Chang-Tong Yang

Syntheses, structural properties and catecholase activity of copper(II) complexes with reduced Schiff base N-(2-hydroxybenzyl)-amino acids

A number of dicopper(II) complexes of reduced Schiff base ligands, N-(2-hydroxybenzyl)-amino acids [Cu2L2(H2O)x].yH2O (L = Sgly (1), D-Sala (2), L-Sala (3), DL-Sala (4), Sab2 (5), Sbal (6), Sab4 (7), Sval (8), Shis (9), Styr (10) and Stryp (11), x= 0-2 & y= 0-2) have been synthesized, and the solid-state structures of, and have been determined. The compounds and are binuclear in which the Cu(II) centres have square-pyramidal geometry with apical sites occupied by aqua ligands. In and one axial site is occupied by water and the other by an oxygen atom of the carboxylate group from the adjacent dimer through oxygen atoms to form 1D helical polymer. Variable temperature magnetic measurements of the dimer and helical polymer showed that they are typical for moderately strong antiferromagnetic coupling. All the complexes show significant catalytic activity on the oxidation of 3,5-di-tert-butylcatechol. The activity measured in terms of Kcat in the range 199-3800 h(-1) has been found to follow the order: 7>6>8>3>5 approximately 2 approximately 1>4 >10 >9 >11. The catalytic activity is found to increase with increasing the length of the methylene side chain of the amino acid in the reduced Schiff base ligands.

Synthesis, characterization and physicochemical properties of copper(II) complexes containing salicylaldehyde semicarbazone

Abstract Copper(II) complexes containing a series of salicylaldehyde semicarbazone ligands have been prepared and characterized by a range of physicochemical techniques. The X-ray structure of [Cu(HBnz2)Cl]·H2O (5) (where HBnz2 is salicylaldehyde-N,N-dibenzyl semicarbazone) shows the complex is monomeric and the copper atom is four coordinated in a distorted square planar geometry. The ligand chelates the copper in a tridentate fashion through the imine N, carbonyl O and phenolato O with the fourth position being occupied by coordinated Cl. The compound [Cu(Ph2)·H2O] (4) (where Ph2 is salicylaldehyde-N,N-diphenyl semicarbazone) is also formulated as a monomer whereas all other complexes are assumed to have a side-by-side dimeric arrangement of the metal chelating with the phenolate bridging the Cu(II) centres.

Chemical and biological studies of the dichloro(2-phenylpyridine) gold(III) complex and its derivatives

Four new derivatives of the type [Au(ppy)X2] (ppy = 2-phenylpyridine) together with [Au(ppy)Cl2] (1) have been synthesized and characterized [X = ac = CH3COO− (2), bz = C6H5COO− (3); mal = CH2(COO−)2 (4), cbdca = C4H6(COO−)2 (5)]. The crystal structures of 2 and 3 are similar in which two carboxylate groups are bound to gold through oxygen, but the two Au–O distances are inequivalent. The crystal structure of 5 shows that gold is bound to σ-C,N-phenylpyridine (ppy) and O,O-cbdca, forming a five-membered and a six-membered chelate ring, respectively. In all four structures the Au(III) center exhibits a square planar coordination geometry and the trans influence of the σ-bonded phenyl group is apparent. The σ-bonded phenyl group contributes to stabilizing these complexes in reducing, biological media. The reaction between 5 and chloride has been investigated by 1H NMR spectroscopy and reveals slow replacement of cbdca by chlorides through an intermediate [Au(ppy)(O-cbdca)Cl]. All five complexes have been tested for cytotoxic properties in vitro against MOLT-4 (human leukemia) and C2C12 (mouse tumour) cell lines. The results show that these complexes have similar cytotoxicity profile to cisplatin against MOLT-4 but are inactive on C2C12, except for complex 5.

Synthesis, characterization, and biological activities of 2-phenylpyridine gold(iii) complexes with thiolate ligandsElectronic supplementary information (ESI) available: ESMS data. See http://www.rsc.org/suppdata/dt/b3/b307610e/

A series of new 2-phenylpyridine Au(III) complexes [Au(ppy)X] with various thiolate ligands has been synthesized and characterized (X = (SCN)(NCS) (1), tlc (thiolactate) (2), tsc (thiosalicylate) (3), dmp (2,3-dimercapto-1-propanol) (4), dms (2,3-dimercaptosuccinic acid) (5), cys (cysteine) (6)). The crystal structure of [Au(ppy)(SCN)(NCS)] (1) shows the two soft carbanion and sulfur donors mutually cis to each other in the thermodynamically most stable isomer. It is noteworthy that the two thiocyanate ions bind to gold through nitrogen (trans to C) and sulfur (trans to N) atom, respectively, with the Au–NCS group linear whereas the Au–SCN is bent. Crystal structures of [Au(ppy)(tsc)]·1.5H2O (3) and [Au(ppy)(cys)]·0.5(Cl− + ClO4− + H2O) (6) show the expected square-planar coordination around the gold atom and the stronger trans influence groups S and C adopting the cis-orientated configuration. Complexes 1–5 have been tested in vitro against MOLT-4 human leukemia and C2Cl2 mouse tumour cell lines, where they are more cytotoxic than the clinically used cisplatin.

