Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra

Nithyanandhan Jayaraj, Mintu Porel, M. Francesca Francesca Ottaviani, Murthy V S N Maddipatla, Alberto Modelli, José P. Da Silva, Balakrishna R. Bhogala, Burjor Captain, Steffen Jockusch, Nicholas J. Turro, Vaidhyanathan Ramamurthy

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by 1H NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6, 6-tetramethylpiperidinyl-N-oxy bromide (CAT1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through 1H NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)2,2,6,6-tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1 @CB7 complex consisting of three lines suggested that probe CAT1 is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for 14N-substituted CAT1 is 5 G, and that for the four-line spectrum for 15Nsubstituted CAT1 is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both 14N- and 15N-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules of CATl@CB8 (i.e., [CAT1@CB8]3) in a triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is a general phenomenon. We are in the process of understanding this unusual phenomenon.

Original languageEnglish
Pages (from-to)13820-13832
Number of pages13
JournalLangmuir
Volume25
Issue number24
DOIs
StatePublished - Dec 15 2009

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line spectra
Paramagnetic resonance
Agglomeration
Salts
Nuclear magnetic resonance
X ray diffraction
spin exchange
Iodides
Complexation
Bromides
Gases
salts
nuclear magnetic resonance
Crystals
Molecules
Geometry
Water
probes
diffraction
iodides

ASJC Scopus subject areas

  • Electrochemistry
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Materials Science(all)
  • Spectroscopy

Cite this

Jayaraj, N., Porel, M., Francesca Ottaviani, M. F., Maddipatla, M. V. S. N., Modelli, A., Da Silva, J. P., ... Ramamurthy, V. (2009). Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra. Langmuir, 25(24), 13820-13832. https://doi.org/10.1021/la9020806

Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra. / Jayaraj, Nithyanandhan; Porel, Mintu; Francesca Ottaviani, M. Francesca; Maddipatla, Murthy V S N; Modelli, Alberto; Da Silva, José P.; Bhogala, Balakrishna R.; Captain, Burjor; Jockusch, Steffen; Turro, Nicholas J.; Ramamurthy, Vaidhyanathan.

In: Langmuir, Vol. 25, No. 24, 15.12.2009, p. 13820-13832.

Research output: Contribution to journalArticle

Jayaraj, N, Porel, M, Francesca Ottaviani, MF, Maddipatla, MVSN, Modelli, A, Da Silva, JP, Bhogala, BR, Captain, B, Jockusch, S, Turro, NJ & Ramamurthy, V 2009, 'Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra', Langmuir, vol. 25, no. 24, pp. 13820-13832. https://doi.org/10.1021/la9020806
Jayaraj N, Porel M, Francesca Ottaviani MF, Maddipatla MVSN, Modelli A, Da Silva JP et al. Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra. Langmuir. 2009 Dec 15;25(24):13820-13832. https://doi.org/10.1021/la9020806
Jayaraj, Nithyanandhan ; Porel, Mintu ; Francesca Ottaviani, M. Francesca ; Maddipatla, Murthy V S N ; Modelli, Alberto ; Da Silva, José P. ; Bhogala, Balakrishna R. ; Captain, Burjor ; Jockusch, Steffen ; Turro, Nicholas J. ; Ramamurthy, Vaidhyanathan. / Self aggregation of supramolecules of Nitroxides@Cucurbit[8]uril revealed by EPR spectra. In: Langmuir. 2009 ; Vol. 25, No. 24. pp. 13820-13832.
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N2 - Supramolecular complexation behavior of cucurbiturils with paramagnetic nitroxide spin probes was examined by 1H NMR, X-ray diffraction studies of crystals, computation, and EPR. Both cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) form a 1:1 complex with 4-(N,N,N-trimethylammonium)-2,2,6, 6-tetramethylpiperidinyl-N-oxy bromide (CAT1). The structure of the complex in the solid state was inferred by X-ray diffraction studies and in the gas phase by computation (B3LYP/6-31G(d)). Whereas ESI-MS data provided evidence for the existence of the complex in solution, indirect evidence was obtained through 1H NMR studies with a structural diamagnetic analogue, 4-(N,N,N-trimethylammonium)2,2,6,6-tetramethyl-N-methylpiperidine iodide (DCAT1). The EPR spectrum of the CAT1 @CB7 complex consisting of three lines suggested that probe CAT1 is associated with host CB7 such that the nitroxide part is exposed to water. The spectral pattern was independent of the concentration of the complex and the presence of salt such as NaCl. The most interesting observation was made with CB8 as the host. In this case, in addition to the expected three-line spectrum, an additional spectrum consisting of seven lines was recorded. The contribution of the seven-line spectrum to the total spectrum was dependent on the concentration of the complex and added salt (NaCl) to the aqueous solution. The coupling constant for the seven-line spectrum for 14N-substituted CAT1 is 5 G, and that for the four-line spectrum for 15Nsubstituted CAT1 is 7.15 G. The only manner by which we could reproduce the observed spectra by simulation for both 14N- and 15N-substituted CAT1@CB8 was by assuming a spin exchange among three nitroxide radicals. To account for this observation, we hypothesize that three CAT1 molecules included within CB8 interact in such a way that there is an association of three supramolecules of CATl@CB8 (i.e., [CAT1@CB8]3) in a triangular geometry that leads to spin exchange between the three radical centers. We have established, with the help of 13 additional examples, that this is a general phenomenon. We are in the process of understanding this unusual phenomenon.

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