Syntheses, crystal structures, photo-physical properties, antioxidant and antifungal activities of Mg(II) 4,4′-bipyridine and Mg(II) pyrazine complexes of the 5,10,15,20 tetrakis(4–bromophenyl)porphyrin

Article abstract of DOI:10.1016/j.ica.2021.120466

This study concerns the synthesis of 5,10,15,20-tetrakis(4-bromophenyl)porphyrin (H₂TBrPP)-based magnesium(II) complexes involving 4,4′-bipyridine (4,4′-bpy) and pyrazine (pyz) ligand, for [Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)₂] (2), respectively. New complexes 1 and 2 were characterized by single crystal X-ray diffraction, elemental analysis, infrared and nuclear magnetic resonance spectroscopies. The photo-physical properties were investigated by UV–visible absorption and emission spectroscopies. These new magnesium(II) complexes exhibit promising antifungal and antioxidant activities.

Full text of DOI:10.1016/j.ica.2021.120466

Inorganica Chimica Acta 525 (2021) 120466
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Syntheses, crystal structures, photo-physical properties, antioxidant and
antifungal activities of Mg(II) 4,4′-bipyridine and Mg(II) pyrazine
complexes of the 5,10,15,20 tetrakis(4–bromophenyl)porphyrin
,
,
Nesrine Amiria *, Fadia Ben Taheurb, Sylviane Chevreuxc d, Carine Machado Rodriguesc,
Vincent Dorcete, Gilles Lemercierc, Habib Nasria
a Laboratory of Physical Chemistry of Materials, University of Monastir, Avenue of the Environment, 5019 Monastir, Tunisia
b Laboratory of Analysis, Treatment and Valorisation of Environmental Pollutants and Products, Faculty of Pharmacy, Monastir University, Tunisia
c University of Reims Champagne Ardenne, ICMR UMR CNRS 7312, BP 1039-51687, Reims, Cedex 2, France
d Chimie Paris Tech, PSL University, CNRS, Institut de Recherche de Chimie Paris, 75005 Paris, France
e Institute of Chemical Sciences of Rennes, UMR 6226, University of Rennes 1, Beaulieu Campus, 35042 Rennes, France
A R T I C L E I N F O
A B S T R A C T
Keywords:
This study concerns the synthesis of 5,10,15,20-tetrakis(4-bromophenyl)porphyrin (H2TBrPP)-based magnesium
(II) complexes involving 4,4′-bipyridine (4,4′-bpy) and pyrazine (pyz) ligand, for [Mg(TBrPP)(4,4′-bpy)] (1) and
[Mg(TBrPP)(pyz)2] (2), respectively. New complexes 1 and 2 were characterized by single crystal X-ray
diffraction, elemental analysis, infrared and nuclear magnetic resonance spectroscopies. The photo-physical
properties were investigated by UV–visible absorption and emission spectroscopies. These new magnesium(II)
complexes exhibit promising antifungal and antioxidant activities.
Porphyrin-based Mg(II) complexes
Pyrazine ligand
4,4′-bipyridine ligand
X-Ray structures
Photo-physical properties
Antioxidant and antifungal activities
1. Introduction
harvesting molecules, so that non-redox magnesium helps in the light
harnessing process. The magnesium complexes attract much attention
Porphyrins and their metal complexes were considered as active
materials used in polymerization [1–3] and they also exhibited impor-
tant function as catalysts, in medicinal and pharmaceutical fields [4–6],
and functional dyes and pigments [7]. For example, iron and manganese
porphyrinic complexes were used as efficient catalysts for hydroxylation
of alkanes and epoxidation of alkenes [8–14]. Having conjugated
configuration, porphyrins and metalloporphyrins are remarkable pre-
cursors in supramolecular chemistry [15,16] and are considered as
excellent components in the design of functional molecular materials
with improved electrochemical and physical–chemical properties [16].
Several projects were reported, including molecular wires [17], chem-
ical sensors [18], semi-conductors [19], photo-induced electron transfer
[20,21], and solar photovoltaic cells [22,23]. Notably several de-
rivatives based on porphyrin had been developed as efficient photo-
sensitizers for photodynamic therapy (PDT) in clinical applications
[24,25]. Structures of magnesium porphyrins are also of interest because
of their relationship to chlorophyll, as highlighted in a recent report
[26]. Nature selects metal magnesium for chlorophyll type light
mainly due to promising photo-physical properties [27,28], and these
properties underlie the interest of the latter as potential photosensitizers
[29]. Interestingly, Mg(II) porphyrin can easily bind with N/O-donor
ligands to produce both five- and six-coordinate complexes [30–34].
Recently, we also reported the preparation of one magnesium de-
rivatives [Mg(TBrPP)(HIm)] five-coordinate [35] and two six-
coordinate magnesium complexes [Mg(TPBP)(L)2] (TPBP
=
5,10,15,20-tetrakis[4(benzoyloxy)phenyl]porphyrin and L = Hexameth-
ylenetetramine -HTMA- or 1,4-diazabicyclo[2.2.2]octane –DABCO-)
[36]. In this context, it was pointed out that these complexes possess
interesting activities against several bacterial species including Escher-
ichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeru-
ginosa. Some examples of magnesium porphyrin-based coordination
dimers, oligomers [37] and polymers [38,39] have been designed, many
of which based on the axial coordination to the magnesium ion of a
metallo-porphyrin through the nitrogen atoms of a bidentate ligand. As
development of brominated porphyrin have been the subject of partic-
ular attention due to their catalytic [40,41], electrochemical and optical
* Corresponding author.
E-mail address: nesamiri@gmail.com (N. Amiri).
https://doi.org/10.1016/j.ica.2021.120466
Received 4 January 2021; Received in revised form 16 April 2021; Accepted 19 May 2021
Available online 23 May 2021
0020-1693/© 2021 Elsevier B.V. All rights reserved.

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
characteristics [42–45], in this paper and in continuation to our work on
functionalization of halogen-substituted porphyrins [35,46], we further
combined the porphyrin framework Mg(TBrPP) (TBrPP = 5,10,15,20-
tetrakis(4-bromophenyl)porphyrin) with two nitrogen based ligands
(4,4′-bpy and pyz) in order to design two novel Mg(II) porphyrins
complexes. X-ray diffraction, spectral and photophysical studies were
performed for these synthetic compounds. Single crystal X-ray diffrac-
tion elucidates the coordination of the Mg(II) ion within these two novel
meso-porphyrin complexes, bearing 4,4′-bpy and pyz molecules in axial
positions to complete the ligand sphere. As far as single crystal structure
is concerned, Mg2+ ion is penta-coordinated in 1 in the form of [Mg
(TBrPP)(4,4′-bpy)], while the same metallic ion is involved in six bonds
in 2, leading to the [Mg(TBrPP)(pyz)2] complex (Fig. 1). These com-
pounds crystallise within the same space group (C2/c). This study pro-
vides further information about the structures of these pyramidal and
octahedral complexes. UV–visible absorption and emission spectros-
copies were also investigated to try to confirm the coordination state of
these structures in diluted solution. Proton nuclear magnetic resonance
(1H NMR) spectroscopy, tends to show that these complexes seem to be
organized in a polymeric (or oligomeric) assembling in these more
concentrated CDCl3 solutions.
