Editing Synthesis Peptide-PEI (section)

== Synthesis of PEG-g-PEI  ==

Dissolve 1 gram of PEI (MW 25,000) (40 μ mol)&nbsp;&nbsp;in 25 mL of a sodium phosphate buffer (pH 8.0).<br>Add 500 ug micrograms of PEG-SSA (100 μ mol, MW&nbsp;5,000) dissolved in 5 mL of dehydrated DMSO &nbsp;to the PEI solution in a drop-wise fashion. 

The<br>reaction was left at room temperature for 4 h. The<br>stoichiometry of the reaction was 1:2.5 (PEI:PEG-SSA).<br>The reaction was stopped by the addition of 60 mL of<br>deionized water followed by dialysis (MWCO 25,000).<br>The<br>conjugate was then freeze-dried and stored at − 20<br>o<br>C until use. The PEG-g-PEI was 1 analyzed by 1 H-NMR<br>using D 2 O as a solvent. The H-NMR spectra were<br>taken using a Brucker DRX 300 spectrometer operating<br>at 300 MHz. The chemical shift ( δ ) was measured in<br>ppm using 3-(trimethyl-silyl) propionic-2,2,3,3-d 4 acid<br>(TSP) sodium salt as an internal reference.<br>Formulation of KALA/PEG-g-PEI/DNA and KALA/PEI/<br>DNA Complexes<br>Ten milliliters of PEI (5 μ g/mL) and DNA (100 μ g/<br>mL) were separately prepared in an HBS (10 mM<br>HEPES, 30 mM NaCl, 1.5 mM sodium phosphate, pH<br>7.4) solution. One mL of the PEI solution was added to<br>1 mL of the DNA solution in a drop-by-drop manner.<br>The weight ratio of PEI and DNA in the solution mix-<br>ture was 1:20 (nitrogen/phosphate ratio = 1:5), and the<br>same amount of PEI was also formulated for making<br>PEG-g-PEI/DNA conjugates. Negatively charged com-<br>plexes were formed at this ratio. After incubation for 15<br>min, the PEI/DNA and PEG-g-PEI/DNA complex parti- 

<br>