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SERS, Raman, IR and DFT investigation of 1-(2-pyridylazo)-2-naphthol and its metal complexes L. Szabó1*, K. Herman1, N. Leopold1, A. Fălămaş1, N. Mircescu1, C. Buzumurgă2, V. Chiş1
1Faculty of Physics, Babeş-Bolyai University, Kogalniceanu 1, 400084 Cluj-Napoca, Romania 2 “Nicolae Stăncioiu" Heart Institute, Moţilor 19-21, 400001 Cluj-Napoca, Romania
*[email protected] Abstract Metal ions determination represents an area of interest in several fields, like environmental protection, food safety or clinical diagnostics. Analytical methodologies for direct determination of metal ions were established over the last decades
including atomic absorption or emission spectroscopy and mass spectrometry. Although these methods are sensitive and accurate, they require tedious sample pre-treatment and expensive equipment. Thus, a significant increase in the
development of optical chemical sensors for heavy metals has been noted in the last years, aiming to their routinely production, low cost, high selectivity and sensitivity. In this work, IR, Raman and SERS spectroscopy is used in conjunction with
quantum chemical calculations in order to characterize the molecular structure, electronic properties and vibrational energies of the 1-(2-pyridylazo)-2-naphthol (PAN) molecule and its complexes with Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II) and
Pb(II). Thus, IR, Raman and SERS spectra of PAN, as well as the SERS spectrum of the Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II) and Pb(II) complex of PAN, were assigned using DFT calculations with the hybrid B3LYP exchange-correlation
functional using the standard 6-31G(d) basis set. The experimental vibrational bands were assigned to the calculated normal modes and a very good correlation was achieved between the experimental and theoretical data. The SERS spectra of
PAN and of its metal chelates were recorded using HeNe laser emitting at 633 nm and hydroxylamine reduced silver colloid [1]. PAN complexes with Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II) and Pb(II) are differentiated by their SERS spectra,
each metal complex showing a particular SERS spectral fingerprint. The molecular electrostatic potential of the molecules has been calculated and used for predicting site candidates of electrophilic attack.
Key words: Metal chelating compounds, heavy metal ion, FTIR, FT-Raman, SERS, DFT, 1-(2-pyridylazo)-2-naphthol (PAN).
Acknowledgement: This work was supported by CNCSIS –UEFISCSU, project number PNII – RU PD_445/2010.
Experimental techniques FT-IR /ATR The FTIR/ATR spectrum of PAN powder sample was recorded at room temperature on a conventional Equinox 55 (Bruker Optik GmbH, Ettlingen, Germany) FTIR spectrometer equipped with a DTGS detector. FT-Raman The FT-Raman spectrum of PAN was recorded in a backscattering geometry with a Bruker FRA 106/S Raman accessory equipped with a nitrogen cooled Ge detector. The 1064 nm Nd:YAG laser was used as excitation source, and the laser power measured at the sample position was 300 mW. The FT-Raman and FTIR/ATR spectra were recorded with a resolution of 4 cm-1 by co-adding 32 scans. SERS SERS spectra were recorded using a DeltaNu Advantage 633 Raman spectrometer (DeltaNu, Laramie, WY) equipped with a HeNe laser emitting at 633 nm. The laser power was 4 mW and the spectral resolution of 10 cm-1. For all SERS measurements 25 µl of analyte were added to 0.5 ml silver colloid. All chemicals used were of analytical reagent grade. The silver colloid was prepared according to the previously reported procedure [1]. The pH value of the silver colloid, measured immediately after preparation, was found to be 8. PAN complexes with Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II) and Pb(II) were prepared by adding 1 ml dilutions of 10-3 M metal salt solution to 2 ml 10-3 M PAN solution, up to obtaining finally 3 ml mixtures at 2:1 PAN:metal salt molar ratio, PAN chelating metal ions at 2:1 ratio.
[1] N. Leopold, B. Lendl, J. Phys. Chem. B 107 (2003) 5723. Computational methods DFT exchange-correlation functionals: B3LYP & BLYP, basis sets: “spectroscopic” 6-31G(d)
Optimized chemical structure of PAN with atom numbering scheme.
FTIR/ATR spectra of PAN
800 1000 1200 1400 1600
648
670
734 75
6 786
810 8
58 873
911 96
498
5
1034
1066
1093
1116
1136
1191
1218
1252
1279
1313
1379
1408
1457
1467
1496
1524
1586 1691
1620
1606
159215
6815
54
1502
1472
1453
1438
1402
1334
1320
129812
6212
5312
3012
0111
5711
4411
3511
09109
810
9110
4510
3698
998
495
4
867
841
796
770
750
728
690
657
Abso
rban
ce (a
.u.)
