Chiral recognition of mesoporous SBA-15 with an incorporated chiral porphyrin

Article abstract of DOI:10.1002/ejic.200600438

The incorporation of a chiral porphyrin into the mesoporous molecular sieves SBA-15 by reactions of the surface OH group with an amino group of the porphyrin and its chiral recognition were studied. The resultant material was analyzed by a combination of

Full text of DOI:10.1002/ejic.200600438

FULL PAPER
DOI: 10.1002/ejic.200600438
Chiral Recognition of Mesoporous SBA-15 with an Incorporated Chiral
Porphyrin
Huan-Bao Fa,[a,d] Lang Zhao,[b] Xing-Qiao Wang,*[a] Ji-Hong Yu,[b] Yi-Bing Huang,[c]
Min Yang,[a] and De-Jun Wang[a]
Keywords: Chiral recognition / Porphyrins / Mesoporous materials / SBA-15
The incorporation of a chiral porphyrin into the mesoporous
molecular sieves SBA-15 by reactions of the surface OH
group with an amino group of the porphyrin and its chiral
recognition were studied. The resultant material was ana-
lyzed by a combination of techniques and it was confirmed
that the channels of SBA-15 have been filled with chiral por-
phyrins, leaving the mesopores unaffected. The investigation
of chiral recognition of the porphyrin and the composite SBA-
15 shows that the incorporated SBA-15 has a clear CD spec-
tral signal of the chiral porphyrin and exhibits different chiral
recognition abilities for small amino acids. The
D-alanine is
more tightly bound to the mesoporous composite SBA-15
than its optical antipode.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
30 nm, high internal surface area of about 700–1000 m2 g–1,
and high thermal and hydrothermal stabilities.
Introduction
Chiral recognition is an attractive subject in the area of
Incorporation of metal complexes into mesoporous SBA-
host-guest chemistry, since it is a fundamental process for 15 for catalytic purposes has been extensively investi-
a range of chemical and biological phenomena.[1–3] Several gated.[21–26] However, studies on the incorporation of chiral
types of host molecules for chiral recognition studies have metal complexes into SBA-15 and their chiral recognitions
been reported[4–10] because of their biological and chemical are limited[27] and there are no reports on incorporation of
importance. Among them, porphyrins are relatively access- chiral porphyrins and their chiral recognitions. It is, there-
ible molecules and have been used in recognition studies for fore, important to study this system and to focus on chiral
the past two decades.[11–16] However, the use of porphyrins recognition of the host for small chiral molecules. It has
for chiral recognition has been restricted due to their poor been proposed that the enantioselectivity of the host for
stability in solution. A useful means to improve the stability amino acids could be effectively enhanced by constructing
of porphyrins is by encapsulating them into microporous a specific chiral environment derived from protected amino
materials such as zeolites, since molecular encapsulating is acids on the host porphyrin. In this research, we designed
an emerging technology with potential applications in sepa- and synthesized a porphyrin that contains an amino acid
ration, chemical sensing, and catalysis.[17] However, for nat- on the porphyrin plane (Figure 1) and incorporated the
ural faujasite and synthetic zeolites X and Y the supercage porphyrin molecule with chiral recognition into the chan-
diameter and the aperture to the cages are only 0.7–1.3 nm, nels of SBA-15 to give it chiral recognition functions. Meth-
which is too small for big complexes such as porphyrin sub- ods reported to date for organic complex fixation include:
strates and products to diffuse in and out.[18] The discovery (a) impregnation,[28,29] (b) attachment to amine ligands pro-
of the mesoporous material SBA-15[19,20] by Zhao and co- vided by the modification of a mesoporous material surface
workers in 1998 provided the materials needed to achieve with an organosilane,[29–31] (c) encapsulation during hydro-
porphyrin incorporation since the SBA-15 has a regular thermal synthesis,[32] (d) ion exchange between the organic
hexagonal array of uniform channels with diameters 4.6– complex cation and the template surfactant species in the
non-calcined mesoporous material,[32] and (e) covalent
bonding of the amine-functionalized porphyrin to sites cre-
[a] College of Chemistry, Jilin University,
ated in mesoporous material by doping with Nb.[33] It is
