Bis(amino acidato)copper(II) compounds in blood plasma: a review of computed structural properties and amino acid affinities for Cu2+ informing further pharmacological research

Neutral bis(amino acidato)copper(II) [Cu(aa)2] coordination compounds are the physiological species of copper(II) amino acid compounds in blood plasma taking the form of bis(l-histidinato)copper(II) and mixed ternary copper(II)-l-histidine complexes, preferably with l-glutamine, l-threonine, l-asparagine, and l-cysteine. These amino acids have three functional groups that can bind metal ions: the common α-amino and carboxylate groups and a side-chain polar group. In Cu(aa)2, two coordinating groups per amino acid bind to copper(II) in-plane, while the third group can bind apically, which yields many possibilities for axial and planar bonds, that is, for bidentate and tridentate binding. So far, the experimental studies of physiological Cu(aa)2 compounds in solutions have not specified their complete geometries. This paper provides a brief review of my group's research on structural properties of physiological Cu(aa)2 calculated using the density functional theory (DFT) to locate low-energy conformers that can coexist in aqueous solutions. These DFT investigations have revealed high conformational flexibility of ternary Cu(aa)2 compounds for tridentate or bidentate chelation, which may explain copper(II) exchange reactions in the plasma and inform the development of small multifunctional copper(II)-binding drugs with several possible copper(II)-binding groups. Furthermore, our prediction of metal ion affinities for Cu2+ binding with amino-acid ligands in low-energy conformers with different coordination modes of five physiological Cu(aa)2 in aqueous solution supports the findings of their abundance in human plasma obtained with chemical speciation modelling.

Cu(II) and Zn(II) Complexes of New 8-Hydroxyquinoline Schiff Bases: Investigating Their Structure, Solution Speciation, and Anticancer Potential

We report the synthesis and characterization of three novel Schiff bases (L1-L3) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with amines containing morpholine or piperidine moieties. These were reacted with CuCl₂ and ZnCl₂ yielding six new coordination compounds, with the general formula ML₂, where M = Cu(II) or Zn(II) and L = L1-L3, which were all characterized by analytical, spectroscopic (Fourier transform infrared (FTIR), UV-visible absorption, nuclear magnetic resonance (NMR), or electron paramagnetic resonance (EPR)), and mass spectrometric techniques, as well as by single-crystal X-ray diffraction. In the solid state, two Cu(II) complexes, with L1 and L2, are obtained as dinuclear compounds, with relatively short Cu-Cu distances (3.146 and 3.171 Å for Cu₂(L1)₄ and Cu₂(L2)₄, respectively). The free ligands show moderate lipophilicity, while their complexes are more lipophilic. The pK_a values of L1-L3 and formation constants of the complex (for ML and ML₂) species were determined by spectrophotometric titrations, with the Cu(II) complexes showing higher stability than the Zn(II) complexes. EPR indicated the presence of several species in solution as pH varied and binding modes were proposed. The binding of the complexes to bovine serum albumin (BSA) was evaluated by fluorescence and circular dichroism (CD) spectroscopies. All complexes bind BSA, and as demonstrated by CD, the process takes several hours to reach equilibrium. The antiproliferative activity was evaluated in malignant melanoma cells (A375) and in noncancerous keratinocytes (HaCaT). All complexes display significant cytotoxicity (IC₅₀ < 10 μM) but modest selectivity. The complexes show higher activity than the free ligands, the Cu(II) complexes being more active than the Zn(II) complexes, and approximately twice more cytotoxic than cisplatin. A Guava ViaCount assay corroborated the antiproliferative activity.

Exploring a new family of designer copper(II) complexes of anthracene-appended polyfunctional organic assembly displaying potential anticancer activity via cytochrome c mediated mitochondrial apoptotic pathway

