Surface pressure–surface area characteristics of a series of autoxidation products of cholesterol

Kamel, A. M.; Felmeister, Alvin; Weiner, Norman

doi:10.1016/s0022-2275(20)39525-0

Cited by 16 publications

(3 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To address monolayer stability, each compression isotherm was completed within approximately 30 min, as a significant onset of oxidation of pure Chol monolayers is known to occur around 45 min after spreading. 25 Similarly, oxidation of Chol mixed in DMPC monolayers was shown to be detectable only after 40 min of air exposure. 33 Isotherm Analysis.…”

Section: ■ Materials and Methodsmentioning

confidence: 96%

“…The standard deviations of the measured mean molecular area (MMA) and surface pressure were ±0.5 A 2 /molecule and ±1 mN/m, respectively. To address monolayer stability, each compression isotherm was completed within approximately 30 min, as a significant onset of oxidation of pure Chol monolayers is known to occur around 45 min after spreading . Similarly, oxidation of Chol mixed in DMPC monolayers was shown to be detectable only after 40 min of air exposure …”

Section: Methodsmentioning

confidence: 99%

“…Although there are numerous studies on mixed PC/sterol monolayers using various experimental techniques, most have been concerned with nonoxidized Chol derivatives. To date, there are only a few theoretical and even fewer experimental published studies on mixed PC/oxysterol monolayers. − For instance, the relationship between the oxidation position on oxysterols, and their condensing and ordering effects on PC monolayers remain largely unexplored. − …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reduced Condensing and Ordering Effects by 7-Ketocholesterol and 5β,6β-Epoxycholesterol on DPPC Monolayers

et al. 2015

View full text Add to dashboard Cite

The exposure of organic-coated marine aerosols containing cholesterol (Chol) to radiation and/or an oxidizing atmosphere results in the formation of oxidized derivatives or oxysterols and will likely change aerosol surface properties. However, the intermolecular interactions between oxysterols and other lipid components and their influence on the surface properties of marine aerosols are not well-known. To address this question, the interfacial behavior and domain morphology of model Langmuir monolayers of two ring-substituted oxysterols, 7-ketocholesterol (7-KChol) and 5β,6β-epoxycholesterol (5,6β-EChol), mixed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) were investigated by means of compression isotherms and Brewster angle microscopy (BAM) over a broad range of surface pressures and sterol molar ratios. Mixed DPPC/cholesterol (Chol) monolayers were also measured for comparison. The results of compression experiments showed that the condensing effect induced on mixed DPPC/sterol monolayers at low surface pressures and for intermediate molar ratios (0.3 ≤ X(sterol) ≤ 0.7) was weaker for oxysterols than for Chol. Additionally, mixed DPPC/oxysterol monolayers exhibited markedly smaller (∼2-3-fold) interfacial rigidity. Examination of the excess free energy of mixing further revealed that DPPC monolayers containing 7-KChol and Chol were thermodynamically more stable at high surface pressures than those with 5,6β-EChol, indicating that the strength of interactions between DPPC and 5,6β-EChol was the smallest. Finally, BAM images in the LE-LC phase of DPPC revealed that in comparison to Chol the addition of small amounts of oxysterols results in larger and less numerous domains, showing that oxysterols are not as effective in fluidizing the condensed phase of DPPC. Taken together, these results suggest that the strength of van der Waals interactions of DPPC alkyl chains with sterols follows the sterol hydrophobicity, with Chol being the most hydrophobic and oxysterols more hydrophilic due to their ketone and epoxy moieties. The difference in the condensing ability and stability of 7-KChol and 5,6β-EChol on DPPC likely originates from the distinct molecular structure and position of oxidation on the steroid nucleus. As suggested by recent MD simulations, depending on the oxidation position, ring-substituted oxysterols have a broader angular distribution of orientation than Chol in bilayers, which could be responsible for the observed reduction in condensing ability.

show abstract

Section: ■ Materials and Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%