Synthesis, characterization and in vitro cytotoxicity studies of platinum(IV) complexes with thiouracil ligands

Reactions of [PtMe₃(bpy)(Me₂CO)][BF₄] (2) with the thionucleobases 2-thiouracil (s²Ura), 4-thiouracil (s⁴Ura) and 2,4-dithiouracil (s²s⁴Ura) resulted in the formation of complexes of the type [PtMe₃(bpy)(L-κS)][BF₄] (L = s²Ura, 3; s⁴Ura, 4; s²s⁴Ura, 5). The complexes were characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt), IR spectroscopy as well as microanalyses. The coordination through the C4S groups (4, 5) was additionally confirmed by DFT calculations, where it was shown that these complexes [PtMe₃(bpy)(L-κS⁴)]⁺ (L = s⁴Ura, s²s⁴Ura) are about 5.8 (4b) and 3.3 kcal/mol (5b), respectively, more stable than the respective complexes, having thiouracil ligands bound through the C2X groups (X = O, 4a; S, 5a). For [PtMe₃(bpy)(s²Ura-κS²)][BF₄] (3) no preferred coordination mode could be assigned solely based on DFT calculations. Analysis of NMR spectra showed the κS² coordination. In vitro cytotoxic studies of complexes 3−5 on nine different cell lines (8505C, A253, FaDu, A431, A549, A2780, DLD-1, HCT-8, HT-29) revealed in most cases moderate activities. However, 3 and 5 showed significant activity towards A549 and A2780, respectively, possessing IC₅₀ values comparable to those of cisplatin. Cell cycle perturbations and trypan blue exclusion test on cancer cell line A431 using [PtMe₃(bpy)(s²s⁴Ura-κS⁴)][BF₄] (5) showed induction of apoptotic cell death. Furthermore, the reaction of [PtMe₃(OAc-κ²O,O′)(Me₂CO)] (6) with 4-thiouracil yielded the dinuclear complex [(PtMe₃)₂(μ-s⁴Ura_-H)₂] (7), which has been characterized by microanalysis, NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopy as well as ESI mass spectrometry. X-ray diffraction analysis of crystals yielded in an isolated case exhibited the presence of a hexanuclear thiouracilato platinum(IV) complex, possessing each three different kinds of methyl platinum(IV) moieties and 4-thiouracilato ligands. This exhibited the ability of 4-thiouracil platinum(IV) complexes to form multinuclear complexes.     

Stereospecific ligands and their complexes. V. Synthesis, characterization and antimicrobial activity of palladium(II) complexes with some alkyl esters of (S,S)-ethylenediamine-N,N′-di-2-propanoic acid

Three new ligands and their palladium(II) complexes of general formula [PdCl₂(R₂-S,S-eddp)] (R = n-propyl, n-butyl and n-pentyl) have been synthesized and characterized by microanalysis, infrared and ¹H and ¹³C NMR spectroscopy. Antimicrobial activity of these ligands and complexes was tested by microdilution method and both minimal inhibitory and microbicidal concentration were determined. These tested complexes demonstrated the significant antifungal activity against pathogenic fungi Aspergillus flavus and Aspergillus fumigatus. On the other hand, these complexes demonstrated moderate antibacterial activity.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Synthesis, characterization, and cytotoxicity of trimethylplatinum(IV) complexes with 2-thiocytosine and 1-methyl-2-thiocytosine ligands

