Method of determining impurities of nitrogen compounds in hydroxyapatite

FIELD: chemistry.

SUBSTANCE: hydroxyapatite sample is irradiated with X-ray, gamma or electron beams, followed by recording the EPR spectrum resulting from exposure of paramagnetic centres on a certified EPR spectrometre. Spectral characteristics the observed EPR spectrum (number of observed lines and their position) are calculated while monitoring measurement error and comparing the obtained spectral characteristics with known spectral characteristics of nitrogen radicals in (poly)crystalline compounds.

EFFECT: possibility of qualitative and quantitative analysis of nitrogen compounds in substances with the structure of hydroxyapatites.

2 dwg

 

The invention relates to physico-chemical methods of analysis, and in particular to methods of determining impurities of nitrogen compounds, in particular nitrates and nitrites, in hydroxiapatite (the gap).

Substances with a structure of hydroxyapatite, CA10(RHO4)6(OH)2are part of the biological tissue. The synthesized HAP is widely used as a preventive component of toothpastes and medical material for filling bone defects, which must be completely biocompatible with human tissues and chemical composition close to the composition of tooth enamel and bone tissue [1, 2].

The invention can be used to control the qualitative composition of natural and synthesized HAP in the sense of the presence of impurities of nitrogen compounds in order to increase the biocompatibility of the synthesized and natural hydroxiapatite, leading to greater efficiency hygienic and preventive measures and treatment with the use of synthetic HAP.

To improve the chemical and phase similarity to the inorganic component of bone tissue using chemical modification of the gap, for example CA10-xNax(RHO4)6-x(CO3)x(OH)2, carbonated hydroxyapatite (hereinafter CGAP), in which the index value x (the degree of carbonization) IU aetsa from 0 to 2 [3, 4].

In some known to the applicant techniques for the synthesis of HAP and CGAP use solutions of the salts of nitric acid (nitrate and nitrite) sodium and/or calcium [5, 6]. It has been shown [5]that in the process of synthesis of hydroxyapatite in a colloidal solution nitrogen compounds can be introduced into the crystalline structure of hydroxyapatite.

Numerous studies (see, for example, [7]) indicate the toxicity of nitrate and nitrite: nitrate in the digestive tract is partially reduced to nitrite (more toxic compounds), and the last to enroll in the blood can cause methemoglobinemia.

In addition, the nitrite in the presence of amines can form N-nitrosamines that are carcinogenic activity that places high demands on the chemical composition of hydroxiapatite as materials, widely used in medical purposes.

Thus, the determination of impurities of nitrogen compounds in the material, widely used in medical purposes, as well as part of a biological tissue, is an important task for biomedical applications.

Of the investigated prior art the applicant is not known how (analogues), similar to the claimed technical solution for the implementation of tasks. The applicant known methods of determination of the composition of nitrate in water (GOST 22688-77, [8]), nitrate and nitrite in feed, feed and feed raw materials (GOST 13496.19-93, [9]), methods for the determination of mass fractions of nitrate and nitrite in cheese (GOST R 51460-99, [10]), in caseino and Caseinates (GOST R 51454-99, [11]).

Known to the applicant and the above solutions are based on the following physical principles and methods: chemical, photometric and ionometric fundamentally different from the claimed technical solution.

Thus, the above methods are intended solely for the safety assessment of food products for humans and animals, while they may not be fully used to achieve the stated technical problem solving.

A known method of electron paramagnetic resonance (EPR) is used to identify the fact of radiation exposure (detection of radiation effects) in the food (meat and meat products containing bone tissue, [12]), to identify a number of inorganic radicals in materials with the structure of hydroxyapatite arising under the action of x-rays or gamma radiation [13-17].

The above methods [8-17] are used for the following purposes:

- to assess the safety of the food supply for humans and animals,

- to identify a number of inorganic radicals in the materials from which the structure of hydroxyapatite, arising under the action of x-rays or gamma radiations, such as carbonate, phosphate and oxygen radicals.

Their main disadvantage is that they are not intended and was not used for the purposes of qualitative and quantitative analysis of the presence of nitrogen compounds in substances with a structure of hydroxiapatite.

The claimed technical solution is aimed at studying the chemical composition of hydroxiapatite used for biomedical research and therapeutic events providing opportunities to improve the controlled characteristics of these materials in order to reduce their toxicity and enhance biological compatibility, ultimately resulting in increased efficiency hygienic and therapeutic measures with the use of gap and CHAP.

