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Conformations of Cyclohexane02:11

Conformations of Cyclohexane

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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...
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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...
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Chair Conformation of Cyclohexane02:02

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The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
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Unsymmetrical bending occurs when the bending moment applied to a structural member does not align with its principal axis. This misalignment leads to complex stress distributions and deflection patterns that differ from those in symmetrical bending, and are essential for designing structures to withstand different loading conditions. In unsymmetrical bending, the neutral axis—where stress is zero—does not necessarily align with the geometric axes of the cross-section. The...
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Formation of Higher-order Actin Filaments01:11

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The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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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...
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Accessing Improbable Foldamer Shapes with Strained Macrocycles.

Ko Urushibara1,2, Yann Ferrand2, Zhiwei Liu3

  • 1Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo, 112-8610, Japan.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|April 27, 2021
PubMed
Summary
This summary is machine-generated.

Alkylation of amide groups in 8-amino-2-quinolinecarboxylic acid oligomers enables macrocycle formation. These cyclic peptides adopt strained, fluxional conformations due to frustrated helix folding.

Keywords:
cis amidefluxionalityfoldamermacrocyclestrained structures

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Area of Science:

  • Supramolecular Chemistry
  • Organic Chemistry
  • Chemical Crystallography

Background:

  • 8-amino-2-quinolinecarboxylic acid oligomers favor helical conformations.
  • Secondary amide alkylation can alter conformational preferences.

Purpose of the Study:

  • To investigate the effect of dimethoxybenzyl (DMB) group alkylation on oligomer conformation.
  • To synthesize and characterize cyclic macrocycles derived from these oligomers.
  • To explore the conformational properties of the resulting macrocycles.

Main Methods:

  • Alkylation of secondary amide functions with DMB groups.
  • Cyclization of modified oligomers to form macrocycles.
  • X-ray crystallography and Nuclear Magnetic Resonance (NMR) spectroscopy for structural analysis.
  • Computational studies including molecular dynamics simulations.

Main Results:

  • Alkylation destabilized helical conformations, facilitating cyclization into hexameric and heptameric macrocycles.
  • Post-deprotection, macrocycles adopted strained conformations, improbable in linear analogues.
  • Homomeric macrocycles exhibited inequivalent monomer units.
  • Experimental and computational methods revealed specific fluxional pathways.

Conclusions:

  • Macrocyclization of 8-amino-2-quinolinecarboxylic acid oligomers leads to unique, strained conformations.
  • The inherent helix-folding propensity is frustrated but partly expressed in these macrocyclic structures.
  • These findings provide insights into the conformational behavior of constrained peptide systems and enable prediction for larger analogues.