Binding Affinities and Spectroscopy of Complexes Formed by Polysiloxanes with Aniline and Chlorophenol Acetates

Article abstract of DOI:10.1134/S0036024418130125

Abstract: The theoretical binding energies of the complexes formed by polysiloxanes with aniline and chlorophenol acetates were calculated at B3LYP/6-31G(d, p) level after the basis set superposition error (BSSE) based on B3LYP/6-31G(d) optimized geometri

Full text of DOI:10.1134/S0036024418130125

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2018, Vol. 92, No. 13, pp. 2718–2722. © Pleiades Publishing, Ltd., 2018.
STRUCTURE OF MATTER
AND QUANTUM CHEMISTRY
Binding Affinities and Spectroscopy of Complexes Formed
by Polysiloxanes with Aniline and Chlorophenol Acetates1
Haiqi Zhanga,b, Qiwen Tenga,c, and Shi Wua,c,*
aDepartment of Chemistry, Zhejiang University, Hangzhou, China
bGlobal Innovation and Technical Center, The Coca-Cola Company, Shanghai, China
cKey Lab of Applied Chemistry of Zhejiang Province, Hangzhou, China
*e-mail: wushi@zju.edu.cn
Received October 31, 2017
Abstract—The theoretical binding energies of the complexes formed by polysiloxanes with aniline and chlo-
rophenol acetates were calculated at B3LYP/6-31G(d, p) level after the basis set superposition error (BSSE)
based on B3LYP/6-31G(d) optimized geometries. The high binding energies of the complexes lead to the long
experimental retention times in gas chromatography (GC). The energy gaps of the complexes are reduced
owing to the formation of the hydrogen bonds. The chemical shifts of the α-C atoms connected to the amino
groups in the NMR spectra of the complexes computed with B3LYP/6-31G(d) method are gradually changed
downfield as the Si–O chain increases. The aromaticities of the benzene rings in the complexes are decreased
due to the transfer of electron clouds from the benzene rings to the Si–O chains based on the nuclear inde-
pendent chemical shifts (NICS) calculated at B3LYP/6-31G(d) level.
DOI: 10.1134/S0036024418130125
INTRODUCTION
polymers are thermodynamically stable, whereas
dimethoxysilanone polymers are kinetically stable [8].
Polysiloxanes possess some excellent properties
such as high-temperature stabilities and low-tempera-
ture flexibilities [1, 2], thus they are widely used as sta-
tionary phases in gas chromatography (GC). For
instance, two CH3O-terminated polysiloxanes have
been used as stationary phases in GC at high tempera-
Most of the studies focus on the properties of poly-
siloxanes as stationary phases, but there are few studies
on the interactions between the stationary phases and
target compounds [9, 10]. Herein, theoretical studies
on the binding affinities of polysiloxanes to target
compounds were performed based on the experimen-
ture of 420°C [3]. Besides the advantage of high-tem- tal results. Spectroscopic characteristics of the com-
plexes formed by polysiloxanes with aniline and chlo-
rophenol acetates were predicted.
perature stabilities, fluorosiloxane and arylenesilox-
ane polymers have shown the wide changeable range
of polarities; therefore, these polysiloxanes are often
utilized as stationary phases in preparative gas chro-
matography [4]. Nowadays, fused silica supports
coated with siloxane-modified copolymers are com-
mercially employed as stationary phases. Further-
more, some new capillary columns coated with sil-
phenylene polymers are also applied, which are equiv-
METHODOLOGY
Experimental Apparatus and Reagents
Aligent HP 6890 gas chromatograph coupled with
MS5975 mass spectrometric detector and equipped
with HP-35MS column (30 m × 0.25 mm × 0.25 μm)
alent to traditional polysiloxanes [5]. Theoretical was used in experiments.
studies have revealed the nature of the polysiloxanes.
The lengths of all the Si–O bonds in polysiloxanes are
equal using ab initio calculations [6]. The Si–O–Si
bonds are bent and the linearization energy barriers
are high in polydimethylsiloxanes by the comparison
between the calculation results and experimental data
[7]. In addition, substituents in polysiloxanes play an
important role in their stabilities. Diphenylsilanone
The reagents used include 2,3,4-trichlorophenol
(2,3,4-TCP), 2,3,5-TCP, 2,4,5-TCP, 2,4,6-TCP, ace-
tic anhydride, n-hexane, methanol, KOH, 2 M.
Experimental Method and Procedures
An intermediate 5 mg/L mixed standard solution
of four trichlorophenol isomers was prepared. Then,
0.5 mL of intermediate was mixed with 20 mL of 2 M
KOH. After that, 2 mL of acetic anhydride was added
1
The article is published in the original.
