Polychromatic Excitation of Delocalized Long-Lived Proton Spin States in Aliphatic Chains

Abstract

Long-lived states (LLS) involving pairs of magnetically inequivalent but chemically equivalent proton spins in aliphatic (CH$_2$)$_n$ chains can be excited by simultaneous application of weak selective radio-frequency (RF) fields at n chemical shifts by polychromatic spin lock induced crossing (poly-SLIC). The LLS are delocalized throughout the aliphatic chain by mixing of intrapair singlet states and by excitation of LLS comprising products of four or six spins. The measured lifetimes T$_{LLS}$ in a model compound are about 5 times longer than T1, and are strongly affected by interactions with macromolecules.