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1.
We synthesized and characterized a series of oligo(phenyl-amide-triazole)s that can fold into a helical conformation guided by halide ions. Their binding models and affinities are highly dependent on the length of the foldamer, media and the inducing capability of halide ions. The short foldamer with one helical turn shows a 1:1 binding stoichiometry to all halides, while the longer foldamer with two or three helical turns in principle can form 1:2 complexes with chloride anions even bromide anions with an enhancement on binding affinities. A result of quantitative NOE calculations imply that the longer foldamer should increase its helical pitch so as to release the electrostatic repulsion between halide ions. 相似文献
2.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(24):6927-6931
The development of foldamer‐based receptors is driven by the design of monomers with specific properties. Herein, we introduce a pyridazine‐pyridine‐pyridazine diacid monomer and its incorporation into helical aromatic oligoamide foldamer containers. This monomer codes for a wide helix diameter and can sequester metal ions on the inner wall of the helix cavity. Crystallographic studies and NMR titrations show that part of the metal coordination sphere remains available and may then promote the binding of a guest within the cavity. In addition to metal coordination, binding of the guest is assisted by cooperative interactions with the helix host, thereby resulting in significant enhancements depending on the foldamer sequence, and in slow guest capture and release on the NMR time scale. In the absence of metal ions, the pyridazine‐pyridine‐pyridazine monomer promotes an extended conformation of the foldamer that results in aggregation, including the formation of an intertwined duplex. 相似文献
3.
Folding‐Induced Modulation of Excited‐State Dynamics in an Oligophenylene–Ethynylene‐Tethered Spiral Perylene Bisimide Aggregate 下载免费PDF全文
Minjung Son Benjamin Fimmel Dr. Volker Dehm Prof. Dr. Frank Würthner Prof. Dr. Dongho Kim 《Chemphyschem》2015,16(8):1757-1767
The excited‐state photophysical behavior of a spiral perylene bisimide (PBI) folda‐octamer ( F8 ) tethered to an oligophenylene–ethynylene scaffold is comprehensively investigated. Solvent‐dependent UV/Vis and fluorescence studies reveal that the degree of folding in this foldamer is extremely sensitive to the solvent, thus giving rise to an extended conformation in CHCl3 and a folded helical aggregate in methylcyclohexane (MCH). The exciton‐deactivation dynamics are largely governed by the supramolecular structure of F8 . Femtosecond transient absorption (TA) in the near‐infrared region indicates a photoinduced electron‐transfer process from the backbone to the PBI core in the extended conformation, whereas excitation power‐ and polarization‐dependent TA measurements combined with computational modeling showed that excitation energy transfer between the unit PBI chromophores is the major deactivation pathway in the folded counterpart. 相似文献
4.
Base‐Free Non‐Noble‐Metal‐Catalyzed Hydrogen Generation from Formic Acid: Scope and Mechanistic Insights 下载免费PDF全文
Dörthe Mellmann Enrico Barsch Prof. Dr. Matthias Bauer Dr. Kathleen Grabow Dr. Albert Boddien Anja Kammer Peter Sponholz Dr. Ursula Bentrup Dr. Ralf Jackstell Dr. Henrik Junge Prof. Dr. Gábor Laurenczy Prof. Dr. Ralf Ludwig Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13589-13602
The iron‐catalyzed dehydrogenation of formic acid has been studied both experimentally and mechanistically. The most active catalysts were generated in situ from cationic FeII/FeIII precursors and tris[2‐(diphenylphosphino)ethyl]phosphine ( 1 , PP3). In contrast to most known noble‐metal catalysts used for this transformation, no additional base was necessary. The activity of the iron catalyst depended highly on the solvent used, the presence of halide ions, the water content, and the ligand‐to‐metal ratio. The optimal catalytic performance was achieved by using [FeH(PP3)]BF4/PP3 in propylene carbonate in the presence of traces of water. With the exception of fluoride, the presence of halide ions in solution inhibited the catalytic activity. IR, Raman, UV/Vis, and EXAFS/XANES analyses gave detailed insights into the mechanism of hydrogen generation from formic acid at low temperature, supported by DFT calculations. In situ transmission FTIR measurements revealed the formation of an active iron formate species by the band observed at 1543 cm?1, which could be correlated with the evolution of gas. This active species was deactivated in the presence of chloride ions due to the formation of a chloro species (UV/Vis, Raman, IR, and XAS). In addition, XAS measurements demonstrated the importance of the solvent for the coordination of the PP3 ligand. 相似文献
5.
