Molecular Devices

1
Molecular Devices
Chennai, September 14, 2005
K.L. Sebastian IPC Department, IISc http//ipc.iis
c.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
Height 8 nm Width 10 n
4
ROLLER
MOLECULAR
What do you mean?
5
Consider Hypostrophene-it is fluxional -perhaps
we can use this property!
To explain, let us start with Pentaprismane
6
Pentaprismane (C10H10) D5h
Hypostrophene C2v
7
(No Transcript)
8
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
(No Transcript)
10
Rolling Motion
Rolling-TS Eact 18 kcal/mol
Translation-TS Eact 65.5 kcal/mol
11
Molecular Roller
12
(No Transcript)
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
Cope Rearrangement of Semibullvalene
17
Semibullvalene on Al(100)
18
Metal surface cluster of 14 or 32 Al atoms in
two layers Hydrogen atoms at the edges.
B3LYP/Al3-21G, C,H6-31G Ea 21.8 kcal/mol
19
Fluxionality for Rotational Motion
20
Hypostrophene
21
Molecular wheel
22
MOLECULAR WHEEL
Eact 16.0 kcal/mol
23
The activation barriers and rate constants
24
Hopping onto adjacent Ge atoms
Adsorbed to the same site!
Eact 11.9 kcal/mol
25
(No Transcript)
26
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
Perhaps, in an excited state, this might happen
30
Ring too small
31
Eact42.4 kcal/mol
Eact a315 kcal/mol b36.6kcal/mol c33.6kcal/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
(No Transcript)
33
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
(No Transcript)
36
Nature does it well!
37
Biological Molecular Motors
All of them occur in BIOLOGICAL systems
38
Figure from http//ccgb.umn.edu/mwd/cell.html
39
Figures and animation from http//www.sp.uconn.ed
u/terry/images/anim/ATPmito.html
40
ATP Synthase (Rotary)
ATP Synthase
Synthesizes ATP. Rotates while it does this!
41
Kinesin (Walker)
Works like a PORTER at the railway station
See animation at http//mc11.mcri.ac.uk/wrongtrous
ers.html
42
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/molbioc
hem/MBWeb/mb2/part1/myosin.htm
43
Synthetic Molecular Motors
44
Rotaxane
45
Electron Removal
46
Proton Addition
47
(No Transcript)
48
Catenanes
49
Switching by Oxidation-Reduction Reations
50
Catenanes how to have light driven motor?
station
shuttle
51
(No Transcript)
52
K.L. Sebastian Current Science, 87, 232 (2004)
53
Can one have?
Cis-trans isomerization as in Azobenzene could be
useful
54
Molecular Ratchets, Second Law and Detailed
Balance
55

It can undergo ratchet-like internal rotation!
56
(No Transcript)
57
The fact that you can see rotation means that
your initial state is a non-equilibrium one!
So even if you had seen net rotation, that would
not violate the second law!
58
K.L. Sebastian, Physical Review E61, 937 (2000)
59
CONCLUSIONS
Fluxional behavior can be used to get interesting
mechanical motion
Ratchets, Light driven motor
60
 
Acknowledgements
 
               
Dr. Bidisa Das Prof. Ashoka Samuelson