Coordination compounds in medicinal chemistry

Spectroscopic evidence of the interaction of titanium(IV) coordination complexes with a phosphate head group in phospholipids

Biological membranes are potentially involved in the transport of metal ions, such as Ti(IV), and, sometimes, their associated ligands. Understanding the interactions of Ti(IV) ions and complexes with biological membranes provides a basis for elucidating the action mechanism of titanium anticancer drugs. Herein, we investigated the interactions of two neutral titanium(IV) complexes, viz. [H2Ti(Cat)3] (1) and [H2Ti(Napht)3] (2), incorporated into DOPC multi-bilayers using ATR-FTIR spectroscopy. Infrared results showed that complexes 1 and 2, when interacting with DOPC multi-bilayers, highly affected the hydration of the lipid phosphate group and its mobility, revealing that the phosphate group is the main group involved in the interactions of complexes 1 and 2 with DOPC phospholipids. NMR studies involving complex 1 and DOPC dissolved in deuterated DMSO solution were performed, and interactions between the Ti complex and DOPC phosphate group could be evidenced. DFT calculations of model complexes were in good agreement with experimental data, and the stability of three model complexes was estimated. On the basis of the obtained data, it can be suggested that the oxygen atom(s) of the phosphato group of the DOPC ligand acted as donor atoms for Ti.

A comprehensive review on the development of chiral Cu, Ni, and Zn complexes as pharmaceutical agents over the past decades: Synthesis, molecular structure and biological activity

Chirality is a fundamental and widespread geometric structural property in living organisms that most biomacromolecules including nucleic acids, proteins and enzymes, possess. Consequently, the development of chiral drugs capable of binding specific targets have gradually gained wide attention in recent decades due to their selective effects on a broad spectrum of biological events ranging from cell metabolism to cell fate. In this context, the synthesis of chiral compounds as promising therapeutic candidates has assumed a major role in drug discovery. Among them, chiral metal complexes have attracted considerable interest due to their unique and intriguing structural features that could enable overcoming side effects and drug-resistance phenomena of metal-based drugs currently in the market such as cisplatin. In the current scenario, an in-depth overview of non-platinum chiral complexes needs to be presented and carried forward. Therefore, in this perspective article, an update of the scientific development of bioactive chiral copper, zinc and nickel complexes have been reported since they have not been thoroughly reviewed so far. Specifically, we focused the article mainly on metal complexes containing chiral ligands (type 2 chirality) as in literature they are more numerous than those with chirality at the metal center (type 1 chirality). Herein, not only their biological activity but also their mechanism of action is summarized. Furthermore, in the final section of the article we have highlighted copper-based complexes as those with a superior biological activity profile and greater prospects for development as a drug.

Synthesis, DNA binding and biological evaluation of benzimidazole Schiff base ligands and their metal(ii) complexes

Two novel benzimidazole ligands (E)-2-((4-(1H-benzo[d]imidazole-2-yl)phenylimino)methyl)-6-bromo-4-chlorophenol (L1) and (E)-1-((4-(1H-benzo[d]imidazole-2-yl)phenylimino)methyl)naphthalene-2-ol (L2) with their corresponding Cu(ii), Ni(ii), Pd(ii) and Zn(ii) complexes were designed and synthesized. The compounds were characterized by elemental, IR, and NMR (1H & 13C) spectral analyses. Molecular masses were determined by ESI-mass spectrometry, and the structure of ligand L1 was confirmed by single crystal X-ray diffraction analysis. Molecular docking was carried out for the theoretical investigation of DNA binding interactions. The results obtained were verified experimentally by UV/Visible absorption spectroscopy in conjunction with DNA thermal denaturation studies. It was observed that ligands (L1 and L2) and complexes (1-8) were moderate to strong DNA binders, as evident from the binding constants (K b). The value was found to be highest for complex 2 (3.27 × 105 M-1) and lowest for 5 (6.40 × 103 M-1). A cell line study revealed that breast cancer cells were less viable to the synthesized compounds compared to that of standard drugs, cisplatin and doxorubicin, at the same concentration. The compounds were also screened for in vitro antibacterial activity for which complex 2 showed a promising broad-spectrum effect against all tested strains of bacteria, almost in the proximity of the reference drug kanamycin, while the rest of the compounds displayed activity against selected strains.

