Push-pull type manganese(III)corroles: Synthesis, electronic structures and tunable interactions with ctDNA

Article abstract of DOI:10.1142/S1088424617500778

The synthesis of three low symmetry A₂B type Mn(III)triarylcorroles with meso-aryl substituents that provide push-pull electron-donating and -withdrawing properties is reported. An analysis of the structure-property relationships for the optical and redox properties has been carried out through a comparison with the results of theoretical calculations. The results demonstrate that A₂B type Mn(III)triarylcorroles interact strongly with cell-free circulating tumor deoxyribonucleic acid (ctDNA) in solution, and that the interaction constants are enhanced when a stronger electron-donating substituent is introduced at the 10-position of the meso-triarylcorrole ligand.

Full text of DOI:10.1142/S1088424617500778

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2017; 21: 751–758
DOI: 10.1142/S1088424617500778
Published at http://www.worldscinet.com/jpp/
Push–pull type manganese(III)corroles: Synthesis, electronic
structures and tunable interactions with ctDNA
Xu Liang,a,b,*Junjia Fang,a Minzhi Li,a Qiuyun Chen,a John Mack,c,*◊
Nthabeleng Molupe,c Tebello Nyokongc◊ and Weihua Zhua,*
a School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, P. R. China
b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210000, P. R. China
c Centre for Nanotechnology Innovation, Department of Chemistry, Rhodes University, Grahamstown 6140,
South Africa
Received 21 October 2017
Accepted 3 December 2017
ABSTRACT: The synthesis of three low symmetry A2B type Mn(III)triarylcorroles with meso-aryl
substituents that provide push–pull electron-donating and -withdrawing properties is reported. An
analysis of the structure-property relationships for the optical and redox properties has been carried out
through a comparison with the results of theoretical calculations. The results demonstrate that A2B type
Mn(III)triarylcorroles interact strongly with cell-free circulating tumor deoxyribonucleic acid (ctDNA)
in solution, and that the interaction constants are enhanced when a stronger electron-donating substituent
is introduced at the 10-position of the meso-triarylcorrole ligand.
KEYWORDS: Mn(III)corrole, DNA interaction, electronic structure, TDDFT calculation.
fluorescence because of low-lying metal-to-ligand charge
transfer (MLCT) states [9–11]. We have recently reported
the properties of several metal triarylcorroles with push–
pull A2B substitution patterns with different meso-aryl
INTRODUCTION
Corroles are structural analogs of porphyrins that
have a direct pyrrole–pyrrole bond and an extra NH
proton in their inner core, which are perhaps best known
substituents at the 5,15-(A2) and 10-(B) positions [12].
in a manner that results in lower molecular symmetry
The push–pull strategy involves the introduction of
and more intense absorption in the longer wavelength
both electron-donating (push) and withdrawing (pull)
portion of the visible region [1, 2]. Corrole chemistry has
substituents to effectively stabilize the LUMO orbitals
inspired a wide range of applications including organic
and destabilize the HOMO orbitals, and this provides
solar cells, photodynamic therapy, heat absorbers, bio-
one of the most effective strategies for modulating the
imaging and organic catalysis [3–8]. In recent decades,
there has been a strong research focus on the use of
electronic structures of porphyrinoid p-systems. Large
shifts are often observed in the wavelengths of the main
corroles as functional ligands, largely due to their ability
spectral bands and in the redox potentials that can be
to stabilize higher oxidation states of coordinated metal.
readily rationalized through a consideration of how the
Manganese corroles have received considerable attention
alignments of the angular nodal patterns of the frontier
in this regard, since the 3d5 configuration of the Mn(II)
p-MOs influence the effect of introducing the push–pull
ion readily loses electrons to form stable Mn(III),
substituents [13, 14].
