Unless otherwise noted, materials and solvents were obtained from commercial suppliers and used without further purification. All reactions were performed under an inert nitrogen atmosphere. EMD 60F 254 silica gel plates were used for thin layer chromatography and visualized using UV light or ninhydrin stain. Column chromatography was performed using standard grade 60 Å 230 – 400 mesh silica gel (Sorbent Technologies). 1H NMR and 13C NMR spectra were obtained at room temperature on a Bruker Avance III 500 MHz NMR spectrometer. An Agilent 6210 LC-TOF spectrometer was used to acquire electro spray ionization mass spectra (ESI-MS). Matrix-Assisted Laser Desorption Ionization Time-Of-Flight (MALDI-TOF) mass spectrometry was carried out using a Bruker Autoflex III MALDI. Semi-preparative HPLC was performed on a Waters 19 × 250 mm X bridge C18 Column. Analytical HPLC was performed using a Waters 4.6 × 250 mm 5 μM X bridge C18 column using the Varian Prostar 500 system equipped with a Varian 363 fluorescence detector, and a Varian 335 UV/Vis Detector.
The amine functionalized Gd(III) scaffold (4 ) was synthesized according to literature procedure.30 For a detailed synthetic procedure of the peg functionalized scaffold (3 ) and the isothiocyanate functionalized dye (5 ) see the supporting information .
The amine functionalized Gd(III) scaffold (