Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces
An ion-pair model has been proposed explaining the origin of acidic sites at the silica surface–aqueous solution interface. The results of quantum chemical simulation testify the idea on principal role of ion-pair state of water molecules in the hydrolysis of saccharose adsorbed on silica surface. З...
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| Опубліковано в: : | Хімія, фізика та технологія поверхні |
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| Дата: | 2010 |
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Інститут хімії поверхні ім. О.О. Чуйка НАН України
2010
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| Цитувати: | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces / O.M. Tsendra, A.G. Grebenyuk, V.V. Lobanov // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 3. — С. 238-241. — Бібліогр.: 12 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860076978181242880 |
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| author | Tsendra, O.M. Grebenyuk, A.G. Lobanov, V.V. |
| author_facet | Tsendra, O.M. Grebenyuk, A.G. Lobanov, V.V. |
| citation_txt | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces / O.M. Tsendra, A.G. Grebenyuk, V.V. Lobanov // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 3. — С. 238-241. — Бібліогр.: 12 назв. — англ. |
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| container_title | Хімія, фізика та технологія поверхні |
| description | An ion-pair model has been proposed explaining the origin of acidic sites at the silica surface–aqueous solution interface. The results of quantum chemical simulation testify the idea on principal role of ion-pair state of water molecules in the hydrolysis of saccharose adsorbed on silica surface.
Запропоновано модель іонних пар, яка пояснює виникнення кислотних центрів на межі поділу фаз поверхня кремнезему – вода. За допомогою квантово-хімічного моделювання було показано, що дисоційована вода відіграє істотну роль в гідролізі сахарози, адсорбованої на поверхні кремнезему.
Предложена модель ионных пар, объясняющая возникновение кислотных центров на поверхности раздела фаз кремнезем – вода. С помощью квантово-химического моделирования было показано, что диссоциированная вода играет существенную роль в гидролизе сахарозы, адсорбированной на поверхности кремнезема.
|
| first_indexed | 2025-12-07T17:13:50Z |
| format | Article |
| fulltext |
Хімія, фізика та технологія поверхні. 2010. Т. 1. № 3. С. 238–241
_____________________________________________________________________________________________
* Corresponding author oksynka@ukr.net
238 ХФТП 2010. Т. 1. № 3
UDC 544.723
ROLE OF IONIZED STATES OF WATER MOLECULES
IN THE REACTION OF HYDROLYSIS OF SACCHAROSE
ON SILICA SURFACES
O.M. Tsendra*, A.G. Grebenyuk, V.V. Lobanov
Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine
17 General Naumov Street, Kyiv 03164, Ukraine
An ion-pair model has been proposed explaining the origin of acidic sites at the silica surface–
aqueous solution interface. The results of quantum chemical simulation testify the idea on principal role of
ion-pair state of water molecules in the hydrolysis of saccharose adsorbed on silica surface.
INTRODUCTION
The theoretical treatment of adsorption pro-
cesses on solid oxide surfaces becomes conside-
rably complicated when the influence of the li-
quid medium should be taken into account. This
necessity arises every time when a detailed simu-
lation is needed to shed light on the sorption
mechanism and the rate-limiting stages.
Usually, the experimental data available re-
veal a substantial role of the solvent in sorption
phenomena [1, 2]. Water is by far the most im-
portant and frequently used solvent. As a rule, the
solvent is portrayed as an ensemble of neutral
molecules. However, as water and other solvent
molecules have dipole moments they can indeed
get coordinated to reaction sites.
Recently a lot of reports appeared that use
advanced quantum chemical techniques to study
the role of the solvent [3, 4]. These studies reveal
the coexistence of clusters of the solvent in the
state of molecules and ion-pairs (Fig. 1).
Fig. 1. Energy levels. Molecular state vs ion-pair state
Systems containing only molecules are called
"molecular state" systems. Other systems can also
exist that though being electrically neutral as a
whole, have ions together with neutral molecules.
These are the "ion-pair" systems. Ions appear as a
result of proton transfer between molecules. Pro-
vided surface acid-base sites are strong enough,
the energy level of the ion-pair state can be lower
than that of the molecular state.
The most interesting problem in aqueous sys-
tems with ion pairs is to find a minimum number
of water molecules needed to produce stable iso-
lated ion pairs (Н3О
+ and ОН–). There is no defi-
nite answer to this question because the results of
quantum chemical calculations depend on both
the accuracy of the method and the basis set used.
No experimental data are available for verifying
such calculations.
A similar situation could be found in other
systems containing water and ionic substances. A
general conclusion for the systems is that only a
few molecules, from 5 to 10, are enough to pro-
duce the transition from molecular associates to
isolated ion-pairs. A cluster of 8 water molecules
is an example of the existence of isolated ion
pairs (Fig. 2) [5]. All oxygen atoms are located in
the cube vertexes. We can see that in this cluster
both molecular water and ion-pair states can co-
exist with a transition temperature of 259 K.
Similar results about the state (ion-pairs or mo-
lecular) of hydrated complexes of some acids,
bases, and salts can be found elsewhere [6–9].
