Fe+ chemical ionization of peptides

Laser-desorbed peptide neutral molecules were allowed to react with Fe⁺ in a Fourier transform mass spectrometer, using the technique of laser desorption/chemical ionization. The Fe⁺ ions are formed by laser ablation of a steel target, as well as by dissociative charge-exchange ionization of ferrocene with Ne⁺. Prior to reaction with laser-desorbed peptide molecules, Fe⁺ ions undergo 20–100 thermalizin collisions with xenon to reduce the population of excited-state metal ion species. The Fe⁺ ions that have not experienced thermalizing collisions undergo charge exchange with peptide molecules. Iron ions that undergo thermalizing collisions before they are allowed to react with peptides are found to undergo charge exchange and to form adduct species [M + Fe⁺] and fragment ions that result from the loss of small, stable molecules, such as H₂O, CO, and CO₂, from the metal ion-peptide complex.     

Redox Reactions of Quercetin and Quercetin-5'-sulfonic Acid with Fe3 + and Cu2 + Ions and with H2O2

Redox reactions of quercetin and quercetin-5'-sulfonic acid with Fe^{3 +} and Cu^{2 +} ions and with H₂O₂ were studied spectrophotometrically. Oxidation of the flavonoids occurs at the 3-OH and 4-OH groups. The redox reactions are largely influenced by pH. With Fe^{3 +} ions, oxidation occurs in strongly acidic (pH 1-2), and with Cu^{2 +} ions, in weakly acidic (pH 4-5) solutions. Oxidation of quercetin and quercetin-5'-sulfonic acid with Fe^{3 +} and Cu^{2 +} ions is accompanied by complexation. Hydrogen peroxide oxidizes the flavonoids at pH 1-3.5, and at pH > 4 oxidation is insignificant.     

Theoretical and Experimental Study of Complex Ions from Reactions of Al+ (Cu+) with Amine Molecules

The gas phase reactions of metal ions (Al⁺, Cu⁺) with amine molecules [CH₃NH₂=MA, (CH₃)₂NH=DMA] were investigated using a laser ablation‐molecular beam method. The directly associated product complex ions,Al⁺‐MA and Al⁺‐DMA, and the dehydrogenation product ions, Cu⁺(CH₂NH) and Cu⁺(C₂H₅N), as well as hydrated ion Cu⁺(NC₂H₅·H₂O), have been obtained and recorded from the reactions of the metal ions and organic amine molecules, and density functional theory (B3LYP) calculations have been performed to reveal the optimized geometry, energetics, and reaction mechanism of the title reactions with basis set 6‐311+G(d,p) adopted.     

Chiral discrimination of β‐3‐homo‐amino acids using the kinetic method

Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu²⁺ and Ni²⁺) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [Cu^I(ref)(A)]⁺. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

Retention Characteristics of Co+3, Fe+3, and Cu+2 4-(2-Pyridylazo)Resorcinol (PAR) Complexes on C-18 and Amino Silica Packings

Abstract

Chloroform extraction of Co-PAR, Fe-PAR, and Cu-PAR complexes in a pH 6.5 phosphate buffer implied the first two species were primarily monoanions, but the latter was a dianion. Examination of the literature and retention data of these complexes on C-18 and amino columns confirmed the more anionic nature of Cu-PAR. The Co⁺³ and Cu⁺² complexes were slightly resolved from each other, but the Fe⁺³ complex was retained longer on the C-18 silica. In contrast, the Co⁺³ and Fe⁺³ complexes were not resolved, but the Cu⁺² complex was well-retained on the weak anion exchange amino silica column. Use of short amino and C-18 columns in series provided a good separation of all three complexes. Detection of the metal complexes at 546 nm instead of 254 nm avoided interference by PAR and good detection limits were still maintained.     