Chemical and biological studies of gold(III) complexes with uninegative bidentate N–N ligands

Three new gold(III) complexes with uninegative bidentate N–N ligands ([Au(pla)Cl2] (1), Hpla = picolinamide; [{Au(pz)Cl2}2] (2), Hpz = pyrazole; [{Au(mpz)Cl2}2] (3), Hmpz = 3-methylpyrazole) have been synthesized and characterized spectroscopically. The crystal structure of 1 contains one five-membered chelated ring and two cis-oriented chloride anions. It is the closest Au(III) analogue to cisplatin with an N–H group in the molecule and it forms a hydrogen bond with the carbonyl from adjacent molecule. The crystal structure of 2 shows a symmetrical six-membered Au(N–N)2Au ring. The two N–N bridging bonds and two gold atoms adopt a boat conformation, a configuration which thermodynamically stabilizes the complex. The two gold centres are square planar, each coordinated by two cis-oriented chlorides and nitrogens, respectively. These three new complexes have been tested for cytotoxic properties in vitro against MOLT-4 (human leukemia) and C2C12 (mouse tumour) cell lines. The results show that these complexes are slightly more cytotoxic than the clinically used cisplatin.

Synthesis, characterization and properties of copper(II) complexes containing N,N-di-(2-pyridylmethyl)-glycine and alanine

The multidentate ligands N ,N -di-(2-pyridylmethyl)-glycine (bpg) and N ,N -di-(2-pyridylmethyl)-alanine (bpa) were synthesized as their lithium salts and X-ray structures of these solved. Copper(II) complexes of these ligands have been prepared and structurally characterized. X-ray structures of compounds [Li(bpg)(H2O)]/H2 O( 1) and [Li(bpa)(H2O)]/H2 O( 2) shown the Li(I) ions adopt a distorted trigonal bipyrimidal geometry whereas in the Cu(II) compounds [Cu(bpg)](NO3)/H2 O( 3) and [Cu(bpa)](SO3CF3)/H2 O( 6) the Cu(II) ions are in an approximate square pyramidal geometry. The ligand chelates the copper ion in a tetradentate fashion with two pyridine N atoms, one tertiary imine N atom occupying the equatorial positions, and one carboxylato O atom occupying an axial position. The last equatorial position is occupied by the O atom from the carboxylate group of the neighboring molecule and thus forms a covalently bonded zig/zag chain, coordination polymer. # 2003 Elsevier Science B.V. All rights reserved.

Synthesis, characterization and properties of ternary copper(II) complexes containing reduced Schiff base N-(2-hydroxybenzyl)-α-amino acids and 1,10-phenanthroline

Ternary copper(II) complexes containing reduced Schiff base ligands (N-(2-hydroxybenzyl)-α-amino acid, where α-amino acid = glycine (H2sgly), L-alanine (H2sala) and L-valine (H2sval)) and 1,10-phenanthroline (phen) have been synthesized and characterized. The neutral mononuclear CuII complexes [Cu(L)(phen)]·xH2O (L = sgly (1), sala (2), sval (3)) have been prepared from Cu(OAc)2·H2O, H2L, phen, LiOH in the ratio 1 ∶ 1 ∶ 1 ∶ 2 in H2O–MeOH. The monodeprotonated CuII complexes [Cu(HL)(phen)](ClO4)·xH2O (L = Hsgly (4), Hsala (5), Hsval (6)) have been obtained from Cu(ClO4)2·6H2O, H2L, phen, LiOH in the ratio 1 ∶ 1 ∶ 1 ∶ 1 in H2O–MeOH. The dinuclear CuII complexes [Cu2(L)(phen)3](ClO4)2·xH2O (L = sgly (7), sala (8), sval (9)) were the only product isolated instead of 1–3 when Cu(ClO4)2·6H2O was used in the place of Cu(OAc)2·H2O. The electronic spectral titration experiments indicate that the neutral mononuclear compounds could be converted to protonated 4–6 but not vice versa. The protonated phenolic oxygen is involved in medium to weak interaction with CuII–OH distances, 2.446(3) A in 4, and 2.73(4) and 2.79(4) A in 5. Compound 4 is a mononuclear cation while 5 is a helical coordination polymer in the solid state with the carboxylate group in anti–anti bridging mode. The structures of 1, 4, 5 and 7 have been determined by X-ray crystallography. Variable temperature magnetic measurements of the helical polymer 5 showed very weak ferromagnetic coupling with μeff per Cu remaining constant at 1.80 BM between 300 and 30 K, then a rapid increase to 2.07 BM at 4 K. Fitting to a Heisenberg S = ½ chain model gave a J value of 1.2 cm−1.

Synthesis, Characterization and Biological Activity of Dioxouranium(VI) Complexes of Acyldipyridoxal Hydrazones

Four acyl dipyridoxal hydrozones ligands, H4PLn, have been prepared by condensing the ester of the diacids, hydrazine hydrate and pyridoxal hydrochloride in 1∶2∶2 molar ratio. The UO2 VI complexes of these ligands have been synthesized and characterized by various analytical and spectroscopic methods including X‐ray crystallography. The ligands and UO2 VI complexes have been tested for cytotoxicity. The solid‐state structure of [(UO2)4(PL1)2(H2O)4] · 12H2O has been found to be a cyclic tetramer and this may or may not represent the structure of the bulk sample. The structures of bulk 1–4 have been proposed to be polymeric. All the cytotoxicity testing was very kindly determined by Ms. Jiang Ling at the Biochemistry Department, National University of Singapore. We thank the National University of Singapore for funding this research.