Chelating Binding Research Articles

Calcium-chelating peptides from rabbit bone collagen: characterization, identification and mechanism elucidation

This study aimed to characterize and identify calcium-chelating peptides from rabbit bone collagen and explore the underlying chelating mechanism. Collagen peptides and calcium were extracted from rabbit bone by instant ejection steam explosion (ICSE) combined with enzymatic hydrolysis, followed by chelation reaction to prepare rabbit bone peptide-calcium chelate (RBCP-Ca). The chelating sites were further analyzed by liquid chromatography-tandem mass (LC-MS/MS) spectrometry while the chelating mechanism and binding modes were investigated. The structural characterization revealed that RBCP successfully chelated with calcium ions. Furthermore, LC-MS/MS analysis indicated that the binding sites included both acidic amino acids (Asp and Glu) and basic amino acids (Lys and Arg). Interestingly, three binding modes, namely Inter-Linking, Loop-Linking and Mono-Linking were for the first time found, while Inter-Linking mode accounted for the highest proportion (75.1 %), suggesting that chelation of calcium ions frequently occurred between two peptides. Overall, this study provides a theoretical basis for the elucidation of chelation mechanism of calcium-chelating peptides.

Efficient Hg(Ⅱ) adsorption of polyphenol functionalized Poly(pyrrole methane)s: The role of acid doped ions

A series of doped and dedoped polyphenol functionalized poly(pyrrole methane)s (234HBAs) were designed to investigate the impact of various dopants on mercury adsorption in water. The adsorption performance of dedoped 234HBAs showed no significant difference (ranging from 2961 to 3004 mg·g−1 at 318 K). However, the adsorption capacities of doped 234HBAs for mercury exhibited significant optimization and varied among different dopants (ranging from 3676 to 4103 mg·g−1 at 318 K). In addition to ultra-high adsorption capacity, 234HBAs also exhibited broad working pH range (2–11), fast kinetics (adsorption equilibrium within 10 min), good anti-ion interference and selectivity (Kd > 7.1 × 105 mL·g−1), and excellent regeneration ability (little attenuation of adsorption capacity after 20 cycles). Furthermore, through characterization techniques (FT-IR, XPS) and the density functional theory (DFT) calculation, it was discovered that the presence of doped acid ions enhanced the capture and immobilization of mercury to varying extents besides the robust chelation binding of mercury by the adjacent phenolic hydroxyl groups. Among these ions, oxygen-containing citrate and sulfate exhibited a stronger ability to facilitate the removal of mercury compared with chloride ions. More importantly, this straightforward approach to fabricating functionalized adsorbents for the remediation of mercury-containing wastewater holds significant guiding implications for the treatment of other heavy metal and organic wastewater.

Comparative pangenomic analysis of predominant human vaginal lactobacilli strains towards population-specific adaptation: understanding the role in sustaining a balanced and healthy vaginal microenvironment

The vaginal microenvironment of healthy women has a predominance of Lactobacillus crispatus, L. iners, L. gasseri, and L. jensenii. The genomic repertoire of the strains of each of the species associated with the key attributes thereby regulating a healthy vaginal environment needs a substantial understanding.We studied all available human strains of the four lactobacilli across different countries, isolated from vaginal and urinal sources through phylogenetic and pangenomic approaches. The findings showed that L. iners has the highest retention of core genes, and L. crispatus has more gene gain in the evolutionary stratum. Interestingly, L. gasseri and L. jensenii demonstrated major population-specific gene-cluster gain/loss associated with bacteriocin synthesis, iron chelating, adherence, zinc and ATP binding proteins, and hydrolase activity. Gene ontology enrichment analysis revealed that L. crispatus strains showed greater enrichment of functions related to plasma membrane integrity, biosurfactant, hydrogen peroxide synthesis, and iron sequestration as an ancestral derived core function, while bacteriocin and organic acid biosynthesis are strain-specific accessory enriched functions. L. jensenii showed greater enrichment of functions related to adherence, aggregation, and exopolysaccharide synthesis. Notably, the key functionalities are heterogeneously enriched in some specific strains of L. iners and L. gasseri.This study shed light on the genomic features and their variability that provides advantageous attributes to predominant vaginal Lactobacillus species maintaining vaginal homeostasis. These findings evoke the need to consider region-specific candidate strains of Lactobacillus to formulate prophylactic measures against vaginal dysbiosis for women’s health.