Mn(IV) and Mn(V)corrole structures, which exhibit no
DNA carries the genetic instructions used in the growth,
development, functioning and reproduction of living
◊ꢀSPP full member in good standing
organisms and most viruses [15, 16]. The interactions
between porphyrinoid chromophores and DNA by an
outside binding mode have not been studied in depth.
Several studies have shown, however, that porphyrinoids
can interact with DNA. This approach can be used for
*Correspondence to: Xu Liang, email: liangxu@ujs.edu.cn,
tel: & fax: +86 511-8879-1928; Weihua Zhu, email: sayman@
ujs.edu.cn, tel: & fax: +86 511-8879-1928; John Mack, email:
j.mack@ru.ac.za, fax: +27 46-622-5109.
Copyright © 2017 World Scientific Publishing Company

752
X. LIANG ET AL.
tumor detection and targeting drug delivery in vivo, leading
to tumor cell death without damage to normal tissue.
According to previous studies, cationic metallocorroles
can interact with DNA and induce and then stabilize the
formation of G-quadruplex structures [17, 18]. It has
previously been reported that the introduction of high-
valence metal centers, such as Mn(III), Fe(III) and P(V)
[19–22], can enhance the electronic attraction between
the metallocorrole and DNA. The push–pull substitution
strategy results in strong intramolecular charge transfer and
this provides a new approach for studying the interaction
between DNA and non-cationic metallocorrole, which
is advantageous since the synthesis and purification of
cationic metallocorroles is difficult to achieve. In this study,
the synthesis, optical spectroscopy, electrochemistry, and
TD-DFT calculations of a series of push–pull Mn(III)
triarylcorroles (3a–3c) is reported (Scheme 1) along with
their interaction properties with cell-free circulating tumor
deoxyribonucleic acid (ctDNA) in aqueous solution.
a model complex with a phenyl substituent as the A2
meso-phenyl positions by using the B3LYP functional
with 6-31G(d) basis sets. TD-DFT calculations were
carried out in a similar manner with the CAM-B3LYP
functional, since its long-range correction is known
to provide more accurate predictions in the context of
porphyrinoids with closed shell electronic configurations
for the energies of transitions with significant charge
transfer character [27, 28].
Sample preparation for DNA interaction
Electronic absorption spectroscopy is one of the
most useful techniques for DNA binding studies [29,
30]. All of the experiments involving the interaction of
3a–3c with ctDNA were conducted in buffer solution
(50 mM NaCl, 5 mM tris-HCl, pH = 7.1) at room
temperature. A solution of ctDNA in tris-HCl buffer
solution gave ratios of UV absorbance at 260 and 280 nm
of ca. 1.9, indicating that the DNA was sufficiently free
of protein. The DNA concentration was determined
by absorption spectroscopy using a molar absorption
coefficient (6600 M cm ) at 260 nm. Absorption
EXPERIMENTAL
-1
.
titration measurements were carried out by varying the
concentration of ctDNA-buffer solution upon addition of
50 mL of a 1 × 10-2 M DMSO solutions of 3a–3c and
keeping a fixed complex concentration in tris-HCl buffer
(pH = 7.11). For fluorescence quenching experiments,
the ctDNA was pretreated with ethidium bromide (EB)
for 30 min and 3a–3c were then added to this mixture so
their effect on the emission intensity could be measured
at different temperatures. The quenching properties of
the DNA complex in the presence of EB was analyzed by
using the Stern–Volmer equation.
Chemicals
The reagents and solvents that were used were of
reagent grade and, except where noted, were used without
further purification. Cyclic voltammetry measurements
were carried out in a three-electrode cell using a Chi-
730D electrochemistry station. A glassy carbon disk
electrode was used as the working electrode, and the
counter and reference electrodes were platinum mesh
and a Ag/AgCl electrode, respectively. Magnetic circular
dichroism (MCD) spectra were recorded on a JASCO
J-815 spectrodichrometer equipped with a JASCO
permanent magnet, which produces magnetic fields of up
to 1.60 Tesla with both parallel and antiparallel fields.
