Rot
ation
al (
atropo-) isomers of Mn(III)
meso-tetr
akis(
N-
alkylpyridinium-2-yl)porphyrins
and corresponding met
al-free porphyrin lig
ands (where
alkyl is methyl, ethyl,
n-butyl,
n-hexyl)
and Zn(II)
meso-tetr
akis(
N-methyl(ethyl,
n-hexyl)pyridinium-2-yl)porphyrins were sep
ar
ated
and isol
ated by reverse-ph
ase HPLC. The identity of the rot
ation
alisomers of met
al-free
meso-tetr
akis(
N-methylpyridinium-2-yl)porphyrin w
as est
ablished by
1H NMR spectr
a and bythe cryst
al structure of the f
astest eluting fr
action (
Rf = 7.7%,
Rw = 9.2%,
P2
1/
c,
Z = 8,
a = 14.2846(15) Å,
b= 22.2158(24) Å,
c = 29.369(3) Å,
ages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> = 95.374(2)
![](/im<font color=)
ages/entities/deg.gif">) which, in
accord
ance with
1H NMR interpret
ation, proved tobe the
![](/im<font color=)
ages/gifch
ars/
alph
a.gif" BORDER=0>
![](/im<font color=)
ages/gifch
ars/bet
a2.gif" BORDER=0 ALIGN="middle">
![](/im<font color=)
ages/gifch
ars/
alph
a.gif" BORDER=0>
![](/im<font color=)
ages/gifch
ars/bet
a2.gif" BORDER=0 ALIGN="middle"> isomer. This result, together with elution intensity p
atterns, w
as used to identify the fr
actions of otherMn(III)-porphyrins, Zn(II)-porphyrins,
and corresponding met
al-free lig
ands in the series. All of the
atropoisomerswere inert tow
ard isomeriz
ation which w
as not observ
able for 30 d
ays
at room temper
ature
and re
ached only 50%in 16 d
ays
at 90
![](/im<font color=)
ages/entities/deg.gif">C in the c
ase of the Mn(III)-ethyl
an
alogue. However,
a complete freeze-dry remov
al of themobile ph
ase from the HPLC fr
actions c
aused
an
almost 100% isomeriz
ation. The Mn(III)
meso-tetr
akis(
N-ethylpyridinium-2-yl)porphyrin,
as
a mixture of
atropoisomers (AEOL-10113), h
as been shown to offer protection inoxid
ative stress injury
ascribed to its high re
activity tow
ard superoxide (
kcat = 5.8 × 10
7 M
-1 s
-1)
as
a consequenceof its f
avor
able redox potenti
al (
E1/2 = +228 mV vs NHE). In this work, the
atropoisomers were found to h
avesimil
ar redox potenti
als r
anging from +240 to +220 mV, to be simil
arly potent c
at
alysts of O
2
ages/entities/bull.gif">- disproportion
ation(dismut
ation), with
kcat r
anging from 5.5 × 10
7 to 6.8 × 10
7 M
-1 s
-1,
and not to preferenti
ally bind to biologic
altissue.