2,236 research outputs found
Methyl Reorientation in Methylphenanthrenes: 1. Solid-State Proton Spin-Lattice Relaxation in the 3-Methyl, 9-Methyl, and 3,9-Dimethyl Systems
We have investigated the dynamics of methyl group reorientation in solid methylâsubstituted phenanthrenes. The temperature dependence of the proton spinâlattice relaxation rates has been measured in polycrystalline 3âmethylphenanthrene (3âMP), 9âmethylphenanthrene (9âMP), and 3,9âdimethylphenanthrene (3,9âDMP) at Larmor frequencies of 8.50, 22.5, and 53.0 MHz. The data are interpreted using a DavidsonâCole spectral density which implies either that the correlation functions for intramolecular reorientation are nonexponential or that there is a distribution of exponential correlation times. Comparing the fitted parameters that characterize the relaxation data for the three molecules shows that the individual contributions to the relaxation rate from the 3â and 9âmethyls in 3,9âDMP can be separated and that the parameters specifying each are similar to the equivalent group in the two single methylphenanthrenes. The 9âmethyl group is characterized by effective activation energies of 10.6±0.6 and 12.5±0.9 kJ/mol in 9âMP and 3,9âDMP, respectively, whereas the 3âmethyl group is characterized by effective activation energies of 5.2±0.8 and 5±1 kJ/mol in 3âMP and 3,9âDMP, respectively. The agreement between the fitted and calculated values of the spinâlattice interaction strength, assuming only intramethyl proton dipoleâdipole interactions need be considered, is excellent. A comparison between experimentally determined correlation times and those calculated from a variety of very simple dynamical models is given, and the results suggest, as have several previous studies, that at high temperatures where tunneling plays no role, methyl reorientation is a simple, thermally activated, hopping process. We have also analyzed many published data in methylâsubstituted phenanthrenes, anthracenes, and naphthalenes (14 molecules) in the same way as we did for the phenanthrene data presented here, and a consistent picture for the dynamics of methyl reorientation emerges
Methyl reorientation in methylphenanthrenes. II. Solid-state proton spin-lattice relaxation in the 1-CH3, 9-CH3, and 1-CD3, 9-CH3 systems
We report proton Zeeman relaxation rates R as a function of temperature T at 8.5 and 53 MHz in polycrystalline 1,9-dimethylphenanthrene (1,9-DMP) and l-trideuteriomethyl-9-methylphenanthrene (1, 9-DMP[1-d3]). The data are interpreted using a Davidson-Cole spectral density for intramolecular reorientation and the implications of this are discussed. R vs Tâ1data for 1,9-DMP[1-d3] are used to determine the parameters that characterize the reorientation of the 9-methyl group. By assuming that the parameters characterizing the dynamics of the 9-methyl group are the same in 1,9-DMP and 1,9-DMP[1-d3], we subtract out the R vs Tâ1 contribution of the 9-methyl group in 1,9-DMP to determine the parameters that characterize the dynamics of the 1-methyl group. We find that the barrier for reorientation of the 9-methyl group is larger than the barrier for the 1-methyl group and this is discussed in terms of the various contributions to the barrier
Methyl Reorientation in Methylphenanthrenes: 1. Solid-State Proton Spin-Lattice Relaxation in the 3-Methyl, 9-Methyl, and 3,9-Dimethyl Systems
We have investigated the dynamics of methyl group reorientation in solid methylâsubstituted phenanthrenes. The temperature dependence of the proton spinâlattice relaxation rates has been measured in polycrystalline 3âmethylphenanthrene (3âMP), 9âmethylphenanthrene (9âMP), and 3,9âdimethylphenanthrene (3,9âDMP) at Larmor frequencies of 8.50, 22.5, and 53.0 MHz. The data are interpreted using a DavidsonâCole spectral density which implies either that the correlation functions for intramolecular reorientation are nonexponential or that there is a distribution of exponential correlation times. Comparing the fitted parameters that characterize the relaxation data for the three molecules shows that the individual contributions to the relaxation rate from the 3â and 9âmethyls in 3,9âDMP can be separated and that the parameters specifying each are similar to the equivalent group in the two single methylphenanthrenes. The 9âmethyl group is characterized by effective activation energies of 10.6±0.6 and 12.5±0.9 kJ/mol in 9âMP and 3,9âDMP, respectively, whereas the 3âmethyl group is characterized by effective activation energies of 5.2±0.8 and 5±1 kJ/mol in 3âMP and 3,9âDMP, respectively. The agreement between the fitted and calculated values of the spinâlattice interaction strength, assuming only intramethyl proton dipoleâdipole interactions need be considered, is excellent. A comparison between experimentally determined correlation times and those calculated from a variety of very simple dynamical models is given, and the results suggest, as have several previous studies, that at high temperatures where tunneling plays no role, methyl reorientation is a simple, thermally activated, hopping process. We have also analyzed many published data in methylâsubstituted phenanthrenes, anthracenes, and naphthalenes (14 molecules) in the same way as we did for the phenanthrene data presented here, and a consistent picture for the dynamics of methyl reorientation emerges
The Local Interstellar Ultraviolet Radiation Field
I have used the Hipparcos Input Catalog, together with Kurucz model stellar
atmospheres, and information on the strength of the interstellar extinction, to
create a model of the expected intensity and spectral distribution of the local
interstellar ultraviolet radiation field, under various assumptions concerning
the albedo a of the interstellar grains. (This ultraviolet radiation field is
of particular interest because of the fact that ultraviolet radiation is
capable of profoundly affecting the chemistry of the interstellar medium.) By
comparing my models with the observations, I am able to conclude that the
albedo a of the interstellar grains in the far ultraviolet is very low, perhaps
a = 0.1. I also advance arguments that my present determination of this albedo
is much more reliable than any of the many previous (and conflicting)
ultraviolet interstellar grain albedo determinations. Beyond this, I show that
the ultraviolet background radiation that is observed at high galactic
