PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION
Mesoporous silicas of MCM‑41 type with surface silanol, 3-aminopropyl, and β‑cyclodextrin‑containing groups were prepared by hydrothermal‑assisted base‑catalyzed sol‑gel condensation of structure-forming silanes in the presence of micelles of long‑chain quaternary ammonium salt. Characterization of...
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V.I.Vernadsky Institute of General and Inorganic Chemistry
2023
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Репозитарії
Ukrainian Chemistry Journal| _version_ | 1871465897794732032 |
|---|---|
| author | Roik, Nadiia Belyakova, Liudmyla |
| author_facet | Roik, Nadiia Belyakova, Liudmyla |
| author_institution_txt_mv | [
{
"author": "Nadiia Roik",
"institution": "Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine"
},
{
"author": "Liudmyla Belyakova",
"institution": "Chuiko Institute of Surface Chemistry of NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine"
}
] |
| author_sort | Roik, Nadiia |
| baseUrl_str | https://ucj.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-07-22T08:23:51Z |
| description | Mesoporous silicas of MCM‑41 type with surface silanol, 3-aminopropyl, and β‑cyclodextrin‑containing groups were prepared by hydrothermal‑assisted base‑catalyzed sol‑gel condensation of structure-forming silanes in the presence of micelles of long‑chain quaternary ammonium salt. Characterization of synthesized silica materials was realized by low‑temperature nitrogen adsorption‑desorption and chemical analysis of surface layer. It was found that addition of ‑cyclodextrin‑containing silane into the sol‑gel reaction mixture causes formation of MCM‑41‑type organosilica with higher surface area and hexagonally arranged uniform mesoporous structure. Sorption ability of synthesized silica materials towards sodium cholate and sodium taurocholate was studied in dependence of solution pH and concentration. It was found that sorption increases due to chemical immobilization of oligosaccharide moieties in the surface layer of silica, and achieves maximal values in the pH regions of molecular forms of bile acids prevailing. Experimental sorption results were analyzed using Freundlich, Redlich - Peterson, and Brunauer - Emmett - Teller models. The formation of island-type structures of bile salts with β‑cyclodextrin-containing surface sorption centers due to cooperative interactions between sorbate moieties was proved. |
| doi_str_mv | 10.33609/2708-129X.89.01.2023.18-33 |
| first_indexed | 2025-09-24T17:43:48Z |
| format | Article |
| fulltext |
18 ISSN 2708-129X. Укр. хім. журн., 2023
UDC 544.7 doi: 10.33609/2708-129X.89.01.2023.18-33
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY
IMMOBILIZED β‑CYCLODEXTRIN MOIETIES
FOR BILE SALTS SORPTION
N.V. Roik*, L.O. Belyakova
Chuiko Institute of Surface Chemistry of NAS of Ukraine,
17 General Naumov Str., Kyiv 03164, Ukraine
* E-mail: roik_nadya@ukr.net
Mesoporous silicas of MCM‑41 type with surface silanol, 3-aminopropyl, and β‑cyclo
dextrin‑containing groups were prepared by hydrothermal‑assisted base‑catalyzed sol‑gel
condensation of structure-forming silanes in the presence of micelles of long‑chain quaternary
ammonium salt. Characterization of synthesized silica materials was realized by low‑tempe
rature nitrogen adsorption‑desorption and chemical analysis of surface layer. It was found
that addition of β‑cyclodextrin‑containing silane into the sol‑gel reaction mixture causes
formation of MCM‑41‑type organosilica with higher surface area and hexagonally arranged
uniform mesoporous structure. Sorption ability of synthesized silica materials towards sodi‑
um cholate and sodium taurocholate was studied in dependence of solution pH and concen‑
tration. It was found that sorption increases due to chemical immobilization of oligosaccha‑
ride moieties in the surface layer of silica, and achieves maximal values in the pH regions of
molecular forms of bile acids prevailing. Experimental sorption results were analyzed using
Freundlich, Redlich − Peterson, and Brunauer − Emmett − Teller models. The formation of
island-type structures of bile salts with β‑cyclodextrin-containing surface sorption centers
due to cooperative interactions between sorbate moieties was proved.
Keywords: sol-gel synthesis; MCM‑41; chemical modification; β‑cyclodextrin; bile salts
sorption.
INTRODUCTION. Bile acids (BAs) are
steroid substances with four rings, a five- or
eight-carbon side chains terminated with car‑
boxylic group, and hydroxylic groups, whose
position and number varies among the acids.
The primary BAs (cholic (CA) and chenode‑
oxycholic) are synthesized from cholesterol in
the liver, secreted along with their conjugated
glycine or taurine forms into the bile, concen‑
trated in the gallbladder, and released into the
upper intestine. Primary BAs are converted to
the secondary ones (deoxycholic, lithocholic,
and ursodeoxycholic) at bacterial actions in
the colon. BAs play the important role as bio‑
logical surfactants for dietary fats and oils solu
bilization. They transport in the small bowel
19https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
and undergo almost complete reabsorption in
the distal ileum with subsequent reuptake from
portal blood by the liver [1]. But, the effect of
BAs is not restricted by gastrointestinal tract
and can involve different tissues throughout
the organism. Along with the ability to partici‑
pate in lipids digestion due to the reduction of
the interfacial tension, BAs can serve as signa‑
ling molecules influencing metabolic process‑
es [1]. Enterohepatic circulation of BAs affects
cholesterol metabolism and plays crucial role
in pathogenesis of atherosclerosis. Therefore,
development of strategies for precise control
of BAs content and cholesterol excretion in the
form of neutral sterols or BAs has noticeable
importance in treatment of hypercholestero
lemia.
Despite of many efforts made in the past
decades to improve accuracy and sensitivity
of analysis methods or enhance the efficiency
of BAs content regulation, design of sorption,
separation and detection approaches is still of
current interest. Low content of BAs, which
varies from micromolar in serum and urine to
millimolar in gallbladder bile, and noticeably
different physicochemical properties compli‑
cate their separation and detection.
Among variety of materials used in BAs
sorption silica belongs to the most promising
one because of its attractive properties such as
large surface area and pore volume, easy surface
functionalization, possibility of regeneration.
Along with hydroxylated silica gel [2, 3], iden‑
tification and separation of steroid substances,
in particular cholesterol and bile acids, can be
realized using impregnated [2, 4] and chemi
cally modified silicas [5, 6]. Combination of
contribution from hydrophobic interactions
arising between steroid skeleton of BAs and
hydrophobic areas of sorbent with geometric
complementarity of sorbate and sorption sites
on silica surface can be considered as the most
suitable approach for creation of highly effec‑
tive sorbents. Silica surface can gain the ability
to recognize steroid substances selectively after
chemical immobilization of cyclodextrin (CD)
macromolecules. Cyclodextrins (CDs) are cy‑
clic oligosaccharides consisting of D-(+)-glu‑
copyranose units bounded together by α(1→4)
linkages. Due to the hydrophilic outer surface
and hydrophobic central cavity CDs are able to
form water-soluble inclusion complexes with
many lipophilic compounds, including cho‑
lesterol and BAs, via host-guest interactions.
The stability of supramolecular complexes is
highly influenced by the polarity of the guest
compound and its steric complementarity with
CD cavity. It was proved that CDs retain their
ability for binding of steroid substances after
chemical immobilization into surface layer of
silica carrier [7, 8].
