EPR investigation of Cu(II)-complexes with nitrogen derivatives of dialdehyde starch

A Redox-Active Copper Complex for Orthogonal Detection of Homocysteine Involving Fluorescence and Electrochemical Techniques

The present work reports the synthesis, characterization, and excited state photo-physical studies of two copper(II) compounds, 1 & 2, which show interference-free emission with homocysteine (Hcy). Cu(II) complexes offer an orthogonal detection strategy involving fluorescence and electrochemical methods, paving the way for improved point-of-care diagnostics and early cardiovascular diseases intervention. The reduction-induced emission enhancement (RIEE) of Cu complexes facilitates the fluorescence measurement of Hcy at physiological pH. The fluorogenic redox-active 1 and 2 are deposited onto gold electrode surfaces to construct the electrochemical sensors 1@Au and 2@Au, respectively. Under specific alkaline conditions, a distinct and selective redox peak at 0.6 V (vs Ag/AgCl) emerges for 1@Au upon interaction with homocysteine. Further, square wave voltammetry confirms the non-interference of its congener (cysteine) even at high concentrations (200 µM) while detecting Hcy (5-100 µM), demonstrating its potential for real-world applications. The fabricated 1@Au exhibits excellent sensitivity of 31.88 µA/µM, with an impressive detection limit of 2.26 nM, and a limit of quantification of 6.85 nM toward Hcy. The analytical applicability of the 1@Au is validated by quantifying Hcy levels in human blood plasma samples. The results highlighted the feasibility of the proposed technique as a rapid and portable monitoring of Hcy in diagnosing cardiovascular diseases (CVDs).

Recent advances on the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch: A review

Starch, a natural storage polysaccharide of plant kingdom, has many industrial applications. However, native starch has some inherent shortages, which can be overcome by structural modification. Dialdehyde starch, one kind of oxidized starch produced by periodate oxidation, has good physical properties and bioactivities with wide applications in different fields. Dialdehyde starch is typically achieved by oxidizing native starch slurry through periodate oxidation under controlled reaction conditions. Several factors including the source of starch, the type of oxidant, the molar ratio of oxidant to starch, reaction temperature, reaction time and solution pH value can influence the synthesis of dialdehyde starch. Dialdehyde starch shows different spectroscopic/chromatographic characters and physicochemical properties from native starch. Moreover, dialdehyde starch exhibits good antioxidant activity, antimicrobial activity and cross-linking property. Based on these functional properties, dialdehyde starch has shown application potentials in food packaging, thermoplastic production, enzyme immobilization, heavy metal ion adsorption, drug delivery, wood adhesion and leather tanning. In this review, the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch are summarized for the first time. The future research and development prospects of dialdehyde starch are also discussed.

Biological activity of mixed chelate copper(II) complexes, with substituted diimine and tridentate Schiff bases (NNO) and their hydrogenated derivatives as secondary ligands: Casiopeína's fourth generation

We synthesize and characterize nine copper(II) compounds. Four with general formula [Cu(NNO)(NO₃)] and five mixed chelates [Cu(NNO)(N-N)]⁺, where NNO corresponds to asymmetric salen ligands (E)-2-((2-(methylamino)ethylimino)methyl)phenolate (L1) and (E)-3-((2-(methylamino)ethylimino)methyl)naphthalenolate (LN1); and their hydrogenated derivatives 2-((2-(methylamino)ethylamino)methyl)phenolate (LH1) and 3-((2-(methylamino)ethylamino)methyl)naphthalenolate (LNH1); and N-N correspond to 4,4'-dimethyl-2,2'-bipiridyne(dmbpy) or 1,10-phenanthroline (phen). Using EPR, the geometries of the compounds in solution in DMSO were assigned, [Cu(LN1)(NO₃)] and [Cu(LNH1)(NO₃)] a square-planar, [Cu(L1)(NO₃)], [Cu(LH1)(NO₃)], [Cu(L1)(dmby)]⁺ and [Cu(LH1)(dmby)]⁺ a square-based pyramid; and [Cu(LN1)(dmby)]⁺, [Cu(LNH1)(dmby)]⁺ and [Cu(L1)(phen)]⁺ and elongated octahedral. By X-ray it was observed that [Cu(L1)(dmby)]⁺ and. [Cu(LN1)(dmby)]⁺ presented a square-based pyramidal, and [Cu(LN1)(NO₃)]⁺ a square-planar geometry. The electrochemical study showed that copper reduction process is a quasi-reversible system, where the complexes with hydrogenated ligands were less oxidizing. The cytotoxicity of the complexes was tested by MTT assay, all the compounds showed biological activity in HeLa cell line, the mixed compounds were the more active ones. Naphthalene moiety, imine hydrogenation and aromatic diimine coordination, increased biological activity. A structure-activity relationships were found: Log(IC₅₀) =  - 1.01(E_pc) - 0.35(Conjugated Rings) + 0.87, for Schiff base complexes and Log(IC₅₀) = 0.078(E_pc) - 0.32(Conjugated Rings) + 1.94, for hydrogenated complexes; the less oxidizing species with a great number of conjugated rings presented the best biological activity. Complexes-DNA binding constants were obtained by uv-vis studies using CT-DNA, the results suggested that the complexes can interact through the grooves, except the phenanthroline mixed complex that intercalate with DNA. Gel electrophoresis study with pBR 322 showed that compounds can produce changes in the form of DNA and some complexes can cleave DNA in the presence of H₂O₂.

