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Acta Cryst. (2009). E65, o1534    [ doi:10.1107/S1600536809020959 ]

3,3'-Di-tert-butyl-2'-hydroxy-5,5',6,6'-tetramethylbiphenyl-2-yl benzenesulfonate

P.-S. Chen, C.-H. Lin and B.-T. Ko

Abstract top

In the title compound, C30H38O4S, the hydroxyl group bonded to one phenyl ring and an O atom of the benzenesulfonate group attached to the other phenyl ring of the biphenyl backbone of the structure are involved in an intramolecular O-H...O hydrogen bond. The dihedral angle between the planes of the two aromatic rings of the biphenyl unit is 70.4 (2)°.

Comment top

During the last decade, bulky bis(phenolate) compounds have been attracting considerable attention, mainly due to their importance in the development of coordination chemistry related to catalytic applications. These bulky ligands are designed to provide a steric barrier around active metal center for minimizing the side reaction. Bulky binolate ligand, 5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-bi-2,2'-phenolate (BIPHEN2-) has proved to be important in ring-closing metathesis reactions in both its racemic and resolved forms (La et al., 1998). Recently, a series of binolate metal complexes where the metal atoms are Li, Zn and Al have been synthesized, structurally characterized and studied for the catalytic activity of lactide polymerization (Chisholm et al., 2003). Most recently, Wu and his co-workers, (Wu et al., 2008) have also reported the magnesium complexes supported by mono-benzenesulfonylate phenol ligand and these complexes have been demonstrated as efficient initiators to catalyze ring-opening polymerization of lactides. Our group is interested in the synthesis and preparation of monovalent phenol derived from BIPHEN-H2. Here, we report the synthesis and crystal structure of the title compound, (I), a potential ligand for the preparation of magnesium and zinc complexes.

The structure of (I) is composed of a biphenyl moiety containing a benzenesulfonate and a hydroxyl group (Fig. 1). The dihedral angle between the planes of the two aromatic rings of the biphenyl unit is 70.4 (2)°. There is an intramolecular O—H···O hydrogen bond between the phenol and benzenesulfonate groups (Table 1). The distance of O4···H is substantially shorter than the van der Waals distance of 2.77 Å for the O and H distance. However, the distances O4···H and O4···O1 are around 0.3-0.4 Å longer than that found in the other mono-sulfonylated biaryl derivative with an intermolecular hydrogen-bonded motif (1.97 Å & 2.795 (2) Å; Solinas et al., 2007).

Related literature top

For the use of the binolate ligand 5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-bi-2,2'-phenolate in ring-closing metathesis reactions in both its racemic and resolved forms, see: Chisholm et al. (2003); La et al. (1998); For binolate–metal complexes, see: Chisholm et al. (2003); Wu et al. (2008). For related structures: see: Solinas et al. (2007).

Experimental top

The title compound (I) was synthesized by the following procedures (Scheme 2): 3,3'-di-tert-butyl-5,5',6,6'-tetramethylbiphenyl-2,2'-diol (1.24 g, 3.50 mmol), benzenesulfonyl chloride (0.45 mL, 3.50 mmol) and 4-(dimethylamino)pyridine (DMAP, 0.069 g, 0.57 mmol, catalyst) were dissolved in 50 mL of freshly distilled CH2Cl2 and the resulting solution cooled to 273 K. Neat triethylamine (NEt3, 0.6 mL, 3.85 mmol) was added dropwise to the solution, which was then stirred at ambient temperature for 48 h. The solution was filtered, and the filtrate was washed with 50 mL of water three times. The dichloromethane layer was collected and dried over anhydrous MgSO4 and filtered through Celite again to remove MgSO4. The resulting filtrate was then dried under vacuum to obtain the white solids (yield: 78 %). The resulting solid was crystallized from a toluene solution to yield colourless crystals of (I).

