Home – Home – Jornals – Advanced Search

Trends of CO and CH₄ total column (TC) are estimated from AIRS spectrometer data for the "Eurasia" domain (0-180° E, 0-85° N) for different time periods and seasons. The results are compared with similar estimates obtained from ground-based spectroscopic measurements at IAP RAS stations (ZSS, Zotto, and Beijing), st. Peterhof of St. Petersburg State University, and NDACC stations located in the test domain. According to the findings, the CO TC over Northern Eurasia generally decreased during the period 2003-2015 with a rate of 0.05-1.5%/year depending on the region, while the CH₄ TC increased at a rate of 0.16-0.65%/year. After 2007, there is a trend toward an increase in CO TC in the summer and autumn months in most of mid- and high-latitude Eurasia background areas, as well as an increase in CH₄ TC growth rate. Positive trends in CO cannot be explained by the growth of emissions from fires or anthropogenic emissions. Thus, one of possible causes may be changes in the entire global photochemical system occurring against the backdrop of global climate change, in particular, changes in the "sources/sinks" ratio for small atmospheric components.

Sixth order connectivity indices are calculated for 29 benzotriazole derivatives. Correlations between the connectivity indices, physicochemical characteristics, and retention factors of the mentioned compounds are obtained for reversed-phase high-performance liquid chromatography conditions. Based on the correlations obtained, a predictive calculation of the retention factors of some benzotriazole derivatives is performed.

The structure and internal rotation of the 2-methyl-2-nitropropane molecule is studied by electron diffraction and quantum chemical calculations with the use of microwave and vibrational spectroscopy data. The electron diffraction data are analyzed within the general intramolecular anharmonic force field model and the quantum chemical pseudoconformer model, considering the adiabatic separation of the degree of freedom of large amplitude motion, i.e., the internal rotation of the NO₂ group. The equilibrium eclipsed configuration of the C_s symmetry molecule has the following experimental bond lengths and valence angles: r_e(N=O) = 1.226//1.226(8) Å, r_e(C-N)// r_e(C-C) = 1.520//1.515/1,521(4) Å, ∠_еC-C-N = 109.1/106,1(8)°, ∠_еO=N=O = 124.2(6)°, ∠_eC-C-H_avg = 110(3)°. The equilibrium geometry parameters are well consistent with MP2/cc-pVTZ quantum chemical calculations and microwave spectroscopy data. The thermally average parameters previously obtained within the small vibration model show a satisfactory agreement with the new results. The electron diffraction data used in this work do not allow a reliable determination of the barrier to internal rotation. However, at a barrier of 203(2) cal/mol, which is derived from the microwave study, it follows from the electron diffraction data that the equilibrium configuration must correspond to an eclipsed arrangement of C-C and N=O bonds, which is also consistent with the results of quantum chemical calculations of various levels.

Quantum chemical calculations are performed for the spatial and electron structure of complex compounds of L-histidine and its ionized forms with copper(II) for a variety of compositions within the density functional theory (DFT) using the B3LYP functional and 6-311G(d) basis. The solvent (water) is considered within the PCM approximation. EPR spectroscopy is used to study the equilibrium in the copper(II)-L-histidine system in an aqueous solution at рН 2-11. A comparison between the theoretical calculations and the EPR spectra suggests the following geometry for the coordination environment of the copper(II) ion in the complex compounds: CuHLL - square-planar coordination; CuL₂, CuHLL', and CuLL' - distorted square pyramid; and - octahedral environment.

The procedures are developed and the complexation products are preparatively isolated from GeO₂-H₄Cit-phen-CH₃CN-H₂O (I) and GeO₂-H₄Cit-CuCl₂-phen-C₂H₅OH-H₂O (II) systems (phen is 1,10-phenanthroline, H₄Cit is citric acid). The (Hphen)₂[Ge(HCit)₂]x3H₂O (I) and [Cu(phen)₂Cl]₂[Ge(HCit)₂]x6H₂O (II) complexes are characterized by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction. The compounds are formed from centrosymmetric octahedral [Ge(HCit)₂]^2- anions, Hphen⁺ (I) and [Cu(phen)₂Cl]⁺ (II) cations, and crystallization water molecules. The structural units in the crystals are linked via a system of hydrogen bonds.

The synthesis of an analog of memantine-containing sulfanilamide gives single crystals of a by-product in the form of a salt. The results of the XRD structure determination of the obtained product are presented.

A new dinuclear nitrido-bridged ruthenium complex with pyridine ligands ([PyH][Ru₂N(Py)₄Cl₆] (1) is synthesized by reacting K₃[Ru₂NCl₈(H₂O)₂] (2) and excessive pyridine, then crystallized from dilute hydrochloric acid. Its crystal structure is determined by single crystal X-ray diffraction. The complex crystallizes in the form of red block crystals of the monoclinic symmetry and the space group C2. The nitrido-bridged ruthenium complex has very short Ru-N distances.

While growing 2-ethylbenzimidazole crystals from methanol, polymorph 1с is obtained. In polymorphs 1а-с, 2-ethylbenzimidazole molecules have a different arrangement in the packing and the position of the ethyl group relative to the benzimidazole plane. At the same time, the character (sequence) of intermolecular N-H…N bonds is maintained. In polymorph 1b with four independent molecules, there is an intermolecular Н bond between homonymous molecules. The study of the crystal structure of another benzimidazole derivative (2-(1-hydroxyethyl)benzimidazole (2)) reveals a new polymorph. The results of the comparative analysis of the crystal structures of two polymorphs 2а, 2b are presented.

Tetrakis(hydroxyacetato)bis(dimethyl sulfoxide)dirhodium(II) (1) is synthesized by the reaction of dimethyl sulfoxide (DMSO) with Rh₂(OOCCH₂OH)₄. The complex is characterized by elemental analysis, FT-IR, ESI⁺-MS, ¹H and ¹³C NMR, along with single crystal X-ray diffraction. The ambidentate DMSO ligands are bound to the rhodium center of 1 through their sulfur atoms, which is firstly predicated by its orange color, then confirmed by the observation of an increase in the S-O stretching frequencies, and finally, unambiguously determined by single crystal X-ray diffraction. The structure of 1 contains two similar but crystallographically independent molecules. Both molecules contain lantern dirhodium units, joined equatorially by four bidentate hydroxyacetate ligands and two monodentate DMSO axial ligands. Four hydrogen bonds link the molecules together with d(O⋯O) of 2.767(4)-2.824(4) Å to form a three dimensional network.

A Schiff base, 4-hydroxy-6-methyl-3-[(1E)-1-(2-phenylhydrazinylidene)ethyl]-2H-pyran-2-one, is synthesized and characterized by ¹H and ¹³C NMR, IR spectroscopy, ESI-mass spectrometry and single crystal X-ray diffraction analysis. There are three crystallographically independent molecules in the asymmetric unit, space group C2/c, a = 30.011(2) Å, b = 17.601(2) Å, c = 13.6878(13) Å, β = 92.532(4)°, and Z = 24. The final reliable index is 0.0406 for 5997 reflections. The molecules are linked through intermolecular N-H…O hydrogen bonds into three-linked molecules forming a supramolecular ring.