- Email: [email protected]
Theoretical evaluation of the configurations and Raman spectra of 209 polychlorinated biphenyl congeners
Chemosphere 85 (2011) 412–417
Contents lists available at SciVerse ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Theoretical evaluation of the configurations and Raman spectra of 209 polychlorinated biphenyl congeners Yongchao Lai, Wenxiao Pan, Shouqing Ni, Dongju Zhang, Jinhua Zhan ⇑ Key Laboratory for Colloid & Interface Chemistry of Education Ministry, Department of Chemistry, Shandong University, 250100 Jinan, China
a r t i c l e
i n f o
Article history: Received 13 March 2011 Received in revised form 6 July 2011 Accepted 29 July 2011 Available online 27 August 2011 Keywords: PCBs Configurations Raman spectra Molecular symmetry Normal modes Vibrational spectra
a b s t r a c t Though polychlorinated biphenyls (PCBs) have distributed as threats in the environment to human beings for several decades, monitoring of trace level PCBs in-field is still a challenge. As a potential method for monitoring PCBs at trace levels, Raman spectroscopy has been used to detect several PCBs in the laboratory. To facilitate the development of rapid detection of PCBs by Raman spectroscopy, it is essential to investigate the Raman spectra of all PCB congeners. Herein, the stable configurations and vibrational spectra of all the PCB congeners were calculated by Gaussian 03 program package. Based on molecular symmetry, PCBs are classified into seven groups. The structural features and the normal vibration modes for each group are discussed. Taking the C2-2 group as an example, the wavenumber ranges of the various normal vibration modes in the Raman spectra of PCBs were analyzed. The accuracy of calculated results was verified by experimental Raman spectra of PCB77 standard. This study can elucidate further information to promote the development of Raman spectroscopy in environmental monitoring. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polychlorinated biphenyls (PCBs), as typical persistent organic pollutants (POPs), are a class of organic compounds with 1–10 chlorine atoms substituent on biphenyl. PCBs were widely used for flame retardation and dielectric fluids due to their low inflammability, chemical stability, and solubility in most organic solvents (Diamond et al., 2010; Hites et al., 2010). Although had been banned for many years, PCBs can be found all over the world even in where they are never been used (Chao et al., 2010; Dang et al., 2010; Li et al., 2010; Rodenburg et al., 2010). PCBs are dangerous to human as they could disorder the endocrine system, destroy the immune system and cause cancers (Golden et al., 2003; Leijs et al., 2009). Moreover, more toxic polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) could form from PCBs by partial oxidation (Van den Berg et al., 2006). PCBs at trace levels, which hide in human living environments, can bioaccumulate in the fatty tissue of human through the food chains with tens of thousands of amplifier stage (Van der Oost et al., 2003; Borgå et al., 2005). To fulfill the protection of human health and the environment, it is urgent to develop a simple and quick method for the detection of trace PCBs in people’s living environment, which is the first step in the environmentally sound management of PCBs. Because PCBs have high chemical stability and generally weak interactions with other substances, most analytical methods can not be ⇑ Corresponding author. Tel.: +86 531 88365017; fax: +86 531 88366280. E-mail address: [email protected] (J. Zhan). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.07.067
effectively applied for the detection of PCBs. The common lab-methods to detect trace PCBs are gas–liquid chromatography and highresolution mass spectrometry (Mullins et al., 1984; Takasuga et al., 2006; Rezaei et al., 2008). These methods are based on spatio– temporal separation to achieve separation and detection of PCBs. Raman spectroscopy may be an alternative for the detection of trace level PCBs with spatio–temporal coupling. With the developments of laser and charge-coupled device (CCD) technology, Raman spectrometer can be integrated into a portable instrument, which makes it suitable for rapid detection and in-field test (McCreery, 2000). Raman spectroscopy can be used to identify molecules since the information of Raman shifts is specific to the molecule structures (McCreery, 2000). Commercial portable Raman spectrometers can cover the vibrational region of common organic molecules (200–4000 cm1) (McCreery, 2000). Compared with infrared spectra, Raman spectra of most molecules have narrow line width, low interference by water and high sensitivity to symmetrical molecules. Furthermore, Raman spectra can be used in microscopic analysis as laser for Raman spectroscopy can be focused in a very small volume (<1 lm in diameter) (McCreery, 2000). Owing to these features, Raman spectroscopy becomes an ideal tool for rapid chemical analysis. However, conventional Raman spectroscopy has its disadvantage like the weak signals intensity (Ru and Etchegoin, 2009). Several techniques for enhanced Raman spectroscopy, for example, surface enhanced Raman spectroscopy (SERS), resonance Raman spectroscopy (RRS), tip-enhanced Raman spectroscopy (TERS), have been developed to overcome this disadvantage (Stiles et al., 2008; Ru and Etchegoin, 2009).
