ISSN 0012-5008, Doklady Chemistry, 2006, Vol. 408, Part 1, pp. 65–69. © Pleiades Publishing, Inc., 2006.Original Russian Text © N.V. Pechishcheva, E.V. Osintseva, L.K. Neudachina, Yu.G. Yatluk, L.I. Leont’ev, K.Yu. Shunyaev, A.A. Vshivkov, 2006, published in Doklady AkademiiNauk, 2006, Vol. 408, No. 2, pp. 199–203.

65

Organic compounds of aliphatic aminopolycarbox-ylic acids and their complexes with transition metalions are soluble in water but are barely used for lumi-nescence analysis due to their chemical structure. Aspecial place is occupied by aromatic complexones ofthe class of

N

-aryl-3-aminopropionic acids (AAPAs).Owing to the presence of a benzene ring in the mole-cule and the possibility of formation of an intramolec-ular hydrogen bond with closure of an additional ring,they are expected to possess luminescence properties.

The monitoring of copper content in environmentalobjects is an important task because this metal is animportant biogenic element participating in oxygentransfer in living tissues, while the mechanisms for pre-vention of the toxic effect that were elaborated duringthe evolution of living organisms, are not always imple-mented with the current level of copper entry into theenvironment. Optical methods are often used to deter-mine the copper content in environmental objects [1].Molecular spectroscopy is described by a rather highproductivity and low cost of analysis compared toatomic spectroscopy. Among the molecular spectros-copy methods, luminescence has the lowest detectionlimit and a broad range of quantifiable concentrations.The reproducibility of results typical of molecularabsorption spectroscopy is retained. The luminescencemethods are applicable for determination of traceamounts of copper around the maximum allowableconcentration (MAC) or at lower concentrations inenvironmental objects. However, most of the known

reagents for luminescence determination of the coppercontent in aqueous solutions do not show a high selec-tivity in the presence of other transition metal ions [2,3] and imply handling of toxic organic solvents [4];therefore, procedures include preseparation of samplecomponents by extraction [5]. Due to the high selectiv-ity of complexation of AAPAs with Cu(II) ions, discov-ered in spectrophotometric and potentiometric studies[6, 7], it is reasonable to investigate these compounds asluminescence reagents for copper determination inenvironmental objects.

This study deals with the luminescence properties ofa number of AAPA representatives (Fig. 1). All thestudied reagents were synthesized by previously devel-oped procedures [8, 9], purified by repeated recrystalli-zation from water or 1,2-dichloroethane, and identifiedby elemental analysis and IR and

1

NMR spectroscopy.The content of the target substance in the products was99.5–99.9%. The fluorescence intensity of solutionswas measured using a Fluorat-02-Panorama spectroflu-orimeter.

Solutions of

I

–

IV

were found to exhibit fluores-cence in the wavelength range from 250 to 450 nm. Thepeak intensities of the fluorescence bands change withpH, due to the acid ionization of the compounds in solu-tion [8–10]. As an example, Fig. 2 presents the fluores-cence spectra of 1

×

10

–4

M solutions of

I

–

III

at differ-ent acidities. The fluorescence spectral pattern for

IV

issimilar to that of

II

but the spectral intensity is lower.The spectra of

I

,

II

, and

IV

exhibit two fluorescencebands with different intensities in the UV region, whichcorrespond to the protonated and deprotonated forms ofthe compounds (about 300 and 355 nm, respectively),the intensity of the shorter wavelength peak decreasingand that of the longer wavelength peak increasing withan increase in the solution pH. The fluorescence inten-sity of

III

(Fig. 2c) is much higher than that of

I

,

II

, or

IV

, its maximum being located in the visible spectralregion (

λ

max

= 434 nm). As the pH increases, the peak

Luminescence Properties of Some

N

-Aryl-3-Aminopropionic Acids and Their Use for Determination

of Copper(II) in Drinking and Waste Water

N. V. Pechishcheva

a

, E. V. Osintseva

b

, L. K. Neudachina

b

, Yu. G. Yatluk

c

,

Academician

L. I. Leont’ev

a

, K. Yu. Shunyaev

a

, and A. A. Vshivkov

b

Received August 15, 2005

DOI:

10.1134/S001250080605003X

a

Institute of Metallurgy, Ural Division, Russian Academyof Sciences, ul. Amundsena 101, Yekaterinburg, 620016 Russia

b

Ural State University, pr. Lenina 51, Yekaterinburg, 620083 Russia

c

Institute of Organic Synthesis, Ural Division, Russian Academy of Sciences, ul. S. Kovalevskoi 20, Yekaterinburg, 620219 Russia

CHEMISTRY

66

DOKLADY CHEMISTRY

Vol. 408

Part 1

2006

PECHISHCHEVA et al.

shifts hypsochromically, which is accompanied by anincrease in the intensity.

