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1.
A Kanavarioti 《The Journal of organic chemistry》1998,63(20):6830-6838
The formation of the internucleotide bond in diguanylate synthesis was studied in aqueous solution at pH 8 and 0.2 M Mg2+ in the presence and absence of polycytidylate, poly(C). The investigation was simplified by using guanosine 5'-phosphorylmorpholinamide, mor-pG, which can act only as a nucleophile, and deoxyguanosine 5'-phosphoryl-2-methylimidazolide, 2-MeImpdG, which can act only as an electrophile. The time-dependent product distribution was monitored by high-performance liquid chromatography (HPLC) and liquid chromatography mass spectrometry (LC/MS). In the absence of poly(C) the reaction between mor-pG and 2-MeImpdG yielded small amounts of the dimer mor-pGpdG with a regioselectivity of 2'-5':3'-5' = 3.5. In the presence of poly(C) dimer yields increased and a reversal in regioselectivity occurred; both effects were in proportion to the concentration of the polymer. The results can be quantitatively explained with the proposition that poly(C), acting as the template, catalyzes the reaction between template-bound monomers by about a factor of 4-5 over the reaction in solution and yields dimers with a regioselectivity of 2'-5':3'-5' approximately 0.33. These findings illustrate the intrinsic preference of guanosine monomers to correctly self-assemble on the appropriate template. 相似文献
2.
Kanavarioti A Bernasconi CF Alberas DJ Baird EE 《Journal of the American Chemical Society》1993,115(19):8537-8546
A kinetic study of oligoguanylate synthesis on a polycytidylate template, poly(C), as a function of the concentration of the activated monomer, guanosine 5'-monophosphate 2-methylimidazolide, 2-MeImpG, is reported. Reactions were run with 0.005-0.045 M 2-MeImpG in the presence of 0.05 M poly(C) at 23 degrees C. The kinetic results are consistent with a reaction scheme (eq 1) that consists of a series of consecutive steps, each step representing the addition of one molecule of 2-MeImpG to the growing oligomer. This scheme allows the calculation of second-order rate constants for every step by analyzing the time-dependent growth of each oligomer. Computer simulations of the course of reaction based on the determined rate constants and eq 1 are in excellent agreement with the product distributions seen in the HPLC profiles. In accord with an earlier study (Fakhrai, H.; Inoue, T.; Orgel, L. E. Tetrahedron 1984, 40, 39), rate constants, ki, for the formation of the tetramer and longer oligomers up to the 16-mer were found to be independent of length and somewhat higher than k3 (formation of trimer), which in turn is much higher than k2 (formation of dimer). The ki (i > or = 4), k3, and k2 values are not true second-order rate constants but vary with monomer concentration. Mechanistic models for the dimerization (Scheme I) and elongation reactions (Scheme II) are proposed that are consistent with our results. These models take into account that the monomer associates with the template in a cooperative manner. Our kinetic analysis allowed the determination of rate constants for the elementary processes of covalent bond formation between two monomers (dimerization) and between an oligomer and a monomer (elongation) on the template. A major conclusion from our study is that bond formation between two monomer units or between a primer and a monomer is assisted by the presence of additional next-neighbor monomer units. This is consistent with recent findings with hairpin oligonucleotides (Wu, T.; Orgel, L. E. J. Am. Chem. Soc. 1992, 114, 317). Our study is the first of its kind that shows the feasibility of a thorough kinetic analysis of a template-directed oligomerization and provides a detailed mechanistic model of these reactions. 相似文献
3.
Ahmed A. Abdel-Khalek 《Transition Metal Chemistry》1991,16(2):173-175
The kinetics of the oxidation of [CrIII(H2O)(XOH)], (XOH=N-(2-hydroxycyclohexyl)ethylenediaminetriacetate) to CrVI by periodate have been investigated in aqueous solution at various pH values (6.00–7.20) and temperatures (15.0–35.0°C). The reaction follows the rate law:
相似文献
4.
