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Investigation of structural properties of clinoptilolite rich zeolites in simulated digestion conditions and their cytotoxicity against Caco-2 cells in vitro

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The use of the clinoptilolite rich natural zeolites in biomedical applications such as in anticancer therapy, drug or drug support systems and as nutritive supplement is highly dependent on their behavior in digestive conditions. Aim of this study is to investigate structural stability of clinoptilolite rich natural zeolites in simulated digestion conditions and their interactions with digestive media and with Caco-2 (human colon adenocarcinoma) cells. X-ray Diffraction (XRD), Fourier Transform InfraRed (FTIR), Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) analyses of the clinoptilolite rich zeolite samples showed that zeolites preserved their structural stabilities during in vitro digestion. Slight interactions were detected in UV measurements of the digestive liquid media and FTIR spectra of the intestinal digested media powders. SEM results implied that zeolites might have a role in the aggregation of the digestive enzymes. Cytotoxicity test using colon cancer cells showed that clinoptilolite rich natural zeolites have cytotoxic effect against Caco-2 cells and cytotoxicity did not significantly change with respect to simulated digestion process.
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Investigation of structural properties of clinoptilolite rich zeolites
in simulated digestion conditions and their cytotoxicity against
Caco-2 cells in vitro
Dilek Demirbu
¨ker Kavak Semra U
¨lku
¨
ÓSpringer Science+Business Media, LLC 2012
Abstract The use of the clinoptilolite rich natural zeo-
lites in biomedical applications such as in anticancer
therapy, drug or drug support systems and as nutritive
supplement is highly dependent on their behavior in
digestive conditions. Aim of this study is to investigate
structural stability of clinoptilolite rich natural zeolites in
simulated digestion conditions and their interactions with
digestive media and with Caco-2 (human colon adenocar-
cinoma) cells. X-ray Diffraction (XRD), Fourier Transform
InfraRed (FTIR), Scanning Electron Microscopy (SEM)
and Inductively Coupled Plasma Atomic Emission Spec-
troscopy (ICP-AES) analyses of the clinoptilolite rich
zeolite samples showed that zeolites preserved their
structural stabilities during in vitro digestion. Slight inter-
actions were detected in UV measurements of the digestive
liquid media and FTIR spectra of the intestinal digested
media powders. SEM results implied that zeolites might
have a role in the aggregation of the digestive enzymes.
Cytotoxicity test using colon cancer cells showed that
clinoptilolite rich natural zeolites have cytotoxic effect
against Caco-2 cells and cytotoxicity did not significantly
change with respect to simulated digestion process.
Keywords Zeolite Clinoptilolite Simulated digestion
Caco-2 Cancer cell
1 Introduction
Natural zeolites are porous, crystalline, hydrated alumina
silicates of alkaline or alkaline earth metals. Their framework
consists of SiO
4
and AlO
4
tetrahedra linked through common
oxygen atoms. They act as molecular sieves, have adsorptive,
ion exchange, catalytic properties and their high stability and
low cost make them useful in numerous industrial, agricul-
tural, chemical and environmental applications [13].
In recent years, one of the exciting potential applications
of natural zeolites is in medical area. Natural zeolite clin-
optilolite has been reported to be nutritionally inert
adsorbent and non-toxic to animals [4,5] which make
clinoptilolite very advantageous. Several studies demon-
strated that clinoptilolite supplementation was well toler-
ated by animals such as it resulted significant feed
conversion and promoted biomass production, weight gain
and animal health [611]. Clinoptilolite was used to protect
animals from feed-originated toxins by adsorbing toxic
compounds in gastrointestinal tract and by preventing their
passage to circulatory system [1214]. Also, it was repor-
ted to decrease the deposition of radioactive compounds in
animals administered to the contaminated feed and it
reduced oxidative stress in animals after partial hepatec-
tomy [15,16]. Purified natural clinoptilolite was reported
to be harmless to the human body [17] and was used as
antidiarrheaic drug [18] and as antiacid agent for humans
suffering from the hyperacidity without showing any toxic
or biological hazard [19,20]. A novel use of micronized
clinoptilolite as a potential adjuvant in anticancer therapy
was reported [21]. It was used in anticancer treatment of
mice and dogs suffering from cancer and it resulted pro-
longed of life span and improvement of health status.
It is clear that biological effect of natural zeolite will
depend on its behavior in physiological systems where
D. D. Kavak (&)
Food Engineering Department, Engineering Faculty,
Afyon Kocatepe University, ANS Campus, 03200
Afyonkarahisar, Turkey
e-mail: dkavak@aku.edu.tr
S. U
¨lku
¨
Chemical Engineering Department, Engineering Faculty,
Izmir Institute of Technology, Gulbahce Koyu, 35430 Urla
Izmir, Turkey
123
J Porous Mater
DOI 10.1007/s10934-012-9602-1
digestive system has prior importance. Available data
primarily focus on using zeolites as drugs or drug supports
[18,19,22]. However, investigations of natural zeolite’s
behavior only in simple buffer solutions or in batch
experiments for medical purposes will be insufficient to
reflect the complicated digestion media where there were
also digestive enzymes or bile salts.
Aim of the present study is to investigate the structural
stability of clinoptilolite rich natural zeolites in complex
simulated digestion conditions and their possible interac-
tions with digestive media considering the gastric and
intestinal digestion as a continuous process. Additionally,
cytotoxic effects of zeolite’s digested and nondigested
forms against colon cancer cells (Caco-2) were investi-
gated in vitro. Regarding the novel uses of zeolites in
biochemical applications, this study will be focused on the
behavior of clinoptilolite rich zeolites in complicated
simulated digestion conditions for their further uses as
drugs/drug release matrices and in cancer therapies. In this
study, special interest has been devoted to clinoptilolite-
rich natural zeolite because of the abundance of the raw
material in our country. 50 billion tons of raw material
reserve having high mineral purity and homogeneity in
Go
¨rdes basin (Western Anatolia) was estimated [23].
2 Materials and methods
2.1 Materials
Clinoptilolite rich mineral specimens were obtained from
Go
¨rdes region of Western Anatolia. The mineral was
mainly made up of clinoptilolite (80–85 %) and addition-
ally, quartz (5–10 %), and analcime ?mordenite (\5%)
[24]. It was ground and sieved at 45–75 lm size. Porcine
bile extract, pepsin and pancreatin, NaOH, NaHCO
3
, HCl
used in digestion experiments were purchased from Sigma
(Germany). In cell culture studies Caco-2 (Human, colon
adenocarcinoma cell line) cells were purchased from
S¸ ap Institute (Turkey). Dulbecco’s Modified Eagles Med-
ium (DMEM), fetal bovine serum (FBS), PBS buffer, ty-
ripsin, L-glutamine and penicillin/streptomycin antibiotics
were purchased from Biological Industries (Israel). MTT
(3-(4,5-dimethylthiazolyl-2)-2,5-diphenyl tetrazolium bro-
mide) solution and dimethyl sulfoxide (DMSO) were pur-
chased from Sigma (Germany).
