共查询到20条相似文献,搜索用时 15 毫秒
1.
Ashutosh Gupta R. P. Singh V. B. Singh Brijesh Kumar Mishra N. Sathyamurthy 《Journal of Chemical Sciences》2007,119(5):457-465
The reaction of ground-state atomic oxygen [O(3
P
2)] with methyl, ethyl, n-propyl and isopropyl radicals has been studied using the density functional method and the complete basis set model. The
energies of the reactants, products, reaction intermediates and various transition states as well as the reaction enthalpies
have been computed. The possible product channels and the reaction pathways are identified in each case. In the case of methyl
radical the minimum energy reaction pathway leads to the products CO + H2 + H. In the case of ethyl radical the most facile pathway leads to the products, methanal + CH3 radical. For propyl radical (n- and iso-), the minimum energy reaction pathways would lead to the channel containing ethanal + methyl radical. 相似文献
2.
Dr. Feryel Soualmia Alain Guillot Dr. Nazarii Sabat Clémence Brewee Dr. Xavier Kubiak Dr. Michael Haumann Dr. Xavier Guinchard Dr. Alhosna Benjdia Dr. Olivier Berteau 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(31):e202200627
B12-dependent radical SAM enzymes are an emerging enzyme family with approximately 200,000 proteins. These enzymes have been shown to catalyze chemically challenging reactions such as methyl transfer to sp2- and sp3-hybridized carbon atoms. However, to date we have little information regarding their complex mechanisms and their biosynthetic potential. Here we show, using X-ray absorption spectroscopy, mutagenesis and synthetic probes that the vitamin B12-dependent radical SAM enzyme TsrM catalyzes not only C- but also N-methyl transfer reactions further expanding its synthetic versatility. We also demonstrate that TsrM has the unique ability to directly transfer a methyl group to the benzyl core of tryptophan, including the least reactive position C4. Collectively, our study supports that TsrM catalyzes non-radical reactions and establishes the usefulness of radical SAM enzymes for novel biosynthetic schemes including serial alkylation reactions at particularly inert C−H bonds. 相似文献
3.
The organometallic radical: (3,5-di-t-butyl-0-benzoquinone)tetracarbonyl-rhenium(0) and its triphenylphosphine substituted derivatives were studied by EPR spectroscopy. The unpaired electron is shown to be localized in the organic 1,2-diketone ligand. The rate of carbonyl substitution by triphenylphosphine at the unsubstituted rhenium radical indicates a second order reaction. The activation parameters are ΔH* =19.1±0.8Kcal/mole and ΔS*-3.0±1.5 eu/mole. 相似文献
4.
A free-radical reaction of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate with electron rich alkynes giving cyclopentene systems is described. This reaction can be achieved with p-toluenesulfonyl chloride and phenyldisulfide as radical precursors. 相似文献
5.
Enrique Saldívar‐Guerra Jos Bonilla Fabiola Becerril Gregorio Zacahua Martha Albores‐Velasco Roberto Alexander‐Katz Leticia Flores‐Santos Larissa Alexandrova 《Macromolecular theory and simulations》2006,15(2):163-175
Summary: The range of validity of two popular versions of the nitroxide quasi‐equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, kc[P][N] = kd[P N], where P, N and P N are living, nitroxide radicals and dormant species respectively, with kinetic constants kc and kd, is found valid only for small values of the equilibrium constant K (10−11–10−12 mol · L−1) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, kc[P][N] = kd[P N]0 was found to be remarkably good up to values of K around 10−8 mol · L−1. This upper bound is numerically found to be 2–3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico‐chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested.
6.
