Separation of β-Blocker Enantiomers on Silica Modified...

152

ISSN 1061-9348, Journal of Analytical Chemistry, 2018, Vol. 73, No. 2, pp. 152–159. © Pleiades Publishing, Ltd., 2018.Original Russian Text © I.A. Anan’eva, Ya.A. Polyakova, E.N. Shapovalova, A.G. Mazhuga, O.A. Shpigun, 2018, published in Zhurnal Analiticheskoi Khimii, 2018, Vol. 73,No. 2, pp. 113–120.

Separation of β-Blocker Enantiomers on Silica Modified with Gold Nanoparticles with Immobilized Macrocyclic Antibiotic Vancomicin

I. A. Anan’eva*, Ya. A. Polyakova, E. N. Shapovalova, A. G. Mazhuga, and O. A. ShpigunDepartment of Chemistry, Moscow State University, Moscow, 119991 Russia

*e-mail: [email protected] May 12, 2017; in final form, July 20, 2017

Abstract⎯A new chiral sorbent based on mercaptosilica modified by gold nanoparticles, then treated by3-mercaptopropionic acid and macrocyclic antibiotic vancomycin, was obtained. The enantioseparation ofisomeric β-blockers (nadolol, atenolol, metoprolol, alprenolol, oxprenolol, and pindolol) by HPLC wasstudied on the synthesized sorbent. The effect of the composition of the mobile phase (nature and concen-tration of the organic solvent, concentration and pH of the buffer solution) on retention times of β-blockerenantiomers, selectivity of separation, and resolution of chromatographic peaks were studied. The best sepa-ration was achieved for pindolol and metoprolol. The procedure was used to determine the pindolol enantio-mers in the preparation “Visken,” and metoprolol in the “Vazocardin” preparation.

Keywords: β-blockers, enantiomers, high-performance liquid chromatography, macrocyclic antibiotic, van-comycin, gold nanoparticlesDOI: 10.1134/S1061934818020028

Current trends in the development of the phar-maceutical industry indicate a growing need inobtaining optically pure dosage forms. Many syn-thetic drugs occur as of two or more spatial isomers.The pharmacological activity of racemic drugs isusually associated with the action of only one enan-tiomer. The second one either has less pronouncedactivity, or is not active at all, or exhibits other phar-macological effects [1].

One of the best methods for separating enantio-mers is liquid chromatography using sorbents mod-ified with a chiral selector. The nature of the selec-tor and the method of modification have a signifi-cant effect on the enantioselectivity. A well-knownclass of chiral selectors is provided by glycopeptideantibiotics, which include vancomycin, teicoplanin,ristocetin A, etc. They have successfully proventhemselves as chiral selectors in HPLC and capil-lary electrophoresis for the enantioseparation of awide range of pharmaceuticals [2–5]. The presenceof various fragments capable of different types ofinteractions with the substances to be separated intheir structure ensure the separation of a wide rangeof optically active compounds, including aminoacids and their derivatives, β-blockers, profenes,etc. Fixed chiral phases based on antibiotics com-bine the advantages of polysaccharide phases andprotein-modified phases are characterized by

high capacity and productivity, as well as stability,possibility of using a wide range of solvents, andseparation of enantiomers into different HPLC ver-sions [6].

The most popular antibiotic is vancomycin, whichis associated with its availability and relatively low costas compared to others. Vancomycin contains variousfunctional groups, such as carboxy-, hydroxy-,amino-, amide, which are responsible for ionization atdifferent pH values and buffer solutions. The pKa val-ues of vancomycin are 2.9 (carboxyl group), 7.2, 8.6(amino group), 9.6, 10.4, and 11.7 (phenolic groups);the isoelectric point is 7.2 [7]. The structuralformula of vancomycin is presented in Scheme 1. Themolecule contains 18 chiral centers, five aromaticrings (A–E), surrounded by three inclusion cavities,and two saccharide residues. The separation of enan-tiomers from various classes of organic compounds(acids, amines, amides, etc.) on sorbents with vanco-mycin occurs due to the formation of hydrogen bonds,π–π interactions, hydrophobic interactions, and theformation of inclusion complexes. The mechanism ofenantiomer separation on sorbents with macrocyclicantibiotics is not completely clear, because a largenumber of chiral centers make difficult the interpreta-tion of the data on enantioseparation.

