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41.
Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set. 相似文献
42.
Małgorzata Pazderska-Szabłowicz Agnieszka Białkowska Ewa Kita 《Transition Metal Chemistry》2006,31(3):413-420
New chromium(III) complexes, [Cr(C2O4)2(2-hnic)]2− and [Cr(C2O4)2(3-hpic)]2− (where 2-hnic = O,O′-bonded 2-hydroxynicotinic acid and 3-hpic = N,O-bonded 3-hydroxypicolinic acid), were obtained and characterized
in solution. The acid-catalyzed aquation of the both complexes leads to liberation of the appropriate pyridinecarboxylic acid
and formation of cis-[Cr(C2O4)2(H2O)2]−. Kinetics of these reactions were studied spectrophotometrically in the 0.1–1.0 M HClO4 range, at I = 1.0 M. In the case of [Cr(C2O4)2(2-hnic)]2−, a slow chelate-ring opening at the Cr–O (phenolate) bond is followed by a fast Cr–O (carboxylate) bond breaking. The rate
law: kobs = kHQH[H+] was established, where kH is the acid-catalyzed rate constant and QH is the protonation constant of the coordinated phenolate oxygen atom. In the case of [Cr(C2O4)2(3-hpic)]2−, the reversible chelate-ring opening at Cr–N bond is followed by the rate determining step – the one-end bonded ligand liberation.
The rate law for the first step was determined: kobs = k1+k−1/Q1[H+], where k1 and k−1 are the rate constants of the chelate-ring opening and closure and Q1 is the protonation constant of the pyridine nitrogen atom. The aquation mechanisms are proposed and the effect of ligand
coordination mode on complex reactivity is discussed. 相似文献
43.
Anna Doga Katarzyna Baranowska Agnieszka Pladzyk Katarzyna Majcher 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(7):m259-m263
The complexes [2‐(1H‐imidazol‐4‐yl‐κN3)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)cobalt(II), [Co(C12H27O3SSi)2(C5H9N3)], and [2‐(1H‐imidazol‐4‐yl‐κN3)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)zinc(II), [Zn(C12H27O3SSi)2(C5H9N3)], are isomorphous. The central ZnII/CoII ions are surrounded by two S atoms from the tri‐tert‐butoxysilanethiolate ligand and by two N atoms from the chelating histamine ligand in a distorted tetrahedral geometry, with two intramolecular N—H...O hydrogen‐bonding interactions between the histamine NH2 groups and tert‐butoxy O atoms. Molecules of the complexes are joined into dimers via two intermolecular bifurcated N—H...(S,O) hydrogen bonds. The ZnII atom in [(1H‐imidazol‐4‐yl‐κN3)methanol]bis(tri‐tert‐butoxysilanethiolato‐κ2O,S)zinc(II), [Zn(C12H27O3SSi)2(C4H6N2O)], is five‐coordinated by two O and two S atoms from the O,S‐chelating silanethiolate ligand and by one N atom from (1H‐imidazol‐4‐yl)methanol; the hydroxy group forms an intramolecular hydrogen bond with sulfur. Molecules of this complex pack as zigzag chains linked by N—H...O hydrogen bonds. These structures provide reference details for cysteine‐ and histidine‐ligated metal centers in proteins. 相似文献
44.
Marianne Stranger Agnieszka Krata Velichka Kontozova-Deutsch Felix Deutsch Anna Worobiec Edward Roekens 《Microchemical Journal》2008,90(2):93-98
Nitrogen dioxide (NO2) concentrations were used to evaluate the air quality before and after the infrastructural change of an important traffic artery in Mortsel, Antwerp (Belgium). During the reconstruction works two pairs of traffic lanes were reduced to one in each direction. Two sampling campaigns were conducted: the first one before the works in 2003 and the second one in 2005, after the road works were finished. Sampling was performed on a weekly base with the use of passive diffusion tubes on the streets, and also indoors in nearby houses. The samples were analyzed by ion chromatography, from which data the NO2 concentrations in air could be calculated. These results were compared with NO2 values from the air monitoring station 42R801 of the Flemish Environment Agency in Borgerhout, Antwerp. On the base of different NO2 concentrations, correlated well with the traffic density, sampling locations were classified into three groups as follows: 1) ‘heavily polluted’ (heavy traffic); 2) ‘moderately polluted’ (medium traffic); or 3) ‘less polluted’ (low traffic density). Sampling sites located further from the road works, enclosed to the group ‘less polluted’, showed the lowest NO2 concentrations. The highest NO2 level was found for the locations close to reconstruction works, which belonged to the group ‘heavily polluted’. The contribution of NO2 was at the same level before and after the road works. During the first campaign it ranged from 30 ± 7 µg/m3 to 71 ± 11 µg/m3 and during the second sampling it was between 36 ± 17 µg/m3 and 73 ± 17 µg/m3. These modernization works had no impact on preventing the traffic-related pollutant as NO2 and as a consequence no significant effect on the air quality in the studied region. It has been proven that the impact of traffic on the air quality is unmistakably high and simply reduction of the number of the traffic lanes, intended to discourage the traffic flow, had apparently no environmentally advantageous effect. 相似文献
45.