Exploring Titanium(IV) Complexes as Potential Antimicrobial Compounds

Due to the rapid mutation of pathogenic microorganisms, drug-resistant superbugs have evolved. Antimicrobial-resistant germs may share their resistance genes with other germs, making them untreatable. The search for more combative antibiotic compounds has led researchers to explore metal-based strategies centered on perturbing the bioavailability of essential metals in microbes and examining the therapeutic potential of metal complexes. Given the limited knowledge on the application of titanium(IV), in this work, eight Ti(IV) complexes and some of their corresponding ligands were screened by the Community for Open Antimicrobial Drug Discovery for antimicrobial activity. The compounds were selected for evaluation because of their low cytotoxic/antiproliferative behavior against a human non-cancer cell line. At pH 7.4, these compounds vary in terms of their solution stability and ligand exchange lability; therefore, an assessment of their solution behavior provides some insight regarding the importance of the identity of the metal compound to the antimicrobial therapeutic potential. Only one compound, Ti(deferasirox)₂, exhibited promising inhibitory activity against the Gram-positive bacteria methicillin-resistant Staphylococcus aureus and minimal toxicity against human cells. The ability of this compound to undergo transmetalation with labile Fe(III) sources and, as a consequence, inhibit Fe bioavailability and ribonucleotide reductase is evaluated as a possible mechanism for its antibiotic effect.

Modified pyridine-triazole and 2,2'-bipyrimidine ligands generating robust titanium complexes constructed around a TiO4N2 core

The synthesis and characterisation of novel chelate nitrogen ligands with phasmidic tails (pyridine-triazole ligand 1b; 2,2'-bipyrimidine ligands 2b and 3b) as well as their titanium(IV) coordination complexes are reported. The analogous ligands 1a, 2a and 3a with methoxy substituents instead of the tails were also synthesized, together with titanium complexes that could be crystallographically characterised. A good agreement is noticed between analytical data of the complexes in solution (NMR) and in the solid state (X-ray diffraction). The complexes are overall robust on phases like alumina or silica, so that they could be characterised by TLC and sometimes chromatographied. Supramolecular architectures were generated from an equimolar solution of titanium(IV) isopropoxide, ligand 1a and a polyphenol ligand 5-H₄, leading to a double-stranded helicate characterised by MS, NMR and crystallography, which was then converted into a trinuclear complex as shown by MS and NMR DOSY data. The liquid-crystalline behaviour of the ligands 1b, 2b and 3b incorporating the long alkyl tails and that of the complexes derived from these ligands have been investigated.

Noble Metals Based Bimetallic and Trimetallic Nanoparticles: Controlled Synthesis, Antimicrobial and Anticancer Applications

Noble bimetallic and trimetallic nanoparticles (NBT-NPs) have superior biomedical applications as compared to their monometallic counterparts. The performance of these nanomaterials depends on their composition, shape and size. Hence, the controlled-synthesis of these nanomaterials is a hot area of research. Till date, no review article in the literature accounts regarding the controlled-synthesis and biomedical applications related to morphology, optimum composition, biocompatibility and versatile chemistry of NBT-NPs. Taking this into contemplation, an effort was made to provide a clear insight into the morphology-controlled synthesis and size/shape-dependent anticancer and bactericidal applications of NBT-NPs. Chemical reduction method for the controlled-synthesis of NBT-NPs is reviewed critically. Furthermore, the potential role of various reaction parameters such as time, reducing agents, stabilizing/capping agents, nature/concentration of precursors, temperature and pH in the shape/size-controlled synthesis of these nanomaterials are discussed. In the second part of this article, anticancer and bactericidal applications of the NBT-NPs are reviewed and the influences of optimum composition, size, surface structure, versatile chemistry and synergism are studied. Finally, the current challenges in the controlled-synthesis and biomedical applications of these nanomaterials, and prospects to resolve related issues are discussed. HighlightsChemical reduction method for the synthesis of NBT-NPs is reviewed.The influences of parameters on the control synthesis of NBT-NPs are discussed.Antibacterial and anticancer applications and cytotoxicity of NBT-NPs are reviewed.Possible solutions for the key challenges are discussed.Outlooks about the synthesis and biomedical applications of NBT-NPs are discussed.