ARTICLES

JOURNAL OF ANALYTICAL CHEMISTRY Vol. 73 No. 2 2018

SEPARATION OF β-BLOCKER ENANTIOMERS 153

Scheme 1. Structural formula of vancomycin.

The enantioselectivity of sorbents on the basis ofmacrocyclic antibiotics can be regulated by changingnot only the structure of the antibiotic, but also of themethod of its immobilization. A great influence onenantioselectivity is provided by the method of immo-bilization and the length and nature of the spacer, con-necting the selector and the carrier. The methods ofthe immobilization of antibiotics described in the lit-erature [8–10] have a number of drawbacks: often syn-thesis is carried out at a temperature of 95 to 105°C,which may result in the partial decomposition of anti-biotics; when the antibiotic is fixed on a silica surface,there remain free silanol groups that unpredictablycontribute to retention; many methods of immobiliza-tion require considerable time for the complete pro-ceeding of the reaction, sometimes up to a week [11].A promising, but still little-studied method of obtain-ing sorbents for HPLC is the immobilization of goldnanoparticles (GNP) stabilized with various ligands onthe surface of the substrate. It was shown [12–17] thatsuch sorbents possess good efficiency and reduce theduration of the analysis.

The aim of this work was to synthesize a new chiralsorbent on the basis of silica modified with GNP withimmobilized antibiotic vancomycin and to study itschromatographic properties on the example of theseparation of β-blocker enantiomers.

EXPERIMENTALEquipment. The work was performed on a Shi-

madzu LC-20 Prominence liquid chromatograph(Japan) with a SPD-M20A diode array detector. Datacollection and chromatogram processing were carriedout using the Shimadzu LC Solution software.

Reagents and solutions. Kromasil 100-5-Sil silica(spherical, particle size 5 μm, surface area 300 m2/g,pore size 100 Å, Ekachemicals, Sweden) was used as amatrix for the synthesis of the sorbent.

The following reagents were used for the synthesisof the sorbent: HAuCl4 · 3H2O of reagent grade,Na3C6H5O7 · 5.5H2O of high-purity grade (bothMerck salts, Germany), 3-mercaptopropyltrimethox-ysilane (95%, Acros Organics, United States), 3-mer-captopropionic acid of reagent grade, N,N'-dicyclo-hexylcarbodiimide of reagent grade, 4-(dimethyl-amino) pyridine of reagent grade, vancomycinhydrochloride, and ethyl alcohol of reagent grade(Sigma-Aldrich, United States).

For the preparation of buffer solutions, exactweighed portions of solid and liquid ammonium ace-tate preparations of analytical grade (Labtekh, Rus-sia), potassium dihydrogen phosphate, potassiumhydrogen phosphate trihydrate, phosphoric acid(85%), acetic acid (Reakhim, Russia), and triethyl-amine (99%, Acros Organics, United States) wereused.

Trimethylamine (99%, Acros Organics, UnitedStates), acetonitrile, methanol, isopropanol “forchromatography” (Panreac, Spain), β-blocker solu-tions (nadolol, atenolol, metoprolol, alprenolol,oxprenolol, and pindolol) (Sigma-Aldrich, UnitedStates) with a concentration of 1 mg/mL in organicsolvents, prepared from precisely weighed portionswere used.

To obtain the sorbent, silica was preliminarilymodified with 3-mercaptopropyltrimethoxysilane andthen sequentially treated with GNP stabilized withcitrate ions and with 3-mercaptopropionic acid. The

OOO

NH

ONH

O

OH

NH

ONH CH3

Cl

O

OH

HOOH

O

O

HOH2N

O

NH2

O

NHO

NH

ClHO

NH

O

HOOH

OHHOOC

C

B

A

ED

154


ANAN’EVA et al.

antibiotic was immobilized on the obtained sorbent bythe formation of an amide bond between the‒COOH-group of acid and ‒NH2-groups of vanco-mycin.