2519 Jiefang Road, Changchun 130021, China
[b] Key Laboratory of Inorganic Synthesis & Preparative Chemis-
try, Jilin University,
well known that the interior surface of SBA-15 is covered
with OH groups, so reduction of the nitro group on the
porphyrin circumference led to the formation of aminogen
with amino groups linking to OH groups of the SBA-15
through hydrogen bonding. In this paper, we report the re-
sults of our studies on the incorporation of a chiral porphy-
Changchun 130023, China
[c] Key Laboratory of Molecular Enzymology and Engineering,
Changchun 130021, China
[d] College of Chemistry and Chemical Engineering, Chongqing
University,
Chongqing 400044, China
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H.-B. Fa, L. Zhao, X.-Q. Wang, J.-H. Yu, Y.-B. Huang, M. Yang, D.-J. Wang
FULL PAPER
rin into SBA-15, and chiral recognition of the mesoporous strutlike arrays (Figure 3, a) exist. The SBA-15 after incor-
composite SBA-15/porphyrin using a combination of tech- poration of chiral porphyrin is shown in Figure 4. When
niques such as X-ray diffraction (XRD), transmission elec- comparing this to Figure 3, it is clear that the hexagonal
tron microscopy (TEM), UV/Vis spectroscopy, nitrogen ad- structure of SBA-15 is preserved after the chiral porphyrin
sorption, and circular dichroism (CD) spectroscopy. At the incorporation. However, the TEM images of Figure 4 (part
same time, the enantioselectivity of the chiral porphyrin for b [110], and part a [100]) show that the hexagonal channels
an amino acid ester in solution was studied for comparison of SBA-15/porphyrin become shaggier. The observed differ-
with the SBA-15/porphyrin.
ence can probably be attributed to incorporation of the chi-
ral porphyrin into the channels of SBA-15.
Figure 3. TEM images of SBA-15 along the (a) [100] and (b) [110]
directions.
Figure 1. Chemical structure of the chiral porphyrin (R = Boc).
Results and Discussion
General Features of the Synthesized Material
The X-ray powder diffraction (XRD) patterns of SBA-
15 before (Figure 2, b) and after (Figure 2, a) the incorpora-
tion of the chiral porphyrin are given in Figure 2. The XRD
patterns of pure SBA-15 and SBA-15/porphyrin show
strong (100) peaks, suggesting that framework stability of
the mesoporous material is well maintained when the chiral
Figure 4. TEM images of SBA-15 with incorporated chiral porphy-
porphyrin is incorporated into the channels of SBA-15. It rin along the (a) [100] and (b) [110] directions.
is to be noted that the relative intensities of (110) and (200)
scattering reflections were dramatically decreased for the
composite consisting of both the porphyrin and SBA-15
when compared to the same bands for pure SBA-15. The
change is interpreted as indicating that the porphyrins are
dispersed in the mesoporous channels. TEM measurements
were used to analyze the structure of the SBA-15. From the
TEM image (Figure 3), it is seen that large ordering do-
mains with highly ordered hexagonal (Figure 3, b) and
UV/Vis diffuse reflectance spectrum of the chiral porphy-
rin, SBA-15/porphyrin, and pure SBA-15 are given in Fig-
ure 5. The pure SBA-15 has no characteristic absorption
bands over the entire spectral region (Figure 5, a). The chi-
ral porphyrin itself has the Soret bands (438 nm) and four
Q-bands (526, 573, 662, 729 nm) (Figure 5, c). The SBA-
15/porphyrin has absorption bands at 425 (Soret band),
518, 560, and 698 nm (Figure 5, b). Compared with the
pure complex, the Soret band of the chiral porphyrin in
SBA-15 is shifted toward shorter wavelengths. This can be
attributed to interactions of the porphyrin with the interior
surface hydroxyl groups of SBA-15. It has been shown that
oxide supports have strong perturbations on the absorption
maxima and molar absorption coefficients.[34] A compari-
son of the characteristic absorption bands of the chiral por-
phyrin incorporated SBA-15 with that of the chiral porphy-
rin confirms the incorporation of the chiral porphyrin into
the SBA-15 channels. When the chiral porphyrin was incor-
porated, interactions of the ligands of the porphyrin with
their local chemical environment changed the symmetry of
the porphyrin. Because of these interactions, the polarity of
the surroundings of the porphyrin is increased, as evidenced
by the shifts of the absorption bands toward higher energy
(shorter wavelength) in the UV/Vis spectra given above.
Figure 2. XRD patterns of SBA-15 samples with (a) and without
(b) the incorporated chiral porphyrin.
