Peroxo derivatives of hydroxyapatite and calcium hydrophosphate

Article abstract of DOI:10.1134/S003602361105024X

Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized by IR spectroscopy, powder X-ray diffraction, and TGA to be used as biocompatible and antibacterial medicaments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A wide range of hydrogen peroxide percentages in stable mixtures of mCa ₅(PO₄)₃(OH) + nCaHPO₄ ? H ₂O₂ ? H₂O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.

Full text of DOI:10.1134/S003602361105024X

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 5, pp. 673–679. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.S. Skogareva, G.P. Pilipenko, I.V. Shabalova, T.A. Tripol’skaya, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 5, pp. 720–727.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Peroxo Derivatives of Hydroxyapatite and Calcium Hydrophosphate
L. S. Skogareva, G. P. Pilipenko, I. V. Shabalova, and T. A. Tripol’skaya
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
Received November 30, 2009
Abstract—Hydroxyapatite and calcium hydrophosphate peroxo solvates were synthesized and characterized
by IR spectroscopy, powder Xꢀray diffraction, and TGA to be used as biocompatible and antibacterial mediꢀ
caments in manufacturing calcium phosphate bioceramics for implantations in orthopedics and dentistry. A
wide range of hydrogen peroxide percentages in stable mixtures of mCa5(PO4)3(OH) + nCaHPO4 ⋅ H2O2 ⋅
H2O (ranging from 0.5 to 18%) allows composites to be prepared with a tailored active oxygen content.
DOI: 10.1134/S003602361105024X
Bone tissues are multicomponent systems comꢀ substitution by a newly formed bone. The investigaꢀ
prising organic and inorganic materials, the major tions of HA and other calcium phosphates are also
ones being the collagen protein and nanocrystalline important for the reason that these compounds are
hydroxyapatite (Ca5(OH)(PO4)3, HA). Depending on involved not only in tooth and bone formation (calciꢀ
fication), but also in pathologic formation of kidney
stones or cavities in dente.
the HA crystal size, its lines in Xꢀray diffraction patꢀ
terns are either narrow and strong (above 60 nm, tooth
enamel) or broad and of low intensity (10–60 nm,
bone and dente). The crystallinity of synthetic HA is
controlled by the synthesis time and temperature and
range from fully amorphous to nanocrystalline (both
states have diffuse Xꢀray diffraction patterns). When
synthesis is carried out in a dynamic mode [1], particle
aggregation is inhibited and nanocrystals are formed.
Jager et al. [2] employed solidꢀstate NMR spectrosꢀ
copy to find out that hydroxyapatite nanocrystals conꢀ
sist of HA crystals coated with a disordered (unobservꢀ
able by Xꢀray diffraction) surface layer which contains
water and hydrogen phosphate. Hydroxyapatites preꢀ
pared from solution may be either stoichiometric
(ratio Ca/P = 1.67) or nonstoichiometric. Nonstoꢀ
ichiometric apatites are distinguished from stoichioꢀ
2−
On the other hand, hydrogen peroxide is known to
play a considerable role in biochemical processes.
H2O2 formation is observed in all metabolic states. A
peroxide transformation raw includes formation of a
peroxide ion from active oxygen to transform then to
H2O2 either spontaneously or by superoxide dismuꢀ
tase. Studies of the mechanism underlying the activaꢀ
tion of neuron receptors by insulinꢀinduced H2O2 are
now underway [10].
Incorporation of peroxide ions into the apatite
structure or creation of HA mixtures with peroxideꢀ
containing phosphates will allow the creation of comꢀ
posites having antiseptic and antiꢀinflammatory activꢀ
ities and of bone recovery stimulators. There are a
number of works on hydroxyapatite containing peroxꢀ
ide and superoxide ions [11–18]. All of the methods
employed were based on synthesis under severe condiꢀ
metric apatites by higher percentages of
ions
HPO4
3−
that substitute for
ions in the structure and by
PO4
lower Ca/P and OH/P ratios. Ca2+ cations can be subꢀ
stituted by Mg2+, Ba2+, and other cations, and
anions can be substituted by Cl–, F–,
tions: Hydroxyapatite was calcined at 600–1400 С
°
followed by reacting anhydrous hydroxyapatite with
3−
PO4
oxygen at room or elevated temperature. By the data of
2−, and other
2−
CO3
the aboveꢀcited works, the presence of
ions (in an
O2
anions. Carbonate hydroxyapatites have been syntheꢀ
sized [3–6] to imitate natural bone systems in living
bodies, as well as HAs having therapeutic agents (e.g.,
antibiotics [7]). Extensive information on hydroxyapꢀ
atite is found in [8, 9].