It was found that each form of the compound (theprotonated or deprotonated one) has an optimal fluores-cence excitation wavelength. The fluorescence parame-ters for solutions of

I

–

IV

are presented in Table 1. Thedifferences in the AAPA fluorescence can be due to thenature of the substituent in the benzene ring and theability of the compounds to form intramolecular hydro-gen bonds, which increase the structure rigidity andpromote electron delocalization, which stabilizes thefluorescing form of the molecule. The introduction ofelectron-donating substituents into the molecule of

I

(

−

ëH

3

, –OCH

3

)

(Table 1) results in a slight bathochro-mic shift of the fluorescence bands (5–7 nm). An elec-tron-withdrawing substituent (–COOH) in the structureof ligand

I

, which is furthermore able to be involved ina hydrogen bond with the amino group, induces agreater bathochromic shift of the bands and a pro-nounced increase in the fluorescence intensity.

Complexation with copper(II) ions was found todecrease the fluorescence intensity of solutions of

I

–

III

. Presumably, this is accompanied by cleavage of theintramolecular hydrogen bond in the AAPA molecule,while the presence of an unpaired electron in Cu(II)facilitates its participation in a radiationless electrontransition upon collision with an excited reagent mole-cule. The intensity of the fluorescence of

IV

does notchange in the presence of Cu(II) ions; therefore, thiscompound cannot be used for analytical purposes. Aninversely proportional dependence between the Cu(II)concentration in the solution and the fluorescence was

found for deprotonated

I

–

III

, while for the protonatedcompounds no such correlation holds. The greatesteffect of Cu(II) ions on the fluorescence of AAPA wasobserved in the pH range 5.0–7.0 (Fig. 3). The extent offluorescence quenching by Cu(II) cations at pH 6 is86% for

I

, 33% for

II

, and 98% for

III

, which does notcoincide with the pattern of variation of the stability ofCu(II) chelates (

is 5.64, 7.15, and 6.31, respec-tively [7]). Apparently, this may be due to structuralfactors that require further investigation.

The results obtained were used to develop a proce-dure for determination of Cu(II) cations in natural andwaste waters. A constant pH value (6.0) was maintainedusing an ammonium acetate buffer solution, which hasa lower influence on the sensitivity of copper determi-nation than a borate phosphate or acetate (

ëç

3

ëééç–äéç

) buffer. The greatest slope of the calibration plotand the least variance of its points are the main criteriafor choosing the concentration of the buffer solution.The optimal conditions for the fluorimetric determina-tion of copper using compounds

I

–

III

are summarizedin Table 2. The range of Cu(II) concentrations deter-mined by the fluorescence method with

I

–

III

(0.005–3 mg/dm

3

) is lower than that for spectrophotometricprocedures using AAPAs [7, 11], covering the MACs inhousehold water [12] and drinking water [13](1 mg/dm

3

). A study of the influence of some possiblewater components on the fluorescence intensity ofCu(II) complexes with

I

–

III

showed that Cu(II) deter-mination is not interfered with by molar excesses of theions given in Table 3. Compounds

I

and

II

exhibit inmost cases equal selectivities with respect to Cu(II)ions, being much more selective than

III

. This fact isconsistent with the statement that a group capable ofcoordinating metal cations in the

ortho

position of thebenzene ring of the AAPA molecule decreases theligand selectivity with respect to Cu(II) ions [6, 7].

The results of comparative determination of copperin waste water from a metallurgical plant containingnickel ions by the fluorimetric method using compound

II

and by the atomic absorption method and the resultsof Cu(II) determination in an artificial mixture based onnatural drinking water and containing

ëu

2+

(1.27 g/cm

3

wasadded using a standard specimen), Ca

2+

(30–100 mg/dm

3

),

Kstlog

O

HN CH2 CH2 CONH2

CH3

COOH

HN CH2 CH2 COOH

NCH2

CH2

CH2 COOH

CH2 COOH

CH3

CH3

NCH2

CH2

CH2 COOH

CH2 COOH

III

III IV

Fig. 1.

I

,

N

,

N-

Di(2-carboxyethyl)aniline;

II

,

N

,

N-

di(2-carboxyethyl)-3,4-xylidine;

III

,

N-

(2-carboxyethyl)-

o

-aminobenzoic acid;

IV

,

N-

(2-carbamoylethyl)-

o

-anisidine.

