Coumarin-modified ruthenium complexes: Synthesis, characterization, and antiproliferative activity against human cancer cells.

Among ruthenium complexes studied as anticancer metallodrugs, NKP-1339, NAMI-A, RM175, and RAPTA-C have already entered clinical trials due to their potent antitumor activity demonstrated in preclinical studies and reduced toxicity in comparison with platinum drugs. Considering the advantages of ruthenium-based anticancer drugs and the cytostatic activity of organometallic complexes with triazole- and coumarin-derived ligands, we set out to synthesize Ru(II) complexes of coumarin-1,2,3,-triazole hybrids (L) with the general formula [Ru(L)(p-cymene)(Cl)]ClO4. The molecular structure of the complex [Ru(2a)(p-cymene)(Cl)]ClO4 (2aRu) was determined by single-crystal X-ray diffraction, which confirmed the coordination of the ligand to the central ruthenium(II) cation by bidentate mode of coordination. Coordination with Ru(II) resulted in the enhancement of cytostatic activity in HepG2 hepatocellular carcinoma cells and PANC-1 pancreatic cancer cells. Coumarin derivative 2a positively regulated the expression and activity of c-Myc and NPM1 in RKO colon carcinoma cells, while the Ru(II) half-sandwich complex 2cRu induced downregulation of AKT and ERK signaling in PANC-1 cells concomitant with reduced intracellular levels of reactive oxygen species. Altogether, our findings indicated that coumarin-modified half-sandwich Ru(II) complexes held potential as anticancer agents against gastrointestinal malignancies.

Dissimilar effect of organometallic ruthenium complexes on the viability of MDR and non-MDR experimental models.

Ruthenium complexes containing triphenylphosphine diamide ligands were prepared, characterized, and tested for their biological activity against various cancer cell lines and the malaria parasite, Plasmodium falciparum. The effect of M (mono-substituted) and B (bis-substituted) complexes on the human cervical carcinoma (HeLa) cell line was investigated using the MTT assay. Five (B2, B3, B5, B6, and B13) of the 24 synthesized ruthenium complexes showed significant effects with IC50 values ranging between 0.3 and 2.3 µM. Evaluation of the potential biomolecular targets of B2 and B13 by fluorescence spectroscopy revealed relevant interactions with BSA and only a weak affinity for ctDNA. Complexes M2, B2, M13 and B13 were selected for further biological characterization. Their effect on the viability of two ovarian cancer cell lines was compared to normal cell lines, denoting their selectivity. Upon treatment of four different drug-resistant gynaecological cancer cell lines, differing in their multidrug-resistant phenotypes, the efficacy of the bis-substituted complexes was shown to be greater than their mono-substituted counterparts. The non-MDR cells are sensitive to all the tested complexes, compared to MDR cells which are less sensitive. Upon investigation of complexes M2, M13, B2, and B13 against sensitive and multidrug-resistant parasite strains of P. falciparum, the bis-substituted complexes were again shown to be the most potent, with submicromolar activity against both strains. Furthermore, the resistance indexes for the complexes were approximately equal to 1, which is at least 5-fold lower than chloroquine diphosphate, suggesting the ability of these complexes to retain their activity in resistant forms of the parasite.

Turn-on fluorescence of ruthenium pyrene complexes in response to bovine serum albumin.

Two novel pyrene triphenylphosphine ruthenium conjugates act as fluorescent turn-on beacons for serum albumin, being non-fluorescent in aqueous media but exhibiting strong emission upon binding to BSA. The selective cytotoxicity of the compounds against tumour cells is enhanced upon irradiation by UV-light, paving the way for application in photodynamic therapy under two-photon excitation.

Synthesis, characterisation and biological evaluation of monometallic Re(I) and heterobimetallic Re(I)/Fe(II) complexes with a 1,2,3-triazolyl pyridine chelating moiety.