latitudes must be extragalactic in origin, as it cannot be backscatter of the
interstellar radiation field.Comment: Astrophysical Journal, in press; 9 figures + 16 text page
Numerical modelling of Auriga's Wheel - a new ring galaxy
We model the formation of Auriga's Wheel - a recently discovered collisional
ring galaxy. Auriga's Wheel has a number of interesting features including a
bridge of stars linking the neighbouring elliptical to the ring galaxy, and
evidence for components of expansion and rotation within the ring. Using
N-body/SPH modelling, we study collisions between an elliptical galaxy and a
late-type disk galaxy. A near direct collision, with a mildy inclined disk, is
found to reasonably reproduce the general system morphology ~50 Myr following
the collision. The collision must have a relatively low velocity (initially
~150 km s^{-1}) in order to form the observed bridge, and simultaneously match
the galaxies separation. Our best-match model suggests the total disk galaxy is
~5 times more massive than the elliptical. We find that the velocity of
expansion of the ring is sensitive to the mass of the elliptical, while
insensitive to the encounter velocity. We evolve our simulation beyond the
current epoch to study the future destiny of the galaxy pair. In our model, the
nucleus moves further away from the plane of the ring in the direction of the
stellar bridge. The nucleus eventually merges with the elliptical galaxy ~100
Myr after the present time. The ring continues to expand for ~200 Myr before
collapsing back. The low initial relative velocity of the two galaxies will
eventually result in a complete merger.Comment: Accepted to MNRAS, March 9th, 2012. 17 pages, 16 figures, no table
Therapeutic Rescue of Misfolded Mutants: Validation of Primary High Throughput Screens for Identification of Pharmacoperone Drugs
Functional rescue of misfolded mutant receptors by small non-peptide molecules has been demonstrated. These small, target-specific molecules (pharmacological chaperones or "pharmacoperones") serve as molecular templates, promote correct folding and allow otherwise misfolded mutants to pass the scrutiny of the cellular quality control system (QCS) and be expressed at the plasma membrane (PM) where they function similarly to wild type (WT) proteins. In the case of the gonadotropin releasing hormone receptor (GnRHR), drugs that rescue one mutant typically rescue many mutants, even if the mutations are located at distant sites (extracellular loops, intracellular loops, transmembrane helices). This increases the value of these drugs. These drugs are typically identified, post hoc, from "hits" in screens designed to detect antagonists or agonists. The therapeutic utility of pharmacoperones has been limited due to the absence of screens that enable identification of pharmacoperones per se.We describe a generalizable primary screening approach for pharmacoperone drugs based on measurement of gain of activity in stable HeLa cells stably expressing the mutants of two different model G-protein coupled receptors (GPCRs) (hGnRHR[E(90)K] or hV2R[L(83)Q]). These cells turn off expression of the receptor mutant gene of interest in the presence of tetracycline and its analogs, which provides a convenient means to identify false positives.The methods described and characterized here provide the basis of novel primary screens for pharmacoperones that detect drugs that rescue GPCR mutants of specific receptors. This approach will identify structures that would have been missed in screens that were designed to select only agonists or antagonists. Non-antagonistic pharmacoperones have a therapeutic advantage since they will not compete for endogenous agonists and may not have to be washed out once rescue has occurred and before activation by endogenous or exogenous agonists
Thinking like a consumer: Linking aquatic basal metabolism and consumer dynamics
The increasing availability of high-frequency freshwater ecosystem metabolism data provides an opportunity to identify links between metabolic regimes, as gross primary production and ecosystem respiration patterns, and consumer energetics with the potential to improve our current understanding of consumer dynamics (e.g., population dynamics, community structure, trophic interactions). We describe a conceptual framework linking metabolic regimes of flowing waters with consumer community dynamics. We use this framework to identify three emerging research needs: (1) quantifying the linkage of metabolism and consumer production data via food web theory and carbon use efficiencies, (2) evaluating the roles of metabolic dynamics and other environmental regimes (e.g., hydrology, light) in consumer dynamics, and (3) determining the degree to which metabolic regimes influence the evolution of consumer traits and phenology. Addressing these needs will improve the understanding of consumer biomass and production patterns as metabolic regimes can be viewed as an emergent property of food webs
Indirect Regulation of Environmental Hazards Through the Provision of Information to The Public: The Case of SARA, Title III
Title III of the Superfund Amendments and Reauthorization Act of 1986 seeks to reduce the risks of chemical accidents through a strategy of indirect regulation that relies on providing the public with information about chemical hazards. For this strategy to be effective, citizens must aggressively utilize the information provided to monitor industrial practices and press for risk reduction. Since prior research suggests it is very difficult to evoke the degree of citizen action that would be required to make a strategy of indirect regulation successful, and since the federal legislation provided no funds for implementation, there is a question o/whether the structures set up by Title III are sufficient to achieve its objectives. This article reports the results of a national study that examined selected aspects of the implementation of Title III in an effort to assess the likely outcome of its attempt at indirect regulation. Our focus is on the degree to which the Title Ill-mandated Local Emergency Planning Committees are pursuing policies that are likely to get the necessary information to citizens and foster community debate on hazardous materials issues
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