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Chiral Recognition of Mesoporous SBA-15 with an Incorporated Chiral Porphyrin
FULL PAPER
and confirms that the porphyrin was successfully incorpo-
rated into the interior surface of the channels of SBA-15.
There is a slight decrease of the average pore size (DBJH
)
from 9.8 to 9.0 nm (Figure 6, B), which indicates that some
of the nanometer-shaggier void space of the host silica is
open, although a portion of the channels may be blocked by
the porphyrin molecules. The space is important for guest
molecules to diffuse into the host silica, and to contact chi-
ral porphyrin molecules for reactions to proceed.
Table 1. Physical and surface properties of selected samples.
SBET [m2 g–1]
Vt [cm3 g–1]
DBJH [nm]
[a]
Sample
SBA-15
SBA-15/porphyrin 427
540
0.88
0.66
9.8
9.0
Figure 5. UV/Vis absorption spectra of SBA-15 before (a) and after
(b) the incorporation of chiral porphyrin, and also the chiral por-
phyrin on its own (c).
[a] SBET, BET specific surface area; Vt, total pore volume; DBJH
pore diameter calculated using the BJH method.
,
The CD spectra of the chiral porphyrin in solution and
the SBA-15/porphyrin in the solid phase are given in Fig-
ure 7. The SBA-15 incorporating chiral porphyrin gives CD
signals while the pure SBA-15 does not have CD signals.
This also confirms the results that the porphyrin has been
In order to understand better the texture of the mesopo-
rous composite SBA-15/porphyrin, the nitrogen isothermal
adsorption technique was employed. Nitrogen adsorption/
desorption isotherms for SBA-15 and SBA-15/porphyrin
are shown in Figure 6. When porphyrins were incorporated
into SBA-15, the sharpness of the inflection was signifi-
cantly reduced at the P/P0 range from 0.45 to 0.9, and the
inflections were shifted slightly toward lower P/P0 ranges.
The inflection point of the relative pressure is related to a
diameter in the mesopore range, and the sharpness of these
steps indicates the uniformity of the mesopore size distribu-
tion.[35,36] Compared to pure SBA-15, the mesoporous com-
posite SBA-15/porphyrin showed a reduction of sharpness,
indicating less uniformity of the mesopore size distribution.
Table 1 summarizes the results of N2 adsorption analyses.
After incorporation of chiral porphyrin into SBA-15, the
S
BET, Vt, and DBJH values for SBA-15/porphyrin were
427 m2 g–1, 0.66 cm3 g–1, and 9.0 nm, respectively, and
540 m2 g–1, 0.88 cm3 g–1, and 9.8 nm for pure SBA-15,
respectively. Therefore, all parameters of SBA-15/porphyrin
decreased compared with pure SBA-15. This is fully consis-
Figure 7. Circular dichroism spectra of the chiral porphyrin (solid
line) (1×10–6 ) in chloroform and the SBA-15/porphyrin (dash
tent with the results of the XRD, UV/Vis, and TEM studies dot line) (solid state) at 298 K.
Figure 6. A: Nitrogen adsorption isotherms of pure SBA-15 (a) and SBA-15/porphyrin (b). B: Pore size distribution of the samples
calculated from the adsorption branch of the isotherms using the BJH algorithm.
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FULL PAPER
1
1
1
1
successfully incorporated into the channels of SBA-15. The
great change in peak shape of the chiral porphyrin upon
incorporation also demonstrates that incorporation has in-
deed occurred. Difference in peak shape is likely attribut-
able to the influence of the channel of mesoporous material
by interactions of porphyrins with OH groups of the SBA-
15.
=
·
+
(1)
A0 – A K·a CL
a
where A0 is the absorbance of the porphyrin 3 solution at
425 nm, A is the absorbance in the presence of a guest at
concentration CL, and a is a constant. The quantity 1/(A0 –
A) has a linear relation to 1/CL; the association constant,
K, can be obtained from the ratio of the intercept to the
slope. The results of the association constant of - and -
AlaOCH3, are KD = 9526 and KL = 3834, respectively,
which are much larger than that of ZnTPP.[40,41] This is be-
cause the electronic effect is more significant than the steric
repulsion between the side chain of the amino acid ester
and the branch group of the porphyrin. The association
constant of -AlaOCH3 is larger than that of its optical
antipode. The structure of the -enantiomer of the guest
molecules can be better aligned with the chiral porphyrin.
