Rafael Navarro-Gonzalez

Nitrogen fixation by volcanic lightning in the early Earth

We examine an unusual mechanism to fix nitrogen in the early Earth by lightning discharges occurring inside explosive volcanic clouds containing gases characteristic of Hawaiian volcanoes as a model of Archean volcanic volatiles. The products are predicted on thermodynamic equilibrium assumptions of the chemical species frozen out as the lightning channel rapidly expands and cools to ∼ 2400°C. Volcanic lightning is simulated in the laboratory by flowing the gas mixture into a microwave discharge cavity where the gases are excited and then the products are analyzed downstream by chemical ionization mass spectrometry. Nitric oxide was found to be the major product formed with an energy yield of ∼1 × 1016 molecule J−1. It is estimated that about 1012−1013 g of NO could have been produced annually by volcanic clouds occurring about 4 Gyr ago.

Pyrolysis of alanine and α-aminoisobutyric acid: identification of less-volatile products using gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry

Abstract In addition to volatile low-molecular-weight decomposition compounds, α -aminoisobutyric acid (Aib) and alanine (Ala) pyrolysis at 500°C under nitrogen atmosphere leads to less-volatile products resulting from amino acid intermolecular condensation. The major pathway is the formation of cyclic dipeptides piperazine-2,5-diones with the yields of 1% for Aib and 68% for Ala. To identify other pyrolysis products, they have been extracted by chloroform and analyzed by means of the coupled technique of gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry with auxiliary computer simulation of IR spectra and 1 H and 13 C nuclear magnetic resonance spectroscopy. In the case of Aib, the condensation has been also found to produce a linear dipeptide Aib-Aib, which undergoes further decarboxylation and the loss of H 2 NCH(CH 3 ) 2 and hydroxyl moiety. Formation of small amounts of the bicyclic amidines hexahydroimidazo[1,2- a ]pyrazine-3,6-diones via amino acid condensation has been detected as well. The presence of α -hydrogen atom in Ala residue facilitates dehydrogenation reactions for the related PD and bicyclic amidine, whereas in the case of Aib the dehydrogenated compounds have not been found. Further pathways of PD pyrolysis can lead to 4- and 5-membered lactams and hydantoins.

Computer simulation of IR spectra as a useful tool for GC/FTIR/MS identification of unusual amidine products of amino acid condensation

Sublimation of simple aliphatic amino acids (Ala, Aib, Val, Nva, and Leu) at 230 - 250 degrees Celsius under reduced pressure in the presence of silica as a catalyst yields cyclic dipeptides (or piperazine-2,5-diones) as major products. In addition, two types of unusual products have been detected. To determine their structures, we utilized a coupled GC/FTIR/MS technique which enables gas- chromatographic separation along with on-line characterization by FTIR and mass spectra of the products. Based on the spectral data obtained, we suggested the condensation products to be substituted bicyclic and tricyclic amidines, hexahydroimidazo[1,2-a]pyrazine- 3,6-diones and hexahydroimidazo[1,2-a]imidazo-[1,2- d]pyrazine-3,8-diones. To verify this supposition we simulated the IR spectra using the PM3 semi-empirical method. The calculated spectra appeared to be in very good agreement with the experimental ones, reflecting adequately general features of the latter and confirming the proposed amidine structure of the condensation products.