Synthesis, crystal structures, DNA binding and cleavage activity of l-glutamine copper(II) complexes of heterocyclic bases

Ternary l-glutamine (l-gln) copper(II) complexes [Cu(l-gln)(B)(H₂O)](X) (B = 2,2′-bipyridine (bpy), , 1; B = 1,10-phenanthroline (phen), , 2) and [Cu(l-gln)(dpq)(ClO₄)] (3) (dpq, dipyridoquinoxaline) are prepared and characterized by physicochemical methods. The DNA binding and cleavage activity of the complexes have been studied. Complexes 1-3 are structurally characterized by X-ray crystallography. The complexes show distorted square pyramidal (4+1) CuN₃O₂ coordination geometry in which the N,O-donor amino acid and the N,N-donor heterocyclic base bind at the basal plane with a H₂O or perchlorate as the axial ligand. The crystal structures of the complexes exhibit chemically significant hydrogen bonding interactions besides showing coordination polymer formation. The complexes display a d-d electronic band in the range of 610-630 nm in aqueous-dimethylformamide (DMF) solution (9:1 v/v). The quasireversible cyclic voltammetric response observed near −0.1 V versus SCE in DMF-TBAP is assignable to the Cu(II)/Cu(I) couple. The binding affinity of the complexes to calf thymus (CT) DNA follows the order: 3 (dpq) > 2 (phen) ? 1 (bpy). Complexes 2 and 3 show DNA cleavage activity in dark in the presence of 3-mercaptopropionic acid (MPA) as a reducing agent via a mechanistic pathway forming hydroxyl radical as the reactive species. The dpq complex 3 shows efficient photo-induced DNA cleavage activity on irradiation with a monochromatic UV light of 365 nm in absence of any external reagent. The cleavage efficiency of the DNA minor groove binding complexes follows the order: 3 > 2 ? 1. The dpq complex exhibits photocleavage of DNA on irradiation with visible light of 647.1 nm. Mechanistic data on the photo-induced DNA cleavage reactions reveal the involvement of singlet oxygen (¹O₂) as the reactive species in a type-II pathway.     

Synthesis, crystal structure and photo-induced DNA cleavage activity of ternary copper(II)-thiosemicarbazone complexes having heterocyclic bases

New ternary copper(II) complexes of formulations [Cu(Ph-tsc)B] (B=1,10-phenanthroline, phen (1); dipyridoquinoxaline, dpq (2); dipyridophenazine, dppz (3); Ph-H₂tsc, salicylaldehyde-N(4)-phenylthiosemicarbazone) and [Cu(Me-tsc)(phen)] (4, Me-H₂tsc, salicylaldehyde-N(4)-methylthiosemicarbazone) are prepared, and their DNA binding and cleavage properties studied. Complex 1 has been characterized by single crystal X-ray crystallography. The molecular structure shows a distorted square pyramidal (4 + 1) geometry of the complex with the dianionic NSO-donor N(4)-phenyl-substituted thiosemicarbazone binding at the basal plane and the NN-donor planar heterocyclic base (phen) displaying axial-equatorial coordination. The one-electron paramagnetic complexes exhibit axial EPR spectra and show a d-d band near 580 nm for the phen and near 720 nm for the dpq, dppz complexes in their electronic spectra in DMF. The complexes show quasireversible cyclic voltammetric response near 0.08 V vs. SCE in DMF-0.1 M TBAP assignable to the Cu(II)/Cu(I) couple. The Ph-tsc complexes display good binding propensity to calf thymus (CT) DNA. They also show oxidative cleavage of supercoiled (SC) pUC19 DNA in dark under aerobic condition in the presence of mercaptopropionic acid. The complexes exhibit light-induced DNA cleavage activity at 312 and 532 nm. Mechanistic investigations reveal DNA minor groove binding for the phen and dpq complexes, and major groove binding for the dppz species. The complexes are cleavage inactive under argon atmosphere. In the ternary structure, the thiosemicarbazones, dpq and dppz act as photosensitizers, while the planar heterocyclic bases are binder to DNA. The mechanistic pathways involved and the role of metal in the DNA cleavage reactions are discussed.     

