organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

1,4-Bis(3-methyl­phen­yl)piperazine-2,5-dione

aCollege of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, People's Republic of China
*Correspondence e-mail: pubsliu@163.com

(Received 20 May 2012; accepted 11 June 2012; online 16 June 2012)

The asymmetric unit of the title compound, C18H18N2O2, consists of two independent mol­ecules, each of which is located about a center of inversion. The mol­ecules are not planar, showing dihedral angles of 55.84 (9) and 54.10 (8)° between the piperazinedione and the aromatic rings. The piperazine N atoms exhibit a planar configuration. The crystal packing is stabilized by inter­molecular C—H⋯O hydrogen bonds.

Related literature

For background to the applications of piperazinedione and its derivatives, see: Acharya et al. (2001[Acharya, A. N., Ostresh, J. M. & Houghten, R. A. (2001). J. Comb. Chem. 3, 612-623.]); Fischer (2003[Fischer, P. M. (2003). J. Pept. Sci. 9, 9-35.]); Krchnak et al. (1996[Krchnak, V., Weichsel, A. S., Cabel, D., Flegelova, Z. & Lebl, M. (1996). Mol. Div. 1, 149-164.]); Paradisi et al. (2002[Paradisi, F., Piccinelli, F., Porzi, G. & Sandri, S. (2002). Tetrahedron Asymmetry, 13, 497-502.]). For the syntheses and structures of piperazinediones, see: Wen et al. (2006[Wen, Y.-H., Zhang, S.-S., Yu, B.-H., Li, X.-M. & Liu, Q. (2006). Asian J. Chem. 18, 1032-1038.]); Zhang et al. (2007[Zhang, S.-S., Wen, Y.-H., Tang, X.-F. & Li, X.-M. (2007). Chin. J. Chem. 25, 714-717.]).

[Scheme 1]

Experimental

Crystal data
  • C18H18N2O2

  • Mr = 294.34

  • Monoclinic, P 21 /n

  • a = 12.6608 (15) Å

  • b = 6.1508 (7) Å

  • c = 19.223 (2) Å

  • β = 95.142 (2)°

  • V = 1490.9 (3) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.09 mm−1

  • T = 153 K

  • 0.38 × 0.12 × 0.10 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.968, Tmax = 0.991

  • 7835 measured reflections

  • 2836 independent reflections

  • 2078 reflections with I > 2σ(I)

  • Rint = 0.029

Refinement
  • R[F2 > 2σ(F2)] = 0.052

  • wR(F2) = 0.137

  • S = 1.02

  • 2836 reflections

  • 199 parameters

  • H-atom parameters constrained

  • Δρmax = 0.19 e Å−3

  • Δρmin = −0.22 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
C8—H8B⋯O1i 0.97 2.53 3.494 (2) 173
C14—H14A⋯O2i 0.93 2.45 3.325 (3) 158
Symmetry code: (i) x, y+1, z.

Data collection: SMART (Bruker, 2001[Bruker (2001). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2001[Bruker (2001). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

Piperazinediones form an important class of biologically active natural products (Fischer et al., 2003), and represent important precursors for the synthesis of peptides and non-natural amino acids (Paradisi et al., 2002). Recently, piperazinediones have gained importance in drug discovery (Krchnak et al., 1996), and opioid receptor agonists and antagonists (Acharya et al., 2001). Here, we report the crystal structure of the title compound.

The title compound consists of two crystallographically independent C18H18N2O2 molecules in the asymmetric unit of the centrosymmetric space group P21/n (Fig. 1). Each molecule is located on a center of inversion. All bond lengths and angles of two independent molecules are comparable with those in the related compounds (Wen et al., 2006; Zhang et al., 2007). The molecules are not planar showing dihedral angles of 55.84 (9)° and 54.10 (8)° between the piperazinedione and the aromatic rings, which is different from the ortho-substituted isomer 1,4-bis(2-methylphenyl)piperazine-2,5-dione (Wen et al., 2006). The sum of the bond angles around N1 (360.00°) and N2 (359.98°) indicates the piperazine N atoms have also a planar configuration, different from the normal pyramidal configuration of the N atom. This difference is mainly due to the π-conjugation effects arising from the presence of the two C=O double bonds. In addition, the crystal packing exhibit intermolecular C—H···O hydrogen bonds (Table 1, Fig. 2).