2.2. X-ray diffraction study
Crystals of complexes (1) and (2) suitable for single crystal X-ray
diffraction were obtained by methods described above. Purple-blue
crystals of dimensions smaller than 0.2 mm were selected for the X-
ray diffraction experiment. Data collections for (1) and (2) were per-
formed on a Bruker APEX-II diffractometer and a Bruker D8 Venture
diffractometer, respectively. All diffractometers were equipped with
graphite monochromated Mo Kα radiation (λ = 0.71073 Å) and intensity
data for all compounds were collected by the narrow frame method at
low temperature (150 and 100 K respectively). All structures were
solved by direct method using SIR97 and SHELXS-97 [47,48] and
refined by full-matrix least-squares on F2 using the SHELXL-97 program
[48]. Data were corrected for absorption effects by the Multi-Scan
method (SADABS) [49]. The crystallographic data are available free of
charge on the Cambridge Crystallographic Data Centre (CCDC), under
references 1,824,510 (1) and 1,877,063 (2).
2.3. Antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH)
method
The synthesized complexes were screened in vitro for their antifungal
activity to evaluate their inhibiting potential against fungal species
including three yeasts strains (C. krusei, C. albicans and C. neoformans)
and two fungal strains (A. brasiliensis and A. fumigatus). The antioxidant
activity of the complexes was also investigated through scavenging ef-
fect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals.
The antioxidant activity of the free base porphyrin and their mag-
nesium complexes was evaluated using DPPH radical scavenging ac-
tivity method. In the experiments, different concentrations (25, 50, 75
and 100 µg/mL) of our compounds were prepared. A volume of 2 mL of
each sample was mixed with 2 mL of 0.1 M sodium acetate buffer (pH =
5.5). Then, 1 mL of 0.5 M methanol DPPH solution was added. The re-
action mixture was shaken vigorously and kept in completely dark for
30 min. Then the absorbance was measured at 517 nm in a spectro-
photometer. The percentage of radical scavenging activity (RSA %) was
calculated according to the following equation:
2. Materials and methods
2.1. Spectroscopies, spectrometry and photo-physical measurements
1H NMR spectra were recorded on a Bruker (Advance 400dpx spec-
trometer) at 400 MHz. FT-IR spectra were recorded in the region of
400–4000 cmꢀ 1 on a Nicolet Impact 410 spectrophotometer. UV–Vis
spectra were measured with a Varian Cary 5000 spectrophotometer and
fluorescence spectra and quantum yield measurements were performed
using a Varian Cary Eclipse luminescence spectrophotometer. Elemental
analyses were carried out on a Flash EA 1112 Series Thermo Electron
fitted with a Porapak column 2 m PTFE + MX5 microbalance Mettler
Toledo. MALDI-ToF-MS measurements were performed using a SYNAPT
G2-Si option MALDI (Waters Corp., Manchester, UK) equipped with a
337 nm UV nitrogen laser producing 3-ns pulses. The samples were also
analyzed by ESI/Q-ToF HRMS method, performed on a Waters SYNAPT
G2-Si High Resolution Mass Spectrometry equipped with electrospray
ionization (ESI) source (Waters Corp., Manchester, UK).
RSA % = [(AC ꢀ ꢀ AS)/AC ] x 100
Where, AC is the absorbance of the control (methanol DPPH solu-
tion) and AS is the absorbance of the sample.
2.4. Antifungal activity
Yeasts Strains: three yeasts strains, C. krusei ATCC6258, C. albicans
ATCC90028 and C. neoformans ATCC14116 were cultured on Sabouraud
◦
agar at 37 C (optimal temperature for yeast growth) for 48 h. Then,
pure colonies were suspended in 10 mL of physiological medium (9 g
NaCl in 1 L distilled water), mixed well for 5 min and suspensions were
adjusted to 0.5 McFarland standard turbidity. One milliliter of yeast
suspension was spread over Sabouraud agar medium plates and incu-
bated for 30 min at 37 ◦C. Then, 6 mm diameters wells were dug in agar
Fig. 1. Molecular structures of [Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)2] (2).
2

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
3
medium using sterile glassy borer. The Mg(II) complexes were prepared
in DMSO (1 mg/mL) and introduced into the respective wells, one of the
wells was supplemented with DMSO as control. These plates were placed
in a 37 ◦C incubator for 48 h to allow yeast growth. After 48 h, the di-
ameters of the clear zone of inhibition surrounding the sample were
measured in millimeters by digital caliper.
MHz]: δ(ppm) 7.90 (d, 8H, JHmHo = 8.4 Hz, Hm–Hm’), 8.01 (d, 8H,
3JHoHm = 8.4 Hz, Ho–Ho’), 8.36 (d, 8H, JHbHa = 5.3 Hz, Hb-ligand),
3
8.54 (d, 8H, 3JHaHb = 5.3 Hz, Ha-ligand), 8.79 (s, 8H, Hβ). UV–vis (in
CH2Cl2) [λmax, nm, (
ε
, Mꢀ 1 cmꢀ 1)]: 427 (4.61 × 106), 565 (1.47 × 105),
604 (6.60 × 104). Anal. Calcd. For C64H42Br4MgN8O: C, 59.9; H, 3.3; N,
8.7. Found: C, 59.6; H, 3.5; N, 9.0. FTIR cmꢀ 1: 3120 (CH 4,4′-bpy),
ν
Fungal Strains: two fungi strains, A. brasiliensis ATCC16404 and
A. fumigatus ATCC204305 were cultured on inclined Sabouraud agar in
2928 and 2855 ν(CH porphyrin), 1497 ν
(CN 4,4′-bpy), 1016 (δCCH
porphyrin), 794 (δCCH 4,4′-bpy).
