6
794 J. Phys. Chem. A, Vol. 114, No. 25, 2010
Błoch-Mechkour et al.
to participate appreciably in the now rapidly established
equilibrium, most probably conformer 3, of URS .
(2) Agerbrink, N.; Olsen, C. E.; Sorensen, H. J. Agric. Food Chem.
+
1998, 46, 1563.
3) Regal, K. A.; Laws, G. M.; Yuan, C.; Yost, G. S. Chem. Res.
(
Table 3 lists also the relative free energies of conformers 1-3
Toxicol. 2001, 14, 1014.
•
of DIM-C (in the gas phase, as solvation is less important than
(4) Leete, E. J. Am. Chem. Soc. 1959, 81, 6023.
index.htm. Accessed June 2010.
+
in URS ). Here, conformer 1 is largely favored over 2 and 3,
•
+•
but if DIM-C is formed from DIM then the conformational
distribution may deviate strongly from the one that prevails at
equilibrium.
(6) See: http://www.cancer.gov/search/ResultsClinicalTrialsAdvanced.
aspx? protocolsearchid)3883031. Accessed June 2010.
(7) Goyal, R. N.; Kumar, A.; Gupta, P. J. Chem. Soc., Perkin Trans.
2
001, 2, 618.
TD-DFT calculations show that the different conformers of
+
(8) Shen, X.; Lind, J.; Mer e´ nyi, G. J. Phys. Chem. 1987, 81, 4403.
URS absorb at different wavelengths (in Figure 8e the
(
9) Solar, S.; Getoff, N.; Surdhar, P. S.; Armstrong, D. A.; Singh, A.
absorptions of the two most stable confomers are indicated by
black and red bars), thus confirming our assertion that the pair
of bands observed around 500 nm in EtOH and in the ionic
J. Phys. Chem. 1991, 95, 3639.
(10) Jovanovic, S. V.; Steenken, S. J. Phys. Chem. 1992, 96, 6674.
(11) Czerwinska, M.; Sikora, A.; Szajerski, P.; Zielonka, J.; Adamus,
J.; Marcinek, A.; Piech, K.; Bednarek, P.; Bally, T. J. Org. Chem. 2000,
+
liquid is due to two conformers of URS . In fact, these bands
7
1, 5312.
+
correspond to the first excited state of URS , which is attained
(
12) Harley-Mason, J.; Bu’lock, J. D. Biochem. J. 1952, 51, 430.
essentially by HOMO f LUMO electron promotion (higher
excited states are due to promotion of the electron from lower
lying doubly occupied MOs to LUMO).
(13) Bally, T. In ReactiVe Intermediate Chemistry; Moss, R. A., Platz,
M. S., Jones, M., Eds.; Wiley & Sons: New York, 2004.
(
14) Marcinek, A.; Zielonka, J.; G e¸ bicki, J.; Gordon, C. M.; Dunkin,
I. R. J. Phys. Chem. A. 2001, 105, 9305.
15) Schuler, R. H.; Patterson, L. K.; Janata, E. J. Phys. Chem. 1980,
84, 2088.
Similar calculations predict that the three conformers of DIM-
C absorb at very similar wavelengths, albeit with very different
(
•
(
16) Karolczak, S.; Hodyr, K.; £ubis, R.; Kroh, J. Radioanal. Nucl.
transition moments (see Figure 8). In this case, the ca. 400 nm
band corresponds to the third excited state, which is attained
essentially by HOMO f LUMO electron promotion (lower-
lying states involve excitation of electron from doubly occupied
MOs to the SOMO, but these give rise to transitions with very
weak oscillator strength, see Supporting Information).
Chem. 1986, 101, 177.
(
17) Neta, P.; Huie, R. E.; Ross, A. B. J. Phys. Chem. Ref. Data 1988,
1
7, 1027.
(18) Wardman, P. J. Phys. Chem. Ref. Data 1989, 18, 1637.
(
(
(
19) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
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21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.;
Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.;
Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford,
S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, ReV B.01, Gaussian, Inc., Pittsburgh, 2003.
