Oxovanadium(<Emphasis Type="SmallCaps">iv</Emphasis>) cations in heterometallic and heteroligand complex formation

The formation of heterometallic oxovanadium(iv) diethylenetriaminepentaacetates with titanium(iii), chromium(iii), cobalt(ii), nickel(ii), and manganese(ii) cations in aqueous solutions was studied by spectrophotometry and pH-metry. The stabilizing influence of heterometallic chelation on an unstable oxidation state of Ti ⁱⁱⁱ and the labilizing effect of oxovanadium(iv) cations on the coordination of Cr ⁱⁱⁱ cations by the carboxylate ligand anions in the heterometallic complex were shown. The optimum conditions for the formation of the heterometallic dtpa complexes were selected and their thermodynamic stability was estimated. The states of the oxovanadium(iv) cations in the monoand heteroligand systems involving polyamine, polyaminopolycarboxylate, and alkylpolyphosphonate ligands were studied. Specific features of ligand coordination and formation of the mixed-ligand chelates were investigated. A variety of molecular compositions of complex oxovanadium(iv) oxyethylenediphosphonate particles formed in ranges of pH 2.2—3.0, 4.5—5.5, and 6.3—6.4 was found. The preferability of formation of polynuclear oxovanadium(iv) oxyethylidenediphosphonates, viz., binuclear particles with oxovanadium(iv) cation to ligand molar ratios of 2 : 1 and 2 : 5 and trinuclear particles with a molar ratio of components of 3 : 2, was shown.     

Complexing properties of 1-[5-(hydrazidomethylsulfinyl)pentyl]-3,5-dimethylisocyanurate with cobalt(<Emphasis Type="SmallCaps">ii</Emphasis>), nickel(<Emphasis Type="SmallCaps">ii</Emphasis>), and iron(<Emphasis Type="SmallCaps">iii</Emphasis>)

Composition and thermodynamic stability of complexes of 1-[5-(hydrazidomethylsulfinyl)pentyl]-3,5-dimethylisocyanurate with cobalt(ii), nickel(ii), and iron(iii) in H₂O—DMSO medium (60 vol.% DMSO) was studied by spectrophotometry, potentiometric titration, and mathematical modeling (CPESSP program). The geometries of all studied structures were optimized by the MM2 molecular mechanics method to obtain the primary target data (estimates) on coordination pattern of 1-[5-(hydrazidomethylsulfinyl)pentyl]-3,5-dimethylisocyanurate in complexes with cobalt(ii), nickel(ii), and iron(iii). Cobalt(ii) and nickel(ii) formed the 1 : 1 complexes; while iron(iii) under experimental conditions excluding redox reactions gave the 1 : 1 and 1 : 2 complexes. All complexes contain ligands in neutral form.     

Formation of homo- and heteronuclear complexes of 1-hydroxyethylidene-1,1-diphosphonic acid with Mn<Superscript>II</Superscript> and Fe<Superscript>III</Superscript> in aqueous solutions

Systems based on 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), iron(iii)—HEDP and manganese(ii)—iron(iii)—HEDP, were studied by pH-potentiometry combined with mathematical modeling and NMR. Diverse and highly stable heteronuclear iron manganese complexes were found to exist in the heteronuclear system. The formation of the MnH₃L₂^3–, FeMnH₃L₂⁰, Fe₂MnHL₃^3–, and MnL^2– complexes was established. The relaxation efficiency coefficient REC₂ (relaxivity) of these complexes was evaluated at ~2000 mol^–1 s^–1 L. Therefore, these systems hold promise as MRI contrast agents.     

