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ARGENTINA FCENA-UNNE Theoretical analysis of measurable NMR spectroscopic parameters in medium-size acyclic hydrocarbons and H-bonded aminoacids * , Patricio F. Provasi * , Marina Sanchez * and Gustavo A. Aucar Stephan P. A. Sauer # * Physics

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Theoretical analysis of measurable NMR spectroscopic parameters in medium-size acyclic hydrocarbons and H-bonded aminoacids

Gustavo A. Aucar

*, Patricio F. Provasi*, Marina Sanchez* and

Stephan P. A. Sauer#

* Physics Department - Northeastern University – Argentina # Chemistry Department - Copenhagen University – Denmark

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NMR Spectroscopy – Phenomenology
Experimental and Theoretical description

NR theory Ramsey mechanisms Requirements for reliable calculations

Polarization propagator approach

Long-range F-F and C-F couplings. Shieldings. Its application

to QCs.

H-bonded aminoacids

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NMR Spectroscopy – Periodic Table

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NMR Spectroscopy – Phenomenology

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NMR Spectroscopy – Spectral origin

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NMR Spectroscopy – Spectral lines

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NMR Spectroscopy – Experiments

Spectroscopic parameters:

Indirect nuclear spin couplings: J [Hz] Nuclear magnetic shieldings: [ ppm] (Chemical shift: )

Gas – liquid – solid

For solids the main spin-spin relaxation is dip-dip interactions. Decoherence times: For solids, few milliseconds For liquid, several seconds

Measurements. First order spectra. Error bars

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NMR Spectroscopy – Theoretical studies

Electronic mechanisms Non relativistic theory. Ramsey: FC, SD, PSO, SDO Reliable calculations from ab initio methods: Electronic correlation (MCSCF, SOPPA, EOM-CCSD) Basis sets Rovibrational effects Relativity

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NMR Spectroscopy – Fluorinated organic compounds

Growing interest of Fluorinated organic compounds: Biological activity Fluorine incorporated to:

Alpha-helices, proteins and bioactive small molecules as NMR probes for aggregation, microenvironmental structure and binding site interactions.

Unusually large F-F couplings in unsaturated compounds Previous studies on the application of NMR as quantum computers (QC) Nuclear spins as quantum bits The need for nonvanishing J-couplings in molecules of reasonable size.

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NMR quantum computers

The inherent power of a QC relies on the fact that the dimension of the Hilbert space

grows exponentially with the number of particles allowing large-scale parallelization by exploiting the superposition principle of QM. Madi et al. JCP 109, 10603 (1998).

Design of molecular NMR quantum computers: Several criteria:

1. Prefered nuclei: 1H, 13C, 15N, 19F (I = ½ and high natural abundance)
2. Solubility.
3. Large J coupling between every pair of spins used as qubits.
4. Chemical shift not close between qubits.
5. Long enough spin-spin relaxation time. Liquid systems are the most

suitable.

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NMR quantum computers – previous studies

R. C. Mawhinney and G. Schreckenbach; Magn. Reson. Chem. 42, S88 (2004): “The two

main challenges in NMR QC are the control of pulse imperfections and the design of molecular systems with the proper spectral properties“

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NMR quantum computers – previous studies

R. C. Mawhinney and G. Schreckenbach; Magn. Reson. Chem. 42, S88 (2004): “The two

main challenges in NMR QC are the control of pulse imperfections and the design of molecular systems with the proper spectral properties“

I. L. Chuang et al. PRL 85, 5452 (2000): “Experimental realization of an order-finding

algorithm with an NMR QC“. Finding the order of permutation.

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NMR Spectroscopy – New candidates

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NMR Spectroscopy – J(F-F) couplings

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NMR Spectroscopy – J(F-F) couplings

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NMR Spectroscopy – J(F-F) couplings

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NMR Spectroscopy – J(F-F) couplings and shieldings

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NMR Spectroscopy – J(C-F) couplings and shieldings

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NMR Spectroscopy – Shieldings

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NMR Spectroscopy – H-bonded nucleic acid

Hidrogen bonds Stabilization of protein and nucleic acid secondary structure Modulate the speed and specificity of enzymatic reactions NMR parameters J coupling through H bonds is very important for structure determination. Trans-hydrogen bond 3hJNC exist in proteins, like human ubiquitin (J ~ 0.25 to 0.92 Hz);

Cornilescu et al JACS 121, 2949 (1999), Cordier and Grzesiek JACS 121, 1601 (1999).

Which are the mechanisms that controls the trans-hydrogen bonds in proteins? Is it possible to predict their values?

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NMR Spectroscopy – H-bonded nucleic acid

Dingley and Grzesiek, JACS 120, 8293 (1998). J-correlation exp. for 69-nucleotide T1 domain

f the potato spindle tuber viroid.
Exp. d(N3 – N1) = 2.82 A

J(N3 – N1) = 6.7 0.5 [Hz]

Exp. d(N3 – N1) = 2.95 A

J(N3 – N1) = 6.3 0.2 [Hz]

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NMR Spectroscopy – H-bonded nucleic acid

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NMR Spectroscopy – H-bonded nucleic acid

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NMR Spectroscopy – H-bonded Fa-Fa

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NMR Spectroscopy – H-bonded Fa-Fi

d(N1 – N2): Ours 2.899 A

Exp. 2.82 A – 2.95 A

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NMR Spectroscopy – H-bonded Fa-Fa

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NMR Spectroscopy – H-bonded Fa-Fa

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NMR Spectroscopy – H-bonded Fa-Fa

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Theoretical analysis of ... Summary

Measurable NMR spectroscopic parameters in unsaturated fluorinated compounds

We have predicted measurable long-range F-F and C-F J-couplings (J > 1 Hz) in unsaturated

compounds for distances longer than 1.2 nm.

The number of bond-separation between measurable coupled F-F and C-F nuclei is N > 9, which

is longer than previous findings.

Fluorine substituted polyenes and polyynes are good candidates to be used as NMR QC.

... H-bonded aminoacids (Formamide-Formamide; Formamide-Formamidine)

Correlated ab initio calculations of NMR spectroscopic parameters of fragments of H-bonded

aminoacids are available and give reliable results.

H-bonded H, O and C change their magnetic properties for Fa-Fa and Fa-Fi in such a way that it

can be used not only for conformational studies but as a magnetic sensor.

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Theoretical analysis of ...

Sponsorship: National Research Council CONICET - Argentina Secretaria General de Ciencia y Técnica – UNNE – Argentina Danish Research Council - Denmark