Chirality Transfer from Chiral Monoamines to an m-Phthalic Diamide-Linked Zinc Bisporphyrinate with a Benzylamide Substituent

Article abstract of DOI:10.1021/acs.inorgchem.7b00815

An m-phthalic diamide-linked bisporphyrin with a benzylamide substituent has been designed and synthesized. It has two types of carbonyl groups. In the solution of this zinc bisporphyrinate, these carbonyl groups are involved in the formation of two diffe

Full text of DOI:10.1021/acs.inorgchem.7b00815

Article
pubs.acs.org/IC
Chirality Transfer from Chiral Monoamines to an m‑Phthalic Diamide-
Linked Zinc Bisporphyrinate with a Benzylamide Substituent
Qingyun Hu,† Congcong Zhuo,† Yong Wang,*,† Chuanjiang Hu,*,†,‡ and Jianping Lang*,†
†State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical
Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, P. R. China
‡Applied Technology College of Soochow University, Suzhou 215325, Jiangsu P.R. China
S
* Supporting Information
ABSTRACT: An m-phthalic diamide-linked bisporphyrin with a
benzylamide substituent has been designed and synthesized. It has two
types of carbonyl groups. In the solution of this zinc bisporphyrinate,
these carbonyl groups are involved in the formation of two different Zn−
O coordination interactions: one is formed between neighboring zinc
bisporphyrinates; another is formed within zinc bisporphyrinate. The
chirality sensing abilities of this zinc porphyrinate to a number of chiral
monoamines have been examined. When zinc bisporphyrinate was mixed
with a series of chiral monoamines, the signs of the circular dichroism
spectra for the chiral monoamines of the same handedness with an aryl
group as the substituent are just opposite to those with an alkyl group as
the substituent. NMR studies reveal that stepwise coordinations lead to
1:1 and 1:2 host−guest complexes. The structure of the 1:1 host−guest
complex was confirmed by crystallography, it is the first time that a 1:1
host−guest complex formed between zinc bisporphyrinate and a chiral monoamine has been crystallographically characterized.
The structure reveals that there is an intramolecular hydrogen bond between the amide oxygen and the coordinated NH2. We
further investigated the chirality transfer mechanism by density functional theory calculations. Our studies suggest that the
interactions between the linker and guests in this bisporphyrin system are crucial in the chirality transfer process, and the nature
of the bulkiest substituent of chiral monoamines makes a difference. For R-type guests, with an alkyl group, the steric repulsion
makes the conformer A more energetically favorable, which leads to the anticlockwise twist and negative Cotton effect. However,
with an aryl group, the π−π interaction makes the conformer B more energetically favorable, which leads to the clockwise twist
and positive Cotton effect.
satisfy this requirement in bisporphyrin systems. However, for
monoamines, it is usually more difficult because the amine
group can only provide one binding site. So, (an)other
interaction(s) is (are) required. For example, in the ethane-
bridged bisporphyrin system developed by Borovkov and co-
workers, besides the coordination interaction, the short linkage
causes steric interactions between the ethyl groups of the
porphyrin and the substituents of the ligand, which result in the
induced supramolecular chirality.6,10,11 For the biphenol-
bridged metal-free bisporphyrin system developed by Borhan
and co-workers, there are both hydrogen-bonding and steric
interactions between the monoamines and host molecule,
which leads to stereodifferentiation.12
INTRODUCTION
■
Porphyrins have been widely used in chirality recognition,
induction, and transfer in recent years.1−5 Because porphyrins
have distinct spectroscopic properties, such as a red-shifted and
intense UV−vis absorption, circular dichroism (CD) spectros-
copy provides a convenient method for studying porphyrin
systems. Bisporphyrins have an advantage in these studies
especially for chiral guests without chromophores, such as
diamines, diols, and amino alcohols, because they can provide
two strong chromophores. However, for monodentate guests,
such as monoamines, studies are usually more difficult because
there is only one coordination site. Only a limited number of
porphyrin systems have been reported for chiral mono-
amines.6−12 Some studies reported that these chiral guests
need to be converted to their chemical derivatives before
measurement.7−9 However, a few systems can have chirality-
sensing ability for monoamines without chemical deriva-
tions.6,10−12
It is still a great challenge to design bisporphyrin systems
suitable for chiral monoamines that can lead to two-point or
multipoint interactions between the hosts and guests. If the
linker in the bisporphyrin is close to the coordination site, there
will also be interactions between the linker and guest when the
In order to have effective chirality sensing, host−guest
interactions generally require at least two-point fixation.
Diamines or diols could provide two coordination sites to
Received: March 30, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Synthetic Route for Compound III and Its Zinc Complex
guest is coordinated to the metalloporphyrin. That could
provide two-point or multipoint interactions. Then the chirality
could be transferred from the guest to the corresponding host−
guest complexes.
EXPERIMENTAL SECTION
■
Material and Physical Methods. All reagents were obtained from
commercial sources without further purification unless otherwise
noted. Triethylamine (Et3N) was distilled over potassium hydroxide,
and methylene chloride was treated with CaH2 before use. Zinc 5-(2-
aminophenyl)-10,15,20-triphenylporphyrinate was synthesized accord-
ing to reported methods.14 Elemental analyses (carbon, hydrogen, and
nitrogen) were performed with an Elementar Vario EL III analytical
instrument. 1H NMR spectra were recorded at room temperature,
using an Agilent 400 MHz spectrometer in CDCl3 with
tetramethylsilane (TMS) as the internal standard; chemical shifts are
expressed in ppm relative to TMS (0 ppm). Two-dimensional NMR
spectra were recorded on a Bruker AVANCE 600 MHz NMR
instrument. UV−vis spectra were recorded with a Shimadzu UV-3150
spectrometer. CD spectra were recorded on a PMT model J-815
spectropolarimeter at 298 K. Scanning conditions were as follows: date
pitch = 0.2 nm; bandwidth = 2 nm; response time = 1 s; scanning
speed = 50 nm/min.
We have been working on this in recent years and have
recently developed several amide-linked zinc bisporphyrins and
trisporphyrinate.13−17 These have all shown chirality transfer
ability from chiral monoamines to their host−guest complexes.
In the case of zinc trisporphyrinate, we obtained the crystal
structure of its 1:3 host−guest complex, and the crystal
structure reveals that the porphyrin subunits adopt a trans
configuration. However, it is difficult to explain the
corresponding chirality transfer mechanism for such a multi-
chromophore system in low symmetry. On the other hand, for
the zinc bisporphyrinate system having only two porphyrin
subunits, the corresponding chirality transfer mechanism could
be relatively easy to investigate. However, our previous studies
did not get any crystal structures of their host−guest complexes
for the bisporphyrin system, so we did not obtain an accurate
host−guest binding mode. Herein, in order to obtain more
insight on the chirality transfer mechanism for these systems,
we have designed and synthesized the bisporphyrin III, as
shown in Scheme 1. The bisporphyrin III is derived from m-
phthalic diamide-linked bisporphyrin, and it has both features
of previously studied amide-linked bisporphyrin and trispor-
phyrin: two porphyrin subunits and three amide groups. These
amide groups can be classified as types A and B, which could
have different roles in the chirality transfer process. We have
studied their chiral-sensing abilities to five chiral monoamines
(3-methyl-2-butylamine, the guest 1; 3,3-dimethyl-2-butyl-
amine, the guest 2; 1-cyclohexylethylamine, the guest 3; 1-
phenylethylamine, the guest 4; 1-(2-naphthyl)ethylamine, the
guest 5). We obtained the crystal structure of the host−guest
crystal structure of [Zn2-III]·1R. Further investigation on the
chirality transfer mechanism was made by UV−vis and NMR
spectroscopy and density functional theory (DFT) calculations.