Heteronuclear complexation in the system 1-hydroxyethylidenediphosphonic acid—manganese(<Emphasis Type="SmallCaps">ii</Emphasis>)—gadolinium(<Emphasis Type="SmallCaps">iii</Emphasis>) in aqueous solution

pH-Potentiometric method in combination with mathematical modeling was used to study the system manganese(ii)—gadolinium(iii)—1-hydroxyethylidenediphosphonic acid (HEDP, H₄L). When both cations simultaneously are present in the solution, the accumulation of heteronuclear forms with the ratio of Gd: Mn: HEDP equal to 1: 1: 1, 1: 1: 2, and 1: 1: 3 was observed already in the strongly acidic pH region, while from homonuclear forms only five complexes were detected in the solution, namely, MnL₂^6–, GdH₄L₂^–, GdH₂L⁺, KGd₂HL₂↓, and K₃Gd₂L₂(OH)↓. It was concluded that heteronuclear complexes are much stronger and replace homonuclear forms in solution.     

Effect of Amino Acids on the Phase Behavior of Aqueous Biphasic Systems Composed of 1-Butyl-3-methylimidazolium Tetrafluoroborate and Sodium Citrate

Ionic liquids (ILs) based aqueous biphasic systems (ABSs) have been successfully applied to the extraction and purification of biomolecules. Although much research has focused on the effect of ILs on the phase formation, there are few reports that describe the phase behavior of quaternary IL-based ABS systems using amino acids (AAs) as additives. Here, 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim]BF₄) formed an ABS with sodium citrate (Na₃C₆H₅O₇) with the aid of AAs. The phase behavior and physical properties of the ABS were investigated at 298 K. The capacity of the AA to create the ABS (area of biphasic region) increases with increasing in solubility and decrease with the molecular weight of the ILs and follows the trend glycine?>?l-alanine?≈?l-lysine?>?l-threonine?>?l-proline?≈?l-arginine?>?none. Moreover, the pH of the top and bottom phases containing l-proline as additive are nearly neutral; l-threonine, glycine, and l-alanine result in mildly acidic environments, while l-arginine and l-lysine provide basic pH conditions. The results show that the effects of the addition of the AAs can be considerable and important in the simulation, design calculation and pH control of ABS for efficient separation and extraction processes.     

Concise synthesis of two natural steroidal glycosides isolated from <Emphasis Type="Italic">Allium schoenoprasum</Emphasis>

Two natural steroidal glycosides, diosgenin 3-O-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-β-d-glucopyranoside (1) and laxogenin 3-O-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-β-d-glucopyranoside (2) with important cytotoxic activity against the HCT 116 and HT-29 human colon cancer cell lines have been efficiently synthesized via straightforward sequential glycosylation reaction with the combined use of N-phenyltrifluoroacetimidates and trichloroacetimidates donors at room temperature. All structures of the synthesized new compounds were identified by ¹H NMR, ¹³C NMR and HRMS spectra.     

Kinetics and mechanism of interactions of some monofunctional Au(III) complexes with sulphur nucleophiles

Kinetics of the substitution reactions between monofunctional Au(III) complexes, [Au(dien)Cl]²⁺, [Au(bpma)Cl]²⁺ and [Au(terpy)Cl]²⁺ (dien?=?3-azapentane-1,5-diamine, bpma?=?di-(2-picolyl) amine, terpy?=?2,2′;6′,2″-terpyridine), and biologically relevant sulphur ligands, namely glutathione (GSH), l-methionine (l-Met) and l-cysteine (l-Cys), were studied in 0.1 M HCl (pH?=?1.0). The reactions were followed under pseudo-first-order conditions as a function of ligand concentration and temperature using stopped-flow spectrophotometry. The [Au(terpy)Cl]²⁺ complex proved to be more reactive than the [Au(bpma)Cl]²⁺ and [Au(dien)Cl]²⁺ complexes. The reactivities of the nucleophiles follow the same order for all three complexes, viz. l-Met?>?GSH?>?l-Cys. Values of the activation parameters of the reactions support an associative substitution mechanism. In order to confirm that these monofunctional Au(III) complexes undergo a single substitution process in strongly acidic medium, the reaction between [Au(terpy)Cl]²⁺ and l-Met was studied by HPLC. At pH?=?1.0, only one reaction product was detected.     

