Anion Exchange-Adsorption on Low Capacity Anion Exchangers: Separation of Organic Acids,Amino Acids,Small Chain Peptides

Abstract

The variables that influence the retention of organic analyte anions on a macroporous, high surface area polystyrenedivinyl-benzene copolymer that is chemically modified by attaching tetraalkylammonium groups to the copolymer surface are identified and studied as a function of anion exchange capacity. A combined adsorption-anion exchange retention of the organic analyte anion is possible providing the analyte has both a hydrophophic center and an anionic charge site. As the column anion exchange capacity (0 to 173 μeq of anion exchange sites/column was studied) increases, analyte retention due to adsorption decreases and retention due to anion exchange increases. The factors influencing organic analyte anion retention by adsorption are low anion exchange capacity and mobile phase solvent composition, type of organic modifier, and pH for analytes that are weak organic acids. For anion exchange the major factors are a high anion exchange     

Non-aqueous capillary electrophoresis of p-quinone anion radicals.

The electrophoretic detection of two kinds of p-quinone anion radicals arising from the electrolysis of benzoquinone and chloranil was achieved by employing an acetonitrile medium. Sufficient dehydration of a running solution was necessary for the detection of the benzoquinone anion radical. Oxygen in the running solution also caused a serious decrease in the amount of the benzoquinone anion radical during electrophoresis. The addition of methanol as a hydrogen-donor decreased the electrophoretic mobility of the benzoquinone anion radical significantly, while that of the chloranil anion radical was little changed. This result is interpreted in terms of hydrogen-bonding interaction between the p-quinone anion radicals and methanol, reflecting the magnitude of their proton-accepting ability (benzoquinone anion radical > chloranil anion radical).     

含氮杂环类阴离子受体*

含氮杂环类阴离子受体是目前超分子阴离子识别领域研究的热点之一。此类受体具有主体结构丰富、可调节性强、识别范围广、选择性强、灵敏度高等优点。本文综述了以吡咯、吲哚、咪唑、吡唑等含氮杂环为识别基团的阴离子受体的设计原理、识别性能和机理,展望了该领域的发展方向。     

Anion-templated assembly of interpenetrated and interlocked structures

The rational development of a general anion templation strategy for the construction of a variety of interpenetrated and interlocked molecular structures based upon the coupling of anion recognition with ion-pairing is described. The success of this anion templation methodology is demonstrated with the halide anion directed assembly of a series of novel [2]pseudorotaxanes containing pyridinium, pyridinium nicotinamide, imidazolium, benzimidazolium and guanidinium threading components and anion binding macrocyclic ligands. Interlocked [2]rotaxane and [2]catenane molecular structures are also synthesised using this anion templation protocol. These interlocked structures feature unique topologically defined hydrogen bond donating binding domains that exhibit a high degree of selectivity for chloride, the templating anion. A series of rhenium(I) bipyridyl containing [2]pseudorotaxane assemblies and a [2]rotaxane further highlight the potential this strategic anion templation approach has in future chemical sensor design and fabrication.     

Exploiting the Catenane Mechanical Bond Effect for Selective Halide Anion Transmembrane Transport

The first examples of [2]catenanes capable of selective anion transport across a lipid bilayer are reported. The neutral halogen bonding (XB) [2]catenanes were prepared via a chloride template-directed strategy in an unprecedented demonstration of using XB⋅⋅⋅anion interactions to direct catenane assembly from all-neutral components. Anion binding experiments in aqueous-organic solvent media revealed strong halide over oxoanion selectivity, and a marked enhancement in the chloride and bromide affinities of the catenanes relative to their constituent macrocycles. The catenanes additionally displayed an anti-Hofmeister binding preference for bromide over the larger iodide anion, illustrating the efficacy of employing sigma-hole interactions in conjunction with the mechanical bond effect to tune receptor selectivity. Transmembrane anion transport studies conducted in POPC LUVs revealed that the catenanes were more effective anion transporters than the constituent macrocycles, with high chloride over hydroxide selectivity, which is critical to potential therapeutic applications of anionophores. Remarkably these outperform existing acyclic halogen bonding anionophores with regards to this selectivity. Record chloride over nitrate anion transport selectivity was also observed. This represents a rare example of the direct translation of intrinsic anion binding affinities to anion transport behaviour, and demonstrates the key role of the catenane mechanical bond effect for enhanced anion transport selectivity.     

