Complexation Of Ammonium Ions Research Articles

Determining the effects of salt, buffer, and temperature on the complexation of methylated ammonium ions and methyllysines by sulfonated calixarenes

Sulfonated calixarenes have long been used as effective binders of ammonium ions in aqueous solution. Recently, the utility of sulfonated calix[4]arenes and calix[6]arenes as specific agents for binding biologically important ammonium ions, and especially post-translationally methylated amino acids, peptides, and proteins, has suggested that they might have important roles to play in the control and understanding of biological pathways. We report here binding data in various buffer systems that attempt to shed light on the roles of buffer and salt in the recognition processes of these hosts. We also report studies on trimethyllysine binding that explore the effects of near physiological salt concentrations and temperatures. These studies provide an understanding of disparate data on these systems and also demonstrate the ability of a sulfonated calixarene to bind trimethyllysine strongly under aqueous conditions that closely replicate the salt concentrations, pH, and temperature of the human body.

Rational Design of a Nonbasic Molecular Receptor for Selective NH4+/K+ Complexation in the Gas Phase

A new molecular receptor (1) for ammonium recognition has been designed and constructed by using only carbon atoms. This molecular receptor can co-exist in two different isoenergetic conformations but, upon complexation, the conformers are no longer isoenergetic, and a basket-shaped conformation becomes clearly more stable. The pre-organised tetrahedral structure of this basket-shaped molecule favours the complexation of ammonium ions by N-H⋅⋅⋅π interactions with the four phenyl groups of the host. A similar behaviour is not observed in a similar, but less pre-organised, reference molecule. ESI-MS competition experiments show that 1 is able to bind NH(4)(+) over K(+) selectively. This is the first example of a neutral molecular receptor that shows a remarkable NH(4)(+)/K(+) selectivity. DFT-calculations provide insight into the nature of host-guest interactions of both 1⋅NH(4)(+) and 1⋅K(+) complexes as well as in the mechanism involved in multiple cation-π interactions and the influence of these interactions on the conformational stability and the selective binding of the host.

The effects of Cu(II) ion as an additive on NH3 loss and CO2 absorption in ammonia-based CO2 capture processes

Chemical CO2 absorption is one of the most cost- and energy-intensive processes in carbon capture and storage (CCS) technology. Among various absorption processes, ammonia-based processes attract much attention, due to many benefits: high CO2 absorption rate and low energy consumption for ammonia regeneration. Ammonia-based processes, however, have a problem to be solved for practical implementation due to the high vapor pressure of ammonia, which incurs ammonia loss during regeneration. In this study, the effect of Cu(II) ion as an additive on NH3 loss and CO2 absorption was investigated to examine the potential of Cu(II) ion to enhance the economic performance of ammonia-based processes. Continuous operations were conducted with and without the addition of Cu(II) ion. The results showed that the addition of Cu(II) ion noticeably decreased NH3 loss in the regeneration process due to the complexation of copper and ammonium ions, i.e., [Cu(NH3)4]2+. The Cu(II) addition also increased the CO2 absorption capacity in the absorption process because ammonia concentration remained higher. In conclusion, Cu(II) ion can be used to reduce ammonia make-up cost and to enhance CO2 absorption performance in ammonia-based CO2 capture processes.

Complexation of Oxonium and Ammonium Ions by Lower-rim Calix[4]arene Amino Acid Derivatives

Complexation of oxonium and ammonium cations with two calix[4]arene amino acid derivatives, namely 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis-(O-methyl-D-α-phenylglycylcarbonylmethoxy)-calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-26,28,25,27-(O-methyl-L-leucylcarbonylmethoxy)calix[4]¬arene (2), in acetonitrile and methanol was studied by means of spectrophotometric and calorimetric titrations at 25 °C. The classical molecular dynamics simulations of the macrocycles and the corresponding complexes with NH4+ and H3O+ were carried out in order to investigate their possible structures in solution. The examined calix[4]arene derivatives were shown to be rather efficient binders for H3O+ cation and moderately efficient for NH4+ in acetonitrile, whereas the complexation of these cations in methanol could not be observed. The structures of the complexes obtained by means of molecular dynamics simulations suggested the involvement of ether and carbonyl oxygen atoms in the complexation of both NH4+ and H3O+. An inclusion of an acetonitrile molecule into the hydrophobic cavity of the free and complexed ligands was observed as well. The difference in binding affinities of 1 and 2 towards NH4+ and H3O+ ions could be explained by taking into account cation solvation, difference in their size and in the strength of hydrogen bonding between cations and the ligand binding sites.

