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Alexander J M Miller - One of the best experts on this subject based on the ideXlab platform.

  • cation controlled catalysis with Crown Ether containing transition metal complexes
    Chemical Communications, 2019
    Co-Authors: Changho Yoo, Henry M Dodge, Alexander J M Miller
    Abstract:

    Transition metal complexes that incorporate Crown Ethers into the supporting ligands have emerged as a powerful class of catalysts capable of cation-tunable reactivity. Cations held in the secondary coordination sphere of a transition metal catalyst can pre-organize or activate substrates, induce local electric fields, adjust structural conformations, or even modify bonding in the primary coordination sphere of the transition metal. This Feature Article begins with a non-comprehensive review of the structural motifs and catalytic applications of Crown Ether-containing transition metal catalysts, then proceeds to detail the development of catalysts based on “pincer-Crown Ether” ligands that bridge the primary and secondary coordination spheres.

  • mapping the binding modes of hemilabile pincer Crown Ether ligands in solution using diamagnetic anisotropic effects on nmr chemical shift
    Inorganic Chemistry, 2017
    Co-Authors: Andrew M Camp, Peter S. White, Matthew R Kita, Javier Grajeda, Diane A Dickie, Alexander J M Miller
    Abstract:

    A protocol for identifying ligand binding modes in a series of iridium pincer complexes bearing hemilabile aza-Crown Ether ligands has been developed using readily accessible NMR methods. The approach was tested on a collection of 13 structurally diverse pincer–Crown Ether complexes that include several newly characterized species. New synthetic routes enable facile interconversion of coordination modes and supporting ligands. Detailed structural assignments of five complexes reveal that the difference in chemical shift (Δδ) between geminal protons in the Crown Ether is influenced by diamagnetic anisotropy arising from halides and other ligands in the primary coordination sphere. The average difference in chemical shift between diastereotopic geminal protons in the Crown Ether macrocycle (Δδavg), as determined through a single 1H–13C HSQC experiment, provides information on the pincer ligand binding mode by establishing whEther the macrocycle is in close proximity to the metal center. The Δδavg values for...

  • cation modulated reactivity of iridium hydride pincer Crown Ether complexes
    Journal of the American Chemical Society, 2014
    Co-Authors: Matthew R Kita, Alexander J M Miller
    Abstract:

    Complexes of a new multidentate ligand combining a rigid, strongly donating pincer scaffold with a flexible, weakly donating aza-Crown Ether moiety are reported. The pincer-Crown Ether ligand exhibits tridentate, tetradentate, and pentadentate coordination modes. The coordination mode can be changed by Lewis base displacement of the chelating Ethers, with binding equilibria dramatically altered through lithium and sodium cation–macrocycle interactions. Cation-promoted hydrogen activation was accomplished by an iridium monohydride cation ligated in a pentadentate fashion by the pincer-Crown Ether ligand. The rate can be controlled on the basis of the choice of cation (with lithium-containing reactions proceeding about 10 times faster than sodium-containing reactions) or on the basis of the concentration of the cation. Up to 250-fold rate enhancements in H/D exchange rates are observed when catalytic amounts of Li+ are added.

Feihe Huang - One of the best experts on this subject based on the ideXlab platform.

  • a Crown Ether appended super gelator with multiple stimulus responsiveness
    Advanced Materials, 2012
    Co-Authors: Shengyi Dong, Bo Zheng, Donghua Xu, Mingming Zhang, Feihe Huang
    Abstract:

    A Crown Ether appended super gelator is designed and synthesized. It can gel a variety of organic solvents and shows excellent gelation properties with both low critical gelation concentration and short gelation time. Due to the introduction of the Crown Ether moiety and a secondary ammonium unit, the supramolecular gels show reversible gel-sol transitions. The supramolecular gels can also be molded into shape-persistent and free-standing objects.

  • supramolecular polymers constructed by Crown Ether based molecular recognition
    Chemical Society Reviews, 2012
    Co-Authors: Bo Zheng, Shengyi Dong, Feng Wang, Feihe Huang
    Abstract:

    Supramolecular polymers, polymeric systems beyond the molecule, have attracted more and more attention from scientists due to their applications in various fields, including stimuli-responsive materials, healable materials, and drug delivery. Due to their good selectivity and convenient enviro-responsiveness, Crown Ether-based molecular recognition motifs have been actively employed to fabricate supramolecular polymers with interesting properties and novel applications in recent years. In this tutorial review, we classify supramolecular polymers based on their differences in topology and cover recent advances in the marriage between Crown Ether-based molecular recognition and polymer science.

