Ammonium Guests Research Articles

Ab Initio Study of Conformers of p-tert-Butylcalix[4]crown-6-ether Complexed with Alkyl Ammonium Cations

The structures and energies of p-tert-butylcalix[4]crown-6-ether(1) in various conformers and their alkyl ammonium complexes have been calculated by ab initio HF/6-31G quantum mechanics method. We have tried to obtain the relative affinity of partial-cone and 1,3-alternate conformers of 1 for alkyl ammonium guests by comparison with its cone-shaped analogue. We have also calculated the relative complexation efficiency of these host-guest complexes focusing on the binding sites of <TEX>$crown-\sigma-enther$</TEX> moiety or benzene-rings pocket of the host molecule 1. These calculations revealed that the crown moiey has better complexation efficiency than upper rim part of calyx[4]arene that is in similar trend to the cone-shaped complexes.

Enantioselective complexation of chiral linear hosts containing monosaccharide moieties with chiral organic amines

New chiral linear hosts ( 1– 3 , a : peracetylated derivatives, b : permethylated derivatives) containing monosaccharide end groups were designed on the basis of the structural features of permethylated 1 F-fructonystose (MeFruNys), which shows a remarkable chiral discrimination ability, and then synthesized. The chiral discrimination ability of their hosts toward chiral organic ammonium guests were evaluated using FAB mass spectrometry and 1H NMR. Their hosts showed chiral discrimination for some guests. As the contrasting compounds ( 4 and 5 ) hardly showed any chiral discrimination, it was clarified that the structural features extracted from MeFruNys are very significant factors for chiral recognition. The 1H NMR shift induced by adding a potassium ion (counter anion: SCN −) in (CD 3) 2CO suggested that the cation moiety of the chiral guests was located at the binding site consisting of the –O–C–C–O– units and the ring-oxygens of the saccharide moieties. The structure of the complex of host 1b with 1-(1-naphthyl)ethylammonium ion (NEA +) was estimated by the 1H NMR induced shifts and the molecular dynamics simulation.

Synthesis and Binding Properties of iiii (4i) Stereoisomers of Phosphonato Cavitands − Cooperative Effects in Cation Complexation in Organic Solvents

Syntheses and host-guest properties of tetrabridged phosphorylated cavitands in their iiii (4i) configurations are described. The tetraphosphonato cavitands 2 and 3, with the four P=O bonds oriented inwards (4i stereoisomer) were prepared in 25% and 53% yields respectively, from the corresponding resorc[4]arenes, dichloro(phenyl)phosphane oxide and base. The formation of the 4i stereoisomers is solvent-dependent and is attributable to the capability of an ammonium guest to form an inclusion complex. Only the iiio (3io) stereoisomer of 3 was isolated otherwise, in low yield. These phosphonato cavitands, in their 4i configurations, are particularly efficient extractants for metal ions. The free energies of complexation of 3 with alkali metal and ammonium cations in chloroform solution are in the range from −43.3 (Li+) to −52.4 kJ mol−1 (CH3NH3+). High binding constants, 1H, 31P and 133Cs NMR studies in solution and single-crystal X-ray analysis clearly demonstrated that the aromatic cavity of the host and the four hard donor P=O groups act cooperatively to ensure the encapsulation of the cationic guests. In the solid, the 2·Cs+ complex showed the Cs+ ion inside the aromatic cavity, interacting strongly with the four phosphoryl groups. The 2·CH3NH3+ complex showed the methyl group of the guest oriented inside the cavity, with the stability of the complex supported by a complex H bond pattern involving H2O molecules and the anion.

Squaramide as a binding unit in molecular recognition

Urea and squaramide are used as building blocks of powerful hosts which are involved in the molecular recognition of quaternary ammonium guests. Complexes of urea and squaramide with ammonium cations were studied using both high level MP2/6-311+G** ab initio and molecular interaction potential with polarization and MEP calculations, in order to explore the physical nature of the interactions. The same procedure was applied to ammonium complexes with water and benzene as prototype models of crown ethers and calixarenes. Our findings reveal that either urea or squaramide are better binding units for the recognition of ammonium cations than water or benzene.

