Abstract
The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M-1 for CB7•1 and 2.1 ± 1.0 × 108 M-1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl) cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.
| Original language | English |
|---|---|
| Pages (from-to) | 5624-5632 |
| Number of pages | 9 |
| Journal | Langmuir |
| Volume | 27 |
| Issue number | 9 |
| DOIs | |
| State | Published - May 3 2011 |
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ASJC Scopus subject areas
- Electrochemistry
- Condensed Matter Physics
- Surfaces and Interfaces
- Materials Science(all)
- Spectroscopy
Cite this
Controlling the extent of spin exchange coupling in 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[ n ]uril hosts. / Yi, Song; Captain, Burjor; Ottaviani, M. Francesca; Kaifer, Angel.
In: Langmuir, Vol. 27, No. 9, 03.05.2011, p. 5624-5632.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Controlling the extent of spin exchange coupling in 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[ n ]uril hosts
AU - Yi, Song
AU - Captain, Burjor
AU - Ottaviani, M. Francesca
AU - Kaifer, Angel
PY - 2011/5/3
Y1 - 2011/5/3
N2 - The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M-1 for CB7•1 and 2.1 ± 1.0 × 108 M-1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl) cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.
AB - The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M-1 for CB7•1 and 2.1 ± 1.0 × 108 M-1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl) cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.
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U2 - 10.1021/la2005198
DO - 10.1021/la2005198
M3 - Article
C2 - 21462968
AN - SCOPUS:79955152288
VL - 27
SP - 5624
EP - 5632
JO - Langmuir
JF - Langmuir
SN - 0743-7463
IS - 9
ER -