Cation- -Binding Hosts Binding Hosts Cation Classes of cyclic and - - PowerPoint PPT Presentation

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Cation- -Binding Hosts Binding Hosts Cation Classes of cyclic and - - PowerPoint PPT Presentation

Jul 27, 2023 474 likes •690 views

Cation- -Binding Hosts Binding Hosts Cation Classes of cyclic and acyclic ligands Crown ethers Podands Corands 18<N 6 2 6 corand-6> 14<N 4 2 2 3 2 corand-4> 18<O 3 N 3 2 6 corand-6> [18]ane-N 6 tetraza[14]crown-4

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SLIDE 1

Cation Cation-

  • Binding Hosts

Binding Hosts

Classes of cyclic and acyclic ligands

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SLIDE 2
  • Podands
  • Corands

Crown ethers

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SLIDE 3

Azacorands

18<N626corand-6> [18]ane-N6

hexacyclen

14<N42232corand-4> tetraza[14]crown-4 cyclam 18<O3N326corand-6>

  • Lariat ethers (corand-podand

hybrids)

BiBLE (bi-bracchial lariat ether)

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SLIDE 4
  • Cryptands

Crypt from the Latin crypta, meaning concealed, private

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SLIDE 5
  • Crown Ethers

Crown Ethers

Accidental synthesis of the first crown ether, dibenzo[18]crown-6, by Pedersen JACS, 1967, 89, 7017

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SLIDE 6

Common crown ethers

Space-filling model of complex between 18-C-6 and K+

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SLIDE 7
  • Chem. Rev. 2004, 104, 2723-2750

Crown ether-metal ion binding: the hole size relationship

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SLIDE 8

X-ray crystal structures of [18]crown-6 containing (a) Na+, (b) K+, (c) Cs+ and (d) two Li+ ions (phenolate salt). Na–O bond lengths are significantly longer than optimal.

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SLIDE 9

Methods for synthesizing the crown Methods for synthesizing the crown ethers (R ethers (R – – V are organic linker groups). V are organic linker groups).

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SLIDE 10
  • Lariat Ethers and

Lariat Ethers and Podands Podands

The term podand was coined by Vögtle and Weber in 1979, referring to acyclic hosts with pendant binding sites, e.g. X-ray molecular structure of the europium(III) podand complex [Eu(H2O)3(3.12)]3+. Podand hosts generally exhibit less cation affinity than their cyclic analogues, as a result of their lack of preorganisation, but they may adopt similar wrapping conformations to the crown ethers in the presence of suitable metal cations.

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Endgroup Concept Compared to crown ethers, podands show higher degree of flexibility, allowing them to adopt non-binding open conformations. If the podand is terminated by a rigid functionality (e.g. aryl, ester, amide), however, binding is enhanced by the extra degree of organization given to the podand host by the rigidifying endgroup.

O O O HO OH O O O O O O O Ca2+ N N N N N O O O MeO O O O MeO O O O OMe

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SLIDE 12

The term lariat ether (from Spanish la reata, lasso) refers to a crown ether or similar macrocyclic derivative with one or more accompanying appendages designed to enhance metal cation complexation ability by giving some three- dimensionality to the binding, e.g.

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SLIDE 13

Examples of lariat ether synthesis

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SLIDE 14

Simultaneous four-bond coupling to produce BiBLE ligands

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SLIDE 15

A lariat ether-based flouremetric sensor

Log K (M-1) Ca2+ 7.6 Sr2+ 6.8 Ba2+ 6.9

  • Org. Lett. 2002, 4, 2641-2644

Measured in CH3CN/CHCl3 (99:1)

(1 : 1 binding)

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SLIDE 16

Crown ethers in molecular devices Crown ethers in molecular devices

  • A spirobenzopyran-based crown

ether for ion sensing

  • A saxitoxin sensor
  • A luminescent sensor for ion pairs
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SLIDE 17
  • A molecular “AND” logic gate
  • J. Org. Chem. 2006, 71, 3970-3972.
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SLIDE 18
  • Viologen-rotaxane switches
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SLIDE 19
  • Science. 2004, 303, 1845-1849.
  • A molecular elevator
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SLIDE 20

Feringa, Angew. Chem. 2010, asap article

  • A molecular motor with a self-complexing lock