- Conductance study of binding of some Rb+ and Cs+ ions by macrocyclic polyethers in acetonitrile solution
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A conductance study of the interaction between Rb+ and Cs+ ions and 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6), dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) in acetonitrile solution has been carried out at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6 > 18C6 > DB30C10 > DB18C6 ~ DB24C8 for Rb+ ion and DC18C6 > 18C6 > DB30C10 ~ DB24C8 > DB18C6 for Cs+ ion. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The complexes with the 18-crowns are both enthalpy and entropy stabilized while, in the case of large crown ethers, the corresponding complexes are enthalpy stabilized but entropy destabilized.
- Shamsipur, Mojtaba,Saeidi, Mahboubeh
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- A Conductance Study of the Association of Alkali Cations with 1,13-Dibenzo-24-Crown-8 in Acetonitrile
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A conductance study concerning the association of Na+, K+, Rb+, and Cs+ with 1,13-dibenzo-24-crown-8 in acetonitrile has been carried out at 35, 30, 25, 20, and 15 deg C.The observed molar conductivities Λ were found to decrease significantly for mole ratios less than unity.A model involving 1:1 stoichiometry has been used to analyze the conductivity data.The stability constant, K, and the molar conductivity Λc for each 1:1 complex were determined from the conductivity data by using a nonlinear least squares curve fitting procedure.The binding sequence, based on the value of log K at 25 deg C, is found to be Rb+>Cs+>K+>Na+.Values of ΔH0 and ΔS0 are reported and their significance is discussed.
- Tawarah, K. M.,Mizyed, S. A.
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- Which One is Bulkier: The 3,5-Dimethylphenyl or the 2,6-Dimethylphenyl Group? Development of Size-Complementary Molecular and Macromolecular [2]Rotaxanes
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We developed novel size-complementary molecular and macromolecular rotaxanes using a 2,6-dimethylphenyl terminal group as the axle-end-cap group in dibenzo-24-crown-8-ether (DB24C8)-based rotaxanes, where the 2,6-dimethylphenyl group was found to be less bulky than the 3,5-dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6-dimethylphenyl group as the axle-end-cap were synthesized using unsubstituted and fluorine-substituted DB24C8. Base-induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size-complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate-determining step was that in which the wheel is getting over the end-cap group, and deslipping proceeded via a hopping-over mechanism. Finally, the present deslipping behavior was applied to a stimulus-degradable polymer as an example for the versatile utility of this concept in the context of stimulus-responsive materials.
- Sato, Hiroki,Aoki, Daisuke,Takata, Toshikazu
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- Multi-gram syntheses of four crown ethers using K+ as templating agent
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Dibenzo-30-crown-10 (DB30C10, 1c), dibenzo-24-crown-8 (DB24C8, 1a), 4-carbomethoxydibenzo-24crown-8 (1b) and a new crown ether, 4-carbomethoxydibenzo-30-crown-10 (1d), were synthesized by a simple, high yielding, three-step method. Potassium ions from the highly soluble KPF6 were employed to template the cyclization step, which resulted in very high isolated yields (80-90%).
- Wessels, Hanlie R.,Gibson, Harry W.
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- Interactions between protonated Amine, aza crown ether, and cryptand with dibenzocrown ether studied by a new spectrophotometric technique
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The stability constants for the complexation of a diprotonated diamine, a diaza crown ether, and a cryptand with dibenzo-18-crown-6 and dibenzo-24-crown-8, have been studied in aqueous solution using a new spectrophotometric technique. Because of the complex formation, the solubility of the dibenzocrown ethers increases. Complex formation is possible between diamines and dibenzocrown ethers with both 1:1 and 2:1 stoichiometry. However, experimental data are insufficient to decide on the actual stoichiometry of the complexes formed. By computing the stability constants and comparing them with the corresponding results for monoamines, it is possible to decide on the actual stoichiometry of the complexes. Under the experimental conditions only 1:1 complexes with diamines are formed.
- Buschmann,Cleve,Mutihac,Schollmeyer
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- Is the tert-butyl group bulky enough to end-cap a pseudorotaxane with a 24-crown-8-ether wheel?
