Herein we report the synthesis and characterization of light responsive metal organic framework (MOF) single crystals containing the photochromic diarylethene 1,2-bis(2,5-dimethyl-thien-3-yl)perfluorocyclopentene. Polarized light microscopy on single crystals indicates that the photochrome is preferentially aligned along the c-axis of the host.
The
solution chemistry and solid-state structures of the CoII, FeII, and NiII complexes of 7,13-bis(carbamoylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane
(L) are reported as members of a new class of paramagnetic
chemical exchange saturation transfer (paraCEST) MRI contrast agents
that contain transition metal ions. Crystallographic data show that
nitrogen and oxygen donor atoms of the macrocyclic ligand coordinate
to the metal ions to generate complexes with distorted pentagonal
bipyramidal geometry for [Co(L)]Cl2·2H2O or [Fe(L)](CF3SO3)2. The NiII complex [Ni(L)](CF3SO3)2·H2O features a
hexadentate ligand in a distorted octahedral geometry. The proton
NMR spectra of all three complexes show highly dispersed and relatively
sharp proton resonances. The complexes were further characterized
by monitoring their dissociation under biologically relevant conditions
including solutions containing phosphate and carbonate, ZnCl2, or acidic conditions. Solutions of the paraCEST agents in 20 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic
acid (pH 7.4) and 100 mM NaCl showed highly shifted and intense CEST
peaks at 59, 72, and 92 ppm away from bulk water for [Co(L)]2+, [Ni(L)]2+, and [Fe(L)]2+, respectively at 37 °C on a 11.7 T NMR
spectrometer. CEST spectra with corresponding rate constants for proton
exchange are reported in 4% agarose gel (w/w), rabbit serum, egg white,
or buffered solutions. CEST phantoms of 4 mM complex in buffer, 4%
agarose gel (w/w), or rabbit serum on a 4.7 T MRI scanner at 37 °C,
are compared. The most substantial change was observed for the reactive
[Ni(L)]2+, which showed reduced CEST contrast
in rabbit serum and egg white. The complexes with the least highly
shifted CEST peaks ([Co(L)]2+ and [Ni(L)]2+) showed a reduction in CEST contrast in 4%
agarose gel (w/w) compared to that in buffered solutions, while the
CEST effect for [Fe(L)]2+ in 4% agarose gel
(w/w) was not substantially different.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.