Bioceramics based on hydroxyapatite and calcium
phosphates are excellent biocompatible materials for
use in traumatic surgery, orthopedic surgery, dentistry,
and cranyoplastic for substituting for bone defects of
amount of about 1%) induces a small contraction of
the HA unit cell, a decrease in the OH group content
2−
O2
(on account of the substitution of
for OH– inside
channels), and vacancy generation. In the context of
design of tooth pastes, the destructive and whitening
effects of H2O2 solutions have been studied on dente
[19] and hydroxyapatite ceramics [20].
Inasmuch as the biological activity of peroxideꢀ
various origins. An advantage of such bioceramics over containing HA composites will be controlled not only
other synthetic materials is believed to be a high affinꢀ by peroxyapatite itself but also by a peroxo compound
ity to the bone tissue and biodegradability followed by of an impurity (hydrogen phosphate), in this work we
673

674
SKOGAREVA et al.
study peroxo derivatives of HA and calcium hydroꢀ ateꢀfree water under stirring with a magnetic stirrer.
phosphate and develop methods for their synthesis Upon completion of the reaction, the product was colꢀ
under the mild conditions of a reaction with H2O2 lected on a filter, washed with water until Cl– ions disꢀ
solutions. An important problem is to prepare stable appeared, and dried in air to constant weight. Yield:
peroxo compounds having Oact contents safe for a livꢀ 2.430 g. The results of analyses were as follows:
For CaHPO4 · 2H2O anal. calcd., %: Ca2+, 23.29;
PO43–, 55.18.
ing body. Our studies will provide implantations that
would combine the functions of a biocompatible and
antibacterial material.
Found, %: Ca2+, 23.41; PO43–, 55.08.
Preparation of CaHPO4
99.7% H2O2 solution cooled to
CaHPO4 2H2O was poured in portions under stirring
with a magnetic stirrer. The suspension was kept at 0 С
for 3 h, after which the solid phase was collected on a
filter, washed with cool ethanol and diethyl ether, and
dried over anhydrone inside a vacuum desiccator. The
product was obtained as a colorless substance in a
0.280 g yield. The results of analyses were as follows:
For CaHPO4 · H2O2 · H2O anal. calcd., %: Oact,
8.51; H2O2, 18.09; Ca2+, 21.31; PO43–, 50.82.
Found, %: Oact, 8.36; H2O2, 17.78; Ca2+, 21.19;
PO43–, 50.98.
⋅
H2O2
⋅ H2O. To 4 mL of a
0 С, 0.305 g (1.77 mol) of
°
EXPERIMENTAL
⋅
Syntheses were carried out using 12%, 25%, 45%,
66%, 72%, 92%, and 99.7% hydrogen peroxide soluꢀ
tions. The initial materials used were commercially
available chemicals: CaCl2 (pure grade) and
(NH4)2HPO4 (chemically pure grade).
Preparation of crystalline hydroxyapatite (HA)
(proceeding from the procedure described in [21] with
account to [11, 12]). Solutions were prepared from
stoichiometric amounts of CaCl2 (1.995 g of the anhydꢀ
rous salt per 100 mL carbonateꢀfree water) and
(NH4)2HPO4 (1.425 g per 100 mL of carbonateꢀfree
water). Each solution was adjusted to pH of 10–12 by
adding 26% aqueous ammonia. To the solution of the
°
Oact was determined permanganatometrically [22,
3−
PO4
23].
was determined gravimetrically by precipiꢀ
tating magnesium ammonium phosphate and then
calcium salt heated to 85
°
С, the phosphate solution
igniting it to Mg2P2O7; Ca2+ was determined gravimetꢀ
heated to 85 was dropped under vigorous stirring
°
С
with a magnetic stirrer. The suspension was kept at this rically as calcium oxalate [24].
temperature for 20 h. A solid phase was filtered off and
washed with carbonateꢀfree water until Cl– ions were
absent. The product squeezed on a glass filter correꢀ
IR spectra were recorded as KBr pellets on Specord
Mꢀ80 in the region 400–4000 cm–1.