Bioorganometallic complexes have attracted considerable interest and have shown promise for potential application in the treatment and diagnosis of cancer, as well as bioimaging agents, some acting as theranostic agents. The series of novel ferrocene, benzimidazo[1,2-a]quinoline and fluorescein derivatives with bidentate pyridyl-1,2,3-triazole and 2,2'-dipyridylamine and their tricarbonylrhenium(I) complexes was prepared and fully characterised by NMR, single-crystal X-ray diffraction, UV-Vis and fluorescence spectroscopy in biorelevant conditions. The fluorescein and benzimidazo[1,2-a]quinoline ligands and their complexes with Re(I) showed interactions with ds-DNA/RNA and HSA, characterised by thermal denaturation measurements, fluorimetric and circular dichroism titrations. The binding constants revealed that addition of Re(I) increases the affinity of fluorescein but decreases the affinity of benzimidazo[1,2-a]quinoline. The complexation of Re(I) had the opposite effect on fluorescein and benzimidazo[1,2-a]quinoline ligands' fluorimetric sensitivity upon biomacromolecule binding, Re(I) fluorescein complex emission being strongly quenched by DNA/RNA or HSA, while emission of Re(I) benzimidazo[1,2-a]quinolone complex was enhanced, particularly for HSA, making it a promising fluorescent probe. Some mono- and heterobimetallic complexes showed considerable antiproliferative activity on colon cancer cells (CT26 and HT29), with ferrocene dipyridylamine complexes exhibiting the best inhibitory activity, comparable to cisplatin. The correlation of the cytotoxicity data with the linker type between the ferrocene and the 1,2,3-triazole ring suggests that direct binding of the metallocene to the 1,2,3-triazole is favourable for antitumor activity. The Re(I) benzimidazo[1,2-a]quinolone complex showed moderate antiproliferative activity, in contrast to the Re(I) fluorescein complex, which exhibited weak activity on CT26 cells and no activity on HT29 cells. The accumulation of the Re(I) benzimidazo[1,2-a]quinolone complex in the lysosomes of CT26 cells indicates the site of its bioactivity, thus making this complex a potential theranostic agent.

Tuning the coordination properties of chiral pseudopeptide bis(2-picolyl)amine and iminodiacetamide ligands in Zn(II) and Cu(II) complexes.

Seven bis(2-picolyl)amine (bpa) and five iminodiacetamide (imda) ligands were prepared with different modifications in their side chain structure. The coordination properties of the ligands (L) were influenced by changes in the aliphatic linker length (C1, C2, or C3), amide group isomers and type of chiral terminal group. Complexation with Cu(II) afforded two polymorphs of a ML complex which features tetradentate coordination of a ligand with C2 linkers, while crystal structures of three trans-fac ML2 complexes with Cu(II) and Ni(II) show tridentate coordination of ligands with a C3 linker. The stoichiometry and stereochemistry of Zn(II) and Cu(II) complexes was further studied in solution by NMR and UV-Vis spectroscopy. DFT calculations gave an insight into the relative stability of isomers, as well as potential hydrogen bonding between two ligands in a ML2 complex. Furthermore, ML complexes of Cu(II) exhibited DNA cleavage activity.

Induction of Λ-helicity in a zinc complex with an alanine-appended aminopyridine ligand.

The crystal structure of tris[dimethyl 5-({1-[(pyridin-2-yl-κN)carbamoyl-κO]ethyl}carbamoyl)benzene-1,3-dicarboxylate]zinc(II) dinitrate acetonitrile trisolvate, [Zn(C19H19N3O6)3](NO3)2·3CH3CN or [Zn(L)3](NO3)2·3CH3CN, (1), has been determined by single-crystal X-ray diffraction. The neutral ligand L coordinates to the Zn2+ cation in a bidentate fashion via the pyridine N atom and an amide O atom, forming a six-membered chelate ring. The Λ-helical chirality of the Zn2+ coordination sphere is induced by pendant L-alanine residues through stacking interactions between the arene groups of two coordinated ligands, assisted by a hydrogen bond between amide groups bonded to the stacked arene rings. The third ligand is coordinated to the Zn2+ cation by the same six-membered chelate ring, but in the opposite direction with respect to the analogous chelate rings of the first two coordinated ligands. Besides ionic interactions between [ZnL3]2+ complexes and NO3- anions, several types of hydrogen bonds and intermolecular stacking interactions contribute to the stability of the solid-state phase.

Comparison of Nonheme Manganese- and Iron-Containing Flavone Synthase Mimics.