413
Y. Lai et al. / Chemosphere 85 (2011) 412–417
Much work has been done to detect PCBs by Raman spectroscopy (Bantz and Haynes, 2009; Yang and Meng, 2010; Zhou et al., 2010a,b), while the lack of Raman spectra of PCBs greatly hinders this convenient and powerful technique. To promote the progress of PCBs monitoring by Raman spectroscopy, an overall study of all PCB congeners’ Raman spectra is needed. It is difficult to gather all Raman spectra of 209 PCB congeners by measuring standard samples. Fortunately, computational chemistry provides a royal road to approach Raman spectra of all 209 PCB congeners. Gaussian program package is considered to be reliable software in computational chemistry for geometry optimization and vibrational spectra calculation of organic molecules (Tomasi et al., 2005). Herein, Gaussian 03 program package was used to obtain stable configurations and vibrational spectra of all 209 PCB congeners (Frisch et al., 2004). The vibration modes of PCBs were analyzed with Gauss View 4.1 software. PCBs were divided into several groups based on their molecular symmetries. Raman spectra of characteristic PCBs were discussed and compared to experimental Raman data. The outcomes of this study can be applied as a database for further applications of Raman spectroscopy in detection of PCBs. 2. Computational details All PCB congeners were arranged by their congener numbers which were adopted from CAS Registry database (Chemical Abstracts Service, 2010; Mills et al., 2007). The geometry optimization and vibrational spectra were calculated using Gaussian 03 program package (Frisch et al., 2004). The popular B3LYP functional with the standard basis set 6-311G (d, p) was used to optimize structures of PCBs followed by the vibrational frequency calculation (Lee et al., 1988; Becke, 1993). Previous work indicated that the B3LYP hybrid functional can obtain reliable frequency information (Szczepaniak et al., 2000; Kapitán et al., 2006; Udeochu et al., 2007; Liu et al., 2010). The scale factor for vibration frequencies was obtained from calculated and experimental
vibrational frequency of biphenyl. The visualization of output files and normal modes analysis were carried out by the GaussView 4.1. 3. Results and discussion We optimized configurations of all PCB congeners by performing the Gaussian calculations. The calculated results are shown in Supplementary material. Chemical structures of PCBs are shown in Fig. 1. The ten possible positions, on which chlorine atoms can substitute, are shown in Fig. 1 by numbers assigned to the carbon atoms. Based on molecular symmetry, 209 PCB congeners are classed into seven groups. The summary structural features of each group are shown in Table 1. Biphenyl, the parent molecule of PCBs, has D2 symmetry. When chlorine substituents are introduced, the symmetry of most PCBs is decreased especially when chlorine substitutions are not symmetrical. There are only four molecules with D2d symmetry and three PCB congeners in D2 group. The symmetry of the other PCBs is lower than the biphenyl molecule. It should be aware that the PCB molecules with identity operation which belong to C1 group reach to 106 kinds. When chlorine substituents are introduced to one benzene ring of biphenyl, the number of possible frameworks is 20. According to their symmetries, they can be divided into two groups. Each group can be divided into two subgroups. All possible frameworks are shown in Fig. 2. Group X has mirror symmetrical structure while Group Y does not have. The subgroups marked with b have two chlorine substituents at 2 and 6 positions, which makes the two benzene ring planes perpendicular to each other. When h, k, i and j are used to represent the numbers of Xa, Xb, Ya and Yb respectively, the evolution of 209 PCB congeners and biphenyl (biphenyl included) from the 20 frameworks can be expressed as follows: hþkþiþj X
" m ¼ k þ h þ ab þ
k X
!# mk
m¼1
m¼1
þ
h X
! mh
m¼1
þ ði þ jÞ þ ½kði þ jÞ þ hj " ! ! # j i X X mi þ m j þ hi þ ij þ m¼1
m¼1
¼ k þ h þ hk þ C 2k þ C 2h þ ði þ jÞ þ ½kði þ jÞ þ hj þ C 2i þ C 2j þ hi þ ij Fig. 1. Chemical structures of PCBs molecules.
¼ 4 þ 4 þ 22 þ 6 þ 12 þ 56 þ 106 ¼ 210 ¼ C 220
ð1Þ
Table 1 Classification of 209 PCB congeners assorted by molecule group and their symmetry elements and normal modes of vibration. Group
Symmetry elementsa
PCB congeners numberb
Normal modes of vibrationc
D2d
54, 155, 202, 209
10A1 + 3A2 + 4B1 + 10B2 + 33E
15, 80, 169
15A + 13B1 + 16B2 + 16B3
10, 30, 32, 65, 73, 75, 104, 116, 117, 121, 125, 152, 165, 166, 168, 186, 188, 192, 193, 204, 205, 208
20A1 + 8A2 + 16B1 + 16B2
C2-1 C2-2 Cs
E, S4, C2, 2C 02 , 2rd E, C2 (z), C2 (y), C2 (x) E, C2, rv (xz), rv (yz) E, C2 E, C2 E, rh
28A + 32B 31A + 29B 37A0 + 23A00
C1
E
3, 14, 38, 39, 81, 127, 4, 11, 40, 47, 52, 77, 128, 133, 136, 153, 194, 197 19, 24, 27, 46, 50, 51, 53, 62, 64, 69, 71, 89, 93, 94, 96, 98, 100, 102, 103, 112, 113, 115, 119, 134, 140, 142, 143, 145, 147, 148, 150, 151, 154, 160, 161, 163, 164, 173, 177, 178, 179, 181, 182, 184, 185, 187, 190, 191, 195, 198, 199, 200, 201, 203, 206, 207 1, 2, 5, 6, 7, 8, 9, 12, 13, 16, 17, 18, 20, 21, 22, 23, 25, 26, 28, 29, 31 33, 34, 35, 36, 37, 41, 42, 43, 44, 45, 48, 49, 55, 56, 57, 58, 59, 60, 61, 63, 66, 67, 68, 70, 72, 74, 76, 78, 79, 82, 83, 84, 85, 86, 87, 88, 90, 91, 92, 95, 97, 99, 101, 105, 106, 107, 108, 109, 110, 111, 114, 118, 120, 122, 123, 124, 126, 129, 130, 131, 132, 135, 137, 138, 139, 141, 144, 146, 149, 156, 157, 158, 159, 162, 167, 170, 171, 172, 174, 175, 176, 180, 183, 189, 196
D2 C2v
60 A
a The meanings of symmetry elements. E: identity; C2: 2-fold symmetry axis; S4: 4-fold Rotation–reflection axis; rd: dubbed dihedral plane of symmetry; rv dubbed vertical plane of symmetry; rh: horizontal plane of symmetry. b PCB congeners number comes from chemical abstracts service (CAS) registry database. c The 60 normal vibration modes are divided according to the irreducible representation.
414
Y. Lai et al. / Chemosphere 85 (2011) 412–417
Fig. 2. The 20 possible frameworks when chlorine substituents are introduced to one benzene ring of biphenyl.
The various formula entries in the above expression represent the numbers of PCBs contained in each group. The first formula entry (k) is representative of the numbers of PCBs contained in D2d group, whose structures have two benzenes with the same Xb framework. The numbers of PCBs (D2) with two same Xa frameworks are symbolized by the second formula entry (h). PCBs in C2v group (the third formula entry: hk þ C 2k ) have two origins. The first is the mutual combination of Xa and Xb frameworks,
while the other comes from internal mutual composition of Xb frameworks. Internal mutual composition of Xa frameworks (the fourth formula entry: C 2k ) is the numbers of PCBs with C2-1 group. The fifth formula entry (i + j) represents the numbers of PCBs contained in C2-2, whose structures have two benzenes with the same Ya or Yb framework. The numbers of PCBs in Cs group are marked by the sixth formula entry kði þ jÞ þ hj. PCBs in this group have only one framework with mirror symmetrical structure and one
Y. Lai et al. / Chemosphere 85 (2011) 412–417
415
Fig. 4. Experimental and calculated Raman spectra of PCB77 and the corresponding normal vibration modes for main peaks.