Enantiomeric Excess Determination for Monosaccharides Using Chiral Transmission to Cold Gas-Phase Tryptophan in Ultraviolet Photodissociation

Chiral transmission between monosaccharides and amino acids via photodissociation in the gas phase was examined using a tandem mass spectrometer fitted with an electrospray ionization source and a cold ion trap in order to investigate the origin of the homochirality of biomolecules in molecular clouds. Ultraviolet photodissociation mass spectra of cold gas-phase noncovalent complexes of the monosaccharide enantiomers glucose (Glc) and galactose (Gal) with protonated l-tryptophan H⁺(l-Trp) were obtained by photoexcitation of the indole ring of l-Trp. l-Trp dissociated via C_α–C_β bond cleavage when noncovalently complexed with d-Glc; however, no dissociation of l-Trp occurred in the homochiral H⁺(l-Trp)(l-Glc) noncovalent complex, where the energy absorbed by l-Trp was released through the evaporation of l-Glc. This enantioselective photodissociation of Trp was due to the transmission of chirality from Glc to Trp via photodissociation in the gas-phase noncovalent complexes, and was applied to the quantitative chiral analysis of monosaccharides. The enantiomeric excess of monosaccharides in solution could be determined by measuring the relative abundance of the two product ions in a single photodissociation mass spectrum of the cold gas-phase noncovalent complex with H⁺(l-Trp), and by referring to the linear relationships derived in this work.

Open image in new window

Graphical Abstract ?

     

Synthesis and structure of the iron(<Emphasis Type="SmallCaps">iii</Emphasis>) tris-chelate complex based on 1,1´-ferrocenediylbis(phenylphosphinic acid)

The previously unknown isomorphous tris{µ²-[1,1´-ferrocenediylbis(phenylphosphinato)]}-iron(iii) complexes as solvates with methanol and DMSO were synthesized and characterized.     

Purification of Two Novel Sugar Acid-binding Lectins from <Emphasis Type="Italic">Haplomitrium Mnioides</Emphasis> (bryophyte,Plantae) and their Preliminary Characterization

Two novel sugar acid-binding lectins were purified from Haplomitrium mnioides (Lindb.) Schust. using a procedure consisting of ammonium sulfate precipitation, G-50 gel filtration, hydroxyapatite chromatography, and HW-50 gel filtration. We reported their partial physicochemical properties: molecular weight, affinity for carbohydrates and organic acids, pH stability, and dependence of their hemagglutination activity on metal ions. We also determined their N-terminal amino acid sequences. H. mnioides lectins (HMLs) were monomers (one with a molecular weight of approximately 27 kDa, and the other with a molecular weight of approximately 105 kDa) under both nonreducing and reducing conditions. They were named HML27 and HML105, respectively. Both HMLs had an affinity for N-acetylneuraminic acid, d-glucuronic acid, d-glucaric acid, bovine submaxillary mucin, heparin, and organic acids, such as citrate, 2-oxoglutaric acid, and d-2-hydroxyglutarate. Furthermore, HML27 had an affinity for α-d-galacturonic acid, d-malate, l-malate, and pyruvate, while HML105 had an affinity for d-gluconic acid. HML27 and HML105 are novel plant lectins: they have an affinity for sugar acids and organic acids and specifically recognize the carboxyl group, and there is no homology between their N-terminal amino acid sequences and those of the previously described lectins and agglutinins.     

Photoredox catalysis via consecutive 2LMCT- and 3MLCT-excitation of an Fe(iii/ii)–N-heterocyclic carbene complex