2718

BINDING AFFINITIES AND SPECTROSCOPY
2719
methods in Gaussian 03 program [12] have been suc-
cessfully used to elucidate the electronic structures of
boron nitride nanotubes [13], graphyne fluorides [14],
quinoline derivatives [15], copper complexes [16],
tetra-tetrazole complexes [17] and cyclodextrin com-
plexes [18]. They are also used to investigate dispersion
interactions in Xe-aromatic molecules [19], proton
transfer in nitrofurazan and glycoluril [20, 21], pyrrole
adsorption on aluminum nitride [22], and the func-
tionalization of fullerenes [23, 24]. Based on the
B3LYP/6-31G(d) optimized geometries, the 13C
NMR spectra of the complexes were calculated using
the gauge-independent atomic orbital (GIAO) [25] at
B3LYP/6-31G(d) level. The NICS values of the com-
plexes were computed at B3LYP/6-31G(d) level
employing a dummy atom [26] at the center of the
phenyl ring in the host (Fig. 1).
H Si O x Si Oy
H
Fig. 1. The structural scheme of hosts 1–6 (host 1: x = 0,
y = 1; host 2: x = 1, y = 1; host 3: x = 1, y = 2; host 4: x =
1, y = 3; host 5: x = 1, y = 4; host 6: x = 1, y = 5).
to the vial of the above mixture. After 30 s the vial was
opened to release gas, and 5 mL of n-hexane was
added for the liquid–liquid extraction. Then the mix-
ture was agitated for 30 min using a mechanical shaker.
After the two-phase separation, 1 mL of hexane was
added to 2 mL of the mixture in each vial, respectively.
Then, the analysis of the extracts was performed with
GCMS.
RESULTS AND DISCUSSION
Retention Time
The retention times of 2,3,4-TCP, 2,3,5-TCP,
2,4,5-TCP, and 2,4,6-TCP acetates on the HP-35MS
capillary column are 8.470, 7.979, 8.049, and
7.432 min, respectively. 2,4,6-TCP acetate elutes first,
and then 2,3,5-TCP acetate elutes. The retention time
of 2,3,4-TCP acetate is the longest. HP-35MS column
is a medium polar column, and thus the retention
times of these TCP acetates are related to their polari-
ties. The strong polarities of the target compounds
result in the effective interaction between the station-
ary phase and the target compounds. Hence, 2,3,4-
TCP acetate with the strongest polarity displays the
longest retention time. The sequence of the retention
times for these TCP acetates is in good agreement with
other experimental results [27].
Theoretical Method
The binding energy of the complex is defined as the
difference of the energies between the complex and the
two separated monomers. Dimethyl polysiloxane sta-
tionary phases are non-polar, and the polarities of the
stationary phases are increased with the increase in the
proportion of diphenyl polysiloxanes. On one hand,
the same target compound can be separated by differ-
ent stationary phases in order to choose an appropriate
column. On the other hand, different target com-
pounds can be separated by the same stationary
phase so as to obtain the sequence of retention times.
Herein, the stationary phases were defined as hosts,
and the target compounds were defined as guests.
Complexes 1–6 were designed in the 1 : 1 proportion
by hosts 1–6 (Fig. 1) with aniline. Complexes 7–12
were formed by host 3 with 2,3,4-TCP, 2,3,5-TCP,
2,3,6-TCP, 2,4,5-TCP, 2,4,6-TCP, and 3,4,5-TCP
acetates, respectively. The stationary phase of the HP-
35MS column is a polymer which consists of 65%
polydimethylsiloxane and 35% polydiphenylsiloxane.
Host 3 is an oligomer which comprises two dimethyl-
siloxanes and one diphenylsiloxane. Hence, host 3
includes the components similar to HP-35MS. In the
initial geometries of the complexes, one of the hydro-
gen atoms on the amino group in aniline or on the
methyl group in trichlorophenol acetates was inserted
near the oxygen atom located at the end of the Si–O
chain in the hosts.
Binding Energies of Complexes
The stabilities of the complexes depend on the
number and strength of the hydrogen bonds. The opti-
mized lengths of the Si–O bond except the end Si–O
bond in host 3 are located in the range of 0.165–
0.166 nm, which is close to the calculation value
0.166 nm [6]. In complex 1, the lengths of the two
hydrogen bonds are 0.206 and 0.292 nm. In complex
2, the lengths of the three hydrogen bonds are 0.207,
0.294, and 0.297 nm. Complex 2 owns more hydrogen
bonds than complex 1, thus the binding energy of
complex 2 is higher than that of complex 1 (Table 1).
