Stoichiometry Of Complexes Research Articles

Isohexide-Based Tunable Chiral Platforms as Amide- and Thiourea-Chiral Solvating Agents for the NMR Enantiodiscrimination of Derivatized Amino Acids.

New arylamide- and arylthiourea-based chiral solvating agents (CSAs) were synthesized starting from commercially available isomannide and isosorbide. The two natural isohexides were transformed into the three amino derivatives, having isomannide, isosorbide, and isoidide stereochemistry, then the amino groups were derivatized with 3,5-dimethoxybenzoyl chloride or 3,5-bis(trifluoromethyl)phenyl isothiocyanate to obtain the CSAs. Bis-thiourea derivative containing the 3,5-bis(trifluoromethyl)phenyl moiety with exo-exo stereochemistry was remarkably efficient in the differentiation of NMR signals (NH and acetyl) of enantiomers of N-acetyl (N-Ac) amino acids in the presence of 1,4-diazabicyclo[2,2,2]octane (DABCO). Nonequivalences in the ranges of 0.104-0.343 ppm and 0.042-0.107 ppm for NH and acetyl groups, respectively, allowed for very accurate enantiomeric excess determination, and a reliable correlation was found between the relative positions of signals of enantiomers and their absolute configuration. Therefore, a complete stereochemical characterization could be performed. Dipolar interactions detected in the ternary mixture CSA/N-Ac-valine/DABCO led to the identification of a different interaction model for the two enantiomers, involving the formation of a one-to-one substrate/CSA complex for (S)-N-Ac-valine and a one-to-two complex for (R)-N-Ac-valine, as suggested by the complexation stoichiometry.

Gelation of copolymers of acrylamide and sodium acrylate upon coordination with Cu2+ ions in concentrated solutions

The phase state of Cu2+ complexes with acrylamide and sodium acrylate copolymers at different copolymer concentrations and components molar ratios was studied. The change in complex stoichiometry from 2 to 3 carboxylate groups per Cu2+ ion was detected with an increase of copolymer concentration. In the concentrated solutions of copolymers, gelation is observed upon addition of Cu2+ ions, with the lowest concentration of copper required for gelation decreasing with the increase in copolymer concentration. These hydrogels are attributed to the formation of meta-stable inter-polymer metal complexes, which are able to persist due to a low segment mobility. The phase separation of complexes is shown to be associated with the bidentate coordination of carboxylate groups to Cu2+ ions, while the hydrogels formed in concentrated solutions mostly consist of bridging structures. Gelation threshold corresponds to the second critical concentration of poly(acrylamide-co-sodium acrylate) and is lower for copolymers with the higher molecular weight. Low acrylate content in the copolymers prevents collapse of the hydrogels caused by the salting-out effect. A higher gel content can be reached by increasing the copolymer concentration or the molar ratio of copper ions to carboxylate groups, with the latter reducing the swelling degree.

Chromene Carbohydrazide- Schiff Base as a Highly Selective Turn-Off Fluorescence Chemosensor for In3+ Ion and its Application.

A new 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide design to synthesize a simple Schiff-base condition. The synthesized molecules' (probe L) photophysical properties were investigated in various solvent systems and solvent-poor-solvent assays. Probe L exhibits the absorbance band at 440nm and the emission band at 488nm in DMSO: H2O (7:3, v/v). Further, probe L shows selective turn-off emission recognition of In3+ ions in DMSO: H2O (7:3, pH = 7.4). By Job's plot and ESI mass analysis, probe L forms a 1:2 stoichiometry complex with an estimated association constant of 4.04 × 104 M- 2 with In3+ ions. Metal induces CHEQ (chelation-caused fluorescence quenching) to reduce the intensity of probe L's emission, and the estimated quenching constant was 4.52 × 104 M- 1. The limit of detection was found to be 5.93 nM; the time response of the sensor is instantaneous, and its reversible nature was confirmed using EDTA additions. Solid substrates (test strips) were designed and tested for fast, reliable, user-friendly, and real-time sensing of In3+ ions for on-site applications. The binding mechanism of probe L with In3+ ions was investigated using 1H NMR titration and DFT/TD-DFT studies.

