Elena V. Basiuk

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.

‘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.

A Bridged High-Spin Complex Bis-[Ni(II)( rac-5,5,7,12,12,14-hexamethyl- 1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicarboxylate Diperchlorate Monohydrate

A bridged high-spin complex,bis-[Ni(II)(rac-5,5,7,l2,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicarboxylate diperchlorate monohydrate has been obtained by reaction of [Ni(II)(rac-5,5,7, 12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)](ClO4)2 and 2,5-pyridinedicarboxylic acid in aqueousalkaline (NH4OH) medium. C39H77Cl2N9Ni2O13, chemical formula weight 1068.42, orthorhombic, P212121, a = 11 .423(3) Å,b = 14.770(6) Å, c = 31.608(7) Å,α = β = γ =90.00°, V = 5333(3) Å3, Z = 4, Dcalc = 1.331 g cm-3, μcalc = 0.869 mm-1, F(000) = 2272, T = 293(2), R = 0.0870 for 2686 observed reflections [I > 2σ(I)]. The complexincludes two folded [Ni(rac- Me6[14]aneN4)]2+ units havingopposite diastereomeric configuration. They are bridged through a dianion of2,5-pyridinedicarboxylic acid, with one Ni-atom coordinated to the O-atom ofthe 2-carboxylic group and the pyridine N-atom (forming a 5-membered chelatering), and with the second Ni-atom coordinated to both O-atoms of the 5-carboxylic group (forming a 4-membered chelate ring). Hydrogen bonding involving macrocyclic NH groups, both 2- and 5-carboxylic groups, perchlorate anions and water molecules gives rise to the formation of an infinite supramolecular network in the title compounds crystals.

Solvent-free one-step covalent functionalization of graphene oxide and nanodiamond with amines

We attempted amide functionalization of the carboxylic groups present in graphene oxide (GO) and nanodiamond (ND) by means of a solvent-free gas-phase treatment with two aromatic amines 1-aminopyrene (AP) and 2-aminofluorene (AF), and also with one aliphatic amine, 1-octadecylamine (ODA), for comparison. The procedure was carried out under moderate vacuum, at temperatures of 150–180 °C, using short reaction times of about 2 h. The amine treatment generally gave rise to changes in Fourier-transform infrared (FTIR), Raman, ultraviolet-visible, and X-ray photoelectron spectra (XPS), to a variable degree depending on the particular sample. Thermogravimetric analysis showed the highest amine content for GO and ND treated with ODA, which turned out to be roughly one order of magnitude higher than in the case of aromatic AF and AP. Considerable changes in sample morphology after functionalization were observed by transmission electron and atomic force microscopy. Based on the analysis of FTIR and XPS spectra, we concluded that amidation is the only possible route for ND functionalization with AF, AP and ODA, whereas we found spectroscopic evidence for an alternative reaction channel on GO sheets, which is amine addition onto epoxy bridges.

Nanostructured Diamine−Fullerene Derivatives: Computational Density Functional Theory Study and Experimental Evidence for their Formation via Gas-Phase Functionalization

Nanostructure derivatives of fullerene C(60) are used in emerging applications of composite matrices, including protective and decorative coating, superadsorbent material, thin films, and lightweight high-strength fiber-reinforced materials, etc. In this study, quantum chemical calculations and experimental studies were performed to analyze the derivatives of diamine-fullerene prepared by the gas-phase solvent-free functionalization technique. In particular, the aliphatic 1,8-diamino-octane and the aromatic 1,5-diaminonaphthalene, which are diamines volatile in vacuum, were studied. We addressed two alternative mechanisms of the amination reaction via polyaddition and cross-linking of C(60) with diamines, using the pure GGA BLYP, PW91, and PBE functionals; further validation calculations were performed using the semiempirical dispersion GGA B97-D functional which contains parameters that have been specially adjusted by a more realistic view on dispersion contributions. In addition, we looked for experimental evidence for the covalent functionalization by using laser desorption/ionization time-of-flight mass spectrometry, thermogravimetric analysis, and atomic force microscopy.

