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1.
Hong-Ying Duan Shi-Tao Han Dr. Tian-Guang Zhan Dr. Li-Juan Liu Prof. Dr. Kang-Da Zhang 《Angewandte Chemie (International ed. in English)》2023,62(5):e202212707
Exploring new noncovalent bonding motifs with reversibly tunable binding affinity is of fundamental importance in manipulating the properties and functions of supramolecular self-assembly systems and materials. Herein, for the first time, we demonstrate a unique visible-light-switchable telluro-triazole/triazolium-based chalcogen bonding (ChB) system in which the Te moieties are connected by azobenzene cores. The binding strengths between these azo-derived ChB receptors and the halide anions (Cl−, Br−) could be reversibly regulated upon irradiation by visible light of different wavelengths. The cis-bidentate ChB receptors exhibit enhanced halide anion binding ability compared to the trans-monodentate receptors. In particular, the telluro-triazolium-based ChB receptor can achieve both high and significantly photoswitchable binding affinities for halide anions, which enable it to serve as an efficient photocontrolled organocatalyst for ChB-assisted halide abstraction in a Friedel–Crafts alkylation benchmark reaction. 相似文献
2.
Mario Leclerc Robert E. Prud'homme Alain Soum Michel Fontanille 《Journal of Polymer Science.Polymer Physics》1985,23(10):2031-2041
The geometric structure of polymethylacetylene (PMA), polypentylacetylene (PPA), and poly(t-butylacetylene) (PTA) was investigated by 1H NMR, 13C NMR, and IR spectroscopies. It was shown that both NMR techniques can be used to determine the trans isomer content of PPA and PTA, whereas the 1H NMR and IR methods can be used for PMA. A calibration curve was constructed by using the 965- and 720-cm?1 bands of the IR spectrum of PPA, and could be used in future work for the same purpose if the samples had molecular weights similar to that of the one used in this study. The isomerization kinetics of PTA was investigated and cis→ trans activation energies of 88 and 121 kJ/mol were calculated in solution and in the solid state, respectively. Heat treatment of the PMA and PPA samples always leads to a cis→ trans isomerization with a 100% trans content under extreme conditions. Moreover, a cis→ trans isomerization of PTA was induced in CCl4, CDCl3, toluene, and benzene, but a trans→ cis isomerization was induced in decalin. The reversible isomerization of PTA covered a trans isomer concentration ranging form 25 to 60%. 相似文献
3.
Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by 1H NMR in CDCl3 and MeCN-d3. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability. 相似文献
4.
Host–Guest Chemistry of a Bis‐Calix[4]pyrrole Derivative Containing a trans/cis‐Switchable Azobenzene Unit with Several Aliphatic Bis‐Carboxylates 下载免费PDF全文
Grazia Cafeo Franz H. Kohnke Giovanni Mezzatesta Aldo Profumo Camillo Rosano Antonino Villari Andrew J. P. White 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(14):5323-5327
The azobenzene unit used as a photochemically and thermally switchable linker in the assembly of a bis‐calix[4]pyrrole receptor provides a means to modulate the binding of bis‐carboxylates of significant biological importance in cancer research. Conversely, the complexation of different bis‐anionic guests has significant kinetic effects on both the photochemical and thermal trans/cis isomerization of the azobenzene unit. 相似文献
5.
Coordination‐Driven Macrocyclization for Locking of Photo‐ and Thermal cis→trans Isomerization of Azobenzene 下载免费PDF全文
Dr. Masaki Yamamura Koji Yamakawa Yuki Okazaki Prof. Dr. Tatsuya Nabeshima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16258-16265
Both trans and cis isomers of azobenzene‐linked bis‐terpyridine ligand L1 were incorporated in rigid macrocycles linked by FeII(tpy)2 (tpy: terpyridine) units. The complex of the longer trans‐ L1 is dinuclear [(trans‐ L1 )2 ? FeII2], whereas the complex of the shorter cis‐ L1 is mononuclear [cis‐ L1? FeII]. The complex cis‐ L1? FeII was not only thermally stable but also photochemically inactive. These results indicate a perfectly locked state of cis‐azobenzene. The stable macrocyclic structure of cis‐ L1? FeII causes locking of the isomerization. To the best of our knowledge, this is first example of dual locking of photo‐ and thermal isomerization of cis‐azobenzene. 相似文献
6.