Fig. 3. The calculated Raman spectra of 12 types of PCBs in C2-2 group.
framework with two chlorine substituents at 2 and 6 positions (these two structural features may appear in the same framework). PCBs with C1 group (the seventh formula entry: C 2i þ C 2j þ hi þ ij) have four sources: the internal mutual composition of Ya frameworks, the internal mutual composition of Yb frameworks, the mutual combination of Xa and Ya frameworks, the mutual combination of Ya and Yb frameworks. For PCB molecules with D2d symmetry, the symmetry elements are E, S4, C2, 2C2 and 2rd. Two benzene ring planes are perpendicular to each other. The main axis in D2d group is the 2-fold symmetry axis (C2), through 4,40 carbon atoms. The other two C2 axes located in the middle of two benzene rings, are perpendicular to the main axis and go halves with dihedral angle between two benzene ring planes. The 4-fold Rotation–reflection axis (S4) coincides with the main axis. Two dubbed dihedral planes of symmetry (rd) overlap with one benzene ring plane and halve the other benzene
ring. For PCB molecules with D2 symmetry, the symmetry elements are E, C2 (z), C2 (y), C2 (x) and the positions of three C2 axises are similar to D2d. As the dihedral angle between two benzene ring planes do not equal 90°, S4 and 2rd symmetry elements do not appear in this group. The symmetry elements in PCB molecules with C2v symmetry are E, C2, rv (xz), rv (yz). The main axis (C2) is through 4,40 carbon atoms while the two dubbed dihedral planes of symmetry (rd) locate in two planes of benzene ring. According to the location of C2 axis, PCB molecules with C2 symmetry can be divided into two groups: C2-1and C2-2. The C2 axis in C2-1 group also goes through 4,40 carbon atoms while the C2 axis is perpendicular to the line through 4,40 carbon atoms in C2-2 group. For PCB molecules with Cs symmetry, the rh overlaps benzene ring plane which do not have symmetrically chlorine substituents. Raman spectra of all PCBs are calculated after geometry optimizations. The data are put in Supplementary material as Gaussian output files, which can be visualized with GaussView software. As all PCBs have 22 atoms, the normal vibrational modes in PCB congener are ca. 60. In PCB molecules, only the bridge bond of two benzene groups can rotate. The symmetry elements in each
416
Y. Lai et al. / Chemosphere 85 (2011) 412–417
group locate in same positions. So the vibration modes are only determined by groups which are shown in the Table 1. The inversion center symmetry elements can not exist in PCB congeners, which suggest that vibrational spectra of PCBs do not follow the rule of mutual exclusion. In other words, most normal vibrational modes of PCBs are both infrared active and Raman active. The vibrational scale factor is set at 0.981 by comparing calculated Raman spectra of biphenyl with the spectra in database (Spectral Database for Organic Compounds, 2010). The C2-2 group was selected as an example to analyze the Raman spectra of PCBs. Normal vibration modes analysis was performed with GaussView. The Raman spectra of 12 types of PCBs in C2-2 group are illustrated in Fig. 3. It should be noticed that high toxic PCBs which have more chlorine substituents at 3, 4, 5, while less chlorine substituents at 2, 6 positions have high intensities in Raman spectra. According to the irreducible representation, the 60 vibration modes can be divided into 31A + 29 B. From high frequency to low frequency, Raman spectra of this group can be divided to five regions (There are some overlaps between diverse regions). The first region is the stretching vibrations of C–H bond in 3050–3200 cm1. The normal modes (different from the peak numbers) of this region are equal to the hydrogen atom numbers in PCBs. With the increase of chlorine substituents, Raman shift of vibration mode in this region moves to higher wavenumber. The width distribution of all peaks in this region partly reflects the number of hydrogen atoms in PCBs: the more hydrogen atoms, the broader width distribution. The second region ranges from 1400 to 1650 cm1. The peaks in this region mainly refer to the benzene framework vibration. The peaks around in 1600 cm1 move to low wavenumbers with chlorine substituents increasing. The third region, which mainly related to the bridge bond vibrations and the rocking vibrations of C–H, locates in 1100–1400 cm1. With the increase of chlorine substituents, the main peak of this region moves to lower wavenumbers. The out-of-plane bending vibrations of C–H bonds and the deformation vibrations of benzene rings located in 600– 1100 cm1 belong to the fourth region. The positions of Raman peaks in this region change with the number and position of chlorine substituents. The highest peak in this region is caused by the triangular breathing vibrations of benzene ring. In the last region (0–600 cm1), the out-of-plane bending vibrations of C–C, the relative vibrations of two benzene rings and the various vibrations of C–Cl are expressed. Those vibration modes intersect with each other in this area and relate to the number and position of substituents. In order to verify the accuracy of theoretical results, we compare calculated Raman spectra of PCB77 with experimental Raman spectra (Ocean Optics miniaturized Raman system with semiconductor laser in 785 nm wavelength). Raman spectra collected from PCB77 standard are shown in Fig. 4. Main peaks in experimental data are marked and in good agreement with calculated values. The normal vibration modes corresponding to main peaks in the experimental Raman spectra are analyzed with Gaussview and the schematic diagrams of these normal modes are also given in Fig. 4.
4. Conclusions By calculations, the configurations and vibration information of all PCB congeners were obtained. The files containing calculated results can be found in the Supplementary material which is designed as a database. One can get the symmetry elements and vibration spectra for each PCB congener from these files. Moreover, the animations of each normal vibration mode can be illustrated with Gaussview. This work may be a foreshadowing of PCBs’ detection by Raman spectroscopy.
Acknowledgments We thank the financial support from National Natural Science Foundation of China (NSFC 21075077), National Basic Research Program of China (973 Program 2007CB936602), Shandong Provincial Natural Science Foundation for Distinguished Young Scholar (JQ201004), and Independent Innovation Foundation of Shandong University (IIFSDU-2009JQ011).
