Interaction of Al(III) with the peptides AspAsp and AspAspAsp

Analysis of protonation equilibria of some alanyl dipeptides in water and aqueous ethanol mixtures

The protonation constants are one of the most fundamental properties of biological molecules. The determination of the constants of the dipeptide is interesting and necessary for a full understanding of its activities in biological process. In this study, the protonation constants of some aliphatic alanine dipeptides (alanyl-alanine, alanyl-phenylalanine, alanyl-valine, alanyl-leucine, and alanyl-methionine) were studied in water and ethanol-water mixtures (20%ethanol-80%water;40%ethanol-60%water;60%ethanol-40%water, (v/v)) at 25 ± 0.1 °C under nitrogen atmosphere and ionic strength at 0.10 mol L^-1 by potentiometry. The constants of the systems were calculated using Best computer program. The effects of the different amino acids bound to the alanine on the acidity of the alanyl dipeptides were investigated. The constants were influenced by changes in solvent composition and their variations were discussed in terms of solvent and structural properties.

Building the uracil skeleton in primitive ponds at the origins of life: carbamoylation of aspartic acid

A large set of nucleobases and amino acids is found in meteorites, implying that several chemical reservoirs are present in the solar system. The "geochemical continuity" hypothesis explores how protometabolic paths developed from so-called "bricks" in an enzyme-free prebiotic world and how they affected the origins of life. In the living cell, the second step of synthesizing uridine and cytidine RNA monomers is a carbamoyl transfer from a carbamoyl donor to aspartic acid. Here we compare two enzyme-free scenarios: aqueous and mineral surface scenarios in a thermal range up to 250 °C. Both processes could have happened in ponds under open atmosphere on the primeval Earth. Carbamoylation of aspartic acid with cyanate in aqueous solutions at 25 °C gives high N-carbamoyl aspartic acid yields within 16 h. It is important to stress that, while various molecules could be efficient carbamoylating agents according to thermodynamics, kinetics plays a determining role in selecting prebiotically possible pathways.

Water-soluble optical sensors: keys to detect aluminium in biological environment

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

Highly selective fluorescent peptide-based chemosensors for aluminium ions in aqueous solution

Two novel fluorescent peptide-based chemosensors, including A (2-amino-benzoyl-Ser-Glu-Glu-NH₂) and B (2-amino-benzoyl-Ala-Glu-Pro-Glu-Ala-Glu-Pro-NH₂) were synthesized and characterized by nuclear magnetic resonance (NMR) spectra. These fluorescent probes exhibited excellent selective and sensitive responses to Al³⁺ ions over other metal ions in aqueous buffered solutions. The limits of detection for both chemosensors towards the Al³⁺ ions were in the order of ∼10^-7 M (A: 155 nM and B: 195 nM), which clearly indicates that these probes have significant potential for biological applications. They also displayed high binding affinity (1.3029 × 10⁴ M^-1 and 1.7586 × 10⁴ M^-1 relevant to A and B respectively). These two chemosensors are great analytical probes that produce turn-on responses upon binding to Al³⁺ ions through an intramolecular charge transfer (ICT) mechanism. In addition, the application of both chemosensors was examined over a wide range of pH. The fluorescent peptide-based probes and Al³⁺ form a 1:1 coordination complex according to the ESI-MS and Job's plot analysis. Notably, upon addition of Al³⁺ to these chemosensors, a fluorescence enhancement of approximately 8-fold was observed and the binding mode was determined using NMR titration and fluorescence emission data.

Highly sensitive and selective detection of Al(III) ions in aqueous buffered solution with fluorescent peptide-based sensor

A fluorescent sensor based on a tripeptide (SerGluGlu) with a dansyl fluorophore detected selectively Al(III) among 16 metal ions in aqueous buffered solutions without any organic cosolvent. The peptide-based sensor showed a highly sensitive turn on response to aluminium ion with high binding affinity (1.84×10(4)M(-1)) in aqueous buffered solutions. The detection limit (230nM, 5.98ppb) of the peptide-based sensor was much lower than the maximum allowable level (7.41μM) of aluminium ions in drinking water demanded by EPA. The binding mode of the peptide sensor with aluminium ions was characterized using ESI mass spectrometry, NMR titration, and pH titration experiments.

Protonation equilibria of biologically active ligands in mixed aqueous organic solvents

The review is mainly concerned with the protonation equilibria of biologically active ligands like amino acids, peptides, DNA constituents, and amino acid esters in nonaqueous media. Equilibrium concentrations of proton-ligand formation as a function of pH were investigated. Also, thermodynamics associated with protonation equilibria were also discussed.