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(Chemical equation presented) Although rotaxane chemists have long believed that the tert-butyl group is bulkier than the cavity of dibenzo-24-crown-8- ether (DB24C8), it is essentially smaller than the cavity of DB24C8. The tert-butyl (or 4-tert-butylphenyl) group can actually function as an end-cap of DB24C8-based rotaxanes when the intercomponent interaction is effectively operative. When such attractive interaction is removed, deslippage occurs.
- Tachibana, Yuya,Kihara, Nobuhiro,Furusho, Yoshio,Takata, Toshikazu
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- Disaggregation reaction of [2]Pseudorotaxanes composed of dibenzo[24]crown-8 and dialkylammonium having isopropyl end groups
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[2]Pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and dialkylammonium having isopropyl end groups are converted into the component molecules in C6D6 solution containing PF6 - anion.
- Suzaki, Yuji,Takagi, Atsuko,Osakada, Kohtaro
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- Discrepancy Regarding the Dethreading of a Dibenzo-24-crown-8 Macrocycle through a Perfluorobutyl End in [2]Pseudorotaxanes
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Here are reported the synthesis and characterization of four new dibenzo-24-crown-8 (DB24C8)-based ammonium-containing pseudorotaxanes, for which one of the two encircled axle's extremities consists of a perfluorobutyl moiety. The subsequent dethreading of the DB24C8 over the perfluorobutyl extremity was studied. Although the perfluorobutyl extremity of an ammonium-containing axle did not allow threading of DB24C8, dethreading of a perfluorobutyl extremity-containing pseudorotaxane was possible and its rate depended on both the strength of the template-to-DB24C8 complex and the nature of the axle. In particular, dethreading process may be assisted by the presence, in the threaded axle, of a poor secondary site of interaction for the DB24C8 and this assistance proved to be higher when this site is close to the DB24C8.
- Coutrot, Frédéric,Gauthier, Maxime
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supporting information
(2021/10/23)
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- Synthesis of Isomeric Dinitro and Diamino Derivatives of Polycyclic Crown Ethers: Dibenzo-18-crown-6 and Dibenzo-24-crown-8
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Specific features of the synthesis of polycyclic crown ethers dibenzo-18-crown-6 and dibenzo-24-crown-8 and their dinitro and diamino derivatives have been studied. A mixture of isomers of dibenzocrown ether derivatives was obtained and separated. The spectral and thermal characteristics of the synthesized compounds and the kinetics of synthesis of dibenzo-24-crown-8 by the two-component condensation of pyrocatechol with 1-chloro-2-[2-(2-chloroethoxy)ethoxy]ethane in an alcoholic medium in the presence of a KOH template agent were studied.
- Glushko,Sadovskaya, N. Yu.,Blokhina,Zhila, M. Yu.,Belus’,Vashchenkova,Shmelevaa
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p. 1595 - 1600
(2018/11/10)
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- Directional molecular transportation based on a catalytic stopper-leaving rotaxane system
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Ratchet mechanism has proved to be a key principle in designing molecular motors and machines that exploit random thermal fluctuations for directional motion with energy input. To integrate ratchet mechanism into artificial systems, precise molecular design is a prerequisite to control the pathway of relative motion between their subcomponents, which is still a formidable challenge. Herein, we report a straightforward method to control the transportation barrier of a macrocycle by selectively detaching one of the two stoppers using a novel DBU-catalyzed stopperleaving reaction in a rotaxane system. The macrocycle was first allowed to thread onto a semidumbbell axle from the open end and subsequently thermodynamically captured into a nonsymmetrical rotaxane. Then, it was driven energetically uphill until it reached a kinetically trapped state by destroying its interaction with ammonium site, and was finally quantitatively released from the other end when the corresponding stopper barrier was removed. Although the directional transportation at the present system was achieved by discrete chemical reactions for the sake of higher transportation efficiency, it represents a new molecular transportation model by the strategy of using stopper-leavable rotaxane.
