Investigation on the Inclusions of PCB52 with Cyclodextrins by

13122

J. Phys. Chem. A 2010, 114, 13122–13128

Investigation on the Inclusions of PCB52 with Cyclodextrins by Performing DFT Calculations and Molecular Dynamics Simulations Peng Liu, Dongju Zhang,* and Jinhua Zhan* Key Lab of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong UniVersity, Jinan, 250100, People’s Republic of China ReceiVed: September 28, 2010; ReVised Manuscript ReceiVed: NoVember 2, 2010

The effective enrichment and identification of lowly concentrated polychlorinated biphenyls (PCBs) in the environment is attracting enormous research attention due to human health concerns. Cyclodextrins (CDs) are known to be capable of forming inclusion complexes with a variety of organic molecules. The purpose of this study is to provide theoretical evidence of whether CDs as host molecules can include the guest molecules PCBs to form stable host-guest inclusion complexes, and if so, whether the general infrared and Raman techniques are suitable for the direction of CD-modified PCBs. Focusing on a representative PCB molecule, 2,2′,5,5′-tetrachlorobiphenyl (PCB52), we carried out density functional theory calculations and molecular dynamics (MD) simulations on its complexes with R-, β-, and γ-CDs with different host-guest stoichiometry ratios, including 1:1, 1:2, 2:1, and 2:2. On the basis of both the optimized geometries and calculated energy changes raised from encapsulating the guest molecule into the cavities of CDs, the CDs are believed to be suitable hosts for accommodating PCB52 guest molecules. The stability of inclusion complexes depends on both the type of CD and host-guest stoichiometry ratio. MD simulations give a clear picture of the scene on how the PCB52 molecule enters the cavity of β-CD. The vibrational analyses on the 1:1 complexes of CDs provide information for the spectral characterization of the inclusion complexes: Raman spectroscopy can deliver the characteristic bands of PCB52, whereas IR spectroscopy cannot uniquely assign them, implying that Raman spectroscopy is a useful technique for the identification of CD-modified PCBs. The present theoretical results are expected to provide guidance for the relevant experimental research. 1. Introduction Polychlorinated biphenyls (PCBs) are a class of chlorinated aromatic hydrocarbon chemicals that are now known as part of the most well-known persistent organic pollutants (POPs).1-6 PCBs were once widely used from the 1930s to the 1970s in hundreds of industrial and commercial applications (mainly as dielectric fluids in capacitors and transformers) due to their nonflammability, chemical stability, high boiling point, and electrical insulating properties. Concern over the toxicity, environmental persistence, and bioaccumulation7-11 of PCBs has led to the progressive restrictions on the use of PCBs since the 1970s. Although the manufacture, marketing, and use of PCBs have been banned for many years in most countries, concerns over these chemicals are never interrupted because of their persistence in the environment and accumulation in the animal food chain on a nearly global scale. So controlling and reducing the PCB pollution remain a focus of environmental attention. At present, the effective enrichment and identification of lowly concentrated PCBs in the environment is attracting a great deal of research attention due to human health concerns. Cyclodextrins (CDs) are homochiral cyclic oligosaccharides, which usually consist of six or more R-D-glycopyranose units. The most common natural CDs are R-, β-, γ-CDs consisting of six, seven, and eight R-D-glycopyranose units by the R-1, 4-linkage, respectively. CDs are often described as a truncated cone with a polar outside and an apolar cavity (Figure 1). Due * To whom correspondence should be addressed. (D.Z.) Phone: +86-531-88365833.Fax:+86-531-88564464.E-mail:[email protected]. (Z.J.) Phone: +86-531-88365017. Fax: +86-531-88564464. E-mail: [email protected].