Modification of silica with 3-mercaptopropyltrime-thoxysilane. A weighed portion of silica (3.000 g) wassuspended in 300.0 mL of a freshly distilled toluene ina 300.0 mL three-necked flask, the suspension wasbrought to the boil, 3.0 mL of 3-mercaptopropyltri-methoxysilane were added, and the mixture was boiledfor 4 h under an argon atmosphere. The modified sil-ica was then filtered through a glass porous filter underan argon atmosphere.

Modification of thiolated silica with gold nanoparti-cles (10 nm) stabilized with citrate ions. The resultingthiolated silica (about 2.100 g) was suspended in150.0 mL of a solution of freshly prepared GNP withthorough mixing by a mechanical overhead stirrer atroom temperature under an inert atmosphere. Themixture was stirred for 24 h and filtered through a glassporous filter. The filter cake was washed successivelywith water and ethyl alcohol and dried at 50°C for 24h.

Modification of gold nanoparticles on silica with3-mercaptopropionic acid. The resulting silica was sus-pended in 100.0 mL of water and 5.0 mL of 3-mercap-topropionic acid was added with vigorous stirring for1 h. The resulting solution was filtered; the substanceon the filter was washed successively with water andethyl alcohol and dried at room temperature for 24 h.

Immobilization of vancomycin on thiolated silicamodified with gold nanoparticles (10 nm). 100 mg of awater-soluble antibiotic vancomycin, a triple excess(35 mg per given amount of antibiotic) of N,N'-dicy-clohexylcarbodiimide and catalytic amounts of4-(dimethylamino) pyridine were added to the result-ing silica at vigorous stirring. The resulting solutionwas stirred for 24 h at room temperature, the violet

precipitate was separated by filtration on a Buchnerfunnel with a glass filter bottom and washed with waterand then with ethanol. The sorbent was dried for 24 hand stored in a dry bag in air. Results of elementalanalysis: 6.3% C, 1.37% H, 1.64% S, and 0.64% N.The elemental analysis data showed that the vancomy-cin immobilization density was 51 mmol/g. At that74% of vancomycin reacted with the modified surfaceof silica introduced into the reaction.

A micrograph of the sorbent SiO2–S–Au–S–van-comycin is shown in Fig. 1a. One can see that gold isuniformly distributed over the surface of silica . In thespectrum of diffuse reflection (Fig. 1b), there is a pro-nounced intense maximum at 540 nm, characteristicof GNP. The consideration of the maps of the distri-bution of gold on the surface of silica by SEM (Fig. 2a)makes it possible to more clearly see that the entiresurface of silica is covered with gold, while there are asmall number of gold aggregates on the surface, and acertain amount of gold is distributed over the bulk.The sulfur distribution map (Fig. 2b) also clearlyshows that the maximal sulfur concentration isobserved on the silica spheres themselves.

Analysis of medicinal products “Visken” and “Vazo-cardin.” A tablet of a preparation was ground in a por-celain mortar to a homogeneous state. The resultingpowder was quantitatively transferred to a conical f laskwith 25.0 mL of acetonitrile. The suspension was pro-cessed in an ultrasonic bath for 15 min, an aliquot por-tion of 2.0 mL was centrifuged for 5 min at 1500 rpm.The supernatant was then filtered and 20 μL of the fil-trate was introduced into a chromatography column.Chromatographic conditions: phosphate buffer solu-tion (25 mM, pH 4.0)–CH3CN (95 : 5, by volume),mobile phase f low (MP) 0.5 mL/min, detector wave-length 270 nm. The sum of peak areas of two enantio-mers was calculated from the chromatogram,.

Fig. 1. (a) Micrograph obtained by scanning electron microscopy (SEM), and (b) diffuse reflectance spectrum of SiO2–S–Au–S–COOH–vancomycin sorbent.

