Fumaric acid

FeCl₃·6H₂O (Acros
Organics, 99%), fumaric acid (Acros Organics, 99%), Pluronic F127
(Sigma-Aldrich, average Mw = 12,600 g/mol, Aldrich), acetic acid (Thermo
Scientific, 99.7%), poly(ethylene glycol) diacrylate (Sigma-Aldrich,
average Mn = 250), PEGDA₂₅₀, poly(ethylene glycol) diacrylate
(Sigma-Aldrich, average Mn = 700) PEGDA₇₀₀, TMPTA (Sigma
Aldrich), and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Sigma-Aldrich,
97%) were purchased and used without further purification.

Iron(III) chloride hexahydrate (FeCl₃.6H₂O, 99 + % extra pure), fumaric acid (99% +) and aniline (99.5%, extra pure) were purchased from Acros Organics. Cobalt(II) nitrate hexahydrate (Co(NO₃)₂·6H₂O, 98%) was purchased from Roth, 2,5-dihydroxiterephthalic acid (DHTPA) and tetramethylurea (TMU) from Fluorochem and dimethylsulfoxide (DMSO, 99%) from Fisher Scientific. Copper(II) acetate hydrate (Cu(OAc)₂·H₂O, 98.1%) was purchased from BLDpharm and N,N-dimethylformamide (DMF, 99.9% GLR), methanol (MeOH, 99.8%), acetonitrile (GC HPLC GGR) and tetrahydrofuran (THF, HPLC GGR) from Labkem. Ethanol (EtOH, denatured) was purchased from Chem-labs. Acetylsalicylic acid (ASA), 4-aminosalicylic acid (4-ASA, 99%) and naproxen sodium were purchased from Aldrich. All reagents were used without further purification except for ethanol that was distilled in order to remove the denaturant.

DL-arginine 98% was purchased from Alfa Aesar (Schiltigheim, France), L-arginine 98%, fumaric acid 97% and D-Methionine 98% were purchased from Acros Organics (Geel, Belgium), ¹³C₆-L-arginine.HCl 99% was purchased from Cambridge Isotope Laboratories (Andover, MA, USA). Methanol and ethanol were of HPLC grade and purchased from VWR (Fontenay-sous-Bois, France). Analytical grade formic acid was purchased from Sigma Aldrich (Saint-Quentin Fallavier, France). Water was ultra-purified (18.2 MΩ) with an Elga system from Veolia water solution & technologies (Saint-Maurice, France).