Single-Conformation Spectroscopy of a Diastereomeric Lignin Monomer: Exploring the Hydrogen Bonding Architectures in a Triol Chain Jacob C. Dean, Evan G. Buchanan, William H. James III, Anna Gutberlet, Bidyut Biswas, P.V. Ramachandran, and Timothy S. Zwier Zwier Research Group, Purdue University Ohio State Dean, J.C.; Buchanan, E.G.; James, W.H. III; Gutberlet, A.G.; Biswas, B.; Ramachandran, P.V.; Zwier, T.S. J. Phys. Chem. A 2011, Submitted.

Lignin: Natural Aromatic Heteropolymer Second-most abundant biopolymer in nature Plant rigidity, macro-structure, and water/nutrient transport Spectroscopic methods for conformational preferences and spectroscopic signatures Vanholme, R, et. al. Plant Physiol , Rodrigo, C; James, W.H.; Zwier, T.S. J. Am. Chem. Soc. 2011, 133,

1-(4-hydroxy-3-methoxyphenyl)propane-1,2,3-triol (HMPPT) β -O-4 derivative: precursor to capped dimers and larger oligomers H-bonding motifs and their signatures Diastereomer-specific conformational preferences: chirality effects on populations α β γ * * 3 α β γ γ - β - α chain

HMPPT Conformational Families 4 DFT M05-2X/6-31+G(d)

R2PI Spectroscopy in the S 0 -S 1 region: RS- vs. RR-HMPPT Significantly different Intensities of red-shifted conformers different between diastereomers 60 cm -1 shift between large origins: immediate indication of shifting of conformational preferences RS-HMPPT RR-HMPPT 5

Conformation-specific UV Spectroscopy: RS-HMPPT R2PI A B C (IR-UV) D E 6 Five conformers found Most vibronic structure is quite similar Origin transitions spread over ~250 cm -1

Conformation-specific IR in the OH stretch Region: RS-Chains γ α/β as α/β ss OH--OCH 3 γα/β as α/β ss α1α1 γ2γ2 β2β2 E γ-β-α (syn) D α-β-γ (syn) A α-β-γ (anti) IRIG β1β1 γ1γ1 α2α2 DFT M05-2X/6-31+G(d) Scale factor: (triol) D: 0.17 kJ/mol A: 2.27 kJ/mol 7 E1: 2.68 kJ/mol E2: 3.08 kJ/mol

Conformation-specific IR in the OH stretch Region: RS-Cycles B cw cycle (syn) C ccw cycle (syn) αβ γβ α γ B: 0 kJ/mol C: 1.77 kJ/mol DFT M05-2X/6-31+G(d) Scale factor: (triol) 8 IRIG

Conformation-specific UV Spectroscopy: RR-HMPPT R2PI A B C X6 (IR-UV) D X6 (IR-UV) 9 Four conformers found Most of intensity is in conformers A and B blue-shifted by ~ 200 cm -1 from C D barely noticeable if not for unique IR absorption (IR-UV HB)

Conformation-specific IR in the OH stretch Region: RR-HMPPT A: 0 kJ/mol C: 7.69 kJ/mol D: 5.02 kJ/mol DFT M05-2X/6-31+G(d) Scale factor: (triol) 10 B: 1.46 kJ/mol

IRIG Spectroscopy: Fractional Abundances of Conformers RS Conformer F i RS RR Conformer F i RR A0.20 ± 0.02A+D0.54 ± 0.03 B0.14 ± 0.02B0.43 ± 0.03 C0.08 ± 0.02C0.03 ± 0.01 D0.30 ± 0.03 E0.28 ± 0.02 RS-HMPPT 11 Chains: α - β - γ 34% γ - β - α 28% Cycles: 22% γ - β - α 97% α - γ - β - π : 3% Difference Significantly different conformational preferences Single chiral site can completely rearrange preferences

Diastereomer-specific Effects on Conformational Preferences 12 CycleC1C2 C3′ Z Ilyushin, V.V. et al. J. Mol. Spectrosc. 2008, 251,

Diastereomer-specific Effects on Conformational Preferences 13 CycleC1C2 C3′ Z RR (A) Ilyushin, V.V. et al. J. Mol. Spectrosc. 2008, 251,

Conformational Families Observed β-γ-αβ-γ-αα-β-γα-β-γγ-β-αγ-β-αα-γ-β-πα-γ-β-πα-β/γ-βα-β/γ-ββ-α-γβ-α-γ H-bonded chains H-bonded cycles clockwise (αγβ) counter-clockwise (αβγ) RS-HMPPT RR-HMPPT

Conclusions Conformational preferences function of three factors: The global minimum RR(A) is stabilized by having all three factors optimal Conformational preferences dramatically change with change in chirality at single center 15 Dean, J.C.; Buchanan, E.G.; James, W.H. III; Gutberlet, A.G.; Biswas, B.; Ramachandran, P.V.; Zwier, T.S. J. Phys. Chem. A 2011, Submitted. 1)2)3)

Acknowledgements Prof. Tim Zwier Evan G. Buchanan Dr. William H. James III Dr. Anna Gutberlet Dr. Bidyut Biswas Prof. P.V. Ramachandran Dr. Chirantha Rodrigo Deepali Mehta Nathan Kidwell Josh Sebree Di Zhang Joe Korn Department of Energy 16

Future Work: Dimer Units and Forward 17 ± Pinoresinol: Lignin dimer unit

Pinoresinol RIDIRS and IRIGS 18

RS-B RS-C RR-B (C1) RR-D (Z) RS-E (C2) RS-E 2 (Z) RS-D (C1) RR-A (C1) RR-C RS-A (C1) CycleC1 C2 C3′ Z a) b)

20

The Strategy and Program Strategy: fit Chi-Squared space to a parabola and use the second derivative and the variance of the fit to determine the coefficient errors. ConformerFiFi A0.201 ± B0.140 ± C0.075 ± D0.295 ± E0.289 ± 0.020

Two Dimensions We should expect a parabola in two-dimension. However, by changing two variables at the same time we become more confident in our error analysis. Same result as 1-D