to the hydrophilic hydroxyl groups outside, CDs can be dissolved in water, where the apolar cavities inside provide a hydrophobic matrix, making CDs (host molecules) able to encapsulate a variety of poorly water-soluble organic compounds (guest molecules),12,13 whose sizes are suitable for the cavities of CDs. The formation of the host-guest inclusion complexes can obviously increase the solubility of some organic molecules in the water, which lead to extensive applications of CDs in a range of fields. For example, in pharmaceutics, CDs can not only improve the hydrophilicity of highly lipophilic drugs, but also increase the stability and reduce the toxicity of some drugs.14-18 In the food industry, CDs are used to increase the solubility of vitamins, colorants, and unsaturated fats, and to eliminate the bitter tastes of the foods.12,19-21 Another particularly important application of CDs is in the field of environmental sciences. By forming the inclusion complexes, CDs can enhance the bioavailability of some hydrophobic organic pollutants, improve the transport of several low-polarity organic compounds in the soil,22-28 and lodge and immobilize toxic compounds inside the cavities to promote their decomposition. A lot of efforts have been devoted to the study of inclusion complexes of CDs with various organic compounds.29 However, as far as we know, the concern for the inclusion complexes of CDs with PCBs are comparatively scarce.11,30-33 The existing experimental studies showed that CDs can significantly enhance the biological degradation of PCBs in soil reactors,30-32 and that CDs are good reagents to enhance the mobilization of PCB compounds from soil.33 Recently, Kida et al. found that some kinds of PCBs were completely removed from insulating oil by channel-type γ-cyclodextrin.11 These experimental studies

10.1021/jp109306v  2010 American Chemical Society Published on Web 11/19/2010

Inclusions of PCB52 with Cyclodextrins

J. Phys. Chem. A, Vol. 114, No. 50, 2010 13123

Figure 1. Sketch map of β-CD and optimized structures for PCB52 and R-, β-, and γ-CD molecules with geometric dimensions from the B3LYP/ 6-31G(d,p) calculations.

have provided useful information for understanding the influence of CDs on the properties of PCBs, but our knowledge about CD-PCB complexes is so limited so that the solubilization effect of CDs for PCBs is still unclear. Therefore, it is highly desirable for theoretically study the molecular behavior between CDs and PCBs, which are still not experimentally accessible at present. In this work, we present a combined quantum chemical and molecular dynamics study of the host-guest interaction between R-, β-, γ-CDs and PCB52, an ortho-substituted, noncoplanar, 2,2′,5,5′-tetrachlorobiphenyl, which was generally used as a model molecule of PCBs in some studies.4,9,34-37 To the best of our knowledge, there are no reports in the literature on such a topic. We focus our attention on the following: (i) Do these three natural CDs have a unique ability to accommodate PCB52 molecule to form stable host-guest inclusion complexes? (ii) If so, how do the individual geometrical and conformational characteristics of the host and guest change? And what are the details of the molecular behavior of PCB52 inside the CD cavities? (iii) Are the general infrared and Raman techniques suitable for the direction of CD-modified PCBs? Theoretical results from the present study would be very useful for understanding the host-guest behavior between CDs and PCBs. 2. Computational Details The isolated R-, β-, γ-CDs and PCB52 are first optimized, respectively, and then the optimized PCB molecule is attached to CDs to obtain the local minimum structures for the inclusion complexes. The starting structures of R-, β-, and γ-CDs are their crystallographic geometries.38-40 Considering the fact that for the general CD-substrate inclusion complexes, the ratio of the host/guest is generally 1:1, 1:2, 2:1, and in some cases, it is 2:2,29 here we studied all the four possible CD-PCB52 stoichiometry complexes.

Our density functional theory (DFT) calculations were performed using both the MS Dmol3 code41 and Gaussian 03 program package.42 For the Dmol3 calculations, the total energies, equilibrium geometries, and electronic structures are obtained based on local density approximation (LDA). The exchange-correlation energy in the LDA was parametrized by Perdew and Wang’s scheme,43 and all-electron Kohn-Sham wave functions were expanded in a double numerical basis set including the polarization function (DND). For the numerical integration, the MEDIUM quality mesh size of the program was adopted. The tolerances of energy, the change of the maximum force on the atom, and the maximal displacement were set to 2 × 10-5 Hartree, 4 × 10-3 Hartree/Å, and 5 × 10-3 Å, respectively. Solvent effects of the complexation in aqueous solution are estimated using the COSMO model.44,45 For the Gaussian calculations, we used the popular B3LYP functional46,47 combined with the standard basis set 6-31G(d,p). Previous investigations indicated that the B3LYP/6-31G(d,p) method can reliably describe the host-guest interaction of CDs with organic compound molecules.48,49 In consideration of the expensive computation cost, the Gaussian calculations are only performed for the three 1:1 complexes, including the geometry optimization and vibrational spectral analysis. The molecular dynamics simulations were performed with the Discover module of Materials Studio 4.4 software package (from Accelrys Inc.), using the COMPASS force field.50 This force field was validated to describe the inclusion interactions of cyclodextrin.51 Periodic boundary conditions, with a 28.8 × 28.8 × 28.8 Å cubic box as the basic unit cell in the NPT ensemble, were used. This dimension is large enough to prevent the direct interactions between a molecule and its periodic images. The nonbonded interactions were calculated using an atom-based method and the cutoff distance was set to 12.0 Å.