The present article describes the systematic study on design and synthesis, physicochemical properties and spectroscopic features, and potential anticancer activities of a family of novel copper(II)-based designer metal complexes [Cu₂(acdp)(μ-Cl)(H₂O)₂] (1), [Cu₂(acdp)(μ-NO₃)(H₂O)₂] (2) and [Cu₂(acdp)(μ-O₂CCF₃)(H₂O)₂] (3) of anthracene-appended polyfunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol). Synthesis of 1-3 was accomplished under facile experimental conditions, preserving their overall integrity in solution. The incorporation of polycyclic anthracene skeleton within the backbone of organic assembly increases lipophilicity of resulting complexes, thereby dictating the degree of cellular uptake with improved biological activity. Complexes 1-3 were characterized by elemental analysis, molar conductance, FTIR, UV-Vis absorption/fluorescence emission titration spectroscopy, PXRD and TGA/DTA studies, including DFT calculations. The cellular cytotoxicity of 1-3 when studied in HepG2 cancer cell line showed substantial cytotoxic effects, whereas no such cytotoxicity was observed when exposed to normal L6 skeletal muscle cell line. Thereafter, the signaling factors involved in the process of cytotoxicity in HepG2 cancer cells were investigated. Alteration of cytochrome c and Bcl-2 protein expression levels along with modulation of mitochondrial membrane potential (MMP) in the presence of 1-3, strongly suggested the possibility of activating mitochondria-mediated apoptotic pathway involved in halting the cancer cell propagation. However, when a comparative assessment on their bio-efficacies was made, 1 showed higher cytotoxicity, nuclear condensation, DNA binding and damage, ROS generation and lower rate of cell proliferation compared to 2 and 3 in HepG2 cell line, indicating that the anticancer activity of 1 is significantly higher than that of 2 and 3.

Toxic metals that interact with thiol groups and alteration in insect behavior

Toxic metals, such as mercury (Hg), lead (Pb), cadmium (Cd), and copper (Cu), are widespread in the biosphere, and human activities have contributed to their continuous release into the ecosystems. Metal-induced toxicity has been extensively studied in mammals; however, the effects of these metals on insects' behavior have been explored to far lesser degree. As the main mechanism of toxicity, the cationic metals, explored in this review, have high affinity for thiol-containing molecules, disrupting the function of several proteins and low-molecular-weight thiol-containing molecules. Existing literature has corroborated that Hg, Pb, Cd, and Cu can disrupt locomotor and mating behaviors, but their effects on insects' memory and learning have yet to be fully characterized. Though field studies on metal-induced toxicity in insects are limited, results from Drosophila melanogaster as an experimental model suggest that insects living in contaminated environments can have behavioral foraging and reproductive deficits, which may cause population decline. In this review, we address the interaction between metals and endogenous thiol groups, with emphasis on alterations in insect behavior.

Reaction of N-Acetylcysteine with Cu2+: Appearance of Intermediates with High Free Radical Scavenging Activity: Implications for Anti-/Pro-Oxidant Properties of Thiols

We studied the kinetics of the reaction of N-acetyl-l-cysteine (NAC or RSH) with cupric ions at an equimolar ratio of the reactants in aqueous acid solution (pH 1.4−2) using UV/Vis absorption and circular dichroism (CD) spectroscopies. Cu2+ showed a strong catalytic effect on the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTSr) consumption and autoxidation of NAC. Difference spectra revealed the formation of intermediates with absorption maxima at 233 and 302 nm (ε302/Cu > 8 × 103 M−1 cm−1) and two positive Cotton effects centered at 284 and 302 nm. These intermediates accumulate during the first, O2-independent, phase of the NAC autoxidation. The autocatalytic production of another chiral intermediate, characterized by two positive Cotton effects at 280 and 333 nm and an intense negative one at 305 nm, was observed in the second reaction phase. The intermediates are rapidly oxidized by added ABTSr; otherwise, they are stable for hours in the reaction solution, undergoing a slow pH- and O2-dependent photosensitive decay. The kinetic and spectral data are consistent with proposed structures of the intermediates as disulfide-bridged dicopper(I) complexes of types cis-/trans-CuI2(RS)2(RSSR) and CuI2(RSSR)2. The electronic transitions observed in the UV/Vis and CD spectra are tentatively attributed to Cu(I) → disulfide charge transfer with an interaction of the transition dipole moments (exciton coupling). The catalytic activity of the intermediates as potential O2 activators via Cu(II) peroxo-complexes is discussed. A mechanism for autocatalytic oxidation of Cu(I)−thiolates promoted by a growing electronically coupled −[CuI2(RSSR)]n− polymer is suggested. The obtained results are in line with other reported observations regarding copper-catalyzed autoxidation of thiols and provide new insight into these complicated, not yet fully understood systems. The proposed hypotheses point to the importance of the Cu(I)−disulfide interaction, which may have a profound impact on biological systems.