Related literature top

For background to the applications of piperazinedione and its derivatives, see: Acharya et al. (2001); Fischer et al. (2003); Krchnak et al. (1996); Paradisi et al. (2002). For the syntheses and structures of piperazinediones, see: Wen et al. (2006); Zhang et al. (2007).

Experimental top

The title compound was prepared according to the literature method (Wen et al., 2006). Colourless single crystals of the title compound suitable for X-ray diffraction study were obtained by slow evaporation of an ethanol solution over a period of 20 d.

Refinement top

All H atoms were positioned geometricallyand constrained to ride on their parent atoms, with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C) for aromatic H atoms, with C—H = 0.97 Å and Uiso(H) = 1.2Ueq(C) for methylene H atoms, and with C—H = 0.96 and Uiso(H) = 1.5Ueq(C) for methyl H atoms.

Structure description top

Piperazinediones form an important class of biologically active natural products (Fischer et al., 2003), and represent important precursors for the synthesis of peptides and non-natural amino acids (Paradisi et al., 2002). Recently, piperazinediones have gained importance in drug discovery (Krchnak et al., 1996), and opioid receptor agonists and antagonists (Acharya et al., 2001). Here, we report the crystal structure of the title compound.

The title compound consists of two crystallographically independent C18H18N2O2 molecules in the asymmetric unit of the centrosymmetric space group P21/n (Fig. 1). Each molecule is located on a center of inversion. All bond lengths and angles of two independent molecules are comparable with those in the related compounds (Wen et al., 2006; Zhang et al., 2007). The molecules are not planar showing dihedral angles of 55.84 (9)° and 54.10 (8)° between the piperazinedione and the aromatic rings, which is different from the ortho-substituted isomer 1,4-bis(2-methylphenyl)piperazine-2,5-dione (Wen et al., 2006). The sum of the bond angles around N1 (360.00°) and N2 (359.98°) indicates the piperazine N atoms have also a planar configuration, different from the normal pyramidal configuration of the N atom. This difference is mainly due to the π-conjugation effects arising from the presence of the two C=O double bonds. In addition, the crystal packing exhibit intermolecular C—H···O hydrogen bonds (Table 1, Fig. 2).

