Synthesis and properties of novel Schiff base oligomers based on oligo‐4‐hydroxybenzaldehyde

Condensation of oligo‐4‐hydroxybenzaldehyde with aniline, 2‐chloroaniline, 2‐aminophenol, 2‐aminotoluene, 4‐aminotoluene, and 4‐nitroaniline gave the corresponding Schiff base oligomers (OFAP, OKAP, OHAP, OOAP, OTAP, and ONAP, respectively). The products were characterized by ¹H NMR, Fourier transform infrared, ultraviolet–visible, and elemental analyses. The number‐average molecular weight, mass‐average molecular weight, and polydispersity index (PDI) values of the Schiff base oligomers were determined. Thermogravimetric analysis was used to compare the thermal stability of the oligomers, which showed the Schiff base oligomers to be resistant to thermooxidative decomposition. Weight loss of 5% and 50% occurred at temperatures of 122 and 475 °C; for OFAP, at 118 and 453 °C; for OKAP, at 182 and 491 °C; for OHAP, at 150 and 452 °C; for OOAP, at 132 and 401 °C; for OTAP, and at 193 and 414 °C for ONAP. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1120–1125, 2004     

Synthesis and magnetic properties of poly(p‐phthaloyl‐disacetylaceton‐ethylenediimine) metal complexes

Macrocyclic Schiff‐base ligand, bisacetylaceton‐ethylenediimine (BAE) and its transition metal complexes M(BAE) (M = Cu²⁺, Ni²⁺) were synthesized. The complexes having characteristics of aromatic systems and well‐defined one‐dimensional structures, reacted with p‐phthaloyl chloride, to obtain polymer complexes. The complexes were characterized by elemental analysis, inductively coupled plasma (ICP), FT‐IR, and thermal analysis and show good thermal stability. ESR spectra analysis discovered that there are free radicals in the chain of polymers, indicating that a weak magnetic spin‐exchange interaction operates between the metal ions and free radicals. It is found that, as the bridging p‐phthaloyl group is able to propagate the magnetic exchange interaction, the polymer complexes show paramagnetic properties by measurement of temperature dependence of the magnetic property, and obey Curie–Weiss law. Copyright © 2001 John Wiley & Sons, Ltd.     

Magnetocaloric properties of dendrimer complexes of Fe(III) with substituted Schiff base

In dendrimer complexes of iron (III) with Schiff base (three complexes of iron (III) based on azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine, a significant magnetocaloric effect (MCE) and heat capacity was found the first time. It was found that the magnitude of MCE depends on the nature of the counter-ion of the complex. MCE were measured with a microcalorimeter over the temperature range of 278–320 K and in a magnetic induction of 0–1.0 T. The temperature dependences of the MCE dendrimer complexes of iron (III) with Schiff base were obtained for the first time. For all the samples studied, the existence of extreme temperature dependence of MCE in the range of temperatures 300–350 K, which is possibly the result of the magnetic phase transition, is shown. The correlation between the thermotropic mesomorphism with the magnetic phase transition in complexes has been established.     

Some divalent metal(II) complexes of novel potentially tetradentate Schiff base N,N′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde: Synthesis,spectroscopic characterization and bioactivities

A novel tetradentate dianionic Schiff base ligand, N ,N ′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde (H₂L) and some first row d‐transition metal chelates (Co(II), Cu(II), Ni(II) and Zn(II)) were synthesized and characterized using various physicochemical and spectroscopic methods. The spectroscopic data suggested that the parent Schiff base ligand coordinates through both deprotonated carboxylic oxygen and imine nitrogen atoms. The free Schiff base and its metal chelates were screened for their antimicrobial activities for various pathogenic bacteria and fungi using the agar well diffusion method. The antibacterial and antifungal activities of all the newly synthesized compounds are significant compared to the standard drugs ciprofloxacin and nystatin. The antioxidant activities of the compounds were determined by reduction of 1,1‐diphenyl‐2‐picrylhydrazyl and compared with that of vitamin C as a standard. DNA binding ability of the novel Schiff base and its complexes was investigated using absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and thermal denaturation. The obtained results clearly demonstrate that the binding affinity with calf thymus DNA follows the order: Cu(II) complex > Ni(II) complex > Zn(II) complex > Co(II) complex >H₂L. Furthermore, the DNA cleavage activity of the newly synthesized ligand and its metal complexes was investigated using supercoiled plasmid DNA (pUC18) gel electrophoresis.     