Why does fluoride anion accelerate transmetalation between vinylsilane and palladium(II)-vinyl complex? Theoretical study

Transmetalation between palladium(II)-vinyl complex and vinylsilane was theoretically investigated with the DFT and MP2 to MP4 methods to clarify the reaction mechanism and the reasons why fluoride anion accelerates the Pd-catalyzed cross-coupling reaction between vinyl iodide and vinylsilane. This transmetalation occurs with a very large activation barrier (45.8 kcal/mol) and a very large endothermicity (25.6 kcal/mol) in the absence of fluoride anion, where the potential energy change resulting from the solvation effect is evident. This is consistent with the experimental fact that this cross-coupling reaction does not proceed well in the absence of fluoride anion. The effects of fluoride anion were investigated in three possible reaction courses. In the first course, fluorovinylsilicate anion is formed before the transmetalation, and it reacts with the palladium(II)-vinyl complex. In the second course, an iodo ligand is substituted for fluoride anion, and then the transmetalation occurs between the palladium(II)-fluoro-vinyl complex and vinylsilane. In the third course, fluoride anion attacks the Si center of vinylsilane in the transition state of the transmetalation between the palladium(II)-iodo-vinyl complex and vinylsilane. Our theoretical calculation suggests that fluorovinylsilicate anion is not formed in the case of trimethylvinylsilane. In the second and third cases, the transmetalation occurs with a moderate activation barrier (E(a)) and a considerably large exothermicity (E(exo)): E(a) = 25.3 kcal/mol and E(exo) = 5.7 kcal/mol in the second course, and E(a) = 12.7 kcal/mol and E(exo) = 24.8 kcal/mol in the third course, indicating that fluoride anion accelerates the transmetalation via the second and third reaction courses. The acceleration of transmetalation by fluoride anion is clearly interpreted in terms of the formation of a very strong Si-F bond and the stabilization of the transition state by the hypervalent Si center, which is induced by the fluoride anion. Our computational results show that hydroxide anion accelerates the transmetalation in a manner similar to that observed with fluoride anion. From these results, we predict that the electronegative anion accelerates this transmetalation because the electronegative group forms a strong covalent bond with the silyl group and facilitates the formation of the hypervalent Si center in the transition state.     

Structure and reactivity of benzoylnitrene radical anion in the gas phase

The open-shell benzoylnitrene radical anion, readily generated by electron ionization of benzoylazide, undergoes unique chemical reactivity with radical reagents and Lewis acids in the gas phase. Reaction with nitric oxide, NO, proceeds by loss of N2 and formation of benzoate ion. This novel reaction is also observed to occur with phenylnitrene anion, forming phenoxide. Similar reactivity was observed in the reaction between benzoylnitrene radical anion and NO2, forming benzoate ion and nitrous oxide. Electronic structure calculations indicate that the reaction has a high-energy barrier that is overcome by the energy released by bond formation. Benzoylnitrene radical anion also transfers oxygen anion to NO and NO2 as well as to CS2 and SO2. In contrast, phenylnitrene anion reacts with carbon disulfide by C+ or CS+ abstraction, forming S- or S2-. Electronic structure calculations indicate that benzoylnitrene in the ground state resembles a slightly polarized benzoate anion, but with a free radical localized on the nitrogen.     

On the interaction of electrons with betaine zwitterions

Betaine is a permanent zwitterion. The molecular betaine anion has been generated in a hybrid, infrared desorption-electron photoemission source and its photoelectron spectrum recorded. The photoelectron spectrum of the betaine anion is characteristic of a dipole bound anion, and its vertical detachment energy was measured to be 0.29+/-0.03 eV. Calculations by Rak, Skurski, and Gutowski [J. Chem. Phys. 114, 10673 (2001)] had found the betaine anion to be a dipole bound anion with a vertical detachment energy of 0.28 eV. We also measured the vertical detachment energy of deprotonated betaine to be approximately 1.9 eV.     