Synthesis of a novel cage-functionalized chiral binaphthol host: a potential new agent for enantioselective recognition of chiral ammonium salts

Optically active, cage-functionalized crown ether (R)-3 which contains a 1,1′-bi-2-naphthol moiety has been prepared. Subsequently, the ability of (R)-3 to selectively recognize the enantiomers of guest ammonium salts, i.e., 4 and 5 in transport experiments was studied. Host (R)-3 displays significantly enhanced enantiomeric selectivity toward complex formation with 4 vis-à-vis complex formation with 5. The relative energetics of various relevant host–guest complexes have been investigated computationally.

Amphiphilic Cup-Shaped [(4-Alkylphenyl)azo]-Substituted Calixarenes: Self-Assembly and Host−Guest Chemistry at the Air−Water Interface

Chromophoric, amphiphilic [(4-alkylphenyl)azo]-substituted calixarenes 1−4 form stable monolayers at the air−water interface of a Langmuir trough. Monolayer limiting areas and collapse pressures are controlled with changes in pH and electrolyte concentration of the subphase. At pH = 8.2 or higher, deprotonation of the hydroxyls of the calixarene produces more polar headgroups, which result in larger mean molecular areas and increases in film collapse pressures. Similar effects result from increasing the concentration of electrolyte in the subphase. Effects of potential guests on monolayer assembly of [(4-alkylphenyl)azo]-substituted calixarenes at the air−water interface were investigated. The limiting area of tetrakis[(4-octylphenyl)azo]calix[4]arene decreases in the presence of N,N,N-trimethylanilinium iodide while no change is detected for tetramethylammonium iodide or N,N,N-trimethyl-N-(2-naphthyl)ammonium iodide. Interactions of the amphiphilic calixarenes and potential ammonium guests are discussed.

Thermodynamic and NMR studies of solvent effect on enantiomeric recognition for chiral organic ammonium guests by chiral diketopyridino-18-crown-6 type ligands at 25.0°C

Abstract Three chiral diketopyridino-18-crown-6 type macrocycles have been shown to exhibit a high degree of enantiomeric recognition toward α-(1-naphthyl)ethylammonium perchlorate (NapEt) in various ratios of chloroform/methanol (CDCl3/CD3OD) and 1,2-dichloroethane/methanol (C2H4Cl2/CH3OH) solvent mixtures (from 100% to 10% methanol component). In most cases, differences in log K values (Δlog K) for (R)− and (S)-NapEt complexation with the chiral macrocycles are larger than 0.5. The degree of the enantiomeric recognition indicated by the Δlog K value changes noticeably with the binary solvent components. The recognition is better in the solvents having a moderate methanol component than in the binary solvents having either a high or a low methanol component. The highest degree of recognition is observed in 6/4 (v/v) CDCl3/CD3OD and C2H4Cl2/CH3OH solvent mixtures and in a 7/3 (v/v) C2H4Cl2/CH3OH mixture for chiral (S,S)-1 macrocycle. Thermodynamic parameters determined in solvent mixtures of C2H4Cl2/CH3OH...

Molecular recognition of alkyl- and arylakyl-amines in dischloromethane and chloroform by calix[4]-crown ethers

The calix[4]-crown-6 ether 2 exhibited pronounced molecular recognition properties toward alkylamines. –ΔG° values obtained for the solvent extraction of alkylamines into dichloromethane by compound 2 ranged up to 9.7. kcal mol–1. This binding strength generally decreased with the increasing size of the alkyl chain of the ammonium guest. 1H NMR titrations of compound 2 with alkyl- or arylalkyl-ammonium guest in CDCl3 revealed that the primary binding site is the central part of the crown moiety. Host 2 exhibited a much larger discrimination than the dibenzo-18-crown-6 ether, favouring linear over other isomeric amines. Transport selectivity between buty- and tert-butyl-ammonium guests was found to be greater than a 70-fold excess, as assessed by the competitive transport through chloroform liquid membrane.