(a)

0.5 μm

18.86 nm

17.78 nm

14.05 nm

14.05 nm8.89 nm13.33 nm

9.94 nm

2.5

2.0

1.5

1.0

0.5400 500 600 700

(b)

λ, nm

F



RESULTS AND DISCUSSIONThe chromatographic properties of the obtained

sorbent were studied on an example of the separationof enantiomers of β-blockers, the structural formulasof which are presented in Scheme 2. β-Adrenoblock-ing agents (or β-blockers) belong to the class ofN-hydroxypropylamines. They are used to bindadrenoreceptors of the cardiac and/or smooth muscle,

while they inhibit the action of adrenoagents, such asamphetamine, epinephrine, catecholamines, etc.β-Blockers may reduce the strength and temp of con-traction of the heart muscle [18, 19]. Most β-blockersare chiral; their enantiomers have various pharmaco-logical effects. Because of these differences, the sepa-ration of isomers of β-andrene-blocking agents isimportant [20, 21].

Scheme 2. Structural formulas of studied β-blockers.

The optimization of the separation of substancescontaining more than one functional group on vanco-mycin sorbents is recommended to begin with a polar

organic version of chromatography, where the con-centration of the organic modifier in the MP exceeds90% [22]. The best initial MP is methanol with addi-

O NHOH

O NHOH

O

OH2N

OOH

NH

OOH

NHHN

OOH

NHO

HOOH

OOH

NH

Alprenolol Oxprenolol

Atenolol Pindolol

Metoprolol Nadolol

Fig. 2. Maps of the distribution of (a) gold and (b) sulfur on the surface of SiO2–S–Au–S–COOH–vancomycin obtainedby SEM.

10 μm

(a)

10 μm

(b)

156


ANAN’EVA et al.

tions of glacial acetic acid and triethylamine (0.1% byvolume). All β-blockers under investigation are elutedby this MP on the synthesized sorbent in less than1 min. Reducing the amount of acid and amine addi-tives down to 0.01% did not result in an increase inretention and enantioseparation. In this connection,we switched to the reversed-phase version of HPLC.Since enantioseparation in this version of chromatog-raphy depends on the pH of the buffer solution, itsconcentration, nature of the buffer solution andorganic modifier, the effect of all these factors on theresolution of peaks and the selectivity of separation ofthe enantiomers was investigated. Based on the data of[22, 23], triethylamine–acetate buffer solution(TEAA) (50 mM, pH 4.0) with an addition of 5 vol %of acetonitrile by volume was chosen as the startingMP. This MP ensures the separation of the enantio-mers of four β-blockers: pindolol, metoprolol, oxpre-nolol, and alprenolol. At that, the resolution for theseblockers does not exceed 0.5, and the times for theoutputs of the components vary from 1.5 to 3 min. Inthe case of atenolol and nadolol, RS was less than 0.2.As the concentration of acetonitrile increases, theretention of blockers decreases, which corresponds topatterns of reversed-phase chromatography. Whenacetonitrile is replaced with methanol or isopropanolin the mobile phase, the resolution of enantiomericpeaks is reduced.

The resolution of enantiomeric peaks may be influ-enced by the nature and concentration of the buffersolution. 50 mM TEAA, FB, and ammonium acetatebuffer solution (AAB) with pH 4.0 and 5 vol % of ace-tonitrile were used as an eluent in the separation ofβ-blocker enantiomers; the results are shown in Fig. 3.It turned out that, with the replacement of TEAA byAAB, the enantioseparation of nadolol and atenololsignificantly improves. For four blockers (pindolol,metoprolol, alprenolol, and oxprenolol), a better sep-

aration was achieved when PB (RS varies from 0.84 to0.92, respectively) was used, for nadolol (RS = 0.76)and atenolol (RS = 0.69), with AAB.

The dependence of the resolution of peaks ofβ-blocker enantiomers on the concentration of thebuffer solution is shown in Fig. 4. The concentrationof the buffer solution was varied in the range 10–100 mM. One can see that there is a certain concentra-tion of the buffer solution, which ensures the maximalseparation of enantiomers. For pindolol, metoprolol,oxprenolol, alprenolol, and nadolol, a better resolu-tion of peaks was observed with 25 mM PB (RS =0.72–0.92) and for atenolol, with 50 mM AAB (RS =0.53). The concentration of the buffer solution alsoaffects the retention of β-blockers: with increasingconcentration, the retention of the test compoundsslightly increases. It is also worth noting that the reten-tion of compounds correlates well with the change inhydrophobicity: more hydrophobic blockers are lon-ger retained on the sorbent. However, the difference inthe retention times of β-blockers is small. This patternconfirms the implementation of the reversed-phaseretention mechanism. A slight increase in the time ofrelease of test compounds with an increase in the con-centration of the buffer solution may be explained bythe enhancement of hydrophobic interactions.

