14,131 research outputs found
Bacteriorhodopsin folds through a poorly organized transition state.
The folding mechanisms of helical membrane proteins remain largely uncharted. Here we characterize the kinetics of bacteriorhodopsin folding and employ Ï-value analysis to explore the folding transition state. First, we developed and confirmed a kinetic model that allowed us to assess the rate of folding from SDS-denatured bacteriorhodopsin (bRU) and provides accurate thermodynamic information even under influence of retinal hydrolysis. Next, we obtained reliable Ï-values for 16 mutants of bacteriorhodopsin with good coverage across the protein. Every Ï-value was less than 0.4, indicating the transition state is not uniquely structured. We suggest that the transition state is a loosely organized ensemble of conformations
Crystallization of the Wahnstr\"om Binary Lennard-Jones Liquid
We report observation of crystallization of the glass-forming binary
Lennard-Jones liquid first used by Wahnstr\"om [G. Wahnstr\"om, Phys. Rev. A
44, 3752 (1991)]. Molecular dynamics simulations of the metastable liquid on a
timescale of microseconds were performed. The liquid crystallized
spontaneously. The crystal structure was identified as MgZn_2. Formation of
transient crystallites is observed in the liquid. The crystallization is
investigate at different temperatures and compositions. At high temperature the
rate of crystallite formation is the limiting factor, while at low temperature
the limiting factor is growth rate. The melting temperature of the crystal is
estimated to be T_m=0.93 at rho=0.82. The maximum crystallization rate of the
A_2B composition is T=0.60+/-0.02.Comment: 4 pages, 4 figures; corrected typo
Exponential distributions of collective flow-event properties in viscous liquid dynamics
We study the statistics of flow events in the inherent dynamics in
supercooled two- and three-dimensional binary Lennard-Jones liquids.
Distributions of changes of the collective quantities energy, pressure and
shear stress become exponential at low temperatures, as does that of the event
"size" . We show how the -distribution controls the
others, while itself following from exponential tails in the distributions of
(1) single particle displacements , involving a Lindemann-like length
and (2) the number of active particles (with ).Comment: Accepter version (PRL
Spectral methods for the wave equation in second-order form
Current spectral simulations of Einstein's equations require writing the
equations in first-order form, potentially introducing instabilities and
inefficiencies. We present a new penalty method for pseudo-spectral evolutions
of second order in space wave equations. The penalties are constructed as
functions of Legendre polynomials and are added to the equations of motion
everywhere, not only on the boundaries. Using energy methods, we prove
semi-discrete stability of the new method for the scalar wave equation in flat
space and show how it can be applied to the scalar wave on a curved background.
Numerical results demonstrating stability and convergence for multi-domain
second-order scalar wave evolutions are also presented. This work provides a
foundation for treating Einstein's equations directly in second-order form by
spectral methods.Comment: 16 pages, 5 figure
New Understanding of Large Magellanic Cloud Structure, Dynamics and Orbit from Carbon Star Kinematics
We derive general expressions for the LMC velocity field which we fit to
kinematical data for 1041 carbon stars. We demonstrate that all previous
studies of LMC kinematics have made unnecessary over-simplifications that have
led to incorrect estimates of important structural parameters. We compile and
improve LMC proper motion estimates to support our analysis. We find that the
kinematically determined position angle of the line of nodes is 129.9 +/- 6.0
deg. The LMC inclination changes at a rate di/dt = -103 +/- 61 deg/Gyr, a
result of precession and nutation induced by Milky Way tidal torques. The LMC
rotation curve V(R) has amplitude 49.8 +/- 15.9 km/s, 40% lower than what has
previously (and incorrectly) been inferred from e.g. HI. The dynamical center
of the carbon stars is consistent with the center of the bar and the center of
the outer isophotes, but not with the HI kinematical center. The enclosed mass
inside 8.9 kpc is (8.7 +/- 4.3) x 10^9 M_sun, more than half of which is due to
a dark halo. The LMC has a larger vertical thickness than has traditionally
been believed. Its V/sigma is less than the value for the Milky Way thick disk.
We discuss the implications for the LMC self-lensing optical depth. We
determine the LMC velocity and orbit in the Galactocentric rest frame and find
it to be consistent with the range of velocities that has been predicted by
models for the Magellanic Stream. The Milky Way dark halo must have mass >4.3 x
10^{11} M_sun and extent >39 kpc for the LMC to be bound. We predict the LMC
proper motion velocity field, and discuss techniques for kinematical distance
estimation. [ABRIDGED]Comment: 57 pages, LaTeX, with 11 PostScript figures. Submitted to the
Astronomical Journa
Synthesis and alkyne-coupling chemistry of cyclomanganated 1- and 3-acetylindoles, 3-formylindole and analogues
The syntheses are reported of new cyclomanganated indole derivatives (1-acetyl-ÎșO-indolyl-ÎșC2)dicarbonylbis(trimethylphosphite)manganese (2), (1-methyl-3-acetyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (4), (3-formyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (5a) and (1-methyl-3-formyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (5b). The unusually complicated crystal structure of 5b has been determined, the first for a cyclomanganated aryl aldehyde.
The preparations of a mitomycin-related pyrrolo-indole and related products by thermally promoted and oxidatively (Me3NO) initiated alkyne-coupling reactions of the previously known complex (1-acetyl-ÎșO-indolyl-ÎșC2)tetracarbonylmanganese (1) are reported for different alkynes and solvents. X-ray crystal structures are reported for the dimethyl acetylenedicarboxylate coupling product of 1 (dimethyl 1-methyl-l-hydroxypyrrolo[1,2a]-indole-2,3-dicarboxylate; 6a), and an unusually-cyclised triple insertion product 8 from the coupling of acetylene with 4, in which a cyclopentadiene moiety is η3-allyl-coordinated to Mn through only one double bond and an exocyclic carbon, but which rearranges on heating to an η5-cyclopentadienyl complex
Strong pressure-energy correlations in liquids as a configuration space property: Simulations of temperature down jumps and crystallization
Computer simulations recently revealed that several liquids exhibit strong
correlations between virial and potential energy equilibrium fluctuations in
the NVT ensemble [U. R. Pedersen {\it et al.}, Phys. Rev. Lett. {\bf 100},
015701 (2008)]. In order to investigate whether these correlations are present
also far from equilibrium constant-volume aging following a temperature down
jump from equilibrium was simulated for two strongly correlating liquids, an
asymmetric dumbbell model and Lewis-Wahnstr{\"o}m OTP, as well as for SPC water
that is not strongly correlating. For the two strongly correlating liquids
virial and potential energy follow each other closely during the aging towards
equilibrium. For SPC water, on the other hand, virial and potential energy vary
with little correlation as the system ages towards equilibrium. Further proof
that strong pressure-energy correlations express a configuration space property
comes from monitoring pressure and energy during the crystallization (reported
here for the first time) of supercooled Lewis-Wahnstr{\"o}m OTP at constant
temperature
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