Synthesis, relaxometric and photophysical properties of a new pH-responsive MRI contrast agent: the effect of other ligating groups on dissociation of a p-nitrophenolic pendant arm.
Two gadolinium(III) chelates, GdNP-DO3A (1-methlyene-(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triAcetate) and GdNP-DO3AM (1-methlyene(p-NitroPhenol)-1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide), containing a single nitrophenolic pendant arm plus either three acetate or three amide pendant arms were synthesized and characterized. The properties of the gadolinium, terbium, and dysprosium complexes of these ligands were examined as a function of pH. The extent and mechanism of the changes in water relaxivity with pH of each gadolinium complex was found to differ substantially for the two complexes. The water relaxivity of Gd(NP-DO3A) increases from 4.1 mM(-1) s(-1) at pH 9 to 7.0 mM(-1) s(-1) at pH 5 as a result of acid-catalyzed dissociation of the nitrophenol from the lanthanide. The nitrophenol group in Gd(NP-DO3AM) does not dissociate from the metal center even at pH 5; therefore, the very modest increase in relaxivity in this complex must be ascribed to an increase in prototropic exchange rate of the bound water and/or phenolic protons.
Woods
Mark
M
Macrocyclics, 2110 Research Row, Suite 425, Dallas, Texas 75235, USA.
Kiefer
Garry E
GE
Bott
Simon
S
Castillo-Muzquiz
Aminta
A
Eshelbrenner
Carrie
C
Michaudet
Lydie
L
McMillan
Kenneth
K
Mudigunda
Siva D K
SD
Ogrin
Doug
D
Tircsó
Gyula
G
Zhang
Shanrong
S
Zhao
Piyu
P
Sherry
A Dean
AD
D000588:Amines / Q000737:chemistry; D003287:Contrast Media / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005682:Gadolinium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008163:Luminescent Measurements; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009596:Nitrophenols / Q000138:chemical synthesis / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry
C492702:(1-methylene-(4-nitrophenol)-1,4,7,10-tetraazacyclododecane-4,7,10-triacetamide)gadolinium(III); C492701:(1-methylene-(4-nitrophenol)-1,4,7,10-tetraazacyclododecane-4,7,10-triacetate)gadolinium(III); D000588:Amines; D003287:Contrast Media; D009596:Nitrophenols; D009942:Organometallic Compounds; D005682:Gadolinium