Cytotoxicity, cellular uptake, and subcellular localization of a nitrogen oxide and aminopropyl-β-lactose derivative ruthenium complex used as nitric oxide delivery agent

This work investigates how the luminescent ruthenium-nitrite complexes cis-[Ru(py-bodipy)(dcbpy)₂(NO₂)](PF₆) (I) and cis-[Ru(py-bodipy)(dcbpy-aminopropyl-β-lactose)₂(NO₂)](PF₆) (II) behave toward the melanoma cancer cell line B16F10. The chemical structure and purity of the synthesized complexes were analyzed by UV-Visible and FTIR spectroscopy, MALDI, HPLC, and ¹H NMR. Spectrofluorescence helped to determine the fluorescence quantum yields and lifetimes of each of these complexes. In vitro MTT cell viability assay on B16F10 cancer cells revealed that the complexes possibly have a tumoricidal role. The metal-nitrite complexes evidenced the dichotomous NO nature: at high concentration, NO exerted a tumoricidal effect, whereas cancer cells grew at low NO concentration. Flow cytometry or fluorescence microscopy aided cellular uptake calculation. Cell staining followed by fluorescence microscopy associated with organelle markers such as DAPI and Rhodamine 123 detected preferential intracellular localization of the ruthenium-nitrite py-bodipy and aminopropyl lactose derivative ruthenium complex in mitochondria. Thus, the cytotoxicity of compounds (I) and (II) against B16F10 cancer cell line show concentration-dependent results. The present studies suggest that nitric oxide ruthenium derivative compounds could be new potential chemotherapeutic agents against cytotoxic cells.

A robust Ti(iv)-based mesogen constructed around a TiO4N2 core

A Ti(iv)-complex with thermotropic liquid crystal properties is reported.

CATALOGIC 301C model - validation and improvement

In Europe, REACH legislation encourages the use of alternative in silico methods such as (Q)SAR models. According to the recent progress of Chemical Substances Control Law (CSCL) in Japan, (Q)SAR predictions are also utilized as supporting evidence for the assessment of bioaccumulation potential of chemicals along with read across. Currently, the effective use of read across and QSARs is examined for other hazards, including biodegradability. This paper describes the results of external validation and improvement of CATALOGIC 301C model based on more than 1000 tested new chemical substances of the publication schedule under CSCL. CATALOGIC 301C model meets all REACH requirements to be used for biodegradability assessment. The model formalism built on scientific understanding for the microbial degradation of chemicals has a well-defined and transparent applicability domain. The model predictions are adequate for the evaluation of the ready degradability of chemicals.

A ubiquitous metal, difficult to track: towards an understanding of the regulation of titanium(iv) in humans

Despite the ubiquitous nature of titanium(iv) and several examples of its beneficial behavior in different organisms, the metal remains underappreciated in biology. There is little understanding of how the metal might play an important function in the human body. Nonetheless, a new insight is obtained regarding the molecular mechanisms that regulate the blood speciation of the metal to maintain it in a nontoxic and potentially bioavailable form for use in the body. This review surveys the literature on Ti(iv) application in prosthetics and in the development of anticancer therapeutics to gain an insight into soluble Ti(iv) influx in the body and its long-term impact. The limitation in analytical tools makes it difficult to depict the full picture of how Ti(iv) is transported and distributed throughout the body. An improved understanding of Ti function and its interaction with biomolecules will be helpful in developing future technologies for its imaging in the body.

Substitutional impact on biological activity of new water soluble Ni(II) complexes: Preparation, spectral characterization, X-ray crystallography, DNA/protein binding, antibacterial activity and in vitro cytotoxicity

