Thermodynamic and structural characterization of amino acid-linked dialkyl lipids.
Using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), we determined some thermodynamic and structural parameters for a series of amino acid-linked dialkyl lipids containing a glutamic acid-succinate headgroup and di-alkyl chains: C12, C14, C16 and C18 in CHES buffer, pH 10. Upon heating, DSC shows that the C12, C14 and annealed C16 lipids undergo a single transition which XRD shows is from a lamellar, chain ordered subgel phase to a fluid phase. This single transition splits into two transitions for C18, and FTIR shows that the upper main transition is predominantly the melting of the hydrocarbon chains whereas the lower transition involves changes in the headgroup ordering as well as changes in the lateral packing of the chains. For short incubation times at low temperature, the C16 lipid appears to behave like the C18 lipid, but appropriate annealing at low temperatures indicates that its true equilibrium behavior is like the shorter chain lipids. XRD shows that the C12 lipid readily converts into a highly ordered subgel phase upon cooling and suggests a model with untilted, interdigitated chains and an area of 77.2A(2)/4 chains, with a distorted orthorhombic unit subcell, a=9.0A, b=4.3A and beta=92.7 degrees . As the chain length n increases, subgel formation is slowed, but untilted, interdigitated chains prevail.
Tristram-Nagle
Stephanie
S
Department of Biological Sciences, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA. stn@cmu.edu
Lewis
Ruthven N A H
RN
Blickenstaff
Joseph W
JW
Diprima
Michael
M
Marques
Bruno F
BF
McElhaney
Ronald N
RN
Nagle
John F
JF
Schneider
James W
JW
D000596:Amino Acids / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002855:Chromatography, Thin Layer; D008055:Lipids / Q000737:chemistry*; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014961:X-Ray Diffraction
D000596:Amino Acids; D008055:Lipids