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Related Concept Videos

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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...
Atomic Nuclei: Types of Nuclear Relaxation01:28

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Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H 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.
Conformations of Cyclohexane02:11

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Repressible Operon: trp Operon01:21

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The trp operon in Escherichia coli exemplifies a repressible operon. It regulates the synthesis of tryptophan through repressor-mediated transcriptional control and attenuation. This dual regulatory mechanism ensures tryptophan biosynthesis occurs only when needed, conserving cellular resources.Structure of the trp OperonThe trp operon consists of five structural genes (trpE, trpD, trpC, trpB, and trpA) that encode enzymes for tryptophan biosynthesis. These genes are transcribed as a single...
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Conformations of Cycloalkanes

Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that was based on the...

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PCR Mutagenesis, Cloning, Expression, Fast Protein Purification Protocols and Crystallization of the Wild Type and Mutant Forms of Tryptophan Synthase
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Conformational relaxation paths in tryptamine.

Marcel Böhm1, Robert Brause, Christoph Jacoby

  • 1Heinrich-Heine-Universität, Institut für Physikalische Chemie I, D-40225 Düsseldorf, Germany.

The Journal of Physical Chemistry. A
|December 19, 2008
PubMed
Summary
This summary is machine-generated.

The study determined tryptamine conformer fluorescence intensities under varying supersonic expansion conditions. Conformer interconversion rates were calculated, revealing discrepancies with RRKM theory due to anharmonic coupling.

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15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale

Published on: April 19, 2021

Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Spectroscopy

Background:

  • Tryptamine exists in multiple conformations with varying fluorescence intensities.
  • Understanding conformer interconversion is crucial for interpreting experimental data.

Purpose of the Study:

  • To investigate the relative fluorescence intensities of tryptamine conformers.
  • To determine conformer interconversion rates under supersonic expansion.
  • To evaluate the applicability of statistical theories in predicting these rates.

Main Methods:

  • Supersonic expansion experiments varying stagnation pressure and nozzle temperature.
  • Ab initio calculations to determine potential energy surfaces, local minima, and transition states.
  • Statistical theories (e.g., RRKM) to calculate conformer interconversion rates.

Main Results:

  • Relative fluorescence intensities of tryptamine conformers are highly dependent on experimental conditions.
  • Calculated interconversion rates (k(T), k(E)) were obtained from ab initio data.
  • RRKM theory significantly overestimated interconversion rates, suggesting limitations.

Conclusions:

  • Vibrational cooling and interconversion rates are of similar magnitude in observed cases.
  • Anharmonic coupling of vibrational modes in tryptamine likely explains RRKM theory's overestimation.
  • Refined theoretical models are needed for accurate prediction of conformer dynamics.