2.2 Simulated digestion and characterization
experiments
Simulated digestion experiments were performed by the
modification of the procedure reported by Ferruzzi et al.
[25]. Gastric fluid was prepared with 0.1 M HCl and
3.2 mg ml
-1
pepsin. pH adjustment was made using 0.1 N
NaOH where final pH of gastric fluid was 2.0. Digestion
experiments were performed with zeolite against control
experiments (without zeolite). Final zeolite concentrations
in simulated digestion conditions were 3 g (100 ml)
-1
.
Gastric fluids were incubated at 37 °C in a water bath
shaking at 95 rpm for 1 h. Samples obtained after this step
were named as gastric digested samples coded with ‘‘G’
throughout the text. Then, the pH of the gastric digested
fluid was raised to 5.5 by adding 1 M NaHCO
3
followed by
the addition of a mixture of bile extract and pancreatin
(including amylase, lipase and protease) prepared in 0.1 M
NaHCO
3
. Final concentrations for the bile extract and
pancreatin were 2.4 and 0.4 mg ml
-1
, respectively. The pH
of each sample was increased to 7.5 by the addition of 1 N
NaOH. Samples were incubated at 95 rpm at 37 °C for 2 h
to complete the intestinal phase of the in vitro digestion
process. Samples obtained after this step were called as
digested samples and coded with ‘‘D’’ throughout the text.
Simulated gastric and intestinal digestion media were
analyzed for their UV absorption properties. 100 ll of each
sample obtained immediately after gastric and intestinal
digestion steps were put in 96-well plates. Samples were
analyzed in triplicate for their UV absorption spectra in the
range of 200–380 nm by microplate reader (Varioskan,
Thermo).
After simulated digestion procedure, solid (zeolite) and
liquid phases of the gastric and intestinal digested media
were separated by centrifugation (Rotofix 32, Hettich, UK)
at 800 g for 5 min. Both zeolite and liquid phases were
frozen at -18 °C for 2 h and freeze dried for 24 h by
lyophilizator (Telstar Cryoduos Lyobeta 50, Spain). Then
they were kept ?4°C until the day of analyzes. Mineral-
ogy and the crystallinity of the zeolite samples were
determined by powder X-ray diffraction techniques
(Philips X-Pert Pro) using CuKaradiation in the range of
2h:2
o
-40°with 0.2°step size. Elementary composition of
control (untreated) and digested zeolite samples were
determined by ICP-AES (96, Varian). Solid (zeolite) pha-
ses and lyophilized liquid phase powders were analyzed by
scanning electron microscopy (SEM) to view the surface
morphology. Photographs were taken at an accelerating
voltage of 15 kV, depending upon the sample at different
magnifications in a Phillips XL30S FEG electron micro-
scope. IR characterizations were carried out between 400
and 4,000 cm
-1
by Shimadzu FTIR-8201 model Fourier
Transform Infrared Spectrometer.
2.3 Cell culture experiments
Caco-2 cells (human colon adenocarcinoma cells) were
cultured in DMEM supplemented with 10 % FBS, 1 %
L-glutamine, 1 % nonessential amino acids, and 50 lg/ml
J Porous Mater
123
penicillin–streptomycin. The cell cultures were maintained
at 37 °C in a 95 % humidified atmosphere with 5 % CO
2
where they were seeded onto collagen-coated 25 cm
2
area
culture flasks. Caco-2 cells were fed twice weekly and were
subcultured (passaged) with 0.25 % trypsin and 0.2 %
EDTA (5–10 min) at 37 °C and seeded in new flasks for
every 10–14 days.
For the zeolite treatments, cells were harvested by
trypsinization after 80 % confluency was reached. They
were seeded at a density of 10
5
cells/cm
2
in 96-well plates
(Becton–Dickinson, Meylan, France). Zeolite samples
were sterilized and added in culture media so that the final
zeolite concentrations were 25, 50 and 75 mg/ml. They
incubated with cell culture media for 24 h at 37 °C. After
incubation treated media was distributed into wells in
triplicate where Caco-2 cells were seeded. Positive and
negative controls were prepared and incubated in the
same manner as the experimental specimens. After 24, 48
and 72 h incubation, MTT cell proliferation assay was
performed.
2.4 MTT cell proliferation assay
Caco-2 cell viability was measured by MTT cell prolifer-
ation assay. The yellow tetrazolium salt; MTT (3-(4,5-
dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide)
was reduced by metabolically active cells, in part by the
action of dehydrogenase enzymes, to generate reducing
equivalents such as NADH and NADPH. The resulting
intracellular purple formazan was solubilized and quanti-
fied by spectrophotometric means. 20 ll MTT solution was
added to each well and shaken to thoroughly mix the MTT
into the media. Cells were incubated under 95 % humidi-
fied air and 5 % CO
2
atmosphere at 37 °C for 4 h to allow
the MTT to be metabolized in accordance with the man-
ufacturer’s instructions. Cell media was dumped and for-
mazan dye was resuspended in dimethyl sulfoxide (DMSO)
and well was shaken to thoroughly mix the formazan into
the solvent. Optical density was measured at 540 nm by
Multiskan Spectrum (Thermo) which was directly corre-
lated with cell quantity.
3 Results and discussion
3.1 Changes in UV absorption spectra of liquid phase
in simulated digestion studies
UV spectra of the digestive media incubated with zeolite
were analyzed to investigate the possible interactions
between protein structures and zeolites such as adsorption.
Digestive media without zeolite incubation was used as
control. Changes in the maxima of the UV absorption
spectra of liquid digestion media might indicate the chan-
ges in the amount of enzyme levels. Results of the UV
spectra of liquid digestion are given in Fig. 1. UV absor-
bance at around 270 nm corresponds to the digestive
enzymes in protein structure. Results in Fig. 1for digestion
fluids (D and DZ) indicate that there is not a considerable
interaction with zeolite and digestion fluid which was
consisted of amylase lipase and protease. This is also
important for the digestive role of enzymes. For gastric
media including pepsin enzyme (G), slight fluctuations in
absorbance values were observed with zeolite incubation.
