Infrared Spectroscopy of Alanine in Solid Parahydrogen Shin Yi Toh, Ying-Tung Angel Wong, Pavle...
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Transcript of Infrared Spectroscopy of Alanine in Solid Parahydrogen Shin Yi Toh, Ying-Tung Angel Wong, Pavle...
Infrared Spectroscopy of Alanine in Solid
Parahydrogen
Shin Yi Toh, Ying-Tung Angel Wong, Pavle Djuricanin, and Takamasa Momose
Department of ChemistryUniversity of British ColumbiaVancouver, BC, Canada.
Introduction
Motive – To study amino acids in relation to interstellar chemistry
Start with simple amino acid β-alanine
β-alanine in Astrochemistry:
• Found in various classes of carbonaceous meteorites.• Most abundant type of amino acid in CI chondrites (class of
carbonaceous meteorites).• Formed preferentially over α-alanine in ion-molecule reactions with
smaller molecules found in interstellar medium.
[1] J.G. Lawless, Geochim. Cosmochim. Ac., 37, 2207 (1978).[2] O. Botta, Z. Martins, and P. Ehrenfreund, Meteorit. Planet. Sci., 42, 81 (2007).[3] V. Blagojevic, S. Petrie, and D.K. Bohme, Mon. Not. R. Astron. Soc., 339, L7 (2003).
Computation:• First began with Ramek (1990) M. Ramek, J. Mol. Struct. (Theochem), 208, 301 (1990)
• Derived 20 stable conformers of β-alanine at HF/4-31G level of theory.
Gas Phase Spectroscopy: • McGlone and Godfrey (1995)
S.J. McGlone and P.D. Godfrey, J. Am. Chem. Soc., 117, 1043 (1995)
• Free-expansion jet spectrometry; observed conformers I, V.
• Sanz et al. (2006) M.E. Sanz, A. Lesarri, M.I. Peña, and V. Vaquero, J. Am. Chem. Soc., 128, 3812 (2006)
• Fourier transform microwave spectroscopy; found conformers II and III, in addition to I, V.
Matrix-isolation spectroscopy:• Dobrowolski et al. (2008) J.C. Dobrowolski, M.H. Jamróz, R. Kolos, J.E. Rode, and J. Sadlej, Chem. Phs. Chem., 9, 2042 (2008)
• Matrix-isolation IR spectroscopy (argon matrices); detected at least 3 conformers: I, II, IV.
• Stepanian et al. (2012) S. G. Stepanian, A. Y. Ivanov, D. A. Smyrnova, and L. Adamowiez, J. Mol. Struct., 1025, 6 (2012)
• Matrix-isolation FT-IR spectroscopy (argon matrices) + irradiation + matrix annealing + deuteration; detected the presence of at least 5 conformers: I, II, IV, V, VII.
Previous studies on β-alanine
Using solid pH2 matrix-isolation FT-IR spectroscopy, we aim to:
• determine the gas-phase conformational composition of β-alanine, and compare to that in argon matrix.
• investigate the outcomes of UV photochemistry on gas-phase β-alanine.
Objective
In on this study
Parahydrogen as matrix host
• The soft and more inert property of pH2 allow for the trapping of highly energetic states possibility of more conformers detection.
Matrix isolation spectroscopy of amino acids:
• Identify vibrational frequency of different conformers
• Identify stable conformer under various condition (low temperature, UV irradiation, etc)
Method
Experimental
18mm
1.6mm
Cartridge Heater
NTC Thermistor
Ortho-Para Converter:• Operates at 14K – triple
point of hydrogen• Magnetic catalyst:
(FeOH)O• Yields parahydrogen gas of
99.95% purity
Knudsen Cell:• Β-alanine sublimation
temperatures - 390±1K or 380±1K
Method
D 2 la
mp
• FT-IR spectrometer: KBr beamsplitter, MIR glowbar light source, liquid cooled MCT detector. 0.2 cm-1 resolution, 1000 scans, approx. 5000-700 cm-1 range
• UV-irradiation with D2 lamp (λ = 180 – 270 cm-1)
Method
Computational
• Theoretical frequencies and intensities calculated for the 11 lowest energy β-alanine conformers at the B3LYP/aug-cc-pVTZ level of theory.
