Gamma Radiolysis of C60 fullerene in water and ...

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Mar 26, 2013 - Actinium Chemical Research srl, Via Casilina. 1626/A, 00133 Rome, Italy high energy radiation C60 reacts with the free radicals gen-.
J Radioanal Nucl Chem (2013) 298:1073–1083 DOI 10.1007/s10967-013-2484-0

Gamma Radiolysis of C60 fullerene in water and water/ammonia mixtures: relevance of fullerene fate in ices of interstellar medium S. Iglesias-Groth F. Cataldo



Y. Hafez



G. Angelini



Received: 28 January 2013 / Published online: 26 March 2013 Akade´miai Kiado´, Budapest, Hungary 2013

Abstract The c radiolysis of fullerene C60 dispersed in H2O, H2O/NH3, H2O/methanol and H2O/NH3/methanol was studied at 250 and 500 kGy. It was found that C60 originally insoluble in the above mentioned hosting matrix became soluble as a consequence of multiple hydroxylation and oxidation reaction produced by the free radicals generated by the radiolysis of the hosting matrix. The changes undergone by C60 were studied by infrared spectroscopy (FT-IR) and by electronic absorption spectroscopy. The astrochemical con-sequences of the present study are that C60 ejected in the interstellar medium for instance from protoplanetary and planetary nebulae can condense together with water and other ices in dense molecular clouds. Under the action of

high energy radiation C60 reacts with the free radicals generated from the matrix where it is embedded it is solubilized and consequently its carbon content becomes available for further abiotic processes of synthesis of molecules of astrobiological interest. The behavior of C60 appears comparable to that of common PAHs which are also hydroxylated and oxidized under similar conditions.

Keywords Astrochemistry Water ices Fullerene Radiolysis Free radicals Hydroxylated fullerenes Fullerol

Introduction S. Iglesias-Groth Instituto de Astrofısica de Canarias, Via Lactea s/n, 38205 La Laguna, Spain e-mail: [email protected]

Fullerenes C60 and C70 are known to be present in different astrophysical environments ranging from young planetary nebulae [1], planetary nebulae in general [2], reflection nebulae [3], protoplanetary nebulae [4] and R Coronae Borealis

S. Iglesias-Groth Departamento de Astrofısica, Universidad de La Laguna (ULL), 38206 La Laguna, Spain

stars [5]. Fullerene C60 and PAHs were detected simultaneously and in mixture in several planetary nebulae [6] and consequently both fullerenes and PAHs may share the same destiny once ejected in the interstellar medium also thanks to

Y. Hafez National Center for Astronomy, KACST, P.O. Box 6086, Riyadh 11442, Saudi Arabia G. Angelini Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300, 00016 Monterotondo Stazione Rome, Italy F. Cataldo (&) INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy e-mail: [email protected] F. Cataldo Actinium Chemical Research srl, Via Casilina 1626/A, 00133 Rome, Italy

the excellent stability of C60 toward high energy radiation [7]. Indeed, it is thought that PAHs and derivatives in the dense clouds of the interstellar medium form agglomerates embedded in ices or freeze out on to dust grains, together with volatile species such as H2O, CO, CO2 and NH3. The ices and dust are processed by the ultraviolet radiation and by the cosmic rays forming hundreds of molecular species of astrobiological interest [8]. For example, Bernstein et al. [9] showed the formation of 1-naphthol and naphthoquinone by UV irradiation of naphthalene in water ice. Bernstein et al. [10, 11] have also reported about the UV photolysis or proton bombardment of the PAH coronene in ice mixture and reported

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the formation of alcohol, ketone, carboxyl derivatives. If ammonia is present in the ice, then also amino, cyano and isocyano derivatives were detected. More recently, Guennoun et al. [12] were able to identify more precisely some photoproducts of UV-processed coronene embedded in water ice matrix reporting 1,10-dihydrocoronene and 1,10 coronenquinone. Ashbourn et al. [13] have reported about the UV irradiation products formed from anthracene and water ice and reported the formation of ketones (9-anthrone, 1,4-anthraquinone, and 9,10-anthraquinone) and alcohols (1-anthrol and 2anthrol). Bouwman et al. [14, 15] and Cuylle et al. [16] have UV-irradiated some of PAHs in pure water ice, in mixed water/ ammonia ices and in pure ammonia ice. In pure water cations of PAHs are generated leading to the corresponding photoproducts while in pure ammonia anions of PAHs are formed leading to ammonia-related photoproducts. Stable PAHs cation of quaterrylene was generated in water ices and studied in a wide range of temperatures [17]. Thus, it is talking about ionmediated solid state astrochemistry [18] and there are also favorable energetics in the H-addition reactions to PAHs cations in ices [19] so that oxidized PAHs are accompanied also by partially hydrogenated PAHs. The general trend in the oxidation of organic compounds embedded in water ices is not limited to PAHs since also the heterocyclic compound pyrimidine, once irradiated in water ice, it produces the nucleobase uracil, an oxidized pyrimidine derivative [20] and quinoline irradiated in water ice yields hydroxyquinoline and quinoline-N-oxide [21].

An extreme consequence of complex ices mixture irradiation is the formation of amino acids mixture as shown for instance by Nuevo et al. [22]. Furthermore, Chen et al. [23] have shown that naphthalene (the smallest PAH) trapped in water/ammonia ice mixture under high energy radiation processing leads to the formation of amino acids. In the present paper we explore for the first time the reactivity of C60 fullerene with water and with water/ ammonia mixtures under the reasonable assumption that C60 largely available in the circumstellar and in the interstellar medium condenses in dense clouds together with ices and is processed by radiation. The aim of the present work is therefore to demonstrate that also C 60 fullerene plays a key role at least as carbon source for the formation of complex molecules since it is transformed in the ISM into other products more useful for the abiotic synthesis of molecules relevant from the astrobiological point of view.

http://link.springer.com/article/10.1007%2Fs10967013-2484-0

J Radioanal Nucl Chem (2013) 298:1073–1083