In the present work, mesoporous silica na‑
noparticles (MSNs) of MCM‑41 type with sur‑
face β‑CD‑containing groups were prepared by
base‑catalyzed sol‑gel condensation of struc‑
ture‑forming silanes in the presence of cetyl‑
trimethylammonium bromide (CTAB) as tem‑
plate. To identify the pH region most suitable
for selective recognition of bile salts (BSs) and
elucidate the contribution of β‑CD‑containing
sites in sorption efficiency of synthesized mate‑
rials in the conditions of gastrointestinal tract,
sorption of sodium cholate (NaC) and sodium
taurocholate (NaTC) was studied in depen
dence of pH value and sorbate concentration.
EXPERIMENT AND DISCUSSIONS OF
THE RESULTS. Materials. Tetraethyl orthosili‑
cate (TEOS) (Merck, purity ≥ 99 %), 3‑amino‑
propyltriethoxysilane (APTES) (Merck, puri‑
ty ≥ 99 %), cetyltrimethylammonium bromide
20 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
(Merck, purity ≥ 97 %), 1,1'‑carbonyldiimi‑
dazole (CDI) (Merck, purity ≥ 98 %), sodium
cholate (Frontier Scientific, purity ≥ 98 %),
sodium taurocholate (Frontier Scientific, puri‑
ty ≥ 98 %), aqueous ammonia 25 % (Reakhim,
analytical grade), ethanol 96 % (Reakhim,
chemical grade), hydrochloric acid 37 % (Re
akhim, chemical grade), phosphoric acid 85 %
(Reakhim, analytical grade), sulfuric acid 98 %
(Reakhim, chemical grade), disubstituted so‑
dium phosphate (Reakhim, analytical grade),
and monosubstituted potassium phosphate
(Reakhim, analytical grade), sodium car‑
bonate (Reakhim, analytical grade), sodium
hydroxide (Reakhim, analytical grade), potas‑
sium ferricyanide (Reakhim, analytical grade),
glucose (Reakhim, analytical grade) were
employed without preliminary purification.
β‑Cyclodextrin (Fluka, purity ≥ 99 %) was
used after drying in an oven at 373 K for 2 h.
N,N′‑dimethylformamide (DMF) (Reakhim,
analytical grade) was dried by activated NaA
molecular sieves for 24 h.
Sol‑gel synthesis of mesoporous silica mate
rials. The high‑quality mesoporous silicas of
MCM‑41 type were prepared by hydrother‑
mal‑assisted base‑catalyzed sol‑gel conden‑
sation of structure‑forming silanes in the
presence of micelles of long‑chain quaternary
ammonium salt as structure directing agents.
Molar compositions of the initial gel reaction
mixtures at synthesis of silica materials are rep‑
resented in Table 1.
Table 1.
Molar compositions of reaction mixtures at synthesis of silica materials.
Silica Molar composition of reaction mixture
MSN‑C16 0.1 TEOS : 0.02 CTAB : 0.54 NH4OH : 0.56 C2H5OH : 14.4 H2O
NH2‑MSN‑C16 0.096 TEOS : 0.004 APTES : 0.012 CTAB : 0.54 NH4OH : 14.4 H2O
CD‑NH2‑MSN‑C16 0.098 TEOS : 0.002 β‑CD‑silane : 0.012 CTAB : 0.54 NH4OH : 14.4 H2O
MSNs with surface silanol and 3-amino‑
propyl groups were synthesized using CTAB
as pore‑forming agent (Table 1). For this, the
batch of CTAB was placed into a conical ves‑
sel and dissolved in mixture of deionized water
and ethanol. After that, 25 % aqueous ammo‑
nium solution was poured into the reaction
vessel and TEOS or its mixture with APTES
was slowly added during 15 min under vigo
rous stirring. The resultant reaction slurry was
stirred at 293 K for 2 h, then transferred into a
polypropylene bottle and aged at 373 K with‑
out stirring for 24 h. After hydrothermal treat‑
ment synthesized MSN‑C16 and NH2‑MSN‑C16
silicas were filtered, washed with deionized
water and dried in air at 373 K for 2 h.
Silica material of MCM‑41‑type with chemi
cally immobilized β‑CD‑containing moieties
was synthesized according to the described ear‑
lier procedures using β‑CD‑silane along with
TEOS as silica source (Table 1). For β‑CD‑si‑
lane synthesis, the batch of β‑CD was dissolved
in minimal volume of DMF and treated with
equimolar quantity of CDI (taken with 5% ex‑
cess) dissolved in DMF at 293 K for 2 h. Then,
equimolar quantity of APTES was added into
the reaction flask at continuous stirring to link
with activated oligosaccharide. The solution
21https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
was stirred at 293 K for 20 h and used for sol-
gel synthesis of CD‑NH2‑MSN‑C16 silica.
Removal of long‑chain quaternary ammo‑
nium salt from the pore volume of mesoporous
silicas was realized by extraction in acid‑etha‑
nol medium. Briefly, the batch of the as‑syn‑
thesized material (1 g) was stirred with a solu‑
tion of hydrochloric acid (8 ml) and ethanol
(92 ml) at 293 K for 24 h. After separation of
silica particles from solution by filtration the
extraction procedure was repeated two more
times. The resulting mesoporous silica was fil‑
tered, washed with deionized water until the
absence of halogen ions in filtrate (negative
probe with silver nitrate), and dried in the air
at 373 K for 5 h.
Characterization of mesoporous silica ma-
terials. Nitrogen adsorption‑desorption iso‑
therms were measured at 77 K with a Kel‑
vin‑1042 Sorptometer. Prior to the analysis,
silica materials were outgassed under vacuum
at 413 K for 20 h. The values of Brunauer − Em‑
mett − Teller (BET) specific surface area were
calculated using adsorption data registered in
the region of relative pressures from 0.06 to
0.99 in increment of 0.015. The pore size dis‑
tribution curves were obtained from analysis
of the adsorption branch of the isotherms by
density functional theory (DFT) algorithm.
The total pore volumes of synthesized MSNs
were determined from the amount of adsorbed
nitrogen at a relative pressure of about 0.99.
The content of surface 3‑aminopropyl groups
was determined from the results of the poten
tiometric titration with 0.01 M HCl. Briefly, the
batch of mesoporous organosilica (0.5 g) was
placed into a volumetric flask and poured with
0.01 M HCl (25 ml). The resulting suspension
was stirred at 294 K for 24 h to attain equilib‑
rium. рН of starting and equilibrium solutions
were measured by an Ionometer I−120.1. The
content of 3‑aminopropyl groups chemically
immobilized on silica surface was calculated
by the equation:
1 2
2
10 10pH pH
NH
( ) VC
m
− −− ⋅
= , (1)
where
1 2
2
10 10pH pH
NH
( ) VC
m
− −− ⋅
=is the content of 3‑aminopropyl
groups of silica, mol⋅g−1; pH1 and pH2 are the
рН of starting and equilibrium solutions, cor‑
respondingly; V is the volume of solution, l;
m is the batch of silica, g.
