Theoretical studies of the functionalized derivatives of fullerene C24H24 by attaching a variety of chemical groups

Journal of Molecular Structure: THEOCHEM 893 (2009) 26–30

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Theoretical studies of the functionalized derivatives of fullerene C24H24 by attaching a variety of chemical groups Xiao Jun Li *, Geng Sheng Jiao Department of Chemistry and Chemical Engineering, Weinan Teachers University, Weinan, Shaanxi 714000, PR China

a r t i c l e

i n f o

Article history: Received 25 June 2008 Received in revised form 11 September 2008 Accepted 14 September 2008 Available online 20 September 2008 Keywords: C24H24 fullerene Derivative Structure Thermochemistry DFT

a b s t r a c t Based on the D6d-symmetrical C24H24 fullerene, its derivatives, which have been exohedrally functionalized by replacing one of its H atoms with –CH2OH, –CONH2, –COOH, and –COH, have been firstly calculated using the hybrid DFT-B3LYP functional in conjunction with 6-31G(d) basis sets. Present calculations show that the C24H23(COOH) is the most stable under the values of DH and De. The calculated HOMO– LUMO energy gaps of the derivatives with –CH2OH and –COOH groups are same as in the case of the not functionalized C24H24 cluster. In addition, the C24H23(CONH2) displays the largest dipole moment (3.32 D), and the vertical electron affinities of the functionalized derivatives are all very higher. These can promote new development in the fields of the bio-medical applications. Ó 2008 Elsevier B.V. All rights reserved.

1. Introduction After the fullerene C60 was prepared using laser vaporization methods in 1985 [1], the fullerene materials have attracted a great deal of attentions. Because the fact that they can be produced in large quantities with full control over size and morphology, and they have also possessed a large number of interesting properties that could lead to the development of novel technologies. For example, the previous studies have found the formation of a large number of organic derivatives, and have significantly expanded the scope of carbon clusters [2–7]. The derivatives containing metal atoms have enhanced the stability of their endohedral fullerenes [8–11], which might find interesting applications in medicinal chemistry, materials science, and nanotechnology [12]. Additionally, the derivatives of some other fullerenes have also been extensively studied theoretically. For instance, Xu et al. [13,14] have investigated C50NCH3, C50CH2, and C50NH complexes by mean of semiempirical AM1 methods and ab initio calculations, respectively. The structure and thermodynamic stability of Glycine–C60 and C60(glycine)n (where n = 1–4) have been calculated by Hu and Ruckenstein [15] and Messaouda et al. [16], respectively. And several kinds of functionalized fullerenes have been recently synthesized for their possible application in electronic and optical devices as well as for developing possible applications in biology and medicine [17–20].

* Corresponding author. Tel.: +86 913 2133073. E-mail address: [email protected] (X.J. Li). 0166-1280/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2008.09.013

To our knowledge, there do not have the theoretical investigation on the derivatives of fullerene C24H24 by attaching a variety of organic groups. In a previous study, the C24 cluster has been extensively calculated theoretically. Many ab initio and density functional theory (DFT) calculations have been directed toward the structure and stability of its isomers [21–24]. In addition, the ground-state structures of C24 and C24H2m have also been predicted [25–28]. In this paper, we investigate the chemical derivatives of C24H24 fullerene (Fig. 1) using the hybrid DFT-B3LYP functional in conjunction with 6-31G(d) basis sets. Four neutral chemical groups have been introduced in the C24H24 fullerene, namely (i) –CH2OH, (ii) –CONH2, (iii) –COOH, and (iv) –COH by replacing a single H atom on C. The choice origins from the observation that these chemical groups are commonly present in both natural and synthetic molecules, which have the ability to interact non-covalently with the side-chain residues of biological receptors [29]. And computer-aided drug design [30] has greatly contributed to the development of molecules that can selectively bind the active site of their putative receptors through the interactions. Hence, for understanding these interactions, we need to assess how the electronic structures of C24H24 fullerene are being affected by the chemical groups. 2. Computational details The hybrid density functional form used here is Becke’s threeparameter hybrid exchange functional [31] with the Lee, Yang, and Parr’s correlation functional [32] (B3LYP). All the calculations

