Electrospray mass spectrometric studies of L-carnosine (beta-alanyl-L-histidine) complexes with copper(II) or zinc ions in aqueous solution

Speciation of Serum Copper and Zinc-Binding High- and Low-Molecular Mass Ligands in Dairy Cows Using HPLC-ICP-MS Technique

The objective of the present study was assessment of the major copper and zinc species in dairy cow blood serum using a hybrid high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) technique. A total of seventeen 5-6-year-old female Simmental cows, cultivated in the Southern Ural region, were examined. Speciation of serum Cu and Zn was performed using chromatographic PerkinElmer Series 200 system equipped with Agilent Bio SEC-5 Column and docked with NexION 300D mass spectrometer. Analysis of serum ⁶³Cu species revealed four major fractions containing 2.5% (A), 15.6% (B), 75.6% (C), and 11.9% (D) of total copper levels. The revealed fractions could be assigned to tetrameric and dimeric macroglobulin, ceruloplasmin, albumin, and low molecular mass (LMM) copper compounds, respectively. Minor fraction (E) containing <1% of total serum Cu levels may be represented by low-molecular mass Cu species. Speciation analysis also revealed four Zn fractions containing 6.3% (A), 16.9% (B), 71% (C), and 3% (D) of total Zn levels that may be attributed to zinc-bound tetrameric and dimeric macroglobulin, albumin, and Zn-amino acid compounds. Correlation analysis demonstrated that relative levels (%) of Zn-B (dimeric α2-macroglobulin), Zn-C (albumin), and Zn-D (LMM) fractions correlate inversely with Cu-A (monomeric α2-macroglobulin) (r = -0.600), Cu-D (albumin) (r = -0.696), and Cu-C (ceruloplasmin) (r = -0.652), respectively. The obtained data demonstrate the particular features of Zn and Cu transport in dairy cows that may be used for assessment of dietary status of trace elements.

Anti-cancer actions of carnosine and the restoration of normal cellular homeostasis

Carnosine is a naturally occurring dipeptide found in meat. Alternatively it can be formed through synthesis from the amino acids, β-alanine and L-histidine. Carnosine has long been advocated for use as an anti-oxidant and anti-glycating agent to facilitate healthy ageing, and there have also been reports of it having anti-proliferative effects that have beneficial actions against the development of a number of different cancers. Carnosine is able to undertake multiple molecular processes, and it's mechanism of action therefore remains controversial - both in healthy tissues and those associated with cancer or metabolic diseases. Here we review current understanding of its mechanistic role in different physiological contexts, and how this relates to cancer. Carnosine turns over rapidly in the body due to the presence of both serum and tissue carnosinase enzymes however, so its use as a dietary supplement would require ingestion of multiple daily doses. Strategies are therefore being developed that are based upon either resistance of carnosine analogs to enzymatic turnover, or else β-alanine supplementation, and the development of these potential therapeutic agents is discussed.

Zinc enhances carnosine inhibitory effect against structural and functional age-related protein alterations in an albumin glycoxidation model

Age-related complications including protein alterations seen in diabetes and Alzheimer's disease are a major issue due to their accumulation and deleterious effects. This report aims to investigate the effect of zinc supplementation on the anti-glycoxidation activity of carnosine on the in vitro model of albumin-based protein modification. Besides, the therapeutic effect of this combination was tested through the addition of the molecules in tandem (co-treatment) or post initiation (post-treatment) of the protein modification process. Glycation was induced via the addition of glucose to which carnosine (5 mM) alone or with various zinc concentrations (125, 250, and 500 μM) were added either at 0 h or 24 h post-glycation induction. On the other hand, protein oxidation was induced using chloramine T (20 mM) and treated in the same way with carnosine and zinc. The different markers of glycation (advanced glycation end products (AGEs), dityrosine, and beta-sheet formation (aggregation)) and oxidation (AOPP, advanced oxidation protein products) were estimated via fluorescence and colorimetric assays. Zinc addition induced a significant enhancement of carnosine activity by reducing albumin modification that outperformed aminoguanidine both in the co- and post-treatment protocols. Zinc demonstrated a supplementary effect in combination with carnosine highlighting its potential in the protection against age-related protein modifications processes such as the ones found in diabetes.

