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41.
Acyclic nucleosides of 4‐nitro‐1H‐imidazole and 4‐nitropyrazole have been synthesized by nucleophilic addition of the appropriate 4‐nitroazole to (?)‐(S)‐(hydroxymethyl)oxirane in the presence of a catalytic amount of potassium carbonate. (+)‐(R)‐3‐(4‐nitro‐1H‐imidazol‐1‐yl)propane‐1,2‐diol and (+)‐(R)‐3‐(2‐methyl‐4‐nitro‐1H‐imidazol‐1‐yl)propane‐1,2‐diol were also obtained in an independent reaction starting from appropriate 1,4‐dinitro‐1H‐imidazole and (+)‐(R)‐3‐aminopropane‐1,2‐diol. (+)‐(R)‐3‐(4‐Nitropyrazol‐1‐yl)propane‐1,2‐diol was also obtained by direct noncatalyzed addition of 4‐nitropyrazole to (?)‐(S)‐(hydroxymethyl)oxirane, whereas the (S)‐enantiomer was obtained by reaction of 4‐nitropyrazole with (+)‐(S)‐1,2‐O‐isopropylideneglycerol under Mitsunobu reaction conditions, followed by a cleavage of the isopropylidene group with 80% AcOH. Racemization during any of these syntheses has not been observed. 3‐(4‐Nitroazol‐1‐yl)propane‐1,2‐diols were incorporated into a 26‐mer oligonucleotide. UV Thermal melting studies of duplexes of the oligonucleotides with 4‐nitropyrazole or 4‐nitro‐1H‐imidazole paired with four natural bases showed moderately decreased stabilities of the duplexes. A narrow range of melting temperatures, typically being within 2° for each acyclic nucleoside, fulfill one of the requirements of using acyclic 4‐nitroazoles as general bases. Single incorporation of 4‐nitroazoles into a 14‐mer triplex forming oligonucleotide resulted in considerably decreased triplex stabilities. 相似文献
42.
Krzysztof Matyjaszewski Przemysaw Kubisa Stanisaw Penczek 《Journal of polymer science. Part A, Polymer chemistry》1975,13(4):763-784
Polymerization of THF in CCl4 solvent was initiated with 1,3-dioxolan-2-ylium eations with AsF6?, PF6?, and SbF6? anions as well as with esters of fluorosulfonic and trifluoromethanesulfonic acids. With these esters polymerization proceeds with a marked acceleration period, due to slow initiation. The corresponding rate constants of initiation and their dependence on the polarity of the THF/CCl4 mixture were determined. The rate constant of propagation on the macroion-pairs (kp±) of the polytetrahydrofurylium cation with AsF6?, PF6?, and SbF6? and CF3SO3?, anions was found to be independent in CCl4 solvent on the anion structure and given by the expression: kp± = 2.93 × 10?2 exp {?4.7 × 103/T} at [THF]0 = 8.0M. This constant depends on the polarity of the polymerization mixture, and at 25°C for the THF-CCl4 system, kp± = 1.78 × 10?2 exp {?4.9/D}; thus, in CCl4 at [THF]0 = 8.0M, and at 25° kp± = 4.0 × 10?21/mole-sec. In the polymerization with derivatives of CF3SO3H (able to form the corresponding macroester) the overall polymerization rate is much lower than that with complex anions because of the reversible conversion of the macroion-pairs into the macroester (internal return). The macroester is much less reactive than the macroionpair (102–103 times) in the monomer addition reaction. At [THF]0 = 8.0M and at 25°C, 96.5% of the growing species exists in the macroester form. Polymerization of THF initiated with derivatives of CF3SO3H is a subject of a strong special salt-effect. At a sufficiently high ratio of [AgSbF6] to [I]0, where the initiator I is C2H5OSO2CF3, the overall polymerization rate is equal to that observed for the polymerization of THF on the macroion-pairs, since the internal return within the triflate ion-pair (the macroester formation) is eliminated and polymerization proceeds on the macroion-pairs with SbF6- anions exclusively. 相似文献
43.
