Metallkomplexe von Farbstoffen. VIII �bergangsmetallkomplexe des Curcumins und seiner Derivate

Synthesis of a light-responsive platinum curcumin complex, chemical and biological investigations and delivery to tumor cells by means of polymeric nanoparticles

Platinum-based anticancer drugs are common in chemotherapy, but problems such as systemic toxicity and acquired resistance of some tumors hamper their clinical applications and therapeutic efficacy. It is necessary to synthesize Pt-based drugs and explore strategies to reduce side effects and improve pharmacokinetic profiles. Photo-responsive chemotherapeutics have emerged as an alternative strategy against several cancers, as photoactivation offers spatial selectivity and fewer side effects. Here, we combine chemical synthesis and nanotechnology to create a multifunctional platinum drug delivery system based on the novel metal complex [Pt(ppy)(curc)] (ppy = deprotonated 2-phenylpyridine, curc = deprotonated curcumin)] embodying the naturally occurring bioactive molecule, curcumin. The ultrasonication method coupled with the layer-by-layer technology was employed to produce nanocolloids, which demonstrated a good biocompatibility, higher solubility in aqueous solution, stability, large drug loading, and good biological activity in comparison with the free drug. In vitro release experiments revealed that the polymeric nanoformulation is relatively stable under physiological conditions (pH = 7.4 and 37 °C) but sensitive to acidic environments (pH = 5.6 and 37 °C) which would trigger the release of the loaded drug. Our approach modifies the bioavailability of this Pt-based drug increasing its therapeutic action in terms of both cytotoxic and anti-metastasis effects.

Theoretical study of the impact of metal complexation on the reactivity properties of Curcumin and its diacetylated derivative as antioxidant agents

The chemical behavior of Curcumin and its derivatives as antioxidant and metal chelator has become the subject of intense experimental research. In this work, a theoretical study was conducted with the aim to investigate whether the acetylation of the aromatic group in Curcumin, which makes it more lipophilic, will alter its biological activities. Also, we selected from the literature metal complexes of Curcumin and its diacetylated derivative with Ga(III) and In(III), in order to discriminate the molecular active sites of the investigated molecules in which the oxidative process occurs and to obtain information about their antioxidation mechanisms. The geometrical structures and electronic properties of these compounds have been obtained using the density functional theory (DFT) method, known for its accurate results. As our other objective is to understand the factors driving biological behavior of all the studied compounds as well as the impact of the metal complexation of Curcumin and its diacetylated derivative, we provided here evidences to explain experimental observations from a molecular reactivity perspective.

Ruthenium(II) 1,4,7-trithiacyclononane complexes of curcumin and bisdemethoxycurcumin: Synthesis, characterization, and biological activity

Two cationic ruthenium(II) 1,4,7-trithiacyclononane ([9]aneS₃) complexes of curcumin (curcH) and bisdemethoxycurcumin (bdcurcH), namely [Ru(curc)(dmso-S)([9]aneS₃)]Cl (1) and [Ru(bdcurc)(dmso-S)([9]aneS₃)]Cl (2) were prepared from the [RuCl₂(dmso-S)([9]-aneS₃)] precursor and structurally characterized, both in solution and in the solid state by X-ray crystallography. The corresponding PTA complexes [Ru(curc)(PTA)([9]aneS₃)]Cl (3) and [Ru(bdcurc)(PTA)([9]aneS₃)]Cl (4) have been also synthesized and characterized (PTA = 1,3,5-triaza-7-phosphaadamantane). Bioinorganic studies relying on mass spectrometry were performed on complexes 1-4 to assess their interactions with the model protein lysozyme. Overall, a rather limited reactivity with lysozyme was highlighted accompanied by a modest cytotoxic potency against three representative cancer cell lines. The moderate pharmacological activity is likely connected to the relatively high stability of these complexes.