RESULTS AND DISCUSSION
The presence of hydroxyl groups on oxide sur-
faces (including silica) and their possible
Role of Ionized States of Water Molecules in the Reaction of Hydrolysis
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 3 239
a
b
c
Fig. 2. Isomeric forms of the (H2O)8 cluster [6] (a, b)
and equilibrium (c) of isomeric forms of the
(H2O)8 cluster (phase transition at 259 K)
hydration in clusters pose the question on the
possible formation of ion-pairs within the surface
layer and their possible role in chemical trans-
formation of adsorbed species.
Let us analyze an example of such a trans-
formation, namely the hydrolysis of saccharose
catalyzed by acid silanol groups, by means of
quantum chemistry. A general scheme of the
process should be as follows:
С12Н22О11 + Н2О C6Н12О6 + C6Н12О6
Fru
(fructose)
Glc
(glucose)
Sacch
(saccharose)
T, K
SiO2
surface
Calculations were carried out using the density
functional theory method. All initial geometry
optimizations and zero point vibrational en-
ergy corrections were performed by the
B3LYP/ 6-31G**method [10] widely used for
studying similar systems with hydrogen bonding
and proton transfer. Silica surface was simulated
with an adamantane-like structure of
(SiO2)9·8H2O (A) [11].
Equilibrium structures and total energies of
reagents and products were calculated in both the
gas phase (vacuum) and an aqueous environment.
For the latter the effect of the solvent was taken
into account using the continuous self-consistent
reaction field theory (SCRF). The results in Fig. 3
show two effects: (i) the solvent noticeably de-
creases the sum of the total energies of the initial
species (Sacch and water); (ii) the presence of an
aqueous environment results in a reversal of the
sign of the energy change of the reaction, that
now becomes more feasible.
gas phase
aqueous medium
Energy values, a.u.
Fig. 3. Energies of saccharose hydrolysis in gas phase
and in aqueous medium
The second part of the research was devoted to
studies of the structure and formation energy of the
adsorption complexes of glucose adsorbed on a
dehydrated silica surface. Despite the presence of
weak acidic silanol groups on silica, no point was
found on the potential energy surface of the system
O.M. Tsendra, A.G. Grebenyuk, V.V. Lobanov
_____________________________________________________________________________________________
240 ХФТП 2010. Т. 1. № 3
(А+Sacch) related to a proton transfer from a si-
lanol group to a Saccharose molecule. This result
can be explained by a high value of the energy for
deprotonation of the silanol group, 1129.3 kJ/mol
as theoretically calculated (or 1400±25 kJ/mol as
experimentally determined [12]).
Complicate physicochemical processes at the
water/silica interface are known to define the
structure and properties of water adsorption com-
plexes. It was shown in some theoretical works
that in an aqueous shell near silica surface the
existence is possible of ion pairs along with po-
lymolecular adsorption complexes of individual
water molecules. The structure of the former is
built of H3O
+ ions and superficial ≡SiO– groups
which in water are separated by a few water
molecules. (Fig. 4) According to the results of the
calculations, in such structures the Si–O bond is
substantially shorter (1.56 Å) than the Si–OH one
(1.66 Å). The length of the shortest hydrogen
(O···HOH) bond is of 1.75 Å. A characteristic of
the ionized states is that the energy of isolation of
protons from the water molecules separating the
charged centers is far lower (975.8 kJ/mol as cal-
culated) than that of isolated silanol groups
(1129.3 kJ/mol). This proves that intermediate
water molecules have an enhanced acidity as
compared to isolated silanol groups.
1,75 А
1,56 А
+
–
∆E(H+)=975.8 kJ/mol
∆E(H+)=1129,3 kJ/mol
1,66 А
Fig. 4. Structure of a water cluster around isolated
silanol group in ion-pair state
The reaction of disaccharide hydrolysis itself
can be considered monomolecular. It consists in the
breaking up of a glycoside bond of the protonated
molecule that results into the formation of a mono-
saccharide molecule and a carbenium ion. Interac-
tion of the latter with water molecules within the
reaction zone produces another monosaccharide
molecule and the recovery of the silanol groups.
The calculated formation energy of the adsorp-
tion complex of saccharose on hydrated silica surface
is of 50.9 kJ/mol. In the case of a dehydrated surface
the deprotonation energy is lower (41.0 kJ/mol).
Calculations show a synchronous elongation
of the bonds of the glycoside oxygen atom and
the carbon atom of the glucose residue. Therefore
the hydrolysis should occur by a simultaneous
transfer of two protons, as it occurs in most pro-
cesses of ion-pair formation. Thus, formed fruc-
tose molecule would be kept near silica surface
by hydrogen bonding (Fig. 5).
The results of computations on the total energy
of adsorption complex as a function of the O–H
bond length of one of the intermediate water mole-
cules are shown in the Fig. 6.
