TANGO sequence

The original COLOC sequence did not attempt to suppress l J(C, H) correlation peaks using a low-pass J filter, which is part of the HMBC experiment (section 5.8.3). The authors who proposed the COLOC sequence [5.170] stated that there would be no practical improvement using additional 1J(C, H) suppression elements [2]. However, several modified COLOC experiments have been published to suppress H(C, H) correlation peaks and spectrum artefacts that are introduced by pulse imperfections. The "BIRD-COLOC" sequence [3] uses two BIRD units to suppress the one-bond IH, correlation peaks [5.182]. The alternative "TANGO-COLOC [5.183] is similar to the "BIRD-COLOC" experiment except that a TANGO unit replaces the first BIRD unit. The S-COLOC sequence [5.94] utilizes the COLOC-TANGO sequence plus an additional 180° pulse to enhance the constant-time procedure. 

This section on building blocks will examine BIRD related sequence units and filter elements. It might appear strange to separate the BIRD and TANGO sequence element from other filters but the BIRD element is an extremely versatile element being used for both filter and purging elements and as such, merits a section in its own right. 

The numbering of the amino acids in porcine pepsin used in this manuscript follows Tangos sequencing results (27,28). 

Open the configuration file ch5622a.cfg and simulate the TANGO-COLOC experiment. Use the file ch5622b.cfg to calculate the S-COLOC sequence spectrum. 

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