Refinement top

The H atoms were placed in idealized positions and constrained to ride on their parent atoms, with C—H = 0.93 and 0.96 Å allowing Uiso(H) = 1.2 and 1.5Ueq(C) for aryl and methyl groups, respectively; for hydroxy group, O—H = 0.82 Å and Uiso(H) = 1.2Ueq(O).

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT-Plus (Bruker, 2008); data reduction: SAINT-Plus (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. A view of the molecular structure of (I) with the atomn umbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
[Figure 2] Fig. 2. The formation of the title compound.
3,3'-Di-tert-butyl-2'-hydroxy-5,5',6,6'-tetramethylbiphenyl-2-yl benzenesulfonate top
Crystal data top
C30H38O4SF(000) = 1064
Mr = 494.66Dx = 1.215 Mg m−3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3976 reflections
a = 9.9909 (7) Åθ = 2.5–22.8°
b = 13.3610 (11) ŵ = 0.15 mm−1
c = 20.2884 (16) ÅT = 296 K
β = 93.428 (3)°Columnar, colourless
V = 2703.4 (4) Å30.30 × 0.20 × 0.18 mm
Z = 4
Data collection top
Bruker APEXII CCD
diffractometer		6653 independent reflections
Radiation source: fine-focus sealed tube3695 reflections with I > 2σ(I)
graphiteRint = 0.055
φ and ω scansθmax = 28.4°, θmin = 1.8°
Absorption correction: multi-scan
(SADABS; Bruker, 2008)		h = −13→8
Tmin = 0.964, Tmax = 0.973k = −17→17
24566 measured reflectionsl = −26→26
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)] = 0.056Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.164H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0774P)2 + 0.1593P]
where P = (Fo2 + 2Fc2)/3
6653 reflections(Δ/σ)max < 0.001
316 parametersΔρmax = 0.33 e Å−3
0 restraintsΔρmin = −0.31 e Å−3
Crystal data top
C30H38O4SV = 2703.4 (4) Å3
Mr = 494.66Z = 4
Monoclinic, P21/cMo Kα radiation
a = 9.9909 (7) ŵ = 0.15 mm−1
b = 13.3610 (11) ÅT = 296 K
c = 20.2884 (16) Å0.30 × 0.20 × 0.18 mm
β = 93.428 (3)°
Data collection top
Bruker APEXII CCD
diffractometer		6653 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2008)		3695 reflections with I > 2σ(I)
Tmin = 0.964, Tmax = 0.973Rint = 0.055
24566 measured reflectionsθmax = 28.4°
Refinement top
R[F2 > 2σ(F2)] = 0.056H-atom parameters constrained
wR(F2) = 0.164Δρmax = 0.33 e Å−3
S = 1.02Δρmin = −0.31 e Å−3
6653 reflectionsAbsolute structure: ?
316 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Experimental. 1H NMR (CDCl3, ppm): δ 7.20-7.46 (6H, m, ArH), 6.68 (1H, s, ArH), 5.00 (1H, s, OH), 2.32 (1H, s, CH3), 1.77 (1H, s, CH3), 1.74 (1H, s, CH3), 1.59 (9H, s, C(CH3)3), 1.50 (1H, s, CH3), 1.45 (9H, s, C(CH3)3).

