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Asian Journal of Chemistry Asian Journal Asian Journal of Chemistry; Vol. 28, No. 3 (2016), 555-561 ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2016.19405 Chemical Evolution of Aminoacetonitrile to Glycine under Discharge onto Primitive Hydrosphere: Simulation Experiments Using Glow Discharge T. MUNEGUMI Department of Science Education, Naruto University of Education, Naruto, Tokushima 772-8502, Japan Corresponding author: Fax: +81 88 6876022; Tel: +81 88 6876418; E-mail: [email protected] Received: 15 June 2015; Accepted: 31 July 2015; Published online: 5 December 2015; AJC-17650 Aminoacetonitrile is an important precursor of abiotic amino acids, as shown in the mechanism that was developed to explain the results of the Miller-type spark-discharge experiment. In present experimental setup, a spark discharge is generated in a simulated reducing atmosphere to yield hydrogen cyanide, aldehyde and ammonia; in a second step, a solution-phase reaction proceeds via aminoacetonitrile to give amino acids. However, when the same experiment is carried out in a non-reducing atmosphere, the yield of amino acids is very low. Contact glow discharge electrolysis onto the aqueous phase, which simulates an energy source for chemical evolution, converted aminoacetonitrile via glycinamide to glycine. The mechanism of glycinamide formation was explained by considering the addition of hydrogen and hydroxyl radicals to the C-N triple bond and subsequent transformation into the amide, which was then oxidized to the amino acid. This research suggests that amino acid amides and amino acids can be obtained through oxidation-reduction with H and OH radicals in the primitive hydrosphere whether under reducing or non-reducing conditions. Keywords: Aminoacetonitrile, Chemical evolution, Contact glow discharge electrolysis. INTRODUCTION have actually proceeded in a primitive hydrosphere, if the primitive atmosphere would have supplied the majority of The formation of primitive amino acids has been discussed materials for amino acid formation on the primitive earth. with respect to both terrestrial [1,2] and extra terrestrial [2,3] On the other hand, the presence of amino acids and their origins. The results of simulation experiments involving Miller- precursors in interstellar solid medium [15,16], interstellar gas type spark-discharge [4,5] in an assumed reducing atmosphere phase [17-20], comets [21,22] and meteorites [23-25] has been (CH4, NH3, H2O, H2), glow discharge onto aqueous solutions reported. Experiments involving use of high-energy particles [6] and other energy sources [2,7,8] have supported the [26,27] and ultraviolet light [28-30] to irradiate simulated conclusion of a terrestrial origin of amino acids. Although the interstellar media have provided results that support formation same Miller-type spark-discharge experiment gave very low of amino acids and their precursors. The survival of such yield of amino acids [9] in an assumed non-reducing [10] compounds within extra terrestrial bodies during atmospheric atmosphere (CO2, N2, H2O), the value of Miller-type spark- entry to earth has been discussed [31,32]. Several experiments discharge has been supported by the research results [11] that that have been designed to simulate atmospheric entry have the early earth atmosphere would have been more hydrogen- supported the conclusion that amino acids remain intact, rich and reducing rather than non-reducing. On the contrary, although the amount of degradation might depend on the size a recent report [12] on the oxidation state of Hadean magmas of the extra terrestrial bodies and on the nature of the amino suggests that the early earth atmosphere would have been acids [33-42]. oxidizing. Discussion about whether the early atmosphere had Aminoacetonitrile is known to be an important precursor been reducing or non-reducing is still controversial. Amino for abiotic amino acid formation [3,43,44] and subsequent acid formation processes under Miller-type spark-discharge peptide formation (Fig. 2) [45] in the primitive earth and conditions has been explained by a two-step mechanism (Fig. interstellar medium [46]. Herein, the formation of glycine from 1): the first step is the formation of acetaldehyde and hydrogen aminoacetonitrile via glycinamide in aqueous solutions cyanide in the gas phase and the second step is a Strecker-type induced by contact glow discharge electrolysis (CGDE; also synthesis in the solution phase [13,14] to give aminoacetonitrile, termed Harada discharge [47-50]) as a simulation energy source which hydrolyzes to glycine. Amino acid formation would in a chemical evolutionary process is reported. The author uses 556 Munegumi Asian J. Chem. Contact glow discharge electrolysis (CGDE): A glass NH3 H2 reaction vessel (114 × 35 mm i.d.) was used for CGDE as Electric reported previously [49,50]. The reaction mixture (20 mL) Gas phase discharge CH4 H2O containing aminoacetonitrile (20 mM) and inorganic salt buffer (200 mM, pH 1-10) in the reaction vessel was cooled in an ice-water bath to 10-30 °C. After bubbling argon gas through the reaction mixture for 15 min, discharge electrolysis (440- 520 V, 20-30 mA) was carried out between the platinum anode O C H NH3 HC N above the solution and the platinum cathode in the solution H over bubbling argon gas. Electric power was supplied by a Model PS-1515 (Toyo Solid State, Tokyo) power supply. An H aliquot of the reaction solution was taken at regular time intervals and analyzed with an amino acid analyzer. H N C C N 2 Hydrolysis of aminoacetonitrile at room temperature Solution phase H Aminoacetonitrile without CGDE: Aqueous solutions containing 20 mM amino- +H2O acetonitrile in 200 mM buffer were stirred with bubbling argon. An aliquot (about 0.200 mL) of the reaction solution was taken H O at regular time intervals and analyzed with an amino acid H2NCC NH2 analyzer. H Glycinamide Amino acid analysis: The composition of amino compounds in the reaction mixtures were analyzed with a JLC-300 amino +H2O, -NH3 acid analyzer (JEOL, Tokyo, Japan). Typical chromatograms H O of standard compounds and of a reaction mixture are shown in Fig. 3. Glycine, aminoacetonitrile, glycinamide and ammonia H2NCC OH were almost baseline separated; their typical retention times H Glycine were as follows: glycine (39.6 min), aminoacetonitrile (73.9 min), glycinamide (77.0 min) and ammonia (80.1 min). Eluted Fig. 1. Plausible reaction pathway of amino acid formation in solution under Miller type discharge compounds were reacted with ninhydrin to enable detection by measuring absorption at 570 nm. Concentration of ammonia H in the reaction mixtures were determined by drawing the initial CH2O + NH3 + HCN H2N C C N concentration out of the actual concentration at each reaction H time. Aminoacetonitrile (a) Standard H H H HNCH-CONH H H 22 2 n H2N C C N N C C N C C OH H H NH n H O n R Polyglycine H 570 nm N C C OH H Polypeptide 0 O n 12 24 36 48 60 72 84 96 108 120 Fig. 2. Aminoacetonitrile as an important intermediate in the formation of (b) Standard HNCH-CN polypeptides 22 570 nm 0 an inert gas, argon atmosphere as a reaction condition to 12 24 36 48 60 72 84 96 monitor the solution phase reactions less susceptible to whether 108 120 HNCH-CONH the atmosphere is reducing or non-reducing. The results demons- (c) 22 2 HNCH-COOH 22 HNCH-CN22 NH trate that amino acid amides and amino acids are formed 570 nm 3 dominantly by oxidation-reduction rather than hydrolysis of 0 12 24 36 48 60 72 84 96 aminoacetonitrile. Retention time (min) 108 120 Fig. 3. Typical chromatograms (a, b) of standard compounds and (c) of a EXPERIMENTAL reaction mixture after exposure to CGDE. A JLC-300 amino acid analyzer was used for analysis. Eluted compounds were reacted with Inorganic buffer solutions (200 mM) were prepared from ninhydrin to enable detection by measuring absorption at 570 nm sulfuric acid (pH 1), sodium hydrogen phosphate (pH 4-7) and sodium carbonate (pH 10-11). The inorganic salts and RESULTS AND DISCUSSION aminoacetonitrile sulfate were purchased from Tokyo Kasei Co., Ltd. (Tokyo, Japan). Glycinamide hydrochloride was Contact glow discharge electrolysis onto aminoaceto- purchased from Kokusan Chemical Co., Ltd. (Tokyo, Japan). nitrile solution: The changes in concentration of amino- Glycine was purchased from Wako Pure Chemical Industries, acetonitrile and products during the CGDE at pH 10 were Ltd. (Osaka, Japan). plotted against the reaction time (Fig. 4(d)). After 60 min Vol. 28, No. 3 (2016) Chemical Evolution of Aminoacetonitrile to Glycine 557 (a) CGDE onto aminoacetonitrile solution at pH 1 (b) CGDE onto aminoacetonitrile solution at pH 6 100 100 80 80 ) % 60 60 HNCHCN22 H22 NCH CONH 2 HNCHCN22 Gly 40 H22 NCH CONH 2 40 Gly NH3 NH3 Yield and recovery ( Yield and recovery (%) recovery and Yield 20 20 0 0 0 20 40 60 80 0 20 40 60 80 Reaction time (min) Reaction time (min) (c) CGDE onto aminoacetonitrile solution at pH 8 (d) CGDE onto aminoacetonitrile solution at pH 10 100 Gly 100 H22 NCH CN H NCH CONH 80 22 2 80 NH3 60 60 H22 NCH CN H22 NCH CONH 2 40 40 Gly NH3 Yield and and recovery(%) Yield Yield and recovery(%) 20 20 0 0 0 20 40 60 80 0 20 40 60 80 Reaction time (min) Reaction time (min) Fig. 4. CGDE onto aqueous solutions containing aminoacetonitrile (20 mM) at pH 1, 6, 8 and 10. Conditions of CGDE: 400-440 V, 20 A reaction, the amount of aminoacetonitrile decreased to 45 % into other compounds. The identities of these compounds are (9 mM) compared with the initial concentration; at this point, not known; however, the negative response to analysis with amino acid analysis revealed the presence of glycine (0.14 ninhydrin suggests that the compounds do not contain an amino mM, 0.7 %) and glycinamide (2.9 mM, 14.5 %).
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