Antibacterial poly(ethylene terephthalate) surfaces obtained from thymyl methacrylate polymerization 下载免费PDF全文
Sophie Bedel Bénédicte Lepoittevin Ludovic Costa Olivier Leroy Diana Dragoe Jérôme Bruzaud Jean‐Marie Herry Morgan Guilbaud Marie‐Noëlle Bellon‐Fontaine Philippe Roger 《Journal of polymer science. Part A, Polymer chemistry》2015,53(17):1975-1985
Thymol, an antibacterial agent was used for the preparation of a methacrylic monomer. The conventional and atom transfer radical (ATRP) polymerizations of this monomer were studied using different conditions. Then, the functionalization of poly(ethylene terephthalate) (PET) films by “grafting from” ATRP using this monomer was investigated. In this aim, a three steps procedure was developed. The surfaces were first treated by NH3 plasma treatment to incorporate primary amino functions. Then, in a second step, ATRP initiator was grafted by reaction with bromoisobutyryl bromide. Surface initiated ATRP of thymyl methacrylate was performed in solution in the presence of a sacrificial initiator. The efficiency of these reactions was confirmed by X‐ray photoelectron spectroscopy. Wetting properties and surface energy were found to vary systematically depending to the type of functionalization and grafting. The poly(thymyl methacrylate)‐grafted PET surfaces exhibit resistance to bacterial adhesion toward Pseudomonas aeruginosa, Listeria monocytogenes, and Staphylococcus aureus strains. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1975–1985 相似文献
7.
Thomas Junkers Lin Zang Edgar H.H. Wong Nico Dingenouts Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2011,49(22):4841-4850
The preparation of ABA‐type block copolymers via tandem enhanced spin capturing polymerization (ESCP) and nitroxide‐mediated polymerization (NMP) processes is explored in‐depth. Midchain alkoxyamine functional polystyrenes (Mn = 6200, 12,500 and 19,900 g mol?1) were chain extended with styrene as well as tert‐butyl acrylate at elevated temperature NMP conditions (T = 110 °C) generating a tandem ESCP‐NMP sequence. Although the chain extensions and thus the block copolymer formation processes function well (yielding in the case of the chain extension with styrene number average molecular weights of up to 20,800 g mol?1 (PDI = 1.22) when the 6200 g mol?1 precursor is used and up to 67,500 g mol?1 (PDI = 1.36) when the 19,900 g mol?1 precursor is used and 21,600 g mol?1 (PDI = 1.17) as well as 37,100 g mol?1 (PDI = 1.21) for the tert‐butyl acrylate chain extensions for the 6200 and 12,500 g mol?1 precursors, respectively), it is also evident that the efficiency of the block copolymer formation process decreases with an increasing chain length of the ESCP precursor macromolecules (i.e., for the 19,900 g mol?1 ESCP precursor no efficient chain extension with tert‐butyl acrylate can be observed). For the polystyrene‐block‐tert‐butyl acrylate‐block‐polystyrene polymers, the molecular weights were determined via triple detection SEC using light scattering and small‐angle X‐ray scattering. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
8.
The rate constant k
CO of decarbonylation of phenylacetyl radicals generated by photolysis of dibenzyl ketone was measured by laser flash photolysis technique in six solvents in a wide temperature range. The pre-exponential factors A and activation energies E
a of decarbonylation were found for all solvents. The k
CO value decreases with an increase in the dielectric constant of the solvent, whereas an increase in the ability of the solvent for hydrogen bonding increases k
CO. The results of quantum-chemical calculations confirm the mutual compensation of the contributions of specific and nonspecific solvations to the activation energy of decarbonylation in alcohols. 相似文献
9.
Takashi Kaneko Hiroyuki Tatsumi Toshiki Aoki Eizo Oikawa Hajime Yoshiki Naoki Yoshioka Eishun Tsuchida Hiroyuki Nishide 《Journal of polymer science. Part A, Polymer chemistry》1999,37(2):189-198
4‐[(3,5‐Di‐tert‐butyl‐4‐hydroxyphenyl)(3,5‐di‐tert‐butyl‐4‐oxo‐cyclohexa‐ 2,5‐dienylidene)methyl]styrene (abbreviated as (p‐vinylphenyl)hydrogalvinoxyl) was polymerized using AIBN as an initiator to give a bright yellow polymer with M w = 3.2 × 104. The polymer was oxidized to give the corresponding polyradical derivative, whose spin concentration could be increased up to about 70 mol % depending on oxidative conditions. ESR signal line‐width in the solid state was greatly increased below 200 K for the polyradical with a high spin concentration (> 50 mol %). The magnetization and magnetic susceptibility indicated weak antiferromagnetic interaction among the radical sites. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 189–198, 1999 相似文献
10.