Synthesis, structure, DNA binding and DNA cleavage activity of oxovanadium(IV) N-salicylidene-S-methyldithiocarbazate complexes of phenanthroline bases

Ternary oxovanadium(IV) complexes [VO(salmdtc)(B)] (1-3), where salmdtc is dianionic N-salicylidene-S-methyldithiocarbazate and B is N,N-donor phenanthroline bases like 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3), are prepared, characterized and their DNA binding and DNA cleavage activity studied. Complex 3 is structurally characterized by single-crystal X-ray crystallography. The molecular structure shows the presence of a vanadyl group in six-coordinate VN₃O₂S coordination geometry. The S-methyldithiocarbazate Schiff base acts as a tridentate NSO-donor ligand in a meridional binding mode. The N,N-donor heterocyclic base displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo-group. The complexes show a d-d band in the range of 675-707 nm in DMF. They exhibit an irreversible oxidative cyclic voltammetric response near 0.9 V due to the V(V)/V(IV) couple and a quasi-reversible reductive V(IV)/V(III) redox couple near −1.0 V vs. SCE in DMF-0.1 M TBAP. The complexes show good binding propensity to calf thymus DNA giving binding constant values in the range of 7.4 × 10⁴-2.3 × 10⁵ M⁻¹. The thermal denaturation and viscosity binding data suggest DNA surface and/or groove binding nature of the complexes. The complexes show poor chemical nuclease activity in dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide. The dpq and dppz complexes show efficient DNA cleavage activity in UV-A light of 365 nm via a type-II mechanistic pathway involving formation of singlet oxygen (¹O₂) as the reactive species.     

Synthesis, crystal structure and photo-induced DNA cleavage activity of ternary copper(II) complexes of NSO-donor Schiff bases and NN-donor heterocyclic ligands

New ternary copper(II) complexes [CuLⁿB](ClO₄) (1-3), where HLⁿ is the NSO donor Schiff base derived from the condensation of 2-mercaptoethylamine hydrochloride with salicylaldehyde (HL¹) or 2-hydroxy-3-methoxybenzaldehyde (HL²) and B is NN-donor heterocyclic base like 2,2′-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2) or 2,9-dimethyl-1,10-phenanthroline (dmp, 3), are prepared, structurally characterized by X-ray crystallography and their DNA cleavage activity studied. The complexes show distorted square-pyramidal (4 + 1) CuN₃OS coordination geometry in which the NSO-donor Schiff base is bonded at the basal plane and the NN-donor heterocyclic base displays axial-equatorial mode of bonding [Cu-S distance: ∼2.4 Å]. The one-electron paramagnetic (μ_eff = ∼1.9 μ_B) complexes display axial EPR spectra in DMF glass at 77 K giving g_∥ = ∼2.2 (A_∥ = 162 G) and g_⊥ = ∼2.0, indicating {d_x²-y²}¹ ground state. The complexes exhibit visible spectral d-d band in MeCN near 650 nm and two charge transfer bands near 400 nm. Complexes 1 and 2 display quasireversible cyclic voltammetric response in DMF-Tris buffer (1:4 v/v, pH 7.2) for the Cu(II)/Cu(I) couple at ca. −0.1 V vs. SCE. Complex 3 exhibits an irreversible reduction process forming [Cu^I(dmp)₂]⁺. Binding of 1-3 to calf thymus DNA shows the relative order: 2 (phen) ? 3 (dmp) > 1 (bpy). Complex 2 efficiently cleaves supercoiled pUC19 DNA in the presence of mercaptopropionic acid (MPA) forming hydroxyl radical or on irradiation with light of 312, 532 and 632.8 nm wavelength in a type-II process. Complexes 1 and 3 are cleavage inactive.     

