research communications
H-purin-9-ido)magnesium
of tetraaquabis(1,3-dimethyl-2,6-dioxo-3,7-dihydro-1aDepartment of Chemistry and Chemical Engineering, Minjiang University, Fuzhou 350108, People's Republic of China
*Correspondence e-mail: lby@mju.edu.cn
The title complex, [Mg(C7H7N4O2)2(H2O)4], lies across an inversion centre and the MgII atom is coordinated in a slightly distorted octahedral environment by four aqua ligands in the equatorial sites and two 1,3-dimethyl-2,6-dioxo-3,7-dihydro-1H-purin-9-ide ligands, through imidazole ring N atoms, in the axial sites. An intramolecular O—H⋯O hydrogen bond forms an S(7) graph-set motif. In the crystal, O—H⋯O and O—H⋯N hydrogen bonds link complex molecules forming a three-dimensional network incorporating R42(8) and R22(18) graph-set motifs.
CCDC reference: 1050901
1. Chemical context
Co-crystallization represents a crystal engineering approach for modifying properties of active pharmaceutical ingredients (APIs) (Sun, 2013). Metal coordination is an alternative strategy without changing chemical structures of APIs (Ma & Moulton, 2007). Theophylline is a methylxanthine drug in the treatment of asthma and chronic obstructive pulmonary disease (Barnes, 2003). In this study, we reacted theophylline with the MgII ion in a basic solution to give rise to a tetraaqua mononuclear MgII complex, (I).
2. Structural commentary
The molecular structure of (I) is shown in Fig. 1. The complex lies across an inversion centre and the MgII atom is coordinated in a slightly distorted octahedral environment (Table 1) by four aqua ligands in the equatorial sites and two 1,3-dimethyl-2,6-dioxo-3,7-dihydro-1H-purin-9-ide ligands, through imidazole ring N atoms [N1 and N1(−x + 1, −y, −z + 1)], in the axial sites. The symmetry-unique purine ring system is essentially planar, with a maximum deviation of 0.030 (2) Å for N3 and the bonded methyl C atoms C4 and C5 deviate from this mean plane by −0.118 (3) and 0.136 (2) Å, respectively.
3. Supramolecular features
In the crystal, the coordinating water molecules are involved in various hydrogen-bonding interactions (Table 2). A (8) graph-set motif (Bernstein et al., 1995) is formed through [O4⋯O1iii = 2.829 (3) Å and O4⋯O1iv = 2.780 (2) Å; symmetry codes: (iii) −x, −y, −z; (iv) x, y, z + 1] between a coordinating water molecule and a carbonyl group of a symmetry-related theophylline group. The mononuclear units are connected into a layer parallel to (010) (Fig. 2), which is further connected into a three-dimensional structure (Fig. 3) by hydrogen-bonding interactions between coordinating water molecules and symmetry-related imidazole groups [O3⋯N2ii = 2.809 (3) Å; symmetry code: (ii) x, −y + , z + ].
4. Database survey
A search of the Cambridge Structural Database (Version 5.36, November 2014; Groom & Allen, 2014) revealed 16 metal complexes of theophylline, including ternary, polynuclear complexes and coordination polymers but only five are mononuclear complexes. The most closely related compound to the title complex, in terms of the ligand types is triaquabis(theophylline)copper(II) dihydrate (WEZYIJ; Begum & Manohar, 1994). The title compound is the first reported to date of a complex of theophylline with an alkaline-earth metal.
5. Synthesis and crystallization
Theophylline (180 mg, 1 mmol) was dissolved in water (20 ml). An aqueous solution (15 ml) of NaOH (40 mg, 1 mmol) was added slowly. MgCl2·6H2O (102 mg, 0.5 mmol) in water (15 ml) was then added. The resulting solution was kept in air and, after several days, colourless block-shaped crystals were obtained.
6. Refinement
Crystal data, data collection and structure . H atoms bonded to C atoms were positioned geometrically (C—H = 0.95–0.98 Å) with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(C). H atoms bonded to O atoms were located in difference Fourier maps and were refined with a distance restraint of O—H = 0.87 (1) Å. The isotropic displacement parameters were refined freely.
details are summarized in Table 3Supporting information
CCDC reference: 1050901
10.1107/S2056989015003758/lh5752sup1.cif
contains datablocks I, LOU. DOI:Structure factors: contains datablock I. DOI: 10.1107/S2056989015003758/lh5752Isup2.hkl
Co-crystallization represents a crystal engineering approach for modifying properties of active pharmaceutical ingredients (APIs) (Sun, 2013). Metal coordination is an alternative strategy without changing chemical structures of APIs (Ma & Moulton, 2007). Theophylline is a methylxanthine drug in the treatment of asthma and chronic obstructive pulmonary disease (Barnes, 2003). In this paper, we reacted theophylline with the MgII ion in a basic solution to give rise to a tetraaqua mononuclear MgII complex, (I).