Kaisa Helttunen Riia Annala Aku Suhonen Juho Iloniemi Elina Kalenius Gemma Aragay Pablo Ballester Heikki M. Tuononen Maija Nissinen 《化学:亚洲杂志》2019,14(5):647-654
The anion‐binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1H NMR spectra of the foldamers in [D6]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the release of ordered solvent molecules solvating the free foldamer and the anion to the bulk solution upon complex formation. The introduction of electron‐withdrawing substituents in foldamers 2 and 3 had only a slight effect on the thermodynamic constants for chloride binding compared to the parent receptor. Remarkably, the binding of chloride to foldamer 3 not only produced the expected 1:1 complex but also open aggregates with 1:2 (host:anion) stoichiometry. 相似文献
6.
Ionic Liquid‐Carbon Nanotube Modified Screen‐Printed Electrodes and Their Potential for Adsorptive Stripping Voltammetry 下载免费PDF全文
Compared with paraffin oil, the use of ionic liquids as a binder in carbon paste type electrodes was shown to greatly enhance the accumulation of analytes, as illustrated with 17α‐ethynylestradiol as a model. The ionic “liquid” n‐octyl‐pyridinium hexafluorophosphate [C8py][PF6] was most efficient among several ionic liquids investigated. Such preconcentration allowed a [C8py][PF6]‐multiwalled carbon nanotubes (MWCNTs) (95 : 5 w/w) composite electrode to be useful for adsorptive stripping voltammetry. Screen‐printed electrodes modified with [C8py][PF6]‐MWCNTs were developed and were able to achieve high sensitivity during adsorptive stripping voltammetric measurements under optimised conditions. 相似文献
7.
Reaction of copper halides CuX (X=Cl, Br, I) with tri(2‐pyridylmethyl)amine) (TPMA) in THF under N2 affords a series of monomeric copper(I) complexes CuX(TPMA) (X=Cl ( 1 ), Br ( 2 ) and I ( 3 )). Treatment of [CuCl(TPMA)] ( 1 ) with 0.5 equivalent of 1,4‐diisocyanobenzene following by equimolar amount of NaBF4 affords a novel binuclear complex [(TPMA)Cu(μ‐1,4‐CNC6H4NC)Cu(TPMA)](BF4)2 ( 4 ). The copper(I) halide TPMA complexes show interesting fluxional behaviors in temperature dependence in the 1H NMR spectrum that can be explained by the dissociation and reassociation of the pyridyl group and alkylamine nitrogen of TPMA ligand. The crystal structures of 1 , 3 and 4 are determined by an X‐ray diffractometer. Complexes 1 and 3 are distorted tetrahedral coordinates with strong bonding between three pyridyl N atoms and the corresponding halide donor. Crystallographic results of 4 clearly indicates two Cu(I) ions are bridged by 1,4‐diisocyanobenzene, forming a centro‐symmetrical homobinuclear complex with a “dangling” uncoordinated pyridyl group. 相似文献
8.
Ming‐Sheng Hsu Yi‐Wei Cao Hsuang‐Wen Wang Ya‐Sin Pan Bo‐Hong Lee Cheng‐Liang Huang Prof. 《Chemphyschem》2010,11(8):1742-1748
Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl?, Br?, and I? are about 3×10?4 M , 1×10?6 M , and 1.5×10?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates. 相似文献
9.
