ОПТИКА И СПЕКТРОСКОПИЯ, 2015, том 118, № 3, с. 385-409
^ СПЕКТРОСКОПИЯ ^^^^^^^^^^
КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
УДК 543.42
FT-IR SPECTROSCOPIC AND DFT COMPUTATIONAL STUDY ON SOLVENT EFFECTS ON 8-HYDROXY-2-QUINOLINECARBOXYLIC ACID © 2015 г. S. Badoglu and §. Yurdakul
Department of Physics, Faculty of Science, Gazi University, Teknikokullar, 06500Ankara, Turkey E-mail: senayy@gazi.edu.tr Received June 2, 2014
Solvent effects on the spectroscopic, structural, and electronic properties of 8-hydroxy-2-quinolinecarbox-ylic acid (8HQC) were analyzed theoretically and experimentally. Density functional theory (DFT) B3LYP/6-311++G(d, p) used within polarized continuum model (pCm) to characterize the solvent effects in benzene, diethyl ether, ethanol, and water. Experimental FT-IR spectra in ethanolic and aqueous solutions were recorded and compared with solid phase experimental data. Nucleus independent chemical shifts were calculated as aromaticity indices. Our results show that the spectroscopic, structural, and electronic properties of 8HQC are solvent dependent.
DOI: 10.7868/S003040341503006X
INTRODUCTION
Theoretical investigations have much applicability in many areas of chemistry such as spectroscopic assignments and characterization of molecular structures [1, 2]. Solvent effects often play an important role in determining conformations, reaction rates, equilibrium constants, and other chemical and biochemical entities [3]. As most chemical reactions occur in the solution phase, the study of solvent effects is very important. These kinds of effects are also considered as pivotal tools for drug design in the pharmaceutical industry because they affect the release, transport and degree of absorption of the drug in the organism, which is important for future development and formulation efforts of the drugs [4].
Currently, a continuum treatment of the solvent through the self-consistent reaction field (SCRF) model is widely employed while studying solvent effects [5]. SCRF continuum models can treat solute's electronic distribution quantitatively. The polarizable continuum model (PCM) by Miertus, Scrocco, and Tomasi was the first proposed SCRF method [6]. The PCM has proven itself as a reliable tool for describing electrostatic solute-solvent interactions. Employing PCM solvation model within the density functional theory (DFT) is a widely used way for modeling solvent effects [7].
To the best of our knowledge, there are no published data available on solvent effects on the spectroscopic, structural, and electronic properties of 8HQC.
In the first part of this paper, we present a theoretical study on the geometrical parameters, vibrational frequencies, and energetics of 8-hydroxy-2-quinoline-carboxylic acid (8HQC) in various solvents. 8HQC contains benzene and pyridine rings besides hydroxyl and carboxylic acid moieties. 8HQC and its derivatives can be used as effective stabilizers against the photo fading of indicator dyes [8, 9]. Also they can be used as the precursor of anti-inflammatory substances [10]. We have used the DFT within the PCM to calculate those properties in four different solvents, and compared the computed data with their counterparts in the gas phase. Nucleus independent chemical shifts (NICS) were calculated as aromaticity indices. The solvents chosen were benzene (e = 2.2706), ether (e = 4.24), ethanol (e = 24.852), and water (e = 78.3553). In the second part, solution phase experimental FT-IR spectra of the compound were recorded in ethanol and in water, and then compared with the solid phase experimental data. Experimental frequencies were assigned on the basis of the potential energy distributions obtained from DFT-PCM calculations. Theoretical electronic properties were reinvestigated by including solvent both explicitly and implicitly.
