Fortho), 29.57 (m, 2F, Fortho); Vis. l/nm: 406(100), 525(10.1), 556(8.1);
Maldi TOF LRMS, m/z: observed 1158.5; mp > 260 °C].
‡ In a saddled (sad) conformation the pyrrole rings alternately tilt up and
down relative to the 24-atom porphyrin plane while the meso carbons
remain in plane. In a ruffled (ruf) conformation the pyrrole rings twist about
the axis that bisects opposing nitrogen atoms and the meso carbons
alternately shift up and down out-of-plane; L. Sun, W. Jentzen, J. A.
Shelnutt, The Normal Coordinate Structural Decomposition Engine (http:/
/jasheln.unm.edu).
§ Crystallographic details: 2[C51H13Cl2F15N6NiO2]·1.5[C6H14],
M =
2468, monoclinic, space group C2/c, a = 31.037(5), b = 22.693(4), c =
30.799 Å, b = 100.047(4)°, V = 21359(6) Å3, Z = 8. Data were collected
on a Bruker SMART 1000 diffractometer [l(Mo-Ka) = 0.71073 Å] at
91(2) K to 2qmax = 63° [total measured reflections = 121513, (±h, ±k, ±l)].
A 2qmax cutoff of 45° was applied affording 13875 independent data (Rint
=
0.238) of which 9065 had I > 2s(I). The structure was solved by direct
methods and refined (based on F2) by full matrix least-squares methods with
1248 parameters (Bruker SHELXTL V. 5.10). Hydrogens were generated
by idealized geometry with the exception of the lone amino hydrogen on
each of the two PQ molecules in the asymmetric unit; these were found on
a difference map and refined freely with their bond lengths fixed at 0.91(2)
Å. Final R factors were R1 = 0.123 (observed data), wR2 = 0.349 (all data)
b209238g/ for crystallographic data in CIF or other electronic format.
Fig. 2 Hydrogen bonding in the PQ crystal between the amine hydrogen
(H11A) of the molecule in the on configuration with the cyano nitrogen
(N6) of the molecule in the off configuration (C6F5 rings not shown).
Selected distances (Å): N6–N11 2.868(12), N6–H11A 2.00(5), N11–H11A
0.91(2).
1 C. S. Raman, P. Martasek and B. S. S. Masters, The Porphyrin Handbook,
ed. K. M. Kadish, K. M. Smith and R. Guilard, Academic Press, Boston,
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Kadish, K. M. Smith and R. Guilard, Academic Press, Boston, 2000, vol.
7, p. 167; T. L. Poulos, The Porphyrin Handbook, ed. K. M. Kadish, K.
M. Smith and R. Guilard, Academic Press, Boston, 2000, vol. 4, p. 189;
M. Sundramorth, K. Kishi. M. H. Gold and T. L. Poulos, J. Mol. Biol.,
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Zamocky, L. M. Nybury, C. Herzog, P. M. Alzari, C. Betzel, F. Koller
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E. D. Getzoff, Science, 1995, 270, 59.
2 Y. F. Li, W. Zhou, R. E. Blankenship and J. P. Allen, J. Mol. Biol., 1997,
271, 456; S. M. Prince, M. Z. Papiz, A. A. Freer, G. McDermott, A. M.
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Klukas, W. Saenger and N. Krauss, Nature, 2001, 411, 909.
3 For examples, see: K. M. Barkigia, M. D. Berber, J. Fajer, C. J. Medforth,
M. W. Renner and K. M. Smith, J. Am. Chem. Soc., 1990, 112, 8851; K.
M. Barkigia, M. W. Renner, L. R. Furenlid, C. J. Medforth, K. M. Smith
and J. Fajer, J. Am. Chem. Soc., 1993, 115, 3627; P. Ochsenbein, K.
Ayougou, D. Mandon, J. Fischer, R. Weiss, R. N. Austin, K. Jayaraj, A.
Gold, J. Terner and J. Fajer, Angew. Chem., Int. Ed., 1994, 33, 384; M. O.
Senge, T. Ema and K. M. Smith, J. Chem. Soc. Chem. Commun., 1995,
733; M. W. Grinstaff, M. G. Hill, E. R. Birnbaum, W. P. Schaeffer, J. A.
Labinger and H. B. Gray, Inorg. Chem., 1995, 34, 4896; D. J. Nurco, C.
J. Medforth, T. P. Forsyth, M. M. Olmstead and K. M. Smith, J. Am.
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(H11A) of the molecule in the on configuration with the cyano
nitrogen (N6) of the quinone in the off configuration (Fig. 2). If
this explanation is correct, the simple PQ dyad thus also
exemplifies the potential structural effects that the ubiquitous
hydrogen bonds in proteins may induce in vivo.