SIFT studies of the reactions of H3O+, NO+ and O+2 with a series of volatile carboxylic acids and esters

We report the results of a selected ion flow tube (SIFT) study of the reactions of H₃O⁺, NO⁺ and O⁺₂ with some nine carboxylic acids and eight esters. We assume that all the exothermic proton transfer reactions of H₃O⁺ with all the acid and esters molecules occur at the collisional rate, i.e. the rate coefficients, k, are equal to k_c; then it is seen that k values for most of the NO⁺ and O⁺₂ reactions also are equal to or close to k_c. The major ionic products of the H₃O⁺ reactions with both the acids and esters are the protonated parent molecules, MH⁺, but minor channels are also evident, these being the result of H₂O elimination from the excited (MH⁺)1 in some of the acid reactions and an alcohol molecule elimination (CH₃OH or C₂H₅OH) in some of the ester reactions. The NO⁺ reactions with the acids and esters result in both ion-molecule association producing NO⁺M in parallel with hydroxide ion (OH⁻) transfer with some of the acids, and parallel methoxide ion (CH₃O⁻) and ethoxide ion (C₂H₅O⁻) transfer as appropriate with some of the esters. The O⁺₂ reactions proceed by dissociative charge transfer with the production of two or more ionic fragments of the parent molecules, the different isomeric forms of both the acid and the ester molecules resulting in different product ions.     

Catalytic concept of mineralizing effects

The subject of this work is the mechanism of phase transformations and chemical reactions of pure aluminas and kaolinite doped by Cu^{2 +}, Mn^{3 +}/Mn^{2 +} and Fe^{3 +}/Fe^{2 +} ions. Accelerated phase transformations of metastable aluminas and mullite formation of metal doped samples are explained by catalytic mechanism in terms of Jahn-Teller effect.     

Novel method for [M + Cu]+ ion formation by matrix-assisted laser desorption ionization

Direct deposition of a MALDI sample onto a copper sample stage and irradiation with UV light (337 nm) produces copper adduct ions of both the matrix and analyte molecules. This technique for introducing Cu⁺ into the gas-phase avoids suppression of ion signal that accompanies addition of metal salts to the sample solution. We observe good correlation between the number of basic residues in peptides and the number of Cu⁺ ions that add to the peptide. For example, the peptide KRQHPG contains three basic residues and forms ions with up to three Cu⁺ adducts. Postsource decay experiments demonstrate that for arginine containing peptides, arginine anchors the Cu⁺ ion. That is, all metastable ions contain the arginine complexed to Cu⁺ and the only immonium ion observed is that of arginine–Cu⁺. In addition, preliminary calculations indicate that guanidine has the highest Cu⁺ ion affinity followed by histidine.     

Influence of transition metal ions on the textural properties of alumina and aluminasilicates

Accelerated phase transformations and chemical reactions of metastable aluminas and kaolinite, doped with Cu^{2 +}, Mn^{3 +}/Mn^{2 +} and Fe^{3 +}/Fe^{2 +} ions, are accompanied with accelerated decrease of surface area and pore volume values. The phenomena in metal ion doped samples are explained by a catalytic mechanism, in terms of the Jahn-Teller effect. This revised version was published online in June 2006 with corrections to the Cover Date.     

An Electrochemiluminescence Assay Based on the Interactionof Diaminotoluene Isomers with Gold(I) and Copper(II) Ions

A novel assay for the determination of 2,4- and 3,4-diaminotoluene (DAT) isomers based on the low-level electrochemiluminescence (ECL) reaction of these molecules with the group IB transition metal ions Au⁺and Cu⁺², respectively, in aqueous solution is described. DAT isomers were screened for ECL against a repertoire of 32 metals, including metal ions such as Cu⁺², Eu⁺³, Mg⁺², Ru⁺³, and Tb⁺³associated with other known ECL complexes, at 1:3 added metal ion:ligand molar ratios. The 1:3 molar ratio presumed tris-bidentate octahedral metal coordination complex formation, which generally yielded optimal ECL intensity. The apparent specificity of Au⁺for 2,4-DAT and Cu⁺²for 3,4-DAT, as indicated by ECL measurements, may be partly based on ionic size as Au⁺has nearly twice the ionic diameter of Cu⁺²and thus may form a coordination complex with themeta,but not theorthoDAT. Other DAT isomers were screened and exhibited mildly enhanced ECL with various metal ions, including group IB transition metal ions, but these ECL enhancements were not statistically significant. In some cases, titration of DAT ligands with Cu⁺²and Au⁺over broad concentration ranges produced nonlinear ECL response curves. Despite low-level ECL, sensitivities in the ppm range for Au⁺, Cu⁺², and their respective DAT isomers were achieved. Time dependence was observed for some of the ECL reactions, including the Ru(III)–bipyridine model system, in which the ECL intensity grew markedly over several hours. No ECL enhancements over background were observed with two dinitrotoluene isomers or an aminonitrotoluene screened against the same set of 32 metals. This novel ECL approach may have applications in the determination of some aminoaromatics from degradation of explosives (e.g., TNT) as well as detection and quantitation of various transition metals in industrial wastewater streams and groundwater supplies. In terms of fundamental science, the present data are probably of interest as an example of size-dependent molecular recognition of metal ions which can be detected by ECL.     

