Wen-Chou Hung

National Chung Hsing University, 臺中市, Taiwan, Taiwan

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Publications (12)32.14 Total impact

  • Saikat Dutta · Wen-Chou Hung · Bor-Hunn Huang · Chu-Chieh Lin
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    ABSTRACT: A good synergy of a catalytic system’s components, such as ancillary ligands and leaving groups at the active site of a catalyst, is of fundamental importance in the ring-opening polymerization (ROP) of lactides and lactones. This article surveys recent advances in the metal-promoted ROP of lactide and glycolide for the preparation of poly(lactide) (PLA), poly(glycolide) (PGA), and their copolymer poly(lactide-co-glycolide) (PLGA). First, there is a general discussion on mechanisms, the undesirable effects of side reactions on the rate of polymerization, and how the first generation of ROP catalysts such as SnOct2 [tin(II) 2-ethylhexanoate, also known as tin(II) octoate] work as efficient initiators. Then, the study focuses on the ROP capability of monomeric and multinuclear complexes of Li, Ca, Mg, Zn, Al, and Ti metals for the efficient preparation of PLA. Special emphasis is given to the factors controlling polymer molecular weight, molecular weight distribution, and the suppression of transesterification side reactions and epimerization of monomers. Surpassing the pure model nature of many structurally well-defined catalytic systems such as bis(phenoxide)-Li, bis(phenoxide)-Mg, trispyrazolylborate-Mg/Zn, and β-diketiiminate-Mg/Zn, the applicability and performance of N,O-donor Schiff base Mg/Zn systems in the production of PLAs are highlighted. The emerging “structure-polymerization” activity is also addressed. Special attention is given to Ca, Mg, and Zn initiators which, due to their biocompatibility, are considered the safest to be used in the preparation of PLAs for biomedical purposes. Likewise, the polymerization activity of the metal initiators is evaluated on the basis of the Lewis acidic properties of the central metal. Alternatives like trivalent lanthanide systems with ancillary ligands such as bis(amidinate), β-ketoiminate, bis(phenolate), and Schiff bases are considered. Some recently investigated coordination complexes of Cu, Ni, Ag, and Au metals used in the solvent-free melt polymerization of lactide are discussed in terms of structure–activity relationships. The substantial role of the ligand geometry on the stereocontrol of the rac-lactide polymerization is addressed to finally summarize the key components essential for obtaining PLAs of desired microstructure from rac- and meso-lactides. The development of glycolide ROP catalysts based on Sn, Zn, Sm, and Bi is addressed and their effectiveness in producing copolyesters of lactide and glycolide such as PLGA assessed.
    01/2011: pages 219-283;
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    ABSTRACT: A series of lithium and sodium complexes with OOO-tridentate bis(phenolate) ligands have been synthesized and fully characterized. The reaction of 2,2'-dihydroxy-3,3',5,5'-tetrakis[(1-methyl-1-phenyl)ethyl]dibenzyl ether (L(1)-H(2)) with different ratios of (n)BuLi in toluene or tetrahydrofuran (THF) gave [Li(2)(L(1)-H)(2)] (1), [Li(4)L(1)(2)] (2), and [Li(2)L(1)(THF)(3)] (3), respectively. Similarly, [Na(L(1)-H)(THF)] (4), [Na(2)(L(1)-H)](2) (5), and [Na(4)L(1)(2)] (6) were prepared by the reaction of L(1)-H(2) and NaN[Si(CH(3))(3)](2) or sodium metal. In addition, the reaction of 2,2'-dihydroxy-3,3',5,5'-tetra-tert-butyldibenzyl ether (L(2)-H(2)) with (n)BuLi in toluene or THF yields Li(2)(L(2)-H)(2)] (7) and [Li(2)(L(2)-H)(2)(THF)(2)] (8), respectively. Further treatment of 7 with 2 mol equiv of benzyl alcohol provides [Li(2)(L(2)-H)(2)(BnOH)(2)] (9). Complexes 1-4 and 6-9 have been structurally characterized by single-crystal X-ray analysis. The dinuclear nature of complexes 1 and 3 was confirmed from their molecular structure. Complexes 2 and 6 illustrate tetranuclear species; however, complex 4 shows a mononuclear feature. A p-π interaction exists from the phenyl ring of the 2-(methyl-1-phenylethyl) groups to the central metal in complexes 2, 4, and 6, which could effectively stabilize the metal center. Among them, complexes 1, 2, and 5-9 displayed efficient catalytic behavior for the ring-opening polymerization of L-lactide in the presence of benzyl alcohol. Experimental results indicate that among these alkali-metal complexes, the sodium compound 6 displays a rapid catalytic polymerization of L-lactide in "living" fashion, yielding poly(L-lactide) with a controlled molecular weight and narrow polydispersity indices for a wide range of monomer-to-initiator ratios.