Probing the coordination properties of glutathione with transition metal ions (Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+) by density functional theory

Complexes formed by reduced glutathione (GSH) with metal cations (Cr(2+), Mn(2+),Fe(2+),Co(2+),Ni(2+),Cu(2+),Zn(2+),Cd(2+),Hg(2+)) were systematically investigated by the density functional theory (DFT). The results showed that the interactions of the metal cations with GSH resulted in nine different stable complexes and many factors had an effect on the binding energy. Generally, for the same period of metal ions, the binding energies ranked in the order of Cu(2+)>Ni(2+)>Co(2+)>Fe(2+)>Cr(2+)>Zn(2+)>Mn(2+); and for the same group of metal ions, the general trend of binding energies was Zn(2+)>Hg(2+)>Cd(2+). Moreover, the amounts of charge transferred from S or N to transition metal cations are greater than that of O atoms. For Fe(2+),Co(2+),Ni(2+),Cu(2+),Zn(2+),Cd(2+) and Hg(2+) complexes, the values of the Wiberg bond indices (WBIs) of M-S (M denotes metal cations) were larger than that of M-N and M-O; for Cr(2+) complexes, most of the WBIs of M-O in complexes were higher than that of M-S and M-N. Furthermore, the changes in the electron configuration of the metal cations before and after chelate reaction revealed that Cu(2+), Ni(2+),Co(2+) and Hg(2+) had obvious tendencies to be reduced to Cu(+),Ni(+),Co(+) and Hg(+) during the coordination process.

Complexation of Al(III) with reduced glutathione in acidic aqueous solutions

The complexation of reduced glutathione (GSH) in its free and Al(III)-bound species in acidic aqueous solutions was characterized by means of multi-analytical techniques: pH-potentiometry, multinuclear ((1)H, (13)C and (27)Al) and two-dimensional nuclear Overhauser enhancement NMR spectroscopy ((1)H, (1)H-NOESY), electrospray mass spectroscopy (ESI-MS), and ab initio electronic structure calculations. The following results were found. In the 25 degrees C 0.1M KCl and 37 degrees C 0.15M NaCl ionic medium systems, Al(3+) coordinates with the important biomolecule GSH through carboxylate groups to form various mononuclear 1:1 (AlHL, AlH(2)L and AlH(-1)L), 1:2 (AlL(2)) complexes, and dinuclear (Al(2)H(5)L(2)) species, where H(4)L(+) denotes totally protonated GSH. Besides the monodentate complexes through carboxylate groups, the amino groups and the peptide bond imino and carbonyl groups may also be involved in binding with Al(3+) in the bidentate and tridentate complexes. The present data reinforce that the glycine carboxylate group of GSH has a higher microscopic complex formation constant than gamma-glutamyl carboxylate. Compared with simple amino acids, the tripeptide GSH displays a greater affinity for the Al(3+) ion and thus may interfere with aluminum's biological role more significantly.

The protonation equilibria of selected glycine dipeptides in ethanol-water mixture: solvent composition effect

Knowledge of the protonation constants of small dipeptide is important, interesting and necessary for complete understanding of the physiochemical behavior of dipeptide. In this study, the protonation constants of some aliphatic dipeptides (Gly-Gly, Gly-Val, Gly-Leu, Gly-Thr, Gly-Phe and Gly-Met) were studied in water and ethanol-water mixtures [20% ethanol-80% water, 40% ethanol-60% water, 60% ethanol-40% water, (v/v)] at 25 +/- 0.1 degrees C under nitrogen atmosphere and ionic strength at 0.10 mol dm(-3) by potentiometry. The constants of the systems were calculated by using BEST computer program, and distribution species diagrams were produced using the SPE computer program. The protonation constants were influenced by changes in solvent composition, and their variations were discussed in terms of solvent and structural properties. The concentration distribution of the various species in ethanol-water mixtures was evaluated.