Fluorescence Sensing of Monosaccharides by Bis-boronic Acids Derived from Quinolinium Dicarboxamides: Structural and Spectroscopic Studies.

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M-1) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Cover Feature: Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands (Chem. Eur. J. 27/2022)

Photochemical cis–trans isomerization was used to switch a divalent lectin ligand between its two forms, which show contrasting binding properties to the plant lectin wheat germ agglutinin (WGA), as visualized by the yin-yang symbol. Whereas the E isomer (obtained under irradiation with green light) is able to bridge adjacent binding sites of WGA leading to a high-affinity chelating binding mode, the Z isomer (obtained under UV light irradiation) crosslinks two lectin molecules associated with a much lower binding affinity. More information can be found in the Research Article by V. Wittmann and co-authors (DOI: 10.1002/chem.202200267).

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor–ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, which can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, which has recently been introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E/Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.

Click functionalized biocompatible gadolinium oxide core-shell nanocarriers for imaging of breast cancer cells.

Site-specific delivery using functionalized nanocarriers is in high demand in imaging applications of modern clinical research. To improve the imaging capabilities of conventionally used contrast agents and expand the targeting accuracy, functional gadolinium oxide based nanocarriers originated from homogeneous core shells structures (Gd2O3@SiO2@Fe3O4) were developed using a multilayer formation approach. The synthesis and chemical configuration for the covalent binding of macrocyclic chelating agents and estrogen targeting molecules on these nanocarriers were designed by a two-step chemical synthesis method. Initially, SiO2@Fe3O4 structures were prepared and encapsulated with a homogenous thin Gd2O3 overlayer. The exterior surface of the as-prepared carriers offered chemical binding with a breast cancer specific estrogen molecule, covalently grafted through a Click-Chemistry protocol. In the next step, to enhance the diagnostic imaging capabilities of these carriers, thiocyanate-linked chelator molecule, DOTA, was attached to the surface of estrogen bound Gd2O3@SiO2@Fe3O4 using basic reaction conditions. The active amino groups before and after conjugation of estrogen molecules on the surface were quantified using a fluorescamine based approach. Due to the covalent binding of the macrocyclic chelator to the Gd2O3@SiO2@Fe3O4 surface, core shell carriers showed potential radiolabeling efficiency using positron emitter radionuclide, gallium-68 (68Ga). Intracellular uptake of estrogen-conjugated carriers was evaluated with MCF7 breast cancer cell lines using confocal laser scanning microscopy and fluorescent flow cytometry. In addition, in vitro cytotoxicity studies of functional nanocarriers as compared to bare nanoparticles showed reduced toxicity to HEK-293 cells demonstrating the role of surface attached molecules in preventing direct exposure of the Gd2O3 surface to the cells. The as-developed gadolinium based nanocarriers presented excellent capabilities as biocompatible target-specific imaging probes which indicates great potential in the field of dual-mode contrast agents.

Intracanal bonding with therapeutic adhesives and new dentin conditioners

The EDTMP (ethylenediamine-tetra-methylene phosphonate) is a molecule similar to EDTA (ethylenediamine-tetra-acetic acid), but with phosphonates, thereby presenting efficient chelating action and binding adequately to proteins, such as collagen. The objective of this study was to evaluate EDTMP as new etching solution to aid ion-releasing adhesive containing beta-tri-calcium phosphate (β-TCP) fillers used for intrarradicular dentin bonding. Thirty extracted single-rooted human teeth were prepared, and glass-fiber posts were adhesively luted with Scotchbond Multipurpose (SBMP, 3 M) adhesive after etching with 37% phosphoric acid for 15s, 15% EDTA or 15% EDTMP for 120s, and SBMP adhesive incorporated or not with β-TCP. RelyX ARC (3 M) was used as resin cement. The restored roots were cut horizontally in 1 mm-thick slabs and submitted to push-out bond strength test after 24h and 6 months of water storage. Interfacial silver nanoleakage was investigated in scanning electron microscopy. Micro-Raman spectroscopy was employed to track mineralization at the hybrid layer. Data were submitted to two-way ANOVA and Tukey’s test (p<0.05). EDTMP without β-TCP achieved the overall highest bond strength in both storage times. The addition of β-TCP impaired the improvements of EDTMP. The presence of carbonated apatite (peak at 1090 cm -1 ) was found in EDTMP without β-TCP, thereby suggesting remineralization. Little silver impregnation was observed in general across groups. Conclusion : EDTMP could be an optimal alternative as root dentin etchant for luting glass-fiber posts with improvements in dentin bond stability.