X.J. Li, G.S. Jiao / Journal of Molecular Structure: THEOCHEM 893 (2009) 26–30

Fig. 1. Optimized structure of C24H24.

in this work have adopted the 6-31G(d) basis sets. Based on the D6d-symmetrical C24H24 fullerene, its derivatives, which have been exohedrally functionalized by replacing one of its H atoms with –CH2OH, –CONH2, –COOH, and –COH, have been calculated at the B3LYP/6-31G(d) level of theory. Some properties have been investigated for the stable structures, including the optimized structures, vibrational frequencies, dipole moments, reaction energies, zero-point corrected dissociation energies, the HOMO– LUMO energy gaps, and vertical electron affinities (VEA). All the stationary point geometries have been analyzed by the evaluation of their harmonic vibrational frequencies at the same theoretical level. All calculations were performed using Gaussian 03 [33] program package. The default numerical integration grid (75,302) of Gaussian 03 was applied. 3. Results and discussion 3.1. Optimized structures of C24H24 and its derivatives Fowler et al. [28] have reported the ground-state structure of C24H24 fullerene which is D6d symmetry, we have found that it has a 1A1 electronic state at B3LYP/6-31G(d) level of theory. And its structure is shown in Fig. 1, the bond lengths of C–C calculated by B3LYP are 1.560, 1.565, and 1.544 Å for the 12 equivalent C–C bond lengths, which are ones of two hexagons, close to two hexagons, and the middle of structure, respectively. All the bond distances of C–H predicted by B3LYP are both 1.095 Å. The optimized structures of functionalized derivatives are shown in Fig. 2. Let us first assess in what extent the highly symmetric D6d structures of C24H24 is being distorted by replacing one of its H atoms with each one of the four chemical groups mentioned above. When a single H atom is replaced with the –CH2OH group (Fig. 2a), the three C–C distances linked to C1 atom are almost unchanged, being 1.571, 1.547, and 1.547 Å, respectively. While the optimized bond length are 1.530 Å for C1–C2 bond, 1.426 Å for C2–O bond, 0.969 Å for O–H bond, and 1.103 Å for the two equivalent C2–H1 and C2–H2 bonds in the –CH2OH group. Thus, this cluster has a Cs symmetry with 1A0 state. The C1–C2–O bond angle is 109.3°, the C2–O–H bond angle is 107.9°, and the H–C–H bond angle is 107.3°. Additionally, the corresponding C1–C2–O–H dihedral angle is 180°. The optimized structure of the derivative functionalized with a –CONH2 group is shown in Fig. 2b. The cluster has a C1 symmetry with 1A state, because –NH2 group is slightly distorted relative to