The molecular structure of (I) is shown in Fig. 1. The complex lies across an inversion centre and the the MgII atom is coordinated in a slightly distorted octahedral environment by four aqua ligands in the equatorial sites and two 1,3-dimethyl-2,6-dioxo-3,7-dihydro-1H-purin-9-ide ligands, through imidazole ring N atoms [N1 and N1(-x + 1, -y, -z + 1)], in the axial sites. The symmetry-unique purine ring system is essentially planar, with a maximum deviation of 0.030 (2) Å for N3 and the bonded methyl C atoms C4 and C5 deviate from this mean plane by -0.118 (3) and 0.136 (2) Å, respectively.
In the crystal, the coordinating water molecules are involved in various hydrogen-bonding interactions. A synthon with graph-set motif R42(8) (Bernstein et al., 1995) is formed through [O4···O1iii = 2.829 (3) Å and O4···O1iv = 2.780 (2) Å; symmetry codes: (iii) -x, -y, -z; (iv) x, y, z + 1] between a coordinating water molecule and a carbonyl group of a symmetry-related theophylline group. The mononuclear units are connected into a layer parallel to (???) (Fig. 2), which is further connected into a three-dimensional structure (Fig. 3) by hydrogen-bonding interactions between coordinating water molecules and symmetry-related imidazole groups [O3···N2ii = 2.809 (3) Å; symmetry code: (ii) x, -y+1/2, z+1/2].
A search of the Cambridge Structural Database (Version 5.36, November 2014; Groom & Allen, 2014) revealed 16 metal complexes of theophylline including ternary, polynuclear complexes and coordination polymers but only five are mononuclear complexes. The most closely related compound to the title complex, in terms of the ligand types is triaquabis(theophylline)copper(II) dihydrate (WEZYIJ; Begum & Manohar, 1994). The title compound is the first
reported to date of a complex of theophylline with an alkaline-earth metal.Theophylline (180 mg, 1 mmol) was dissolved in water (20 ml). An aqueous solution (15 ml) of NaOH (40 mg, 1 mmol) was added slowly. MgCl2·6H2O (102 mg, 0.5 mmol) in water (15 ml) was then added. The resulting solution was kept in air and, after several days, colourless block-shaped crystals were obtained.
H atoms bonded to C atoms were positioned geometrically (C—H = 0.95–0.98 Å) with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(C). H atoms bonded to O atoms were located in difference Fourier maps and were refined with a distance restraint of O—H = 0.87 (1) Å. The isotropic displacement parameters were refined freely.
Data collection: CrystalClear (Rigaku, 2000); cell
CrystalClear (Rigaku, 2000); data reduction: CrystalClear (Rigaku, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).Fig. 1. The molecular structure of the title complex, shown with 30% probability displacement ellipsoids [symmetry code: (A) x, -y, -z + 1). | |
Fig. 2. Part of the crystal structure, showing hydrogen bonds in two dimensions (dashed lines). | |
Fig. 3. Part of the crystal structure, showing the overall three-dimensional hydrogen-bonded structure (dashed lines). |
[Mg(C7H7N4O2)2(H2O)4] | F(000) = 476 |