Synthesis and characterization of new iridium(III) complexes containing the fragment [Cp*IrCl2] and the ligands 2- and 4-aminobenzonitryl and 2- and 4-aminopyridine

We report the synthesis and characterization of six new iridium(III) complexes of stoichiometry, [Ir(Cp*Cl2(2abn)] (1), [Cp*Cl2Ir(µ-2abn)IrCl2Cp*] (2), [IrCp*Cl2(4abn)] (3), [Cp*Cl2Ir(µ-4abn)IrCl2Cp*] (4), [IrCp*Cl2(2-ampy)] (5) and [IrCp*Cl2(4-ampy)] (6) (Cp* =pentamethylcyclopentadienyl anion; 2- and 4abn = 2- and 4-aminobenzonitrile, respectively; 2- and 4-ampy = 2- and 4-aminopyridine, respectively). The new compounds have been prepared from [(IrCp*Cl)(µ-Cl)]2 by the addition of the ligands in appropriate proportions in dichloromethane and then precipitated using hexane. They have been characterized by C, H, N elemental analyses, thermogravimetric analysis, infrared spectroscopy,1H and 1H-1H Cosy nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry (ESI), and in the case of 1 and 5, by single-crystal X-ray diffraction, confirming the proposed structure. To the best of our knowledge, 1 is the first reported crystal structure of a neutral Cp*Ir complex with a benzonitrile-based ligand coordinated through the -CN group. The cytotoxic behavior of all compounds was studied against HeLa cells, but no measurable biological activity could be established.

Benzimidazolium bromide derivative inclusion complexes with native and modified beta-cyclodextrins

The interactions between four native and modified beta-cyclodextrins and a benzimidazolium bromide salt were analyzed through UV-Vis and NMR Spectroscopy. The new benzimidazolium salt was obtained by simple and efficient conversion of N-1 substituted 5,6-dimethylbenzimidazole with phenacyl bromide in acetone. In all cases, the complexes stoichiometry was 1:1, as determined from UV-Vis titrations. Based on the values for association constants, the strength of the interactions with benzimidazolium bromide was weakest with the methyl substituted beta-cyclodextrin and strongest with the sulfobutylether substituted beta-cyclodextrin. Through-space NOE experiments were used to investigate the structural aspects of inclusion process. The obtained NOE correlations indicate coexistence of two inclusion modes: one with the phenacyl group inside the cyclodextrin cavity and the second one with dimethyl-substituted benzene ring inside the cavity. The imidazole ring and the ethyl substituent have been proven to remain outside the cyclodextrin cavity in both inclusion modes.

Cyclodextrin-Enabled Enantioselective Complexation Study of Cathinone Analogs.

The characteristic alkaloid component of the leaves of the catnip shrub (Catha edulis) is cathinone, and its synthetic analogs form a major group of recreational drugs. Cathinone derivatives are chiral compounds. In the literature, several chiral methods using cyclodextrins (CDs) have been achieved so far for diverse sets of analogs; however, a comprehensive investigation of the stability of their CD complexes has not been performed yet. To characterize the enantioselective complex formation, a systematic experimental design was developed in which a total number of 40 neutral, positively, and negatively charged CD derivatives were screened by affinity capillary electrophoresis and compared according to their cavity size, substituent type, and location. The functional groups responsible for the favorable interactions were identified in the case of para-substituted cathinone analog mephedrone, flephedrone, and 4-methylethcathinone (4-MEC) and in the case of 3,4-methylendioxy derivative butylone and methylenedioxypyrovalerone (MDPV). The succinylated-β-CD and subetadex exhibited the highest complex stabilities among the studied drugs. The complex stoichiometry was determined using the Job's plot method, and the complex structures were further studied using ROESY NMR measurements. The results of our enantioselective complex formation study can facilitate chiral method development and may lead to evaluate potential CD-based antidotes for cathinone analogs.

Cryo-EM of soft-landed β-galactosidase: Gas-phase and native structures are remarkably similar.

Native mass spectrometry (MS) has become widely accepted in structural biology, providing information on stoichiometry, interactions, homogeneity, and shape of protein complexes. Yet, the fundamental assumption that proteins inside the mass spectrometer retain a structure faithful to native proteins in solution remains a matter of intense debate. Here, we reveal the gas-phase structure of β-galactosidase using single-particle cryo-electron microscopy (cryo-EM) down to 2.6-Å resolution, enabled by soft landing of mass-selected protein complexes onto cold transmission electron microscopy (TEM) grids followed by in situ ice coating. We find that large parts of the secondary and tertiary structure are retained from the solution. Dehydration-driven subunit reorientation leads to consistent compaction in the gas phase. By providing a direct link between high-resolution imaging and the capability to handle and select protein complexes that behave problematically in conventional sample preparation, the approach has the potential to expand the scope of both native mass spectrometry and cryo-EM.

CombFold: predicting structures of large protein assemblies using a combinatorial assembly algorithm and AlphaFold2

Deep learning models, such as AlphaFold2 and RosettaFold, enable high-accuracy protein structure prediction. However, large protein complexes are still challenging to predict due to their size and the complexity of interactions between multiple subunits. Here we present CombFold, a combinatorial and hierarchical assembly algorithm for predicting structures of large protein complexes utilizing pairwise interactions between subunits predicted by AlphaFold2. CombFold accurately predicted (TM-score >0.7) 72% of the complexes among the top-10 predictions in two datasets of 60 large, asymmetric assemblies. Moreover, the structural coverage of predicted complexes was 20% higher compared to corresponding Protein Data Bank entries. We applied the method on complexes from Complex Portal with known stoichiometry but without known structure and obtained high-confidence predictions. CombFold supports the integration of distance restraints based on crosslinking mass spectrometry and fast enumeration of possible complex stoichiometries. CombFold’s high accuracy makes it a promising tool for expanding structural coverage beyond monomeric proteins.

Characterization of Large Immune Complexes with Size Exclusion Chromatography and Native Mass Spectrometry Supplemented with Gas Phase Ion Chemistry.

Large immune complexes formed by the cross-linking of antibodies with polyvalent antigens play critical roles in modulating cell-mediated immunity. While both the size and the shape of immune complexes are important determinants in Fc receptor-mediated signaling responsible for phagocytosis, degranulation, and, in some instances, autoimmune pathologies, their characterization remains extremely challenging due to their large size and structural heterogeneity. We use native mass spectrometry (MS) supplemented with limited charge reduction in the gas phase to determine the stoichiometry of immune complexes formed by a bivalent (homodimeric) antigen, a 163 kDa aminopeptidase P2 (APP2), and a monoclonal antibody (mAb) to APP2. The observed (APP2·mAb)n complexes populate a wide range of stoichiometries (n = 1-4) with the largest detected species exceeding 1 MDa, although the gas-phase dissociation products are also evident in the mass spectra. While frequently considering a nuisance that complicates interpretation of native MS data, limited dissociation provides an additional dimension for characterization of the immune complex quaternary structure. APP2/mAb associations with identical composition but slightly different elution times in size exclusion chromatography exhibit notable differences in their spontaneous fragmentation profiles. The latter indicates the presence of both extended linear and cyclized (APP2·mAb)n configurations. The unique ability of MS to distinguish between such isomeric structures will be invaluable for a variety of applications where the biological effects of immune complexes are determined by their ability to assemble Fc receptor clusters of certain density on cell surfaces, such as platelet activation by clustering the low-affinity receptors FcγRIIa on their surface.

Exploring Brilliant Blue FCF Assembly with Beta Cyclodextrin, Characterizations and Applications in Biological Systems Using Physicochemical and Computational Methods

AbstractThis research delvedinto the BrilliantBlue FCF (BB) dye encapsulation within the nano hydrophobic cavity of β‐cyclodextrin (β‐CD) utilizing various spectroscopic and physicochemical techniques. Job's plot using UV‐visible and Fluorescence spectroscopy, surface tension, and conductance study confirmed 1 : 1 stoichiometry of theinclusion complex (BBIC).1H NMR and FT‐IR studies demonstrated the possible binding mode of BB into the β‐CD cavity, which wasin good agreement withthe DFT study. The degree of affinity of β‐CD for BB in the ground state and excited state were estimatedfromUV‐visible andFluorescence spectroscopy(binding constant=8113.9451 M−1and10199.563 M−1), andthe negative free binding energyshowedthe encapsulation process to bethermodynamically feasible. PXRD analysis and SEM image studies revealed the formation of the BBIC. After complexation with β‐CD, the photostability of BB was found to be enhanced. The interaction study of BB and BBIC with CT‐DNA revealed the sustained release of BB from the complex. Furthermore, neither BBICnor free BB exhibited a significant cytotoxic effect on the normal cell line HEK‐293. However, BBIC complex (IC50=6.15 μM) showed significant in vitrocytotoxic activity compared to pure BB (IC50=8.90 μM) towards cancer cell line A549.

