A switching cascade of hydrazone-based rotary switches through coordination-coupled proton relays.
Imidazole, a subunit of histidine, plays a crucial role in proton-relay processes that are important for various biological activities, such as metal efflux, viral replication and photosynthesis. We show here how an imidazolyl ring incorporated into a rotary switch based on a hydrazone enables a switching cascade that involves proton relay between two different switches. The switching process starts with a single input, zinc(II), that initiates an E/Z isomerization in the hydrazone system through a coordination-coupled proton transfer. The resulting imidazolium ring is unusually acidic and, through proton relay, activates the E/Z isomerization of a non-coordinating pyridine-containing hydrazone switch. We hypothesize that the reduction in the acid dissociation constant of the imidazolium ring results from a combination of electrostatic and conformational effects, the study of which might help elucidate the proton-coupled electron-transfer mechanism in photosynthetic bacteria.
Department of Chemistry, Dartmouth College, 6128 Burke Laboratory, Hanover, New Hampshire 03755, USA.
Debdas
D
Ray
Justin T
JT
Foy
Russell P
RP
Hughes
Ivan
I
Aprahamian
D055598:Chemical Phenomena; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry; D006835:Hydrazones / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D011522:Protons; D055672:Static Electricity; D015032:Zinc / Q000737:chemistry
D006835:Hydrazones; D007093:Imidazoles; D011522:Protons; D006639:Histidine; D015032:Zinc