Guanidine-phosphate non-covalent interaction in LAP crystal growth solution evidenced from spectroscopy studies

•The aqueous solutions of l-arginine and l-lysine show the fluorescence emission properties.•The fluorescent emission of the similar l-arginine aggregate in LAP solution has an obvious blue shift.•The special interaction between guanidine and Pi is found in LAP molecular.

The similar l-arginine molecule aggregation has been found in l-arginine (LA) and l-arginine phosphate monohydrate (LAP) aqueous solutions. The special fluorescence emission at 380 nm of LA aggregates in LAP solution has been found, compared with the emission of LA solution at 415 nm, which has an obvious blue shift. By comparing the fluorescence spectra of several solutions for l-arginine and l-lysine salts, the interaction between phosphate and guanidine in LAP solution was considered to be the cause of its special fluorescence emission. Meanwhile, when LAP molecule formed in solution, the fluorescence emission wavelength and the UV absorption intensity at 296 nm of l-arginine solutions have mutated. Therefore, the group interaction involved by guanidine has changed the fluorescence properties of l-arginine aggregates in LAP solution, indicating that the specific interaction between phosphate and guanidine exists in LAP molecule.

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