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Solute-Solvent Contact by Intermolecular Cross Relaxation: I. The Nature of the Water-Hydrophobic Interface
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.ORCID iD: 0000-0002-0231-3970
2006 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 7, 074704- p.Article in journal (Refereed) Published
Abstract [en]

Intermolecular cross-relaxation rates between solute and solvent were measured by {H-1} F-19 nuclear magnetic resonance experiments in aqueous molecular solutions of ammonium perfluoro-octanoate and sodium trifluoroacetate. The experiments performed at three different magnetic fields provide frequency-dependent cross-relaxation rates which demonstrate clearly the lack of extreme narrowing for nuclear spin relaxation by diffusionally modulated intermolecular interactions. Supplemented by suitable intramolecular cross-relaxation, longitudinal relaxation, and self-diffusion data, the obtained cross-relaxation rates are evaluated within the framework of recent relaxation models and provide information about the hydrophobic hydration. In particular, water dynamics around the trifluoromethyl group in ammonium perfluoro-octanoate are more retarded than that in the smaller trifluoroacetate

Place, publisher, year, edition, pages
2006. Vol. 125, no 7, 074704- p.
Keyword [en]
molecular-dynamics simulation, overhauser effect measurements, nuclear-spin relaxation, pair correlation-functions, low ionic-strength, nmr relaxation, magnetic-resonance, carboxylic-acids, translational diffusion, electronic relaxation
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5689DOI: 10.1063/1.2336199ISI: 000239914800046Scopus ID: 2-s2.0-33747624412OAI: oai:DiVA.org:kth-5689DiVA: diva2:10136
Note
Uppdaterad från submitted till published: 20100914 QC 20100914Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Molecular Association Studied by NMR Spectroscopy
Open this publication in new window or tab >>Molecular Association Studied by NMR Spectroscopy
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This Thesis presents studies of molecular association in aqueous solution and at the liquid/solid interface. The investigated molecular systems range from self-aggregating surfactants to hydration water in contact with micelles or individual molecules. In most studies, combinations of various NMR methods were applied. These vary from simple chemical shift and intensity measurements to more elaborate self-diffusion and intermolecular cross-relaxation experiments.

Non-ideal mixed micelles of fluorinated and hydrogenated surfactants were studied by an experimental procedure that allows an analysis in terms of micellar structure, using a minimal number of initial assumptions. Quantitative conclusions about micro-phase separation within mixed micelles were obtained within the framework of the regular solution theory. Additionally, NMR was introduced and developed as a powerful method for studying adsorption of surfactants at solid interfaces. Adsorption isotherms for pure and mixed surfactant systems and non-ideal mixing behavior of fluorinated and hydrogenated surfactants at solid surfaces were quantified. Fluorosurfactant-protein association was investigated using the methods described.

Intermolecular cross-relaxation rates between solute and solvent molecules were recorded at several different magnetic fields. The results reveal strong frequency dependence for both small molecules and micelles. This finding demonstrates that intermolecular cross-relaxation is not solely controlled by fast local motions, but also by long-range translational dynamics. Data analysis in terms of recently developed relaxation models provides information about the hydrophobic hydration and micellar structure.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 52 p.
Series
Trita-FYK, 0602
Keyword
NMR, spin relaxation, self-diffusion, intermolecular cross-relaxation, chemical shift, fluorinated surfactants, hydrogenated surfactant, micelle, non-ideal mixing, adsorption, hydration, surfactant-protein association
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-3947 (URN)91-7178-345 8 (ISBN)
Public defence
2006-05-19, F3, Lindstedtsv. 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100914Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2010-09-14Bibliographically approved
2. NMR Studies of Colloidal Systems in and out of Equilibrium
Open this publication in new window or tab >>NMR Studies of Colloidal Systems in and out of Equilibrium
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The Thesis describes (i) the development of add-on instrumentation extending the capabilities of conventional NMR spectrometers and (ii) the application of the designed equipments and techniques for investigating various colloidal systems. The new equipments are:

Novel designs of stopped-flow and temperature–jump inserts intended for conventional Bruker wide-bore superconductive magnets. Both inserts are loaded directly from above into the probe space and can be used together with any 10 mm NMR probe with no need for any auxiliary instruments.

A set of 5 mm and 10 mm 1H – 19F – 2H NMR probes designed for heteronuclear 1H – 19F cross-relaxation experiments in Bruker DMX 200, AMX 300 and DMX 500 spectrometers, respectively.

A two–stage low-pass filter intended for suppressing RF noise in electrophoretic NMR experiments.

The kinetics of micellar dissolution and transformation in aqueous solutions of sodium perfluorooctanoate (NaPFO) is investigated using the stopped-flow NMR instrument. The sensitivity of NMR as detection tool for kinetic processes in micellar solutions is clarified and possible artefacts are analysed. In the NaPFO system, the micellar dissolution is found to proceed faster than 100 ms while surfactant precipitation occurs on the time scale of seconds-to-minutes. The kinetics of the coil-to–globule transition and intermolecular aggregation in a poly (Nisopropylacrylamide) solution are investigated by the temperature-jump NMR instrument. As revealed by the time evolution of the 1H spectrum, the T2 relaxation time and the self-diffusion coefficient D, large (>10 nm) and compact aggregates form in less than 1 second upon fast temperature increase and dissolve in less than 3 seconds upon fast temperature decrease.

The intermolecular 1H – 19F dipole-dipole cross-relaxation between the solvent and solute molecules, whose fast rotational diffusion is in the extreme narrowing limit, is investigated. The solutes are perfluorooctanoate ions either in monomeric or in micellar form and trifluoroacetic acid and the solvent is water. The obtained cross-relaxation rates are frequency-dependent which clearly proves that there is no extreme narrowing regime for intermolecular dipole-dipole relaxation. The data provide strong constraints for the dynamic retardation of solvent by the solute.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 55 p.
Series
Trita-FYK, 0601
Keyword
stopped-flow NMR, temperature-jump NMR, crossrelaxation, NMR, NMR probe, fluorosurfactant, micellar kinetics, micellar structure
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-3898 (URN)91-7178-310-5 (ISBN)
Public defence
2006-04-20, Sal F3, Lindstedtsvägen 26, 10:00
Opponent
Supervisors
Note
QC 20100929Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-29Bibliographically approved

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