Sergio Albeverio Agnieszka Kozak Yuri Kozitsky 《Communications in Mathematical Physics》2004,251(1):1-25
We study the two-dimensional gauge theory of the symmetric group Sn describing the statistics of branched n-coverings of Riemann surfaces. We consider the theory defined on the disc and on the sphere in the large-n limit. A non trivial phase structure emerges, with various phases corresponding to different connectivity properties of the covering surface. We show that any gauge theory on a two-dimensional surface of genus zero is equivalent to a random walk on the gauge group manifold: in the case of Sn, one of the phase transitions we find can be interpreted as a cutoff phenomenon in the corresponding random walk. A connection with the theory of phase transitions in random graphs is also pointed out. Finally we discuss how our results may be related to the known phase transitions in Yang-Mills theory. We discover that a cutoff transition occurs also in two dimensional Yang-Mills theory on a sphere, in a large N limit where the coupling constant is scaled with N with an extra logN compared to the standard t Hooft scaling. 相似文献
46.
Gómez-Zavaglia A Kaczor A Cardoso AL Pinho e Melo TM Fausto R 《The journal of physical chemistry. A》2006,110(26):8081-8092
The structure, preferred conformers, vibrational spectrum, and photochemical behavior of the novel azirine, methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate (MCMAC) were investigated in low-temperature matrixes and in the neat solid amorphous state by infrared spectroscopy and quantum-chemical calculations. Two conformers of the compound were observed in argon, krypton, and xenon matrixes, in agreement with the DFT(B3LYP)/6-311++G(d,p) and MP2/6-311++G(d,p) theoretical calculations. Both conformers were found to exhibit the carboxylic ester group in the cis conformation, differing in the arrangement defined by the O=C-C-Cl dihedral angle (cis and trans, for Ct and Cc forms, respectively). The Ct conformer was found to be the most stable conformer in the gaseous phase as well as in both argon and krypton matrixes, whereas the more polar Cc conformer became the most stable form in the xenon matrix and in the neat solid amorphous phase. In situ broadband UV (lambda > 235 nm) excitation of matrix-isolated MCMAC led to azirine ring C-C and C-N bond cleavages, the latter process corresponding to the most efficient reaction channel. The photochemical cleavage of the C-N bond had never been previously observed in the case of aliphatic 2H-azirines. Two electron withdrawing substituents (methoxycarbonyl group and chlorine atom) are connected to the azirine ring in the novel MCMAC azirine. The simultaneous presence of these two groups accelerates intersystem crossing toward the triplet state where cleavage of the C-N bond takes place. The primary photoproducts resulting from the C-N and C-C ring-opening reactions were also found to undergo further photochemical decarbonylation or decarboxylation reactions. 相似文献
47.
Marta Zalewska Agnieszka Gawin Milena Ściskalska Marcin Moczulski Halina Milnerowicz 《International journal of environmental analytical chemistry》2013,93(14-15):1422-1434
Metallurgy processes are associated with many hazardous and toxic factors, including heavy metals. Exposure to heavy metals can cause damage to different organs, which can be observed through variation in the concentration of proteins in serum. The aim of this study was to evaluate the changes in a serum protein profile of copper smelters exposed to As, Cd and Pb ions, and xenobiotics present in tobacco smoke. A 2.3-fold higher Pb concentration in the blood and a 2.8-fold greater As concentration have been observed in the urine of non-smoking smelters compared to a control group. In the blood of smoking smelters, Cd concentration was 2-fold higher than in non-smoking ones. Serum proteins were separated by capillary electrophoresis, and in the group of non-smoking smelters, a higher amount of α1-globulins was observed. In the group of smoking smelters, fewer α1-globulins were noted. Furthermore, a greater amount of α2-globulins in the serum of smoking and non-smoking workers in relation to the control group was revealed. A positive correlation between the concentration of Cd in the blood and the content of a fraction containing α1- and α2-globulins was revealed. Urine Cd concentration was found to be negatively associated with the α1- and α2-globulins fraction. Observed abnormalities in the proteins profiles of smelters can be important markers when assessing exposure to heavy metals and in the early diagnosis of diseases caused by them. 相似文献
48.
