Metal ion induced FRET On-Off in naphthyl-pyrenyl pendent tetrahomodioxacalix[4]arene

A novel tetrahomodioxacalix[4]arene (7) bearing both naphthyl- and pyrenyl-amide pendants was synthesized as FRET-based fluorometric sensor for Cu²⁺ ion. Intramolecular FRET from the naphthalene emission to the pyrene absorption affords Cu²⁺ ion selectivity over other metal ions. Upon addition of Cu²⁺ ion, the complex solution of 7 gave a significantly decreased pyrene acceptor emission along with an enhancement of naphthalene donor emission via FRET On-Off event.     

新型经由三氮唑连接的含芘基团的杯[4]芳烃：对锌离子的比率荧光识别及其在组合逻辑门中的应用

通过“click”反应合成了两个新的由三氮唑连接的含芘的杯[4]芳烃。 化合物1含有两个芘单元,对Zn2+表现出比率荧光响应,且对Cu2+, Hg2+ 和 Pb2+表现出选择性的荧光淬灭;而化合物2只含一个芘单元,对铜离子有显著的荧光淬灭,对汞离子有中等程度的荧光淬灭。利用化合物1对锌离子和铜离子不同的荧光响应,设计了INH和NOR逻辑门。     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

High field asymmetric waveform ion mobility spectrometry-mass spectrometry: an investigation of leucine enkephalin ions produced by electrospray ionization

High field asymmetric waveform ion mobility spectrometry (FAIMS) provides atmospheric pressure, room temperature, low-resolution separation of gas-phase ions. The FAIMS analyzer acts as an ion filter that can continuously transmit one type of ion, independent of m/z. The combination of FAIMS with electrospray ionization and mass spectrometry (ESI-FAIMS-MS) is a powerful technique and is used in this study to investigate the cluster ions of leucine enkephalin (YGGFL). Separation by FAIMS of leucine enkephalin ions having the same m/z (m/z 556.5), [M + H]⁺ and [2M + 2H]²⁺, was observed. In addition, four complex ions of leucine enkephalin, [2M + H]⁺, [4M + 2H]²⁺, [6M + 3H]³⁺, and [8M + 4H]⁴⁺, all having m/z 1112, were shown to be separated in FAIMS. Fragmentation of ions as the result of harsh conditions within the mass spectrometer interface (FAIMS-MS) was shown to provide similar information to that obtained from MS/MS experiments in conventional ESI-MS.     

Fragmentation of protonated O,O-diethyl O-aryl phosphorothionates in tandem mass spectral analysis

The gas-phase ion chemistry of protonated O,O-diethyl O-aryl phosphorothionates was studied with tandem mass spectrometric and ab initio theoretical methods. Collision-activated dissociation (CAD) experiments were performed for the [M+H]⁺ ions on a triple quadrupole mass spectrometer. Various amounts of internal energy were deposited into the ions upon CAD by variation of the collision energy and collision gas pressure. In addition to isobutane, deuterated isobutane C₄D₁₀ also was used as reagent gas in chemical ionization. The daughter ions [M+H?C₂H₄]⁺ and [M+H?2C₂H₄]⁺ dominate the CAD spectra. These fragments arise via various pathways, each of which involves γ-proton migration. Formation of the terminal ions [M+H?2C₂H₄?H₂O]⁺, [M+H?2C₂H₄?H₂S]⁺, [ZPhOH₂]⁺, [ZPhSH₂]⁺, and [ZPhS]⁺ [Z = substituent(s) on the benzene ring] suggests that (1) the fragmenting [M+H]⁺ ions of O,O-diethyl O-aryl phosphorothionates have protons attached on the oxygen of an ethoxy group and on the oxygen of the phenoxy group; (2) thiono-thiolo rearrangement by aryl migration to sulfur occurs; (3) the fragmenting rear-ranged [M+H]⁺ ions have protons attached on the oxygen of an ethoxy group and on the sulfur of the thiophenoxy group. To get additional support for our interpretation of the mass spectrometric results, some characteristics of three protomers of O,O-diethyl O-phenyl phosphorothionate were investigated by carrying out ab initio molecular orbital calculations at the RHF/3–21G* level of theory.     