EXPERIMENTAL AND COMPUTATIONAL METHODS
8-hydroxy-2-quinolinecarboxylic acid was purchased from Aldrich and used without further purification. FT-IR spectra were recorded between 3500
Table 1. Energies (Hartree) and relative Gibbs energy differences (kcal/mol) of 8HQC in various solvents
Vacuum [13] Benzene Ether Ethanol Water
e 1 2.2706 4.24 24.852 78.3553
Eo -665.767 -665.773 -665.776 -665.780 -665.781
E -665.756 -665.762 -665.765 -665.769 -665.770
H -665.755 -665.761 -665.764 -665.768 -665.769
G -665.803 -665.809 -665.812 -665.816 -665.817
AG(gas-soln) 3.76 8.77 8.30 8.73
E0: sum of electronic and zero-point energies (Eelec + ZPE). E: sum of electronic and thermal energies (E0 + Evib + Erot + Etransl). H: sum of electronic and thermal enthalpies (E + RT). G: sum of electronic and thermal free energies (H — TS).
and 550 cm-1 on a Bruker Vertex 80 spectrometer equipped with a Pike MIRacle ATR accessory. For liquid sample analysis, a solution of 8HQC was prepared at 25 mg/mL and the pure solvent spectrum was recorded as reference before sample measurement. Due to the poor solubility of 8HQC in benzene and ether, experimental FT-IR spectra are only recorded in ethanol and water.
Geometry optimizations, harmonic frequencies, IR spectra in the gas phase and in solution phase were
computed at B3LYP/6-311++G(d, p) for monomer forms and B3LYP/6-31G(d) level for dimer forms by using the Gaussian 09W suite of programs [11]. The solvent effects were evaluated by using the PCM. Geometries were fully optimized without symmetry constraints. The stationary structures were found by ascertaining that all the computed frequencies were real. Assignments for the fundamental vibrational modes were proposed according to their PED (potential energy distribution) values obtained by using the VEDA 4 program [12]. Frontier molecular orbitals properties,
Table 2. Selected geometrical parameters (Ä and degrees) of 8HQC
Parameter Vacuum [13] Benzene Ether Ethanol Water
2C-16O 1.351 1.353 1.354 1.355 1.355
11C-12C 1.510 1.507 1.506 1.504 1.504
12C-14O 1.203 1.206 1.207 1.210 1.210
12C-15O 1.343 1.342 1.341 1.340 1.339
17H-13N 2.183 2.187 2.191 2.198 2.199
21H-13N 2.060 2.049 2.047 2.048 2.049
17H-13N-21H 78.582 78.025 77.837 77.657 77.633
11C-10C-18H 118.783 119.105 119.269 119.475 119.507
18H-10C-19C 122.616 122.341 122.198 122.018 121.990
10C-11C-12C 119.535 119.922 120.067 120.202 120.217
12C-11C-13N 117.117 116.658 116.475 116.277 116.252
11C-12C-14O 122.920 123.293 123.464 123.604 123.625
14O-12C-15O 122.581 122.139 121.877 121.561 121.505
12C-15O-21H 106.994 107.135 107.229 107.443 107.486
Table 3. Scaled vibrational wavenumbers (frequency, cm of 8HQC in different media
Vacuum* Benzene Ether Ethanol Water
Frequ- Iir Frequ- Iir Frequ- Iir Frequ- Iir Frequ- Iir % PED*
ency ency ency ency ency
59 2.14 58 2.77 60 3.27 64 3.91 64 4.06 71r(OCCC)
83 2.92 83 3.80 83 4.40 82 5.51 82 5.71 63r(NCCC)
154 9.83 163 12.55 165 14.45 162 17.15 160 17.65 476(NCC) + 156(CCC) + 136(OCC)
180 1.42 179 1.87 179 2.29 179 3.17 179 3.37 69r(CCCC) + 15r(OCCC)