The MCD sign and Faraday term conventions of Piepho
and Schatz are used throughout [23–25].
Synthesis of 5,15-(m-nitrophenyl)-10-
(3,5-bis-trifluoromethylphenyl)Mn(III)corrole 3a
Synthesisandpurificationof5-(3-nitrophenyl)-dipyrro-
methane were carried out according to literature pro-
cedures [12, 31] to provide a precursor to form A2B
type triarylcorroles. 5-(3-Nitrophenyl)-dipyrromethane
(0.535 g, 2.0 mmol) and 3,5-bis-trifluoromethylbenz-
aldehyde (242 mg, 1.0 mmol) were dissolved in a mixture
Computational methods
The Gaussian 09 software package [26] was used to
carry out DFT geometry optimizations for 3a–3c and
Scheme 1. Synthesis of Mn(III)corroles 3a–3c
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PUSH–PULL TYPE MANGANESE(III)CORROLES
753
of methanol (50 mL) and water (47.5 mL). 2.5 mL of
concentrated hydrochloric acid was slowly added and
the mixture was stirred at room temperature for 1 h
under N2. The solid state compound was collected after
filtration, and dissolved in CHCl3. The organic phase
was washed by NaHCO3 aqueous solution, distilled
water and dried with anhydrous NaSO4. After removal
of the solvent by rotary evaporation, the residue was
dissolved in 20 mL of CH2Cl2 and chloranil (0.74 g,
3.0 mmol) and the mixture was heated at 50°C for 3 h
with progress monitored by TLC plate. After purification
by silica gel column chromatography using CH2Cl2/
hexane (4:1) as the eluent, finally the H3-5,15-(3-
nitrophenyl)-10-(3,5-bis-trifluoromethylphenyl)corrole
2a was obtained by recrystallization from CH2Cl2 and
hexane as a deep-violet solid in 12.1% yield (0.0748 g).
The free base 5,15-(m-nitrophenyl)-10-(3,5-bis-trifluoro-
methyl-phenyl)corrole 2a (0.0350 g, 0.05 mmol) and
MnCl2 (0.0623 g, 0.25 mmol; 5.0 eq) were dissolved in
5 mL DMF and stirred at 120°C for 1 h. After removal of
the solvent, purification by Al2O3 gel (CH2Cl2:hexane =
2:1; v/v) gave the target compound 3a in 90.2%
yield (0.0281 g). MALDI-TOF-MS: m/z = 804.96 (Calcd.
[M]+ = 804.53). Elemental analysis: Found, C, 58.13; H,
2.45; N, 10.52; O, 7.99 (Calculated, C, 58.22; H, 2.38; N,
10.45; O, 7.95).
699.22 (Calcd. [M]+ = 698.56); Elemental analysis: Found,
C, 65.44; H, 3.12; N, 12.36; O, 11.21 (Calculated, C, 65.34;
H, 3.32; N, 12.03; O, 11.45).
Synthesis of 5,15-(m-nitrophenyl)-10-(p-N,N′-
dimethylaminophenyl)Mn(III)corrole 3c
Thegeneralsyntheticprocedurewassimilarwith3a,but
5,15-(m-nitrophenyl)-10-(p-N,N-dimethylaminophenyl)
corrole 2c was used instead. The target compound 3c was
obtained in a 63.2% yield (0.0173 g). MALDI-TOF-MS:
m/z = 711.99 (calcd. [M]+ = 711.61); Elemental analysis:
Found, C, 65.76; H, 3.55; N, 13.79; O, 8.95 (Calculated,
C, 65.83; H, 3.68; N, 13.78; O, 8.99).