Heme and nonheme-type flavone synthase enzymes, FS I and FS II are responsible for the synthesis of flavones, which play an important role in various biological processes, and have a wide range of biomedicinal properties including antitumor, antimalarial, and antioxidant activities. To get more insight into the mechanism of this curious enzyme reaction, nonheme structural and functional models were carried out by the use of mononuclear iron, [FeII(CDA-BPA*)]2+ (6) [CDA-BPA = N,N,N',N'-tetrakis-(2-pyridylmethyl)-cyclohexanediamine], [FeII(CDA-BQA*)]2+ (5) [CDA-BQA = N,N,N',N'-tetrakis-(2-quinolilmethyl)-cyclohexanediamine], [FeII(Bn-TPEN)(CH3CN)]2+ (3) [Bn-TPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-diaminoethane], [FeIV(O)(Bn-TPEN)]2+ (9), and manganese, [MnII(N4Py*)(CH3CN)]2+ (2) [N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine)], [MnII(Bn-TPEN)(CH3CN)]2+ (4) complexes as catalysts, where the possible reactive intermediates, high-valent FeIV(O) and MnIV(O) are known and well characterised. The results of the catalytic and stoichiometric reactions showed that the ligand framework and the nature of the metal cofactor significantly influenced the reactivity of the catalyst and its intermediate. Comparing the reactions of [FeIV(O)(Bn-TPEN)]2+ (9) and [MnIV(O)(Bn-TPEN)]2+ (10) towards flavanone under the same conditions, a 3.5-fold difference in reaction rate was observed in favor of iron, and this value is three orders of magnitude higher than was observed for the previously published [FeIV(O)(N2Py2Q*)]2+ [N,N-bis(2-quinolylmethyl)-1,2-di(2-pyridyl)ethylamine] species.

A ferrocene-based pseudopeptide chiroptical switch.

We present a double-stranded ferrocene pseudopeptide 2b which exhibits stimuli responsive chirality inversion triggered by solvent exchange or acid addition. Compound 2b exists as a mixture of self-assembled fast exchanging oligomers which macroscopically behave as a chiroptical switch with two stable states. The ferrocene group inversion results in a distinct CD signal in the visible part of the spectrum. The inversion is accomplished through a conformational change due to a rearrangement of hydrogen bonding forcing the rotation of ferrocene rings.

Copper(ii) and zinc(ii) complexes of mono- and bis-1,2,3-triazole-substituted heterocyclic ligands.

Chelating 1,4-disubstituted mono- (8a-8d) and bis-1,2,3-triazole-based (9a-11a) ligands were prepared by regioselective copper(i)-catalysed 1,3-dipolar cycloaddition of terminal alkynes with aromatic azides, together with bioconjugate 13a synthesized by amide coupling of l-phenylalanine methyl ester to 11a. Cu(ii) and Zn(ii) complexes were prepared and single crystal structures were determined for complexes 8aCu, 8dCu, 9cCu and 10cCu, as well as the free ligands 10a and 10c. The in situ prepared Zn(ii) complexes were studied by NMR spectroscopy, while the stoichiometry of the Cu(ii) complexes in solution was determined by UV-Vis titrations and confirmed by the electronic structure DFT calculations at the (SMD)/M05-2X/6-31+G(d)/LanL2DZ+ECP level of theory.

Stereochemistry of Hexacoordinated Zn(II), Cu(II), Ni(II), and Co(II) Complexes with Iminodiacetamide Ligands.

Metal complexes of iminodiacetamide (imda) ligands and metal ions Zn(II), Cu(II), Ni(II), and Co(II) were prepared using eight imda ligands (L1-L8) substituted with groups of different steric and electronic properties on the central amine N atom (H atom, methyl, isopropyl, and benzyl) and the para position of the phenyl rings (nitro and dimethylamino). The effect of these substituents on the stoichiometry (ML and ML2), geometry, and stereochemistry (mer, trans-fac, cis-fac) of the complexes was studied in the solid state, in solution, and by density functional theory calculations. Single-crystal and powder X-ray diffraction, thermogravimetry, and IR spectroscopy showed that in the solid state imda ligands preferentially form trans-fac ML2 complexes, with the exception of the cis-fac complex 7Zn. NMR spectroscopy of diamagnetic Zn(II) and paramagnetic Co(II) complexes revealed the formation of both ML and ML2 complexes in solution, which was also confirmed by UV-vis titrations. Variable-temperature NMR was used to study the effect of the substituent on the central amine N atom on the Zn-N bond strength and nitrogen inversion. The relative stabilities of the isomers were rationalized by computations and the optimized structures used for geometry analysis.

Organometallic ruthenium(II)-arene complexes with triphenylphosphine amino acid bioconjugates: Synthesis, characterization and biological properties.