Development of multiple reaction monitoring assay for quantification of carnosine in human plasma

Carnosine, a histidine containing dipeptide, exerts beneficial effects by scavenging reactive carbonyl compounds (RCCs) that are implicated in pathogenesis of diabetes. However, the reduced carnosine levels may aggravate the severity of diabetes. The precise quantification of carnosine levels may serve as an indicator of pathophysiological state of diabetes. Therefore, we have developed a highly sensitive targeted multiple reaction monitoring (MRM) method for quantification of carnosine in human plasma samples. Various mass spectrometry parameters such as ionization of precursor, fragment abundance and stability, collision energy, tube lens offset voltage were optimized to develop a sensitive and robust assay. Using the optimized MRM assay, the lower limit of detection (LOD) and limit of quantification (LOQ) for carnosine were found to be 0.4 nM and 1.0 nM respectively. Standard curves were constructed ranging from 1.0 nM to 15.0 μM and the levels of carnosine in mice and human plasma were determined. Further, the MRM assay was extended to study carnosine hydrolyzing activity of human carnosinases, the serum carnosinase (CN1) and the cytosolic carnosinase (CN2). CN1 showed three folds higher activity than CN2. The MRM assay developed in this study is highly sensitive and can be used for basal plasma carnosine quantification, which can be developed as a novel marker for scavenging of RCCs in diabetes.

Carnosine Supplementation Enhances Post Ischemic Hind Limb Revascularization

High (millimolar) concentrations of the histidine containing dipeptide - carnosine (β-alanine-L-histidine) are present in the skeletal muscle. The dipeptide has been shown to buffer intracellular pH, chelate transition metals, and scavenge lipid peroxidation products; however, its role in protecting against tissue injury remains unclear. In this study, we tested the hypothesis that carnosine protects against post ischemia by augmenting HIF-1α angiogenic signaling by Fe2+ chelation. We found that wild type (WT) C57BL/6 mice, subjected to hind limb ischemia (HLI) and supplemented with carnosine (1g/L) in drinking water, had improved blood flow recovery and limb function, enhanced revascularization and regeneration of myocytes compared with HLI mice placed on water alone. Carnosine supplementation enhanced the bioavailability of carnosine in the ischemic limb, which was accompanied by increased expression of proton-coupled oligopeptide transporters. Consistent with our hypothesis, carnosine supplementation augmented HIF-1α and VEGF expression in the ischemic limb and the mobilization of proangiogenic Flk-1+/Sca-1+ cells into circulation. Pretreatment of murine myoblast (C2C12) cells with octyl-D-carnosine or carnosine enhanced HIF-1α protein expression, VEGF mRNA levels and VEGF release under hypoxic conditions. Similarly pretreatment of WT C57/Bl6 mice with carnosine showed enhanced blood flow in the ischemic limb following HLI surgery. In contrast, pretreatment of hypoxic C2C12 cells with methylcarcinine, a carnosine analog, lacking Fe2+ chelating capacity, had no effect on HIF-1α levels and VEGF release. Collectively, these data suggest that carnosine promotes post ischemic revascularization via augmentation of pro-angiogenic HIF-1α/VEGF signaling, possibly by Fe2+ chelation.

Collision-induced dissociation products of the protonated dipeptide carnosine: structural elucidation, fragmentation pathways and potential energy surface analysis

Collision-induced dissociation (CID) experiments on protonated carnosine, [carnosine + H](+), with several collision energies were shown to yield eleven different fragment ions with the generation of product ions [carnosine-H2O + H](+) and [carnosine-NH3 + H](+) being the lowest energy processes. Energy-resolved CID showed that at slightly higher collision energies the ions [histidine + H](+) and [histidine-H2O-CO + H](+) are formed. At even higher energies four other product ions were observed, however, attained relatively lower abundances. Quantum chemistry calculations, carried out at different levels of theory, were employed to probe fragmentation mechanisms that account for all the experimental data. All the adopted computational protocols give similar energetic trends, and the range of the calculated free energy barrier values for the generation of all the observed product ions is in agreement with the fragmentation mechanisms offered here.