Huiqi Zhang Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4882-4894
The controlled atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) catalyzed by iron halide/N‐(n‐hexyl)‐2‐pyridylmethanimine (NHPMI) is described. The ethyl 2‐bromoisobutyrate (EBIB)‐initiated ATRP with [MMA]0/[EBIB]0/[iron halide]0/[NHPMI]0 = 150/1/1/2 was better controlled in 2‐butanone than in p‐xylene at 90 °C. Initially added iron(III) halide improved the controllability of the reactions in terms of molecular weight control. The p‐toluenesulfonyl chloride (TsC1)‐initiated ATRP were uncontrolled with [MMA]0/[TsC1]0/[iron halide]0/[NHPMI]0 = 150/1/1/2 in 2‐butanone at 90 °C. In contrast to the EBIB‐initiated system, the initially added iron(III) halide greatly decreased the controllability of the TsC1‐initiated ATRP. The ration of iron halide to NHPMI significantly influenced the controllability of both EBIB and TsC1‐initiated ATRP systems. The ATRP with [MMA]0/[initiator]0/[iron halide]0/[NHPMI]0 = 150/1//1/2 provided polymers with PDIs ≥ 1.57, whereas those with [iron halide]0/[NHPMI]0 = 1 resulted in polymers with PDIs as low as 1.35. Moreover, polymers with PDIs of approximately 1.25 were obtained after their precipitation from acidified methanol. The high functionality of the halide end group in the obtained polymer was confirmed by both 1H NMR and a chain‐extenstion reaction. Cyclic voltammetry was utilized to explain the differing catalytic behaviors of the in situ‐formed complexes by iron halide and NHPMI with different molar ratios. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4882–4894, 2004 相似文献
10.
Sung Beom Seo Seungwon Lee Hae‐Geun Jeon Kyu‐Sung Jeong 《Angewandte Chemie (International ed. in English)》2020,59(26):10441-10445
As a synthetic model for intra‐protein interactions that reinforce binding affinities between proteins and ligands, the energetic interplay of binding and folding was investigated using foldamer‐based receptors capable of adopting helical structures. The receptors were designed to have identical hydrogen‐bonding sites for anion binding but different aryl appendages that simply provide additional π‐stacking within the helical backbones without direct interactions with the bound anions. In particular, the presence of electron‐deficient aryl appendages led to dramatic enhancements in the association constant between the receptor and chloride or nitrate ions, by up to three orders of magnitude. Extended stacking within the receptor contributes to the stabilization of the entire folding structure of complexes, thereby enhancing binding affinities. 相似文献
11.
Bappaditya Gole Brice Kauffmann Victor Maurizot Ivan Huc Yann Ferrand 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(24):8147-8151
An aromatic oligoamide sequence composed of a light‐responsive diazaanthracene‐based aromatic β‐sheet flanked by two variable diameter helical segments was prepared. Structural investigations revealed that such oligomers adopt two distinct conformations: a canonical symmetrical conformation with the two helices stacked above and below the sheet, and an unanticipated unsymmetrical conformation in which one helix has flipped to directly stack with the first helix. Photoirradiation of the foldamer led to the quantitative, and thermally reversible, formation of a single photoproduct resulting from the [4+4] cycloaddition of two diazaanthracenes within the aromatic β‐sheet. NMR and crystallographic studies revealed a parallel arrangement of the diazaanthracene photoproduct and a complete conversion into a symmetrical conformation requiring a rearrangement of all unsymmetrical conformers. These results highlight the potential of foldamers, with structures more complex than isolated helices, for the design of photoswitches showing nontrivial nanometer scale shape changes. 相似文献
12.
[Ph3C][B(C6F5)4]: A Highly Efficient Metal‐Free Single‐Component Initiator for the Helical‐Sense‐Selective Cationic Copolymerization of Chiral Aryl Isocyanides and Achiral Aryl Isocyanides 下载免费PDF全文
Dr. Xinwen Yan Prof. Shaowen Zhang Dr. Pengfei Zhang Dr. Xiaolu Wu An Liu Ge Guo Prof. Yuping Dong Prof. Xiaofang Li 《Angewandte Chemie (International ed. in English)》2018,57(29):8947-8952
Commercially available [Ph3C][B(C6F5)4] served as a highly efficient metal‐free and single‐component initiator not only for the carbocationic polymerization of polar and bulky aryl isocyanides with extremely high activity up to 1.2×107 g of polymer/(molcat. h), but also for the helical‐sense‐selective polymerization of chiral aryl isocyanides and copolymerization with achiral aryl isocyanides to afford high‐molecular‐weight functional poly(aryl isocyanide)s with good solubility as well as AIE characteristics and/or a single‐handed helical conformation. 相似文献
13.