CD and UV−Vis Measurements. UV−vis titration experiments
were carried out as follows. Measurements were performed by adding
different aliquots of the optically active monoamine solution to the
host solution in methylene chloride at room temperature. Then UV−
vis spectra were recorded after each addition.
For CD measurements, the background spectrum was taken from
380 to 460 nm with a scan rate of 100 nm/min at 25 °C. A zinc
bisporphyrinate solution was injected into a 1.0 cm quartz cuvette.
Then guests were added to the above solution to form the
corresponding complexes. CD spectra were measured after several
minutes. The resultant CD spectra recorded in millidegrees were
normalized on the basis of the concentrations of zinc bisporphyrinates.
A solid CD spectrum was measured with the following method: KBr
pellets were prepared by grinding a single crystal sample with solid
KBr and applying great pressure to the dry mixture. The thickness of
the KBr pellet was about 0.3 mm. The CD spectrum was then
recorded.
1
1H NMR Titrations. For H NMR titration experiments, portions
of a solution of chiral monoamine in CDCl3 were added to the
solution of [Zn2-III] in CDCl3 in a 5-mm-o.d. NMR tube, and NMR
spectra were recorded after each addition.
Preparation of the Free Base Bisporphyrin I. A solution of 5-
nitroisophthalic acid (0.069 g, 0.36 mmol) in thionyl chloride (8 mL)
B
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
was refluxed under nitrogen for 4 h, followed by the removal of excess
reagent under reduced pressure. The residual white solid was
redissolved in CH2Cl2 (30 mL), and Et3N (150 μL, 1.1 mmol) was
added to the solution described above and stirred for 10 min in an ice
bath. Zinc 5-(2-aminophenyl)-10,15,20-triphenylporphyrinate (0.50 g,
0.78 mmol) was added to the solution under a nitrogen atmosphere
overnight in an ice bath. Then it was washed with water, and the
organic layer was collected and evaporated to dryness under vacuum.
A purple solid was obtained and purified by silica gel chromatography
Preparation of [Zn2-III]. The free base bisporphyrin III (0.50 g,
0.33 mmol) was dissolved in a mixture of CHCl3 (150 mL) and
CH3OH (50 mL). Zn(CH3COO)2 (0.24 g 1.32 mmol) was added to
the solution described above and refluxed for 2 h. Then it was
extracted with water, and the organic layer was collected and
evaporated to dryness under vacuum. The purple solid was obtained
and purified by silica gel chromatography (99:1 CH2Cl2/methanol;
0.51 g, 94% yield). 1H NMR (400 MHz, CDCl3): δ 8.85 (s, 8H), 8.61
(d, J = 4.3 Hz, 4H), 8.37 (d, J = 4.3 Hz, 4H), 8.19 (s, 6H), 8.04 (d, J =
6.9 Hz, 2H), 7.91 (d, J = 7.3 Hz, 2H), 7.85−7.72 (m, 8H), 7.66 (d, J =
16.4 Hz, 10H), 7.49 (t, J = 7.5 Hz, 8H), 7.09 (s, 3H), 6.82 (s, 2H),
6.56 (t, J = 7.4 Hz, 2H), 5.79 (s, 1H), 5.06 (s, 2H), 4.18 (d, J = 7.5 Hz,
2H), 3.78 (s, 1H). 13C NMR (151 MHz, DMSO): δ 161.38, 150.18,
149.91, 149.13, 146.06, 146.04, 145.42, 142.92, 137.62, 135.43, 134.42,
134.01, 133.46, 132.58, 132.01, 131.89, 130.83, 130.48, 130.04, 128.94,
127.45, 127.17, 126.34, 126.22, 123.91, 123.49, 121.48, 120.90, 120.24,
119.26, 118.11, 112.14, 96.90, 93.15, 77.19, 76.98, 76.77, 31.57, 29.67,
14.10, 1.01. UV−vis [CH2Cl2; λmax, nm (log ε, cm−1 M−1)]: 422
(5.60), 556 (4.21), 597 (3.04). Anal. Calcd for C103H65N10O3Zn2: C,
76.30; H, 4.04; N, 8.64. Found: C, 76.35; H, 3.99; N, 8.69.
Preparation of Crystals of [Zn2-III]·1R. [Zn2-III] (50 mg, 0.030
mmol) was dissolved in CH2Cl2 (1 mL), 200 μL of a 0.2 M solution of
(R)-2-amino-3-methylbutane in anhydrous CH2Cl2 was added to the
solution described above, and the mixture was stirred for ∼3 min.
Then it was transferred to 8 mm × 250 mm glass tubes. n-Hexane was
added as a nonsolvent at room temperature. After 3 months, purple
crystals were obtained, which were then isolated by filtration, washed
with n-hexane, and dried under vacuum. (11 mg, 21% yield). Anal.
Calcd for C108H78N11O3Zn2: C, 75.92; H, 4.60; N, 9.02; Found: C,
75.82; H, 4.65; N, 9.05.
X-ray Structure Determination. The measurements of single
crystals were performed on a Bruker APEX-II CCD X-ray
diffractometer by using graphite-monochromated Mo Kα (λ =
0.71073 nm). The structure was determined by direct methods and
refined on F2 using the full-matrix least-squares method with
SHELXTL, version 2014.18 All non-hydrogen atoms were refined
anisotropically; all hydrogen atoms were theoretically added and rode
on their parent atoms. In the structure, the asymmetric unit contains
badly disordered solvent molecules. SQUEEZE19 was used to model all
disordered solvates. The electron count within the interporphyrin
voids was 825e for [Zn2-III]·1R (corresponding roughly to five
molecules of methylene chloride per [Zn2-III]). Details of the crystal
parameters, data collection, and refinements are summarized in Table
1. Complete crystallographic details, atomic coordinates, anisotropic
thermal parameters, and fixed hydrogen-atom coordinates are given in
the CIF file (CCDC 1531702).
