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Interaction of benzene with bilayers. Thermal and structural studies.

Publication ,  Journal Article
McDaniel, RV; Simon, SA; McIntosh, TJ; Borovyagin, V
Published in: Biochemistry
August 17, 1982

The thermal and structural properties of saturated phosphatidylcholine liposomes are significantly altered by benzene. Upon the addition of benzene, the liposomes first swell and then disperse into small multilamellar vesicles. At 20 degrees C these vesicles contain striations or ripples in the plane of the bilayer. Major changes in the thermal behavior of DSPC-benzene liposomes occur near mole ratios of 2:1 and 1:1. At a 2:1 mole ratio, the area under the main endothermic peak, delta Hm, essentially disappears; however, the total heat absorbed, delta Hf, remains approximately equal to that of the control. This occurs because for benzene mole fractions 0.12 less than x less than 0.50, benzene increases the apparent molar heat capacity, Cp, of the gel phase to about 1.2 kcal/(mol . deg). We interpret this increase in heat capacity to be due to an increase in the concentration of defects (or disorder) in the gel phase. At mole fractions of benzene between 0.5 and 0.9, the transition temperature decreases by 20-30 degrees C, and broad, multiple transitions are observed. From 0.5 less than or equal to x less than or equal to 0.9, the apparent molar heat capacity of the liquid-crystal phase increases to that of the defected rippled gel phase. The value of delta Hf approaches the heat of fusion for 2 mol of n-octadecane, suggesting that benzene uncouples the liquid-crystalline acyl chains. The lipids affected by benzene or "boundary lipids" have higher heat capacity than nonperturbed lipids. The apparent molar specific heat, Cp, of 1,2-distearoyl-sn-glycero-3-phosphorylcholine (and 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine) multilamellar vesicles is 0.20 +/- 0.05 kcal/(mol. deg) in the L beta', P beta, and L alpha phases. Cp fluctuates about this value in all three phases upon repeated phase transitions in the same sample. However, the value of Cp in the P beta (rippled) phase exhibits much greater fluctuations in Cp than that in the L alpha phase. We attribute these fluctuations to crystal packing defects.

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Published In

Biochemistry

DOI

ISSN

0006-2960

Publication Date

August 17, 1982

Volume

21

Issue

17

Start / End Page

4116 / 4126

Location

United States

Related Subject Headings

  • X-Ray Diffraction
  • Thermodynamics
  • Pulmonary Surfactants
  • Phosphatidylcholines
  • Liposomes
  • Lipid Bilayers
  • Freeze Fracturing
  • Chemistry, Physical
  • Chemical Phenomena
  • Calorimetry, Differential Scanning
 

Citation

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McDaniel, R. V., Simon, S. A., McIntosh, T. J., & Borovyagin, V. (1982). Interaction of benzene with bilayers. Thermal and structural studies. Biochemistry, 21(17), 4116–4126. https://doi.org/10.1021/bi00260a031
McDaniel, R. V., S. A. Simon, T. J. McIntosh, and V. Borovyagin. “Interaction of benzene with bilayers. Thermal and structural studies.Biochemistry 21, no. 17 (August 17, 1982): 4116–26. https://doi.org/10.1021/bi00260a031.
McDaniel RV, Simon SA, McIntosh TJ, Borovyagin V. Interaction of benzene with bilayers. Thermal and structural studies. Biochemistry. 1982 Aug 17;21(17):4116–26.
McDaniel, R. V., et al. “Interaction of benzene with bilayers. Thermal and structural studies.Biochemistry, vol. 21, no. 17, Aug. 1982, pp. 4116–26. Pubmed, doi:10.1021/bi00260a031.
McDaniel RV, Simon SA, McIntosh TJ, Borovyagin V. Interaction of benzene with bilayers. Thermal and structural studies. Biochemistry. 1982 Aug 17;21(17):4116–4126.
Journal cover image

Published In

Biochemistry

DOI

ISSN

0006-2960

Publication Date

August 17, 1982

Volume

21

Issue

17

Start / End Page

4116 / 4126

Location

United States

Related Subject Headings

  • X-Ray Diffraction
  • Thermodynamics
  • Pulmonary Surfactants
  • Phosphatidylcholines
  • Liposomes
  • Lipid Bilayers
  • Freeze Fracturing
  • Chemistry, Physical
  • Chemical Phenomena
  • Calorimetry, Differential Scanning