◦
Falcon tube 15 mL at 25 C for 7 days (optimal temperature for their
[MgII(TBrPP)(pyz)2]. 0.5 H2O (2): Mg(TBrPP) (20 mg, 0.020
mmol) and pyrazine (90 mg, 1.1 mmol) in 5 mL of dichloromethane
were stirred of 3 h at room temperature. The colour of the reaction
mixture changed from purple to green–blue. Crystals of 2 were prepared
by slow diffusion of n-hexane into the dichloromethane solution. 1H
NMR [CDCl3, 400 MHz]: δ(ppm) 7.14 (s, 8H, Hpyz) 7.96 (d, 8H, 3JHmHo
= 8.4 Hz, Hm–Hm’), 8.11 (d, 8H, 3JHoHm = 8.4 Hz, Ho–Ho’), 8.81 (s, 8H,
growing). The spore of fungal strain was suspended in peptone water
and counted to have 106 spores/mL. Then, one milliliter of fungal sus-
pension was spread over Sabouraud agar medium plates and incubated
for 30 min at 25 ◦C. After that, 6 mm diameters wells were dug in agar
medium using sterile glassy borer. The Mg(II) complexes were prepared
in DMSO (1 mg/mL) and introduced into the respective wells, one of the
wells was supplemented with DMSO as control. These plates were placed
in a 25 ◦C incubator for five days to allow fungal growth. After five days,
the diameters of the clear zone of inhibition surrounding the sample
were measured in millimeters by digital caliper.
Hβ). UV–vis (in CH2Cl2) [λmax, nm, (
ε
, Mꢀ 1 cmꢀ 1)]: 435 (4.46 × 106),
578 (1.69
×
105), 618 (1.04
×
105). Anal. Calcd. for
C
52H35Br4MgN8O0.5C, 55.6; H, 3.1; N, 10.0. Found: C, 55.6; H, 3.0; N,
9.8. FTIR cmꢀ 1: 3061
ν(CH pyz), 2969 and 2918 ν(CH porphyrin), 1482
ν
(CN pyz), 998 (δCCH porphyrin), 794 (δCCH pyz).
2.5. Syntheses and crystallization
3. Results and discussion
Commercially available chemicals and reagents were used without
purification. The solvents were purified using the available literature
methods [50]. The synthesis of 5,10,15,20-tetrakis(4-bromophenyl)
porphyrin macrocycle (H2TBrPP) was performed according to method
already described in the literature [51]. The insertion of the magnesium
ion into porphyrin molecule was done by the heterogeneous method
reported by Lindsey and co-workers [52].
3.1. IR and 1H NMR spectroscopies
In order to give more insights in the structure of porphyrin, metal-
loporphyrin and axially ligated magnesium(II) porphyrin complexes,
detailed IR and 1H NMR studies were performed. FTIR spectrum of the
free base porphyrin H2TBrPP (Fig. S7) show a broad band at 3447 cmꢀ 1
,
Meso-tetrakis(4-bromophenyl)porphyrin (H2TBrPP): 4-Bromoben-
zaldehyde (7 g, 37.8 mmol) was dissolved in acetic acid (150 mL) and
the solution was heated under reflux conditions. Pyrrole (2.6 mL, 37.8
mmol) was added drop-wise and the dark mixture was heated for a
further 30 min. After cooling, the black tarry mixture was filtered to
obtain a purple solid which, after washing with methanol and water,
lead to the porphyrin derivative as purple crystals (15%). 1H NMR
[CDCl3, 400 MHz]: δ (ppm) ꢀ 2.86 (s, 2H, NHpyrro), 7.88 (d, 8H, 3JHoHm
= 8.1 Hz, Hm–Hm’), 8.02 (d, 8H, 3JHoHm = 8.1 Hz, Ho–Ho’), 8.80 (s, 8H,
which is due to overlapping of –NH2 stretching frequencies, 1472 cmꢀ 1
–
due to C
C
stretching frequency and the bands observed
–
around 1000 (camroꢀm1atiacr)e assigned to δ(CCH) vibration modes for the meso-
porphyrin. This assignment is in good agreement with the work of
Boucher and Katz [53]. When the magnesium ion was inserted into the
–
porphyrin ring, the N H vibration frequency of free base porphyrin
disappeared which indicated the formation of magnesium(II) porphyrin
compounds (Fig.S6). The IR spectra of the complexes 1 and 2 containing
4,4′-bipyridine and pyrazine as ligands show additional stretching vi-
, Mꢀ 1 cmꢀ 1)] 419 (4.52 × 106), 515
bration due to the presence of C H group which lies at 3120 cmꢀ 1 and
–
Hβ). UV–vis (in CH2Cl2) [λmax, nm, (
ε
(2.05 × 105), 549 (8.51 × 104), 590 (5.88 × 104), 648 (4.78 × 104). MS
3060 cmꢀ 1. Similarly, the bands located in 1485–1480 cmꢀ 1 spectral
[ESI]: m/z calcd for C44H26Br4N4: 930.32, found: 930.38. FTIR cmꢀ 1
:
range can be attributed to C N vibrations (Fig. S9 and S10).
–
–
3317
ν
(NH porphyrin), 2926 and 2845
ν(CH porphyrin), 966 (δ
1H NMR data of free base porphyrin H2TBrPP, their corresponding
metallated, and axially ligated magnesium(II) porphyrin complexes in
CDCl3 at 298 K is listed in Table S1. The free base porphyrin reveals
characteristic resonances of β-pyrrole protons as singlet at 8.80 ppm; the
NH pyrrole protons are very shielded and are located at ꢀ 2.86 ppm as
low-intensity singlet, and the aromatic protons of the meso-phenyl rings
resonate in the 8.02–7.88 ppm region (Fig. S11). The insertion of mag-
nesium metal ion into porphyrin ring shows the absence of inner imino-
proton signal and results in the slight shift of resonances towards low
CCH
porphyrin), 731 ν(C–Br porphyrin). Anal. Calcd. for C44H26Br4N4: C,
56.8; H, 2.81; N, 6.02. Found: C, 56.5; H, 2.79; N, 6.08.
Meso-tetrakis(4-bromophenyl)porphyrinato magnesium(II) complex
[Mg(TBrPP)]: To a solution of free base porphyrin H2TBrPP (0.5 g,
0.537 mmol) in dichloromethane (80 mL), was added 2 mL of triethyl-
amine followed by 1.35 g (5.25 mmol) of MgBr2.OEt2. The reaction was
stirred at room temperature for 15 min. The evolution of this reaction
was followed by UV–visible spectroscopy, which highlights the gradual
disappearance of a Q band. Indeed, the presence of only three Q bands is
characteristic of a metallated porphyrin [31,35,52]. The solvent was
evaporated and a light-purple solid of the Mg(TBrPP) complex was ob-
1
field (at higher frequency) (Fig. S12). The H NMR spectra of axially
ligated [Mg(TBrPP)L] (L = 4,4′-bpy or pyz) are highly characteristic and
provide structural information of these compounds in solution. This
spectrum shows a slight difference in the proton resonance is observed
depending upon the nature of the axial ligand coordinated to the mag-
nesium atom. In the case of [Mg(TBrPP)(4,4′-bpy)] (1), Fig. S13 in-
dicates that the β-pyrrole protons resonate as a singlet at 8.79 ppm and
the meso-aryl ortho and meta protons resonate as doublet at 8.01 and
7.90 ppm, respectively, which are slightly deshielded compared to Mg
(TBrPP) as well as for H2TBrPP. The spectrum also reveals other char-
acteristic signals of axial 4,4′-bipyridine ligand. The aromatic protons
tained (90%). 1H NMR [CDCl3, 400 MHz]: δ(ppm) 7.94 (d, 8H, 3JHoHm
=
8.35 Hz, Hm–Hm’), 8.09 (d, 8H, 3JHoHm = 8.35 Hz, Ho–Ho’), 8.75 (s, 8H,
Hβ). UV–vis (in CH2Cl2) [λmax, nm, (
ε
, Mꢀ 1 cmꢀ 1)] 426 (4.32 × 106), 563
(1.69 × 105), 603 (1.12 × 105), 651 (4.60 × 104). Anal. Calcd. for
C
44H26Br4MgN4: C, 55.4; H, 2.7; N, 5.9. Found: C, 55.2; H, 2.7; N, 5.6.
