Jan Cz. Dobrowolski

Infrared evidence for CO2 electron donor—acceptor complexes☆

Abstract Frequencies and bandwidths of the ν 3 (CO 2 ) (asymmetric stretching) and ν 2 (CO 2 ) (bending) vibration bands were determined by IR spectroscopy for CO 2 dissolved in more than 35 organic solvents. Two ν 2 (CO 2 ) bands appear for CO 2 solutions in tertiary amides, tertiary amines and DMSO, and the same seems to be true for ketones and esters. The ν 2 (CO 2 ) band at lower wavenumbers was assigned to CO 2 — n -electron donor complexes. In such complexes the electron donors lone pair is directed to the CO 2 carbon atom. The possibility of formation of electron donor—acceptor (EDA) complexes of CO 2 with π-electron donors is also considered.

AB INITIO STUDY ON THE 1 : 2 REACTION OF CO2 WITH DIMETHYLAMINE

Abstract The reaction between CO 2 and the dimethylamine molecule in the presence of a second dimethylamine molecule is modeled by the ab initio RHF/3–21G method. Starting from the most stable 1:2 complex, the most effective reaction pathway turned out to be proton transfer between amine molecules followed by immediate proton transfer from one of the amine molecules to the CO 2 moiety. The activation barrier for this pathway (9.54 kcal mol −1 with respect to the 1:2 complex) is within the range of activation energy values found in kinetic studies for similar reactions with different hydroxylamines (from 9.2 to 13.0 kcal mol −1 ). The reaction product is the cyclic hydrogen bonded complex of dimethylcarbamic acid with dimethylamine.

Recent Advances in Raman Analysis of Plants: Alkaloids, Carotenoids, and Polyacetylenes

This paper demonstrates the special potential of Raman spectroscopy for the study of selected plant metabolites. Carotenoids, which are beneficial components in fruits and vegetables, have been shown to be a significant factor in lowering the risk of various types of cancer and ischemic heart diseases. On the other hand, alkaloids may have various effects on human health, e.g. caffeine is a mild stimulant of the central nervous system and as a result it can influence human behaviour. Polyacetylenes are highly cytotoxic against numerous cancer cell lines and demonstrate antifungal, anti-inflammatory and anti-platelet-aggregatory properties. In most cases, vibrational measurements can be performed directly on plant tissues as well as on fractions isolated from the plant material by hydro-distillation or solvent extraction. Raman spectroscopy techniques allow obtaining spectra which present some characteristic key bands of individual components. Based on such markers related to individual plant substances, spectroscopic analyses in principle allow the discrimination of different species, and even chemotypes among the same species. Moreover, Raman microspectroscopy provides 2- and 3-dimensional images of the investigated plant samples. These maps can be directly compared to the corresponding visual images obtained from a light microscope and offer additional detailed information regarding the local distribution of specific compounds in the surface layers of the analyzed plant tissue.

Spectroscopic Studies on Bioactive Polyacetylenes and Other Plant Components in Wild Carrot Root

Polyacetylenes and other common plant components, such as starch, pectin, cellulose, and lignin, were studied in roots of the wild carrot (Daucus carota) subspecies D. carota subsp. gummifer and D. carota subsp. maximus by Raman spectroscopy. The components were measured in situ, directly in the plant tissue and without any preliminary sample preparation. The analysis was performed on the basis of the intense and characteristic key bands observed in the Raman spectrum. The two main carrot polyacetylenes falcarinol (1) and falcarindiol (2) have similar molecular structures, but their Raman spectra exhibit a small band shift in the symmetric -C≡C-C≡C- mode from 2258 cm⁻¹ to 2252 cm⁻¹. Quantum chemical calculations confirmed that the differences observed between the samples may be due to conformational and environmental changes. The polyacetylenes were also detected by Raman mapping, which visualized the distribution of the compounds across sections of carrot roots. The mapping technique was also applied to assess the distribution of lignin and polysaccharide compounds. The results showed the tissue-specific accumulation of starch and cell wall components such as lignin, pectin, and cellulose.

TAUTOMERISM OF HISTAMINE REVISITED

Abstract The tautomerism of the histamine molecule was explored based on quantum chemical calculations both in the gaseous state and in aqueous medium. Structural optimizations were performed at the ab initio Hartree-Fock (HF) and the second order Moller-Plesset (MP2) perturbation level. The most stable tautomer in aqueous medium appeared to be the N(3) monocation, with strong intramolecular hydrogen bonding. Results from calculations prove that the previous hypothesis on interaction with the hypothetical H 2 receptor remains valid, even though this hypothesis involved a slightly different assumption regarding the structure of the most stable form. The most stable neutral form in aqueous medium turned out to be the opened N(3) gauche structure.

