Guest-responsive intramolecular charge transfer of viologen-crown ether conjugate

Viologen-benzocrown ether conjugate (1) was prepared, in which a phenyl unit in benzocrown ether was incorporated into the nitrogen atom of a bypiridinium unit through a sigma bond. 1 showed a yellow color associated with an intramolecular charge transfer (CT) that responds to alkali and alkaline earth metal ions, especially to Ca²⁺.     

Combination of size selective binding ability of 18-crown-6 dissolved in aqueous phase and extractive properties of an amic acid; toward enhancement of rare earths separation

The separation of La(III), Eu(III) and Er(III) ions by an amic acid, N,N-dioctyldiglycolamic acid (HL), dissolved in carbon tetrachloride has been improved in the presence of 18-crown-6 (18C6) in aqueous phase as a selective masking agent. The interaction between the studied metal ions and 18C6 resulted a shift in the extraction curve of the studied metal ions versus pH toward higher pH region. The displacement of the extraction curves was more pronounced for lanthanum ions and was varied as La(III) > Eu(III) > Er(III). This order of complexing ability of 18C6 toward the studied ions was attributed to the size adaptation of the ions and that of the crown ether cavity. The stability constants of the lanthanide–crown ether complexes in aqueous phase were evaluated. The influence of temperature on the extraction of studied metal ions from aqueous phase in the absence and the presence of 18C6 was tested in the range 298–308 K. This investigation allowed evaluating the thermodynamic parameters associated with the extraction process and those of the complexation of cations by 18C6 in the aqueous phase.     

Steric effects as a basis for improved monovalent cation extraction selectivity in crown ethers

Incorporation into a 20-crown-6 of a bulky substituent capable of impeding cation/anion access to one face of the crown ether cavity is shown to afford compounds exhibiting good extraction selectivity for potassium ion over both alkaline earth cations (Ca²⁺, Sr²⁺) and other alkali metal ions (Na⁺, Cs⁺), an apparent result of diminished flexibility of the crown ether cavity, inhibition of the formation of extractable sandwich complexes with large cations, and the destabilizing effect of forcing charge-neutralizing counter anions to approach from one face of the crown cavity.     

The Claisen rearrangement of protonated allyl phenyl ether

Molecular protonated ions of allyl phenyl ether undergo a Claisen rearrangement both in the ion source and along the flight path. The rearranged ions undergo fragmentation, the predominat loss being ethene, and only a small contribution from loss of carbon monoxide is observed. Collision-induced dissociation spectra are used to verify the structures of the daughter ions. These spectra, together with other evidence of an acid-induced ortho rearrangement, allow a mechanism to be proposed for the ethene loss. In contrast, molecular protonated ions of propargyl phenyl ether lose exclusively carbon monoxide.     

邻氨基二苯醚类重氮盐的水解及分子内缩合反应

用邻氨基二苯醚类化合物进行重氮化水解反应制备邻羟基二苯醚类化合物, 对影响氯代邻氨基二苯醚重氮盐水解反应和分子内关环反应的因素进行了系统研究, 讨论了取代基、金属及其离子催化等对两类反应的影响规律, 揭示了在金属离子催化下, 邻氨基二苯醚类化合物重氮盐发生分子内关环反应的规律, 并推测了反应机理.     

A new cavitand ionophore bearing two rigid crown ether groups

A new cavitand (1) bearing two rigid crown ether groups has been synthesized from tetrahydroxycavitand (2). The binding properties of this cavitand towards alkali metal ions as well as ammonium ion were also examined.     

An intramolecular benzyl rearrangement of 1-(N-benzyloxycarbonylamino)alkylphosphonate diesters under electrospray ionization conditions

The mass spectrometric behavior of eleven 1-(N-benzyloxycarbonyl(Cbz)amino)alkylphosphonate diesters was studied under positive ion electrospray ionization (ESI) conditions. Their fragmentation pathways are depicted and supported by tandem mass spectrometry. Besides the common eliminations of ether, benzyl alcohol, phosphite and an ether plus benzyl alcohol from molecular ions, the title compounds show a tendency to undergo an interesting intramolecular benzyl rearrangement to yield benzylphosphonate ions. The fragmentation patterns do not depend on the substituent attached to the alpha-carbon atom.     

