Analyses of Aliphatic Aldehydes and Ketones in Carbonaceous Chondrites

Abstract

Aliphatic aldehydes and ketones are essential building blocks for the synthesis of more complex organic compounds. In spite of their potentially key role as precursors of astrobiologically-important molecules, such as amino acids and carboxylic acids, this family of compounds has scarcely been evaluated in carbonaceous chondrites. The paucity of such analyses likely derives from the low concentration of aldehydes and ketones in the meteorites, and from the currently used chromatographic methodologies that have not been optimized for meteorite analysis. In this work, we report the development of a novel analytical method to quantify the molecular distribution and compound-specific isotopic analysis of 29 aliphatic aldehydes and ketones. Using this method, we have investigated the molecular distribution and 13 C-isotopic composition of aldehydes and ketones in ten carbonaceous chondrites from the CI, CM, CR and CV groups. The total concentration of carbonyl compounds ranged from 130 to 1000 nmolg-1 of meteorite, with formaldehyde, acetaldehyde, and acetone being the most abundant species in all investigated samples. The 13 C-isotopic values ranged from-67 to +64‰ and we did not observe clear relationships between 13 C-content and molecular weight. Accurately measuring the relative abundances, determining the molecular distribution, and isotopic composition of chondritic organic compounds is central in assessing both their formation chemistry and synthetic relationships.

Methodologies for Analyzing Soluble Organic Compounds in Extraterrestrial Samples: Amino Acids, Amines, Monocarboxylic Acids, Aldehydes, and Ketones

“…These hot-water extractions can be carried out using a reflux set-up or as small aliquots (1–2 mL water for 0.5–1 g of powder). A number of studies have carried out meteorite extractions of polar organic compounds in organic solvents, such as KOH/CH 3 OH mixtures or 1 N NaOH for the extraction of carboxylic acids [61,62,63,64,65], and dichloromethane (DCM) for the extraction of aldehydes and ketones [66]. Relatively non-polar organic species (e.g., hydrocarbons and heterocycles) are typically extracted using either CH 3 OH, DCM, DCM/CH 3 OH mixtures, or benzene/CH 3 OH mixtures [13,67,68,69,70,71,72,73,74].…”

“…Sample purification steps are commonly carried out to remove impurities and isolate soluble organic compounds of interest for chromatographic analysis. Common purification techniques include treating the meteorite extract with activated silica gels (e.g., [65,82]), performing liquid-liquid extractions to isolate specific target molecules (e.g., [61,63]) and removing co-extracted elemental sulfur from solution using copper powder or granules (e.g., [66,70]). These purification steps may be carried out before or after derivatization, depending on the extraction procedure, target analytes, and derivatization chemistry.…”

The Astrophysical Formation of Asymmetric Molecules and the Emergence of a Chiral Bias

“…One of the most likely scenarios involves the Strecker synthesis from aldehydes, ketones, amines and hydrogen cyanide (HCN) [66]. The discovery of several ketones and aldehydes in meteorites is then an important piece of information [74,75,76,77,78,79], as it strengthens the hypothesis that meteoritic amino acids result from a Strecker-type reaction. However, this pathway encounters some drawbacks—discussed in Section 2.3—that need clarification.…”

Prebiotically Plausible Organocatalysts Enabling a Selective Photoredox α‐Alkylation of Aldehydes on the Early Earth

“…Contrary to this assumption, we werea ble to obtain imidazolidine-4-thiones 1a-1l in yields of up to 76 %, thus including aldehydes as ac lass of prebiotically relevant molecules. [13] In this way,a large number of derivatives could be easily accessed, andw e exemplarily synthesized at otal number of 16 imidazolidine-4thiones.S ince only aldehydes or ketones are neededa so rganic feedstock, this procedure demonstrates its potential and relevance for the emerging of the first organocatalysts on the Early Earth.…”

“…Thereby,t he catalysts showing the best selectivity are formed from the prebiotically more abundant smallera ldehydes and ketones. [13] Moreover,t he already observed superiority of the preferentially formed diastereomer (anti-substituted) in terms of catalytic activity is perceived even more strongly regarding its enantioselectivity.U sing the anti-substituted imidazolidine-4-thione 1b, which represents the diastereomer crystallizing as conglomer-ate, gave 3 with 65 % ee comparedt o1 7% ee in case of the syn-substituted isomer.…”