Coordination-induced emission enhancement in copper(I) iodide coordination polymers supported by 2-(alkylsulfanyl)pyrimidines

First examples of copper(i) complexes with 2-(alkylsulfanyl)pyrimidine ligands have been synthesized. Reactions of copper(i) iodide with 2-(methylsulfanyl)pyrimidine (L1) in various metal-to-ligand molar ratios in MeCN afford a ladder-type coordination polymer [Cu2L1I2]n with polymeric chains built from double-stranded (Cu2I2)n ribbons supported on both sides by μ2-N,S-L1 molecules. Although the second ligand, 2-(ethylsulfanyl)pyrimidine (L2), differs from L1 only by a methylene group, its reactions with copper(i) iodide in MeCN yield not only a congenerous coordination polymer, [Cu2L2I2]n, but also [CuL2I]n, in which a similar (Cu2I2)n ribbon is decorated by N-monodentate L2 molecules. Absorption spectra of all compounds represent an interplay of metal + iodine-to-ligand charge transfer (XMLCT) and ligand-centered (LC) and cluster-centered (CC) transitions, while the emission occurs from the excited states of XMLCT nature. The luminescence of [Cu2L1I2]n and [Cu2L2I2]n is blue-shifted and greatly enhanced in comparison with that of [CuL2I]n (quantum yields: 89% and 68% for [Cu2L1I2]n and [Cu2L2I2]nvs. 23% for [CuL2I]n at 77 K), which can be associated with a more rigid μ2-N,S coordination of 2-(alkylsulfanyl)pyrimidine ligands in [Cu2L1I2]n and [Cu2L2I2]n leading to a less distorted T1 state.

Ca2+ Complexation With Relevant Bioligands in Aqueous Solution: A Speciation Study With Implications for Biological Fluids

A speciation study on the interaction between Ca2+ and ligands of biological interest in aqueous solution is reported. The ligands under study are l-cysteine (Cys), d-penicillamine (PSH), reduced glutathione (GSH), and oxidized glutathione (GSSG). From the elaboration of the potentiometric experimental data the most likely speciation patterns obtained are characterized by only protonated species with a 1:1 metal to ligand ratio. In detail, two species, CaLH2 and CaLH, for systems containing Cys, PSH, and GSH, and five species, CaLH5, CaLH4, CaLH3, CaLH2, and CaLH, for system containing GSSG, were observed. The potentiometric titrations were performed at different temperatures (15 ≤ t/°C ≤ 37, at I = 0.15 mol L-1). The enthalpy and entropy change values were calculated for all systems, and the dependence of the formation constants of the complex species on the temperature was evaluated. 1H NMR spectroscopy, MALDI mass spectrometry, and tandem mass spectrometry (MS/MS) investigations on Ca2+-ligand solutions were also employed, confirming the interactions and underlining characteristic complexing behaviors of Cys, PSH, GSH, and GSSG toward Ca2+. The results of the analysis of 1H NMR experimental data are in full agreement with potentiometric ones in terms of speciation models and stability constants of the species. MALDI mass spectrometry and tandem mass spectrometry (MS/MS) analyses confirm the formation of Ca2+-L complex species and elucidate the mechanism of interaction. On the basis of speciation models, simulations of species formation under conditions of some biological fluids were reported. The sequestering ability of Cys, PSH, GSH, and GSSG toward Ca2+ was evaluated under different conditions of pH and temperature and under physiological condition.

Kayser-Fleischer-Ring – kann eine frühe Diagnosestellung den Krankheitsverlauf von Morbus Wilson verbessern?

Morbus Wilson ist eine seltene genetische Erkrankung des Kupferstoffwechsels, die zu einer erhöhten Kupferansammlung im Körper führt. Ablagerungen finden sich vor allem in Leber, zentralem Nervensystem, Niere und Auge. Unbehandelt kann die Erkrankung zu Bewegungsstörungen, Persönlichkeitsveränderungen, Leberversagen bis hin zum Tod führen. Differenzialdiagnostisch kommen viele Erkrankungen infrage. Eine Diagnosefindung ist nur durch spezifische Testverfahren möglich. Der Augenarzt hat somit eine besondere Rolle in der Früherkennung eines Morbus Wilson. In unserer Klinik stellte sich eine 19-jährige Patientin mit einem schwachen, im Verlauf entstehenden Kayser-Fleischer-Kornealring mit sonst unauffälligem ophthalmologischen Befund vor. Die Patientin hatte ein progredientes Leberversagen und erhielt 2 Monate nach Erstvorstellung in der Augenklinik eine Lebertransplantation. Eine frühzeitige augenärztliche Mitbeurteilung mit gründlicher Untersuchung ist von entscheidender Bedeutung für eine schnelle Diagnosestellung. Die Kupferablagerungen finden sich in der Descemet-Membran und beginnen in der Schwalbe-Linie. Der sog. Kayser-Fleischer-Ring zeigt sich an der Descemet-Membran bis zu 5 mm vom Limbus entfernt. Andere mögliche ophthalmologische Manifestationen stellen eine Chalkose der gesamten Descemet, ein Ikterus der Skleren oder eine Sonnenblumenkatarakt dar. Bei fehlenden Kupferablagerungen im Spaltlampenbefund sollte bei einem Verdacht auf einen Morbus Wilson immer auch eine Gonioskopie des Kammerwinkels erfolgen. Eine frühe Diagnosestellung kann Patienten vor unnötigen Komplikationen und Operationen schützen. Behandelt hat der Morbus Wilson eine gute Prognose.