13124

J. Phys. Chem. A, Vol. 114, No. 50, 2010

Liu et al.

The box, containing one β-cyclodextrin, one PCB52, and 800 water molecules corresponding to a density of 1 g/mL, was taken an energy minimization using the conjugate gradient algorithm for achieving equilibration. Constant temperature (298 K) and pressure (1 atm) was controlled using the Andersen method.52 The system was simulated for 5 ns and the integration of the motion equations was performed using the Verlet velocity algorithm53 with a time step of 0.5 fs. 3. Results and Discussion To evaluate the stability of the inclusion complexes, we calculated the complexation energies of each CD-PCB52 complex using the following relationship:

∆Em:n(R,βorγ) ) (mECD + nEPCB52) - Ecomplex

(1)

where ECD, EPCB52, and Ecomplex are the energies of the CD, PCB52, and the inclusion complex, respectively, and m ) n ) 1 for the 1:1 complexes, m ) 1 and n ) 2 for the 1:2 complexes, m ) 2 and n ) 1 for the 2:1 complexes, and m ) n ) 2 for the 2:2 complexes. The larger complexation energy implies the more thermodynamically favorable inclusion complex. Furthermore, in order to investigate the induced deformation for the host and guest by forming the host-guest complex, we define a deformation energy of the host or the guest molecule, ∆Ed, as follows:

∆Ed ) E(x-sing/complex-opt) - E(x-opt)

(2)

where E(x-sing/complex-opt) is the single point energy of the host (CD) or the guest (PCB) at the geometry in the optimized complex, and E(x - opt) is the energy of the host (CD) or the guest (PCB) at its optimized geometry. A smaller deformation energy may indicate an energetically more favorable process. 3.1. Geometries of Isolated CDs and PCB52. We optimized structures of isolated R-, β-, and γ-CDs and PCB52 by performing both the Dmol3 calculations and the Gaussian calculations. It is found that the structural feature of the CDs in crystals and the geometrical parameters of PCB52 are reproduced rather well. In Figure 1, we only show the results from the Dmol3 calculations. As is seen, CDs present truncated cone structures with the wide and narrow rims occupied by the secondary and primary hydroxyl group, respectively. The calculated central cavity diameters of R-, β-, and γ-CDs are 4.43-5.78, 5.57-7.47, and 7.44-8.71 Å, which are in good agreement with the experimental reports, 4.7-5.3, 6.0-6.5, and 7.5-8.3 Å, respectively.12,54 The dipole moments of three CD molecules are calculated to 0.183, 2.402, and 2.086 D, which could be an important driving force in CD complexation. PCB52 is a nonplanar molecule, where the dihedral angle and bond length between the two phenyl rings are 55.7° and 1.466 Å and the ortho- and meta-C-Cl bond lengths are 1.723 and 1.721 Å, respectively, which are in good agreement with the corresponding values (59.0°, and 1.467, 1.746, and 1.746 Å).55 The dimensions of PCB52 in different orientations (Figure 1) are in the range of 4.871-9.256 Å. As is seen from Figure 1, all of the central cavity diameters of CDs except that of the narrow rim of R-CD are larger that the smallest dimension of PCB52 (4.871 Å), indicating that CDs seem to be capable of include PCB52 molecule. As indicated by our MD simulations later, PCB52 molecule prefers to enter the CD cavity from the wide rim. In this case, R-CD is also expected to form the inclusion complex with PCB52 molecule

Figure 2. Optimized 1:1 and 1:2 inclusion complexes (the upper is for the lateral view and the lower shows the structural parameters in each panel) and the calculated complexation energies (in kcal mol-1) in the gas phase and in aqueous solution (in the parentheses).