Muscle histidine-containing dipeptides are elevated by glucose intolerance in both rodents and men

OBJECTIVE

Muscle carnosine and its methylated form anserine are histidine-containing dipeptides. Both dipeptides have the ability to quench reactive carbonyl species and previous studies have shown that endogenous tissue levels are decreased in chronic diseases, such as diabetes.

DESIGN AND METHODS

Rodent study: Skeletal muscles of rats and mice were collected from 4 different diet-intervention studies, aiming to induce various degrees of glucose intolerance: 45% high-fat feeding (male rats), 60% high-fat feeding (male rats), cafeteria feeding (male rats), 70% high-fat feeding (female mice). Body weight, glucose-tolerance and muscle histidine-containing dipeptides were assessed. Human study: Muscle biopsies were taken from m. vastus lateralis in 35 males (9 lean, 8 obese, 9 prediabetic and 9 newly diagnosed type 2 diabetic patients) and muscle carnosine and gene expression of muscle fiber type markers were measured.

RESULTS

Diet interventions in rodents (cafeteria and 70% high-fat feeding) induced increases in body weight, glucose intolerance and levels of histidine-containing dipeptides in muscle. In humans, obese, prediabetic and diabetic men had increased muscle carnosine content compared to the lean (+21% (p>0.1), +30% (p<0.05) and +39% (p<0.05), respectively). The gene expression of fast-oxidative type 2A myosin heavy chain was increased in the prediabetic (1.8-fold, p<0.05) and tended to increase in the diabetic men (1.6-fold, p = 0.07), compared to healthy lean subjects.

CONCLUSION

Muscle histidine-containing dipeptides increases with progressive glucose intolerance, in male individuals (cross-sectional). In addition, high-fat diet-induced glucose intolerance was associated with increased muscle histidine-containing dipeptides in female mice (interventional). Increased muscle carnosine content might reflect fiber type composition and/or act as a compensatory mechanism aimed at preventing cell damage in states of impaired glucose tolerance.

Physiology and pathophysiology of carnosine

Carnosine (β-alanyl-l-histidine) was discovered in 1900 as an abundant non-protein nitrogen-containing compound of meat. The dipeptide is not only found in skeletal muscle, but also in other excitable tissues. Most animals, except humans, also possess a methylated variant of carnosine, either anserine or ophidine/balenine, collectively called the histidine-containing dipeptides. This review aims to decipher the physiological roles of carnosine, based on its biochemical properties. The latter include pH-buffering, metal-ion chelation, and antioxidant capacity as well as the capacity to protect against formation of advanced glycation and lipoxidation end-products. For these reasons, the therapeutic potential of carnosine supplementation has been tested in numerous diseases in which ischemic or oxidative stress are involved. For several pathologies, such as diabetes and its complications, ocular disease, aging, and neurological disorders, promising preclinical and clinical results have been obtained. Also the pathophysiological relevance of serum carnosinase, the enzyme actively degrading carnosine into l-histidine and β-alanine, is discussed. The carnosine system has evolved as a pluripotent solution to a number of homeostatic challenges. l-Histidine, and more specifically its imidazole moiety, appears to be the prime bioactive component, whereas β-alanine is mainly regulating the synthesis of the dipeptide. This paper summarizes a century of scientific exploration on the (patho)physiological role of carnosine and related compounds. However, far more experiments in the fields of physiology and related disciplines (biology, pharmacology, genetics, molecular biology, etc.) are required to gain a full understanding of the function and applications of this intriguing molecule.