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
S0.36621 (6)0.38183 (5)0.17811 (3)0.04538 (19)
O10.65811 (15)0.19585 (13)0.25711 (8)0.0520 (5)
H1A0.57980.21180.26120.078*
O20.39067 (14)0.32215 (11)0.11199 (7)0.0418 (4)
O30.23658 (16)0.42523 (15)0.16868 (11)0.0713 (6)
O40.39560 (19)0.31853 (13)0.23306 (8)0.0614 (5)
C10.7141 (2)0.25910 (17)0.21289 (11)0.0372 (5)
C20.8289 (2)0.31260 (18)0.23429 (11)0.0403 (5)
C30.8784 (2)0.37703 (18)0.18794 (12)0.0438 (6)
H3B0.95350.41510.20080.053*
C40.8245 (2)0.38863 (17)0.12427 (12)0.0425 (6)
C50.7154 (2)0.32891 (18)0.10304 (11)0.0401 (5)
C60.6595 (2)0.26372 (17)0.14839 (11)0.0357 (5)
C70.5539 (2)0.18961 (16)0.12617 (10)0.0354 (5)
C80.5890 (2)0.08878 (18)0.12009 (11)0.0397 (5)
C90.4930 (2)0.01987 (17)0.09643 (11)0.0403 (5)
C100.3647 (2)0.05417 (17)0.07881 (11)0.0401 (5)
H10A0.30200.00760.06250.048*
C110.3231 (2)0.15299 (17)0.08380 (10)0.0360 (5)
C120.4217 (2)0.21839 (16)0.10941 (10)0.0343 (5)
C130.8876 (3)0.4624 (2)0.07860 (14)0.0648 (8)
H13A0.96070.49610.10210.097*
H13B0.82170.51070.06320.097*
H13C0.92030.42720.04160.097*
C140.6595 (3)0.3336 (2)0.03255 (12)0.0587 (7)
H14A0.70950.38140.00860.088*
H14B0.56710.35360.03160.088*
H14C0.66630.26890.01250.088*
C150.7310 (2)0.0537 (2)0.13777 (14)0.0599 (7)
H15A0.78460.10960.15330.090*
H15B0.76840.02560.09940.090*
H15C0.72990.00390.17180.090*
C160.5247 (2)−0.08952 (19)0.08847 (13)0.0549 (7)
H16A0.4457−0.12420.07160.082*
H16B0.5541−0.11720.13050.082*
H16C0.5943−0.09690.05820.082*
C170.8981 (2)0.2976 (2)0.30302 (12)0.0506 (6)
C180.9429 (3)0.1879 (2)0.31150 (15)0.0734 (9)
H18A0.86620.14480.30570.110*
H18B0.98450.17860.35490.110*
H18C1.00590.17200.27910.110*
C191.0244 (3)0.3626 (3)0.31303 (15)0.0776 (10)
H19A1.00020.43190.30830.116*
H19B1.08660.34520.28060.116*
H19C1.06520.35140.35640.116*
C200.8038 (3)0.3252 (3)0.35657 (13)0.0757 (9)
H20A0.77670.39380.35130.114*
H20B0.84920.31640.39920.114*
H20C0.72610.28290.35290.114*
C210.1775 (2)0.18286 (18)0.06284 (12)0.0428 (6)
C220.1001 (2)0.2033 (2)0.12392 (14)0.0609 (8)
H22A0.14260.25670.14890.091*
H22B0.09930.14400.15060.091*
H22C0.00970.22200.11070.091*
C230.1028 (2)0.0976 (2)0.02594 (15)0.0625 (8)
H23A0.01270.11830.01370.094*
H23B0.10090.03990.05400.094*
H23C0.14800.0812−0.01310.094*
C240.1724 (3)0.2737 (2)0.01644 (15)0.0714 (9)
H24A0.21810.32900.03790.107*
H24B0.08060.29170.00570.107*