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other part of the cluster. And the C1–C2–O bond angle is 124.2°, the C1–C2–N bond angle is 115.3°, the C2–N–H1 bond angle is 117.1°, and the C2–N–H2 bond angle is 122.1°. Moreover, the dihedral angles are –8.8° and –169.0° for O–C2–N–H1 and O–C2–N–H2, respectively. The three C–C distances linked to C1 atom are 1.563, 1.557, and 1.558 Å, respectively. The optimized distances are 1.541 Å for C1–C2 bond, 1.224 Å for C2–O bond, 1.374 Å for C2–N bond, and 1.010 and 1.009 Å for N–H1 and N–H2 bonds. The remaining C–C bonds are almost unchanged compare with the C24H24. The geometry of ground state of the derivative functionalized with a –COOH group is displayed in Fig. 2c. The cluster also has a C1 symmetry with 1A state because of the steric repulsion between the C–H bond and –COOH group. For C24H23(COOH), the three C–C bond lengths linked to C1 atom are 1.581, 1.542, and 1.557 Å, respectively. And the optimized distances are 1.516 Å for C1–C2 bond, 1.213 Å for C2–O1 bond, 1.363 Å for C2–O2 bond, and 0.976 Å for O2–H bond in the COOH group. While the C1–C2–O1 bond angle is 127.2°, the C1–C2–O2 bond angle is 111.7°, and the C2–O2–H bond angle is 105.7°. In addition, the dihedral angles are –179.9° and 0.1° for C1–C2–O2–H and O1–C2–O2–H, respectively. Replacement of an H atom with –COH group yields the functionalized derivative displayed in Fig. 2d. Our B3LYP results show a Cs symmetry with 1A’ state for the ground state of C24H23(COH). The three C–C distances linked to C1 atom are 1.556, 1.554, and 1.554 Å, respectively. While the C1–C2 bond distance is 1.517 Å, and the C2–O and C2–H bond distances are 1.212 and 1.116 Å, respectively. Moreover, the corresponding C1–C2–O–H dihedral angle is 180°, the C1–C2–O bond angle is 126.6°, and the C1–C2–H bond angle is 113.4°. From these features, we conclude that these functionalized derivatives do not almost affect the molecular structure of C24H24 fullerene. 3.2. Vibrational frequencies The calculated vibrational frequencies of C24H24 are shown in Fig. 3. According to the group representation theory in chemistry, we can easily deduce that there are 138 kinds of vibrational modes for C24H24 with D6d symmetry, which are 22 e1 + 24e2 + 24e3 + 24e4 + 22 e5 + 8a1 + 4b1 + 3a2 + 7b2. Among these normal modes, the strongest IR absorption peak is e1 mode, which located 3088 cm1. The simulated IR spectra of derivatives functionalized by replacing one of its H atoms with –CH2OH, –CONH2, –COOH, and –COH groups are also shown in Fig. 3. As can be seen from Fig. 3, the IR spectra of the functionalized derivatives are almost the same with the strongest absorption peak of C24H24 located 3088 cm1. Additionally, except for C24H23(CH2OH), the spectra of C24H23(CONH2), C24H23(COOH), and C24H23(COH) appear to be quite similar in general shapes with the absorption peaks located 1783, 1827, and 1816 cm1, respectively. There are no experimental or other theoretical values for comparison. 3.3. Thermochemistry and relative stabilities The reaction energies (DH), zero-point corrected dissociation energies (De), HOMO–LUMO energy gaps (Egap), and vertical electron affinities (VEA) of the functionalized derivatives evaluated by B3LYP method are shown in Table 1. The reaction energies and dissociation energies for the reaction as follows: DH

C24 H23 þ X )* C24 H23 ðXÞ De

DH ¼ HðC24 H23 ðXÞÞ  HðC24 H23 Þ  HðXÞ De ¼ EðC24 H23 Þ þ EðXÞ  EðC24 H23 ðXÞÞ

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X.J. Li, G.S. Jiao / Journal of Molecular Structure: THEOCHEM 893 (2009) 26–30

Fig. 2. Optimized structures of (a) C24H23(CH2OH), (b) C24H23(CONH2), (c) C24H23(COOH), and (d) C24H23(COH).

where X = CH2OH, CONH2, COOH, and COH. Thermodynamic stability is expected when a negative DH, and the more negative the value of DH, the more stable the C24H23(X) clusters. With De, the situation is the opposite, which is the more positive the value of De, the more stable the C24H23(X) clusters. It is can be seen from Table 1, the most negative DH and positive De are 84.74 kcal/mol and 3.65 eV, respectively. So it is implied that C24H23(COOH) is the most stable structure. Meanwhile, other stable order of the functionalized derivatives is C24H23(COH) > C24H23(CH2OH) > C24H23(CONH2). The result agrees similarly with the earlier studies predicted by Slanina et al. [34], and they should stress the fact that the reaction enthalpies give the same stability order as the HOMO/ LUMO gaps. Now let us see the electronic structures of C24H24 and its functionalized derivatives. As shown in Fig. 4, the vibrational modes and orbital energies are put into parentheses. Both HOMO and LUMO orbital of C24H24, C24H23(CH2OH), and C24H23(COOH) are associated with the cage. Moreover, the calculated Egap of them are bigger (shown in Table 1), being 7.75, 7.67, and 7.40 eV, respectively. It is easier to find that, the HOMO and LUMO orbital of C24H23(COH) have their weight on the –COH groups, and the Egap for one is 6.25 eV which is the smallest. These suggest that the values of Egap for C24H23(X) have close relations with the position of the interaction of HOMO and LUMO, and the different character of frontier orbital is interesting for molecular design. In Table 1,