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemosphere.2011.07.067. References Bantz, K.C., Haynes, C.L., 2009. Surface-enhanced Raman scattering detection and discrimination of polychlorinated biphenyls. Vib. Spectrosc. 50, 29–35. Becke, A.D., 1993. Density-functional thermochemistry III. The role of exact exchange. J. Chem. Phys. 87, 5648–5652. Borgå, K., Fisk, A.T., Hargrave, B., Hoekstra, P.F., Swackhamer, D., Muir, D.C.G., 2005. Bioaccumulation factors for PCBs revisited. Environ. Sci. Technol. 39, 4523– 4532. Chao, H.A., Chen, S.C.-C., Chang, C.-M., Koh, T.-W., Chang-Chiend, G.-P., Ouyang, E., Lin, S.-L., Shy, C.-G., Chen, F.-A., Chao, H.-R., 2010. Concentrations of polybrominated diphenyl ethers in breast milk correlated to maternal age, education level, and occupational exposure. J. Hazard. Mater. 175, 492–500. Chemical Abstracts Service, 2010. All PCB congeners were Obtained from a Directed Search of the PCBs Number by SciFinder Scholar 2007 (Access is Provided Through the Subscription of Shandong University), The American Chemical Society. Dang, V.D., Walters, D.M., Lee, C.M., 2010. Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web. Environ. Sci. Technol. 44, 2836– 2841. Diamond, M.L., Melymuk, L., Csiszar, S.A., Robson, M., 2010. Estimation of PCB stocks, emissions, and urban Fate: will our policies reduce concentrations and exposure? Environ. Sci. Technol. 44, 2777–2783. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Montgomery, Jr., J.A., Vreven, T., Kudin, K.N., Burant, J.C., Millam, J.M., Iyengar, S.S., Tomasi, J., Barone, V., Mennucci, B., Cossi, M., Scalmani, G., Rega, N., Petersson, G.A., Nakatsuji, H., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Klene, M., Li, X., Knox, J.E., Hratchian, H.P., Cross, J.B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R. E., Yazyev, O., Austin, A.J., Cammi, R., Pomelli, C., Ochterski, J.W., Ayala, P.Y., Morokuma, K., Voth, G.A., Salvador, P., Dannenberg, J.J., Zakrzewski, V.G., Dapprich, S., Daniels, A.D., Strain, M.C., Farkas, O., Malick, D.K, Rabuck, A.D., Raghavachari, K., Foresman, J.B., Ortiz, J.V., Cui, Q., Baboul, A.G., Clifford, S., Cioslowski, J., Stefanov, B.B., Liu, G., Liashenko, A., Piskorz, P., Komaromi, I., Martin, R.L., Fox, D.J., Keith, T., Al-Laham, M. A., Peng, C.Y., Nanayakkara, A., Challacombe, M., Gill, P.M.W., Johnson, B., Chen, W., Wong, M.W., Gonzalez, C., Pople, J.A., 2004. Gaussian 03, Revision D.01, Gaussian, Inc., Wallingford CT. Golden, R., Doull, J., Waddell, W., Mandel, J., 2003. Potential human cancer risks from exposure to PCBs: a tale of two evaluations. Crit. Rev. Toxicol. 33, 543–580. Hites, R., Hornbuckle, K.C., Robertson, L.W., 2010. Polychlorinated biphenyls (PCBs): sources, exposures, toxicities. Environ. Sci. Technol. 44, 2749–2751. Kapitán, J., Baumruk, V., Bourˇ, P., 2006. Demonstration of the ring conformation in polyproline by the Raman optical activity. J. Am. Chem. Soc. 128, 2438–2443. Lee, C., Yang, W., Parr, R.G., 1988. Development of the colle-salvetti correlationenergy formula into a functional of the electron density. Phys. Rev. B 37, 785– 789. Leijs, M.M., Koppe, J.G., Olie, K., Van Aalderen, W.M.C., De Voogt, P., Ten Tusscher, G.W., 2009. Effects of dioxins, PCBs, and PBDEs on immunology and hematology in adolescents. Environ. Sci. Technol. 43, 7946–7951. Li, Y.-F., Harner, T., Liu, L., Zhang, Z., Ren, N.-Q., Jia, H., Ma, J., Sverko, E., 2010. Polychlorinated biphenyls in global air and surface soil: distributions, air–soil exchange, and fractionation effect. Environ. Sci. Technol. 44, 2784–2790. Liu, P., Zhang, D., Zhan, J., 2010. Investigation on the inclusions of PCB52 with cyclodextrins by performing DFT calculations and molecular dynamics simulations. J. Phys. Chem. A 114, 13122–13128. McCreery, R.L., 2000. Raman Spectroscopy for Chemical Analysis. WileyInterscience, New York. Mills III, S.A., Thal, D.I., Barney, J., 2007. A summary of the 209 PCB congener nomenclature. Chemosphere 68, 1603–1612. Mullins, M.D., Pochini, C.M., McCrindle, S., Romkes, M., Safe, S.H., Safe, L.M., 1984. High-resolution PCB analysis: synthesis and chromatographic properties of all 209 PCB congeners. Environ. Sci. Technol. 18, 468–476. Rodenburg, L.A., Guo, J., Du, S., Cavallo, G.J., 2010. Evidence for unique and ubiquitous environmental sources of 3, 30 -dichlorobiphenyl (PCB 11). Environ. Sci. Technol. 44, 2816–2821.
Y. Lai et al. / Chemosphere 85 (2011) 412–417 Rezaei, F., Bidari, A., Birjandi, A.P., Hosseini, M.R.M., Assadi, Y., 2008. Development of a dispersive liquid–liquid microextraction method for the determination of polychlorinated biphenyls in water. J. Hazard. Mater. 158, 621–627. Ru, E.L., Etchegoin, P., 2009. Principles of Surface Enhanced Raman Spectroscopy and Related Plasmonic Effects. Elsevier, Amsterdam. Spectral Database for Organic Compounds (SDBS), 2010. National Institute of Advanced Industrial Science and Technology
417
Van den Berg, M., Birnbaum, L.S., Denison, M., De Vito, M., Farland, W., Feeley, M., Fiedler, H., Hakansson, H., Hanberg, A., Haws, L., Rose, M., Safe, S., Schrenk, D., Tohyama, C., Tritscher, A., Tuomisto, J., Tysklind, M., Walker, N., Peterson, R.E., 2006. The 2005 world health organization reevaluation of human and mammalian toxic equivalency factors for dioxins and dioxin-like compounds. Toxicol. Sci. 93, 223–241. Van der Oost, R., Beyer, J., Vermeulen, N.P.E., 2003. Fish bioaccumulation and biomarkers in environmental risk assessment: a review. Environ. Toxicol. Pharmacol. 13, 57–149. Yang, Y., Meng, G., 2010. Ag dendritic nanostructures for rapid detection of polychlorinated biphenyls based on surface-enhanced Raman scattering effect. J. Appl. Phys. 107, 044315. Zhou, Q., Yang, Y., Ni, J., Li, Z., Zhang, Z., 2010a. Rapid recognition of isomers of monochlorobiphenyls at trace levels by surface-enhanced Raman scattering using Ag nanorods as a substrate. Nano Res. 3, 423–428. Zhou, Q., Yang, Y., Ni, J., Li, Z., Zhang, Z., 2010b. Rapid detection of 2,3,30 ,4,40 pentachlorinated biphenyls by silver nanorods-enhanced Raman spectroscopy. Physica E 42, 1717–1720.
