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#NOE

2 public questions tagged with this topic.

NMRSpectroscopy

Which statement is FALSE about NOEs?

Nuclear Overhauser Effect provides distance information via through-space dipole-dipole cross-relaxation, decaying as inverse sixth power of internuclear separation, observable up to about 0.5 nanometer. Intensity depends on molecular tumbling and proximity, not on covalent bonds. Through-bond scalar coupling underlies COSY and TOCSY spectra, showing connectivity. Therefore statement describing NOEs as through-bond is false. NOESY experiments exploit dipolar mechanism to generate restraints for three-dimensional structure calculation of proteins, nucleic acids, and polysaccharides, fundamental distinction taught in biophysical chemistry and structural biology courses for interpreting spectra correctly.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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NMRSpectroscopy

Which NOE peak pattern suggests α-helical structure?

In alpha helix, periodicity 3.6 residues per turn places successive amide protons approximately 2.8 angstroms apart, enabling strong dipole-dipole cross-relaxation observed as intense sequential dNN cross-peaks in two-dimensional NOESY. Continuous chain of Ni to Ni+1 NH-NH contacts along entire sequence is hallmark of helix, often accompanied by medium-range i to i+3 and i to i+4 contacts. Beta sheets show different pattern with strong CαH-NH and long-range interstrand contacts. Recognizing continuous amide-amide NOE ladder confirms helical folding in synthetic and natural peptides.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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