Mass spectrometry assay for studying kinetic properties of dipeptidases: characterization of human and yeast dipeptidases

Chemical modifications of substrate peptides are often necessary to monitor the hydrolysis of small bioactive peptides. We developed an electrospray ionization mass spectrometry (ESI-MS) assay for studying substrate distributions in reaction mixtures and determined steady-state kinetic parameters, the Michaelis-Menten constant (K(m)), and catalytic turnover rate (V(max)/[E](t)) for three metallodipeptidases: two carnosinases (CN1 and CN2) from human and Dug1p from yeast. The turnover rate (V(max)/[E](t)) of CN1 and CN2 determined at pH 8.0 (112.3 and 19.5s(-1), respectively) suggested that CN1 is approximately 6-fold more efficient. The turnover rate of Dug1p for Cys-Gly dipeptide at pH 8.0 was found to be slightly lower (73.8s(-1)). In addition, we determined kinetic parameters of CN2 at pH 9.2 and found that the turnover rate was increased by 4-fold with no significant change in the K(m). Kinetic parameters obtained by the ESI-MS method are consistent with results of a reverse-phase high-performance liquid chromatography (RP-HPLC)-based assay. Furthermore, we used tandem MS (MS/MS) analyses to characterize carnosine and measured its levels in CHO cell lines in a time-dependent manner. The ESI-MS method developed here obviates the need for substrate modification and provides a less laborious, accurate, and rapid assay for studying kinetic properties of dipeptidases in vitro as well as in vivo.

The Interaction of the Dipeptide Carnosine With Alkali Metal Ions Studied by Ion Trap Mass Spectrometry

The complexation of alkali metal ions and the proton X+ (X=H, Li, Na, K, Rb, Cs) by β-alanyl-L-histidine (carnosine, Car) was investigated by electrospray ionization mass spectrometry (ESI-MS) and MS/MS fragmentation studies. Collision-induced dissociation (CID) breakdown curves were recorded and the resulting apparent activation energies were compared to DFT calculations of binding energies at the B3LYP/cc-pVDZ level of theory. Additionally, the influence of metal complexation on hydrogen/deuterium exchange of CarX+ with D2O was tested. Our investigations characterize the structures of Car-alkali complexes and elucidate the interaction with the differently sized solvated metal cations.

Effects of dietary supplementation of carnosine on mitochondrial dysfunction, amyloid pathology, and cognitive deficits in 3xTg-AD mice

Background

The pathogenic road map leading to Alzheimer's disease (AD) is still not completely understood; however, a large body of studies in the last few years supports the idea that beside the classic hallmarks of the disease, namely the accumulation of amyloid-β (Aβ) and neurofibrillary tangles, other factors significantly contribute to the initiation and the progression of the disease. Among them, mitochondria failure, an unbalanced neuronal redox state, and the dyshomeostasis of endogenous metals like copper, iron, and zinc have all been reported to play an important role in exacerbating AD pathology. Given these factors, the endogenous peptide carnosine may be potentially beneficial in the treatment of AD because of its free-radical scavenger and metal chelating properties.

Methodology

In this study, we explored the effect of L-carnosine supplementation in the 3xTg-AD mouse, an animal model of AD that shows both Aβ- and tau-dependent pathology.

Principal Findings

We found that carnosine supplementation in 3xTg-AD mice promotes a strong reduction in the hippocampal intraneuronal accumulation of Aβ and completely rescues AD and aging-related mitochondrial dysfunctions. No effects were found on tau pathology and we only observed a trend toward the amelioration of cognitive deficits.

Conclusions and Significance

Our data indicate that carnosine can be part of a combined therapeutic approach for the treatment of AD.

Zinc deposition during ESI-MS analysis of peptide-zinc complexes

Electrospray ionization (ESI) mass spectrometry (MS) has proven to be an extremely powerful technique for studying the stoichiometry and binding strength of peptide-metal complexes. We have found a significant new problem in the ESI-MS of zinc-peptide systems involving the deposition of zinc in the ESI emitter. This deposition of zinc during the experiment removes a significant amount of zinc ions from the solution, impacting the resulting mass spectral intensities used to quantify the amount of the zinc-bound species. Analysis of infused zinc-peptide samples with atomic absorption spectrometry and with a custom-built nanoflow ESI source confirms the alteration of the analyte solutions with positive or negative or no potential applied to the emitter. Ultimately, the location of the zinc deposition was determined to be the stainless steel emitter. The use of a custom-built nanoESI interface using glass emitters was found to mitigate the zinc deposition problem. The phenomenon of metal deposition warrants further investigation as it may not be limited to just zinc and may represent a significant obstacle in the ESI-MS analysis of all protein-metal systems.