The reaction of [PtMe₃(MeOH)(bpy)][BF₄] (1) with the thionucleobases 2-thiocytosine (SCy, 2) and 1-methyl-2-thiocytosine (1-MeSCy, 3) resulted in the formation of the complexes [PtMe₃(bpy)(SCy-κS)][BF₄] (4) and [PtMe₃(bpy)(1-MeSCy-κS)] [BF₄] (5), respectively. The complexes were characterized by ¹H and ¹³C NMR spectroscopy as well as by single-crystal X-ray analyses of 4 · MeOH and 5. In 4 · MeOH two strong hydrogen bonds (N4-H?N3′: N4?N3′ 2.976(7) Å) between the thiocytosine ligands give rise to base pairing thus forming dinuclear cations [{PtMe₃(bpy)(SCy-κS)}₂]²⁺. In both complexes the platinum atom is octahedrally coordinated [PtC₃N₂S] by three methyl ligands, the 2,2′-bipyridine ligand and the κS coordinated nucleobase (configuration index: OC-6-33). The structural investigations gave evidence that the sulfur atoms of the nucleobase ligands in 4 · MeOH and 5 have to be regarded as sp³ and sp² hybridized, respectively. Thus, the ligand in 4 · MeOH has to be considered as the deprotonated thiol-amino form of thiocytosine being reprotonated at N1. In complex 5 the 1-MeSCy is coordinated in its thione-amino form. DFT-calculations of the base-paired dinuclear cation in 4 as well as of 4 itself gave proof of the strength of the hydrogen bond (8.5 kcal/mol) and exhibited that cation-anion interactions influence the conformation of the complex. In vitro cytotoxicity studies of 4 and 5 using nine different human tumor cell lines revealed moderate cytotoxic activity.     

Platinum(IV) complexes with ethylenediamine-N,N′-diacetate diester (R2edda) ligands: Synthesis, characterization and in vitro antitumoral activity

The novel N,N-type bidentate ligand precursors, diethyl, dipropyl esters of ethylenediamine-N,N′-diacetic acid dihydrochloride (HOOCCH₂NHCH₂CH₂NHCH₂COOH · 2HCl, H₂edda · 2HCl), and the corresponding tetrachloroplatinum(IV) complexes, [PtCl₄(R₂edda)] · H₂O (ROOCCH₂NHCH₂CH₂NHCH₂COOR, R = Me, Et, n-Pr), were synthesized. The esters coordinated as bidentate ligands via both N donor atoms. The esters, as well as the complexes, have been characterized by infrared, ¹H and ¹³C NMR spectroscopy and elemental analysis. Solid state structures of both dimethyl and diethyl ester platinum(IV) complexes have been determined by X-ray crystallography. Quantum chemical calculations were performed in order to investigate diastereoselectivity in the formation of the platinum(IV) complexes. The in vitro cytotoxic evaluation of the investigated complexes in human tumor cell lines 1411HP, H12.1 (both testicular germ cell tumors), DLD-1 (colon carcinoma), 518A2 (melanoma), A549 (lung carcinoma) and liposarcoma showed a dose-dependent antiproliferative effect in all cell lines. Remarkably, the highest cytotoxic activity was observed in the cisplatin-resistant cell line 1411HP. In addition, at higher concentrations the treatment with these complexes led to the induction of apoptosis in all cell lines except for DLD-1.     

Studies of mononuclear and dinuclear complexes of dibromodimethylplatinum(IV): Preparation, characterization and crystal structures

A number of complexes of the types [PtBr₂Me₂(N^?N)] (N^?N = 4,4′-di-Me-2,2′-bpy (1); 4,4′-di-t-Bu-2,2′-bpy (2); 2,2′-bpz (3); bpym (4)) and [PtBr₂Me₂(L)₂] (L = H-pz (5); 4-Me-H-pz (6); H-idz (7); H-im (8); H-bim (9); quaz (10)) are reported. Characterization by NMR (¹H, ¹³C and ¹⁹⁵Pt), IR and EI-MS is given. In addition, crystal structures of several of these complexes are described. Furthermore, interactions within these structures including intramolecular hydrogen bonding and π-π stacking interactions are reported. The reactivity of selected mononuclear complexes was investigated and yielded two dinuclear complexes [PPh₄][(PtBrMe₂)₂(μ-Br)(μ-pz)₂] (11) and [(PtBr₂Me₂)₂(μ-bpym)] (12), respectively. The latter complex is accompanied by a solid-state structure. Finally, the thermal stability of all complexes is reported.     