During revision of the manuscript some additional calculations were done with
Gaussian 09, Rev. A02 (see footnote 30).
Conclusions
We have investigated the primary products obtained on
oxidation of the glucobrassicin metabolites (and dietary supple-
ments), I3C and DIM, in addition to that from parent I. The
radical cations from all three compounds were generated by
radiolysis in ionic liquid or Ar matrices at cryogenic temperature,
identified by their electronic absorption spectra and characterized
by excited state quantum chemical calculations.
We found that the radical cations of all three compounds are
completely resistant to (photo-) deprotonation. The N-centered
indolyl radicals of the three compounds can be formed by UV-
photolyisis and deprotonation of the radical cations in aqueous
solution, but no definite evidence was obtained for the formation
(
22) Andersson, K.; Roos, B. O. In Modern Electronic Structure Theory;
World Scientific Publ. Co.: Singapore, 1995; Vol. 2, p 55.
23) Pierloot, K.; Dumez, B.; Widmark, P.-O.; Roos, B. O. Theor. Chim.
2
of radicals that arise by H loss from the CH -groups of I3C,
(
although calculations indicate that this radical should be more
stable than the observed indolyl radical. In the case of I3C, the
C-centered radicals could be generated by protonation of the
radical anion of the corresponding aldehyde. In contrast to
Acta 1995, 90, 87.
(24) Roos, B. O.; Andersson, K.; F u¨ lscher, M. P.; Serrano-Andr e´ s, L.;
Pierloot, K.; Merchan, M.; Molina, V. J. Mol. Struct (THEOCHEM) 1996,
3
88, 257.
25) Karlstr o¨ m, G.; Lindh, R.; Malmqvist, P. -Å.; Roos, B. O.; Ryde,
(
•
+
the radical cation of I3C, DIM seems to be more prone to
U.; Veryazov, V.; Widmark, P.-O.; Cossi, M.; Schimmelpfennig, B.;
Neogrady, P.; Seijo, L. Comput. Mater. Sci. 2003, 28, 222.
(26) Casida, M. E. In Recent AdVances in Density Functional Methods,
Part I; Chong, D. P., Ed.; World Scientific Publ. Co.: Singapore, 1995.
deprotonation on the route to form the red urorosein cation,
+
+
-
URS , by sequential H /e loss.
(
27) Iwasaki, M.; Fukuya, M.; Fujii, S.; Muto, H. J. Phys. Chem. 1973, 77,
739.
28) Vinzenz, A. Z. Physiol. Chem. 1911, 71, 1.
Acknowledgment. This work was supported by grant from
the Polish Ministry of Science and Higher Education (No. N205
03 32/0258). The Fribourg group acknowledges support by
2
(
0
(29) Bally, T., The calculation was done at room temperature, but if
the entropy difference bewteen the conformers is assumed to be close to
zero (which is supported by the gas-phase calculations), the free energy
difference does not change much with temperature.
the Swiss National Science Foundation (project No. 20020-
1
21747).
(
30) At the suggestion of a referee we have recalculated this barrier at
Supporting Information Available: Four additional Figures
the B2PLYP level (with the 6-31G* basis set), accounting for solvation
using the new model, implemented in the Gaussian 09 program, which
makes the reaction field self-consistent with the MP2 density. At this level,
the free energy of activation for conversion of 1 to 2 decreased to 14.5
kcal/mol, in much better accord with experiment. However, it should be
noted that at this level, the relative free energies of the three conformers
are also not the same: 2 is almost at the same free energy as 1, whereas 3
lies only 0.95 kcal/mol higher. It is clear that even these calculations are
fraught with so many approximations that it would be foolhardy to expect
and the complete results of the CASSCF/CASPT2 calculations
are contained in a pdf file, and a text-file contains the Cartesians
and energies of all stationary points discussed in this study, and
the results of TD-DFT calculations. This information is available
free of charge via the Internet at http://pubs.acs.org.
References and Notes
+
perfect agreement with experiment for a molecule the size of URS .
(1) http://lpi.oregonstate.edu/infocenter/phytochemicals/i3c/. Accessed
June 2010.
JP912121Y