Ni(II) complexes with Schiff bases derived from amino sugars

It was found by 1H and 13C NMR spectroscopy that the Schiff base, 2-deoxy-2-(2-hydroxybenzaldimino)-D-glucopyranose exhibits enol-imine-keto-amine and anomeric equilibria in methanolic, and in dimethyl sulfoxide solutions. The reaction of the Schiff base with nickel acetate gave the bidentate, mononuclear Ni(II) complex that was characterized by spectroscopic methods and by cyclic voltammetry. The coordination of the Schiff base to the metal is through the enol-imine tautomeric form, and the anomeric equilibrium remains in dimethyl sulfoxide solutions. This complex was also obtained by reaction of D-glucosamine with Ni(II) salicylaldehydate. The same reaction was employed for the synthesis of bis-N-[2-deoxy-D-galactopyranosyl-2-(2-hydroxybenzaldiminate)]Ni(II). The small paramagnetic shifts of the 1H NMR resonances of the complexes suggest that paramagnetic species are present in low proportions.     

Synthesis, DNA binding, photo-induced DNA cleavage, cytotoxicity and apoptosis studies of copper(II) complexes

Two new Cu(II) complexes, [Cu(acac)(dpq)Cl] () and [Cu(acac)(dppz)Cl] () (acac = acetylacetonate, dpq = dipyrido[3,2-d:20,30-f]quinoxaline, dppz = dipyrido[3,2-a:20,30-c] phenazine), have been synthesized and their DNA binding, photo-induced DNA cleavage activity and cell cytotoxicity are studied. The complexes show good binding propensity to calf thymus DNA in the order: 2(dppz) > 1(dpq). Furthermore, two complexes exhibit efficient DNA cleavage activity on natural light or UV-A (365 nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The photo-induced DNA cleavage activity of the dppz complex 2 is found to be more efficient than its dpq analogue. In vitro study of the photocytotoxicity of two complexes on HeLa cells indicate that both of them have the potential to act as effective anticancer drugs, with IC₅₀ values of 5.25 ± 0.83 μM (1) and 4.40 ± 0.52 μM (2) in the natural light, and 2.57 ± 0.92 μM (1) and 2.18 ± 0.52 μM (2) in UV-A light. In addition, to detect an apoptotic HeLa body, cells were stained with Hoechst 33342 dye.     

Solubility and crystal structure of N-(1-deoxy-beta-D-fructopyranos-1-yl)-l-histidine monohydrate ('D-fructose-l-histidine')

Within a set of food-related Amadori compounds, crystalline N-(1-deoxy-beta-D-fructopyranos-1-yl)-l-histidine monohydrate (Fru-l-HisxH(2)O) has an unusually low solubility in water, which we determined as 0.21 g/100 g at 25 degrees C. The majority of the other fructose-amino acid conjugates have solubilities exceeding 100 g/100 g in water at this temperature. We report the crystal structure data on Fru-l-HisxH(2)O. The conformation of the carbohydrate is the normal (2)C(5) pyranose chair. Bond lengths and valence angles compare well with the average values from a number of pyranose structures. All hydroxyl and carboxyl oxygen atoms, all nitrogen atoms and the water molecule are involved in an extensive hydrogen bonding, which forms a network of infinite chains with small antidromic rings.     

Structural and DNA cleavage of sugar-derived Schiff base ligands and their dinuclear Cu(II) complexes

Neutral dinuclear Cu(II) complexes of Schiff base ligands derived from d-glucose have been synthesized and structurally characterized. These complexes were evaluated for their interaction with DNA, and DNA cleavage was observed even in the presence of radical inhibitors.     

Synthesis, crystal structure and DNA cleavage activity of a novel Ni(II)-Cd(II) coordination polymer

A novel one-dimensional heterometallic complex, {Cd₂[NiL]₂(SCN)₄(H₂O)}_n (1), has been synthesized and characterized by single-crystal X-ray analysis, where L is dianion of 2,3-dioxo-5,6,13,14-dibenzo-9,10-cyclohexyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene. The most striking feature of 1 is that in the structure there is one type of S-S bond (1.823(13) Å) formed by two thiocyanate groups which has not been reported to our knowledge. The DNA cleavage activity of 1 in the presence of H₂O₂ was compared with those of nickel(II) ion, cadmium(II) ion and corresponding mononuclear precursor NiL (2). The DNA cleavage kinetics was studied and the corresponding activation parameters of 1 were obtained.     