RESULTS AND DISCUSSION
Synthesis and characterization
Free base corrole compounds (2a–2c) were synthe-
sized from a reaction of dipyrromethane 1 and the
appropriate aryl-aldehyde (Scheme 1) according to the
literature procedures. Mn(III)corroles (3a–3c) were
then synthesized by a metalation reaction of 2a–2c, and
were purified by Al2O3 gel column chromatography. The
MALDI-TOF MS data for 3a revealed an intense parent
peak at 804.96 (calcd. [M]+ = 804.53), providing direct
evidence that the 5,15-(m-nitrophenyl)-10-(3,5-bis-
trifluoromethyl-phenyl)Mn(III)corrole 3a was success-
fully prepared. Similar parent peaks were also observed
for 3b and 3c. Elemental analyses provided further
evidence that the structures are consistent with those
predicted on the basis of MS data.
Synthesis of 5,15-(m-nitrophenyl)-10-
(p-methoxylphenyl)Mn(III)corrole 3b
The general synthetic procedure is similar to that of 3a,
but 5,15-(m-nitrophenyl)-10-(p-methoxylphenyl) corrole
2b was used instead. The target compound 3b was obtained
in a 90.0% yield (0.0243 g). MALDI-TOF-MS: m/z =
Fig. 1. The nodal patterns of a model complex with a phenyl ring at the B meso-aryl position (−H) at the CAM-B3LYP/6-31G(d)
level of theory
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754
X. LIANG ET AL.
their analogs such as corroles. Michl [33–36] referred
to the p-MOs that are derived from the HOMO and
LUMO of the parent perimeter as the a and -a MOs,
respectively, if angular nodal planes lie on the y-axis,
or as the s and -s MOs for the corresponding MOs that
have significant MO coefficients on the y-axis (Fig. 1).
In marked contrast with what is the case with free base
corroles [3], the a, s, -a and -s MOs do not form the
four frontier p-MOs in the TD-DFT calculations for
3a–3c and there is significant mixing with close lying
3d orbitals of the Mn(III) ion (Fig. 1). The LUMOs are
consistently predicted to be associated primarily with
the 3dxz orbital of the central metal ion (Figs 1 and 2) and
the LUMO+1, LUMO+2 and LUMO+4 are associated
primarily with the electron withdrawing NO2 groups at
the A2 meso-positions and the 3dz2 orbital of the central
metal ion. The LUMO+3 and LUMO+5 are the -a and
-s MOs, respectively, while in contrast, the a and s MOs
consistently correspond to the HOMO−1 and HOMO.
This means that the complexes are expected to undergo
reduction initially at the metal center rather than on the
corrole ligand.
Fig. 2. The predicted MO energies for 3a–3c and a model
complex with a phenyl ring at the B meso-aryl position (−H)
at the CAM-B3LYP/6-31G(d) level of theory. Occupied MOs
are highlighted with small black squares. Gray diamonds are
used to denote average HOMO−LUMO gap values for the a, s,
-a and -s MOs that are associated with the corrole ligand and
are plotted against a secondary axis. The a, s, -a and -s MOs are
highlighted with thick black lines. Gray and longer black lines
are used to denote MOs that are localized primarily on the A2
position meso-aryl rings and the 3d orbitals of the Mn(III) ion,
respectively
A comparison withTD-DFT calculations demonstrates
that the intense bands at around 420 nm and the shoulder
of absorbance to high energy in the spectra of 3a–3c
(Figs 3 and 4 and Table 1) can be readily assigned to the
B transitions. Further evidence can be derived for the
MCD spectra, since there is an intense pair of oppositely-
signed Faraday B0 terms in the MCD spectra (Fig. 1).