Table 1.

Fluorescence characteristics of 1

×

10

–4

M aque-ous solutions of compounds

I

–

IV

(a medium sensitivity ofthe fluorimeter photomultplier)

ReagentProtonated form Deprotonated form

λ

excit/detect

, nm

I

, rel. units

λ

excit/detect

, nm

I

, rel. units

I

210/278 2.7 254/355 25.1

II

215/285 20.6 254/360 3.5

III

220/434 25.4 220/411 107.4

IV

220/298 17.4 237/350 0.8

DOKLADY CHEMISTRY

Vol. 408

Part 1

2006

LUMINESCENCE PROPERTIES 67

2

370350 390 410 430 450 470 490 510 530 550

Wavelength, nm

0

4

6

8

10

12

14

16 (c)

76

4

5

3

2

1

4

250 4100

6

10

1416

222426

(

b

)

7

6

4

5

3

2

1

2018

12

8

2

390370350330310290270

8

260 4000

4

8

14

16

18 (‡)

6

4

5

3

21

12

10

6

2

380360340320300280

I, rel. units

Fig. 2. Fluorescence spectra of 1 × 10–4 M solutions of AAPAs at different pH values: (a) compound I, medium sensitivity, λexcit =210 nm, (1) pH 1.2; (2) pH 2.8; (3) pH 4.3; (4) pH 6.2; (5) pH 7.5; (6) pH 9.0; (b) compound II, maximum sensitivity, λexcit =215 nm, (1) pH 1.2; (2) pH 1.8; (3) pH 2.0; (4) pH 2.5; (5) pH 4.0; (6) pH 5.8; (7) pH 7.3; (8) pH 10.7; (c) compound III, minimumsensitivity, λexcit = 220 nm, (1) pH 1.3; (2) pH 1.8; (3) pH 4.3; (4) pH 5.4; (5) pH 7.2; (6) pH 8.0; (7) pH 8.4.

68

DOKLADY CHEMISTRY Vol. 408 Part 1 2006

PECHISHCHEVA et al.

Mg2+ (<50 mg/dm3), HC (150–300 mg/dm3), andother components (total mineralization 300–600 mg/dm3)are listed in Table 4. Verification of the results by the

O3–

added/found method for drinking water and by an alter-native analytical method (atomic absorption spectros-copy) for waste water showed the absence of a system-atic error.

The method we developed has a broader range ofquantifiable copper concentrations (0.005–3.0 mg/dm3)than the lumocupferron procedure proposed with theFluorat-02 spectrofluorimeter (Lyumeks, St. Peters-burg, Russia) (0.005–0.2 mg/dm3) [4]. This allows oneto determine Cu(II) ions at an MAC level without addi-tional dilution of sample solutions. In addition, thelumocupferron determination is interfered with by sev-enfold molar excesses of nickel(II) or cobalt(II) ions.

Thus, this study extends the scope of molecularluminescence analysis to a new class of organic com-pounds, N-aryl-3-aminopropionic acids, which allowsselective determination of minor amounts of copper inenvironmental objects without the use of organic sol-vent extraction. The determination with N,N-di(2-car-boxyethyl)aniline and N,N-di(2-carboxyethyl)-3,4-xylidine is not interfered with by most of the usual tran-sition metal ions (up to a 200-fold molar excess) or

2

10 2 3 4 5 6 7 8 9

4

6

8

10

12

pH

I, rel. units

1

2

Fig. 3. Fluorescence intensity of reagent III vs. pH(λexcit/detect = 220/411 nm, minimum sensitivity): (1) cIII =

1 × 10–4 M; (2) cIII = cCu(II) = 1 × 10–4 M.

Table 2. Optimal conditions for the fluorimetric determination of copper(II) using I, II, and III (Fluorat-02-Panorama spec-trofluorimeter)

ParameterCompound

I II III

λexcit, nm 237* 215 220λdetect, nm 355 360 411Buffer solution Ammonium acetateConcentration of the buffer solution, mol/dm3 0.1 0.02 0.02pH 6.0Residence time of the solution, min 30 30 60Range of quantifiable concentrations, mg/dm3 0.03–2.5 0.03–2.5 0.005–3.0Sensitivity of the fluorimeter photomultplier Medium Maximum All ranges are used* The optimal wavelength that allows working over the whole range of quantifiable concentrations using one sensitivity of the fluorimeter

photomultplier.

