring the native state, is a ubiquitous problem in biotechnology and biomedical engineering. Providing a mechanistic basis for the pathways that lead to aggregation should allow development of rational approaches for its prevention. We have chosen recombinant human interferon-γ (rhIFN-γ) as a model protein for a mechanistic study of aggregation. In the presence of 0.9 M guanidinium hydrochloride, rhIFN-γ aggregates with first order kinetics, a process that is inhibited by addition of sucrose. We describe a pathway that accounts for both the observed first-order aggregation of rhIFN-γ and the effect of sucrose. In this pathway, aggregation proceeds through a transient expansion of the native state. Sucrose shifts the equilibrium within the ensemble of rhIFN-γ native conformations to favor the most compact native species over more expanded ones, thus stabilizing rhIFN-γ against aggregation. This phenomenon is attributed to the preferential exclusion of sucrose from the protein surface. In addition, kinetic analysis combined with solution thermodynamics shows that only a small (9%) expansion surface area is needed to form the transient native state that precedes aggregation. The approaches used here link thermodynamics and aggregation kinetics to provide a powerful tool for understanding both the pathway of protein aggregation and the rational use of excipients to inhibit the process.

Kinetics and mechanism of polyamide ("peptide") nucleic acid binding to duplex DNA.

To elucidate the mechanism of recognition of double-stranded DNA (dsDNA) by homopyrimidine polyamide ("peptide") nucleic acid (PNA) leading to the strand-displacement, the kinetics of the sequence-specific PNA/DNA binding have been studied. The binding was monitored with time by the gel retardation and nuclease S1 cleavage assays. The experimental kinetic curves obey pseudo-first-order kinetics and the dependence of the pseudo-first-order rate constant, kps, on PNA concentration, P, obeys a power law kps approximately P gamma with 2 < gamma < 3. The kps values for binding of decamer PNA to dsDNA target sites with one mismatch are hundreds of times slower than for the correct site. A detailed kinetic scheme for PNA/DNA binding is proposed that includes two major steps of the reaction of strand invasion: (i) a transient partial opening of the PNA binding site on dsDNA and incorporation of one PNA molecule with the formation of an intermediate PNA/DNA duplex and (ii) formation of a very stable PNA2/DNA triplex. A simple theoretical treatment of the proposed kinetic scheme is performed. The interpretation of our experimental data in the framework of the proposed kinetic scheme leads to the following conclusions. The sequence specificity of the recognition is essentially provided at the "search" step of the process, which consists in the highly reversible transient formation of duplex between one PNA molecule and the complementary strand of duplex DNA while the other DNA strand is displaced. This search step is followed by virtually irreversible "locking" step via PNA2/DNA triplex formation. The proposed mechanism explains how the binding of homopyrimidine PNA to dsDNA meets two apparently mutually contradictory features: high sequence specificity of binding and remarkable stability of both correct and mismatched PNA/DNA complexes.

A quasi stationary approach to drying kinetics of cylindrical food particulates in a heat pump asisted fluid bed dryer

Experiments were undertaken to study drying kinetics of moist cylindrical shaped food particulates during fluidised bed drying. Cylindrical particles were prepared from Green beans with three different length:diameter ratios, 3:1, 2:1 and 1:1. A batch fluidised bed dryer connected to a heat pump system was used for the experimentation. A Heat pump and fluid bed combination was used to increase overall energy efficiency and achieve higher drying rates. Drying kinetics, were evaluated with non-dimensional moisture at three different drying temperatures of 30, 40 and 50o C. Numerous mathematical models can be used to calculate drying kinetics ranging from analytical models with simplified assumptions to empirical models built by regression using experimental data. Empirical models are commonly used for various food materials due to their simpler approach. However problems in accuracy, limits the applications of empirical models. Some limitations of empirical models could be reduced by using semi-empirical models based on heat and mass transfer of the drying operation. One such method is the quasi-stationary approach. In this study, a modified quasi-stationary approach was used to model drying kinetics of the cylindrical food particles at three drying temperatures.

Prediction of fluidization behaviour and a quasi-stationary approach to drying kinetics of irregular particulate food materials

Changes in fluidization behaviour behaviour was characterised for parallelepiped particles with three aspect ratios, 1:1, 2:1 and 3:1 and spherical particles. All drying experiments were conducted at 500C and 15 % RH using a heat pump dehumidifier system. Fluidization experiments were undertaken for the bed heights of 100, 80, 60 and 40 mm and at 10 moisture content levels. Due to irregularities in shape minimum fluidisation velocity of parallelepiped particulates (potato) could not fitted to any empirical model. Also a generalized equation was used to predict minimum fluidization velocity. The modified quasi-stationary method (MQSM) has been proposed to describe drying kinetics of parallelepiped particulates at 30o C, 40o C and 50o C that dry mostly in the falling rate period in a batch type fluid bed dryer.

Development of diagnostic and prognostic algorithms for SF6 puffer circuit breakers from transient waveforms : a validation proposal

- This paper presents a validation proposal for development of diagnostic and prognostic algorithms for SF6 puffer circuit-breakers reproduced from actual site waveforms. The re-ignition/restriking rates are duplicated in given circuits and the cumulative energy dissipated in interrupters by the restriking currents. The targeted objective is to provide a simulated database for diagnosis of re-ignition/restrikes relating to the phase to earth voltage and the number of re-ignition/restrikes as well as estimating the remaining life of SF6 circuit-breakers. The model-based diagnosis of a tool will be useful in monitoring re-ignition/restrikes as well as predicting a nozzle’s lifetime. This will help ATP users with practical study cases and component data compilation for shunt reactor switching and capacitor switching. This method can be easily applied with different data for the different dielectric curves of circuit breakers and networks. This paper presents modelling details and some of the available cases, required project support, the validation proposal, the specific plan for implementation and the propsed main contributions.