interestingly, the C24H24 possess a net dipole moment, and the dipole moment of C24H23(CONH2) is the largest, 3.32 D, followed by those of C24H23(COH), 3.02 D, and C24H23(COOH), 1.80 D. It is worth mentioning that the dipole moment of C24H23(CH2OH) is the smallest, 1.36 D. The VEA (1.97 eV) of C24H24 calculated by B3LYP, is similar to saturated structures, is negative value. That is to say, the C24H24 fullerene cannot form stable anion. At a first approximation, the negative VEA corresponds to the resonant electron scattering energy [35–37]. As can be seen from Table 1, the VEA of the functionalized derivatives with –CH2OH, –CONH2, –COOH, and –COH groups are very higher, being 11.00, 11.03, 10.72, and 10.09 eV, respectively. So they are more stable. To our knowledge, there are no experimental or theoretical data regarding these properties for these functionalized derivatives. Our results may thus provide a reference for further study.

4. Conclusion Based on the D6d-symmetrical C24H24 fullerene, its derivatives functionalized by replacing one of its H atoms with –CH2OH, –CONH2, –COOH, and –COH groups have been firstly calculated using the hybrid DFT-B3LYP functional in conjunction with 631G(d) basis sets. Some properties have been investigated for the

29

500 400 300 200

300

200

220 277

100

100 0

0 0

500

1000

1500

2000

2500

3000

0

3500

500

1500

2000

2500

C24H23(COOH)

300 200

0

3682

652

100

3589 3714

1303 1354

225

100

1642 1783

300

400

1827

400

1136 1208

IR intensity (Km/mol)

500

200

3500

3092

600

C24H23(CONH2)

500

3000

-1

3089

600

1000

Vibrational frequency (cm )

-1

Vibrational frequency (cm )

IR intensity (Km/mol)

2970 2999

IR intensity (Km/mol)

600

C24H23(CH2OH)

400

1097 1066

C24H24

700

IR intensity (Km/mol)

500

3088

800

3083

X.J. Li, G.S. Jiao / Journal of Molecular Structure: THEOCHEM 893 (2009) 26–30

0 0

500

1000

1500

2000

2500

3000

3500

4000

0

500

1000

1500

2000

-1

Vibrational frequency (cm )

3000

3500

4000

-1

3089

600

C24H23(COH)

500 400 300 200

2873

1816

IR intensity (Km/mol)

2500

Vibrational frequency (cm )

100 0 0

500

1000

1500

2000

2500

3000

3500

-1

Vibrational frequency (cm ) Fig. 3. Simulated IR spectra for C24H24, C24H23(CH2OH), C24H23(CONH2), C24H23(COOH), and C24H23(COH).