Wavenumber /cm-1
PAN_FT-IR/ATR
Calculated IR spectrum
SERS, FT-Raman and Calculated Raman spectra of PAN
381
480 60
3
655
679
728
754
855
877
908
984
1002
1016
1050
1092
1153
1181
1229
1255
1310
1330
1357
1386
1433
1449
1477
1550
1574
1592 16
09
1714
161916
0415
9215
781554
1512
1482
1453
1441
1396
1353
1333
1321
1299
12811
262
1252
1228
1201
1100
1090
984
906
89685
6
784
761
727
706
644
60058
656
955
153
952
249
946
044
9422369
349
315
302
252
223
261
317
354
425
463 501 529
553 60
8 648
734
779
810
859
911
964
1034
1116 11
40
1217 1
280
1379 14
37
1496
1523
1550
1585
1615
1691
200 400 600 800 1000 1200 1400 1600
Ram
an In
tens
ityWavenumber (cm-1)
SERS_PAN
FT-Raman_PAN
Calculated Raman spectrum
Optimized chemical structure of Mn(PAN)2 complex
Conclusions PAN was investigated by experimental (FT-IR, FT-Raman and SERS) techniques in conjunction with DFT quantum chemical calculations. In order to assess the detection potential of different metal ions PAN as chelating agent and SERS as detection method, SERS spectra of
different metal complexes of this ionophores were recorded (Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II), Pb(II)) using a silver colloid substratum. Each PAN-metal complex SERS spectrum shows a characteristic spectral fingerprint. Because all PAN-metal compounds indicated standard
marker bands, SERS method may be a new detection technique for Al(III), Ca(II), Mn(II), Fe(III), Cu(II), Zn(II) and Pb(II). For PAN, DFT calculation were made for a good geometric optimization, for the molecular electrostatic potential determination and also for
band assignment.
B3LYP/6-31G(d) calculated 3D electrostatic potential contour map of PAN, in atomic units.
236
382
481
606
660
730
856
985
1051 10
94 1154 12
26 125
613
1013
3313
8814
3414
79
1551
1574
1594
1611
409 45
4
513
538
570
649
761
856
912
1022
1096
1142
1232
1254
1334
1361
1454
1562 1590
1612
234
476 588
644
729
758 85
690
9
984
1016
1093
1154
1229
1255
1330
1356
1450 1
478
1551
1594
455
482
603 654
679 7
3076
081
0 856
911
984
1017
1094
1155
1232
1252
1326 1
360
1449 14
77
1551
1605
454
506
568
644 75
6
859
908
1016
1092
1138
1231
1329
1354
1449
1511
1560 1606
452
509 5
86 645
758
856
909
1018
1093
1140
1230
1326
1358
1450
1508 15
60 1606
238
480
604
645
729
855 9
8410
16
1093 1154
1229
1255
1330
1357
1385
1450
1478
1551
1605
445
477 55
958
763
8 729
757
856 1000
1092
1154
1230
1255
1327
1447
1478
1551
1592
200 400 600 800 1000 1200 1400 1600
Ram
an In
tens
ity
Raman shift /cm-1
SERS-Al(PAN)2
SERS-Ca(PAN)2
SERS-Pb(PAN)2
SERS-Zn(PAN)2
SERS-Mn(PAN)2
SERS-Fe(PAN)2
SERS-Cu(PAN)2
SERS-PAN
SERS spectra of PAN and PAN-metal complexes
232
276
320
367
403
426
452
518
548
596
663
697
722
754
777
879
909
929
964
986
1007
1165 12
0712
43 1266
1312
1399
1424
1466
1499
1529 15
74
221 2
61 317
354
425
463 52
955
3 608 648
734
779
810
858
911 9
64
1034
1116 1139
1217 12
80
1379 14
3714
9615
2315
85
1691
211
250
296
364
445
526 572
649
671
876
975
1033
1096
1127
1232
1262
1296 1
343
1434
1550 1
593
263
325
353
416 467 57
561
567
7
783
885 933
1007
1075 1
150
1205
1232
1289
1326
1383
1446 1497
1532
1575
200
237
270
300
324
516
569
606
782 99
6
1101
1135
1199
1260
1322
1398 14
37
1536 1
590
197
220
271
316
378
440
533
578
656
672
749
773
879 9
8310
29
1096
1125
1168
1238
1274 13
11 1350
1438
1552
1591
229
309
368
446
510 576
652
673
771
878
981
1041
1096
1126
1166
1230
1277 1
307
1353
1440
1469
1556
1594
224
294
378
437
497
519
568
627
649
668
878
973
1000
1032
1099
1124
1149
1232
1271
1297
1338
1436
1540
1594
200 400 600 800 1000 1200 1400 1600
Pb(PAN)2
Cu(PAN)2
Fe(PAN)2
Mn(PAN)2
Ca(PAN)2
Al(PAN)2
Zn(PAN)2
PAN
Ram
an In
tens
ity
Raman shift /cm-1
Calculated Raman spectra of PAN
and PAN-metal complexes B3LYP/6-31G(d) calculated 3D
electrostatic potential contour map of Mn(PAN)2 complex, in atomic units.
Picture of solutions of different PAN-metal complexes: PAN Al(PAN)2 Ca(PAN)2 Mn(PAN)2 Fe(PAN)2 Cu(PAN)2 Zn(PAN)2 Pb(PAN)2
Slide Number 1