Mr = 454.71 | Dx = 1.558 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 2170 reflections |
a = 7.694 (4) Å | θ = 2.7–27.5° |
b = 13.399 (7) Å | µ = 0.16 mm−1 |
c = 9.739 (5) Å | T = 295 K |
β = 105.169 (9)° | Prism, colorless |
V = 969.0 (9) Å3 | 0.2 × 0.2 × 0.2 mm |
Z = 2 |
Rigaku CCD diffractometer | 2153 independent reflections |
Radiation source: fine-focus sealed tube | 1738 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.032 |
Detector resolution: 14.6306 pixels mm-1 | θmax = 27.5°, θmin = 2.7° |
CCD_Profile_fitting scans | h = −8→9 |
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000) | k = −17→17 |
Tmin = 0.949, Tmax = 1.000 | l = −11→12 |
7442 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.049 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.123 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0542P)2 + 0.4099P] where P = (Fo2 + 2Fc2)/3 |
2153 reflections | (Δ/σ)max < 0.001 |
160 parameters | Δρmax = 0.29 e Å−3 |
4 restraints | Δρmin = −0.25 e Å−3 |
[Mg(C7H7N4O2)2(H2O)4] | V = 969.0 (9) Å3 |
Mr = 454.71 | Z = 2 |
Monoclinic, P21/c | Mo Kα radiation |
a = 7.694 (4) Å | µ = 0.16 mm−1 |
b = 13.399 (7) Å | T = 295 K |
c = 9.739 (5) Å | 0.2 × 0.2 × 0.2 mm |
β = 105.169 (9)° |
Rigaku CCD diffractometer | 2153 independent reflections |
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000) | 1738 reflections with I > 2σ(I) |
Tmin = 0.949, Tmax = 1.000 | Rint = 0.032 |
7442 measured reflections |
R[F2 > 2σ(F2)] = 0.049 | 4 restraints |
wR(F2) = 0.123 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | Δρmax = 0.29 e Å−3 |
2153 reflections | Δρmin = −0.25 e Å−3 |
160 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Mg1 | 0.5000 | 0.0000 | 0.5000 | 0.0220 (2) | |
O1 | 0.0856 (2) | −0.02565 (12) | −0.27579 (14) | 0.0366 (4) | |
O2 | 0.2118 (2) | −0.14692 (11) | 0.17770 (15) | 0.0396 (4) | |
O3 | 0.5654 (2) | 0.14587 (11) | 0.56135 (16) | 0.0361 (4) | |
O4 | 0.2306 (2) | 0.02272 (14) | 0.49391 (16) | 0.0419 (4) | |
N1 | 0.4375 (2) | 0.04557 (11) | 0.27257 (16) | 0.0253 (4) | |
N2 | 0.4425 (2) | 0.16133 (12) | 0.09955 (17) | 0.0295 (4) | |
N3 | 0.2518 (2) | 0.07368 (12) | −0.10112 (17) | 0.0277 (4) | |
N4 | 0.1533 (2) | −0.08355 (12) | −0.04781 (17) | 0.0260 (4) | |
C1 | 0.4967 (3) | 0.13335 (14) | 0.2386 (2) | 0.0285 (4) | |
H1 | 0.5733 | 0.1745 | 0.3083 | 0.034* | |
C2 | 0.3344 (2) | 0.01127 (14) | 0.14086 (19) | 0.0231 (4) | |
C3 | 0.3417 (3) | 0.08329 (14) | 0.0411 (2) | 0.0241 (4) | |
C4 | 0.2540 (4) | 0.15494 (17) | −0.2003 (2) | 0.0426 (6) | |
H4A | 0.3623 | 0.1497 | −0.2350 | 0.064* | |
H4B | 0.2543 | 0.2190 | −0.1517 | 0.064* | |
H4C | 0.1468 | 0.1507 | −0.2809 | 0.064* | |
C5 | 0.0602 (3) | −0.17694 (16) | −0.1029 (2) | 0.0379 (5) | |
H5A | −0.0695 | −0.1645 | −0.1367 | 0.057* | |
H5B | 0.0827 | −0.2270 | −0.0269 | 0.057* | |
H5C | 0.1054 | −0.2016 | −0.1819 | 0.057* | |
C6 | 0.1602 (2) | −0.01192 (15) | −0.1483 (2) | 0.0263 (4) | |
C7 | 0.2344 (3) | −0.07757 (14) | 0.1001 (2) | 0.0256 (4) | |