Powder Xꢀray diffraction patterns were recorded on
a Rigaku Xꢀray diffractometer equipped with a RINT
sponded to the composition Ca5(PO4)3(OH)
⋅
48H2O
PO34−
2000 goniometer using Cu
K radiation (anodic voltꢀ
α
(I) (37% of the major material; found, %: ,
age: 50 kV; anodic current: 250 mA); the
10 –90
Thermogravimetric curves for ~30ꢀmg samples
2
θ
range was
20.80%; Ca2+, 14.75%; anal. calcd., %: 20.84 and
14.66%, respectively). A compound of composition
°
°
.
Ca5(PO4)3(OH)
rial) was prepared by exposing compound
⋅
21H2O (II
)
(57% of the major mateꢀ
over anhyꢀ
were recorded on a PaulikꢀPaulikꢀErdey 1500 MOM
instrument in the range from 20 to 500°C at 10 K/min.
I
drone inside a desiccator at room temperature until
the compound appeared as moist clumps. Apatite of
composition Ca5(PO4)3(OH)
(99% of the major material) was prepared by drying
compound to constant weight in air at room temperꢀ
⋅
0.2–0.3H2O (III)
RESULTS AND DISCUSSION
Of the known methods of hydroxyapatite synthesis
(there are wet, dry, and hydrothermal processes [9]), in
this work we used the reaction of CaCl2 with
(NH4)2HPO4 in aqueous ammonia (pH 10–12),
which was either followed by prolonged heating of the
resulting suspension (to obtain crystalline HA) or not
(to obtain amorphous HA). Crystalline compounds
having various degrees of hydration had compositions
I
ature; the presence of water was verified by the appearꢀ
ance of a band at 1640 cm–1 in the IR spectrum.
Preparation of amorphous hydroxyapatite. The
reaction was carried out in the same way as in the synꢀ
thesis of crystalline HA, but at room temperature and
the suspension was filtered just after the synthesis.
Hydroxyapatite peroxo solvates were prepared by
Ca5(PO4)3(OH)
reaction of Ca5(PO4)3(OH)
H2O2 solutions at for 2 h produced peroxo comꢀ
⋅
n
H2O (
n
= 48, 21, or 0.2–0.3). The
reacting 8 mL of an appropriate H2O2 solution with ~1
g
⋅
48H2O ) with 12–92%
(I
of HA at for 2 h, followed by filtering of the susꢀ
0 С
°
0 С
°
pension through a glass filter, washing of the solid
phase by cool ethanol and diethyl ether, and drying
over anhydrone inside a desiccator at 5°С (in a refrigeꢀ
rator).
Preparation of CaHPO4 ⋅ 2H2O. To a solution of
2.039 g (18.37 mmol) of CaCl2 in 100 mL of carbonꢀ
pounds having Oact of from 3.5 to 16.0% (or H2O2 of
from 7.5 to 34.0%, respectively). The H2O2 percentage
in crude (asꢀsynthesized) solvates increased with the
concentration of hydrogen peroxide solutions (Table 1).
When 92% hydrogen peroxide solution was used, the
H2O2 percentage in the product was either virtually the
ateꢀfree water, dropped was a solution of 2.427 g
(18.37 mmol) of (NH4)2HPO4 in 100 mL of carbonꢀ same as for 66% solution (when the product was isoꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 5 2011

PEROXO DERIVATIVES
675
Table 1. Composition of the products produced by reacting Ca5(PO4)3(OH) ⋅ 48H2O with 12–92% hydrogen peroxide solutions
(see Fig. 1)
Oact and H2O2 percentages
in the product after synthesis, %
Composition of the Ca5(PO4)3(OH) ⋅ nH2O ⋅ mH2O2 product
in 1 day after synthesis, %
H2O2 conꢀ
centration, %
PO34–
Ca
2+
O
H O
composition
O
H O
2 2
act
2
2
act
92*
92
66
45
25
12
15.39
7.87
32.72
16.72
33.96
24.90
17.44
7.47
Ca (PO ) (OH)
⋅
12H O
⋅
5.5H O (point A
)
9.67 20.55 31.55 21.65
5.42 11.53
5
4 3
2
2 2
–
–
–
15.97
11.71
8.20
Ca (PO ) (OH)
⋅
⋅
⋅
⋅
11H O
⋅
⋅
7H O (point B
)
11.89 25.28 30.53 20.77
8.04 17.10 34.55 24.47
5.06 10.76 48.74 33.83
1.51 3.21 53.58 38.10
5
4 3
2
2 2
Ca (PO ) (OH)
10H O
4H O (point C
)
5
4 3
2
2 2
Ca (PO ) (OH)
H O 2H O (point D)
⋅
5
4 3
2
2 2
3.51
Ca (PO ) (OH)
0.5H O
⋅
0.5H O (point E
)
5
4 3
2
2 2
* The reaction product was isolated at 0°C.