Although complex 3 possesses the same number of
Full geometry optimization of complexes 1–12 hydrogen bonds to complex 2, the powerful hydrogen
without any symmetry restriction was performed using bond with the length of 0.205 nm (Fig. 2) leads to the
AM1 method. Further optimization of these com- high binding energy of complex 3. The lengths of the
plexes was carried out utilizing Becke three parameters three hydrogen bonds in complex 4 are 0.206, 0.299,
plus Lee, Yang and Parr’s (B3LYP) method [11] with and 0.287 nm. The first two lengths of the hydrogen
6-31G(d) basis set in density function theory (DFT). bonds in complexes 3 and 4 are almost the same, but
Then the binding energies of the complexes were cal- the powerful hydrogen bond with the length of
culated at B3LYP/6-31G(d, p) level after BSSE. These 0.287 nm of complex 4 leads to the high binding
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HAIQI ZHANG et al.
Table 1. The optimized parameters of complexes 1–12 at the B3LYP/6-31G(d, p) level
Parameter
1
2
3
4
5
6
7
8
9
10
11
12
–ΔE, eV
0.234 0.235 0.244 0.265 0.222 0.233 0.229 0.206 0.171 0.209 0.170
0.157
–EHOMO, eV
5.136 5.123 5.042 5.131 5.056 5.048 6.811 6.696 6.625 6.747 6.643 6.830
1.107 1.011
5.569 4.465 4.388 4.636 4.526 4.423 5.910 5.472 5.583 5.579 5.536 5.819
8.824 8.814 8.883 8.670 8.589 8.546 8.822 8.880 8.759 8.821 8.637
–ELUMO, eV –0.433 0.658 0.654 0.495 0.530 0.625 0.902 1.223 1.042 1.167
Eg, eV
–NICS*
* NICS values were calculated at B3LYP/6-31G(d) level.
energy. Complex 5 only includes two hydrogen bonds
with the lengths of 0.206 and 0.294 nm; therefore, the
binding energy of complex 5 is lower than that of com-
plex 4. In complex 6, the lengths of the two hydrogen
bonds are 0.206 and 0.293 nm; hence the binding
energy of complex 6 is a little higher than that of com-
plex 5.
Energy Gaps
The kinetic stabilities of complexes are affected by
the LUMO–HOMO energy gaps. The energy gaps of
hosts 1–6 are 9.106, 6.136, 6.131, 6.108, 6.161, and
6.134 eV, respectively. The energy gaps of complexes 1–6
are all narrower than those of the corresponding hosts,
thus the reactivities of complexes 1–6 are higher than
those of the hosts. The interactions between the hosts
and guest molecules lead to the overlap of the electron
cloud and the decrease in the energy gaps of the com-
plexes, which is supported by the [14]. Complexes 2–
5 possess the narrow energy gaps compared to com-
plex 1 since the presence of the two phenyl rings leads
to the extension of the conjugation system. The energy
gaps of complexes 1–3 and those of complexes 4–6
are respectively decreased with the increase in the Si–
O chain length. But the energy gaps of complexes 4–6
are wide due to the steric effect of the Si–O chain,
compared to those of complexes 1–3.
The binding energies of complexes 1–4 are
increased as the length of the Si–O chain increases,
which provides more possibilities for the formation of
the hydrogen bonds. However, the hosts in complexes 5
and 6 become huge, which occupy much space and
result in steric effects. Also, these hosts contain more
methyl groups on the Si–O chain rather than the phe-
nyl groups, which leads to the decrease in the polarity
of the oligomers. All of the above factors have adverse
effects on the formation of the hydrogen bonds.
Thereby, the moderate chain length and the appropri-
ate ratio between the phenyl and methyl groups are all
important to the binding energies of the complexes.
The energy gap of complex 3 is narrower than that
of complex 7. The guest molecule aniline in complex 3
has little steric effect, which is favorable to the forma-
tion of the hydrogen bonds. The energy gaps of com-
plexes 7 and 12 are wider than those of complexes 8–
11. In complexes 7 and 12, the three adjacent chlorine
Complexes 3 and 7 possess the same host. The
binding energy of complex 7 is lower than that of com-
plex 3. In complex 7, the bulky 2,3,4-TCP acetate
shows a strong steric effect, which reduces the strength
of the hydrogen bonds. In complexes 7–12, complex 7
has the highest binding energy, which results from the
four hydrogen bonds (Fig. 2). Complex 8 owns the two
hydrogen bonds with the lengths of 0.216 and
0.245 nm. Complex 10 has the two hydrogen bonds
with the lengths of 0.205 and 0.244 nm. Owing to the
strong hydrogen bonds, the binding energy of com-
plex 10 is higher than that of complex 8. The lengths of
hydrogen bonds in complexes 9 and 11 are 0.272,
0.279, and 0.239 nm as well as 0.278, 0.273, and
0.239 nm, respectively. Therefore, the binding ener-
gies of these two complexes are close. Complex 12
owns the two hydrogen bonds with the lengths of 0.296
and 0.239 nm. There are no advantages either in the
number or in the strength of the hydrogen bonds com-
pared to the other complexes. Thus, complex 12 has
the lowest binding energy. The binding energies of
complexes 7, 10, 8, and 11 are decreased in sequence,
which is compatible with the decrease in the experi-
mental retention time of the four TCP acetates in this
thesis and in the [26].