Synthesis of calix[4]arene(amido)monocrowns and their photoresponsive derivatives

A series of new calix[4]arene(amido)mono-crown compounds have been synthesized through aminolysis of calix[4]arene esters and intramolecular cyclization of the intermediates. The title compounds were converted into their nitro and azo substituted derivatives to provide novel photoresponsive molecular receptors for transition metal ions. Single crystal X-ray analysis of calix[4]arene(ethyleneamido)mono-crown (2a) revealed that the compound is present in a cone conformation with an amido loop that caps the lower rim of calix[4]arene cavity to result in stacking along axis a and axis c to provide supramolecular aggregates in the solid state. Evaluation of synthesized macrocycles in the solution phase for recognition of transition metal cations (Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Pb²⁺, Hg⁺, Hg²⁺, Pd²⁺, and Pt²⁺) by UV-visible spectroscopy revealed that p-tert-butyl-calix[4]arene mono-(amidocrown) 1c selectively shows a blue shift at 38 nm on interaction with Hg⁺ ions.     

Multiple ionization,charge separation and charge stripping reactions involving polycyclic aromatic compounds

The 70 eV electron ionization mass spectra of polycyclic aromatic compounds are characterized by the presence of relatively stable multiply charged molecular ions [M]ⁿ⁺ (n=2–4). When generated from the compounds benzene, napthalene, anthracene, phenanthrene, 2,3-benzanthracene, 1,2-benzanthracene, chrysene, 9,10-benzophenanthrene and pyrene, the relative abundances of the multiply charged ions increase dramatically with the number of rings. These compounds form multiply charged molecular ions (n=2, 3) which undergo unimolecular decompositions indicative of considerable ionic rearrangement. The main charge separation processes observed here [M]²⁺→m₁⁺+m₂⁺, [M]³⁺˙→m₃⁺+m→+m₄²⁺) involve, in almost every case, one or more of the products [CH₃]⁺, [C₂H₃]⁺˙ and [C₃H₃]⁺. This suggests the existence of preferred structures amongst the metastable parent ions. Information on the relative importance of the various fragmentation pathways is presented here along with translational energy release data. Some tentative structural information about the metastable ions has been inferred from the translational energy release on the assumption that the released energy is due primarily to coulombic repulsion within the transition state structure. For the triply charged ions these interpretations have necessitated the use of a coulombic repulsion model which takes account of an extra charge. Vertical ionization energies for the process [M]ⁿ⁺+G→[M](ⁿ⁺¹)+G+e^? (charge stripping) have also been determined where possible for n=1 and 2 and the results from these experiments allow the derivation of simple empirical equations which relate successive ionization energies for the formation of [M]²⁺ and [M]³⁺˙ to the appearance energy of [M]⁺˙.     

Interaction of angiotensin peptides and zinc metal ions probed by electrospray ionization mass spectrometry

Electrospray ionization-tandem mass spectrometry experiments were used to provide evidence regarding the sites of interactions between zinc metal ions and angiotensin peptides. The electrospray ionization mass spectra of histidine-containing human angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) and angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) in the presence of zinc show abundant multiply charged ions for the zinc-attached peptide [M + aZn²⁺ +(c ? 2a)H⁺]^c+, where a = 1, 2 and c is charge. From collisionally activated dissociation experiments, with both low energy (triple quadrupole mass spectrometry) and high energy collisions (linked scan at constant B/E with a double focusing instrument) of the [M + Zn]²⁺ and [M + Zn + H]³⁺ ions for angiotensin II, a [b ₆ + Zn]²⁺ species is produced as the most abundant product ion, suggesting that the zinc interaction site is in the vicinity of the His⁶ residue. Additionally, tandem mass spectra from the zinc-attached ions for angiotensin I show abundant [b ₆ + Zn]²⁺ and [b ₉ + Zn]²⁺ products, providing evidence that both His⁶ and His⁹ are involved in zinc coordination.     

Fluorescent chemosensor for Cu2+ ion based on iminoanthryl appended calix[4]arene

Calix[4]arene based podands 1a of cone conformation and 1b of 1,3-alternate conformation possessing imine units and bearing anthracene moieties have been synthesized by a 1 + 2 Schiff base condensation in good yields and examined for their cation recognition abilities towards cations such as lithium, sodium, potassium, nickel, cadmium, copper, zinc, lead, silver and mercury ions by UV–vis and fluorescence spectroscopy. The calix[4]arene derivative 1b shows a selective fluorescence enhancement in presence of Cu²⁺ ions among the various metal ions tested (Li⁺, Na⁺, K⁺, Ni²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Ag⁺ and Hg²⁺ ions). The colour of the solution changes from colourless to light yellow in the presence of Cu²⁺ ions. The stoichiometry of the complex formed between 1b and Cu²⁺ was found to be 1:1 as established by Job’s plot.     