Atmospheric pressure gas-phase ammonium/alkyl ammonium exchange studies of some crown ethers complexes using ion mobility spectrometry: A thermodynamic investigation and collision cross section measurements

A systematic evaluation of the intermolecular binding forces responsible for the association of crown ethers (hosts) with alkyl amines (guests) is presented by exchanging the ammonium and alkyl ammonium in the ion source of atmospheric pressure ion mobility spectrometry. The hydrogen bonding interactions of crown ether/alkyl ammonium ion complexes are examined with respect to the macrocyclic size effects of five crown ethers (12-crown-4, 15-crown-5, benzo-15-crown-5, 18-crown-6 and aza-18-crown-6) and the gas-phase basicities of five homologous series of alkyl amines. Our approach is based on a formalism assuming an equilibrium: [host + NH 4] + + [guest + H] + ↔ [host + guestH] + + [NH 4] +. The exchange equilibrium constant for this process was calculated using the relative peak intensities of the corresponding species in the IMS spectra. Determination of the equilibrium constants at different temperature via Van’t Hoff plots led to the standard molar enthalpy change Δ H° that is equivalent to the guest-exchange affinity of different crown ethers. The collision cross-sections are measured for the formation of complexes ions and different alkyl ammonium ions, which are produced. Complexes of 15C5 with two different normal and iso-alkyl amine showed a gas phase selectivity binding to normal alkyl amines relative to iso-alkyl amines.

ChemInform Abstract: Enantioselective Complexation of Organic Ammonium Ions by Simple Tetracyclic Podand Ionophores.

ChemInform Abstract: Enantioselective Complexation of Organic Ammonium Ions by Simple Tetracyclic Podand Ionophores.

Single Electron Transfer and SN2 Reactions: The Importance of Ionization Potential of Nucleophiles.

The importance of single electron transfer energetics in promoting SN2 reactions was probed by a density functional computational study on substitution reactions of quaternary ammonium ion complexes with anionic nucleophiles. Good correlations were found between the ionization potentials (IP) of the nucleophiles when plotted against density functional theory (DFT)-computed reaction activation enthalpies (ΔΗrxn≠) over a range of 15 eV. Poor correlations were found between IPs or proton affinities and central barrier heights (ΔΗcmp≠). Examples of inverted values of ΔΗrxn≠ of primary vs secondary systems were found.

Surprisingly stable ammonium ion complex of a non-cyclic crown-type polyether: solid and solution studies

The first crystal structure of an NH4+ ion complex with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (L), a representative non-cyclic analogue of 18-crown-6, is reported along with the characteristics of the complex’s solution; very interestingly, L forms a more stable complex with the NH4+ ion than does 18-crown-6 by the formation of unique recognition tetrahedral-type hydrogen bonds.

Complexation of Aliphatic Ammonium Ions with a Water‐Soluble Cucurbit[6]uril Derivative in Pure Water: Isothermal Calorimetric, NMR, and X‐ray Crystallographic Study

