812 research outputs found
Excitation energy transfer between monomolecular layers of light harvesting LH2 and LH1-reaction centre complexes printed on a glass substrate
Light-harvesting 2 (LH2) and light-harvesting 1 â reaction centre (RCLH1) complexes purified from the photosynthetic bacterium Rhodobacter (Rba.) sphaeroides were cross-patterned on glass surfaces for energy transfer studies. Atomic force microscopy (AFM) images of the RCLH1 and LH2 patterns show the deposition of monomolecular layers of complexes on the glass substrate. Spectral imaging and fluorescence life-time imaging microscopy (FLIM) revealed that RCLH1 and LH2 complexes, sealed under physiological conditions, retained their native light-harvesting and energy transfer functions. Measurements of the amplitude and lifetime decay of fluorescence emission from LH2 complexes, the energy transfer donors, and gain of fluorescence emission from acceptor RCLH1 complexes, provide evidence for excitation energy transfer from LH2 to RCLH1. Directional energy transfer on the glass substrate was unequivocally established by using LH2-carotenoid complexes and RCLH1 complexes with genetically removed carotenoids. Specific excitation of carotenoids in donor LH2 complexes elicited fluorescence emission from RCLH1 acceptors. To explore the longevity of this novel nanoprinted photosynthetic unit, RCLH1 and LH2 complexes were cross-patterned on a glass surface and sealed under a protective argon atmosphere. The results show that both complexes retained their individual and collective functions and are capable of directional excitation energy transfer for at least 60 days
Wave Mechanics of Two Hard Core Quantum Particles in 1-D Box
The wave mechanics of two impenetrable hard core particles in 1-D box is
analyzed. Each particle in the box behaves like an independent entity
represented by a {\it macro-orbital} (a kind of pair waveform). While the
expectation value of their interaction, ,
satisfies (or , with being the size
of the box). The particles in their ground state define a close-packed
arrangement of their wave packets (with , phase position
separation and momentum ) and experience a
mutual repulsive force ({\it zero point repulsion}) which
also tries to expand the box. While the relative dynamics of two particles in
their excited states represents usual collisional motion, the same in their
ground state becomes collisionless. These results have great significance in
determining the correct microscopic understanding of widely different many body
systems.Comment: 12 pages, no figur
Multicomponent nanoscale patterning of functional lightâharvesting protein complexes by local oxidation lithography
Local oxidation lithography has the potential for patterning proteins on conductive substrates such as silicon with nanometer accuracy, guided by and extending the nanoscale architectures found in native bioenergetic membranes. Such membranes foster energy and electron transfers between two or more types of protein complex, so the potential of this lithographic technique is investigated for copatterning multiple types of protein complex. Composite patterns consisting of lightâharvesting 2 (LH2) and reaction centerâlightâharvesting 1âPufX (RCLH1) complexes purified from Rhodobacter (Rba.) sphaeroides, and lightâharvesting complex II (LHCII) purified from spinach, are fabricated. Atomic force microscopy (AFM) images demonstrate the successful sequential deposition of singleâmolecule layers of RCLH1 and LH2 molecules. In the case of LHCII, a mixture of singleâlayer and multilayer patterns is found on the silicon substrate. Experimental conditions are established for the most efficient substrate surface modification and for protein immobilization. Spectral imaging and fluorescence lifetime imaging microscopy (FLIM) show that the immobilized photosynthetic complexes retain their native lightâharvesting and energy transfer functions, and provide evidence for excitation energy transfer from LH2 to RCLH1. Local oxidation lithography has the capacity to pattern proteins singly, or in small domains, for fabricating bioinspired nanoscale architectures for biosensors and solar cells
Proteorhodopsin overproduction enhances the long-term viability of Escherichia coli
Genes encoding the photoreactive protein proteorhodopsin (PR) have been found in a wide range of marine bacterial species, reflecting the significant contribution that PR makes to energy flux and carbon cycling in ocean ecosystems. PR can also confer advantages to enhance the ability of marine bacteria to survive periods of starvation. Here, we investigate the effect of heterologously produced PR on the viability of Escherichia coli. Quantitative mass spectrometry shows that E. coli, exogenously supplied with the retinal cofactor, assembles as many as 187,000 holo-PR molecules per cell, accounting for approximately 47% of the membrane area; even cells with no retinal synthesize âŒ148,000 apo-PR molecules per cell. We show that populations of E. coli cells containing PR exhibit significantly extended viability over many weeks, and we use single-cell Raman spectroscopy (SCRS) to detect holo-PR in 9-month-old cells. SCRS shows that such cells, even incubated in the dark and therefore with inactive PR, maintain cellular levels of DNA and RNA and avoid deterioration of the cytoplasmic membrane, a likely basis for extended viability. The substantial proportion of the E. coli membrane required to accommodate high levels of PR likely fosters extensive intermolecular contacts, suggested to physically stabilize the cell membrane and impart a long-term benefit manifested as extended viability in the dark. We propose that marine bacteria could benefit similarly from a high PR content, with a stabilized cell membrane extending survival when those bacteria experience periods of severe nutrient or light limitation in the oceans
Distribution and density of the partition function zeros for the diamond-decorated Ising model
Exact renormalization map of temperature between two successive decorated
lattices is given, and the distribution of the partition function zeros in the
complex temperature plane is obtained for any decoration-level. The rule
governing the variation of the distribution pattern as the decoration-level
changes is given. The densities of the zeros for the first two
decoration-levels are calculated explicitly, and the qualitative features about
the densities of higher decoration-levels are given by conjecture. The Julia
set associated with the renormalization map is contained in the distribution of
the zeros in the limit of infinite decoration level, and the formation of the
Julia set in the course of increasing the decoration-level is given in terms of
the variations of the zero density.Comment: 8 pages,8figure
Top-quark spin correlation at Linear Colliders with anomalous couplings
We investigate the feasibility of probing anomalous top-quark couplings of
, , and in terms of an effective
Lagrangian with dimension-six operators at future linear colliders
with a c. m. energy GeV. We first examine the
constraints on these anomalous couplings from the data at LEP
I and from unitarity considerations. We then consider in detail the effects of
anomalous couplings on spin correlations in the top-pair production
and decay with three spin bases: the helicity, beamline and off-diagonal bases.