A significant effect of the pH of MP on retentionand enantioseparation is due to the presence of ioniz-ing groups both in the chiral selector and in the sub-stances to be separated. With an increase in pH in therange 3.5–5.0, the retention times of all β-blockersincrease slightly, the RS dependence on pH is then acurve with a maximum at pH 4.0, dropping to zero atpH 5.0. The absence of separation at pH 3.5 is due tothe fact that, under these conditions, β-blockers areeluted virtually in a dead volume. In the studied pHrange under reversed-phase conditions, vancomycin is

Fig. 3. Influence of the nature of buffer solution in the mobile phase buffer solution (50 mM, pH 4.0)—CH3CN (95 : 5, by vol-ume) on the resolution of the peaks of β-blocker enantiomers on the sorbent SiO2–S–Au–S–COOH–vancomycin.

Pindolol

Metoprolol

Oxprenolol

Alprenolol

Nadolol

Atenolol

1.0

0.8

0.6

0.4

0.2

0TEAA AAB PB

RS



a zwitterion (contains COO–- and -groups), andβ-blocker molecules are positively charged. As pHincreases, the negative charge of vancomycinincreases, which results in an increase in the retentionof β-blockers because of electrostatic interactionsbetween the carboxyl group of vancomycin and theamino group of the blockers. Enantioseparation ismost likely also due to the formation of hydrogenbonds and dipole interactions with amide andhydroxyl groups of vancomycin and due to hydropho-bic interactions. The weak influence of the spatialstructure of β-blockers on retention and virtuallyidentical patterns of the influence of the compositionof MP on the separation suggest a weak role of hydro-phobic and π–π interactions and the predominantionic interactions of the chiral center of blockers, theenvironment of which is identical for all compounds,with one of the participants vancomycin.

Thus, for pindolol, metoprolol, oxprenolol, andalprenolol, the best enantioseparation was achievedwith MP: PB (25 mM, pH 4.0)–CH3CN (96 : 4, byvolume) for nadolol: AAB (25 mM, pH 4.0)–CH3CN(96 : 4, by volume), for atenolol–AAB (50 mM,pH 4.0)–CH3CN (96 : 4, by volume). The chromato-graphic parameters of the separation of β-blockers inthe selected optimal conditions are given in Table 1.One can see that the elution time of all test compoundsdoes not exceed 3 min. The best enantioseparationamong the studied compounds was achieved for pin-dolol (RS = 0.93), metoprolol (RS = 0.92), and oxpre-nolol (RS = 0.91). For the same blockers, the maximalnumber of theoretical plates per meter (16400 for pin-dolol) is achieved. The minimal value of the separatingability of this sorbent was observed for nadolol (RS =

3NH+ 0.71) and atenolol (RS = 0.53), which possess the least

retention.

Procedures for the determination of pindolol andmetoprolol on a synthesized sorbent were developed,and analytical characteristics are presented in Table 2.The proposed procedures ensure the determination ofpindolol and metoprolol in a wide range of concentra-tions with a good reproducibility.

The reproducibility (sr) of the retention time ofβ-blockers on the synthesized sorbent in work for3 months was 2%. The obtained values of RS (0.91–0.93) are acceptable for evaluating the enantiomericcomposition of the pharmaceuticals of β-blockers.The developed procedures were applied to the separa-tion and determination of β-blockers on an example ofthe analysis of pharmaceutical preparations “Visken”and “Vazocardin,” containing pindolol and metopro-lol as active agents, respectively. It is shown that the“Visken” preparation is a racemic mixture with an iso-mer ratio of 48 : 52 (by weight), containing 4.7 ±0.5 mg/tab (n = 5, P = 0.95) of the active ingredient,which agrees with the data declared by the manufac-turer (5 mg). The determination of metoprolol in the“Vazocardin” tablets by the reversed-phase methodshowed that the preparation is also a racemic mixture(ratio of isomers 46 : 54 (by weight), containing 110 ±10 mg/tab (n = 5, P = 0.95) of the active ingredient.Fillers and other concomitant components of thepreparation do not interfere with the determination.The chromatograms of the preparations “Visken” and“Vazocardinum” are presented in Figs. 5 and 6,respectively. The developed procedures are simple; theanalysis of tablets of preparations with sample prepa-ration takes 15–20 min.