Mercury(II) and silver(I) receptors based on tetrathiacalix[4]arene hydrazones

The extraction ability of phenyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards to some alkali, alkaline earth, transition and heavy metal ions has been investigated by picrate extraction method. The synthesized cone-tetrathiacalix[4]arene hydrazones show a high efficiency coupled with an excellent selectivity towards for Ag⁺ and Hg²⁺ ions. The stoichiometry of complexes and the extraction constants have been determined. The influence of calix[4]arene platform’s structure and the electron donor substituents in phenyl fragments on the extraction efficiency has been discussed.     

Chromened t-butylcalix[4]arenes: cooperation effect of chromene and calixarene moieties on photochromism and metal-ion binding ability

Novel t-butylcalix[4]arenes bearing several chromene molecules were synthesized, and their photochromism and metal-ion binding ability were examined with alkali and alkaline-earth metal ions. While the metal-ion binding ability of the t-butylcalix[4]arene moiety facilitated the photoisomerization of the chromene moiety to a great extent, the chromene moiety influenced the metal-ion binding ability of the t-butylcalix[4]arene moiety through lariat effect. Therefore, the metal-ion that induced the most facilitated photoisomerization of the chromene moiety was shifted drastically from Li⁺ to Ba²⁺ with the increase of the incorporated chromene number. Even without metal ions, the interaction among the chromene moieties derived from the cone-conformation of the t-butylcalix[4]arene moiety also facilitated the photoisomerization.     

Supramolecular self-assemblies of stereoisomers of p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim with some metal cations

Novel p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups at the lower rim in cone, partial cone and 1,3-alternate conformations were synthesized and their receptor properties toward metal ions of p- (Al³⁺, Pb²⁺) and d- (Fe³⁺, Co³⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺) elements were investigated by picrate extraction and dynamic light scattering (DLS). It was shown that the p-tert-butyl thiacalix[4]arenes functionalized with hydrazide groups are effective extractants of soft metal cations. The complex stoichiometry depended on the receptor configuration. All the p-tert-butyl thiacalix[4]arene derivatives with hydrazide fragments were able to form nanoscale aggregates but did not show self-association abilities.     

Fragmentation of protonated O,O-dimethyl O-aryl phosphorothionates in tandem mass spectral analysis

A study was carried out on the fragmentation of 12 protonated O,O-dimethyl O-aryl phosphorothionates by tandem quadrupole mass spectrometry. Some of the studied compounds are used in agriculture as pesticides. Energy-resolved and pressure-resolved experiments were performed on the [M + H]⁺ ions to investigate the dissociation behavior of the ions with various amounts of internal energy. On collisionally activated dissociation, the [M + H]⁺ ions decompose to yield the [M + H ? CH₃OH]⁺, (CH₃O)₂PS⁺ (m/z 125), and (CH₃O)₂PO⁺ (m/z 109) ions as major fragments. The ions [M + H ? CH₃OH]⁺ and (CH₃O)₂PS⁺ probably arise from the [M + H]⁺ ions of the O,O-dimethyl O-aryl phosphorothionates with the proton on the sulfur or on the oxygen of the phenoxy group. The origin of the hydroxy proton of the methanol fragment was in many cases, surprisingly, the phenyl group and not the reagent gas. This was confirmed by using deuterated isobutane, C₄D₁₀, as reagent gas in Cl. The fragment ions (CH₃O)₂PO⁺ and [ZPhS]⁺ are the results of thiono-thiolo rearrangement reaction. The precursor ion for the ion (CH₃O)₂PO⁺ arises from most compounds upon chemical ionization, whereas the precursor ion for the ion [ZPhS]⁺ arises only from a few compounds upon chemical ionization. The observed fragments imply that several sites carry the extra proton and that these sites get the proton usually upon ionization. The stability order and some characteristics of three protomers of O,O-dimethyl O-phenyl phosphorothionate were investigated by ab initio calculations at the RHF/3-21G* level of theory.     

