Vladimir A. Basiuk

Mechanisms of amino acid polycondensation on silica and alumina surfaces

Chemisorption products of bifunctional amino acid vapours on the surface of silica and alumina have been studied by the method of infrared spectroscopy. On the basis of the analysis of spectral data it is supposed that heterogeneous polycondensation of amino acids with formation of peptides proceeds under these conditions. The supposition was confirmed by the study of products of interaction of amino acid vapours with silica and alumina by the method of fast atom bombardment mass-spectrometry. It is established that in contrast to alumina the condensation of amino acids into linear peptides on silica surface proceeds only at presence of at least small amounts of water. The most probable mechanisms of extending of peptide chains are proposed on the basis of obtained experimental data.

Pyrolysis of amino acids: recovery of starting materials and yields of condensation products

Abstract The present study relates to the problem of the thermal stability of small biomolecules during their extraterrestrial delivery. It was undertaken in order to make rough estimates of the temperatures under which amino acids can survive during atmospheric entry heating of organics-bearing space bodies in oxygen-free atmosphere. Amino acids tested in the present study were glycine (Gly), α- and β-alanine (Ala and β-Ala, respectively), α-aminoisobutyric acid (Aib), valine (Val), leucine (Leu), proline (Pro), phenylalanine (Phe) and glutamic acid (Glu). Off-line design of pyrolytic experiments was used, with extraction and HPLC quantification of residual amino acids and peptide-type products formed as a result of amino acid dehydration. The lower temperature limit used was 400°C, repeating the experiments with 100°C increments. Of the nine studied amino acids, Glu and β-Ala are the most unstable, pyrolyzing completely at 400°C. At the other extreme was Ala which was still detected at 800°C with 0.4% recovery. At a percent recovery level, Aib and Pro are able to survive 500°C; Gly, 600°C; Val and Leu, 700°C. Formation of cyclic dipeptides piperazine-2,5-diones (PDs) was observed for Gly, Ala, Aib, Val, Leu and Pro; and pyroglutamic acid for Glu. Pro and Ala PDs form in especially high yields (about 80 and 48%, respectively, at 400°C), but as a whole, PD yields are of the same order of magnitude as amino acid recovery. Thermal stability of PDs is also comparable with that of amino acids.

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.

Pyrolysis of valine and leucine at 500°C: identification of less-volatile products using gas chromatography-Fourier transform infrared spectroscopy-mass spectrometry

Abstract The products of valine and leucine pyrolysis at 500°C under nitrogen atmosphere have been analyzed using the methods of high-performance liquid chromatography and gas-chromatography-Fourier transform infrared spectroscopy-mass spectrometry with auxiliary computer simulation of IR spectra. The amino acids do not decompose completely under the above conditions, and are recovered by 10% (Val) and 2% (Leu). Among their pyrolysis products several carboxylic acids, primary and secondary amides have been identified, as well as a number of less-volatile compounds resulting from amino acid intermolecular condensation. Major condensation pathway is the formation of cyclic dipeptides piperazine-2,5-diones with the yields of 5% for Val and 3.5% for Leu, which can further undergo thermal dehydrogenation, dealkylation, rearrangement into hydantoins, loss of HNCO, etc. The formation of small amounts of bicyclic amidines hexahydroimidazo[1,2-a]pyrazine-3,6-diones via amino acid condensation has been also observed. Pathways of their thermal decomposition also include dehydrogenation, dealkylation and loss of HNCO.

Identification of hexahydroimidazo[1,2-a]pyrazine-3,6-diones and hexahydroimidazo[1,2-a]imidazo[1,2-d]pyrazine-3,8-diones, unusual products of silica-catalyzed amino acid thermal condensation and products of their thermal decomposition using coupled high-performance liquid chromatography–particle beam mass spectrometry and gas chromatography–Fourier transform infrared spectroscopy–mass spectrometry

Abstract Sublimation of simple aliphatic amino acids (Ala, Aib, Val and Leu) at 230–250°C under reduced pressure in the presence of silica as a catalyst yields cyclic dipeptides 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 HPLC–particle beam-MS and GC–Fourier transform IR–MS technique with auxiliary computer simulation of IR spectra. Based on the spectral data obtained, we identified the condensation products as 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. Other peaks in the chromatograms has been identified as products of the amidines thermal decomposition. The general decomposition pattern includes dehydrogenation as well as cleavage of the carbon skeleton. The last process primarily affects the 6-membered pyrazine ring causing elimination of CO or HNCO, or/and the loss of α-substituents without or with α-carbon atom.