A series of new water soluble nickel(II) complexes containing triphenylphosphine and 4-methoxysalicylaldehyde-4(N)-substituted thiosemicarbazones were synthesized and characterized. Crystallographic investigations confirmed the structure of the complexes (1-4) having the general structure [Ni(4-Msal-Rtsc)(PPh₃)] (Where R=H (1); CH₃ (2); C₂H₅ (3); C₆H₅ (4)) which showed that thiosemicarbazone ligands coordinated to nickel(II) ion as ONS tridentate bibasic donor. DNA/BSA protein binding ability of the ligands and their new complexes were studied by taking calf-thymus DNA (CT-DNA) and Bovine serum albumin (BSA) through absorption and emission titrations. Ethidium bromide (EB) displacement study showed the intercalative binding trend of the complexes to DNA. From the albumin binding studies, the mechanism of quenching was found as static and the alterations in the secondary structure of BSA by the compounds were confirmed with synchronous spectral studies. The binding affinity of the complexes to CT-DNA and BSA has the order of [Ni(4-Msal-etsc)(PPh₃)] (3) >[Ni(4-Msal-mtsc)(PPh₃)] (2) >[Ni(4-Msal-tsc)(PPh₃)] (1) >[Ni(4-Msal-ptsc)(PPh₃)] (4). In vitro cytotoxicity of the complexes was tested on human lung cancer cells (A549), human cervical cancer cells (HeLa), human liver carcinoma cells (Hep G2). All the complexes exhibited significant activity against three cancer cells. Among them, complex 4 exhibited almost 2.5 fold activity than cisplatin in A549 and HepG2 cell lines. In HeLa cell line, the complexes exhibited significant activity which is less than cisplatin. While comparing the activity of the complexes in A549 and HepG2 cell lines it falls in the order 4>1>2>3>cisplatin. The results obtained from DNA, protein binding and cytotoxicity studies, it is concluded that the cytotoxicity of the complexes as determined by MTT assay were not unduly influenced by the complexes having different binding efficiency with DNA and protein. The complexes exhibited good spectrum of antibacterial activity against four pathogenic bacteria such as E. faecalis (gram +ve), S. aureus (gram +ve), E. coli (gram -ve) and P. aeruginosa (gram -ve).

Monomeric Ti(iv)-based complexes incorporating luminescent nitrogen ligands: synthesis, structural characterization, emission spectroscopy and cytotoxic activities

Novel photoluminescent 2,2′-bipyrimidine ligands and their titanium(iv) complexes are cytotoxic.

Targeting copper induced oxidative damage to proteins by ligation: a novel approach towards chelation therapy for oxidative stress disorders

DIDE and rhodanine prevent the copper induced oxidative damage to proteins by binding copper into a redox inactive state.

In vitro effects of novel ruthenium complexes in Neospora caninum and Toxoplasma gondii tachyzoites

Upon the screening of 16 antiproliferative compounds against Toxoplasma gondii and Neospora caninum, two hydrolytically stable ruthenium complexes (compounds 16 and 18) exhibited 50% inhibitory concentrations of 18.7 and 41.1 nM (T. gondii) and 6.7 and 11.3 nM (N. caninum). To achieve parasiticidal activity with compound 16, long-term treatment (22 to 27 days at 80 to 160 nM) was required. Transmission electron microscopy demonstrated the rapid impact on and ultrastructural alterations in both parasites. These preliminary findings suggest that the potential of ruthenium-based compounds should thus be further exploited.

Rational design of [Co(acacen)L2]+ inhibitors of protein function

Cobalt(III) Schiff base complexes, such as [Co(acacen)L(2)](+), inhibit the function of Zn(II)-dependent proteins through dissociative exchange of the axial ligands with key histidine residues of the target protein. Consequently the efficacy of these compounds depends strongly on the lability of the axial ligands. A series of [Co(acacen)L(2)](+) complexes with various axial ligands was investigated using DFT to determine the kinetics and thermodynamics of ligand exchange and hydrolysis. Results showed excellent agreement with experimental data, indicating that axial ligand lability is determined by several factors: pK(a) of the axial ligand, the kinetic barrier to ligand dissociation, and the relative thermodynamic stability of the complexes before and after exchange. Hammett plots were constructed to determine if the kinetics and thermodynamics of exchange can be modulated by the addition of an electron-withdrawing group (EWG) to either the axial ligand itself or to the equatorial acacen ligand. Results predict that addition of an EWG to the axial ligand will shift the kinetics and thermodynamics so as to promote axial ligand exchange, while addition of an EWG to acacen will decrease axial ligand lability. These investigations will aid in the design of the next generation of [Co(acacen)L(2)](2+), allowing researchers to develop new, more effective inhibitors.