Those interactions might be related to the continuous
changes of the pH and ionic strength of the simulated
digestion media. Thus, active sites on the zeolite and pro-
tein surfaces might be affected. The active sites on zeolite
surface are Si–OH and Al–OH groups. In acidic to neutral
pH range, protonation of negative and neutral surface
hydroxyl groups were reported [26]:
Al OH þHþ
aq ,Al OHþ
2ð1Þ
Si OþHþ
aq ,Si OH:ð2Þ
On the other hand, pepsin has only two basic groups and
20 carboxyl groups and at pH higher than 1 (pI), it has a
negative electrical charge [27]. Therefore, electrostatic
interactions between the COO-groups and Al–OH
2?
groups might be active and might result reduction of the
spectral maxima which corresponds to reduction of free
enzyme level in liquid media. Beside the electrostatic
interactions, there could be hydrogen bonding between
hydroxyl (-OH) groups on the zeolite and H-bond
acceptors on the enzyme depending on the chemical
nature of the protein chains and zeolite. It was important
to note that zeolite has also small amounts of impurities
such as quartz. Quartz might be responsible for the
interaction of pepsin enzyme where it was also reported
to be used in protein adsorption [28].
G
GZ
D
DZ
0
0.5
1
1.5
2
200 220 240 260 280 300 320 340 360 380
wavelength (nm)
Absorbance
Fig. 1 UV spectra of gastric and digestion fluids (Gcontrol gastric
fluid, GZ gastric fluid incubated with zeolite, Dcontrol digestion
fluid, DZ digestion fluid incubated with zeolite
J Porous Mater
123
3.2 Characterization results
XRD results for the digested and non-digested zeolite
samples are given in Fig. 2. Results showed that zeolite
could be identified as clinoptilolite and characteristic
clinoptilolite peaks were recognized at 2h=9.81°, 22.3°,
and 30°. Quartz peak at 2h=26.62°was also identified. In
literature, HCl treatment was reported to decrease the
intensities of the characteristic peaks of zeolites [29].
However, results showed that characteristic peak intensities
of the clinoptilolite were almost same compared to the
control sample after the gastric treatment. It implied that
crystal structure of zeolites were stable after gastric treat-
ment where similar results were also reported [30]. On
contrary, a significant change was observed in the quartz.
HCl was a registered chemical used to purify the quartz
[31]. It might help the diffusion of mineral impurities to the
quartz crystal surface where they formed salts with chlo-
ride ion. Therefore, increase in peak intensity of the quartz
might be related to the purification effect of HCl. At the
later stages of the simulated digestion, with the increase in
pH and with the complexation of the media, this purifica-
tion was probably limited.
FTIR analyze for the gastric and intestinal digested
zeolite samples were performed to investigate structural
changes arised due to the simulated digestion treatments
and results are given in Fig. 3. The 472 and 615 cm
-1
peaks were assigned to the internal and external Si (or Al)–
O double ring respectively. The strong symmetric and
asymmetric stretch vibrations were present at 1,058 cm
-1
.
The water vibrations of zeolite were also observed after
3,450 cm
-1
. In literature, acidic treatments were reported
to result shifts at characteristic peaks position (at 472 and
1,056 cm
-1
) and reduction in peak intensities were repor-
ted as a result of dealumination and partial structural
breakdown [29,32]. However, FTIR spectra showed that
characteristic peaks of zeolite were preserved for all
treatments and there were no significant variations in the
frequencies of assigned bands after gastric and intestinal
digestion processes. Therefore, there were no significant
dealumination and structural breakdown and these results
revealed that zeolites preserved their structural stability
during simulated digestion.
FTIR results were also used to identify possibility of the
adsorption of digestive media constituents onto zeolite
surface. Results in Fig. 3showed that there were no
additional peaks in FTIR spectra of zeolites. Previous
results of the interaction studies indicated that there were
slightly changes in UV absorbance of the gastric media
fluid (at 270 nm, corresponding to digestive enzymes) by
zeolite treatment. However, this possible interaction espe-
cially between enzymes and zeolite should be so weak and
it could not be observed in FTIR spectra.
To investigate possible interactions with the digestion
media and the zeolite, IR spectrum of lyophilized powders
of the digestion fluids were analyzed and results are given
in Fig. 4. In Fig. 4, the main characteristic protein bands of
digestive enzymes such as Amide 1 and Amide 3 are
observed in the region around of 1,650 and 1,350 cm
-1
.
Possible hydrogen bonds to the C=O group were reported
to lower the amide I frequency by 20–30 cm
-1
and
hydrogen bond to the NH group by 10–20 cm
-1
[33].
However, no significant shifts were observed in digestion
media powders with the zeolite treatments. Thus, result
revealed that there was no hydrogen bonding and zeolite
did’t interact with C=O, C–N or N–H of the polypeptide
chains in the digestive enzymes [34] which was also in
CZ
C
QC
C
ZG
C
Q
C
C
ZD
C
QC
8 12162024283236
C ounts (Arbitrary Units)
2θ
Fig. 2 XRD patterns of zeolites; Zcontrol-untreated zeolite, ZG
gastric treated zeolite, ZD digested zeolite (Cclinoptilolite peaks at
2h=9.81°, 22.3°and 30°;Qquartz peak at 2h=26.62°)
ZG
ZD
Z
400 1200 2000 2800 3600
wave number (cm
-1
)
Absorbance (Arbitrary Units)
Fig. 3 Infrared spectra of zeolite samples (Zcontrol-untreated
zeolite, ZG gastric treated zeolite, ZD digested zeolite)
J Porous Mater
123
good agreement with the FTIR results of the zeolite sam-
ples. Amide 2 bands (1,500–1,550 cm
-1
) were not easily
detected on the FTIR spectra because of the possible
deformations with digestive treatment. This might be due
to the proteolitic activity of digestive enzymes or changes
in the pH and ionic strength of the media. Those factors
might be effective in enzyme/protein stability and confor-
mation. Additionally with digestion process using zeolite,
intensities of the protein peaks were reduced. Similar
results were also observed in UV spectrum of some liquid
media samples as slight reduction in their intensities. Those
reductions in the peak intensities might be due to the weak
interactions of the digestion media components with
zeolite.
With the pH change (from pH 2–7.5), there could be
interactions between zeolite and digestive media and
chemical composition of the zeolite might be affected.
These interactions might be attributed to different physi-
cochemical reactions as dissolution, ion exchange, sorp-
tion, and possibly surface precipitation [35]. Changes in the
major elementary composition of zeolites were analyzed
and results are given in Table 1.
Interactions of the zeolite with the digestive media
might depend on Si/Al ratio and also could be related to
acidic and basic sites in its structure which is defined by the
Brønsted and Lewis theory. Such as, Si–O–Al species
represents negative charge of the lattice and structural basic
site. Therefore oxygen from the lattice acts as a proton
acceptor. In simulated digestion experiments, pH adjust-
ments were performed with CaCO
3
and NaOH so that they
were in high amounts in the digestive media. Elementary
composition results showed that Na
?
content of zeolite was
increased especially after intestinal digestion experiments
(79.1 %) which might be attributed to the exchange of this
ion. It was important to note that Al composition was
almost remained constant, however there were slight
decrease in the Si composition with the increase in the pH
of the digestive media. Such as, there was 1.3 and 1.8 %
decrease in Si content compared to untreated-control zeo-
lite (Z) after gastric and intestinal treatments, respectively.
