Proton Flow Research Articles

Beam-energy dependence of the directed flow of protons, antiprotons, and pions in Au+Au collisions.

Rapidity-odd directed flow (v1) measurements for charged pions, protons, and antiprotons near midrapidity (y=0) are reported in sNN=7.7, 11.5, 19.6, 27, 39, 62.4, and 200GeV Au+Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider. At intermediate impact parameters, the proton and net-proton slope parameter dv1/dy|y=0 shows a minimum between 11.5 and 19.6GeV. In addition, the net-proton dv1/dy|y=0 changes sign twice between 7.7 and 39GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.

Proton Conduction in Water Ices under an Electric Field

We report on a first-principles study of the effects produced by a static electric field on proton conduction in ordinary hexagonal ice (phase Ih) and in its proton-ordered counterpart (phase XI). We performed ab initio molecular dynamics simulations of both phases and investigated the effects produced by the field on the structure of the material, with particular attention paid to the phenomenon of proton transfer. We observed that in ice Ih molecules start to dissociate for field intensities around 0.25 V/Å, as in liquid water, whereas fields stronger than 0.36 V/Å are needed to induce a permanent proton flow. In contrast, in ice XI, electric fields as intense as 0.22 V/Å are already able to induce and sustain, through correlated proton jumps, an ionic current; this behavior suggests, somewhat counterintuitively, that the ordering of protons favors the autoprotolysis phenomenon. However, the same is not true for static conductivities. In fact, both crystalline phases show an ohmic behavior in the conduction regime, but the conductivity of ice Ih turns out to be larger than that of ice XI. We finally discuss the qualitative and quantitative importance of the conspicuous concentration of ionic defects generated by intense electric fields in determining the value of the conductivity, also through a comparison with the experimental data available for saline ices.

Structure and function of the bi-directional bacterial flagellarmotor.

The bacterial flagellum is a locomotive organelle that propels the bacterial cell body in liquid environments. The flagellum is a supramolecular complex composed of about 30 different proteins and consists of at least three parts: a rotary motor, a universal joint, and a helical filament. The flagellar motor of Escherichia coli and Salmonella enterica is powered by an inward-directed electrochemical potential difference of protons across the cytoplasmic membrane. The flagellar motor consists of a rotor made of FliF, FliG, FliM and FliN and a dozen stators consisting of MotA and MotB. FliG, FliM and FliN also act as a molecular switch, enabling the motor to spin in both counterclockwise and clockwise directions. Each stator is anchored to the peptidoglycan layer through the C-terminal periplasmic domain of MotB and acts as a proton channel to couple the proton flow through the channel with torque generation. Highly conserved charged residues at the rotor–stator interface are required not only for torque generation but also for stator assembly around the rotor. In this review, we will summarize our current understanding of the structure and function of the proton-driven bacterial flagellar motor.

Flow probe of symmetry energy in relativistic heavy-ion reactions

Flow observables in heavy-ion reactions at incident energies up to about 1 GeV per nucleon have been shown to be very useful for investigating the reaction dynamics and for determining the parameters of reaction models based on transport theory. In particular, the elliptic flow in collisions of neutron-rich heavy-ion systems emerges as an observable sensitive to the strength of the symmetry energy at supra-saturation densities. The comparison of ratios or differences of neutron and proton flows or neutron and hydrogen flows with predictions of transport models favors an approximately linear density dependence, consistent with ab-initio nuclear-matter theories. Extensive parameter searches have shown that the model dependence is comparable to the uncertainties of existing experimental data. Comprehensive new flow data of high accuracy, partly also through providing stronger constraints on model parameters, can thus be expected to improve our knowledge of the equation of state of asymmetric nuclear matter.

Lateral pH gradient between OXPHOS complex IV and F0F1 ATP-synthase in folded mitochondrial membranes

Ion-driven ATP synthesis by rotary F0F1 ATP-synthase powers aerobic life. Since Mitchell's seminal hypothesis, this synthesis has been discussed in terms of the proton-motive force between two bulk phases, each in equilibrium. In active mitochondria, a steady proton flow cycles between pumps and the distant ATP synthase. Here we determine the lateral pH profile along the p-side of cristae in situ by attaching a ratiometric fluorescent pH-sensitive GFP variant to OXPHOS complex IV, a proton pump, and the dimeric F0F1 ATP-synthase, a proton consumer. In respiring HeLa cells, we observe that the local pH at F0F1 dimers is 0.3 units less acidic than that at complex IV. This finding is consistent with the calculated pH profile for steady proton diffusion from CIV to F0F1. The observed lateral variation in the proton-motive force necessitates a modification to Peter Mitchell's chemiosmotic proposal. The experimental technique can be extended to other pH-dependent reactions in membrane microcompartments.