Fe–N-heterocyclic carbene (NHC) complexes attract increasing attention as photosensitisers and photoredox catalysts. Such applications generally rely on sufficiently long excited state lifetimes and efficient bimolecular quenching, which leads to there being few examples of successful usage of Fe–NHC complexes to date. Here, we have employed [Fe(iii)(btz)₃]³⁺ (btz = (3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene))) in the addition of alkyl halides to alkenes and alkynes via visible light-mediated atom transfer radical addition (ATRA). Unlike other Fe–NHC complexes, [Fe(iii/ii)(btz)₃]^3+/2+ benefits from sizable charge transfer excited state lifetimes ≥0.1 ns in both oxidation states, and the Fe(iii) ²LMCT and Fe(ii) ³MLCT states are strong oxidants and reductants, respectively. The combined reactivity of both excited states enables efficient one-electron reduction of the alkyl halide substrate under green light irradiation. The two-photon mechanism proceeds via reductive quenching of the Fe(iii) ²LMCT state by a sacrificial electron donor and subsequent excitation of the Fe(ii) product to its highly reducing ³MLCT state. This route is shown to be more efficient than the alternative, where oxidative quenching of the less reducing Fe(iii) ²LMCT state by the alkyl halide drives the reaction, in the absence of a sacrificial electron donor.

An iron complex with N-heterocyclic carbene ligands engages in efficient photoredox catalysis via excited state electron transfer reactions of its Fe(ii) and Fe(iii) oxidation states.     

Volumetric Investigations on Molecular Interactions of Glycine/<Emphasis Type="SmallCaps">l</Emphasis>-alanine in Aqueous Citric Acid Solutions at Different Temperatures

Apparent molar volumes \((\phi_{V})\) of glycine/l-alanine in water and in aqueous citric acid (CA) solutions of varying concentrations, i.e. (0.05, 0.10, 0.20, 0.30, 0.40 and 0.50) mol·kg^?1 were determined from density measurements at temperatures T?=?(288.15, 298.15, 308.15, 310.15 and 318.15) K and at atmospheric pressure. Limiting partial molar volumes \((\phi_V^{\text{o}})\) and their corresponding partial molar volumes of transfer \((\Delta_{\text{tr}} \phi_{V} )\) have been calculated from the \(\phi_{V}\) data. The negative \(\Delta_{\text{tr}} \phi_{V}\) values obtained for glycine/l-alanine from water to aqueous CA solutions indicate the dominance of hydrophilic–hydrophobic/hydrophobic–hydrophilic and hydrophobic–hydrophobic interactions over ion/hydrophilic–dipolar interactions. Further, pair and triplet interaction coefficients, i.e. \((V_{\text{AB}} )\;{\text{and}}\; (V_{\text{ABB}} )\) along with hydration number \((n_{\text{H}} )\) have also been calculated. The effect of temperature on the volumetric properties of glycine/l-alanine in water and in aqueous CA solutions has been determined from the limiting partial molar expansibilities \((\partial \phi_{V}^{\text{o}} /\partial T)_{p}\) and their second-order derivative \((\partial^{2} \phi_{V}^{\text{o}} /\partial T^{2} )_{{P}}\). The apparent specific volumes \((\nu_{\phi} )\) for glycine and l-alanine tend to approach sweet taste behavior both in the presence of water and in aqueous CA solutions. The \(\nu_{\phi}\) values for glycine/l-alanine increase with increase in concentration of CA at all temperatures studied. This reveals that CA helps in enhancing the sweet taste behavior of glycine/l-alanine which also supports the dominance of hydrophobic–hydrophobic interactions.     

Electrochemical sensing of <Emphasis Type="SmallCaps">D</Emphasis>-penicillamine on modified glassy carbon electrode by using a nanocomposite of gold nanoparticles and reduced graphene oxide

A new electrochemical sensor was developed for determination of D-penicillamine using glassy carbon electrode which had been modified by gold nanoparticles–reduced graphene oxide nanocomposite (AuNPs/RGO/GCE) in aqueous solution. Cyclic voltammetry, transmission electron microscopy and electrochemical impedance spectroscopy were used for characterization of the modified electrode. The results indicated that the kinetic of oxidation reaction of D-penicillamine at the surface of the electrode was controlled by both diffusion and adsorption processes. In 0.1 mol L^?1 phosphate buffer (pH 2.0), the oxidation current increased linearly with concentration of D-penicillamine with a linear range of 5.0 × 10^?6 to 1.1 × 10^?4 mol L^?1 and regression coefficient of R ² = 0.9972. Theoretical detection limit, defined based on 3σ of the blank signal (n = 9) divided by the slope of the linear regression equation, was 3.9 × 10^?6 mol L^?1 D-penicillamine using differential pulse voltammetry. The developed method was successfully applied to the determination of D-penicillamine in pharmaceutical formulation and blood serum samples.     