N,N-Alkylation Clarifies the Role of N- and O-Protonated Intermediates in Cyclen-Based 64Cu Radiopharmaceuticals

Radioisotopes of Cu, such as ⁶⁴Cu and ⁶⁷Cu, are alluring targets for imaging (e.g., positron emission tomography, PET) and radiotherapeutic applications. Cyclen-based macrocyclic polyaminocarboxylates are one of the most frequently examined bifunctional chelators in vitro and in vivo, including the FDA-approved ⁶⁴Cu radiopharmaceutical, Cu(DOTATATE) (Detectnet); however, connections between the structure of plausible reactive intermediates and their stability under physiologically relevant conditions remain to be established. In this study, we share the synthesis of a cyclen-based, N,N-alkylated spirocyclic chelate, H₂DO3A^C4H8, which serves as a model for N-protonation. Our combined experimental (in vitro and in vivo) and computational studies unravel complex pH-dependent speciation and enable side-by-side comparison of N- and O-protonated species of relevant ⁶⁴Cu radiopharmaceuticals. Our studies suggest that N-protonated species are not inherently unstable species under physiological conditions and demonstrate the potential of N,N-alkylation as a tool for the rational design of future radiopharmaceuticals.

Casiopeinas® third generation, with indomethacin: synthesis, characterization, DFT studies, antiproliferative activity, and nanoencapsulation

Seven new Casiopeinas® were synthesized and properly characterized. These novel compounds have a general formula [Cu(N-N)(Indo)]NO3, where Indo is deprotonated indomethacin and N-N is either bipyridine or phenanthroline with some methyl-substituted derivatives, belonging to the third generation of Casiopeinas®. Spectroscopic characterization suggests a square-based pyramid geometry and voltammetry experiments indicate that the redox potential is strongly dependent on the N-N ligand. All the presented compounds show high cytotoxic efficiency, and most of them exhibit higher efficacy compared to the well-known cisplatin drug and acetylacetonate analogs of the first generation. Computational calculations show that antiproliferative behavior can be directly related to the volume of the molecules. Besides, a chitosan (CS)-polyacrylamide (PNIPAAm) nanogel was synthesized and characterized to examine the encapsulation and release properties of the [Cu(4,7-dimethyl-1,10-phenanthroline)(Indo)]NO3 compound. The results show good encapsulation performance in acidic conditions and a higher kinetic drug release in acidic media than at neutral pH. This result can be described by the Peppas-Sahlin model and indicates a release mechanism predominantly by Fick diffusion.

Recognition of antioxidants and photosensitizers in Dyssodia pinnata by EPR spectroscopy

INTRODUCTION

Previous studies report the isolation mainly of terthiophene derivatives and flavonoids from Dyssodia species. Terthiophenes are known as photosensitizers by their capacity to generate singlet oxygen (¹ O₂ ), and flavonoid antioxidant activity is recognized. These opposite properties could represent interesting options in photodynamic therapy.

OBJECTIVE

To determine the antioxidant and photosensitizer activities of extracts and isolates of Dyssodia pinnata by electron paramagnetic resonance (EPR).

METHODOLOGY

Extracts and isolates were evaluated as antioxidants by the interactions with copper ion (Cu²⁺ ) observed in EPR, and by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and the thiobarbituric reactive substances (TBARS) methods. Their abilities as ¹ O₂ producers were also estimated by EPR.

