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ECEN 5341/4341 Lecture 10 Feb 5,2014

. ECEN 5341/4341 Lecture 10 Feb 5,2014. Review of the Effects of Electric Fields on Chemical Reactions. Effects of Shifts in Energy . Review of Chemical Reactions. Changes in Collision Rates =1/z. 1. In a homogeneous solution no effect to first order in a uniform field.

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ECEN 5341/4341 Lecture 10 Feb 5,2014

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  1. . ECEN 5341/4341Lecture 10 Feb 5,2014 Review of the Effects of Electric Fields on Chemical Reactions. Effects of Shifts in Energy

  2. Review of Chemical Reactions

  3. Changes in Collision Rates =1/z • 1. In a homogeneous solution no effect to first order in a uniform field. • 2 Effects at boundaries • 3. Setio and Hsieh show changes at 5V/m of a factor of 5 in enzyme reaction rates at boundary. • 4. Other have shown changes that go as E2ω1/2 for ω<1010 for ω> E2ω-2

  4. Steric Effect, p ∙ p is usually a small number The Langevine Equation for shifts in angle as a Function of energy for a dipole For small fields • L = α V( )

  5. Changes in Energy So at room temperature N1≈N2 for energy states That are separated by hf where f <1010Hz.

  6. Stark Effect The Stark Effect is the Shift in Energy with an Applied Electric field. This shift is usually observed In the optical or infrared Part of the spectrum. The shifts may correspond To transitions in the radio or microwave part of the Spectrum. However the changes in Chemical reaction rates may be Exponential to satisfy the conservation of energy. The energy shifts may be in the Orientation of dipole moments etc. Hyperfine States resulting from nuclear spins lead to Multiple energy levels or broadening of the Lines. Energy shifts typically are so that f ≈ 10-4 E corresponds to transitions Between Stark shifted states.

  7. Zeeman Shifts with Magnetic Fields. The Larmor Precession Frequency

  8. More complete Diagram for Transitions between Energy Levels in Magnetic Fields without Hyperfine States. Figure 1 Shows a simplified diagram for the energy levels for a free radical. (Steiner and Ulrich} In the singlet state, S, the spins are aliened in opposite directions or spin up and spin down parallel to the external magnetic field. In the triplet state both spins are aliened or parallel to the magnetic field.

  9. Changes in Energy with Separation of Particles

  10. Magnetic Field Reaction Rates.

  11. More Realistic Energy Levels For a Free Radical

  12. Magnetic Field Dependence of Recombination Rate

  13. Some Biological Effects 1.Change is growth rates of two kinds of cancer and e-coli by ≈ 25% 2. Changes in free radical lifetimes by changes in the energy required For transitions between states. 3. Changes in free radical concentrations.

  14. E-Coli Growth In Reduced Magnetic Fields.

  15. E-Coli Growth vs Magnetic Field

  16. Free Radicals Are Molecules with Unpaired Spins. These molecules are very important and include molecules such as hemoglobin and chlorophyll Note hemoglobin is parmagnetic without O2 and diamagnetic with it.

  17. Protein Protein Energy levels.

  18. Energy Shifts with Confirmation States

  19. Temperature Effects on Chemical Reaction Rates The power absorbed is given by The rate of change of temperature for Short pulses is given by Changes in Chemical Reactions Rates

  20. Amplifiers • 1. Basic Definition • A small signal is used to extract energy from another source to produce a larger signal. 2. A typical transistor amplifier will extract energy from a DC source. Note with a BJT the control signal is separated in energy from the signal to be controlled. With MOSFET they are separated in space. 3. A parametric amplifier extracts energy from an AC source that is at a higher frequency. 4. A stochastic amplifier extracts energy from a noise source.

  21. Biological Amplifiers • 1. Nerve cells use chemical energy to maintain the potential difference of -50 to -100mV to transmit action potentials which trigger muscles • 2. Inputs from dendrites are summed to trigger action potentials at synapse which fire action potentials • 3. A neural transmitter can release 104 Ca++ ions. • 4. Many biological amplifiers have negative feedback. • Body temperature has a gain of -33 and the gain for blood pressure is -2 • 5. The gain is calculated as Gain =

  22. The Concentration of Electric Fields Across Membranes • Figure 2. A rectangular model for a cell and an approximant equivalent circuit for it. The membranes are typically 5 to 10nm thick while the cell may range from a few micrometers to a centimeter or so in length. The effective membrane resistance (Rm) per unit area takes on values of 0.14 to 15 Ω/m2in the transverse direction. This corresponds to resistivities in the range of ρm = 107 Ω m to ρm= 10 9 Ω m. The relative dielectric constant for the membrane is typically in the range of 2 to 4. Both the surrounding fluid and the interior of a cell have resistivitiesρf of about ρf= 2 Ω m and a relative dielectric constant of 50 to 80.

  23. Currents Through Cells

  24. A Membrane and Cell Model

  25. Parametric Amplifiers • 1

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