  • improved complexation of paraquat derivatives by the formation of Crown Ether based cryptands
    Chemical Communications, 2010
    Co-Authors: Mingming Zhang, Kelong Zhu, Feihe Huang
    Abstract:

    Self-assembly allows the construction of advanced molecular or supramolecular systems from small building blocks. Host–guest recognition, for its self-selectivity, environmental responsiveness and convenient application to complex molecular devices, plays a significant role in self-assembled systems. During this process, the association constant between the host and guest is an important standard to identify the properties of the systems. In order to prepare mechanically interlocked structures and large supramolecular systems efficiently from small molecules based on a host–guest recognition motif, it is necessary to increase host–guest association constants. Crown Ether-based cryptands have been designed and prepared to improve the binding of paraquat derivatives. This feature article aims to describe the design and syntheses of Crown Ether-based cryptand hosts for paraquat derivatives and the application of the cryptand/paraquat recognition motif in the fabrication of threaded structures, molecular switches and supramolecular polymers.

  • responsive supramolecular gels constructed by Crown Ether based molecular recognition
    Angewandte Chemie, 2009
    Co-Authors: Feihe Huang, Shiyong Liu
    Abstract:

    Responsive supramolecular gels were constructed from Crown Ether terminated four-arm star poly(epsilon-caprolactone) (PCL-DB24C8) and dibenzylammonium-terminated two-arm PCL-DBAS (see scheme), exploiting the formation of pseudorotaxane linkages between Crown Ether and ammonium moieties. The resultant supramolecular gels exhibit thermo- and pH-induced reversible gel-sol transition.

Richard F. Browner - One of the best experts on this subject based on the ideXlab platform.

  • Liquid chromatography/electrospray mass spectrometry of organoselenium compounds with postcolumn Crown Ether complexation.
    Analytical Chemistry, 2000
    Co-Authors: Wilson Z. Shou, Michelle M. Woznichak, Richard F. Browner
    Abstract:

    Postcolumn addition is an effective means of alleviating or solving ionization-related problems in liquid chromatography/electrospray ionization mass spectrometry (LC/ESIMS). In the current study, initial attempts to develop a direct LC/ESIMS method for an organoselenium compound, 4-hydroxyphenyl 2-methyl-2-aminoethyl selenide (HOMePAESe), were unsuccessful because of extensive fragmentation which occurred even under the mildest in-source collision-induced dissociation (CID) conditions. To reduce the extent of compound fragmentation, a Crown Ether, 18-Crown-6, was added postcolumn to the system, forming a complex with HOMePAESe, which survived the electrospray ionization process with reduced fragmentation and hence improved sensitivity for the major ions. The general applicability of this Crown Ether complexation approach to clinical samples was demonstrated by the analysis of HOMePAESe in human urine, using a structural analogue, 4-fluorophenyl 2-aminoethyl selenide (FPAESe) as an internal standard. The ...

  • liquid chromatography electrospray mass spectrometry of organoselenium compounds with postcolumn Crown Ether complexation
    Analytical Chemistry, 2000
    Co-Authors: Wilson Z. Shou, Michelle M. Woznichak, Richard F. Browner
    Abstract:

    Postcolumn addition is an effective means of alleviating or solving ionization-related problems in liquid chromatography/electrospray ionization mass spectrometry (LC/ESIMS). In the current study, initial attempts to develop a direct LC/ESIMS method for an organoselenium compound, 4-hydroxyphenyl 2-methyl-2-aminoethyl selenide (HOMePAESe), were unsuccessful because of extensive fragmentation which occurred even under the mildest in-source collision-induced dissociation (CID) conditions. To reduce the extent of compound fragmentation, a Crown Ether, 18-Crown-6, was added postcolumn to the system, forming a complex with HOMePAESe, which survived the electrospray ionization process with reduced fragmentation and hence improved sensitivity for the major ions. The general applicability of this Crown Ether complexation approach to clinical samples was demonstrated by the analysis of HOMePAESe in human urine, using a structural analogue, 4-fluorophenyl 2-aminoethyl selenide (FPAESe) as an internal standard. The ...

Ryota Satake - One of the best experts on this subject based on the ideXlab platform.

Harold H. Schobert - One of the best experts on this subject based on the ideXlab platform.