Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands

Cell nucleus localization and high anticancer activity of quinoline-benzopyran rhodium(III) metal complexes as therapeutic and fluorescence imaging agents

Four novel rhodium(III) complexes, [Rh^III(QB1)Cl₃(DMSO)] (RhN1), [Rh^III(QB2)Cl₃(CH₃OH)]·CH₃OH (RhN2), [Rh^III(QB3)Cl₃(CH₃OH)]·CH₃OH (RhS), and [Rh^III(QB4)Cl₃(DMSO)] (RhQ), bearing quinoline-benzopyran ligands (QB1-QB4) were synthesized and used to develop highly anticancer therapeutic and fluorescence imaging agents. Compared with the QB1-QB4 ligands (IC₅₀ > 89.2 ± 1.7 μM for A549/DDP), RhN1, RhN2, RhS and RhQ exhibit selective cytotoxicity against lung carcinoma cisplatin-resistant A549/DDP (A549CDDP) cancer cells, with IC₅₀ values in the range of 0.08-2.7 μM. The fluorescent imaging agent RhQ with the more extended planar QB4 ligand exhibited high anticancer activity in A549CDDP cells and was found in the cell nucleus fraction, whereas RhS had no fluorescence properties. RhQ and RhS may trigger cell apoptosis by causing DNA damage and initiating the mitochondrial dysfunction pathway. Furthermore, RhQ has a higher antitumor efficacy (ca. 55.3%) than RhS (46.4%) and cisplatin (CDDP, 33.1%), and RhQ demonstrated significantly lower toxicity in vivo than CDDP, making it a promising Rh(III)-based anticancer therapeutic and fluorescence imaging agent.

Spectroscopic Studies for Rhodium (III) Binding to Apo-Transferrin

Transferrin belongs to a class of monomeric glycoproteins, which sequestrate and transport iron inside the body. Apart from iron, transferrin binds with various other metal ions and is assumed to deliver medicinally important metal ions to cells. Hence, the investigation of binding characteristics may provide crucial information for new drug developments. To study the biological impacts of medicinally important metal ions, in this work, we explored the binding behavior of Rh(III) ion with serum apo-transferrin (ApoHST) using FT-IR and UV-Vis spectroscopy. In FT-IR, interaction of Rh(III) with ApoHST was studied at three concentrations (0.25, 0.5, and 1 mM) of metal ion at different time intervals (15, 30, and 60 min). The IR spectra of Rh(III)-ApoHST coordinates revealed a marked reduction in amide I and II band intensities with alterations in band positions. The α-helical part of protein secondary structure reduced considerably (from 53% to 49%, 42%, and 39%), followed by an increment in β-sheet and β-turn components with the increasing concentrations of metal ion. Saturation level reached at 1 mM concentration of Rh(III) ion. In the UV-Vis spectroscopic study, absorption of metal ion-protein coordinates successively raised as concentration of Rh(III) ion increased. The binding constant (K) was calculated as $1.16\times {10}^4{\text{M}}^{-1}$ , which showed a strong binding of the test metal ion with the protein. Upon coordination with a metal ion, the microenvironment of aromatic protein residues changed, which was detected by these spectroscopic techniques. The results revealed the existence of a significant interaction between Rh (III) ion and ApoHST. These research outcome may present new insight into the possible utilization of Rh(III) ion-based compounds in biomedicine. However, more investigations are needed to interpret the exact cellular mechanism.

New rhodium(II)-ED3AP-complex: Crystal structure, characterization and computational chemistry

Only one (trans(O5)-Na[Rh(ed3ap)]?3H2O) of possible two isomers was synthesized and characterized by single crystal X-ray analysis, IR, and UV-Vis spectroscopy. Computational analysis of both isomers was performed with three levels of theory (B3LYP/TZV, BP86/TZV, OPBE/TZV), which gave consistent results. The more stable isomer by total energy and ligand field stabilization energy (LFSE) was trans(O5) which appeared in synthesis. Calculation of excited state energies complied with UV-Vis spectra, especially with OPBE functional. The results of excited state energy pointed out the differences among isomers in means of a splitting pattern of 1T2g excited state term. Both isomers have a strongly delocalized structure according to the natural bonding orbital (NBO) analysis. The trans(O5) geometry has the stabilization of the whole system for roughly 87 kJ/mol and makes this isomer as the only one present in the reaction mixture.

Recent advances in biological activities of rhodium complexes: Their applications in drug discovery research

Unique structure, characteristic reactivity, and facile synthesis of metal complexes have made them efficient ligands in drug development research. Among them, rhodium complexes have a limited history and there are a few discussions about their biological activities documented in the literature. However, investigation of kinetically inert rhodium complexes has recently attracted lots of attention and especially there are various evidences on their anti-cancer activity. It seems that they can be investigated as a versatile surrogates or candidates for the existing drugs which do not affect selectively or suffer from various side effects. In recent years, there has been an increasing interest in the use of mononuclear rhodium (III) organometallo drugs due to its versatile structurally important aspects to inhibit various enzymes. It has been demonstrated that organometallic Rh complexes profiting from both organic and inorganic aspects have shown more potent biological activities than classical inorganic compartments. In this respect, smart design, use of the appropriate organic ligands, and efficient and user-friendly synthesis of organometallic Rh complexes have played crucial roles in the inducing desirable biological activities. In this review, we focused on the recent advances published on the bioactivity of Rh (III/II/I) complexes especially inhibitory activity, from 2013 till now. Accordingly, considering the structure-activity relationship (SAR), the effect of oxidation state (+1, +2, and +3) and geometry (dimer or monomer complexes with coordination number of 4 and 6) of Rh complexes as well as various ligands on in vitro and in vivo studies was comprehensively discussed.