The interaction potential between two planar methyl radicals is investigated based on the available ab initio calculations. Two components contribute to this potential: a bonding potential, V
B, an angle-dependent square of the overlap integral for unoccupied p
s orbitals, and a nonbonding potential, V
NB, a total of the long-range dispersive and short-range repulsive interactions. The analytical form of the potential, valid at longer distances, can be used for evaluation of the matrix elements of functions describing rotational states. 相似文献
11.
Dr. Kubandiran Kolanji Prof. Dr. Martin Baumgarten 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3626-3632
Three 1 N-phenyl nitronyl nitroxide (NN) 4-substituted dithieno[3,2-b:2′,3′-d]pyrrole ( DTP ) derivatives with R1=4-phenyl-, 4H-, and 4-methylthiothiophenyl- ( R1 2 DTP-Ph-NN , R1=H, Ph and MeSTh) were designed, synthesized and characterized. The electrochemical properties were studied by cyclic voltammetry (CV). All the molecules exhibited two main oxidation peaks, first for radical cation and next for dication formation. The cation and dication formation were also confirmed by UV/Vis absorption spectroscopy for Ph2DTP-Ph-NN and MeSTh2DTP-Ph-NN titrated with tris(4-bromophenyl)aminiumhexachloroantimonate (magic blue). In addition, the cation and dication formation were verified by EPR spectroscopy. Finally, the exchange interactions (J/kB) of NN and radical cation were calculated by DFT studies. 相似文献
12.
Zhi Xu Shougen Yin Bin Lei Yan Lu Weixing Chang Jing Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(5):942-948
1,3‐dichloro‐tetra‐n‐butyl‐distannoxane, which contains Sn? Cl bonds, was used as a novel initiator for atom transfer radical polymerization of styrene in bulk. Some interesting results that were thought to be related to the characteristics of the 1,3‐dihalotetra‐alkyl‐distannoxanes had been obtained. The concentration of the 1,3‐dichlorotetra‐n‐butyl‐distannoxane in the bulk solution of styrene was confirmed to be an important factor for the different results of the polymerization. The corrected theoretical molecular weights, which were based on the proposed mechanism, accorded with the GPC results very well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 942–948, 2007 相似文献
13.
Akikazu Matsumoto Katsuhiko Fukushima Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1991,29(12):1697-1706
Radical polymerization of N,N,N′,N′-tetraalkylfumaramides (TRFAm) bearing methyl, ethyl, n-propyl, isopropyl, and isobutyl groups as N-substituents (TMFAm, TEFAm, TnPFAm, TIPFAm, and TIBFAm, respectively) was investigated. In the polymerization of TEFAm initiated with 1,1′-azobiscyclohexane-1-carbonitrile (ACN) in benzene, the polymerization rate (Rp) was expressed as follows: Rp = k [ACN]0.28 [TEFAm]1.26, and the overall activation energy was 102.1 kJ/mol. The introduction of a bulky alkyl group into N-substituent of TRFAm decreased the Rp in the following order: TMFAm > TEFAm > TnPFAm > TIBFAm > TIPFAm ~ 0. The relative reactivities of these monomers were also investigated in radical copolymerization with styrene (St) and methyl methacrylate (MMA). In copolymerization of TRFAm (M2) with St (M1), monomer reactivity ratios were determined to be r1 = 1.07 and r2 = 0.20 for St–TMFAm, and r1 = 1.88 and r2 = 0.11 for St–TEFAm, from which Q2 and e2 values were estimated to be 0.35 and 0.44 for TMFAm, and 0.19 and 0.47 for TEFAm, respectively. The other TRFAm were also copolymerized with St, but copolymerization with MMA gave polymers containing a small amount of TRFAm units. The polymer from TRFAm consists of a less-flexible poly(N,N-dialkylaminocarbonylmethylene) structure. The solubility and thermal property of the polymers were also investigated. 相似文献
14.