- Meng, Zheng,Xiang, Jun-Feng,Chen, Chuan-Feng
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p. 5652 - 5658
(2016/05/24)
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- Neutralization of a sec-ammonium group unusually stabilized by the "rotaxane Effect": Synthesis, structure, and dynamic nature of a "free" sec-amine/crown ether-type rotaxane
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A fifteen-year riddle has been settled: neutralization, the most popular chemical event, of a crown ether/sec-ammonium salt-type rotaxane has been achieved and a completely nonionic crown ether/sec-amine-type rotaxane isolated. A [2]rotaxane was prepared as a typical substrate from a mixture of dibenzo[24]crown-8 ether (DB24C8) and sec-ammonium hexafluorophosphate (PF 6) with a terminal hydroxy group through end-capping with 3,5-dimethylbenzoic anhydride in the presence of tributylphosphane as a catalyst in 90 % yield. A couple of approaches to the neutralization of the ammonium rotaxane were investigated to isolate the free sec-amine-type rotaxane by decreasing the degree of thermodynamic and kinetic stabilities. One approach was the counteranion-exchange method in which the soft counterion PF 6- was replaced with the fluoride anion by mixing with tetrabutylammonium fluoride, thus decreasing the cationic character of the ammonium moiety. Subsequent simple washing with a base allowed us to isolate the free sec-amine-type rotaxane in a quantitative yield. The other approach was a synthesis based on a protection/deprotection protocol. The acylation of the sec-ammonium moiety with 2,2,2-trichloroethyl chloroformate gave an N-carbamated rotaxane that could be deprotected by treating with zinc in acetic acid to afford the corresponding free sec-amine-type rotaxane in a quantitative yield. The structure of the free sec-amine-type rotaxane was fully confirmed by spectral and analytical data. The generality of the counteranion-exchange method was also confirmed through the neutralization of a bisammonium-type [3]rotaxane. The mechanism was studied from the proposed potential-energy diagram of the rotaxanes with special emphasis on the role of the PF 6- counterion. Neutral and free: The neutralization of the ammonium group of crown ether/sec-ammonium salt-type rotaxanes is a simple, yet important issue, which had not been solved to date. Neutral rotaxanes had not been isolated because of their unusual stability; however, the successful synthesis of free amine-type rotaxanes has now been achieved. The key to canceling this strong stabilization is the construction of a multiple equilibrium system and the successful removal of the conjugate acid from the reaction system (see scheme). Copyright
- Nakazono, Kazuko,Takata, Toshikazu
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supporting information; experimental part
p. 13783 - 13794
(2011/02/28)
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- Effect of pressure on [2]pseudorotaxane formation and decomplexation and their corresponding activation volumes
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(Figure presented) In this study, we investigated the effect of pressure on the formation and decomplexation of [2]pseudorotaxanes. High pressure accelerated the formation of [2]pseudorotaxanes in an aprotic nonpolar solvent (CDCl3/CD3CN) via the slipping approach when using two crown ether/secondary ammonium salt systems: dibenzo[24]crown-8/ bis(cyclohexylmethyl)ammonium salt (1a/2a) and tetrabenzo[24]crown-8/ dibenzylammonium salt (1b/2b). The influence of pressure on the rate constants for the formation of the [2]pseudorotaxanes 3a and 3b revealed activation volumes (ΔV-) of -2.5 and -4.6 cm3 mol-1, respectively, at 303 K and zero pressure. We also investigated the effect of pressure on the decomplexation of the [2]pseudorotaxanes 3a and 3b in a polar solvent (DMSO-d6/CDCl3), obtaining activation volumes of -0.9 and -0.4 cm3 mol-1, respectively, at 303 K and zero pressure. Moreover, we calculated the activation parameters for the decomplexation processes on the basis of transition state theory at each pressure.
