1 / 26

PROTEIN PHYSICS LECTURES 5-6 Elementary interactions: hydrophobic & electrostatic;

PROTEIN PHYSICS LECTURES 5-6 Elementary interactions: hydrophobic & electrostatic; SS and coordinate bonds. Hydrophobic effect. Concentration of C 6 H 12 in H 2 O: 50 times less than in gas! WHY?. H 2 O. G int : “ Free energy of interactions ”

frey
Download Presentation

PROTEIN PHYSICS LECTURES 5-6 Elementary interactions: hydrophobic & electrostatic;

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. PROTEIN PHYSICS LECTURES 5-6 Elementary interactions: hydrophobic & electrostatic; SS and coordinate bonds

  2. Hydrophobic effect Concentration of C6H12 in H2O: 50 times less than in gas! WHY? H2O

  3. Gint: “Free energy of interactions” (“mean force potential”) Chemical potential: m G(1) = Gint - T•kBln(V(1))  Gint + T•kBln[C] EQUILIBRIUM for transition of molecule1from A to B: GA(1) = GB(1) chemical potentials inAandBare equal GintAB = GintB – GintA GintAB= kBT•ln([CinA]/[CinB]) ===================================================

  4. Experiment: GintAB= kBT•ln([C1inA]/[C1inB]) SintAB = -d(GintAB)/dT HintAB = GintAB +TSintAB [C] of C6H12 in H2O: 50 times less than in gas; 100000 times less than in liquid C6H12 C6H12 T=2980K=250C

  5. -2/3 Loss: S usual case -2/3 +1/3 H-bond: directed Loss: LARGE E rare case “hydrophobic bond”

  6. High heat capacity d(H)/dT: Melting of “iceberg”

  7. Octanol  Water 20-25 cal/mol per Å2 of molecular accessible non-polar surface

  8. ______ large effect _______ small ______ large

  9. Electrostatics in uniform media: potential 1 = q1/r Interaction of two charges: U = 1q2 = 2q1 = q1q2/r  = 1 vacuum   3 protein   80 water Protein/water interface In non-uniform media: = ? At atomic distances: = ?

  10. CHARGE inside PROTEIN Water => vacuum: U  +100 kcal/mol Water => PROTEIN (ε3) R  1.5 - 2 Å U  +30 - 40 kcal/mol CHARGE inside PROTEIN: VERY BAD

  11. Non-uniform media: eff = ?

  12. j = q/1r

  13. j = (q/1)/r - - - -

  14. j = q/reff in positions: - - - - eff≈40 +-+-+ –+–+– eff≈ 200 !! Good estimate for non-uniform media

  15. effective in non- uniform media

  16. Large distance: Atomic distance:  = 80 = ? intermed. “vacuum”, ε~1? but absence of intermed. dipoles can only increase interaction…

  17. At atomic distances in water: 1) =80 is not a bad approximation (much better than  = 1 or 3 !!) • (salt does not dissolve, if <50 at 3Å!) • [H]1/2=10-1.75 [H]1/2=10-4.25e-Gel/RT •   30-40 at ~2.5Å! Gel = 2.5  ln(10)  RT  6RT  3.5 kcal/mol at 2.5Å

  18. Protein engineering experiments: (r) = pH  2.3RT  eff(r)

  19. Dipole interactions (e.g., H-bonds): (HO)-1/3-H+1/3::::::(OH)-1/3-H+1/3 Quadruple interactions Also: charge-dipole, dipole-quadruple, etc. Potentials: dipole ~ 1/r2 quadruple ~ 1/r3

  20. Electrostatic interactions also occur between charge (q) and non-charged body if its 2 differs from the media’s 1: U ~ q• [1/2– 1/1] •V• (1/r4) at large r In water: repulsion of charges from non-polar molecules (since here 1>>2); in vacuum (where 1<2): just the opposite! 1 + + + - - - 2 V

  21. Debye-Hückel screening of electrostatic by ions: U = [q1q2/r]•exp(-r/D) ; in water: D = 3Å•I-1/2; Ionic strength I = ½iCi(Ziion)2 . Usually:I  0.1 [mol/liter]; D  8Å. Electrostatics is an example of a multi-body (charge1, charge2, media, ions) interaction

  22. Electrostatics is T-dependent; U = (1/)•(q1q2/r) is free energy; TS = T•(-dU/dT) = -T•[d(1/)/dT]•(q1q2/r) = = [dln()/dlnT]•U in water: when T grows from 273o to 293oK (by 7%),  decreases from 88 to 80 (by 10%): TS≈ -1.3U; H  -0.3U In water the entropic term (-TS) is the main for electrostatics!

  23. S-S bonds (Cys-Cys) exchange S-S bond is not stable within a cell

  24. Coordinate bonds (with Zn++, Fe+++,…)

  25. j = q/r1 - - - -

More Related