B. L. Tumanskii A. V. Usatov V. V. Bashilov S. P. Solodovnikov N. N. Bubnov Yu. N. Novikov V. I. Sokolov 《Russian Chemical Bulletin》1997,46(4):836-838
The reaction of phosphoryl radicals with (η2-C60)lrH(CO)(PPh3)2 and (η2-C60IrH(8H12)(PPh3) was shown (ESR) to result in the formation of isomers differing in the constants of hyperfine interaction (HFI) with31P nuclei,g-factors, and linewidths. It is likely that the addition of phosphoryl radicals at a distance of two-three bond lengths from
the metallofragment is predominant.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 870–872, April, 1997. 相似文献
15.
Zuoying Wen Xiaofeng Tang Chengcheng Wang Christa Fittschen Tao Wang Cuihong Zhang Jiuzhong Yang Yang Pan Fuyi Liu Weijun Zhang 《国际化学动力学杂志》2019,51(3):178-188
Photoionization mass spectrometry as a powerful analytical method has been widely utilized and provided valuable insight in the field of gas-phase reactions. Here, a highly sensitive vacuum ultraviolet (VUV) photoionization time-of-flight mass spectrometer combined with a microwave discharge generator and a fast flow tube reactor has been developed to study radical reactions of atmospheric and combustion interests. Two kinds of continuous light sources, the tunable VUV synchrotron radiation at Hefei, China for isomer-specific product detection and a commercial krypton discharge lamp for time-consuming kinetic measurements, are employed as photoionization sources in the apparatus. A multiplexed detection with high sensitivity (the limit of detection ∼0.8 ppb) and high mass resolution (M/ΔM ∼ 2100) has been approached. As representative examples, the self-reaction of the methyl radical, CH3, and the reaction of the methyl radical with molecular oxygen are studied and multiple species including reactive radicals and isomeric/isobaric products are detected and identified. In addition, some preliminary results related to the reaction kinetics are also presented. 相似文献
16.
B. L. Tumanskii R. G. Gasanov V. V. Bashilov M. V. Tsikalova N. N. Bubnov V. I. Sokolov V. P. Gubskaya L. Sh. Berezhnaya V. V. Zverev I. A. Nuretdinov 《Russian Chemical Bulletin》2003,52(7):1512-1515
The radical adducts of the P·(O)(OPri)2 (R·) radicals with C60C[P(O)(OEt)2]2
2 fullerene derivatives were studed by ESR spectroscopy. The number of stable regioisomers of phosphorylfullerenyl radicals formed by addition of the phosphoryl radicals to the C60C[P(O)(OEt)2]2
2 isomers depends on the mutual position of the organophosphorus groups and decreases in the series trans-2 > trans-3 trans-4 > e. The rate constants for addition of the R· radicals to the trans-3 regioisomer (k = 1.7·108 L mol–1 s–1) were determined. 相似文献
17.