Cisplatin enhances the formation of DNA single- and double-strand breaks by hydrated electrons and hydroxyl radicals

The synergistic interaction of cisplatin with ionizing radiation is the clinical rationale for the treatment of several cancers including head and neck, cervical and lung cancer. The underlying molecular mechanism of the synergy has not yet been identified, although both DNA damage and repair processes are likely involved. Here, we investigate the indirect effect of γ rays on strand break formation in a supercoiled plasmid DNA (pGEM-3Zf-) covalently modified by cisplatin. The yields of single- and double-strand breaks were determined by irradiation of DNA and cisplatin/DNA samples with (60)Co γ rays under four different scavenging conditions to examine the involvement of hydrated electrons and hydroxyl radicals in inducing the DNA damage. At 5 mM tris in an N2 atmosphere, the presence of an average of two cisplatins per plasmid increased the yields of single- and double-strand breaks by factors of 1.9 and 2.2, respectively, relative to the irradiated unmodified DNA samples. Given that each plasmid of 3,200 base pairs contained an average of two cisplatins, this represents an increase in radiosensitivity of 3,200-fold on a per base pair basis. When hydrated electrons were scavenged by saturating the samples with N2O, these enhancement factors decreased to 1.5 and 1.2, respectively, for single- and double-strand breaks. When hydroxyl radicals were scavenged using 200 mM tris, the respective enhancement factors were 1.2 and 1.6 for single- and double-strand breaks, respectively. Furthermore, no enhancement in DNA damage by cisplatin was observed after scavenging both hydroxyl radicals and hydrated electrons. These findings show that hydrated electrons can induce both single- and double-strand breaks in the platinated DNA, but not in unmodified DNA. In addition, cisplatin modification is clearly an extremely efficient means of increasing the formation of both single- and double-strand breaks by the hydrated electrons and hydroxyl radicals created by ionizing radiation.

Four NiIIcomplexes with the new cyclam–methylimidazole ligand 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane

Although it has not proved possible to crystallize the newly prepared cyclam–methylimidazole ligand 1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane (LIm1), thetransandcisisomers of an NiIIcomplex, namelytrans-aqua{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate) monohydrate, [Ni(C15H30N6)(H2O)](ClO4)2·H2O, (1), andcis-aqua{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate), [Ni(C15H30N6)(H2O)](ClO4)2, (2), have been prepared and structurally characterized. At different stages of the crystallization and thermal treatment from which (1) and (2) were obtained, a further two compounds were isolated in crystalline form and their structures also analysed, namelytrans-{1-[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}(perchlorato)nickel(II) perchlorate, [Ni(ClO4)(C15H30N6)]ClO4, (3), andcis-{1,8-bis[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane}nickel(II) bis(perchlorate) 0.24-hydrate, [Ni(C20H36N6)](ClO4)2·0.24H2O, (4); the 1,8-bis[(1-methyl-1H-imidazol-2-yl)methyl]-1,4,8,11-tetraazacyclotetradecane ligand is a minor side product, probably formed in trace amounts in the synthesis ofLIm1. The configurations of the cyclam macrocycles in the complexes have been analysed and the structures are compared with analogues from the literature.

Solution equilibria of copper(II) complexation with N,N′-(2,2′-azanediylbis(ethane-2,1-diyl))dipicolinamide: A bio-distribution and dermal absorption study

The protonation equilibria of a pentadentate ligand, N,N'-(2,2'-azanediylbis(ethane-2,1-diyl))dipicolinamide ([H(2)(5555)-N]) and the complexation of this ligand with Cu(II) Ca(II), Zn(II) and Ni(II) have been studied by pH-potentiometry, (1)H NMR spectroscopy and UV-vis spectrophotometry. (1)H NMR detected the protonation of the pyridyl groups and formation of Cu[H(2)(5555)-N]H species at low pH, while amide group deprotonation at higher pH resulted in the formation of Cu[H(2)(5555)-N]H(-1) and Cu[H(2)(5555)-N]H(-2) species in solution. Potentiometric detection of protonated species was limited by the acidic nature of the pyridyl nitrogen donors. From UV-vis spectroscopy it is suggested that the amide nitrogens are coordinated. This conclusion is supported by Molecular Mechanics calculations. Water-octanol partition coefficients for the Cu(II)-[H(2)(5555)-N] system indicated that although the Cu[H(2)(5555)-N]H(-1) species is largely hydrophilic, approximately 54% of the complex goes into the organic phase. This percentage is able to promote dermal absorption of copper with a calculated penetration rate of 1.92x10(-1)cmh(-1). This was confirmed by dermal absorption studies which illustrate the role of hydrophobicity in promoting percutaneous drug administration.