- Tokunaga, Yuji,Wakamatsu, Nanae,Ohiwa, Norihiro,Kimizuka, Osamu,Ohbayashi, Akihiro,Akasaka, Koichiro,Saeki, Susumu,Hisada, Kenji,Goda, Tatsuhiro,Shimomura, Youji
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supporting information; experimental part
p. 4950 - 4956
(2010/10/19)
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- Using photoresponsive end-closing and end-opening reactions for the synthesis and disassembly of [2]rotaxanes: Implications for dynamic covalent chemistry
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We have synthesized two [2]rotaxanes, each possessing a (Z)-α-methylstilbene unit as one of its stoppers, in good yield through the photoisomerization of terminal (E)-α-methylstilbene units of dialkylammonium salts in the presence of the crown ether diben
- Tokunaga, Yuji,Akasaka, Koichiro,Hashimoto, Nobuharu,Yamanaka, Shou,Hisada, Kenji,Shimomura, Youji,Kakuchi, Suzuka
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body text
p. 2374 - 2379
(2009/08/08)
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- Quantitative active transport in [2]rotaxane using a one-shot acylation reaction toward the linear molecular motor
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(Figure Presented) A rotaxane consisting of a crown ether wheel and a secondary ammonium salt axle, on which a neopentyl-type end-cap was placed close to the ammonium moiety, was prepared. When the rotaxane was treated by excess triethylamine, the wheel component thermodynamically moved over the proximate neopentyl group to deconstruct the interlocked structure. The wheel component in the rotaxane, however, quantitatively moved against the proximate end-cap by the action of trifluoroacetic anhydride in the presence of excess triethylamine. This motion, which was driven by the simple one-shot acylation reaction, can be referred as the active transport. When the distant end-cap is of the neopentyl-type, the axle can be thermally dethreaded from the distant end-cap after the acylative transport. The series of the wheel movement controlled by the neopentyl group can be the basic motion of the unidirectional linear molecular motor.
- Makita, Yoshimasa,Kihara, Nobuhiro,Takata, Toshikazu
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supporting information; experimental part
p. 9245 - 9250
(2009/04/11)
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- Do dibenzo[22-30]crown ethers bind secondary ammonium ions to form pseudorotaxanes?
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In this study, we synthesized dibenzo[22-30]crown ethers and dumbbell-like secondary ammonium salts having stoppers of varying bulk. These crown ethers formed pseudorotaxanes with the ammonium ions in solution and in the gas phase, as evidenced using NMR spectroscopy and MS/MS spectrometry, respectively. The association constants in solution were obtained through regulation of the association and dissociation rates by varying the nature of the stopper groups of the dumbbell-like ammonium ions. The [25]- and [26]crown ether/ isopropylphenyl group, the [27]- and [30]crown ether/tert-butylphenyl group, and the [22]- and [23]crown ether/furyl group were matched pairs. 1 HNMR spectra of mixtures (CDCI3/CD3CN) of the crown ethers and their matched ammonium salts indicated the presence of three sets of signals in solution: those of the crown ether, the ammonium salt, and their pseudorotaxane. Integration of pertinent signals allowed the association constants of pseudorotaxanes to be determined readily. Among the [22-30]crown ethers, the highest value of the association constant was that for the [24]crown ether/dibenzylammoniumion system; the [25-30]crown ether/ammonium ion systems exhibited moderate values of their association constants [Kexp - 35-114 M-1 when using (ArCH2)2NH 2+PF6- as the ammonium salt at 27 °C; Kexp = 21 M-1 when using (ArCH2) 2NH2+TsO- at 27 °C]. The [22]- and [23]crown ethers interacted weakly [Kexp = 6-14 M-1 when using (ArCH2)2NH2+TsO - at27°C].
- Tokunaga, Yuji,Yoshioka, Megumi,Nakamura, Tatsuya,Goda, Tatsuhiro,Nakata, Ryuji,Kakuchi, Suzuka,Shimomura, Youji
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experimental part
p. 1377 - 1382
(2009/06/20)
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- Two new "onium" fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: Structures and spectroscopic properties
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Two novel compounds, (L1H)2[SiF6] ·2H2O (1) and (L2H)2[SiF 5(H2O)]2·3H2O (2), resulting from the reactions of H2SiF6 with 4′-aminobenzo-12- crown-4 (L1) and monoaza-12-crown-4 (L2), respectively, were studied by X-ray diffraction and characterised by IR and 19F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L1 and secondary amine group incorporated into the macrocycle L2. The structure of 1 is composed of [SiF6]2- centrosymmetric anions, N-protonated cations (L1H)+, and two water molecules, all components being bound in the layer through a system of NH...F, NH...O and OH...F hydrogen bonds. The [SiF 6]2- anions and water molecules are assembled into inorganic negatively-charged layers via OH...F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF 5(H2O)]-, the labile product of hydrolytic transformations of the [SiF6]2- anion in an aqueous solution. The components of 2, i.e., [SiF5(H2O)] -, (L2H)+, and water molecules, are linked by a system of NH...F, NH...O, OH...F, OH...O hydrogen bonds. In a way similar to 1, the [SiF5(H2O)]- anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH...F and OH...O interactions. The Royal Society of Chemistry.