Synthesis and properties of poly(1‐naphthylacetylene) and poly(9‐anthrylacetylene)

Polymerizations of 1‐naphthylacetylene (1‐NA) and 9‐anthrylacetylene (9‐AA) by various transition metal catalysts were studied, and properties of the polymers were clarified. 1‐NA polymerized with WCl₆‐based catalysts to offer dark purple polymers in good yield. Especially, a binary catalyst composed of WCl₆ and Ph₃Bi gave a polymer with high molecular weight (M_w = 140×10³) and sufficient solubility in common solvents. The use of Mo and Rh catalysts, in contrast, resulted in the formation of insoluble red poly(1‐NA)s. 9‐AA gave insoluble polymers by both WCl₆‐ and MoCl₅‐based catalysts in moderate to good yields. Copolymerization of 9‐AA with 1‐NA by WCl₆–Ph₃Bi provided a soluble copolymer which exhibited the largest third‐order nonlinear optical susceptibilities (χ⁽³⁾(−3ω; ω, ω, ω) = 40×10⁻¹²) among all the substituted polyacetylenes synthesized so far. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 277–282, 1999     

Synthesis and properties of biomimetic poly(L‐glutamate)‐b‐poly(2‐acryloyloxyethyllactoside)‐b‐poly(L‐glutamate) triblock copolymers

A novel class of biomimetic glycopolymer–polypeptide triblock copolymers [poly(L ‐glutamate)–poly(2‐acryloyloxyethyllactoside)–poly(L ‐glutamate)] was synthesized by the sequential atom transfer radical polymerization of a protected lactose‐based glycomonomer and the ring‐opening polymerization of β‐benzyl‐L ‐glutamate N‐carboxyanhydride. Gel permeation chromatography and nuclear magnetic resonance analyses demonstrated that triblock copolymers with defined architectures, controlled molecular weights, and low polydispersities were successfully obtained. Fourier transform infrared spectroscopy of the triblock copolymers revealed that the α‐helix/β‐sheet ratio increased with the poly(benzyl‐L ‐glutamate) block length. Furthermore, the water‐soluble triblock copolymers self‐assembled into lactose‐installed polymeric aggregates; this was investigated with the hydrophobic dye solubilization method and ultraviolet–visible analysis. Notably, this kind of aggregate may be useful as an artificial polyvalent ligand in the investigation of carbohydrate–protein recognition and for the design of site‐specific drug‐delivery systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5754–5765, 2004     

X‐ray characterization and magnetic properties of dioxygen‐bridged CuII and MnIII Schiff base complexes

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi‐metal active sites of various metalloproteins and metalloenzymes. Multinuclear Cu^II and Mn^III compounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen‐bridged binuclear Mn^III complexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear Cu^II complexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen‐bridged copper(II) and manganese(III) Schiff base complexes, namely bis(μ‐4‐bromo‐2‐{[(3‐oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu₂(C₁₀H₁₀BrNO₂)₂], (1), and bis(diaqua{4,4′‐dichloro‐2,2′‐[(1,1‐dimethylethane‐1,2‐diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{μ‐4,4′‐dichloro‐2,2′‐[(1,1‐dimethylethane‐1,2‐diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C₁₈H₁₆Cl₂N₂O₂)(H₂O)₂]₂[Mn₂(C₁₈H₁₆Cl₂N₂O₂)₂(H₂O)₂](ClO₄)₄·2C₂H₅OH, (2), have been synthesized and single‐crystal X‐ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each Cu^II atom is four‐coordinated, with long weak Cu…O interactions of 2.8631 (13) Å linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each Mn^III atom is six‐coordinated. The shortest intra‐ and intermolecular nonbonding Mn…Mn separations are 3.3277 (16) and 5.1763 (19) Å for (2), while the Cu…Cu separations are 3.0237 (3) and 3.4846 (3) Å for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2–300 K and reveal the presence of antiferromagnetic spin‐exchange interactions between the transition metal ions.     

