Vibrational spectroscopy and density functional theory study of 4-mercaptophenol

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Vibrational spectroscopy and density functional theory study of 4-mercaptophenol Ran Li a, Wei Ji a, Lei Chen a, Haiming Lv a,c, Jianbo Cheng b, Bing Zhao a,⇑ a

State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, China The Laboratory of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, China c Center for Composite Material, Harbin Institute of Technology, Harbin, China b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Most of the fundamentals vibrations

4-Mercaptophenol (4-MPH) was designed as a model molecule for theoretical and experimental studies of the molecule structure. Fourier transform infrared (FTIR) and Raman spectra of the compound have been obtained experimentally. Most of the fundamentals vibrations agree well with the predicted frequencies. Hydrogen bond donors and acceptors are predicted.

agree well with the predicted frequencies.  Hydrogen bond donors and acceptors are predicted.  The vibrational spectra of 4-MPH are investigated experimentally and theoretically.

a r t i c l e

i n f o

Article history: Received 10 September 2013 Received in revised form 8 November 2013 Accepted 28 November 2013 Available online 4 December 2013 Keywords: 4-Mercaptophenol FTIR Raman DFT HOMO–LUMO gap Hydrogen bond

a b s t r a c t In this paper, 4-mercaptophenol (4-MPH) was designed as a model molecule for theoretical and experimental studies of the molecule structure. Density functional theory (DFT) calculations have been performed to predict the IR and Raman spectra for the molecule. In addition, Fourier transform infrared (FTIR) and Raman spectra of the compound have been obtained experimentally. All FTIR and Raman bands of the compound obtained experimentally were assigned based on the modeling results obtained at the B3LYP/6-311 + G level. Our calculated vibrational frequencies are in good agreement with the experimental vales. The molecular electrostatic potential surface calculation was performed and the result suggested that the 4-MPH has two hydrogen bond donors and three hydrogen bond acceptors. HOMO–LUMO gap was also obtained theoretically at B3LYP/6-311 + G level. Ó 2013 Elsevier B.V. All rights reserved.

Introduction 4-Mercaptophenol (4-MPH) has been widely used in pharmaceutical synthesis [1–3], molecular self-assembly [4–8], crystal engineering [9–12], and other advanced research areas [13,14]. ⇑ Corresponding author. Tel.: +86 431 8516 8473. E-mail address: [email protected] (B. Zhao). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.11.109

4-MPH, a benzene derivative, contains a hydroxyl (–OH) and a sulfhydryl (–SH) functional group and has been used to synthesize highly functionalized materials [15,16]. 4-MPH has been used to form a monolayer [17–21] that protected gold nanoclusters from aggregating. 4-MPH can be used to obtain directionally or periodically ordered structures of supramolecular systems via hydrogen bonding, halogen bonding, or p–p stacking.

R. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703

Surface-enhanced Raman scattering (SERS) has been widely used as a powerful tool for ultrasensitive chemical analysis, which allows this technique sensitive enough to detect single-molecules [22,23]. Applications of SERS range from nanostructure characterization to chemical–biochemical analysis. 4-MPH has been previously employed as a SERS-signaling molecule used in various fields [24–26]. For the selected enhancement in SERS-based study of molecules, the orientation of the studied molecule on the substrate can be identified. Therefore, the molecular structure information, the vibration mode assignment, and the frontier molecular orbital information of a probe molecular are important for analyzing the complex structure of molecule and the mechanism of the enhancement. Molecular conformation and the frontier molecular orbital data are very important for many applications, but these were extremely hard to get by employing experiment method. Fortunately, such informations can be calculated theoretically using the density functional theory (DFT) which describes the electronic states of atoms, molecules, and materials in terms of the three-dimensional electronic density of the system. DFT is generally accepted as a reliable means for predict the spectrum information and molecular conformation. Wu et al. [27] successfully assigned their corresponding vibrational modes of aflatoxins (AFs) and AFs-Ag complexes by using DFT method at the B3LYP/6-311G level. Our previous works [28,29] also showed the advantage of DFT method in application of obtaining the vibrational informations. Herein, we report the conformational, IR, and Raman study of 4MPH based on DFT calculations at the B3LYP/6-311 + G level. FTIR and confocal Raman spectra of the compound have also been obtained experimentally and accurately assigned using the results of the theoretical calculations. For further application, the energy difference between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the HOMO/ LUMO gap, has also been calculated, which were valuable for explaining the enhancement as mechanism of SERS. In addition, the hydrogen bond donors and receptors are predicted based on the theoretical calculations.