This might be related to the possible dissolution process of
aluminosilicates at the surface layer at the alkaline condi-
tions. The dissolution process for the natural zeolites were
affected by the H
?
or OH
-
in the solutions (Brønsted and
Lewis theory) and they represent acidic or basic behavior.
It was reported that dissolution of Si was related to the
decrease in ionic strength and increase in the pH of the
solution. Additionally Al dissolution was reported to be
increased with the increase in ionic strength but also it
decreased with the decrease in solution pH [26]. Therefore
ionic strength and pH might be effective on slight disso-
lution of Si. However, Si content did not differ statistically
from each other (p\0.05) and dissolution might be con-
sidered as insignificant.
SEM images were recorded for the gastric and intestinal
digested zeolite samples and results are given in Fig. 5.
Results showed that hexagonal clinoptilolite crystals were
identified in wide range of the samples. In simulated
digestion treatment with the changes in pH, zeolites were
subjected to acid or alkali media. Acidic and alkali con-
ditions were reported to be effective in structural losses for
zeolites which were defined by SEM analyzes [36,37].
However, SEM results indicated that there was no struc-
tural deformation. Besides, no protein like structure was
observed on the zeolite surface during scanning which was
also in good agreement with the FTIR results.
SEM images were recorded for the lyophilized digestion
media powders and results of 5,0009magnification were
given in Fig. 6. Surface porosity and irregularity was
observed but there wasn’t a significant factor or relevance
to differentiate the treatment types. On the other hand,
it was interesting to observe that digested powders
PD
PDZ
1200 1600 2000 2400 2800 3200 3600
wave number (cm
-1
)
Absorbance (Arbitrary Units)
Fig. 4 Infrared spectra of simulated digestion fluid powders (PD
powder of control digestion fluid, PDZ powder of digestion fluid
incubated with zeolite)
Table 1 Elementary compositions of zeolite samples
Elements (mg g
-1
) Zeolites
ZZGZD
Na 11.0 ±2.3
a
12.9 ±3.0 19.7 ±2.7
Mg 6.5 ±2.0 6.1 ±1.4 6.4 ±1.7
Al 84.7 ±5.0 81.5 ±2.5 81.8 ±8.4
Si 373.8 ±12.6 368.8 ±4.2 366.9 ±1.5
K 24.2 ±5.2 19.5 ±0.7 18.4 ±3.5
Ca 13.2 ±3.7 13.5 ±2.2 17.0 ±4.0
Zuntreated-control zeolite, ZG gastric treated zeolite, ZD digested
zeolite
a
SD of three replicates
J Porous Mater
123
(without zeolite) were smaller in size but presence of the
zeolite in the digestive media resulted powders to form
aggregates (Fig. 7). Agglomeration is a sign of the exis-
tence of possible and complex interactions between the
protein structures (enzymes) in the aqueous phase due to
zeolite treatments. Proteins are often stable against aggre-
gation over narrow pH ranges and when pH is outside those
ranges, they may aggregate rapidly in solutions [38]. In
simulated digestion process, digestion media contained the
factors to prone aggregation of protein structures such as
varying pH values and ionic strengths. Changes in pH (step
by step; acidic to alkaline) and ionic strength of the media
might have caused exchange of H
?
ions, binding of protons
on the Lewis basic sites, removal of protons from the
surface Bronsted acidic sites or removal of the protons that
arrange the ion exchange (such as Na, K, Ca, Mg) [35]on
zeolites surfaces. Although the exact mechanism was hard
to define, this complex mechanism with zeolite treatments
might have resulted proteins to possess anisotropic charge
distribution on their surfaces and this might have caused
increase in dipoles. Thus protein–protein interactions might
be attractive and lead aggregation to be energetically
favorable [39,40].
3.3 Cytotoxicity results for Caco-2 cells
Caco-2 cells are originated from human digestive system
that having primary importance for biomedical/drug
applications. Possible metabolic events after zeolite expo-
sure might lead to apoptosis or necrosis, and reduction in
the cell viability of those cells. To investigate the effect of
simulated digested clinoptilolite rich mineral on prolifera-
tion of human colon adenocarcinoma cells (Caco-2),
cytotoxicity measurements were performed. Results were
given in Figs. 8and 9.
Results showed that both digested (ZD) and non-
digested control zeolite (Z) were effective against cancer
cell proliferations. Proliferation percentages varied in the
range of 96.1–29.5 % with respect to zeolites, treatment
time and zeolite concentration. Decrease in the cell via-
bility might be related to the effect of zeolite on growth
media. Because Caco-2 cells are enterocytes (absorbtive
cells) and account for majority of the absorption in the
small intestine [41] and they are highly sensitive to the
changes in their microenvironment. Deviations from opti-
mum conditions of Caco-2 cell growth in the culture media
with zeolite treatments might have caused cells to go under
stress and might have affected the Caco-2 cells responses.
It was reported that the proton pumps in the Caco-2 cells
did not rapidly reverse the effect of pH, and the buffering
capacity of the cytoplasm was not strong enough to prevent
the pH change [42]. Since zeolites have amphoteric
behavior, they alter the pH of the aqueous growth media
[30] thus reduction in cell proliferation compared to control
sample might be achieved. Other possible reasons for the
inhibition of cancer cell proliferation with zeolite treatment
Fig. 5 SEM images of zeolites.
acontrol-untreated zeolite (Z);
bdigested zeolite (ZD)
Fig. 6 SEM images of
digestion fluid powders with
95,000 magnification.
aPowder of control digestion
fluid (PD); bpowder of
digestion fluid incubated with
zeolite (PDZ)
J Porous Mater
123
might due to its effect on cancer cell signaling pathways, or
possibility of weak interactions such as van-der Waals,
hydrogen bonding, electrostatic interactions between zeo-
lite and some protein like structures in cell culture media
(such as aminoacids, or growth hormones secreted by the
cells) due to zeolite’s ion exchange and adsorptive prop-
erties. Similar cases were suggested previously [21,43]. It
was reported that decrease in the viability of the tumor
cells with the zeolite treatment might be due to adsorption
of some serum components such as epidermal growth
factor (EGF) by the clinoptilolite.
4 Conclusions
In this study, simulated digestion studies were performed in
order to investigate the behavior clinoptilolite rich zeolites
in in vitro simulated digestion conditions. Possible inter-
actions of the clinoptilolite rich zeolites with digestive
media and cytotoxic effects of their digested/non-digested
forms on colon cancer cells (Caco-2) were analyzed.
