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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

¹H 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...

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

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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.

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pH-induced conformational changes in histamine in the solid state.

Kanchanok Kodchakorn^1,2, Piyarat Nimmanpipug¹, Suttinun Phongtamrug³

¹Department of Chemistry, Faculty of Science and Center of Excellence for Innovation in Analytical Science and Technology, Chiang Mai University Chiang Mai 50200 Thailand piyarat.n@cmu.ac.th.

|May 6, 2022

Summary

This study reveals histamine

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Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability

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Published on: April 2, 2015

Area of Science:

Biochemistry
Crystallography
Physical Chemistry

Background:

Histamine's structure and pH-dependent cation forms are not fully understood due to limited crystal structure data.
Conformational changes are sensitive to pH, impacting histamine's properties.

Purpose of the Study:

To analyze histamine's molecular packing structures at various pH levels.
To investigate the relationship between molecular conformation, hydrogen bonding, and proton conductivity.
To experimentally confirm predicted proton conductivity in histamine.

Main Methods:

X-ray diffraction analysis of histidine (histamine precursor) at different pH.
Vibrational spectroscopy and computational energy calculations.
Experimental measurement of proton conductivity during heating.

Main Results:

Identified diverse molecular conformations and tautomeric phenomena linked to hydrogen bonds.
Confirmed histamine's potential for proton conductivity, as predicted by simulations.
Observed a maximum conductivity of 10⁻⁴ S cm⁻¹ around 60 °C due to effective proton transfer.

Conclusions:

Hydrogen bonding plays a crucial role in histamine's structure and proton transfer capabilities.
Experimental evidence supports histamine's proton conductivity, particularly at elevated temperatures.
This research provides new insights into histamine's physical chemistry and potential applications.