Zulfiqar Majeed William R. McWhinnie Philip R. Lowe 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):e105-e106
The title selenenyl halide complex, 3‐iodo‐2‐phenyl‐3H‐3‐selenaindazole, C12H9IN2Se, has an almost planar conformation and a nearly ideal T‐shape for the Se(INC) moiety [Se—I 2.8122 (12), Se—C 1.881 (7) and Se—N2 2.051 (6) Å; C—Se—N 79.6 (3), C—Se—I 96.8 (2) and N—Se—I 176.17 (17)°]. This arrangement, together with the two selenium lone pairs, leads to a distorted trigonal‐bipyrimidal geometry about the Se atom. Intermolecular interactions are largely limited to stacking forces. 相似文献
14.
In‐Won Park Dr. Jaeduk Yoo Dr. Suman Adhikari Jung Su Park Prof. Jonathan L. Sessler Prof. Chang‐Hee Lee 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):15073-15078
A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl3. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li+, Na+, K+, Cs+, Mg2+, and Ca2+; studied as their perchlorate salts in CD3CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]? (preformed as the tetrabutylammonium (TBA+) complex), little evidence of interaction with the K+ ion was seen. In contrast, when this same complex (i.e., [ 1? F]? as the TBA+ salt) was treated with the Li+ or Na+ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li+, Na+, and K+, treating complex [ 1? F]? with the Cs+ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs+ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]?. In this case, no appreciable interaction was observed with Na+ or K+. In addition, treating [ 1? Cl]? with Li+ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H2O)]2 in which two Li+ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]?, exposure of [ 1? Cl]? to the Cs+ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts. 相似文献
15.
Lihong Huang Jun Hu Le Lang Xiuli Zhuang Xuesi Chen Yen Wei Xiabin Jing 《Macromolecular rapid communications》2008,29(14):1242-1247
The amphiphilic PEG1 500‐b‐EM AP‐b‐PEG1 500 (EM PAP) triblock copolymer of poly(ethylene glycol) (PEG) and emeraldine aniline‐pentamer (EM AP) in its concentrated solution can self‐assemble into a special shape like “sandglass”, as observed by transmission electron microscopy (TEM), field emission scanning electron microscopy (ESEM) and atomic force microscopy (AFM). This “sandglass”‐shaped assembly is composed of several “rods” aggregated in the middle, with every “rod” being about 8 µm in length and 300 nm in diameter. We conclude that the special “sandglass”‐shaped assembly may come into being because of the inducement effect of the crystallization of EM AP segments, by studying electron diffraction (ED) results and wide‐angle X‐ray diffusion (WAXD) characterization of the EM PAP triblock copolymer.
16.
Three aza‐aromatic base adducts of cadmium(II) furoyltrifluoroacetonate, [Cd(4,4′‐bpy)(ftfa)2]n ( 1 ), [Cd(2,2′‐bpy)(ftfa)2] ( 2 ) and [Cd(dmp)(ftfa)2] ( 3 ) (“4,4′‐bpy”, “2,2′‐bpy”, “dmp” and “ftfa” are the abbreviations of 4,4′‐bipyridine, 2,2′‐bipyridine, 2,9‐dimethyl‐1,10‐phenanthroline and furoyltrifluoroacetonate, respectively) have been synthesized and characterized by elemental analysis and IR, 1H NMR and 13C NMR spectroscopy and studied by thermal as well as X‐ray crystallography. The single‐crystal structure of these complexes shows that the coordination number of the CdII ions are six with two N‐donor atoms from aza‐aromatic base ligands and four O‐donors from two the furoyltrifluoroacetonates. The supramolecular features in these complexes are guided/controlled by weak directional intermolecular interactions. 相似文献
17.
Dr. Liam Byrne Dr. Jordi Solà Dr. Thomas Boddaert Dr. Tommaso Marcelli Dr. Ralph W. Adams Prof. Gareth A. Morris Prof. Jonathan Clayden 《Angewandte Chemie (International ed. in English)》2014,53(1):151-155
An N‐terminal L ‐α‐methylvaline dimer induces complete conformational control over the screw sense of an otherwise achiral helical peptide foldamer formed from the achiral quaternary amino acids Aib and Ac6c. The persistent right‐handed screw‐sense preference of the helix enables remote reactive sites to fall under the influence of the terminal chiral residues, and permits diastereoselective reactions such as alkene hydrogenation or iminium ion addition to take place with 1,16‐, 1,31‐, 1,46‐ and even 1,61‐asymmetric induction. Stereochemical information may be communicated in this way over distances of up to 4 nm. 相似文献
18.