Effects of Finite-size Ions and Relative Permittivity in a Nanopore Model of a Polymer Electrolyte Membrane

In this contribution, modified Poisson-Nernst-Planck equations are applied to study the distribution and flow of protons within cylindrical, water-filled nanopores of polymer electrolyte membranes (PEM). The model incorporates finite-size effects and an explicit expression for the relative permittivity. Due to the geometry, the problem decouples into a modified Poisson-Boltzmann equation in the radial direction and the Stokes equation in the axial direction. Ion saturation near pore walls, radial permittivity profiles, conductivity and water drag are properties of particular interest. Shortcomings and the usefulness of continuum models are elucidated and how these models might be employed to simulate macroscopic membrane properties.

Facility for Heavy Ion Collision Experiment at RAON

The Rare Isotope Science Project (RISP) was established in December 2011 in order to carry out the technical design and the establishment of the accelerator complex (RAON) for the rare isotope science in Korea. The rare isotope accelerator at RAON will provide both stable and rare isotope heavy-ion beams the energy range from a few MeV/nucleon to a few hundreds of MeV/nucleon for researches in fields of basic and applied science.Large Acceptance Multipurpose Spectrometer (LAMPS) at RAON is a heavy-ion collision experimental facility for studying nuclear symmetry energy by using rare isotope beams. Two different experimental setups of LAMPS are designed for covering entire energy range at RAON.One is for low energy (< 18.5 MeV/nucleon) heavy-ion collision experiment for day-1 experiments. This experimental setup consists of an array of ΔE-E Si-CsI detectors, a gamma array to cover backward polar angle, and a forward neutron wall.The other is for completing an event reconstruction by detecting all the particles produced in high energy heavy-ion collisions within a large acceptance angle to measure particle spectrum, yield, ratio and collective flow of pions, protons, neutrons, and intermediate fragments at the same time. The experimental setup consists of a superconducting spectrometer, a dipole spectrometer, and a forward neutron wall. A Time Projection Chamber (TPC) will be placed inside of superconducting solenoid magnet of 0.6 T for charged particle tracking. The dipole spectrometer will be located forward of the superconducting spectrometer and it will be composed of a combination of quadrupole, dipole magnets, focal plane detector, tracking stations, and Time-of-Flight (ToF) detector at the end. The neutron wall will be made of 10 layers of plastic scintillators for neutron tracking.In this presentation, the detail physics and design of LAMPS at RAON will be discussed.

Left-right patterning in Xenopus conjoined twin embryos requires serotonin signaling and gap junctions.

A number of processes operating during the first cell cleavages enable the left-right (LR) axis to be consistently oriented during Xenopus laevis development. Prior work showed that secondary organizers induced in frog embryos after cleavage stages (i.e. conjoined twins arising from ectopic induced primary axes) correctly pattern their own LR axis only when a primary (early) organizer is also present. This instructive effect confirms the unique LR patterning functions that occur during early embryogenesis, but leaves open the question: which mechanisms that operate during early stages are also involved in the orientation of later-induced organizers? We sought to distinguish the two phases of LR patterning in secondary organizers (LR patterning of the primary twin and the later transfer of this information to the secondary twin) by perturbing only the latter process. Here, we used reagents that do not affect primary LR patterning at the time secondary organizers form to inhibit each of 4 mechanisms in the induced twin. Using pharmacological, molecular-genetic, and photo-chemical tools, we show that serotonergic and gap-junctional signaling, but not proton or potassium flows, are required for the secondary organizer to appropriately pattern its LR axis in a multicellular context. We also show that consistently-asymmetric gene expression begins prior to ciliary flow. Together, our data highlight the importance of physiological signaling in the propagation of cleavage-derived LR orientation to multicellular cell fields.