The content of β‑CD moieties introduced
into the MSNs at the process of sol‑gel synthe‑
sis was estimated by acid hydrolysis of surface
β‑CD‑containing groups to glucose. For this,
the batch of silica (0.1 g) was refluxed with
1 M H2SO4 (15 ml) at 373 K for 2 h. Then, the
solution was neutralized with 5 M NaOH up
to pH 7, filtered, and diluted up to 50 ml with
water. Aliquot of this solution (2 ml) was held
in the boiling flask with of 0.05 % K3Fe(CN)6
(25 ml) dissolved in 1 % Na2CO3 water solution
at 373 K for 10 min. On cooling concentra‑
tion of glucose was determined as its coloured
complex with potassium ferricyanide from the
value of optical density of the absorption band
at λ = 420 nm. The glucose calibration curve
was plotted over the range 0−0.888 mmol⋅l−1.
Content of grafted β‑CD was calculated by the
equation:
[β‑CD] =
7
C V
m
⋅
⋅
, (2)
where [β‑CD] is the content of β‑CD on the
silica surface, mmol⋅g−1; C is the concen‑
tration of glucose in the solution, mmol⋅l−1;
V is the volume of solution, l; m is the batch of
β‑CD‑containing silica, g.
Sorption studies. UV‑Vis spectra of BSs
in phosphate buffer solutions (PBSs) were
22 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
recorded in 200−600 nm spectral range with
a Specord M‑40 using quarts cells with 5 mm
path length. All spectroscopic measurements
were made with temperature‑controlled cell
holder and water bath. рН of solutions were
measured by an Ionometer I−120.1 that was
calibrated for optimal precision using standard
buffer solutions.
Sorption of BSs on synthesized mesoporous
silica materials in dependence of pH was car‑
ried out from 0.18 mmol⋅l−1 solutions in PBS.
Briefly, batches of silicas (0.02 g) were placed
in 50 ml glass beakers and solutions of BSs in
PBSs (10 ml) with predetermined pH in the
range from 1.0 to 8.0 were added. Prepared
suspensions were shaken at 297 K for equilib‑
rium attainment. Supernatant solutions were
separated by filtering through a 0.22 μm PVDF
syringe filter, treated with concentrated sulfu‑
ric acid to obtain coloured complex [9] and
analyzed at λ = 389 nm. The amount of NaC
or NaTC sorbed on silica surface was calculat‑
ed using calibration curves plotted for each pH
value by the equation:
o eq
BET
( C C ) V
A
m S
− ⋅
=
⋅
, (3)
where A is the content of BS sorbed on silica
surface at equilibrium, mmol⋅m−2; Co and Ceq
are the concentrations of BS at initial moment
and at equilibrium, correspondingly, mmol⋅l−1;
V is the volume of solution, l; m is the batch of
silica, g; SBET is the specific surface area of silica,
m2·g−1.
Equilibrium sorption of BSs on synthesized
MSNs was studied from 0.06−0.3 mmol⋅l−1
solutions with pH 5.0 and 7.4 as described
above for sorption in dependence of pH.
Sorbents characterization. Low-temperature
nitrogen adsorption-desorption isotherm of
MSN‑C16 silica is represented in Figure 1. The
profile of MSN‑C16 isotherm belongs to the
type IV with hysteresis loop of the type H4 as
defined by IUPAC classification (Fig. 1). Ac‑
cording to the pore size distribution plot cal‑
culated by the DFT model, formation of silica
framework with two prevailing pore diameters
takes place (Fig. 2, Table 2).
Fig. 1. Isotherms of low‑temperature nitrogen adsorption-desorption on MSN‑C16 (a), NH2‑MSN‑C16
(b), and CD‑NH2‑MSN‑C16 (c).
[-CD] =
m
VС
7
, (2)
where [-CD] is the content of -CD on the silica surface, mmolg1; C is the concentration of
glucose in the solution, mmoll1; V is the volume of solution, l; m is the batch of -CD-containing
silica, g.
Sorption studies. UV-Vis spectra of BSs in phosphate buffer solutions (PBSs) were recorded in
200600 nm spectral range with a Specord M-40 using quarts cells with 5 mm path length. All
spectroscopic measurements were made with temperature-controlled cell holder and water bath. рН
of solutions were measured by an Ionometer I120.1 that was calibrated for optimal precision using
standard buffer solutions.
Sorption of BSs on synthesized mesoporous silica materials in dependence of pH was
carried out from 0.18 mmoll1 solutions in PBS. Briefly, batches of silicas (0.02 g) were placed in
50 ml glass beakers and solutions of BSs in PBSs (10 ml) with predetermined pH in the range from
1.0 to 8.0 were added. Prepared suspensions were shaken at 297 K for equilibrium attainment.
Supernatant solutions were separated by filtering through a 0.22 μm PVDF syringe filter, treated
with concentrated sulfuric acid to obtain coloured complex [9] and analyzed at = 389 nm. The
amount of NaC or NaTC sorbed on silica surface was calculated using calibration curves plotted for
each pH value by the equation:
BET
o )(
Sm
VCC
A eq
, (3)
where A is the content of BS sorbed on silica surface at equilibrium, mmolm2; Co and Ceq are the
concentrations of BS at initial moment and at equilibrium, correspondingly, mmoll1; V is the
volume of solution, l; m is the batch of silica, g; SBET is the specific surface area of silica, m2·g1.
Equilibrium sorption of BSs on synthesized MSNs was studied from 0.060.3 mmoll1
solutions with pH 5.0 and 7.4 as described above for sorption in dependence of pH.
Sorbents characterization. Low-temperature nitrogen adsorption-desorption isotherm of MSN-C16
silica is represented in Figure 1. The profile of MSN-C16 isotherm belongs to the type IV with
hysteresis loop of the type H4 as defined by IUPAC classification (Fig. 1). According to the pore
size distribution plot calculated by the DFT model, formation of silica framework with two
prevailing pore diameters takes place (Fig. 2, Table 2).
0.0 0.2 0.4 0.6 0.8 1.0
0
100
200
300
400
500
600
V
(c
m
3 g
1
)
p/ps
0.0 0.2 0.4 0.6 0.8 1.0
0
100
200
300
400
500
600
V
(c
m
3 g
1
)
p/ps
0.0 0.2 0.4 0.6 0.8 1.0
0
100
200
300
400
500
600
700
p/ps
V
(c
m
3 g
1
)
a b c
Fig. 1. Isotherms of low-temperature nitrogen adsorption-desorption on MSN-C16 (a), NH2-MSN-C16 (b),
23https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
Addition of APTES in sol‑gel reaction mix‑
ture has noticeable influence on structural pa‑
rameters of resulting NH2‑MSN‑C16 material.
Transformation of isotherm into the type IV
with hysteresis loop of the type H3 is observed.
As can be seen from the pore size distribu‑
tion curve, mesopore diameter controlled by
CTAB template is prevailing (Figs. 2, Table 2).
It should be mentioned that increase of meso‑
pores size is observed (Table 2). Obviously, po‑
rous structure of synthesized material is prede‑
termined not only by the long‑chain alkyltri‑
methyl ammonium salt as structure directing
agent but in the great extent by the presence of
functional silane, which functionalities inter‑
act with template and participate in condensa‑
tion process.
Introduction of β‑CD‑silane, obtained by
coupling of oligosaccharide with equimolar
quantity of APTES, in reaction mixture of sol‑gel
synthesis causes formation of CD‑NH2‑MSN‑C16
material with higher surface area in compari‑
son with NH2‑MSN‑C16 (Table 2). Moreover,
it should be mentioned, that the profiles of
low‑temperature nitrogen adsorption‑desorp‑
tion isotherm obtained for CD‑NH2‑MSN‑C16
is similar to that one for MSN‑C16 (Fig. 1).
