Structure of Water in the Vicinity of Phospholipid Analogue Copolymers As Studied by Vibrational Spectroscopy

Abstract

The structure and hydrogen bonding of water in the vicinity of phospholipid analogue random copolymers [poly(2-methacryloyloxyethyl phosphorylcholine-r-n-butyl methacrylate), Poly(MPC-r-BMA)] with various molecular weights were analyzed in their aqueous solutions and thin films with contours of O−H stretching of Raman and attenuated total reflection infrared (ATR-IR) spectra, respectively. The relative intensity of the collective band (C value) corresponding to a long-range coupling of O−H stretchings of the Raman spectra for the aqueous solution of Poly(MPC-r-BMA) was very close to that for pure water, which is in contrast with the smaller C value in the aqueous solution of ordinary polyelectrolytes. The number of hydrogen bonds collapsed by the presence of one monomer residue (N corr value) of Poly(MPC-r-BMA) (M w 1.3 × 104, 3.0 × 104, and 9.3 × 104) was much smaller than those for ordinary polyelectrolytes and close to those for neutral polymers such as poly(ethylene glycol) and poly(N-vinylpyrrolidone). Furthermore, water-insoluble Poly(MPC-r-BMA) with a large molecular weight (4.2 × 105) could be cast as a thin film (thickness, ca. 10 μm) on a ZnSe crystal for the ATR-IR spectroscopy. At an early stage of sorption of water into the Poly(MPC-r-BMA) film, the O−H stretching band of the IR spectra for the water incorporated in the film was similar to that for free water, which is in contrast with the drastic change in the O−H stretching band of water incorporated in polymer films such as poly(2-hydroxyethyl methacrylate), poly(methyl methacrylate), and poly(n-butyl methacrylate). These results suggest that the phospholipid analogue monomer residues with a zwitterionic structure do not significantly disturb the hydrogen bonding between water molecules in either the aqueous solution or the thin film systems.

Characterization of protein resistant, grafted methacrylate polymer layers bearing oligo(ethylene glycol) and phosphorylcholine side chains by neutron reflectometry

“…Apparently, water plays a crucial role in modulating the interactions between PEO-and PC-enriched surfaces and proteins. 23,24 Comparison of PEO-and PC-based systems with respect to their effectiveness in preventing protein adsorption has been reported previously. 25 Silicon ͑Si͒ surfaces grafted with oligo͑ethylene glycol͒ methyl ether methacrylate ͑OEGMA͒ and 2-methacryloyloxyethyl phosphorylcholine ͑MPC͒, which contain, respectively, PEO and PC sidechains of comparable size, were chosen as the basis for this comparison.…”

“…The highly hydrated layer associated with the PC headgroups is believed to result in decreased protein adsorption and improved biocompatibility. 22 Recently, using polarized Raman and attenuated total reflection infrared spectroscopies, Kitano et al 23,24 investigated the hydrogen-bond network structure of the water molecules in the vicinity of various watersoluble polymers and calculated the number of hydrogen bonds per monomer unit in the water which are "collapsed" ͑N collapsed ͒ by the presence of polymer. They found that in the case of PEO-and PC-containing polymers, N collapsed is practically zero and much smaller than for other polymers, suggesting that PEO-and PC-containing polymers do not significantly disturb the hydrogen bonding between water molecules.…”

Effect of Zwitterionic Polymers on Wound Healing

“…18) The q values were expressed as the mean of 15 portions of the polymer surface and expressed as the meanϮstandard error (S.E.) of three independent polymer films.…”

Effects of dynamics of water molecules at hydrophilic polymer brush surfaces on protein adsorption behavior

“…In this regard, dynamics of water should be considered in order to realize zero protein adsorption surface. Some reports have attempted to clarify hydration state, and it was revealed that hydration state at the surface has strong effect on protein adsorption [3][4][5][6][7][8]. Among them, Ishihara et al clearly demonstrated that the hydrophilic polymer surfaces with high-free water fraction reduced protein adsorption.…”