Molecular-level insights into adsorption of a novel silyl ester donor on essential MgCl2 facets of supported Ziegler–Natta catalysts

This article deals with the adsorption properties of a new silyl ester donor called bis(benzoyloxy)dimethylsilane (BDMS) on the MgCl2 support of the Ziegler–Natta catalysts in both conventional and zip modes of coordination. The results confirmed the strong (by up to 47.6 kcal/mol at PBEh/TZVP) preference of BDMS for bridging over chelating or monodentate binding modes on both tetracoordinate and pentacoordinate Mg atoms. Among the spontaneous events, the lowest but appreciable preference was predicted for monodentate chemisorption on penta-coordinated Mg. The zero-point energy (ZPE) values confirmed that BDMS could be adsorbed more strongly, by 7.0 kcal/mol, on the (110) facet than on the (104) surface of the MgCl2 matrix. The enthalpy changes confirmed the ability of BDMS to effectively stabilize the lateral crystallite terminations. The observed characteristics were explained in terms of the quantum theory of atoms in molecules, natural bond orbital population, reduced density gradient, non-covalent interactions, and charge density difference. While some in-plane redistribution of charges was demonstrated, the electron transfer did not exceed 0.1 e. Overall, BDMS was shown to be more selective than the commonly used phthalate donors.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

Dystroglycan (DG) is a widely expressed high-affinity extracellular matrix receptor that requires extensive glycosylation and additional post-translational processing. In skeletal muscle, DG is part of the dystrophin-glycoprotein complex, which is embedded in the plasma membrane and establishes a continuous link between laminin-G-like (LG) domains of extracellular matrix-resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α-DG via a novel heteropolysaccharide [-GlcA-β1,3-Xyl-α1,3-]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like-acetylglucosaminyltransferase (LARGE). Abnormalities in the post-translational processing of DG lead to an absence or reduction of the matriglycan modification on α-DG, and thereby lead to various forms of glycosylation-deficient muscular dystrophy (secondary dystroglycanopathies). We have used a multidisciplinary approach to provide the first atomic-level insights into the structure of a unique protein-carbohydrate interaction that is essential for the binding of α-DG to the extracellular matrix and proper skeletal muscle function. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin-α2 LG4,5 with high affinity (KD=0.23 µM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin-α2 LG4,5. Dr. Hohenester soaked matriglycan into crystals of LG4,5 to produce a high-resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+-dependent lectin with specificity for GlcA-β1,3-Xyl disaccharides, and that a single glucuronic acid-β1,3-xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+-bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein-carbohydrate interaction. Finally, we used two novel exoglycosidases to provide direct evidence that native α-DG contains unmodified matriglycan and numerous GlcA-Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein-carbohydrate interactions underlying dystroglycanopathies.

Fungal-Metal Interactions: A Review of Toxicity and Homeostasis.