Szyperska A Gajewicz A Mazurkiewicz K Leszczynski J Rak J 《Physical chemistry chemical physics : PCCP》2011,13(43):19499-19507
Electron attachment to trimeric complexes that mimic most frequent hydrogen bonding interactions between an amino acid side chain (AASC) and the Watson-Crick (WC) 9-methyladenine-1-methylthymine (MAMT) base pair has been studied at the B3LYP/6-31++G(d,p) level of theory. Although the neutral trimers will not occur in the gas phase due to unfavorable free energy of stabilization (G(stab)) they should form a protein-DNA complex where entropy changes related to formation of such a complex will more than balance its disadvantageous G(stab). The most stable neutrals possess an identical pattern of hydrogen bonds (HBs). In addition, the proton-acceptor (N7) and proton-donor (N10) atoms of adenine involved in those HBs are located in the main groove of DNA. All neutral structures support the adiabatically stable valence anions in which the excess electron is localized on a π* orbital of thymine. The vertical detachment energies (VDEs) of anions corresponding to the most stable neutrals are substantially smaller than that of the isolated WC MAMT base pair. Hence, electron transfer from the anionic thymine to the phosphate group and as a consequence formation of a single strand break (SSB) should proceed more efficiently in a protein-dsDNA complex than in the naked dsDNA as far as electron attachment to thymine is concerned. 相似文献
49.
The aim of this contribution was the study of the influence of polymer matrix on the photo-induced orientation of azobenzene groups. Notably, an azo-prepolymer bearing hydroxyl groups was selectively confined in self-assembled phases of different block copolymers, randomly-epoxidized polystyrene-b-polybutadiene-b-polystyrene (SBSep) and polystyrene-b-poly-4-vinylpyridine (S4VP). The formation of hydrogen bonds between the azo-prepolymer and poly-4-vinylpyridine block, as well as the effect of the local environment surrounding the azo-prepolymer were investigated by Fourier transform infrared and ultraviolet–visible spectroscopies. In addition, the reversible optical storage properties of the developed materials were also studied. Birefringent properties of the systems based on S4VP were strongly enhanced by intermolecular interactions with the azo-prepolymer. Specifically, the maximum birefringence level attained by a system containing 13 wt% of azobenzene was around 2.3 × 10−2 and its remaining birefringence was nearly three times higher than that of the neat azo-prepolymer. Furthermore, a morphological analysis of the designed materials was carried out by atomic force microscopy. Taking into account that the control of the microdomains ordering in block copolymer films is of current interest, special attention was focused on the influence of different variables on the arrangement of the block copolymer microdomains. 相似文献
50.
Agnieszka Grzelka Marek Cypryk Peter C. Hupfield 《Journal of organometallic chemistry》2004,689(4):705-713
Kinetics studies of the condensation of model hydroxyl-terminated oligosiloxanes, pentamethyldisiloxane-1-ol (MDH) and heptamethyltrisiloxane-1-ol (MD2H), catalysed by protic complex of tetrakis(pentafluorophenyl)borate in the toluene solution were performed. The dominating reaction was condensation, which was accompanied by disproportionation of oligosiloxanols. Water released in the condensation forms separate dispersed phase, but the phase separation and the presence of water does not affect the rate of the polycondensation. Both processes, condensation and disproportionation, show analogous kinetic laws being first order in silanol and half order in catalyst. They exhibit also similar values of activation parameters. The kinetics are explained by the formation of a reactive protic complex of silanol with borate being in fast preequilibrium with an unreactive complex including two borate molecules and the silanol molecules. The equilibrium lies to the side of the unreactive borate complex. 相似文献