Electrospray ionization mass spectrometric observation of ligand exchange of zinc pyrithione with amino acids

Zinc pyrithione (ZnPT) is widely used as an antidandruff or antifouling reagent. However, this compound is considered toxic, such as the teratogenic effect, to aquatic lives, and it is important to clarify the mechanism of its toxicity. In this study, the interactions between ZnPT and amino acids were observed using electrospray ionization mass spectrometry (ESI-MS) in order to obtain information on the activity of ZnPT within the living body. The ZnPT complex ([ZnPT-ligand+Amino acid]+), in which the ligand of ZnPT was exchanged by the amino acid, was detected in ZnPT solutions mixed with one of 20 amino acids by ESI-MS. Histidine and cysteine, in particular, showed a high reactivity with ZnPT, while serine and glycine showed a low reactivity. The complexes of ZnPT and a peptide were also observed by the ESI-MS measurement of the solution containing ZnPT with the peptide. These results would be useful to understand the mechanism of ZnPT toxicities to living creatures.

Carnosine as molecular probe for sensitive detection of Cu(II) ions using localized 1H NMR spectroscopy

Complex formation of carnosine (Csn) with Cu(II) is suspected to be of significant biochemical importance and can be detected by NMR via ion-induced paramagnetic relaxation of Csn signals. Here, we present quantification of the sensitivity achieved with localized (1)H NMR spectroscopy at physiological pH and high ligand-to-metal ratios. While characterizing the highly effective relaxation transfer onto a huge Csn pool due to fast ligand exchange, it is demonstrated that a metal-to-ligand ratio of approximately 100 ppm suffices to reduce Csn signals by approximately 50% in vitro, thus making the dipeptide a sensitive probe for such ions. Variation of the donor accessibility reveals that the paramagnetic effect is transferred onto a approximately 1370-fold donor abundance for a given ion concentration. A method is presented to characterize such effective ligand exchange relaxation transfer. These studies focus on the monomer formation since comparison with (1)H NMR data of human calf muscle demonstrates that the dimer complex is insignificant in vivo. Observed line broadening in living tissue yields an upper limit of ca. 195 ppm for the Csn-related copper concentration in human skeletal muscle.

Environmental effects on a prion's helix II domain: copper(II) and membrane interactions with PrP180-193 and its analogues

An abnormal interaction between copper and the prion protein is believed to play a pivotal role in the pathogenesis of prion diseases. Copper binding has been mainly attributed to the N-terminal domain of the prion protein, but this hypothesis has recently been challenged in some papers which suggest that the C-terminal domain might also compete for metal anchoring. In particular, the segment corresponding to the helix II region of the prion protein, namely PrP180-193, has been shown both to bind copper and to exhibit a copper-enhanced cytotoxicity, as well as to interact with artificial membranes. The present work is aimed at extending these results by choosing the most representative model of this domain and by determining its copper affinity. With this aim, the different role played by the electrostatic properties of the C- and N-termini of PrP180-193 (VNITIKQHTVTTTT) in determining its conformational behaviour, copper coordination and ability to perturb model membranes was investigated. Owing to the low solubility of PrP180-193, its copper affinity was evaluated by using the shorter PrPAc184-188NH2 (IKQHT) analogue as a model. ESI-MS, ESR, UV/Vis, and CD measurements were carried out on the copper(II)/PrPAc184-188NH2 and copper(II)/PrP180-193NH2 systems, and showed that PrPAc184-188NH2 is a reliable model for the metal interaction with the helix II domain. The affinity of copper(II) for the helix II fragment is higher than that for the octarepeat and PrP106-126 peptides. Finally, the different ability of PrP180-193 analogues to perturb the DPPC model membrane was assessed by DSC measurements. The possible biological consequences of these findings are also discussed briefly.