H3A | 0.505 (3) | 0.2015 (13) | 0.557 (3) | 0.058 (8)* | |
H3B | 0.644 (3) | 0.149 (2) | 0.6439 (17) | 0.059 (9)* | |
H4D | 0.188 (4) | 0.007 (2) | 0.566 (2) | 0.072 (10)* | |
H4E | 0.142 (3) | 0.023 (2) | 0.4175 (19) | 0.055 (8)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mg1 | 0.0247 (5) | 0.0223 (4) | 0.0169 (5) | 0.0003 (3) | 0.0018 (3) | 0.0002 (3) |
O1 | 0.0312 (8) | 0.0563 (10) | 0.0181 (7) | −0.0009 (7) | −0.0013 (6) | −0.0023 (6) |
O2 | 0.0501 (9) | 0.0329 (8) | 0.0287 (8) | −0.0141 (7) | −0.0021 (7) | 0.0066 (6) |
O3 | 0.0495 (10) | 0.0243 (7) | 0.0278 (8) | 0.0015 (7) | −0.0020 (7) | −0.0018 (6) |
O4 | 0.0278 (8) | 0.0722 (12) | 0.0239 (9) | 0.0027 (8) | 0.0034 (7) | 0.0008 (8) |
N1 | 0.0292 (9) | 0.0234 (8) | 0.0207 (8) | −0.0013 (6) | 0.0022 (7) | −0.0005 (6) |
N2 | 0.0375 (9) | 0.0255 (8) | 0.0238 (9) | −0.0042 (7) | 0.0052 (7) | 0.0021 (6) |
N3 | 0.0311 (9) | 0.0309 (9) | 0.0189 (8) | 0.0003 (7) | 0.0026 (7) | 0.0055 (6) |
N4 | 0.0252 (8) | 0.0274 (8) | 0.0225 (8) | −0.0018 (6) | 0.0010 (7) | −0.0027 (6) |
C1 | 0.0323 (10) | 0.0253 (10) | 0.0257 (10) | −0.0041 (8) | 0.0037 (8) | −0.0012 (8) |
C2 | 0.0242 (9) | 0.0244 (9) | 0.0193 (9) | 0.0017 (7) | 0.0035 (7) | 0.0005 (7) |
C3 | 0.0248 (9) | 0.0253 (9) | 0.0211 (9) | 0.0040 (7) | 0.0042 (7) | 0.0007 (7) |
C4 | 0.0566 (15) | 0.0412 (13) | 0.0274 (12) | 0.0027 (11) | 0.0064 (10) | 0.0114 (9) |
C5 | 0.0399 (12) | 0.0357 (11) | 0.0332 (12) | −0.0078 (9) | 0.0011 (10) | −0.0100 (9) |
C6 | 0.0202 (9) | 0.0367 (11) | 0.0205 (10) | 0.0047 (8) | 0.0029 (7) | −0.0006 (8) |
C7 | 0.0257 (10) | 0.0274 (9) | 0.0223 (10) | 0.0003 (7) | 0.0039 (8) | 0.0000 (7) |
Mg1—O3i | 2.0672 (17) | N3—C6 | 1.361 (3) |
Mg1—O3 | 2.0672 (17) | N3—C3 | 1.383 (2) |
Mg1—O4i | 2.081 (2) | N3—C4 | 1.459 (3) |
Mg1—O4 | 2.081 (2) | N4—C6 | 1.382 (3) |
Mg1—N1i | 2.2255 (19) | N4—C7 | 1.414 (3) |
Mg1—N1 | 2.2255 (19) | N4—C5 | 1.472 (3) |
O1—C6 | 1.238 (2) | C1—H1 | 0.9500 |
O2—C7 | 1.238 (2) | C2—C3 | 1.381 (3) |
O3—H3A | 0.875 (10) | C2—C7 | 1.416 (3) |
O3—H3B | 0.872 (10) | C4—H4A | 0.9800 |
O4—H4D | 0.873 (10) | C4—H4B | 0.9800 |
O4—H4E | 0.867 (10) | C4—H4C | 0.9800 |
N1—C1 | 1.334 (3) | C5—H5A | 0.9800 |
N1—C2 | 1.398 (2) | C5—H5B | 0.9800 |
N2—C3 | 1.337 (2) | C5—H5C | 0.9800 |
N2—C1 | 1.361 (3) | ||
O3i—Mg1—O3 | 180.00 (3) | C6—N4—C5 | 115.94 (16) |
O3i—Mg1—O4i | 92.02 (7) | C7—N4—C5 | 117.55 (16) |
O3—Mg1—O4i | 87.98 (7) | N1—C1—N2 | 116.97 (17) |
O3i—Mg1—O4 | 87.98 (7) | N1—C1—H1 | 121.5 |
O3—Mg1—O4 | 92.02 (7) | N2—C1—H1 | 121.5 |
O4i—Mg1—O4 | 180.0 | C3—C2—N1 | 107.34 (17) |
O3i—Mg1—N1i | 90.06 (6) | C3—C2—C7 | 120.60 (17) |
O3—Mg1—N1i | 89.94 (6) | N1—C2—C7 | 132.06 (17) |
O4i—Mg1—N1i | 88.69 (6) | N2—C3—C2 | 111.89 (17) |
O4—Mg1—N1i | 91.31 (6) | N2—C3—N3 | 125.57 (17) |
O3i—Mg1—N1 | 89.94 (6) | C2—C3—N3 | 122.53 (17) |
O3—Mg1—N1 | 90.06 (6) | N3—C4—H4A | 109.5 |
O4i—Mg1—N1 | 91.31 (6) | N3—C4—H4B | 109.5 |
O4—Mg1—N1 | 88.69 (6) | H4A—C4—H4B | 109.5 |
N1i—Mg1—N1 | 180.0 | N3—C4—H4C | 109.5 |
Mg1—O3—H3A | 135.0 (19) | H4A—C4—H4C | 109.5 |