Theoretical study on second‐order nonlinear optical properties of spin crossover Fe(III) phenolate‐pyridyl Schiff base complexes

The density functional and ab initio theory were used to investigate the second‐order nonlinear optical (NLO) properties of Schiff base ligands, open‐shell Fe(III), and closed‐shell Ni(II) complexes. The effect of the metal center in complexes is thus manifold: it templates the formation of acentric structures, imparts high thermal stability to the chelate ring, and display higher second‐order NLO response than their ligands. The second‐order NLO response of metal complexes are intensively sensitive to the exchange donor/acceptor because the differences of the extent of charge separation and the intraligand charge transfer processes. Thus, substituted metal complexes could realize “switches on” the second‐order NLO response by exchange donor/acceptor. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Synthesis and catalytic properties of 1‐alkyl‐2‐imidazolineruthenium(II) complexes

New [RuCl₂(imidazoline)(arene)] complexes have been prepared. The complexes were characterized by conventional spectroscopic methods and elemental analyses. Upon reaction with 1,1‐diphenylprop‐2‐ynol they generate catalyst precursors that can perform the cycloisomerization of diallyltosylamide into N‐tosyl‐α‐methylenepyrrolidine. Copyright © 2004 John Wiley & Sons, Ltd.     

双水杨醛缩环己二胺类西佛碱及其配合物的合成、性质研究

合成了两种双水杨醛缩环已二胺类西佛碱N，N’-(二羟苯次甲基)环已二胺(1)和N，N’-二(3，5-二叔丁基-2-羟苯次甲基)环已二胺(2)，以及它们的金属锌配合物(3)和(4)，通过核磁共振、元素分析和红外光谱确定了四种物质的结构，研究了它们的紫外吸收光谱、荧光光谱，测定了(3)和(4)的荧光量子效率．(4)中四个叔丁基的存在使其荧光量子效率提高．此类双西佛碱金属配合物可以应用于有机电致发光材料中．     

Synthesis,structure and DNA cleavage of mononuclear Fe(III) complexes with 1,2,4‐triazole‐base ligand

Two new mononuclear iron(III) complexes, [Fe(HL)₂](ClO₄) · (H₂O)_1.75· CH₃CN (1) and [Fe(HL)Cl₂] · DMF (2) [H₂L = 3‐(2‐phenol)‐5‐(pyridin‐2‐yl)‐1,2,4‐triazole] have been synthesized and characterized by X‐ray single‐crystal structure analysis. The single crystal X‐ray crystallographic studies reveal that the central iron atom has a distorted octahedral environment for 1 and a distorted square pyramidal geometry for 2. The DNA cleavage activity of the iron(III) complexes was measured, indicating that the six‐coordinated iron(III) (complex 1) was cleavage inactive and only five‐coordinated complex 2 effectively promoted the cleavage of plasmid DNA in the presence and/or absence of activating agents (peroxide oxygen) at physiological pH and temperature. The mechanism of plasmid DNA cleavage was also studied by adding standard radical scavengers. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel rhenium(V) tetradentate N2O2 Schiff base monomer and dimer complexes