Metal nanoparticles used as antifungals have increased the occurrence of fungal–metal interactions. However, there is a lack of knowledge about how these interactions cause genomic and physiological changes, which can produce fungal superbugs. Despite interest in these interactions, there is limited understanding of resistance mechanisms in most fungi studied until now. We highlight the current knowledge of fungal homeostasis of zinc, copper, iron, manganese, and silver to comprehensively examine associated mechanisms of resistance. Such mechanisms have been widely studied in Saccharomyces cerevisiae, but limited reports exist in filamentous fungi, though they are frequently the subject of nanoparticle biosynthesis and targets of antifungal metals. In most cases, microarray analyses uncovered resistance mechanisms as a response to metal exposure. In yeast, metal resistance is mainly due to the down-regulation of metal ion importers, utilization of metallothionein and metallothionein-like structures, and ion sequestration to the vacuole. In contrast, metal resistance in filamentous fungi heavily relies upon cellular ion export. However, there are instances of resistance that utilized vacuole sequestration, ion metallothionein, and chelator binding, deleting a metal ion importer, and ion storage in hyphal cell walls. In general, resistance to zinc, copper, iron, and manganese is extensively reported in yeast and partially known in filamentous fungi; and silver resistance lacks comprehensive understanding in both.

Ultrasensitive fluorescence detection of bismuth ion (III) in plasma, urine and medicines by a terbium chelate probe

Abstract A novel, ultrasensitive probe of Bi3+ ion based on the fluorescence of a terbium chelate was presented and synthesized. This terbium chelate probe for Bi3+ is composed of a carbostyril-linked polyaminocarboxylate chelator and fluorescent terbium ion, and is highly fluorescent due to the sensitization of carbostyril to terbium ion. The extremely strong binding of polyaminocarboxylate chelator to Bi3+ replaced the binding of terbium ion, quenching the fluorescence of the probe. The probe based on this principle shows an ultra-high sensitivity for the detection of Bi3+ with a limit of detection as low as 0.1 pM in aqueous solution and 1 pM in urine and plasma solution respectively, at least 100-fold more sensitive than current various assays for Bi3+. The probe can be used to determine trace Bi3+ in medicines, urine and plasma. Due to a long fluorescence lifetime of the probe containing terbium ion, which allows the elimination of various short-lived nonspecific fluorescence via a time-delay measurement, this probe is particularly advantageous for the determination of biological samples like plasma and urine with autofluorescence.

PSMA targeted conjugates based on dextran

BackgroundCurrently, radiotherapy is one of the most popular choices in clinical practice for the treatment of cancers. While it offers a fantastic means to selectively kill cancer cells, it can come with a host of side effects. To minimize such side effects, and maximize the therapeutic effect of the treatment, we propose the use of targeted radiopharmaceuticals. In the study presented herein, we investigate two synthetic pathways of dextran-based radiocarriers and provide their key chemical and physical properties: stability of the bonding of chelating agent and tertiary structure of obtained formulations and its influence on biological properties. Additionally, PSMA small molecule inhibitor was attached and quantified using DELFIA fluorescence assay. Finally, biological properties and radiolabeling yield were studied using confocal microscopy and ITLC-SG chromatography. ResultsTwo types of Dex-conjugates – micelle-like nanoparticles (NPs) and non-folded conjugates – were successfully generated and shown to exhibit cellular effects. The tertiary structure of the conjugates was found to influence the selectivity of PSMA and mediate cell binding as well as cellular uptake mechanisms. NPs were shown to be internalized by other, non – PSMA mediated channels. Simultaneously, the uptake of non-folded conjugates required PSMA inhibitor to pass through cell membrane. The radiochemical yield of NHS coupled DOTA chelator was between 91.3 and 97.7% while the TCT-amine bonding showed higher stability and gave the yields of 99.8–100%. ConclusionsWe obtained novel, dextran-based radioconjugates, and presented a superior method of chelator binding, resulting in exquisite radiochemical properties as well as selective cross-membrane transport.

Synthesis, biological evaluation of antioxidant-antibacterial activities and computational studies of novel anthracene- and pyrene-based Schiff base derivatives.

Schiff base derivatives with anthracene- and pyrene-based units, A1-A6 and P1-P6 were synthesized (89%–99% yields). Schiff base derivatives were designed to possess an heterocyclic moiety on one side to enhance the coordination ability towards metals. To investigate the biological assay of the newly synthesized compounds, their DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, metal chelating, reducing power, antibacterial and DNA binding activities were tested. A6 (63.1%) showed the maximum free radical scavenging activity among all. However, compound P3 at concentration of 200 μg/mL possessed the highest metal chelating (45.8%) activity and power of reduction. In addition, P3 and A6 showed antibacterial activity against all bacteria tested and both compounds were very well bound to CT-DNA. Density functional theory method with B3LYP/6-311++G(d,p) basis set was performed to get information about the structural and electronic properties of the present compounds. In addition, the metal coordination properties of the dimers of the parent Schiff bases were investigated through interactions with Zn2+.