(a)
(b)
4
3
1
3
2
1
2
1 0.205
2 0.297
3 0.296
1 0.276
2 0.247
3 0.238
4 0.285
Fig. 2. The B3LYP/6-31G(d) optimized geometries of
complexes 3 (a) and 7 (b).
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BINDING AFFINITIES AND SPECTROSCOPY
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Complex 2
Complex 3
Complex 4
9.6
200.4 11.8
201.4 10.2
201.5
200.6
Complex 7
Complex 8
Complex 9
11.2
196.3 10.5
200.6 10.1
Complex 10
Complex 11
Complex 12
11.2
203.7 9.8
199.3 8.4
198.1
0
50 100 150 200 0
50 100 150 200 0
50 100 150 200
δ, ppm
13
Fig. 3. The C NMR spectra of some complexes at B3LYP/6-31G(d) level.
atoms on the phenyl ring in the guest molecules may
reduce the electron cloud on the phenyl ring.
Aromaticities
The NICS value is the negative value of the abso-
lute magnetic shielding effect calculated at the center
in an aromatic system, and rings with negative NICS
values are qualified as aromaticity. The calculated
NICS value at the center of benzene is –9.7 ppm,
which agrees with –8.0 ppm [28]. The NICS values at
the same benzene ring center in complexes 1–12
(Table 1) are higher than –9.7 ppm, thus the aroma-
ticities of the benzene rings in complexes 1–12 are
weakened. The electron density on benzene is delocal-
ized, and thus the magnetic shielding effect is reduced
in the presence of the Si–O chain. The NICS value
‒7.4 ppm of mono-substituted benzene using SiH3 is
higher than –8.0 ppm of benzene, which supports our
results [28].
13C NMR Spectra
The electron clouds on the carbon atoms are
changed upon the formation of the hydrogen bonds,
which can be shown in the NMR spectra. The number
of the absorptions in the NMR spectra of complexes 1–
6 is less than that of the absorptions in the NMR spec-
tra of complexes 7–12 (Fig. 3) since there is only one
substituent on the phenyl ring in the guest molecules
of complexes 1–6. The δ signal of the α-C atom which
is connected to the NH2 group in pristine aniline
appears at 157.4 ppm. The δ signals of the α-C atoms
in complexes 1–6 are located within the range of
159.3–161.2 ppm, which are changed downfield com-
pared with the value 157.4 ppm. Upon the formation
of the hydrogen bonds, the strong electronegativity of
the oxygen atom at the end of the Si–O chain leads to
the decrease in the electron density on the NH2 group
and the adjacent α-C atom. Besides, the δ signals of
the α-C atoms in complexes 1, 2, 3, and 4 are located
at 160.0, 160.1, 160.3, and 161.2 ppm, which are grad-
ually changed downfield as the Si–O chain increases.
The NICS values at the benzene ring center in
complexes 4, 5, and 6 are increased with the increase
in the length of the Si–O chain. Thus the aromaticities
of the benzene rings in these complexes are gradually
depressed. Basically, the aromaticities of the benzene
rings are decreased with the decrease in the energy
gaps of the complexes. Thereby, the aromaticities of
the benzene rings affect the kinetic stabilities of the
complexes, which is supported by the conclusion in
The δ signals of the α-C atoms which are linked to the literature [23]. The NICS values at the benzene
the ester groups in complexes 7–12 except complex 11 ring center of complexes 7, 10, and 12 are increased
are changed upfield compared with those of the guest compared with –8.819 ppm of host 3, and thus the
molecules. The oxygen atoms in the ester groups dis- aromaticities of benzene in complexes 7, 10, and 12
play the strong electro-withdrawing effects, which are weakened. The electron density on benzene is
increases the electron density and shielding effect on reduced owing to the formation of the hydrogen
these C atoms.
bonds.
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2722
HAIQI ZHANG et al.
11. A. D. Becke, J. Chem. Phys. 98, 5648 (1993).
CONCLUSIONS
12. Gaussian 03, Rev. B01 (Gaussian Inc., Pittsburgh, PA,
In summary, the binding energies of the complexes
formed by polysiloxanes with aniline and chlorophe-
nol acetates are increased with the increase in the
number and strength of the hydrogen bonds. The
chemical shifts of the α-C atoms which are linked to
the ester groups in the complexes compared with those
of the α-C atoms in the guest molecules are changed
upfield due to the formation of the hydrogen bonds.
The aromaticities of the benzene rings in the complexes
in comparison with the aromaticity of a single benzene
ring are weakened owing to the presence of the substit-
uents. Polysiloxanes show the excellent binding affini-
ties to aniline and chlorophenol acetates, and thus they
are promising stationary phases in GC.
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