H24C0.21520.2572−0.02330.107*
C250.4840 (2)0.47824 (17)0.17560 (11)0.0402 (5)
C260.4767 (3)0.5430 (2)0.12214 (13)0.0592 (7)
H26A0.41300.53310.08740.071*
C270.5643 (3)0.6219 (2)0.12097 (16)0.0681 (8)
H27A0.56140.66480.08480.082*
C280.6552 (3)0.6378 (2)0.17246 (16)0.0652 (8)
H28A0.71400.69170.17150.078*
C290.6605 (3)0.5750 (2)0.22544 (15)0.0627 (8)
H29A0.72230.58690.26070.075*
C300.5747 (2)0.4935 (2)0.22742 (12)0.0492 (6)
H30A0.57910.45020.26340.059*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S0.0427 (3)0.0365 (4)0.0576 (4)−0.0017 (3)0.0083 (3)−0.0061 (3)
O10.0436 (9)0.0635 (12)0.0487 (10)−0.0086 (8)0.0011 (7)0.0110 (9)
O20.0448 (8)0.0324 (9)0.0471 (9)0.0014 (7)−0.0058 (7)−0.0024 (7)
O30.0406 (10)0.0567 (12)0.1176 (17)0.0051 (9)0.0124 (10)−0.0200 (12)
O40.0897 (14)0.0449 (11)0.0511 (11)−0.0069 (10)0.0174 (9)0.0024 (9)
C10.0339 (11)0.0369 (13)0.0409 (13)0.0006 (9)0.0034 (9)0.0030 (10)
C20.0316 (11)0.0422 (14)0.0468 (14)0.0012 (10)0.0004 (10)−0.0057 (11)
C30.0319 (11)0.0409 (14)0.0584 (16)−0.0040 (10)0.0019 (10)−0.0043 (12)
C40.0364 (11)0.0364 (13)0.0553 (15)−0.0015 (10)0.0076 (10)0.0019 (11)
C50.0363 (11)0.0396 (14)0.0443 (13)0.0030 (10)0.0020 (10)0.0005 (11)
C60.0306 (10)0.0349 (13)0.0414 (13)0.0003 (9)0.0008 (9)−0.0021 (10)
C70.0331 (10)0.0340 (12)0.0389 (12)0.0004 (9)0.0013 (9)−0.0002 (10)
C80.0376 (11)0.0406 (14)0.0409 (13)0.0027 (10)0.0034 (9)−0.0022 (11)
C90.0467 (13)0.0344 (13)0.0405 (13)0.0005 (10)0.0086 (10)−0.0035 (10)
C100.0416 (12)0.0361 (13)0.0424 (13)−0.0059 (10)0.0012 (10)−0.0046 (11)
C110.0378 (11)0.0376 (13)0.0322 (11)−0.0017 (10)−0.0008 (9)−0.0033 (10)
C120.0380 (11)0.0292 (12)0.0354 (12)0.0001 (9)0.0011 (9)−0.0002 (9)
C130.0617 (17)0.0595 (19)0.0741 (19)−0.0114 (14)0.0112 (14)0.0113 (15)
C140.0577 (15)0.074 (2)0.0443 (15)−0.0078 (14)0.0011 (12)0.0079 (14)
C150.0458 (14)0.0536 (17)0.0795 (19)0.0144 (12)−0.0017 (13)−0.0046 (15)
C160.0606 (16)0.0386 (15)0.0667 (17)0.0049 (12)0.0130 (13)−0.0053 (13)
C170.0393 (12)0.0666 (18)0.0446 (14)−0.0009 (12)−0.0078 (10)−0.0047 (13)
C180.0639 (17)0.081 (2)0.073 (2)0.0148 (16)−0.0195 (15)0.0068 (17)
C190.0595 (17)0.100 (3)0.070 (2)−0.0212 (17)−0.0197 (15)−0.0072 (18)
C200.0661 (18)0.114 (3)0.0466 (16)0.0055 (18)−0.0005 (14)−0.0178 (17)
C210.0334 (11)0.0445 (14)0.0493 (14)−0.0013 (10)−0.0077 (10)−0.0032 (11)
C220.0354 (12)0.074 (2)0.0736 (19)−0.0008 (13)0.0059 (12)−0.0162 (16)