Table 2. Composition of the products produced by reacting hydroxyapatites with 45% aqueous hydrogen peroxide (see Fig. 2)
Initial hydroxyapatite Hydroxyapatite peroxo solvates
Main
substance
percent
PO34–
Ca
2+
composition
Ca (PO ) (OH) 48H O
composition
10H O 4H O (point A
O
H O
2 2
act
⋅
37
57
98
Ca (PO ) (OH)
⋅
⋅
⋅
⋅
)
8.04 17.10 34.55 24.47
7.08 15.06 41.26 27.53
11.04 23.48 25.64 18.08
5
4 3
2
5
4 3
2
2 2
Ca (PO ) (OH)
⋅
21H O
Ca (PO ) (OH)
4.5H O 3H O (point B)
⋅
5
4 3
2
5
4 3
2
2 2
Ca (PO ) (OH)
⋅
0.25H O
Ca (PO ) (OH)
19.5H O 7.5H O (point C)
⋅
5
4 3
2
5
4 3
2
2 2
lated at
pound was isolated at room temperature). When the
contact time of Ca5(PO4)3(OH) 0.2–0.3H2O with 45
or 66% H2O2 increased to 5 days at , the product
0
°
С
), or oneꢀhalf (when the peroxo comꢀ stoichiometric HAs that have been prepared by a dry
method or from solutions at T > 900 [9, 25, 26], is
°
С
unfavorable for the synthesis of peroxo derivatives by
⋅
5°С
had a very low H2O2 percentage (below 1%), and there
was no difference regardless of whether crystalline or
amorphous HA was used. Evidently, the newly formed
peroxo compounds having high H2O2 percentages
decomposed in prolong contact with the solution.
H2O2 concentration
30
2
After exposure over anhydrone for 1 day at
5 С, the
°
1
products (peroxo solvates) had the compositions as
indicated in Table 1. The maximal H2O2 percentage in
the powdery product was ~25% and corresponded to
B
3
A
20
10
the formula unit Ca5(PO4)3(OH)
⋅
7H2O2 11H2O (for
⋅
C
the reaction with 66% H2O2 solution). The H2O2 perꢀ
centage in peroxyapatite was in direct relation to the
water content of the initial HA. For a 45% H2O2 soluꢀ
1'
D
tion, for example, from Ca5(PO4)3(OH)
obtained was Ca5(PO4)3(OH) 4H2O2 10H2O, and
from Ca5(PO4)3(OH) 21H2O obtained was
Ca5(PO4)3(OH) 3H2O2 · 4.5H2O (Table 2). The comꢀ
position of the product of contacting lowꢀwater
Ca5(PO4)3(OH) 0.25H2O with a 45% H2O2 solution
⋅
48H2O
⋅
⋅
4
5
⋅
,
⋅
E
⋅
0
1
2
3
4
5
6
Time, days
7
8
9
10
(Table 2) signifies the concurrence of hydration and
peroxide solvation. The ordinary desire to increase the
crystallinity of HAs during synthesis, which is proꢀ
vided by the heat treatment of stoichiometric and nonꢀ
Fig. 1. Decomposition curves at 5°C for peroxyapatites
prepared by reacting HA with ( ') 90% H O , ( ) 66%
H O , ( ) 45% H O , ( ) 25% H O , and ( ) 12% H O
1
,
2
1
2
2
5
2
3
4
.