(p-Cymene)-ruthenium bioconjugates ML (1) and ML2 (2), bearing phosphane ligands substituted with chiral or non-chiral amino acid esters, L, were synthetized and characterized by instrumental methods (NMR, CD, MS) and DFT calculations (using the wB97xD functional). Cytotoxic activity of complexes 1 and 2 was investigated by using human cervical carcinoma cell line (HeLa) and MTT assay. Four (2pG, 2pA, 2mG and 2mA) out of ten synthesized ruthenium complexes showed significant toxicity, with IC50 values of 5-30 µM. Evaluation of the potential biomolecular targets of bioconjugates 2 by UV-Vis, fluorescence and CD spectroscopy revealed no measurable interaction with DNA, but micromolar affinity for proteins. The cytotoxicity of bioconjugates 2 is in correlation with their BSA binding constants, i. e. bioconjugates with lower IC50 values show higher binding affinities towards BSA. Compound 2mG with value of IC50 16 µM was selected for further biological characterization. The higher level of toxicity towards tumor compared to normal cell lines indicates its selective activity, important characteristic for potential medical use. It was detected 2mG caused increase of cells in the S phase of cell cycle and consequential decrease of cells in G0/G1 phase. Additionally, 2mG caused dose- and time-dependent increase of SubG0/G1 cell population, suggesting its ability to induce programmed cell death. Further investigation determined autophagy as the mode of cell death. The role of GSH in HeLa cells response to investigated organometallic ruthenium complexes was confirmed using specific regulators of GSH synthesis, buthionine sulfoximine and N-acetyl-cysteine. Pre-treatment of cells with ethacrynic acid and probenecid emphasized the role of GSH in detoxification of 2mG compound. The amount of total ruthenium accumulation in the cell did not correlate with toxicity of 2pG, 2pA, 2mG and 2mA, suggesting structure dependent differences in either cell uptake or kinetics of ruthenium complexes detoxification. We speculate that ruthenium complexes bind protein-based biomolecules further triggering cell death. Based on the gained knowledge, the synthesis and development of more tumor-specific ruthenium-based complexes as potential anticancer drugs can be expected.

Controlling orthogonal self-assembly through cis-trans isomerization of a non-covalent palladium complex dimer.

The trans-configured square-planar complex of dichloropalladium and chiral monodentate phosphine ligands forms self-complementary dimers through 16 hydrogen bonded amides and π-π stacking in chlorinated solvents. The self-assembly is controlled by cis-trans isomerisation of the metal center, where the trans-configuration governs the dimer formation.

Metal-induced supramolecular chirality inversion of small self-assembled molecules in solution.

A non-covalent self-assembled chiral alanyl aminopyridine ligand exhibits supramolecular chirality in solution, independent of the organic solvent used. The supramolecular chirality of the assemblies is completely inverted by complexation to zinc ions. To date, such a supramolecular metal-ligand system has not been reported in the literature.

Hydrophobic-hydrophilic post-cross-linked polystyrene/poly (methyl acryloyl diethylenetriamine) interpenetrating polymer networks and its adsorption properties.

In this study, we developed an effective approach for increasing the equilibrium adsorption capacity of the interpenetrating polymer networks (IPNs) toward polar aromatic compounds. For this purpose, a novel post-cross-linked polystyrene/poly (methyl acryloyl diethylenetriamine) (CMPS_pc/PMADETA) IPNs was synthesized and its adsorption was evaluated from aqueous solution using p-hydroxybenzoic acid as the adsorbate. CMPS_pc/PMADETA IPNs possessed a relatively high Brunauer-Emmett-Teller (BET) surface area and hydrophobic networks as well as hydrophilic networks, inducing a much enhanced adsorption toward p-hydroxybenzoic acid. The equilibrium adsorption capacity of p-hydroxybenzoic acid on CMPS_pc/PMADETA IPNs was remarkably larger than that on its precursors and the equilibrium data were correlated better by Sips model than the Langmuir and Freundlich models. Furthermore, the adsorption was a fast process, and the micropore diffusion model characterized the kinetic data very well. At a feed concentration of 1060.8mg/L and a flow rate of 10.8BV/h, the dynamic adsorption capacity was calculated to be 200.8mg/mL wet resin.

Synthesis and characterization of ML and ML2 metal complexes with amino acid substituted bis(2-picolyl)amine ligands.

Metal complexes with ML or ML2 stoichiometry have been isolated in the reaction of Zn(NO3)2, ZnBr2 or M(NO3)2/NaBF4, M = Zn(ii), Co(ii) or Ni(ii), with either amino acid or amine substituted tridentate nitrogen ligands based on bis(2-picolyl)amine (bpa) or bis(2-quinaldyl)amine (bqa). The stoichiometry (M : L = 1 : 1 or 1 : 2) and stereochemistry (mer, trans-fac or cis-fac) of the products have been studied by NMR and IR spectroscopy, X-ray single crystal analysis and quantum-chemical calculations with an implicit SMD solvation model.