Theoretical modeling of molecular spectra parameters of disubstituted diacetylenes.

Symmetrically disubstituted diacetylenes, X-C≡C-C≡C-X, were studied computationally by using the DFT B3LYP/aug-cc-pVDZ method. For more than 35 substituents the bond lengths, charge density and Laplacian in bond critical points, C≡C stretching vibrational frequencies, (13)C NMR chemical shifts and spin-spin CC coupling constants through diacetylene moiety were calculated and examined by using the substituent sEDA and pEDA descriptors. It is demonstrated that in disubstituted diacetylenes the triple bond length increases with the electron donating and decreases with the electron withdrawing properties of the substituents. The σ-electron repulsion is likely to be responsible for this phenomenon. The electron density of the C-X bond critical point decreases linearly with an increase of the σ-electron donating properties, whereas the Laplacian of electron density in the C≡C bond critical point increases as the sEDA descriptor i.e., σ-electron donating properties of the substituent, are increased. Thus, ρ(C≡C) is locally reduced with an increase of sEDA. The ν(as)(C≡C) and ν(s)(C≡C) mode frequencies decrease with the electron donating and increase with the electron withdrawing properties of the substituents. The calculated chemical shift of the C1-atom, to which the substituent is attached, does not correlate with the substituent descriptors, whereas the δ(C2) deshielding increases when the σ-electron donating properties and C≡C distance are increased. The calculated (1)J(CC) coupling constants decrease with an increase of the triple bond length, the sEDA parameter, and ρ(C-X), whereas they decrease with Laplacian in the C≡C BCP.

The IR evidence of H2O-aromatic hydrocarbons single hydrogen bond

Abstract The ν 3 and ν 1 IR bands of water dissolved in benzene, toluene, cumene, xylenes, CCl 2 FCClF 2 , CCl 4 , CS 2 , CDCl 3 and CH 2 ClCH 2 Cl were observed. On the basis of the ν 3 to ν 1 band intensity ratio it is concluded that in aromatic solvents water forms a single hydrogen bond and acts as the proton donor. Additionally based on band shifts it is suggested that water in CH 2 ClCH 2 Cl, CDCl 3 and CS 2 plays electron donor role.

Infrared study on the double hydrogen bond between the urea molecule and halogenated aliphatic hydrocarbon solvents

Abstract The infrared bands of CO and NH stretching vibrations of urea dissolved in a series of halogen derivatives of aliphatic hydrocarbons were analyzed. From the relationship between the solubility of urea and the structure of the solvent as well as the infrared spectra it is concluded that a double hydrogen bond between one urea and one solvent molecule is formed. In this bond, the solvent molecule is donor of two hydrogen atoms of two polar CH bonds, and the CO group of urea is proton acceptor. The interaction of NH groups with XC solvent groups is predominantly determined by the valence orbital repulsion of N and X atoms, and the polarizability of the halogen atom X.

On two alizarin polymorphs

For centuries alizarin has been used as natural pigment, yet, now it is also used in histochemistry and dermatology, and as a dye for semiconductor solar cells. Here, the crystal structure of the previously known form of alizarin is determined accurately and its new polymorph is discovered. The two polymorphs crystallize into the same monoclinic crystal system. The previously known form is centrosymmetric (P21/c space group) whereas the new one is not (space group Pc). Both crystals are twinned, disordered, and have the molecules packed into the crystal lattices in a comparable way. However the powder patterns of both forms are visibly different. In addition the analysis of the fingerprints of H⋯O intermolecular interactions based on Hirshfeld surfaces also indicates differences in the packing. Yet, these similarities between two forms of alizarin make their vibrational spectra hardly distinguishable.

Genistein complexes with amines: structure and properties

New amine complexes of genistein in the crystal and the solution state have been studied by X-ray crystallography and by 1H and 13C NMR spectroscopy. The gas-phase structures have been modelled with ab initio quantum chemical calculations. The morpholine–genistein hydrogen bonded complex has been investigated by all the above methods whereas the triethylamine, morpholine and piperazine complexes have been investigated with 1H NOE and 13C NMR spectroscopy. The X-ray results show the genistein–morpholine complex to be formed as a result of proton transfer from the genistein OH group at position C7 to the morpholine nitrogen atom. This complex also has the lowest total energy when compared to other possible complexes. The NMR measurements in solution indicate that the protonated amine is in fast exchange between various interaction sites, the most stable complex being formed at position C7 as in the crystal. The ab initio quantum mechanical calculations show that this position is also the best for interactions. The 13C NMR chemical shifts calculated theoretically are in agreement with experimental values.