202 1.39 202 1.49 201 1.50 201 1.45 200 1.43 51r(CCCC) + 16r(NCCC)
272 10.32 269 13.11 267 14.61 263 16.85 262 17.29 456(OCC) + 186(CCC)
297 3.99 297 4.79 297 5.39 297 6.42 297 6.64 52r(CCCC) + 17r(NCCC) + + 13r(OCCC)
331 0.30 332 0.31 333 0.35 333 0.50 333 0.54 33v(CC) + 16 6(OCO)
428 6.81 429 10.84 429 13.98 430 19.43 430 20.41 24r(NCCC) + 14r(CCCC) + + 12r(HCC) + 11r(HOCC)
465 21.27 465 28.55 465 33.52 463 40.72 462 42.04 546(OCC)
491 23.65 480 70.43 474 88.98 466 118.41 465 124.36 39r(HOCC) + 12r(NCCC)
498 28.70 495 2.98 495 1.43 495 0.66 495 0.59 43r(HOCC) + 13r(NCCC)
508 0.72 508 0.95 508 1.14 508 1.55 508 1.64 286(CCC) + 176(OCC)
538 2.79 538 4.07 538 4.95 538 6.18 538 6.40 386(CCC)
569 0.55 568 0.72 568 0.79 567 0.83 567 0.83 436(CCC) + 176(OCC) + 136(NCC)
588 2.75 588 2.33 589 2.17 588 2.15 588 2.18 22r(CCCC) + 21r(OCCC) + + 13r(NCCC)
615 2.85 614 3.70 614 4.21 614 4.96 614 5.09 266(CCC) + 266(OCO)
638 117.87 641 101.06 643 84.10 644 84.12 644 87.80 57r(HOCC)
647 20.40 651 53.25 654 82.44 658 105.97 658 107.57 31r(HOCC) + 14r(OCCC) + + 14r(OCOC)
729 20.26 729 28.88 729 35.08 728 44.57 728 46.34 326(CCC) + 216(OCO)
740 11.40 740 14.81 740 16.38 741 17.83 741 18.01 146(NCC) + 126(OCO) + 12v(CC)
762 43.57 765 53.60 766 60.81 766 71.65 766 73.50 34r(CCCH) + 14r(CCCC) + + 10r(NCCC)
769 0.26 772 0.03 773 0.06 773 0.92 773 1.39 34r(CCCH) + 21r(OCOC)
810 14.05 813 18.79 814 21.46 816 24.67 816 25.19 23r(NCCC) + 11r(CCCH) + + 10r(CCCC) + 10r(NCCC)
870 39.28 870 45.47 870 49.71 868 56.47 868 57.80 71r(CCCH)
883 12.87 883 17.69 883 20.97 882 25.85 882 26.76 536(CCC)
901 0.49 904 0.46 905 0.44 905 0.41 905 0.41 77r(CCCH)
925 1.57 925 1.98 925 2.24 924 2.60 924 2.66 196(NCC) + 13v(CC) + 126(CCC) + + 10v(NC)
983 0.51 988 0.55 990 0.59 992 0.63 992 0.64 71r(CCCH) + 16r(CCCC)
1009 0.01 1011 0.10 1011 0.20 1011 0.37 1011 0.41 82r(CCCH) + 11r(CCCC)
1066 1.84 1065 3.70 1065 5.39 1064 8.33 1064 8.91 43v(CC) + 196(HCC)
1108 19.92 1107 35.24 1106 46.23 1104 63.11 1103 66.26 176(CNC) + 13v(OC) + 116(CCC) + + 106(HCC)
1128 68.31 1128 90.35 1128 104.62 1127 126.46 1127 130.59 51v(CC) + 13v(OC)
1155 4.47 1156 4.10 1155 4.36 1155 5.27 1154 5.52 586(HCC) + 17v(CC)
1188 31.53 1187 48.89 1186 59.48 1183 73.45 1182 75.75 506(HCC) + 116(HOC)
1207 19.92 1203 22.31 1202 26.89 1199 42.34 1198 47.07 286(HCC) + 146(HOC)
Table 3. (Contd.)
Vacuum* Benzene Ether Ethanol Water
Frequency IlR Frequency Iir Frequency Iir Frequency Iir Frequency Iir % PED*
1252 25.30 1250 93.40 1248 157.29 1245 255.87 1244 271.96 26v(CC) + 176(HOC) + 106(HCC)
1262 125.28 1259 119.84 1257 98.67 1255 60.88 1255 54.64 216(HOC) + 21S(HCC) + 13v(OC)
1309 8.41 1308 18.66 1307 27.98 1306 45.09 1305 48.26 106(HCC)
1344 80.75 1340 151.13 1338 199.62 1336 268.23 1336 279.42 27v(NC) + 136(HOC) + 136(HCC)
1379 312.50 1372 441.47 1369 495.12 1366 550.10 1365 558.19 236(HOC) + 15v(CC) + 10v(NC)
1392 182.93 1390 154.17 1389 146.75 1388 133.88 1387 131.85 17v(NC) + 13v(CC) + 136(HOC)
1414 16.84 1413 28.
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