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PROTEIN PHYSICS LECTURE 4

PROTEIN PHYSICS LECTURE 4. HYDROGEN BONDS. WATER molecule:. H-bond energy: 5 kcal/mol ICE sublimation: ( 12 kcal/mol - 2 kcal/mol [vdW] ) /2 10 kcal/mol [CH 3 -CH 2 -OH] - 5 kcal/mol [CH 3 -O-CH 3 ].

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PROTEIN PHYSICS LECTURE 4

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  1. PROTEIN PHYSICS LECTURE 4

  2. HYDROGEN BONDS WATER molecule: H-bond energy:5 kcal/mol ICE sublimation: (12 kcal/mol - 2 kcal/mol[vdW])/2 10 kcal/mol[CH3-CH2-OH] - 5 kcal/mol[CH3-O-CH3] (HO)-1/3-H+1/3::::: O-2/3-H2+2/3: e1/3 2/3  (-1/2-1/4+21/3) ~ 6 kcal/mol

  3. ICE

  4. MODEL OF “FORMED” and “BROKEN” H-BONDS IN WATER IS VERY ROUGH H--O in CCl4 H--Oin ICE H--Oin WATER O--H O--H ::: O

  5. PEPTIDE GROUP ALSO FORMS H-BONDS ACCEPTOR DONOR

  6. EXCHANGE OF H-BONDS

  7. ENERGY: E (E  min) BUT: THEMAL KICKS! Barometric eq.:density (N/V)|E=mgh ~ exp(-E/kBT) Boltzmann: Probability1_STATE(E) ~ exp(-E/kBT) ProbabilityV_STATES(E)~V•exp(-E/kBT) = exp(ln(V) - E/kBT) = exp(-(E – T•kB•ln(V))/kBT) = exp(-(E – T•S)/kBT)

  8. ProbabilityV_STATES(E) ~ V•exp(-E/kBT) = exp(-(E – T•S)/kBT) ENTROPY: S = kB•ln(V) => kB•ln(#STATES) FREE ENEGRY: F = E – TS Probability ~ exp(-F/kBT)  max F  min (under T=const)

  9. H-bonds are formed, when EH< -TSH Just because H-bonds have large energy, only their ENTROPIC part plays a role in water surrounding

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