Zn(II) Curcuminate Complexes with 2,2'-bipyridine and Carboxylates

Two novel zinc(II) compounds with curcuminate (abbreviated as cur-), [Zn(CH3COO)(cur)(bpy)](1)·CH3OH·2H2O (bpy = 2,2'-bipyridine) and [Zn(PhCOO)(cur)(bpy)] (2)·CH3OH, have been synthesized and characterized. Their composition has been determined by single-crystal X-ray structure analysis. Complexes 1 and 2 are similar: in both a five-fold coordination environment of zinc(II) consists of a monodentate carboxylate, a chelating bidentate 2,2'-bipyridine, and curcuminate, which is bound via a deprotonated 1,3-dione moiety. In 1, 2,2'-bipyridine nitrogen atoms and curcuminate oxygen atoms form the base of a square pyramid, whereas the acetate oxygen occupies its apex. The O3N2 donor set in 2 defines a polyhedron which more closely resembles a trigonal bipyramid. The packing in the crystal lattices of both compounds is governed by hydrogen-bonds. Complexes 1 and 2 display higher stability than curcumin in buffered media at pH = 7.0, however, the degradation of coordinated cur- is comparable to that of yellow pigment curcumin (curH) when the pH is raised to 7.2. Both complexes 1 and 2 in DMSO exhibit fluorescence with Stokes shifts of 5367 and 4634 cm-1, respectively.

DNA-binding and in vitro cytotoxic activity of platinum(II) complexes of curcumin and caffeine

Three Pt(II) complexes containing the natural ligands curcumin and caffeine, namely [Pt(curc)(PPh₃)₂]Cl (1), [PtCl(curc)(DMSO)] (2) (curc = deprotonated curcumin) and trans-[Pt(caffeine)Cl₂(DMSO)] (3), were synthesized and fully characterized. The data obtained suggest that, for both 1 and 2, the anion of curcumin is coordinated to the platinum ion via the oxygen atoms of the β-diketonate moiety. Spectroscopic features reveal that in 2 and 3, a DMSO molecule is S-bonded to the metal centre. For 3, all data indicate a square-planar geometry formed by a 9-N bonded caffeine, two trans chloride anions and a DMSO. The three complexes undergo changes in solution upon incubation for 24 h; 1 and 2 release curcumin while 3 isomerizes from trans to cis configuration. The DNA-binding and cytotoxic properties of 1-3 were evaluated in vitro. Despite their structural similarity, curcuminate-containing 1 and 2 exhibit distinct DNA interactions. While 1 appears to intercalate between nucleobase pairs, inducing the oxidative degradation of the biomolecule, 2 behaves as a groove binder, by means of electrostatic forces. Caffeine-containing 3 exhibits a behaviour that is comparable to that of 2. Complexes 1 and 2 showed moderate to high cytotoxicity and selectivity against several cancer cell lines, while 3 is inactive. Compounds 1 and 2 can be further activated by visible-light irradiation.

Comparative solution and structural studies of half-sandwich rhodium and ruthenium complexes bearing curcumin and acetylacetone

Half-sandwich organometallic complexes of curcumin are extensively investigated as anticancer compounds. Speciation studies were performed to explore the solution stability of curcumin complexes formed with [Rh(η⁵-C₅Me₅)(H₂O)₃]²⁺. Acetylacetone (Hacac), as the simplest β-diketone ligand bearing (O,O) donor set, was involved for comparison and its Ru(η⁶‑p‑cymene), Ru(η⁶‑toluene) complexes were also studied. ¹H NMR, UV-visible and pH-potentiometric titrations revealed a clear trend of stability constants of the acac complexes: Ru(η⁶‑p‑cymene) > Ru(η⁶‑toluene) > Rh(η⁵-C₅Me₅). Despite this order, the highest extent of complex formation is seen for the Rh(η⁵-C₅Me₅) complexes at pH 7.4. Formation constant of [Rh(η⁵-C₅Me₅)(H₂curcumin)(H₂O)]⁺ reveals similar solution stability to that of the acac complex. Additionally, structures of two complexes were determined by X-ray crystallography. The in vitro cytotoxicity of curcumin was not improved by the complexation with these organometallic cations.