Analysis of pore size distribution curve proves
that addition of β‑CD‑silane as structure‑form‑
ing agent in sol‑gel reaction mixture results in
organosilica with homogeneous mesoporosity
(Figs. 2, Table 2). Thus, β‑CD‑silane has posi‑
tive impact on structural characteristics of syn‑
thesized CD‑NH2‑MSN‑C16 material.
Fig. 2. Pore size distribution in MSN‑C16 (a), NH2‑MSN‑C16 (b), and CD‑NH2‑MSN‑C16 (c).
Table 2.
Structural characteristics of MCM‑41‑type silicas.
Silica
Low-temperature nitrogen
adsorption-desorption Chemical analysis of surface layer
SBET, m
2·g−1 V, cm3·g−1 D, nm [NH2] [β-CD]
mmol·g−1 μmol·m−2 mmol·g−1 μmol·m−2
MSN‑C16 995 0.75 1.27; 3.54 − − − −
NH2‑MSN‑C16 515 0.91 3.78 0.28 0.54 − −
CD‑NH2‑MSN‑C16 758 1.08 3.78 0.34 0.45 0.029 0.038
Addition of APTES in sol-gel reaction mixture has noticeable influence on structural
parameters of resulting NH2-MSN-C16 material. Transformation of isotherm into the type IV with
hysteresis loop of the type H3 is observed. As can be seen from the pore size distribution curve,
mesopore diameter controlled by CTAB template is prevailing (Figs. 2, Table 2). It should be
mentioned that increase of mesopores size is observed (Table 2). Obviously, porous structure of
synthesized material is predetermined not only by the long-chain alkyltrimethyl ammonium salt as
structure directing agent but in the great extent by the presence of functional silane, which
functionalities interact with template and participate in condensation process.
Introduction of -CD-silane, obtained by coupling of oligosaccharide with equimolar quantity
of APTES, in reaction mixture of sol-gel synthesis causes formation of CD-NH2-MSN-C16 material
with higher surface area in comparison with NH2-MSN-C16 (Table 2). Moreover, it should be
mentioned, that the profiles of low-temperature nitrogen adsorption-desorption isotherm obtained
for CD-NH2-MSN-C16 is similar to that one for MSN-C16 (Fig. 1). Analysis of pore size distribution
curve proves that addition of -CD-silane as structure-forming agent in sol-gel reaction mixture
results in organosilica with homogeneous mesoporosity (Figs. 2, Table 2). Thus, -CD-silane has
positive impact on structural characteristics of synthesized CD-NH2-MSN-C16 material.
1 10 100
0.0
0.1
0.2
0.3
0.4
0.5
dV
/d
D
(c
m
3 g
n
m
1
)
D (nm)
1 10 100
0.00
0.05
0.10
0.15
0.20
0.25
D (nm)
dV
/d
D
(c
m
3 g
n
m
1
)
1 10 100
0.0
0.2
0.4
0.6
0.8
1.0
D (nm)
dV
/d
D
(c
m
3 g
n
m
1
)
a b c
Fig. 2. Pore size distribution in MSN-C16 (a), NH2-MSN-C16 (b), and CD-NH2-MSN-C16 (c).
Table 2.
Structural characteristics of MCM-41-type silicas.
Silica
Low-temperature nitrogen
adsorption-desorption Chemical analysis of surface layer
SBET,
m2·g1 V, cm3·g1 D, nm [NH2] [-CD]
mmol·g1 μmol·m2 mmol·g1 μmol·m2
MSN-C16 995 0.75 1.27; 3.54
NH2-MSN-C16 515 0.91 3.78 0.28 0.54
CD-NH2-MSN-C16 758 1.08 3.78 0.34 0.45 0.029 0.038
Sorption of bile salts by mesoporous silica materials. The effect of the solution acidity on the
sorption of BSs by synthesized MSNs was studied in PBSs with predetermined pH in the range
from 1.0 to 8.0 (Fig. 3). It was found that sorption of NaC by MSNs with surface silanol and
3-aminopropyl groups is insufficient (Fig. 3).
and CD-NH2-MSN-C16 (c).
24 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
Sorption of bile salts by mesoporous silica ma-
terials. The effect of the solution acidity on the
sorption of BSs by synthesized MSNs was stu
died in PBSs with predetermined pH in the range
from 1.0 to 8.0 (Fig. 3). It was found that sorp‑
tion of NaC by MSNs with surface silanol and
3‑aminopropyl groups is insufficient (Fig. 3).
The profiles of NaTC sorption curves
on MSNs differ from that ones obtained for
NaC (Fig. 3). Slight decrease of MSN‑C16 and
NH2‑MSN‑C16 sorption is observed in acidic
medium. Obviously, this is related with the
difference in physico‑chemical characteristics
reflecting protolytic (acid ionization constant
Ka) and hydrophobic/hydrophilic properties
(critical micelle concentration CMC, oc‑
tanol‑water partition coefficient Po/w) of BSs
(Table 3).
Fig. 3. Effect of pH on NaC (a) and NaTC (b) sorption by MSN‑C16 (curve 1), NH2‑MSN‑C16 (curve 2),
and CD‑NH2‑MSN‑C16 (curve 3) from PBSs at 297 K.
Table 3.
Physico‑chemical parameters of bile acids.
Bile
acid Structure pKa [10] CMC,
mmol⋅l−1 [11]
log Po/w
(HBA) [12]
log Po/w
(BA−) [12]
CA
HO
H
OH
OH
O
OH
H
H
H
4.6 11−13 2.02 1.1
TCA
S
O
O
OHN
H
HO OH
O
OH
H
H
H
1.4 6−10 not
determinable −0.50
1 2 3 4 5 6 7 8
0.00
0.01
0.02
0.03
0.04
3
2
pH
A
(
m
ol
m
)
1
1 2 3 4 5 6 7 8
0.00
0.01
0.02
0.03
0.04
3
2
1
pH
A
(
m
ol
m
2
)
a b
Fig. 3. Effect of pH on NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2),
and CD-NH2-MSN-C16 (curve 3) from PBSs at 297 K.
The profiles of NaTC sorption curves on MSNs differ from that ones obtained for NaC (Fig. 3).
Slight decrease of MSN-C16 and NH2-MSN-C16 sorption is observed in acidic medium. Obviously,
this is related with the difference in physico-chemical characteristics reflecting protolytic (acid
ionization constant Ka) and hydrophobic/hydrophilic properties (critical micelle concentration
CMC, octanol-water partition coefficient Po/w) of BSs (Table 3).
Table 3.
Physico-chemical parameters of bile acids.