since its cavity diameter (5.78 Å) of the wide rim is larger than the smallest dimension of PCB52. 3.2. Host-Guest Complexes in 1:1 and 1:2 Stoichiometry Ratios. The optimized geometries for the complexes of 1:1 and 1:2 stochiometries obtained from the Dmol3 calculations in vacuum are shown in Figure 2, where the calculated complexation energies are given below the geometries. As seen in Figure 2, in all three 1:1 stochiometry complexes, R-CD-PCB52, β-CDPCB52, and γ-CD-PCB52, a considerable part of PCB molecule is embedded inside the CD cavities. For R-CD, due to the limited cavity dimension, only one phenyl ring of PCB52 is accommodated in the cavity and the other lies on the top edge of the R-CD. With the increasing cavity size, β-CD can include more part of PCB52, whereas in the situation of γ-CD, the molecule completely enters the cavity and is included in the most effective way. As shown in Figure 2, the orientations of PCB52 in three complexes are different from each other, indicating that the conformations of PCB52 in inclusion complexes are sensitive for the cavity size of CDs. In Figure 2, we showed the shortest distance between CDs and the molecules, i.e., the lengths of the H-bonds between the glycosidic oxygen atoms of CDs and the H atoms on the phenyl ring of PCB52 included in CD cavities, which vary in the range of 2.0-2.7 Å. These H-bonds may be mainly responsible for the different orientations of PCB52 in three CD cavities, although the initial driving force for forming the inclusion complexes is the electrostatic interaction and van der Waals interaction between the hosts and guest molecules. The calculated complexation energies for 1:1 stochiometry complexes are in the range of ∼35-50 kcal mol-1 in vacuum



TABLE 1: Deformation Energies (in kcal mol-1) of the CDs and PCB52 in the Complexes in Gas Phase and in Aqueous Solution (In the Parentheses) CD-I R-CD-PCB52 β-CD-PCB52 γ-CD-PCB52 β-CD-2PCB52 γ-CD-2PCB52 2R-CD-PCB52 2β-CD-PCB52 2γ-CD-PCB52 2β-CD-2PCB52 2γ-CD-2PCB52

1.35 (1.14) 1.62 (2.20) 5.14 (5.26) 3.84 (3.50) 5.31 (5.35) 27.77 (19.29) 25.29 (16.58) 32.98 (18.26) 36.58 (36.13) 34.25 (21.97)

CD-II

PCB52-I

27.24 (19.58) 25.17 (16.76) 33.09 (17.69) 49.76 (39.44) 32.47 (21.97)

0.76 (0.34) 0.15 (0.15) 0.45 (0.31) 0.27 (0.44) 0.10 (0.16) 4.51 (4.95) 0.14 (0.18) 0.20 (0.86) 4.16 (7.99) 1.10 (3.50)

PCB52-II

1.05 (0.84) 0.44 (0.52)

6.41 (5.17) 2.81 (2.96)

and ∼28-40 kcal mol-1 in water solution. These large energy changes upon complexation indicate that all three CDs could form stable complexes with PCB52. However, we calculated the deformation energies of the host and the guest molecules, which are also important indexes indicating the driving forces leading to the inclusion complexes. As shown in Table 1, in all situations, PCB52 needs only an energy smaller than 1.0 kcal mol-1 for conformational adaptation inside the CD cavities. In contrast, the deformation energies of CDs are slightly larger. However, the largest one is only ∼5 kcal mol-1. These small deformation energies imply the favorable processes for forming the stable 1:1 inclusion complexes for all three CD hosts again. Figure 2 also shows two 1:2 stochiometry complexes, β-CD2PCB52 and γ-CD-2PCB52. Note that no stable R-CD-2PCB52 complex was found from the present calculations. This may be because the cavity of R-CD is too small to accommodate two PCB52 molecules simultaneously. In β-CD-2PCB52, only very small parts of two PCB52 molecules enter the cavity of β-CD. In the strict sense, such a complex is not the real “inclusion complex”, because the most parts of two PCB52 molecules are exposed outside of the cavity. This fact implies that β-CD prefers the 1:1 complexation to 1:2 complexation. In contrast, in γ-CD2PCB52 two guest molecules are covered by γ-CD by ∼50% to form the effective 1:2 inclusion complex, and the calculated complexation energy for γ-CD-2PCB52 (74.1 kcal mol-1) is larger than that for the β-CD-2PCB52 complex (58.7 kcal mol-1). These results suppose that one γ-CD host can effectively include two PCB52 guest molecules due to its relatively larger cavity than those of R- and β-CDs. The calculated deformation energies of the host- and guest- molecules are shown in Table 1. Similar to those in the 1:1 complex, for γ-CD-2PCB52, the deformation energies are small, confirming that the conformational adaptations of γ-CD and PCB52 molecules in the 1:2 complex are not significant and thus the complex is expected to form easily. 3.3. Host-Guest Complexes in 2:1 and 2:2 Stoichiometry Ratios. It is noted that in the 1:1 and 1:2 complexes discussed above, a relevant part of PCB52 molecule remains outside the cavities of the CDs. Can the exposed part be further included by a second CD molecule? To further understand the properties of CD-PCB52 inclusion complexes, we also studied 2:1 and 2:2 host-guest systems. By adding a second CD molecule to the optimized 1:1 and 1:2 complexes, we built the initial 2:1 and 2:2 complexes, where two CDs are oriented in the widerrim-to-wider-rim manner. Figure 3 shows the optimized stable geometries for these two-CD complexes. Clearly, in all of these complexes, the guest molecule is completely covered by CDs. Depending on the complex composition and the types of CDs, the calculated complexation energies vary from 170 to 280 kcal mol-1, which are much larger than those of the one-CD complexes discussed above. The high stability of these two-