Induced circular dichroism detection of chiral ammonium guests through inclusion in calix[n]arene cavities

p-Sulfonatocalix[n]arenes include chiral quaternary ammonium guests in water and give the induced circular dichroism (ICD) spectra specific to the guest chirality and shape; the ICD bands arise from guest-induced asymmetric deformation of the benzene array in calix[n]arenes.

Diester-calix[4]arenediquinone complexation and electrochemical recognition of group 1 and 2, ammonium and alkyl ammonium guest cations.

The synthesis, metal, ammonium and alkyl ammonium cation coordination chemistry and electrochemical recognition studies of a new diester-calix[4]arenediquinone receptor are described.

Novel acyclic receptors for aromatic amines using peptidic frameworks

The synthesis, characteristics and recognition ability of a novel class of acyclic peptidic receptors designed to complex aromatic ammonium guests using a combination of hydrogen-bonding, electrostatic and π–π interactions is described.

Enantioselective Optode Membranes with Enantiomer Selectivity for (R)‐ and (S)‐l‐Phenylethylammonium Ions

AbstractThe recently developed general principle of ion‐selective optode membranes, based on conventional ionophores, was employed to design a new approach to the determination of enantiomeric excess. Highly lipophilic chiral crown derivatives, exhibiting a high selectivity for a chiral ammonium guest cation, are combined with a H+‐selective chromoionophore in a plasticized PVC membrane. The enantiomer recognition process is translated by this sensor with an optical transduction into a signal easily measured by a conventional spectrophotometer, and enantiomeric excess can be determined without the need for polarized light. Characteristics and a theoretical description of these new optode membranes are given.

ChemInform Abstract: Amine Selective Coloration with Chromoacerands

Amine selective complexation of some azophenol-dyed crowns with concurrent coloration and molecular structures of two sec. amine-dyed crown complexes are reported as well as selective colorations of enantiomeric amines with chiral azophenol crowns and of diamines with bisazophenol crown. INTRODUCTION A variety of complexes and inclusion compounds between tcationic or neutral guest and neutral host, e.g. crowns, cryptands, cyclodextrins, and antibiotics has been studied to develop the phase-transfer catalysis and to elucidate the mechanism of enzyme/substrate and naturally occurring ionophore /metal cation interactions so far. On the other hand, studies on complexation involving the coulombic attractive force between oppositely charged hosts and guests have been expected to draw a new trend in molecular recognition, since this additional binding force will affect the stability and selectivity of the complex other than ion-dipole interaction and/or hydrogen bonding. Previously we reported design and syntheses of a series of ligands which c selectively bind a given metal ion and undergo concurrently color ch gel e.g. lithium ion selective color tion with azophenol-dyed crowns?7 and azophenol spherand-like cyclophanefj, sion with benzothiazolylphenol crowns,'j and their application to lithium ion analyses. BP thium ion specific fluorescent emisAMINE SELECTIVE COMPLEXATION-COLORATION5 Now we wish to report selective complexation of protonated amines by the use of azophenol crowns 1-6 and podand 7 which have a phenol group in the cavity to yield the corresponding ammonium phenolate complex 1 0 (Scheme 1 ). The colored complex 1 0 must be differentiated from simple ion-dipole type complexes by an additional binding force, that is, coulombic interaction between the host phenolate anion and the guest ammonium cation. We recently observed such a perching type complexation of protonated amines by the phenolate anion and ether oxygens of the azophenol crowns.