MS [ESI+]: m/z calcd for C44H25Br4N4Mg: 951.8552, found: 951.8566.
FTIR cmꢀ 1: 2969 and 2818
ν(CH porphyrin), 991 ν(δCCH porphyrin), 720
ν
(C-Br porphyrin).
[MgII(TBrPP)(4,4′-bpy)](4,4′-bpy⋅H2O) (1): Mg(TBrPP) (20 mg,
(C H) of the 4,4 -bpy ring are shifted to the weak field at 8.54 and 8.36
′
–
0.020 mmol) was mixed with the bidentate ligand 4,4-bipyridine (90
mg, 0.57 mmol) in 5 mL of dichloromethane. The mixture was stirred at
room temperature for 3 h. Crystals were obtained by slow diffusion of n-
hexane through the dichloromethane solution. 1H NMR [CDCl3, 400
ppm. Chemical shift and peak integration of Ha and Hb protons of 4,4′-
bpy ligand indicates that Mg(TBrPP) complex and 4,4′-bpy ligand form a
polymer chain in CDCl3 solution, the repetitive unit being [Mg(TBrPP)
(4,4′-bpy)] which have been previously reported in the litterature [38].
3

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
Similarly, for compound 2 [Mg(TBrPP)(pyz)2], the β-pyrrole protons,
the meso-aryl ortho and the meta protons resonate at around 8.81, 8.11,
evidenced. In these reported structures, the zinc(II) is coordinated with
4 N of the porphyrin ring and the N atom of the 4,4′-bipyridine axial
ligand, forming a pyramid as a coordination polyhedra of zinc(II). To the
best of our knowledge, our study is the first attempt to determine the
crystal structure of a five-coordinate Mg(II) complex, (Mg-porphyrin)
(4,4′-bpy), (4,4′-bpy = 4,4′-bipyridine) and the crystal structure of a six-
coordinate complex, (Mg-porphyrin)(pyz), (pyz = pyrazine). The type of
solid state structure formed is directed by the nature of the ligand
(especially its electronic properties) and may be the solvent used. The
structure of complex 1 involving a 4,4′-bipyridyl ligand, Mg-porphyrin,
which is coordinated by one nitrogen atom (N57) of a pyridine cycle to
the magnesium atom forms a five-coordinate complex. On the other
hand, the pyrazine ligand which leads to the formation of a six-
coordinate complex through coordination of Mg-porphyrin, by one ni-
trogen atom (N3) of a first pyrazine heterocycle and the nitrogen atom
(N3i) of a second pyrazine. It has to be pointed out that the same trend
concerning the difference in coordination mode of 4,4′-bipyridine and
pyrazine ligand was already reported in the literature for meso-{tetrakis
[4-(benzoyloxy)phenyl]porphyrinato} zinc(II) complexes [58].
–
and 7.96 ppm, respectively (see Fig. S14). The aromatic protons (C H)
of the pyrazine ring are also shifted to the weak field at around 7.14
ppm. The same behaviour of polymerization in quite concentrated
CDCl3 solution (10-3 M used for NMR) is highligthed and the repetitive
unit being [Mg(TBrPP)(pyz)], observing chemical shift and peak inte-
gration of Hpyz. To conclude, in solution (concentration in CDCl3 around
10-3 M), the NMR characterization is in agreement with a polymeric
architecture of both complexes. Due to the high molecular weight of the
edifice and the low energy Mg-NL interaction (axial ligand, see Table 1),
mass spectrometry measurements (MALDI-ToF) only allowed us to evi-
dence the parent Mg(TBrPP) motif (see supplementary material in the
ESI, Figures. S1-S2 and Figures S3-S4, for compounds 1 and 2, respec-
tively). This observation is in good agreement with the quite low energy
Mg-NL bond and long Mg-NL distances; 2.143 Å and 2.350 Å for complex
1 and complex 2, respectively and compared to an average distance of
2.07 Å for the Mg-Nporph bond (see Table 1).
The ORTEP drawings of 1 and 2 are illustrated by Figs. 2 and 3. First,
it has to be pointed out that one molecule of the free ligand (in excess for
the synthesis) is present in both structures (Crystals were obtained from
the reaction media, before purification); it may has a role in the stabi-
lization of the structure via H bonds, that are depicted below and in the
supplementary material (see Fig. S16 and S18 in the ESI). The coordi-
nation geometry around the Mg(II) cation in 1 is pyramid with a square
base (Fig. 2), where the four donor N atoms of pyrrole rings of the TBrPP
porphyrin occupy the equatorial positions. The donor N atom of axial
4,4′-bpy ligand occupy the apical position.
3.2. Crystal structure description of compounds 1 and 2
Single crystal XRD analysis of complexes 1 and 2 was done and the
data are given in Table S2. Complexes 1 and 2 crystallize in the mono-
clinic crystal system in the same C2/c space group. Selected bond
lengths and angles for both complexes are listed in Table S3. For 1, the
asymmetric unit is made of one half of the [Mg(TBrPP)(4,4′-bpy)]
complex, one free 4,4′-bpy molecule and one water molecule. The
asymmetric unit of 2 contains half a molecule of the porphyrin, one
ligand pyrazine molecule coordinated to the magnesium(II) center and
one half free molecule of the same ligand. As shown in Table 1, mag-
nesium metalloporphyrins with monodentate axial ligands are present
in solid state as five-coordinate species type [Mg(Porph)(X)] (X =
neutral or anionic ligand) in most cases [30,31,35] and as six-coordinate
derivative type [Mg(Porph)(L)2] (L = neutral axial monodentate ligand)
in few cases i.e. [Mg(TPP)(py)2] [54] and [Mg(TPP)(4-pic)2] complexes
(TPP = 5,10,15,20-tetraphenylporphyrin, py = pyridine and 4-pic = 4-
picoline) [34].