Cervilla A Pérez-Plá F Llopis E Piles M 《Dalton transactions (Cambridge, England : 2003)》2004,(9):1461-1465
The kinetic study of the spontaneous reduction of some neutral tris-dithiolene complexes [ML3] of molybdenum(VI) and tungsten(VI), (L = S2C6H4(2-), S2C6H3CH3(2-) and S2C2(CH3)2(2-); M = Mo or W) by tetrabutylammonium hydroxide in tetrahydrofuran-water solutions demonstrates that OH- is an effective reductant. Their reduction is fast, clean and quantitative. Depending upon both the molar ratio in which the reagents are mixed and the amount of water present, one- or two-electron reductions of these tris-dithiolene complexes were observed. If Bu4NOH is present in low concentration or/and at high concentrations of water, the total transformation of the neutral M(VI) complex into the monoanionic M(V) complex is the only observed process. Stopped-flow kinetic data for this reaction are consistent with the rate law: -d[ML3]/dt = d[ML3-]/dt = k[ML3][Bu4NOH]. The proposed mechanism involves nucleophilic attack of OH- to form a mono-anionic seven-coordinate intermediate [ML3OH]-, which interacts with another molecule of [ML3] to generate the monoanionic complex [ML3]- transfering the oxygen from coordinated OH- to water. Hydrogen peroxide was identified as the reaction product. The molybdenum complexes are more difficult to reduce than their corresponding tungsten complexes, and the values of k obtained for the molybdenum and tungsten series of complexes increase as the ene-1,2-dithiolate ligand becomes more electron-withdrawing (S2C6H4(2-) > S2C6H3CH3(2-) > S2C2(CH3)2(2-)). This investigation constitutes the only well-established interaction between hydroxide ion and a tris(dithiolene) complex, and supports a highly covalent bonding interaction between the metal and the hydroxide ion that modulates electron transfer reactions within these complexes. 相似文献
5.
Vergleichende Untersuchung der Bromaddition an symmetrisch substituierte Stilben- und Tolan-Derivate
Hansjörg Sinn Siegfried Hopperdietzel Dieter Sauermann 《Monatshefte für Chemie / Chemical Monthly》1965,96(3):1036-1055
The addition of bromine to multiple bond systems is generally maintained to be an electrophilic reaction. Assuming an electrophilic mechanism however leads to difficulties with reactions on the CC triple bond system. In addition, the few existing investigations show a strong influence of trace contaminations. Through the principle of preliminary reactions, proven in polymer reactions, it was possible to obtain pure bromobenzene solutions of stilbene, tolane, p,p′-dimethyl-stilbene and-tolane, m,m′-dimethyl-stilbene and-tolane, p,p′-dibrom-stilbene and-tolane, m,m′-dinitro-stilbene and-tolane, p,p′-dinitro-stilbene and-tolane, as well as of bromine. With such solutions, for all cases of brominations, the rate law obtained ([c] = concentration of unsaturated compound) was
$$d[Br_2 ]/dt = d[c]/dt = k[Br_2 ]^2 [c]$$ 相似文献
6.
G. Adefikayo Ayoko 《Transition Metal Chemistry》1990,15(6):421-424
Summary The kinetics of oxidation of hypophosphorus and arsenious acids by 12-tungstocobaltate(III) anion have been studied in aqueous hydrochloric acid at constant ionic strength (I=2.0 M NaCl). The reactions obey the second-order rate law d[oxidant]/dt=2k [oxidant] [reductant]. Variation of [H+] in the range 0.10–1.50 M has no effect on the rates. Possible mechanistic interpretations of these observations are suggested. 相似文献
7.
《European Polymer Journal》1987,23(2):153-158
The polyesterifications of cinnamylsuccinic acid with 1,4-tetramethylene glycol in both equimolar and non-equimolar ratios were investigated over the range of 130–180°C in the absence and the presence of p-toluenesulphonic acid as catalyst. The kinetic equations were: d[COOH]/dt = k1[COOH][OH]2 and d[COOH]/dt = k2[COOH]2 for uncatalyzed and acid-catalyzed polyesterifications, respectively. The apparent rate constants for uncatalyzed and acid-catalyzed reactions were evaluated by using the method of least squares for various values of initial molar ratios between [OH] and [COOH]. The activation parameters were also calculated. 相似文献
8.
