Transcript WG09-VanesaVAQUERO-VARA.pptx

COMPREHENSIVE SPECTROSCOPIC
CHARACTERIZATION OF
MODEL AROMATIC
SUBSTITUENTS OF LIGNIN
Jacob C Dean, Vanesa Vaquero-Vara, Rachel Clayton, Polina Navotnaya, Alex Parobek,
Kelly M Hotopp, Brian C Dian, Timothy S Zwier
Department of Chemistry, Purdue University
West Lafayette, IN 47906
WG09 – 67th International Symposium Molecular Spectroscopy
Motivation
Lignin – component of the secondary cell walls of plants.
Three main precursors of lignin (studied in Zwier´s laba,b).
O H
OH
OH
O
O
O H
O
Lignin
OH
OH
Coumaryl alcohol
Coniferyl alcohol
Sinapyl alcohol
Different ratios – different physical properties.
Biosynthesis of lignin is NOT WELL UNDERSTOOD.
It is a radical polymerization process.
a
b
C. P. Rodrigo, et al. J. Am. Chem. Soc. 2011, 133, 2632.
J. C. Dean, et al., J. Phys. Chem A. 2011, 115, 8464.
1
Motivation
OH
O
O
2,6-dimethoxyphenol
(dmp)
OH
Sinapyl alcohol
2-methoxyphenol
(mp)
4-methyl-2,6-dimethoxyphenol
(mdmp)
2
Intensity (arb. units)
Intensity (arb. units)
LIF
Experimental study: electronic spectrum
LIF
?
IR-UV
LIF HB
Difficult assignment
Not clear progressions
Large geometry change in ES
Two different excited states?
000 (?)
36000
IR-UV HB
36200
36400
-1
Wavenumber (cm )
36600
36800
36600
36800
REMPI
36000
36200
36400
-1
Wavenumber (cm )
Clear assignment.
c E.
Fujimaki et al., J. Chem. Phys. 1999, 110, 4238.
3
Experimental study: electronic spectrum
Only one conformation
Intensity (arb. units)
IRIGS
RIDIRS
1100
1200
1300
1400
-1
Wavenumber (cm )
1500
1600
4
Experimental study: electronic spectrum
Dispersed fluorescence
-1
Intensity (arb. units)
Monitoring transition at 36370 cm
Smoothed
• No sharp peaks, broadening
• Red-shifted emission
• Something is happening!
0
2000
4000
-1
Relatve Wavenumber (cm )
6000
5
Experimental study: LIF Excitation spectrum
Intensity (arb. units)
4-Methyl-2,6-dimethoxyphenol
LIF
• Complete loss of sharp features
• Still detecting fluorescence
• Second ES?
36000
36200
36400
-1
Wavenumber (cm )
36600
36800
6
Experimental study: rotational spectrum
7.5-18.5 GHz rotational spectrum (S0)
dmp
Texp ~ 105°
7
Experimental study: rotational spectrum
716 - 615
818 - 717
808 - 707
Three potential sources of internal rotation
8
Experimental study: rotational spectrum
7.5-18.5 GHz rotational spectrum (S0)
mp
322 - 211
505 - 414
515 - 414
752 - 743
9
Experimental study: rotational spectrum
7.5-18.5 GHz rotational spectrum
dmp (OD)
10
Experimental study: rotational spectrum
μa changes sign with the rotation of the –OH group
(μa antisymmetric)
b
<ψ´ | μg | ψ´´>
a
a-type rotational transition only allowed
between different vibrational levels
11
Experimental study: rotational spectrum
Δν ~ 1 MHz
716 - 615
818 - 717
Δν
808 - 707
ΔE(v´-v´´)
V2
Splitting related to the
separation between
both levels.
V2
v´
v´´
12
Experimental study: rotational spectrum
ΔE (MHz)
V2 / cm-1
55
1207
R = CH(CH3)2 (Propofol) e
104.1
1200
R = OCH3 (dmp) f
0.48
1965
7.97
1513
R = H (Phenol) d
R
R
d
4-hydroxypyridine
g
d
E. Mathier, et al., J. Mol. Spect. 1971, 37, 63.
Lesarri, et al., J. Am. Chem. Soc. 2010, 132, 13417.
f Present work.
g R. Sanchez, et al., Chem. Phys. Lett. 2006, 425, 6.
e A.
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Conclusions and Future Goals
■ Complete spectroscopic characterization of model lignin compounds.
▪ “Clean” spectroscopy of the mp.
▪ Addition of a methoxy rotor in the dmp→ effect on the electronic
rotational spectrum.
▪ Addition of a methyl rotor in the mdmp→ effect on the electronic spectrum.
14
Conclusions and Future Goals
■ Complete spectroscopic characterization of model lignin compounds.
▪ “Clean” spectroscopy of the mp.
▪ Addition of a methoxy rotor in the dmp→ effect on the electronic
rotational spectrum.
▪ Addition of a methyl rotor in the mdmp→ effect on the electronic spectrum.
■ Calculations on dmp - relative energies and structures of Sn.
15
Conclusions and Future Goals
■ Complete spectroscopic characterization of model lignin compounds.
▪ “Clean” spectroscopy of the mp.
▪ Addition of a methoxy rotor in the dmp→ effect on the electronic
rotational spectrum.
▪ Addition of a methyl rotor in the mdmp→ effect on the electronic spectrum.
■ Calculations on dmp - relative energies and structures of Sn.
■ Photoexcitation + MW spectroscopy
of monolignols and model compounds.
(a)
MW CP
probe
(a) J. A. Sebree, et al., J. Am. Chem. Soc. 2012, 134, 1153.
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Acknowledgements
Professor Timothy S. Zwier
The Zwier Group
Evan Buchanan (WF12,WG08)
Zachary Davis (TF10)
Jacob Dean (TF09,WG10)
Joseph Gord (MF08)
Nathan Kidwell (TG09,FB07)
Joseph Korn
Dr Ryoji Kusaka (TD09)
Deepali Mehta (TG10)
James Redwine
Nicole Shimko
Patrick Walsh
Di Zhang (FB08)
Polina Navotnaya
Rachel Clayton
Alex Parobek
THANK YOU
FOR YOUR ATTENTION!