The steric repulsion between the larger groups in the por-
phyrin and the -enantiomer is unfavorable for “close bind-
ing” of the host and guest. Accordingly, the association of
the porphyrin with the -guest becomes weaker and the as-
sociation constant smaller than that with the -guest.
Chiral Recognition
To investigate comparatively the chiral recognition of the
chiral porphyrin and mesoporous composite SBA-15/por-
phyrin for chiral amino acids, visible spectroscopy and cir-
cular dichroism spectra were employed to study the
enantioselectivity of  and  amino acids.
Figure 8 shows circular dichroism spectra of porphyrin 1
before and after linking -BocAla. The porphyrin 1 has no
spectral signal, but porphyrin 3 has a strong CD spectral
signal with a split Cotton effect around its Soret band when
chiral amino acid is linked with porphyrin 1 by covalent
bonding. The interaction between the excited states of chro-
mophores in unsymmetrical environments gives circular di-
chroism curves with split Cotton effects.[37] There is strong
exciton-coupled action between the porphyrin ring and the
acylamide group. Porphyrin 3 exhibits complex curves
around its Soret band (Figure 8, b). According to the Tin-
oco law,[38] the coupling between the electric and magnetic
transition moments of the acylamide group and the electric
transition moments of porphyrin chromophores leads to
the observed Cotton effects.[13,39]
Figure 9. UV/Vis titration of the chiral porphyrin with -AlaOCH3
in chloroform at 298 K: [3] = 2×10–6 ; [-AlaOCH3] = 0, 0.1, 0.2,
0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, and 1.4×10–4 .
Figure 8. Circular dichroism spectra of porphyrin 1 (a) and chiral
porphyrin 3 (b) (1×10–6 ).
Absorption spectra of chiral porphyrins binding with
amino acid esters of varying concentrations are shown in
Figure 9 and Figure 10, which suggest a stepwise binding
of the chiral porphyrin with - and -alanine methyl ester
(AlaOCH3), respectively. The absorption spectral change in
the Soret region shows an increase in intensity of the ab-
Figure 10. UV/Vis titration of chiral porphyrin with -AlaOCH3
in chloroform at 298 K: [3] = 1×10–6 ; [-AlaOCH3] = 0, 0.1, 0.2,
0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, and 1.4×10–4 .
The chiral porphyrin has a higher enantioselectivity in
sorption band at 465 nm with a decrease of the absorption organic solutions, however, the tedious preparation, high
at 425 nm, displaying an isosbestic point at 440 nm, which cost, and weak stability of the porphyrin, and also the weak
indicates 1:1 complexation between the host and guest solubility of some amino acids in organic solutions obstruct
molecules. The association constant K is given by Equa- the application of porphyrins in chiral recognition for
tion (1).
amino acids. A good approach to circumvent this problem
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Chiral Recognition of Mesoporous SBA-15 with an Incorporated Chiral Porphyrin
FULL PAPER
is to incorporate porphyrins into SBA-15, facilitating the their liquid phase are evidently different (inset of Figure 11
host-guest separation. To investigate the enantioselectivity and Figure 12). The linear regression parameter for -ala-
of the mesoporous material SBA-15/porphyrin for chiral nine is 0.19, and –0.47 for -alanine. All these results indi-
amino acids, a 10–3  solution of -alanine and -alanine cated that -alanine couples more strongly with the meso-
in distilled water was prepared. This solution (10 mL) of - porous material, which is consistent with the results of the
alanine and -alanine was mixed with SBA-15 (5.6 mg) af- porphyrin with the amino acid ester. When the porphyrin
ter incorporation of chiral porphyrin 3. While the mixture was not incorporated into the SBA-15, the changes in the
was stirred in a round-bottomed flask at room temperature, CD spectra of the alanines were the same. The observed
the solution was monitored by the CD technique. The difference is attributed to incorporation of the chiral por-
changes in the CD spectra with time are shown in Figure 11 phyrin. The branch groups of the chiral porphyrin provide
and Figure 12. Figure 11 gives the CD spectra of -alanine a chiral cavity for the guest molecules (small amino acids).
with a positive response. As time passes, the response inten-
sity of the solution of -alanine decreases. The intensity at
Conclusions
30 min is half the intensity at 0 min. This indicates that -
alanine is absorbed into the channel and onto the surface
of the mesoporous material.