Neil W. Owens Adrian Lee Kirk Marat Dr. Frank Schweizer Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(40):10649-10657
The conformations of peptides and proteins are often influenced by glycans O‐linked to serine (Ser) or threonine (Thr). (2S,4R)‐4‐Hydroxyproline (Hyp), together with L ‐proline (Pro), are interesting targets for O‐glycosylation because they have a unique influence on peptide and protein conformation. In previous work we found that glycosylation of Hyp does not affect the N‐terminal amide trans/cis ratios (Ktrans/cis) or the rates of amide isomerization in model amides. The stereoisomer of Hyp—(2S,4S)‐4‐hydroxyproline (hyp)—is rarely found in nature, and has a different influence both on the conformation of the pyrrolidine ring and on Ktrans/cis. Glycans attached to hyp would be expected to be projected from the opposite face of the prolyl side chain relative to Hyp; the impact this would have on Ktrans/cis was unknown. Measurements of 3J coupling constants indicate that the glycan has little impact on the Cγ‐endo conformation produced by hyp. As a result, it was found that the D ‐galactose residue extending from a Cγ‐endo pucker affects both Ktrans/cis and the rate of isomerization, which is not found to occur when it is projected from a Cγ‐exo pucker; this reflects the different environments delineated by the proline side chain. The enthalpic contributions to the stabilization of the trans amide isomer may be due to disruption of intramolecular interactions present in hyp; the change in enthalpy is balanced by a decrease in entropy incurred upon glycosylation. Because the different stereoisomers—Hyp and hyp—project the O‐linked carbohydrates in opposite spatial orientations, these glycosylated amino acids may be useful for understanding of how the projection of a glycan from the peptide or protein backbone exerts its influence. 相似文献
7.
Georg Gescheidt Axel Lamprecht Jürgen Heinze Barbara Schuler Michael Schmittel Susanne Kiau Christoph Rüchardt 《Helvetica chimica acta》1992,75(5):1607-1612
ESR and cyclic voltammetry investigations show that isomerization of the radical cation of cis-1,1′-azonorbornane (cis- 1 ) to the trans-radical ion proceeds too fast in solution for direct investigation of the cis-radical ion even at ?78°. The facile isomerization of the radical cation is in agreement with PM 3 calculations proposing an activation barrier of only 17 kJ/mol. As a consequence, quantitative cis → trans isomerization of 1,1′-azonorbornane can effectively be accomplished by addition of catalytic amounts of one-electron oxidants. This is the first evidence for a radical-cation-catalyzed cis → trans isomerization of azo compounds. 相似文献
8.
The isomerization of cis-Pt(PPh3)2(I)(CH2P(O)(OCH3)2), 1 , was studied by an NMR technique. An Arrhenius plot for the isomerization gives an activation energy of 99.2 KJ/mol, ΔH≠ = 97 KJ/mol and ΔS≠ = ?8.3 J/mol-K. Under a CO atmosphere the cis isomer catalytically isomerized to its trans form. Free PPh3 did not catalyze the cis-trans isomerization. In the proposed isomerization mechanism the reaction goes through an intramolecular assisted phosphine dissociation, followed by dimer formation. The addition of phosphine to the dimer then completes the isomerization of the original monomer from cis to trans. 相似文献
9.
E. A. Katayev G. V. Kolesnikov V. N. Khrustalev M. Yu. Antipin R. K. Askerov A. M. Maharramov K. E. German G. A. Kirakosyan I. G. Tananaev T. V. Timofeeva 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):385-389
The synthesis and anion binding properties of a neutral macrocyclic receptor bearing H-bond donor coordination sites are described.
The anion binding studies by use of UV-vis and 99Tc NMR methods revealed that the receptor can coordinate perrhenate and pertechnetate in dimethylsulfoxide and chloroform
solutions with the relatively high binding constants, viz. log K
a > 4. The coordination mode of the perrhenate to the receptor was determined by a single-crystal X-ray diffraction analysis. 相似文献
10.