1
(pure CH2Cl2; 0.27 g, 52% yield). H NMR (400 MHz, CDCl3): δ
8.82 (d, J = 8.9 Hz, 8H), 8.71 (d, J = 4.4 Hz, 4H), 8.53 (d, J = 4.5 Hz,
4H), 8.18 (d, J = 7.4 Hz, 6H), 8.10 (dd, J = 16.4, 7.0 Hz, 8H), 7.96 (d,
J = 7.4 Hz, 2H), 7.83−7.76 (m, 6H), 7.71 (dd, J = 12.7, 6.9 Hz, 10H),
7.61 (t, J = 6.9 Hz, 4H), 7.49 (t, J = 7.5 Hz, 2H), 7.30 (s, 2H), 6.62 (s,
2H), 6.58 (s, 1H), −2.91 (s, 4H). 13C NMR (151 MHz, DMSO): δ
163.71, 145.79, 141.55, 138.32, 136.42, 136.32, 136.28, 134.66, 134.50,
134.37, 132.18, 131.64, 129.37, 128.46, 128.33, 127.39, 127.28, 127.21,
126.43, 125.43, 123.28, 120.64, 120.13, 116.10, 40.39, 40.25, 40.11,
39.97, 39.84, 39.70, 39.56, 31.36, 22.47, 14.37. UV−vis [CH2Cl2; λmax
,
nm (log ε, cm−1 M−1)]: 418 (5.86), 517 (4.59), 553 (4.07), 594
(4.16). Anal. Calcd for C96H63N10O4: C, 81.17; H, 4.47; N, 9.86.
Found: C, 81.20; H, 4.50; N, 9.88.
Preparation of the Free Base Bisporphyrin II. The free base
bisporphyrin I (0.50 g, 0.35 mmol) was dissolved in 20 mL of
concentrated HCl, and 2.3 g of SnCl2·2H2O was added. The bright-
green solution was stirred at room temperature for 45 min and then
heated at 65 °C for 30 min. After the solution was cooled in an ice
bath, concentrated ammonia was added to bring the suspension to pH
10. The brown-violet mixture was stirred for 1 h with 50 mL of
CHC13. The organic layer was separated, washed twice with water, and
dried over Na2SO4. After filtration, the solvent was removed on a
rotary evaporator. The purple solid was obtained and purified by
1
column chromatography (silica, pure CH2Cl2; 0.39 g, 80% yield). H
NMR (400 MHz, DMSO): δ 8.92 (s, 2H), 8.74 (t, J = 22.5 Hz, 8H),
8.62 (s, 8H), 8.19 (s, 2H), 8.13 (s, 6H), 8.04 (t, J = 9.9 Hz, 4H), 7.98
(d, J = 6.9 Hz, 2H), 7.82 (d, J = 6.2 Hz, 6H), 7.77 (s, 8H), 7.66 (s,
6H), 7.61−7.55 (m, 2H), 7.52 (d, J = 7.7 Hz, 2H), 5.66 (s, 1H), 5.54
(s, 2H), 3.90 (s, 2H), −3.02 (s, 4H). 13C NMR (151 MHz, DMSO): δ
166.04, 147.23, 141.63, 141.58, 138.77, 136.27, 135.77, 135.36, 134.56,
131.56, 129.18, 128.50, 128.37, 127.43, 127.33, 126.00, 124.63, 120.62,
120.10, 116.27, 114.39, 113.06, 40.37, 40.23, 40.09, 39.96, 39.82,
39.68, 39.54. UV−vis [CH2Cl2; λmax, nm (log ε, cm−1 M−1)]: 417
(5.77), 517 (4.05), 551 (3.82), 529 (3.96). Anal. Calcd for
C96H65N10O2: C, 82.92; H, 4.71; N, 10.07. Found: C, 82.95; H,
4.74; N, 10.09.
Preparation of the Free Base Bisporphyrin III. The reaction
was performed under anaerobic conditions. The free base bisporphyrin
II (0.50 g, 0.36 mmol) was dissolved in anhydrous methylene chloride
(50 mL). Et3N (150 μL, 1.07 mmol) was added to the solution
described above, the mixture was stirred for 15 min in an ice bath, and
then benzoyl chloride (46 μL, 0.40 mmol) was added. The mixture
was slowly warmed to room temperature, and the reaction was
monitored by thin-layer chromatography (TLC). After 8 h, the
reaction was complete. The solution was rotor-evaporated to dryness
under vacuum. The purple solid was obtained and purified by column
Computational Methods. All calculations are on the basis of the
crystal structural data. To simplify the calculations, we only consider a
single bisporphyrin molecule, and we did not calculate the aggregated
species. We first performed DFT calculations on the free host [Zn2-
III]. Then we did calculations on the corresponding 1:1 ([Zn2-III]·1R
and [Zn2-III]·4R) and 1:2 ([Zn2-III]·(1R)2 and [Zn2-III]·(4R)2)
complexes. Full optimizations on these structures were performed by
DFT at the level of B3LYP/6-31G* using the Gaussian09 suite of
programs.20 We employed DFT with no symmetry constraints to
investigate the optimized geometries.
1
chromatography (silica, pure CH2Cl2; 0.26 g, 48% yield). H NMR
(400 MHz, CDCl3): δ 8.88−8.79 (m, 4H), 8.76 (d, J = 4.0 Hz, 4H),
8.69 (d, J = 4.0 Hz, 4H), 8.55 (d, J = 3.7 Hz, 4H), 8.25−8.15 (m, 6H),
8.11 (s, 4H), 7.99 (d, J = 6.7 Hz, 4H), 7.88 (d, J = 7.4 Hz, 2H), 7.83−
7.73 (m, 6H), 7.69 (s, 10H), 7.54 (s, 4H), 7.44 (t, J = 7.4 Hz, 2H),
7.39 (s, 2H), 7.06 (t, J = 7.3 Hz, 1H), 6.54 (t, J = 7.5 Hz, 2H), 6.24 (s,
1H), 6.16 (s, 2H), 5.78 (s, 1H), 5.67 (d, J = 7.6 Hz, 2H), −2.86 (s,
4H). 13C NMR (151 MHz, DMSO): δ 163.54, 163.34, 142.13, 141.75,
138.03, 137.43, 135.09, 135.03, 134.72, 134.59, 134.51, 132.63, 131.95,
130.97, 129.38, 127.89, 127.72, 127.70, 126.83, 126.76, 126.60, 125.71,
123.07, 120.97, 120.93, 120.69, 120.57, 119.45, 112.64, 77.28, 77.07,
76.86. UV−vis [CH2Cl2; λmax, nm (log ε, cm−1 M−1)]: 417 (5.53), 515
(4.10), 552 (3.16), 590 (2.54). Anal. Calcd for C103H69N10O3: C,
82.77; H, 4.65; N, 9.37. Found: C, 82.81; H, 4.68; N, 9.32.