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tional [32]. The triple split valence basis set of 6-311 + G was adapted. The frequency calculation was performed at the same level. All calculations were carried out with the aid of the Gaussian 09 program [33]. The molecular electrostatic potential (MEP) were obtained by the WFA [34] software package. Potential energy distribution (PED) calculation was carried out by the VEDA 4 (Vibrational Energy Distribution Analysis) [35]. The method for calculating scaling factors was same as that proposed by Scott and Radom [36]. Results and discussion 4-MPH is di-substituted aromatic compound, containing a hydroxyl and a sulfhydryl group. Potential energy scans performed along on the C2–C3–O11–H12 and C5–C6–S13–H14 dihedral angles, from 0° to 180°, with an increment of ten degrees. The DFT calculated potential energy curves were shown in Fig. 1. Herein, the horizontal and axes refer to torsion angles and the potential energy difference, respectively. In addition, we labeled all the atoms of 4-MPH with number, which were shown in Fig. 1. The potential energy difference is obtained by subtracting the energy of the dihedral-confined geometry from the energy of the optimized geometry. The optimized geometries from two curves are the same one with none imaginary frequency at the same calculation level, suggesting that optimized geometry is the real global energy minima. Molecular geometry The optimized geometry of 4-MPH is also shown in Fig. 1, and the corresponding structural parameter of bond lengths, bond

Experimental Materials 4-Mercaptophenol (4-MPH, 97%) was obtained from Sigma. All other chemicals were of analytical grade and were purchased from Beijing Chemical Reagent Factory and used without further purification. Instruments Raman spectra of 4-MPH were recorded on a LabRam Aramis Raman Microscope system (Horiba–JobinYvon) equipped with a multichannel air cooled charge-coupled device (CCD) detector. Spectra were excited using the 633 nm line of a HeNe narrow bandwidth laser (Melles Griot). The Raman spectra were collected at room temperature with the laser power at the sample position typically at 400 lW with an average spot size diameter of 1 lm. The typical acquisition time used in this work was 30 s. The FTIR spectra of 4-MPH were recorded as KBr disks at room temperature by a Bruker IFS-66V FT-IR spectrometer, equipped with a DTGS detector at a resolution of 4 cm1. Theoretical method All the geometries we got in this work were optimized by DFT method of B3LYP which is the hybrid of Becke’s three-parameter exchange functional [30,31] with the Lee–Yang–Parr correlation func-

Fig. 1. Torsional potential energy curve for 4-MPH calculated at the B3LYP/6311 + G level.

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R. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703

Table 1 The optimized structural parameters of 4-mercaptophenol calculated at the B3LYP/6-311 + G level. BL

Value (Å)

BA

Value (°)

BA

Value (°)

Dihedral

Value (°)

Dihedral

Value (°)

C1–C2 C1–C6 C2–C3 C3–C4 C4–C5 C5–C6 C1–H7 C2–H8 C4–H9 C5–H10 C3–O11 C6–S13 O11–H12 S13–H14

1.3933 1.3953 1.3954 1.3963 1.3893 1.3992 1.0831 1.0861 1.0832 1.0833 1.3669(1.3696) 1.8026(1.7875) 0.9629 1.3513

C1–C2–C3 C2–C3–C4 C3–C4–C5 C4–C5–C6 C1–C6–C5 C2–C1–C6 C2–C1–H7 C6–C1–H7 C1–C2–H8 C3–C2–H8 C3–C4–H9 C5–C4–H9 C4–C5–H10 C6–C5–H10

119.9 119.9 119.8 120.7 119.0 120.5 119.8 119.7 119.9 120.2 119.1 121.1 119.7 119.6

C2–C3–O11 C4–C3–O11 C1–C6–S13 C5–C6–S13 C3–O11–H12 C6–S13–H14

122.7 117.3 120.0 120.9 109.9 97.4

C6–C1–C2–C3 C1–C2–C3–C4 C2–C3–C4–C5 C4–C5–C6–C1 C2–C1–C6–C5 C3–C4–C5–C6 C6–C1–C2–H8 H7–C1–C2–C3 H8–C2–C3–C4 H7–C1–C6–C5 C2–C3–C4–H9 H9–C4–C5–C6 H10–C5–C6–C1 C3–C4–C5–H10