Table 1 Dipole moments, Reaction energies (DH), Zero-point corrected dissociation energies (De), HOMO–LUMO energy gaps (Egap), and vertical electron affinities (VEA) of C24H24 and its derivatives Clusters

State

Dipole (Debye)

DH (kcal mol1)

De (eV)

Egap (eV)

VEA (eV)

C24H24 C24H23(CH2OH) C24H23(CONH2) C24H23(COOH) C24H23(COH)

1

0.00 1.36 3.32 1.80 3.02

– 77.09 76.74 84.74 78.08

– 3.30 3.30 3.65 3.34

7.75 7.67 7.07 7.40 6.25

1.97 11.00 11.03 10.72 10.09

A1 1 0 A 1 A 1 A 1 0 A

stable structures, including the optimized structures, vibrational frequencies, dipole moments, reaction energies, zero-point corrected dissociation energies, the HOMO–LUMO energy gaps, and vertical electron affinities (VEA). Present calculations show that the C24H23(COOH) is the most stable under the values of DH and De. The calculated HOMO–LUMO energy gaps of the derivatives

with –CH2OH and –COOH groups are same as in the case of the not functionalized C24H24 cluster. Moreover, their corresponding HOMO and LUMO are associated with the cage. The C24H23(CONH2) displays the largest dipole moment (3.32 D), and the VEA of the functionalized derivatives are all very higher. Thus, it would be possible to produce novel species for bio-medical applications by

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Fig. 4. (a–e) HOMO and (f–j) LUMO plots of (a and f) C24H24, (b and g) C24H23(CH2OH), (c and h) C24H23(CONH2), (d and i) C24H23(COOH), and (e and j) C24H23(COH).

attaching selected chemical groups. We hope that our results may provide a reference for further experimental and theoretical work as well as efforts directed toward the synthesis of these derivatives. Acknowledgement This work was financially supported from the start-up fund (No. 08YKZ009) of Weinan Teachers University of China. References [1] H.W. Kroto, J.R. Heath, S.C. OflBrien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] M. Fanti, Z. Zerbetto, J.P. Galaup, J. Rice, P. Birkett, N. Wachter, R. Taylor, J. Chem. Phys. 116 (2002) 7621. [3] J.E. Riggs, Y.P. Sun, J. Chem. Phys. 112 (2000) 4221. [4] P.F. Coheur, J. Lievin, R. Colin, B. Razbirib, J. Chem. Phys. 118 (2003) 550. [5] R.H. Xie, G.W. Bryant, C.F. Cheung, V.H. Smith, J. Zhao, J. Chem. Phys. 121 (2004) 2849. [6] B. Sitharaman, R.D. Bolskar, I. Rusakova, L.J. Wilson, Nano Lett. 4 (2004) 2373. [7] E. Toth, R.D. Bolskar, A. Borel, G. Gonzalez, L. Helm, A.E. Merbach, B. Sitharaman, L.J. Wilson, J. Am. Chem. Soc. 127 (2005) 799. [8] Yu.N. Makurin, A.A. Sofronov, A.I. Gusev, A.L. Ivanovsky, Chem. Phys. 270 (2001) 293. [9] M.H. Lin, Y.N. Chiu, S.T. Lai, J.M. Xiao, M.Z. Fu, J. Mol. Struct. (Theochem) 422 (1998) 57. [10] T. Guo, R.E. Smalley, G.E. Scuseria, J. Chem. Phys. 99 (1993) 352. [11] K.M. Kadish, R.S. Ruo, Fullerenes: Chemistry Physics and Technology, Wiley Interscience, New York, 2000. [12] H. Prinzbach, A. Weiler, P. Landenberger, F. Wahl, J. Woorth, L.T. Scott, M. Gelmont, D. Olevano, B.V. Issendor, Nature 407 (2000) 60. [13] X. Xu, Z. Shang, R. Li, Z. Cai, X. Zhao, J. Mol. Struct. (Theochem) (2008), doi:10.1016/j.theochem.2008.05.022. [14] X. Xu, Z. Shang, R. Li, Z. Cai, X. Zhao, J. Mol. Struct. (Theochem) 760 (2006) 99. [15] Y.H. Hu, E. Ruckenstein, J. Mol. Struct. (Theochem) 850 (2008) 67. [16] M.B. Messaouda, F. Moussa, B. Tangour, H. Szwarc, M. Abderrabba, J. Mol. Struct. (Theochem) 809 (2007) 153.

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