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Inclusion of Chloromethane Guests Affects Conformation and Internal Dynamics of Cryptophane-D Host
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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2012 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 27, 7898-7913 p.Article in journal (Refereed) Published
Abstract [en]

Cryptophane-D is composed of two nonequivalent cyclotribenzylene caps bound together by three OCH2CH2O bridges in a syn arrangement. Host-guest complexes with chloroform and dichloromethane were investigated in solution by NMR spectroscopy. Variable temperature NMR. H-1 and C-13 spectra showed effects of chemical exchange between the free and bound guest and of conformational exchange for the host, strongly and specifically affected by guest binding. We found in particular that the carbon-13 chemical shifts for the linkers connecting the two cyclotribenzylene units are very informative. The NMR results were supported by DFT calculations. The guest exchange was also studied quantitatively, either by EXSY measurements (for chloroform as guest) or by line-shape analysis (for dichloromethane as guest). In the case of chloroform guest, we also investigated cross relaxation between the guest and host protons, as well as carbon 13 longitudinal relaxation and heteronuclear NOE at three different fields. The results were interpreted in terms of orientation and dynamics of the guest inside the host cavity. Putting together various types of evidence resulted in remarkably detailed insight into the process of molecular recognition of the two guests by cryptophane-D host.

Place, publisher, year, edition, pages
2012. Vol. 116, no 27, 7898-7913 p.
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-80433DOI: 10.1021/jp303469xISI: 000306264200016OAI: oai:DiVA.org:su-80433DiVA: diva2:556098
Note

AuthorCount:6;

Available from: 2012-09-24 Created: 2012-09-19 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Chloromethane Complexation by Cryptophanes: Host-Guest Chemistry Investigated by NMR and Quantum Chemical Calculations
Open this publication in new window or tab >>Chloromethane Complexation by Cryptophanes: Host-Guest Chemistry Investigated by NMR and Quantum Chemical Calculations
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Host–guest complexes are widely investigated because of their importance in many industrial applications. The investigation of their physico–chemical properties helps understanding the inclusion phenomenon. The hosts investigated in this work are cryptophane molecules possessing a hydrophobic cavity. They can encapsulate small organic guests such as halo–methanes (CH2Cl2, CHCl3). The encapsulation process was investigated from both the guest and the host point of view. With the help of Nuclear Magnetic Resonance (NMR), the kinetics of complex formation was determined. The information was further used to obtain the activation energies of the processes. Having done this on five different cryptophanes, it is possible to relate the energies to structural differences between the hosts. Via the dipolar interaction between the guest’s and host’s protons, one can get information on the orientation of the guest inside the cavity. Moreover, the dynamics of the guest can be further investigated by its relaxation properties. This revealed restricted motion of the guest inside the host cavity. Not only the nature of the guest plays an important role. The host is also changing its properties upon encapsulation. All the cryptophanes investigated here can exchange rapidly between many conformers. These conformers have different–sized cavities. Quantum chemical optimization of the structure of the conformers makes volume estimation possible. Not only the cavity volumes, but also the quantum-chemically obtained energies and the calculated chemical shifts of the carbon–13 atoms can be helpful to follow the changes of the host upon complex formation. The host cannot be considered as a rigid entity. Analysis of variable temperature proton and carbon-13 spectra shows that the encapsulation can be considered as a mixture of conformational selection and induced fit. The structures of the formed complexes are further investigated by means of two-dimensional nuclear Overhauser spectroscopy (NOESY). The complex formation, its kinetics and thermodynamics are found to be a complicated function of structure elements of the host, the cavity size and the guest size and properties.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2012. 57 p.
Keyword
Host–guest complexes, inclusion phenomenon, cryptophanes, NMR, kinetics, activation energy, dipolar interaction, exchange, quantum chemical optimization, calculated chemical shifts, NOESY, cavity size
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-81472 (URN)978-91-7447-598-2 (ISBN)
Public defence
2012-11-30, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 5: Manuscript.

 

Available from: 2012-11-08 Created: 2012-10-22 Last updated: 2013-08-23Bibliographically approved

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