Tuesday, November 6, 2007 - 5:30 PM
278g

Selective Ester Cleavage In Phospholipids -- Towards The Development Of Phosphate Functionalized Polymers

Vijitha Mohan and Keisha B. Walters. Dave C. Swalm School of Chemical Engineering, Mississippi State University, 330 Swalm, Box 9595, Mississippi State, MS 39762

The goal of this research is to selectively cleave the phosphate ester bond in phospholipids via non-enzymatic methods. The released polar phosphate molecule can be used to functionalize polymeric surfaces for stimuli-responsive and bioaffinity applications. The phosphoglycerides phosphatidyl choline, ethanolamine, and serine are investigated in this study. Lithium and zinc halides were combined with potassium hydroxide in solution and the catalytic effect of the resultant lithium and zinc hydroxide on ester cleavage was evaluated. The cleavage reaction was monitored as a function of reaction temperature and time using attenuated total reflectance and transmission FTIR spectroscopy. Carbonyl (C=O) and phosphonyl (P=O) stretching of the phospholipid ester functionalities can be observed at 1737 cm-1 and 1230 cm-1, respectively. Ratios of the C=O and P=O peak heights to the aliphatic hydrocarbon (C-H scissoring bend) peak at 1465 cm-1 allows the carboxylate ester and phosphate ester cleavage to be monitored and quantified. The peak height ratio (PHR) of the phosphonyl (P=O) group decreases from 1 to 0 during the reaction of phosphatidyl choline and lithium chloride indicating cleavage of the phosphate ester bond under mild conditions (2 h, 30 °C). Successful cleavage then allows the polar phosphate groups to be used in the synthesis of phosphate functionalized polymers via substitution reactions. Thin polymer films are produced by first forming a thiol self assembled monolayer (SAM) on gold surfaces and then performing surface-confined polymerization. The grafted polymers have cleavable pendant groups and by controlling the extent of pendant group substitution, grafted polymer layers with varying phosphate content are produced.