Differential toxicity of novel aluminium compounds in hippocampal culture

The dependence of aluminium (Al) toxicity on its chemical form has been implicated in previous studies, but the complex chemistry of Al in solutions of biological preparations has hampered a reliable assessment. Here, we assessed the toxicity of select and pure Al(III) citrate compounds, well-characterized at physiological pH, and compared it with Al from standard solution (in HCl). Cell death rates of neurones and glia were established in hippocampal cultures following 3h incubations in a HEPES-buffered solution and 24h incubations in full culture medium. Overall, Al toxicity was found to vary considerably between compounds, with duration of exposure, medium type, and cell type as factors. While Al (from atomic absorption standard solution) induced the highest levels of cell death, AlCit1, ((NH(4))(5)[Al(C(6)H(4)O(7))(2)].2H(2)O) was the most toxic citrate compound, and affected viability of neurones more than glia (viability at 500 microM/3h-neurones: 40%; glia: 60%). AlCit2 (K(4)[Al(C(6)H(4)O(7))(C(6)H(5)O(7))].4H(2)O) did not show any toxicity after 3h, but severe toxicity after 24h in both cell types (viability at 500 microM/24h-neurones: 50%, glia: 30%). AlCit3 ((NH(4))(5)[Al(3)(C(6)H(4)O(7))(3)(OH)(H(2)O)].(NO(3)).6H(2)O), exhibited a cell type specific toxicity profile, and only affected neuronal viability at both time points (neuronal viability at 500 microM/3h: 20%). The medium type and presence of serum (FBS) was also found to contribute to the toxicity pattern, with serum providing partial protection. Since the Al(III) compounds introduced here are assumed to form in vivo, our data raise further awareness for the toxicity of Al(III) in general, and for the importance of Al speciation and cell type specific actions in its toxicity.

Metal ion selectivity of oligopeptides

Metal binding affinity and selectivity of peptides are reviewed with a special emphasis on the high structural variety of peptide complexes. The most common structural type of these complexes is built up by the deprotonation and metal ion coordination of subsequent amide groups in the form of fused five-membered chelate rings. The metal ion selectivity of this process and the role of various anchoring groups are discussed in detail. The highest metal binding affinity of peptides is connected to the presence of two anchoring groups in appropriate location (the "double anchor"): e.g. the NH2-Xaa-Xaa-His/Cys/Asp/Met-Xaa sequence. Among the side chain donor functions, the imidazole of histidyl and thiolate of cysteinyl residues are the most effective ligating groups and their involvement in metal binding results in a great variety of different macrochelate or loop structures and/or formation of various polynuclear complexes. Examples of these structural motifs and their possible applications have been thoroughly discussed.

Evaluation of the speciation status of aluminium(III) ions in isolated osteoarthritic knee-joint synovial fluid

High field 1H NMR spectroscopy demonstrated that the equilibration of added Al(III) ions in osteoarthritic (OA) knee-joint synovial fluid (SF) resulted in its complexation by citrate and, to a much lesser extent, tyrosine and histidine. The ability of these ligands, together with inorganic phosphate, to compete for the available Al(III) in terms of (1) thermodynamic equilibrium constants for the formation of their complexes and (2) their SF concentrations was probed through the use of computer speciation calculations, which considered low-molecular-mass binary and ternary Al(III) species, the predominant Al(III) plasma transport protein transferrin, and also relevant hydrolysis and precipitation processes. It was found that, at relatively low added Al(III) concentrations, citrate species were more favoured, whilst phosphate species became dominant at higher levels. The significance of these findings with regard to the in vivo corrosion of aluminium-containing metal alloy joint prostheses (e.g., TiAlV alloys) is discussed.

Copper(II) complexes of oligopeptides containing aspartyl and glutamyl residues. Potentiometric and spectroscopic studies

Copper(II) complexes of di-, tri- and tetra-peptides built up from Asp and/or Glu residues were studied by potentiometric and various spectroscopic techniques including UV-visible, circular dichroism and electron paramagnetic resonance measurements. The ligands contain two to five carboxylate functions and it generally results in the enhanced metal binding ability of the ligands, which is especially true for the oligopeptides of aspartic acid. In the case of peptides containing aspartyl residue in the N-terminal position the stability enhancement is reflected in the equilibrium data of the species [CuL] containing the (NH(2),beta-COO(-))-coordination mode in a 6-membered chelate. In the case of AspAsp and AspAspAsp the (NH(2),N(-),beta-COO(-)) and (NH(2),N(-),N(-),beta-COO(-))-coordination modes will be favoured, which contain (5,6) and (5,5,6)-joined chelate ring systems, respectively. The outstanding stability of the latter binding mode and the high negative charge of the corresponding species suppresses the metal ion coordination of the third amide function of AspAspAspAsp. It is also important to note that the presence of side chain carboxylate functions results in the formation of carboxylato-bridged polynuclear complexes in medium pH range. The extent of oligomerisation can be significantly enhanced by the increase of concentration and by the decrease of temperature.