Native Capillary Electrophoresis-Mass Spectrometry of Near 1 MDa Non-Covalent GroEL/GroES/Substrate Protein Complexes.

Protein complexes are essential for proteins' folding and biological function. Currently, native analysis of large multimeric protein complexes remains challenging. Structural biology techniques are time-consuming and often cannot monitor the proteins' dynamics in solution. Here, a capillary electrophoresis-mass spectrometry (CE-MS) method is reported to characterize, under near-physiological conditions, the conformational rearrangements of ∽1 MDa GroEL upon complexation with binding partners involved in a protein folding cycle. The developed CE-MS method is fast (30min per run), highly sensitive (low-amol level), and requires ∽10 000-fold fewer samples compared to biochemical/biophysical techniques. The method successfully separates GroEL14 (∽800 kDa), GroEL7 (∽400 kDa), GroES7 (∽73kDa), and NanA4 (∽130 kDa) oligomers. The non-covalent binding of natural substrate proteins with GroEL14 can be detected and quantified. The technique allows monitoring of GroEL14 conformational changes upon complexation with (ATPγS)4-14 and GroES7 (∽876 kDa). Native CE-pseudo-MS3 analyses of wild-type (WT) GroEL and two GroEL mutants result in up to 60% sequence coverage and highlight subtle structural differences between WT and mutated GroEL. The presented results demonstrate the superior CE-MS performance for multimeric complexes' characterization versus direct infusion ESI-MS. This study shows the CE-MS potential to provide information on binding stoichiometry and kinetics for various protein complexes.

Beyond copper: examining the significance of His-mutations in mycobacterial GroEL1 HRCT for Ni(II) complex stability and formation.

Recently, we have studied the coordination chemistry of the Cu(II)-histidine-rich C-terminal tail (HRCT) complex of the mycobacterial GroEL1 protein. The structure of this domain differs significantly compared to the well-known methionine-glycine-rich GroEL chaperonin - it was predicted that mycobacterial GroEL1 could play a significant role in the metal homeostasis of Mycobacteria, especially copper. However, we found that this particular domain's pattern also repeats in a number of Ni(II)-binding proteins. Here, we present the studies concerning the properties of GroEL1 HRCT as a ligand for Ni(II) ions. For this purpose, we chose eight model peptides: L1 - Ac-DHDHHHGHAH, L2 - Ac-DKPAKAEDHDHHHGHAH, and 6 mutants of the latter in the pH range of 2-11. We examined the stoichiometry, stability, and spectroscopic features of copper complexes. We noticed that similar to the Cu(II)-complex, the presence of a Lys5 residue significantly increases the stability of the system. The impact of His mutations was also examined and carefully studied using NMR spectroscopy. His9 and His13 are the crucial residues for Ni(II) binding, whereas His12 has minimal relevance in complex formation.

Luminescent and time-resolved determination of gemifloxacin mesylate in pharmaceutical formulations and spiked blood plasma samples using a lanthanide complex as a probe.

A novel luminescence-based analytical methodology was established employing a europium(III) complex with 3-allyl-2-hydroxybenzohydrazide (HAZ) as the coordinating ligand for the quantification of gemifloxacin mesylate (GMF) in pharmaceutical preparations and human plasma samples spiked with the compound. The stoichiometry of the europium complex with HAZ was determined via the Job plot and exhibited a metal-to-ligand ratio of 1 : 2. The analytical procedure relies on a rapid and significant enhancement of luminescence by the Eu(AZ)2 complex when it interacts with gemifloxacin mesylate, which allowed for the rapid detection of 96 samples within approximately 2 minutes. The thermodynamic parameters of the complexation of GMF with Eu(AZ)2 were evaluated and showed that the complexation of GMF was spontaneous with a negative ΔG. The binding constant K was 4.27 × 105 L mol-1 and DFT calculations supported GMF binding and the formation of Eu(AZ)2-GMF without further ligand exchange. The calibration graph for the luminescence quantitation of GMF was linear over a wide concentration range of 0.11-16 μg mL-1 (2.26 × 10-7 to 3.30 × 10-5 mol L-1), with a limit of quantification (LOQ) of 110 ng mL-1 (230 nmol L-1) and a detection limit (LOD) of 40 ng mL-1 (82 nmol L-1). The proposed method showed good accuracy with an average recovery of 99% with relative standard deviations of less than 5% in spiking experiments, even in complex pharmaceutical dosage forms such as tablets and in human blood plasma. Herein, the ability of the suppression of the luminescence background by using the long lag times of the lanthanide probe in a time-resolved detection scheme provided reliable and precise results, which suggests its potential for use in further real or patient samples.

