Fourier transform infrared study on the thermotropic behaviour of fully hydrated 1-palmitoyl-2-[10-(pyren-1-y)decanoyl]- sn-glycero-3-phosphatidylcholine

Fourier transform infrared (FTIR) spectroscopy was used to study the thermotropic behaviour of fully hydrated 1-palmitoyl-2-[10-(pyren-1-yl)-decanoyl]- sn-glycero-3-phosphatidylcholine (PPDPC) in the temperature range of 3–30°C. Several changes in the spectral features of PPDPC were observed. Major alterations analogous to the gel-to-liquid crystalline phase transition of saturated phosphatidylcholines were evident at approximately 16°C in both the wavenumbers and the halfbandwidths of five different vibrational modes of PPDPC, viz. asymmetric and symmetric CH 2 stretching, CO stretching, and CH 2 bending. Also the pyrene ring deformation mode changed at this temperature. Using Fourier self-deconvolution technique we resolved the carbonyl stretching mode into two bands at approx. 1741 and 1726 cm −1. These bands are due to conformational differences in the ester linkages of the two acyl chains, and are further assigned on the basis of literature data to the sn-1 and sn-2 carbonyl groups, respectively. The ratio of the relative intensities of these two bands is shown to depend on the phase state of the phospholipid.