A combination of techniques such as XRD, TEM, UV/
Vis, nitrogen adsorption, and CD spectroscopy was em-
ployed to confirm that we have successfully incorporated
chiral porphyrins into the interior surface of the channels
of mesoporous molecular sieves SBA-15. The SBA-15 has
a clear CD spectra signal after the incorporation and shows
different chiral recognition abilities for small amino acids
such as - and -alanine. The above experiments demon-
strate that the -alanine is more tightly bound to the host
than its optical antipode, which is consistent with the re-
sults of porphyrins in organic solutions. The investigation
provides an available model for the application of chiral re-
cognition.
Experimental Section
Materials and Physical Measurements: All reagents and solvents
were of commercial reagent grade and used without further purifi-
cation. Boc-alanine(BocAla) was purchased from Aldrich. The
SBA-15 was synthesized according to ref.[19]
Figure 11. CD spectra of -alanine at different times after being
stirred with SBA-15/porphyrin. Inset shows the CD decrease
(∆CD) vs. time (min).
The powder diffraction of the solid materials was examined by
using a Rigaku D/MAX X-ray powder diffractometer with a Cu-Kα
X-ray source (λ = 0.154 18 nm). Transmission electron microscopic
(TEM) images were performed with a JEOL JEM2011 electron
microscope operating at 200 kV. UV/Vis spectra of solutions were
collected with a Perkin–Elmer Lambda 2 spectrometer. Diffuse re-
flectance UV/Vis spectra of solids were recorded with a Perkin–
Elmer Lambda 9 spectrometer. Circular dichroism (CD) spectra
were performed with a JASCO-715 spectropolarimeter equipped
with a thermostat cell compartment. Nitrogen adsorption measure-
ments at 77 K were performed with a NOVA 2000e volumetric ad-
sorption analyzer, samples were outgassed for 6 h in the degas port
of the adsorption apparatus.
Synthesis of the Chiral Porphyrin: The synthesis procedure for the
chiral porphyrin is illustrated in Scheme 1.The synthesis was based
on the following procedures: The unsymmetrically phenyl-substi-
tuted porphyrin 1 was synthesized according to an adaptation of
the general Rothemund method for synthesis of meso-tetraphen-
ylporphyrins.[42] o-Hydroxybenzaldehyde (4.9 g, 1 equiv.) and p-ni-
trobenzaldehyde (6.1 g, 3 equiv.) were added to refluxing propionic
acid (300 mL). Once the aldehydes had completely dissolved,
freshly distilled pyrrole (6 mL, 4 equiv.) was added within 20 min
and refluxed for 1 h. The reaction mixture was then cooled and
allowed to stand overnight. After diluting with distilled water
Figure 12. CD spectra of -alanine solution at different times after
being stirred with SBA-15/porphyrin. Inset shows the CD decrease
(∆CD) vs. time (min).
Comparing this with Figure 12, the CD spectra of -ala-
nine exhibit a negative response and a mirror image of -
alanine. The signal intensity of -alanine also decreases
with time. However, the difference is obvious compared
with -alanine in that the intensity at 30 min is very weak,
nearly one ninth of that at 0 min (Figure 12). Also for the
same 30 min, the changes of concentration of alanines in (500 mL) and adjusting the pH to 6–7 with aqueous sodium hy-
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Scheme 1. Synthesis of the tailed chiral amino acid porphyrin chloroform at 298 K.
droxide (6 molL–1), filtration and hot water washing was per-
formed five times. The obtained powder mixture, which was black-
purple in color, was then dried in a vacuum oven at 80 °C over-
night. The dried powder was extracted with chloroform until the
extracts became colorless. After distilling off the solvents under a
reduced pressure with a rotary evaporator, a black-purple crude
product was obtained. The crude product was separated using silica
gel column chromatography eluted first with dichloromethane fol-
lowed by elution with a chloroform solution. The second elution
was collected and the solvents evaporated to dryness, and the prod-
uct was chromatographed a second time by column chromatog-
raphy and then TLC. Porphyrin 1 was obtained at the end and
dried in a vacuum oven at 80 °C overnight.
neutralized with concentrated aqueous ammonia. Chloroform
(20 mL) was added to the hot suspension and the mixture was
stirred for 1 h. The chloroform layer was separated, the aqueous
layer extracted several times with chloroform, and all chloroform
extracts were combined and filtered. The chloroform solution was
reduced in volume (10 mL) on a rotary evaporator, washed first
with dilute aqueous ammonia then twice with water, dried with
anhydrous sodium sulfate, and evaporated under reduced pressure.