RESULTS

Terthiophenes were obtained from hexane (DPH) and acetone (DPA) extracts, and flavonoids from DPA and methanol (DPM) extracts. The interaction with Cu²⁺ of extracts and isolated compounds of Dyssodia pinnata showed two effects in EPR: reduction and chelation; flavonoids exhibited both effects, while terthiophenes showed only reduction. DPA, DPM, and flavonoids were active in DPPH and TBARS assays. Quercetagetin-7-O-β-glucoside showed the highest antioxidant and chelating activities, 3-glycosidated flavonoids were less active. Upon irradiation extracts and terthiophenes induced ¹ O₂ formation.

CONCLUSION

Flavonoid reducing activity on Cu²⁺ and free radical scavenging capacity were related to the number of hydroxy groups and to the conjugation between the B and C rings. All tested flavonols showed a major complex with Cu²⁺ , with the most probable site of chelation between the 5-hydroxy and 4-oxo groups. Extracts and terthiophene derivatives showed photosensitizer activity. Thus, EPR is useful to evaluate free radical scavenging and pro-oxidant properties.

endo- versus exo-Cyclic coordination in copper complexes with methylthiazolylcarboxylate tacn derivatives

Three tacn (1,4,7-triazacyclononane)-based ligands substituted by methylthiazolylcarboxylate (tha) and/or methylthiazolyl (th) arms have been examined for copper complexation with the aim to study the impact of carboxylate groups on the complexation of Cu(ii), which can present an endo- or exo-cyclic coordination. Two new ligands have been synthesised: H₃no3tha, tacn bearing three methylthiazolylcarboxylate arms, and H₂no1th2tha, tacn with one methylthiazolyl and two methylthiazolylcarboxylate arms, while Hno2th1tha had already been described. Their complexation behaviour with 1 or 1.5 equivalents of metal was studied on the basis of preliminary results showing the tendency of tha arms to form exocyclic polynuclear species. The solid state studies of the Cu(ii) and Zn(ii) complexes were investigated and some of their structures were characterised by X-ray diffraction. The physicochemical properties of the complexes in solution were also investigated by means of potentiometric measurements, UV-vis spectroscopy, EPR and computational studies, NMR characterisation of the corresponding Zn(ii) complexes and redox behaviour by electrochemistry. Mono- and tri-nuclear complexes ML and M₃L₂ were formed and isolated, highlighting the tendency of methylthiazolylcarboxylate arms, when carried by a tacn platform, to form exo-cyclic and polynuclear complexes. However, this exhaustive study evidences that the "out of cage" and "in cage" present different behaviour in terms of stability.

Bioinspired Oxidation of Methane in the Confined Spaces of Molecular Cages

Non-heme iron, vanadium, and copper complexes bearing hemicryptophane cavities were evaluated in the oxidation of methane in water by hydrogen peroxide. According to ¹H nuclear magnetic resonance studies, a hydrophobic hemicryptophane cage accommodates a methane molecule in the proximity of the oxidizing site, leading to an improvement in the efficiency and selectivity for CH₃OH and CH₃OOH compared to those of the analogous complexes devoid of a hemicryptophane cage. While copper complexes showed low catalytic efficiency, their vanadium and iron counterparts exhibited higher turnover numbers, ≤13.2 and ≤9.2, respectively, providing target primary oxidation products (CH₃OH and CH₃OOH) as well as over-oxidation products (HCHO and HCOOH). In the case of caged vanadium complexes, the confinement effect was found to improve either the selectivity for CH₃OH and CH₃OOH (≤15%) or the catalytic efficiency. The confined space of the hydrophobic pocket of iron-based supramolecular complexes plays a significant role in the improvement of both the selectivity (≤27% for CH₃OH and CH₃OOH) and the turnover number of methane oxidation. These results indicate that the supramolecular approach is a promising strategy for the development of efficient and selective bioinspired catalysts for the mild oxidation of methane to methanol.

New Copper Compounds with Antiplatelet Aggregation Activity

BACKGROUND

Ischemic heart disease, cerebrovascular accident, and venous thromboembolism have the presence of a thrombotic event in common and represent the most common causes of death within the population.

OBJECTIVE

Since Schiff base copper(II) complexes are able to interact with polyphosphates (PolyP), a procoagulant and potentially prothrombotic platelet agent, we investigated the antiplatelet aggregating properties of two novel tridentate Schiff base ligands and their corresponding copper( II) complexes.