For compound 2, the close interaction sphere of the Mg(II) cation is
described as a distorted octahedron, in which the equatorial positions
are occupied by four pyrrole nitrogen atoms and the other two come
from two N-donor atoms of the pyrazine ligand (Fig. 3).
Selected structural features for some magnesium porphyrin with
axial nitrogen ligand are listed in Table 1. The most important structural
feature in these complexes is that the axial Mg-Nax bond for the 4,4′-bpy
complex is shorter than those for pyrazine, being 2.143(5) and 2.350(4)
Å, respectively (Fig. 4). The axial Mg-Nax bond of [Mg(TPP)(4,4′-bpy)]
(1), is in good agreement with Mg—Nax bond length (2.143(5) Å)
observed in previously studied similar five-coordinate complexes
[31,35,37].
Previously, a linear one-dimensional (1D) polymeric chains of
magnesium tetra-porphyrins mediated by bipyridine and pyrazine li-
gands have been observed in the X-ray structure of the six-coordinate
complexes in which Mg-porphyrins units are aligned parallel [38,55].
In the case of tetrakis(ethyl-4(4-butyryl)oxypheny)porphyrine
(H2TEBOP) [56] and (4,4′-bipyridine)(5,10,15,20-tetratolylphenylpor-
phyrinato)zinc(II) [57], Zn(II) complexes with penta-coordination was
Several other examples were reported in the literature for long
Mg—Nax bonds in six-coordinate Mg–porphyrin systems. For example,
the Mg—Nax bond length in [Mg(TPP)(pip)2] is 2.419(4) Å [34]. For
[Mg(TPP)(4-pic)2], [Mg(TPP)(Py)2] and [Mg(OEP)(Py)2], the Mg—Nax
bonds are 2.386(4), 2.369(4) and 2.389(2) Å, respectively [33,34,54],
which are both very similar to that in [Mg(TBrPP)(pyz)2]. The average
Mg–Np bond length for complex 1 is 2.090(3) Å and the displacement of
the Mg(II) atom from the mean porphinato core is 0.478 Å. These
structural parameters are characteristic of five-coordinate magnesium
(II) porphyrins [31,35,59]. For complex 2, the Mg(II) ion is approx-
imatively in the plane of the porphyrin core, involving a Mg-Np bond
(2.070(3) Å) very close to the one in complex 1; these bonds are
consistent with those already reported and obtained for other Mg(II)-
porphyrins complexes (see Table 1).
Table 1
Selected bond lengths [Å] in several penta and hexa-coordinate magnesium
porphyrin complexes.a.
Compound
b
M__Np
M__NcL
Reference
[Mg(TBrPP)(4,4′-bpy)] (1)
2.090(3)
2.094(2)
2.1187(16)
2.1108(15)
2.0962(13)
2.108(5)
2.070(3)
2.065(2)
2.071(6)
2.071(3)
2.071(3)
2.063(2)
2.068(2)
2.074(3)
2.066(1)
2.143(5)
this work
[35]
[Mg(TPP)(HIm)]
2.120(3)
[Mg(TPP)(N3)]-
1.997(2)
[31]
[Mg(TPP)(NCO)]-
[Mg(TPP)(NCS)]-
2.0471(17)
2.0817(15)
2.055(3)
[31]
[31]
[Mg(TPP)(NCO)]-
[Mg(TBrPP)(pyz)2] (2)
[Mg(TPBP)(4,4′-bpy)2]
[Mg(TPP)(1-MeIm)2]
[Mg(TPP)(pip)2]
[37]
The 4,4′-bpy ligand in complex 1 is twisted with a dihedral angle of
ca. 39.90◦ between the two pyridyl cycles (Fig. 5), while the values of
this dihedral angle in several 4,4′-bpy complexes range between 24◦ and
46◦ [60–63]. The values of the dihedral angle between the projection of
the_p_ lane of the pyridyl group of the 4,4′-bpy axial ligand and the nearest
Mg Np vector is ca. 40.84◦. The two pyrazine planes for the complex 2
are nearly coplanar. The dihedral angle between the plane defined by
N1, Mg, and Npyz and the plane of the major pyrazine is 27.05◦ (Fig. 5).
The dihedral angle between the plane of the pyrazine ligand and the 24-
atom mean porphyrin plane is 86.05◦.
2.350(4)
this work
[55]
2.319(3)–2.290(3)
2.297(8)
[34]
2.419(4)
[34]
[Mg(TPP)(4-pic)2]
[Mg(TPP)(py)2]
2.386(2)
[34]
2.369(2)
[54]
[Mg(OEP)(py)2]
2.389(2)
[33]
[Mg(TPBP)(HTMA)2]
[Mg(TPBP)(BABCO)2]
2.438(3)
[36]
2.437(1)
[36]
a
Distances in [Å]; bAverage equatorial metal–nitrogen pyrrole distance; cDistance
between the metal and the nitrogen of the N-donor ligand.
Scheidt and Lee [64] have shown that the porphyrin macrocycle
4

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
Fig. 2. ORTEP diagrams of complex 1. Ellipsoids are drawn at the 40%.
Fig. 3. ORTEP diagrams of complex 2; ellipsoids are drawn at the 40%.
presents four major deformations: (i) the ruffling distortion (ruff) is
indicated by the values of the meso-carbon atoms above and below the
porphyrin mean plane; (ii) the doming distortion (dom) is often
observed in five-coordinate complexes when the axial ligand causes a
displacement of the metal center out of the mean plane, and the nitrogen
atoms are also displaced toward the axial ligand, (iii) the saddle
distortion (sad) involves the displacement of the pyrrole rings alter-
nately above and below the mean porphyrin macrocycle so that the
pyrrole nitrogen atoms are out of the mean plane, (iv) in the waving
beta-carbons from the least-squares plane of C20N4 pophyrinato core are
± 0.012 Å.
The stability and the cohesion of the free ligand of 4,4′-bpy and the
water molecule for the complex 1 are provided by intra-molecular
–
hydrogen bonds and by weak C H⋅⋅⋅Cg
π interactions (Fig. S15).