Protective effect of orally administered carnosine on bleomycin-induced lung injury

Carnosine is an endogenously synthesized dipeptide composed of beta-alanine and L-histidine. It acts as a free radical scavenger and possesses antioxidant properties. Carnosine reduces proinflammatory and profibrotic cytokines such as transforming growth factor-beta (TGF-beta), IL-1, and TNF-alpha in different experimental settings. In the present study, we investigated the efficacy of carnosine on the animal model of bleomycin-induced lung injury. Mice were subjected to intratracheal administration of bleomycin and were assigned to receive carnosine daily by an oral bolus of 150 mg/kg. One week after fibrosis induction, bronchoalveolar lavage (BAL) cell counts and TGF-beta levels, lung histology, and immunohistochemical analyses for myeloperoxidase, TGF-beta, inducible nitric oxide synthase, nitrotyrosine, and poly(ADP-ribose) polymerase were performed. Finally, apoptosis was quantified by terminal deoxynucleotidyltransferase-mediated UTP end-labeling assay. After bleomycin administration, carnosine-treated mice exhibited a reduced degree of lung damage and inflammation compared with wild-type mice, as shown by the reduction of 1) body weight, 2) mortality rate, 3) lung infiltration by neutrophils (myeloperoxidase activity and BAL total and differential cell counts), 4) lung edema, 5) histological evidence of lung injury and collagen deposition, 6) lung myeloperoxidase, TGF-beta, inducible nitric oxide synthase, nitrotyrosine, and poly(ADP-ribose) polymerase immunostaining, 7) BAL TGF-beta levels, and 8) apoptosis. Our results indicate that orally administered carnosine is able to prevent bleomycin-induced lung injury likely through its direct antioxidant properties. Carnosine is already available for human use. It might prove useful as an add-on therapy for the treatment of fibrotic disorders of the lung where oxidative stress plays a role, such as for idiopathic pulmonary fibrosis, a disease that still represents a major challenge to medical treatment.

Copper(II) interaction with unstructured prion domain outside the octarepeat region: speciation, stability, and binding details of copper(II) complexes with PrP106-126 peptides

Copper(II) complexes of the neurotoxic peptide fragments of human and chicken prion proteins were studied by potentiometric, UV-vis, CD, and EPR spectroscopic and ESI-MS methods. The peptides included the terminally blocked native and scrambled sequences of HuPrP106-126 (HuPrPAc106-126NH2 and ScrHuPrPAc106-126NH2) and also the nona- and tetrapeptide fragments of both the human and chicken prion proteins (HuPrPAc106-114NH2, ChPrPAc119-127NH2, HuPrPAc109-112NH2, and ChPrPAc122-125NH2). The histidyl imidazole-N donor atoms were found to be the major copper(II) binding sites of all peptides; 3N and 4N complexes containing additional 2 and 3 deprotonated amide-N donors, respectively, are the major species in the physiological pH range. The complex formation processes for nona- and tetrapeptides are very similar, supporting the fact that successive deprotonation and metal ion coordination of amide functions go toward the N-termini in the form of joined six- and five-membered chelates. As a consequence, the peptide sequences investigated here, related to the neurotoxic region of the human PrP106-126 sequence, show a higher metal-binding affinity than the octarepeat fragments. In the case of the HuPrP peptide sequences, a weak pH-dependent binding of the Met109 residue was also detected in the 3N-coordinated complexes.

Interactions between Carnosine and Captopril on Free Radical Scavenging Activity and Angiotensin-converting Enzyme Activity in vitro

Interactions between carnosine (beta-alanyl-L-histidine), being plentiful in skeletal muscles and neuronal tissues, and captopril, a widely used angiotensin-converting enzyme (ACE) inhibitor, were examined concerning free radical scavenging activity and ACE activity in vitro. Not only captopril, but also carnosine, at concentrations less than those ordinarily found in muscles and neuronal tissues, significantly scavenged 2,2'-azinobis (3-ethylbenzothiazoline-6-sulphonate) (ABTS) radical cations, and inhibited ACE activity. Cupric ions reversed the ABTS scavenging activity of carnosine and captopril, whereas cupric ions strengthened the inhibitory action of carnosine on ACE activity. In contrast, cupric ions antagonized the inhibition of ACE activity induced by ethylenediaminetetraacetic acid, indicating that the inhibitory effect of carnosine on ACE activity is not related to the chelating action of carnosine. On the other hand, carnosine and captopril synergistically enhanced the free radical scavenging activity, but not the inhibitory effect on the ACE activity. These data suggest that carnosine in its concurrent use with captopril could act as a beneficial free radical scavenger, with less danger of overdose, in the inhibition of ACE activity.