Synthesis and in vitro antitumoral activity of novel O,O'-di-2-alkyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate ligands and corresponding platinum(II/IV) complexes

Syntheses of two novel ligand precursors O,O'-diisopropyl- (1a) and O,O'-diisobutyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate dihydrochloride monohydrate (1b) and the corresponding dichloroplatinum(II) (2a and 2b) and tetrachloroplatinum(IV) complexes (3a and 3b) are described here. The substances were characterized by IR, (1)H and (13)C spectroscopy and elemental analysis. Crystal structures were determined for 1a and the corresponding platinum(IV) complex, 3a. In vitro antiproliferative activity was determined against tumor cell lines: human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, rested and stimulated normal immunocompetent cells (human peripheral blood mononuclear PBMC cells) using KBR test (Kenacid Blue Dye binding test). The IC(50)(microM) values for the most active compound 3a were: 30.48+/-2.54; 12.26+/-2.60; 13.68+/-3.22; 80.18+/-24.07 and 71.30+/-21.70, respectively.     

Synthesis and transition metal complexes of 3,3-bis(1-vinylimidazol-2-yl)propionic acid, a new N,N,O ligand suitable for copolymerisation

The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ³-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)₃] (6), [Mn(bvip)(CO)₃] (7) and [Cu(bvip)₂] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)₅] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres.     

Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2^′:6,2^′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)₂] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)₂](I)₂ (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO₃)₂ · 4H₂O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO₃)₂(H₂O)] (3) and [Mn(bpea)(NO₃)₂] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.     

Synthesis, X-ray crystal structure and NMR characterisation of mononuclear Pd(II) and Pt(II) complexes of didentate ligands with NN′-donor set

Two new 3,5-dimethylpyrazolic derived ligands that are N1-substituted by diamine chains, 1-[2-(diethylamino)ethyl]-3,5-dimethylpyrazole (L1) and 1-[2-(dioctylamino)ethyl]-3,5-dimethylpyrazole (L2) were synthesised. Reaction of the ligands, L1 and L2, with [MCl₂(CH₃CN)₂] yielded [MCl₂(L)] (M = Pd(II), Pt(II)) complexes. These complexes were characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹⁹⁵Pt{¹H} NMR spectroscopies. The crystal structure of [PdCl₂(L1)] was determined by single-crystal X-ray diffraction methods. The structure consists of mononuclear units. The Pd(II) atom is coordinated by a pyrazolic nitrogen, an amine nitrogen and two chlorine atoms in a cis disposition. In this structure, C-H?Cl, C-H?H-C and C-H?C-H intermolecular interactions have been identified.     

Supramolecular architectures based on di-, tri- and tetrameric complexes with N,N′-diacylhydrazide ligands

Five new complexes, [Co₃(HL₁)₂(Py)₈]·4CH₃OH (1), [Ni₃(HL₁)₂(Py)₄]₂·2DMF (2), [Co₃(H₂L₂)₂(Py)₈]·2NO₃ (3), [Ni₂(HL₂)(Py)₆] (4) and [Cu₄(HL₂)₂(Py)₄]·4DMF (5) (H₄L₁ = N-propionyl-4-hydroxysalicylhydrazide, H₄4-hopshz; H₅L₂ = N-(3-carboxy-cis-2-propenoyl)-4-hydroxysalicylhydrazide, H₅4-hocpshz) have been obtained from two N,N′-diacylhydrazide ligands and characterized by elemental analysis, FT-IR, X-ray diffraction and antimicrobial activities. These di-, tri-, and tetrameric complexes are connected into three-dimensional supramolecular architectures with interesting topologies through O-H?O, C-H?O and C-H?π interactions. 1-3 are linear trimeric complexes with the ligands triply-deprotonated. Topological analysis indicates that they exhibit 2D (4,4), 3D (6,8)-connected (3³4⁹5²6)(3⁴4¹²5⁷6⁴7) and 8-connected (4²⁵6³) net, respectively. 4 and 5 possess dimeric and tetrameric structures, which are extended into 7-connected (3³4¹³5³6) and 4-connected (4,4) net, respectively.     