Experimental Determination of the Ion Selectivity of an ATP-Synthase Membrane Rotor by Isothermal Titration Calorimetry

ATP synthases are rotating nanomachines that couple ATP synthesis or hydrolysis to the transmembrane flow of protons or sodium ions down or against their electrochemical gradient. The key coupling element is a membrane-embedded subcomplex, the c-ring. We have recently proposed a principle that explains the ion selectivity of the c-ring, and validated this through functional studies of several ATP synthases. Specifically, we have proposed that a conserved Glu/Asp confers a universal H+ selectivity to all c-ring binding sites, and that additional amino-acids, which vary among species, have evolved to modulate this selectivity. In particular, we have shown that polar groups can suppress the H+ selectivity of the c-ring by a factor of 1-103. Thus, the enzyme becomes coupled to Na+, due to the large excess of Na+ over H+ under physiological conditions. Here, we further assess this theory by directly measuring the selectivity of a representative c-ring through Isothermal Titration Calorimetry. Specifically, we characterized the c-ring from the ATP synthase of Ilyobacter tartaricus. From titrations at different pH values, we established that Kd(Na+) ∼ 0.3 mM while Kd(H+) ∼ 0.3 μM, confirming the notion that this prototypical Na+-coupled c-ring is in fact H+ selective, although to a much smaller degree than those actually H+-driven. Comparing our results with those obtained for Enterococcus hirae demonstrates that, as predicted by our theory, the I. tartaricus c-ring is 100 times less Na+ selective. The weaker affinity for Na+ of the I.tartaricus ring is also coherent with the 10-fold difference in Km(Na+) values between these enzymes, at high pH. Taken together, these experiments demonstrate that the c-ring is the main determinant of the physiological ion specificity of rotary ATPases, and provide a conclusive validation of our theory.

Asymmetric bi-layer PFSA membranes as model systems for the study of water management in the PEMFC.

New bi-layer PFSA membranes made of Nafion® NRE212 and Aquivion™ E79-05s with different equivalent weights are prepared with the aim of managing water repartition in the PEMFC. The membrane water transport properties, i.e. back-diffusion and electroosmosis, as well as the electrochemical performances, are compared to those of state-of-art materials. The actual water content (the inner water concentration profile across the membrane thickness) is measured under operation in the fuel cell by in situ Raman microspectroscopy. The orientation of the equivalent weight gradient with respect to the water external gradient and to the proton flow direction affects the membrane water content, the water transport ability and, thus, the fuel cell performances. Higher power outputs, related to lower ohmic losses, are observed when the membrane is assembled with the lower equivalent weight layer (Aquivion™) at the anode side. This orientation, corresponding to enhanced water transport by back-flow while electroosmosis remains unaffected, results in the higher hydration of the membrane and of the anode active layer during operation. Also, polarization data suggest a different water repartition in the fuel cell along the on-plane direction. Even if the interest in multi-layer PFSA membranes as perspective electrolytes for PEMFCs is not definitively attested, these materials appear to be excellent model systems to establish relationships between the membrane transport properties, the water distribution in the fuel cell and the electrochemical performances. Thanks to the micrometric resolution, in situ Raman microspectroscopy proves to be a unique tool to measure the actual hydration of the membrane at the surface swept by the hydrated feed gases during operation, so that it can be used as a local probe of the water concentration evolution along the gas distribution channels according to changing working conditions.

Towards a ‘proton flow battery’: Investigation of a reversible PEM fuel cell with integrated metal-hydride hydrogen storage

An innovative concept for integrating a metal hydride storage electrode into a reversible proton exchange membrane (PEM) fuel cell is described and investigated experimentally. This new concept has the potential to increase roundtrip efficiency compared to the conventional hydrogen-based electrical energy storage system by eliminating the intermediate steps of hydrogen gas production, storage, and recovery. As only an inflow of water is needed in the charge mode, and air in discharge mode, the system is called a ‘proton flow battery’. A hydrogen storage electrode was fabricated from a novel composite metal hydride–nafion material, and found to have acceptably high proton and electron conductivities. Its hydrogen storage capacity was measured to be 0.6 wt% of hydrogen, although the amount of hydrogen recovered to run the device in fuel cell mode was much lower. These results provide initial confirmatory evidence that the proton flow battery concept is technically feasible, though additional research is still required to enhance both storage capacity and reversibility.

The Creation of Proton Hopping from a DrugReceptor Encounter

We extend recent modeling studies of proton hopping, used to describe the functioning of membrane channels and axon nerve conduction, to offer an explanation of the initiation of the nerve impulse at an effector-ligand encounter. This encounter is proposed to create a hydronium ion in the vicinity of the effector and ligand, which leads to a continuous flow of protons, called proton hopping, through water adjacent to this encounter. This proton hopping is proposed to be the message carried from the encounter to the axon of a particular nerve system associated with that particular effector-ligand system.