A sensitive electrochemical sensor for lead based on gold nanoparticles/nitrogen-doped graphene composites functionalized with <Emphasis Type="SmallCaps">l</Emphasis>-cysteine-modified electrode

Glassy carbon electrodes (GCEs) modified with l-cysteine (l-cys)/gold nanoparticles (AuNPs)/nitrogen-doped graphene (NG) composite were prepared to fabricate a novel electrochemical sensor for lead. AuNPs were uniformly dispersed into NG and l-cys was successfully decorated on AuNPs through the S–Au bond. The l-cys/AuNPs/NG exhibited a well-distributed nanostructure and high responsivity toward Pb(II). The results indicated that l-cys/AuNPs/NG/GCE exhibited the highest peak current, reflecting that the l-cys/AuNPs/NG composites showed the best response signal toward Pb²⁺. Under optimized conditions, a linear relationship between the current intensity and Pb²⁺ concentration was obtained in a range of 0.5–80 μg L^?1 with a detection limit of 0.056 μg L^?1 (S/N = 3). The analytical interference procedure and practical application were investigated using the prepared electrode, which exhibited an acceptable result.     

Hydrophilic sulfonated bis-1,2,4-triazine ligands are highly effective reagents for separating actinides(iii) from lanthanides(iii) via selective formation of aqueous actinide complexes

We report the first examples of hydrophilic 6,6′-bis(1,2,4-triazin-3-yl)-2,2′-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) ligands, and their applications as actinide(iii) selective aqueous complexing agents. The combination of a hydrophobic diamide ligand in the organic phase and a hydrophilic tetrasulfonated bis-triazine ligand in the aqueous phase is able to separate Am(iii) from Eu(iii) by selective Am(iii) complex formation across a range of nitric acid concentrations with very high selectivities, and without the use of buffers. In contrast, disulfonated bis-triazine ligands are unable to separate Am(iii) from Eu(iii) in this system. The greater ability of the tetrasulfonated ligands to retain Am(iii) selectively in the aqueous phase than the corresponding disulfonated ligands appears to be due to the higher aqueous solubilities of the complexes of the tetrasulfonated ligands with Am(iii). The selectivities for Am(iii) complexation observed with hydrophilic tetrasulfonated bis-triazine ligands are in many cases far higher than those found with the polyaminocarboxylate ligands previously used as actinide-selective complexing agents, and are comparable to those found with the parent hydrophobic bis-triazine ligands. Thus we demonstrate a feasible alternative method to separate actinides from lanthanides than the widely studied approach of selective actinide extraction with hydrophobic bis-1,2,4-triazine ligands such as CyMe₄-BTBP and CyMe₄-BTPhen.     

