Infrared Spectra of
K+(Tryptamine)(H2O)n and
K+(Tryptamine)(H2O)nAr
Cluster Ions
Amy L. Nicely and James M. Lisy
OSU International Symposium on
Molecular Spectroscopy
June 16, 2008
Outline
Motivation
 Apparatus and formation of cluster ions
 Supporting calculations
 K+(Tryptamine)(H2O)n vs
K+(Tryptamine)(H2O)nAr experimental and
calculated IR spectra

Motivation

Extension of previous studies
 K+(H2O)n
 K+(Indole)(H2O)n

Biological significance
 Neurotransmitters
(serotonin)
 Amino acids (tryptophan)
Triple quadrupole mass spectrometer
LaserVision OPO/A
Tunable: 1.35-10 µm




Neutral clusters are formed via a
Nd3+:YAG Laser
(1064 nm)
supersonic expansion
10 Hz, 10 ns pulse width
Tryptamine in sample heater (~115 °C)
Fully expanded neutral clusters collide with alkali cations
produced via thermionic emission
MS-MS method: select ion cluster, dissociate with IR laser,
detect fragment ion
Evaporative Cooling
En [K+(Tryp)(H2O)n]
En [K+(Tryp)(H2O)2Arn]
ΔE ≈ BE Ar
ΔE ≈ BE H2O
Energy
●
Cooling efficiency determined by the evaporating ligands’ binding energy
Most weakly bound ligand evaporates to cool cluster, removes both mass and
energy
Energy
●
Efinal [K+(Tryp)(H2O)2]
0-
0- Efinal [K+(Tryp)(H2O)2Ar]
H2O evap. =
larger energy loss
Ar evap. =
smaller energy loss
Terminal temperature
~300-400 K
Terminal temperature
~40-100 K
Calculation details

Preliminary structures generated using SPARTAN 02

Geometries optimized, frequencies and energies
calculated at B3LYP/6-31+G* level with GAUSSIAN
03

SWIZARD used to apply Gaussian lineshape with 5100 cm-1 peak width to scaled calculated frequencies

Thermodynamics data obtained using THERMO.PL
perl script
Hydrated Biomolecules
Tryptamine has nine
conformers which
differ in side chain
orientation and lone
pair position
Favored conformer
in neutral gas-phase
experiments
Not observed in
neutral gas-phase
experiments
Zwier, T.S., et. al., Science 2004, 303, 1169-1173.
K+(Tryptamine) spectra
NH
AGph(in)
AGph(in)
NH2 asym
NH2 sym
In the presence of K+, the
two lowest-energy
K+(Tryptamine) isomers are
built from those not seen in
neutral experiments
AGpy(in)
Simulated
K+(Tryp)Ar3
3250
AGpy(in)
3350
Experimental
3450
3550
-1
Frequency (cm )
3650
Experimental spectrum
shows presence of both
isomers, in good agreement
with the calculated spectra
Temperature Dependence
“Tagging” the cluster ions
with an argon atom reduces
the internal energy
K+(Tryp)(H2O)1
"warm"
By changing the effective
temperature of the cluster
ions, different isomers may
be thermodynamically
favored, resulting in different
spectral features
K+(Tryp)(H2O)1Ar
"cold"
2800
3000
3200
3400
3600
-1
Frequency (cm )
3800
Identifying the OH and NH features
Gas-phase H 2 O
 sym  3657 cm
K+(Tryp)(H2O)
-1
 asym  3756 cm-1
NH
+
K (H 2O)Ar
 sym  3636 cm-1
 asym  3710 cm-1
OH νasym
OH νsym
Vaden, T.D., Weinheimer, C.J. and Lisy, J.M.,
J. Chem. Phys. 2004, 121, 3102-3107.
NH2 asym
3250
3350
3450
3550
Frequency (cm-1)
3650
3750
Identifying the OH and NH features
K+(Tryp)(H2O)
NH
OH νasym/ νfree
OH νsym
3350
3450
3550
3650
3750
Frequency (cm-1)
Miller, D.J., Lisy, J.M., J. Chem. Phys.
2006, 124, 184301.
3250
NH2 asym
3350
3450
OH πhydrogen
bond
3550
Frequency (cm-1)
3650
3750
Identifying the OH and NH features
K+(Tryp)(H2O)Ar
???
NH
OH πhydrogen
bond
3250
3350
3450
3550
Frequency (cm-1)
OH νasym
OH νsym
3650
OH νfree
3750
38
Relative Free Energies
Relative Free Energies (kJ/mol)
25
20
15
10
5
0
0
50
100
150
200
250
300
Temperature (K)
1A
1B
1C
1D
1E
350
400
1E
1E
1B
1B
1A
1C
1A
1D
1C
K+(Tryp)(H2O)Ar
K+(Tryp)(H2O)
2700
2900
3100
3300
Frequency (cm-1)
3500
3700
3900
1D
00
Simulated Spectra
K+(Tryp)(H2O)
1D
K+(Tryp)(H2O)Ar
1A
~87%
~50%
1E
~35%
1C
~13%
1C
~15%
2900
3100
3300
3500
-1
Frequency (cm )
3700
2700
3900
2900
3100
3300
3500
-1
Frequency (cm )
3700
3900
K+(Tryp)(H2O)2 Spectra
K+(Tryp)(H2O)2
"warm"
Significant
differences observed
again between the
warm and cold
spectra
K+(Tryp)(H2O)2Ar
"cold"
2800
3000
3200
3400
3600
-1
Frequency (cm )
3800
No new features
compared with n=1
spectra, but there is
some additional
splitting and
broadening
K+(Tryp)(H2O)2
2A
2B
~43%
~30%
2C
~27%
2800
3000
3200
3400
Frequency (cm-1)
3600
3800
K+(Tryp)(H2O)2Ar
2A
2B
~37%
~37%
2E
2F
~7%
2800
3000
3200
3400
Frequency (cm-1)
3600
3800
~3%
2G
~17%
Conclusions
K+ stabilizes the high-energy tryptamine
conformers
 K+…Tryp and K+…OH2 interactions favored over
Tryp…OH2 interactions
 Temperature dependence

temperatures  favors “free” water molecules
and π-hydrogen bonds
 Low temperatures  favors hydrogen-bonded
water molecules, traps higher-energy isomers
 High
Acknowledgements



Dr. Jim Lisy
Dr. Dotti Miller
Lisy Group Members
 Mr.
Jason Rodriguez
 Mr. Jordan Beck
 Mr. Oscar Rodriguez, Jr.

Mr. Brian E. Nicely

Funding
 NSF
CHE-0415859
 NSF CRIF-0541659
 UIUC Department of
Chemistry
 UIUC Graduate College
Block Grant
Competition between interactions
vs.
K+(Tryptamine)
(Tryptamine)(H2O)
Meerts, W.L., et. al., J. Am. Chem. Soc. 2005, 127, 10356-10364.
K+(Tryptamine)(H2O) structure maximizes
potassium interactions
K+Tryptamine(H2O)2
Relative Free Energies (kJ/mol)
20
10
0
0
50
100
150
200
250
300
Temperature (K)
2A
2B
2C
2D
2E
2F
2G
350
400
2700
2900
3100
3300
3500
-1
Frequency (cm )
3700
3900