Electronically regulated thermally and light-gated electron transfer from anions to naphthalenediimides

Anion-induced electron transfer (ET) to π-electron-deficient naphthalenediimides (NDIs) can be channeled through two distinct pathways by adjusting the Lewis basicity of the anion and the π-acidity of the NDI: (1) When the anion and NDI are a strong electron donor and acceptor, respectively, positioning the HOMO of the anion above the LUMO of the NDI, a thermal anion → NDI ET pathway is turned ON. (2) When the HOMO of a weakly Lewis basic anion falls below the LUMO of an NDI but still lies above its HOMO, the thermal ET is turned OFF, but light can activate an unprecedented anion → (1)*NDI photoinduced ET pathway from the anion's HOMO to the photogenerated (1)*NDI's SOMO-1. Both pathways generate NDI(?-) radical anions.     

A proton-driven amino acid pump: lipophilic primary ammonium cation—crown ether complex as a new type of anion-transport carrier

A lipophilic primary ammonium cation—crown ether complex was shown to mediate effectively active and passive transport of amino acid derivatives via proton/amino acid anion cotransport as well as anion/amino acid anion countertransport. It may offer a new chemical analog to amino group-containing carrier proteins and a prototype for an anion separation membrane.     

含氮鎓阴离子受体的研究进展

含氮鎓阴离子受体是目前阴离子识别领域研究的热点之一,此类受体具有主体结构修饰的灵活性和多样性,能更好的发挥氢键、疏水作用、静电作用、π-π作用、阴离子-π作用的协同效应等优点。本文详细评述了咪唑鎓和吡啶鎓两类含氮鎓受体的设计、结构及其阴离子识别作用的研究进展。     

Anion-templated assembly of a [2]catenane

The first example of a [2]catenane structure to be synthesized using anion templation is described. The nature of the anion template is demonstrated to be crucial to the assembly process, with only chloride anion producing the [2]catenane in acceptable yield. Anion binding studies reveal a dramatic catenation effect on anion selectivity properties as compared to a noncatenated acyclic receptor.     

Tuning anion‐π interaction via halogen substituent effects in cyanuric acids and its derivatives

Several anion‐π complexes of isocyanuric acid, thioderivatives and their halogen substituted derivatives with chloride anion have been studied. The geometric and energetic features, charges transfer from chloride anion to the aromatic rings and “atoms‐in‐molecules” analysis are performed and discussed for these complexes. The results show that the strength of the anion‐π interaction between cyanuric derivatives and chloride anion can be tuned by halogen‐substituting. The localized molecular orbital energy decomposition analyses shows that, in the total interaction, exchange and electrostatic energies are the dominant stabilizing forces, and the polarization energies also make a favorable contribution. Finally, solvent effect significantly weakens the anion‐π interaction between the isocyanuric derivatives and chloride anion, especially in polar solvents. © 2015 Wiley Periodicals, Inc.     

Amide-based ligands for anion coordination

Anion recognition is an active area of research in supramolecular chemistry. The rapidly increasing amount of structural data now allows anion coordination chemistry to be formalized in terms of coordination numbers and geometries based on hydrogen-bonding interactions between the host (ligand) and the guest (anion). This Minireview targets just one class of anion receptors, namely, amide-based ligands. The structural data for a series of five anion shapes are compiled according to coordination number, and distinct commonalities are observed within a given anion topology. The results also indicate a number of similarities between the coordination of anions and transition-metal ions.     

Synthesis of an Anionic Receptor Based on Phenylhydrazone Group and Its Recognition Property for Acetate

A colorimetric anion receptor was synthesized by a simple method where the phenylhydrazone moiety was need as binding sites. The anion recognition via hydrogen-bonding interactions can be easily monitored by anion complexation induced changes in UV-vis absorption spectra. Moreover, the hydrogen bond formation between the phenylhydrazone N-H and acetate or fluoride anion was described on the basis of ^1H NMR experiments.     

