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Related Concept Videos

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

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

1.2K
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...
1.2K
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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

1.6K
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.
1.6K
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

15.1K
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
15.1K
UV–Vis Spectroscopy of Conjugated Systems01:32

UV–Vis Spectroscopy of Conjugated Systems

8.2K
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent of conjugation in...
8.2K
Properties of Enantiomers and Optical Activity02:24

Properties of Enantiomers and Optical Activity

21.0K
It is essential to understand the difference between chiral and achiral interactions and the implications thereof in optical activity and their applications. Just as our feet, which are chiral, interact uniquely with chiral objects, such as a pair of shoes, but identically with achiral socks, enantiomers of a molecule exhibit different properties only when they interact with other chiral media. An example of a significant implication from this facet is the phenomenon known as optical activity,...
21.0K
UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

2.7K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
2.7K

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Flexural Rigidity Measurements of Biopolymers Using Gliding Assays
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Three Conformations of Polyglutamic Acid Monitored by Vibrational Optical Activity.

Andrii S Kurochka1, Jana Hudecová2, Josef Kapitán2

  • 1Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo Náměstí 2, 16610 Prague, Czech Republic.

Analytical Chemistry
|December 12, 2025
PubMed
Summary
This summary is machine-generated.

Polyglutamic acid (PGA) folding was studied using vibrational optical activity. This technique, combined with computational methods, offers a powerful way to analyze protein structure, including amyloid fibrils.

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Area of Science:

  • Biophysics
  • Spectroscopy
  • Computational Chemistry

Background:

  • Polyglutamic acid (PGA) serves as a model for peptide and protein folding studies.
  • Vibrational optical activity (VOA) is a key technique for analyzing molecular conformation in solution.

Purpose of the Study:

  • To investigate PGA behavior across different protonation states.
  • To advance spectroscopic methodologies for protein structure analysis.
  • To explore the VOA of PGA fibrils.

Main Methods:

  • Acquisition of infrared (IR), vibrational circular dichroism (VCD), Raman, and Raman optical activity (ROA) spectra.
  • Molecular dynamics (MD) and density functional theory (DFT) computations for spectral interpretation.
  • Measurement of ROA spectra for both PGA enantiomers and fibrils.

Main Results:

  • Distinct ROA patterns were observed for PGA fibrils, verifiable with both enantiomers.
  • Computational models successfully linked spectral features to molecular geometry.
  • Simulated spectra largely reproduced experimental data, despite challenges in fibril VOA simulation.

Conclusions:

  • VOA combined with spectral simulations is an effective tool for studying protein geometry, including aggregates like amyloid fibrils.
  • Advancements in VOA for amyloid fibrils could enhance understanding of their biological roles in neurodegenerative diseases.