Figure 3. Optimized 2:1 and 2:2 inclusion complexes (the upper is for the lateral view and the lower shows the structural parameters in each panel) and the calculated complexation energies (in kcal mol-1) in gas phase and in aqueous solution (in the parentheses).

CD complexes not only derives from the dipole-dipole interaction and the H-bond interaction between the host and the guest but also those between two CDs, where there are many hydrogen bonds formed by hydroxyl H atoms from one CD and hydroxyl O atoms from the other CD. Their stability increases with the increasing number of R-D-glycopyranose units, i.e., γ-CD complexes are the most stable. The calculated deformation energies are shown in Table 1. Compared to the one-CD complexes, the energy demands of the host and guest molecules are generally larger than those in the one-CD complexes, in particular, for the host CD molecules. For example, each β-CD in 2β-CD-PCB52 needs 25.2 kcal mol-1 to include one PCB52 molecule, whereas it only needs 3.8 kcal mol-1 in β-CD-PCB52. The high energy demand is attributed to the relatively large conformational change of CDs induced by the dipole-dipole interaction and the H-bond interaction between two CDs. The calculated largest CD deformation energy is 50.0 kcal mol-1 in the 2:2 complex, 2β-CD-2PCB52. However, the complexation energies released to form stable complexes are enough for compensating these energy demands. So from an energetic point of view, the formations of two-CD complexes are very favorable processes. 3.4. Solvent Effect on the Inclusion Complexes. From the discussions above so far, the host-guest complexes shown in Figures 2 and 3 have been proven to be stable in the gas-phase. To evaluate the influence of the solvent effect on the stability of the inclusion complexes, we reoptimized the gas-phase

13126


Liu et al.

Figure 4. Snapshots of the geometries of β-CD-PCB52 complex obtained from the MD runs in water. The water molecules are not shown for clarity.

inclusion complexes using the COSMO solvent model and calculated the complexation energies and deformation energies in aqueous solution. The results show that the solvent does not have a significant effect on the geometries for all complexes shown in Figures 2 and 3. All inclusion complexes obtained in the gas-phase are still stable in aqueous solution, indicating the intrinsic capability of CDs for including PCB52 molecule. The calculated complexation energies (see values in the parentheses in Figures 2 and 3) in aqueous solution are monotonously smaller than those in gas-phase: they reduce by 6.7-12.7 kcal mol-1 for 1:1 and 1:2 complexes and by 32.6-55.9 kcal mol-1 for 2:1 and 2:2 complexes. It is well-known that water molecules are hydrogen-bonded to each other and of large dipole moments. So in the water solvent of PCB52-CD complexes, water-water interactions are more favorable than water-CD interactions, making the inclusion complexes less stable than those in gas phase. In this scenario, we conjecture that water may not be the optimized solvent for the inclusions of PCB52 with CDs. From an application’s point of view, optimizing the solvent of the inclusion complexes is an important challenge in this field, which deserves our further study. The same trend is also observed for the deformation energies of CD molecules in two-CD complexes, which are 0.5-15.4 kcal mol-1 smaller than those in gas phase (see Table 1) depending on the type of CDs. However, the solvent effect is not significant for the deformation energies of the guest molecule in all complexes and for the CD molecules in one-CD complexes. These results indicate that the solvent has more important influence on CDs than on PCB52. This fact is in agreement with the larger dipole moments of CDs, which possess the stronger dipole-dipole interaction with the polar solvent molecules than PCB52. 3.5. The Formation Process of Inclusion Complexes. To better understand the formation process of CD-PCB52 inclusion complexes, we carried out MD simulations for the representative β-CD/PCB52 system in water solvent. Computational results provide the evidence again that β-CD and PCB52 can form the stable host-guest inclusion complex, β-CD-PCB52 in the water solvent. Figure 4 shows a series of pivotal snapshots in the process of forming the complexes. The original centroid distance of β-CD and PCB52 was sited at about 11 Å, and along with the simulation progress, the two molecules begin to get close with each other. When the simulation are carried out to about 150 ps, PCB52 molecule has finally entered into the cavity of β-CD. This process can be proved by the trajectory of distance between the centers of mass of β-CD and PCB52 versus