In-depth synthetic, physicochemical and in vitro biological investigation of a new ternary V(IV) antioxidant material based on curcumin

Curcumin is a natural product with a broad spectrum of beneficial properties relating to pharmaceutical applications, extending from traditional remedies to modern cosmetics. The biological activity of such pigments, however, is limited by their solubility and bioavailability, thereby necessitating new ways of achieving optimal tissue cellular response and efficacy as drugs. Metal ion complexation provides a significant route toward improvement of curcumin stability and biological activity, with vanadium being a representative such metal ion, amply encountered in biological systems and exhibiting exogenous bioactivity through potential pharmaceuticals. Driven by the need to optimally increase curcumin bioavailability and bioactivity through complexation, synthetic efforts were launched to seek out stable species, ultimately leading to the synthesis and isolation of a new ternary V(IV)-curcumin-(2,2'-bipyridine) complex. Physicochemical characterization (elemental analysis, FT-IR, Thermogravimetry (TGA), UV-Visible, NMR, ESI-MS, Fluorescence, X-rays) portrayed the solid-state and solution properties of the ternary complex. Pulsed-EPR spectroscopy, in frozen solutions, suggested the presence of two species, cis- and trans-conformers. Density Functional Theory (DFT) calculations revealed the salient features and energetics of the two conformers, thereby complementing EPR spectroscopy. The well-described profile of the vanadium species led to its in vitro biological investigation involving toxicity, cell metabolism inhibition in S. cerevisiae cultures, Reactive Oxygen Species (ROS)-suppressing capacity, lipid peroxidation, and plasmid DNA degradation. A multitude of bio-assays and methodologies, in comparison to free curcumin, showed that it exhibits its antioxidant potential in a concentration-dependent fashion, thereby formulating a bioreactivity profile supporting development of new efficient vanado-pharmaceuticals, targeting (extra)intra-cellular processes under (patho)physiological conditions.

Targeting curcumin to specific tumour cell environments: the influence of ancillary ligands

Tumour-activation of prodrugs has the potential to improve the efficacy of anticancer agents while minimising systemic toxicity. Cobalt complexes are of interest in this respect as chaperones to deliver and release anticancer agents in the low oxygen, reducing environment of solid tumours. In addition to being able to release a cytotoxic ligand under the conditions of the tumour microenvironment, it is fundamental that the chaperone complex must also be able to penetrate through multiple cell layers to deliver the cytotoxin to all regions of the tumour. Herein, we report an investigation of the distribution and metabolism of two chaperone complexes of the anticancer agent curcumin within monolayer tumour cells and multicellular tumour spheroids. Using a combination of X-ray fluorescence microscopy, confocal fluorescence microscopy, and X-ray absorption spectroscopy, we demonstrate how the nature of the chaperone complex can profoundly influence the cellular uptake, distribution, and release mechanism of curcumin, providing key insights into the design of this class of prodrug.

The evaluation of Cr-curcumin-DNA complexation by experimental and theoretical approaches

Chromium(III) chloride mediates DNA-DNA cross-linking. Some chromium complexes promote programmed cell death in specific ligand environment through binding to DNA. One strategy that can be supposed for reduction of Cr³⁺ binding affinity to DNA is using curcumin as a chelator. In the current study, the [Cr(Curcumin)(EtOH)₂](NO₃)₂ (CCC) was synthesized and characterized by UV/Vis, FT-IR, CHN and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Cr³⁺ and curcumin in solution. Binding interaction of this complex with calf thymus-DNA (CT-DNA) was investigated using UV/Vis, circular dichroism (CD), FT-IR and cyclic voltammetry. The intrinsic binding constants of CCC with DNA, measured by UV/Vis and cyclic voltammetry, were 1.60 × 10⁵ and 1.13 × 10⁵, respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favoured. CD analysis revealed that only Λ-CCC interacts with DNA and Δ-CCC form has no tendency towards DNA. Based on FT-IR studies, it was understood that CCC interacts with DNA via minor groove binding. The docking simulation was carried out for finding the binding mode of CCC to DNA, too. All of data demonstrated that the curcumin significantly reduced the affinity of Cr³⁺ to the DNA and the form of Δ-CCC has no interaction with DNA.

