4th EucheMs chemistry congress

Monday, 27-Aug 2012
s812
chem. Listy 106, s587–s1425 (2012)
Physical, theoretical and Computational Chemistry
Biointerface and Colloids
o - 1 0 6
new KinetiC StudieS of the nitroSAtion of
CoMPLex MoLeCuLeS
M. GonzALez JiMenez 1 , J. ArenAS-vALGAnón 1 ,
i. f. CéSPedeS-CAMACho 1 , e. CALLe 1 , J. CASAdo 1
1 Facultad de Ciencias Químicas, Química Física, Salamanca,
Spain
The report by Magee and Barnes (Magee, P. N.; Barnes,
J. M. Br. J. Cancer. 1956, 10, 114) that dimethylnitrosamine
induces liver cancer when fed to rats prompted the study of the
Chemistry and Biology of nitroso compounds. Since then,
biologists have mainly been interested in the use of these
compounds as models for producing a broad range of cancers,
whereas chemists are more interested first in the mechanisms of
formation of nitroso compounds and then in blocking or inhibiting
the mechanisms of these species (Lijinsky, W. (Chemistry and
Biology of N-nitroso compounds, Cambridge Univ. Press.,
Cambridge, 1992).
While N-nitrosation reactions are well known, the
mechanism for generating C-and O-nitroso compounds are
subject to discussion, especially when a molecule has several
competing potentially nitrosatable groups (Williams, D. L. H.,
Nitrosation reactions and the chemistry of nitric oxide, Elsevier,
Amsterdam, 2004; González Jiménez, M. et al., Org. Biomol.
Chem. 2011, 9, 7680).
In this work, the nitrosation mechanisms of ethylbenzene,
2-phenethylamine and tyramine (2-(4-hydroxyphenyl)ethylamine)
in perchloric aqueous solutions of sodium nitrite were
investigated. The mechanisms for the reactions of N-nitrosation
and aromatic C-nitrosation are proposed and discussed. The
activation of the aromatic ring and the basicity of the substrate
proved to be crucial factors in the rate of the C-nitrosation
reaction, which was sometimes faster than that of N-nitrosation.
Nitrosation reactions were followed kinetically by
UV-visible spectrography, measuring the absorbance of the
reaction products with a spectrophotometer equipped with a
thermoelectric six-cell holder temperature-control system
(± 0.1 ºC).
Acknowledgments: The authors thank the Spanish Ministerio
de Ciencia e Innovación and the European Regional
Development Funds (Project CTQ2010-18999) for supporting
the research reported in this article. M.G.-J. and J.A.-V. thank
the Spanish Ministerio de Economía y Competitividad for a
PhD Grant.
Keywords: kinetics; nitrosation; catecholamines; tyramine;
Biointerface and Colloids
4 th EucheMs chemistry congress
o - 1 0 7
Low-teMPerAture, SoLid-StAte nMr of the
v49A BACteriorhodoPSin MutAnt
v. L. Mooney 1 , M. n. SAndBerG 2 , S. SenGuPtA 1 ,
e. A. fry 1 , n. L. wAGner 2 , r. r. BirGe 2 , K. w. ziLM 1
1 Yale University, Chemistry, New Haven CT, USA
2 University of Connecticut, Chemistry, Storrs CT, USA
Bacteriorhodopsin is a proton pump which activates when
absorption of a photon causes isomerization of the all-trans retinal
ligand present in the protein’s binding pocket. The V49A mutant
changes the retinal binding pocket, resulting in alterations in the
retinal isomer composition and in the kinetics of the protein’s
photoactivation mechanism. It has also been suggested that the
V49A mutation disrupts the interaction between the retinal-K216
protonated Schiff base and its counterion, D85. For these reasons,
we chose to investigate the retinal environment in the V49A
mutant using solid-state NMR. After acquiring 1D and
2D 13C spectra of the dark-adapted bacteriorhodopsin mutant
possessing a retinal ligand labeled at positions C8-C15, C19 and
C20, we were able to assign many of the peaks due to labeled
carbons. We found that both all-trans and 13-cis retinal isomers
are present and that some of the labeled carbons chemical shifts
differ from those previously seen in wild-type bacteriorhodopsin.
Our results thus far indicate that the environments of certain
carbons along the retinal chain in the V49A bacteriorhodopsin
mutant are significantly different from those in wild-type
bacteriorhodopsin. Experiments are currently underway to resolve
the identities and chemical shifts of overlapping peaks. This data
should provide insight into the interaction of the protonated Schiff
base and the D85 counterion in the V49A mutant and also the
changes in the retinal isomer composition. In addition, the
sensitivities of our 1D and 2D spectra are such that we are now
able to investigate other bacteriorhodopsin mutants’ retinal
environments.
Keywords: NMR spectroscopy; Schiff bases; Chromophores;
Membrane proteins;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc