HSQC may also be used in relaxation analysis in the studies of molecular dynamics of proteins, the determination of ionization constant, and other studies. 1H—13C HSQC This experiment provides correlations between a carbon and its attached protons. The constant time (CT) version of 1H—13C HSQC is normally used as it circumvents the issue of splitting of signal due to homonuclear 13C—13C J couplings which reduces spectral resolution. The "constant time" refers to the entire evolution period between the two INEPT steps which is kept constant in this experiment. If this evolution period is set to be the inverse of the J-coupling constant, then the sign of the magnetization of those carbons with an odd number of aliphatic carbon attached will be opposite to those with an even number. For example, if the Cβ of leucine appears as a positive peak (2 aliphatic carbons attached), then the Cγ (3 aliphatic carbons attached) and Cα (1 aliphatic carbons attached) would appear negative. HSQC in lipid NMR 1H—31P HSQC The use of 1H—31P HSQC is relatively uncommon in lipidomics, however use of 31P in lipidomics dates back to the 1990s. The use of this technique is limited with respect to mass spectrometry due to its requirement for much bigger sample size, however the combination of 1H—31P HSQC with mass spectrometry is regarded as a thorough approach to lipidomics and techniques for 'dual spectroscopy' are becoming available. See also Protein NMR Nuclear Magnetic Resonance Protein structure Structural biology References General references Protein NMR Spectroscopy : Principles and Practice (1995) John Cavanagh, Wayne J. Fairbrother, Arthur G. Palmer III, Nicholas J. Skelton, Academic Press External links Protein NMR Protein NMR spectra Biochemistry methods Spectroscopy Protein structure Nuclear magnetic resonance experiments