High‐Fidelity Multistate Switching with Anion–Anion and Acid–Anion Dimers of Organophosphates in Cyanostar Complexes

The acid–base switching of complexes formed from anti‐electrostatic anion–anion homodimers of organophosphates and cyanostar macrocycles was investigated for the first time. High‐fidelity 2:2 complexes were selected by using suitably sized organo substituents. Reversible and direct switching occurs with triflic acid and hydroxide base. An unexpected acid⋅⋅⋅anion heterodimer was discovered with weaker picric acid, which helped reveal some of the elementary steps. Switching can also proceed in a cooperative (strong anion then weak acid) or stepwise manner (weak acid then strong anion).     

Reactions des derives du phosphore trivalent avec les composes a halogene positif—V : α-Cyano α-haloimides, α-cyano α-halolactames et phosphites d'alcoyle,phenylphosphonite de dimethyle et diphenylphosphinite de methyle

Trialkylphosphites react with α-cyano α-haloimides or lactames and generale a halophosphonium cation and a mesomeric anion. The attack at phosphorus of the cation by the oxygen anion gives a phosphorane which leads to phosphates or to alkylation products of the imide. In one case, where the phosphorus atom and the oxygen anion are sterically hindered, the attack of the cation occurs on the nitrogen atom of the anion and leads to a ketenimine.     

Conversion of MT-sulfone to a trifluoromethyl group by IF5: the application of an MT-sulfone anion as a trifluoromethyl anion equivalent

An MT-sulfone group was converted to a trifluoromethyl group by treatment with IF(5) after an alkylation reaction. Therefore, an MT-sulfone anion can be used as a trifluoromethyl anion equivalent. The formal asymmetric Michael-addition of a trifluoromethyl anion to crotonaldehyde was also performed.     

Anion induced capsular self-assemblies

Researchers world-wide have employed diverse strategies to achieve various anion binding hosts and anion induced supramolecular architectures due to the increasing appreciation of anion receptor chemistry. Intellectual discovery of molecular capsules for the recognition of different guest species has opened up a new field of research in the area of supramolecular chemistry. This feature article aims to provide an overview of the current status and recent achievements made by us and others in the last decade in the area of anion induced construction of supramolecular capsules and anion binding in molecular capsules.     

Fragmentation pathways of deprotonated amide‐sulfonamide CXCR4 inhibitors investigated by ESI‐IT‐MSn,ESI‐Q‐TOF‐MS/MS and DFT calculations

Amide‐sulfonamides provide a potent anti‐inflammatory scaffold targeting the CXCR4 receptor. A series of novel amide‐sulfonamide derivatives were investigated for their gas‐phase fragmentation behaviors using electrospray ionization ion trap mass spectrometry and quadrupole time‐of‐flight mass spectrometry in negative ion mode. Upon collision‐induced dissociation (CID), deprotonated amide‐sulfonamides mainly underwent either an elimination of the amine to form the sulfonyl anion and amide anion or a benzoylamide derivative to provide sulfonamide anion bearing respective substituent groups. Based on the characteristic fragment ions and the deuterium–hydrogen exchange experiments, three possible fragmentation mechanisms corresponding to ion‐neutral complexes including [sulfonyl anion/amine] complex ( INC‐1 ), [sulfonamide anion/benzoylamide derivative] complex ( INC‐2 ) and [amide anion/sulfonamide] complex ( INC‐3 ), respectively, were proposed. These three ion‐neutral complexes might be produced by the cleavages of S–N and C–N bond from the amide‐sulfonamides, which generated the sulfonyl anion (Route 1), sulfonamide anion (Route 2) and the amide anion (Route 3). DFT calculations suggested that Route 1, which generated the sulfonyl anion (ion c ) is more favorable. In addition, the elimination of SO₂ through a three‐membered‐ring transition state followed by the formation of C–N was observed for all the amide‐sulfonamides.