Alexandru D. Asandei Isaac W. Moran 《Journal of polymer science. Part A, Polymer chemistry》2005,43(23):6028-6038
Bisketonate and alkoxide Ti(III) complexes derived from Zn reduction of Ti(IV) precursors were evaluated as catalysts for the living radical polymerization (LRP) of styrene initiated by Ti‐catalyzed epoxide radical ring opening and mediated by reversible termination with Ti(III). No polymerization occurred with tris(2,2,6, 6‐tetramethyl‐3,5‐heptanedionato)titanium (III), whereas dichlorobis(2,2,6,6‐tetramethyl‐3,5‐heptanedionato)titanium (IV) affords only a free radical polymerization. Preliminary living features were displayed by (iPrO)2TiCl2. Investigations of the effect of epoxide/Ti/Zn ratios, temperature, and nature of the epoxide demonstrated that (iPrO)3TiCl provides a linear dependence of Mn on conversion over a wide range of conditions with an optimum for [Sty]/[epoxide group]/[Ti]/[Zn] = 50/1/2/4 at 90 °C. However, the polydispersity could not be reduced below 1.4–1.5, with an initiator efficiency of 0.15. These results were rationalized in terms of a combination of decreased Ti oxophilicity and ligand exchange. The lowered oxophilicity decreases the initiation rate and broadens Mw/Mn. The fast alkoxide exchange promotes a weak dependence of the polymerization on reaction conditions and generates macromolecular Ti species with reduced ability to mediate LRP. Thus, while monofunctional epoxides provide homogeneous polymerizations and narrower Mw/Mn, difunctional initiators may lead to gel formation at high conversion. Nonetheless, all polymerizations were light gray to colorless and afforded white polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6028–6038, 2005 相似文献
18.
Weijie Zhao Ming Fang Junpo He Junyu Chen Wei Tang Yuliang Yang 《Journal of polymer science. Part A, Polymer chemistry》2010,48(19):4141-4149
Tandem atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMRP) were used to synthesize a polystyrene‐co‐poly(acrylic acid) (poly(St‐co‐AA)) network, in which the two components were interconnected by covalent bond. First, a specific cross‐linker, 1,4‐bis(1′‐(4″‐acryloyloxy‐2″,2″,6″,6″‐tetramethylpiperidinyloxy)ethyl)benzene (di‐AET), a bifunctional alkoxyamine possessing two acrylate groups, was copolymerized with tert‐butyl acrylate through ATRP to prepare a precursor gel. The gel was then used to initiate the NMRP of styrene to prepare poly(St‐co‐(t‐BA)) conetwork, in which the cross‐linkages are composed of polystyrene segments. Finally, the poly(St‐co‐(t‐BA)) conetwork was hydrolyzed to produce amphiphilic poly(St‐co‐AA) conetwork. The resulting gels show swelling ability in both organic solvent and water, which is characteristic of amphiphilic conetworks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4141–4149, 2010 相似文献
19.
Yuichi Yamamura Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2008,46(6):2015-2024
Tripodal imidazole containing ligands, bis((2‐pyridyl)methyl)(1‐methylimidazole‐2‐yl)methyl)amine (BPIA) and bis(1‐methylimidazole‐2‐yl)methyl)((2‐pyridyl)methyl)amine (BIPA), were synthesized and used for copper catalyzed atom transfer radical polymerization (ATRP) of n‐butyl acrylate (nBA). The molecular weights of poly(n‐butyl acrylate) (PnBA) catalyzed by CuBr/BPIA and CuBr/BIPA complexes increased linearly with nBA conversions and they were close to theoretical values with low polydispersities. ATRP equilibrium rate constant (KATRP) measurements showed that bothCuBr/BPIA and CuBr/BIPA complexes had high KATRP values, similar to that of CuBr/tri(2‐pyridylmethyl)amine (TPMA), which is one of the ATRP most active ligands. Activators regenerated by electron transfer (ARGET) ATRP of nBA with CuBr2/BPIA and CuBr2/BIPA complexes were also conducted and polymerization reached high nBA conversions, resulting in PnBA with low polydispersities. This suggests that the copper complexes with BPIA and BIPA were sufficiently stable and active to conduct ATRP when catalyst concentration was low. ARGET ATRP to form high molecular weight PnBA with CuBr2/BPIA and CuBr2/BIPA complexes was also successful. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2015–2024, 2008 相似文献
20.
Addition of CCl4 to 2S-methoxycarbonyl-N-(trans-cinnamoyl)pyrrolidine in the presence of Fe(CO)5 or Fe2(CO)9 results in predominant formation of one of four possible optical isomers of the adduct PhCHClCH(CCl3)C(O)R (R=2S-methoxycarbonylpyrrolidyl).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1390–1392, July, 1995. 相似文献