Saturated α cyano 4 hydroxycinnamic acid

The concentrated amphiphilic polymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic segments in 20 ml DMF (~27 wt%) were dropped into cold deionized water (60 mL) with 600 rpm magnetic stirring to form the core-shell nanoparticles (NP₁, NP₂, and NP₃), respectively. The nanoparticle solutions then were dialyzed against deionized water (standard regenerated cellulose (RC) dialysis membrane with 3.5 kDa cutoff, Spectrum Chemical) at room temperature for 24 h to form NPA coacervates via nanoparticle assembly. To determine the successful synthesis and the molecular weight of the hydrophobic segment of the amphiphilic polymers, 1.5 μL of the hydrophobic segment in methanol (1 mg/ml) was premixed with 1.5 μL of matrix solution (saturated α-cyano-4-hydroxycinnamic acid, Sigma). Then this mixture was applied to a ground steel target that was ready for mass spectrometry. Finally, the analyses of air-dried samples were performed in an AutoFlex Speed LRF MALDI-TOF mass spectrometer (Bruker Daltonics, Germany) under reflector mode.

A 1-μl aliquot of the supernatant of each sample was spotted on the MALDI-TOF MS steel target plate (Bruker Daltonics) in quadruplicate and covered with 1 μl of matrix solution (saturated α-cyano-4-hydroxycinnamic acid [Sigma-Aldrich Chemie]), 50% (v/v) acetonitrile, 2.5% (v/v) trifluoroacetic acid (Sigma-Aldrich Chemie), following which HPLC-grade water was added. The sample was then analyzed on a Microflex LT MALDI-TOF Mass Spectrometer device (Bruker Daltonics). Details on sample loading, MALDI-TOF MS parameters and MS spectra analysis are given in Additional file 1: Data file.