Table 3. Divisible molar excesses of ions that do not interfere with the fluorimetric determination of Cu(II) using compounds I−III

Com-pound

Cations

Ni2+ Co2+ Al3+ Cr3+ Cd2+ Fe3+ K+ Na+ Ca2+ Mg2+ Zn2+

I 100 200 10 200 0.5 5000 10000 – – –II 100 10 50 – 0.5 2000 2000 2000 2000 2000III <1 3 5 1 50 0.1 1000 1000 100 100 1000

Com-pound

Cations Anions

Mn2+ Ba2+ F– Cl– CH3COO–

I – – 20 1000 5000 10000 – –

II 500 1000 10 0.5 5000 1000 1000 5000 – 300

III 50 200 50 <1 1000 5 –

NH4+

HCO3– NO3

– SO42– NO2

– PO43–

DOKLADY CHEMISTRY Vol. 408 Part 1 2006

LUMINESCENCE PROPERTIES 69

alkali and alkaline earth metals (up to a 5000-foldexcess) or the most common anions. AAPAs can beused to determine Cu(II) in drinking and waste water.

ACKNOWLEDGMENTS

This work was supported by the Russian Founda-tion for Basic Research and the Government of Sver-dlovskaya oblast (project no. 03–04–96095, Ural),the program of the Ministry of Education of the Rus-sian Federation “Universities of Russia” (projectno. UR.05.01.438), and BRHE 2004 (grant no. Y2–C–05–08).

REFERENCES

1. Podchainova, V.N. and Simonova, L.N., Med’ (Copper),Moscow: Nauka, 1990.

2. Kim, H.-S. and Choi, H.-S., Talanta, 2001, vol. 55, no. 4,pp. 163–169.

3. Sandor, M., Geistmann, F., and Schuster, M., Anal.Chem. Acta, 2003, vol. 486, no. 1, pp. 11–19.

4. Izmerenie massovoi kontsentratsii khimicheskikh ve-shchestv lyuminestsentnymi metodami v ob”ektakhokruzhayushchei sredy Sb. metodicheskikh ukazanii.(Measurements of Concentrations of Chemical Sub-stances in Environmental Objects, Collection of Meth-

odological Manuals), Moscow: Minzdrav Rossii, 1997,pp. 67–76.

5. Cao, Q.-E., Wang, K., Hu, Z., and Xu, Q., Talanta, 1998,vol. 47, pp. 921–927.

6. Skorik, Yu.A., Podberezskaya, N.V., andRomanenko, G.V., Zh. Neorg. Khim., 2003, vol. 48,no. 2, pp. 246–251.

7. Neudachina, L.K., Osintseva, E.V., Skorik, Yu.A., andVshivkov, A.A., Zh. Anal. Khim., 2005, vol. 60, no. 3,pp. 271–277.

8. Melkozerov, V.P., Neudachina, L.K., and Vshivkov, A.A.,Zh. Obshch.. Khim., 1997, vol. 67, no. 1, pp. 98–103.

9. Skorik, Yu.A., Neudachina, L.K., Vshivkov, A.A., et al.,Zh. Fiz. Khim., 1999, vol. 73, no. 12, pp. 2284–2286.

10. Skorik, Yu.A., Neudachina, L.K., and Vshivkov, A.A.,Zh. Org. Khim., 1999, vol. 69, no. 2, pp. 296–301.

11. Skorik, Yu.A., Neudachina, L.K., Korotovskikh, E.V.,and Vshivkov, A.A., Zavod. Lab., 2001, vol. 67, no. 3,pp. 15–16.

12. Obobshchennyi perechen’ PDK i OBUV vrednykh vesh-chestv dlya vody rybokhozyaistvennykh vodoemov. GN12-04-11 (List of MACs and PELs of Hazardous Sub-stances for Fish Industry Waters), Moscow: MinzdravRossii, 1990.

13. GOST (State Standard) 2874-82. Voda pit’evaya.Gigienicheskie trebovaniya i kontrol’ za kachestvom(Drinking Water. Hygienic Requirements and QualityControl), Moscow: Izd-vo Standartov, 1982.

Table 4. Results of Cu(II) determination in drinking and waste waters by the fluorescence procedure using II and by atomicabsorption spectroscopy (AAS)

Object Copper added, mg/dm3

Copper found by AAS, mg/dm3

Fluorescence method

copper found, mg/dm3 n SR

±∆ forP = 0.95

Drinking water* 1.27 – 1.36 8 0.19 0.16

Waste water – 2.28 ± 0.05 2.24 7 0.13 0.12

* TU 9185-004-41645795-01.