Functionalized basket-shaped hosts. Synthesis and complexation studies with (alkali) metal and ammonium and diammonium ions

Functionalized basket-shaped hosts have been synthesized from the concave building block 1,3:4,6-bis(3,6-dihydroxy-1,2-xylylene)tetrahydro-3a,6a-diphenylimidazo[4,5-d]imidazole-2,5(1H,3H)-dione (1). To this end, N-substituted 1,4,10,13-tetraoxa-7-azatridecamethylene bridges were attached to the 3,6- and 3',6'-positions of the xylylene rings of 1. The substituents at the nitrogen atom in the bridge include: 5-hydroxy-3-oxapentyl, benzyl, hydrogen, 5-(N-(benzyloxycarbonyl)-L-histidyl)-3-dioxapentyl, and 5-acetyl-3-oxapentyl. The baskets complex alkali metal and ammonium guests, as well as aliphatic and aromatic diammonium guests, all in a 1:1 ratio. Using the picrate extraction technique, free energies of binding for the new hosts with 19 guests were determined. Extremely strong binding (-ΔG° values up to 18 kcal mol −1 ) was observed for the complexes between the hosts and o-phenylenediammonium dipicrate. The host with histidyl substituents easily forms a 1:1 complex with Zn(OTf) 2

Bis-monensin: Synthesis of new chiral receptor from naturally occurring monensin ionophore

Bis-monensin derivatives were synthesized and characterized for the first time as chiral receptor molecules. Among them, o-xylene-bridged bis-monensin exhibited particularly excellent chiral recognition ability by the inclusion of chiral ammonium guest cations in its central cavity.

Amine selective coloration with chromoacerands

Abstract

Synthesis and Properties of Optically Active Coronands Incorporating Sulfoxide and Sulfoximine Functionality

A number of optically active coronands incorporating sulfoxide and sulfoximine functionality have been prepared and their association constants for complexes with alkali metal and ammonium picrates have been measured. Some of these complexes have association constants greater than 70000 1. mol-1 with selectivity for lithium and sodium cations, but no stereoselectivity has been observed for complexes with racemic ammonium guests. The X-ray crystal structure of one of the sulfoxide coronands is reported.

Liquid chromatography with crown ether-containing mobile phases : IV. Role of pH, alkali metal ion and pairing anion in retention of guest substances in reversed-phase high-performance liquid chromatography

The effects of pH and added electrolytes (alkali metal chlorides, ion-pair agents) on the retention of various organic guest compounds in reversed-phase high-performance liquid chromatography with crown ether-containing mobile phases have been investigated. The capacity factor ( k) of a guest compound bearing a primary amino group was markedly increased by the presence of a crown ether (18-crown-6) in the mobile phase the pH of which was varied between 2.4 and 4.9 by addition of hydrochloric, perchloric, or trichloroacetic acid. The pH vs. k profiles indicated that the retention of a guest ammonium cation associated with the crown ether was decreased with increasing proton concentration owing to ion exclusion. However, in the mobile phase acidified with trichloroacetic acid (TCA), a slight increase in the k value was observed in the low-pH region (<3.5) owing to ion-pairing between the crown ether-associated ammonium cation and the TCA anion. The addition of a hydrophobic anion ( e.g. heptanesulphonate) to the crown ether-containing mobile phase caused the retention of the primary amino compound to be more enhanced than in normal reversed-phase ion-pair chromatography, and the degree of change in the retention was characteristic of the class of amino group and the chemical structure around the amino group in the guest molecule. The addition of an alkali metal ion to the crown ether-containing mobile phase caused the guest ammonium cation to compete with the alkali metal ion in binding to the crown ether, resulting in a change in the retention which depended on the kind of alkali metal ion and the structure of the guest molecule; addition of K + or Rb + gave rise to a significant decrease in the k values of primary amino compounds, while Na + produced almost no apparent change, and Li + brought about an enhanced retention. The guest compounds bearing either a sterically hindered primary amino group or a secondary amino group received very weak effects from any of the alkali metal ions tested.

Structural selectivity in the formation of inclusion complexes by tricyclic derivatives of diaza-12-crown-4

The tricyclic host molecules (1c—e) form inclusion complexes with suitable guest ammonium salts and with copper(II) chloride; complex formation with the bisammonium salts (4) is accompanied by host recognition of the length of the guest molecule.