Probing Protein Complexes Composition, Stoichiometry, and Interactions by Peptide-Based Mass Spectrometry.

The characterization of a protein complex by mass spectrometry can be conducted at different levels. Initial steps regard the qualitative composition of the complex and subunit identification. After that, quantitative information such as stoichiometric ratios and copy numbers for each subunit in a complex or super-complex is acquired. Peptide-based LC-MS/MS offers a wide number of methods and protocols for the characterization of protein complexes. This chapter concentrates on the applications of peptide-based LC-MS/MS for the qualitative, quantitative, and structural characterization of protein complexes focusing on subunit identification, determination of stoichiometric ratio and number of subunits per complex as well as on cross-linking mass spectrometry and hydrogen/deuterium exchange as methods for the structural investigation of the biological assemblies.

Are the metal identity and stoichiometry of metal complexes important for colchicine site binding and inhibition of tubulin polymerization?

Quite recently we discovered that copper(II) complexes with isomeric morpholine-thiosemicarbazone hybrid ligands show good cytotoxicity in cancer cells and that the molecular target responsible for this activity might be tubulin. In order to obtain better lead drug candidates, we opted to exploit the power of coordination chemistry to (i) assemble structures with globular shape to better fit the colchicine pocket and (ii) vary the metal ion. We report the synthesis and full characterization of bis-ligand cobalt(III) and iron(III) complexes with 6-morpholinomethyl-2-formylpyridine 4N-(4-hydroxy-3,5-dimethylphenyl)-3-thiosemicarbazone (HL1), 6-morpholinomethyl-2-acetylpyridine 4N-(4-hydroxy-3,5-dimethylphenyl)-3-thiosemicarbazone (HL2), and 6-morpholinomethyl-2-formylpyridine 4N-phenyl-3-thiosemicarbazone (HL3), and mono-ligand nickel(II), zinc(II) and palladium(II) complexes with HL1, namely [CoIII(HL1)(L1)](NO3)2 (1), [CoIII(HL2)(L2)](NO3)2 (2), [CoIII(HL3)(L3)](NO3)2 (3), [FeIII(L2)2]NO3 (4), [FeIII(HL3)(L3)](NO3)2 (5), [NiII(L1)]Cl (6), [Zn(L1)Cl] (7) and [PdII(HL1)Cl]Cl (8). We discuss the effect of the metal identity and metal complex stoichiometry on in vitro cytotoxicity and antitubulin activity. The high antiproliferative activity of complex 4 correlated well with inhibition of tubulin polymerization. Insights into the mechanism of antiproliferative activity were supported by experimental results and molecular docking calculations.

Stoichiometry validation of supramolecular complexes with a hydrocarbon cage host by van ’t Hoff analyses

Defining chemical processes with equations is the first important step in characterizing equilibria for the assembly of supramolecular complexes, and the stoichiometry of the assembled components must be defined to generate the equation. Recently, this subject has attracted renewed interest, and statistical and/or information-theoretic measures were introduced to examine the validities of the equilibrium models used during curve fitting analyses of titration. The present study shows that these measures may not always be appropriate for credibility examinations and that further reformation of the protocols used to determine the overall stoichiometry is necessary. Hydrocarbon cage hosts and their chloroform complexes formed via weak CH-π hydrogen bonds were studied, which allowed us to introduce van ’t Hoff analyses for effective validation of the stoichiometries of supramolecular complexes. This study shows that the stoichiometries of supramolecular complexes should be carefully examined by adopting multiple measures with different origins.

Modulation of excimer formation and photostability of avobenzone inside the nanocavities of cyclodextrins