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules

We studied the electronic and conductance properties of two thiophene-curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO-LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO-LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.

The in vitro antitumor activity of arene-ruthenium(II) curcuminoid complexes improves when decreasing curcumin polarity

The antitumor activity of ruthenium(II) arene (p-cymene, benzene, hexamethylbenzene) derivatives containing modified curcumin ligands (HCurcI=(1E,4Z,6E)-5-hydroxy-1,7-bis(3,4-dimethoxyphenyl)hepta-1,4,6-trien-3-one and HCurcII=(1E,4Z,6E)-5-hydroxy-1,7-bis(4-methoxyphenyl)hepta-1,4,6-trien-3-one) is described. These have been characterized by IR, ESI-MS and NMR spectroscopy. The X-ray crystal structure of HCurcI has been determined and compared with its related Ru complex. Four complexes have been evaluated against five tumor cell lines, whose best activities [IC₅₀ (μM)] are: breast MCF7, 9.7; ovarian A2780, 9.4; glioblastoma U-87, 9.4; lung carcinoma A549, 13.7 and colon-rectal HCT116, 15.5; they are associated with apoptotic features. These activities are improved when compared to the already known corresponding curcumin complex, (p-cymene)Ru(curcuminato)Cl, about twice for the breast and ovarian cancer, 4.7 times stronger in the lung cancer and about 6.6 times stronger in the glioblastoma cell lines. In fact, the less active (p-cymene)Ru(curcuminato)Cl complex only shows similar activity to two novel complexes in the colon cancer cell line. Comparing antitumor activity between these novel complexes and their related curcuminoids, improvement of antiproliferative activity is seen for a complex containing CurcII in A2780, A549 and U87 cell lines, whose IC₅₀ are halved. Therefore, after replacing OH curcumin groups with OCH₃, the obtained species HCurcI and its Ru complexes have increased antitumor activity compared to curcumin and its related complex. In contrast, HCurcII is less cytotoxic than curcumin but its related complex [(p-cymene)Ru(CurcII)Cl] is twice as active as HCurcII in 3 cell lines. Results from these novel arene-Ru curcuminoid species suggest that their increased cytotoxicity on tumor cells correlate with increase of curcuminoid lipophilicity.

Anthraquinones and Derivatives from Marine-Derived Fungi: Structural Diversity and Selected Biological Activities

Anthraquinones and their derivatives constitute a large group of quinoid compounds with about 700 molecules described. They are widespread in fungi and their chemical diversity and biological activities recently attracted attention of industries in such fields as pharmaceuticals, clothes dyeing, and food colorants. Their positive and/or negative effect(s) due to the 9,10-anthracenedione structure and its substituents are still not clearly understood and their potential roles or effects on human health are today strongly discussed among scientists. As marine microorganisms recently appeared as producers of an astonishing variety of structurally unique secondary metabolites, they may represent a promising resource for identifying new candidates for therapeutic drugs or daily additives. Within this review, we investigate the present knowledge about the anthraquinones and derivatives listed to date from marine-derived filamentous fungi's productions. This overview highlights the molecules which have been identified in microorganisms for the first time. The structures and colors of the anthraquinoid compounds come along with the known roles of some molecules in the life of the organisms. Some specific biological activities are also described. This may help to open doors towards innovative natural substances.

Organometallic rhodium(III) and iridium(III) cyclopentadienyl complexes with curcumin and bisdemethoxycurcumin co-ligands

A series of half-sandwich cyclopentadienyl rhodium(III) and iridium(III) complexes of the type [Cp*M(curc/bdcurc)Cl] and [Cp*M(curc/bdcurc)(PTA)][SO3CF3], in which Cp* = pentamethylcyclopentadienyl, curcH = curcumin and bdcurcH = bisdemethoxycurcumin as O^O-chelating ligands, and PTA = 1,3,5-triaza-7-phosphaadamantane, is described. The X-ray crystal structures of three of the complexes, i.e. [Cp*Rh(curc)(PTA)][SO3CF3] (5), [Cp*Rh(bdcurc)(PTA)][SO3CF3] (6) and [Cp*Ir(bdcurc)(PTA)][SO3CF3] (8), confirm the expected "piano-stool" geometry. With the exception of 5, the complexes are stable under pseudo-physiological conditions and are moderately cytotoxic to human ovarian carcinoma (A2780 and A2780cisR) cells and also to non-tumorigenic human embryonic kidney (HEK293) cells, but lack the cancer cell selectivity observed for related arene ruthenium(II) complexes.

