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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
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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...
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High-Resolution Mass Spectrometry (HRMS)01:15

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The resolution of a mass spectrometer depends on the efficiency of separating ions with different ion masses. The mass of an atom is approximated to the sum of the masses of protons and neutrons inside, considering the masses of protons and neutrons as equal. However, the masses of the proton (1.6726 × 10−24 g) and neutron (1.6749 × 10−24 g) are not truly equal. There is a minor error in the expression of atomic masses relative to the simplest atom of hydrogen. For...
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¹H NMR: Complex Splitting01:13

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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.
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Chemical Shift: Internal References and Solvent Effects01:17

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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons01:03

¹H NMR Chemical Shift Equivalence: Homotopic and Heterotopic Protons

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Protons in identical electronic environments within a molecule are chemically equivalent and have the same chemical shift. The replacement test is a useful tool to identify chemical equivalence and predict NMR spectra. A substituent replaces each of the protons being examined and the resulting molecules are compared. If the same molecule is obtained, the protons are equivalent or homotopic. Replacement of any hydrogens in ethane by chlorine yields chloroethane because all six protons are...
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Exploiting subtle structural differences in heavy-atom derivatives for experimental phasing.

Jimin Wang1, Yue Li1, Yorgo Modis1

  • 1Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.

Acta Crystallographica. Section D, Biological Crystallography
|July 10, 2014
PubMed
Summary
This summary is machine-generated.

This study presents a novel method for improving experimental phasing in protein structure determination using subtle differences between weak derivative data sets. This approach enhances the resolution of isomorphous signals, making it broadly applicable for challenging structures.

Keywords:
data set mergingheavy-atom derivativesisomorphous replacementphase combinationphasingsingle anomalous dispersion (SAD)

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Area of Science:

  • Structural biology
  • Crystallography
  • Biophysics

Background:

  • Single isomorphous replacement (SIR) and single-wavelength anomalous diffraction (SAD) methods are crucial for protein structure determination.
  • These methods face challenges when using weak derivative data sets, often yielding low-resolution or noisy experimental maps.

Purpose of the Study:

  • To describe a novel approach for experimental phasing by exploiting subtle structural differences in highly isomorphous derivatives.
  • To provide a detailed explanation of the methodology and the underlying principles for its effectiveness.

Main Methods:

  • Merging three isomorphous uranium-derivative data sets for glycoprotein E2 from bovine viral diarrhea virus.
  • Treating merged data as independent SAD and pairwise SIR data sets to enhance experimental maps.
  • Detailed analysis of subtle structural variations between derivative data sets.

Main Results:

  • Improved interpretability of initial experimental maps through the novel phasing approach.
  • Demonstrated that the effective resolution of isomorphous signals can exceed that of individual anomalous signals.
  • Successfully applied the method to a challenging structure determination.

Conclusions:

  • The developed phasing strategy effectively leverages subtle differences in weak derivative data.
  • This method offers a significant advancement for experimental phasing, particularly for difficult protein structures.
  • The approach is broadly applicable to structure determination challenges involving weak derivatives in macromolecular crystallography.