Dielectric properties of (C60 + C70)-ferroelectric liquid crystal composite

Abstract A stable composite of fullerene and ferroelectric liquid crystal (FLC) has been obtained. Analysis of the frequency dependence of imaginary part of complex dielectric permittivity showed that orientation of the liquid crystal (LC) in the composite is close to homeotropic. At temperatures above 329 K, the composite conductance is determined by the conductance of fullerene. At 344 K, the composite conductance is 3.2 × 10−8 Ω−1 m−1, and the activation energy for the temperature dependence of conductance is 0.99 eV. At temperatures below 329 K, the composite properties are determined by the LC, and the frequency dependences of the components of complex dielectric permittivity showed dispersion due to rotation of molecular dipoles around the helicoid (Goldstone mode) axis. The relaxation time is close to 1 msec and almost equal to the value obtained for homeotropically oriented LC.

Regioselectivity in Azahydro(60)fullerene Derivatives: Application of General-Purpose Reactivity Indicators

To attempt theoretical predictions of the regioselectivity pattern in molecules with multiple reactive sites, the energies of formation of all possible isomers are usually considered. This means that the computing becomes highly demanding if high theoretical levels are used. The study objective was to predict the regioselectivity in the reaction of hydrogen addition onto azahydro[60]fullerene C 59H n+1 N ( n = 0-4) systems using a new reactivity indicator termed general-purpose reactivity indicator, Xi Delta N<or=0,alpha (kappa), proposed by Anderson et al. ( J. Chem. Theory Comput. 2007, 3, 358). Because Xi Delta N<or=0,alpha (kappa) combines the information from the electrostatic potential and the Fukui function, this indicator is a two-parameter model that depends on the atomic charges and Fukui values calculated. We used the gradient-corrected BLYP and BOP functionals to approximate the electronic density of the systems, and these densities were employed to determinate the parameters. In terms of regioselectivity, the preferential addition sites at every hydrogenation step on C 59H n+1 N ( n = 0-4) shows that 1,4-adducts are more stable than 1,2-adducts. However, we show that the multiple additions are only feasible up to a C 59H 5N (tetraddition) product. Consequently, the application of this indicator not only helps to avoid systematic computational studies by comparing energies of formation in several isomersmany of which are not currently supported by experimental resultsbut also provides an insight of how the pattern of addition is achieved. Comparisons with traditional indicators show that the application of Xi Delta N<or=0,alpha (kappa) performs much better for predicting reactivity in the aza[60]fullerene derivatives studied.

(C-rac-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane-κ4N)(nicotinato-O,O′)nickel(II) perchlorate

In the title compound, [Ni(C(6)H(4)NO(2))(C(16)H(36)N(4))]ClO(4), the macrocyclic unit adopts a folded conformation, allowing the two carboxyl O atoms to occupy two neighbouring coordination sites and thus form an additional four-membered chelate ring. The less crowded side of the macrocycle (that with the two asymmetric C-H groups) is directed towards the nicotinate anion and the asymmetric C-CH(3) groups are directed away from it. The macrocyclic NH groups neighbouring the C-CH(3) groups are also directed away from the nicotinate anion, while those NH groups which are near to the geminal methyl groups are directed towards the nicotinate anion. Although the complex does not include water molecules, three types of hydrogen bond were found, involving NH groups of the macrocyclic ligand, pyridine N atoms and O atoms of the perchlorate anions.

Graphene oxide and nanodiamond: same carboxylic groups, different complexation properties

DFT calculations (PBE functional with the empirical correction by Grimme) were employed to explain why our attempts to coordinatively functionalize nanodiamond (ND) with tetraazamacrocyclic cations [Ni(cyclam)]2+ and [Ni(tet b)]2+, and to generate paramagnetic hybrid materials in this way, failed, contrary to the successful functionalization of graphene oxide (GO) reported previously (Appl. Surf. Sci., 2016, 371, 16–27). The explanation offered is based on the comparison of binding energies for low-spin (singlet) and high-spin (triplet) complexes of model carboxylate ions GO− and ND− with the two tetraazamacrocycles. The formation energies were interpreted in terms of ΔΔE3−1 values, which characterize the difference in stability for the triplet and singlet complexes (negative values mean that triplet state is more stable, and positive, that singlet state is more stable). While the results obtained do not rule out completely the possibility of forming high-spin [Ni(cyclam)]2+ carboxylate derivatives on ND, in the case of [Ni(tet b)]2+ comparison of the ΔΔE3−1 values explicitly demonstrated that the formation of high-spin complex is highly unfavorable with ND− contrary to GO− model: ΔΔE3−1 values obtained are 13.22 and −4.64 kcal mol−1, respectively. For comparison, similar data are presented for a series of simpler carboxylates. In addition to binding energies and ΔΔE3−1 values, for all the systems studied we analyzed Ni–O distances, spin density plots and HOMO−LUMO parameters.