For background to the applications of piperazinedione and its derivatives, see: Acharya et al. (2001); Fischer et al. (2003); Krchnak et al. (1996); Paradisi et al. (2002). For the syntheses and structures of piperazinediones, see: Wen et al. (2006); Zhang et al. (2007).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound, with atom labels and 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. The packing diagram of the title compound, viewed down the c axis, showing the intermolecular hydrogen bonds (dashed lines).
1,4-Bis(3-methylphenyl)piperazine-2,5-dione top
Crystal data top
C18H18N2O2F(000) = 624
Mr = 294.34Dx = 1.311 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 1825 reflections
a = 12.6608 (15) Åθ = 3.2–23.9°
b = 6.1508 (7) ŵ = 0.09 mm1
c = 19.223 (2) ÅT = 153 K
β = 95.142 (2)°Block, colourless
V = 1490.9 (3) Å30.38 × 0.12 × 0.10 mm
Z = 4
Data collection top
Bruker SMART CCD area-detector
diffractometer
2836 independent reflections
Radiation source: fine-focus sealed tube2078 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.029
phi and ω scansθmax = 25.7°, θmin = 1.9°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 1515
Tmin = 0.968, Tmax = 0.991k = 77
7835 measured reflectionsl = 2312
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.052Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.137H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0664P)2 + 0.2932P]
where P = (Fo2 + 2Fc2)/3
2836 reflections(Δ/σ)max < 0.001
199 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.22 e Å3
Crystal data top
C18H18N2O2V = 1490.9 (3) Å3
Mr = 294.34Z = 4
Monoclinic, P21/nMo Kα radiation
a = 12.6608 (15) ŵ = 0.09 mm1
b = 6.1508 (7) ÅT = 153 K
c = 19.223 (2) Å0.38 × 0.12 × 0.10 mm
β = 95.142 (2)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
2836 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
2078 reflections with I > 2σ(I)
Tmin = 0.968, Tmax = 0.991Rint = 0.029
7835 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0520 restraints
wR(F2) = 0.137H-atom parameters constrained
S = 1.02Δρmax = 0.19 e Å3
2836 reflectionsΔρmin = 0.22 e Å3
199 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O20.14816 (10)0.1901 (2)0.50117 (7)0.0517 (4)
N20.09833 (10)0.5171 (2)0.54147 (8)0.0372 (4)
O10.53271 (11)1.1732 (2)0.59161 (8)0.0571 (4)
N10.58560 (11)1.5000 (2)0.55280 (8)0.0423 (4)
C150.19661 (13)0.5530 (3)0.58423 (9)0.0369 (4)
C160.08291 (13)0.3358 (3)0.50265 (9)0.0383 (4)
C140.25272 (14)0.7430 (3)0.57627 (10)0.0432 (5)
H14A0.22750.84700.54380.052*
C60.67677 (14)1.5123 (3)0.60368 (10)0.0434 (5)
C70.52080 (14)1.3255 (3)0.55088 (11)0.0431 (5)
C10.75220 (14)1.3485 (3)0.60645 (10)0.0442 (5)
H1A0.74161.22800.57740.053*
C100.23305 (13)0.4011 (3)0.63376 (9)0.0410 (5)
H10A0.19420.27480.63910.049*
C130.34654 (15)0.7763 (3)0.61707 (11)0.0499 (5)
H13A0.38530.90260.61160.060*
C80.56977 (15)1.6836 (3)0.50490 (11)0.0487 (5)
H8A0.63451.70260.48210.058*
H8B0.56081.81300.53260.058*
C170.02008 (14)0.6913 (3)0.54148 (11)0.0480 (5)
H17A0.05320.82360.52670.058*
H17B0.00380.71340.58930.058*
C120.38306 (15)0.6248 (3)0.66558 (11)0.0505 (5)
H12A0.44680.64930.69240.061*
