Photosynthetic organisms fuel their metabolism with light energy and have developed for this purpose an efficient apparatus harvesting sunlight. The atomic structure of the apparatus, as it evolved in purple bacteria, has been constructed through a combination x-ray crystallography, electron microscopy, modeling. detailed overall architecture reveals hierarchical aggregate pigments that utilizes, shown femtosecond spectroscopy quantum physics, elegant mechanisms primary absorption transfer...

A diagnostic criterion was developed to distinguish between an intermediate formed in over-all reaction path and a product parallel electrochemical reaction. It utilizes the method of rotating-disk electrode with concentric ring, first proposed by Frumkin Nekrassov. From dependence currents at disk ring on rate rotation, individual rates reactions can be obtained.

Absorption of light by light-harvesting complexes and transfer electronic excitation to the photosynthetic reaction center (RC) constitute primary process photosynthesis. This is investigated on basis an atomic level structure so-called unit bacterium Rhodobacter sphaeroides. The combines in intracytoplasmic membrane a nanometric assembly three pigment−protein complexes: (i) center, (ii) ring-shaped complex LH-I, (iii) multiple copies similar complex, LH-II. has been modeled using known for...

The dynamics of pigment-pigment and pigment-protein interactions in light-harvesting complexes is studied with a novel approach which combines molecular (MD) simulations quantum chemistry (QC) calculations. MD an LH-II complex, solvated embedded lipid bilayer at physiological conditions (with total system size 87,055 atoms) revealed pathway water molecule into the B800 binding site, as well increased dimerization within B850 BChl ring, compared to found for crystal structure. fluctuations...

The zinc/KOH‐zincate electrode reaction was investigated under high purity conditions with galvanostatic and potentiostatic transient techniques in the 0.1–3.0M 0.0001–0.5M zincate concentration range. exchange current density found to be between 8 370 mA/cm2, 40 mV/decade anodic 120 cathodic nominal Tafel slopes; an overpotential range of ± 100 mV covered. orders were 1 for zincate, −1 hydroxyl ions. A four‐step mechanism, consistent kinetic data, is suggested. It consists four consecutive...

Cathodic and anodic Tafel parameters, stoichiometric numbers, decay kinetics have been determined on rhodium, iridium, platinum‐rhodium alloy electrodes. Two regions of constant for a given substrate were observed. The catalytic activity the substrates in acid solution above about 1.4v (vs. N.H.E.) was On side, tends to behave as Rh, cathodic side Pt. Time behavior conventional except surface, where from resembled that number Ir, Pt‐Rh 2. Rate‐determining steps unambiguously by criteria...

A rotating disk electrode with a concentric ring has been used to determine the role of hydrogen peroxide in reduction oxygen at platinum electrodes alkaline solution. Oxygen proceeds along two parallel reaction paths comparable rates. In one paths, is intermediate which partially reduced water. other, reduces water without as an intermediate. path intermediate, first part probable sequence steps shown be

The rotating disk electrode with a concentric ring is used to analyze the role of in reduction O2 acid solutions. No formed as an intermediate reaction path oxygen water. Only when residual impurities from not sufficiently purified solutions are adsorbed at does parallel appear which that reduce further any significant rate. mechanism involves first charge transfer step rate‐controlling under Temkin conditions adsorption.

We propose a new algorithm for obtaining proton titration curves of ionizable residues. The is pH replica-exchange method (PHREM), which based on the constant Mongan et al. (J Comput Chem 2004;25:2038-2048). In original method, simulations different replicas are performed at temperatures, and temperatures exchanged between replicas. our PHREM, values, pHs PHREM was applied to blocked amino acid two protein systems (snake cardiotoxin turkey ovomucoid third domain), in conjunction with...

This study focuses on voltage cycling induced degradation of cathodes with different loading (0.4 and 0.1 mgPt/cm2) when applying square wave or triangular based accelerated stress tests (ASTs) between 0.6 1.0 VRHE. The the H2/O2 H2/air performance upon extended (up to 30000 cycles) was analyzed in terms loss contributions from ORR kinetics, O2 mass transport resistances proton conduction cathode. extent cathode thinning due carbon support corrosion determined by post mortem electrode...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOXYGEN ADSORPTION RELATED THE UNPAIRED d-ELECTRONS IN TRANSITION METALSM. L. B. Rao, A. Damjanovic, and J. O'M. BockrisCite this: Phys. Chem. 1963, 67, 11, 2508–2509Publication Date (Print):November 1, 1963Publication History Published online1 May 2002Published inissue 1 November 1963https://pubs.acs.org/doi/10.1021/j100805a520https://doi.org/10.1021/j100805a520research-articleACS PublicationsRequest reuse permissionsArticle...

In photosynthetic light-harvesting systems carotenoids and chlorophylls jointly absorb light transform its energy within about a picosecond into electronic singlet excitations of the only. This paper investigates this process for complex II purple bacterium Rhodospirillum molischianum, which structure and, hence, exact arrangement participating bacteriochlorophylls have recently become known. Based on CI expansions states individual chromophores (bacteriochlorophylls carotenoids) as well an...

The Qy excitation energies of the 96 chlorophyll molecules in photosystem I Synechococcus elongatus, both and out their protein environments, were obtained by using semiempirical INDO/S method crystal structure geometries. dipole−dipole approximation was used to calculate coupling between states chlorophylls; case closely separated chlorophylls dimer calculations determine couplings. effective Hamiltonian for excitations constructed, enabling tentative assignment red calculation absorption...

Biological cells contain nanoscale machineries that exhibit a unique combination of high efficiency, adaptability to changing environmental conditions, and reliability. Recent progress in obtaining atomically resolved structures provide an opportunity for atomic-level explanation the biological function cellular underlying physical mechanisms. A prime example this regard is apparatus with which purple bacteria harvest light sun. Its highly symmetrical architecture close interplay...

To study the mechanism and kinetics of electrocrystallization, electrochemical measurements were supplemented with in situ microscopic observations growing copper electrodeposits. The growth was followed on main crystal planes single crystals up to an average thickness deposit corresponding 10 coulomb/cm2. Highly purified solutions used.