Several rhenium(V) oxo complexes with tetradentate N(2)O(2) Schiff base ligands were synthesized and characterized. The general synthetic procedure involved reaction of [NBu(4)][ReOCl(4)] with a tetradentate Schiff base ligand (L(1) = N,N'-ethylenebis(acetylacetoneimine), (acac(2)en) or L(2) = N,N'-propylenebis(acetylacetoneimine) (acac(2)pn)) in ethanol solution to generate complexes of the form trans-ReOX(L) where X = Cl(-), MeO(-), ReO(4)(-), or H(2)O. The product isolated from the reaction was found to be dependent on the reaction conditions, in particular the presence or absence of water and/or base. The mu-oxo-Re(2)O(3)(L)(2) dimers were synthesized and characterized for chemical and structural comparison to the related monomers. Conversion of the monomer to its dimer analogue was followed qualitatively by spectrophotometry. The complexes were characterized by (1)H and (13)C NMR, UV-vis, and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. The crystallographic data reported for the structures are as follows: trans-[ReO(OH(2))(acac(2)en)]Cl (H(20)C(12)ClN(2)O(4)Re) 1, triclinic (Ponemacr;), a = 7.2888(6) A, b = 9.8299(8) A, c = 10.8195(9) A, alpha = 81.7670(10) degrees, beta = 77.1510(10) degrees, gamma = 87.6200(10) degrees, V = 747.96(11) A(3), Z = 2; trans-[ReO(OReO(3))(acac(2)en)] (H(18)C(12)N(2)O(7)Re(2)) 2, monoclinic (P2(1)/c), a = 7.5547(4) A, b = 8.7409(5) A, c= 25.7794(13) A, beta = 92.7780(10) degrees, V = 1700.34(16) A(3), Z = 4; trans-[ReOCl(acac(2)pn)] (H(20)C(13)N(2)O(3)ClRe) 3, monoclinic (P2(1)/c), a = 8.1628(5) A, b = 13.0699(8) A, c = 28.3902(17) A, beta = 97.5630(10) degrees, V = 3002.5(3) A(3), Z = 8; trans-[ReO(OMe)(acac(2)pn)] (H(23)C(14)N(2)O(4)Re) 4, monoclinic (P2(1)/c), a = 6.7104(8) A, b = 27.844(3) A, c = 8.2292(9) A, beta = 92.197(2) degrees, V = 1536.4(3) A(3), Z = 4; trans-[mu-oxo-Re(2)O(3)(acac(2)en)(2)] (H(36)C(24)N(4)O(7)Re(2)) 5, monoclinic (P2(1)/n), a = 9.0064(5) A, b = 12.2612(7) A, c = 12.3695(7) A, beta = 90.2853(10) degrees, V = 1365.94(13) A(3), Z = 2; and trans-[mu-oxo Re(2)O(3)(acac(2)pn)(2)] (H(40)C(26)N(4)O(7)Re(2)) 6, monoclinic (P2(1)/n), a = 9.1190(5) A, b = 12.2452(7) A, c = 12.8863(8) A, beta = 92.0510(10) degrees, V = 1438.01(14) A(3), Z = 2.     

Nickel(II) Schiff base complex supported on nano‐titanium dioxide: A novel straightforward route for preparation of supported Schiff base complexes applying 2,4‐toluenediisocyanate

For the first time, a novel, straightforward and inexpensive route for immobilization of metals in Schiff base complex form is reported applying 2,4‐toluenediisocyanate as a precursor of primary amine group. A nickel(II) Schiff base complex supported on nano‐TiO₂ was designed and synthesized as an effective heterogeneous nanocatalyst for organic reactions, and well characterized using various techniques such as Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray analysis and thermogravimetric analysis. The catalytic efficiency of the complex was evaluated in selective oxidation of sulfide to sulfoxide by hydrogen peroxide as an oxidant under solvent‐free conditions at room temperature, which successfully resulted in high yield and high conversion of products. Effective factors including solvent type, oxidant and catalyst amount were also optimized. The catalyst shows outstanding reusability and could be impressively recovered for six consecutive cycles without significant change of its catalytic efficiency.     

Synthesis and electrochemistry of vanadium(IV) Schiff base complexes

The electrochemical properties of vanadyl(IV) derivatives, namely salen Schiff base complexes of the type [VO(Salen)] (5-BrSalen, 5-NO₂Salen, 5-MeOSalen, salpn (bis(salicylaldehyde)-1,3-propanediamine, 5-BrSalpn, 5-NO₂Salpn, 5-MeOSalpn, Me₂Salen, Salophen, 5-BrSalophen, and 5-MeOSalophen) were investigated. The equatorial Schiff base ligands affect the oxidation potentials via interaction with the d-orbitals of the vanadyl metal ion. The cathodic peak potential (E_pc) becomes less negative according to the sequence MeO- < H- < Br- < NO_2?.     

Synthesis of phenanthroline‐terminated polymers and their Fe(II)‐complexes

Well‐defined mono‐ and bifunctional, phenanthroline‐terminated poly(ethylene glycol) and polyisobutylene capable of polymer network formation were synthesized. The starting materials mono‐ and bi‐phenanthroline‐ (phen) terminated poly(ethylene glycols) (mPEG‐phen, phen‐PEG‐phen) and polyisobutylenes (PIB‐phen, phen‐PIB‐phen) were prepared by the Williamson synthesis and characterized by means of ¹H NMR and MALDI‐TOF mass spectrometry. According to UV–Vis spectrophotometry and ESI‐TOF mass spectrometry, the phenanthroline‐terminated polymers underwent quantitative complex formation with ferrous ions in solution. The aqueous solution of mPEG‐phen shows self‐assembly behavior. Important parameters, such as critical micelle concentration and hydrodynamic radius of the aggregates were also determined. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2709–2715, 2010     