    Inorganic Chemistry 10/2010; 49(20):9416-25. DOI:10.1021/ic1011154 · 4.79 Impact Factor
  • Po-Yu Li · Ping-Shan Lai · Wen-Chou Hung · Wei-Jhe Syu
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    ABSTRACT: Multiple drug resistance (MDR) seriously reduces the efficacy of many chemotherapeutic agents for cancer. P-Glycoprotein, an efflux pump overexpressed on the cell surface, plays an important role in drug resistance, but several surfactants, such as vitamin E TPGS, can inhibit P-glycoprotein. In this study, a polylactide-surfactant block copolymer poly(l-lactide)-vitamin E TPGS (PLA-TPGS) was synthesized using bidentate sulfonamide zinc ethyl complex as an efficient catalyst, and its self-assembled nanoparticles were used as carriers of doxorubicin. We first found that the activity of P-glycoprotein in drug-resistant breast cancer MCF-7/ADR cells was decreased after incubation with PLA-TPGS nanoparticles. In addition, the nuclear accumulation and cytotoxicity of doxorubicin were significantly increased by encapsulation into the nanoparticles. The enhanced efficacy of the doxorubicin-loaded PLA-TPGS nanoparticles may result from the combination of inhibition of efflux and increased entry of doxorubicin into the nucleus in drug-resistant MCF-7/ADR cells. Therefore, this innovative delivery system has potential to act as a nanomedicine for therapy of both drug-sensitive and drug-resistant cancer.
    Biomacromolecules 10/2010; 11(10):2576-82. DOI:10.1021/bm1005195 · 5.75 Impact Factor
  • Min-Yi Shen · Ya-Liu Peng · Wen-Chou Hung · Chu-Chieh Lin
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    ABSTRACT: A series of magnesium complexes have been prepared and characterized, in which [(EDBP-Me)Mg(mu-OBn)](2) (4) has shown high activity toward the ring-opening polymerization (ROP) of epsilon-caprolactone and L-lactide. 2,2'-Ethylidene-bis(4,6-di-tert-butylphenol)-monomethyl ether ([EDBP-(Me)H]) is prepared by the reaction of 2,2'-ethylidene-bis(4,6-di-tert-butylphenol) (EDBP-H(2)) with dimethyl sulfate. The reaction of [EDBP-(Me)H] with (n)Bu(2)Mg yields [(EDBP-Me)Mg(n)Bu](2), which further reacts with benzyl alcohol and N,N-dimethylethylenediamine giving complexes [(EDBP-Me)Mg(mu-OBn)](2) (4) and {[EDBP(Me)]Mg(mu-Me(2)NCH(2)CH(2)NH)}(2) (5), respectively. Experimental results indicate that the activity of complex 4 toward cyclic esters is higher than that of [(mu-EDBP)Mg](2)/(BnOH).
    Dalton Transactions 11/2009; 44(44):9906-13. DOI:10.1039/b912443h · 4.20 Impact Factor
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    ABSTRACT: Four metal benzylalkoxides, [L2M2(μ-OBn)2] (M = Mg or Zn), based on NNO-tridentate ketiminate ligands are synthesized and characterized. X-ray crystal structural studies of [(L1)2Mg2(μ-OBn)2] (1a) and [(L1)2Zn2(μ-OBn)2] (1b) (L1-H = (Z)-4-((2-(dimethylamino)ethylamino)(phenyl)methylene)-3-methyl-1-phenyl-pyrazol-5-one) reveal that both complexes 1a and 1b are dinuclear species whereas the geometry around the metal center is penta-coordinated bridging through the benzylalkoxy oxygen atoms in the solid structure. The activities and stereoselectivities of these four complexes toward the ring-opening polymerization of L-lactide and rac-lactide are investigated. Polymerization of L-lactide initiated by these four metal benzyloxides proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. The kinetic studies for the polymerization of L-lactide with compound 1a show first order in both compound 1a and lactide concentrations with the polymerization rate constant, k, of 6.94 M/min. Besides, experimental results demonstrate that among these metal benzylalkoxides, complex 1a exhibits the highest stereoselectivity with a Pr up to 87% and complex 1b possesses the highest activity indicating that the terminal group of NNO-tridentate ketimine ligands exerts a significant influence on both the reactivity and stereoselectivity of these complexes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2318–2329, 2009
    Journal of Polymer Science Part A Polymer Chemistry 05/2009; 47(9):2318 - 2329. DOI:10.1002/pola.23314 · 3.54 Impact Factor
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    Yueh-Hsuan Tsai · Wen-Chou Hung · Chu-Chieh Lin
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    ABSTRACT: The Cu atom of the title complex, [Cu(C(13)H(19)N(2)O(2))(C(10)H(8)N(2))]ClO(4), has a distorted square-pyramidal geometry with all three of the donor atoms from the N,N',O-tridentate Schiff base ligand in the equatorial positions and the bipyridine N atoms in an equatorial-axial binding mode. The Cu atom is 0.1801 (11) Å above the N(3)O mean basal plane.
    Acta Crystallographica Section E Structure Reports Online 05/2009; 65(Pt 5):m578. DOI:10.1107/S1600536809014573 · 0.35 Impact Factor
  • Wen-Chou Hung · Chu-Chieh Lin
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    ABSTRACT: A series of magnesium benzyl alkoxides, [LMg(mu-OBn)](2) (1-8), supported by NNO-tridentate Schiff-base ligands are prepared by the reactions of Mg(OBn)(2) with one molar equivalent of related Schiff-base ligands (L(1)H-L(8)H) in toluene. The molecular structures of compounds 2, 3, 7, and 8 are characterized by X-ray structure determination. All of these compounds are crystallized as penta-coordinated dimers, and the central magnesium atoms are bridged by the oxygen atoms of benzyl alkoxides. The catalytic activities of complexes 1-8 toward the ring-opening polymerization of l-lactide are investigated. Experimental results indicate that the reactivity of [LMg(mu-OBn)](2) (1-8) is dramatically affected by the electronic effect of the substituents on the Schiff-base ligands, and 4 has the highest activity among them.
    Inorganic Chemistry 01/2009; 48(2):728-34. DOI:10.1021/ic801397t · 4.79 Impact Factor
  • Jincai Wu · Yi-Zhen Chen · Wen-Chou Hung · Chu-Chieh Lin
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    ABSTRACT: A series of sterically bulky phenols (1a−f; EDBP-RTs-H = 2,4-di-tert-butyl-6-(1-(3,5-di-tert-butyl-2-hydroxyphenyl)ethyl)phenyl benzenesulfonate) were synthesized. Their related n-butylmagnesium complexes [(μ-EDBP-RTs)MgnBu]2 (2a−f) and magnesium alkoxides [(EDBP-RTs)Mg(μ-OBn)]2 (3a−f) were prepared and structurally characterized. In the presence of THF, coordination of [(EDBP-RTs)Mg(μ-OBn)]2 (3e) with THF gave the pentacoordinated magnesium complex [(EDBP-RTs)Mg(μ-OBn)(THF)]2 (4). Crystal structures of 2a−c,e, 3a−c,f, and 4 have been determined. Experimental results show that magnesium alkoxides (3a−f) are very reactive initiators toward ROP of l-lactide, with a quantitative yield of polymer (1000 equiv) in less than 4 min.
    Organometallics 08/2008; 27(19). DOI:10.1021/om800482j · 4.25 Impact Factor
  • Wen-Chou Hung · Chu-Chieh Lin
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    ABSTRACT: The NiII atom in the title complex, [Ni(C17H17ClNO)2], is tetracoordinated by two N atoms and two O atoms from two bidentate salicylideneiminate ligands, forming a square-planar environment. The asymmetric unit consists of two half-molecules; in each molecule the Ni atom lies on a centre of symmetry.
    Acta Crystallographica Section E Structure Reports Online 12/2007; 63(12). DOI:10.1107/S1600536807060680/gk2118Isup2.hkl · 0.35 Impact Factor
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    ABSTRACT: Three new metal alkoxides, [(MMPEP)Al(μ-OCH2C6H4CH2Cl)]2 (1), [(MMPEP–H)Li·(BnOH)]2 (2) and [(MMPEP–H)Li·(HOCH2C6H4CH2Cl)]2 (3) (MMPEP–H2: 2,2′-methylene-bis{4,6-di(1-methyl-1-phenylethyl)phenol}) have been synthesized and characterized. Complex 1 was prepared by the reaction of [(MMPEP)Al(CH3)(Et2O)] with p-(chloromethyl)benzyl alcohol. Followed by the reaction of MMPEP–H2 with nBuLi, BnOH or p-(chloromethyl)benzyl alcohol was added to give complexes 2 and 3, respectively. Complex 1 has shown excellent catalytic activity towards ring-opening polymerization (ROP) of ɛ-caprolactone. Both complexes 2 and 3 are active for ROP of l-lactide. Block copolymers of poly(ɛ-caprolactone)-b-polyacrylonitrile (PCL-b-PAN) and poly(l-lactide)-b-polyacrylonitrile can be synthesized by combining a technique of atom transfer radical polymerization (ATRP) and ROP using a double-headed initiator. Microphase-separated morphology of PCL-b-PAN has been observed by transmission electron microscopy, indicating the formation of self-assembled nanostructure.
    Polymer 07/2007; 48(15-48):4401-4411. DOI:10.1016/j.polymer.2007.05.044 · 3.77 Impact Factor
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    Wen-Chou Hung · Shu-Ling Lai · Chu-Chieh Lin
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    ABSTRACT: The title complex, [Zn(2)(C(2)H(5))(2)(C(12)H(16)BrN(2)O)(2)], is dimeric, bridged through the O atoms of the phenolate anions. The molecule lies on a crystallographic twofold rotation axis. Each Zn atom is penta-coordinated by two N atoms and two bridging O atoms of the tridentate salicylideneiminate ligands and one C atom from an ethyl group, forming a distorted square-pyramidal environment.
    Acta Crystallographica Section E Structure Reports Online 01/2007; 64(Pt 1):m129-30. DOI:10.1107/S1600536807065208 · 0.35 Impact Factor
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    ABSTRACT: Palladium-catalyzed Suzuki cross-coupling reactions employing Schiff-bases as ligands toward a series of substituted arylbromides and boronic acids were pursued. In the presence of a N,O-bidentate ligand, 2-[1-(2,4,6-trimethyl-phenylimino)-ethyl]-phenol 5, the catalytic reactions could be carried out efficiently at room temperature with a wide array of arylbromides, even with electronically deactivated arenes. A deprotonated 5, 5′, chelated palladium acetate complex, [5′Pd(II)(OAc)(solv)] 8, was proposed as a precursor of a genuine catalytically active species.
    ChemInform 10/2005; 61(40):9484-9489. DOI:10.1016/j.tet.2005.08.005