–
–
Starting with the hydrogen bonds, O H⋅⋅⋅N and C H⋅⋅⋅O type links
were evidenced; the oxygen atom of the water molecule acting as both
–
an O H donor (O1–H1A⋅⋅⋅N39 and O1–H1B⋅⋅⋅N32) and a O1 acceptor
(C7–H7⋅⋅⋅O1 and C55–H55⋅⋅⋅O1) (Table 2 and Fig. S16). The distances
between hydrogen and the acceptor atom X (X = O or N) are varying
between 1.94 and 2.55 Å. On the other hand, free 4,4′-bpy molecule and
porphyrin are linked one to the other by intra-molecular C8–H8⋅⋅⋅N32
hydrogen bond (H8⋅⋅⋅N32 distance range is 2.48 Å). The analysis of the
[Mg(TBrPP)(4,4′-bpy)] complex reveals that phenyl rings could form a
distortions (wav), the four fragments “(β-carbon)-(
α-carbon)- (meso-
carbon)-( -carbon)-(β-carbon)” are alter natively above and below the
α
24-atoms of the C20N4 least squares plane (PC plane). Additional
quantitative information of two structures are given in Fig. 5, which
displays the detailed displacements of each porphyrin core atom (in
units of 0.01 Å) from the 24-atom mean planes. The top panels show that
porphyrin core of [MgII(TBrPP)(4,4’-bpy)] (1) presents major doming
(dom) and comparably small saddle (sad) distortions. Formal diagram of
the porphyrinato core of [MgII(TBrPP)(pyz)2] (2) show a quasi-planar
conformation of porphyrin macrocycle, the displacement of meso and
–
π contact (Fig. S16). In this complex there are C H⋅⋅⋅Cg
weak C–Br⋯ Cg
π
interactions between hydrogen atoms and five-membered pyrrole
rings, but also between hydrogen atom and six-membered chelate ring.
We find three intermolecular interactions as an H acceptor; two
–
C
H⋅⋅⋅Cg π interactions involving carbon atoms (C30 and C38) from
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N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
4. Photophysical properties
4.1. Absorption spectroscopy
The UV–Vis absorption spectra of the free base porphyrin base
H2TBrPP, [Mg(TBrPP)] and complexes 1 and 2 recorded in dichloro-
methane are shown in Fig. 6. The λmax values of these species are listed in
Table S4 and compared to several other meso-porphyrins and magne-
sium metalloporphyrins. The electronic spectra of free base porphyrin
Table 2
Inter-and intra-molecular interactions for 1.
D–H⋅⋅⋅A
D–H
H⋅⋅⋅A
D⋅⋅⋅A
D–H⋅⋅⋅A
O1-H1A… N39 [i]
O1-H1B… N32
C7-H7… O1
0.97
1.94
2.13
2.55
2.48
2.50
2.890(5)
2.967(6)
3.266(6)
3.389(6)
3.195(6)
166
0.97
144
0.95
133
C8-H8… N32
0.95
159
C55-H55… O1[ii]
0.95
130
C–X⋅⋅⋅Cg (
π
)
X⋅⋅⋅Cg (
π
)
C⋅⋅⋅Cg (
π
)
)
C–X⋅⋅⋅Cg (
101.18
160.24
π)
Fig. 4. Coordination polyhedron of the Mg2+ species in complexes 1 (left) and
2. (right).
C20-Br2… Cg4[iii]
C20-Br2… Cg24[iv]
3.7937(16)3.4629(19)
4.569(5)
5.305(5)
–
–
H⋅⋅⋅Cg (
C
H⋅⋅⋅Cg (
π
)
H⋅⋅⋅Cg (
π
)
C⋅⋅⋅Cg (
π
C
π)
C2-H2… Cg3 [v]
2.90
3.708(5)
3.657(6)
3.549(6)
144
134
134
free 4,4′-bipyridine and the centroids of the pyrrole of the meso-
C30-H30… Cg2 [vi]
C38-H38… Cg1 [vi]
2.93
2.82
porphyrin where five-membered pyrrole rings are H acceptors, and one
C2–H2⋅⋅⋅Cg8
π interaction involving a carbon atom (C2) of pyrrole and
A = acceptor, D = donor, X = heteroatom, Cg = centroid.
the centroid of 4,4′- bipyridine coordinated of neighbouring molecule
where six-membered rings are H acceptors (C⋅⋅⋅Cg vary between 3.549
(6) and 3.708(5) Å).
Cg1: is the centroid of the N1/C1-C4 five-membered ring, Cg2: is the centroid of the
N2/C6-C9 five-membered ring. Cg3: N39/C38-C40 six-membered ring, Cg4: N57/
C56-C56 a six-membered ring. Cg24: N50/C51-C51 a six-membered ring.
Symmetry codes: (i):1-x,-y,-z, (ii): -x,y,-1/2-z; (iii): 1-x,-y,-z; (iv); 1 + x,y,z; (v): 1/
2 + x,1/2 + y,z; (vi): 1/2-x,1/2-y,-z.
Similarly, the molecular structure and crystal packing for complex 2
–
(Fig. S17) are stabilised by inter- and intramolecular C H⋅⋅⋅N hydrogen
–
bond, and by a weak C H⋅⋅⋅Cg
π interactions (Table 3 and Fig. S18).
Remarkably, the free pyrazine nitrogen N5 is linked by intermolecular
C16–H16⋅⋅⋅N5 hydrogen bond with the C16 carbon of the neighbouring
porphyrin, and this same free ligand is linked by weak C26–H26⋅⋅⋅Cg23
Table 3
Inter-and intra-molecular interactions for 2.
D–H A
D–H
H A
D A
D–H A
π
interaction involving a carbon atom (C26) from pyrazine coordinated
where six-membered ring for free pyrazine is H acceptors. Neighbouring
C16-H16… N5 [i]
0.93
2.61
3.460(7)
153
–
–
C
H Cg (
π
)
H Cg (
π
)
C Cg (
π
)
C
H Cg (
π
)
porphyrins are linked one to the other by weak C18–H18⋅⋅⋅Cg1
π
C18-H18… Cg1 [ii]
2.722.95
3.480(5)
140
interaction.
C26-H26… Cg23 [iii]
3.550(6)
123
A = acceptor, D = donor, X = heteroatom, Cg = centroid.
Cg1: is the centroid of the N1/C2-C5 five-membered ring, Cg23: is the centroid of the
N1/C27-C27 a six-membered ring. Symmetry codes: (i): x,1 + y,z; (ii):-x,1-y,1-z;
(iii): -x,1 + y,1/2-z.
Fig. 5. Diagram of the porphyrin cores of complexes (1) and (2) showing the mean plane displacements of the Mg(II) ion and the core atoms shown in Å units and the
dihedral angle between the two pyridyl moieties of the 4,4′-bpy molecules and the dihedral angle of the nearest Mg__Npyz vector.
6

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
Fig. 6. UV–vis absorption spectra of H2TBrPP, [Mg(TBrPP)], [Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)2] (2), in CH2Cl2 solution at concentrations around 10-6
mol.L-1
.
contain one intense band around 400 nm (the Soret or B-band) corre-
sponding to strongly allowed transitions to S2 state, followed by four
low intensity absorption bands at 515 nm, 549 nm, 590 nm, and 648 nm
attributed to Qy (1,0), Qy (0,0), Qx (1,0) and Qx (0,0), respectively (Q-
bands). When the metal ion was inserted into the porphyrin ring, the
number and intensity of the Q bands were found to decrease [31,35,52],
while the intense Soret band showed a red shift up to 7 nm (Fig. 6).