Oxovanadium(IV) complexes of curcumin for cellular imaging and mitochondria targeted photocytotoxicity

Oxovanadium(IV) complexes [VO(R-tpy)(cur)](ClO4) (1, 2) of curcumin (Hcur) and terpyridine ligands (R-tpy) where R is phenyl (phtpy in 1) or p-triphenylphosphonium methylphenyl bromide (C6H4CH2PPh3Br) (TPP-phtpy in 2) were prepared and characterized and their DNA photocleavage activity, photocytotoxicity and cellular localization in cancer cells (HeLa and MCF-7) were studied. Acetylacetonate (acac) complexes [VO(R-tpy)(acac)](ClO4) of phtpy (3) and TPP-phtpy (4) were prepared and used as the control species. These complexes showed efficient cleavage of pUC19 DNA in visible light of 454 nm and near-IR light of 705 nm. Complexes 1 and 2 showed significant photocytotoxicity in visible light of 400-700 nm. FACS analysis showed sub-G1/G0 phase cell-cycle arrest in cancer cells when treated with 1 and 2 in visible light in comparison with the dark controls. Fluorescence microscopic studies revealed specific localization of the p-triphenylphosphonium complex 2 in the mitochondria of MCF-7 cancer cells whereas no such specificity was observed for complex 1.

Metal complexes of curcumin--synthetic strategies, structures and medicinal applications

This Tutorial Review presents an overview on the synthesis, characterization and applications of metal complexes containing curcumin (=1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) and its derivatives as ligands. Innovative synthetic strategies leading to soluble and crystallizable metal curcumin complexes are outlined in detail. Special emphasis is placed on the highly promising and exciting medicinal applications of metal curcumin complexes, with the three most important areas being anticancer activity and selective cytotoxicity, anti-Alzheimer's disease activity, and antioxidative/neuroprotective effects. Overall, this Tutorial Review provides the first general overview of this emerging and rapidly expanding field of interdisciplinary research.

Formation of curcumin molecular ion under electrospray ionisation conditions in the presence of metal cations

Electrospray ionisation (ESI) mass spectra obtained for solutions containing curcumin, copper cation and other metal cations, namely Co2+, Ni2+, Mn2+ and Zn2+, have shown an abundant curcumin molecular ion at m/z 368. This ion was not formed for solutions containing curcumin and copper cations or for those containing curcumin and other metal cations. To the best of our knowledge, it is the first example of a system in which copper cations and other metal cations promote formation of organic radical cation under ESI conditions.

Improved separation of the curcuminoids, syntheses of their rare earth complexes, and studies of potential antiosteoporotic activity

The first reported homogenous rare earth curcumin (HCurc; ((1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione)) complexes with the formula ML3, where M(3+) is Eu(III), Gd(III) or Lu(III), were synthesized and characterized by mass spectrometry, infrared spectroscopy and, in the case of the lutetium complex, (1)H NMR spectroscopy. Most importantly an improved separation of the three curcuminoids, HCurc, HDMC ((1E,6E)-1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)hepta-1,6-diene-3,5-dione) and HBDMC ((1E,6E)-1,7-bis(4-hydroxyphenyl)hepta-1,6-diene-3,5-dione) was realized using a combination of normal-phase column and phosphate-impregnated preparative-thin layer chromatographies. The toxicities of the metal curcumin complexes and ligands were investigated in MG-63 cells, an osteoblast-like cell line, for potential activity as antiosteoporotic agents.