Overall results in this study indeed showed that the zeolites
preserved their structural stability under given simulated
digestion conditions. Additionally, cell culture studies
indicated that clinoptilolite rich zeolite and its digested
forms were both effective to inhibit colon cancer cell
proliferation. Proliferation percentages reduced and varied
in the range of 96.1–29.5 % with respect to zeolites,
treatment time and zeolite concentration. However,
agglomeration formation suggested the existence of pos-
sible and complex interactions among the protein structures
(enzymes) in aqueous digestion media phase as a result of
zeolite treatments. Considering potential biomedical
applications of the clinoptilolite rich natural zeolites such
as in drug systems or cancer therapy, this study is a primary
step to understand possible interactions with complicated
digestive media and their cytotoxicity against colon cancer
cells. Further studies would be at the perspective of
enzyme activity and cellular responses in molecular level
regarding the pH and ionic strength which would be helpful
to identify the detailed mechanism.
Acknowledgments This study was financially supported by Turkish
Republic Prime Ministry State Planning Organization (DPT-
2003K120690, Determination of Effects of Zeolite on Health at
Cellular and Molecular Level). The authors gratefully acknowledge to
Prof. Serdar O
¨ZC¸ ELI
˙K (Izmir Institute of Technology, Department of
Chemistry, Turkey) for his kind contributions.
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Fig. 7 SEM images of
digestion fluid powders with
9100 magnification. aPowder
of control digestion fluid (PD);
bpowder of digestion fluid
incubated with zeolite (PDZ)
73,5
65,0
57,7
100,0
50,5 46,2
39,0
54,5
32,7 29,5
0
20
40
60
80
100
120
control 25(m
g
/ml) 50(m
g
/ml) 75(m
g
/ml)
Caco-2 Cell Proliferation (%)
24h 48h 72h
Fig. 8 Cell proliferation (%) for Caco-2 cells incubated with control
zeolite (Z) treated culture media (incubation times: 24, 48 and 72 h;
zeolite concentrations: 25, 50 and 75 mg/ml)
96,1
83,1 79, 7
100,0
49,9 47, 5
49,5
52,6 51, 5
43,2
0
20
40
60
80
100
120
control 25(mg/ml) 50(mg/ml) 75(mg/ml)
Caco-2 Cell Proliferation (%)
24h 48h 72h
Fig. 9 Cell proliferation (%) for Caco-2 cells incubated with digested
zeolite (ZD) treated culture media (incubation times: 24, 48 and 72 h;
zeolite concentrations: 25, 50 and 75 mg/ml)
J Porous Mater
123
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... Figure 2 illustrates the mechanism of a zeolite dissolution in hydrochloric acid as described by Hartman and Fogler (2006). (Hartman and Fogler, 2006) According to the results from the experiment performed by Kavak and Ulku (2013), the presence of zeolites in the gastrointestinal fluid did not show substantial interaction such as in the chemical composition of the zeolites and in the amount of enzyme levels in the fluid. A change in the Ideal International E-Publication www.isca.co.in pH and ionic strength could be due to the protonation of the negative and neutral surface hydroxyl groups of the active sites on the zeolites (Kavak and Ulku, 2013). ...
... (Hartman and Fogler, 2006) According to the results from the experiment performed by Kavak and Ulku (2013), the presence of zeolites in the gastrointestinal fluid did not show substantial interaction such as in the chemical composition of the zeolites and in the amount of enzyme levels in the fluid. A change in the Ideal International E-Publication www.isca.co.in pH and ionic strength could be due to the protonation of the negative and neutral surface hydroxyl groups of the active sites on the zeolites (Kavak and Ulku, 2013). ...
... Therefore, the question whether the antiproliferative activity of the synthesized nanozeolite will remain after passing through the gastrointestinal tract is an additional concern. A study by Kavak and Ulku (2013) showed an insignificant decrease in the antiproliferative activity of digested zeolite. Thus, a slight decrease in the antiproliferation activity would be expected, but most importantly the synthesized nanozeolite must have low toxicity against the normal cells for it to function as an anticancer adjuvant alternative to the clinoptilolite. ...
Book
Full-text available
Zeolites are three dimensional, crystalline solids, made from interlinked tetrahedral of alumina and silica. They form with many different crystalline structures and have a unique ability to act as molecular sieves. Generally, zeolites are grouped into two major categories, namely natural and synthetic zeolites.
... Figure 2 illustrates the mechanism of a zeolite dissolution in hydrochloric acid as described by Hartman and Fogler (2006). (Hartman and Fogler, 2006) According to the results from the experiment performed by Kavak and Ulku (2013), the presence of zeolites in the gastrointestinal fluid did not show substantial interaction such as in the chemical composition of the zeolites and in the amount of enzyme levels in the fluid. A change in the Ideal International E-Publication www.isca.co.in pH and ionic strength could be due to the protonation of the negative and neutral surface hydroxyl groups of the active sites on the zeolites (Kavak and Ulku, 2013). ...
... (Hartman and Fogler, 2006) According to the results from the experiment performed by Kavak and Ulku (2013), the presence of zeolites in the gastrointestinal fluid did not show substantial interaction such as in the chemical composition of the zeolites and in the amount of enzyme levels in the fluid. A change in the Ideal International E-Publication www.isca.co.in pH and ionic strength could be due to the protonation of the negative and neutral surface hydroxyl groups of the active sites on the zeolites (Kavak and Ulku, 2013). ...
... Therefore, the question whether the antiproliferative activity of the synthesized nanozeolite will remain after passing through the gastrointestinal tract is an additional concern. A study by Kavak and Ulku (2013) showed an insignificant decrease in the antiproliferative activity of digested zeolite. Thus, a slight decrease in the antiproliferation activity would be expected, but most importantly the synthesized nanozeolite must have low toxicity against the normal cells for it to function as an anticancer adjuvant alternative to the clinoptilolite. ...
Chapter
Full-text available
This paper provides an updated review on the synthesis of hierarchical mesoporous Zeolite. The hierarchical structure enhances the zeolite’s structure based on pore volume and size without severe penalization of the micropore volume, making it more efficient. Hierarchical mesoporous zeolites allow diffusion of bulky molecules compared to microporous zeolites. They are more stable hydrothermally than conventional mesoporous zeolites. They are widely used in fast pyrolysis of biomass and product upgrading such as zeolite cracking and hydrodeoxygenation as well as catalysis in general. We discussed synthesis routes including template and template-free methods, factors influencing mesophase formation and zeolite crystallization, metal modification, hierarchy factor etc. Moreover, future developments such as scale-up, cheaper synthesis catalyst design as well as eco-friendly processes were also discussed.