Fig. 4. The influence of the buffer solution concentration in the MP buffer solution (pH 4.0)—CH3CN (96 : 4, by volume) onthe resolution of the peaks of the enantiomers of (1) pindolol, (2) metoprolol, (3) alprenolol, (4) nadolol, (5) oxprenolol, and(6) atenolol on the sorbent SiO2–S–Au–S–COOH–vancomycin, (1)–(5) PB, (6) AAB.

1.0

0.8

0.6

0.4

0.2

0 20 40 60 80 100

1

2

34

5

6

RS

c, mM

158


ANAN’EVA et al.

Table 1. Chromatographic parameters of the separation of β-blockers on a SiO2–S–Au–S–COOH–vancomycin column

β-Blocker tr1 (tr2), min RS α N1(N2), tp/m MP

Nadolol 1.62(1.85)

0.62(0.85) 0.71

1.38 8200(9700)

AAB (25 mM, pH 4.0)–CH3CN (96 : 4, by volume)

Atenolol 1.57(1.73)

0.57(0.73) 0.53

1.28 7600(10500)

AAB (50 mM, pH 4.0)–CH3CN (96 : 4, by volume)

Metoprolol 2.11(2.40)

1.11(1.40) 0.92

1.27 10100(13200)

PB (25 mM, pH 4.0)–CH3CN (96 : 4, by volume)

Alprenolol 2.23(2.58)

1.23(1.58) 0.81

1.28 10700(12600)

Oxprenolol 2.10(2.43)

1.10(1.43) 0.91

1.30 13000(16300)

Pindolol 1.94(2.22)

0.94(1.22) 0.93

1.30 16 400(13200)

1 2( )' 'k k

Fig. 5. Chromatogram of the preparation “Visken”: col-umn (100 × 4.6 mm) SiO2–S–Au–S–COOH–vancomy-cin; MP–PB (25 mM, pH 4.0)–CH3CN (96 : 4, by vol-ume), f low rate 0.5 mL/min.

175

145

115

85

55

25

–50 2 4 6

A, arb.units

t, min

Table 2. Performance characteristics of the procedures for determination of pindolol and metoprolol (n = 3, P = 0.95)

β-Blocker Analytical range, mg/L Equation of calibration curve r sr

Pindolol 0.001–500 y = (1819 ± 30)с − (0.3 ± 0.7) 0.9994 0.06

Metoprolol 0.005–100 y = (1278 ± 15)с + (13 ± 3) 0.9998 0.05

Fig. 6. Chromatogram of the preparation “Vazocardin”:column (100 × 4.6 mm) SiO2–S–Au–S–COOH–vanco-mycin, MP–PB (25 mM, pH 4.0)–CH3CN (96 : 4, by vol-ume), f low rate 0.5 mL/min.

115

95

75

55

35

15

–50 1 2 3 4 5

A, arb.units

t, min



ACKNOWLEDGMENTSThis work was supported by the Russian Founda-

tion for Basic Research, project no. 15-03-05979а,and Russian Science Foundation, project no. 17-14-01316 (physicochemical studies of sorbents).

REFERENCES1. Lehninger, A. and Cox, N., Principles of Biochemistry,

New York: Worth, 1993, p. 58.2. Ilisz, I., Berkecz, R., and Peter, A., J. Chromatogr. A,

2009, vol. 1216, p. 1845.3. Armstrong, D.W., Tang, Y.B., Chen, S.S., Zhou, Y.W.,

Bagwill, C., and Chen, J.R., Anal. Chem., 1994, vol. 66,p. 1473.

4. Shapovalova, E.N., Fedorova, I.A., Priporova, A.A.,Anan’eva, I.A., and Shpigun, O.A., Analitika Kontrol’,2016, vol. 20, no. 2, p. 168.

