Reducing acquisition and processing duration in solid-state NMR: a critical point for wider use
Résumé
The VCT-CPMAS (Variable contact time- Cross Polarization Magic Angle Spinning) sequence (Figure 1) allows studying the kinetics of polarization transfers 1H-> 13C and thus, gaining information on structural organization and interactions of polysaccharides and their assemblies [1]. This sequence belongs to a family of pseudo-2D sequences, which have two major drawbacks limiting their use, especially on series of samples: •The long acquisition time which may be incompatible with the availability of the equipment. •The length and the tedious aspect of the signal processing which requires a significant investment in human resources. In order to reduce these constraints and thus allow a wider use of this experiment, the objective was to improve two aspects : •The optimization of acquisition parameters (number of scans, recycling time, number of points in the time dimension) to speed up the experiment while yielding acceptable results. •The automation of repetitive, tedious and time-consuming steps inherent to pseudo-2D solid-state NMR sequences. The acquisition time using VCT-CPMAS for cellulose samples using 20 contact times has been reduced from 23 hours to 4 hours, making it possible to consider a larger number of contact times useful to model the polarization transfer kinetics. This time reduction can be very helpful also in case of a larger number of samples in order to take better account of their biological variability. Homemade Python scripts available on a Galaxy bioinformatic intern platform made it possible to speed up the processing of data batches, notably by formatting files and optimizing data modelling. This pipeline allowed saving almost 50% in time in the processing of a collection of 5 celluloses samples. This pipeline will be inserted in an executable file to further disseminate its use and the all approach will be evaluated on more complex samples (i.e. lignocellulosic material) with others complex NMR sequences.