FORMATION OF PEPTIDE BONDS IN SPACE: A COMPREHENSIVE STUDY OF FORMAMIDE AND ACETAMIDE IN Sgr B2(N)

Abstract

Extensive observations of acetamide (CH 3 CONH 2 ) and formamide (NH 2 CHO) have been conducted toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope (SMT) and the 12 m antenna of the Arizona Radio Observatory. Over the frequency range 65-280 GHz, 132 transitions of acetamide have been observed as individual, distinguishable features, although in some cases they are partially blended. The unblended transitions in acetamide indicate V LSR = 63.2 ± 2.8 km s −1 and ΔV 1/2 = 12.5 ± 2.9 km s −1 , line parameters that are very similar to that of formamide (NH 2 CHO) and other organic species in Sgr B2(N). For formamide, 79 individual transitions were identified over the same frequency region. Rotational diagram analyses indicate the presence of two components for both species in Sgr B2(N). For acetamide, the colder component (E u < 40 K) exhibits a rotational temperature of T rot = 17 ± 4 K and a column density of N tot = 5.2 ± 3.5 × 10 13 cm −2 ; the higher energy component has T rot = 171 ± 4 K and N tot = 6.4 ± 4.7 × 10 14 cm −2 . In the case of formamide, T rot = 26 ± 4 K and N tot = 1.6 ± 0.7 × 10 14 cm −2 for the colder component with T rot = 134 ± 17 K and N tot = 4.0 ± 1.2 × 10 14 cm −2 for the warmer region. The fractional abundances of acetamide are f (H 2 ) = 1.7 × 10 −11 and 2.1 × 10 −10 for the cold and warm components, and in formamide, f (H 2 ) = 5.3 × 10 −11 and 1.3 × 10 −10 . The similarity between the abundances and distributions of CH 3 CONH 2 and NH 2 CHO suggests a synthetic connection. The abundance of acetamide, moreover, is only a factor of three lower than that of formaldehyde, and very similar to acetaldehyde and ketene. CH 3 CONH 2 is therefore one of the most abundant complex organic species in Sgr B2(N), and could be a possible source of larger peptide molecules, as opposed to amino acids.

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

“…In our spectrum, most of these transitions are significantly blended with emission from other species and only a few transitions can be reliably identified. The temperature is however not very well constrained in our data and we set it to the value derived by Halfen et al (2011) for their warm component, which is very close to the temperature we derive for formamide (see Sect. 4.4.37).…”

“…The detected signals were interpreted as coming from a low-excitation (∼8 K) halo surrounding both hot cores. Halfen et al (2011) published a detailed analysis of the emission of acetamide based on their spectral survey of Sgr B2(N) performed with the ARO 12 m telescope (HPBW ∼ 60 at 100 GHz) and the SMT at 3, 2, and 1 mm. They claim the detection of 132 transitions of acetamide, the majority of them being "partially blended", and they identify two temperature components based on a rotation-diagram analysis (17 ± 4 and 171 ± 4 K, respectively).…”

Some Insights Into Formamide Formation Through Gas-Phase Reactions in the Interstellar Medium

“…The identification of more than 80 amino acids in meteorites, such as Murchison (Cooper et al 1992), is a positive clue about the presence of amino acids in space. In contrast, molecules with a peptide bond (NH-C=O), such as formamide (Rubin et al 1971) and acetamide (Hollis et al 2006), have been detected in interstellar clouds, and Halfen et al (2011) recently highlighted their importance as prototypes for peptide bond formation. Because of these compounds' relatively large abundance, Halfen et al suggest that they could be a possible source of larger peptide molecules that do not involve amino acids.…”

Infrared spectrum of formamide in the solid phase

“…Formamide was first detected (in 1971) in the gas phase in Sgr B2 and later in the long period comet C/1995 O1 Hale- Bopp (2000) and in the young stellar object W33A (1999), and recently (2004) there has been a tentative report of ice bound formamide in ISO-SWS spectra of the protostellar source NGC 7538 IRS9 [3][4][5][6].…”