Adrian‐Mihail Stadler Dr. Juan Ramírez Dr. Jean‐Marie Lehn Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5369-5378
The shape of ligand strands composed of six‐membered aza‐heterocycles (het) connected at the α and α′ positions by hydrazone (hyz) units is determined in a predictable fashion by the nature of the heterocyclic groups (pyridine, pyrimidine, pyrazine etc.), and covers the range from extended linear to compact helical structures. The binding of metal ions to the coordination subunits, defined by the het‐hyz sequences, leads to marked shape changes by inter‐converting bent and linear conformations of the subunits, thus inducing relative motions of strand domains either in the same (con‐sense, “twirling”) or in opposite (dis‐sense, “flapping”) directions. The amplitude of the motion induced by metal‐ion binding and release and the relative directions of the formal motions can be controlled by the nature of the heterocyclic units. Thus, motions around a central 4,6‐disubstituted pyrimidine are dis‐sense motions, whereas there are con‐sense motions around a central 2,5‐disubstituted pyrazine unit, as illustrated by model ligands 1 and 2 , respectively. The more extended helical 3 and undulating (zigzag shape) 4 ligands undergo larger‐amplitude motions combining the relative displacements displayed by 1 and 2 . Ligands 3 and 4 form linear tetranuclear PbII and ZnII complexes, thus producing an extension motion. The same holds for [Ru( 4 )(terpy)4](PF6)8 (terpy=terpyridine). Reversible acid–base‐triggered molecular motions have been generated with [Zn4( 4 )(OTf)8] (TfOH=triflic acid). 相似文献
19.
Leopoldo Suescun Alvaro W. Mombrú Raúl A. Mariezcurrena Helena Pardo Silvia Russi Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):179-181
The crystal structure of the title compound, [NiCl(C12H8N2)2(CH4N2S)]2(NO3)Cl·2C2H6O, is formed by [Ni(phen)2(thiourea)Cl]+ cations (phen = 1,10‐phenanthroline), chloride and nitrate counter‐ions, and ethanol solvate molecules. The Ni atom is octahedrally coordinated to two bidentate phen ligands, a monodentate thiourea and a chloride ion. Both the chloride and nitrate anions, which provide charge balance, are located at special positions on a twofold symmetry axis. Hydrogen bonds play a key role in the packing and conformation of the cation and create a three‐dimensional network. 相似文献
20.
Ming‐Shou Ho Chain‐Shu Hsu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6596-6611
Three kinds of chiral saccharide‐containing liquid crystalline (LC) acetylenic monomers were prepared by click reaction between 2‐azidoethyl‐2,3,4,6‐tetraacetyl‐β‐D ‐galactopyranoside and 1‐biphenylacetylene 4‐alkynyloxybenzoate. The obtained monomers were polymerized by WCl6‐Ph4Sn to form three side‐chain LC polyacetylenes containing 1‐[2‐(2,3,4,6‐tetraacetyl‐β‐D ‐galactopyranos‐1‐yl)‐ethyl]‐1H‐[1,2,3]‐triazol‐4′‐biphenyl 4‐alkynyloxybenzoate side groups. All monomers and polymers show a chiral smectic A phase. Self‐assembled hiearchical superstructures of the chiral saccharide‐containing LCs and LCPs in solution state were studied by field‐emission scanning electron microscopy. Because of the LC behavior, the LC molecules exhibit a high segregation strength for phase separation in dilute solution (THF/H2O = 1:9 v/v). The self‐assembled morphology of LC monomers was dependent upon the alkynyloxy chain length. Increasing the alkynyloxy chain length caused the self‐assembled morphology to change from a platelet‐like texture ( LC‐6 ) to helical twists morphology ( LC‐11 and LC‐12 ). Furthermore, the helical twist morphological structure can be aligned on the polyimide rubbed glass substrate to form two‐dimensional ordered helical patterns. In contrast to LC monomers, the LCP‐11 self‐assembled into much more complicate morphologies, including nanospheres and helical nanofibers. These nanofibers are evolved from the helical cables ornamented with entwining nanofibers upon natural evaporation of the solution in a mixture with a THF/methanol ratio of 3:7. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6596–6611, 2009 相似文献