Bile acid Structure pKa [10] CMC, mmoll1
[11]
log Po/w
(HBA) [12]
log Po/w
(BA) [12]
CA
4.6 1113 2.02 1.1
TCA
1.4 610 not
determinable 0.50
Lower values of CMC and octanol-water partition coefficients for molecular and dissociated
species of conjugated TCA in comparison with unconjugated CA indicates its less pronounced
tendency to self-association and higher affinity to hydrophilic surface groups of sorbent. At the
same time, conjugation of CA with taurine reduces the pKa value and enhances solubility of product
in aqueous medium drastically. So, contrary to the CA, for which molecular protolytic form is
predominant below pH 4.6, negatively charged dissociated form of TCA is prevailing in all studied
pH range. Analysis of the effect of pH on BSs sorption in the context of protolytic properties of
sorbate and sorbent evidences that increase of NaC and NaTC sorption by MSN-C16 and
NH2-MSN-C16 is mainly associated with hydrogen bonds formation and electrostatic interactions
between non-ionized silanol (pKa = 6.9) and protonated 3-aminopropyl groups (pKa = 3.8) of silica
25https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
Lower values of CMC and octanol‑water
partition coefficients for molecular and disso‑
ciated species of conjugated TCA in compa
rison with unconjugated CA indicates its less
pronounced tendency to self‑association and
higher affinity to hydrophilic surface groups of
sorbent. At the same time, conjugation of CA
with taurine reduces the pKa value and enhanc‑
es solubility of product in aqueous medium
drastically. So, contrary to the CA, for which
molecular protolytic form is predominant be‑
low pH 4.6, negatively charged dissociated form
of TCA is prevailing in all studied pH range.
Analysis of the effect of pH on BSs sorption in
the context of protolytic properties of sorbate
and sorbent evidences that increase of NaC and
NaTC sorption by MSN‑C16 and NH2‑MSN‑C16
is mainly associated with hydrogen bonds for‑
mation and electrostatic interactions between
non‑ionized silanol (pKa = 6.9) and protonat‑
ed 3‑aminopropyl groups (pKa = 3.8) of silica
surface, correspondingly, and anionic forms of
BAs (Fig. 3). Further accumulation of bile acids
anions in solution and negatively charged
functional groups on silica surface at pH > 5
causes reduction in their sorption on MSN‑C16
and NH2‑MSN‑C16 as the result of electrostatic
repulsion arising between negatively charged
sorbate and silica surface (Fig. 3).
Chemical immobilization of β‑CD‑con‑
taining moieties in the surface layer of
MCM‑41‑type silica results in noticeable in‑
crease of BSs sorption on CD‑NH2‑MSN‑C16
in comparison with parent materials (Fig. 3). It
can be related with the formation of inclusion
complexes between surface β‑CD‑containing
groups and molecular or anionic forms of BSs
supplied from solution. As seen from Figure 3,
NaC and NaTC sorption on β‑CD‑containing
MSNs in dependence of solution pH differ no‑
ticeably. Contribution of surface supramolecu‑
lar complexes formation in total NaC sorption
on CD‑NH2‑MSN‑C16 is more pronounced in
acidic medium than in neutral one. Obvious‑
ly, cholate anions, which prevail in a solution
with pH exceeding pKa (Table 3), form weaker
surface inclusion complexes with β‑CD‑con‑
taining groups as theirs localization in the
β‑CD cavity is less favorable due to the lower
hydrophobicity in comparison with molecu‑
lar form of CA. Decrease of NaTC sorption on
CD‑NH2‑MSN‑C16 begins at much lower pH
values than for NaC (Fig. 3). Such differences
in pH‑dependent curves are due to the appear‑
ance and accumulation of taurocholate anions
in strongly acidic medium.
It should be pointed out that substantial
difference in sorption of NaC and NaTC by
β‑CD‑containing silicas, which is observed at
pH~2, gradually decreases with pH rise. So,
the ability of CD‑NH2‑MSN‑C16 silica for se‑
lective sorption of BSs can be considered only
in highly acidic medium and reduces signifi‑
cantly at pH values from 4 to 8 (Fig. 3). This
phenomenon can be clarified by comparison
of inclusion complexes formation on silica sur‑
face with that ones in a solution. Quantitative
estimation of “β‑CD−BS” inclusion complexes
stability in solutions by means of isothermal
calorimetric and spectroscopic titrations as
well as 1H-NMR and 13C‑NMR measurements
was realized by authors [13, 14]. The maximal
sorption efficiency of BSs by MSNs, which is
achieved in the pH range from 4 to 5 for NaC
and at pH 2 for NaTC, is predetermined by
their protolytic properties and formation of
stable supramolecular inclusion complexes.
Whereas, the absence of drastic difference
in sorption ability of β‑CD‑containing silica
material towards NaC and NaTC in neutral
26 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
medium is in a good agreement with the ex‑
perimental results obtained for inclusion com‑
plexes of BSs with β‑CD in PBS, according to
which the same order of stability constant val‑
ues was observed.
In the human small intestine, the pH level
varies from 4.0 to 8.3. The mean pH in the
proximal small intestine consists of 6.6, where‑
as in the terminal ileum it equals to 7.5. Al‑
though the highest values of BSs sorption were
achieved in weakly acidic and acidic medi‑
um for NaC and NaTC, correspondingly, the
sorption studies were performed at pH 5.0
(BAs are present in different protolytic forms)
and pH 7.4 (both BAs are fully dissociated),
to provide useful information for simulation
of BSs sorption in the gastrointestinal tract.
As seen from the experimental data ob‑
tained for BSs sorption on MSNs, isotherms
have different shape reflecting influence of
sorbate and sorbent nature and affinity arising
between them on sorption process (Figs. 4, 5).
Extremely low values of BSs sorption by
MSN‑C16 and NH2‑MSN‑C16 at concentra‑
tions up to 0.17 mmol⋅l−1 is indicative of weak
sorbate‑sorbent interactions at pH 5 and 7.4
(Fig. 4, 5). Increase of NaC and NaTC concen‑
trations results in gradual rise of isotherms.
This phenomenon may be caused by coope
rative interactions of BSs sorbed on silica
surface with that ones supplied from solution
(Figs. 4, 5).
Fig. 4. Isotherms of NaC (a) and NaTC (b) sorption by MSN‑C16 (curve 1), NH2‑MSN‑C16 (curve 2),
and CD‑NH2‑MSN‑C16 (curve 3) from PBSs with pH 5.0 at 297 K.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05 3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 4. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16 (curve 3) from PBSs with pH 5.0 at 297 K.
CD-NH2-MSN-C16 demonstrates enhanced affinity to sorbate at both studied pH values.
Complexity in structure of surface layer of CD-NH2-MSN-C16 in comparison with parent silica
materials causes substantial changes in the profiles of BSs sorption curves (Figs. 4, 5). Noticeable
enhancement of BSs sorption by MSNs with chemically immobilized oligosaccharide moieties
begins in the region of small concentrations of sorbate and acquires rapid growth above
0.2 mmoll1 (Figs. 4, 5). It can be attributed to the formation of inclusion complexes with
participation of surface β-CD-containing groups reinforced by cooperative interactions of sorbed
BSs with supplied from solution ones. Thus, even negatively charged cholate and taurocholate
anions, which prevail in solution at pH 7.4, participate in surface inclusion complexes formation
and make noticeable contribution to the total sorption on CD-NH2-MSN-C16. It should be noted that
NaC sorption on CD-NH2-MSN-C16 is slightly higher than that of NaTC. It can be explained by the
differences in BSs structure and physico-chemical properties (Table 3).
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
C (mmoll1)
A
(
m
ol
m
2
)
2
3
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Figure 5. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2),
and CD-NH2-MSN-C16 (curve 3) from PBSs with pH 7.4 at 297 K.
The experimental isotherms were analyzed using Freundlich, Redlich Peterson, and
Brunauer Emmett Teller (BET) equations. The Freundlich isotherm theory describes monolayer
sorption on heterogeneous surface with energetically non-equivalent sorption sites. Redlich
Peterson model can predict sorption either on heterogeneous or homogenous sites of silica surface
CD‑NH2‑MSN‑C16 demonstrates enhanced
affinity to sorbate at both studied pH values.