A pyrene-based dual chemosensor for colorimetric detection of Cu2+ and fluorescent detection of Fe3+

A pyrene based chemosensor was designed and synthesized. The pyrene fluorophore was connected with a pyridine unit through a Schiff base structure to give the sensor (L). L was tested with a variety of metal ions and exhibited high colorimetric selectivities for Cu²⁺ and Fe³⁺ over other ions. Upon binding with Cu²⁺ or Fe³⁺, L showed an obvious optical color change from colorless to pink for Cu²⁺ or orange for Fe³⁺ over a wide pH range from 3 to 12. Moreover, the fluorescence of L at 370 nm decreased sharply after bonding with Fe³⁺, while other metal ions including Cu²⁺ had no apparent interference. Thus, using such single chemosensor, Cu²⁺ and Fe³⁺ can be detected independently with high selectivity and sensitivity. The limits of detection toward Cu²⁺ and Fe³⁺ were 8.5 and 2.0 μM, respectively. DFT calculation results also proved the formation of stable coordination complexes and the phenomenon of fluorescence quenching by Fe³⁺. Furthermore, L was also successfully used as a bioimaging reagent for detection of Fe³⁺ in living cells.     

A Dinuclear Ruthenium(II) Complex as a One‐ and Two‐Photon Luminescent Probe for Biological Cu2+ Detection

A new dinuclear Ru^II polypyridyl complex, [(bpy)₂Ru(H₂bpip)Ru(bpy)₂]⁴⁺ ( RuH₂bpip , bpy=2,2‐bipyridine, H₂bpip=2,6‐pyridyl(imidazo[4,5‐f][1,10]phenanthroline), was developed to act as a one‐ and two‐photon luminescent probe for biological Cu²⁺ detection. This Ru^II complex shows a significant two‐photon absorption cross section (400 GM) and displays a remarkable one‐ and two‐photon luminescence switch in the presence of Cu²⁺ ions. Importantly, RuH₂bpip can selectively recognise Cu²⁺ in aqueous media in the presence of other abundant cellular cations (such as Na⁺, K⁺, Mg²⁺, and Ca²⁺), trace metal ions in organisms (such as Zn²⁺, Ag⁺, Fe³⁺, Fe²⁺, Ni²⁺, Mn²⁺, and Co²⁺), prevalent toxic metal ions in the environment (such as Cd²⁺, Hg²⁺, and Cr³⁺), and amino acids, with high sensitivity (detection limit≤3.33×10^?8 M ) and a rapid response time (≤15 s). The biological applications of RuH₂bpip were also evaluated and it was found to exhibit low cytotoxicity, good water solubility, and membrane permeability; RuH₂bpip was, therefore, employed as a sensing probe for the detection of Cu²⁺ in living cells and zebrafish.     

Study of Host-Guest Complexation of Alkaline Earth Metal Ion,Aluminum Ion and Transition Metal Ions with Crown Ethers by Fast Atom Bombardment Mass Spectrometry

Complexations of crown ethers with alkali metal ions have been investigated extensively by FAB mass spectrometry over the past decade, but very little attention has been paid to reactions of crown ethers with other classes of metal ions such as alkaline earth metal ions, transition metal ions and aluminum ions. Although fast atom bombardment ionization mass spectrometry has proven to be a rapid and convenient method to determine the binding interactions of crown ethers with metal ions, problems in reliabilities for quantitative measurements of” binding strength for the host-guest complexes have been described in the literature. Thus, in this paper, applications of FAB/MS for investigating the complexation of crown ethers with various classes of metal ions is discussed. Extensive fragmentations for neutral losses such as C₂H₄O or C₂H₄ molecules from the host-guest complexes could be observed. The reason is attributed to the energetic bombardment processes of FAB occuring in the formation of these complexes. Complexes of cyclen with metal ions also show neutral losses of C₂H₄NH molecules leading to fragment ions. Transition metal ions usually form (Crown + MCl)⁺ type of ions, alkaline earth metal ions can form both (Crown + MCl)⁺ and (Crown + MOH)⁺ type of ions. But for aluminum ions, only (Crown + Al(OH)₂)⁺ type of ions could he observed.     