Medicinal Thiols: Current Status and New Perspectives

The thiol (-SH) functional group is found in a number of drug compounds and confers a unique combination of useful properties. Thiol-containing drugs can reduce radicals and other toxic electrophiles, restore cellular thiol pools, and form stable complexes with heavy metals such as lead, arsenic, and copper. Thus, thiols can treat a variety of conditions by serving as radical scavengers, GSH prodrugs, or metal chelators. Many of the compounds discussed here have been in use for decades, yet continued exploration of their properties has yielded new understanding in recent years, which can be used to optimize their clinical application and provide insights into the development of new treatments. The purpose of this narrative review is to highlight the biochemistry of currently used thiol drugs within the context of developments reported in the last five years. More specifically, this review focuses on thiol drugs that represent the standard of care for their associated conditions, including N-acetylcysteine, 2,3-meso-dimercaptosuccinic acid, British anti-Lewisite, D-penicillamine, amifostine, and others. Reports of novel dosing regimens, delivery strategies, and clinical applications for these compounds were examined with an eye toward emerging approaches to address a wide range of medical conditions in the future.

Enhanced Copper-Temozolomide Interactions by Protein for Chemotherapy against Glioblastoma Multiforme

Current treatment of recurrent glioblastoma multiforme (GBM) demands dose-intense temozolomide (TMZ), a prodrug of 5-(3-methyltriazen-1-yl) imidazole-4-carboxamide (MTIC), based on the spontaneous hydrolysis of TMZ at basic pH. However, how to control the activity of MTIC remains unknown, which poses a particular challenge to search a reliable MTIC receptor. We reported that copper, for the first time, is found to recognize and bind MTIC in the process of TMZ degradation, which means copper can play an important role in enhancing the bioavailability of MTIC derived from TMZ. Using apoferritin as a model copper-bound protein, we studied the copper-TMZ interaction in protein and observed efficient MTIC immobilization with high binding efficiency (up to 92.9% based on original TMZ) and capacity (up to 185 MTIC moieties per protein). The system was stable against both alkaline and acidic pH and could be activated by glutathione to liberate MTIC, which paves a way to deliver a DNA-alkylating agent for both TMZ-sensitive and TMZ-resistant GBM chemotherapy. Our study provides a new insight for understanding the potential relationship between the special GBM microenvironment (specific copper accumulation) and the therapeutic effect of TMZ.

Exploring various ligand classes for the efficient sequestration of stannous cations in the environment

Metal pollution, coming from both natural and anthropogenic sources, has become one of the most serious environmental problems. Various strategies have been tested with the aim of removing heavy metals from environment. In this contribution, containing a robust experimental work together with a critical literature analysis, the sequestering ability of a variety of ligands towards Sn²⁺ cation will be evaluated in the conditions of several natural fluids, i.e. sea water, fresh water, human blood plasma, urine and saliva. 13 structural and 11 thermodynamic descriptors will be selected for a total of thirty-eight molecules belonging to different classes (carboxylic acids, amines, amino acids, phosphonates, polyelectrolytes etc. …). For the filling of those missing data relative to the 11 thermodynamic descriptors, different strategies will be adopted, including simple correlations and Nipals algorithm. The evaluation of the sequestering ability of the ligands is assessed in terms of estimation of pL_0.5 (total concentration of ligand required to bind the 50% of metal in solution), an empirical parameter that takes into account all the side reactions in solutions and does not depend on the speciation scheme. Partial least square calculations were performed to model the pL_0.5 and to determine its correlation with the abovementioned descriptors. The possibility to design and build up new tailor-made molecules capable of effectively sequester Sn²⁺ in various conditions is crucial for practical applications in biosphere, hydrosphere and lithosphere.

