Metal-to-metal electron transfer in a cyanido-bridged {Fe2Co2} square complex followed by X-ray diffraction and absorption techniques.

The switching properties of a cyanido-bridged Fe/Co square molecule were investigated by single-crystal X-ray diffraction and X-ray absorption spectroscopy at both Fe and Co K-edges. Combining these two techniques, a complete picture of the thermal-, light- and X-ray-induced metal-to-metal electron transfer is obtained, illustrating the concerted role played by the Fe and Co sites.

Two-photon absorption properties of multipolar triarylamino/tosylamido 1,1,4,4-tetracyanobutadienes.

The synthesis and characterization of four new tetracyanobutadiene (TCBD) derivatives (1, 3c and 4b-c) incorporating tosylamido and 4-triphenylamino moieties are reported. Along with those of five closely related or differently branched TCBDs derivatives (2, 3a-b, 4c and 5), their linear and (third-order) nonlinear optical properties were investigated by electronic absorption spectroscopy and Z-scan measurements. Among these compounds, the tri-branched compounds 3c and 5 are the most active two-photon absorbers, with effective cross-sections of 275 and 350 GM at 900 nm, respectively. These properties are briefly discussed with the help of DFT calculations, focussing on structural and electronic factors, and contextualized with results obtained previously for related compounds.

Molecular docking, DFT and antimicrobial studies of Cu(II) complex as topoisomerase I inhibitor.

Herein, we report the synthesis and single crystal X-ray structure of Cu(II)-picolinic acid complex, 1 as a potent topoisomerase I inhibitor. The complex 1 crystallized in the triclinic crystal system with space group P-1. Comparative in vitro binding studies of complex 1 with CT DNA and tRNA were carried out revealing an electrostatic binding mode with higher binding propensity towards tRNA. The intrinsic bonding constant value, Kb was calculated to be 4.36 × 104 and 8.78 × 104 M-1 with CT DNA and tRNA respectively. DNA cleavage activity was carried out with a pBR322 plasmid DNA substrate to ascertain the cleaving ability. Furthermore, Topo-I inhibition assay of complex 1, performed via gel electrophoresis revealed a significant inhibitory effect on the enzyme catalytic activity at a minimum concentration of 15 µM. The DFT studies were carried out to provide better insight in the electronic transitions observed in the absorption spectrum of the complex 1. Molecular docking studies were carried out with DNA, RNA and Topo-I to determine the specific binding preferences at the target site and complement the spectroscopic studies. The antimicrobial potential of complex 1 was screened against E. coli, S. aureus, P. aeruginosa, B. subtilis and C. albicans; and compared with doxycycline, exhibiting an excellent maximum zone of inhibition of 28 mm against E. coli.Communicated by Ramaswamy H. Sarma.

Correction: Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity.

Correction for 'Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity' by Farukh Arjmand et al., Dalton Trans., 2020, 49, 9888-9899, DOI: 10.1039/d0dt01527j.

Copper(ii) l/d-valine-(1,10-phen) complexes target human telomeric G-quadruplex motifs and promote site-specific DNA cleavage and cellular cytotoxicity.

Chiral l-/d-valine-(1,10-phen)-Cu(ii) complexes that target G-quadruplex DNA were synthesized and thoroughly characterized by UV-vis, IR, EPR, ESI-MS, elemental analysis and single crystal X-ray spectroscopy. Complexes 1a and 1b crystallized in the monoclinic P21/c and C2 space groups, respectively. On the basis of Wolfe-Shimer analyses, the binding affinities of 1a and 1b with G-quadruplex telomeric DNA were determined, and 1a exhibited significantly higher binding as compared to 1b. Site selective cleavage of G4-DNA was demonstrated by employing the time-dependent PAGE assay, with 1a exhibiting a significantly higher cleavage rate from A1 to G22 (4.32 (±0.13) µM h-1) than 1b (4.29 (±0.11) µM h-1). The DNA cleavage profile demonstrated that both complexes perform non-random double-strand cleavage by following first-order kinetics (kobs = 0.9432 min-1 for 1a and kobs = 0.6574 min-1 for 1b). Molecular docking simulations were performed with both parallel and anti-parallel topologies of the quadruplex to provide a clear insight on G-quadruplex-complex interactions. Complexes 1a and 1b were found to interact strongly at the minor groove cavity of the quadruplex with preferential selectivity for the parallel vs. anti-parallel quadruplex. The cytotoxic activities of complexes 1a and 1b were evaluated on a few notably important human cancer cell lines, viz, breast (MCF-7), pancreatic strains (BxPC3, AsPC1) and liver (Huh7) by an MTT assay. Both 1a and 1b exhibited pronounced cytotoxic activity with remarkably low IC50 values (1-3 µM) for all tested cancer strains.