Enhancing the photocytotoxic potential of curcumin on terpyridyl lanthanide(III) complex formation

Lanthanide(III) complexes [Ln(R-tpy)(cur)(NO3)2] (Ln = La(III) in 1, 2; Gd(III) in 5, 6) and [Ln(R-tpy)(scur)(NO3)2] (Ln = La(III) in 3, 4; Gd(III) in 7, 8), where R-tpy is 4′-phenyl-2,2′:6′,2′′-terpyridine (ph-tpy in 1, 3, 5, 7), 4′-(1-pyrenyl)-2,2′:6′,2′′-terpyridine (py-tpy in 2, 4, 6, 8), Hcur is curcumin (in 1, 2, 5, 6) and Hscur is diglucosylcurcumin (in 3, 4, 7, 8), were prepared and their DNA photocleavage activity and photocytotoxicity studied. Complexes [La(ph-tpy)(cur)(NO3)2] (1) and [Gd(ph-tpy)(cur)(NO3)2] (5) were structurally characterized. The complexes in aqueous-DMF showed an absorption band near 430 nm and an emission band near 515 nm when excited at 420 nm. The complexes are moderate binders to calf-thymus DNA. They cleave plasmid supercoiled DNA to its nicked circular form in UV-A (365 nm) and visible light (454 nm) via (1)O2 and ˙OH pathways. The complexes are remarkably photocytotoxic in HeLa cells in visible light (λ = 400–700 nm) and are non-toxic in the dark. FACScan analysis of the HeLa cells treated with 2 and 4 showed cell death via an apoptotic pathway. Nuclear localization of 1–4 is evidenced from confocal imaging on HeLa cells. The hydrolytic instability of curcumin gets significantly reduced upon binding to the lanthanide ions while retaining its photocytotoxic potential.

Synthesis and characterization of ligational behavior of curcumin drug towards some transition metal ions: chelation effect on their thermal stability and biological activity

Complexes of Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with curcumin ligand as antitumor activity were synthesized and characterized by elemental analysis, conductometry, magnetic susceptibility, UV-Vis, IR, Raman, ESR, (1)H-NMR spectroscopy, X-ray diffraction analysis of powdered samples and thermal analysis, and screened for antimicrobial activity. The IR spectral data suggested that the ligand behaves as a monobasic bidentate ligand towards the central metal ion with an oxygen's donor atoms sequence of both -OH and C=O groups under keto-enol structure. From the microanalytical data, the stoichiometry of the complexes 1:2 (metal:ligand) was found. The ligand and their metal complexes were screened for antibacterial activity against Escherichia Coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa and fungicidal activity against Aspergillus flavus and Candida albicans.

Ruthenium-arene complexes of curcumin: X-ray and density functional theory structure, synthesis, and spectroscopic characterization, in vitro antitumor activity, and DNA docking studies of (p-cymene)Ru(curcuminato)chloro

The in vitro antiproliferative activity of the title compound on five tumor cell lines shows preference for the colon-rectal tumor HCT116, IC(50) = 13.98 μM, followed by breast MCF7 (19.58 μM) and ovarian A2780 (23.38 μM) cell lines; human glioblastoma U-87 and lung carcinoma A549 are less sensitive. A commercial curcumin reagent, also containing demethoxy and bis-demethoxy curcumin, was used to synthesize the title compound, and so (p-cymene)Ru(demethoxy-curcuminato)chloro was also isolated and chemically characterized. The crystal structure of the title compound shows (1) the chlorine atom linking two neighboring complexes through H-bonds with two O(hydroxyl), forming an infinite two-step network; (2) significant twist in the curcuminato, 20° between the planes of the two phenyl rings. This was also seen in the docking of the Ru-complex onto a rich guanine B-DNA decamer, where a Ru-N7(guanine) interaction is detected. This Ru-N7(guanine) interaction is also seen with ESI-MS on a Ru-complex-guanosine derivative.

