The Delicate Balance of Hydrogen Bond Forces in D-Threoninol 19 Di Zhang, Vanesa Vaquero Vara, Brian C. Dian and Timothy S. Zwier Zwier Research Group, Purdue University

HO – CH 2 – CH – CH – OH – CH 3 – NH 2 (S) Artificial ¨DNA¨: Acyclic threoninol nucleic acid (aTNA)* Threonine *H. Kashida et al., Angew. Chem. Int. Ed. 2011, 50, 1285 D-Threoninol: Reduced form of D-Threonine 20

D-Threoninol: Evolution of the structure HO – CH 2 – CH 2 – OH (1) HO – CH 2 – CH 2 – CH – OH (3) – CH 3 W. Caminati et al., J. Mol. Struct. 1982, 78, 197 HO – CH 2 – CH 2 – CH 2 – OH (2) W. Caminati et al., J. Mol. Spectr. 1995, 171, 394 W. Caminati et al., J. Mol. Spectr. 1981, 90(2), 572 ? HO – CH 2 – CH – CH – OH – CH 3 – NH 2 (S) 21 HO – CH 2 – CH– CH 2 – OH (2) OH – V. Ilyushin et al. J. Mol. Spectr. 2008, 251, 129

Calculational Methods 1.Force field calculation in Amber * force field was performed first at low computational cost with MacroModel commercial program suite stable conformation structures were filtered out with a given energy threshold (50kJ mol -1 ). 3.Full geometry optimizations were performed using MP2 with G(d,p) basis set.

Predicted lower energy conformers and relative energies with respect to the global minimum cw ccw

1)Pulse Generation 2)Molecular Interaction 3)Detection instrumentation

Rotational spectrum of D-threoninol from GHz

Predicted lower energy conformers and relative energies with respect to the global minimum cw ccw

Hyperfine structures with their respective 2 2,0 ← 1 1,1 rotational transitions

Hyperfine structures with their respective 3 1,3 ← 2 1,2 rotational transitions

Hyperfine structures with their respective 5 1,4 ← 4 1,3 rotational transitions

Hyperfine structure with its respective 5 1,4 ← 4 1,3 rotational transition

cyclechain 1→3→2 1→2→3 3→2→1 MP2/ G(d,p) cyclechain 1→3→2 3→2→1 1→2→3 2→1→3 MP2/aug-cc-pVTZ V.V.Ilyushin et al. J.Mol.Spec. 251 (2008) 129 ① ② ③ ① ② ③ Conclusions ① Substituted alkyl chains allow the formation of networks of intramolecular hydrogen bonds ② Cycles are lowest in energy in both tri-substituted cases ③ Chains are only slightly higher in energy Observe several chain conformers Near energies Compensation between 3 weak H bonds and 2 strong H bonds ④ Presence of NH 2 : a)Better H-bond acceptor b)Poorer H-bond donor H-bond length Distorted structure 2.34Å 2.35Å 2.08Å 2.28Å2.17Å 2.57Å 2.17Å 2.12Å

Prof. Tim Zwier Dr. Vanessa Vaquero Vara Dr. Ryoji Kusaka Evan G. Buchanan Zachary Davis James Redwine Jacob Dean Deepali Mehta Nathan Kidwell Di Zhang Joe Korn Nicole Shimko Patrick Walsh Joseph Gord Acknowledgments

Conclusions I Observed 7 conformers of D-threoninol Two hydrogen bonded cycles Five hydrogen bonded chains Rotational constants A,B,C provide information on the conformation of the molecules Quadrupole coupling constants χ gg (g= a,b,c) provide a different and independent way to identify different conformers

III +sc -sc 402 cm cm -1 *Zero point corrected energies at MP2/ G(d,p) Predicted lower energy conformers and relative energies with respect to the global minimum

MP2/ G(d,p) 3exp1 23exp10exp19exp13exp5 A (MHz) (11) (69) ( 68) (84) (53) (27) (42) B (MHz) (97) (12) (20) (89) (23) (13) (21) C (MHz) (13) (11) ( 32) (76) (25) (17) (20) Δ (kHz)0.178(28)0.167(30)-0.301( 67)0.309(49)0.212(25) Configuration +sc –sc II 3 +sc –sc I 3 +sc I 2 -sc –sc I 2 +sc II 2 -sc +sc I 2 -sc –sc II 2

MP2/ G(d,p) A (MHz) B (MHz) C (MHz) Configuration+sc -sc +sc -sc -sc +sc