A multi-approach study of the interaction of the Cu(II) and Ni(II) ions with alanylglycylhistamine, a mimicking pseudopeptide of the serum albumine N-terminal residue

The protonation equilibria of alanylglycylhistamine (Ala-Gly-Ha) and the complexation of this ligand with Cu(II) and Ni(II) have been studied by pH-potentiometry, 1H and 14N NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), UV-Vis spectrophotometry and electron paramagnetic resonance (EPR). From pH approximately 2-12, the following complexes: MLH, MLH(-1), MLH(-2) and MLH(-3) are successively formed in aqueous solutions, the ligand under its neutral form being noted L. At physiological pH, the MLH(-2) complex is predominant. The coordination in this complex is assumed by one amino, two deprotonated peptide and one imidazole nitrogen atoms. The ESI-MS study confirmed the formation of the MLH(-1), MLH(-2) and MLH(-3) complexes. The structure of MLH(-2) was determined by single crystal X-ray analysis. CD and UV-Vis techniques allowed us to propose that the imidazole-N3 nitrogen acts as the anchor group for the coordination to the metal(II) ions rather than the amino group. At high pH values, the further deprotonation of the N-H imidazole group, leading to the formation of MLH(-3), occurs, as revealed by 1H NMR spectroscopy.

Coordination features of difunctionalized beta-cyclodextrins with carnosine: ESI-MS and spectroscopic investigations on 6A,6D-di-(beta-alanyl-L-histidine)-6A,6D-dideoxy-beta-cyclodextrin and 6A,6C-di-(beta-alanyl-L-histidine)-6A,6C-dideoxy-beta-cyclodextrin and their copper(II) complexes

The synthesis and characterization of two beta-cyclodextrins (beta-CD) functionalized with two units of carnosine (beta-alanyl-L-histidine) through the amino group, 6A,6C-(beta-alanyl-L-histidine)-6A,6C-dideoxy-beta-cyclodextrin (ACCDAH) and 6A,6D-(beta-alanyl-L-histidine)-6A,6D-dideoxy-beta-cyclodextrin (ADCDAH), are reported. NMR and C.D. data of the ligands indicate a different interaction of dipeptide chains with upper rim and cavity of beta-CD. Analogously, spectroscopic and electrospray ionization mass spectrometry data show different copper(II) complex species formed by the two regioisomers. The ability of carnosine-cyclodextrin derivatives to bind copper ions in a head-to-tail fashion induces the formation of oligomeric species (up to hexamers) in the case of ACCDAH, where the two carnosine moieties are adjacent, while in the ADCDAH case the mutual interaction between the peptidic chains of two ADCDAH molecules allows the almost exclusive formation of a copper-assisted self-assembled dimeric species.

Copper(II) complexes of peptide fragments of the prion protein. Conformation changes induced by copper(II) and the binding motif in C-terminal protein region

In this paper, we report the characterization of copper(II) complexes with two prion (PrP) protein peptide fragment analogues (VNITKQHTVTTTT), one with the N-terminus acetylated and the C-terminus amidated (PrP Ac180-193NH2) and the other with both the C- and N-termini free (PrP 180-193). Such peptide sequence almost entirely encompasses the PrPC's helix 2 in the C-terminal region. The stoichiometry, the binding modes and the conformational features of the copper(II) complexes with the above mentioned two peptides were investigated by electrospray ionization-mass spectrometry (ESI-MS), UV-visible (UV-Vis) spectrometry and electron paramagnetic resonance (EPR) spectrometry as well as by circular dichroism (CD) measurements. The binding site location of copper(II) in the structured region of the protein can be here suggested on the basis of our findings that show the involvement of His 187 residue. The similarity of the EPR parameters suggests that the anchoring imidazole residue drives the copper(II) coordination environment towards a common binding motif in different regions of the prion protein.