Yue Zhu Min Pu De-Cai Fang Yong-Qiang Ji Jing He David G. Evans 《Structural chemistry》2010,21(4):817-825
Abstract
The cis–trans isomerization pathways of 3,3′-azobenzene disulphonate in the S0 and T1 states are studied by DFT method at the B3LYP/6-31G(d,p) level. In the S0 state, the cis–trans isomerization concerns the complex pathway that is characterized by the inversion of one NNC angle combined with rotation around the NC bond, and the three sequential transition states are also found on the potential energy profile. Therefore, the cis–trans isomerization of 3,3′-azobenzene disulphonate can be understood in terms of a pathway involving successive rotation, inversion, and rotation processes. The energy barrier of the S0 state is 22.79 kcal mol−1. In the T1 state, the isomerization mainly concerns the rotational pathway around the NN double bond, and the two isomers are connected through only one transition state. The isomerization of the T1 state is related to a lower energy barrier, 5.02 kcal mol−1, but requires a change in spin-multiplicity. 相似文献11.
V. I. Bakhmutov V. A. Burmistrov K. K. Babievsky K. A. Kochetkov B. A. Kvasov V. M. Belikov E. I. Fedin 《Magnetic resonance in chemistry : MRC》1978,11(6):308-312
Fast Z, E-isomerization of α-nitro-β-indolylacrylates in polar solvents has been studied by dynamic 1H NMR spectroscopy. With indolylnitroacrylates having no substituents at the ring nitrogen atom, isomerization proceeds via intermediate formation of a mesomeric anion and ionization of the N? –H bond as the rate determining step. For methyl-substituted indolylnitroacrylates, no general isomerization mechanism can be suggested, and isomerization pathways depend on the structures of isomerizing species. 相似文献
12.
The rate of selenium catalyzed cis-trans isomerization of stilbene, 2-styrylfuran and 2-styryI-thiophene in decahydronaphthalene has been studied in the temperature range 170-190° by gas chromatographic analysis. Rate constants were pseudo first order and gave the following reactivity order: e(.s-stilbene < cis-2-styrylthiophene < cis-2-styrylfuran. In all cases the reaction orders with respect to selenium are temperature dependent. For catalyzed cis-stilbene isomerization the activation energy is ca. 15 kcal. mole?1 lower than for thermal isomerization. The hypothesis that cis-2-styrylfuran isomerizes through a triplet state is proposed. 相似文献
13.
Anion binding to a receptor based on stiff-stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and 1H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors. 相似文献
14.
Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br?2 · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO2H=CR'CO2H) in aqueous solution. 相似文献
15.
The equilibrium energetics and the kinetics of cis-trans isomerization of some bis(dialkylsulfide)dihaloplatinum(II) complexes have been examined by 1H-NMR. spectroscopy. The isomers are stable in chloroform but each form isomerizes to an equilibrium mixture when free dialkylsulfide is added. The cis to trans process is endothermic and the position of the equilibrium is markedly dependent on the nature of the donor atoms and of the solvent. The rate of isomerization of Pt(Me2S)2Cl2 is first order in complex and in Me2S. The isomerization proceeds by a double displacement mechanism as it is shown that the tris(dimethylsulfide)chloroplatinum(II) cation is an isolable intermediate of the reaction. When free Me2S is added to trans-Pd(Me2S)2Cl2, isomerization does not occur and one observes instead a fast ligand exchange. Its mechanism is the usual associative one for substitutions in square planar d8complexes. 相似文献
16.
Poater A Ragone F Correa A Szadkowska A Barbasiewicz M Grela K Cavallo L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14354-14364
The mechanism of the trans to cis isomerization in Ru complexes with a chelating alkylidene group has been investigated by using a combined theoretical and experimental approach. Static DFT calculations suggest that a concerted single‐step mechanism is slightly favored over a multistep mechanism, which would require dissociation of one of the ligands from the Ru center. This hypothesis is supported by analysis of the experimental kinetics of isomerization, as followed by 1H NMR spectroscopy. DFT molecular dynamics simulations revealed that the variation of geometrical parameters around the Ru center in the concerted mechanism is highly uncorrelated; the mechanism actually begins with the transformation of the square‐pyramidal trans isomer, with the Ru?CHR bond in the apical position, into a transition state that resembles a metastable square pyramidal complex with a Cl atom in the apical position. This high‐energy structure collapses into the cis isomer. Then, the influence of the N‐heterocyclic carbene ligand, the halogen, and the chelating alkylidene group on the relative stability of the cis and trans isomers, as well as on the energy barrier separating them, was investigated with static calculations. Finally, we investigated the interconversion between cis and trans isomers of the species involved in the catalytic cycle of olefin metathesis; we characterized an unprecedented square‐pyramidal metallacycle with the N‐heterocyclic carbene ligand in the apical position. Our analysis, which is relevant to the exchange of equatorial ligands in other square pyramidal complexes, presents evidence for a remarkable flexibility well beyond the simple cis–trans isomerization of these Ru complexes. 相似文献
17.