C230.0447 (14)0.0646 (19)0.0760 (19)−0.0079 (13)−0.0155 (13)−0.0168 (15)
C240.0560 (16)0.073 (2)0.082 (2)−0.0045 (15)−0.0219 (15)0.0193 (17)
C250.0418 (12)0.0325 (13)0.0460 (13)0.0005 (10)−0.0003 (10)−0.0050 (11)
C260.0673 (17)0.0497 (17)0.0584 (17)−0.0112 (14)−0.0145 (13)0.0060 (14)
C270.081 (2)0.0491 (18)0.074 (2)−0.0146 (15)0.0029 (16)0.0102 (15)
C280.0588 (17)0.0476 (18)0.090 (2)−0.0145 (13)0.0143 (16)−0.0160 (17)
C290.0523 (15)0.0607 (19)0.073 (2)−0.0030 (14)−0.0115 (13)−0.0236 (17)
C300.0505 (14)0.0503 (16)0.0462 (14)0.0018 (12)−0.0036 (11)−0.0071 (12)
Geometric parameters (Å, °) top
S—O41.4161 (18)C16—H16B0.9600
S—O31.4215 (18)C16—H16C0.9600
S—O21.5920 (16)C17—C201.526 (4)
S—C251.748 (2)C17—C191.535 (4)
O1—C11.376 (3)C17—C181.538 (4)
O1—H1A0.8200C18—H18A0.9600
O2—C121.422 (3)C18—H18B0.9600
C1—C61.389 (3)C18—H18C0.9600
C1—C21.398 (3)C19—H19A0.9600
C2—C31.388 (3)C19—H19B0.9600
C2—C171.532 (3)C19—H19C0.9600
C3—C41.378 (3)C20—H20A0.9600
C3—H3B0.9300C20—H20B0.9600
C4—C51.397 (3)C20—H20C0.9600
C4—C131.516 (3)C21—C221.524 (3)
C5—C61.407 (3)C21—C231.532 (3)
C5—C141.505 (3)C21—C241.535 (4)
C6—C71.497 (3)C22—H22A0.9600
C7—C121.398 (3)C22—H22B0.9600
C7—C81.399 (3)C22—H22C0.9600
C8—C91.394 (3)C23—H23A0.9600
C8—C151.517 (3)C23—H23B0.9600
C9—C101.388 (3)C23—H23C0.9600
C9—C161.506 (3)C24—H24A0.9600
C10—C111.390 (3)C24—H24B0.9600
C10—H10A0.9300C24—H24C0.9600
C11—C121.394 (3)C25—C301.362 (3)
C11—C211.544 (3)C25—C261.386 (3)
C13—H13A0.9600C26—C271.371 (4)
C13—H13B0.9600C26—H26A0.9300
C13—H13C0.9600C27—C281.360 (4)
C14—H14A0.9600C27—H27A0.9300
C14—H14B0.9600C28—C291.362 (4)
C14—H14C0.9600C28—H28A0.9300
C15—H15A0.9600C29—C301.389 (4)
C15—H15B0.9600C29—H29A0.9300
C15—H15C0.9600C30—H30A0.9300
C16—H16A0.9600
O4—S—O3119.60 (12)H16B—C16—H16C109.5
O4—S—O2109.22 (10)C20—C17—C2110.6 (2)
O3—S—O2105.99 (10)C20—C17—C19107.8 (2)
O4—S—C25110.79 (11)C2—C17—C19111.7 (2)
O3—S—C25107.77 (11)C20—C17—C18109.8 (2)
O2—S—C25101.95 (10)C2—C17—C18109.8 (2)
C1—O1—H1A109.5C19—C17—C18107.1 (2)
C12—O2—S124.34 (13)C17—C18—H18A109.5
O1—C1—C6119.32 (19)C17—C18—H18B109.5
O1—C1—C2118.01 (19)H18A—C18—H18B109.5
C6—C1—C2122.6 (2)C17—C18—H18C109.5
C3—C2—C1115.2 (2)H18A—C18—H18C109.5
C3—C2—C17122.5 (2)H18B—C18—H18C109.5
C1—C2—C17122.2 (2)C17—C19—H19A109.5
C4—C3—C2124.7 (2)C17—C19—H19B109.5
C4—C3—H3B117.7H19A—C19—H19B109.5