2
2
2
2
2
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 5 2011

676
H2O2 concentration
SKOGAREVA et al.
or 3.34%, respectively. Further, we will demonstrate
that a stable peroxyapatite having this peroxide perꢀ
centage has not been found, which cannot rule out
partial substitutions of OOH groups for OH in HA.
30
Highꢀhydrogen peroxide hydroxyapatite peroxo
solvates are unstable: the almost complete decomposiꢀ
C
tion of the peroxide component (to 0.5–1% H2O2
)
occurs within 3–7 days of storage at (Fig. 1). The
5 С
°
20
lower the degree of hydration of the HA to be reacted
with hydrogen peroxide, the higher the peroxyapatite
decomposition rate (Fig. 2). Peroxyapatite containing
about 1% H2O2 loses oneꢀhalf its Oact within 10 days
A
B
while stored at
5 С; within the following 40 days, the
°
1
H2O2 percentage remains virtually unchanged; that is,
quite a stable peroxide compound is formed, although
having a low H2O2 percentage. From the viewpoint of
preparing a useful medicament, this low percentage of
an oxidizing agent is favorable because of being safe for
a living body. The peroxo solvate isolated from lowꢀ
concentration hydrogen peroxide solutions, also havꢀ
ing a low H2O2 percentage, evolves water and oxygen
while stored over anhydrone, and its composition
approaches the starting Ca5(PO4)3(OH). When the
peroxo compound having 11.9% Oact (25.3% H2O2) is
heated in a polythermal mode, to the decomposition
of the peroxide part of the molecule there corresponds
10
2
3
0
1
2
3
4
Time, days
5
6
7
Fig. 2. Decomposition curves at
prepared by reacting 45% H O with
Ca (PO ) (OH) ⋅ 50H O (samples were stored under anhyꢀ
drone in (
and with (
bottle).
5°С for peroxyapatites
2
(
1,
2)
2
5
4 3
2
1
3
) uncovered and (
2
) covered weighing bottles)
a strong exotherm at 40–70
the dehydration endotherm, which ends at 95
°
С on the background of
)
Ca (PO ) (OH)
⋅ 0.25H O (in an uncovered
5
4 3
2
°
С.
The Xꢀray diffraction pattern of crystalline HA
coincides with the patterns found in the literature [2,
12, 27]. For amorphous hydroxyapatite, the Xꢀray difꢀ
fraction pattern contains, on the background of a halo,
reaction with H2O2, on account of ruling out the presꢀ
ence of water to be substituted.
Thus, binding of peroxide groups follows the solvaꢀ as few as eight broad reflections (d, Å/Irel: 3.435/48,
tion scenario (H2O2 molecules substitute for water 3.106/23, 2.809/100, 2.259/20, 1.935/28, 1.836/35,
molecules). There is indirect evidence that a hydropꢀ 1.713/22, and 1.449/20). For a stable peroxo comꢀ
eroxo group does not substitute for a hydroxo group in pound of hydroxyapatite having ~1% H2O2, the Xꢀray
apatite: for 0.25 mole of H2O2 to substitute for 0.25 mol diffraction pattern displays no additional lines apart
of water in the solvate Ca5(PO4)3(OH) 0.25H2O, the from HA lines. Since structural alterations affect the
⋅
calculated H2O2 percentage should be 0.78% (actually, biological transformation of a material, the retention
we have 0.88%). For the product of composition of the HA structure in lowꢀH2O2 peroxyapatite is a
Ca10(PO4)6(OОH)2 or Ca10(PO4)6(ОН)(OОH) to be positive factor on account of proving the constancy of
obtained, the H2O2 percentage would have been 6.57 properties of bioperoxycomposites.
Table 3. Composition of the products produced by reacting CaHPO4 ⋅ 2H2O with aqueous hydrogen peroxide
O
, %
H O , %
2 2
act
H2O2
Product composition
concentration, %
found
calcd.
found
calcd.