Load‐sensitive coupling of proton translocation and torque generation in the bacterial flagellar motor

The Salmonella flagellar motor consists of a rotor and about a dozen stator elements. Each stator element, consisting of MotA and MotB, acts as a proton channel to couple proton flow with torque generation. A highly conserved Asp33 residue of MotB is directly involved in the energy coupling mechanism, but it remains unknown how it carries out this function. Here, we show that the MotB(D33E) mutation dramatically alters motor performance in response to changes in external load. Rotation speeds of the MotA/B(D33E) and MotA(V35F)/B(D33E) motors were markedly slower than the wild-type motor and fluctuated considerably at low load but not at high load, whereas the rotation rate of the wild-type motor was stable at any load. At low load, pausing events were frequently observed in both mutant motors. The proton conductivities of these mutant stator channels in their 'unplugged' forms were only half of the conductivity of the wild-type channel. These results suggest that the D33E mutation induces a load-dependent inactivation of the MotA/B complex. We propose that the stator element is a load-sensitive proton channel that efficiently couples proton translocation with torque generation and that Asp33 of MotB is critical for this co-ordinated proton translocation.

Basic Properties of Rotary Dynamics of the Molecular Motor Enterococcus hirae V1-ATPase

V-ATPases are rotary molecular motors that generally function as proton pumps. We recently solved the crystal structures of the V1 moiety of Enterococcus hirae V-ATPase (EhV1) and proposed a model for its rotation mechanism. Here, we characterized the rotary dynamics of EhV1 using single-molecule analysis employing a load-free probe. EhV1 rotated in a counterclockwise direction, exhibiting two distinct rotational states, namely clear and unclear, suggesting unstable interactions between the rotor and stator. The clear state was analyzed in detail to obtain kinetic parameters. The rotation rates obeyed Michaelis-Menten kinetics with a maximal rotation rate (Vmax) of 107 revolutions/s and a Michaelis constant (Km) of 154 μM at 26 °C. At all ATP concentrations tested, EhV1 showed only three pauses separated by 120°/turn, and no substeps were resolved, as was the case with Thermus thermophilus V1-ATPase (TtV1). At 10 μM ATP (<<Km), the distribution of the durations of the ATP-waiting pause fit well with a single-exponential decay function. The second-order binding rate constant for ATP was 2.3 × 10(6) M(-1) s(-1). At 40 mM ATP (>>Km), the distribution of the durations of the catalytic pause was reproduced by a consecutive reaction with two time constants of 2.6 and 0.5 ms. These kinetic parameters were similar to those of TtV1. Our results identify the common properties of rotary catalysis of V1-ATPases that are distinct from those of F1-ATPases and will further our understanding of the general mechanisms of rotary molecular motors.

Mass Hierarchy in Identified Particle Distributions in Proton-Lead Collisions

We study the mass dependence for identified particle average transverse momentum and harmonic flow coefficients in proton-lead (p-Pb) collisions, recently measured at the LHC. The collective mechanism in the p-Pb system predicts a specific mass ordering in these observables: the growth of the average transverse momentum with the particle mass and a mass splitting of the elliptic flow coefficient, i.e., smaller differential elliptic flow of protons than pions for p(T)<2 GeV. This provides an opportunity to distinguish between the collective scenario and the mechanism based on the initial gluon dynamics in the evolution of the p-Pb system.

Hypothesis of Lipid-Phase-Continuity Proton Transfer for Aerobic ATP Synthesis

The basic processes harvesting chemical energy for life are driven by proton (H(+)) movements. These are accomplished by the mitochondrial redox complex V, integral membrane supramolecular aggregates, whose structure has recently been described by advanced studies. These did not identify classical aqueous pores. It was proposed that H(+) transfer for oxidative phosphorylation (OXPHOS) does not occur between aqueous sources and sinks, where an energy barrier would be insurmountable. This suggests a novel hypothesis for the proton transfer. A lipid-phase-continuity H(+) transfer is proposed in which H(+) are always bound to phospholipid heads and cardiolipin, according to Mitchell's hypothesis of asymmetric vectorial H(+) diffusion. A phase separation is proposed among the proton flow, following an intramembrane pathway, and the ATP synthesis, occurring in the aqueous phase. This view reminiscent of Grotthus mechanism would better account for the distance among the Fo and F1 moieties of FoF1-ATP synthase, for its mechanical coupling, as well as the necessity of a lipid membrane. A unique active role for lipids in the evolution of life can be envisaged. Interestingly, this view would also be consistent with the evidence of an OXPHOS outside mitochondria also found in non-vesicular membranes, housing the redox complexes.