METHODS

The Schiff base ligands (L1) and (L2), as well as their corresponding copper(II) complexes (C1) and (C2), were synthesized and characterized by chemical analysis, X-ray diffraction, mass spectrometry, and UV-Visible, IR and far IR spectroscopy. In addition, EPR studies were carried out for (C1) and (C2), while (L1) and (L2) were further analyzed by 1H and 13C NMR. Tests for antiplatelet aggregation activities of all of the four compounds were conducted.

RESULTS

X-ray diffraction studies show that (L1) and (L2) exist in the enol-imine tautomeric form with a strong intramolecular hydrogen bond. NMR studies show that both ligands are found as enol-imine tautomers in CDCl3 solution. In the solid state, the geometry around the copper(II) ion in both (C1) and (C2) is square planar. EPR spectra suggest that the geometry of the complexes is similar to that observed in the solid state by X-ray crystallography. Compound (C2) exhibited the strongest antiplatelet aggregation activity.

CONCLUSION

Schiff base copper(II) complexes, which are attracting increasing interest, could represent a new approach to treat thrombosis by blocking the activity of PolyP with a potential anticoagulant activity and, most importantly, demonstrating no adverse bleeding events.

The impact of biochemical composition and nature of paramagnetic species in grains on stress tolerance of oat cultivars

The aim of this work was to investigate the relationships between the chemical composition of oat grains and the tolerance to oxidative stress of oat genotypes. The studies were based on the results of biochemical analyses and both EPR and Raman spectroscopies on whole grains and their parts (embryo, endosperm, seed coat) originating from oat genotypes with different sensitivities to stress. We found that the amounts of fats and especially unsaturated fatty acids, proteins rich in glutamic acid and glycine, as well as phenolics and tocopherols were higher in grains of the tolerant genotype. Moreover, fats and proteins were distributed not only in embryos, but also in endosperms. The grains of tolerant genotypes exhibited high antioxidant activity and contained greater amounts of β-glucan. EPR data pointed to higher concentrations of various kinds of stable organic radicals (semiquinone, tyrosyl and carbon-centered radicals) in whole grains (and their parts) of sensitive genotypes. EPR spectra revealed the character of interactions of paramagnetic transition metal ions Fe(III) and Mn(II) with organic and inorganic structures of grains. The quantitative EPR measurements showed the dependence between the amount of radical species and the content of transition metal ions, mainly Fe(III) bonded to inorganic structures.

The use of dialdehyde starch derivatives in the phytoremediation of soils contaminated with heavy metals

Products of the reaction between dialdehyde starch and Y-NH2 compounds (e.g. semicarbazide or hydrazine) are effective ligands for metal ions. The usefulness of these derivatives was tested in the experiment, both in terms of the immobilization of heavy metal ions in soil and the potential application in phytoextraction processes. The experimental model comprised maize and the ions of such metals as: Zn(II), Pb(II), Cu(II), Cd(II), and Ni(II). The amount of maize yield, as well as heavy metal content and uptake by the aboveground parts and roots of maize, were studied during a three-year pot experiment. The results of the study indicate the significant impact of heavy metals on reduced yield and increased heavy metal content in maize. Soil-applied dialdehyde starch derivatives resulted in lower yields, particularly disemicarbazone (DASS), but in heavy metal-contaminated soils they largely limited the negative impact of these metals both on yielding and heavy metal content in plants, particularly dihydrazone (DASH). It was demonstrated that the application of dihydrazone (DASH) to a soil polluted with heavy metals boosted the uptake of Zn, Pb, Cu, and Cd from the soil, hence there is a possibility to use this compound in the phytoextraction of these metals from the soil. Decreased Ni uptake was also determined, hence the possibility of using this compound in the immobilization of this metal. The study showed that dialdehyde starch disemicarbazone was ineffective in the discussed processes.

Facile synthesis of monodisperse functional magnetic dialdehyde starch nano-composite and used for highly effective recovery of Hg(II)

By covalently linking dialdehyde starch and amine functionalized Fe3O4 nanoparticle, and modifying with aminothiourea functional group, the novel monodisperse nano-composite has been successfully synthesized without any toxic crosslinking agent. The resulting nano-composite was characterized by means of the Fourier transform infrared spectra (FT-IR), transmission electron microscope (TEM), X-ray diffraction (XRD), elemental analysis and vibrating sample magnetometer (VSM). As the new kind of low-cost and environmentally friendly adsorbent with the excellent monodispersity in aqueous phase, the obtained nano-composite has shown not only the good adsorption capacity for Hg(II) on high initial concentration, but also the strong removal ability on low concentration. Moreover, the unique selectivity for Hg(II) among the mixed metal ions solution and good regeneration performance of nano-composite has also been demonstrated by batch experiments.