0.1 0.3 0.1 1.3 0.8 0.9 179.9 179.8 179.7 179.4 179.5 179.7 178.6 179.0

C2–C1–C6–S13 C4–C5–C6–S13 C1–C2–C3–O11 O11–C3–C4–C5 H9–C4–C5–H10 H7–C1–C2–H8 H8–C2–C3–O11 O11–C3–C4–H9 H10–C5–C6–S13 H7–C1–C6–S13 C2–C3–O11–H12 C4–C3–O11–H12 C1–C6–S13–H14 C5–C6–S13–H14

177.6 178.0 179.9 179.7 0.4 0.1 0.1 0.3 1.9 2.6 0.4 179.5 101.4 81.9

Note: BL is bond length, BA is bond angle. The data in parentheses are from phenol and thiophenol calculated at the same level.

angles, and dihedral angles are shown in Table 1. The C–C bonds were not equal and varied from 1.3893 to 1.3992 Å, whereas the C–H bonds are still almost identical except the C2–H8 bond which was longer owing to the interaction with O–H bond. The C–O bond was slightly shortened whereas the C–S bond was elongated compared to the phenol and thiophenol, respectively. The C–C–C and C–C–H bond angles indicated slight deformation of the ring. The O–H was found to lie in the phenyl ring (dihedral angle formed by C–C–O–H is 179.5°), whereas the S–H bond was nearly perpendicular (dihedral angle formed by C–C–S–H is 81.9°) to the ring.

Vibrational assignments The 4-MPH consists of 14 atoms, which undergoes 36 normal modes of vibrations. The optimized 4-MPH is not symmetrical because the S–H bond does not lie in the plane of the ring. We restricted the molecule into C2v symmetry is convenient for spectrum discussion and vibrational assignments, thus the 36 normal modes of vibrations are distributed as:

Cvib ¼ 13A1 þ 3A2 þ 8B1 þ 12B2 Assuming that the molecule is C2v symmetry, all of the 36 fundamental vibrations were Raman active. Amongst these vibrations, 33 were active in IR as the three A2 modes were IR inactive. The observed and calculated vibration modes are shown in Table 2 and the calculated frequencies 901–2999 and 3000–4000 cm1 were multiplied by the scaling factors 0.9726 and 0.9325, respectively. The IR spectra in Fig. 2 shows a number of bands appearing at 421, 518, 642, 664, 823, 926, 1010, 1101, 1166, 1225, 1260, 1360, 1434, and 1584 cm1. The Raman bands in Fig. 3 were observed at 243, 331, 380, 544, 638, 701, 816, 830, 919, 1007, 1077, 1082, 1172, 1178, 1261, 1291, 1489, 1585, and 1602 cm1. As can be seen from Figs. 2 and 3, most of the fundamentals vibrations observed in Raman and FTIR spectra agreed well with the theoretically predicted frequencies. A1 species The fundamental m10 arises from a typical C–S stretch coupled with 6a vibration were observed in both IR and Raman spectra

Table 2 Experimental and theoretical vibrational frequencies (cm1) of 4-mercaptophenol at the B3LYP/6-311 + G level. No.

FT-IR

m36 m34 m33 m32 m31 m30 m29 m28 m27 m25 m24 m23 m22 m21 m20 m19 m17 m14 m13 m12 m10 m9 m8 m6 m5 m3 a b

a

Experimental

1584 1434 1360 1260 1225 1166 1101 1010 926 823 664 642 518 421

Theo.

Sym. constrained

Vibrational assignmentsb

PED

4160(A1) 3223(B2) 3193(B2) 3192(A1) 2810(A1) 1620(A1) 1592(B2) 1501(A1) 1419(B2) 1307(B2) 1306(B2) 1180(A1) 1196(B2) 1114(B2) 1054(A1) 1004(A1) 942(B1) 840(B1) 795(A1) 686(B1) 628(A1) 500(B1) 438(B2) 381(A1) 1139(B1) 262(B2)

mO–H 20b 7b 7b mS–H 9b 9a 18a 18b, bC–O 14 18a, mC–O 8a 15, bC–O 19a 9b, mC–S 9b 5, bC–S 17b 10a 4 6a, mC–S 16b 16a, bO–H, cS–H mC–S, bC–S sC–O bC–S, bC–O

mO–H(92) 20b(92) 7b(92) 7b(96) mS–H(91) 9b(82) 9a(82) 18a(88) 18b(79), bC–O(14) 14(90) 18a(73), mC–O(18) 8a(91) 15(59), bC–O(27) 19a(91) 9b(79), mC–S(11) 9b(94) 5(88), bC–S(5) 17b(90) 10a(90) 4(90) 6a(78), mC–S(14) 16b(95) 16a(60), bO–H(16), cS–H(18) mC–S(46), bC–S(33) sCCOH(93) bC–S(43.7), bC–O(21)

Raman 3070 3055 2980 2569 1602 1585 1489 1261 1178 1172 1082 1077 1007 919 830 816 701 638 544 380 331 243

The theoretical frequencies are scaled. The wilson notation is employed.

