Optimization of identity operation in NMR spectroscopy via genetic algorithm: Application to the TEDOR experiment

Abstract

Identity operation in the form of π pulses is widely used in NMR spectroscopy. For an isolated single spin system, a sequence of even number of π pulses performs an identity operation, leaving the spin state essentially unaltered. For multi-spin systems, trains of π pulses with appropriate phases and time delays modulate the spin Hamiltonian to perform operations such as decoupling and recoupling. However, experimental imperfections often jeopardize the outcome, leading to severe losses in sensitivity. Here, we demonstrate that a newly designed Genetic Algorithm (GA) is able to optimize a train of π pulses, resulting in a robust identity operation. As proof-of-concept, we optimized the recoupling sequence in the transferred-echo double-resonance (TEDOR) pulse sequence, a key experiment in biological magic angle spinning (MAS) solid-state NMR for measuring multiple carbon-nitrogen distances. The GA modified TEDOR (GMO-TEDOR) experiment with improved recoupling efficiency results in a net gain of sensitivity up to 28% as tested on a uniformly 13C, 15N labeled microcrystalline ubiquitin sample. The robust identity operation achieved via GA paves the way for the optimization of several other pulse sequences used for both solid- and liquid-state NMR used for decoupling, recoupling, and relaxation experiments.

Discrimination of six tea categories coming from different origins depending on polyphenols, caffeine, and theanine combined with different discriminant analysis

“…The genetic algorithm operated on a specific problem by encoding its solution into a simple chromosome-like data structure and applying recombination operators to optimize the outcomes in an iterative manner, [16] thereby serving as a stochastic searching method that simulates the process of biological natural selection and genetic mechanisms. [17,18] In the genetic algorithm, there were 100 individuals in each generation and each set of solution with greatest fitness was more likely to be transmitted to the next generation until fit some convergence.…”

Optimization of band-selective homonuclear dipolar recoupling in solid-state NMR by a numerical phase search

“…27,47 Phase modulation, matching, or incrementation generates new categories of sequences, including cosine modulated rotary resonance (CMpRR), constant phase increment (CPI), four pulse recoupling (FPR), three pulse recouplin (TPR), and two phase modulated recoupling (TOPR). [48][49][50][51] The optimization of RF phases using genetic algorithms 52,53 or optimal control [54][55][56][57][58] may also improve the performance of recoupling sequences.…”

Enhancing the sensitivity of multidimensional NMR experiments by using triply-compensated π pulses

“…In contrast, the G5 is relatively short ( 1 H π pulse of 144 μs) and is applied at the same power level as a hard π/2 pulse, which is sufficiently short to avoid signal losses due to transverse relaxation. Importantly, the G5 pulse was developed via GA optimization 30,31 and is designed to operate on both inversion of longitudinal magnetization and refocusing of transverse magnetization 27 . Although the Gaussian cascade pulse (Q3) is also able to operate on both longitudinal and transverse magnetization, the bandwidth of the G5 pulse is 20% wider while using ~75% of the maximum RF amplitude necessary for the Q3 π pulses 14 .…”