C110.32667 (14)0.4345 (3)0.67562 (10)0.0443 (5)
C50.69087 (17)1.6911 (3)0.64691 (11)0.0563 (6)
H5A0.64051.80150.64500.068*
C90.92602 (17)1.1862 (4)0.65370 (13)0.0715 (7)
H9A0.90371.07510.62050.107*
H9B0.93531.12430.69970.107*
H9C0.99201.24720.64200.107*
C40.78057 (19)1.7042 (4)0.69301 (12)0.0656 (7)
H4A0.79011.82300.72290.079*
C20.84310 (15)1.3621 (4)0.65189 (10)0.0507 (5)
C180.36529 (18)0.2729 (4)0.73046 (12)0.0676 (7)
H18A0.31670.15280.72980.101*
H18B0.36970.34120.77550.101*
H18C0.43410.22100.72110.101*
C30.85602 (18)1.5430 (4)0.69520 (12)0.0637 (6)
H3A0.91661.55520.72610.076*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O20.0451 (8)0.0387 (7)0.0687 (9)0.0118 (6)0.0098 (7)0.0062 (7)
N20.0339 (8)0.0303 (8)0.0456 (9)0.0019 (6)0.0069 (7)0.0003 (7)
O10.0545 (8)0.0430 (8)0.0724 (10)0.0054 (6)0.0018 (7)0.0148 (7)
N10.0392 (8)0.0338 (8)0.0535 (10)0.0026 (6)0.0027 (7)0.0021 (7)
C150.0342 (9)0.0362 (9)0.0392 (10)0.0025 (7)0.0029 (8)0.0016 (8)
C160.0383 (9)0.0311 (9)0.0445 (11)0.0019 (7)0.0019 (8)0.0034 (8)
C140.0472 (11)0.0374 (10)0.0439 (10)0.0030 (8)0.0015 (9)0.0029 (9)
C60.0432 (10)0.0423 (10)0.0455 (11)0.0072 (8)0.0087 (9)0.0010 (9)
C70.0400 (10)0.0313 (9)0.0592 (12)0.0005 (8)0.0102 (9)0.0007 (9)
C10.0455 (11)0.0457 (11)0.0413 (11)0.0040 (9)0.0031 (9)0.0003 (9)
C100.0378 (10)0.0401 (10)0.0441 (10)0.0011 (8)0.0018 (9)0.0047 (9)
C130.0447 (11)0.0495 (11)0.0544 (12)0.0134 (9)0.0009 (10)0.0011 (10)
C80.0428 (10)0.0357 (10)0.0672 (14)0.0047 (8)0.0027 (10)0.0067 (10)
C170.0431 (10)0.0355 (10)0.0621 (13)0.0075 (8)0.0134 (10)0.0099 (9)
C120.0364 (10)0.0625 (13)0.0506 (12)0.0052 (9)0.0078 (9)0.0038 (10)
C110.0387 (10)0.0530 (12)0.0401 (10)0.0060 (9)0.0025 (8)0.0015 (9)
C50.0569 (13)0.0472 (12)0.0662 (14)0.0086 (10)0.0129 (11)0.0103 (11)
C90.0516 (13)0.0829 (17)0.0775 (17)0.0030 (12)0.0078 (12)0.0164 (14)
C40.0691 (15)0.0647 (15)0.0635 (15)0.0252 (12)0.0093 (13)0.0206 (12)
C20.0451 (11)0.0616 (13)0.0454 (11)0.0088 (10)0.0037 (9)0.0078 (10)
C180.0633 (14)0.0744 (15)0.0606 (14)0.0066 (12)0.0191 (12)0.0146 (13)
C30.0527 (13)0.0801 (17)0.0565 (13)0.0237 (12)0.0040 (11)0.0001 (13)
Geometric parameters (Å, º) top
O2—C161.221 (2)C8—C7ii1.499 (3)
N2—C161.346 (2)C8—H8A0.9700
N2—C151.445 (2)C8—H8B0.9700
N2—C171.459 (2)C17—C16i1.500 (2)
O1—C71.221 (2)C17—H17A0.9700
N1—C71.349 (2)C17—H17B0.9700
N1—C61.446 (2)C12—C111.393 (3)
N1—C81.460 (2)C12—H12A0.9300
C15—C101.383 (2)C11—C181.499 (3)
C15—C141.383 (2)C5—C41.379 (3)
C16—C17i1.500 (2)C5—H5A0.9300
C14—C131.379 (3)C9—C21.505 (3)
C14—H14A0.9300C9—H9A0.9600
C6—C51.380 (3)C9—H9B0.9600
C6—C11.386 (3)C9—H9C0.9600
C7—C8ii1.499 (3)C4—C31.375 (3)
C1—C21.384 (3)C4—H4A0.9300
C1—H1A0.9300C2—C31.391 (3)
C10—C111.387 (2)C18—H18A0.9600
C10—H10A0.9300C18—H18B0.9600
C13—C121.369 (3)C18—H18C0.9600
C13—H13A0.9300C3—H3A0.9300
C16—N2—C15121.08 (14)N2—C17—C16i118.32 (15)
C16—N2—C17122.92 (14)N2—C17—H17A107.7
C15—N2—C17115.97 (14)C16i—C17—H17A107.7
C7—N1—C6120.45 (16)N2—C17—H17B107.7
C7—N1—C8123.32 (15)C16i—C17—H17B107.7
C6—N1—C8116.22 (14)H17A—C17—H17B107.1
C10—C15—C14120.26 (16)C13—C12—C11121.34 (17)
C10—C15—N2120.36 (15)C13—C12—H12A119.3
C14—C15—N2119.37 (15)C11—C12—H12A119.3
O2—C16—N2123.79 (16)C10—C11—C12117.77 (17)