Fig. 5. Proton transfer from the ionized hydrated com-
plex formed around silanol group to the ad-
sorbed saccharose molecule
Fig. 6. Dependence of the total energy of the adsorp-
tion complex on the O-H bond length of one of
the intermediate water molecules
Role of Ionized States of Water Molecules in the Reaction of Hydrolysis
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 3 241
The activation energy of the reaction of sac-
charose hydrolysis on hydrated silica is rather
high (178 kJ/mol) and therefore it is only feasible
at relatively high temperatures.
CONCLUSIONS
When adsorbed over silica surface, water
gains acidic properties and acts as a catalyst for
saccharose hydrolysis.
The application of the idea of ionized states
to the hydrated layer of silica surfaces enables
simulating a complex set of physical and chemi-
cal processes occurring on solid surfaces. These
phenomena cannot be simulated using ordinary
theoretical techniques that considering only neut-
ral water molecules.
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Received 02.07.2010, accepted 17.08.2010
Роль іонізованих станів молекул води в гідролізі сахарози на поверхні кремнезему
О.М. Цендра, А.Г. Гребенюк, В.В. Лобанов
Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України
вул. Генерала Наумова 17, Київ 03164, Україна, oksynka@ukr.net
Запропоновано модель іонних пар, яка пояснює виникнення кислотних центрів на межі поділу фаз повер-
хня кремнезему – вода. За допомогою квантово-хімічного моделювання було показано, що дисоційована вода
відіграє істотну роль в гідролізі сахарози, адсорбованої на поверхні кремнезему.
Роль ионизированных состояний молекул воды в гидролизе сахарозы
на поверхности кремнезема
О.М. Цендра, А.Г. Гребенюк, В.В. Лобанов
Институт химии поверхности им. А.А. Чуйко Национальной академии наук Украины
ул. Генерала Наумова 17, Киев 03164, Украина, oksynka@ukr.net
Предложена модель ионных пар, объясняющая возникновение кислотных центров на поверхности раздела
фаз кремнезем – вода. С помощью квантово-химического моделирования было показано, что диссоциированная
вода играет существенную роль в гидролизе сахарозы, адсорбированной на поверхности кремнезема.
|
| id | nasplib_isofts_kiev_ua-123456789-28984 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 2079-1704 |
| language | English |
| last_indexed | 2025-12-07T17:13:50Z |
| publishDate | 2010 |
| publisher | Інститут хімії поверхні ім. О.О. Чуйка НАН України |
| record_format | dspace |
| spelling | Tsendra, O.M. Grebenyuk, A.G. Lobanov, V.V. 2011-11-27T16:07:03Z 2011-11-27T16:07:03Z 2010 Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces / O.M. Tsendra, A.G. Grebenyuk, V.V. Lobanov // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 3. — С. 238-241. — Бібліогр.: 12 назв. — англ. 2079-1704 https://nasplib.isofts.kiev.ua/handle/123456789/28984 544.723 An ion-pair model has been proposed explaining the origin of acidic sites at the silica surface–aqueous solution interface. The results of quantum chemical simulation testify the idea on principal role of ion-pair state of water molecules in the hydrolysis of saccharose adsorbed on silica surface. Запропоновано модель іонних пар, яка пояснює виникнення кислотних центрів на межі поділу фаз поверхня кремнезему – вода. За допомогою квантово-хімічного моделювання було показано, що дисоційована вода відіграє істотну роль в гідролізі сахарози, адсорбованої на поверхні кремнезему. Предложена модель ионных пар, объясняющая возникновение кислотных центров на поверхности раздела фаз кремнезем – вода. С помощью квантово-химического моделирования было показано, что диссоциированная вода играет существенную роль в гидролизе сахарозы, адсорбированной на поверхности кремнезема. en Інститут хімії поверхні ім. О.О. Чуйка НАН України Хімія, фізика та технологія поверхні Теорія хімічної будови, реакційної здатності та хімічного модифікування поверхні твердих тіл Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces Роль іонізованих станів молекул води в гідролізі сахарози на поверхні кремнезему Роль ионизированных состояний молекул воды в гидролизе сахарозы на поверхности кремнезема Article published earlier |
| spellingShingle | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces Tsendra, O.M. Grebenyuk, A.G. Lobanov, V.V. Теорія хімічної будови, реакційної здатності та хімічного модифікування поверхні твердих тіл |
| title | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces |
| title_alt | Роль іонізованих станів молекул води в гідролізі сахарози на поверхні кремнезему Роль ионизированных состояний молекул воды в гидролизе сахарозы на поверхности кремнезема |
| title_full | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces |
| title_fullStr | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces |
| title_full_unstemmed | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces |
| title_short | Role of Ionized States of Water Molecules in the Reaction of Hydrolysis of Saccharose on Silica Surfaces |
| title_sort | role of ionized states of water molecules in the reaction of hydrolysis of saccharose on silica surfaces |
| topic | Теорія хімічної будови, реакційної здатності та хімічного модифікування поверхні твердих тіл |
| topic_facet | Теорія хімічної будови, реакційної здатності та хімічного модифікування поверхні твердих тіл |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/28984 |
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