These results thus demonstrate that a single neighboring
‘residue’ can indeed induce a more distorted conformational
landscape in porphyrins, as suggested by Raman et al.,1 for
eNOS, and further illustrate the plasticity of the macrocycles as
well as their acute sensitivity to their microenvironment
increasingly observed both in vitro and in vivo.1–4 These
evidently facile interconversions and multiplicities of con-
formational surfaces (‘surfing’) also raise the caveat that site-
directed mutations in proteins may not be structurally innocent
by affecting the conformations and hence the properties of the
porphyrinic prosthetic groups and chromophores.3,4,8
This work was supported by the Division of Chemical
Sciences, US Department of Energy, under contract DE-AC02-
98CH10886 (at BNL) and NSF grant CHE-99-04076.
Notes and references
† PQ synthesis: condensation of pyrrole (4 eq.), pentafluorobenzaldehyde
(3 eq.), and 2-nitrobenzaldehyde (1 eq.) in refluxing acetic acid gave
5-(2-nitrophenyl)-10,15,20-tri(pentafluorophenyl)porphyrin (1) in 6%
yield7 [1H NMR, CDCl3: d 22.77 (s, 2H, NH), 7.99 (m, 2H, phenyl H),
8.25, 8.52 (m, 1H each, phenyl H), 8.78, 8.84 (d, 2H each, Cb H), 8.93 (br,
4H, Cb H); 19F NMR, CDCl3: d 3.84 (m, 6F, Fmeta), 13.82 (m, 3F, Fpara),
28.52 (m, 2F, Fortho), 28.71 (m, 1F, Fortho), 29.15 (m, 1F, Fortho), 29.44 (m,
2F, Fortho); Vis. l/nm: 412 (100), 510 (7.2), 542 (1.1), 586 (2.3), 642 (0.4),
mp > 260 °C]. Nickel insertion into 1 with Ni(II) acetylacetonate (20 eq.) in
refluxing xylenes afforded Ni(II) nitroporphyrin 2 in 91% yield [1H NMR,
CDCl3: d 7.96, 7.98 (m, 1H each, phenyl H), 8.19, 8.43 (m, 1H each, phenyl
H), 8.69, 8.66 (d, 2H each, Cb H), 8.76 (br, 4H, Cb H);19F NMR, CDCl3: d
3.86 (m, 6F, Fmeta), 13.74 (m, 3F, Fpara), 28.51 (m, 2F, Fortho), 28.71 (m, 1F,
Fortho), 29.15 (m, 1F, Fortho), 29.44 (m, 2F, Fortho), Vis. l/nm: 404 (100), 526
(7.4), 560 (5.1), mp > 260 °C]. Under an atmosphere of H2(g), 2 was stirred
with palladium on carbon in CH2Cl2 and yielded a mixture of reduced
macrocycle Ni(II) 5-(2-aminophenyl)-10,15,20-tri(pentafluorophenyl)por-
phyrinoids (3). Under inert atmosphere, this mixture was reacted with an
excess of DDQ in CH2Cl2 and afforded PQ in 18% yield from 2 [PQ: 1H
NMR, CDCl3: d 7.48 (s, 1H, amino H, exchangeable with D2O), 7.60 (d,
1H, phenyl H), 7.91 (m, 2H, phenyl H), 8.33 (d, 1H, phenyl H), 8.75 (m, 6H,
Cb H), 8.88 (d, 2H, Cb H); 19F NMR, CDCl3: d 4.61 (m, 6F, Fmeta), 14.43
(t, 3F, Fpara), 28.65 (m, 2F, Fortho), 28.86 (m, 1F, Fortho), 29.28 (m, 1F,
4 For reviews, see: J. Fajer, J. Porphyrins Phthalocyanines, 2000, 4, 382;
J. A. Shelnutt, X. Z. Song, J. G. Ma, S. L. Jia, W. Jentzen and C. J.
Medforth, Chem. Soc. Rev., 1998, 27, 31 and references therein.
5 A. K. Wertsching, A. S. Koch and S. G. Dimagno, J. Am. Chem. Soc.,
2001, 123, 3932.
6 R. Huber, Eur. J. Biochem., 1990, 187, 283.
7 J. P. Collman, J. I. Brauman, K. M. Doxsee, T. R. Halbert, E.
Bunnenberg, R. E. Linder, G. N. LaMar, J. D. Gaudio, G. Lang and K.
Spartalian, J. Am. Chem. Soc., 1980, 102, 4182.
8 S. Gentemann, N. Y. Nelson, L. Jacquinod, D. J. Nurco, S. H. Leung, C.
J. Medforth, K. M. Smith, J. Fajer and D. Holten, J. Phys. Chem. B, 1997,
101, 1247; K. M. Barkigia, D. J. Nurco, M. W. Renner, D. Melamed, K.
M. Smith and J. Fajer, J. Phys. Chem. B, 1998, 102, 322; J. L. Retzek, S.
Gentemann, C. J. Medforth, K. M. Smith, V. S. Chirvony, J. Fajer and D.
Holten, J. Phys. Chem B, 2000, 104, 6690.
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