According to the literature, the five-coordinated magnesium(II)
tetraporphyrin-based complex exhibits an increased Soret intensity with
slightly red shifted (3–6 nm) Q-bands. For the hexa-coordinated Mg-
porphyrin analogue, both Soret and Q-bands are red shift (around 10
nm and 10 to 18 nm, respectively) [65]. Fig. 6 illustrates the UV–visible
optical absorption spectral changes observed during the complexation of
MgTBrPP with 4,4′-bipyridine or pyrazine ligand. This spectral change is
an indication of the formation of new species. Upon addition of the 4,4′-
bpy ligand, a marked color variation from purple to blue-green is
observed (at concentrations 1.22 10-6 mol.L-1). The Soret band (427 nm)
revealed a larger intensity much than obtained with the individual
spectrum of MgTBrPP, while the visible Q-bands (565 and 604 nm) were
red shifted by 2 nm leading to the formation of new complex 1:1 (4,4′-
bpy: complex 1) binding stoichiometry.
These spectral features are characteristic of a pentacoordinated
specie. The important characteristics were consistently observed upon
adding an amount of pyrazine to a solution of MgTBrPP. It can be
observed (i) a marked color variation from purple to blue-green (at
concentrations 1.24 10-6 mol.L-1), and (ii) the red shift of the Soret band
Fig. 7. Emission spectra of H2TBrPP (λexc = 420 nm) , Mg(TBrPP) (λexc = 427 nm), complexes 1 (λexc = 429 nm) and 2 (λexc = 434 nm) in a 10-6 mol.L-1
dichloromethane solution.
7

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
from 426 nm to 435 nm and the Q bands (563 and 603 nm to 578 and
618 nm) indicating transformation to an hexa-coordinated complex. It
can also be concluded that the neutral complexes spectra [Mg(TBrPP)
(L)] (L = 4,4′-bpy or pyrazine) exhibit larger red shifts of the Soret and Q
bands than those of the anionic complexes of the type [Mg(TPP)(X)], in
which X is a pseudo-halide (N–3, NCO–, NCS–, NCO–) [31,66] ligand
(Table S4).
atom such as bromine, reduces fluorescence quantum yield (see
Table S5).
5. Biological studies
5.1. Antioxidant activity of complexes 1 and 2 by DPPH radical
scavenging method
4.2. Spectrofluorometry
1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay is a simple,
rapid and suitable method extensively used to assess the antioxidant
properties of compounds. The quite stable DPPH nitrogen centered
radical posseses a characteristic absorption which decreases when
exposed to antioxidants [72]. It reacts with hydrogen donating functions
resulting in a colour change from purple to yellow. The intensity of this
phenomena is related to the number of captured electrons [73], i.e., the
greater the free radical scavenging capacity of an antioxidant com-
pounds, the more reduction of DPPH and the less purple colour of the
sample.
Excited-state processes in porphyrins are extremely important for
their application in molecular devices. Thus, the fluorescence emission
data [67–69] of the porphyrins provide significant information on the
singlet excited state properties. The emission spectra of the free base
porphyrin, metallo-porphyrin and complexes 1 and 2 are reported in
Fig. 7. The values of fluorescence quantum yields (Φ ) of these synthe-
sized complexes were measured in dichloromethanef, using MgTPP as
reference (Φ = 0.15) [31,70] and are summarized in Table S5.
f
As previously reported, upon excitation at 420 nm the free base
porphyrin H2TBrPP exhibit two emission bands at 654 and 720 nm [35]
corresponding to Q (0,0) and Q (0,1) transitions, respectively, the in-
tensity of the Q (0,0) being higher than the Q (0,1) transition (Fig. S19
a). The spectra is typical of many free-base porphyrins [36,68,69]. The
major emission peaks for [Mg(TBrPP)] appear at 612 and 660 nm for Q
(0,0) and Q (0.1) bands, respectively, upon excitation at 427 nm
(Fig. S19b). As shown in Table S4 and Fig. 7, the main impact of the
magnesium insertion resides in the large blue shift (~42 nm) for the
strongest emission band Q (0,0) and ~ 60 nm for the second band Q
(0,1). The axially ligated metallo-porphyrins (complexes 1 and 2) results
in two emission bands (from S2 excited state to fundamental state S0)
centered at 613 nm (S2 [Q (0,0)] to S0) and 660 nm (S2 [Q (0,1)] to S0)
for complex 1 when excited at 429 nm, and at 612 nm (S2 [Q (0,0)] to
S0) and 663 nm (S2 [Q (0,1)] to S0) for complex 2 when excited at 434
nm (Figs. S19c and d).
In the present study, the scavenging activity of the free base
porphyrin base H2TBrPP, Mg(TBrPP), [Mg(TBrPP)(4,4′-bpy)] (1), and
[Mg(TBrPP)(pyz)2] (2) against DPPH were evaluated at different con-
centrations (in a range comparable to usual literature assays) from 25 to
100 µg/mL (i.e. from approximatively 10-5 to 10-4 M). The antioxidant
activity efficiency is quantified and reported Fig. 8.
As expected, free radical scavenging activity of these complexes was
concentration dependent. Free radical scavenging rate increases with
increasing concentration of the inclusion compound solution. The
highest antioxidant activity was obtained for Mg-porphyrin compounds
with respect to H2TBrPP free base porphyrin. Axial ligand presence af-
fects also antioxidant activity. As shown Fig. 8, the amount of DPPH
radical of the complex 1 at the concentration of 25 and 50 µg/mL was
found to be 13% and 24%, respectively, which was slightly weaker than
for complex 2 (20% and 25%) at the same concentrations. However, at
100 µg/mL, the DPPH scavenging activity of [Mg(TBrPP)(4,4′-bpy)] (1)
reached 60%, which was significantly higher than that of [Mg(TBrPP)
(pyz)2] (2) (40%) at the same concentration. These results confirm
previous reports from Ferruzzi et al. [74] and Endo et al. [75] who
determined in vitro the antioxidant activity of natural chlorophyll de-
rivatives. They evidenced that the magnesium might alter the electron-
donating ability from the conjugated porphyrin system, which
strengthen the apparent antioxidant activity of chlorophylls. By com-
parison with already well-known antioxidants, our new complexes
remained a little bit less active in the same range of concentration. As far
as radical scavenging activity is concerned and at a concentration of 100
These bands exhibit similar behaviour to [Mg(TBrPP)] (Fig. S19) and
to those already reported in the literature for [MgII(TPP)(THF)2] [71]
and [MgII(TPP)(NCO)]- [37] for example. In the 350–700 nm spectral
range, the excitation spectra are similar to the absorption spectra,
indicating that it corresponds to similar electron transition process
(Fig. S19). The fluorescence quantum yields (Φ ) of H2TBrPP,
f
[MgII(TBrPP)] and for the obtained complexes are in the range
0.050–0.065; these values do not depend on the nature of the axial
ligand, but they depend more largely on the nature of the phenyl sub-
stitution in the meso position, that is to say, compounds including heavy
Fig. 8. Emission DPPH radical scavenging activity of H2TBrPP, Mg(TBrPP), complexes 1 and 2.