The analysis of the weaker bands at lower energy in
the visible region and near-infrared (500–800 nm) is
complicated by the presence of ligand-to-metal charge
transfer (LMCT) bands (Fig. 4), since the LUMO is
predicted to be associated primarily with the 3dxz orbital
of the central metal ion (Figs 1 and 2). Regular Mn(III)-
meso-triphenyl-corroles have weaker bands that lie at
ca. 640 nm, and 3a has similar spectral properties in this
regard. The coupled pairs of oppositely-signed Faraday
B0 terms in the 550–600 nm region of the MCD spectra of
3a–3c can be assigned to the Q transition (Fig. 3), while
Optical spectra and TD-DFT calculations
The electronic structures and optical spectra of
porphyrinoids can be readily rationalized by using
Gouterman’s 4-orbital model [32] and Michl’s perimeter
model [33–36]. The electronic structures and optical
properties of corroles are reasonably similar to those
of porphyrins [37]. The p-MOs associated with the 15
atom 18 p-electron inner ligand perimeter are arranged
in an ML = 0, 1, 2, 3, 4, 5, 6, 7 sequence in
ascending energy terms that is determined by the
angular nodal properties. Since the HOMO and LUMO
have ML values of 4 and 5, respectively, Gouterman’s
4-orbital model predicts the presence of an allowed B
transition (DML = 1) at high energy and a forbidden Q
transition (DML = 9) at low energy for porphyrins and
Fig. 3. Magnetic circular dichroism (MCD) and UV-visible absorption spectra of Mn(III)corroles 3a–3c in CH2Cl2
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PUSH–PULL TYPE MANGANESE(III)CORROLES
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0.1 M tetra-n-butylammonium perchlorate (TBAP) as
a supporting electrolyte (Fig. 5), to provide further
information about the electronic structure of synthetic
Mn(III)corroles. 3a–3c have similar electrochemical
properties to those that have been reported previously
for similar complexes [38]. The first reduction steps of
A2B type metal corrole complexes have been reported to
occur at the central metal, and the second at ca. 1.0 V
involves reduction of the meso-nitrophenyl rings, while
the first oxidation step forms a [Mn(III)corrole]+ p-cation
[39]. The HOMO and LUMO of 3a–3c are predicted to
be a corrole p-system and Mn(III) 3d orbitals (Fig. 2),
respectively, so similar trends in the redox properties
are anticipated in this context. When electron-donating
and -withdrawing substituents are introduced at the B
meso-position, there is an increase or decrease in the
electron density on the p-conjugation system of the
corrole ligand, respectively, and a decrease or increase
in the dipole moment of the complex [40, 41]. The cyclic
voltammogram for 3a has a first reversible [Mn(III)
corrole]/[Mn(II)corrole]- reduction step at 0.32 V (in
o-DCB) (Fig. 5), while there is a negative shift of the
E1/2 values for 3b–3c to 0.25 V (3b) and 0.20 V (3c),
respectively, when electron-donating substituents are
introduced at the B meso-position. The trend in the
gaps between the first reduction and oxidation steps
(Fig. 5) is consistent with the slight red shift of both
the Q and B bands that is observed in the spectroscopic
characterization and theoretical calculations of 3b and
3c (Figs 2–4 and Table 1) which have more pronounced
push–pull properties.
Fig. 4. The TD-DFT calculations for 3a–3c and a model
complex with a phenyl ring at the B meso-aryl position (−H).
Large gray squares are used to highlight the Q and B bands,
while black circles are used to denote transitions that are
associated with the 3d orbitals of the Mn(III) ion. Small gray
diamonds are used for transitions associated with the LUMO+1
and LUMO+2 that are localized on the A2 position meso-phenyl
rings. The simulated spectra were generated with the Chemcraft
program with a fixed bandwidth of 2000 cm-1
ctDNA interaction
the weak broader bands to the red that vary significantly
in their band centers are probably associated with LMCT
transitions, since the gap between the a/s and -a/-s MOs
do not vary significantly in the TD-DFT calculations
(Fig. 2). Upon increasing the electron-donating ability of
the B position meso-substituent to form 3c, the broader
absorption bands extend beyond 800 nm and can be
assigned to LMCT transitions possibly due to slight
changes in the energies of the occupied frontier MOs
(Fig. 2). The +/−/+/− sign sequence that is observed
for the Faraday B0 terms that have been assigned to
the Q and B transitions in the MCD spectra (Fig. 3 and
Table 1) is consistent with what would be expected based
on the relative magnitudes of the splittings (Fig. 2) of the
a and s MOs (the DHOMO value in Michl’s terminology)
and the -a and -s MOs (the DLUMO value). Michl [33–
36] has demonstrated that a +/−/+/− sign sequence is
observed when DLUMO > DHOMO as is the case with
3a–3c (Fig. 2).
