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Detection of a branched alkyl molecule in the interstellar medium: iso-propyl cyanide

Science  26 Sep 2014:
Vol. 345, Issue 6204, pp. 1584-1587
DOI: 10.1126/science.1256678

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Carbon chains branch out on space dust

Meteorites found on Earth contain a wide range of complex constituent molecules, including amino acids. Astrochemists proposed the existence of these molecules in interstellar space in the 1980s, but detections have been elusive. Belloche et al. used the ALMA telescope array in Chile to observe the massive star-forming region Sgr B2. There, the vast quantities of gas enabled detection of even sparsely distributed species such as iso-propyl cyanide. Despite being difficult to detect, such nonlinear organic molecules may be common. The formation of branched molecules is important, given the analogous structure of familiar amino acids — some of the building blocks for life.

Science, this issue p. 1584

Abstract

The largest noncyclic molecules detected in the interstellar medium (ISM) are organic with a straight-chain carbon backbone. We report an interstellar detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an abundance 0.4 times that of its straight-chain structural isomer. This detection suggests that branched carbon-chain molecules may be generally abundant in the ISM. Our astrochemical model indicates that both isomers are produced within or upon dust grain ice mantles through the addition of molecular radicals, albeit via differing reaction pathways. The production of iso-propyl cyanide appears to require the addition of a functional group to a nonterminal carbon in the chain. Its detection therefore bodes well for the presence in the ISM of amino acids, for which such side-chain structure is a key characteristic.

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