... Purified natural clinoptilolite was reported to be harmless to the human body and recommended as an antidiarrheal drug and as antiacid agent for humans suffering from hyperacidity and showed no toxic or biological hazards [5,6,15]. Among the studies performed, those related to the use of clinoptilolite in cancer treatment, have special value; in animal models clinoptilolite treatment has improved health, prolonged life-spans and decreased tumor size [16][17][18][19][20]. Therefore, to identify the mechanism underlying the therapeutic effects of clinoptilolite-rich minerals, investigation of the interactions between clinoptilolite rich minerals and bioactive molecules related to health and diseases is crucial for the formulation of new materials for biomedical applications. ...
... The surface morphology and macropore size of clinoptilolite-rich minerals were estimated with a Phillips XL30S FEG electron microscope. Chemical composition (by ICP-AES 96, Varian), mineralogy and crystallinity (by X-Pert Pro, Philips), IR characterization (by FTIR-8201, Shimadzu) and Thermogravimetric (by TGA-51/51H, Shimadzu) analyses were performed as previously described [17]. Zeta potential measurements of the mineral samples were measured using 5 mg/mL samples in potassium phosphate buffer solution at pHs 5.5, 6.8 and 8 with a Zetasizer 3000 HAS analyzer (Malvern Instruments), where pH 6.8 is the optimum pH for GUS activity (recommended by the purchaser instructions) and pH 5.5-8 is the pH range simulating the fasted and fed states of gastrointestinal media. ...
... Purified natural clinoptilolite was reported to be harmless to the human body and recommended as an antidiarrheal drug and as antiacid agent for humans suffering from hyperacidity and showed no toxic or biological hazards [5,6,15]. Among the studies performed, those related to the use of clinoptilolite in cancer treatment, have special value; in animal models clinoptilolite treatment has improved health, prolonged life-spans and decreased tumor size [16][17][18][19][20]. Therefore, to identify the mechanism underlying the therapeutic effects of clinoptilolite-rich minerals, investigation of the interactions between clinoptilolite rich minerals and bioactive molecules related to health and diseases is crucial for the formulation of new materials for biomedical applications. ...
... The surface morphology and macropore size of clinoptilolite-rich minerals were estimated with a Phillips XL30S FEG electron microscope. Chemical composition (by ICP-AES 96, Varian), mineralogy and crystallinity (by X-Pert Pro, Philips), IR characterization (by FTIR-8201, Shimadzu) and Thermogravimetric (by TGA-51/51H, Shimadzu) analyses were performed as previously described [17]. Zeta potential measurements of the mineral samples were measured using 5 mg/mL samples in potassium phosphate buffer solution at pHs 5.5, 6.8 and 8 with a Zetasizer 3000 HAS analyzer (Malvern Instruments), where pH 6.8 is the optimum pH for GUS activity (recommended by the purchaser instructions) and pH 5.5-8 is the pH range simulating the fasted and fed states of gastrointestinal media. ...
Article
The adsorption of the bacterial-glucuronidase (GUS) enzyme, which is thought to be responsible for the production of reactive metabolites related to some diseases and cancer development, by clinoptilolite-rich mineral was investigated. Batch experiments were performed to analyze of the effects of the clinoptilolite amount and particle size, initial GUS concentration, shaking rate, pH and temperature on the adsorption equilibrium and kinetics. Adsorption equilibrium data were interpreted in terms of Langmuir and Freundlich isotherms; and they were well represented by the Langmuir isotherm model. The percentage of GUS removal by the clinoptilolite-rich mineral was changed in the range of 9.4–54.4% depending on its initial concentration. The kinetic data were analyzed using external film diffusion, intraparticle diffusion, pseudo-first-order and pseudo-second-order models and both external film and intraparti-cle diffusion appeared to be effective in GUS adsorption. Thermodynamic studies indicated that GUS adsorption is exothermic, physical and spontaneous at the temperatures investigated (288–310 K).
... The stability of natural zeolite (clinoptilolite) in simulated digestion conditions and their interactions with digestive media and with Caco-2 (human colon adenocarcinoma) cells was investigated. 182 The cytotoxicity test using colon cancer cells showed that the natural clinoptilolite has cytotoxic effect against Caco-2 cells, and cytotoxicity did not significantly change with respect to simulated digestion process. 182 Non-toxic nanosized zeolites with interesting physicochemical properties offer considerable advantages in everyday life uses as stated by Cola et al. 183 In summary, most of the toxicity tests were performed on five types of nanosized zeolites (LTA, MOR, LTL, FAU and MFI) ( Table 1). ...
... 182 The cytotoxicity test using colon cancer cells showed that the natural clinoptilolite has cytotoxic effect against Caco-2 cells, and cytotoxicity did not significantly change with respect to simulated digestion process. 182 Non-toxic nanosized zeolites with interesting physicochemical properties offer considerable advantages in everyday life uses as stated by Cola et al. 183 In summary, most of the toxicity tests were performed on five types of nanosized zeolites (LTA, MOR, LTL, FAU and MFI) ( Table 1). The low cytotoxic activity of nanosized zeolites with different sizes, compositions and shapes is expected to enlarge their future industrial and medical applications. ...
Article
Full-text available
This review highlights recent developments in the synthesis and unconventional applications of nanosized microporous crystals including framework (zeolites) and layered (clays) type materials. Owing to their microporous nature nanosized zeolites and clays exhibit novel properties, different from those of bulk materials. The factors controlling the formation of nanosized microporous crystals are first revised. The most promising approaches from the viewpoint of large-scale production of nanosized zeolites and clays are discussed in depth. The preparation and advanced applications of nanosized zeolites and clays in free (suspension and powder forms) and fixed (films) forms are summarized. Further the review emphasises the non-conventional applications of new porous materials. A comprehensive analysis of the emerging applications of microporous nanosized crystals in the field of semiconductor industry, optical materials, chemical sensors, medicine, cosmetics, and food industry is presented. Finally, the future needs and perspectives of nanosized microporous materials (zeolites and clays) are addressed.
... Purified natural clinoptilolite was reported to be harmless to the human body and recommended as an antidiarrheal drug and as antiacid agent for humans suffering from hyperacidity and showed no toxic or biological hazards [5,6,15]. Among the studies performed, those related to the use of clinoptilolite in cancer treatment, have special value; in animal models clinoptilolite treatment has improved health, prolonged life-spans and decreased tumor size [16][17][18][19][20]. Therefore, to identify the mechanism underlying the therapeutic effects of clinoptilolite-rich minerals, investigation of the interactions between clinoptilolite rich minerals and bioactive molecules related to health and diseases is crucial for the formulation of new materials for biomedical applications. ...