Figure 5. (a) Distance between the centroids of β-CD and PCB52 versus simulation time and (b) the distribution function for the distance between the centroid of β-CD and PCB52.

simulation time, see Figure 5a. After the PCB52 molecule located into the β-CD, the distance between the centers mass of the two molecules fluctuated at about 1.5 Å. The distribution function for the distance between the centers mass (Figure 5b) also shows that the most probability of the distance is between 0.5 Å and 1.5 Å along the simulation. 3.5. Infrared and Raman Spectra of the Inclusion Complexes. To provide information for the spectral characterization of CD-PCB52 inclusion complexes, we here evaluate suitabilities of the Infrared (IR) and Raman spectra for detecting the inclusion complexes. Figures 6 and 7 show calculated IR and Raman spectra of the free CD molecules, 1:1 complexes, and the free PCB52 molecule, where band frequencies and band intensities are given in the region 200-4000 cm-1 for IR spectra and 200-1800 cm-1 for Raman spectra. As seen in Figure 6, compared to PCB52, IR signals of CDs are much stronger due to their much larger molecular weights. As a result, the bands of the inclusion complexes mainly present the spectra features of the CDs, i.e., CD bands change only slightly upon complexation. Moreover, characteristic IR bands of PCD52 all are in the range of the strong absorption bands of CD molecules, and hence the resultant spectra of the complexes have a superposition of host and guest bands. Thus, bands which could be assigned to the guest molecule in the complexes are easily masked by the CD spectrum bands. These results seem to indicate that IR techniques are not suitable for direction of PCB52-CD complexes. The situation is different for these complexes with the corresponding Raman spectra, which are shown in Figure 7. The characteristic Raman bands of PCB52 occur at 1640, 1260, and 1070 cm-1, thereinto, the peak appearing at the highest wavenumber, 1640 cm-1, is the strongest, which corresponds to the intramolecular C-C bond stretching vibrations of PCB52. Interestingly, these Raman bands, in particular the strongest one, are also evident in the spectra of the host-guest complexes with


Figure 6. Calculated IR spectra for the inclusion complexes: (a) R-CDPCB52, (b) β-CD-PCB52, and (c) γ-CD-PCB52 at the B3LYP/6-31G(d, p) level of theory.

comparable intensities with the free PCB52. In other words, in the Raman spectra of the complexes, the PCB52 bands stick out, implying that Raman spectroscopy is an applicable technique for the identification of CD-modified PCBs. 4. Conclusions DFT calculations and MD simulations were carried out on the inclusion complexes of the most common cyclodextrins R-, β-, and γ-CDs with the model molecule of PCBs (PCB52) to better understand the complexation of PCBs by CDs. The


Figure 7. Calculated Raman spectra for the inclusion complexes: (a) R-CD-PCB52, (b) β-CD-PCB52, and (c) γ-CD-PCB52 at the B3LYP/ 6-31G(d, p) level of theory.

theoretical results confirm that the CDs have the ability to accommodate PCB52 molecules. The stability of the inclusion complexes depends on both the type of CD and the host-guest stoichiometry ratio. While R-CDs preferentially form 1:1 and 2:1 complexes and β-CD stably include the guest molecule with 1:1, 2:1, and 2:2 stoichiometries, γ-CD is proven to have the capability to form all four, 1:1, 1:2, 2:1, and 2:2, complexes. The complex of γ-CD is generally the most stable compared to those of R- and β-CD with the same stoichiometry ratio with the sole exception being for 1:1 complexes, of which R-CDPCB52 is the energetically most stable. MD simulations give a