- Gelmboldt, Vladimir O.,Ganin, Eduard V.,Fonari, Marina S.,Simonov, Yurii A.,Koroeva, Larisa V.,Ennan, Alim A.,Basok, Stepan S.,Shova, Sergiu,Kaehlig, Hanspeter,Arion, Vladimir B.,Keppler, Bernhard K.
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p. 2915 - 2924
(2008/02/10)
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- A rotaxane synthesis based on stilbene photoisomerization. A photoswitchable catch and release process
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A [2]rotaxane, having (Z)-α-methylstilbene as a stopper, is (1) synthesized in good yield by using a (E)- to (Z)-stilbene photoisomerization process, and (2) dissociated by reverse photoisomerization from (Z)- to (E)-stilbene.
- Tokunaga, Yuji,Akasaka, Koichiro,Hisada, Kenji,Shimomura, Youji,Kakuchi, Suzuka
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p. 2250 - 2251
(2007/10/03)
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- Supramolecular daisy chains
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Two series of self-complementary daisy chain monomers, in which a secondary ammonium ion-containing arm is grafted onto a macrocycle with either a [24]- or [25]crown-8 constitution, have been synthesized. In the solid- and 'gas'-phases, the parent [24]crown-8-based monomer forms dimeric superstructures, as revealed by X-ray crystallography and mass spectrometry, respectively. Elucidation of the complicated solution-phase behavior of this compound was facilitated by the synthesis and study of both deuterated, and fluorinated, analogues. These investigations revealed that the cyclic dimeric superstructure also dominates in solution, except when extremes of either concentration (low), temperature (high), or solvent polarity (highly polar, e.g., dimethyl sulfoxide) are employed. Whereas, upon aggregation, the [24]crown-8-based daisy chain monomers have the capacity to form stereoisomeric superstructures further complicating the study of this series of compounds. The assembly of [25]crown-8-based monomers gives only achiral superstructures. The weaker association exhibited between secondary dialkylammonium ions and crown ethers with a [25]crown-8 constitution, however, resulted in limited oligomerization-only dimeric and trimeric superstructures were formed at experimentally attainable concentrations-of [25]crown-8-based daisy chain monomers.
- Cantrill,Youn,Stoddart,Williams
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p. 6857 - 6872
(2007/10/03)
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- The self-assembly of fullerene-containing [2]pseudorotaxanes: Formation of a supramolecular C60 dimer
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With its unique chemical and physical properties. C60 is an attractive molecule to be incorporated into molecular assemblies and supramolecular arrays. This paper reports the syntheses of a C60 derivative with the macrocyclic polyether dibenzo-24-crown-8 (DB24C8) attached to the carbon sphere and of a C60 adduct with a dibenzylammonium salt covalently bonded to the carbon allotrope. The C60 DB24C8 conjugate forms a stable, pseudorotaxane-like 1 : 1 complex (ΔGo = -16.6 kJ mol-1. T = 298 K, CDCl3-CD3CN 1 : 1) with dibenzylammonium hexafluorophosphate. Evidence for this superstructure was provided by 1H NMR spectroscopic studies in solution and by mass spectrometric investigations in the gas phase. Equally, the C60 dibenzylammonium conjugate threads through the cavity of DB24C8 to form a 1 : 1 complex with a pseudorotaxane-like geometry (ΔGo = -23.3 kJ mol-1, CDCl3). Furthermore, the C60 DB24C8 adduct and the C60 dibenzylammonium conjugate interact with each other by means of hydrogen bonding and ion-dipole interactions to form the first supramolecular C60 dimer (ΔGo = -17.0 kJ mol-1, CDCl3-CD3CN 90 : 10). In all three cases, the dibenzylammonium component is threaded through the cavity of the crown ether macrocycle. When DB24C8 is complexed to the C60 dibenzylammonium conjugate, the luminescence associated with the catechol rings of the crown ether is partially quenched upon complex formation. We have profited from this special feature to monitor reversible, acid-base induced dethreading/rethreading processes.