C2—C3—H3B117.7C17—C19—H19C109.5
C3—C4—C5118.6 (2)H19A—C19—H19C109.5
C3—C4—C13119.5 (2)H19B—C19—H19C109.5
C5—C4—C13121.9 (2)C17—C20—H20A109.5
C4—C5—C6119.0 (2)C17—C20—H20B109.5
C4—C5—C14120.5 (2)H20A—C20—H20B109.5
C6—C5—C14120.5 (2)C17—C20—H20C109.5
C1—C6—C5119.66 (19)H20A—C20—H20C109.5
C1—C6—C7118.98 (19)H20B—C20—H20C109.5
C5—C6—C7120.87 (19)C22—C21—C23105.9 (2)
C12—C7—C8118.76 (19)C22—C21—C24110.9 (2)
C12—C7—C6122.01 (19)C23—C21—C24106.9 (2)
C8—C7—C6119.20 (18)C22—C21—C11109.74 (18)
C9—C8—C7119.73 (19)C23—C21—C11111.5 (2)
C9—C8—C15119.5 (2)C24—C21—C11111.68 (19)
C7—C8—C15120.8 (2)C21—C22—H22A109.5
C10—C9—C8118.4 (2)C21—C22—H22B109.5
C10—C9—C16119.3 (2)H22A—C22—H22B109.5
C8—C9—C16122.3 (2)C21—C22—H22C109.5
C9—C10—C11124.8 (2)H22A—C22—H22C109.5
C9—C10—H10A117.6H22B—C22—H22C109.5
C11—C10—H10A117.6C21—C23—H23A109.5
C10—C11—C12114.52 (19)C21—C23—H23B109.5
C10—C11—C21120.42 (19)H23A—C23—H23B109.5
C12—C11—C21125.1 (2)C21—C23—H23C109.5
C11—C12—C7123.7 (2)H23A—C23—H23C109.5
C11—C12—O2118.27 (18)H23B—C23—H23C109.5
C7—C12—O2117.67 (18)C21—C24—H24A109.5
C4—C13—H13A109.5C21—C24—H24B109.5
C4—C13—H13B109.5H24A—C24—H24B109.5
H13A—C13—H13B109.5C21—C24—H24C109.5
C4—C13—H13C109.5H24A—C24—H24C109.5
H13A—C13—H13C109.5H24B—C24—H24C109.5
H13B—C13—H13C109.5C30—C25—C26120.8 (2)
C5—C14—H14A109.5C30—C25—S120.40 (19)
C5—C14—H14B109.5C26—C25—S118.62 (18)
H14A—C14—H14B109.5C27—C26—C25119.3 (2)
C5—C14—H14C109.5C27—C26—H26A120.3
H14A—C14—H14C109.5C25—C26—H26A120.3
H14B—C14—H14C109.5C28—C27—C26120.3 (3)
C8—C15—H15A109.5C28—C27—H27A119.9
C8—C15—H15B109.5C26—C27—H27A119.9
H15A—C15—H15B109.5C27—C28—C29120.2 (3)
C8—C15—H15C109.5C27—C28—H28A119.9
H15A—C15—H15C109.5C29—C28—H28A119.9
H15B—C15—H15C109.5C28—C29—C30120.7 (3)
C9—C16—H16A109.5C28—C29—H29A119.6
C9—C16—H16B109.5C30—C29—H29A119.6
H16A—C16—H16B109.5C25—C30—C29118.6 (3)
C9—C16—H16C109.5C25—C30—H30A120.7
H16A—C16—H16C109.5C29—C30—H30A120.7
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1A···O40.822.373.107 (2)150
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O1—H1A···O40.822.373.107 (2)150
Acknowledgements top

We gratefully acknowledge financial support from the National Science Council, Taiwan (NSC97-2113-M-033-005-MY2) and from the Project of Specific Research Fields in Chung Yuan Christian University (No. CYCU-97-CR-CH).

references
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