Contents lists available at SciVerse ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Theoretical evaluation of the configurations and Raman spectra of 209 polychlorinated biphenyl congeners Yongchao Lai, Wenxiao Pan, Shouqing Ni, Dongju Zhang, Jinhua Zhan ⇑ Key Laboratory for Colloid & Interface Chemistry of Education Ministry, Department of Chemistry, Shandong University, 250100 Jinan, China
a r t i c l e
i n f o
Article history: Received 13 March 2011 Received in revised form 6 July 2011 Accepted 29 July 2011 Available online 27 August 2011 Keywords: PCBs Configurations Raman spectra Molecular symmetry Normal modes Vibrational spectra
a b s t r a c t Though polychlorinated biphenyls (PCBs) have distributed as threats in the environment to human beings for several decades, monitoring of trace level PCBs in-field is still a challenge. As a potential method for monitoring PCBs at trace levels, Raman spectroscopy has been used to detect several PCBs in the laboratory. To facilitate the development of rapid detection of PCBs by Raman spectroscopy, it is essential to investigate the Raman spectra of all PCB congeners. Herein, the stable configurations and vibrational spectra of all the PCB congeners were calculated by Gaussian 03 program package. Based on molecular symmetry, PCBs are classified into seven groups. The structural features and the normal vibration modes for each group are discussed. Taking the C2-2 group as an example, the wavenumber ranges of the various normal vibration modes in the Raman spectra of PCBs were analyzed. The accuracy of calculated results was verified by experimental Raman spectra of PCB77 standard. This study can elucidate further information to promote the development of Raman spectroscopy in environmental monitoring. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction Polychlorinated biphenyls (PCBs), as typical persistent organic pollutants (POPs), are a class of organic compounds with 1–10 chlorine atoms substituent on biphenyl. PCBs were widely used for flame retardation and dielectric fluids due to their low inflammability, chemical stability, and solubility in most organic solvents (Diamond et al., 2010; Hites et al., 2010). Although had been banned for many years, PCBs can be found all over the world even in where they are never been used (Chao et al., 2010; Dang et al., 2010; Li et al., 2010; Rodenburg et al., 2010). PCBs are dangerous to human as they could disorder the endocrine system, destroy the immune system and cause cancers (Golden et al., 2003; Leijs et al., 2009). Moreover, more toxic polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) could form from PCBs by partial oxidation (Van den Berg et al., 2006). PCBs at trace levels, which hide in human living environments, can bioaccumulate in the fatty tissue of human through the food chains with tens of thousands of amplifier stage (Van der Oost et al., 2003; Borgå et al., 2005). To fulfill the protection of human health and the environment, it is urgent to develop a simple and quick method for the detection of trace PCBs in people’s living environment, which is the first step in the environmentally sound management of PCBs. Because PCBs have high chemical stability and generally weak interactions with other substances, most analytical methods can not be ⇑ Corresponding author. Tel.: +86 531 88365017; fax: +86 531 88366280. E-mail address: [email protected] (J. Zhan). 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.07.067
effectively applied for the detection of PCBs. The common lab-methods to detect trace PCBs are gas–liquid chromatography and highresolution mass spectrometry (Mullins et al., 1984; Takasuga et al., 2006; Rezaei et al., 2008). These methods are based on spatio– temporal separation to achieve separation and detection of PCBs. Raman spectroscopy may be an alternative for the detection of trace level PCBs with spatio–temporal coupling. With the developments of laser and charge-coupled device (CCD) technology, Raman spectrometer can be integrated into a portable instrument, which makes it suitable for rapid detection and in-field test (McCreery, 2000). Raman spectroscopy can be used to identify molecules since the information of Raman shifts is specific to the molecule structures (McCreery, 2000). Commercial portable Raman spectrometers can cover the vibrational region of common organic molecules (200–4000 cm1) (McCreery, 2000). Compared with infrared spectra, Raman spectra of most molecules have narrow line width, low interference by water and high sensitivity to symmetrical molecules. Furthermore, Raman spectra can be used in microscopic analysis as laser for Raman spectroscopy can be focused in a very small volume (<1 lm in diameter) (McCreery, 2000). Owing to these features, Raman spectroscopy becomes an ideal tool for rapid chemical analysis. However, conventional Raman spectroscopy has its disadvantage like the weak signals intensity (Ru and Etchegoin, 2009). Several techniques for enhanced Raman spectroscopy, for example, surface enhanced Raman spectroscopy (SERS), resonance Raman spectroscopy (RRS), tip-enhanced Raman spectroscopy (TERS), have been developed to overcome this disadvantage (Stiles et al., 2008; Ru and Etchegoin, 2009).