One-dimensional copper(II) coordination polymers bridged both by mu-trans-oxamidates and phenyldicarboxylates: Synthesis, crystal structure and DNA binding studies

Two new one-dimensional copper(II) polymers with formulae of [Cu₂(H₂O)₂(dmapox)(ipa)₂]_n (1) and [Cu₂(H₂O)₂(dmapox)(tpa)₂]_n (2), where dmapox, ipa and tpa stand for the dianion of N,N′-bis[3-(dimethylamino)propyl]oxamide, isophthalic acid and terephthalic acid respectively, have been synthesized and characterized by elemental analysis, conductivity measurement, IR and electronic spectral studies. The crystal structures of the two complexes have been determined by X-ray single-crystal diffraction. The structures of 1 and 2 consist of one-dimensional copper(II) coordination polymeric chain constructed both by the bis-tridentate trans-dmapox and bis-monodentate phenyldicarboxylate bridging ligands. In the two complexes, the environment around the copper(II) atoms can be described as distorted square-pyramid and the Cu···Cu separations through μ-trans-dmapox and phenyldicarboxylato bridging ligands are 5.245(5) Å and 8.212(3) Å for 1, 5.237(8) Å and 11.171(1) Å for 2, respectively. The binding properties of the two copper(II) polymers with herring sperm DNA (HS-DNA) have been investigated by using absorption and emission spectral and electrochemical techniques and viscometry. The results show that the two copper(II) complexes interact with the HS-DNA in the mode of intercalation with the intrinsic binding constants of 1.22(±0.2) × 10⁴ M⁻¹ and 1.45(±0.3) × 10⁴ M⁻¹ for 1 and 2, respectively.     

Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(L)(B)] (1-3), where H₂L is a Schiff base ligand 2-(2-hydroxybenzylideneamino)phenol and B is 1,10-phenanthroline (phen for 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq for 2) or dipyrido[3,2-a:2′,3′-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO₃N₃ coordination geometry. The complexes show a d-d band within 800-850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)-V(IV) and a reductive response within −1.1 to −1.3 V due to V(IV)-V(III) couple in DMF-0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 × 10⁴ to 1.2 × 10⁵ M⁻¹. The complexes do not show any “chemical nuclease” activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via ¹O₂ pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO^• pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC₅₀ value of 13 μM, while it is less toxic in dark (IC₅₀ = 97 μM).     

Synthesis, characterization and l-lactide polymerization behavior of bis(amidinate) rare earth metal amide complexes

A family of neutral and solvent-free bis(amidinate) rare earth metal amide complexes with a general formula [RC(N-2,6-Me₂C₆H₃)₂]₂LnN(SiMe₃)₂ (R = phenyl (Ph), Ln = Y (1), Nd (2); R = cyclohexyl (Cy), Ln = Y (3), Nd (4)) were synthesized in high yields by one-pot salt metathesis reaction of anhydrous LnCl₃, amidinate lithium salt [RC(N-2,6-Me₂C₆H₃)₂]Li, and NaN(SiMe₃)₂ in THF at room temperature. Single crystal structural determination of complexes 1, 2 and 4 revealed that the central metal adopts distorted pyramidal geometry. In the presence of 1 equivalent of ⁱPr-OH, all these complexes were active for l-lactide polymerization in toluene at 70 °C to give high molecular weight (M_n > 10⁴) polymers.     

Tris-ruthenium(II)/copper(II) multimetallic porphyrin: Synthesis, characterization, DNA binding and supercoiled DNA photocleavage studies