- Diederich, Francois,Echegoyen, Luis,Gomez-Lopez, Marcos,Kessinger, Roland,Stoddart, J. Fraser
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p. 1577 - 1586
(2007/10/03)
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- An Improved Method for Preparing Dibenzo Crown Ethers
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In synthesis of symmetrical and unsymmetrical dibenzo crown ethers, the use of dimethyl sulfoxide as a solvent in cyclization allows an increase in the yields, a significant reduction in the reaction time, and simplification of refining.
- Kotlyar,Gorodnyuk,Grigorash,Chuprin
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p. 1135 - 1138
(2007/10/03)
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- Dialkylammonium-Ionen/Kronenether-Komplexe: Vorlaeufer einer neuen Familie "mechanisch" verknuepfter Molekuele
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Keywords: Einschlusskomplexe; Kronenether; Rotaxane; Selbstorganisation; Wasserstoffbruecken
- Ashton, Peter R.,Campbell, Paul J.,Chrystal, Ewan J. T.,Glink, Peter T.,Menzer, Stephan,et al.
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p. 1997 - 2001
(2007/10/03)
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- 13-AMINO-1,4,7,10-BENZOTETRAOXA-15-CYCLODODECENE
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A separation was performed for benzo-12-crown-4 and dibenzo-24-crown-8 obtained as a mixture by the reaction of pyrocatechol with 1,8-dichloro-3,6-dioxaoctane.Nitro and amino derivatives of benzo-12-crown-4 were obtained.
- Markovich, I. S.,Filyagina, N. A.,Blokhina, L. I.,Dziomko, V. M.,Poponova, R. V.,et al.
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p. 147 - 148
(2007/10/02)
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- Photoresponsive Crown Ethers. 4. Influence of Alkali Metal Cations on Photoisomerization and Thermal Izomerization of Azobis(benzocrown ether)s
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Five photoresponsive azobis(benzocrown ether)s 1(4,4), 1(5,5), 1(6,6), 2(5,5) and 2(6,6), were synthesized, where numbers in parentheses denote the number of oxygens in benzocrown ethers, and crown series 2 have two tert-butyl groups in the 2 and 2' position of the azo linkage.We have found that (i) in the presence of alkali metal cations, the concentration of cis isomers (cis percent) under the photostationary state is enhanced and the rate of thermal cis-to-trans isomerization (k) is supressed, the optima cis-1(5,5) and cis-1(6,6) being observed for Rb+ and Cs+, respectively, (ii) Rb+ and Cs+ are extracted most efficiently from an aqueous solution to an organic phase (o-dichlorobenzene) with cis-1(5,5) and cis-1(6,6), respectively, (iii) cis percent and k of 2(5,5) and 2(6,6) are affected by alkyli metal cations smaller than those of corresponding 1(5,5) and 1(6,6), and (iv) cis percent and k of 1(4,4) are less affected by added alkali metal cations and the extractability is very low.The increase in cis percent and the supression of the thermal isomerization rate are rationalized in terms of the "tying effect" of complexed cations requiring the additional energy to disrupt the crown-cation interaction.The correlation of the extractability with cis percent and k implies that alkali metal cations are extracted under photoirradiation as intramolecular 1:2 cation/crown complexes and the ion selectivity is associated with the fitness between the ion size and the size of the spatial cavity provided by two crown ethers of cis form.The ion selectivity suggests (i) the cavity size of cis-1(6,6) is greater than that of cis-(5,5) and (ii) the cavity sizes of crown series 2 are smaller than those of crown series 1 probably owing to the steric repulsion of the tert-butyl groups.Hence, the ion selectivity in the photocontrolled solvent extraction is effected by the crown ring size and the steric crowding around the azo linkage.
- Shinkai, Seiji,Ogawa, Toshiyuki,Kusano, Yumiko,Manabe, Osamu,Kikukawa, Kiyoshi,et al.
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p. 1960 - 1967
(2007/10/02)
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