Developing scandium and yttrium coordination chemistry to advance theranostic radiopharmaceuticals

The octadentate siderophore analog 3,4,3-LI(1,2-HOPO), denoted 343-HOPO hereafter, is known to have high affinity for both trivalent and tetravalent lanthanide and actinide cations. Here we extend its coordination chemistry to the rare-earth cations Sc3+ and Y3+ and characterize fundamental metal–chelator binding interactions in solution via UV-Vis spectrophotometry, nuclear magnetic resonance spectroscopy, and spectrofluorimetric metal-competition titrations, as well as in the solid-state via single crystal X-ray diffraction. Sc3+ and Y3+ binding with 343-HOPO is found to be robust, with both high thermodynamic stability and fast room temperature radiolabeling, indicating that 343-HOPO is likely a promising chelator for in vivo applications with both metals. As a proof of concept, we prepared a 86Y-343-HOPO complex for in vivo PET imaging, and the results presented herein highlight the potential of 343-HOPO chelated trivalent metal cations for therapeutic and theranostic applications.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

(DG) is a widely expressed high‐affinity extracellular matrix receptor that requires extensive glycosylation and additional post‐translational processing. In skeletal muscle, DG is part of the dystrophin‐glycoprotein complex, which establishes a continuous link between laminin‐G‐like (LG) domains of extracellular matrix‐resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α‐DG via a novel heteropolysaccharide [‐GlcA‐β1,3‐Xyl‐α1,3‐]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like‐acetylglucosaminyltransferase (LARGE). We have used a multidisciplinary approach to provide the first atomic‐level insights into the structure of a unique protein‐carbohydrate interaction that is essential for the binding of α‐DG to the extracellular matrix. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin‐α2 LG4,5 with high affinity (Kd=0.23 μM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin‐α2 LG4,5. We provided Dr. Hohenester with enough matriglycan to soak into crystals of LG4,5 and to produce a high‐resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+‐dependent lectin with specificity for GlcA‐β1,3‐Xyl disaccharides, and that a single glucuronic acid‐β1,3‐xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+‐bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein‐carbohydrate interaction as measured by NMR. Finally, we used two novel exoglycosidases to provide direct evidence that native α‐DG contains unmodified matriglycan and numerous GlcA‐Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Abnormalities in the post‐translational processing of DG lead to an absence or reduction of the matriglycan modification on α‐DG, and thereby lead to various forms of muscular dystrophy (secondary dystroglycanopathies). Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein‐carbohydrate interactions.Support or Funding InformationDr. Campbell is an investigator of the Howard Hughes Medical Institute. This work was supported in part by a Paul D. Wellstone Muscular Dystrophy Cooperative Research Center grant.

Precipitation-free high-affinity multivalent binding by inline lectin ligands.

Multivalent ligand–protein interactions are a key concept in biology mediating, for example, signalling and adhesion. Multivalent ligands often have tremendously increased binding affinities. However, they also can cause crosslinking of receptor molecules leading to precipitation of ligand–receptor complexes. Plaque formation due to precipitation is a known characteristic of numerous fatal diseases limiting a potential medical application of multivalent ligands with a precipitating binding mode. Here, we present a new design of high-potency multivalent ligands featuring an inline arrangement of ligand epitopes with exceptionally high binding affinities in the low nanomolar range. At the same time, we show with a multi-methodological approach that precipitation of the receptor is prevented. We distinguish distinct binding modes of the ligands, in particular we elucidate a unique chelating binding mode, where four receptor binding sites are simultaneously bridged by one multivalent ligand molecule. The new design concept of inline multivalent ligands, which we established for the well-investigated model lectin wheat germ agglutinin, has great potential for the development of high-potency multivalent inhibitors as future therapeutics.