Radiochemical Study of Reactions of Diethylsilylium Ions with Dibutyl Ether in the Gas and Liquid Phases

Reactions of diethylsilylium ions with dibutyl ether in the gas and liquid phases were studied radiochemically. These reactions, as those with benzene and alcohols, are accompanied by partial rearrangement of diethylsilylium ions into monoethylsilylium and dimethylsilylium ions. The extent of transformations of the (C₂H₅)₂SiT⁺ ions decreases in going from benzene to dibutyl ether, which is due to the higher energy of adduct formation with the ether, compared to benzene.     

Colorimetric and fluorometric chemosensors for selective signaling toward Ca and Mg by aza-crown ether acridinedione-functionalized gold nanoparticles

The aza-crown ether acridinedione-functionalized gold nanoparticles (ACEADD-GNPs) 6 have been synthesized and investigated as a fluorescent chemosensor for metal ions. A blue shift along with an intensity enhancement of emission and color change are observed in the presence of both Ca²⁺ and Mg²⁺ ions. The enhanced fluorescence intensity is attributed to the photoinduced electron transfer (PET) suppression through space and color change of the suspension from red to blue due to shifted surface plasmon resonance (SPR) with aggregation of nanoparticles by the sandwich complexation.     

Ion-molecule reactions of oxygenated chemical ionization reagents with vincamine

The ion-molecule reactions of ions from acetone, dimethyl ether, 2-methoxyethanol, and vinyl methyl ether with vincamine were investigated. Reactions with dimethyl ether result in [M+13]⁺ and [M+45]⁺ products, reactions with 2-methoxyethanol produce [M+13]⁺ and [M+89]⁺ ions, and reactions with acetone or vinyl methyl ether ions generate predominantly [M+43]⁺ ions. Collision-activated dissociation and deuterium labeling experiments allowed speculation about the product structures and mechanisms of dissociation. The methylene substitution process was shown to occur at the hydroxyl oxygen and the phenyl ring of vincamine for dimethyl ether reactions, but the methylene substitution process was not favored at the hydroxyl oxygen for the 2-methoxyethanol reactions, instead favored at the 12 phenyl position. The reaction site is likely different for the 2-methoxyethanol ion due to its capability for secondary hydrogen-bonding interactions. For the [M+45]⁺ and [M+89]⁺ ions, evidence suggests that charge-remote fragmentation processes occur from these products. In general, the use of dimethyl ether ions or 2-methoxyethanol ions for ionmolecule reactions prove highly diagnostic for the characterization of vincamine; both molecular weight and structural information are obtained. Limits of detection for vincamine with dimethyl ether chemical ionization via this technique on a benchtop ion trap gas chromatography-tandem mass spectrometer are in the upper parts per trillion range.     

Skeletal rearrangements of protonated molecular ions of some ethers

Skeletal rearrangements are reported of protonated molecular ions in the chemical ionization mass spectra of allyl cyclohexyl ether, benzyl cyclohexyl ether, t-butyl cyclohexyl ether and dibenzyl ether.     

Recovery of perrhenate ions with a macrocellular anion exchanger based on epoxidized monoethanolamine vinyl ether, allyl glycidyl ether, and polyethyleneimine

Sorption of perrhenate ions by a new anion exchanger based on epoxidized monoethanolamine vinyl ether, allyl glycidyl ether, and polyethyleneimine was studied. It was found that the anion exchanger has a high sorption capacity for rhenium ions.     

New fluorescent benzocrown ether derivatives of tetrathiafulvalene: facile synthesis and recognition properties

Two new fluorescent crown ether derivatives of tetrathiafulvalene (TTF) (2a and 2b) were synthesized and characterized; their electrochemical response to Na⁺ ions and fluorescence properties were investigated. The mechanism of the strong fluorescence has also been explored.     

