Weak nuclear spin singlet relaxation mechanisms revealed by experiment and computation

Abstract

Nuclear spin singlet states are often found to allow long-lived storage of nuclear magnetization, which can form the basis of novel applications in spectroscopy, imaging, and in studies of dynamic...

Limits of the quantum cognition hypothesis: 31P singlet order lifetimes of pyrophosphate from experiment and simulation

“…6. Light sensitive silver phosphate salt 1 was prepared from 18 O phosphoric acid by a simple precipitation method (20). Subsequent benzylation in the presence of excess benzyl chloride provided the triester 2 in 75% yield (21).…”

“…To overcome this challenge, we unsymmetrically labeled PPi with the 18 O isotope. The increased mass of the 18 O nuclei relative to the abundant 16 O isotope was expected to induce a small chemical shift difference between the neighboring 31 P nuclei, sufficiently large to allow creation and read-out of SO. This strategy was used previously for pairs of 13 C nuclei (10).…”

“…This strategy was used previously for pairs of 13 C nuclei (10). The tetrasodium salt of the unsymmetrically labelled 18 O-PPi (uPPi) was synthesized as described in the Materials and Methods section below and prepared in D2O under highly alkaline conditions to avoid potentially interfering effects due to proton exchange, which can accelerate SO relaxation (11). An excess of potassium cations, relative to the sodium cations from the tetrasodium salt, was found to promote longer SO lifetimes than if sodium ions alone were present.…”

Limits of the quantum cognition hypothesis: 31P singlet order lifetimes of pyrophosphate from experiment and simulation

“…Other known relaxation contributions to R1 and RS are described below. MD simulations following the procedure of Kharkov et al (18) gave the contribution of intermolecular dipolar relaxation between 31 P and 2 D solvent spins as 5.14×10 -3 s -1 . The 31 P-31 P dipolar relaxation contribution, relevant only for R1, was determined to be 1.60×10 -3 s -1 .…”

31P spin–lattice and singlet order relaxation mechanisms in pyrophosphate studied by isotopic substitution, field shuttling NMR, and molecular dynamics simulation

“…2 Disentangling the relative contributions of each can be difficult, and the spin-rotation mechanism has been under-explored, especially in flexible molecules in solution. 3,4 Progress has been made recently in accurately computing relaxation rates with molecular dynamics (MD) simulations and ab initio calculations in small molecules and ions, [5][6][7][8][9] and it has been demonstrated that very few (if any) adjustable parameters may be required in order to do so. 9 Nuclear spin singlet order (SO) relaxation has been of particular interest, since it offers the opportunity of potentially achieving particularly long magnetization storage mechanisms (the SO relaxation time T S has been shown in some cases to be up to two orders of magnitude larger than T 1 ).…”