13128


clear picture of the scene on how the PCB52 molecule enters the cavity of the β-CD. The IR spectra of 1:1 inclusion complexes mainly present the spectra features of the CDs and give only slight indication for bands of the guest molecule. In contrast, the characteristic Raman bands of the guest molecule are remarkably prominent in the Raman spectra of the inclusion complexes. Raman spectroscopy can be used for the identification of CD-modified PCBs, whereas IR spectroscopy is not suitable for such an application. Acknowledgment. This work was supported by the National Basic Research Program of China (973 Program) (Grant No. 2007CB936602), and the National Natural Science Foundation of China (Nos. 20873076 and 20773078). References and Notes (1) Van den Berg, M.; Birnbaum, L.; Bosveld, A. T. C.; Brunstrom, B.; Cook, P.; Feeley, M.; Giesy, J. P.; Hanberg, A.; Hasegawa, R.; Kennedy, S. W.; Kubiak, T.; Larsen, J. C.; van Leeuwen, F. X. R.; Liem, A. K. D.; Nolt, C.; Peterson, R. E.; Poellinger, L.; Safe, S.; Schrenk, D.; Tillitt, D.; Tysklind, M.; Younes, M.; Warn, F.; Zacharewski, T. EnViron. Health Perspect. 1998, 106, 775. (2) Zhang, Q. Z.; Li, S. Q.; Qu, X. H.; Shi, X. Y.; Wang, W. X. EnViron. Sci. Technol. 2008, 42, 7301. (3) Qu, X. H.; Wang, H.; Zhang, Q. Z.; Shi, X. Y.; Xu, F.; Wang, W. X. EnViron. Sci. Technol. 2009, 43, 4068. (4) Llansola, M.; Montoliu, C.; Boix, J.; Felipo, V. Chem. Res. Toxicol. 2010, 23, 813. (5) Hyun, S.; Kim, M.; Baek, K.; Lee, L. S. Chemosphere 2010, 78, 423. (6) Vasilyeva, G. K.; Strijakova, E. R.; Nikolaeva, S. N.; Lebedev, A. T.; Shea, P. J. EnViron. Pollut. 2010, 158, 770. (7) Fischer, L. J.; Seegal, R. F.; Ganey, P. E.; Pessah, I. N.; Kodavanti, P. R. S. Toxicol. Sci. 1998, 41, 49. (8) Safe, S. H. Crit. ReV. Toxicol. 1994, 24, 87. (9) Menzel, R.; Yeo, H. L.; Rienau, S.; Li, S.; Steinberg, C. E. W.; Stu¨rzenbaum, S. R. J. Mol. Biol. 2007, 370, 1. (10) Kohler, H.; Knodler, C.; Zanger, M. Arch. EnViron. Contam. Toxicol. 1999, 36, 179. (11) Kida, T.; Nakano, T.; Fujino, Y.; Matsumura, C.; Miyawaki, K.; Kato, E.; Akashi, M. Anal. Chem. 2008, 80, 317. (12) Thorsteinn Lofsson, T.; Brewster, M. E. J. Pharm. Sci. 1996, 85, 1017. (13) Szejtli, J. Pure Appl. Chem. 2004, 76, 1825. (14) Stella, V. J.; Rajewski, R. A. Pharm. Res. 1997, 14, 556. (15) Messner, M.; Kurkov, S. V.; Jansook, P.; Loftsson, T. Int. J. Pharm. 2010, 387, 199. (16) Al Omari, M. M.; El-Barghouthi, M. I.; Zughul, M. B.; Davies, J. E. D.; Badwan, A. A. J. Inclusion Phenom. Macrocycl. Chem. 2009, 64, 305. (17) Zhou, H. W.; Lai, W. P.; Zhang, Z. Q.; Li, W. K.; Cheung, H. Y. J. Comput. Aided Mol. Des. 2009, 23, 153. (18) Vyas, A.; Saraf, S.; Saraf, S. J. Incl. Phenom. Macrocycl. Chem. 2008, 62, 23. (19) Szente, L.; Szejtli, J. Trends Food Sci. Technol. 2004, 15, 137. (20) Szejtli, J.; Szente, L. Eur. J. Pharm. Biopharm. 2005, 61, 115. (21) de Vos, P.; Faas, M. M.; Spasojevic, M.; Sikkema, J. Int. Dairy J. 2010, 20, 292. (22) Brusseau, M. L.; Wang, X.; Hu, Q. EnViron. Sci. Technol. 1994, 28, 952. (23) Reid, B. J.; Stokes, J. D.; Jones, K. C.; Semple, K. T. EnViron. Sci. Technol. 2000, 34, 3174.

