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J-coupling (also called indirect dipole dipole coupling) is the coupling between two nuclear spins due to the influence of bonding electrons on the magnetic field running between the two nuclei. In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges J-coupling contains information about dihedral angles which can be estimated using Karplus equation. In Aerospace engineering, the Dihedral is the Angle between the two wings see Dihedral. The Karplus equation, named after Martin Karplus, describes the correlation between 3 J-coupling constants and dihedral torsion angles in

Contents

Discovery

In October 1951, EL Hahn and D. Year 1951 ( MCMLI) was a Common year starting on Monday. Events of 1951 January E. Maxwell reported a spin echo experiment which indicates the existence of an interaction between two protons in dichloroacetaldehyde. In the echo experiment, two short, intent pulses of radiofrequency are applied to spin ensemble at the nuclear resonance condition and are separated by time interval of τ. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz The echo appears with a given maximum amplitude at time 2τ. For each setting of τ, the maximum of the echo signal is measured and plotted as a function of τ. If the spin ensemble consists of magnetic moment, a monotonic decay in the echo envelope is obtained. In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current In Hahn-Maxwell experiment, the decay was modulated by two frequencies: one frequency was in correspondence with the difference in chemical shift between two non equivalent spins and a second frequency, J, that was smaller and independent of magnetic field strength. In Nuclear magnetic resonance (NMR the chemical shift describes the dependence of nuclear magnetic energy levels on the electronic environment in a Molecule. (J/2π = 0. 7 cycle per second)

Such interaction came as a great surprise. The direct interaction between two magnetic dipole is dependent on the relative position of two nuclei in such a way that when averaged on all various orientation of the molecule it equals to zero.

In November 1951, NF Ramsey and EM Purcell, proposed a mechanism that explained the observation and gave rise to an interaction of the form I1. I2. The mechanism is the magnetic interaction between each nucleus and the electron spin of its own atom together with the exchange coupling of the electron spins with each other.

In 1990s, direct evidence has been found for the presence of J-couplings between magnetically active nuclei on both sides of the hydrogen bond. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen [1][2]Initially, it was surprising to observe such couplings across hydrogen bonds since we usually associate J-couplings with the presence of purely covalent bonds. However, it is now well established that the H-bond J-couplings follow the same electron-mediated polarization mechanism as their covalent counterparts. [3]

J-coupling Hamiltonian

The hamiltonian of a molecular system may be taken as:

H = D1 +D2 +D3.

D1 = electron orbital-orbital, spin-orbital, spin-spin and electron spin-external field interactions

D2 = magnetic interactions between nuclear spin and electron spin

D3 = direct interaction of nuclei with each other

for a singlet molecular state and frequent molecular collisions, D1 and D3 are almost zero. The full form of J-coupling interaction between spins Ij and Ik on the same molecule is:

H = 2π Ij. Jjk. Ik

where Jjk is the j-coupling tensor, a 3x3 real matrix. It depends on molecular orientation. In isotropic liquid it reduces to a number, so called scalar coupling. In 1D NMR, scalar coupling leads to oscillations in FID as well as splitting of lines in the spectrum.

Measurement of J-coupling

The Quantitative J correlation developed by Ad Bax et al. Ad Bax (born as Adriaan Bax June 14 1956 is the Chief of the Section on Biophysical NMR Spectroscopy at the National Institutes of Health. in 1994 is commonly the method of choice for accurate measurements of J couplings. [4][5]

References

Classics:

Other references:

  1. ^ P. Blake, B. Lee, M. Summers, M. Adams, J. -B. Park, Z. Zhou and A. Bax (1992). "Quantitative measurement of small through-hydrogen-bond and ‘through-space’ 1H-113Cd and 1H-199Hg J couplings in metal-substituted rubredoxin from Pyrococcus furiosus". Journal of Biomolecular NMR 2 (5): 527–533. Journal of Biomolecular NMR publishes research on technical developments and innovative applications of Nuclear magnetic resonance spectroscopy for the study doi:10.1007/BF02192814. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  2. ^ P. R. Blake, J. B. Park, M. W. W. Adams and M. F. Summers (1992). "Novel observation of NH--S(Cys) hydrogen-bond-mediated scalar coupling in cadmium-113 substituted rubredoxin from Pyrococcus furiosus". J. Am. Chem. Soc. 114 (12): 4931–4933. The Journal of the American Chemical Society (usually abbreviated as J doi:10.1021/ja00038a084. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  3. ^ Andrew J. Dingley, Florence Cordier and Stephan Grzesiek (2001). "An introduction to hydrogen bond scalar couplings". Concepts in Magnetic Resonance 13 (2): 103–127. doi:10.1002/1099-0534(2001)13:2<103::AID-CMR1001>3.0.CO;2-M. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  4. ^ E. de Alba and N. Tjandra (2006). "Interference between Cross-correlated Relaxation and the Measurement of Scalar and Dipolar Couplings by Quantitative J". Journal of Biomolecular NMR 35 (1): 1–16. Journal of Biomolecular NMR publishes research on technical developments and innovative applications of Nuclear magnetic resonance spectroscopy for the study doi:10.1007/s10858-006-0028-4. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  5. ^ G. W. Vuister and A. Bax (1993). "Quantitative J correlation: a new approach for measuring homonuclear three-bond J(HNHα) coupling constants in 15N-enriched proteins". J. Am. Chem. Soc. 115 (17): 7772–7777. The Journal of the American Chemical Society (usually abbreviated as J doi:10.1021/ja00070a024. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  

See also

Magnetic dipole-dipole interaction, also called dipolar coupling, refers to the direct interaction between two Magnetic dipoles The Energy of the interaction The residual dipolar coupling between two spins in a molecule occurs if the molecules in solution exhibit a partial alignment leading to an incomplete averaging of spatially anisotropic Exclusive correlation spectroscopy (ECOSY is an NMR correlation experiment introduced by O
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