Studies of interaction between Rh(I) and human serum albumin in a “nanostructured biocatalyst” active in the hydroformylation reaction

The interaction between Rh(CO)(2)(acac=acetylacetonate ion) and human serum albumin (HSA) in a hydrosoluble nanostructured biocatalyst active in homogeneous hydroformylation was characterised by means of matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS), high performance liquid chromatography mass spectrometry (HPLC-MS) and scanning electron microscopy (SEM). MALDI-TOFMS substantiates that the biocatalyst consists of a tetrameric structure of HSA that could bind up to 89 Rh(CO)(2)(+) units. A comparison between samples of pure HSA and the biocatalyst, both tryptic digested, showed a significant change in the tertiary structure of the protein in the HSA/Rh adduct, probably ascribable to the interaction of Rh(I) ions with sulphur atoms in the HSA moiety. SEM observations confirmed an evident denaturation of the protein and an outstanding correspondence between the surface distribution of Rh and S atoms; this is indirect evidence that the metal ion interacts strongly mainly with the sulphur atoms. Furthermore, an excellent agreement between calculated and measured (SEM) S/Rh elemental mean ratio was observed. Finally, an electrostatic interaction between Rh(I) and sulphur atoms was ruled out by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) findings.

Acridine Orange based platinum(II) complexes inducing cytotoxicity and cell cycle perturbation in spite of GSTP1 up-regulation

A series of new ionic Pt(II) complexes of general formula [Pt(II)(A)n(Cl)(AO)]X (A=en, NH3; n=1, 2; X-=BF4-, NO3-, PF6-, CF3SO3-), 1-5, containing Acridine Orange (AO) bound to the metal atom through the endocyclic N atom, have been tested in human melanoma cells (M14, JR8 and PLF2), human neuroblastoma cell line SH-SY5Y and its cis-platin resistant subline SH-SY5Yres. The Pt(II) compounds, and in particular complexes 1 and 4, exhibit higher cytotoxic activity at lower concentration compared to cis-DDP in melanoma cells, affecting cell growth behavior and causing cell cycle perturbation. Moreover, M14 and JR8 cell lines were not able to rescue the impairment due to the new Pt(II) complexes since perturbation of cell cycle phases and cell proliferation inhibition were found after 72 h of recovery time. In order to evaluate whether GSTP1 may play a role in chemo-resistance of our melanoma model, we investigated the effect of the treatment with these Pt(II) compounds on GSTP1 gene expression. Up-regulation of GSTP1, evaluated by Qreal-time PCR was observed after treatment with complexes 1 and 4, showing that the effect of these Pt(II) compounds is GSTP1 indipendent. The lack of resistance of the new Pt(II)-AO complexes and their cytotoxicity, cell growth and cell cycle recovery in melanoma cells provide the basis for the development of new platinum anticancer compounds, directed to those tumors that over express GSTs enzymes.