Chiral NMR discrimination of pyrrolidines using (18-crown-6)-2,3,11,12-tetracarboxylic acid

The compound (18-crown-6)-2,3,11,12-tetracarboxylic acid is shown to be an effective chiral NMR solvating agent for determining the enantiomeric excess of chiral pyrrolidines. Enantiomeric discrimination is observed in both the ¹H and ¹³C NMR spectra. The neutral amine is mixed with the crown ether in an NMR tube and a neutralization reaction between the two produces the corresponding ammonium and carboxylate ions. An association of these ions accounts for the chiral recognition. Pyrrolidines with one or two substituent groups α to the nitrogen atom are not inhibited from binding to the crown ether. Chiral discrimination was observed in the NMR spectra of pyrrolidines that have a stereogenic center α or β to the nitrogen atom. Dibasic substrates are likely converted to their diprotonated form in the presence of the crown ether, and both ammonium sites appear to associate with the crown ether moiety.     

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li⁺ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li⁺. The channels attract and enrich Li⁺ ions by up to orders of magnitude. As a result, our material sieves Li⁺ out of various common ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺ and Al³⁺. Moreover, by spontaneously enriching Li⁺ ions, it realizes an effective Li⁺/Na⁺ selectivity of 1422 in artificial seawater where the Li⁺ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.     

Synthesis and Characterization of a Novel Thermo‐Sensitive Copolymer of N‐Isopropylacrylamide and Dibenzo‐18‐crown‐6‐diacrylamide

Summary: A series of novel, thermo‐sensitive copolymers with different molar ratios of N‐isopropylacrylamide (NIPAM) and hydrophobic cis‐dibenzo‐18‐crown‐6‐diacrylamide (cis‐DBCAm) were prepared via free‐radical copolymerization. cis‐DBCAm with polymerizable end groups was successfully synthesized by reacting the corresponding amino crown ether with acryloyl chloride. The copolymers were characterized by FT‐IR and elemental analysis, and the thermo‐sensitivities of the copolymers were evaluated by measuring their lower critical solution temperatures (LCSTs) in the absence or presence of various metal ions. The results indicated that incorporation of cis‐DBCAm lowered LCSTs, and that the LCSTs of the copolymers decreased with the increase in cis‐DBCAm content in the copolymers. When the cavities of the crown ether units captured either K⁺ or Cs⁺ ions, the LCST of the respective copolymer–metal ion complex was further decreased, whereas the capture of Na⁺ or Li⁺ ions did not have a significant influence on the LCSTs of the copolymers.

Incorporation of cis‐DBCAm into PNIPAM resulted in a lower LCST. The LCST was decreased more when the cavities of the crown ether units captured K⁺ ions.     

Protonation and rearrangement of the tricyclo[4.2.2.2]dodeca-3,7,9,11-tetraene scaffold

The biplanemers 2a,b contain enol ether substructures, which permit facile protonations of the π electron system. The subsequent ether cleavage is characterized by rearrangements of the polycyclic scaffold of the carbenium ions or the electroneutral primary products. Apart from the expected products 3a and 5a, a series of unexpected ketones and diketones (4a′, 9b, 10b, 11b, and 12b) were obtained.     

Effects of functional group interactions on the gas-phase methylation and dissociation of acids and esters

Functional group interactions have been observed to affect gas-phase ion-molecule chemistry in a quadrupole ion trap mass spectrometer. Gas-phase methylation and collisionactivated dissociation reactions of a series of related acids and esters allows an evaluation of the structural factors that influence reactivity and functional group interactions of these compounds. Examination of the [M+H]⁺ or [M+15]⁺ product ions by collision-activated dissociation has provided insight into the conformations from which diacids and diesters undergo electrophilic addition. Collision-activated dissociation has provided not only more detailed information on the structures of the ions, but also the data necessary for confident mechanistic interpretation. Labeling studies were done to probe fragmentation pathways. Upon activation of the [M+CD₃]⁺ products of dimethyl maleate and dimethyl succinate, formed from reaction of the neutrals with CD₃OCD ₂ ⁺ ions, a rapid interfunctional group methyl transfer causes scrambling of the methyls prior to elimination of dimethyl ether or methanol. The [M+15]⁺ ions of dimethyl maleate are believed to lose dimethyl ether through a rate-determining 1,6-methyl transfer, whereas the [M+15]⁺ ions of dimethyl succinate eliminate methanol through a rate-determining 1,5-proton transfer.     