Transport of metal ions through cation exchange membranes containing episulfide (or thiol) groups and/or triethylenetetramine side chains

Two types of cation exchange membranes bearing sulfonic acid groups were prepared. One membrane (EA membrane), having episulfide groups beside sulfonic acid groups, was prepared with 2,3-epithiopropylmethacrylate (ETMA)-2-acrylamide-2-methylpropane sulfonic acid (AMPS) copolymers and the another one (EA-TTA membrane) having thiol groups, triethylenetetramide (TTA) side chains, and carboxyl groups beside sulfonic acid groups was prepared by treating EA membranes with TTA in a water-1,4-dioxane mixture solution. The transport of metal ions such as K⁺, Li⁺, Ag⁺, Ca²⁺, and Cu²⁺ through the membranes was investigated. The transport rate of Ag⁺ through the EA membranes was considerably lower than those of other metal ions from solution. High selective transport of Ag⁺ from mixed solution could be observed using the EA and EA-TTA membranes. Transport of Cu²⁺ and Ca²⁺ through the EA-TTA membrane was depressed by an electrostatic repulsion between ammonium groups in the membranes and metal ions when HNO₃ or sodium ethylenediamine tetraacetate was used as receiving solution.     

Amino acid influence on copper binding to peptides: Cysteine versus arginine

Matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) and theoretical calculations [density functional theory (DFT)] were utilized to investigate the influence of cysteine side chain on Cu⁺ binding to peptides and how Cu⁺ ions competitively interact with cysteine (−SH/SO₃H) versus arginine. Results from theoretical and experimental (fragmentation reactions) studies on [M+Cu]⁺ and [M+2Cu−H]⁺ ions suggest that cysteine side chains (−SH) and cysteic acid (−SO₃H) are important Cu⁺ ligands. For example, we show that Cu⁺ ions are competitively coordinated to the −SH or SO₃H groups; however, we also present evidence that the proton of the SH/SO₃H group is mobile and can be transferred to the arginine guanidine group. For [M+2Cu−H]⁺ ions, deprotonation of the −SH/SO₃H group is energetically more favorable than that of the carboxyl group, and the resulting thiolate/sulfonate group plays an important role in the coordination structure of [M+2Cu−H]⁺ ions, as well as the fragmentation patterns.     

Synthesis, coordination properties, and analytical applications of mixed donor macrocycles containing the 1,10-phenanthroline sub-unit

The coordination properties towards different metal ions of a new class of mixed N/S-, and N/S/O-donor macrocycles containing the 1,10-phenanthroline sub-unit in the cyclic framework are reviewed. The conformational constraints imposed by the heteroaromatic fragment onto the aliphatic portion of the ring determine the coordination mode of these ligands which can stabilise low-valent Ni⁺, Pd⁺, Pt⁺, and Rh⁺ metal complexes. Structural and thermodynamic aspects of the coordination chemistry of these ligands are considered together with possible applications as building blocks in the synthesis of multi-centred systems, and as template in the construction of extended polyiodide networks. However, solution studies demonstrate the inability of these ligands to work as selective and specific fluorescent chemosensors for heavy transition and post-transition metal ions and the formation constants evaluated for the formation of 1:1 complexes with Pb²⁺, Cd²⁺, Hg²⁺, Cu²⁺, and Ag⁺ in acetonitrile are of the same order of magnitude. Nevertheless, some of these macrocyles are extremely effective to recognise Cu²⁺ or Ag⁺ over the other metal ions in transport processes, and have been successfully used as neutral ionophore in the construction of PVC-based ionselective electrodes and supported liquid membranes for analytical detection and separation, respectively, of these metal ions.     

A highly selective colorimetric sensor to Fe3+ and Co2+ in aqueous solutions

Five aromatic azo dyes with hydroxyl groups (1–5) were designed and synthesized by coupling reactions. The relationships between structures of the compounds and the spectroscopic properties were investigated. The absorption spectra of these compounds upon titration with K⁺, Ca²⁺, Al³⁺, Mg²⁺, Ni²⁺, Mn²⁺, Cd²⁺, Cr³⁺, Fe³⁺, Cu²⁺, Zn²⁺, Co²⁺, Hg²⁺, and Pb²⁺ ions in neutral aqueous solutions were reported. The results are coincident with the calculation results using the density functional theory method. The high selectivity, excellent water solubility and simple synthetic process make 1-[(2-Hydroxyl)phenylazo]-2-naphthol (5) a potential sensor for sensing Fe³⁺ and Mn²⁺ with the naked eye. 1-[(2-hydroxyl)phenylazo]-2-naphthol-6-sulfonic acid (3) shows high selectivity for the colorimetric detection of Fe³⁺ and Co²⁺ among the tested metal ions. The detection limitations of 3 for determining Co²⁺ and Fe³⁺ were calculated to be 2.8 × 10^?7 and 5.6 × 10^?7 mol/L, respectively.     

