Related Experiment Video
Updated: Jun 14, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Detecting columnar deformations in a supermesogenic octapode by proton NMR relaxometry
A Van-Quynh1, P J Sebastião, D A Wilson
1Centro de Física da Matéria Condensada, Universidade de Lisboa, Av. Gama Pinto, 1649-003, Lisboa, Portugal. aquynh@cii.fc.ul.pt
The European Physical Journal. E, Soft Matter
|March 20, 2010
Summary
Proton NMR relaxometry reveals distinct molecular dynamics in supermesogen phases. Even isotropic phases exhibit local nematic order, while columnar phases show restricted collective fluctuations due to elastic columnar deformations.
Area of Science:
- Materials Science
- Supramolecular Chemistry
- Physical Chemistry
Background:
- Supermesogens are complex liquid crystalline materials with unique properties.
- Understanding molecular dynamics is crucial for designing advanced materials.
- Proton NMR relaxometry is a powerful tool for probing molecular motion.
Purpose of the Study:
- To investigate the molecular dynamics of a supermesogenic octapode in its isotropic and mesophase states.
- To adapt and apply low-molar-mass liquid crystal relaxation mechanisms to supermolecular systems.
- To differentiate the dynamic behaviors across various mesophases using proton NMR dispersions.
Main Methods:
- Proton (1H) nuclear magnetic relaxation (NMR) dispersions were employed.
- Spin-lattice relaxation time (T(1)) was measured across a range of Larmor frequencies.
- Relaxation mechanisms were analyzed and adapted for supermolecular liquid crystals.
Main Results:
- High-frequency NMR data (above 10MHz) showed similar behavior across all phases, attributed to local reorientations.
- Low-frequency NMR data (below 10MHz) revealed distinct phase-dependent dynamics.
- Isotropic and nematic phases exhibited order director fluctuations (ODF), indicating local nematic order in the isotropic phase via cybotactic clusters.
- Columnar hexagonal phase dynamics were dominated by elastic columnar deformations (ECD), restricting collective fluctuations.
Conclusions:
- Proton NMR relaxometry effectively distinguishes molecular dynamics in different mesophases of supermesogens.
- The isotropic phase of the octapode exhibits local nematic order, suggesting the formation of cybotactic clusters.
- The columnar hexagonal phase demonstrates restricted collective dynamics due to elastic columnar deformations, highlighting the influence of molecular packing.
Related Concept Videos
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:19NMR Spectroscopy Of Amines
In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...
01:15NMR Spectroscopy: Chemical Shift Overview
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
For instance, the proton...