The role of different H-bonds in phases II, III, IV, and V of triammonium hydrogen disulfate, (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), has been studied by X-ray diffraction and (1)H solid-state MAS NMR. The proper space group for phase II is C2/c, for phases III and IV is P2/n, and for phase V is P onemacr;. The structures of phases III and IV seem to be the same. The hydrogen atom participating in the O(-)-H(+).O(-) H-bond in phase II of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) at room temperature is split at two positions around the center of the crucial O(-)-H(+).O(-) H-bonding, joining two SO(4)(2)(-) tetrahedra. With decreasing temperature, it becomes localized at one of the oxygen atoms. Further cooling causes additional differentiation of possibly equivalent sulfate dimers. The NH(4)(+) ions participate mainly in bifurcated H-bonds with two oxygen atoms from sulfate anions. On cooling, the major contribution of the bifurcated H-bond becomes stronger, whereas the minor one becomes weaker. This is coupled with rotation of sulfate ions. In all the phases of (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2), some additional, weak but significant, reflections are observed. They are located between the layers of the reciprocal lattice, suggesting possible modulation of the host (NH(4)(+))(3)H(+)(SO(4)(2)(-))(2) structure(s). According to (1)H MAS NMR obtained for phases II and III, the nature of the acidic proton disorder is dynamic, and localization of the proton takes place in a broader range of temperatures, as can be expected from the X-ray diffraction data. 相似文献
44.
Maksymilian Chruszcz Krzysztof Lewinski 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m150-m151
The structural data for sodium 2‐hydroxy‐5‐nitrobenzylsulfonate monohydrate, Na+·C7H6NO6S?·H2O, which mimics an artificial substrate for human arylsulfatase A, viz. p‐nitrocatechol sulfate, reveal that the geometric parameters of the substrate and its analogue are very similar. Two water molecules, the phenolic O atom and three sulfonate O atoms form the coordination sphere of the Na+ ion, which is a distorted octahedron. The Na+ cations and the O atoms join to form a chain polymer. 相似文献
45.
Anna Rakowska Robert Filipek Krzysztof Sikorski Marek Danielewski Renata Bachorczyk 《Mikrochimica acta》2004,145(1-4):183-186
The interdiffusion process in thin and thick (500nm–60µm) Au–Ni layers deposited on different substrates is studied using the EDS technique. In-depth X-ray analysis based on the Pouchou and Pichoir method is applied for obtaining the concentration profiles in nanometre scale multi-layers. A theoretical analysis using the Darken method is employed for modelling interdiffusion in the Au–Ni system. Computer simulations, where intrinsic diffusivities of the Au and Ni are functions of composition, are presented and compared with experimental results. 相似文献
46.
Abstract— Benoxaprofen [2-(4-chlorophenyl)-α-methyl-5-benzoxazole acetic acid] is an anti-inflammatory drug that causes acute phototoxicity in many patients. Photolysis studies in organic solvents (ethanol, benzene, dimethylsulfoxide) showed that benoxaprofen underwent both Type I and Type II reactions. Irradiation of an anerobic solution of benoxaprofen in ethanol resulted in hydrogen abstraction from the solvent to yield hydroxyethyl and ethoxyl radicals. In the presence of oxygen, superoxide, singlet oxygen and hydroxyethyl radicals were detected. Photolysis of benoxaprofen in air-saturated benzene or dimethylsulfoxide gave superoxide. However, under anerobic conditions the drug yielded a carbon-centered radical in benzene that could not be identified. These findings suggest that both oxygen-dependent and oxygen-independent processes may be important in the phototoxic reactions of benoxaprofen. 相似文献
47.