Transition metal complexes of neocryptolepine analogues. Part I: synthesis, spectroscopic characterization, and invitro anticancer activity of copper(II) complexes

New generation of copper(II) complexes with aminoalkylaminoneocryptolepine as bidentate ligands has been synthesized and it is characterized by elemental analyses, magnetic moment, spectra (IR, UV-Vis, (1)H NMR and ESR) and thermal studies. The IR data suggest the coordination modes for ligands which behave as a bidentate with copper(II) ion. Based on the elemental analysis, magnetic studies, electronic and ESR data, binuclear square planar geometry was proposed for complexes 7a, 7b, square pyramidal for 9a, 9b and octahedral for 8a, 8b, 10a, 10b. The molar conductance in DMF solution indicates that all complexes are electrolyte except 7a and 7b. The ESR spectra of solid copper(II) complexes in powder form showed an axial symmetry with (2)B1g as a ground state and hyperfine structure. The thermal stability and degradation of the ligands and their metal complexes were studied employing DTA and TG methods. The metal-free ligands and their copper(II) complexes were tested for their in vitro anticancer activity against human colon carcinoma (HT-29). The results showed that the synthesized copper(II) complexes exhibited higher anticancer activity than their free ligands. Of all the studied copper(II) complexes, the bromo-substituted complex 9b exhibited high anticancer activity at low micromolar inhibitory concentrations (IC50=0.58μM), compared to the other complexes and the free ligands.

Preparation and structure investigation of novel Schiff bases using spectroscopic, thermal analyses and molecular orbital calculations and studying their biological activities

Two novel Schiff's bases (EB1 and L1) as new macrocyclic compounds were prepared via condensation reactions between bisaldehyde (2,2'-(ethane-1,2-diylbis(oxy))dibenzaldehyde): firstly with hydrazine carbothioamide to give (EB1), secondly with 4,6-diaminopyrimidine-2-thiol to give (L1). EB1 has a general formula C₁₈H₂₀N₆O₂S₂ of mole mass=416.520, and IUPAC name ((N,N'Z,N,N'E)-N,N'-(((ethane1,2diylbis(oxy))bis(2,1phenylene))bis(methanylylidene))bis(1hydrazinylmethanethioamide). L1 has a general formula C₂₀H₁₆N₄O₂S of mole mass=376.10; and IUPAC name 1,2-bis(2-vinylphenoxy)ethane4,6-diaminopyrimidine-2-thiol). The structures of the compounds obtained were characterized based on elemental analysis, FT-IR and (1)H NMR spectra, mass, and thermogravimetric analysis (TG, DTG). The activation thermodynamic parameters, such as, ΔE(*), ΔH(*), ΔS(*) and ΔG(*) were calculated from the TG curves using Coats-Redfern method. It is important to investigate their structures to know the active groups and weak bond responsible for their biological activities. The obtained thermal (TA) and mass (MS) practical results are confirmed by semi-empirical MO-calculation using PM3 procedure, on the neutral and positively charged forms of these novel Schiff bases. Therefore, comparison between MS and TA helps in selection of the proper pathway representing the decomposition of these compounds to give indication about their structures and consequently their biological activities. Their biological activities have been tested in vitro against Escherichia coli, Proteus vulgaris, Bacillissubtilies and Staphylococcus aurous bacteria in order to assess their antimicrobial potential.

DFT calculations and experimental FT-IR, dispersive-Raman and EPR spectral studies of Copper (II) chloride complex with 3-amino-1-methylbenzene

In this study, we present the synthesis and the characterization of Copper (II) chloride complex with 3-amino-1-methylbenzene (3A1MB). This complex was characterized by vibrational and EPR spectroscopic techniques and elemental analysis. The molecular structure and spectrometry of this complex: Cu(3A1MB)2Cl2 and its ligand: 3A1MB have been investigated theoretically by performing DFT/B3LYP calculations. Cu(3A1MB)2Cl2 has been optimized as two conformers and the more stable conformer is determined. The optimized geometries and calculated vibrational frequencies have been evaluated via comparison with experimental values, and the normal modes were assigned on the basis of the percent potential energy distribution (PED). A good agreement between calculated and experimental data is observed.