RESULTS AND DISCUSSION
■
CD Spectral Studies. In this study, five types of chiral
monoamines were used as guests, and they have different
substituents X. Each host and each enantiopure amine were
mixed in methylene chloride, and the corresponding CD
spectra were recorded. Because the formation constants for
binding monoamines to zinc porphyrinates are in general
around 103 L/mol21 and the concentrations of porphyrin used
in our CD measurements are around 10−6 mol/L, a large excess
of guests are required to completely convert the host to the
corresponding host−guest complex. In our experiments, more
C
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
comparison, the free base bisporphyrin III was also measured
by UV−vis spectroscopy. The spectrum is provided in Figure
S11, which does not show such a shoulder. This suggests that
zinc is involved in the formation of such a shoulder. Generally,
the coordination of zinc porphyrin to oxygen or nitrogen leads
to bathochromic shifts compared to four-coordinate zinc
porphyrins.22 In our case, such a shoulder at longer wavelength
could be caused by the Zn−O coordination interactions.
As shown in Figure 2, when the concentration of [Zn2-III]
increased, the intensity of the shoulder increased, and the
intensity of the peak at 421 nm deceased. Such a concentration-
dependent spectral change suggests that the Zn−O bond is
formed between neighboring zinc bisporphyrinates, and
aggregation through the coordination interactions occurs in
solution. Such a coordination mode was actually found in our
previous studies.14,16 So, the following equilibrium (1) exists in
solution. [Zn2-III]n is the aggregated species, and [Zn2-III] is
the single zinc bisporphyrinate molecule.
Table 1. Crystal Data and Structural Refinement Data of
[Zn2-III]·1R
crystal
[Zn2-III]·1R
C108 H78 N12 O3 Zn2
1722.56
0.71073
223(2)
chemical formula
fw
wavelength (Å)
temperature (K)
cryst syst
space group
a (Å)
monoclinic
C2
36.298(3)
15.1343(11)
26.262(2)
90
b (Å)
c (Å)
α (deg)
β (deg)
133.414(4)
90
γ (deg)
V (Å3)
10479.7(15)
4
Z
density (Mg/m3)
1.092
abs coeff (mm−1
)
0.509
[Zn2‐III]n ⇌ n[Zn2‐III]
(1)
F(000)
3576.0
UV−vis spectroscopic titrations also have been performed
between [Zn2-III] and five chiral monoamines. A representative
example of the spectral change of [Zn2-III] induced by the
addition of 1R is shown in Figure 3. (Others are provided in
Figures S12−S15.) Before the addition, the spectrum of [Zn2-
III] shows one strong Soret band at 421 nm and one shoulder
at 431 nm. During the titration, the electronic spectra showed
that the intensity of the band at 421 nm decreased and the
intensity at 431 nm increased with increasing the ligand
concentrations.
data collection θ range (deg) 2.41−27.51
index ranges
reflns collected
Rint
−47 ≤ h ≤ 47, −19 ≤ k ≤ 19, −34 ≤ l ≤ 34
301609
0.0622
indep reflns
data/restraints/param
GOF on F2
24236
24236/92/1181
1.024
a
R1 [I > 2σ(I)]
0.0346
wR2
peak/hole (e/Å3)
0.0871
0.491/−0.462
When guests are mixed with zinc bisporphyrinate, the
following two equilibria could be in the solution because there
are two zinc binding sites:
Flack parameter
0.032(6)
a
2
2
2
R1 = (Fo − Fc)/Fo; wR2 = w(Fo − Fc2)2/w(F0 ) ]1/2
.
K1
[Zn2‐III] + L ⇌ [Zn2‐III]·L
than 1000 equiv of guests was generally used. Their titration
CD spectra and the corresponding plots of the CD intensity as
a function of the equivalents of guests are provided in the
Supporting Information. These figures show that the CD
intensities reached a maximum at a large excess of guests, which
suggested that all zinc bisporphyrinates were converted to the
corresponding host−guest complexes. The spectra in Figure 1
show clear signals with typical bisignate Cotton effects in the
Soret band region. The CD spectral data are listed in Table 2.
These results reveal the following features: (1) For a pair of
enantiomers of chiral amines, the CD spectra showed similar
shapes and intensities but opposite signs. (2) More
importantly, when the substituent X is an aryl group or an
alkyl group, the signs of the resulting CD are different. For the
R-type chiral monoamines, when X is an alkyl group, such as
1R, 2R, and 3R, the longer-wavelength peak of the Soret band
is negative and the shorter-wavelength peak is positive.
However, when X is an aryl group, such as 4R and 5R, the
signs of CD are just opposite to those with X as an alkyl group.
As follows, we have investigated the chirality transfer
mechanism through UV−vis spectra, NMR studies, the crystal
structure, and DFT calculations.
(2)
K2
[Zn2‐III]·L + L ⇌ [Zn2‐III]·(L)2
(3)
where L represents a guest.
However, because of the self-aggregation process [equili-
brium (1)] in solution, the equilibria in solution became more
complicated. The binding constants for the above two equilibria
are difficult to determine. In fact, in the titration spectra, we did
not observe clear isosbestic points. This is possibly due to the
self-aggregation process. Self-aggregation through Zn−O bonds
is further confirmed by NMR studies.
NMR Studies. For the free base bisporphyrin III and its
complex [Zn2-III], the 1H NMR spectra are presented in
Figure 4. In this bisporphyrin, all protons are aromatic protons
except the NH protons. The resonances for the aromatic
protons are generally located in the 7−9 ppm region.16
However, for the bisporphyrin III and its complex [Zn2-III],
some resonances are located in the 3−7 ppm region. Because
the linker is between two porphyrin subunits, the ring current
effect of porphyrin could cause such upfield shifts. So, these
resonances are assigned to the protons of the linker. Detailed
1
1
UV−vis Spectral Studies and Self-Aggregation Proc-
ess for the Host. UV−vis spectra of [Zn2-III] were measured
at different concentrations, as shown in Figure 2. The spectra of
[Zn2-III] show one strong Soret band at 421 nm and one
shoulder at 431 nm, which are similar to those reported for m-
phthalic diamide-linked zinc bisporphyrinates14 but different
from those for the oxalic amide-linked species.13 For
assignments are based on H and H−1H COSY NMR, which
are presented in the Supporting Information. Compared with
the free base bisporphyrin III, most signals for the zinc
bisporphyrinate [Zn2-III] remain unchanged, while the
resonances of H12, H(14,16), and H(22,26) shift remarkably
upfield to 3.80, 5.08, and 4.28 ppm, respectively. Such upfield
shifts suggest that these protons are even much closer to the
D
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. CD spectra of a solution of [Zn2-III] (1.75 × 10−6 mol/L) and a large excess of guests in methylene chloride at 298 K. (A) 2500 equiv of
1S, (dashed line) or 1R (solid line); (B) 1600 equiv of 2S (dashed line) or 2R (solid line); (C) 1535 equiv of 3S (dashed line) or 3R (solid line);
(D) 1340 equiv of 4S (dashed line) or 4R (solid line); (E) 1550 equiv of 5S (dashed line) or 5R (solid line).
porphyrin plane in zinc bisporphyrinate than in free base
bisporphyrin, which could be due to coordination of the
carbonyl oxygen atom to the neighboring zinc porphyrinate. In
addition, 1H NMR spectra at different concentrations have also
been measured. In these spectra, most resonances do not
change, but the resonance of H12 shows slight shifts.