Cobalt(II) complexes with the non-steroidal anti-inflammatory drug diclofenac and nitrogen-donor ligands

The interaction of the non-steroidal anti-inflammatory drug sodium diclofenac with CoCl2 in the absence or presence of the nitrogen-donor ligands 2,2′-bipyridine, 1,10-phenanthroline, 2,2′-bipyridylamine, pyridine or imidazole resulted in the formation of six mononuclear Co(II) complexes. The complexes were characterized by diverse physicochemical and spectroscopic techniques and single-crystal X-ray crystallography revealing a monodentate or a bidentate chelating binding mode of the diclofenac ligands. The scavenging activity of the complexes was evaluated in vitro against the free radicals of 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and hydroxyl; the complexes present significant scavenging activity of ABTS and hydroxyl radicals. The interaction of the complexes with calf-thymus (CT) DNA and bovine serum albumin (BSA) was also investigated; the complexes can bind tightly to CT DNA via intercalation and can bind to BSA tightly and reversibly.

Zinc-oxaprozin compounds: Synthesis, structure and biological activity

Four novel zinc complexes, namely [Zn(oxa)2(MeOH)4] (1), [Zn(oxa)2(H2O)(bipy)]·MeOH·2.5H2O (2·MeOH·2.5H2O), [Zn(oxa)2(bipyam)]·1.25MeOH (3·1.25MeOH) and [Zn(oxa)2(phen)] (4), with the non-steroidal anti-inflammatory drug oxaprozin (Hoxa) and a N,N′-donor heterocyclic ligand, such as 2,2′‑bipyridylamine (bipyam), 1,10‑phenanthroline (phen) or 2,2′‑bipyridine (bipy), were characterized with physicochemical techniques, various spectroscopies and single-crystal X-ray crystallography. In these coordination compounds, the oxaprozin ligands are coordinated to zinc ion in a monodentate or a bidentate chelating binding mode. The antioxidant activity of the complexes was evaluated via their ability to scavenge in vitro 1,1‑diphenyl‑2‑picrylhydrazyl, hydroxyl and 2,2′‑azinobis‑(3‑ethylbenzothiazoline‑6‑sulfonic acid) radicals. The complexes bind to calf-thymus DNA via intercalation as suggested via a series of studies employing UV–vis spectroscopy, DNA-viscosity measurements and competition with ethidium bromide. The complexes may bind to serum albumins tightly and reversibly in order to get transferred through the bloodstream.

Novel SPME fibers based on a plastic support for determination of plasma protein binding of thiosemicarbazone metal chelators: a case example of DpC, an anti-cancer drug that entered clinical trials.

Solid-phase microextraction (SPME) is an alternative method to dialysis and ultrafiltration for the determination of plasma protein binding (PPB) of drugs. It is particularly advantageous for complicated analytes where standard methods are not applicable. Di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) is a lead compound of novel thiosemicarbazone anti-cancer drugs, which entered clinical trials in 2016. However, this agent exhibited non-specific binding on filtration membranes and had intrinsic chelation activity, which precluded standard PPB methods. In this study, using a simple and fast procedure, we prepared novel SPME fibers for extraction of DpC based on a metal-free, silicon string support, covered with C18 sorbent. Reproducibility of the preparation process was demonstrated by the percent relative standard deviation (RSD) of ≤ 9.2% of the amount of DpC extracted from PBS by several independently prepared fibers. The SPME procedure was optimized by evaluating extraction and desorption time profiles. Suitability of the optimized protocol was verified by examining reproducibility, linearity, and recovery of DpC extracted from PBS or plasma. All samples extracted by SPME were analyzed using an optimized and validated UHPLC-MS/MS method. The developed procedure was applied to the in vitro determination of PPB of DpC at two clinically relevant concentrations (500 and 1000ng/mL). These studies showed that DpC is highly bound to plasma proteins (PPB ≥ 88%) and this did not differ significantly between both concentrations tested. This investigation provides novel data in the applicability of SPME for the determination of PPB of chelators, as well as useful information for the clinical development of DpC. Graphical abstract.