3575(A) 3078(A) 3068(A) 2940(A) 2564(A) 1592(A) 1577(A) 1481(A) 1410(A) 1275(A) 1245(A) 1159(A) 1155(A) 1088(A) 1074(A) 997(A) 924(A) 833(A) 811(A) 674(A) 642(A) 504(A) 423(A) 374(A) 324(A) 253(A)

R. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703

Fig. 2. The comparison of the experimental FT-IR spectrum (black) of 4-MPH with the theoretical IR spectrum (red, B3LYP/6-311++G). The theoretical spectrum has been shifted to improve the visual comparison. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3. The comparison of the experimental Raman spectrum (black) of 4-MPH with the theoretical Raman spectrum (red, B3LYP/6-311++G). The theoretical spectrum has been shifted to improve the visual comparison. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

and appeared at ca. 642 and 638 cm1, respectively. Potential energy distribution (PED) results suggested that the C–S stretch also corresponds to m6 and m20. Two stretching vibrational modes of the A1 species, m31 and m36 were assigned to the S–H and O–H stretch, respectively, and could only be observed in the Raman spectra. Normal modes, m13, m23, m30, and m32 were attributed to 10a, 8a, 9b, and 7b, and appeared at ca. 816, 1178, 1602, and 2980 cm1, respectively. The remaining vibrational modes of A1 species were observed in both the IR and Raman spectra at ca. 1007 and 1489 cm1, and assigned to 9b and 18a, respectively. A2 species In the proposed FTIR and Raman spectra of 4-MPH, three vibration modes (m7, m16, and m18) of A2 species could not be observed in either the IR or Raman spectra. These vibrational modes were IR inactive, and their Raman activities were extremely low. B1 species The fundamental m1 mode arises from the C–S torsional vibration, with a theoretical frequency of 65 cm1. The fundamental m2 mode, at 117 cm1, arises from C–S and C–O out-of-plane

701

Fig. 4. The natural charge population of 4-MPH calculated at the B3LYP/6-311 + G level.

Fig. 5. The molecular electrostatic potential (MEP) of 4-MPH calculated at the B3LYP/6-311 + G level from different observational orientation. (A) top, (B) bottom, (C) left, (D) right, (E) front and (F) back. The color scheme is red > 0.0559 a.u. > yellow > 0.0 a.u. > green > 0.0058 > blue. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

bending coupled with 17a. The fundamental m4 mode, at 300 cm1, arises from C–S and C–O out-of-plane bending coupled with skeletal C–C out-of-plane bending. The fundamental m16 (905 cm1) and m26 (1328 cm1) modes are 10b coupled with C–S in-plane bending and 14 coupled with C–O in-plane bending, respectively. The above-mentioned modes were difficult to observe in both the IR and Raman spectra; therefore, they are omitted from Table 2. The remaining three fundamental B1 modes of vibration are observed in both the IR and Raman spectra, in the range from 500 to 1350 cm1. The fundamental m9 (504 cm1), m12 (674 cm1), and m14 (833 cm1) modes arise from motion related to benzene ring of 16b, 4, and 17b, respectively. B2 species The fundamental m3 and m5 modes observed in the Raman spectrum are C–S and C–O in-plane bending coupled with 17b and C–O

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R. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703

Fig. 6. Plots of the frontier orbitals of 4-MPH calculated at the B3LYP/6-311 + G level.