Fluorescence studies were used to quantify the
interaction between EB-ctDNA and 3a–3c (Fig. 6),
by using the Stern–Volmer static equation, I0 /I = 1 +
K[Q], where I0 is the original intensity of EB-ctDNA
compound at 602 nm, I is the fluorescence intensity upon
addition of the Mn(III)corrole to the solution, and [Q]
is the concentration of 3a–3c which act as fluorescence
quenchers. The quenching constants (K) for 3a–3c have
been found to be K = 3.49 × 105, 4.54 × 105, and 4.58 ×
10 L mol for 3a–3c, respectively. The binding ability
between ctDNA and Mn(III)corroles increases with
the electron donating ability of the meso-substituent at
the B meso-position. There are three possible reasons
for the observed fluorescence decrease. Firstly, the
formation of a chemical bonded Mn(III)-EB complex
causes fluorescence quenching; secondly, Mn(III)corrole
binding with EB-ctDNA forms a new non-fluorescent
EB-ctDNA-Mn(III)corrole complex, which decreased
the fluorescence intensity of EB-ctDNA; and thirdly,
the Mn(III)corrole competes with EB in binding with
DNA and the intercalated EB was excluded from the
DNA double helix, resulting in decreases in the observed
fluorescence intensity. These results are noteworthy
5
-1
.
Electrochemistry
Cyclic voltammetry (CV) measurements were
carried out in o-dichlorobenzene (o-DCB) containing
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756
X. LIANG ET AL.
Table 1. TD-DFT spectra of 3a–3c and a model complex with a phenyl ring the B meso-aryl position (−H) with the CAM-B3LYP
functional and 6-31G(d) basis sets
b
Banda
#
Calcc
Expd
Wave Functione =
3a
—
Qx
Qy
Bx
1
—
—
—
—
—
Ground state
10 20.7 482 (0.05) ≈16.7 ≈600 42% s → -a; 27% a → -a; 9% s → Ldxz; …
11 22.4 446 (0.01)
14 27.3 368 (0.19)
17.5 572 42% a → -a; 35% s → -s; …
50% s → L+1NO ; 8% a → L+1 ; 7% H−4 → Ldxz; 7% s → -s; 7% s →
-a; 6% a → -s; …
NO
2
2
23.1 432
2
25.0 400 27% a → -s; 26% a → L+1NO ; 12% a → L+4dz ; 8% s → -a; …
2
By
19 28.7 349 (0.18)
3b
—
Qx
Qy
Bx
1
8
—
—
—
—
—
Ground state
20.2 495 (0.07) ≈16.7 ≈600 28% s → -a; 14% a → -a; 13% s → -s; 10% a → Ldxz; 6% s → Ldxz; …
11 21.9 457 (0.01)
15 27.0 370 (0.18)
17.4 576 40% a → Ldxz; 15% a → -a; 12% a → Ldxz; 10% s → -s; …
18% s → -s; 17% H−2dyz → Ldxz; 15% H−5 → Ldxz; 10% H−2dyz → a; 8%
23.2 431
a → L+2NO ; …
2
25.3 395 47% a → -s; 16% s → -a; 10% a → L+1NO ; …
2
By
19 28.4 352 (0.48)
3c
—
1
8
—
—
—
—
—
Ground state
Qx
20.1 499 (0.07)
16.8 594 31% s → -a; 14% a → -a; 11% a → Ldxz; 11% s → -s; 7% s → L+4dz2
6% s → Ldxz; …
;
2
2
Qy
Bx
By
11 21.8 460 (0.01) ≈17.4 ≈575 42% a → L+4dz ; 15% a → -a; 12% s → L+4dz ; 10% s → -s; …
23.5 425 31% s → -s; 16% H−5 → Ldxz; 12% a → L+1NO ; 11% a → L+2 ; …
NO
2
2
16 26.9 371 (0.25)
19 28.3 354 (0.54)
25.7 389 50% a → -s; 12% s → -a; 8% s → -s; …
−H
—
Qx
Qy
Bx
1
—
—
—
—
—
—
—
—
—
Ground state
10 20.6 485 (0.07)
11 22.2 450 (0.01)
15 26.7 374 (0.23)
