核磁共振光譜在蛋白質化學的應用

1、principle

According to Zeeman effect, nuclear spectroscopy would split into several components due to different energy in magnetic field.

∆E=[-(-1/2)γℏH]-[-(1/2)γℏH]=γℏH

(γ: const. ; H: strength of magnetic field)

After some complex operations, we can get at that the frequency of spectroscopy is associated with strength of magnetic field; also, ‘γ’varies from one kind of atomic to another.

υ=γH/2π

2、NMR spectrometer

Inside the facility, superconducting magnet provide magnetic field for sample tube. With the intention of getting stronger current, it’s important to reduce heat, thus, between the receiver and outside, 4K liquid helium and 77K liquid nitrogen is added.

3、Spectrum and structure

Each type of hydrogen in amino acid, like the ones added after nitrogen or those bonded with alpha carbon, has different spectrum. (We use Fouler transform to form the spectrum.) Thus, we can sequence and get at the structure of protein that we want to know.

4、Dimensional NMR Spectroscopy

After Fouler transform, we can get the result of spectrum. The use of 1D spectrum is like point three. In addition, 2D spectrum can not only display the structure but also have superior contribution to the experiment.

TOCSY: When two hydrogen atoms are in three bonds, they would have interaction. The spots that doesn’t appear on midline mean that there are two atoms having interaction.

NOESY: Two atomics in certain distance can be shown on the spectrum.