Study binding of Al-curcumin complex to ds-DNA, monitoring by multispectroscopic and voltammetric techniques

In this work a complex of Al3+ with curcumin ([Al(curcumin) (EtOH)2](NO3)2) was synthesized and characterized by UV-vis, FT-IR, elemental analysis and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Al3+ and curcumin in solution. For binding studies of this complex to calf thymus-DNA various methods such as: UV-vis, fluorescence, circular dichroism (CD), FT-IR spectroscopy and cyclic voltammetry were used. The intrinsic binding constant of ACC with DNA at 25°C was calculated by UV-vis and cyclic voltammetry as 2.1×10(4) and 2.6×10(4), respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favored. The CD results showed that only the Δ-ACC interacts with DNA and the Δ-ACC form has not any tendency to interact with DNA, also the pure curcumin has not any stereoselective interaction with CT-DNA. Fluorimetric studies showed that fluorescence enhancement was initiated by a static process in the ground state. The cyclic voltammetry showed that ACC interact with DNA with a binding site size of 2. From the FT-IR we concluded that the Δ-ACC interacts with DNA via partial electrostatic and minor groove binding. In comparison with previous works it was concluded that curcumin significantly reduced the affinity of Al3+ to the DNA.

Copper curcuminoids containing anthracene groups: fluorescent molecules with cytotoxic activity

The coordination chemistry of the new curcuminoid ligand, 1,7-(di-9-anthracene-1,6-heptadiene-3,5-dione), abbreviated 9Accm has been studied, resulting in two new copper-9Accm compounds. Compound 1, [Cu(phen)Cl(9Accm)], was synthesized by reacting 9Accm with [Cu(phen)Cl(2)] in a 1:1 ratio (M:L) and compound 2, [Cu(9Accm)(2)], was prepared from Cu(OAc)(2) and 9Accm (1:2). UV-vis, electron paramagnetic resonance (EPR), and superconducting quantum interference device (SQUID) measurements were some of the techniques employed to portray these species; studies on single crystals of free 9Accm, [Cu(phen)Cl(9Accm)] and [Cu(9Accm)(2)(py)] provided detailed structural information about compounds 1 and 2·py, being the first two copper-curcuminoids crystallographically described. In addition the antitumor activity of the new compounds was studied and compared with free 9Accm for a number of human tumor cells. To provide more insight on the mode of action of these compounds under biological conditions, additional experiments were accomplished, including studies on the nature of their interactions with calf thymus DNA by UV-vis titration and Circular Dichroism. These experiments together with DNA-binding studies indicate electrostatic interactions between some of these species and the double helix, pointing out the weak nature of the interaction of the compounds with CT-DNA. The intrinsic fluorescence of the free ligand and both copper compounds provided valuable information over the cellular process and therefore, fluorescence microscopy studies were performed using a human osteosarcoma cell line. Studies in vitro using this technique suggest that the action of these molecules seems to occur outside the nuclei.

Curcumin as the OO bidentate ligand in "2 + 1" complexes with the [M(CO)3]+ (M = Re, 99mTc) tricarbonyl core for radiodiagnostic applications

The synthesis and characterization of "2 + 1" complexes of the [M(CO)(3)](+) (M = Re, (99m)Tc) core with the β-diketones acetylacetone (complexes 2, 8) and curcumin (complexes 5, 10 and 6, 11) as bidentate OO ligands, and imidazole or isocyanocyclohexane as monodentate ligands is reported. The complexes were synthesized by reacting the [NEt(4)](2)[Re(CO)(3)Br(3)] precursor with the β-diketone to generate the intermediate aqua complex fac-Re(CO)(3)(OO)(H(2)O) that was isolated and characterized, followed by replacement of the labile water by the monodentate ligand. All complexes were characterized by mass spectrometry, NMR and IR spectroscopies, and elemental analysis. In the case of complex 2, bearing imidazole as the monodentate ligand, X-ray analysis was possible. The chemistry was successfully transferred at (99m)Tc tracer level. The curcumin complexes 5 and 6, as well as their intermediate aqua complex 4, that bear potential for radiopharmaceutical applications due to the wide spectrum of pharmacological activity of curcumin, were successfully tested for selective staining of β-amyloid plaques of Alzheimer's disease. The fact that the complexes maintain the affinity of the mother compound curcumin for β-amyloid plaques prompts for further exploration of their chemistry and biological properties as radioimaging probes.