Liu et al. (24) Wang, J. M.; Marlowe, E. M.; Miller-Maier, R. M.; Brusseau, M. L. EnViron. Sci. Technol. 1998, 32, 1907. (25) Ehlers, G. A. C.; Loibner, A. P. EnViron. Pollut. 2006, 141, 494. (26) Semple, K. T.; Doick, K. J.; Wick, L. Y.; Harms, H. EnViron. Pollut. 2007, 150, 166. (27) Dean, J. R.; Scott, W. C. Trends Anal. Chem. 2004, 23, 609. (28) Leitgib, L.; Gruiz, K.; Fenyvesi, E.; Balogh, G.; Mura´nyi, A. Sci. Total EnViron. 2008, 392, 12. (29) Song, L. X.; Bai, L.; Xu, X. M.; He, J.; Pan, S. Z. Coord. Chem. ReV. 2009, 253, 1276. (30) Fava, F.; Gioia, D. D.; Marchetti, L. Biotechnol. Bioeng. 1998, 58, 345. (31) Fava, F.; Bertin, L.; Fedi, S.; Zannoni, D. Biotechnol. Bioeng. 2003, 81, 381. (32) Fava, F.; Ciccotosto, V. F. Appl. Microbiol. Biotechnol. 2002, 58, 393. (33) Ehsan, S.; Prasher, S. O.; Marshall, W. D. Chemosphere 2007, 68, 150. (34) Aarts, J. M. M. J. G.; Denison, M. S.; Cox, M. A.; Schalk, M. A. C.; Garrison, P. M.; Tullis, K.; de Haan, L. H. J.; Brouwer, A. Eur. J. Pharmacol. EnViron. Toxicol. Pharmacol. 1995, 293, 463. (35) Yilmaz, B.; Sandal, S.; Chen, C.; Carpenter, D. O. Toxicology 2006, 217, 184. (36) Sandal, S.; Yilmaz, B.; Carpenter, D. O. Mutat. Res. 2008, 654, 88. (37) Lores, M.; Llompart, M.; Gonzalez-Garcia, R.; Gonzalez-Barreiro, C.; Cela, R. Chemosphere 2002, 47, 607. (38) Harata, K. Bull. Chem. Soc. Jpn. 1975, 48, 2409. (39) Lindner, K.; Saenger, W. Carbohydr. Res. 1982, 99, 103. (40) Harata, K. Bull. Chem. Soc. Jpn. 1987, 60, 2763. (41) The DMol3 is a registered software product of Accelrys, Inc. (42) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; 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. Gaussian03, ReVision D. 01; Gaussian, Inc.: Pittsburgh, PA, 2004. (43) Perdew, J. P.; Wang, Y. Phys. ReV. B 1992, 45, 13244. (44) Klamt, A.; Schu¨u¨rmann, G. J. Chem. Soc., Perkin Trans. 1993, 2, 799. (45) Delley, B. Mol. Simul. 2006, 32, 117. (46) Becke, A. D. J. Chem. Phys. 1992, 96, 2155. (47) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785. (48) Weinzinger, P.; Weiss-Greiler, P.; Snor, W.; Viernstein, H.; Wolschann, P. J. Incl. Phenom. Macrocycl. Chem. 2007, 57, 29. (49) Snor, W.; Liedl, E.; Weiss-Greiler, P.; Viernstein, H.; Wolschann, P. Int. J. Phytorem. 2009, 381, 146. (50) Sun, H. J. Phys. Chem. B 1998, 102, 7338. (51) Sellner, B.; Zifferer, G. J. Phys. Chem. B 2008, 112, 710. (52) Andersen, H. C. J. Chem. Phys. 1980, 72, 2384. (53) Verlet, L. Phys. ReV. 1967, 159, 98. (54) Lindner, K.; Saenger, W. Carbohydr. Res. 1982, 99, 103. (55) Miao, X. S.; Chu, S. G.; Xu, X. B.; Jin, X. L. Acta Crystallogr. 1996, C52, 2582.

JP109306V

Investigation on the Inclusions of PCB52 with Cyclodextrins by

Recommend Documents