characterization of ion-driven conformations in diphenylacetylene molecular switches arron wolk...
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Characterization of Ion-Driven Conformations in Diphenylacetylene
Molecular Switches
Arron Wolk
Johnson Lab
Yale University
Hydrogen Bonding in Supramolecular Complexes
• Infrared predissociation of cryogenically cooled ions
• Accessing the vibrational transitions of amide functionalities in supramolecular complexes
Catalytic Cycles
Host-GuestInteractions
Protein Folding
SolventInteractions
Electospray Ionization
Andersen, Biopolymers, 2006
N-H ••• O=C Bonds
Hydrogen Bond Linkages
Electrostatic InteractionsC-O ••• Na+
Rizzo, JACS, 2011
Cryogenic Mass Spectrometry: H2-Tagging in a Quadrupole Ion Trap
Wiley-McLarenextraction region
Ion optics
To time-of-flightand 2-D infrared analysis
Electrosprayneedle
Heated capillary
90° ionbender
RF only quadrupolesH2/He filled 3-D quadrupoleion trap with temperature
control to 8 KEinzel
Octopoles
1st skimmer
2nd skimmerDifferential
aperture
50 K heat shield
1x10-5 1.5x10-23x10-7Pressure (Torr) 1.5 760
•Adapted from Lai-Sheng Wang’s H2 tagging instrument
•Paul trap interfaced to our standard TOF experiment.
•Molecular H2 tag, analogous to Ar tag in previous predissociation experiments.
•We have interfaced our Ar tagging, TOF instrument to a new electrospray ionization source
Trapping, Cooling, and Tagging
He/H2 buffer gas
RF
RF
Pulsedvalve
Ions in Ions out
Paul Trap at 10K
100’s of collisions for translational cooling
1,000-10,000’s of collisionsfor internal energy cooling
72 74 76 78
Time of Flight (s)
30 ms
50 ms
40 ms
20 ms
10 ms
doubly-chargedparent
a)
b)
c)
d)
e)
trap residence time:
Sig
nal I
nten
sity
(ar
bitr
ary
units
)
hydrogen adduct formation
5
10
15
*
The Diphenylacetylene Scaffold
• Rigid scaffold limits conformational complexity
• Creates specific acceptor-donor interactions
• An ideal molecular switch backbone that responds with a conformation switch
Donor1
Acceptor
Donor2
?
O
O
O
NH
NH
O
NH
OR
Urea Amide
Lactone
NH
NH
O
NH
O
O
O
O
R
Cl-
Sodium Complex
νesterC=O
ν C=O
νCH
νfreeC=O
FreeNH
DonorNH
Photon Energy, cm-1
1200 1500 1800 2100 2400 2700 3000 3300 3600
Carbonyl Region NH Region
O
O
O
NH
NH
O
NH
OR
Na+
B3LYP/6-31+G(d,p)
A Neutral Analog
3000 3300 36001600 1650 17001750
B3LYP/6-31+G(d,p)
Na+ Complex
Free NH
Urea NHs
TMA+ Complex
Photon Energy, cm-1
Acceptor Possible Donors
•Acceptor redshifts •Two donors redshift•Remaining carbonyls largely unaffected
Donor NH Perturbation
1700 3200 3300 3400 3500Photon Energy (cm-1)
N-H
N-H
C=O
ν NHfree
O
O
O
NH
N
O
N
O
N
H H
O
O
O
NH
N
O
N
O
N
H H
O2N
Larger ShiftAcceptor Responds!
Electrostatic Potential:Positive Counterions
+-Na+ Complex TMA+ Complex
Na+
TMA+
A Story of Electrostatics
Cations Anions
O
O
O
NH
NH
O
NH
OR
Na+ TMA+ Cl- I-
Charge Solvationvs.
Double H-bond
Steric effectsversus
double H-bond
Three cation solvators Three cation solvators
The Chloride Anion
1650 1700 1750 2700 2850 3000 3150 3300 3450
Photon Energy (cm-1)
esterνCH
Free NH
Conformation Switch
Donor NHs
νamide
νurea
• Only one neutral NH h-bond donor
• Acceptor blueshifts, losing a hydrogen bond
•Spectator C=O’s blueshift
O
O
O
NH
N
O
N
O
N
H H
B3LYP/6-31+G(d,p)
NN
O
N
O
Cl
O
O
O
HHH
NN
O
N
O
Cl
O
O
O
HHH
O2N
TMA+
Cl-
Surveying Charge Solvation
+
-
Na+ TMA+
Cl-
2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600Photon Energy, cm-1
Switch*•Cl-
Switch•Cl-
Switch•Br-
Switch•I-
Halide SeriesDonor acidity drops
AcceptorProton Affinitydrops
Conclusions• Gained microscopic picture of an amide-based molecular
switch accommodating a charge center• Observed conformation switch in gas-phase• Future studies:
O
O
O
NH
N
O
N
OR
H H
Anion-DependentSwitching
Cl-
Molecular Switch Dynamics
Versatile Hydrogen Bond Framework
RO
O
NH
N
O O
NH
pH-DependentSwitching
RO
O
NH
N
O O
Fe H
Oxidation-DependentSwitching
O
O
NH
N
O O
H
Fluorescence Studies:Materials Mimic
N
O
R1
HN
O
NH
N
O
O
R2
H
H
R3
N
R3
O
H
Hydrogen-Bonded Scaffold Mimic
H+ e-
hv
Thank You• Ian Jones and Andrew Hamilton• Etienne Garand, Mike Kamrath, Chris Leavitt, and Mark
Johnson
Comparison to FTIR