8

N. Amiri et al.
Inorganica Chimica Acta 525 (2021) 120466
µg/mL, Vitamin C (Vit C) and Butylated Hydroxy-Toluene (BHT) for
example reach approximatively 80 and 70%, respectively [76,77]. As
already inspected and mentioned in the literature [78], the radical
scavenging activity (and related prevention of oxidative damage) is
correlated to the standard reduction potential (E◦) of the species; this
one can be finely tuned with the nature of the surrounding ligands (E◦’)
in order to adapt the best to the E◦ values of ROS of interest. We assume
this study is original illustration of this point.
A. fumigatus. Moreover, our complexes are slightly more active than Mn
(III) and Co(II)-based porphyrins derivatives reported by Karimipour
et al. (A. fumigatus between 9 mm and 11 mm) [82] but remain in the
same principles explaining the activity increase for the metal complexes
[83–85]. According to the Overtone’s concept for cell permeability
[83,84] and due to the liphophilicity as an important factor in controling
the antifungal activity, the lipid membrane surrounding the cell, favours
the passage of only the lipid-soluble materials. Tweedy’s chelation
theory [85] shows that the polarity of the metal ion will be reduced to a
greater extent due to overlap of the porphyrin orbital and partial sharing
of the positive charge of the metal ion with donor group. However, in
Mg-porphyrin compounds, Mg(II) is almost completely neutralized by
the porphyrin. Therefore, the polarity is minimized and the lipo-
solubility of Mg-porphyrin compounds are significantly increased. This
increase in lipophilicity enhances the penetration of the complexes into
lipid membranes and disturb the respiration process of the cell. In this
study, Mg-porphyrin compounds were more reactive than the non-
metallateded H2TBrPP porphyrin ligand.
5.2. Antifungal activity
The antifungal activities of the free base porphyrin H2TBrPP, Mg
(TBrPP), [Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)2] (2) were
quantitatively assessed by the presence, or absence of inhibition zones
against three yeasts strains (C. krusei ATCC6258, C. albicans ATCC90028
and C. neoformans ATCC14116) and two fungal strains (A. brasiliensis
ATCC16404 and A. fumigatus ATCC204305). The diameters of inhibition
zones observed with the well diffusion method are shown in Fig. 9.
Porphyrin derivatives have been reported to possess significant
antifungal activity [79,80]. We synthesized analogues in an attempt to
find newer and better antifungal agents. In the present research work,
several compounds were evaluated for antifungal activity. The results
reveal that the yeasts strain C. albicans was the most sensitive and the
strain C. neoformans was the most resistant. In fact, no zone of inhibition
was observed for our compounds on this yeast strain (Fig. 9). Based on
zones of inhibition results, the lowest activity is observed for the free
base porphyrin H2TBrPP. Contrariwise, the Mg(TBrPP), starting mate-
rial and complexes 1 and 2 displayed nearly the same zones of in-
hibitions against all strains (yeasts and fungal). These magnesium
derivatives showed a zone inhibition diameter between 13 and 16 mm
and of 11 to 12 mm against C. albicans and C. krusei, respectively. They
also inhibited A. brasiliensis (12–13 mm) and A. fumigatus (13–15 mm).
These complexes exhibit less antifungal activity than the standard drug
Nystatin [81], who owns 29 and 19 mm in diameter of zone inhibition
against C. albicans and A. fumigatus, respectively. The literature survey
revealed that antifungal activity of these magnesium complexes was
comparable and in some cases even superior, to previously synthesized
and studied metalloporphyrins. For example, Singh et al. [81], synthe-
sized tetra-porphyrins derivatives [M: 2H, Cu(II), Co(II), Ni(II)] and
investigated their antifungal properties. According to the results these
complexes produced diameters of zones of inhibition between 15 mm
and 22 mm against C. albicans and between 10 mm and 19 mm against
6. Conclusion
In the present work, two new magnesium(II) porphyrin complexes,
[Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)2] (2) have been pre-
pared and characterized in solution and at the solid state (X-ray
diffraction structures). The UV–visible spectrum of these latter exhibits
red-shifted Soret band compared to the [Mg(TBrPP)]. The fluorescence
data are very similar to those of already reported magnesium porphyrin
complexes. The single crystal molecular structures show clearly that: (i)
the five-coordinate species 1 involving one molecule of the complex [Mg
(TBrPP)(4,4′-bpy)], two free 4,4′-bipyridine ligand and two water
–
–
–
molecule linked together by O H⋅⋅⋅N, C H⋅⋅⋅O and C H⋅⋅⋅N hydrogen
–
bonds and C H⋅⋅⋅
π interactions., (ii) the six-coordinate species 2
comprised by one molecule of the complex [Mg(TBrPP)(pyz)2] (2) and
one free pyrazine ligand which are linked together by hydrogen bonds of
–
C
–
H⋅⋅⋅N type and C H⋅⋅⋅π interactions. For quite concentrated solution
(NMR), compounds 1 and 2 seem to lead to low energy bonds-based
polymeric species The biological studies reveal that the magnesium
complexes may be a good candidate as antioxidant and antifungal agent,
especially the [Mg(TBrPP)(4,4′-bpy)] complex (1, involving the most
stable Mg-NL axial bond), which is the most active one. Indeed, these
complexes present a high antioxidant activity according to the DPPH
assay. The biological activities obtained from present work could be
Fig. 9. In vitro antifungal activity of H2TBrPP, Mg(TBrPP), [Mg(TBrPP)(4,4′-bpy)] (1) and [Mg(TBrPP)(pyz)2] (2) at concentrations around 10-3 mol.L-1.
9

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Inorganica Chimica Acta 525 (2021) 120466
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agents.
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CRediT authorship contribution statement
Nesrine Amiri: Writing - original draft. Fadia ben Taheur: Data
curation. Sylviane Chevreux: Data curation, Writing - review & editing.
Carine Machado Rodrigues: Methodology. Vincent Dorcet: Method-
ology. Gilles Lemercier: Formal analysis, Writing - review & editing.
Habib Nasri: Supervision.
`
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Declaration of Competing Interest
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The authors declare that they have no known competing financial
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N.A. thanks The Tunisian Ministry of Higher Education and Scientific
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Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120466.
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