H Munakata T Kanzaki S Nakagawa H Imai Y Uemori 《Chemical & pharmaceutical bulletin》2001,49(12):1573-1580
We synthesized two water-soluble porphyrins appending platinum(II) complexes [alpha,beta-(4a) and alpha,alpha-(4b) 5,15-bis(2-trans-[PtCl(NH3)2]N-2-aminoethylaminocarbonylphenyl) 2,3,7,8,12,13,17,18-octamethylporphyrin] and studied their reactions with a variety of nucleic acids [disodium adenosine-5'-monophosphate (AMP), disodium guanosine-5'-monophosphate (GMP), disodium thymidine-5'-monophosphate (TMP), disodium cytidine-5'-monophosphate (CMP), synthetic polymer poly(dG)-poly(dC), poly(dA)-poly(dT)] by 1H-NMR, UV-vis and FAB-MS spectroscopies. Based on the denaturation experiments of synthetic nucleic acid polymers, we conclude that the presence of the porphyrins (5.6 microM) does not cause significant changes in the melting temperature of poly(dA)-poly(dT) (28 microM) (deltaT=1 degrees C) and shows reannealing. On the other hand, gradual melting of poly(dG)-poly(dC) (28 microM) occurs at a low temperature (deltaT= -27 degrees C) in the presence of the porphyrins (5.6 microM), and the solutions do not show reannealing phenomena. The results of UV-vis and 1H-NMR experiments revealed that the porphyrins bind to guanine bases and that the porphyrins bind to GMP more strongly than to the other nucleotides. The binding modes between the porphyrins and synthetic nucleic acids are affected more by the coordination of the nucleobase [poly(dG)-poly(dC)] to the Pt(II) in the porphyrins than by Coulomb and hydrophobic interactions. 相似文献
9.
本文研究了VO[OCH2C(CH3)3]2Cl-Ali-Bu3催化丁二烯、丙烯交替共聚合的动力学特征,测定了单体和催化剂的反应级数,建立了聚合速度方程,并求得了-80℃-20℃温度范围内的一级速率常数K和总活化能ET. 相似文献
10.
Total syntheses of the epoxyquinoid dimers, epoxyquinols A, B, and epoxytwinol A (RKB-3564 D), have been accomplished employing [4 + 2] and [4 + 4] dimerization of 2H-pyran epoxyquinol monomers. Modifications of 2H-pyran precursors have been explored, including alteration of epoxy alcohol and diene stereochemistry. A stable 2H-pyran prepared by alteration of the epoxyquinol 2H-pyran nucleus was evaluated as a diene in Diels-Alder cycloaddition with reactive dienophiles. Extensive studies for improving the [4 + 4] dimerization of selectively protected 2H-pyran monomers to afford the novel epoxyquinoid dimer epoxytwinol A were carried out, and valuable insight regarding competitive [4 + 2] and [4 + 4] dimerization processes has been obtained. In addition, chemical reactivities and structural modifications of epoxyquinol dimers have been evaluated, including [2 + 2] photocycloaddition and [3,3] sigmatropic rearrangement, indicating the possibility for production of novel structural diversity from dimeric epoxyquinoid natural product frameworks. 相似文献
11.
The synthesis of the epoxyquinol dimer RKB-3564 D (3) is reported, employing an alkoxysilanol protecting group to redirect the inherently favored [4 + 2] dimerization of 2H-pyran monomers to a [4 + 4] manifold. Preliminary mechanistic studies indicate that the [4 + 4] dimerization may occur through a stepwise, ionic process. 相似文献
12.
Kinetics on the cheletropic addition of sulfur dioxide to (E)-1-methoxybutadiene (1) to give the corresponding sulfolene 2 (2-methoxy-2,5-dihydrothiophene-1,1-dioxide) gave the rate law d[2]/dt = k[1][SO(2)](x)() with x = 2.6 +/- 0.2 at 198 K. Under these conditions, no sultine 3 [(2RS,6RS)-6-methoxy-3,6-dihydro-1,2-oxathiin-2-oxide] resulting from a hetero-Diels-Alder addition was observed, and the cheletropic elimination 2 --> 1 + SO(2) did not occur. Ab initio and DFT quantum calculations confirmed that the cheletropic addition 1 + SO(2) --> 2 follows two parallel mechanisms, one involving two molecules of SO(2) and the transition structure with DeltaG(++) = 18.2 +/- 0.2 kcal/mol at 198 K (exptl); 22.5-22.7 kcal/mol [B3LYP/6-31G(d,p)], the other one involving three molecules of SO(2) with DeltaG(++) = 18.9 +/- 0.1 kcal/mol at 198 K (exptl); 19.7 kcal/mol [B3LYP/6-31G(d,p)]. The mechanism involving only one molecule of SO(2) in the transition structure requires a higher activation energy, DeltaG(++) = 25.2 kcal/mol [B3LYP/6-31G(d,p)]. Comparison of the geometries and energetics of the structures involved into the 1 + SO(2) --> 2, 3 and 1 + 2SO(2) --> 2, 3 + SO(2) reactions obtained by ab initio and DFT methods suggest that the latter calculation techniques can be used to study the cycloadditions of sulfur dioxide. The calculations predict that the hetero-Diels-Alder addition 1 + SO(2) --> 3 also prefers a mechanism in which three molecules of SO(2) are involved in the cycloaddition transition structure. At 198 K and in SO(2) solutions, the entropy cost (TDeltaS(++)) is overcompensated by the specific solvation by SO(2) in the transition structures of both the cheletropic and hetero-Diels-Alder reactions of (E)-1-methoxybutadiene with SO(2). 相似文献
13.