Our results show that the polarized beams are more suitable for exploring the
effects of different new operators. For polarized beams, the helicity basis
yields the best sensitivity.Comment: 23 pages, 10 figures, references adde
Radiative Corrections to Double Dalitz Decays: Effects on Invariant Mass Distributions and Angular Correlations
We review the theory of meson decays to two lepton pairs, including the cases
of identical as well as non-identical leptons, as well as CP-conserving and
CP-violating couplings. A complete lowest-order calculation of QED radiative
corrections to these decays is discussed, and comparisons of predicted rates
and kinematic distributions between tree-level and one-loop-corrected
calculations are presented for both pi-zero and K-zero decays.Comment: 25 pages, 18 figures, added figures and commentar
Augmenting light coverage for photosynthesis through YFP-enhanced charge separation at the Rhodobacter sphaeroides reaction centre.
Photosynthesis uses a limited range of the solar spectrum, so enhancing spectral coverage could improve the efficiency of light capture. Here, we show that a hybrid reaction centre (RC)/yellow fluorescent protein (YFP) complex accelerates photosynthetic growth in the bacterium Rhodobacter sphaeroides. The structure of the RC/YFP-light-harvesting 1 (LH1) complex shows the position of YFP attachment to the RC-H subunit, on the cytoplasmic side of the RC complex. Fluorescence lifetime microscopy of whole cells and ultrafast transient absorption spectroscopy of purified RC/YFP complexes show that the YFP-RC intermolecular distance and spectral overlap between the emission of YFP and the visible-region (QX) absorption bands of the RC allow energy transfer via a Förster mechanism, with an efficiency of 40±10%. This proof-of-principle study demonstrates the feasibility of increasing spectral coverage for harvesting light using non-native genetically-encoded light-absorbers, thereby augmenting energy transfer and trapping in photosynthesis
Structural modulation of the photophysical and electronic properties of pyrene-based 3D metal-organic frameworks derived from s-block metals
Materials in which charge delocalization and migration can be tuned are critical for electronic applications. Crystalline framework materials containing Ï-rich polycyclic aromatic moieties, such as pyrene, can provide a pathway for fast anisotropic charge transport. The extent of interchromophore interaction for structurally distinct assemblies of the Ï-conjugated aromatic ligand 4,4âČ,4âČâČ,4âČâČâČ-(1,3,6,8-pyrenetetrayl) tetrabenzoic acid (H4TBAPy) was studied within two novel metalâorganic frameworks (MOFs), Na(TBAPy)(DMF) and K(TBAPy)(DMF), via steady-state and time-resolved spectroscopic techniques. Single-crystal X-ray diffraction was used to determine the structures of K(TBAPy)(DMF) and Na(TBAPy)(DMF), which both form 3D MOFs comprising 1D rod-like SBUs surrounded by columnar stacks of TBAPy that are aligned in an eclipsed and x-shaped (staggered) geometry, respectively. Spectroscopic and computational results indicate significant chromophore interactions and potentially fast charge transport. Furthermore, distinct transient emission decay profiles are observed and are attributed to significant differences in the stacking orientation of the organic ligands in the two MOFs. Lastly, the study identifies design principles that may be exploited in the rational construction of s-block based MOFs for microelectronic and sensing applications.Christopher N. Coleman, Patrick C. Tapping, Michael T. Huxley, Tak W. Kee, David M. Huang, Christian J. Doonan and Christopher J. Sumb
Discovery of New Natural Products by Intact-Cell Mass Spectrometry and LC-SPE-NMR: Malbranpyrroles, Novel Polyketides from Thermophilic Fungus Malbranchea sulfurea
Six photosensitive polyketides, malbranpyrroles A-F, were discovered from the thermophilic fungus Malbranchea sulfurea by using intact-cell desorption/ionization on silicon mass (ICD-MS) and LC-SPE-NMR. These two strategies facilitate the searching and structural determination of unstable natural products. The ICD-MS indicated that only brown hyphae of M. sulfurea can produce malbranpyrroles. The biosynthetic pathway of malbranpyrroles was evidenced by (13)C isotope precursors and amino acid feeding experiments. The cytotoxicity data revealed that the conformation of the conjugated system in malbranpyrroles does not affect cytotoxic potency against cancer cell lines. In addition, the chlorine atom was shown to be the pharmacophore for cytotoxicity
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