Hydration-Induced Gel States of the Dienic Lipid 1,2-Bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine and Their Characterization Using Infrared Spectroscopy

Abstract

The lyotropic phase behavior of the dienic lipid 1,2-bis(2,4-octadecadienoyl)-sn-glycero-3-phosphorylcholine (DODPC) has been investigated by means of IR spectroscopy at 25 °C. Gradual hydration has been realized exposing the lipid to an atmosphere of variable relative humidity (RH). Upon scans of decreasing RH, the liquid crystalline lipid undergoes the chain-freezing transition to a metastable gel state. By storage of the sample at low RH, the gel transforms to a crystalline subgel designated as SGI. Subsequent hydration induces the conversion to a second subgel (SGII). The subgel phases are characterized by the dense packing of the acyl chains as indicated by the correlation field splitting of the CH2 rocking and bending modes. Band shifts of phosphate group vibrations as well as the splitting of the carbonyl stretching mode are correlated with the hydration of the polar region of the bilayer given in terms of the molar ratio of water to lipid. The ν1,3(OH) absorption band of water yields qualitative information about the water−lipid interaction. The drastic sharpening of this band in the SGI phase was attributed to the reduction of water binding sites on the lipid, leading to a more uniform population of water molecules adsorbed onto the lipid headgroup. The external conditions of phase transformation of DODPC were compared with corresponding data of dimyristoylphosphatidylcholine (DMPC) having the same number of subsequent methylene segments in the acyl chains. Apparent differences can be attributed to the influence of the diene groups representing a rigid spacer inserted between the methylene chains and the ester groups of the lipid, i.e., in a position near the polar/apolar interface of the bilayer.

IR and NMR Studies on the Action of Hypochlorous Acid on Chondroitin Sulfate and Taurine

“…The relatively high sensitivity of the IR spectroscopy in comparison to the NMR spectroscopy makes it a reliable tool for the detection of chloramine formation, despite some experimental problems arising from the presence of the intense water absorption which can, however, be overcome by the use of the attenuated total reflection (ATR) technique (18).…”

“…Absorbance spectra of the sample were calculated using the respective single-channel spectra of the empty ATR crystal (without sample) as background. Selected absorption bands are characterized in terms of the wavenumber at maximum absorbance (18). …”

Hydration and Lyotropic Melting of Amphiphilic Molecules: A Thermodynamic Study Using Humidity Titration Calorimetry

“…The sample undergoes the freezing transition at a RH which is distinctly reduced in comparison with that of the melting transition. The formation of crystalline structures of long chain amphiphiles is typically accompanied by marked nonequilibrium effects such as "phase transitions upon storage" and freezing/melting hystereses (12,(22)(23)(24). We did not study this effect systematically by, e.g., the variation of the scan rate, because the phase behavior of DTAB in thermodynamic equilibrium is not in the center of interest of the present investigation.…”

“…The samples for ITC, gravimetry, and FTIR measurements are assumed to possess virtually identical physicochemical properties owing to the very similar conditions of preparation. The ATR crystal was mounted into a BioRad FTS-60a Fourier transform infrared spectrometer (Digilab, MA) using a commercial horizontal Benchmark unit (Graseby Specac, U.K.) which has been modified to realize a definite relative humidity (RH) and temperature at the crystal surface coated with the sample (12). Absorption spectra were recorded as a function of RH in steps of 3% at constant temperature.…”

“…In this way, the degree of hydration of the polar/apolar interface can be varied continu-ously between the anhydrous and fully hydrated state of the amphiphiles. We used this sample conditioning method to study structural details of the lyotropic phase behavior of lipids by means of infrared spectroscopy and X-ray analysis (12)(13)(14). The results show that the properties of the amphiphilic aggregates decisively depend on the amount of water which forms the hydration shell.…”