The gas-phase derivatization procedure was employed for direct (i.e., without chemical activation of terminal carboxylic groups) amidization of oxidized single-walled carbon nanotubes (SWNTs) with simple aliphatic amines. The procedure includes treatment of SWNTs with amine vapors under reduced pressure and a temperature of 160-170 °C. Applicability of infrared (IR) spectroscopy and temperature-programmed desorption mass spectrometry (TPD-MS) for chemical characterization of the derivatized SWNTs was analyzed. It was concluded that IR spectra of oxidized SWNTs treated with amines under different conditions (described here and elsewhere) cannot correspond to amide derivatives on SWNT tips because of the very low concentration of the terminal groups relative to the whole sample mass, which implies a negligible contribution to the IR spectra. The bands detectable in the case of long-chain amines correspond to amine molecules physisorbed because of strong hydrophobic interactions of their hydrocarbon chains with SWNT walls. Energetically preferable adsorption sites are the channels inside SWNTs, according to MM+ molecularmechanics modeling. TPD-MS provided additional information on the chemical state of the amines. Heating of the amine-treated SWNTs at >200 °C causes cleavage of alkenes from the amine residues: nonene and pentene form in the case of nonylamine and dipentylamine, respectively. For the short-chain amine (dipentylamine), only one chemical form was detected, whereas two forms (amide and physisorbed amine) can be distinguished for the SWNTs treated with nonylamine. The content of physisorbed nonylamine is about 1 order of magnitude higher than the amide content. According to the results of two-level ONIOM quantum-chemistry-molecular-mechanics calculations, the direct formation of amides on armchair SWNT tips is more energetically favorable than that on the zigzag tips, although the activation barriers are of approximately equal height.

Abstract. 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 massspectrometry. 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 Ieast small amounts of water. The most probable mechanisms of extending of peptide chains are proposed on the basis of obtained experimental data.

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To describe quantitatively the adsorption of prebiotically important compounds of low molecular weight (amino acids, short linear peptides, cyclic dipeptides, the Krebs's cycle and other carboxylic acids, nucleosides and related phosphates) on silica surface from diluted neutral aqueous solutions, equilibrium constants (K) and free energies (-delta G) of adsorption were determined from the retention values measured by means of high-performance liquid chromatography on a silica gel column and from the isotherms measured under static conditions. For most carboxylic acids (including amino acids and linear peptides) -delta G values were negative and K < 1, thus showing very weak adsorption. Cyclic dipeptides (2,5-piperazinediones) exhibited higher adsorbability; -delta G > 0 and K > 1 were found for most of them. Influence of the structure of alpha-substituent on the adsorbability is analyzed. A linear dependence of -delta G on the number of aliphatic carbon atoms in a sorbate molecule was found for the series of aliphatic bifunctional amino acids, related dipeptides and 2,5-piperazinediones, as well as for the row from glycine to triglycyl glycine. The adsorption of nucleosides and their phosphates is characterized by much higher K and -delta G values (of the order of 10(2) and 10(4), respectively). The adsorption data available from our work and literature are summarized and discussed with implications to the Bernal's hypothesis on the roles of solid surfaces in the prebiotic formation of biopolymers from monomeric 'building blocks'.