45
0.25
6.91
8.01
8.33
0.53
14.68
17.03
17.72
72
6.92
7.72
8.51
14.72
16.42
18.09
CaHPO
CaHPO
CaHPO
⋅
⋅
⋅
0.8H O
⋅
⋅
1.2H O
2
4
4
4
2
2
92
0.9H O
1.1H O
2
2
2
99.7
H O
⋅
H O
2
2 2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 5 2011

PEROXO DERIVATIVES
677
Table 4. Xꢀray diffraction data for CaHPO4 ⋅ H2O2 ⋅ H2O
, Å , Å
In the IR spectra of the initial hydroxyapatite of
composition Ca5(PO4)3(OH) 0.2–0.3H2O and perꢀ
⋅
d
I
d
I
rel
rel
oxyapatite (3.92% Oact or 8.34% H2O2), there are phosꢀ
phate bands: ν1 = 958 cm–1 (nondegenerate symmetrical
stretching P–O vibrations); ν3 = 1040, 1094 cm–1 (with
a shoulder; triply degenerate antisymmetrical stretchꢀ
ing P–O vibrations; in the peroxide derivative, splitꢀ
ting of ν3 disappears); ν2 = 472 cm–1 (with a shoulder;
doubly degenerate vibrations of bound OPO); and
ν4 = 564 (with a shoulder), 604 cm–1 (triply degenerꢀ
ate vibrations of bound OPO). The stretching vibraꢀ
8.064
7.607*
4.371
4.238*
4.021
3.750*
3.184
3.046*
2.962
2.851*
2.796
2.734
2.707
2.585
2.498
2.476
100
18
20
4
3
1
49
5
8
2
1
10
7
4
4
3
2.383
2.333
2.273*
2.157
2.150*
2.102
2.010*
1.960
1.893
1.860
1.717
1.682
1.668
1.643
1.586
1.433
3
1
7
3
2
6
4
3
4
7
2
1
1
2
3
2
tions of hydroxyls appear at 3408 cm–1
and 3568 cm–1 (OH)HA); the band at 632 cm–1 was
assigned to the libration vibrations of OH. The bendꢀ
ing vibrations of water (H–O–H) appear as a band at
(
ν
(OH)H2O)
(
ν
δ
1640 cm–1. The appearance of a weak band (someꢀ
times, as a shoulder) at 876 cm–1 in all HA and peroxyaꢀ
patite samples is indicative of a minor hydrogen phosꢀ
phate impurity. The characteristic band at 1460 cm–1
does not appear. The spectra are characteristic of comꢀ
pounds having phosphate and hydroxide groups [28]
and coincide with literature data for HA [2, 11, 12,
29–33]. The vibrations of the peroxide part of apatite
peroxo solvate do not appear in IR spectra.
* Reflections from impurity CaHPO ⋅ 2H O.
4
2
For understanding the mechanism of reactions of Table 5. Vibration frequencies (cm–1) in the IR spectra of
CaHPO4 ⋅ 2H2O and CaHPO4 ⋅ H2O2 ⋅ H2O
phosphates with hydrogen peroxide, it was important
to elucidate the reaction pathways: whether the reacꢀ
tion involve substitution of H2O2 for water molecules
or addition of H2O2 molecules. A suitable subject for
this purpose was calcium hydrophosphate. It appeared
that anhydrous CaHPO4, obtained by dehydration of
CaHPO · 2H O CaHPO · H O · H O
Assignment
4
310 w
344 w
360 s
2
4
2
2
2
316 m
Ca–O(H O)
2
360 m
394 w
412 m
446 w
458 w
CaHPO4 2H2O at 170–180°С, does not react with
⋅
402 w
416 w
99.7% H2O2 solution; that is, addition of hydrogen
peroxide to hydrophosphate does not occur in a pracꢀ
tically anhydrous medium. Below, we will make it clear
that, in order for a peroxo compound to be obtained,
solvation water should be present in the initial phosꢀ
phate molecule or aqueous H2O2 solutions should be
used. As for HA, here binding of peroxo groups by calꢀ
cium hydrophosphate occurs via the substitution of
hydrogen peroxide for water. Since water molecules in
the structure of layered calcium hydrophosphate dihyꢀ
drate are bound with calcium ions and are arranged
OPO bound
OPO bound
528 v.s.
576 v.s.
664 s
528 v.s.
582 s
736 s
788 v.s.
872 v.s.
984 v.s.
868 v.s.
ν
s(P–O)
HPO24−
between planes formed by
and Ca2+ ions,
1004 v.s.
1056 v.s.