Flash column chromatography (silica gel, chloroform, the second
elution) afforded 21.7 mg (89%) of pure porphyrin 3.
C52H46N8O4 (846.36): calcd. C 73.74, H 5.47, N 13.23; found C
73.58, H 5.39, N 13.34. Visible spectrum (CHCl3): λ = 650, 590,
550, 515, 425 nm. IR (KBr): ν = 3429 (N–H), 3359 (CON–H), 3216
˜
(pyrrole N–H), 2921 (–CH3), 2850 (–CH2–), 1700 (C=O) cm–1.
MALDI-TOF-MS: m/z = 847.4 [M + 1]+.
C44H27N7O7 (765.20): calcd. C 69.02, H 3.55, N 12.80; found C
68.85, H 3.50, N 12.63. Visible spectrum (CHCl3): λ = 650, 590,
550, 515, 425 nm. IR (KBr): ν = 3442 (–OH), 3317 (pyrrole N–
˜
Incorporation of Chiral Porphyrin into SBA-15: SBA-15 (100 mg)
was mixed with porphyrin 3 (10 mg) in a round-bottomed flask
(20 mL), and then chloroform (10 mL) was added and stirred for
48 h at room temperature. The solid was filtered and washed with
chloroform until no absorption of porphyrin in the UV/Vis spec-
trum was seen from the solution. The solid was dried at room tem-
perature. The original white powders of SBA-15 turned jade-green
after adding the chiral porphyrin, which indicated inclusion of the
porphyrins into the SBA-15 frameworks.
H) 2921 (C–H), 2850, (–CH2–), 1515, 1346 (–NO2) cm–1. MALDI-
TOF-MS: m/z = 765.5 [M + 1]+.
BocAla (30 mg) was dissolved in thionyl chloride (50 mL). This
solution was stirred at reflux for 12 h. Thionyl chloride was then
removed by distillation under reduced pressure. The crude product
was redissolved in benzene (60 mL) and triethylamine (5 mL). A
solution of porphyrin 1 (50 mg) in benzene (10 mL) was added.
The reaction was stirred for 10 h at reflux. The mixture separated
into benzene and water. The organic layer was evaporated under
reduced pressure. Flash column chromatography (silica gel, dichlo-
romethane/ethanol, 3:1) afforded 14.1 mg (23%) of pure porphyrin
2.
For quantitative determination of the porphyrin incorporated into
the SBA-15, a mesoporous composite SBA-15/porphyrin sample
(14 mg) was dissolved in aqueous sodium hydroxide solution (8 )
to destroy the framework. Thus the porphyrin in the mesoporous
composite was released. The porphyrin was extracted with chloro-
form (10 mL), and the solution was diluted to 1/5 its concentration
with chloroform. The OD value of the porphyrin at 425 nm is
0.3141. A reference solution was made with chiral porphyrin
(0.5 mg) dissolved in chloroform (100 mL) and its OD value at
425 nm was measured to be 0.5022. By comparing this with the
reference, the amount of porphyrin encapsulated in SBA-15 was
determined to be 11.2 mgg–1 using Beer’s law. Because there is no
C element in pure SBA-15, the C elemental analysis of the mesopo-
C52H40N8O10 (936.29): calcd. C 66.66, H 4.30, N 11.96; found C
66.57, H 4.23, N 12.01. Visible spectrum (CHCl3): λ = 650, 590,
550, 515, 425 nm. IR (KBr): ν = 3375 (CON–H), 3317 (pyrrole N–
˜
H), 2923 (–CH3), 2852 (–CH2–), 1699 (C=O) cm–1. MALDI-TOF-
MS: m/z = 937.2 [M + 1]+.
Porphyrin 2 (24 mg) was dissolved in concentrated hydrochloric
acid (36%, 20 mL) at room temperature, in a beaker, followed by
addition of excess SnCl2·2H2O (100 mg). The resulting green mix-
ture was quickly heated to 65–70 °C for 25 min, then cautiously
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Chiral Recognition of Mesoporous SBA-15 with an Incorporated Chiral Porphyrin
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Received: May 11, 2006
Published Online: September 7, 2006
Eur. J. Inorg. Chem. 2006, 4355–4361
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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