Synthesis and biological evaluation of novel ferrocenyl curcuminoid derivatives

With the purpose to improve the biological activities of curcumin, eight novel ferrocenyl curcuminoids were synthesized by covalent anchorage of three different ferrocenyl ligands. We evaluated their cytotoxicity on B16 melanoma cells and normal NIH 3T3 cells, their inhibition of tubulin polymerization and their effect on the morphology of endothelial cells. The presence of a ferrocenyl side chain was clearly shown to improve the biological activity of most of their corresponding organic curcuminoid analogues.

Syntheses, characterization and biological activities of rare earth metal complexes with curcumin and 1,10-phenanthroline-5,6-dione

Three new solid complexes have been synthesized by the reaction of rare earth(III) nitrate with the first ligand curcumin (HL) and the second ligand 1,10-phenanthroline-5,6-dione (L') in alcohol solution (pH=6.5-7.0). The composition of the complexes has been characterized by elemental analysis, molar conductivity, thermogravimetric analysis, IR, UV-vis methods. The results reveal that beta-diketone group of the first ligand to coordinates with rare earth ions in bidentate mode after deprotonated. But the second ligand uses its two N atoms coordinates with rare earth ions in bidentate mode. The general formula of the complexes is REL(3)L' (RE=Sm, Eu, Dy). The results of antibacterial activity indicated that the complexes have excellent antibacterial ability for the testing bacterium than that of curcumin. The result of agarose gel electrophoresis suggested that the complex of SmL(3)L' can cleave the plasmid DNA at physiological pH and temperature. And it was found that the cleavage process of plasmid DNA was sensitive to pH, however, adding radical scavengers almost had no effect on the DNA cleavage reaction, therefore, the cleavage of DNA by SmL(3)L' does not produce diffusible hydroxyl radicals via the Fenton reaction.

Chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts of cytotoxic ruthenium arene complexes containing O,O-chelating ligands

The synthesis and X-ray structures of a half-sandwich Ru(II)p-cymene beta-diketonato complex as chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts are reported. Structural features which contribute to stabilisation of adducts through non-covalent, weak interactions are discussed. The X-ray crystal structure of the cytotoxic complex [(eta(6)-p-cym)Ru(Ph(2)acac)Cl] (1), where Ph(2)acac=1,3-diphenyl-1,3-propanedionate and p-cym=para-cymene, shows that the phenyl rings of the acac-type ligand form a hydrophobic face, conferring lipophilic character on the complex. The structure of the aqua adduct [(eta(6)-p-cym)Ru(Ph(2)acac)H(2)O]CF(3)SO(3).H(2)O.Et(2)O (4.H(2)O.Et(2)O), a possible activated species, possesses a comparatively short Ru-OH(2) bond. In the structure of [(eta(6)-p-cym)Ru(Ph(2)acac)9EtG-N7]CF(3)SO(3).2tol (5.2tol), where tol=toluene and 9EtG=9-ethylguanine, a comparatively long Ru-N7 bond is observed in addition to weak G CH8cdots, three dots, centeredO (Ph(2)acac) H-bonds. The crystal structure of [(eta(6)-p-cym)Ru(acac)9EtA-N7]PF(6) (6), where acac=acetylacetonate and 9EtA=9-ethyladenine, a rare example of a ruthenium complex containing monodentate adenine, shows a strong H-bonding interaction between N6Hcdots, three dots, centeredO(acac), which may contribute to the selectivity of {(eta(6)-p-cym)Ru(acac)}(+) towards adenine bases.

Curcumin and cyclopalladated complexes: a recipe for bifunctional biomaterials

The first examples of binuclear and mononuclear ortho-palladated complexes based on a functionalized 2-phenylquinoline ligand have been synthesized and fully characterized. Conjugating cyclopalladated fragments to curcumin family biologically active beta-diketones gives in one single molecule two different functionalities. The structural variations based on the curcuminoid structure have been tested for their in vitro cytotoxic activity. The activity of complexes comprised of a cyclopalladated fragment conjugated to functionalized bioactive ligands, represents the potential of organometallic systems in generating new bifunctional biomaterials.