Bis-4-aza[6]helicene: A Bis-helicenic 2,2'-Bipyridine with Chemically Triggered Chiroptical Switching Activity.

A novel enantiopure bis-helicenic 2,2'-bipyridine system was prepared using a Negishi coupling. Thanks to the bipyridine unit, the coordination with ZnII and protonation processes were studied, revealing efficient tuning of photophysical (UV/visible and emission) and chiroptical properties (electronic circular dichroism and circularly polarized emission) of the system. The coordination/decoordination and protonation/deprotonation processes appeared reversible, thus constituting novel chiroptical switches.

Directed ortho C-H borylation catalyzed using Cp*Rh(iii)-NHC complexes.

Cp*Rh(NHC) complexes with bulky chiral bidentate NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. These unprecedented rhodium(iii) complexes demonstrated high selectivity in pyridine-directed ortho-C-H borylation of arenes under mild conditions.

Enantiopure Cycloiridiated Complexes Bearing a Pentahelicenic N-Heterocyclic Carbene and Displaying Long-Lived Circularly Polarized Phosphorescence.

A fused π-helical N-heterocyclic carbene (NHC) system was prepared and examined through its diastereoisomerically pure cycloiridiated complexes. The latter display light-green phosphorescence with unusually long lifetimes and circular polarization that depends on both the helical NHC P/M stereochemistry and the iridium Δ/Λ stereochemistry. These unprecedented features are attributed to extended π conjugation within the helical carbenic ligand and efficient helicene-NHC-Ir interaction.

Metal Confinement through N-(9-Alkyl)fluorenyl-Substituted N-Heterocyclic Carbenes and Its Consequences in Gold-Catalysed Reactions Involving Enynes.

A series of gold(I) and gold(III) complexes containing bulky bis-N,N'-(9-alkylfluorenyl) heterocyclic carbene (R F-NHC) ligands have been prepared in high yields from appropriate imidazolinium, imidazolium and benzimidazolium salts. In all complexes, the carbene ligand provides high steric protection of the Au-X bond trans to the carbenic C atom. Irrespective of the metal oxidation state, the complexes showed high efficiency in a tandem 3,3-rearrangement/Nazarov reaction of an enynyl acetate. One of the AuIII complexes, [AuCl3 (R F-NHC)], was further found to be suitable for the efficient cyclisation of a propargylcarboxamide. Furthermore, unlike related NHC-gold(I) complexes based on conventional bulky N-heterocyclic carbenes (notably, 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-(bis-tert-butyl)imidazol-2-ylidene (ItBu)), the studied [AuI Cl(R F-NHC)] complexes catalysed the conversion of a 1,6-enyne in the presence of indole into a single product; this arises from the embracing character of the ligand, which prevents indole addition on one of the catalytic intermediates. A structure/selectivity relationship was established for all carbenes tested that took into account percent buried volumes and topographic steric maps. The results illustrate the high potential of confining NHCs in organic synthesis.

Synthesis and Chiroptical Properties of Hexa-, Octa-, and Deca-azaborahelicenes: Influence of Helicene Size and of the Number of Boron Atoms.

Four members of a new class of cycloborylated hexa-, octa-, and deca-helicenes (1 a-d) have been prepared in enantiopure form, along with two cycloplatinated deca-helicenes (1 d', 1 d1 ), further extending the family of cycloplatinated hexa- and octa-helicenes reported previously. The azabora[n]helicenes display intense electronic circular dichroism and large optical rotations; the dependence of the optical activity on the size of the helix (n=6, 8, 10) and the number of boron atoms (1 or 2) has been examined in detail both experimentally and theoretically. The photophysical properties (nonpolarized and circularly polarized luminescence) of these new fluorescent organic helicenes have been measured and compared with the corresponding organometallic phosphorescent cycloplatinated derivatives (1 a1 -d1 ).

Electronic and chiroptical properties of chiral cycloiridiated complexes bearing helicenic NHC ligands.

The first helicene-NHC-iridium complexes have been prepared in enantiopure forms. Their stereochemical, electronic, and chiroptical features were characterized experimentally and via first-principles calculations, highlighting the helical and iridium-centered chirality.

Iron Alkynyl Helicenes: Redox-Triggered Chiroptical Tuning in the IR and Near-IR Spectral Regions and Suitable for Telecommunications Applications.

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 µm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged.

Synthesis, Chemistry, and Photochemistry of Methylcyanobutadiyne in the Context of Space Science.

An alternative preparation of methylcyanobutadiyne (MeC5N), a molecule present in the interstellar medium, was established in order to circumvent tedious steps from previous methods. The possibility of forming methylcyanoacetylene and MeC5N by gas-phase photolysis was evaluated from relevant acetylene derivatives in the context of space science. The reactivity of MeC5N toward simple nucleophiles was investigated. The exclusive formation of E adducts was observed, together with a solvent dependence for the regioselectivity of the addition.