The porphyrin, meso-5-(pentafluorophenyl)-10, 15, 20-tris(4-pyridyl)porphyrin has been used to synthesize two new metalloporphyrin complexes. Insertion of copper(II) into the porphyrin center gives the copper(II) porphyrin. Coordination of three [Ru(bipy)₂Cl]⁺ moieties (where bipy = 2,2′-bipyridine) to the pyridyl nitrogens of the copper(II) porphyrin gives the target complex. Electronic transitions associated with the copper(II) porphyrin and the triruthenium copper(II) porphyrin include an intense Soret band and a less intense Q-band in the visible region of the spectrum. An intense π-π∗ transition in the UV region associated with the bipyridyl groups and a metal to ligand charge transfer (MLCT) band appearing as a shoulder to the Soret band are observed for the ruthenated copper(II) porphyrin. Electrochemical properties associated with the multimetallic complex include a redox couple in the cathodic region with E_1/2 = −0.86 V versus Ag/AgCl attributed to the porphyrin and a redox couple in the anodic region E_1/2 = 0.88 V versus Ag/AgCl due to the Ru^III/II couple. DNA titrations indicate the triruthenium copper(II) porphyrin interacts with DNA potentially through a groove binding mechanism. Irradiation of aqueous solutions of the target complex and supercoiled DNA at a 10:1 base pair to complex ratio with visible light above 400 nm indicates that the complex causes nicking of the DNA helix.     

Bis(pyrazolyl) palladium(II), platinum(II) and gold(III) complexes: Syntheses, molecular structures and substitution reactions with l-cysteine

A series of pyrazolyl palladium(II), platinum(II) and gold(III) complexes, [PdCl₂(3,5-R₂bpza)] {R = H (1), R = Me (2), bpza = bis-pyrazolyl acetic acid}, [PtCl₂(3,5-R₂bpza)] {R = H (3a), R = Me (4)}, [AuCl₂(3,5-R₂bpza)]Cl {R = H (5a), R = Me (6a)} and [PdCl₂(3,5-R₂bpzate)] {R = Me (7)} have been synthesised and structurally characterised. Single crystal X-ray crystallography showed that the pyrazolyl ligands exhibit N^N-coordination with the metals. Anticancer activities of six complexes 1-6a were investigated against CHO cells and were found to have low activities. Substitution reactions of selected complexes 1, 2, 3a and 5a with l-cysteine show that the low anticancer activities compounds and that the rate of substitution with sulfur-containing compounds is not the cause of the low anticancer activities.     

Synthesis, crystal structure and properties of the novel chiral 3D coordination polymer with S-carboxymethyl-l-cysteine

Reaction of fresh Mn(OH)₂ precipitate and S-carboxymethyl-l-cysteine (H₂SCMC) in aqueous solution afforded a novel chiral 3D coordination polymer Mn(H₂O)(SCMC) 1, which crystallizes in the acentric polar space group P2₁ with cell constants a = 5.079(1) Å, b = 9.617(2) Å, c = 8.649(2) Å, β = 94.40(3)°, V = 421.2(1) Å³, Z = 2, and exhibit a SHG effect and ferroelectricity (a remnant polarization P_r = 0.0159 uC cm⁻², coercive field E_c = 0.83 kV cm⁻², saturation of the spontaneous polarization P_s = 0.234 uC cm⁻²). To the best of our knowledge, the present compound represents the first example of S-carboxymethyl-l-cysteine coordination polymers that exhibit possible ferroelectric behavior. The structural analysis revealed that the Mn²⁺ ions in 1 are each coordinated by one N atom and five O atoms of four S-carboxymethyl-l-cysteine ligand bridges four symmetry-related Mn²⁺ ions to form 3D MOF of 6⁶ topology type with irregular chiral channels extending along [1 0 0]. The temperature-dependent magnetic susceptibilities shows that 1 obeys Curie-Weiss law χ_m = C/(T − Θ) with C = 4.23 cm³ mol⁻¹ K and Θ = −5.86 K and the best fit gave a weak antiferromagnetic coupling (J = −0.282(5) cm⁻¹) among Mn ions.     