1132 v.s.
1452 v.s.
hydrogen peroxide molecules that have substituted for
water may also be coordinated to the metal atom.
1060 v.s.
1132 v.s.
ν
as(P–O)
The reactions of CaHPO4
99.7% H2O2 solutions at yield peroxo compounds
of compositions CaHPO4 · 0.8H2O2 1.2H2O,
CaHPO4 0.9H2O2 1.1H2O, and CaHPO4 H2O2
⋅
2H2O with 72%, 92%,
0 С
°
δ
δ
(OOH)
⋅
1220 s
1648 v.s.
1723 w
2926 w
3168 s
3284 s
3504 s
3544 s
⋅
⋅
⋅
⋅
1644 v.s.
(H–O–H)
H2O, respectively (Table 3). A double treatment of
CaHPO4 · 2H2O with 99.7% H2O2 yields an unstable
solvate CaHPO4 H2O2. There is mention in the literꢀ
⋅
2832 s
ν
ν
(OH)(H O )
2 2
ature that an unstable compound was prepared from
CaHPO4 and 30% H2O2 whose composition
3136 s.br.
(OH)(H O)
2
(
CaHPO4 0.5H2O2) was derived from the Oact perꢀ
⋅
3408 s
3536 s
ν
(OH)(HPO )
4
centage solely [34]. In case where 45% H2O2 was used,
the product contained as little as 0.25% Oact (0.53%
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 5 2011

678
SKOGAREVA et al.
In the IR spectra of CaHPO4
agreement with [35]) and CaHPO4 H2O2
Table 5), there are bands of hydrophosphate ions (the
⋅
2H2O (in good
⋅
⋅
H2O (Fig. 3,
1
2−
most characteristic band of the
ion appears at
HPO4
~870 cm–1), water, hydrogen peroxide, and Ca–O
bond in the lowꢀfrequency part of the spectrum. Of the
two most characteristic vibrations of hydrogen peroxꢀ
ide, only one vibration ( (ООН)) appears in the IR
δ
spectrum of the peroxide derivative at 1452 cm–1. The
presence of carbonate ions, which absorb in the same
region, is ruled out: they are absent in the initial calꢀ
cium hydrophosphate and hydrogen peroxide soluꢀ
tions. The band associated with the stretching vibraꢀ
tions
appear on the background of a strong band at 868 cm–1
νs(P–O))
The results we obtained on calcium peroxohydroꢀ
ν
(О–О) (in the region ~880 cm–1) does not
2
(
.
phosphate allowed us to explain the formation of perꢀ
oxyapatite having a stable composition and a low H2O2
percentage: impurity calcium hydrogen phosphate,
the occurrence of which was verified spectroscopically,
forms a stable peroxide derivative.
Since the H2O2 percentage in stable peroxyapatite
is not high (0.5%), a sufficiently stable calcium hydroꢀ
phosphate peroxo solvate is a suitable additive to HA
for manufacturing bioceramic composites having a
tailored H2O2 percentage. Mixtures of hydroxyapatite
3600 2800 2000 1600 1200
4000 3200 2400 1800 1400 1000 600
, cm–1
800
400
with CaHPO4
⋅
H2O2 H2O were prepared in two ways,
⋅
by means of (1) mechanical blending of HA with calꢀ
cium peroxohydrophosphate and (2) incomplete
ν
hydrolysis of CaHPO4 2H2O (by heating with carꢀ
⋅
Fig. 3. IR spectra of (
1)
CaHPO
⋅
2H O and (
2)
CaHPO
4
⋅
4
2
bonateꢀfree water in a weight ratio of the solid material
to water of 1 : 100; the produced phosphoric acid was
repeatedly washed off with water) followed by reacting
a (HA + hydrophosphate) solid mixture with a hydroꢀ
gen peroxide solution (a process is known for preparꢀ
ing HA via hydrolysis of poorly soluble calcium orthoꢀ
H O H O
⋅
.