Observation of an unusually facile fragmentation pathway of gas-phase peptide ions: a study on the gas-phase fragmentation mechanism and energetics of tryptic peptides modified with 4-sulfophenyl isothiocyanate (SPITC) and 4-chlorosulfophenyl isocyanate (SPC) and their 18-crown-6 complexes

Various peptide modifications have been explored recently to facilitate the acquisition of sequence information. N-terminal sulfonation is an interesting modification because it allows unambiguous de novo sequencing of peptides, especially in conjunction with MALDI-PSD-TOF analysis; such modified peptide ions undergo fragmentation at energies lower than those required conventionally for unmodified peptide ions. In this study, we systematically investigated the fragmentation mechanisms of N-terminal sulfonated peptide ions prepared using two different N-terminal sulfonation reagents: 4-sulfophenyl isothiocyanate (SPITC) and 4-chlorosulfophenyl isocyanate (SPC). Collision-induced dissociation (CID) of the SPC-modified peptide ions produced a set of y-series ions that were more evenly distributed relative to those observed for the SPITC-modified peptides; y(n-1) ion peaks were consistently and significantly larger than the signals of the other y-ions. We experimentally investigated the differences between the dissociation energies of the SPITC- and SPC-modified peptide ions by comparing the MS/MS spectra of the complexes formed between the crown ether 18-crown-6 (CE) and the modified peptides. Upon CID, the complexes formed between 18-crown-6 ether and the protonated amino groups of C-terminal lysine residues underwent either peptide backbone fragmentation or complex dissociation. Although the crown ether complexes of the unmodified ([M + CE + 2H]2+) and SPC-modified ([M* + CE + 2H]2+) peptides underwent predominantly noncovalent complex dissociation upon CID, the low-energy dissociations of the crown ether complexes of the SPITC-modified peptides ([M' + CE + 2H]2+) unexpectedly resulted in peptide backbone fragmentations, along with a degree of complex dissociation. We performed quantum mechanical calculations to address the energetics of fragmentations observed for the modified peptides.     

A Bis(p-tert-butyloctahomotetraoxacalix[8]arene) Capsule with [(UO2)2(OH)2] Links and a Disordered [Rb4(H2O)4] Inner Core

p-tert-Butyloctahomotetraoxacalix[8]arene (LH⁸) reacts with uranyl nitrate hexahydrate in the presence of rubidium hydroxide to give a mixed complex that can be viewed as a tetrauranate dimer [(UO²)⁴(LH⁴)²(OH)⁴] containing four disordered rubidium ions and water molecules. Two uranyl ions are complexed in an “external” fashion by each macrocycle, each of them bound to two phenoxide groups and one ether group, as well as to two bridging hydroxide ions. The latter ensure the formation of a dimeric capsule that contains the disordered set of alkali metal ions. Apart from water molecules, the Rb⁺ ions are bound to the uranyl oxo groups directed towards the inner cavity, and to phenol and ether oxygen atoms from the macrocycle. The resulting octanuclear complex presents an unprecedented geometry evidencing the assembling potential of uranyl ions.

p-tert-Butyloctahomotetraoxacalix[8]arene (LH₈) reacts with uranyl nitrate hexahydrate in the presence of rubidium hydroxide to give a mixed complex that can be viewed as a tetrauranate dimer [(UO₂)₄(LH₄)₂(OH)₄] containing four disordered rubidium ions and water molecules. Two uranyl ions are complexed in an “external” fashion by each macrocycle, each of them bound to two phenoxide groups and one ether group, as well as to two bridging hydroxide ions. The latter ensure the formation of a dimeric capsule that contains the disordered set of alkali metal ions. Apart from water molecules, the Rb^+| ions are bound to the uranyl oxo groups directed towards the inner cavity, and to phenol and ether oxygen atoms from the macrocycle. The resulting octanuclear complex presents an unprecedented geometry evidencing the assembling potential of uranyl ions.