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Molecular Devices

Molecular Devices. Chennai, September 14, 2005. K.L. Sebastian IPC Department, IISc http://ipc.iisc.ernet.in/~kls. Outline. Motivation – examples from biology Molecular Rollers and Rocker Molecular Wheel Molecular Rattle . Fluxionality for Rotational Motion

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Molecular Devices

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  1. Molecular Devices Chennai, September 14, 2005 K.L. Sebastian IPC Department, IISc http://ipc.iisc.ernet.in/~kls

  2. Outline • Motivation – examples from biology • Molecular Rollers and Rocker • Molecular Wheel • Molecular Rattle • . Fluxionality for Rotational Motion • Nature does it very well! (Biological Molecular Motors) • Synthetic Molecular Motors • Light driven molecular motor

  3. Is that a flower? It is a motor Height ~ 8 nm Width ~ 10 n

  4. Seems rather difficult, perhaps we can try to use fluxionality! Can one design molecules that would prefer to roll on a surface? MOLECULAR ROLLER What do you mean?

  5. God! He is crazy!! ConsiderHypostrophene-itis fluxional -perhaps we can use this property! To explain, let us start with Pentaprismane

  6. H hypostrophene pentaprismane Symmetry is broken! It can bebroken inFIVEdifferent ways! Pentaprismane (C10H10) D5h Hypostrophene C2v

  7. Five degenerate minima! It should be possible to jump from one to the other It does! Known asDegenerate Cope Rearrangement

  8. Activation energy B3LYP/6-31G** (kcal/mol) 25.31 GS TS Rate constant Degenerate Cope Rearrangement for Hypostrophene Rate constant ~ 1.8 X 10-5 sec-1 Activation energy Q and Q* are the partition functions of GS and TS

  9. Think of Hypostropheneadsorbedon Al(100)

  10. Rolling Motion Rolling-TS Eact ~ 18 kcal/mol Translation-TS: Eact ~ 65.5 kcal/mol

  11. Same thing can happen with syn-TOD! Molecular Roller

  12. Syn-TOD Cubane C2v Td Activation energy B3LYP/6-31G** (kcal/mol) GS 24.25 TS

  13. Activation energy 13.6 kcal/mol (B3LYP/6-31G** C,H and 3-21G for Al) TS

  14. MOLECULAR ROLLERS We conclude that: Hypostrophene and tricyclooctadiene when chemisorbed on Al(100) surface should behave as ‘Molecular roller’ Bidisa Das, K.L Sebastian, Chemical Physics Letters, 330, 433 (2000).

  15. MOLECULAR ROCKER

  16. GS GS TS Activation energy B3LYP/6-31G** (kcal/mol) 5.5 Cope Rearrangement of Semibullvalene

  17. Semibullvalene on Al(100)

  18. MOLECULAR ROCKER Metal surface: cluster of 14 or 32 Al atoms in two layers Hydrogen atoms at the edges. B3LYP/Al:3-21G, C,H:6-31G** Ea = 21.8 kcal/mol

  19. Fluxionality for Rotational Motion Fe(CO)3 Fe(CO)3 Fe(CO)3 Fe(CO)3 moving around hypostrophene

  20. 203i cm-1 4.3 kcal/mol 33.6 kcal/mol Hypostrophene

  21. Molecular wheel

  22. C5H5Ge(CH3)3is known to be fluxional! MOLECULAR WHEEL Eact ~ 16.0 kcal/mol

  23. M atom bonded to Cp and basis-sets used rate constant at 298.15 K (sec-1) Eact (kcal/mol) Si (C,H: 6-31G** & Si: 6-31G**) 14.04 3.2X102 Ge (C,H: 6-31G** & Ge: 6-31G**) 12.21 1.6X103 Sn (C,H: 6-31G** & Sn: 3-21G) 5.74 3.7X108 The activation barriers and rate constants

  24. Cyclopentadienyl adsorbed on Ge surface, should move like awheel! Hopping onto adjacent Ge atoms Adsorbed to the same site! Eact ~ 11.9 kcal/mol

  25. M atom bonded to Cp and basis-sets used Rate constant (sec-1) 298.15 K Eact (kcal/mol) Si (C,H: 6-31G** & Si: 6-31G**) 13.45 8.5X102 Ge (C,H: 6-31G** & Ge: 6-31G**) 11.90 1.9X104 Sn (C,H: 6-31G** & Sn: 3-21G) 5.97 2.5X108

  26. Molecular Wheel Sn That is not bad! Why don’t you call it amolecular “seal”? Ea = 5.97 kcal/mol B. Das and K.L. Sebastian: CPL 357, 25 ( 2002)

  27. We conclude that : The cyclopentadienyl co-adsorbed with hydrogen on Si/Ge/Sn (111) surfaces would form a system where the five membered ring can undergo spinning motion with low activation energies. Bidisa Das, K.L Sebastian, Chemical Physics Letters, 357, 25 (2002).

  28. Molecular Rattle A B B A B A

  29. H+ - Does not happen! Ionization potential of H too large! - H+ Perhaps, in an excited state, this might happen

  30. Li+ Replace H with Li! - - Li+ Ring too small

  31. Eact~42.4 kcal/mol Eact a:315 kcal/mol b:36.6kcal/mol c:33.6kcal/mol These are the molecules that we studied but activation energies for the ‘umbrella inversion’ kind of motion was found to be high. M. Oda, Pure & Appl. Chem. 58, 7 (1986), T.Z. Ktaz, P. A. Garratt, J. Am. Chem. Soc. 85, 2852 (1963).

  32. C9H9-

  33. Molecular Rattle Proton going through benzene (C6H7+) Mahapatra, Sathyamurthy, Current Science, 1995 Ea = 11.7 kcal/mol B. Das and K.L. Sebastian: CPL, 365, 320 (2002)

  34. Cyclononatetraenyl-lithium The activation barrier for the ‘umbrella inversion’ in this case is ~11.5 kcal/mol Normal mode analysis: 276 cm-1(GS), 274i cm-1(TS) 1D through ring motion calc.: 277 cm-1(GS), 267i cm-1 (TS)

  35. Nature does it well!

  36. We know of several, efficient molecular motors! Biological Molecular Motors All of them occur in BIOLOGICAL systems

  37. Figure from: http://ccgb.umn.edu/~mwd/cell.html

  38. Energy from photosynthesis Figures and animation from: http://www.sp.uconn.edu/~terry/images/anim/ATPmito.html

  39. Most powerful known motor ATP Synthase (Rotary) ATP Synthase Synthesizes ATP. Rotates while it does this!

  40. Proteins that WALK! Kinesin (Walker) Works like a PORTER at the railway station See animation at http://mc11.mcri.ac.uk/wrongtrousers.html

  41. Proteins that PUSH! Myosin Myosin For an animation, see the CD of the book: Molecular Biology of the Cell by B. Alberts et. Al. See also: http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/myosin.htm

  42. NO WAY near the natural ones! Synthetic Molecular Motors

  43. shuttle station stopper station Rotaxane

  44. +e -e Electron Removal

  45. Proton Addition - H+ + H+

  46. Either electron removal or proton addition

  47. 2-catenane 3-catenane Catenanes

  48. -e +e Switching by Oxidation-Reduction Reations

  49. Leigh et. al. Nature, 424, 174 (2003) Excitation of the station leads to unbinding! Catenanes – how to have light driven motor? station shuttle

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