JESS, a Joint Expert Speciation System – VI: thermodynamically-consistent standard Gibbs energies of reaction for aqueous solutions

A large, open-access, sustainable database of relative Gibbs energies is developed for over 50 000 aqueous chemical species, including many metal–ligand complexes.

Fluorescence “off” and “on” signalling of esculetin in the presence of copper and thiol: a possible implication in cellular thiol sensing

The fluorescence intensity of esculetin was drastically reduced in the presence of a copper ion, which was regenerated in the presence of GSH. The copper–esculetin system was able to detect GSH in a cellular model.

Glutathione limits aquacopper(I) to sub-femtomolar concentrations through cooperative assembly of a tetranuclear cluster

The tripeptide glutathione (GSH) is a crucial intracellular reductant and radical scavenger, but it may also coordinate the soft Cu(I) cation and thereby yield pro-oxidant species. The GSH-Cu(I) interaction is thus a key consideration for both redox and copper homeostasis in cells. However, even after nearly four decades of investigation, the nature and stability of the GSH-Cu(I) complexes formed under biologically relevant conditions remain controversial. Here, we revealed the unexpected predominance of a tetranuclear [Cu₄(GS)₆] cluster that is sufficiently stable to limit the effective free aquacopper(I) concentration to the sub-femtomolar regime. Combined spectrophotometric-potentiometric titrations at biologically realistic GSH/Cu(I) ratios, enabled by our recently developed Cu(I) affinity standards and corroborated by low-temperature phosphorescence studies, established cooperative assembly of [Cu₄(GS)₆] as the dominant species over a wide pH range, from 5.5 to 7.5. Our robust model for the glutathione-Cu(I) equilibrium system sets a firm upper limit on the thermodynamic availability of intracellular copper that is 3 orders of magnitude lower than previously estimated. Taking into account their ability to catalyze the production of deleterious superoxide, the formation of Cu(I)-glutathione complexes might be avoided under normal physiological conditions. The actual intracellular Cu(I) availability may thus be regulated a further 3 orders of magnitude below the GSH/Cu(I) affinity limit, consistent with the most recent affinity determinations of Cu(I) chaperones.

Half-sandwich complexes of iridium and ruthenium containing cysteine-derived ligands

The dimers [{(ηⁿ-ring)MCl}₂(μ-Cl)₂] ((ηⁿ-ring)M = (η⁵-C₅Me₅)Ir, (η⁶-p-MeC₆H₄iPr)Ru) react with the modified cysteines S-benzyl-l-cysteine (HL1) or S-benzyl-α-methyl-l-cysteine (HL2) affording cationic complexes of the formula [(ηⁿ-ring)MCl(κ²N,S-HL)]Cl (1, 2) in good yield. Addition of NaHCO₃ to complexes 1 and 2 gave equilibrium mixtures of neutral [(ηⁿ-ring)MCl(κ²N,O-L)] (3, 4) and cationic [(ηⁿ-ring)M(κ³N,O,S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO₃ to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-l-cysteine (HL3) and NaHCO₃ to the dimers [{(ηⁿ-ring)MCl}₂(μ-Cl)₂] affords the neutral compounds [(ηⁿ-ring)MCl(κ²O,S-L3)] ((ηⁿ-ring)M = (η⁵-C₅Me₅)Ir (5a), (η⁶-p-MeC₆H₄iPr)Ru (5b)). Complexes of the formula [(ηⁿ-ring)MCl(κ³N,O,S-L)][SbF₆] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF₆ to the solutions of compounds 5 or to the mixtures of complexes 3/6Cl and 4/7Cl. The amide proton of compounds 8aSb and 8bSb can be removed by addition of NaHCO₃ affording the neutral complexes [(ηⁿ-ring)M(κ³N,O,S-L3-H)] ((ηⁿ-ring)M = (η⁵-C₅Me₅)Ir (9a), (η⁶-p-MeC₆H₄iPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers [{(ηⁿ-ring)MCl}₂(μ-Cl)₂] with HL3 and two equivalents of NaHCO₃. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (R_Ir,R_C,R_S)-[(η⁵-C₅Me₅)Ir(κ³N,O,S-L1)][SbF₆] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound [(η⁵-C₅Me₅)Ir(κ³N,O,S-L3-H)] (9a) undergoes have been determined through variable temperature ¹H NMR studies.