in black and white
Main menu
Share a book About us Home
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics

The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
Previous << 1 .. 157 158 159 160 161 162 < 163 > 164 165 166 167 168 169 .. 240 >> Next

well as substitution on the porphyrin ring, can influence the ability of
given anions to bind as axial ligands and thereby alter the
potentiometric anion selectivity. When a relatively simple
Table 4. Typical Selectivity Coefficients, Log /Cpotx,y for the Liquid-
Membrane Electrodes Based on Porphyrins and Quarternary Ammonium Salts
Anion Porphyrins
(TPP)Sn15 (TPP)Mn15 Sapphyrin118 (-3) (TPP)Mn104 (TPP)Sn114
Salicylate 0.0 0.0 -0.6
-0.1 -1.4 0.0
Cl- -3.8 -2.1 <-2.0
-3.2 -2.8 -2.1
Br- -3.7 -1.8 <-2.0
-2.8 -2.7 - 1.4
I -3.7 -0.6 <-2.0
-2.4 0.1
I04 -3.6 -0.3
CIO4 -3.4 -0.6 -0.7
-2.4 -2.1 1.8
SCN- -2.5 -0.8 - 1.7
0.0 0.7
Salicylurate - 1.5 -0.5
- 1.1
Benzoate - 1.4
Citrate -3.8
- 1.8
Acetate -2.2
Lactate -4.0
Hydroxybenzoate - 1.4
3,5-dinitrobenzoate 0.0
N03- <-2.0 -
3.26 -2.6
unhindered porphyrin structure was employed (eg., TPP), moderate
deviations from the Hofmeister pattern were evident. When additional
hydrophobic character in the form of methyl groups is added around the
coordination sites, a marked increase in the response to both salicylate
and SCN~ is observed.112 Such increases occur without concomitant changes
in the toward other lipophilic anions (4, IO4, I ). This implies that
the coordination of salicylate and SCN ions are stabilized by the
presence of methyl groups.
Metalloporphyrins in which anion accessibility to one side of the
metal is partially impaired (tetrahalonaphthyl porphyrins), showed a
response to 4 and IO4 further reduced when response toward SCN- is
enhanced.15 This suggests that anions are capable of binding as sixth
ligands and that selectivity can be varied by controlling which anions
can coordinate at this site. When one side of the metal ion is totally
blocked (capped) with an intermolecu-larly bound electron donating one
axial ligand, selectivity of the electrode reverts back to the classical
Hofmeister pattern. A strong axial ligand coordination on one side of the
metal weakens the interactions of ligand at the other axial site.
Consequently, the analyte anions can enter the membrane phase
predominately as solvated counter ions with little or no affinity for the
central metal atom.
It has been reported that protonated expanded porphyrins recognize
anions through a charge-charge interaction and hydrogen-bonding
formation. The observed response of protonated expanded porphyrins are
thought to arise as the result of electrostatic attractions between the
analyte anions and the positively charged expanded porphyrins. A n-n
interaction and hydrogen-bonding formation between the expanded
porphyrins and analytes ions are probably responsible for the observed
characteristic potentiometric selectivities for the electrodes.119-120
Sapphyrin, 22--electron aromatic pentapyrrolic expanded porphyrin
which uptakes two protons at most, is an excellent anion receptor for
fluoride, phosphate and phenylphosphate.121 Rubyrin, a 26-71-electron
aromatic hexapyrrolic macrocycle which uptakes two protons, recognizes
chloride and triphenylro-sarin.120 A fully conjugated 24-n-electron
hexapyrrolic macrocycle uptakes three protons and recognizes chloride.
Protonated sapphyrin acts as an efficient carrier for the transport of
fluoride anion, GMP and AMP.120122 The systemic studies of potentiometric
responses of expanded porphyrin-based electrodes towards benezoates,
geometrical isomers, positional isomers, chloroacetates and inorganic
anions show that the expanded porphyrin-incorporated membranes responded
to these anions upon protonation at the membrane-sample solution
Expanded-porphyrin electrodes can discriminate anions based on their
Previous << 1 .. 157 158 159 160 161 162 < 163 > 164 165 166 167 168 169 .. 240 >> Next