On the basis of these NMR spectral changes, we proposed
one possible mode for the self-aggregation of [Zn2-III], as
shown in Figure 5. In the structural formula, there are two types
of carbonyl groups. In solution, both carbonyl oxygen atoms are
coordinated to zinc: the A-type carbonyl group involves
“intermolecular” interactions; the B-type carbonyl group
involves “intramolecular” Zn−O coordination interactions.
Such coordination interactions cause H12, H(14,16), and
H(22,26) to locate above the adjacent porphyrin plane, and the
ring current effect causes their resonances to shift upfield
compared with the free base bisporphyrin.
As is also shown in Figure 5, when the B-type carbonyl
oxygen atom is coordinated to zinc, coordination interactions
lead to the adjacent phenyl ring above the plane of the subunit
P1. H22 and H26 are closer to the shielding cone of the
porphyrin ring than H23 and H25, which is similar to that in
the crystal structure of [Zn2-III]·1R (vide infra). As a result, the
resonances of H22 and H26 shift more upfield than those of
H23 and H25.
On the other hand, “intermolecular” interactions are
concentration-dependent, while “intramolecular” interactions
are not. When we change the concentrations, the resonances of
these protons behave differently. The proton H12 is close to
the A-type carbonyl group, and “intermolecular” interactions
lead to its shift upon changes in the concentration. On the
E
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
with different “n” values in solution, and there could also be
equilibria between them, which makes the equilibria more
complicated in solution.
Table 2. Observed CD Spectral Data of the Complexes of
a
[Zn2-III] (1.75 × 10−6 M) with Chiral Monoamines in
Methylene Chloride at 298 K
1H NMR titration experiments were performed between
[Zn2-III] and 1R. When the guest was added to the [Zn2-III]
solution, there were some resonances located in the −4 to 0
ppm region, as shown in Figure S20, which is similar to our
studies on previously reported amide-linked bisporphyrin
systems. Obviously, the large upfield shifts of these protons
are due to coordination of the guests to zinc porphyrinate. The
detailed titration spectra shown in Figure 6 gave us more
information on the coordination interactions. During titration,
the resonances of the protons of the linker in the host have
shown remarkable shifts. When the host−guest ratio is below
1:1, the resonance of H12 has the largest shift; when the ratio is
over 1:1, the resonance of H(22,26) has the largest shift. When
the guest is in a large excess, the resonance pattern is very
similar to that of the free base porphyrin III. This suggests that
the NMR spectral changes during titration are caused by
replacing the Zn−O bonds with the Zn−N (from amine)
bonds. While the structural formula suggests that H12 is close
to the A-type carbonyl, H(22,26) is close to the B-type
carbonyl. The above studies suggest that, during titration, the
A-type carbonyl oxygen atom was first replaced by one
monoamine to form the 1:1 complex, and then the B-type
carbonyl oxygen atom was replaced by another monoamine to
form the 1:2 host−guest complex.
λmax, nm (Δε, cm−1 M−1
)
b
first cotton
second cotton
Aobs
1R
1S
2R
2S
3R
3S
4R
4S
5R
5S
432 (−142)
431 (+143)
431 (−234)
431 (+248)
433 (−50)
433 (+53)
423 (+70)
421 (−68)
424 (+160)
423 (−150)
425 (+68)
424 (−70)
419 (−160)
419 (+163)
422 (−452)
420 (+443)
−212
+211
−394
+398
−118
+123
+357
−356
+950
−926
431 (+197)
431 (−193)
430 (+498)
429 (−483)
a
The corresponding host−guest ratios are the same as those in Figure
b
1. Aobs = Δε1 − Δε2. This value represents the total amplitude of the
experimentally observed CD couplets.
1
The H NMR titration experiments were also performed
between [Zn2-III] and 4R. Their spectra (Figure S22) show
changes similar to those for 1R. This suggests that 4R is also
coordinated to [Zn2-III] in a stepwise fashion, leading to the
formation of 1:1 and 1:2 host−guest complexes during
titration.
1
Figure 2. UV−vis spectra of [Zn2-III] in 0.1 mm, 1 mm, and 1.0 cm
quartz cells at different concentrations in methylene chloride. The
intensities are normalized on the basis of the concentrations of [Zn2-
III]: (A) 1.5 × 10−7 mol/L; (B) 6.0 × 10−7 mol/L; (C) 1.5 × 10−6
mol/L; (D) 1.5 × 10−5 mol/L; (E) 1.5 × 10−4 mol/L.
On the basis of the H NMR titration results, Job plots for
the titration of 1R or 4R into a [Zn2-III] solution are shown in
Figures S23 and S24. The plots showed a broad peak around
0.3−0.5 mole fraction but not at 0.33, as was expected for a 1:2
host−guest complex. This is possibly due to the limitation of
Job plots. Actually, there were some reports on the limited
applicability of this method.23−25 Because there are several
equilibria and too many species (including the aggregated
species) in solution, the Job plot method is not suitable for this
system.
X-ray Crystal Structure of [Zn2-III]·1R. In order to
understand the chirality transfer mechanism, we need to obtain
the binding mode of the host−guest complexes. One of the
best ways to get the binding mode is through the crystal
structure. We tried to obtain crystal structures for the host−
guest complexes. For one of the alkyl-substituted guests, 1R, we
obtained single crystals of [Zn2-III]·1R.
The structure of [Zn2-III]·1R was solved in a chiral space
group, C2. One asymmetric unit contains one zinc
bisporphyrinate molecule. The bisporphyrin host molecule
has two zinc porphyrinate subunits that are linked by an m-
phthalic diamide group. Interestingly, both zinc atoms are five-
coordinate, but their axial ligations are different. As shown in
Figure 7, for the subunit P1, the axial ligand is the N1 atom of
the chiral guest. The ligand adopts an “inside” binding mode
(the ligand is facing the linker). For the subunit P2, the axial
ligation is from the B-type carbonyl oxygen O013 of the amide
group of the linker. Because of coordination, the phenyl rings
composed of C21, C22, C23, C24, C25, and C26 are over the
plane of the porphyrin subunit P2, and C22/C26 and their
Figure 3. UV−vis spectral change of [Zn2-III] (1.50 × 10−6 M) upon
the addition of 1R as the host−guest molar ratios are from 1:0 to
1:850.
other hand, the protons close to the B-type carbonyl group,
such as H24, H(22,26), and H(23,25), do not show clear shifts
because the B-type carbonyl group involves “intramolecular”
Zn−O coordination interactions. “Intermolecular” interactions
can result in self-aggregation, as shown in equilibrium (1),
which may lead to the formation of a dimer, trimer, or even
polymer. It is likely that there are several aggregated species
F
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 4. 1H NMR spectra for compound III (A; 3.3 × 10−3 M) and [Zn2-III] at different concentrations: (B) 4.6 × 10−3 M; (C) 1.2 × 10−3 M; (D)
0.92 × 10−3 M; (E) 0.45 × 10−3 M. The inset shows the proton numbering scheme of the linker in the host. The arrows show the shifts of the
relevant protons.
method,28 the anticlockwise twist will lead to a negative Cotton
effect. This is consistent with our experimental results.