New mannose derivatives: The tetrazole analogue of mannose-6-phosphate as angiogenesis inhibitor.

Two novel compounds with mannose-derived structure, bearing a tetrazole (compound 3) and a sulfone group (compound 4) in terminal position, have been prepared from methyl α-d-mannopyranoside in reduced number of steps. The angiogenic activity of 3 and 4 has been screened using the chick chorioallantoic membrane (CAM) method. Tetrazole 3 has been identified to possess a promising bioactivity, being identified as angiogenesis inhibitor, with 68% of neovascular vessels when compared to control (PBS).

Synthesis and Structural Properties of Aza[n]helicene Platinum Complexes: Control of Cis and Trans Stereochemistry.

The synthesis and structural characterization of azahelicene platinum complexes obtained from cis-PtCl2(NCEt)(PPh3) and from ligands that differ in terms of both the position of the nitrogen atom and the number of fused rings are reported. These square-planar complexes of the general formula PtCl2(nHm)(PPh3) (n = 4, 5; m = 5, 6) display mainly a cis configuration. However, by X-ray crystallographic analysis, we show that for both PtCl2(4H6)(PPh3) and PtCl2(5H6)(PPh3) there is chirality control of the cis/trans stereochemistry. Indeed, starting from a racemic mixture of aza[6]helicene, platinum complexes with a cis configuration are invariably obtained, and the more thermodynamically stable trans isomers are formed when using enantiopure ligands. We further corroborated these results by NMR analysis in solution.

Latent ruthenium-indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand.

A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions.

"Hummingbird" behaviour of N-heterocyclic carbenes stabilises out-of-plane bonding of AuCl and CuCl units.

An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the AuX rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH⋅⋅⋅Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl⋅⋅⋅H bonds are likely to cooperate with the H⋅⋅⋅Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere.

Alkylfluorenyl substituted N-heterocyclic carbenes in copper(I) catalysed hydrosilylation of aldehydes and ketones.

Copper(i) complexes featuring N-heterocyclic carbenes (NHCs) in which the nitrogen atoms are substituted by a 9-ethyl-9-fluorenyl group (EF) have been synthesised and tested in the hydrosylilation of functionalized and/or sterically demanding ketones and aldehydes. These reactions, carried out with triethylsilane as hydride source, were best achieved with the imidazolylidene copper complex in which the EF substituents can freely rotate about the corresponding N-CEF bonds. The remarkable stability of the active species, which surpasses that of previously reported Cu-NHC catalysts is likely to rely on the ability of the NHC side arms to protect the copper centre during the catalytic cycle by forming sandwich-like intermediates, but also on its steric flexibility facilitating approach of encumbered substrates. TONs up to 1000 were reached.

Mechanistic insights into a novel chromone-appended Cu(II) anticancer drug entity: in vitro binding profile with DNA/RNA substrates and cytotoxic activity against MCF-7 and HepG2 cancer cells.

A new chromone-appended Cu(ii) drug entity () was designed and synthesized as a potential anticancer chemotherapeutic agent. The structural elucidation was carried out thoroughly by elemental analysis, FT-IR, EPR, ESI-MS and single crystal X-ray crystallography. Complex resulted from the in situ methoxylation reaction of the 3-formylchromone ligand and its subsequent complexation with the copper nitrate salt in a 2 : 1 ratio, respectively. crystallized in the monoclinic P21/c space group possessing the lattice parameters, a = 8.75 Å, b = 5.07 Å, c = 26.22 Å, α = γ = 90°, ß = 96.3° per unit cell. Furthermore, in vitro interaction studies of with ct-DNA and tRNA were carried out which suggested more avid binding propensity towards the RNA target via intercalative mode, which was reflected from its Kb, K and Ksv values. The gel electrophoretic mobility assay was carried out on the pBR322 plasmid DNA substrate, to ascertain the cleaving ability and the mechanistic pathway in the presence of additives, and the results revealed the efficient cleaving ability of via the oxidative pathway. In vitro cell growth inhibition via the MTT assay was carried out to evaluate the cytotoxicity of complex and IC50 values were found to be in the range of 5-10 µg mL(-1) in HepG2 and MCF-7 cancer cell lines, which were found to be much lower than the IC50 values of previously reported similar Cu(ii) complexes. Additionally, in the presence of , reactive oxygen species (ROS) and thiobarbituric acid reactive substance (TBARS) levels in the tested cancer cell lines increased significantly, coupled with reduced glutathione (GSH) levels. Thus, our results suggested that ROS plays an important role in cell apoptosis induced by the Cu(ii) complex and validates its potential to act as a robust anticancer drug entity.