413
Y. Lai et al. / Chemosphere 85 (2011) 412–417
Much work has been done to detect PCBs by Raman spectroscopy (Bantz and Haynes, 2009; Yang and Meng, 2010; Zhou et al., 2010a,b), while the lack of Raman spectra of PCBs greatly hinders this convenient and powerful technique. To promote the progress of PCBs monitoring by Raman spectroscopy, an overall study of all PCB congeners’ Raman spectra is needed. It is difficult to gather all Raman spectra of 209 PCB congeners by measuring standard samples. Fortunately, computational chemistry provides a royal road to approach Raman spectra of all 209 PCB congeners. Gaussian program package is considered to be reliable software in computational chemistry for geometry optimization and vibrational spectra calculation of organic molecules (Tomasi et al., 2005). Herein, Gaussian 03 program package was used to obtain stable configurations and vibrational spectra of all 209 PCB congeners (Frisch et al., 2004). The vibration modes of PCBs were analyzed with Gauss View 4.1 software. PCBs were divided into several groups based on their molecular symmetries. Raman spectra of characteristic PCBs were discussed and compared to experimental Raman data. The outcomes of this study can be applied as a database for further applications of Raman spectroscopy in detection of PCBs. 2. Computational details All PCB congeners were arranged by their congener numbers which were adopted from CAS Registry database (Chemical Abstracts Service, 2010; Mills et al., 2007). The geometry optimization and vibrational spectra were calculated using Gaussian 03 program package (Frisch et al., 2004). The popular B3LYP functional with the standard basis set 6-311G (d, p) was used to optimize structures of PCBs followed by the vibrational frequency calculation (Lee et al., 1988; Becke, 1993). Previous work indicated that the B3LYP hybrid functional can obtain reliable frequency information (Szczepaniak et al., 2000; Kapitán et al., 2006; Udeochu et al., 2007; Liu et al., 2010). The scale factor for vibration frequencies was obtained from calculated and experimental
vibrational frequency of biphenyl. The visualization of output files and normal modes analysis were carried out by the GaussView 4.1. 3. Results and discussion We optimized configurations of all PCB congeners by performing the Gaussian calculations. The calculated results are shown in Supplementary material. Chemical structures of PCBs are shown in Fig. 1. The ten possible positions, on which chlorine atoms can substitute, are shown in Fig. 1 by numbers assigned to the carbon atoms. Based on molecular symmetry, 209 PCB congeners are classed into seven groups. The summary structural features of each group are shown in Table 1. Biphenyl, the parent molecule of PCBs, has D2 symmetry. When chlorine substituents are introduced, the symmetry of most PCBs is decreased especially when chlorine substitutions are not symmetrical. There are only four molecules with D2d symmetry and three PCB congeners in D2 group. The symmetry of the other PCBs is lower than the biphenyl molecule. It should be aware that the PCB molecules with identity operation which belong to C1 group reach to 106 kinds. When chlorine substituents are introduced to one benzene ring of biphenyl, the number of possible frameworks is 20. According to their symmetries, they can be divided into two groups. Each group can be divided into two subgroups. All possible frameworks are shown in Fig. 2. Group X has mirror symmetrical structure while Group Y does not have. The subgroups marked with b have two chlorine substituents at 2 and 6 positions, which makes the two benzene ring planes perpendicular to each other. When h, k, i and j are used to represent the numbers of Xa, Xb, Ya and Yb respectively, the evolution of 209 PCB congeners and biphenyl (biphenyl included) from the 20 frameworks can be expressed as follows: hþkþiþj X
" m ¼ k þ h þ ab þ
k X
!# mk
m¼1
m¼1
þ
h X
! mh
m¼1
þ ði þ jÞ þ ½kði þ jÞ þ hj " ! ! # j i X X mi þ m j þ hi þ ij þ m¼1
m¼1
¼ k þ h þ hk þ C 2k þ C 2h þ ði þ jÞ þ ½kði þ jÞ þ hj þ C 2i þ C 2j þ hi þ ij Fig. 1. Chemical structures of PCBs molecules.
¼ 4 þ 4 þ 22 þ 6 þ 12 þ 56 þ 106 ¼ 210 ¼ C 220
ð1Þ
Table 1 Classification of 209 PCB congeners assorted by molecule group and their symmetry elements and normal modes of vibration. Group
Symmetry elementsa
PCB congeners numberb
Normal modes of vibrationc
D2d
54, 155, 202, 209
10A1 + 3A2 + 4B1 + 10B2 + 33E
15, 80, 169
15A + 13B1 + 16B2 + 16B3
10, 30, 32, 65, 73, 75, 104, 116, 117, 121, 125, 152, 165, 166, 168, 186, 188, 192, 193, 204, 205, 208
20A1 + 8A2 + 16B1 + 16B2
C2-1 C2-2 Cs
E, S4, C2, 2C 02 , 2rd E, C2 (z), C2 (y), C2 (x) E, C2, rv (xz), rv (yz) E, C2 E, C2 E, rh
28A + 32B 31A + 29B 37A0 + 23A00
C1
E
3, 14, 38, 39, 81, 127, 4, 11, 40, 47, 52, 77, 128, 133, 136, 153, 194, 197 19, 24, 27, 46, 50, 51, 53, 62, 64, 69, 71, 89, 93, 94, 96, 98, 100, 102, 103, 112, 113, 115, 119, 134, 140, 142, 143, 145, 147, 148, 150, 151, 154, 160, 161, 163, 164, 173, 177, 178, 179, 181, 182, 184, 185, 187, 190, 191, 195, 198, 199, 200, 201, 203, 206, 207 1, 2, 5, 6, 7, 8, 9, 12, 13, 16, 17, 18, 20, 21, 22, 23, 25, 26, 28, 29, 31 33, 34, 35, 36, 37, 41, 42, 43, 44, 45, 48, 49, 55, 56, 57, 58, 59, 60, 61, 63, 66, 67, 68, 70, 72, 74, 76, 78, 79, 82, 83, 84, 85, 86, 87, 88, 90, 91, 92, 95, 97, 99, 101, 105, 106, 107, 108, 109, 110, 111, 114, 118, 120, 122, 123, 124, 126, 129, 130, 131, 132, 135, 137, 138, 139, 141, 144, 146, 149, 156, 157, 158, 159, 162, 167, 170, 171, 172, 174, 175, 176, 180, 183, 189, 196
D2 C2v
60 A
a The meanings of symmetry elements. E: identity; C2: 2-fold symmetry axis; S4: 4-fold Rotation–reflection axis; rd: dubbed dihedral plane of symmetry; rv dubbed vertical plane of symmetry; rh: horizontal plane of symmetry. b PCB congeners number comes from chemical abstracts service (CAS) registry database. c The 60 normal vibration modes are divided according to the irreducible representation.
414
Y. Lai et al. / Chemosphere 85 (2011) 412–417
Fig. 2. The 20 possible frameworks when chlorine substituents are introduced to one benzene ring of biphenyl.
The various formula entries in the above expression represent the numbers of PCBs contained in each group. The first formula entry (k) is representative of the numbers of PCBs contained in D2d group, whose structures have two benzenes with the same Xb framework. The numbers of PCBs (D2) with two same Xa frameworks are symbolized by the second formula entry (h). PCBs in C2v group (the third formula entry: hk þ C 2k ) have two origins. The first is the mutual combination of Xa and Xb frameworks,
while the other comes from internal mutual composition of Xb frameworks. Internal mutual composition of Xa frameworks (the fourth formula entry: C 2k ) is the numbers of PCBs with C2-1 group. The fifth formula entry (i + j) represents the numbers of PCBs contained in C2-2, whose structures have two benzenes with the same Ya or Yb framework. The numbers of PCBs in Cs group are marked by the sixth formula entry kði þ jÞ þ hj. PCBs in this group have only one framework with mirror symmetrical structure and one
Y. Lai et al. / Chemosphere 85 (2011) 412–417
415
Fig. 4. Experimental and calculated Raman spectra of PCB77 and the corresponding normal vibration modes for main peaks.