Influence of Sulfolane on ESI-MS Measurements of Protein–Ligand Affinities

The results of an investigation into the influence of sulfolane, a commonly used supercharging agent, on electrospray ionization mass spectrometry (ESI-MS) measurements of protein–ligand affinities are described. Binding measurements carried out on four protein–carbohydrate complexes, lysozyme with β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-β-d-GlcNAc-(1→4)-d-GlcNAc, a single chain variable fragment and α-d-Gal-(1→2)-[α-d-Abe-(1→3)]-α-d-Man-OCH₃, cholera toxin B subunit homopentamer with β-d-Gal-(1→3)-β-d-GalNAc-(1→4)[α-d-Neu5Ac-(2→3)]-β-d-Gal-(1→4)-β-d-Glc, and a fragment of galectin 3 and α-l-Fuc-(1→2)-β-d-Gal-(1→3)-β-d-GlcNAc-(1→3)-β-d-Gal-(1→4)-β-d-Glc, revealed that sulfolane generally reduces the apparent (as measured by ESI-MS) protein–ligand affinities. To establish the origin of this effect, a detailed study was undertaken using the lysozyme–tetrasaccharide interaction as a model system. Measurements carried out using isothermal titration calorimetry (ITC), circular dichroism, and nuclear magnetic resonance spectroscopies reveal that sulfolane reduces the binding affinity in solution but does not cause any significant change in the higher order structure of lysozyme or to the intermolecular interactions. These observations confirm that changes to the structure of lysozyme in bulk solution are not responsible for the supercharging effect induced by sulfolane. Moreover, the agreement between the ESI-MS and ITC-derived affinities indicates that there is no dissociation of the complex during ESI or in the gas phase (i.e., in-source dissociation). This finding suggests that supercharging of lysozyme by sulfolane is not related to protein unfolding during the ESI process. Binding measurements performed using liquid sample desorption ESI-MS revealed that protein supercharging with sulfolane can be achieved without a reduction in affinity.

Open image in new window

Graphical Abstract ?

     

Interaction of the Ni<Superscript>2+</Superscript> ion with citric acid in an aqueous solution

The formation of nickel citrate complexes was studied at ionic strength values of 0.1 and 0.3 mol/l (Et₄NCl) and 298.15 K by potentiometric titration. The NiCit^?, NiHCit, and NiH₂Cit⁺ complexes were formed in a Ni²⁺ ion-citric acid (H₃Cit) system. The thermodynamic formation constants of the nickel(II) citrate complexes were calculated in an aqueous solution at \(I = 0:\log \beta _{NiCit^ - }^0 \) = 6.86 ± 0.12 (Ni²⁺ + Cit^3? ai NiCit^?), logK ₁ ⁰ = 4.18 ± 0.10 (Ni²⁺ + HCit^2? ai NiHCit), and logK ₂ ⁰ = 2.24 ± 0.11 (Ni²⁺ + H₂Cit^? ai NiH₂Cit⁺). The spectral properties of the Ni²⁺-H₃Cit system were studied by spectrometry. The conditions of calorimetric determination of the thermal effects of formation of the nickel citrate complexes in an aqueous solution were optimized on the basis of the calculated stability constants of the Ni(II) complexes with H₃Cit.     

Enantiomeric pairs of copper(II) polypyridyl-alanine complex salts: anticancer studies

The anticancer properties of two previously characterized pairs of optically pure chiral complex salts [Cu(phen)(ala)(H₂O)]X·xH₂O (phen?=?1.10-phenanthroline; X?=?NO₃^?; ala: l-alanine (l-ala) 1 and d-alanine (d-ala) 2; and (X?=?Cl^?; ala: l-ala, 3 and d-ala, 4; x?=?number of lattice water molecules) are reported herein, together with the crystal structure of the d-enantiomer 4. Unlike cisplatin which is ineffective against MCF-7 cancer cells with the absence of caspase-3 protein expression, these two pairs of complex salts were effective against this cell line and they were able to induce an increase in intracellular ROS, loss in mitochondrial membrane potential, cell cycle arrest mainly at SubG1 phase , caspase-9 activation, and caspase-3/caspase-7-independent apoptosis. Screening of 1 on the NCI-60 panel of human cancer cell lines showed that it was effective against most of the cell lines. MTT-NCI modified assay screening was also done on other cancer cell lines, viz. A549, CNE1, and HepG2, and two normal cell lines, viz. MCF-10A and CHANG. The effects of chirality of these Cu(II) compounds, especially the greater selectivity of d-enantiomers over the l-counterparts, on their anticancer properties are also reported herein.     

Tyrosine alkyl esters as prodrug: the structure and intermolecular interactions of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine methyl ester compared to <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine and its ethyl and <Emphasis Type="Italic">n</Emphasis>-butyl esters

l-Tyrosine alkyl esters are used as prodrugs for l-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of l-tyrosine methyl ester has been determined and compared to published structures of l-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P2₁2₁2₁, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å³ with Z′ = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of l-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because l-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine.