1,721,411 research outputs found
Synthesis, characterisation and ROP catalytic evaluation of Cu(II) complexes bearing 2,2ʹ-diphenylglycine-derived moieties
Full text linkThe treatment of CuX2 (X = Cl, Br) with an equimolar amount of 2-2ʹ-diphenylglycine (DpgH) in EtOH at reflux afforded, after work up, the complexes [CuCl(Dpg)(EtOH)]2 (1) and [(CuBr2)2(Dpg)2Cu(EtOH)4] (2), respectively. The compounds were obtained microanalytically pure in low to moderate yield (13 and 27%, respectively) and were fully characterised. Synthetic attempts towards Cu-alkoxide species led to the isolation of the heterobimetallic species [(CuCl2)(Dpg)Li(THF)]·THF (3·THF). Finally, complex 4, bearing an imine ligand derived from the decarboxylation of DpgH, was serendipitously obtained from the synthesis of 3. These complexes were found to be inactive in the homo- and co-ring opening polymerization (ROP) of cyclic esters (ε-caprolactone and rac-lactide) and epoxides (propylene oxide and cyclohexene oxide). Compounds 1 and 2 were shown to be non-toxic against cancerous cell lines HCT116 and HT-29
Synthesis and characterization of Schiff-base complexes as medical imaging precursors
No full textSchiff-base compounds have been utilized in the medical field as antibiotics, antifungal, anti-inflammatory and antiviral agents. The presence of nitrogen, oxygen and sulphur atoms in chelating Schiff-base compounds showed great biological activities. Furthermore, their derivative metal complexes have exhibited greater effects in many reported cases. Some Schiff-base complexes have been reported as medical imaging agents. The aim of my work is to synthesis novel Schiff base ligands and their metal derivatives that have the potential to be used as medical imaging precursors. A novel macrocyclic Schiff-base ligand was developed from 3,5- diformyl-4-hydroxybenzoic acid and 2,2’-oxydianiline. Also, a novel crystal structure for a known macrocyclic Schiff-base was synthesized from 2,2’-oxydianiline and 4-tert-butyl-2,6-diformylphenol. Finally, a novel copper Schiff-base complex synthesized
Ring Opening Polymerization of Lactides and Lactones by Multimetallic Titanium Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2)
Full text linkThe reactions of the titanium alkoxide [Ti(OR)4] (R = Me, nPr, iPr, tBu) with the acids 2,2’-Ph2C(X)(CO2H), where X = OH and NH2, i.e., benzilic acid (2,2’-diphenylglycolic acid, L1H2), and 2,2’-diphenylglycine (L2H3), have been investigated. The variation of the reaction stoichiometry allows for the isolation of mono-, bi-, tri or tetra-metallic products, the structures of which have been determined by X-ray crystallography. The ability of the resulting complexes to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and r-lactide (r-LA) has been investigated. In the case of ε-CL, all catalysts except that derived from [Ti(OnPr)4] and L2H3, i.e., 7, exhibited an induction period of between 60 and 285 min, with 7 exhibiting the best performance (>99% conversion within 6 min). The PCL products are moderate- to high-molecular weight polymers. For r-LA, systems 1, 3, 4 and 7 afforded conversions of ca. 90% or more, with 4 exhibiting the fastest kinetics. The molecular weights for the PLA are somewhat higher than those of the PCL, with both cyclic and linear PLA products (end groups of OR/OH) identified. Comparative studies versus the [Ti(OR)4] starting materials were conducted, and although high conversions were achieved, the control was poor
Synthesis and characterization of Schiff-base complexes as medical imaging precursors
Full text linkSchiff-base compounds have been utilized in the medical field as antibiotics, antifungal, anti-inflammatory and antiviral agents. The presence of nitrogen, oxygen and sulphur atoms in chelating Schiff-base compounds showed great biological activities. Furthermore, their derivative metal complexes have exhibited greater effects in many reported cases. Some Schiff-base complexes have been reported as medical imaging agents. The aim of my work is to synthesis novel Schiff base ligands and their metal derivatives that have the potential to be used as medical imaging precursors. A novel macrocyclic Schiff-base ligand was developed from 3,5- diformyl-4-hydroxybenzoic acid and 2,2’-oxydianiline. Also, a novel crystal structure for a known macrocyclic Schiff-base was synthesized from 2,2’-oxydianiline and 4-tert-butyl-2,6-diformylphenol. Finally, a novel copper Schiff-base complex synthesized
New catalysts bearing chelate ligands for ring opening polymerization studies.
Full text linkChapter 1: The accumulation of traditional polymer (plastic) pollution has led people to start looking for biodegradable plastics as alternatives. This first chapter provides information on the concept and the development of biodegradable polymers. It also highlights the development of efficient catalysts based on Sn/Al/Ti/Zn metals for producing biodegradable aliphatic polyester and the key ring-opening polymerization mechanisms, including coordination-insertion, cationic, anionic mechanisms. Moreover, this chapter delivers a comprehensive review of metal complexes bearing 2,2’-diphenylglycine or benzilic acid ligands, with particular focus on the binding modes of Ph2C(X)(CO2H) (X = NH2, OH) in these complexes. These complexes’ application as catalysts for the ring-opening polymerisation of cyclic esters is summarised. Lastly, the characterisation methods used in this work are discussed.Chapter 2: Here, the Schiff-base compounds 2,4-di-tert-butyl-6-(((3,4,5-trimethoxyphenyl)imino)methyl)phenol (L1H), 2,4-di-tert-butyl-6-(((2,4,6-trimethoxyphenyl)imino)methyl)phenol (L2H), 2,4-di-tert-butyl-6-(((2,4-dimethoxyphenyl)imino)methyl)phenol) (L3H) derived from anilines bearing methoxy substituents have been employed in the preparation of alkylaluminium and zinc complexes. Molecular structure determinations reveal mono-chelate aluminium complexes of the type [Al(Ln)(Me)2] (L1, 1; L2, 2; L3, 3), and bis(chelate) complexes for zinc, namely [Zn(Ln)2] (L1, 5; L2, 6; L3, 7). All complexes have significant activity at 50 C and higher activity at 100 C for the ring-opening polymerisation (ROP) of -caprolactone (-CL) with good control over the molar mass distribution (Mw/Mn 99 % conversion at 100 C, whilst 10 and 11 were inactive under the same conditions. All complexes show moderate activities towards the ROP of r-LA at 160 C, with 9-11 producing heterotactic enriched PLA while 12 afforded isotactic enriched PLA.Chapter 4: The reactions of the titanium alkoxides [Ti(OR)4] (R = Me, nPr, iPr, tBu) with the L4H2 or L5H3 have been investigated. Variation of the reaction stoichiometry allows for the isolation of mono-, bi-, tri or tetra-metallic products, the structures of which have been determined by X-ray crystallography. The ability of the resulting complexes to act as catalysts for the ROP of -CL and r-LA has been investigated. In the case of -CL, all catalysts except that derived from [Ti(OnPr)4] and L5H3 i.e. 19, exhibited an induction period of between 60 and 285 min., with 19 exhibiting the best performance (>99% conversion within 6 min.). The PCL products are moderate to high molecular weight polymers. For r-LA, there was no induction period, and systems 13, 15, 16 and 19 afforded conversions of ca. 90% or more, with 16 exhibiting the fastest kinetics. The molecular weights for the PLA are somewhat higher than those of the PCL, with both cyclic and linear PLA products (end groups of OR/OH) identified. Comparative studies versus the [Ti(OR)4] starting materials were conducted and although high conversions were achieved, the control was poor.Chapter 5: The better performing catalysts from chapters 2-4 are selected and compared with other reported catalysts with similar ligand systems. The evaluation of these catalysts is based on the ROP of -CL. Various factors, including polymerisation rate, molecular weight and distribution of polymer products, catalyst efficiency, and catalyst stability have been considered
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
New catalysts bearing chelate ligands for ring opening polymerization studies.
Full text linkChapter 1: The accumulation of traditional polymer (plastic) pollution has led people to start looking for biodegradable plastics as alternatives. This first chapter provides information on the concept and the development of biodegradable polymers. It also highlights the development of efficient catalysts based on Sn/Al/Ti/Zn metals for producing biodegradable aliphatic polyester and the key ring-opening polymerization mechanisms, including coordination-insertion, cationic, anionic mechanisms. Moreover, this chapter delivers a comprehensive review of metal complexes bearing 2,2’-diphenylglycine or benzilic acid ligands, with particular focus on the binding modes of Ph2C(X)(CO2H) (X = NH2, OH) in these complexes. These complexes’ application as catalysts for the ring-opening polymerisation of cyclic esters is summarised. Lastly, the characterisation methods used in this work are discussed.Chapter 2: Here, the Schiff-base compounds 2,4-di-tert-butyl-6-(((3,4,5-trimethoxyphenyl)imino)methyl)phenol (L1H), 2,4-di-tert-butyl-6-(((2,4,6-trimethoxyphenyl)imino)methyl)phenol (L2H), 2,4-di-tert-butyl-6-(((2,4-dimethoxyphenyl)imino)methyl)phenol) (L3H) derived from anilines bearing methoxy substituents have been employed in the preparation of alkylaluminium and zinc complexes. Molecular structure determinations reveal mono-chelate aluminium complexes of the type [Al(Ln)(Me)2] (L1, 1; L2, 2; L3, 3), and bis(chelate) complexes for zinc, namely [Zn(Ln)2] (L1, 5; L2, 6; L3, 7). All complexes have significant activity at 50 C and higher activity at 100 C for the ring-opening polymerisation (ROP) of -caprolactone (-CL) with good control over the molar mass distribution (Mw/Mn 99 % conversion at 100 C, whilst 10 and 11 were inactive under the same conditions. All complexes show moderate activities towards the ROP of r-LA at 160 C, with 9-11 producing heterotactic enriched PLA while 12 afforded isotactic enriched PLA.Chapter 4: The reactions of the titanium alkoxides [Ti(OR)4] (R = Me, nPr, iPr, tBu) with the L4H2 or L5H3 have been investigated. Variation of the reaction stoichiometry allows for the isolation of mono-, bi-, tri or tetra-metallic products, the structures of which have been determined by X-ray crystallography. The ability of the resulting complexes to act as catalysts for the ROP of -CL and r-LA has been investigated. In the case of -CL, all catalysts except that derived from [Ti(OnPr)4] and L5H3 i.e. 19, exhibited an induction period of between 60 and 285 min., with 19 exhibiting the best performance (>99% conversion within 6 min.). The PCL products are moderate to high molecular weight polymers. For r-LA, there was no induction period, and systems 13, 15, 16 and 19 afforded conversions of ca. 90% or more, with 16 exhibiting the fastest kinetics. The molecular weights for the PLA are somewhat higher than those of the PCL, with both cyclic and linear PLA products (end groups of OR/OH) identified. Comparative studies versus the [Ti(OR)4] starting materials were conducted and although high conversions were achieved, the control was poor.Chapter 5: The better performing catalysts from chapters 2-4 are selected and compared with other reported catalysts with similar ligand systems. The evaluation of these catalysts is based on the ROP of -CL. Various factors, including polymerisation rate, molecular weight and distribution of polymer products, catalyst efficiency, and catalyst stability have been considered
New pre-catalysts derived from calixarenes : synthesis, structural and polymerization studies
Full text linkIn this thesis, a series of V, Ti, Li and Pb compounds have been synthesized and fully characterized. The catalytic performance of these pre-catalysts towards different polymerization reactions, including ring opening polymerization (ROP) of cyclic esters, ethylene polymerization and co-polymerization of propylene oxide and CO2 are studied.Chapter 1 presents the history and research achievements of both calixarene and metallocalixarene compounds, with particular reference to polymerization reactions catalyzed by such coordination complexes, including ethylene polymerization, ring opening polymerization of cyclic esters and co-polymerization of propylene oxide and CO2.In Chapter 2, reactions of larger calix[n]arenes with vanadium precursors are studied. In particular, the reaction of Na[VO(tBuO)4] (generated in-situ from VOCl3 and NaOtBu) with p-tert-butyltetrahomodioxacalix[6]areneH6 (LO6H6) afforded, after work-up (in MeCN), the mixed-metal complex [(VO)2(μ-O)Na2(LO6)(MeCN)4]·5(MeCN) (1·5MeCN), whilst the oxo complex {[VO]4LO6} (2·6MeCN) was isolated via the use of [VO(OnPr)3]. Reaction of LO6H6 with [V(Np-CH3C6H4)(OtBu)3] afforded the complex {[V(Np-CH3C6H4)]2LO6} (3·7MeCN·0.5CH2Cl2). Use of similar methodology afforded the imido complexes {[V(Np-RC6H4)]2LO6} (R = OMe (4); CF3 (5); Cl (6); F (7)); on one occasion, reaction of [V(Np-CH3C6H4)(OEt)3] with LO6H6 afforded the product [VO(L6O’)]2·4MeCN (8·4MeCN) (L6O’ = 2-(p-CH3-C6H4NCH)-4-tBu-C6H2O-6-CH2)-4-tBuC6H2OH) in which LO6 has been cleaved. For comparative catalytic ring opening polymerization (ROP) studies, the known complexes [VOL3] (L3H3 = oxacalix[3]arene) (I), [V(Np-CH3-C6H4)L3]2 (II), [Li(MeCN)4][V2(O)2Li(MeCN)(L6H2)2] (L6H6 = p-tert-butylcalix[6]areneH6) (III) and [(VO)2L8H] (L8H8 = p-tert-butylcalix[8]areneH8) (IV) have also been prepared. ROP studies, with or with or without external alcohol present, indicated that complexes 1 to 8 exhibited moderate to good conversions for ε-Cl, δ-VL and the co-polymerization thereof. Within the imido series, a positive influence was observed when electron withdrawing substituents were present. These systems afforded relatively low molecular weight products and were also inactive toward the ROP of rac-lactide. In the case of ethylene polymerization, complexes 3, 5 and 7 exhibited highest activity when screened in the presence of dimethylaluminium chloride/ethyltrichloroacetate; the activity of 4 was much lower. The products were highly linear polyethylene with Mw in the range 74-120x103 Da.In Chapter 3, a number of metallocalix[n]arenes, where n = 4, 6, or 8, of titanium and vanadium have been screened for their ability to act as catalysts for the co-polymerization of propylene oxide and CO2 to form cyclic/polycarbonates. The vanadium-containing catalysts, namely [VO(L4Me)] (V), [(VO2)L8H6] (VI), [Na(NCMe)6]2[(Na(VO)4L8)(Na(NCMe))3]2 (VII), [VO(-OH)L4S/H2]2∙6CH2Cl2 (9/), [(VO)2(μ-O)Na2(LO6)(MeCN)4] (1), {[V(Np-CH3C6H4)]2LO6} (3) and [V(Np-RC6H4)Cl3] (R = Cl (VIII), OMe (IX), CF3 (X)), where L4H4 = p-tert-butylcalix[4]areneH4, L8H8 = p-tert-butylcalix[8]areneH8, L4SH4 = p-tert-butylthiacalix[4]areneH4, performed poorly, affording, in the majority of cases, TONs less than 1 at 90 oC over 6 h. In the case of the titanocalix[8]arenes, {(TiX)2[TiX(NCMe)]2(μ3-O)2(L8)} (X = Cl (10), Br (XI), I (XII)), which all adopt a similar ladder-type structure, the activity under the same conditions is somewhat higher (TONs > 6) and follows the trend Cl > Br > I; by comparison the non-calixarene species [TiCl4(THF)2] (XIII) was virtually inactive. The molecular structures of the complexes [HNEt3]2[VO(-O)L4SH2]2∙3CH2Cl2 (9∙3CH2Cl2), [VO(-OH)L4S/H2]2∙6CH2Cl2 (9/) (where L4S/H2 is a partially oxidized form of L4SH4) and {(TiCl)2[TiCl(NCMe)]2(μ3-O)2(L8)}·6.5MeCN (10·6.5MeCN) are reported.In Chapter 4, the coordination chemistry of azacalix[n]arenes is studied focusing on reactions with titanium precursors. Reaction of excess [Ti(OiPr)4] with L6OH6 afforded, after work-up (MeCN), the complex [Ti2(OiPr)2(MeCN)L6O]∙3.5MeCN (11∙3.5MeCN), whilst the oxo complex [Ti4O4(L6O)2]∙MeCN (12∙MeCN) was isolated via a fortuitous synthesis involving the use of two equivalents of [Ti(OiPr)4]. Reactions of p-methyl-dimethyldiazacalix[6]areneH6 (L6NH6) with [TiF4] (four equivalents), [TiCl4(THF)2] (two equivalents) or [TiBr4] (>four equivalents) resulted in the titanium-based azacalix[n]arene complexes [Ti4F14L6NH2(H)2]∙2.5MeCN (13∙2.5MeCN), [Ti2X4(H2O)2OL6NH2(H)2] (X = Cl (14∙5MeCN), Br (15∙4.5MeCN) and [Ti4Br12L6N(H)2(MeCN)6]∙7MeCN (16∙7MeCN), respectively. Reaction of four equivalents of [TiF4] with L3H4 (L4NH4 = p-methyl-dimethyldiazacalix[4]areneH4) afforded the product [Ti2F2(μ-F)3L4N(H)2(SiF5)]∙2MeCN (17∙2MeCN). These complexes have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA). Generally, the titanium complexes bearing oxacalixarene exhibited better activities than the azacalixarene-based pre-catalysts. For ε-CL, δ-VL and r-LA, moderate activity at 130 °C over 24 h was observed for 11-16. In the case of the co-polymerization of ε-CL with r-LA, 11-16 afforded reasonable conversions and high molecular weight polymers; 17 exhibited lower catalytic performance due to low solubility. None of the complexes proved to be active in the polymerization of ω-pentadecalactone (ω-PDL) under the conditions employed herein.In Chapter 5, a variety of lithiated calix[n]arenes, where n = 6 or 8, have been isolated, structurally characterized and screened for their ability to act as catalysts for the ring opening polymerization (ROP) of the cyclic esters ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and r-lactide (r-LA). In particular, interaction of L6H6 with LiOtBu in THF afforded [Li14(L6H)2(CO3)2(THF)6(OH2)6]·14THF (18·14THF), whilst L8H8 afforded [Li10(L8)(OH)2(THF)8]·7THF (19·7THF). Similar use of de-butylated calix[8]areneH8 (deBuL8H8) led to an elongated dimer [Li18(deBuL8)2(OtBu)2(THF)14]·4THF (20·4THF). Interaction of L8H8 with LiOH·H2O afforded [Li4(L8H4)(OH2)4(THF)6]·5.5THF (21·5.5THF), whilst addition of Me3Al to the solution generated from L8H8 and LiOtBu led to the isolation of [(AlMe2)2Li20(L8H2)2(OH2)4(O2–)4(OH)2(NCMe)12]·10MeCN (22·10MeCN). These complexes have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-CL, δ-VL and r-LA. For ε-CL, δ-VL and r-LA, moderate activity for ROP at 130 °C over 8 h was observed for 18-21. In the case of ROP using the mixed-metal (Li/Al) system 22, better conversions and high molecular weight polymers were achieved. None of the complexes proved to be active in the ROP of ω-pentadecalactone (ω-PDL) under the conditions employed herein.In Chapter 6, the lead coordination chemistry of large calix[n]arenes is studied. Reaction of [LiPb(OiPr)3]2 (generated in-situ from Pb(OiPr)2 and LiOiPr) with either L4H4 or L6H6 resulted in the heterometallic lithium/lead complexes [Pb4Li2(L4)4H6(MeCN)3]∙4.5MeCN (23∙4.5MeCN) and [Pb8Li10Cl2(L6)4(H)8(O)4(H2O)2(MeCN)4]∙14MeCN (24∙14MeCN), respectively. Reaction of five equivalents of [Pb(OiPr)2] with L6OH6 afforded [Pb13(L6O)3O4(iPrOH)]∙11MeCN (25∙11MeCN). Reaction of L8H8 with [Pb(OtBu)2] or {Pb[N(TMS)2]} (TMS = SiMe3) afforded the products [Pb12(L8)2O4]∙8.7C7H8 (26∙8.7C7H8) or [Pb6(SiMe3)2(L8)O2Cl2] (27), respectively. Reaction of {Pb[N(TMS)2]} (generated in-situ from (Me3Si)2NH, nBuLi and PbCl2) with L6H6 afforded, after work-up (MeCN), the mixed-metal complex [Pb5Li(L6)O2.5Cl0.5]∙4.75MeCN (28·4.75MeCN). Complexes 23-27 have been screened for their potential to act as pre-catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) and the copolymerization thereof. Generally, the lithiated complexes 23 and 24 exhibited better activities than the other pre-catalysts screened herein. For ε-CL and δ-VL, moderate activity at 130 °C over 24 h was observed for 23-27. In the case of the co-polymerization of ε-CL with δ-VL, 23-27 afforded reasonable conversions and high molecular weight polymers. The catalysts 23-27 also be proved to be active in the ROP of the rac-lactide (r-LA), the activity trend was found to be 24 >23 >25 >26 ≈ 27.Chapter 7 presents the experimental section.Chapter 8 Appendix
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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