torsion vibration, respectively. The fundamental m8, m24, and m27 modes observed in the IR spectrum are arise from O–H in-plane bending coupled with S–H out-of-plane bending coupled with 16a, C–O stretching coupled with 18a, and C–O in-plane bending coupled with 18b, respectively. The fundamental m21, m33, and m34 modes observed in the Raman spectrum are benzene ring vibration of 19a, 7b, and 20b, respectively. The fundamental m25 mode has been assigned to benzene ring vibration of 14, observed both in IR and Raman spectra and appears at ca. 1260 and 1261 cm1, respectively. The fundamental m22 mode is benzene ring vibration of 15 coupled with C–S in-plane bending, and observed in IR and Raman spectra at ca. 1166 and 1172 cm1, respectively. The fundamental m29 mode is C–O in-plane bending coupled with 9a, and they could also be observed both in IR and Raman spectra at ca. 1584 and 1585 cm1. The fundamental m11 mode with a theoretical frequency of 650 cm1 is assigned to 6b but the peak could not be found in the IR and Raman spectra. HOMO–LUMO gap HOMO–LUMO gap results in a significant degree of electric excitation and charge transfer. In most cases, even in the absence of inversion symmetry, the strongest band in the Raman spectrum is weak in the IR spectrum and vice versa. Changes in the HOMO–LUMO gap by connecting with some noble metal or semiconductor or some other means result in the change of the charge transfer degree, intensity and position of the peak. The frontier molecular orbitals are shown in Fig. 6 and the HOMO–LUMO gap estimated to be 5.69 eV at B3LYP/6-311 + G level.

sulfydryl functional group) and three hydrogen accepters (the p electron cloud of the benzene ring, and the lone pair on the O and S atom in the hydroxyl and sulfhydryl group). Conclusion In this work, the structural parameters of 4-mercaptophenol (4MPH) have been obtained at the B3LYP/6-311 + G level of theory. The sulfhydryl hydrogen was found to lie perpendicular to the plane of the phenyl ring, whereas the hydroxyl hydrogen was found to be in the plane of the ring. When the S covalently bonded to the substrate, the hydroxyl was away from the plane owing to the low rotation energy barrier (14.7 kJ/mol). In addition, modeling performed for 4-MPH at the B3LYP/6-311 + G level allowed the assignments of the IR and Raman bands of the compound, and was accurate in predicting harmonic vibrational frequencies and the normal modes along with the vibrational spectra were well resolved. The HOMO–LUMO gap is predicted to be 5.69 eV at the B3LYP/6-311 + G level. Furthermore, based on the MEP map, we found that 4-MPH has two potential hydrogen donors and three hydrogen acceptors. Acknowledgements This work was supported by the National Natural Science Foundation (Grant Nos. 21272991, 21221063) of P.R. China; Specialized Research Fund for the Doctoral Program of Higher Education (20110061110017); the 111 project (B06009), the Development Program of the Science and Technology of Jilin Province (20110338).

Hydrogen bond donor and accepter

References

Hydrogen bond is an important intermolecular interaction in supramolecular systems and charge transfer and the corresponding change in electric structure directly effect on the spectra. The natural population analysis results show in Fig. 4, the atom number labeling consist with Fig. 1. The mapping of molecular electrostatic potential onto the iso-electron density surface simultaneously displays electrostatic potential distribution, molecular shape, size, and dipole moments of the molecule and it provides a visual method to understand the relative polarity of the molecule. The total electron density and molecular electrostatic potential (MEP) surfaces of the molecules under investigation are constructed using B3LYP/6-311 + G method. The total electron density mapped with 5 electrostatic potential surface of 4-MPH is shown in Fig. 5. The color scheme in Fig. 5 of MEP is red > 0.0559 a.u. > yellow > 0.0 a.u. > green > 0.0058 > blue. The MEP map indicates that 4-MPH has two potential hydrogen donors (the hydrogen atom in the hydroxyl and the hydrogen atom in the

