196 research outputs found
The Methanol-Trimethoxyborane Azeotrope as a Solvent for Acid-Catalyzed Reactions. Methyl Esterification
Carboxylic acids UIIldergo a rapid and complete acid-catalyzed
methyl esterification in the methanol-trimethoxyborane azeotrope.
The reaction is first order in cariboxylic acid and first order in
strong acid catalyst. Rate constants are very similar to those in
methanol alone. These observations suggest that the mechanism
is the same as that in solvent, methanol-AAc 2. The reaction can be
made the basis of a convenient preparation of methyl esters. It has
been used to prepare methyl benzoate, methyl lactate, and the
methyl ester of phenylalanine. Acid-catalyzed acetal and ketal
formation in the azeotrope is fast but incomplete. Methyl etherification
of tertiary alcohols seems too limited, structurally, to be
generally useful. No acid-catalyzed addition of methanol to acetonitrile
or acrylonitrile could be observed
The Methanol-Trimethoxyborane Azeotrope as a Solvent
The methanol-trimethoxyborane azeotrope is an ea.sily prepa.
red solvent of strong H-bond donor and weak H-bond acceptor
properties. It has a low viscosity and low boiling point, and is
completely transparent in the visible and uv at wave lengths above
220 nm. It has a dieLectric constant of 9 and ion pair formation
constants between 103 and 104 for simple electrolytes. The glass
electrode pH-meter can be used in this solvent, with the ordinary
calomel reference electrode. Indicator acidity measurements are
somewhat complicated by the forma•tion of H-bonded ion pairs.
The solvent is useful for measuning the relative acidity of
strong acids; CH3S020H and CF3S020H are readily differentiated.
It should be useful for other physico-chemical measurements and
also in preparative chemistry
Observation of ferromagnetic resonance in strontium ruthenate (SrRuO3)
We report the observation of ferromagnetic resonance (FMR) in SrRuO3 using
the time-resolved magneto-optical Kerr effect. The FMR oscillations in the
time-domain appear in response to a sudden, optically induced change in the
direction of easy-axis anistropy. The high FMR frequency, 250 GHz, and large
Gilbert damping parameter, alpha ~ 1, are consistent with strong spin-orbit
coupling. We find that the parameters associated with the magnetization
dynamics, including alpha, have a non-monotonic temperature dependence,
suggestive of a link to the anomalous Hall effect.Comment: submitted to Phys. Rev. Let
Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements
We report time-resolved Kerr effect measurements of magnetization dynamics in
ferromagnetic SrRuO3. We observe that the demagnetization time slows
substantially at temperatures within 15K of the Curie temperature, which is ~
150K. We analyze the data with a phenomenological model that relates the
demagnetization time to the spin flip time. In agreement with our observations
the model yields a demagnetization time that is inversely proportional to T-Tc.
We also make a direct comparison of the spin flip rate and the Gilbert damping
coefficient showing that their ratio very close to kBTc, indicating a common
origin for these phenomena
Interleukin-1 receptor-associated kinase-M suppresses systemic lupus erythematosus
Interleukin-1 receptor-associated kinase (IRAK)-M suppresses Toll-like receptor (TLR)-mediated activation of innate immunity during infection. A similar role was hypothesised for IRAK-M in autoimmunity
Cultural factors that affected the spatial and temporal epidemiology of kuru
Kuru is a prion disease which became epidemic among the Fore and surrounding linguistic groups in Papua New Guinea, peaking in the late 1950s. It was transmitted during the transumption (endocannibalism) of dead family members at mortuary feasts. In this study, we aimed to explain the historical spread and the changing epidemiological patterns of kuru by analysing factors that affected its transmission. We also examined what cultural group principally determined a family’s behaviour during mortuary rituals. Our investigations showed that differences in mortuary practices were responsible for the initial pattern of the spread of kuru and the ultimate shape of the epidemic, and for subsequent spatio-temporal differences in the epidemiology of kuru. Before transumption stopped altogether, the South Fore continued to eat the bodies of those who had died of kuru, whereas other linguistic groups, sooner or later, stopped doing so. The linguistic group was the primary cultural group that determined behaviour but at linguistic boundaries the neighbouring group’s cultural practices were often adopted. The epidemiological changes were not explained by genetic differences, but genetic studies led to an understanding of genetic susceptibility to kuru and the selection pressure imposed by kuru, and provided new insights into human history and evolution
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