The kinetics and mechanism of the ligand substitution reaction of aquapentacyanoruthenate(II) with d-penicillamine in aqueous medium

The kinetics of the formation of the light orange–coloured complex [Ru(CN)5D-PA]3− are studied spectrophotometrically through substitution of a coordinated H2O molecule in aquapentacyanoruthenate(II) [Ru(CN)5OH2]3− by interaction with D-penicillamine [D-PA] in aqueous medium at 490 nm (λmax of [Ru(CN)5D-PA]3−). The reaction is monitored under pseudo-first-order conditions, taking [D-PA] in excess over [Ru(CN)5OH23−]. The effects of various reaction parameters on the rate of the reaction are investigated. Experimental observations reveal that the variation in [D-PA] obeyed the first-order rate law while it is found to be invariant with [Ru(CN)5OH23−] in the whole experimental range. With ionic strength variation, as the reaction advances a decrease in the reaction rate is noticed. The product stoichiometry is assigned as 1:1. The ease of substitution at an H2O molecule in [Ru(CN)5OH23−] is considered on the basis of the electronic effect generated through interactions of the M–OH2 bond. A provisional mechanism based on the calculated results is proposed based on the slowest step of the reaction.

Comparative study of binding interactions between three organometallic rhodium(III) complexes with curcuminoid ligands and human serum albumin

Organometallic rhodium(III) complexes with curcuminoid ligands attracted considerable attention in biological-related fields and the variation of curcuminoid ligands may regulate the biological activity of these organometallic rhodium(III) complexes. To deeply evaluate the biological influences of these complexes, the binding interactions between three rhodium(III) complexes with curcuminoid ligands and human serum albumin (HSA) were comparably investigated by spectroscopic and electrochemical techniques. The results suggested that the intrinsic fluorescence of HSA was quenched by three complexes through static fluorescence quenching mode. Three complexes bonded with Sudlow's site I of HSA to form ground-state compounds under the binding forces of van der Waals interactions, hydrogen bonds formation, and protonation. Finally, the native conformational structure and the thermal stability of HSA were all changed. Space steric hindrance of complexes took part in the differences of the fluorescence quenching processes, and the chemical polarity of the complexes played a vital role in the variations of the structure and biological activity of HSA. These results illustrated the molecular interactions between protein and organometallic rhodium(III) complexes with curcuminoid ligands, offering new insight about the prospective applications of analogical rhodium(III) complexes in biomedicine areas.

Rhodium at the chemistry-biology interface

As a rare element with no known natural biological function, rhodium has a limited history in biological chemistry and chemical biology. However, rhodium complexes have unique structure and reactivity attributes, and chemists have increasingly used these attributes to probe and perturb living systems. This brief review focuses on recent advances in the use of rhodium complexes in biological contexts, including medicinal chemistry, protein science, and chemical biology. In particular, we highlight both structure- and reactivity-driven approaches to biological probes and discuss how coordination environment affects molecular properties in a biological environment.

A Rhodium(III) Complex as an Inhibitor of Neural Precursor Cell Expressed, Developmentally Down-Regulated 8-Activating Enzyme with in Vivo Activity against Inflammatory Bowel Disease

We report herein the identification of the rhodium(III) complex [Rh(phq)₂(MOPIP)]⁺ (1) as a potent and selective ATP-competitive neural precursor cell expressed, developmentally down-regulated 8 (NEDD8)-activating enzyme (NAE) inhibitor. Structure-activity relationship analysis indicated that the overall organometallic design of complex 1 was important for anti-inflammatory activity. Complex 1 showed promising anti-inflammatory activity in vivo for the potential treatment of inflammatory bowel disease.

Expanding the family of bis-cyclometalated chiral-at-metal rhodium(iii) catalysts with a benzothiazole derivative

Synthetic access to previously elusive single enantiomers of an octahedral chiral-at-metal rhodium(iii) complex containing two cyclometalated 2-phenylbenzothiazoles and two acetonitrile ligands is reported. The complex is a superior chiral Lewis acid catalyst compared to its benzoxazole congener which can be rationalized with a higher steric congestion around the coordination sites.

Synthesis, characterization, in vitro cytotoxicity, in silico ADMET analysis and interaction studies of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and its zinc(ii) complex with human serum albumin: combined spectroscopy and molecular docking investigations

The binding site of new complex Zn(ii) of 5-dithiocarbamato-1,3,4-thiadiazole-2-thiol and HAS.

Rhodium(I) N-Heterocyclic Carbene Bioorganometallics as in Vitro Antiproliferative Agents with Distinct Effects on Cellular Signaling

Organometallics with N-heterocyclic carbene (NHC) ligands have triggered major interest in inorganic medicinal chemistry. Complexes of the type Rh(I)(NHC)(COD)X (where X is Cl or I, COD is cyclooctadiene, and NHC is a dimethylbenzimidazolylidene) represent a promising type of new metallodrugs that have been explored by advanced biomedical methods only recently. In this work, we have synthesized and characterized several complexes of this type. As observed by mass spectrometry, these complexes remained stable over at least 3 h in aqueous solution, after which hydrolysis of the halido ligands occurred and release of the NHC ligand was evident. Effects against mitochondria and general cell tumor metabolism were noted at higher concentrations, whereas phosphorylation of HSP27, p38, ERK1/2, FAK, and p70S6K was induced substantially already at lower exposure levels. Regarding the antiproliferative activity in tumor cells, a clear preference for iodido over chlorido secondary ligands was noted, as well as effects of the substituents of the NHC ligand.