[1] C. Chen, Y.Z. Liu, K.S. Shia, H.Y. Tseng, Bioorg. Med. Chem. Lett. 12 (2002) 2729. [2] F. Sobrio, T. Quentin, M. Dhilly, T. Bourdier, S. Tymciu, D. Debruyne, L. Barré, Nucl. Med. Biol. 35 (2008) 377. [3] J.Z. Vlahakis, R.T. Kinobe, K. Nakatsu, W.A. Szareka, I.E. Crandall, Bioorg. Med. Chem. Lett. 16 (2006) 2396. [4] J.R.I. Lee, T.Y. Han, T.M. Willey, D. Wang, R.W. Meulenberg, J. Nilsson, P.M. Dove, L.J. Terminello, T.V. Buuren, J.J.D. Yoreo, J. Am. Chem. Soc. 129 (2007) 10370. [5] T. Yonezawa, H. Matsune, N. Kimizuka, Adv. Mater. 15 (2003) 499. [6] R. Paolesse, D. Monti, L.L. Monica, M. Venanzi, A. Froiio, S. Nardis, C.D. Natale, E. Martinelli, A. D’Amico, Chem. Eur. J. 8 (2002) 2476. [7] W. Ni, R.A. Mosquera, J. Pérez-Juste, L.M. Liz-Marzán, J. Phys. Chem. Lett. 1 (2010) 1181. [8] Y. Lin, V.K. Daga, E.R. Anderson, S.P. Gido, J.J. Watkins, J. Am. Chem. Soc. 133 (2011) 6513. [9] A.S. Angeloni, M. Laus, D. Caretti, E. Chiellini, G. Galli, Chirality 3 (1991) 307. [10] J. Küther, R. Seshadri, W. Tremel, Angew. Chem. Int. Ed. 37 (1998) 3044. [11] J. Küther, R. Seshadri, G. Nelles, W. Assenmacher, H.J. Butt, W. Mader, W. Tremel, Chem. Mater. 11 (1999) 1317. [12] H.R. Kricheldorf, N. Probst, Macromol. Chem. Phys. 196 (1995) 3511. [13] C. Lu, N. Wu, X. Jiao, C. Luo, W. Cao, Chem. Commun. (2003) 1056. [14] Y. Feng, L. Liu, Y. Fang, Q.X. Guo, J. Phys. Chem. A 106 (2002) 11518.

R. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 698–703 [15] A.S. Belov, I.G. Belaya, V.V. Novikov, Z.A. Starikova, E.V. Polshin, A.V. Dolganov, E.G. Lebed, Inorg. Chim. Acta 394 (2013) 269. [16] E.R. Zubarev, J. Xu, A. Sayyad, J.D. Gibson, J. Am. Chem. Soc. 128 (2006) 4958. [17] R. Guo, Y. Song, G. Wang, R.W. Murray, J. Am. Chem. Soc. 127 (2005) 2752. [18] R. Guo, R.W. Murray, J. Am. Chem. Soc. 127 (2005) 12140. [19] D. Barriet, C.M. Yam, O.E. Shmakova, A.C. Jamison, T.R. Lee, Langmuir 23 (2007) 8866. [20] J.J. Calvente, G. López-Pérez, P. Ramírez, H. Fernández, M.A. Zón, W.H. Mulder, R. Andreu, J. Am. Chem. Soc. 127 (2005) 6476. [21] H.G. Choi, J.P. Amara, T.M. Swager, K.F. Jensen, Langmuir 23 (2007) 2483. [22] S.M. Nie, S.R. Emory, Science 275 (1997) 1102–1106. [23] K. Kneipp, Y. Wang, H. Kneipp, L.T. Perelman, I. Itzkan, R.R. Dasari, M.S. Feld, Phys. Rev. Lett. 78 (1997) 1667–1670. [24] K. Kim, H.B. Lee, K.S. Shin, Langmuir 24 (2008) 5893. [25] W. Ji, Y. Kitahama, X. Han, X. Xue, Y. Ozaki, B. Zhao, J. Phys. Chem. C 116 (2012) 24829. [26] N. Guijarro, T. Lana-Villarreal, T. Lutz, S.A. Haque, R. Gómez, J. Phys. Chem. Lett. 3 (2012) 3367. [27] X. Wu, S. Gao, J. Wang, H. Wang, Y. Huang, Y. Zhao, Analyst 137 (2012) 4226. [28] Z. Zhuang, W. Ruan, N. Ji, X. Shang, X. Wang, B. Zhao, Vib. Spectrosc. 49 (2009) 118. [29] Z. Zhuang, J. Chenga, X. Wang, B. Zhao, X. Han, Y. Luo, Spectrochim. Acta. A 67 (2007) 509.

[30] [31] [32] [33]

703

A.D. Becke, Phys. Rev. A 38 (1988) 3098. A.D. Becke, J. Chem. Phys. 98 (1993) 5648. C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery, Jr, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, GAUSSIAN 09 (Revision A.02), Gaussian Inc, Wallingford CT, 2009. [34] F.A. Bulat, A. Toro-Labbe, T. Brinck, J.S. Murray, P. Politzer, J. Mol. Model. 16 (2010) 1679. [35] M.H. Jamróz, Spectrochim. Acta. A 114 (2013) 220. [36] A.P. Scott, L. Radom, J. Phys. Chem. 100 (1996) 16502.