Aqueous Spectroscopy and Redox Properties of Carboxylate-Bound Titanium

The aqueous chemistry of Ti(III) and Ti(IV) in two different chemical environments is investigated given its relevance to environmental, materials, and biological chemistry. Complexes of titanium with the carboxylate ligands citrate and oxalate, found ubiquitously in Nature, were synthesized. The redox properties were studied by using cyclic voltammetry. All the titanium citrate redox couples are quasi-reversible. Electrospray mass spectrometry of the Ti(III) citrate solution shows the presence of a 1:2 Ti/cit complex in solution, in contrast to the predominant 1:3 Ti/cit complex with Ti(IV). The change in the coordination of the ligand to the metal on reduction may explain the quasi-reversible behavior of the electrochemistry. The redox potentials for Ti(IV) citrate in water vary with pH. At pH 7, the approximate E(1/2) is less than -800 mV. This stated change in redox properties is considered in light of the previously reported Ti(IV) citrate solution speciation. Analogous speciation behavior is suggested from the EPR spectroscopy of Ti(III) citrate aqueous solutions. The g tensors are deduced for several pH-dependent species from the simulated data. The X-ray crystal structure of a Ti(III)(2) oxalate dimer Ti(2)(mu-C(2)O(4))(C(2)O(4))(2)(H(2)O)(6).2H(2)O (3), which crystallizes from water below pH 2, is reported. Complex 3 crystallizes in a monoclinic P2(1)/c space group with a = 9.5088(19) Angstroms, b = 6.2382(12) Angstroms, c = 13.494(3) Angstroms, V = 797.8(3) Angstroms(3), and Z = 2. The infrared spectroscopy, EPR spectroscopy, and cyclic voltammetry on complex 3 are reported. The cyclic voltammetry shows an irreversible redox couple approximately -196 mV which likely corresponds to the Ti(IV)(2)/Ti(III)Ti(IV) couple. The EPR spectroscopy on solid complex 3 shows a typical S = 1 triplet-state spectrum. The solid follows non-Curie behavior, and the antiferromagnetic coupling between the two metal centers is determined to be -37.2 cm(-1). However, in solution the complex follows Curie behavior and supports a Ti(III)Ti(IV) oxidation state for the dimer.

Titanium(IV) Citrate Speciation and Structure under Environmentally and Biologically Relevant Conditions

The water-soluble complexes of Ti(IV) with citrate are of interest in environmental, biological, and materials chemistry. The aqueous solution speciation is revealed by spectropotentiometric titration. From pH 3-8, given at least three equivalents of ligand, 3:1 citrate/titanium complexes predominate in solution with successive deprotonation of dangling carboxylates as the pH increases. In this range and under these conditions, hydroxo- or oxo-metal species are not supported by the data. At ligand/metal ratios between 1:1 and 3:1, the data are difficult to fit, and are consistent with the formation of such hydroxo- or oxo- species. Stability constants for observed species are tabulated, featuring log beta-values of 9.18 for the 1:1 complex [Ti(Hcit)](+), and 16.99, 20.41, 16.11, and 4.07 for the 3:1 complexes [Ti(H(2)cit)(3)](2-), [Ti(H(2)cit)(Hcit)(2)](4-), [Ti(Hcit)(2)(cit)](6-), and [Ti(cit)(3)](8-), respectively (citric acid = H(4)cit). Optical spectra for the species are reported. The complexes exhibit similar yet distinct spectra, featuring putative citrate-to-Ti(IV) charge-transfer absorptions (lambda(max) approximately 250-310 nm with epsilon approximately 5000-7000 M(-)(1) cm(-1)). The prevailing 3:1 citrate/titanium ratio in solution is supported by electrospray mass spectrometry data. The X-ray crystal structure of a fully deprotonated tris-citrate complex Na(8)[Ti(C(6)H(4)O(7))(3)].17H(2)O (1) (or Na(8)[Ti(cit)(3)].17H(2)O) that crystallizes from aqueous solution at pH 7-8 is reported. Compound 1 crystallizes in the triclinic space group P, with a = 11.634(2) Angstroms, b = 13.223(3) Angstroms, c = 13.291(3) Angstroms, V = 1982.9(7) Angstroms(3), and Z = 2.

Oxidative DNA damage of mixed copper(II) complexes with sulfonamides and 1,10-phenanthroline. Crystal structure of [Cu(N-quinolin-8-yl-p-toluenesulfonamidate)2(1,10-phenanthroline)]

Mixed coordination compounds of Cu(II) with sulfonamides and 1,10-phenanthroline as ligands have been prepared and characterised. Single crystal structural determination of the complex [Cu(N-quinolin-8-yl-p-toluenesulfonamidate)(2)(phen)] shows Cu(II) ions are located in a highly distorted octahedral environment, probably as a consequence of the Jahn-Teller effect. The FT-IR and electronic paramagnetic resonance (EPR) spectra are also discussed. The mixed complexes prepared undergo an extensive DNA cleavage in the presence of ascorbate and hydrogen peroxide. Two of the complexes have higher nucleolytic efficiency than the bis(o-phenanthroline)copper(II) complex.