Speciation and Coordination Chemistry of Uranyl(VI)−Citrate Complexes in Aqueous Solution

The pH dependence of uranyl(VI) complexation by citric acid was investigated using Raman and attenuated total reflection FTIR spectroscopies and electrospray ionization mass spectrometry. pH-dependent changes in the nu(s)(UO(2)) envelope indicate that three major UO(2)(2+)-citrate complexes with progressively increasing U=O bond lengths are present over a range of pH from 2.0 to 9.5. The first species, which is the predominant form of uranyl(VI) from pH 3.0 to 5.0, contains two UO(2)(2+) groups in spectroscopically equivalent coordination environments and corresponds to the [(UO(2))(2)Cit(2)](2)(-) complex known to exist in this pH range. At pH values >6.5, [(UO(2))(2)Cit(2)](2)(-) undergoes an interconversion to form [(UO(2))(3)Cit(3)](3)(-) and (UO(2))(3)Cit(2). ESI-MS studies on solutions of varying uranyl(VI)/citrate ratios, pH, and solution counteranion were successfully used to confirm complex stoichiometries. Uranyl and citrate concentrations investigated ranged from 0.50 to 50 mM.

The potential of organic (electrospray- and atmospheric pressure chemical ionisation) mass spectrometric techniques coupled to liquid-phase separation for speciation analysis

The use of mass spectrometry based on atmospheric pressure ionisation techniques (atmospheric pressure chemical ionisation, APCI, and electrospray ionisation, ESI) for speciation analysis is reviewed with emphasis on the literature published in and after 1999. This report accounts for the increasing interest that atmospheric pressure ionisation techniques, and in particular ESI, have found in the past years for qualitative and quantitative speciation analysis. In contrast to element-selective detectors, organic mass spectrometric techniques provide information on the intact metal species which can be used for the identification of unknown species (particularly with MS-MS detection) or the confirmation of the actual presence of species in a given sample. Due to the complexity of real samples, it is inevitable in all but the simplest cases to couple atmospheric pressure MS detection to a separation technique. Separation in the liquid phase (capillary electrophoresis or liquid chromatography in reversed phase, ion chromatographic or size-exclusion mode) is particularly suitable since the available techniques cover a very wide range of analyte polarities and molecular mass. Moreover, derivatisation can normally be avoided in liquid-phase separation. Particularly in complex environmental or biological samples, separation in one dimension is not sufficient for obtaining adequate resolution for all relevant species. In this case, multi-dimensional separation, based on orthogonal separation techniques, has proven successful. ESI-MS is also often used in parallel with inductively coupled plasma MS detection. This review is structured in two parts. In the first, the fundamentals of atmospheric pressure ionisation techniques are briefly reviewed. The second part of the review discusses recent applications including redox species, use of ESI-MS for structural elucidation of metal complexes, characterisation and quantification of small organometallic species with relevance to environment, health and food. Particular attention is given to the characterisation of biomolecules and metalloproteins (metallothioneins and phytochelatins) and to the investigation of the interaction of metals and biomolecules. Particularly in the latter field, ESI-MS is the ideal technique due to the softness of the ionisation process which allows to assume that the detected gas-phase ions are a true representation of the ions or ion-biomolecule complexes prevalent in solution. It is particularly this field, important to biochemistry, physiology and medical chemistry, where we can expect significant developments also in the future.

Electrospray ionization mass spectrometry in studies of aluminium(III)-ligand solution equilibria

Electrospray ionization mass spectrometry (ESI-MS) has been applied to the study of solution equilibria between Al(III) and the two ligands 4-hydroxy-3-pyridinecarboxylic acid (4H3P) and 3-hydroxy-4-pyridinecarboxylic acid (3H4P). The results compare well with the speciation data obtained from potentiometric, UV-visible spectroscopy, and NMR measurements. This agreement suggests the applicability of ES-MS to the study of more complicated aluminium-ligand systems.