Communication
Dalton Transactions
More far-reaching support for the notion of electroneutral- exhibit a marked off/on magnetic relationship in aqueous solu-
ity at neutral pH may be obtained by determining the specific tion. The results herein are currently transferred to the explora-
conductivity of 1 (Table 1). Indeed, conductimetry has already tion of molecular candidates for a responsive, magnetogenic
been considered early on as a useful means for characterizing probe operating in vivo.
coordination compounds, but in those days studies in water
We thank Christophe Bucher, for assistance with the acqui-
were excluded for fear of “complex hydrolysis or lack of solubi- sition of cyclovoltammograms, and Laurence Canaple and
lity”.39 A more recent report demonstrates electroneutrality of Olivier Beuf for help with T1 measurements by MRI.
a lanthanide chelate in aqueous solution by conductimetry.40
Thus, an aqueous sample containing [1 × 2 HBF4] (crystals;
4 mM) was adjusted with NaOH to pH 7 and compared to a
reference sample containing hydrotetrafluoroboric acid (HBF4)
References
at the same concentration (8 mM), also adjusted to pH 7 by
use of NaOH. Both gave almost identical conductivites
(1.221 mS cm−1 (1); 1.242 mS cm−1 (HBF4)). By contrast,
1 M. Port, J.-M. Idee, C. Medina, C. Robic, M. Sabatou and
C. Corot, BioMetals, 2008, 21, 469–490.
2 T. Courant, G. V. Roullin, C. Cadiou, M. Callewaert,
M. C. Andry, C. Portefaix, C. Hoeffel, M. C. de Goltstein,
M. Port, S. Laurent, L. Vander Elst, R. N. Muller,
M. Molinari and F. Chuburu, C. R. Chim., 2013, 16, 531–
539.
analysis of
a sample of cationic reference complex 5
([FeII(TPTACN)]2+ × 2 BF4 at 4 mM), also adjusted to neutral pH
via NaOH titration, furnished a conductance 2.2 times higher
(2.721 mS cm−1), thus confirming the electroneutral quality of
1 at physiological pH, one of the prime objectives of this study.
Finally, complexes 1 and 2 were tested for their contact toxi-
city in a classic cell viability test (Fig. 3). While low-spin
complex 1 does not show any contact toxicity up to 4 mM con-
centration in the culture medium, even high-spin complex 2
(powder) shows appreciable biotolerance with an LD50 of
4 mM. These data bode well for the employment of nicotinate
pendent arms in future magnetogenic probes responding to
an enzyme activity of one’s choice and thus destined for bio-
logical applications.
3 C. Geraldes and S. Laurent, Contrast Media Mol. Imaging,
2009, 4, 1–23.
4 H. Toftlund, Coord. Chem. Rev., 1989, 94, 67–108.
5 H. Toftlund and J. J. McGarvey, in Spin Crossover in Tran-
sition Metal Compounds I: Vol 1 (Topics in Current Chem-
istry), Springer, Berlin/Heidelberg, 2004, vol. 233,
pp. 151–166.
6 F. Touti, P. Maurin and J. Hasserodt, Angew. Chem., Int. Ed.,
2013, 52, 4654–4658.
7 J. Hasserodt, J. L. Kolanowski and F. Touti, Angew. Chem.,
Int. Ed., 2014, 53, 60–73.
8 F. Touti, A. K. Singh, P. Maurin, L. Canaple, O. Beuf,
J. Samarut and J. Hasserodt, J. Med. Chem., 2011, 54, 4274–
4278.
9 W. R. Scheidt and C. A. Reed, Chem. Rev., 1981, 81, 543–
555.
In conclusion, a pair of structurally analogous macrocyclic
iron(II) complexes is presented that exhibit electroneutrality at
neutral pH and high stability in physiological media. This
instance of an electroneutral low-spin iron(II) complex has
been made possible through the incorporation of nicotinate
pendent arms. They allow for external charge compensation of
the iron center without impeding the experimenter’s ability to 10 W. R. Scheidt, J. Porphyrins Phthalocyanines, 2008, 12, 979–
render the iron center low-spin. Both complexes are highly tol- 992.
erated by mammalian cells at concentrations up to 4 mM for 11 V. V. Novikov, O. A. Varzatskii, V. V. Negrutska,
the low-spin and 2 mM for the high-spin complex. They
Y. N. Bubnov, L. G. Palchykovska, I. Y. Dubey and
Y. Z. Voloshin, J. Inorg. Biochem., 2013, 124, 42–45.
12 K. Wieghardt, E. Schoffmann, B. Nuber and J. Weiss, Inorg.
Chem., 1986, 25, 4877–4883.
13 L. Christiansen, D. N. Hendrickson, H. Toftlund,
S. R. Wilson and C. L. Xie, Inorg. Chem., 1986, 25, 2813–
2818.
14 V. Stavila, M. Allali, L. Canaple, Y. Stortz, C. Franc,
P. Maurin, O. Beuf, O. Dufay, J. Samarut, M. Janier and
J. Hasserodt, New J. Chem., 2008, 32, 428–435.
15 C. Gateau, M. Mazzanti, J. Pecaut, F. A. Dunand and
L. Helm, Dalton Trans., 2003, 2428–2433.
16 A. Nonat, C. Gateau, P. H. Fries and M. Mazzanti, Chem. –
Eur. J., 2006, 12, 7133–7150.
17 A. Nonat, M. Giraud, C. Gateau, P. H. Fries, L. Helm and
M. Mazzanti, Dalton Trans., 2009, 8033–8046.
18 V. Placide, A. T. Bui, A. Grichine, A. Duperray, D. Pitrat,
C. Andraud and O. Maury, Dalton Trans., 2015, 44, 4918–
4924.
Fig. 3 MTS cell viability test over 24 h for 1 and 2.
Dalton Trans.
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