Synthesis, crystal structure, antibacterial assay and DNA binding activity of new binuclear Cu(II) complexes with bridging oxamidate

Two new binuclear copper complexes, [Cu₂(oxpn)(bpy)(pic)(H₂O)](pic) (1) and [Cu₂(oxpn)(Me₂bpy)(pic)](pic) (2) [H₂oxpn = N,N′-bis(3-aminopropyl)oxamide; Hpic = 2,4,6-trinitrophenol; bpy = 2,2′-bipyridine; Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine], have been synthesized and characterized by elemental analyses, conductivity measurements, IR, UV-visible spectroscopy and single crystal X-ray analyses. Both complexes have similar molecular structures. In complex 1, the central two Cu(II) atoms are bridged by cis-oxpn²⁻ with the Cu1-Cu2 separation of 5.221 Å and the polyhedron of each copper atom is a square-pyramid. Similarly, complex 2 is a cis-oxpn²⁻-bridged binuclear complex with the Cu1-Cu2 separation of 5.196 Å. Cu1(II) central atom situated in a tetrahedral geometry is four-coordinated and Cu(II) atom situated in a square-pyramidal geometry is five-coordinated. Hydrogen bonding interactions and π-π stacking interactions link the binuclear copper complex 1 or 2 into a 2D infinite network. The antibacterial assays indicate that the two complexes showed better activities than their ligands. The interactions of the two binuclear complexes with herring sperm DNA (HS-DNA) have been studied by UV absorption titration, fluorescence titration and viscosity measurements. The results suggest that the two binuclear complexes bind to HS-DNA via an intercalative mode.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

Efficient synthesis of 2-deoxy-L-erythro-pentose (2-deoxy-L-ribose) from L-arabinose

An efficient and practical route for the large-scale synthesis of 2-deoxy-L-erythro-pentose (2-deoxy-L-ribose) starting from L-arabinose was developed using Barton-type free-radical deoxygenation reaction as a key step. The radical precursor, a phenoxythiocarbonyl ester, was prepared in situ, and the most efficient deoxygenation was achieved by slow addition of tributyltin hydride to the reaction mixture.     

Double-strand DNA cleavage induced by oxindole-Schiff base copper(II) complexes with potential antitumor activity

Some oxindole-Schiff base copper(II) complexes have already shown potential antitumor activity towards different cells, inducing apoptosis in a process modulated by the ligand, and having nuclei and mitochondria as main targets. Here, three novel copper(II) complexes with analogous ligands were isolated and characterized by spectroscopic techniques, having their reactivity compared to the so far most active complex in this class. Cytotoxicity experiments carried out toward human neuroblastoma SH-SY5Y cells confirmed its pro-apoptosis property. DNA cleavage studies were then performed in the presence of these complexes, in order to verify the influence of ligand structural features in its nuclease activity. All of them were able to cause double-strand DNA scissions, giving rise to nicked circular Form II and linear Form III species, in the presence of hydrogen peroxide. Additionally, DNA Form II was also detected in the absence of peroxide when the most active complex, [Cu(isaepy)₂]²⁺ 1, was used. In an effort to better elucidate their interactions with DNA, solutions of the different complexes titrated with DNA had their absorption spectra monitored. An absorbance hyperchromism observed at 260 nm pointed to the intercalation of these complexes into the DNA structure. Further, investigations of 2-deoxy-d-ribose (DR) oxidation catalyzed by each of those complexes, using 2-thiobarbituric acid reactive species (TBARS) method, and detection of reactive oxygen species (ROS) formation by spin-trapping EPR, suggested that their mechanism of action in performing efficiently DNA cleavage occurs preferentially, but not only by oxidative pathways.     

Purification and Characterization,of Rice Bran Lipase II

A species of rice bran lipase (lipase II) was purified by ammonium sulfate precipitation, followed by successive chromatographies on DEAE-cellulose, Sephadex G–75 and CH-Sephadex C–50. Both polyacrylamide disc electrophoresis and ultracentrifugation demonstrated that the enzyme protein is homogeneous. The isoelectric point of the enzyme was 9.10 by ampholine electrophoresis. The sedimentation coefficient of the enzyme was evaluated to be 2.60 S, and the molecular weight to be 33,300 according to Archbald’s method. The enzyme showed the optimum pH between 7.5 and 8.0, and the optimum temperature at about 27°C. It was stable over the pH range from 5 to 9.5 and below 30°C. In substrate specificity, the enzyme exhibited a high specificity toward triglycerides having short-carbon chain fatty acids, although it was capable of hydrolyzing the ester bonds in the rice and olive oil.