O2—C16—C17i117.46 (16)C10—C11—C18121.18 (18)
N2—C16—C17i118.75 (15)C12—C11—C18121.04 (17)
C13—C14—C15119.16 (17)C4—C5—C6119.2 (2)
C13—C14—H14A120.4C4—C5—H5A120.4
C15—C14—H14A120.4C6—C5—H5A120.4
C5—C6—C1120.31 (18)C2—C9—H9A109.5
C5—C6—N1120.09 (18)C2—C9—H9B109.5
C1—C6—N1119.54 (16)H9A—C9—H9B109.5
O1—C7—N1123.53 (18)C2—C9—H9C109.5
O1—C7—C8ii118.20 (16)H9A—C9—H9C109.5
N1—C7—C8ii118.26 (17)H9B—C9—H9C109.5
C2—C1—C6120.76 (18)C3—C4—C5120.5 (2)
C2—C1—H1A119.6C3—C4—H4A119.7
C6—C1—H1A119.6C5—C4—H4A119.7
C15—C10—C11120.95 (17)C1—C2—C3118.2 (2)
C15—C10—H10A119.5C1—C2—C9120.7 (2)
C11—C10—H10A119.5C3—C2—C9121.12 (19)
C12—C13—C14120.50 (18)C11—C18—H18A109.5
C12—C13—H13A119.8C11—C18—H18B109.5
C14—C13—H13A119.8H18A—C18—H18B109.5
N1—C8—C7ii118.38 (15)C11—C18—H18C109.5
N1—C8—H8A107.7H18A—C18—H18C109.5
C7ii—C8—H8A107.7H18B—C18—H18C109.5
N1—C8—H8B107.7C4—C3—C2121.0 (2)
C7ii—C8—H8B107.7C4—C3—H3A119.5
H8A—C8—H8B107.1C2—C3—H3A119.5
C16—N2—C15—C1055.7 (2)C14—C15—C10—C110.8 (3)
C17—N2—C15—C10126.27 (19)N2—C15—C10—C11179.35 (17)
C16—N2—C15—C14125.74 (19)C15—C14—C13—C120.9 (3)
C17—N2—C15—C1452.3 (2)C7—N1—C8—C7ii2.2 (3)
C15—N2—C16—O21.0 (3)C6—N1—C8—C7ii177.36 (16)
C17—N2—C16—O2178.81 (19)C16—N2—C17—C16i1.3 (3)
C15—N2—C16—C17i179.17 (17)C15—N2—C17—C16i179.26 (16)
C17—N2—C16—C17i1.3 (3)C14—C13—C12—C110.5 (3)
C10—C15—C14—C131.6 (3)C15—C10—C11—C120.6 (3)
N2—C15—C14—C13179.86 (17)C15—C10—C11—C18178.63 (19)
C7—N1—C6—C5126.3 (2)C13—C12—C11—C101.3 (3)
C8—N1—C6—C554.1 (2)C13—C12—C11—C18177.93 (19)
C7—N1—C6—C156.7 (2)C1—C6—C5—C40.3 (3)
C8—N1—C6—C1122.93 (19)N1—C6—C5—C4177.27 (19)
C6—N1—C7—O11.7 (3)C6—C5—C4—C31.1 (3)
C8—N1—C7—O1178.69 (18)C6—C1—C2—C30.8 (3)
C6—N1—C7—C8ii177.35 (17)C6—C1—C2—C9178.7 (2)
C8—N1—C7—C8ii2.2 (3)C5—C4—C3—C20.9 (4)
C5—C6—C1—C20.7 (3)C1—C2—C3—C40.0 (3)
N1—C6—C1—C2176.35 (17)C9—C2—C3—C4179.4 (2)
Symmetry codes: (i) x, y+1, z+1; (ii) x+1, y+3, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C8—H8B···O1iii0.972.533.494 (2)173
C14—H14A···O2iii0.932.453.325 (3)158
Symmetry code: (iii) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC18H18N2O2
Mr294.34
Crystal system, space groupMonoclinic, P21/n
Temperature (K)153
a, b, c (Å)12.6608 (15), 6.1508 (7), 19.223 (2)
β (°) 95.142 (2)
V3)1490.9 (3)
Z4
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.38 × 0.12 × 0.10
Data collection
DiffractometerBruker SMART CCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.968, 0.991
No. of measured, independent and
observed [I > 2σ(I)] reflections
7835, 2836, 2078
Rint0.029
(sin θ/λ)max1)0.610
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.052, 0.137, 1.02
No. of reflections2836
No. of parameters199
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.19, 0.22

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2001), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C8—H8B···O1i0.97002.53003.494 (2)173.00
C14—H14A···O2i0.93002.45003.325 (3)158.00
Symmetry code: (i) x, y+1, z.
 

Acknowledgements

The project was supported by the Promotive Research Fund for Excellent Young and Middle-Aged Scientists of Shandong Province (BS2011CL019).

References

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