Itoh T Shichi T Yui T Takahashi H Inui Y Takagi K 《The journal of physical chemistry. B》2005,109(8):3199-3206
The present study is an investigation of a reversible thermal color change induced in lamella hybrids of poly(diacetylenecarboxylates) incorporated in layered double hydroxide (LDH) nanosheets. These poly-[m,n]/LDH hybrids prepared by the photo- or gamma-ray-induced polymerization of diacetylenecarboxylates, i.e., CH(3)(CH(2))(m)()(-)(1)CC-CC(CH(2))(n)()(-)(1)CO(2)(-) (mono-[m,n]), and intercalated in LDH lamella sheets, were observed to develop colors ranging from yellow to blue. The change in color was found to depend greatly on the alkyl carbon numbers of the mono-[m,n] (m,n = 10,11; 5,11; 10,5; 16,1) values. Moreover, the conformational alignment of the mono-[m,n] within the LDH was observed to be a crucial factor in color development, which was greatly affected by the intercalation degrees and extent of poly(ene-yne) linkage elongation of the polymers. For the poly-[m,n]/LDH hybrids investigated, a reversible color change was found to occur repeatedly and remarkably for the poly-[10,11]/LDH hybrid. This color change occurred at temperatures between ca. 20 and 80 degrees C back and forth from purple red to bright orange, in stark contrast to the irreversible color change for poly-[10,11] without LDH. Moreover, DSC and Raman spectroscopic studies of the LDH hybrids showed that the thermochromic temperature corresponded to the phase transition temperature of 80 degrees C. XRD analysis also indicated that the poly-[m,n]/LDH hybrid could retain its lamella structure during such thermochromic color changes, enabling conformational recovery in the polymer chains by a cooling down of the hybrids to temperatures lower than the transition temperature, while the nonhybrid poly-[10,11] powders exhibited an irreversible color change at 60 degrees C, above which the polymer powder turned amorphous. 相似文献
14.
Among the many mechanisms for the oxidation of guanine derivatives (G) assisted by transition metals, Ru(III) and Pt(IV) metal ions share basically the same principle. Both Ru(III)- and Pt(IV)-bound G have highly positively polarized C8-H's that are susceptible to deprotonation by OH(-), and both undergo two-electron redox reactions. The main difference is that, unlike Pt(IV), Ru(III) is thought to require O(2) to undergo such a reaction. In this study, however, we report that [Ru(III)(NH(3))(5)(dGuo)] (dGuo = deoxyguanosine) yields cyclic-5'-O-C8-dGuo (a two-electron G oxidized product, cyclic-dGuo) without O(2). In the presence of O(2), 8-oxo-dGuo and cyclic-dGuo were observed. Both [Ru(II)(NH(3))(5)(dGuo)] and cyclic-dGuo were produced from [Ru(III)(NH(3))(5)(dGuo)] accelerated by [OH(-)]. We propose that [Ru(III)(NH(3))(5)(dGuo)] disproportionates to [Ru(II)(NH(3))(5)(dGuo)] and [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)], followed by a 5'-OH attack on C8 in [Ru(IV)(NH(3))(4)(NH(2)(-))(dGuo)] to initiate an intramolecular two-electron transfer from dGuo to Ru(IV), generating cyclic-dGuo and Ru(II) without involving O(2). 相似文献
15.
《Current Opinion in Colloid & Interface Science》2007,12(1):29-42
The role of local environment on mobility of chain molecules is illustrated by considering the case of a miscible mixture of two polymers. The historical background, observed dynamic responses to mixing, and theoretical explanations for these responses are outlined. Two miscible blend systems: poly(isoprene) [PI]/poly(vinyl ethylene) [PVE] and poly(ethylene oxide) [PEO]/poly(methyl methacrylate) [PMMA] are reviewed in detail, with available data consolidated in a set of figures. Unusual features of the PEO/PMMA blend are discussed. 相似文献
16.
The kinetics of substitution of aqua ligands fromcis-diaqua-bis(biguanide)cobalt(III) and chromium(III) ions by aspartic acid in EtOH–H2O media have been studied spectrophotometrically in the 30 to 45°C range. We propose the following rate law for the anation
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