2
2
2
H2O2). The Xꢀray diffraction pattern for CaHPO4
H2O2 H2O is displayed in Table 4. At room temperaꢀ
ture, the compound loses less than 1.5% of Oact within
⋅
⋅
six months; the stable calcium peroxohydrophosphate phosphates [8, 36, 37]). For selecting the optimal and
corresponds to CaHPO4 0.8H2O2 1.2H2O
⋅
⋅
.
stable composition of CaHPO4 H2O2 H2O to be
⋅
⋅
used by the first method, mixtures of these compounds
were prepared in ratios of 1 : 1, 1 : 2, 1 : 3, 1 : 4, and 2 : 1.
For ratios of 1 : 4 and 2 : 1, the compositions containꢀ
ing 7.6 and 3.1% H2O2, respectively, were stable during
the time of the experiment, namely, for 8 days. A simꢀ
ilar mixture (2 : 1) containing 4% H2O2 did not change
its composition within at least three months. Accordꢀ
ing to the second method, the ratio of the product
Under the TGA conditions, the initial CaHPO4
⋅
2H2O is dehydrated in the range 160–190°С (with a
strong endotherm); at 390–410°C, the newly formed
calcium hydrophosphate decomposes at 390–410°C
to yield Ca2Р2O7 (with a weak endotherm). The weight
loss upon heating to 500
tion 2CaHPO4 2H2O
24.3). The DTA curve for CaHPO4
tures one weak exotherm at 135–145
°
С
is 24.8% (for the overall reacꢀ
Ca2Р2O7 + 5H2O, calcd., %:
⋅
→
⋅
H2O2
°С
⋅
H2O feaꢀ
(HA) to the initial compound (CaHPO4 2H2O) varies
⋅
(associated
depending on the duration and temperature of the
water treatment of calcium hydrophosphate; pure
hydroxyapatite is the limiting case. The products of the
reaction of such the mixtures with H2O2 contain perꢀ
oxyapatite and calcium peroxohydrophosphate. Speꢀ
cial mention should be made that the major amount of
H2O2 in the mixtures is on account of calcium peroxꢀ
ohydrophosphate. The hydrogen peroxide percentꢀ
ages in the mixtures range quite widely, from 0.5% for
pure peroxyapatite to 18% for calcium peroxohydroꢀ
with the decomposition of the peroxide part of the
material) and two endotherms (a strong one associated
with the end of dehydration at 145–150
one associated with calcium pyrophosphate formation
at 400–420 ). The weight loss in the range 90–150
is 27.9% (for the reaction CaHPO4 H2O2 H2O
CaHPO4 + 2H2O + 1/2O2 calcd., %: 27.7). The overall
weight loss is 31.3% (for the reaction 2CaHPO4 H2O2
H2O Ca2Р2O7 + 5H2O + O2 calcd., %: 31.0).
°
С and a weak
°
С
°
С
⋅
⋅
→
⋅
⋅
→
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 5 2011

PEROXO DERIVATIVES
679
15. C. Rey, J.ꢀC. Trombe, and G. Montel, C. R. Acad. Sci.,
phosphate. This makes it possible to prepare composꢀ
ites for manufacturing bioceramics having tailored
active oxygen percentages.
Ser. C 273 (17), 1081 (1971).
16. J.ꢀC. Gourdon, C. Rey, C. Chachaty, et al., C. R. Acad.
Sci., Ser. B 276 (13), 559 (1973).
Porous ceramics are preferred for clinical practices
on account of their higher surface activities.
Macroporous implantations transformable to new
bone and comprising hydroxyapatite and tricalcium
phosphate have been prepared [38–40]. Our prepared
calcium peroxohydrophosphate has a moderate denꢀ
sity (1.2 g/cm3) and a higher solubility in lowꢀacidity
media than hydroxyapatite and its peroxide derivative.
When used in biocomposites, these properties may
appear favorable on account of enhancing an increase
in porosity of the material immediately in contact with
the medium of the body, the better intergrowth of the
body tissue into pores, and thereby greater biocompatꢀ
ibility.
17. J. Dugas and C. Rey, J. Phys. Chem. 81 (14), 1417
(1977).
18. Y. Matsumura, H. Kanai, and J. B. Moffat, J. Mol.
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20. J. M. Yanurudin, K. Ozeki, H. Aoki, et al., BioꢀMed.
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Mir, Moscow, 1985).
22. W. C. Schamb, C. N. Satterfield, and R. Wentworth,
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ACKNOWLEDGMENTS
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The authors are thankful to N.A. Minaeva for carryꢀ
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