2 aminoethyl phosphonic acid

A stock solution of 500 mM 2-aminoethyl phosphonic acid (Sigma-Aldrich) was prepared in 1× Milli Q water (MQ, Millipore) and adjusted to pH 10 using sodium hydroxide. 75 μl of 0.5 M 2-aminoethyl phosphonic acid (Sigma-Aldrich) was incubated with 20 μl of 400 mM azidobutyric acid NHS (N-Hydroxysuccinimide) ester (Lumiprobe) in dimethylsulfoxide (Sigma-Aldrich) and 45 μl MQ. The reaction was incubated for at least 2 h at room temperature in the dark rotating, resulting in approximately 50 mM stocks of phosphonate-azide.

Thiol-poly (ethylene glycol)-N-Hydroxysuccinimide and thiol-poly (ethylene glycol)-nitrilotriacetic acid (MW 3400 Da) were purchased from Biochempeg Scientific, Inc. (Watertown, MA). 2-aminoethylphosphonic acid and dopamaine hydrochloride were purchased from Sigma Aldrich, Inc. (St. Louis, MO). All organic solvents [N-methylmorpholine (99%), 200-proof ethanol (99.5%, ACS), acetone (ACS), isopropanol (ACS), tetraethylammonium hydroxide (10% in water), and N,N-dimethylformamide (99.8%)], iron (III) chloride hexahydrate, iron (II) chloride hexahydrate, regenerated cellulose dialysis tubing [6,000–8,000 Da, and 3,500 Da Molecular Weight Cut-Off (MWCO)], HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] buffer (1 M, pH 8), and hydrochloric acid were purchased from Fisher Scientific.