Magnesium-Catalyzed Mild Reduction of Tertiary and Secondary Amides to Amines

The first example of a catalytic hydroboration of amides for their deoxygenation to amines is reported. This transformation employs an earth-abundant magnesium-based catalyst. Tertiary and secondary amides are reduced to amines at room temperature in the presence of pinacolborane (HBpin) and catalytic amounts of ToMMgMe (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). Catalyst initiation and speciation is complex in this system, as revealed by the effects of concentration and order of addition of the substrate and HBpin in the catalytic experiments. ToMMgH2Bpin, formed from ToMMgMe and HBpin, is ruled out as a possible catalytically relevant species by its reaction with N,N-dimethylbenzamide, which gives Me2NBpin and PhBpin through C–N and C–C bond cleavage pathways, respectively. In that reaction, the catalytic product benzyldimethylamine is formed in only low yield. Alternatively, the reaction of ToMMgMe and N,N-dimethylbenzamide slowly gives decomposition of ToMMgMe over 24 h, and this interaction is also ruled out as a catalytically relevant step. Together, these data suggest that catalytic activation of ToMMgMe requires both HBpin and amide, and ToMMgH2Bpin is not a catalytic intermediate. With information on catalyst activation in hand, tertiary amides are selectively reduced to amines in good yield when catalytic amounts of ToMMgMe are added to a mixture of amide and excess HBpin. In addition, secondary amides are reduced in the presence of 10 mol % ToMMgMe and 4 equiv of HBpin. Functional groups such as cyano, nitro, and azo remain intact under the mild reaction conditions. In addition, kinetic experiments and competition experiments indicate that B–H addition to amide C═O is fast, even faster than addition to ester C═O, and requires participation of the catalyst, whereas the turnover-limiting step of the catalyst is deoxygenation

A Photometrically and Morphologically Variable Infrared Nebula in L483

We present narrow and broad K-band observations of the Class 0/I source IRAS 18148-0440 that span 17 years. The infrared nebula associated with this protostar in the L483 dark cloud is both morphologically and photometrically variable on a time scale of only a few months. This nebula appears to be an infrared analogue to other well-known optically visible variable nebulae associated with young stars, such as Hubble's Variable Nebula. Along with Cepheus A, this is one of the first large variable nebulae to be found that is only visible in the infrared. The variability of this nebula is most likely due to changing illumination of the cloud rather than any motion of the structure in the nebula. Both morphological and photometric changes are observed on a time scale only a few times longer than the light crossing time of the nebula, suggesting very rapid intrinsic changes in the illumination of the nebula. Our narrow-band observations also found that H_2 knots are found nearly twice as far to the east of the source as to its west, and that H_2 emission extends farther east of the source than the previously known CO outflow.Comment: 19 pages, 6 figures, 1 tabl

The Variable Reflection Nebula Cepheus A East

We report K'-band imaging observations of the reflection nebula associated with Cepheus A East covering the time interval from 1990 to 2004. Over this time the reflection nebula shows variations of flux distribution, which we interpret as the effect of inhomogeneous and varying extinction in the light path from the illuminating source HW2 to the reflection nebula. The obscuring material is located within typical distances of approximately 10 AU from the illuminating source.Comment: 22 pages, including 6 figures, accepted for publication in The Astronomical Journa

The Probable Detection of SN 1923A: The Oldest Radio Supernova?

Based upon the results of VLA observations, we report the detection of two unresolved radio sources that are coincident with the reported optical position of SN 1923A in M83. For the source closest to the SN position, the flux density was determined to be 0.30 +/- 0.05 mJy at 20 cm and 0.093 +/- 0.028 mJy at 6 cm. The flux density of the second nearby source was determined to be 0.29 +/- 0.05 at 20 cm and 0.13 +/- 0.028 at 6 cm. Both sources are non-thermal with spectral indices of alpha = -1.0 +/- 0.30 and -0.69 +/- 0.24, respectively. SN 1923A has been designated as a Type II-P. No Type II-P (other than SN 1987A) has been detected previously in the radio. The radio emission from both sources appears to be fading with time. At an age of approximately 68 years when we observed it, this would be the oldest radio supernova (of known age) yet detected