T. Lóránd F. Aradi Á. Szöllösy G. Tóth T. Kónya 《Monatshefte für Chemie / Chemical Monthly》1996,127(8-9):971-977
Summary The acid and base catalyzed isomerization of some tricyclic 2-pyrazolines with N-Carbamoyl-,N-thiocarbamoyl-and N-phenyl substituents was investigated. Starting fromcis ortrans 3-H, 3a-H diastereomers, equilibrium mixtures ofcis andtrans diastereomers were prepared which were separated and subsequently studied by1H NMR and13C NMR spectroscopy. A mechanism for the isomerization of the pyrazolines is suggested, supported by a deuterium exchange at C-3a.
Isomerisierung von einigen substituierten 4,5-Dihydropyrazolen
Zusammenfassung Die Isomerisierung einiger tricyclischer 2-Pyrazoline mit N-Carbamoyl-, N-Thiocarbamoyl-und N-Phenyl-substituenten unter saurer und basischer Katalyse wurde untersucht. Ausgehend von dencis odertrans 3-H,3a-H-Diastereomeren wurdencis- undtrans Gleichgewichtsgemische gewonnen, die getrennt und durch1H- und13C-NMR-Spektroskopie untersucht wurden. Ein Mechanismus für die Isomerisierung von Pyrazolinen wird vorgeschlagen, der durch den Deuteriumaustausch in Position 3a-C unterstützt wird.相似文献
18.
Titskii G. D. Gaidash T. S. Matvienko V. N. Matveev A. A. 《Theoretical and Experimental Chemistry》2002,38(3):179-184
Equilibrium photoisomerization of trans-DASP into cis-DASP occurs in a solution. In presence of picric and trifluoroacetic acids in acetonitrile, cis-DASP isomerizes into trans-DASPH+ cation. The reaction is inhibited by three molecules of PicOH. Acid-catalyzed mechanism of isomerization is confirmed by semiempirical calculation (PM3) of changes in standard heats of the separate steps. 相似文献
19.
Chengshuo Shen Dr. Emmanuel Anger Dr. Monika Srebro Dr. Nicolas Vanthuyne Dr. Loïc Toupet Prof. Christian Roussel Prof. Jochen Autschbach Prof. Régis Réau Dr. Jeanne Crassous 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16722-16728
Homochiral and heterochiral cis‐bis‐cycloplatinated‐[6]helicene derivatives 1 b1, 2 , as representative examples of platina[6]helicenes that share a common platinum center, have been prepared. A diastereo‐ and enantioselective synthesis, which combines CH activation and dynamic isomerization from heterochiral structure 1 b2 into homochiral structure 1 b1 , is also described. Overall, this isomerization process results in the transfer of chiral information from one helicene moiety to the other one. The chiroptical properties of homochiral (P)‐ and (M)‐ 1 b1 were greatly modified upon oxidation into their corresponding (P)‐ and (M)‐diiodo‐PtIV complexes ( 5 ). The changes were also analyzed by performing theoretical calculations. C? H activation in the synthesis of organometallic helicenes is further demonstrated by the preparation of cis‐bis‐cycloplatinated‐[8]helicene 1 c . 相似文献
20.
Jing Wu Lyle Isaacs Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11675-11680
Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the formation of purple‐colored CB[7] ? cis‐ 1? 2 H+ and CB[7] ? cis‐ 3? 2 H+ complexes, respectively. The high binding affinity and selectivity displayed by CB[7] toward 1 and 3 pays the >10 kcal mol?1 thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large pKa shifts and high pH responsiveness, which are characteristic of cucurbit[n]uril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4 – 10 . This indicator displacement assay is capable of quantifying the pseudoephedrine ( 5 ) content in Sudafed tablets over the 5–350 μM range. 相似文献