Study of adduct ions of meso-phenyl-substituted tetrabenzoporphyrins by fast-atom bombardment mass spectrometry

Mass spectra of meso-phenyl-substituted tetrabenzoporphyrins were investigated by fast-atom bombardment mass spectrometry and tandem mass spectrometry. A cluster of adduct ions with mass-to-charge ratio values higher than the corresponding molecular ions of the porphyrins has been observed. The mass number differences among the series of cluster ions are constant depending on the para-phenyl substituents. Under certain conditions, dimers or trimers of molecular ions with low abundances have been detected. To trace the origin of the adduct ions, a series of experiments based on mass spectrometry have been carried out. The mass spectrum of tetrabenzoporphyrin showed no adduct ions with mass number differences of 90 even with the addition of phenylacetic acid. The mass spectrum of meso-tetraphenylte-trabenzoporphyrin ¹³C-labeled at the meso carbons showed adduct ions with mass number differences of 91. Product spectra of [2M + H]⁺ or [3M + H]⁺ of porphyrins exhibited adduct ions. All these results suggest that fragmentations of [2M + H]⁺ or [3M + H]⁺ may be one of the many possible routes to form the adduct ions, and the mass number differences among the series of these cluster ions should correspond to the benzyl group from the meso positions of meso-phenyl-substituted tetrabenzoporphyrins.     

Gas-phase reactivity and molecular modeling studies on triply protonated dodecapeptides that contain four basic residues

Gas-phase deprotonation and hydrogen/deuterium (H/D) exchange reactions for ions from three model dodecapeptides were studied by Fourier transform ion cyclotron resonance mass spectrometry. Molecular dynamics calculations were employed to provide information on conformations and Coulomb energies. The peptides, (KGG)₄, (K₂G₄)₂, and K₄G₈, each contain four high basicity lysine residues and eight low basicity glycine residues; however, in the present work only three lysine residues were protonated. Proton transfer reactions with a series of reference amines revealed apparent gas-phase acidities in a narrow range of 207. 3–209. 6 kcal/mol, with deprotonation efficiencies following the order [K₄G₈+3H]³⁺ > [(KGG)₄+3H]³⁺ > [(K₂G₄)₂+3H]³⁺. The three ions also react similarly with d ₄-methanol: each exchanged a maximum of 23–25 of their 25 labile hydrogens, with the first 15–17 exchanges occurring at rate constants of (1. 6–2. 6) × 10^?11 cm³ molecule^?1 s^?1. The experimental results agree with molecular modeling findings of similar conformations and Coulomb energies for the three peptide ions. The [M+3H]³⁺ data are compared to data obtained previously in our laboratory for the “fully” protonated [M+4H]⁴⁺ (Zhang, X.; Ewing, N. P.; Cassady, C. J. Int. J. Mass Spectrom. Ion Phys., in press). For (KGG)₄ and (K₂G₄)₂, there is a marked difference in H/D exchange reactivity between 3+ ions and 4+ ions. The 4+ ions, which have diffuse conformations, slowly exchange only 14 hydrogens, whereas their more compact 3+ counterparts exchange 23–25 hydrogens at a 5-times greater rate. In contrast, the 3+ and 4+ ions of K₄G₈ have similar compact conformations and exchange reactivity. The results indicate that a multiply hydrogen-bonded intermediate between the deuterating reagent and the peptide ion is necessary for facile H/D exchange. The slower, incomplete H/D exchange of [(KGG)₄+4H]⁴⁺ and [(K₂G₄)₂+4H]⁴⁺ is attributed to the inability of their protonated lysine n-butylamino groups (which extend away from the peptide backbone) to form this intermediate.     

Synthesis,supramolecular complexation and DFTstudies of a bis(pyrene)-appended ‘capped’ triazole-linked calix[4]arene as Zn2+ and Cd2+ fluorescent chemosensors

ABSTRACT

A new bimodal triazole-bridged pyrene-appended calix[4]arene 2g has been synthesised and characterised and complexation studies showed that the binding of Cd²⁺ and Zn²⁺ occurs as demonstrated by enhanced monomer and declining excimer emission fluorescence spectral changes. With several other metal ions, quenching of both monomer and excimer emissions occurred. The observed monomer formation in the fluorescence spectra seen with Zn²⁺ and Cd²⁺ is possibly linked not just to the diminished parallel orientations of the pyrene rings but with the magnitude of the resulting HOMO-LUMO gaps and other parameters measured by DFT calculations.     