5. Shapovalova, E.N., Fedorova, I.A., Priporova, A.A.,Ananieva, I.A., and Shpigun, O.A., Moscow Univ.Chem. Bull. (Engl. Transl.), 2017, vol. 72, no. 1, p. 56.

6. Allenmark, S.G., Chromatographic Enantioseparation:Methods and Applications, Chichester: Horwood, 1998.

7. Aboul-Enein, H.Y. and Ali, I., Chromatographia, 2000,vol. 52, p. 679.

8. Berthod, A., Kullman, J.P., Armstrong, D.W.,Gaspati, F., D’Acquarica, I., Misiti, D., andCarotti, A., J. Chromatogr. A, 2002, vol. 897, p. 113.

9. D’Acquarica, I., J. Pharm. Biomed. Anal., 2000, vol. 23,p. 3.

10. Svenson, L.A. and Owens, P.K., Analyst, 2000,vol. 125, p. 1037.

11. Kuznetsov, M.A., Cand. Sci. (Chem.) Dissertation,Moscow: Moscow State Univ., 2008.

12. Anan’eva, I.A., Elfimova, Ya.A., Mazhuga, A.G.,Rudakovskaya, P.G., Shapovalova, E.N., Zyk, N.V.,and Shpigun, O.A., Sorbtsionnye Khromatogr. Protsessy,2011, vol. 11, no. 3, p. 281.

13. Elfimova, Ya.A., Pichugina, D.A., Anan’eva, I.A.,Mazhuga, A.G., and Shpigun, O.A., Russ. J. Phys.Chem. A, 2012, vol. 86, no. 10, p. 1623.

14. Elfimova, Ya.A., Anan’eva, I.A., Mazhuga, A.G., andShpigun, O.A., Zavod. Lab., Diagn. Mater., 2012,vol. 78, no. 6, p. 20.

15. Shapovalova, E.N., Ananieva, I.A., Elfimova, Ya.A.,Grineva, L.A., Mazhuga, A.G., and Shpigun, O.A.,Moscow Univ. Chem. Bull. (Engl. Transl.), 2012, vol. 67,no. 2, p. 72.

16. Polyakova, Ya.A., Ananieva, I.A., Shapovalova, E.N.,Mazhuga, A.G., and Shpigun, O.A., Moscow Univ.Chem. Bull. (Engl. Transl.), 2016, vol. 71, no. 1, p. 54.

17. Majouga, A., Pichugina, D., Ananieva, I., Kurilova, S.,Shpigun, O., Kuz’menko, N., and Zyk, N., J. Manuf.Technol. Management, 2010, vol. 21, no. 8, p. 950.

18. Kharkevich, D.A., Farmakologiya (Pharmacology),Moscow: Meditsina, 1987.

19. Armstrong, D.W., Chen, S., Chang, C., and Chang, S.,J. Liq. Chromatogr., 1992, vol. 15, no. 3, p. 545.

20. Mashkovskii, M.D., Lekarstvennye sredstva (Medi-cines), Moscow: Medgiz, 1954.

21. Pham-Huy, C., Radenen, B., Sahui-Gnassi, A., andClaude, J., J. Chromatogr. B: Biomed. Sci. Appl., 1995,vol. 665, p. 125.

22. Aboul-Enein, H.Y. and Ali, I., Farmaco, 2002, vol. 57,p. 513.

23. Bosakova, Z., Curinova, E., and Tesarova, E., J. Chro-matogr. A, 2005, vol. 1088, p. 94.

Translated by V. Kudrinskaya

本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP

图书馆。

图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具

http://www.xuebalib.com/cloud/http://www.xuebalib.com/http://www.xuebalib.com/cloud/http://www.xuebalib.com/http://www.xuebalib.com/vip.htmlhttp://www.xuebalib.com/db.phphttp://www.xuebalib.com/zixun/2014-08-15/44.htmlhttp://www.xuebalib.com/

Separation of β-Blocker Enantiomers on Silica Modified with Gold Nanoparticles with Immobilized Macrocyclic Antibiotic Vancomicin学霸图书馆link:学霸图书馆

Separation of β-Blocker Enantiomers on Silica Modified...

Documents

Transcript of Separation of β-Blocker Enantiomers on Silica Modified...