Results and Discussions
0.05
0.04
0.03
0.02
0.01
0.00Abs
orba
nce,
relat
ive un
it
18001780176017401720Wavenumber, cm
-1
0.25
0.20
0.15
0.10
0.05
0.00
IV
I
III
I
IV
Para-H2Ar
II
III not observed in
Ar
0.10
0.08
0.06
0.04
0.02
0.00Abso
rban
ce, r
elativ
e unit
830820810800790780Wavenumber, cm
-1
III
VII IV
II
I
ν (C=O) regionω(NH2) region
Conformational Composition
Results and Discussions
11601150114011301120111011001090
Wavenumber, cm-1
Para-H2Ar
Para-H2Ar
III
II & I
IV
VIIVII
II
I
IV
Deposition Spectra
UV-Irradiation Difference Spectra
Ab
sorb
an
ce, re
lativ
e u
nit
ν (C-O) region
UV PhotochemistryConformer I II III IV VIIPopulation before UV 1.00 0.63 0.19 0.36 0.11Population after UV 0.73 0.46 0.25 0.49 0.03Change in population - 0.27 -0.17 +0.06 +0.13 -0.08 All population numbers are normalized to the population of conformer I at deposition.
Results and Discussions
Temperature dependence of conformational population
40
30
20
10
Exp
erim
enta
l pop
ulat
ion
ratio
, %
390388386384382380
Sublimation temperature, K
Conformer I Conformer II Conformer III Conformer IV Conformer VII
Conformer I II III IV VIIΔEZPE, kJ/mol 0.0 2.0 7.4 3.9 5.4
Boltzmann distribution at 390 K, % 46.4 25.4 4.7 14.1 9.0Boltzmann distribution at 380K, % 47.5 25.4 4.5 13.8 8.7
Conformational Studies:• Five conformers of β-alanine were identified: I, II, IV, III, and VII.• Conformer III was found for the first time under matrix isolation
technique.• Conformer V: possibility of inconclusive assignment by previous
research.
UV Photochemistry:• Conformational change:
• I & II IV• VII III
Sublimation Temperature:• Trend follows Boltzmann distribution. With increasing temperature:
• Lowest energy conformer (conformer I) decrease.• Higher energy conformers (conformer II, IV, III, and VII) increase.
• Useful technique for conformational studies of other similar molecules: • Aid in identifying the most stable conformer.
Conclusions
Advantages:• Conserves the room temperature conformations of the gas-phase sample.
• Lighter collision of the host molecule to the gaseous sample preserve the highly energized states of the target molecule.
• More profound isomerization of amino acids under UV irradiation in pH2 matrix compare to in Ar matrix.
• Comparable spectra line-width of the sample with that performed in Ar matrix.• Expectation: narrower line-width.
Disadvantage:• No matrix annealing experiment.
• The range of temperature change without distorting the pH2 crystal is very narrow (4-7K) as compared to solid Ar (4-40K).
Alternative technique – sublimation temperature experiment• Preservation of amino acids’ conformational population at sublimation
temperature due to the softer collision effect on the sample.
Summary of Parahydrogen as matrix host for studies of amino acids
UV Photolysis on β-alanine
Current Work
Aside from conformational changes, β-alanine also seems to photodissociate into CO2 molecule and other fragments. We are now performing computation calculations on some possible candidates in hope to assign these β-alanineUV photolysis products.
Ab
sorb
an
ce,
rela
tive
inte
nsi
ty
24002350230022502200 Wavenumber, cm
-1
CO2
At Deposition
After 4hrs UV Irradiation
185018481846184418421840
New product peakfrom UV photolysis
Using similar experimental settings and concepts as the ones employed for gas phase β-alanine, we aim to further expand the present spectroscopic knowledge on amino acids by conducting solid parahydogen matrix-isolation FTIR spectroscopy on other simple amino acids. We also aim to study the zwitterion form of the molecules in study. Currently under investigation:
• α-alanine
• β-alanine zwitterion
Future Work
Acknowledgement
Supervisor: Takamasa Momose
Collaborator: Ying-Tung Angel Wong
Technician: Pavle Djuricanin