Molecular Dynamics Studies of the Stability of Water/<i>n</i>-Heptane Interfaces with Adsorbed Naphthenic Acids

Li, Zhiying; Cranston, Blair; Zhao, Liyan; Choi, Phillip

doi:10.1021/jp053048d

Cited by 11 publications

(5 citation statements)

References 26 publications

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“…The simulation geometry is similar to that applied previously (ref and refs therein) and has been used in many studies. − The size of the simulation cell was kept constant to accommodate the EE molecules on each interface (fixed area per lipid of 80 and 100 Å 2 − and Lz = 26 nm) to ensure that interactions across the z axis were negligible for each surface density considered at a fixed number of water molecules.…”

Section: Methodsmentioning

confidence: 99%

V-Shaped Molecular Configuration of Wax Esters of Jojoba Oil in a Langmuir Film Model

et al. 2018

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The aim of the present work was to understand the interfacial properties of a complex mixture of wax esters (WEs) obtained from Jojoba oil (JO). Previously, on the basis of molecular area measurements, a hairpin structure was proposed as the hypothetical configuration of WEs, allowing their organization as compressible monolayers at the air-water interface. In the present work, we contributed with further experimental evidence by combining surface pressure (π), surface potential (Δ V), and PM-IRRAS measurements of JO monolayers and molecular dynamic simulations (MD) on a modified JO model. WEs were self-assembled in Langmuir films. Compression isotherms exhibited π at 100 Å/molecule mean molecular area ( A) and a collapse point at π ≈ 2.2 mN/m and A ≈ 77 Å/molecule. The Δ V profile reflected two dipolar reorganizations, with one of them at A > A due to the release of loosely bound water molecules and another one at A < A < A possibly due to reorientations of a more tightly bound water population. This was consistent with the maximal SP value that was calculated according to a model that considered two populations of oriented water and was very close to the experimental value. The orientation of the ester group that was assumed in that calculation was coherent with the PM-IRRAS behavior of the carbonyl group with the C═O oriented toward the water and the C-O oriented parallel to the surface and was in accordance with their orientational angles (∼45 and ∼90°, respectively) determined by MD simulations. Taken together, the present results confirm a V shape rather than a hairpin configuration of WEs at the air-water interface.

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Section: Methodsmentioning

confidence: 99%

V-Shaped Molecular Configuration of Wax Esters of Jojoba Oil in a Langmuir Film Model

et al. 2018

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“…The simulation geometry is similar to that proposed by Feller and co-workers 33 and has been used in many recent studies. [34][35][36] Although computationally more expensive than the effective monolayer geometry employed by Kaznessis et al, 26 the present simulation box permits the study of CPZ-containing and CPZ-free monolayers simultaneously, thus facilitating comparison. Because of the significant molecular volume of CPZ, the surface densities on each monolayer may differ in this approach.…”

Section: Methods and Computational Detailsmentioning

confidence: 99%

Molecular Dynamics Simulations of Neutral Chlorpromazine in Zwitterionic Phospholipid Monolayers

2006

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Molecular dynamics simulations have been performed to investigate the interactions between chlorpromazine (CPZ), a neuroleptic drug used in the treatment of psychiatric disorders, and dipalmitoylphosphatidylcholine (DPPC), a zwitterionic phospholipid, in Langmuir monolayers. The results from simulations carried out at different monolayer surface densities were able to capture important features of the CPZ-lipid interaction. We find that neutral (unprotonated) CPZ is preferentially located in the lipid tail region of the phospholipids, in little contact with the aqueous phase, and that the orientation of its rigid ring structure and tail conformation vary with lipid surface density. CPZ is found to promote ordering of the lipid tails for all surface densities because of a reduction in the effective surface area per lipid upon addition of the drug. Similar effects have been observed in previous studies of cholesterol in DPPC monolayers, in which lipid tails were seen to order around the solute. This feature, however, is quite distinct from what we observe for the most dense monolayer considered here (area per lipid of 50 A(2)), for which we find that CPZ promotes a local distortion of the lipid tails in its immediate vicinity and a concomitant ordering of lipid tails located further away from the solute. This view is further supported by the results obtained for an approximated nonlinear vibrational sum frequency generation susceptibility, which showed greater tail disorder close to CPZ.

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“…This result is especially important if one seeks to simulate naphthenate content in crude oils with surrogate surfactant molecules. At this point, there is no consensus on what represents a good surrogate for naphthenates [33,34].…”

Section: Toluene Microemulsions With Binary Mixtures Of Sdhs and Testmentioning

confidence: 99%

The Characteristic Curvature of Ionic Surfactants

Acosta

Yuan

Bhakta

2008

J Surfact & Detergents

142

219

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Characterizing the hydrophilic-lipophilic nature of a surfactant molecule has been a challenge for colloid scientists and technologists. The hydrophilic-lipophilic balance (HLB), the packing factor, the phase inversion temperature (PIT) and the natural curvature of the surfactant are all terms that seek to address this issue. In this article we build on the hydrophilic-lipophilic difference concept (HLD) (Salager et al. Langmuir, 16, 5534-5539, 2000) to develop a methodology to determine a characteristic curvature (Cc) for ionic surfactants based on the phase behavior of mixed ionic surfactant microemulsions. In essence, the method consists of evaluating the shift in optimal electrolyte concentration as a function of the mole fraction of the test surfactant in a mixture with a reference surfactant, sodium dihexyl sulfosuccinate (SDHS) and applying the appropriate HLD equation for ionic surfactant mixtures to determine Cc. The values of Cc were determined for a range of surfactants, including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), sodium naphthenate, and others. The method was also extrapolated to nonionic additives and hydrophilic linkers. It was observed that the calculated values of Cc were similar to those predicted by group contribution models, however the proposed method can be used even for complex surfactant mixtures. Finally, when Cc values were compared to apparent packing factor and HLB values, it was found that Cc is correlated with the apparent packing factor of ionic surfactants, and that Cc correlates with the HLB value for nonionic amphiphiles.The physical interpretation of Cc, and its potential application in the Net-Average Curvature equation of state for oil-surfactant-water systems is discussed.

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Molecular Dynamics Studies of the Stability of Water/n-Heptane Interfaces with Adsorbed Naphthenic Acids

Cited by 11 publications

References 26 publications

V-Shaped Molecular Configuration of Wax Esters of Jojoba Oil in a Langmuir Film Model

V-Shaped Molecular Configuration of Wax Esters of Jojoba Oil in a Langmuir Film Model

Molecular Dynamics Simulations of Neutral Chlorpromazine in Zwitterionic Phospholipid Monolayers

The Characteristic Curvature of Ionic Surfactants

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