51% s → -a; 27% a → -s; 11% s → Ldxz; …
2
49% a → -a; 29% s → -s; 8% s → L+4dz ; …
23% s → L+2NO ; 19% a → L+1 ; 17% s → -s; 11% H−5 → Ldxz; 10%
NO
2
2
s → L+1NO ; 5% a → -s; …
2
—
—
2
2
By
19 28.5 351 (0.33)
34% a → -s; 15% H−3dxy → L+19dx –y ; 12% s → -a; 7% H−3dxy → L+23;
6% a → L+1NO ; …
2
a — The band assignment is described in the text. b — Numbers for each state within the TD-DFT calculation are assigned in terms of
-1
ascending energy. c — For each calculated spectral band, energies (103 cm ), wavelengths (nm) and in parentheses oscillator strengths (f) are
.
-1
provided. d — The experimentally observed energies (103 cm ) and wavelengths (nm) in Fig. 1. e — The wave functions based on the
.
eigenvectors predicted by TD-DFT. Only one-electron transitions that contribute more than 5% are included. Those associated exclusively
with the a, s, -a and -s MOs of Michl’s perimeter model [33–36] are highlighted with bold fonts. NO2 superscripts are used to denote MOs that
2
2
2
are localized on the A2 position meso-aryl rings, while dxy, dxz, dyz, dz and dx are used denote MOs that are primarily associated with the 3d
–y
orbitals of the Mn(III) ion.
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PUSH–PULL TYPE MANGANESE(III)CORROLES
757
Fig. 5. Cyclic voltammetry measurements of Mn(III)corroles 3a (left), 3b (middle) and 3c (right) in o-dichlorobenzene (o-DCB)
Fig. 6. Fluorescence spectra of EB-ctDNA solution upon addition of Mn(III)corroles 3a–3c
since they demonstrate that binding with porphyrinoid
chromophores with strong intramolecular charge transfer
properties could result in less efficient photocleavage by
singlet oxygen and hydroxyl radicals.
province (No. BK20160499), the fund from the state key
laboratory of Coordination Chemistry (No. SKLCC1710)
and an NRF of South Africa CSUR grant (93627). The
theoretical calculations were carried out at the Centre for
High Performance Computing in Cape Town.
CONCLUSIONS
A series of Mn(III)triarylcorroles containing asym-
metric push–pull meso-substitutions have been synthe-
sized and characterized. A detailed analysis of the
UV-visible absorption and MCD spectra, cyclic voltam-
metry measurements, and the results of DFT and
TD-DFT calculations has been carried out to identify the
key trends in the redox and optical properties. Evidence
for normally forbidden LMCT bands associated with
the Mn(III) ion was observed in the NIR region of the
optical spectra of 3b and 3c, which have strong push–
pull properties. This study demonstrates that A2B type
Mn(III)triarylcorroles efficiently bond with ctDNA in
solution and that the bonding properties can be readily
modified by adjusting the push–pull properties of the
meso-aryl rings.
REFERENCES
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Scientific Foundation of China (Nos. 21701058,
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