Structural,Electronic, and Optical Properties of Metallo Base Pairs in Duplex DNA: A Theoretical Insight

Using density functional theory calculations, we investigated the structural, energetic, electronic, and optical properties of recently synthesized duplex DNA containing metal‐mediated base pairs. The studied duplex DNA consists of three imidazole (Im) units linked through metal (Im‐M‐Im, M=metal) and four flanking A:T base pairs (two on each side). We examined the role of artificial base pairing in the presence of two distinctive metal ions, diamagnetic Ag⁺ and magnetic Cu²⁺ ions, on the stability of duplex DNA. We found that metal‐mediated base pairs form stable duplex DNA by direct metal ion coordination to the Im bases. Our results suggest a higher binding stability of base pairing mediated by Cu²⁺ ions than by Ag⁺ ions, which is attributed to a larger extent of orbital hybridization. We furthermore found that DNA modified with Im‐Ag⁺‐Im shows the low‐energy optical absorption characteristic of π–π*orbital transition of WC A:T base pairs. On the other hand, we found that the low‐energy optical absorption peaks for DNA modified with Im‐Cu²⁺‐Im originate from spin–spin interactions. Additionally, this complex exhibits weak ferromagnetic coupling between Cu²⁺ ions and strong spin polarization, which could be used for memory devices. Moreover, analyzing the role of counter ions (Na⁺) and the presence of explicit water molecules on the structural stability and electronic properties of the DNA duplex modified with Im‐Ag⁺‐Im, we found that the impact of these two factors is negligible. Our results are fruitful for understanding the experimental data and suggest a potential route for constructing effective metal‐mediated base pairs in duplex DNA for optoelectronic applications.     

Molecular Dynamics Simulations of Metal Ion Binding to the His‐tag Motif

In our previous study, we have observed that the chelation of various metal ions to the His‐tag motifs mostly involves the i and i+2 His residues for Ni²⁺, Cu²⁺, Zn²⁺ and Co²+. In the present study, various 200 ps molecular dynamics simulations were further conducted to investigate the chelating pathway of various metal ions to the His‐tag motif with 6 His residues (His‐tag6) and the binding affinities of these metal binding pockets towards these metal ions. The results indicate that His‐tag6 with the chelated metal ion located in positions His(2,4) or His(3,5) exhibits the strongest affinity for Ni²+ and Cu²+.K⁺ was found to be preferred to chelate in His(1,3) and His(3,5) coordinations. However, Fe³+ was found to have higher affinity towards His(1,3) and His(2,4) binding pockets. Our results also suggest that Ni²⁺ exhibits the highest binding affinity towards His‐tag6 over the other metal ions. Most of the structural variations of the His‐tag6 motif were from the Histidyl side chains during metal ion binding. In addition, there is an inverse linear correlation between the final chelated distance and the charge/volume ratio of metal ion. There is a negative correlation between the metal binding affinity and the averaged potential energy generated from the MD simulations.     

Perturbation of the intramolecular hydrogen bonds of glucose by Cu+ association

A density functional theory study of glucose and glucose–Cu⁺ complexes has been performed to investigate the changes undergone by the set of intramolecular hydrogen bonds of the neutral system upon Cu⁺ association. The geometries of the different species investigated were optimized at the B3LYP/6‐31G(d,p) level. The same level of theory was used to obtain the harmonic vibrational frequencies and to analyze the electron charge density by means of the atoms in molecules theory. We have shown that the interaction with Cu⁺ strongly perturbs the set of intramolecular hydrogen bonds of the neutral. Some of these changes are a direct consequence of the conformational changes induced by the metal, which result in the breaking of some of the existing bonds or in the formation of new ones. The most important point, however, is that the intramolecular hydrogen bonds that remain are perturbed to a different extent. In general, all hydrogen bonds in which the OH donor interacts directly with the metal cation are significantly stabilized while the remaining ones become weaker. These changes influence the relative stability of the complexes as well as its capacity to interact with other systems. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001