... The surface morphology and macropore size of clinoptilolite-rich minerals were estimated with a Phillips XL30S FEG electron microscope. Chemical composition (by ICP-AES 96, Varian), mineralogy and crystallinity (by X-Pert Pro, Philips), IR characterization (by FTIR-8201, Shimadzu) and Thermogravimetric (by TGA-51/51H, Shimadzu) analyses were performed as previously described [17]. Zeta potential measurements of the mineral samples were measured using 5 mg/mL samples in potassium phosphate buffer solution at pHs 5.5, 6.8 and 8 with a Zetasizer 3000 HAS analyzer (Malvern Instruments), where pH 6.8 is the optimum pH for GUS activity (recommended by the purchaser instructions) and pH 5.5-8 is the pH range simulating the fasted and fed states of gastrointestinal media. ...
Article
The adsorption of the bacterial β-glucuronidase (GUS) enzyme, which is thought to be responsible for the production of reactive metabolites related to some diseases and cancer development, by clinoptilolite-rich mineral was investigated. Batch experiments were performed to analyze of the effects of the clinoptilolite amount and particle size, initial GUS concentration, shaking rate, pH and temperature on the adsorption equilibrium and kinetics. Adsorption equilibrium data were interpreted in terms of Langmuir and Freundlich isotherms; and they were well represented by the Langmuir isotherm model. The percentage of GUS removal by the clinoptilolite-rich mineral was changed in the range of 9.4-54.4% depending on its initial concentration. The kinetic data were analyzed using external film diffusion, intraparticle diffusion, pseudo-first-order and pseudo-second-order models and both external film and intraparticle diffusion appeared to be effective in GUS adsorption. Thermodynamic studies indicated that GUS adsorption is exothermic, physical and spontaneous at the temperatures investigated(288-310 K).
... The infrared spectrum was used to identify the functional groups present in the zeolite by their specific vibration. (Saleh 2011) Through Fig. 4, it is possible to notice a band in the range of 3640-3620 cm −1 that can be associated with the vibration of free O-H groups represented by water (Kavak and Ülkü 2013). In the range of 1750-1600 cm −1 , it is noticed that the presence of vibration due to the presence ...
Article
Full-text available
Diazepam has been detected in water sources around the world affecting the quality of drinking water. Even in small quantities, recent studies have proven the negative effects of the drug on human body. Since traditional water and sewage treatment do not remove this type of contaminant, it became interesting to evaluate forms to remove them from water sources. A cheap and eco-friendly alternative to remove this drug from the water is through adsorption using the natural clinoptilolite zeolite as an adsorbent. This work goal was to study the characterizations of clinoptilolite, such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), and Fourier transform infrared spectroscopy (FTIR) and analyze the potential of this material as an adsorbent. Kinetic studies and isotherm analysis were performed in batch. The results showed the potential of the natural zeolite to remove the pollutant in an aqueous medium reaching a maximum adsorption capacity of 8.25 mg g−1. The adsorption process followed a pseudo-second-order kinetics indicating that the adsorption was based on a chemisorption process. The isotherms curves shown favorable adsorption and the Langmuir isotherm model fit the experimental data better.
... Zeolites are hydrated aluminosilicates of alkali and alkali earth metals, with infinite, three-dimensional and crystalline structures (Demirbüker-Kavak & Ülkü, 2013). It is well known that zeolites act as ion exchange materials due to their structural properties with high specific surface area and high ion-exchange capacity, and therefore they are widely used to remove metal ions from the aqueous medium (Top & Ülkü, 2004). ...
Article
Full-text available
The effect of zeolite treatment on color change, 5‐hydroxymethyl furfural (HMF), total phenolic compounds (TPCs), ionic composition and texture of sweet pear pekmez was investigated for two different zeolite concentrations during pekmez production. HMF was not detected in clarified pear juice and pekmez samples subjected to 5 g/L (5ZP) and 10 g/L (10ZP) zeolite adsorption. HMF content of pekmez sample without zeolite treatment (PP) was measured as 2.76 ± 0.07 mg/kg. The addition of zeolite just after the clarification results in the reduction of the HMF content of pekmez samples. The highest TPC was determined as 4,958.1 ± 167 mg GAE/kg dry weight in PP sample. Application of zeolite together with conventional clarification resulted in 31.4% and 33.2% reduction in TPC of 5ZP and 10ZP, respectively, compared to PP samples. Zeolite application improved the color quality of pekmez samples. While the amount of fluoride, chloride, bromide, and potassium decreased with the zeolite treatment, the amount of calcium, sodium and magnesium in pekmez samples increased significantly. Zeolite treatment did not significantly affect the texture of the samples. Practical applications Pekmez is concentrated fruit juice with long shelf life and high nutritional value. HMF formation is a very important problem that must be prevented or eliminated in the pekmez production process. This study provides the pear pekmez production process and determination of some important quality features such as color change and amount of HMF and metal ions. Besides, zeolite treatment is applied for the first time during pekmez processing. The results reveal that zeolite treatment is useful means to reduce undesirable metal ions and HMF formation during pekmez production while improving the color quality. Consequently, the use of zeolite in pekmez production has great potential to produce the high quality and safe pear pekmez.
... Arcoya et al. reported a decrease of the characteristic peaks by HCl treatment, however our results show no modification of the characteristic peak intensities, probably due to the stability of crystal structure [26,29]. Our results are in line with those of Kavak et al., who reported that the characteristic peak intensities of clinoptilolite in the control sample were nearly the same as those of samples exposed to gastric fluids [19]. ...
Article
Full-text available
This study presents the effect of thermal treatment (450, 500, 600, 750, and 800 °C) on a Romanian clinoptilolite-rich natural zeolite, along with the interaction of raw and thermally treated zeolites with simulated gastric fluid (SGF, pH = 1.20) at different zeolite to SGF ratios and exposure times. The zeolites were characterized using gravimetric analysis, X-ray fluorescence, powder X-ray diffraction (pXRD), and Fourier transform infrared (FT-IR) spectroscopy. The chemical composition of the zeolite subjected to thermal treatment did not change significantly with the increase of temperature. Structural changes were not detectable by pXRD and FT-IR analyses in the zeolites thermally treated up to 500 °C, while above 600 °C a gradual structural breakdown of zeolite was noticed. At high temperatures, the broad, low-intensity peaks in pXRD patterns indicated the partial amorphization of the crystalline structure. The pXRD and FT-IR analyses showed that the crystalline structure of zeolites remains unaffected after their exposure to SGF. The results revealed that the amounts of Fe, Na, Mg, K, Ca, Al, and Si released depends mainly on the zeolite to SGF ratio, and to a lower extent on the thermal treatment temperature, while the exposure time of 1 to 7 days does not have a significant impact on the elements released in SGF.