Complexity in structure of surface layer of
CD‑NH2‑MSN‑C16 in comparison with parent
silica materials causes substantial changes in
the profiles of BSs sorption curves (Figs. 4, 5).
Noticeable enhancement of BSs sorption by
MSNs with chemically immobilized oligosac‑
charide moieties begins in the region of small
concentrations of sorbate and acquires rapid
27https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
growth above 0.2 mmol⋅l−1 (Figs. 4, 5). It can
be attributed to the formation of inclusion
complexes with participation of surface β‑CD‑
containing groups reinforced by cooperative
interactions of sorbed BSs with supplied from
solution ones. Thus, even negatively charged
cholate and taurocholate anions, which pre‑
vail in solution at pH 7.4, participate in surface
inclusion complexes formation and make no‑
ticeable contribution to the total sorption on
CD‑NH2‑MSN‑C16. It should be noted that
NaC sorption on CD‑NH2‑MSN‑C16 is slightly
higher than that of NaTC. It can be explained
by the differences in BSs structure and physi‑
co‑chemical properties (Table 3).
Figure 5. Isotherms of NaC (a) and NaTC (b) sorption by MSN‑C16 (curve 1), NH2‑MSN‑C16 (curve 2),
and CD‑NH2‑MSN‑C16 (curve 3) from PBSs with pH 7.4 at 297 K.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05 3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 4. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16 (curve 3) from PBSs with pH 5.0 at 297 K.
CD-NH2-MSN-C16 demonstrates enhanced affinity to sorbate at both studied pH values.
Complexity in structure of surface layer of CD-NH2-MSN-C16 in comparison with parent silica
materials causes substantial changes in the profiles of BSs sorption curves (Figs. 4, 5). Noticeable
enhancement of BSs sorption by MSNs with chemically immobilized oligosaccharide moieties
begins in the region of small concentrations of sorbate and acquires rapid growth above
0.2 mmoll1 (Figs. 4, 5). It can be attributed to the formation of inclusion complexes with
participation of surface β-CD-containing groups reinforced by cooperative interactions of sorbed
BSs with supplied from solution ones. Thus, even negatively charged cholate and taurocholate
anions, which prevail in solution at pH 7.4, participate in surface inclusion complexes formation
and make noticeable contribution to the total sorption on CD-NH2-MSN-C16. It should be noted that
NaC sorption on CD-NH2-MSN-C16 is slightly higher than that of NaTC. It can be explained by the
differences in BSs structure and physico-chemical properties (Table 3).
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
C (mmoll1)
A
(
m
ol
m
2
)
2
3
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Figure 5. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2),
and CD-NH2-MSN-C16 (curve 3) from PBSs with pH 7.4 at 297 K.
The experimental isotherms were analyzed using Freundlich, Redlich Peterson, and
Brunauer Emmett Teller (BET) equations. The Freundlich isotherm theory describes monolayer
sorption on heterogeneous surface with energetically non-equivalent sorption sites. Redlich
Peterson model can predict sorption either on heterogeneous or homogenous sites of silica surface
The experimental isotherms were analyzed
using Freundlich, Redlich − Peterson, and Bru
nauer − Emmett − Teller (BET) equations. The
Freundlich isotherm theory describes mon‑
olayer sorption on heterogeneous surface with
energetically non‑equivalent sorption sites.
Redlich − Peterson model can predict sorption
either on heterogeneous or homogenous sites
of silica surface for which the mechanism of
sorption has hybrid character. The modified
BET isotherm equation for multilayer sorp‑
tion from liquid phase assumes that solvent is
weakly sorbed on silica surface.
To find out the isotherm model that can de‑
scribe experimental sorption isotherms in the
best way and give precise values of equilibri‑
um sorption parameters, analysis of the line‑
ar form of Freundlich equation or nonlinear
regression analysis of Redlich − Peterson and
BET equations was realized (Tables 4−7). Es‑
timated statistical error function, the correla‑
tion coefficient (R2), of linearized Freundlich
model is significantly lower compared to that
ones obtained at non-linear modeling of ex‑
perimental results with Redlich − Peterson and
BET equations.
28 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
Table 4.
Parameters of BSs sorption on MSNs at pH 5.0 (the Freundlich and Redlich − Peterson
models).
Equilibrium sorption model Freundlich Redlich − Peterson
Linear form of equation 1
eq F eqlg A lg K lg C
n
= + 1
R eq
eq
R eq
K C
A
a C β=
+
Sorption parameters KF n R2 KR aR β R2 χ2
NaC
MSN‑C16 0.035 0.876 0.915 0.036 0.002 4.6⋅10−13 0.719 11.136
NH2‑MSN‑C16 0.091 0.505 0.646 0.061 6.674⋅10−4 1⋅10−12 0.529 17.849
CD‑NH2‑MSN‑C16 0.055 2.112 0.811 0.167 3.9⋅10−17 0.01 0.862 19.312
NaTC
MSN‑C16 0.077 0.645 0.989 0.036 1.7⋅10−15 0.01 0.918 2.397
NH2‑MSN‑C16 0.166 0.751 0.943 0.130 0.191 1⋅10−16 0.790 0.790
CD‑NH2‑MSN‑C16 0.038 3.086 0.784 7.97⋅103 9.41⋅104 0.279 0.797 14.758
Aeq − amount of BS sorbed on silica surface, µmol⋅m−2; Ceq − concentration of BS in the solution after
equilibrium attainment, mmol/l; KF − the Freundlich constant that indicates the extent of surface heteroge‑
neity, 1⋅m−2; 1/n − measure of sorption intensity, which can be between 0 and 1; KR and aR − the Redlich −
Peterson isotherm constants, l⋅m−2 and l⋅mmol−1, correspondingly; β − exponent that lies between 0 and 1
Table 5.
Parameters of BSs sorption on MSNs at pH 7.4 (the Freundlich and Redlich − Peterson
models).
Equilibrium sorption model Freundlich Redlich − Peterson
Linear form of equation 1
eq F eqlg A lg K lg C
n
= + 1
R eq
eq
R eq
K C
A
a C β=
+
Sorption parameters KF n R2 KR aR β R2 χ2
NaC
MSN‑C16 0.055 0.777 0.835 0.046 0.124 1⋅10−14 0.810 6.866
NH2‑MSN‑C16 0.077 0.897 0.784 0.091 0.127 1⋅10−16 0.705 12.656
CD‑NH2‑MSN‑C16 0.054 1.762 0.953 3.32⋅103 4.244⋅104 0.234 0.929 4.069
NaTC
MSN‑C16 0.035 1.251 0.847 0.053 0.023 1⋅10−16 0.852 5.382
NH2‑MSN‑C16 0.077 1.212 0.941 0.110 4.021⋅10−6 4.1⋅10−9 0.914 2.684
CD‑NH2‑MSN‑C16 0.084 1.108 0.980 0.113 0.096 1⋅10−16 0.943 3.624
29https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
Table 6.
Parameters of BSs equilibrium sorption on MSNs at pH 5.0 (the Brunauer − Emmett −
Teller model).
