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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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Figure 130. Langmuir-Blodgett film sensor response at varying NH3
concentrations. Reprinted with permission from Nappa, .; Valentine, |.
S. j. Am. Chem. Soc. 1978, 100, 5075. ic) 1978 American Chemical Society.
areas is based upon incorporation of metalloporphyrins into electrode
membranes, where ion-porphvrin interactions can be monitored
polentiometrically. or where electrochemical reactions with analyte
substrates can be mediated by the porphyrin. As with gas sensors, this is
a research area where molecular-recognition studies will allow for
continued progress.
n - ? A 6 8 'I!)
Figure 128. Collman s "picnic basket" porphyrins.
Chou et al.
Figure 131. Response of porphyrin array towards 14 chemical species.
Reprinted with permission from Natale, C. D.; Macagnano, A.; Repole, G.;
Saggio, G.; D'Amico, A.; Paolesse, R.; Boschi, T. Mater. Sci. Eng. 1998,
5, 209.
a. Anion Detection
Detection of anions in solution via potentiometric techniques has been
widely studied. If lipophilic elec-trode-membrane materials are employed,
the selectivity of the detector is based upon the solubility of the
anions in the membrane layer. This gives rise to the Hofmeister pattern,
whereby lipophilic anions are preferentially incorporated into the
membrane, in the order CIO4 > 4 >
I >Br >1 >\234 Deviation from Hofmeister selectivity can be
achieved by incorporating a range of compounds, including porphyrins,
metallocorrins and phthalocyanines, into the membrane. The varying
affinities that anions have for the chosen macrocycle metal center can
change the ion preference of the material. Porphyrins are also utilized
because their synthetic versatility allows for creation of size-selective
pockets about the metal center, lending additional selectivity. For
instance, Meyerhoff and coworkers have examined various synthetic
manganese porphyrins by incorporating them into PVC polymer membranes.235
The porphyrins, shown in Figure 133, were chosen to give a wide range of
steric access and / or hydrophobicity to the metal-center anion-ligation
site. The tetraphenylporphyrins (Figure 133) deviate from the Hofmeister
trend due to selectivity imparted by axial
binding to the manganese center. The tetrahalonaphthylpor-phyrins
(Mn(TXNP)Cl) are even more exclusive of perchlorate and iodate, owing to
their more hindered metal centers. Meanwhile Mn(TDDPP)Cl and Mn(TDDIP)Cl,
which contain nitrogenous axial ligands, destabilize anion coordination
to the metal, restoring the Hofmeister selectivity. Improved affinity for
salicylate was subsequently achieved by incorporation of Sn(TPP)Cl2 into
the electrode membranes.236
Zheng and coworkers have employed a similar methodology and have
demonstrated that PVC membranes doped with indium tetraphenylporphyrin
show high relative sensitivity to nitrite ions.237 Manganese and indium
porphyrins immobilized in silicone by Paeng et al. have been used for the
potentiometric analysis of serum chloride levels.238
Studies of synthetic porphyrin-based anion receptors should form the
basis for more effective sensors. Metallo-cene-substituted porphyrins
examined by Beer and coworkers have proven successful in the solution-
phase binding of ions such as chloride, bromide and nitrate.239 The
cobaltocenium-substituted and ferrocene-substituted porphyrins (Figure
134) bind ions in solution, as shown by 'H NMR and electrochemical
studies. The latter measurements reveal that the porphyrin and ferrocene
41 / Porphyrin Materials Chemistry
Sn4* Co3* Cr3*
Mn3* Fe3* (c)
# Ru2* Zn2*
(c) $
Aa2* 2H*(FB)
Pyridine Hexylamine
Triethyl- Tributyl-
phosphite phosphine
Figure 132. Black and white projection of color change fingerprints for a
series of ligating vapors. In color, the differences between analytes are
considerably more distinct.
potentials vary with the bound ion. Studies of the various atropisomers
of the ferrocene-substituted zinc porphyrin have shown interesting
isomer-dependent selectivities. For example, the a,a,a,/? isomer shows a
preference for nitrate over chloride, where the other atropisomers show a
preference for spherical ions such chloride and bromide. In related work,
Sessler and coworkers have shown sapphyrins to be potentially useful
receptors for anion sensing. These expanded species are more basic than
their porphyrin counterparts, and hence readily form dicationic species
in solution.-40 The positively charged dication core forms a site for
anion binding. A deca-alkyl sapphyrin was originally shown to bind
fluoride ion, as shown by the crystal structure in Figure 135.241 The ion
is believed to be
stabilized via a combination of electrostatic and hydrogen-bonding
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