Water State In Confined Regions Of Lipids Bilayers Observed By FTIR Spectroscopy

FRIAS, M DE LOS ANGELES; DISALVO, E ANIBAL

Sendai

Conferencia; 14th International Association of Colloid and Interface Scientists, Conference. (IACIS); 2012

The presence of water pockets or defects in lipid bilayers may explain the insertion charged and polar peptides and aminoacids. The properties of these confined regions of water have not yet been analyzed. FTIR spectroscopy provides visualization at molecular level of the order-disorder increase due to the trans-gauche isomers in the lipid acyl chains. It is assumed that the increase of conformational isomers enhances water penetration beyond the polar head group region. In this condition, water may be present in different states according to the hydrophobic hydrophilic character of the wall it is facing. FTIR spectroscopy gives directly changes in water states following the bands at 3600 cm-1 parallel to the changes in the CH2 region. In this work we analyze the different water populations occurring below and above the phase transition of phosphatidylcholines and phosphatidylethanolamines of similar chain lengths. FTIR spectroscopy is a valuable tool to obtain molecular information without adding perturbing probes. Thus, direct changes in water states can be evaluated by the position and width of the 3400-3800 cm-1 bands parallel to the changes in the CH2 region (the band at the 2400 nm). FTIR spectroscopy is especially suitable for identifying H-bonds between interfacial water molecules and phospholipid headgroups. Generally speaking, the formation of a H-bonded complex between two atoms A and B, A–H. . .B, leads to a weakening of the A–H bond and, thereby, a downshift of the frequency of the A–H stretching vibration by a few tens of cm-1. The width in frequency of the 1,3(OH) band reflects the distribution in strength of the H-bonds between phospholipid and interfacial water molecules. The data were analyzed using the mathematical software provided by the instrument. In cases where absorption bands appeared to be a summation of components, a combination of Fourier deconvolution and curve-fitting procedures were used to obtain estimates of the position of the component bands and to reconstruct the contours of the original band envelope.