This presentation has been moved. To view this presentation, please visit http://pubs.acs.org/iapps/liveslides/pages/index.htm?mscNo=jz300541t Tracking of Proton Transfer Reaction in Supercooled RNA Nucleoside

1. Tracking of Proton Transfer Reaction
in Supercooled RNA Nucleoside
Z. Wojnarowska*
M. Paluch (presenter)
P. Wlodarczyk, M. Dulski, R. Wrzalik
Institute of Physics, University of Silesia,
ul. Uniwersytecka 4, 40-007 Katowice, Poland
C. M. Roland
Naval Research Laboratory, Chemistry Division,
Code 6120, Washington DC 20375-5342, USA
*zwojnaro@us.edu.pl
J. Phys. Chem. Lett. 2012, 3, 2288–2292 1

2. Motivation of tautomerization
investigation
Examples of tautomerization : Importance:
 physics
 chemistry (chelating agents)
 pharmacology
(various tautomers-different drug activity)
amide-imidic acid tautomerism  molecular biology
(noncanonic RNA/DNA tautomers-incorrect base pairing
- genetic disease, cancer, or drug resistance)
keto-enol tautomerism
the same atoms RNA chain
but in different Problem:
arrangement
How to track the proton transfer
reaction of RNA nucleoside experimentally?
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3. Experimental setup
Examined sample: β-uridine Measurements:
lactam-lactim tautomerism
Sample preparation:
crystal; T<Tm liquid; T=Tm glass; T<Tg
dielectric spectrometer
(http://www.novocontrol.com/)
capacitor filled
heating with β-uridine
quick cooling
(Tm=438 K)
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4. Results
Measurement in a wide Isothermal time-dependent
temperature range: dielectric measurement :
f max  1 2  
T>Tg
supercooled
liquid state
During the sample equilibration:
 εs is increasing
   s     N   2
Structural relaxation process originates
from the cooperative motions Consequently:
of the molecule and is related
 dipole moment of the sample increases
to the glass transition of β-uridine
 concentration of isomers with larger
Tg  T (   100 s )  324 K dipol moment is getting higher
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5. Data analysis
Step I: Analyzis of kinetic curves Step II: Determination of Ea
BDS
measurements
refractive index
measurements
The isothermal εs=f(t) and n=f(t) dependence Arrhenius equation:
reflects the kinetics
of the β-uridine tautomerization Ea
ln k  ln k0 
RT
Determination of the rate constants k:
 s  A1  exp( k1  t )  A2  exp( k 2  t )  C
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6. Results interpretation
Does proton transfer during the uridine equilibration involve
the lactam-lactim conversion or its opposite?
Experiment: First tautomerization Second tautomerization
pathway: pathway:
 the population of isomers
having larger a dipole
moment increases during
chemical equilibration
DFT calculations:
 for both noncanonical
tautomeric structures the
dipole moments are higher Δε=216 kJ/mol Δε=182 kJ/mol
than that calculated for the Δμ=1.1 D Δμ=1.7 D
lactam form
conversion of lactam to both
Good agreement Lower Ea higher
lactims transpires during probability of
the time dependent between EaBDS and EaDFT
incorrect base
measurements pairing
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7. Biological consequences
of amide-imidic acid conversion
Different electrostatic potentials on Translation mechanism:
the tautomers molecular surfaces:
Corectly:
mRNA: UCC → tRNA: AGG →serine
Consequently: If U in mRNA is replaced by its
 different H-bonds formation abilities, noncanonical tautomer:
 tautomer 2 is very similar to adenosine, mRNA: UCC (read as ACC) → tRNA:
and therefore can mimic this nucleoside UGG →trypsin
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8. Conclusions
The dielectric spectroscopy
technique offers a new approach
to the study of proton transfer
reactions of RNA and DNA M.Paluch
compounds, and consequently for Z. Wojnarowska
investigations of possible point
mutations.
C.M. Roland
Acknowledgments P. Wlodarczyk
The work at NRL was supported
by the Office of Naval
Research. Z.W. and M.P. are deeply thankful
for the financial support received from the
National Science Center (Grant MAESTRO2).
R. Wrzalik
M. Dulski
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