Fig. 3. The calculated Raman spectra of 12 types of PCBs in C2-2 group.
framework with two chlorine substituents at 2 and 6 positions (these two structural features may appear in the same framework). PCBs with C1 group (the seventh formula entry: C 2i þ C 2j þ hi þ ij) have four sources: the internal mutual composition of Ya frameworks, the internal mutual composition of Yb frameworks, the mutual combination of Xa and Ya frameworks, the mutual combination of Ya and Yb frameworks. For PCB molecules with D2d symmetry, the symmetry elements are E, S4, C2, 2C2 and 2rd. Two benzene ring planes are perpendicular to each other. The main axis in D2d group is the 2-fold symmetry axis (C2), through 4,40 carbon atoms. The other two C2 axes located in the middle of two benzene rings, are perpendicular to the main axis and go halves with dihedral angle between two benzene ring planes. The 4-fold Rotation–reflection axis (S4) coincides with the main axis. Two dubbed dihedral planes of symmetry (rd) overlap with one benzene ring plane and halve the other benzene
ring. For PCB molecules with D2 symmetry, the symmetry elements are E, C2 (z), C2 (y), C2 (x) and the positions of three C2 axises are similar to D2d. As the dihedral angle between two benzene ring planes do not equal 90°, S4 and 2rd symmetry elements do not appear in this group. The symmetry elements in PCB molecules with C2v symmetry are E, C2, rv (xz), rv (yz). The main axis (C2) is through 4,40 carbon atoms while the two dubbed dihedral planes of symmetry (rd) locate in two planes of benzene ring. According to the location of C2 axis, PCB molecules with C2 symmetry can be divided into two groups: C2-1and C2-2. The C2 axis in C2-1 group also goes through 4,40 carbon atoms while the C2 axis is perpendicular to the line through 4,40 carbon atoms in C2-2 group. For PCB molecules with Cs symmetry, the rh overlaps benzene ring plane which do not have symmetrically chlorine substituents. Raman spectra of all PCBs are calculated after geometry optimizations. The data are put in Supplementary material as Gaussian output files, which can be visualized with GaussView software. As all PCBs have 22 atoms, the normal vibrational modes in PCB congener are ca. 60. In PCB molecules, only the bridge bond of two benzene groups can rotate. The symmetry elements in each
416
Y. Lai et al. / Chemosphere 85 (2011) 412–417
group locate in same positions. So the vibration modes are only determined by groups which are shown in the Table 1. The inversion center symmetry elements can not exist in PCB congeners, which suggest that vibrational spectra of PCBs do not follow the rule of mutual exclusion. In other words, most normal vibrational modes of PCBs are both infrared active and Raman active. The vibrational scale factor is set at 0.981 by comparing calculated Raman spectra of biphenyl with the spectra in database (Spectral Database for Organic Compounds, 2010). The C2-2 group was selected as an example to analyze the Raman spectra of PCBs. Normal vibration modes analysis was performed with GaussView. The Raman spectra of 12 types of PCBs in C2-2 group are illustrated in Fig. 3. It should be noticed that high toxic PCBs which have more chlorine substituents at 3, 4, 5, while less chlorine substituents at 2, 6 positions have high intensities in Raman spectra. According to the irreducible representation, the 60 vibration modes can be divided into 31A + 29 B. From high frequency to low frequency, Raman spectra of this group can be divided to five regions (There are some overlaps between diverse regions). The first region is the stretching vibrations of C–H bond in 3050–3200 cm1. The normal modes (different from the peak numbers) of this region are equal to the hydrogen atom numbers in PCBs. With the increase of chlorine substituents, Raman shift of vibration mode in this region moves to higher wavenumber. The width distribution of all peaks in this region partly reflects the number of hydrogen atoms in PCBs: the more hydrogen atoms, the broader width distribution. The second region ranges from 1400 to 1650 cm1. The peaks in this region mainly refer to the benzene framework vibration. The peaks around in 1600 cm1 move to low wavenumbers with chlorine substituents increasing. The third region, which mainly related to the bridge bond vibrations and the rocking vibrations of C–H, locates in 1100–1400 cm1. With the increase of chlorine substituents, the main peak of this region moves to lower wavenumbers. The out-of-plane bending vibrations of C–H bonds and the deformation vibrations of benzene rings located in 600– 1100 cm1 belong to the fourth region. The positions of Raman peaks in this region change with the number and position of chlorine substituents. The highest peak in this region is caused by the triangular breathing vibrations of benzene ring. In the last region (0–600 cm1), the out-of-plane bending vibrations of C–C, the relative vibrations of two benzene rings and the various vibrations of C–Cl are expressed. Those vibration modes intersect with each other in this area and relate to the number and position of substituents. In order to verify the accuracy of theoretical results, we compare calculated Raman spectra of PCB77 with experimental Raman spectra (Ocean Optics miniaturized Raman system with semiconductor laser in 785 nm wavelength). Raman spectra collected from PCB77 standard are shown in Fig. 4. Main peaks in experimental data are marked and in good agreement with calculated values. The normal vibration modes corresponding to main peaks in the experimental Raman spectra are analyzed with Gaussview and the schematic diagrams of these normal modes are also given in Fig. 4.
4. Conclusions By calculations, the configurations and vibration information of all PCB congeners were obtained. The files containing calculated results can be found in the Supplementary material which is designed as a database. One can get the symmetry elements and vibration spectra for each PCB congener from these files. Moreover, the animations of each normal vibration mode can be illustrated with Gaussview. This work may be a foreshadowing of PCBs’ detection by Raman spectroscopy.
Acknowledgments We thank the financial support from National Natural Science Foundation of China (NSFC 21075077), National Basic Research Program of China (973 Program 2007CB936602), Shandong Provincial Natural Science Foundation for Distinguished Young Scholar (JQ201004), and Independent Innovation Foundation of Shandong University (IIFSDU-2009JQ011).
Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemosphere.2011.07.067. References Bantz, K.C., Haynes, C.L., 2009. Surface-enhanced Raman scattering detection and discrimination of polychlorinated biphenyls. Vib. Spectrosc. 50, 29–35. Becke, A.D., 1993. Density-functional thermochemistry III. The role of exact exchange. J. Chem. Phys. 87, 5648–5652. Borgå, K., Fisk, A.T., Hargrave, B., Hoekstra, P.F., Swackhamer, D., Muir, D.C.G., 2005. Bioaccumulation factors for PCBs revisited. Environ. Sci. Technol. 39, 4523– 4532. Chao, H.A., Chen, S.C.-C., Chang, C.-M., Koh, T.-W., Chang-Chiend, G.-P., Ouyang, E., Lin, S.-L., Shy, C.-G., Chen, F.-A., Chao, H.-R., 2010. Concentrations of polybrominated diphenyl ethers in breast milk correlated to maternal age, education level, and occupational exposure. J. Hazard. Mater. 175, 492–500. Chemical Abstracts Service, 2010. All PCB congeners were Obtained from a Directed Search of the PCBs Number by SciFinder Scholar 2007 (Access is Provided Through the Subscription of Shandong University), The American Chemical Society. Dang, V.D., Walters, D.M., Lee, C.M., 2010. Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web. Environ. Sci. Technol. 44, 2836– 2841. Diamond, M.L., Melymuk, L., Csiszar, S.A., Robson, M., 2010. Estimation of PCB stocks, emissions, and urban Fate: will our policies reduce concentrations and exposure? Environ. Sci. Technol. 44, 2777–2783. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Montgomery, Jr., J.A., Vreven, T., Kudin, K.N., Burant, J.C., Millam, J.M., Iyengar, S.S., Tomasi, J., Barone, V., Mennucci, B., Cossi, M., Scalmani, G., Rega, N., Petersson, G.A., Nakatsuji, H., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Klene, M., Li, X., Knox, J.E., Hratchian, H.P., Cross, J.B., Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Stratmann, R. E., Yazyev, O., Austin, A.J., Cammi, R., Pomelli, C., Ochterski, J.W., Ayala, P.Y., Morokuma, K., Voth, G.A., Salvador, P., Dannenberg, J.J., Zakrzewski, V.G., Dapprich, S., Daniels, A.D., Strain, M.C., Farkas, O., Malick, D.K, Rabuck, A.D., Raghavachari, K., Foresman, J.B., Ortiz, J.V., Cui, Q., Baboul, A.G., Clifford, S., Cioslowski, J., Stefanov, B.B., Liu, G., Liashenko, A., Piskorz, P., Komaromi, I., Martin, R.L., Fox, D.J., Keith, T., Al-Laham, M. A., Peng, C.Y., Nanayakkara, A., Challacombe, M., Gill, P.M.W., Johnson, B., Chen, W., Wong, M.W., Gonzalez, C., Pople, J.A., 2004. Gaussian 03, Revision D.01, Gaussian, Inc., Wallingford CT. Golden, R., Doull, J., Waddell, W., Mandel, J., 2003. Potential human cancer risks from exposure to PCBs: a tale of two evaluations. Crit. Rev. Toxicol. 33, 543–580. Hites, R., Hornbuckle, K.C., Robertson, L.W., 2010. Polychlorinated biphenyls (PCBs): sources, exposures, toxicities. Environ. Sci. Technol. 44, 2749–2751. Kapitán, J., Baumruk, V., Bourˇ, P., 2006. Demonstration of the ring conformation in polyproline by the Raman optical activity. J. Am. Chem. Soc. 128, 2438–2443. Lee, C., Yang, W., Parr, R.G., 1988. Development of the colle-salvetti correlationenergy formula into a functional of the electron density. Phys. Rev. B 37, 785– 789. Leijs, M.M., Koppe, J.G., Olie, K., Van Aalderen, W.M.C., De Voogt, P., Ten Tusscher, G.W., 2009. Effects of dioxins, PCBs, and PBDEs on immunology and hematology in adolescents. Environ. Sci. Technol. 43, 7946–7951. Li, Y.-F., Harner, T., Liu, L., Zhang, Z., Ren, N.-Q., Jia, H., Ma, J., Sverko, E., 2010. Polychlorinated biphenyls in global air and surface soil: distributions, air–soil exchange, and fractionation effect. Environ. Sci. Technol. 44, 2784–2790. Liu, P., Zhang, D., Zhan, J., 2010. Investigation on the inclusions of PCB52 with cyclodextrins by performing DFT calculations and molecular dynamics simulations. J. Phys. Chem. A 114, 13122–13128. McCreery, R.L., 2000. Raman Spectroscopy for Chemical Analysis. WileyInterscience, New York. Mills III, S.A., Thal, D.I., Barney, J., 2007. A summary of the 209 PCB congener nomenclature. Chemosphere 68, 1603–1612. Mullins, M.D., Pochini, C.M., McCrindle, S., Romkes, M., Safe, S.H., Safe, L.M., 1984. High-resolution PCB analysis: synthesis and chromatographic properties of all 209 PCB congeners. Environ. Sci. Technol. 18, 468–476. Rodenburg, L.A., Guo, J., Du, S., Cavallo, G.J., 2010. Evidence for unique and ubiquitous environmental sources of 3, 30 -dichlorobiphenyl (PCB 11). Environ. Sci. Technol. 44, 2816–2821.
Y. Lai et al. / Chemosphere 85 (2011) 412–417 Rezaei, F., Bidari, A., Birjandi, A.P., Hosseini, M.R.M., Assadi, Y., 2008. Development of a dispersive liquid–liquid microextraction method for the determination of polychlorinated biphenyls in water. J. Hazard. Mater. 158, 621–627. Ru, E.L., Etchegoin, P., 2009. Principles of Surface Enhanced Raman Spectroscopy and Related Plasmonic Effects. Elsevier, Amsterdam. Spectral Database for Organic Compounds (SDBS), 2010. National Institute of Advanced Industrial Science and Technology
417
Van den Berg, M., Birnbaum, L.S., Denison, M., De Vito, M., Farland, W., Feeley, M., Fiedler, H., Hakansson, H., Hanberg, A., Haws, L., Rose, M., Safe, S., Schrenk, D., Tohyama, C., Tritscher, A., Tuomisto, J., Tysklind, M., Walker, N., Peterson, R.E., 2006. The 2005 world health organization reevaluation of human and mammalian toxic equivalency factors for dioxins and dioxin-like compounds. Toxicol. Sci. 93, 223–241. Van der Oost, R., Beyer, J., Vermeulen, N.P.E., 2003. Fish bioaccumulation and biomarkers in environmental risk assessment: a review. Environ. Toxicol. Pharmacol. 13, 57–149. Yang, Y., Meng, G., 2010. Ag dendritic nanostructures for rapid detection of polychlorinated biphenyls based on surface-enhanced Raman scattering effect. J. Appl. Phys. 107, 044315. Zhou, Q., Yang, Y., Ni, J., Li, Z., Zhang, Z., 2010a. Rapid recognition of isomers of monochlorobiphenyls at trace levels by surface-enhanced Raman scattering using Ag nanorods as a substrate. Nano Res. 3, 423–428. Zhou, Q., Yang, Y., Ni, J., Li, Z., Zhang, Z., 2010b. Rapid detection of 2,3,30 ,4,40 pentachlorinated biphenyls by silver nanorods-enhanced Raman spectroscopy. Physica E 42, 1717–1720.