Equilibrium sorption model Brunauer − Emmett − Teller
Equation 1 1
m S eq
eq
L eq L eq S eq
A K C
A
( K C )( K C K C )
=
− − +
Parameters KS KL Am R2 χ2
NaC
MSN‑C16 0.049 1.957 0.207 0.919 3.213
NH2‑MSN‑C16 0.089 3.787 0.016 0.999 0.003
CD‑NH2‑MSN‑C16 220.217 3.379 0.01 0.941 8.262
NaTC
MSN‑C16 0.028 1.110 0.708 0.967 0.974
NH2‑MSN‑C16 2.832 2.772 0.014 0.989 0.597
CD‑NH2‑MSN‑C16 2.923⋅106 2.898 0.01 1 3.228⋅10−4
KS − term for the energy of interaction with the surface, l⋅mmol−1; KL − equilibrium constant for sur‑
face sorption‑desorption, l⋅mmol−1.
Table 7.
Parameters of BSs sorption on MSNs at pH 7.4 (the Brunauer − Emmett − Teller model).
Equilibrium sorption model Brunauer − Emmett −Teller
Equation 1 1
m S eq
eq
L eq L eq S eq
A K C
A
( K C )( K C K C )
=
− − +
Parameters KS KL Am R2 χ2
NaC
MSN‑C16 0.021 1.816 0.638 0.939 2.214
NH2‑MSN‑C16 0.059 2.414 0.290 0.946 2.299
CD‑NH2‑MSN‑C16 120.785 2.721 0.009 0.988 0.662
NaTC
MSN‑C16 1.152⋅107 3.442 0.003 1 2.904⋅10−4
NH2‑MSN‑C16 82.704 3.360 0.007 0.988 0.368
CD‑NH2‑MSN‑C16 23.635 2.855 0.009 0.979 1.318
30 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
High R2 values obtained for Freundlich
model clearly indicates a pronounced hetero
geneous nature of BSs sorption on MSNs.
Whereas, close values of the correlation co‑
efficients estimated by Redlich‑Peterson and
BET models prove ambiguous nature of BSs
sorption on synthesized silica materials due
to the hydrogen bonds formation or electro‑
static interactions between different surface
functional groups of silica sorbents and BSs
as well as surface inclusion complexes forma‑
tion followed by stacking of sorbed moieties of
BSs and supplied from solution ones. In most
cases, the highest values of correlation coeffi‑
cients were obtained at applying of BET mo
del to the isotherms of BSs sorption on MSNs
(Tables 6, 7). To ensure the suitability of BET
model for precise description of experimental
sorption isotherms, the results of Chi square
test (χ2) were analyzed. According to the data
represented in Tables 4−7, application of BET
theory gives smaller χ2 values than modelling
of experimental isotherms with Redlich‑Pe‑
terson equation. So, an assessment of statisti‑
cal error functions proves that the best fit for
BSs sorption process on MSNs is attained at
BET model application. It can be assumed that
sorption of BSs proceeds due to the formation
of island-type supramolecular structures with
β‑CD-containing surface centers in which
cooperative interactions play crucial role.
Comparison of sorption data calculated by
BET model with experimental ones is repre‑
sented in Figures 6, 7.
Fig. 6. Isotherms of NaC (a) and NaTC (b) sorption by MSN‑C16 (curve 1), NH2‑MSN‑C16 (curve 2),
and CD‑NH2‑MSN‑C16(curve 3) from PBSs with pH 5.0 calculated by nonlinear regression analysis of
BET equation.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
C (mmoll1)
A
(
m
ol
m
2
)
3
2
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 6. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16(curve 3) from PBSs with pH 5.0 calculated by nonlinear regression analysis of BET
equation.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
A
(
m
ol
m
2
)
C (mmoll1)
3
2
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 7. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16 (curve 3) from PBSs with pH 7.4 calculated by nonlinear regression analysis of BET
equation
CONCLUSIONS. In the present paper, sorption of NaC and NaTC by periodic mesoporous
organosilicas with chemically immobilized β-CD was studied. It was established that introduction
of oligosaccharide moieties in surface layer of silica sorbent leads to the substantial enhancement of
BSs sorption. The most pronounced difference in NaC and NaTC sorption was registered in highly
acidic medium (pH~2) with different protolytic forms of BAs. Substantial increase of pH leads to
the accumulation of cholate and taurocholate anions in solution and causes convergence of NaC and
NaTC sorption values. Slight prevailing of NaC sorption on CD-NH2-MSN-C16 in comparison with
NaTC which is observed at pH 5 and 7 was explained by differences in surface inclusion complexes
stability. Sorption of BSs on synthesized silica materials was analyzed using Freundlich,
Redlich-Peterson, and BET models. An assessment of statistical error functions showed that the
best fit for BSs sorption process is attained at BET model application. Obtained results let us
assume formation of island-type supramolecular structures of BSs with β-CD-containing surface
sorption centers in PBSs with pH 5.0 and 7.4.
31https://ucj.org.ua
N.V. Roik, L.O. Belyakova UCJ № 01 / Vol. 89
Fig. 7. Isotherms of NaC (a) and NaTC (b) sorption by MSN‑C16 (curve 1), NH2‑MSN‑C16 (curve 2),
and CD‑NH2‑MSN‑C16 (curve 3) from PBSs with pH 7.4 calculated by nonlinear regression analysis of
BET equation
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
C (mmoll1)
A
(
m
ol
m
2
)
3
2
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 6. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16(curve 3) from PBSs with pH 5.0 calculated by nonlinear regression analysis of BET
equation.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
A
(
m
ol
m
2
)
C (mmoll1)
3
2
1
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.01
0.02
0.03
0.04
0.05
3
2
1
C (mmoll1)
A
(
m
ol
m
2
)
a b
Fig. 7. Isotherms of NaC (a) and NaTC (b) sorption by MSN-C16 (curve 1), NH2-MSN-C16 (curve 2), and
CD-NH2-MSN-C16 (curve 3) from PBSs with pH 7.4 calculated by nonlinear regression analysis of BET
equation
CONCLUSIONS. In the present paper, sorption of NaC and NaTC by periodic mesoporous
organosilicas with chemically immobilized β-CD was studied. It was established that introduction
of oligosaccharide moieties in surface layer of silica sorbent leads to the substantial enhancement of
BSs sorption. The most pronounced difference in NaC and NaTC sorption was registered in highly
acidic medium (pH~2) with different protolytic forms of BAs. Substantial increase of pH leads to
the accumulation of cholate and taurocholate anions in solution and causes convergence of NaC and
NaTC sorption values. Slight prevailing of NaC sorption on CD-NH2-MSN-C16 in comparison with
NaTC which is observed at pH 5 and 7 was explained by differences in surface inclusion complexes
stability. Sorption of BSs on synthesized silica materials was analyzed using Freundlich,
Redlich-Peterson, and BET models. An assessment of statistical error functions showed that the
best fit for BSs sorption process is attained at BET model application. Obtained results let us
assume formation of island-type supramolecular structures of BSs with β-CD-containing surface
sorption centers in PBSs with pH 5.0 and 7.4.