Krzysztof Ejsmont Magorzata Broda Andrzej Domaski Janusz B. Kyzio Jacek Zaleski 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):o545-o548
The two isomeric compounds 4‐amino‐ONN‐azoxybenzene [or 1‐(4‐aminophenyl)‐2‐phenyldiazene 2‐oxide], i.e. the α isomer, and 4‐amino‐NNO‐azoxybenzene [or 2‐(4‐aminophenyl)‐1‐phenyldiazene 2‐oxide], i.e. the β isomer, both C12H11N3O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X‐ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the molecules are different due to rotation along the Ar—N bonds. In the α isomer, the benzene rings are twisted by 31.5 (2) and 14.4 (2)° towards the plane of the azoxy group; the torsion angles along the Ar—N bond in the β isomer are 24.3 (3) and 23.5 (3)°. Quantum‐mechanical calculations indicate that planar conformations are energetically favourable for both isomers. The N—H?O hydrogen bonds observed in both networks may be responsible for the deformation of these flexible molecules. 相似文献
48.
49.
Valensin D Luczkowski M Mancini FM Legowska A Gaggelli E Valensin G Rolka K Kozlowski H 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1284-1293
Potentiometric and spectroscopic data have shown that octarepeat dimer and tetramer are much more effective ligands for Cu(II) ions than simple octapeptide. Thus, the whole N-terminal segment of prion protein due to cooperative effects, could be more effective in binding of Cu(II) than simple peptides containing a His residue. The gain of the Cu(II) binding by longer octarepeat peptides derives from the involvement of up to four imidazoles in the coordination of the first Cu(II) ion. This type of binding increases the order of the peptide structure, which allows successive metal ions for easier coordination. 相似文献
50.
Bill E Bothe E Chaudhuri P Chlopek K Herebian D Kokatam S Ray K Weyhermüller T Neese F Wieghardt K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):204-224
The bidentate ligands N-phenyl-o-phenylenediamine, H(2)((2)L(N)IP), or its analogue 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, ((4)L(N)IP), react with [Co(II)(CH(3)CO(2))(2)]4H(2)O and triethylamine in acetonitrile in the presence of air yielding the square-planar, four-coordinate species [Co((2)L(N))(2)] (1) and [Co((4)L(O))(2)] (4) with an S=1/2 ground state. The corresponding nickel complexes [Ni((4)L(O))(2)] (8) and its cobaltocene reduced form [Co(III)(Cp)(2)][Ni((4)L(O))(2)] (9) have also been synthesized. The five-coordinate species [Co((2)L(N))(2)(tBu-py)] (2) (S=1/2) and its one-electron oxidized forms [Co((2)L(N))(2)(tBu-py)](O(2)CCH(3)) (2 a) or [Co((2)L(N))(2)I] (3) with diamagnetic ground states (S=0) have been prepared, as has the species [Co((4)L(O))(2)(CH(2)CN)] (7). The one-electron reduced form of 4, namely [Co(Cp)(2)][Co((4)L(O))(2)] (5) has been generated through the reduction of 4 with [Co(Cp)(2)]. Complexes 1, 2, 2 a, 3, 4, 5, 7, 8, and 9 have been characterized by X-ray crystallography (100 K). The ligands are non-innocent and may exist as catecholate-like dianions ((2)L(N)IP)(2-), ((4)L(N)IP)(2-) or pi-radical semiquinonate monoanions ((2)L(N)ISQ)(*) (-), ((4)L(N)ISQ)(*) (-) or as neutral benzoquinones ((2) L(N)IBQ)(0), ((4) L(N)IBQ)(0); the spectroscopic oxidation states of the central metal ions vary accordingly. Electronic absorption, magnetic circular dichroism, and EPR spectroscopy, as well as variable temperature magnetic susceptibility measurements have been used to experimentally determine the electronic structures of these complexes. Density functional theoretical (DFT) and correlated ab initio calculation have been performed on the neutral and monoanionic species [Co((1)L(N))(2)](0,-) in order to understand the structural and spectroscopic properties of complexes. It is shown that the corresponding nickel complexes 8 and 9 contain a low-spin nickel(II) ion regardless of the oxidation level of the ligand, whereas for the corresponding cobalt complexes the situation is more complicated. Spectroscopic oxidation states describing a d(6) (Co(III)) or d(7) (Co(II)) electron configuration cannot be unambiguously assigned. 相似文献