Effect of p-tert-butylcalix[4]arene fitted with phosphinoyl pendant arms as synergistic agent in the solvent extraction of trivalent lanthanoids with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione and structural study of solid complexes by IR,NMR and X-ray

The synergistic solvent extraction of five selected lanthanoid ions (La³⁺, Nd³⁺, Eu³⁺, Ho³⁺ and Lu³⁺) with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (HL) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl₃ has been studied. It was found that in presence of this phosphorus-containing calix[4]arene the lanthanoid ions have been extracted as [LnL₃S₂]. The values of the equilibrium constants and the separation factor have been calculated. The influence of the synergistic agent on the extraction process has been discussed.     

Combining Ion Mobility Spectrometry with Hydrogen-Deuterium Exchange and Top-Down MS for Peptide Ion Structure Analysis

The gas-phase conformations of electrosprayed ions of the model peptide KKDDDDIIKIIK have been examined by ion mobility spectrometry (IMS) and hydrogen deuterium exchange (HDX)-tandem mass spectrometry (MS/MS) techniques. [M+4H]⁴⁺ ions exhibit two conformers with collision cross sections of 418 Ų and 471 Ų. [M+3H]³⁺ ions exhibit a predominant conformer with a collision cross section of 340 Ų as well as an unresolved conformer (shoulder) with a collision cross section of ~367 Ų. Maximum HDX levels for the more compact [M+4H]⁴⁺ ions and the compact and partially-folded [M+3H]³⁺ ions are ~12.9, ~15.5, and ~14.9, respectively. Ion structures obtained from molecular dynamics simulations (MDS) suggest that this ordering of HDX level results from increased charge-site/exchange-site density for the more compact ions of lower charge. Additionally, a new model that includes two distance calculations (charge site to carbonyl group and carbonyl group to exchange site) for the computer-generated structures is shown to better correlate to the experimentally determined per-residue deuterium uptake. Future comparisons of IMS-HDX-MS data with structures obtained from MDS are discussed with respect to novel experiments that will reveal the HDX rates of individual residues. Graphical Abstract

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Ion-molecule reactions in the gas phase. part XXII. Reactivity of the cis- and trans-indanediols with dimethyl ether ions

Specific reactivity of cis- and trans-indanediols has been investigated under dimethyl ether (DME) chemical ionization conditions. Several unusual species, such as [M + 29]⁺ and [M + 27]⁺ ions, are produced in high yield. From DME pressure variations and tandem mass spectrometry experiments (low-energy collisions with Ar and NH₃) including some labeled compounds, it appears that [M + 29]⁺ ions are generated by nucleophilic substitution according to a S_Ni pathway from the proton bound[M + DMEH]⁺ adduct ion. On the other hand, [M + 27]⁺ ions are produced from the covalent [M + DME ? H]⁺ adduct ions via a stepwise process inducing a water loss. This latter dehydration occurs from the adducts prepared by [DME ? H]⁺ attachment to the homobenzylic hydroxy site, which allows internal proton transfer from the charged position to the benzylic hydroxy group, promotingthe loss of water. In addition, trans indanediol labeled with ¹⁸O has been used to obtain evidence for the regioselectivity of both water-loss mechanisms from the benzylic site.     

Structural determination of oxofatty acids by charge-remote fragmentations

A strategy is described to locate the carbonyl position in oxofatty acids by utilizing charge-remote fragmentations of various molecular ions that are desorbed by fast atom bombardment (FAB). Oxofatty acids were cationized with alkali metal ions (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) to form [M+2Met?H]⁺ or alkaline earth metal ions (Mg²⁺, Ca²⁺, Sr²⁺ or Ba²⁺) to form [M+Met?H]⁺ in the gas phase. The cationized acids undergo charge-remote fragmentations upon high-energy activation, giving a product-ion pattern that has a gap corresponding to the oxo position and bordered by two high-intensity peaks. One of the peaks corresponds to an ion that is formed by the cleavage of the C-C bond β to the oxo position and proximal to the charge (β ion), whereas the other is formed from the cleavage of the C-C bond γ to the oxo position and distal to the charge (γ′ ion). The oxo position is easily determined by identifying the gap and the β and γ′ ions. Furthermore, there are two competing patterns of fragments in a CAD spectrum of an oxofatty acid or ester [M+Li]⁺ ion. These arise because Li⁺ attaches to either the oxo or the carboxylic end, as was confirmed by ab initio molecular orbital calculations. The results demonstrate that control of the fragmentation can be guided by an understanding of metal-ion affinities. Collisional activation of the anionic carboxylates gives results that are similar to those for positive ions, showing that the process is not related to the charge status. Collisional activation of [M+H]⁺ ions does not give structural information because the charge migrates, leading to charge-mediated fragmentations.