Syntheses and activity of some platinum(IV) complexes with N-methyl derivate of glycine and halogeno ligands against HeLa, K562 cell lines and human PBMC

Four platinum(IV) complexes, trans,trans-dichlorobis(N,N-dimethylglycinato)platinum(IV), trans,trans-[Pt(dmgly)₂Cl₂] (1) and trans,trans-dibromobis(N,N-dimethylglycinato)platinum (IV), trans,trans-[Pt(dmgly)₂Br₂] (2), as well as, trans,trans-dichlorobis(N-methylglycinato)platinum(IV), trans,trans-[Pt(sar)₂Cl₂] (3) and trans,trans-dibromobis(N-methylglycinato)platinum(IV), trans,trans-[Pt(sar)₂Br₂] (4) (with configuration index for all complexes OC-6-14), were synthesized and characterized by elemental analysis, infrared and ¹H NMR spectroscopy. In the aim to assess the selectivity in the antitumor action of these complexes, the antiproliferative action of these compounds was determined to human adenocarcinoma HeLa cells; to human myelogenous leukemia K562 cells and to normal immunocompetent cells; i.e., on human PBMC. The details of the crystal structure synthesized trans,trans-[Pt(sar)₂Br₂] complex were also reported here. In the crystal structure of trans,trans-[Pt(sar)₂Br₂], the Pt(IV) ion had a deformed octahedral coordination with both N-methylglycinates and bromides bonded trans to one another and with the N-Pt-Br bond angles of 84.1(4) and 95.9(4)°. The trans,trans-[Pt(sar)₂Br₂] complex molecules form 2D-layers with multiple N-H?O and C-H?O hydrogen bonds.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Coordination diversity of N-phosphoryl-N′-phenylthiourea (LH) towards Co, Ni and Pd cations: Crystal structure of ML2-N,S and ML2-O,S chelates

Thiourea, PhNHC(S)NHP(O)(OPrⁱ)₂ (LH) chelates of Co^II, Ni^II, and Pd^II ions have been obtained and investigated by single-crystal X-ray diffraction, UV, IR, NMR spectroscopy, and EI mass-spectrometry. The unusual 1,3-N,S-coordination via sulfur and NP(O) nitrogen atoms has been found in the trans-square-planar NiL₂ and PdL₂ complexes, whereas the 1,5-O,S-coordination is realized in the tetrahedral CoL₂ complex. DFT calculations have revealed significant stabilization of the 1,3-N,S-structures due to stronger crystal field and the NH-OP hydrogen bonds.     

Synthesis, structural characterisation and biological studies of new mononuclear platinum(II) complexes with sterically hindered heterocyclic ligands

Three novel cisplatin analogues were synthesized, designed according to an approach which violates the “classical” structure-activity relationship, by replacing the diamine ligands with a planar N donor heterocycle giving a sterically hindered complex. Moreover, the sterical hindrance of antitumor drug candidates potentially makes them less susceptible to deactivation by sulphur-containing proteins and helping to overcome resistance mechanisms. The resulting mononuclear complexes of sterically hindered polidentate heterocyclic N ligands [PtCl(bbp)]Cl (1) [bbp = 2,6-bis(2-benzimidazolyl)pyridine], [PtCl₂(dptdn)](H₂O) (2) [dptdn = sodium 5,6-diphenyl-3-(2′-pyridyl)-1,2,4-triazine-4″,4″′-disulfonate] and [(dptdn)(dpt)Pt]Cl₂(H₂O) (3) [dpt = 5,6-diphenyl-3-(2′-pyridyl)-1,2,4-triazine] have been prepared and structurally characterised. Both neutral and ionic complexes are present, with monofunctional (1) and bifunctional Pt(II) moieties (2) and coordinatively saturated Pt(II) ions in the mixed ligand complex (3), whose size and shape enable them to behave as novel scaffolds for DNA binding. All complexes were tested “in vitro” for their biological activity on human HT29 colorectal carcinoma and HepG2 hepatoma cells. The complexes (1) and (3), endowed with a positive charge, showed a potent cytotoxic activity and reduced cell viability with an efficacy higher than that of cisplatin; whilst the neutral bifunctional compound (2) was inactive. IC50 values have been calculated for the active compounds. The cytotoxic effects were confirmed by the accumulation of treated cells in subG0/G1 phase of cell cycle, by the loss of mitochondrial potential (Δψ_m) and by the chromatin condensation or fragmentation observed by means of fluorescence microscopy after Hoechst 33258 nuclear staining. A study on intracellular platinum uptake in HT29 cell line has been also performed and data obtained strongly suggest that the cytotoxicity of new tested complexes reported in this work is based on a different pharmacodynamic pattern with respect to cisplatin.     

Structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif

The structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of 2-organochalcogenomethylpyridine ligands is described. Complexes with a methyl group in the 6-position of the pyridyl ring, 6-MepyCH₂ER, form dimeric complexes [trans-PdX₂(μ-6-MepyCH₂SePh-N,Se)]₂ (X = Br (1), I (2)) or mononuclear complexes trans-PdI₂(6-MepyCH₂SR-N)₂ (R = Me (5), Ph (6)). Absence of a 6-methyl substituent results in the bidentate configuration observed for PdI₂(pyCH₂SePh-N,Se) (3) and PdI₂(4-MepyCH₂SMe-N,S) (4). Related platinum(II) complexes are mononuclear including PtCl₂(6-MepyCH₂SPh-N,S) (8) as an analogue of trimeric [trans-PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃. Differences between palladium and platinum appear to result from a combination of steric and electronic factors.     

Synthesis, structure and catalytic activity of low-spin dicyano iron(III) complexes of N,N-bis(quinolyl)malonamide derivatives

Two low-spin Fe(III) dicyano-dicarboxamido complexes have been prepared from N,N^′-bis(8-quinolyl)malonamide derivatives. Crystal structures show that the four nitrogen donors available to complex the metal are arranged in the equatorial plane with the two cyanides trans to each other in the axial positions when the malonyl moiety is disubstituted. In contrast, the unsubstituted malonyl results in only three nitrogens in the equatorial plane with the fourth in an apical position and the two cyanides occupying cis sites, one equatorial and the other axial. NMR analyses show that the solid state structure of both complexes is retained in solution. Both types of configurational complexes catalyze cyclic olefin oxidations with H₂O₂ but only the cis-dicyano complex catalyzes stilbene oxidation with formation of epoxides, diols and benzaldehyde.     

Preparation, properties and crystal structure of two isomers of R,R,S,S- and R,S,R,S-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1,0]tetracosane)copper(II)]

Two isomers (R,S,R,S- and R,R,S,S-) of five coordinate complex [Cu(L)Cl]⁺ have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of R,S,R,S-[Cu(L)Cl]⁺ shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of R,R,S,S-[Cu(L)Cl]⁺. R,S,R,S-[Cu(L)Cl]⁺ is significantly distorted to trigonal-bipyramidal structure, whereas R,R,S,S-[Cu(L)Cl]⁺ retains almost square-planar geometry. The average bond distance of Cu-N in basal plane of R,S,R,S-[Cu(L)Cl]⁺ is longer by 0.024 Å than that of R,R,S,S-[Cu(L)Cl]⁺, whereas the bond distance of Cu-Cl in former is shorter by 0.200 Å than that in latter. The isolated square-planar complexes of R,R,S,S- and R,S,R,S-[Cu(L)](ClO₄)₂ are converted to the R,R,S,S- and R,S,R,S-[Cu(L)Cl]⁺ by the addition of Cl⁻ in nitromethane solution with the rate constants, k=1.70 (±0.02) and 8.31 (±0.07) M⁻¹ s⁻¹, respectively.     