Avobenzone (AVZ), a UVA filter, is extensively used in sunscreen lotion and protects the skin from harmful UVA radiation. Despite their importance in sunscreen formulation, less attention has been given to its light induced excited state properties. Herein, we have explored the photophysical properties of AVZ in aqueous solutions and cyclodextrins (CDs) complexes by employing steady-state, time-resolved fluorescence, and molecular modelling tools followed by photostability analysis. AVZ exhibits dual emission from monomer and excimer forms in aqueous solutions. Spectroscopic studies revealed that AVZ forms multiple inclusion complexes with β-CD and γ-CD depending upon the host’s cavity size. These versatile host–guest complexes resulted in the modulation of the excimer formation of AVZ. The presence of α-CD and β-CD complexes with AVZ inhibited the excimer forms. In contrast, γ-CD facilitated excimer formation because its larger cavity could encapsulate the AVZ dimer. Stoichiometry and association constants for multiple host–guest complexes were determined using Benesi-Hildebrand (BH) plot. Job’s plot was used to confirm the stoichiometry of complexes. Time correlated single photon counting (TCSPC) technique was used to depict the excited state lifetime values of AVZ:CD inclusion complexes. Furthermore, these inclusion complexes were characterized by Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Molecular docking followed by semiempirical calculations confirm the experimental results on stoichiometries and binding constants of host–guest complexes. UV light-induced absorption kinetics revealed that the photostability of AVZ inside the β-CD cavity is much better than other inclusion complexes of CDs. Overall, the present study helps us in further understanding of excited state behavior of AVZ inside hydrophobic nanocavities.

Structure and dynamics of endogenous cardiac troponin complex in human heart tissue captured by native nanoproteomics

Protein complexes are highly dynamic entities that display substantial diversity in their assembly, post-translational modifications, and non-covalent interactions, allowing them to play critical roles in various biological processes. The heterogeneity, dynamic nature, and low abundance of protein complexes in their native states present challenges to study using conventional structural biology techniques. Here we develop a native nanoproteomics strategy for the enrichment and subsequent native top-down mass spectrometry (nTDMS) analysis of endogenous cardiac troponin (cTn) complex directly from human heart tissue. The cTn complex is enriched and purified using peptide-functionalized superparamagnetic nanoparticles under non-denaturing conditions to enable the isotopic resolution of cTn complex, revealing their complex structure and assembly. Moreover, nTDMS elucidates the stoichiometry and composition of the cTn complex, localizes Ca2+ binding domains, defines cTn-Ca2+ binding dynamics, and provides high-resolution mapping of the proteoform landscape. This native nanoproteomics strategy opens a paradigm for structural characterization of endogenous native protein complexes.

Synthesis, structures and DFT study of copper coordination with bis- benzimidazole based thiones and selones: Scope for nonstoichiometric Cu2-xSe nanoparticles

The newly synthesized benzimidazole-based [E2]-donor ligands (E = S or Se) (L1 − L4) on reaction with copper(II) chloride and copper(II) acetate involved reduction of Cu(II) to Cu(I) and yielded copper(I) complexes. The ligands L1 − L3 formed stable 20-membered metallocyclic binuclear Cu(I)-complexes of stoichiometry, [Cu2Cl2(L1-L3)2] (5–7) and [Cu2(OAc)2(L1-L3)2] (9–11). Interestingly, L4 ligand yielded a stable complex, [Cu2Cl2(L4)2] (8) with a chloride anion, but with acetate it formed an unstable complex, [Cu2(OAc)2(L4)2] (12). ESI-mass of coordination compounds 5–12, supported the characteristic molecular ion peaks/fragmented peaks for their ions. NMR study of ligands and complexes, single crystal x-ray crystallography of ligands L1, L2, L4 and complex 6, as well as DFT studies of all ligands and complexes are reported for characterization of ligands and complexes (1–12). Compound 12 with –NCH2CH2OH moiety in the ligand L4 showed very unusual behavior as compared to the compound 11 with –NCH3 moiety in the ligand L3. It degraded under mild conditions to form copper selenide (Cu2-xSe) nanoparticles in the solution, which were characterized using various techniques, such as TEM, SEM and EDX. The plausible mechanism for the instability of the complex 12 even at low temperature (at 0 °C), leading to the formation of Cu2-xSe nanoparticles, has been discussed in this paper.

Extraction properties of polyphosphorylated pyridines in nitric acid media

The extraction of U(VI), Th(IV), Am(III), and Eu(III) with solutions of phosphorylated pyridines from nitric acid solutions has been studied. The stoichiometry of the extractable complexes was established. In terms of their extraction ability, these compounds are inferior to bis(diphenylphosphinyl)methane, but they are signi cantly superior to carbamoylmethylphosphine oxides. An increase in the number of phosphine oxide groups in the molecules of phosphorylated pyridines leads to a signi cant decrease in their extraction ability and selectivity in the extraction of Am(III) and Eu(III) from nitric acid solutions.