While the claimed technical solution provides the following features:

- detect impurity content of nitrogen compounds in natural and synthesized hydroxiapatite;

assessment of quantitative indicators;

- the ability to control the qualitative composition of the synthesized materials with the structure of hydroxyapatite in the sense of the presence of admixtures of nitrogen compounds in the synthesis process, and the process of cleaning materials from inclusions that can is t to be used when deciding on the admissibility of the use of synthetic HAP and CGAP in biomedical applications and will make recommendations for improving the production technology of materials structure hydroxyapatite to minimize toxicity and to increase the biological compatibility with natural materials, leading, ultimately, to increase the effectiveness of hygienic and therapeutic measures using hydroxiapatite.

The claimed method for the determination of impurities of nitrogen compounds in the hydroxyapatite is in the irradiation of a sample of hydroxyapatite x-ray, gamma or electron rays with the subsequent registration of the EPR spectrum arising under irradiation of paramagnetic centers in a certified EPR spectrometer, the calculation of the spectral characteristics of the observed EPR spectrum (the number of observed lines and their position) to control the error of the measurement and the comparison of the obtained spectral characteristics with known spectral characteristics of nitrogen radicals in the (poly)crystalline compounds [19, 20].

The claimed method is characterized by the following sequence of steps:

a) placing a sample of hydroxyapatite in a standard quartz ampoule of an EPR spectrometer;

b) irradiation of a sample of hydroxyapatite x-ray, gamma or electron beams (with the observance of sanitary-hygienic norms) at room temperature, the radiation dose is 10±5 kGy (kilogray);

C) registration of the EPR spectrum in a certified EPR spectrometer, allowing Provo is resolved measurements in continuous or pulsed modes of operation;

g) calculating parameters of the EPR spectrum (the number of observed lines, n, the values of the g-tensor and hyperfine interaction tensor A)

d) the control error of the measurement results;

(e) comparison of the obtained parameters, known for nitrogen radicals, such as NO32-in irradiated crystalline matrices (the number of observed lines, n, the values of the g-tensor and hyperfine interaction tensor A: n=3, g||=2.005(1), g=2.009(1), And||=6.65(20) MT And=3.4(5) MTL).

It should be noted that the change in the sequence of operations a) and b) does not modify the technical result.

Achieved technical result is the identification of the presence of impurities of nitrogen compounds in the gap and CGAP based on the recording of the spectra of paramagnetic centers obtained by irradiating the above-mentioned materials, x-ray, gamma or electron rays, the EPR method and the estimation of the number of these centers on the measurement of the amplitude (intensity) components of the observed EPR spectrum.

The applicant for the first time in the composition of hydroxyapatite (HAP) and materials with a structure similar to the structure of hydroxyapatite (CHAP), based on the registration by the EPR method were found paramagnetic centers, which, according to the applicant, due to cash what chii impurities of nitrogen compounds to the above compounds.

List of figures graphical images

Figure 1. presents the steady state spectra the EPR X-band (frequency microwave 9.6 GHz, T=300K) in nanocrystals CHAP Ca10Nax(PO4)6-x(OH)2(CO3)xwith the average size of nanocrystallites 30 nm for different values of degrees of carbonization in the range x=0-2 mol.%, subjected to x-ray irradiation with a dose of 10 kGy (a-g), and the spectrum of the unirradiated sample gap for comparison (h). On the x-axis value of the magnetic field (in millitesla), on the y - axis the amplitude of the first derivative of the absorption signal (in arbitrary units). Spectra for different values of degrees of carbonization of x are shifted along the ordinate axis for convenience of visual perception.

Figure 2 presents EPR spectra obtained using the methods of detection of the spin echo at the frequency of the microwave 9.6 GHz at T=300K in nanocrystals CHAP CA10PAx(RHO4)6-x(OH)2(CO3)xwith the average size of nanocrystallites 30 nm for different values of degrees of carbonization in the range x=0-2 mol.%, subjected to x-ray irradiation with a dose of 10 kGy (a-f) and the spectrum of the unirradiated sample gap for comparison (f). Specify the parallel and perpendicular components of the component values of g-tensor and hyperfine tensor structure of A. For x-axis values of the s magnetic field (millitesla), on the y - axis the amplitude of the spin echo signal (in arbitrary units). Spectra for different values of degrees of carbonization of x are shifted along the ordinate axis for convenience of visual perception.

