Gradient‐enhanced TROSY described with Cartesian product operators

TROSY, Transverse Relaxation Optimized Spectroscopy, was developed more than a decade ago. Since that time, the 15 N‐ 1 H HSQC‐TROSY experiment has become the standard “fingerprint” correlation spectrum for proteins of high molecular weight. In addition, its implementation in protein triple resonance experiments has pushed the boundaries of NMR assignment up to about 100 kDa, making NMR a highly relevant technique in structural biology. TROSY exploits the dipole‐CSA cross‐correlated relaxation properties of the NH system and selects for the narrowest of the HSQC J‐correlation quartet in both dimensions. The original publications and reviews of TROSY use shift operators and/or single transition product operators to describe the TROSY coherence pathways selections. In this review, we offer a familiar Cartesian product operator approach to comprehensively describe all of the events in the modern TROSY pulse sequence such as multiplet selection, gradient coherence selection, gradient quadrature, and sensitivity enhancement. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38: 280–288, 2011.