3 2 versus 2 2 Addition of Metal Oxides Across CC Double Bonds

1
32 versus 22 Addition of Metal Oxides
Across CC Double Bonds
ACS National Meeting, Chicago August 26, 2001

• Dirk V. Deubel and Gernot Frenking
• University of Calgary, Canada
• University of Marburg, Germany

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Outline

• Objective
• Methods
• Metal oxide additions to ethylene
• Metal oxide additions to activated double bonds
• Summary

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Visualization of MD Results Movie

• Chaotic nature of molecular motion
• High-frequency motions such as C-H vibrations
  often uninteresting
• Remove unwanted high-frequency motions
• - Constrained dynamics Freeze interatomic
  distance to equilibrium value, MM chapter 6.5,
  or
• - Restrained dynamics Add penalty terms to the
  force field for deviations from the reference
  value, MM chapter 8.7, or
• - Filter trajectory using Fourier analysis
  techniques

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Filter Trajectory Using Fourier Analysis
Techniques

• Convert trajectory x(t) to frequency function
  X(?)
• Remove high frequencies from frequency function
  X(?)
• Convert modified frequency function X(?) to
  modified trajectory x(t)
• Use discrete Fourier transform for discontinuous
  trajectory

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Chain Amphiphiles

• Biological interest Cell membranes
• Industrial interest Insulators in
  semiconductors, filtration devices,
  anti-reflective coatings, fabric softeners
• Consist of polar head group and lipophilic
  hydrocarbon tail
• Many degrees of conformational freedom in the
  hydrocarbon tail
• Example Palmitic acid

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Chain Amphiphiles Form Various Phases

• Mono-, bi-, and multiple layers
• Langmuir-Blodgett films layers adsorbed on
  solid
• Micelles
• Dynamic properties of layers
• - perpendicular
• - lateral
• - conformational changes

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MD Simulation of Chain Amphiphiles I

• Energy E of a chain in the mean field consists of
  the following contributions
• E Eint Evdw Erep Espc Elb
• Eint internal energy of the chain,
• Calculated using standard force fields
• Evdw van-der-Waals interactions between
• chains,
• Calculated using Maier-Saupe potential

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MD Simulation of Chain Amphiphiles II

• E Eint Evdw Erep Espc Elb
• Erep repulsive contribution due to lateral
  pressure
• Calculated from cross-sectional area A of the
  chain and the lateral pressure ?
• Erep A ?
• The approach using the first three terms is
  denoted mean-field approach (Marcelja)
• E Eint Evdw Erep

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MD Simulation of Chain Amphiphiles III

• E Eint Evdw Erep Espc Elb
• Espc specific intermolecular interactions,
• e.g., hydrogen bridges in head-to-head
  arrangements,
• Calculated using force field methods
• Elb interaction between lipid and solid in
  Langmuir-Blodgett films,
• Calculated, e.g., using a Lennard-Jones potential

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Summary

• MD simulations of conformationally flexible
  molecules such as peptides or chain amphiphiles
  are important in biochemistry and in the chemical
  industry
• High-frequency motions such as C-H vibrations can
  be removed from trajectories for visualization
  purposes, using Fourier analysis techniques
• MD simulations of lipid layers can be performed
  using the mean-field approach (E Eint Evdw
  Erep)
• MD simulations of Langmuir-Blodgett films require
  additional concepts to model the interactions
  between lipid and solid