Orientation of specifically 13C=O labeled phosphatidylcholine multilayers from polarized attenuated total reflection FT-IR spectroscopy

Abstract

Oriented multilayers of 1-myristoyl-2(1-13C)-myristoyl-sn-glycero-3-phosphatidylcholine (2[1-13C]DMPC) and 1-palmitoyl-2(1-13C)-palmitoyl-sn-glycero-3-phosphatidylcholine (2[1-13C]DPPC) were investigated by use of attenuated total reflection infrared spectroscopy with polarized light. Experiments were performed with the aim to determine the orientation of the two ester groups in these phospholipids in the solid state and in the hydrated state at temperatures below and above the respective gel to liquid-crystalline phase transitions. Substitution of the naturally occurring 12C carbonyl carbon atom by 13C in the ester group of the sn-2 chain of DMPC and DPPC shifts the infrared absorption of the carbonyl double bond stretching vibration to lower frequency. This results in two well-resolved ester C=O bands which can be assigned unequivocally to the sn-1 and sn-2 chains as they are separated by more than 40 cm-1. The two ester CO-O single bond stretching vibrations of the molecular fragments-CH2CO-OC-are also affected and the corresponding infrared absorption band shifts by 20 cm-1 on 13C-labeling of the carbonyl carbon atom. From the dichroic ratios of the individual ester bands in 2(1-13C)DMPC and 2(1-13C)DPPC we were able to demonstrate that the sn-1 and sn-2 ester C=O groups are similarly oriented with respect to the bilayer plane, with an angle greater than or equal to 60 degrees relative to the bilayer normal. The two CO-O single bonds on the other hand have very different orientations. The CH2CO-OC fragment of the sn-1 chain is oriented along the direction of the all-trans methylene chain, whereas the same molecular segment of the sn-2 carbon chain is directed toward the bilayer plane. This orientation of the ester groups is retained in the liquid-crystalline phase. The tilt angle of the hydrocarbon all-trans chains, relative to the membrane normal, is 25 degrees in the solid state of DMPC and DPPC multibilayers. In the hydrated gel state this angle varies between 26 degrees and 30 degrees, depending on temperature. Neither the orientation of the phosphate group, nor that of the choline group varies significantly in the different physical states of these phospholipids.

Electrostatic interactions in phospholipid membranes revealed by coherent 2D IR spectroscopy

“…2 A). The elongation of these resonances along the diagonal direction of the 2D IR spectrum confirms the inhomogeneous character of the absorption bands of the carbonyl moieties (10,11,16). Each resonance has a negative (blue) contribution due to ground-state bleaching and to stimulated emission from the first excited state and a Author contributions: V…”

“…The absorption band shows a clear inhomogeneous character and can be described as a superposition of several substates (5-7). The carbonyl stretching line-shapes in membranes could yield direct information about molecular architecture and fluctuations in the membrane interface (10,11), provided that the origin of the spectral inhomogeneity of the carbonyl IR response in phospholipid membranes is understood. The inhomogeneity was attributed to differences in the local environment of the sn-1 and sn-2 carbonyl moieties stemming from the packing arrangements (6,8), the local chain conformations (8,9,(12)(13)(14), the relative positions of the two CAO groups with respect to the interface (9,15), and the degree of hydration (16,17).…”

Application of the DSC and spectroscopy methods in the analysis of the protective effect of extracts from the blueberry fruit of the genus Vaccinium in relation to the lipid membrane

“…The wave number for vibrations of completely dry lipid is just over two units less than that of completely hydrated lipid membrane (a liposome). The half width of the band depends on the ''stiffness'' of the polar head, namely on the capacity to move along the skeleton -N-C-C-O-P-O- [28][29][30].…”

“…In spectra thus prepared we examined four bands: vibrations of CH 2 and CH 3 groups of alkyl chains-located in the range of 3000-2800 cm -1 , vibrations of the carbonyl group (C=O)-located in the range of 1780-1700 and 1300-1200 cm -1 [26][27][28][29][30].…”

FT-IR spectroscopy of lipoproteins—A comparative study

“…It is known that Asp and Glu residues are exposed toward the polar environment [12]. HDL 3 is the smallest particle of four lipoproteins and has two molecules of apo A- is usually attributed to P=O stretching vibration [10,16] or asymmetric PO 2 -stretching [5,19]. The band B at 1171 cm for LDL and VLDL particles.…”