Examples of specific performance

Were obtained EPR spectra in a stationary mode of the spectrometer, an X-band Bruker Elexsys 580 with an operating frequency of 9.6 GHz, synthesized nanocrystals CHAP CA10PAx(RHO4)6-x(OH)2(CO3)xwith the size of the nanocrystallites 30(5) nm [6] with degrees of carbonization x=0-2 mol.% according to the standard recommendations [18]. EPR spectra of nanocrystals of hydroxyapatite subjected to x-ray irradiation with a dose of 10(1) GSR presented in figure 1. The spectra differ significantly from the EPR spectra presented in numerous works, for example [17], the study of irradiated carbonated hydroxyapatite. To determine the nature of the observed new paramagnetic centers in the X-band was used the technique of pulsed EPR with detection of the amplitude of the primary electron spin echo (Figure 2).

Range of EPR samples with x=0 (gap) is described by the spin Hamiltonian axial symmetry [20]:

H=g||βHzSz+gβ(HxSx+HySy)+A||SzIz+A(SxIx+SyIy),

where S=1/2, I=1; parameter : the Rami of the Hamiltonian g ||=2.005, g=2.009, A||=6.65 MT, A=3.4 MT (see Figure 2.).

The parameters of the spin Hamiltonian were determined under the assumption that the principal directions of the tensors g and a match.

The line shape of the EPR spectrum characteristic of the spectra of powder and is caused by averaging over all possible orientations of the paramagnetic centre. The three lines in the spectrum due to the hyperfine interaction of the magnetic moment of the unpaired electron paramagnetic center with a magnetic moment of the nitrogen nucleus with spin I=1.

The parameters of the observed EPR spectrum (g - tensor, the tensor of the hyperfine interaction And the presence of three lines in the spectrum correspond to the characteristics of the radical NO32-in the irradiated crystal KNO3and other crystalline matrices [19, 20], the characteristic feature of which is axial symmetry. Such radicals was first observed in samples of synthetic hydroxyapatite. The presence of NO3groups in the hydroxyapatite can be explained by the method of synthesis of the investigated nanocrystals, in which the original solution contains components Sa(NO3)2and (NH4NO3[6].

With the increase of the degree of carbonization EPR spectrum is transformed and there is a significant reduction in the intensity (amplitude) spectrum NR3that can be associated with a decrease in the introduction of nitrogen is s groups in the crystal lattice of CHAP increasing the degree of carbonization. This allows for a comparative quantitative assessment of the content of nitrogen compounds for different samples by comparing the amplitudes (intensities) of the EPR signals.

Thus, the claimed technical solution allows to achieve the set objectives, namely:

to determine qualitatively and quantitatively assess the presence of a content of nitrogen compounds in natural and synthesized hydroxiapatite;

- to monitor the qualitative composition of the synthesized materials with the structure of hydroxyapatite in the sense of the presence of admixtures of nitrogen compounds in the synthesis process, and the process of cleaning materials from inclusions that can be used by consumers when making decisions about the permissibility of the use of synthetic HAP in biomedical applications and will make recommendations to the manufacturers, for example, synthetic HAP and CHAP to improve the technology of production of materials with the structure of hydroxyapatite to minimize toxicity and to increase the biological compatibility with natural materials, leading, ultimately, to increase the effectiveness of hygienic and therapeutic measures with the use of gap.

The claimed technical solution meets the criterion of "novelty" requirements for inventions, because the set statement, the data characteristics are not known studied by the applicant of the technical level.

The claimed technical solution meets the criterion of "inventive step" presented to the invention, since it is not obvious to a person skilled in this technical field.

The claimed technical solution meets the criterion of "industrial applicability", presented to the invention, since the stated objectives have been fulfilled by the applicant in the laboratory of EPR spectroscopy of Kazan (Volga region) Federal University.

Sources of information

1. J.P.Lafon, E. Champion and D. Bemache-Assollant, Processing ofAB-type carbonated hydroxyapatite CA10-x(RHO4)6-x(CO3)x(OH)2-x-2y(CO3)y, ceramics with controlled composition. J. Eur. Cer. Soc, 28 (1), pp.13 9-147 (2008).

