Advanced

Polarization Transfer Solid-State NMR for Studying Surfactant Phase Behavior.

Nowacka, Agnieszka LU ; Choudhary, Parveen LU ; Norrman, Jens LU ; Martin, Rachel W and Topgaard, Daniel LU (2010) In Langmuir 26(22). p.16848-16856
Abstract
The phase behavior of amphiphiles, e.g., lipids and surfactants, at low water content is of great interest for many technical and pharmaceutical applications. When put in contact with air having a moderate relative humidity, amphiphiles often exhibit coexistence between solid and liquid crystalline phases, making their complete characterization difficult. This study describes a (13)C solid-state NMR technique for the investigation of amphiphile phase behavior in the water-poor regime. While the (13)C chemical shift is an indicator of molecular conformation, the (13)C signal intensities obtained with the CP and INEPT polarization transfer schemes yield information on molecular dynamics. A theoretical analysis incorporating the effect of... (More)
The phase behavior of amphiphiles, e.g., lipids and surfactants, at low water content is of great interest for many technical and pharmaceutical applications. When put in contact with air having a moderate relative humidity, amphiphiles often exhibit coexistence between solid and liquid crystalline phases, making their complete characterization difficult. This study describes a (13)C solid-state NMR technique for the investigation of amphiphile phase behavior in the water-poor regime. While the (13)C chemical shift is an indicator of molecular conformation, the (13)C signal intensities obtained with the CP and INEPT polarization transfer schemes yield information on molecular dynamics. A theoretical analysis incorporating the effect of molecular segment reorientation, with the correlation time τ(c) and order parameter S, shows that INEPT is most efficient for mobile segments with τ(c) < 0.01 μs and S < 0.05, while CP yields maximal signal for rigid segments with τ(c) > 10 μs and/or S > 0.5 under typical solid-state NMR experimental conditions. For liquid crystalline phases, where τ(c) < 0.01 μs and 0 < S < 0.3, the observed CP and INEPT intensities serve as a gauge of S. The combination of information on molecular conformation and dynamics permits facile phase diagram determination for systems with solid crystalline, solid amorphous, anisotropic liquid crystalline, and isotropic liquid (crystalline) phases as demonstrated by experiments on a series of reference systems with known phase structure. Three solid phases (anhydrous crystal, dihydrate, gel), two anisotropic liquid crystalline phases (normal hexagonal, lamellar), and two isotropic liquid crystalline phases (micellar cubic, bicontinuous cubic) are identified in the temperature-composition phase diagram of the cetyltrimethylammonium succinate/water system. Replacing the succinate counterion with DNA prevents the formation of phases other than hexagonal and leads to a general increase of τ(c). (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
26
issue
22
pages
16848 - 16856
publisher
The American Chemical Society
external identifiers
  • wos:000283837800034
  • pmid:20925371
  • scopus:78650373256
ISSN
0743-7463
DOI
10.1021/la102935t
language
English
LU publication?
yes
id
6fc2b515-0d33-4310-b7ad-2294c9e1d584 (old id 1711366)
date added to LUP
2010-11-08 12:48:59
date last changed
2018-07-08 03:04:03
@article{6fc2b515-0d33-4310-b7ad-2294c9e1d584,
  abstract     = {The phase behavior of amphiphiles, e.g., lipids and surfactants, at low water content is of great interest for many technical and pharmaceutical applications. When put in contact with air having a moderate relative humidity, amphiphiles often exhibit coexistence between solid and liquid crystalline phases, making their complete characterization difficult. This study describes a (13)C solid-state NMR technique for the investigation of amphiphile phase behavior in the water-poor regime. While the (13)C chemical shift is an indicator of molecular conformation, the (13)C signal intensities obtained with the CP and INEPT polarization transfer schemes yield information on molecular dynamics. A theoretical analysis incorporating the effect of molecular segment reorientation, with the correlation time τ(c) and order parameter S, shows that INEPT is most efficient for mobile segments with τ(c) &lt; 0.01 μs and S &lt; 0.05, while CP yields maximal signal for rigid segments with τ(c) &gt; 10 μs and/or S &gt; 0.5 under typical solid-state NMR experimental conditions. For liquid crystalline phases, where τ(c) &lt; 0.01 μs and 0 &lt; S &lt; 0.3, the observed CP and INEPT intensities serve as a gauge of S. The combination of information on molecular conformation and dynamics permits facile phase diagram determination for systems with solid crystalline, solid amorphous, anisotropic liquid crystalline, and isotropic liquid (crystalline) phases as demonstrated by experiments on a series of reference systems with known phase structure. Three solid phases (anhydrous crystal, dihydrate, gel), two anisotropic liquid crystalline phases (normal hexagonal, lamellar), and two isotropic liquid crystalline phases (micellar cubic, bicontinuous cubic) are identified in the temperature-composition phase diagram of the cetyltrimethylammonium succinate/water system. Replacing the succinate counterion with DNA prevents the formation of phases other than hexagonal and leads to a general increase of τ(c).},
  author       = {Nowacka, Agnieszka and Choudhary, Parveen and Norrman, Jens and Martin, Rachel W and Topgaard, Daniel},
  issn         = {0743-7463},
  language     = {eng},
  number       = {22},
  pages        = {16848--16856},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Polarization Transfer Solid-State NMR for Studying Surfactant Phase Behavior.},
  url          = {http://dx.doi.org/10.1021/la102935t},
  volume       = {26},
  year         = {2010},
}