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101.
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
102.
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
103.
Wojtczak BA Andrysiak A Grüner B Lesnikowski ZJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(34):10675-10682
A general approach to the synthesis of nucleoside conjugates containing carborane and metallocarborane complexes, based on Huisgen 1,3-dipolar cycloaddition ("chemical ligation"), is described. Boron-cluster-donors bearing terminal azide or ethynyl groups were prepared in the ring-opening reaction of dioxane-boron-cluster adducts and an azide anion or suitable alkynol-derived alcoholate nucleophile. Analogous derivatives bearing terminal sulfhydryl groups were also prepared. Nucleosides with various spacers containing terminal azide or ethynyl groups, located within nucleobases or sugar residues, were used as boron-cluster acceptors. The proposed methodology provides a convenient way to synthesize libraries of boron-cluster-modified nucleosides for various applications. 相似文献
104.
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
105.
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
106.
Mina Roueinfar Hayley N. Templeton Julietta A. Sheng Ka Lok Hong 《Molecules (Basel, Switzerland)》2022,27(3)
The clustered regularly interspaced short palindromic repeat (CRISPR)/Cas system is best known for its role in genomic editing. It has also demonstrated great potential in nucleic acid biosensing. However, the specificity limitation in CRISPR/Cas has created a hurdle for its advancement. More recently, nucleic acid aptamers known for their high affinity and specificity properties for their targets have been integrated into CRISPR/Cas systems. This review article gives a brief overview of the aptamer and CRISPR/Cas technology and provides an updated summary and discussion on how the two distinctive nucleic acid technologies are being integrated into modern diagnostic and therapeutic applications 相似文献
107.
Agnieszka Wróblewska Egbert Meissner Eugeniusz Milchert 《Journal of fluorine chemistry》2006,127(3):345-350
The influence of technological parameters on the dehydroiodination of perfluoroalkylethene iodides (CF3)2CF(CF2CF2)nCH2CH2I, where n = 1, 2, 3 and 4, has been investigated. The most advantageous conditions for the two-stage oxidation of (CF3)2CF(CF2CF2)nCHCH2, with ozone in the first stage, followed by the oxidation with hydrogen peroxide to the perfluorocarboxylic acids, were determined. The effects of temperature and time on the conversion of perfluoroalkylethenes during the oxidation with ozone were studied. In the second stage, the selectivity of transformation (of each homologue) to the perfluorocarboxylic acid in relation to the theoretical amount resulting from a quantity of perfluoroalkylethene used and the conversion of perfluoroalkylethene in the temperature range of 10-80 °C has been determined. 相似文献
108.
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
109.
Chibowski E Wiacek A Holysz L Terpilowski K 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7662-7671
Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential. 相似文献
110.
Multiblock poly(ester-block-amide)s (PEA) elastomers comprising hard blocks of oligoamide and oligoester soft segments were prepared and their structure-property relations were analysed. The polycondensation reaction of oligoesters (prepared from 1,4-butanediol and dimerized fatty acid) with oligolaurolactam (PA12) gave copolymer series with variable blocks content (the soft segments content was varied from 24 to 60 wt.%). PEAs are the phase system composed of crystallised sequences of oligoamide (hard segment phase) as well as oligoesters (soft segment phase). Mixing between the hard and soft phases was studied by thermal and mechanical measurements (DSC, DMTA). These results have indicated on a multiphase structure of investigated materials. The relationship between the observed thermal and tensile properties and the soft/hard segments content indicated on an increase of the phase separation with soft segments content. 相似文献