Special issues on Photosynthesis Education honoring Govindjee

The special issues in volumes 116 and 117 of Photosynthesis Research are all dedicated to Photosynthesis Education. They honor Professor Govindjee, at his 80th birthday on October 24, 2013, for his contributions, dedication, and enthusiasm about photosynthesis, for which he has been called ‘‘Mr. Photosynthesis’’. He is a master educator of our time. The depth of his knowledge and understanding of all aspects of photosynthesis, ‘‘From Photons to a Leaf’’ is enormous. He is also the de facto Ambassador of Photosynthesis to the rest of the World. Govindjee, as he prefers to be called, is a renowned scientist who has made outstanding and significant contributions to photosynthesis research and education. Govindjee has authored or co-authored more than 400 publications which have brought understanding to many aspects of photosynthesis (for a list since 1994, see his webpage at: http://www.life.illinois.edu/govindjee/recent_ papers.html). This includes, most dramatically, his work on exploitation of light emission (chlorophyll fluorescence, delayed fluorescence and thermoluminescence) of plants and algae for understanding photosynthesis. In cooperation with his co-workers, he showed a unique role of bicarbonate in the electron and proton flow on the electron acceptor side of Photosystem II (PSII), and, in his early work on the minimum quantum requirement of oxygen evolution, he proved that Nobel-Laureate Otto Warburg was wrong and that his own professor Robert Emerson was right: i.e. a minimum of 8–12 photons, not 3–4, is required for the evolution of one oxygen molecule. His research, with many collaborators, included the discovery of a shortwavelength form of chlorophyll (Chl) a functioning in the Chl b-containing system, now called PS II, and of the twolight effects in Chl a fluorescence and NADP reduction in chloroplasts. Further, again, with his coworkers, he discovered the existence of different spectral fluorescing forms of Chl a, was the first to measure the temperature dependence of excitation energy transfer down to liquid helium temperature (4 K), the first to provide the current theory for thermoluminescence in plants, and the first to make picosecond measurements of the primary photochemistry of PSII. Equally important, Govindjee has played a key role in global dissemination of research through collaboration with scientists all over the world, and through his lucid lectures on the basics of photosynthesis, as well as on the history of ‘‘Photosynthesis Research’’. A major characteristic of Govindjee is his availability to help anyone and everyone who writes to him; always ready to respond to emails that he receives. In addition, we marvel at his tremendous accomplishments in terms of communication of ideas, and the unsurpassed marathon job he has done editing, which includes numerous books on Photosynthesis, S. I. Allakhverdiev Controlled Photobiosynthesis Laboratory, Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow 127276, Russia e-mail: suleyman.allakhverdiev@gmail.com

Mapping water's path through a pore protein

X-ray crystallography reveals why aquaporins permit the passage of water but stem the flow of protons.

Elliptic flow of protons and antiprotons in Au + Au collisions at [formula omitted] within alternative scenarios of three-fluid dynamics

Analysis of elliptic flow of protons and antiprotons in Au + Au collisions is performed in a wide range of incident energies sNN=7.7–62.4 GeV. Simulations has been done within the three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS involving deconfinement transition: an EoS with the first-order phase transition and that with a smooth crossover transition. It is found that the proton data are reproduced approximately to the same extent within all of the scenarios, including the hadronic one, while the deconfinement scenarios look certainly preferable for the antiproton elliptic flow. The fact that difference between elliptic flows of protons and antiprotons decreases with the incident energy rise is a consequence of reducing baryon stopping rather than an onset of deconfinement.

Effect of momentum dependent interactions and nucleonic cross-section on directed flow [formula omitted

The descriptive analysis for the effect of momentum dependent interactions and nucleonic cross-section (isospin dependent and isospin-independent) on the neutron–proton directed flow (v1), within the framework of the isospin dependent quantum molecular dynamics model is presented. Our study shows that, the directed flow of both neutrons and protons is affected by the momentum dependence of nuclear equation of state and the isospin dependence of nucleon–nucleon cross-section. A soft momentum dependent (SM) equation of state is found to be more compatible with the experimental data.