CONCLUSIONS. In the present paper,
sorption of NaC and NaTC by periodic me
soporous organosilicas with chemically immo‑
bilized β-CD was studied. It was established
that introduction of oligosaccharide moieties
in surface layer of silica sorbent leads to the
substantial enhancement of BSs sorption. The
most pronounced difference in NaC and NaTC
sorption was registered in highly acidic medi‑
um (pH~2) with different protolytic forms of
BAs. Substantial increase of pH leads to the ac‑
cumulation of cholate and taurocholate anions
in solution and causes convergence of NaC and
NaTC sorption values. Slight prevailing of NaC
sorption on CD‑NH2‑MSN‑C16 in comparison
with NaTC which is observed at pH 5 and 7
was explained by differences in surface inclu‑
sion complexes stability. Sorption of BSs on
synthesized silica materials was analyzed using
Freundlich, Redlich‑Peterson, and BET mo
dels. An assessment of statistical error func‑
tions showed that the best fit for BSs sorption
process is attained at BET model application.
Obtained results let us assume formation of
island-type supramolecular structures of BSs
with β‑CD-containing surface sorption centers
in PBSs with pH 5.0 and 7.4.
ACKNOWLEDGEMENT. The work
was performed with the financial
support of the National Academy of
Sciences of Ukraine within the state budget
theme “Controlled functionalization of car‑
bon and inorganic nanomaterials and phy
sicochemistry of supramolecular systems
and composites based on them”, State regist
ration number − 0119U100272.
32 ISSN 2708-129X. Укр. хім. журн., 2023
PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED
β‑CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTIONPHISICAL CHEMISTRY
ВПОРЯДКОВАНІ МЕЗОПОРИСТІ ОРГАНО‑
КРЕМНЕЗЕМИ З ХІМІЧНО ІММОБІЛІЗОВА‑
НИМ β-ЦИКЛОДЕКСТРИНОМ ДЛЯ СОРБЦІЇ
СОЛЕЙ ЖОВЧНИХ КИСЛОТ
Н. В Роїк*, Л. О. Бєлякова
Інститут хімії поверхні ім. О. О. Чуйка
Національної академії наук України,
вул. Генерала Наумова, 17, Київ 03164,
Україна
* E-mail: roik_nadya@ukr.net
Одержано мезопористі органокремне
земи типу MCM‑41 з поверхневими сила‑
нольними, 3-амінопропільними та β‑цикло
декстринвмісними групами золь-гель-кон‑
денсацією структуроутворюючих силанів
у присутності міцел довголанцюгової чет‑
вертинної амонієвої солі за умов лужного
каталізу та подальшого гідротермального
оброблення. Синтезовані кремнеземні ма‑
теріали охарактеризовано з використан‑
ням методів низькотемпературної адсорб
ції‑десорбції азоту та хімічного аналізу по‑
верхневого шару. Показано, що додавання
β‑циклодекстринвмісного силану у реак‑
ційну суміш зумовлює формування крем‑
незему типу МСМ‑41 із більшою питомою
поверхнею та гексагонально впорядкова‑
ною однорідною мезопористою структу‑
рою. Сорбційну здатність синтезованих
кремнеземних матеріалів відносно холату
та таурохолату натрію було вивчено залеж‑
но від рН розчину та його концентрації.
Встановлено, що сорбція зростає завдя‑
ки хімічній іммобілізації олігосахаридних
груп у поверхневому шарі кремнезему та
досягає максимальних значень у діапазонах
рН, де переважають молекулярні форми
жовчних кислот. Експериментально одер‑
жані результати сорбції проаналізовано з
використанням моделей Фрейндліха, Ред‑
ліха − Петерсона та Брунауера − Еммета −
Теллера. Доведено формування структур
острівкового типу солей жовчних кислот з
β‑циклодекстринвмісними поверхневими
сорбційними центрами завдяки коопера‑
тивним взаємодіям між молекулами сор‑
бату.
Ключові слова: золь-гель-синтез;
MCM‑41; хімічне модифікування; β‑цикло‑
декстрин; сорбція солей жовчних кислот.
REFERENCES
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Стаття надійшла 15.02.2023.
|
| id | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-515 |
| institution | Ukrainian Chemistry Journal |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-07-23T01:09:20Z |
| publishDate | 2023 |
| publisher | V.I.Vernadsky Institute of General and Inorganic Chemistry |
| record_format | ojs |
| resource_txt_mv | ucjorgua/09/b5aca5486ce6aa37be306aee45394709.pdf |
| spelling | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-5152026-07-22T08:23:51Z PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION Roik, Nadiia Belyakova, Liudmyla sol-gel synthesis; MCM 41; chemical modification; β cyclodextrin; bile salts sorption. Mesoporous silicas of MCM‑41 type with surface silanol, 3-aminopropyl, and β‑cyclodextrin‑containing groups were prepared by hydrothermal‑assisted base‑catalyzed sol‑gel condensation of structure-forming silanes in the presence of micelles of long‑chain quaternary ammonium salt. Characterization of synthesized silica materials was realized by low‑temperature nitrogen adsorption‑desorption and chemical analysis of surface layer. It was found that addition of ‑cyclodextrin‑containing silane into the sol‑gel reaction mixture causes formation of MCM‑41‑type organosilica with higher surface area and hexagonally arranged uniform mesoporous structure. Sorption ability of synthesized silica materials towards sodium cholate and sodium taurocholate was studied in dependence of solution pH and concentration. It was found that sorption increases due to chemical immobilization of oligosaccharide moieties in the surface layer of silica, and achieves maximal values in the pH regions of molecular forms of bile acids prevailing. Experimental sorption results were analyzed using Freundlich, Redlich - Peterson, and Brunauer - Emmett - Teller models. The formation of island-type structures of bile salts with β‑cyclodextrin-containing surface sorption centers due to cooperative interactions between sorbate moieties was proved. V.I.Vernadsky Institute of General and Inorganic Chemistry 2023-02-24 Article Article Physical chemistry Физическая xимия Фізична xімія application/pdf https://ucj.org.ua/index.php/journal/article/view/515 10.33609/2708-129X.89.01.2023.18-33 Ukrainian Chemistry Journal; Vol. 89 No. 1 (2023): Ukrainian Chemistry Journal; 18-33 Украинский химический журнал; ##issue.vol## 89 ##issue.no## 1 (2023): Ukrainian Chemistry Journal; 18-33 Український хімічний журнал; Том 89 № 1 (2023): Український хімічний журнал; 18-33 2708-129X 2708-1281 en https://ucj.org.ua/index.php/journal/article/view/515/262 Copyright (c) 2023 Nadiia Roik, Liudmyla Belyakova https://creativecommons.org/licenses/by-nc/4.0 |
| spellingShingle | Roik, Nadiia Belyakova, Liudmyla PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title | PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title_full | PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title_fullStr | PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title_full_unstemmed | PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title_short | PERIODIC MESOPOROUS ORGANOSILICAS WITH CHEMICALLY IMMOBILIZED β CYCLODEXTRIN MOIETIES FOR BILE SALTS SORPTION |
| title_sort | periodic mesoporous organosilicas with chemically immobilized β cyclodextrin moieties for bile salts sorption |
| topic_facet | sol-gel synthesis MCM 41 chemical modification β cyclodextrin bile salts sorption. |
| url | https://ucj.org.ua/index.php/journal/article/view/515 |
| work_keys_str_mv | AT roiknadiia periodicmesoporousorganosilicaswithchemicallyimmobilizedbcyclodextrinmoietiesforbilesaltssorption AT belyakovaliudmyla periodicmesoporousorganosilicaswithchemicallyimmobilizedbcyclodextrinmoietiesforbilesaltssorption |