Synthesis, characterization, DFT studies and DNA binding of mixed platinum (II) complexes containing quinoxaline and 1,2-dithiolate ligands

The complexes Pt(pq)Cl2(1) and Pt(pq)(bdt) (2) (where pq = 2-(2'pyridyl)quinoxaline and bdt=benzene-1,2-dithiolate) have been synthesized and fully characterized by UV-visible (UV-Vis), Fourier Transformer Infrared Spectra (FTIR), 1 and 2D NMR and cyclic voltammetry (CV). Interactions of the tested systems (the aforementioned complexes 1 and 2) and the free ligands pq and bdt with double stranded calf thymus DNA (CT-DNA) were studied by UV-spectrophotometric (melting curves) and circular dichroism (CD) measurements. The results suggest that both complexes 1 and 2, are able to form adducts with DNA and to distort the double helix by changing the base stacking. Complex 2 forms stronger adducts to CT-DNA than complex 1 and this is probably due to the substitution of the chlorine atoms of 1 by the 1,2-dithiolate ligand (bdt) in 2. The latter induces an extensive distortion in the planarity of 2 as density functional theory (DFT) calculations reveal. Besides, the light absorbing complex 2 possess intense mixed metal ligand to ligand charge transfer (MM'LLCT) transition in the visible region of the spectrum and could act as photoluminescent metal-based probe for the study of DNA binding. Thus, the photocleavage of DNA by 2 has been studied by UV-Vis and CD spectra and monitored by agarose gel electrophoresis. Under our experimental conditions, it is unclear that complex 2 can photocleave DNA. Furthermore, the ability of 2 to inhibit proliferation of human tumor cell lines was tested and the results indicate some cytoxytic effect on the SF-286 cells.     

Magnetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of tridentate NNS Schiff base ligands formed from 2-acetylpyrazine and S-methyl- and S-benzyldithiocarbazates

New copper(II) complexes of general empirical formula, [Cu(NNS)X] (NNS = anionic forms of the 2-acetylpyrazine Schiff bases of S-methyl- and S-benzyldithiocarbazate, Hapsme and Hapsbz) and X = Cl⁻, Br⁻, NCS⁻ and NO₃⁻ have been synthesized and characterized. X-ray crystal structures of the free ligand, Hapsbz and the complexes, [Cu(apsbz)(NO₃)]_∞, [Cu(apsme)(NCS)]₂ and [Cu(apsme)Cl]₂ have been determined. In the solid state, the Schiff base, Hapsbz remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. X-ray diffraction shows that the [Cu(apsbz)(NO₃)]_∞ complex is a novel coordination polymer in which one of the nitrogen atoms of the pyrazine ring bridges two adjacent copper(II) ions. The Schiff base is coordinated to the copper(II) ion in its iminothiolate form via the thiolate sulfur atom, the azomethine nitrogen atom and one of the pyrazine nitrogen atoms, the overall geometry of each copper atom in the polymer being close to a square-pyramid. The complexes, [Cu(apsme)X]₂ (X = NCS⁻, Cl⁻) are dimers in which each copper atom adopts a five-coordinate near square-pyramidal geometry with an N₃S₂ coordination environment. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. A nitrogen atom of a unidentate thiocayanate or chloride ligand and a bridging sulfur atom from a second ligand completes the coordination sphere. Room temperature μ_eff values for the complexes in the solid state are in the range 1.70-2.0 μ_B typical of uncoupled or weakly coupled Cu(II) centres. Variable temperature susceptibility studies show that the chain complex displays weak ferromagnetic coupling across the pyrazine bridges, while the S-bridged dinuclear compounds display either weak ferromagnetic or weak antiferromagnetic coupling that relates to subtle bridging geometry differences. EPR studies of frozen DMF solutions give rather similar g and A_Cu values for all compounds indicative of Cu(d_x²-y²) ground state orbitals on the Cu centers.