Synthesis, characterization and magnetic properties of novel μ-isophthalato oxovanadium(IV) binuclear complexes

Four novel oxovanadium(IV) binuclear complexes have been synthesized, namely [(VO)₂(IPHTA) (L)₂SO₄ (L denotes 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen); 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy) and 5-nitro-1,10-phenanthroline (NO₂-phen)), where IPHTA is the isophthalate dianon. Based on elemental analyses, molar conductivity measurements, IR and electronic spectra studies, it is proposed that these complexes have IPHTA-bridged structures and consist of two vanadium(IV) atoms in a square-pyramidal environment. The complexes [(VO)₂(IPHTA)(Me₂bpy)₂]SO₄ (1) and [(VO)₂(IPHTA)(bpy)₂]SO₄ (2) were characterized by variable temperature magnetic susceptibility (4–300 K) and the data could be well fitted by the least-squares method to a susceptibility equation derived from the spin Hamiltonian operator, . The exchange integral, J, was found to be −26.8 cm⁻¹ for (1) and −31.0 cm⁻¹ for (2). These results are commensurate with antifferomagnetic interactions between two oxovanadium(IV) ions within each molecule. The influence of different terminal ligands on magnetic interactions between the metals of this kind of complexes is also discussed.     

Synthesis of novel ladder polymers of poly(3,4‐dihydro‐2H‐pyran‐2‐methanol)

Polydi(3,4‐dihydro‐2H‐pyran‐2‐methyl) esters of oxalic, adipic, and phthalic acids were prepared at different temperatures in the presence of different cationic initiators, namely, the boron trifluoride/diethyl ether complex system, anhydrous ferric chloride, and p‐toluene sulfonic acid. The obtained polymers were hydrolyzed under basic conditions, and the polydispersity indices of these polymers were determined before and after hydrolysis. The results are discussed to shed some light on the ability to use this analysis to investigate the precise structure of the obtained polymers and to predict the ability of these polymers to form ladder or semiladder polymers. Characteristics of such polymers were dependent, to some extent, on the type of crosslinks and the cationic initiators used for polymerization as well as the reaction temperature. It seems possible to optimize the conditions leading to formation of ladder or semiladder polydi(3,4‐dihydro‐2H‐pyran‐2‐methyl) esters of oxalic acid and adipic acid, respectively. The ladder structure was confirmed through determination of the polydispersity index before and after hydrolysis of the polymer formed at different temperatures and through computer‐aided molecular modeling. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3909–3915, 2002     

Synthesis and characterization of novel biodegradable block copolymer poly(ethylene glycol)‐block‐poly(L‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylene carbonate)

An amphiphilic block copolymer, poly(ethylene glycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate) [PEG‐b‐P(LA‐co‐MBC)], was synthesized in bulk by the ring‐opening polymerization of L ‐lactide with 2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate (MBC) in the presence of poly(ethylene glycol) as a macroinitiator with diethyl zinc as a catalyst. The subsequent catalytic hydrogenation of PEG‐b‐P(LA‐co‐MBC) with palladium hydroxide on activated charcoal (20%) as a catalyst was carried out to obtain the corresponding linear copolymer poly(ethyleneglycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylenecarbonate) [PEG‐b‐P(LA‐co‐MCC)] with pendant carboxyl groups. DSC analysis indicated that the glass‐transition temperature (T_g) of PEG‐b‐P(LA‐co‐MBC) decreased with increasing MBC content in the copolymer, and T_g of PEG‐b‐P(LA‐co‐MCC) was higher than that of the corresponding PEG‐b‐P(LA‐co‐MBC). The in vitro degradation rate of PEG‐b‐P(LA‐co‐MCC) in the presence of proteinase K was faster than that of PEG‐b‐P(LA‐co‐MBC), and the cytotoxicity of PEG‐b‐P(LA‐co‐MCC) to chondrocytes from human fetal arthrosis was lower than that of poly(L ‐lactide). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4771–4780, 2005