Mg1—O3—H3B | 111.8 (19) | H4B—C4—H4C | 109.5 |
H3A—O3—H3B | 103 (3) | N4—C5—H5A | 109.5 |
Mg1—O4—H4D | 122 (2) | N4—C5—H5B | 109.5 |
Mg1—O4—H4E | 125.3 (19) | H5A—C5—H5B | 109.5 |
H4D—O4—H4E | 108 (3) | N4—C5—H5C | 109.5 |
C1—N1—C2 | 102.20 (16) | H5A—C5—H5C | 109.5 |
C1—N1—Mg1 | 119.32 (12) | H5B—C5—H5C | 109.5 |
C2—N1—Mg1 | 138.26 (13) | O1—C6—N3 | 121.81 (19) |
C3—N2—C1 | 101.59 (16) | O1—C6—N4 | 120.91 (19) |
C6—N3—C3 | 119.72 (16) | N3—C6—N4 | 117.28 (17) |
C6—N3—C4 | 120.00 (17) | O2—C7—N4 | 118.96 (17) |
C3—N3—C4 | 120.28 (17) | O2—C7—C2 | 127.74 (18) |
C6—N4—C7 | 126.42 (16) | N4—C7—C2 | 113.31 (17) |
Symmetry code: (i) −x+1, −y, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3A···N2ii | 0.88 (1) | 1.97 (1) | 2.809 (3) | 160 (3) |
O3—H3B···O2i | 0.87 (1) | 1.80 (1) | 2.668 (2) | 173 (3) |
O4—H4E···O1iii | 0.87 (1) | 1.93 (1) | 2.780 (2) | 168 (3) |
O4—H4D···O1iv | 0.87 (1) | 1.96 (1) | 2.829 (3) | 178 (3) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) x, −y+1/2, z+1/2; (iii) −x, −y, −z; (iv) x, y, z+1. |
Mg1—O3i | 2.0672 (17) | Mg1—N1i | 2.2255 (19) |
Mg1—O4i | 2.081 (2) | ||
O3i—Mg1—O3 | 180.00 (3) | O4—Mg1—N1i | 91.31 (6) |
O3—Mg1—O4i | 87.98 (7) | O3—Mg1—N1 | 90.06 (6) |
O3—Mg1—O4 | 92.02 (7) | O4—Mg1—N1 | 88.69 (6) |
O4i—Mg1—O4 | 180.0 | N1i—Mg1—N1 | 180.0 |
O3—Mg1—N1i | 89.94 (6) |
Symmetry code: (i) −x+1, −y, −z+1. |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3A···N2ii | 0.875 (10) | 1.970 (14) | 2.809 (3) | 160 (3) |
O3—H3B···O2i | 0.872 (10) | 1.800 (11) | 2.668 (2) | 173 (3) |
O4—H4E···O1iii | 0.867 (10) | 1.926 (12) | 2.780 (2) | 168 (3) |
O4—H4D···O1iv | 0.873 (10) | 1.956 (11) | 2.829 (3) | 178 (3) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) x, −y+1/2, z+1/2; (iii) −x, −y, −z; (iv) x, y, z+1. |
Experimental details
Crystal data | |
Chemical formula | [Mg(C7H7N4O2)2(H2O)4] |
Mr | 454.71 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 295 |
a, b, c (Å) | 7.694 (4), 13.399 (7), 9.739 (5) |
β (°) | 105.169 (9) |
V (Å3) | 969.0 (9) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.16 |
Crystal size (mm) | 0.2 × 0.2 × 0.2 |
Data collection | |
Diffractometer | Rigaku CCD diffractometer |
Absorption correction | Multi-scan (CrystalClear; Rigaku, 2000) |
Tmin, Tmax | 0.949, 1.000 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7442, 2153, 1738 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.650 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.049, 0.123, 1.09 |
No. of reflections | 2153 |
No. of parameters | 160 |
No. of restraints | 4 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.29, −0.25 |
Computer programs: CrystalClear (Rigaku, 2000), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), X-SEED (Barbour, 2001).
Acknowledgements
The authors are grateful for grants from the Research Project for Young and Middle-aged Faculty of Fujian Province (JA14250) and the Undergraduate Innovative Research Program of Minjiang University (201310395059).
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