Solid-State CD Spectrum. For [Zn2-III]·1R, we also did
CD measurements on several single-crystal samples. For these
measurements, the signals were all weak. However, they did
show CD signals in the Soret band region. One of them is given
in Figure 8. The CD spectrum shows the same sign and similar
shape as the solution CD spectra. This confirms the chirality of
the single crystal.
Computational Studies on the Chirality Transfer
Mechanism. In order to gain more insight into the chirality
transfer mechanism for this system, we did further inves-
tigations by DFT calculations. On the basis of the crystal
structure, we did calculations on the host, 1:1 and 1:2 host−
guest complexes for the guests 1R and 4R. All of the optimized
structures are displayed in Figures 9 and 10. We found that, in
Figure 5. Proposed binding mode for [Zn2-III]. The A-type carbonyl
group involves “intermolecular” interactions, and the B-type carbonyl
group involves “intramolecular” Zn−O coordination interactions.
all of these optimized structures, except the zinc atoms
coordinated by amines, other zinc atoms are all coordinated
by the amide oxygen atom. Such a coordination mode was
actually found for zinc trisporphyrinate as well.29
As shown in Figure 9A, for the free host [Zn2-III], the
optimized structure is in low symmetry, which leads to a
conformer with a noncentrosymmetric (chiral) configuration.
Such conformers exist as a pair of enantiomers, namely, the
conformers A and B. For the conformer A, the two porphyrin
protons H22/H26 are closer to the porphyrin center than C23/
C25 and H23/H25 (vide supra). So, this coordination mode is
consistent with our NMR studies. Besides the coordination
interaction, the guest 1R also involves hydrogen-bonding
subunits adopt an anticlockwise twist; for the conformer B, the
interactions. There is an intramolecular hydrogen bond
two porphyrin subunits adopt a clockwise twist. However, the
solution consists of a racemic mixture, which is optically
inactive.
between N1 and the carbonyl oxygen O012. The correspond-
ing distance N1···O012 is 2.919(4) Å, and the bond angle N1−
H1B···O012 is 159°. These interactions could be the major
factors stabilizing the “inside” binding mode for the 1:1
complex.
The C5−C15−C5′−C15′ torsion angle can be used to
present the dihedral angle between the two transition moments
of the chromophores for the effective exciton coupling
interactions in the bisporphyrin system.26,27 In this structure,
two porphyrin subunits form an anticlockwise twist with the
C5−C15−C5′−C15′ torsion angle (here it is C1M3−C1M1−
C2M1−C2M3) of −147°. On the basis of the exciton chirality
When the chiral guest 1R is mixed with the host, both
conformers A and B could interact with it and form the
corresponding 1:1 complexes, the conformer A·1R and the
conformer B·1R. Their optimized structures are shown in
Figure 9B. In both cases, coordination and hydrogen-bonding
interactions are maintained like those in the crystal structure.
The calculations suggest that the conformer A·1R is more
energetically favorable, which is 1.96 kJ/mol lower than the
conformer B·1R.
G
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 6. 1H NMR spectral changes of [Zn2-III] (4.4 × 10−3 M) upon the addition of 1R in CDCl3 at 298 K as the host−guest molar ratios are from
1:0 to 1:8.2.
Figure 8. CD spectrum of the single crystal of [Zn2-III]·1R in the KBr
pellet.
between the guest and the porphyrin plane. (2) Another is
between the guest and the linker. In order to minimize the
steric repulsions between the guest and the porphyrin plane, in
both conformers A·1R and B·1R, the least bulky group
(hydrogen) is facing the porphyrin plane and the bulkiest group
(isopropyl) is away from the porphyrin plane. However, as
shown in Figure 9B, the orientations of the isopropyl groups in
two conformers are different. In the conformer A·1R, it is away
from the linking phenyl. However, in the conformer B·1R, it
Figure 7. ORTEP view for [Zn2-III]·1R with 50% probability thermal
tilts toward the linking phenyl. The former orientation may
ellipsoids. A hydrogen bond is shown as a dashed line. The arrows
cause less steric repulsion between the guest and the linker and
show the direction of the effective transition moments along the C5···
lower its energy. Therefore, the conformer A·1R should be the
C15 axis (here labeled as C1M1···C1M3 and C2M1···C2M3). Some
major contributor to the CD spectra.
phenyl rings and some hydrogen atoms have been omitted for clarity.
In the conformer A·1R, the two porphyrin subunits adopt an
anticlockwise twist with a C5−C15−C5′−C15′ torsion angle of
What structural differences cause the difference in energy for
these two conformers? For the chiral monoamines used in this
work, the chirogenic carbon center is bonded to four different
groups: NH2, CH3, H, and X. For the case of 1R, X is an
isopropyl group [CH(CH3)2], an alkyl substituent. Because of
the coordination interaction, the position of NH2 is fixed. Then
the major differences are caused by the orientations of the other
three groups. The bulkiness order is H < CH3 < CH(CH3)2.
When the guest 1R is coordinated to zinc porphyrinate, two
parts of the steric repulsions have to be considered: (1) One is
−144°. On the basis of the exciton chirality method,28 this
anticlockwise twist will lead to a negative Cotton effect. This is
also consistent with our experimental results.
When the 1:1 complex further reacts with a guest, both
conformers A·(1R)2 and B·(1R)2 of the 1:2 complexes will
form. As shown in Figure 9C, in the optimized structures, the
two guest molecules are not equivalent. One is similar to that in
the 1:1 complex; besides the coordination interaction, it also
forms a hydrogen bond with the A-type carbonyl oxygen atom.
The second replaces the coordination site of the B-type
H
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 10. Chirality transfer mechanism based on DFT calculations
for 4R. Hydrogen atoms of the chiral carbon atoms are marked by red
circles. (A) Host [Zn2-III] existing as a pair of enantiomers, the
conformers A and B. (B) Optimized 1:1 host−guest complexes for
[Zn2-III]·4R. The conformer B·4R is more energetically favorable,
which leads to the clockwise twist. (C) Optimized 1:2 host−guest
complex for [Zn2-III]·(4R)2. The conformer B·(4R)2 is more
energetically favorable, which leads to the clockwise twist.
Figure 9. Chirality transfer mechanism based on DFT calculations for
1R. Hydrogen atoms of the chiral carbon atoms are marked by red
circles; arrows show the orientations of the isopropyl groups. (A) Host
[Zn2-III], which exists as a pair of enantiomers in solution. The
conformer A forms an anticlockwise twist, and the conformer B forms
a clockwise twist. (B) Optimized 1:1 host−guest complexes for [Zn2-
III]·1R. The conformer A·1R is more energetically favorable, which
leads to the anticlockwise twist. (C) Optimized 1:2 host−guest
complex for [Zn2-III]·(1R)2. The conformer A·(1R)2 is more
energetically favorable, which leads to the anticlockwise twist.
