Glutamic acid

Urea was purchased from Solaribio (Beijing, China). The L-AAs discussed in our work were obtained from Macklin (Shanghai, China), including alanine (Ala), phenylalanine (Phe), glycine (Gly), proline (Pro), lysine (Lys), cysteine (Cys), serine (Ser), histidine (His), arginine (Arg), leucine (Leu), isoleucine (Ile), valine (Val), methionine acid (Met), aspartic acid (Asp), asparagine (Asn), glutamic acid (Glu), glutamine (Gln), tryptophan (Trp), threonine (Thr), and tyrosine (Tyr). Peptides were synthesized by Anhui Guoping Pharmaceutical Co., Ltd. (Anqing, China), including alanyl-alanine (Ala-Ala), phenylalanyl-phenylalanine (Phe-Phe), and alanyl-glycyl-proline (Ala-Gly-Pro). Cell culture media DMEM and RPMI 1640 were purchased from Corning (USA).

Tannic acid (TA), Cu(NO₃)₂·3H₂O, ethanol, hydrogen peroxide (30 wt%), 3,3′,5,5′-tetramethylbenzidine (TMB), L-proline, glycine, cysteine, alanine, glutamic acid, NaCl, KCl, MnCl₂·4H₂O, CaCl₂, glucose and L-glutathione reduced were purchased from Macklin Biochemical Co., Ltd. Ammonia solution (25–28 wt%) and formaldehyde (37–40 wt%) were purchased from Tianjin Zhiyuan Chemical Co., Ltd. Pluronic^® F127 was purchased from Sigma-Aldrich. The qualitative filter paper was purchased from Whatman. All the reagents were used without further purification. Deionized water from a Milli-Q Plus system (Millipore) was used in all experiments.