2. R.Z.LeGeros, Properties of osteoconductive biomaterials: calcium phosphates, Clin. Orthoped. rel. Res, 395 (1), pp.81-98 (2002).

3. I.R.Gibson, W.Bonfield, Novel synthesis and characterization of an AB-type carbonate-substituted hydroxyapatite. J.Biomed. Mater. Res. 59(4), 697-708 (2002).

4. L.G.Ellies, D.G.A.Nelson, J.D.B.Featherstone, Crystallographic structure and surface morphology of sintered carbonated apatites. J.Biomed. Mater. Res. 22 (6), 541-553 (1988).

5. Eshveleba, Mpharane, Whipplei, Juditial, Vchebanov, Neelin, Luggageonline, Have, Gwiin, Suboleski, Mccallahan, Bioresorbability powder materials based on Ca10-xNax(PO4)6-x(CO3)x(OH)2. Scientific notes of the KSU. A series of natural science 152 (1), 79-98 (2010).

6. E.S.Kovaleva, M.P.Shabanov, V.I.Putlyaev, Y.D.Tretyakov, V.K.Ivanov, N.I.Silkin, Bioresorbabl carbonated hydroxyapatite Ca 10-xNax(PO4)6-x(CO3)x(OH)2. Cent. Eur. J. Chem. 7(2), 168-174 (2009).

7. The industrial forces AL., Volkov N.V. and other Harmful chemicals. Inorganic compounds of the elements V-VIII groups. Reference edition. Edited Wahiawa and other L.: Chemistry, 1989, 592 S.

8. GOST 18826-73 drinking Water. Methods for the determination of nitrate content.

9. GOST 13496.19-93 Feed, feed, feed raw materials. Methods for the determination of nitrates and nitrites.

10. GOST R 51460-99 Cheese. The method of determining the mass fraction of nitrates and nitrites.

11. GOST R 51454-99 - State and Caseinates. The method of determining the mass fraction of nitrates and nitrites.

12. GOST R 52529-2006 meat and Meat products. The method of electron paramagnetic resonance to detect radiation-processed meat containing the bone.

13. .Mengeot, R.H.Bartram, O.R.Gilliam, Paramagnetic holelike defect in irradiated calcium hydroxyapatite single crystals. Phys. Rev. 11 (11), pp.4110-4124(1975).

14. F. Callens, G. Vanhaelewyn, P. Matthys, E. Boesman, EPR of Carbonate Derived Radicals: Applications in. Dosimetry, Dating and Detection of Irradiated Food. Applied magnetic resonance, 14 (2), pp.235-254 (1998)

15. P.Moens, F.Callens, S.V.Doorslaer, P.Matthys, ENDOR study of an O-ion observed in x-ray-irradiated carbonated hydroxyapatite powders. Phys. Rev. 53 (11), pp.5190-5197 (1996).

16. D.U.Schramm, J.Terra, A.M.Rossi, D.E.Ellis. Configuration of CO2-radicals in gamma-irradiated A-type carbonated apatites: theory and experimental EPR and ENDOR studies Phys. Rev. B, 63, pp.024107-024133, (2000).

17. D.U.Schram, A.M.Rossi. Electron spin resonance (ESR) studies of CO2-radicls in irradiated A-and B-type carbonate-containing apatites Applied radiation and isotopes, 52, pp.1085-1091 (2000).

18. GOST R 22.3.04-95 safety emergency control population. Dosimetric method for the determination of absorbed doses of external gamma radiation spectra of electron paramagnetic resonance tooth enamel.

19. P.W.Aktins, M.C.R.Symons. The structure of inorganic radicals. An application of electron spin resonance to the study of molecular structure, Amsterdam: Elsevier publishing company, 1967.

20. J.A.Weil, J.R.Bolton. Electron Paramagnetic Resonance: Elementary Theory and Practical Applications, 2nd Edition. J.Wiley, 2007. ISBN 978-0471754961.

The method for determining impurities of nitrogen compounds in the hydroxyapatite, which consists in the irradiation of a sample of hydroxyapatite x-ray, gamma or electron rays with the subsequent registration of the EPR spectrum arising under irradiation of paramagnetic centers in a certified EPR spectrometer, the calculation of the spectral characteristics of the observed EPR spectrum (the number of observed lines and their position) to control the error of the measurement and the comparison of the obtained spectral characteristics with known spectral characteristics of nitrogen radicals in the (poly)crystalline compounds.



 

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