Pyrolysis of poly-glycine and poly-l-alanine: analysis of less-volatile products by gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry

Abstract Pyrolysis of poly-glycine and poly- l -alanine at 500°C under nitrogen atmosphere gives rise to volatile low-molecular-mass decomposition products, as well as to less-volatile compounds which have been analyzed by the coupled technique of gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry. All identified products are nitrogen compounds, 5-membered mono- N -heterocycles being the most frequently encountered ones. In the case of poly-glycine, we found acetamide, a dimethyl 2-pyrrolidinone, N -methyl succinimide, piperazine-2,5-dione derived from glycine, and barbituric acid. In the case of poly- l -alanine pyrolysis, the compounds identified were N -methyl, 2,3,5-trimethyl, 2-ethyl-4-methyl and 3-ethyl-2,5-dimethyl pyrrole, 4-methyl and 2,6-dimethyl pyridine, propanamide, a trimethyl 2-pyrrolidinone, 3-ethyl-5-methylhydantoin, and piperazine-2,5-dione derived from alanine. The formation of piperazine-2,5-diones (diketopiperazines) is one of the major pyrolytic pathways.

POSSIBLE ROLE OF VOLCANIC ASH.GAS CLOUDS IN THE EARTH'S PREBIOTIC CHEMISTRY

Volcanic ash-gas clouds represent versatile local atmospheric environments appropriate for abiotic synthesis of rather complex organic molecules due to the simultaneous presence of various gaseous reagents, catalytically active inorganic particles, electric discharges, pressure and temperature gradients. They are relatively readily attainable for the scientists, contrary to objects or events of space origin (interstellar and planetary dust, meteoritic/cometary impacts,etc.), providing excellent opportunities forin situ studies and grounded simulating experiments. This paper reviews the available data on this environment, its most important chemical and physical parameters. Based on this analysis, it is suggested in brief experimental conditions for the simulation.

Pyrolysis of simple amino acids and nucleobases: survivability limits and implications for extraterrestrial delivery

Abstract The idea of extraterrestrial delivery of organic matter to the early Earth is strongly supported by the detection of a large variety of organic compounds in the interstellar medium, comets, and carbonaceous chondrites. Whether organic compounds essential for the emergence and evolution of life, particularly amino acids and nucleic acid bases found in the meteorites, can be efficiently delivered by other space bodies is unclear and depends primarily on capability of the biomolecules to survive high temperatures during atmospheric deceleration and impacts to the terrestrial surface. In the present study we estimated survivability of simple amino acids (glycine, Lalanine, α-aminoisobutyric acid, L-valine and L-leucine), purines (adenine and guanine) and pyrimidines (uracil and cytosine) under rapid heating to temperatures of 400-1000°C under N2 or CO2 atmosphere. We have found that most of the compounds studied cannot survive the temperatures substantially higher than 700°C; however at 500600°C, the recovery can be at a percent level (or even 10%-level for adenine, uracil, alanine, and valine). The final fate of amino acids and nucleobases during the atmospheric deceleration and surface impacts is discussed depending on such factors as size of the space body, nature and altitude of the heating, chemical composition of the space body and of the atmosphere.

‘Green’ derivatization of carbon nanotubes with Nylon 6 and L-alanine

Amide derivatives of L-alanine and e-caprolactam were readily obtained on diamine-functionalized oxidized single-walled and pristine multi-walled carbon nanotubes through a one-step direct amidation reaction, which employs thermal activation at 160–200 °C instead of chemical activation, avoids the use of organic solvents, and requires a few hours only for completion. In the case of e-caprolactam, amino groups attached to the nanotubes initiated polymerization into Nylon 6. The functionalized nanotubes were characterized by infrared and Raman spectroscopy, scanning and transmission electron microscopy, atomic force microscopy, thermal gravimetric analysis and differential scanning calorimetry.

Behavior of amino acids when volatilized in the presence of silica gel and pulverized basaltic lava.

To evaluate the types of amino acid thermal transformations caused by silicate materials, we studied the volatilization products of Aib, L-Ala, L-Val and L-Leu under temperatures of up to 270 °C in the presence of silica gel as a model catalyst and pulverized basaltic lava samples. It was found that silica gel catalyzes nearly quantitative condensation of amino acids, where piperazinediones are the major products, whereas lava samples have much lower catalytic efficiency. In addition bicyclic and tricyclic amidines and several products of their subsequent thermal decomposition have been identified using the coupled technique of GC-FTIR-MS and HPLC-PB-MS, with auxiliary computer simulation of IR spectra and NMR spectroscopy. The decomposition is due to dehydrogenation, elimination of the alkyl substituents and dehydration as well as cleavage of the bicyclic ring system. The imidazole ring appears to be more resistant to thermal decomposition as compared to the pyperazine moiety, giving rise to the formation of different substituted imidazolones. The amidines were found to hydrolyze under treatment with concentrated HCl, releasing the starting amino acids and thus behaving as amino acid anhydrides. The thermal transformations cause significant racemization of amino acid residues. Based on our observations, the formation of amidine-type products is suggested to be rather common in the high-temperature experiments on amino acid condensation.