(1R)2 should be the major contributor to the CD spectra. In
the conformer A·(1R)2, the two porphyrin subunits adopt an
anticlockwise twist with a C5−C15−C5′−C15′ torsion angle of
−157°. On the basis of the exciton chirality method,28 this
anticlockwise twist will lead to a negative Cotton effect. This is
also consistent with our experimental results.
Why are the signs of the CD signals different when the
substituent is an aryl group compared to an alkyl group? In the
calculations, (R)-1-phenylethylamine (4R) was used as the
guest with an aryl substituent. When the chiral guest 4R is
mixed with the host, this leads to 1:1 and 1:2 complexes. For
the 1:1 complexes, the optimized structures are the conformer
A·4R and the conformer B·4R, as shown in Figure 10B. In both
cases, hydrogen bonds are maintained. However, different from
the case of 1R, there are also π−π interactions between the
phenyl ring of the guest and the phenyl ring of the linker. Such
types of π−π interactions were also found in the reported
carbonyl oxygen atom but does not form any hydrogen bond.
The calculations suggest that the conformer A·(1R)2 is more
energetically favorable, which is 3.96 kJ/mol lower than the
conformer B·(1R)2. Similar to the case of their 1:1 complex, the
difference could be also caused by the orientations of the
isopropyl groups. Besides the different orientations of the
isopropyl group of the first guest coordinated in the subunit P1,
the isopropyl group of the second guest coordinated in the
subunit P2 also adopts different orientations in both con-
formers. As shown in Figure 9C, in the conformer A·(1R)2, the
isopropyl group is away from the benzylamide substituent.
However, in the conformer B·(1R)2, it tilts toward this
substituent. The former orientation may cause less steric
repulsions and lower its energy. Therefore, the conformer A·
I
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
amide-linked zinc trisporphyrinate complex.17 The calculations
suggest that the conformer B·4R is more energetically
favorable, which is 6.48 kJ/mol lower than the conformer A·4R.
For the chiral guest 4R, X is a phenyl group. Because of the
coordination and π−π interactions, the positions of NH2 and
the phenyl group are fixed, and then the major differences
between the conformer A·4R and the conformer B·4R are
caused by the orientations of the methyl group and the
hydrogen atom. The bulkiness order is H < CH3. In their
optimized structures, as shown in Figure 10B, the methyl group
is facing the porphyrin plane in the conformer A·4R, while it is
away from the porphyrin plane in the conformer B·4R. Such an
orientation may cause less steric repulsion for the conformer B·
4R and, hence, lower its energy. Therefore, the conformer B·4R
could be the major contributor for the CD signal. In the
conformer B·4R, the two porphyrin subunits adopt a clockwise
twist with a C5−C15−C5′−C15′ torsion angle of 154°. On the
basis of the exciton chirality method,28 the above conformer
will lead to a positive Cotton effect.
could control chirality transfer by adjusting the linker. Further
studies on the functionalization of the linker are under
investigation.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b00815.
CD, UV−vis, and NMR spectra, calculation data, relative
energies, and Cartesian coordinates (PDF)
Accession Codes
CCDC 1531702 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
When both conformers of the 1:1 complex further react with
a guest, both conformers A·(4R)2 and B·(4R)2 of the 1:2
complexes will form. As shown in Figure 10C, the two guest
molecules in the optimized structures are not equivalent. One is
similar to that in the 1:1 complex; besides coordination
interaction, it also involves hydrogen-bonding and π−π
interactions. The other one only involves coordination and
π−π interactions but does not form any hydrogen bonds. The
calculations suggest that the conformer B·(4R)2 is more
energetically favorable, which is about 0.92 kJ/mol lower than
the conformer A·(4R)2. Similar to the case of their 1:1 complex,
the difference could also be caused by the orientations of the
methyl group and hydrogen, as shown in Figure 10C. The
methyl group is facing the porphyrin plane in the conformer A·
(4R)2, while it is away from the porphyrin plane in the
conformer B·(4R)2. Such an orientation may cause less steric
repulsion for the conformer B·(4R)2 and, hence, lower its
energy. In the conformer B·(4R)2, the two porphyrin subunits
adopt an anticlockwise twist with a C5−C15−C5′−C15′
torsion angle of 168°. On the basis of the exciton chirality
method,28 this clockwise twist will lead to a positive Cotton
effect. This is also consistent with our experimental results.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: yowang@suda.edu.cn.
*E-mail: cjhu@suda.edu.cn.
*E-mail: jplang@suda.edu.cn.
■
ORCID
Chuanjiang Hu: 0000-0001-7126-3789
Jianping Lang: 0000-0003-2942-7385
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Nature Science Foundation of China for
financial support (Grants 21271133, 21305098, and
21531006), the Natural Science Foundation of Jiangsu
Province (Grant BK2016127502), and the Local Joint
Engineering Laboratory for Novel Functional Polymeric
Materials and the Priority Academic Program Development
of Jiangsu Higher Education Institutions. The authors are
grateful for the useful comments of the Editor and reviewers.
CONCLUSION
REFERENCES
■
■
(1) Hembury, G. A.; Borovkov, V. V.; Inoue, Y. Chirality-Sensing
Supramolecular Systems. Chem. Rev. 2008, 108, 1−73.
(2) Berova, N.; Pescitelli, G.; Petrovic, A. G.; Proni, G. Probing
molecular chirality by CD-sensitive dimeric metalloporphyrin hosts.
Chem. Commun. 2009, 5958−5980.
(3) Liu, M. H.; Zhang, L.; Wang, T. Y. Supramolecular Chirality in
Self-Assembled Systems. Chem. Rev. 2015, 115, 7304−7397.
(4) Borovkov, V. Supramolecular Chirality in Porphyrin Chemistry.
Symmetry 2014, 6, 256−294.
(5) Rosaria, L.; D’Urso, A.; Mammana, A.; Purrello, R. Chiral
memory: induction, amplification, and switching in porphyrin
assemblies. Chirality 2008, 20, 411−419.
(6) Borovkov, V. V.; Hembury, G. A.; Inoue, Y. Origin, Control, and
Application of Supramolecular Chirogenesis in Bisporphyrin-Based
Systems. Acc. Chem. Res. 2004, 37, 449−459.
In conclusion, we have designed and synthesized a new m-
phthalic diamide-linked zinc bisporphyrinate. It can function as
a chirality probe for a series of chiral monoamines. For the
chiral monoamines with the same handedness, the signs of their
CD signals for those with an aryl group as the substituent (X)
are opposite to those with an alkyl group as the substituent.