The Crab pulsar and its pulsar-wind nebula in the optical and infrared

We investigate the emission mechanism and evolution of pulsars that are associated with supernova remnants. We used imaging techniques in both the optical and near infrared, using images with very good seeing (<0.6) to study the immediate surroundings of the Crab pulsar. In the case of the infrared, we took two data sets with a time window of 75 days, to check for variability in the inner part of the Crab nebula. We also measure the spectral indices of all these wisps, the nearby knot, and the interwisp medium, using our optical and infrared data. We then compared the observational results with the existing theoretical models. We report variability in the three nearby wisps located to the northwest of the pulsar and also in a nearby anvil wisp in terms of their structure, position, and emissivity within the time window of 75 days. All the wisps and the inner knot display red spectra with similar spectral indices. Similarly, the interwisp medium regions also show red spectra similar to those of the wisps. Also, based on archival HST data and our IR data, we find that the inner knot remains stationary for a time period of 13.5 years. The projected average velocity relative to the pulsar for this period is < 8 km/s. By comparing the spectral indices of the structures in the inner Crab with the current theoretical models, we find that the Del Zanna et al. (2006) model for the synchrotron emission fits our observations, although the spectral index is at the flatter end of their modelled spectra.Comment: 8 pages, 5 figure

Cultivating compliance: governance of North Indian organic basmati smallholders in a global value chain

Focusing on a global value chain (GVC) for organic basmati rice, we study how farmers’ practices are governed through product and process standards, organic certification protocols, and contracts with buyer firms. We analyze how farmers’ entry into the GVC reconfigures their agencements (defined as heterogeneous arrangements of human and nonhuman agencies which are associated with each other). These reconfigurations entail the severance of some associations among procedural and material elements of the agencements and the formation of new associations, in order to produce cultivation practices that are accurately described by the GVC’s standards and protocols. Based on ethnography of two farmers in Uttarakhand, North India, we find that the same standards were enacted differently on the two farmers’ fields, producing variable degrees of (selective) compliance with the ‘official’ GVC standards. We argue that the disjuncture between the ‘official’ scripts of the standards and actual cultivation practices must be nurtured to allow farmers’ agencements to align their practices with local sociotechnical relations and farm ecology. Furthermore, we find that compliance and disjuncture were facilitated by many practices and associations that were officially ungoverned by the GVC

On the origin of variable gamma-ray emission from the Crab Nebula

The oblique geometry of pulsar wind termination shock ensures that the Doppler beaming has a strong impact on the shock emission. We illustrate this using recent relativistic MHD simulations of the Crab Nebula and also show that the observed size, shape, and distance from the pulsar of the Crab Nebula inner knot are consistent with its interpretation as a Doppler-boosted emission from the termination shock. If the electrons responsible for the synchrotron gamma-rays are accelerated only at the termination shock then their short life-time ensures that these gamma-rays originate close to the shock and are also strongly effected by the Doppler beaming. As the result, bulk of the observed synchrotron gamma-rays of the Crab Nebula around 100 MeV may come from its inner knot. This hypothesis is consistent with the observed optical flux of the inner knot provided its optical-gamma spectral index is the same as the injection spectral index found in the Kennel & Coroniti model of the nebula spectrum. The observed variability of synchrotron gamma-ray emission can be caused by the instability of the termination shock discovered in recent numerical simulations. Given the small size of the knot, it is possible that the September 2010 gamma-ray flare of the Crab Nebula also came from the knot, though the actual mechanism remains unclear. The model predicts correlation of the temporal variability of the synchrotron gamma-ray flux in the Fermi and AGILE windows with the variability of the unpulsed optical flux from within 1 arcsec of the Crab pulsar.Comment: submitted to MNRAS, typos corrected, new references added, additional issues discusse