Article
Batch experiments were carried out to understand the potential values of clinoptilolite rich mineral and its surfactant modified forms in the removal of Gram-positive and Gram-negative bacteria. Zeta potential and Fourier Transform IR analysis were performed to explain the possible interactions between the bacteria and the zeolite samples. The results revealed that hydrogen bonding was significant mechanism in the removal of bacteria with clinoptilolite rich mineral and anionic surfactant modified clinoptilolite rich mineral whereas both attractive electrostatic forces and hydrogen bonding were dominant mechanism in the removal of bacteria with cationic surfactant modified clinoptilolite rich mineral. Cationic and anionic surfactant modified clinoptilolite rich mineral are promising materials in removal of bacteria studies.
Article
Full-text available
The effects of clinoptilolite in pig's diets were examined on sixty Landrace x Yorkshire crossbred pigs of both sexes divided into two groups: 1. control group, with basal diets; 2. treatment, with basal diets supplemented with 5 g clinoptilolite per 1 kg diet (Cp group). Feed and water were available ad libitum. Individual live weights were recorded on days 45, 90 and 135 of the experiment. Feed consumptions were recorded weekly. Blood was drawn from the anterior vena cava of each pig at day 135 for the determination of serum biochemical parameters. During the first 90 days of the experiment pigs from the Cp group had higher body weight gain (BWG) compared with the control group (+2.5% and +7.0%, respectively) but in the finishing phase of growing their growth parameters were significantly lower (-4.8%). Blood serum biochemical parameters from all experimental pigs were generally within the normal range. Higher triglyceride concentration, lower total cholesterol concentration and increased activity of AST were recorded in the serum of the Cp group.
Article
Full-text available
Samples of natural clinoptilolite modified by treatment with NH4Cl or HCl solutions, followed by thermal treatments, have been characterized, and their catalytic activity evaluated, in o-xylene isomerization and ethanol dehydration reactions. The substitution of the compensating cations by NH4+ does not produce structural changes in the original material, but it opens the channels and increases its acidity and thermal stability. The treatment with HCl increases both the acidity and the effective diameter of the channels and pores but it produces an important loss of zeolite phase. Calcination of the acidic forms above 973 K leads to the breakdown of the zeolite structure. Catalaytic activity of the samples is related to the surface acidity. -from Authors
Article
Full-text available
Samples of natural clinoptilolite modified by treatment with NH4C1 or HCI solutions, followed by thermal treatments, have been characterized, and their catalytic activity evaluated, in o-xylene isomerization and ethanol dehydration reactions. The substitution of the compensating cations by NH4 ~ does not produce structural changes in the original material, but it opens the channels and increases its acidity and thermal stability. The treatment with HCI increases both the acidity and the effective diameter of the channels and pores but it produces an important loss of zeolite phase. Calcination of the acidic forms above 973 K leads to the breakdown of the zeolite structure. Catalytic activity of the samples is related to the surface acidity. For the original and NH4Cl-treated samples, however, the conversion of o-xylene is limited by the access of the reactant inside the channels of the zeolite. A comparative study with modified sepiolite in dehydration of ethanol has also been performed.
Article
Batch sorption experiments were performed in order to understand the potential value of local clinoptilolite rich mineral and its bacteria loaded form in Cr(VI) sorption. The results indicated that Cr(VI) sorption capacities of the sorbents were increased after bacteria loading and the clinoptilolite rich mineral is a promising material in Cr(VI) sorption. Zeta potential and Fourier Transform IR (FTIR) analysis were performed to explain the possible mechanism involved in the Cr(VI) sorption. The results revealed that non-electrostatic forces played a significant role rather than the electrostatic forces. The existence of non-electrostatic forces was confirmed by the FTIR results.
Article
The nature of the interactions between whey proteins and kaolinite surfaces was investigated by adsorption–desorption experiments at room temperature, performed at the isoelectric point (IEP) of the proteins and at pH 7. It was found that kaolinite is a strong adsorbent for proteins, reaching the maximum adsorption capacity at the IEP of each protein. At pH 7.0, the retention capacity decreased considerably. The adsorption isotherms showed typical Langmuir characteristics. X-ray diffraction data for the protein–kaolinite complexes showed that protein molecules were not intercalated in the mineral structure, but immobilized at the external surfaces and the edges of the kaolinite. Fourier transform IR results indicate the absence of hydrogen bonding between kaolinite surfaces and the polypeptide chain. The adsorption patterns appear to be related to electrostatic interactions, although steric effects should be also considered.
Article
In this study, water vapor adsorption properties of the clinoptilolite rich zeolite tuff, from Bigadic (Turkey), and its modified forms were examined. The modified forms were obtained by treating the tuff with HCl solutions (0.032, 0.16, 0.32, 1.6 or 5 M) at 25, 40, 75 and 100 °C for 3 h. Infrared spectroscopy and water vapor adsorption were used for the characterization of the zeolites. Langmuir, BET and Dubinin–Raduschevich methods were applied in the analysis of water vapor adsorption data. Applications of Dubinin Raduschevich equation to the water adsorption data displayed that the super-micropore volume was not very sensitive to acid treatment. It was found out that the Langmuir surface area and ultra-micropore volume depend on the degree of the removal of aluminum from the structure.
Article
The ammonium form of ferrierite (obtained from K,Na-ferrierite, Tosoh) was modified with aqueous solution of hydrochloric acid of different concentration. It has been demonstrated that ferrierite is amenable to HCl solution treatment, while retaining its high crystallinity (XRD, SEM). Dealumination proceeded smoothly and 60% of aluminium was easily removed from the sample just upon 0.25M HCl treatment. 29Si NMR revealed that during the acid treatment the aluminium atoms were removed preferentially from Si(2Al) and Si(1Al) TB positions. Acidity of the samples was assessed by sorption of CO and ammonia and using FT IR spectroscopy. Studies of m-xylene transformations showed increased activity of the samples with increasing level of dealumination. Such behaviour was attributed to a particular morphology of the parent ferrierite. Dealumination of zeolite with the plate-like morphology yields a highly active material, coupled with high para-selectivity after the first acid treatment.
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Aqueous interactions of natural zeolitic material in as-received and modified forms were studied. The zeolitic materials was interacted with acidic (hydrochloric acid, lactic acid, acetic acid) and basic (sodium hydroxide) solutions. Ion exchange, adsorption, complex formation, precipitation and cation hydrolysis were possible interaction mechanisms affected by the amount and cation content of zeolite and pH. The dominant mechanisms seemed to be ion exchange and adsorption in HCl solution when zeolite was used in the as-received form, but dissociation of outer-sphere complexes when modified zeolite was used. In lactic acid, acetic acid as well as the basic solution, cation hydrolysis and complex formation were additional mechanism in the interactions.
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