NMR studies suggest that stepwise coordination leads to the
1:1 and 1:2 complexes. The crystal structure of a 1:1 host−
guest complex reveals that this bisporphyrin adopts a trans
configuration and the NH2 of the amine is involved in both
coordination and hydrogen-bonding interactions. DFT calcu-
lations suggest that, in the host−guest complexes, the nature of
the bulkiest group X makes a difference. When X is an alkyl
group, the steric repulsion causes the conformer B·1R to be
more energetically favorable, which leads to a clockwise twist;
when X is an aryl group, it can form π−π interactions with the
phenyl ring of the linker, which causes the conformer A·4R to
be more energetically favorable and leads to an anticlockwise
twist. Our studies suggest that, in this bisporphyrin system, the
interactions between the linker and guests are crucial, and we
(7) Kurtan, T.; Nesnas, N.; Li, Y.-Q.; Huang, X.; Nakanishi, K.;
Berova, N. Chiral Recognition by CD-Sensitive Dimeric Zinc
Porphyrin Host. 1. Chiroptical Protocol for Absolute Configurational
Assignments of Monoalcohols and Primary Monoamines. J. Am. Chem.
Soc. 2001, 123, 5962−5973.
(8) Kurtan, T.; Nesnas, N.; Koehn, F. E.; Li, Y.-Q.; Nakanishi, K.;
Berova, N. Chiral Recognition by CD-Sensitive Dimeric Zinc
J
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Porphyrin Host. 2. Structural Studies of Host-Guest Complexes with
Chiral Alcohol and Monoamine Conjugates. J. Am. Chem. Soc. 2001,
123, 5974−5982.
(9) Tanasova, M.; Yang, Q.; Olmsted, C. C.; Vasileiou, C.; Li, X.;
Anyika, M.; Borhan, B. An Unusual Conformation of α-Haloamides
Due to Cooperative Binding with Zincated Porphyrins. Eur. J. Org.
Chem. 2009, 2009, 4242−4253.
(10) Borovkov, V. V.; Lintuluoto, J. M.; Fujiki, M.; Inoue, Y.
Temperature Effect on Supramolecular Chirality Induction in Bis(zinc
porphyrin). J. Am. Chem. Soc. 2000, 122, 4403−4407.
(11) Borovkov, V. V.; Lintuluoto, J. M.; Inoue, Y. Supramolecular
Chirogenesis in Zinc Porphyrins: Mechanism, Role of Guest Structure,
and Application for the Absolute Configuration Determination. J. Am.
Chem. Soc. 2001, 123, 2979−2989.
(12) Anyika, M.; Gholami, H.; Ashtekar, K. D.; Acho, R.; Borhan, B.
Point-to-Axial Chirality Transfer-A New Probe for ″Sensing″ the
Absolute Configurations of Monoamines. J. Am. Chem. Soc. 2014, 136,
550−553.
(25) Ulatowski, F.; Dąbrowa, K.; Bałakier, T.; Jurczak, J. Recognizing
the Limited Applicability of Job Plots in Studying Host−Guest
Interactions in Supramolecular Chemistry. J. Org. Chem. 2016, 81,
1746−1756.
(26) Matile, S.; Berova, N.; Nakanishi, K.; Fleischhauer, J.; Woody, R.
W. Structural Studies by Exciton Coupled Circular Dichroism over a
Large Distance: Porphyrin Derivatives of Steroids, Dimeric Steroids,
and Brevetoxin B. J. Am. Chem. Soc. 1996, 118, 5198−5206.
(27) Pescitelli, G.; Gabriel, S.; Wang, Y. K.; Fleischhauer, J.; Woody,
R. W.; Berova, N. Theoretical analysis of the porphyrin-porphyrin
exciton interaction in circular dichroism spectra of dimeric
tetraarylporphyrins. J. Am. Chem. Soc. 2003, 125, 7613−7628.
(28) Berova, N.; Polavarapu, P. L.; Nakanishi, K.; Woody, R. W.
Comprehensive Chiroptical Spectroscopy; John Wiley & Sons, Inc.:
Hoboken, NJ, 2012.
(29) Li, L.; Hu, C. J.; Shi, B.; Wang, Y. Rationalization of chirality
induction and inversion in a zinc trisporphyrinate by a chiral
monoalcohol. Dalton Trans. 2016, 45, 8073−8080.
(13) Jiang, J.; Feng, Z.; Liu, B.; Hu, C.; Wang, Y. Chiral recognition
of amino acid esters by a novel oxalic amide-linked bisporphyrin.
Dalton Trans. 2013, 42, 7651−7659.
(14) Jiang, J.; Fang, X.; Liu, B.; Hu, C. m-Phthalic Diamide-Linked
Zinc Bisporphyrinate: Spontaneous Resolution of Its Crystals and Its
Application in Chiral Recognition of Amino Acid Esters. Inorg. Chem.
2014, 53, 3298−3306.
(15) Liu, B.; Jiang, J.; Fang, X.; Hu, C. Absolute Configurational
Assignments of Amino Acid Esters by a CD-Sensitive Malonamide-
Linked Zinc Bisporphyrinate Host. Chin. J. Chem. 2014, 32, 797−802.
(16) Fang, X. S.; Han, Z.; Xu, C. L.; Li, X. H.; Wang, Y.; Hu, C. J.
Discrimination between alkyl and aryl substituents of chiral mono-
amines by m-phthalic diamide-linked zinc bisporphyrinates. Dalton
Trans. 2015, 44, 12511−12515.
(17) Han, Z.; Li, L.; Shi, B.; Fang, X. S.; Wang, Y.; Hu, C. J.
Crystallographic and Spectroscopic Studies of a Host-Guest Complex
Consisting of a Novel Zinc Trisporphyrinate and a Chiral Monoamine.
Inorg. Chem. 2016, 55, 3730−3737.
(18) Sheldrick, G. M. Crystal structure refinement with SHELXL.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(19) Spek, A. L. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 9−
18.
(20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, G. H.; Caricato, M.; Li, X.; Hratchian,
H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J.
E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
̈
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian09, revision C.01; Gaussian, Inc.: Wallingford, CT, 2010.
(21) Borovkov, V. V.; Lintuluoto, J. M.; Sugeta, H.; Fujiki, M.;
Arakawa, R.; Inoue, Y. Supramolecular Chirogenesis in Zinc
Porphyrins: Equilibria, Binding Properties, and Thermodynamics. J.
Am. Chem. Soc. 2002, 124, 2993−3006.
(22) Nardo, J. V.; Dawson, J. H. Magnetic circular dichroism
spectroscopy as a probe of axial ligation in porphyrin complexes:
zinc(II) tetraphenylporphyrin complexes with oxygen and nitrogen
donor ligands. Spectrosc.: Int. J. 1983, 2, 326.
(23) Ingham, K. C. On the application of Job’s method of continuous
variation to the stoichiometry of protein-ligand complexes. Anal.
Biochem. 1975, 68, 660−663.
(24) Gil, V. M. S.; Oliveira, N. C. On the use of the method of
continuous variations. J. Chem. Educ. 1990, 67, 473−478.
K
DOI: 10.1021/acs.inorgchem.7b00815
Inorg. Chem. XXXX, XXX, XXX−XXX