When protein-based biomineralization meets hydrothermal synthesis: the nanostructures of the as-prepared materials are independent of the protein types.

Proteins were proved to be type-independent templates for the biomineralization of iron ions into hematite mesocrystals with tunable structures and morphologies under hydrothemal conditions. Our finding could pave the way for the synthesis of mesocrystals with controlled stuctures and morphologies using templates of low-cost proteins.

Reversible site-specific tagging of enzymatically synthesized RNAs using aldehyde-hydrazine chemistry and protease-cleavable linkers.

The investigation of RNA structure, dynamics and biological function often requires the site-specific incorporation of non-natural moieties. Here we describe the functionalization of RNA transcripts by aldehyde-hydrazine chemistry using a simple initiator nucleotide that carries an acetal-protected aldehyde function. This initiator nucleotide was efficiently incorporated into RNA, and the modified RNAs were quantitatively coupled to a peptide derivative displaying a hydrazine moiety at one end, a biotin tag at the other, and a trypsin-cleavable sequence in between. RNA conjugates could be easily isolated by affinity chromatography on streptavidin agarose and quantitatively cleaved off the support by trypsin treatment without detectable RNA degradation. The strategy described here may allow the incorporation of various new features into enzymatically synthesized RNA under mild conditions.

Helically chiral ferrocene peptides containing 1'-aminoferrocene-1-carboxylic acid subunits as turn inducers.

We present a detailed structural study of peptide derivatives of 1'-aminoferrocene-1-carboxylic acid (ferrocene amino acid, Fca), one of the simplest organometallic amino acids. Fca was incorporated into di- to pentapeptides with D- and L-alanine residues attached to either the carboxy or amino group, or to both. Crystallographic and spectroscopic studies (circular dicroism (CD), IR, and NMR) of about two dozen compounds were used to gain a detailed insight into their structures in the solid state as well as in solution. Four derivatives were characterized by single-crystal X-ray analysis, namely Boc-Fca-Ala-OMe (16), Boc-Fca-D-Ala-OMe (17), Boc-Fca-beta-Ala-OMe (18), and Boc-Ala-Fca-Ala-Ala-OMe (21) (Boc=tert-butyloxycarbamyl). CD spectroscopy is an extremely useful tool to elucidate the helical chirality of the metallocene core. Unlike in all other known ferrocene peptides, the helical chirality of the ferrocene is governed solely by the chirality of the amino acid attached to the N terminus of Fca. Depending on the degree of substitution of both cyclopentadiene (Cp) rings, different hydrogen-bonding patterns are realized. (1)H NMR and IR spectroscopy, together with the results from X-ray crystallography, give detailed information regarding not only the hydrogen-bonding patterns of the compounds, but also the equilibria between different conformers in solution. Differences in chemical shifts of NH protons in dimethyl sulfoxide ([D(6)]DMSO) and CDCl(3), that is, the variation ratio (vr), is used for the first time as a measure of the hydrogen-bonding strength of individual COHN bonds in ferrocenoyl peptides. In dipeptides with one intramolecular hydrogen bond between the pendant chains, for example, in dipeptide 16, an equilibrium between hydrogen-bonded and open forms is observed, as testified by a vr value of around 0.5. Higher peptides, such as tetrapeptide 21, are able to form two intramolecular hydrogen bonds stabilizing one single conformation in CDCl(3) solution (vr approximately 0). Due to the low barrier of Cp-ring rotation, new and unnatural hydrogen-bonding patterns are emerging. The systematic work described herein lays a solid foundation for the rational design of metallocene peptides with unusual structures and properties.

Insertion of an internal dipeptide into PNA oligomers: thermal melting studies and further functionalization.

The solid phase synthesis of PNA oligomers with the internal dipeptide Gly-Phe is presented and the interaction with complementary DNA investigated. UV absorbance melting experiments with different but complementary DNA sequences show that stable PNA x DNA duplexes are only obtained when there is no DNA base opposite the dipeptide unit. Instead, the dipeptide spacer forms a loop-like structure within the duplex. Further functionalization with N-heterocyclic ligands is described. p-Nitro-phenylalanine is introduced in place of Phe during solid phase synthesis and subsequently reduced to p-amino-phenylalanine. Reaction with activated acids provides the ligand conjugates in high yield and purity. This strategy opens a universal route to a large number of internal substitutions in PNA chemistry.