Complexation of a water-soluble cucurbituril (CB) derivative, cyclohexanocucurbit[6]uril (CB*[6]), the cavity dimensions of which are essentially the same as those of CB[6], with various organic mono- and diammonium ions has been studied by isothermal titration calorimetry and 1H NMR spectroscopy. The binding affinity of CB*[6] with the guest molecules in water is 3-5 and 2-3 orders of magnitude higher than those of CB[6] in 50 % formic acid and in 0.05 M NaCl solution, respectively, which is mainly due to the larger enthalpic gains upon complex formation in the absence of interfering ions, such as protons and Na+. In particular, the binding constant (K) of spermine to CB*[6] was measured to be 3.4 x 10(12) M(-1), which is the highest binding constant ever reported for CB[6] or its derivatives. We also obtained the X-ray crystal structures of alpha,omega-alkanediammonium ions (C(n)DA2+, n=4-8) and spermine complexes with CB[6], in which the aliphatic chains of the guest molecules take an extended or partially bent conformation inside the CB[6] cavity, depending on the chain length. The hexamethylene chain of C6DA2+ takes a twisted conformation, which not only allows strong ion-dipole interactions between the ammonium groups and the carbonyl groups at the portals, but also increases hydrophobic interactions between the alkyl part of the guest and the inner wall of the host, which results in the largest enthalpic gain among alpha,omega-alkanediammonium ions. The thermodynamic parameters associated with the complexation are discussed in relation to the binding modes and conformations of the aliphatic chain of the guest molecules inside the host, which were investigated by 1H NMR spectroscopy and X-ray crystallography.

Complex Formation of Crown Ethers and Cryptands with Alkali Metal and Ammonium Ions in Chloroform

The complex formation between different crown ethers and the cryptand [222] with alkali metal and ammonium ions in chloroform has been investigated by means of calorimetric titrations. The stability constants, reaction enthalpies and entropies for complex formation in chloroform have been determined. The complexation of alkali metal ions is favored by enthalpic contributions and influenced by both the ligand and the nature of the cation. The reaction enthalpies for complex formation of different ammonium salts with cryptand [222] are higher compared to the corresponding values for the reaction with different 18-crown-6 derivatives in chloroform due to the complete encapsulation of ammonium ion by the cryptand [222]. The benzo group attached to the crown ethers and the nature of the anion borne by the ammonium ion influence complex formation of ammonium with crown ethers. In the case of ammonium salts, competitive measurements have been carried out to underline the influence of the anion upon the complex formation. From the reaction enthalpies for complexation of ammonium ions, the contributions for the formation of hydrogen bonds are calculated using experimental data.

Calix[6]arene Tris-carboxylic Acid Derivatives: X-ray and NMR Characterization of their Remarkable Host-guest Properties Toward Ammonium Ions

The ability of calix[6]arene tris-carboxylic acid derivatives to include ammonium guests has been investigated both in solution and in the solid state. NMR studies and crystallographic data showed that the highly flexible calix[6]arene structures can be shaped in a well defined cone conformation thanks to the formation of an ion-paired cap between the carboxylate groups of the calixarene and their ammonium counter-ions. The resulting supramolecular edifices exhibit remarkable host-guest properties toward ammonium ions even in polar and protic solvents. The recognition process has been rationalized in the solid state by the combination of hydrogen bonding, electrostatic and CH–π interactions, and a remarkable C 3-complementarity between the well-organized binding carboxylates of the host and the ammonium guest. Very interestingly, the endo-cavity complexation of large polycyclic ammonium ions as well as bioactive ammonium ions has been clearly demonstrated through NMR spectroscopy. Finally, the tuning of the nature of the ammonium ions involved in the supramolecular cap led to highly responsive molecular receptors.

Molecular recognition of ammonium ion by tetrahomodioxacalix[4]biscrown

The first theoretical study on the conformational features and the complexation behaviors upon ammonium ion binding of tetrahomodioxacalix[4]biscrown-4 has been performed using molecular dynamic simulations and density functional theory. The conformational analyses show that the relative stability and the geometry of the ammonium ion complexes are directly contributed by the number of putative hydrogen bonds between oxygen lone pairs and ammonium hydrogens.

Ammonium Ion Complexes of Tetraethyl Resorcarene: An Ab Initio Study

The complexation of various ammonium ions with a resorcarene host was evaluated by ab initio calculations. The approximations of the binding locations and the interaction energies for each guest are reported. The supramolecular complex formation also affects the conformation of the resorcarene host.

Mass Spectrometric Investigation of Noncovalent Complexation between a Tetratosylated Resorcarene and Alkyl Ammonium Ions

Noncovalent complexation between tetratosylated tetraethyl resorcarene (1) and primary, secondary, and tertiary alkyl ammonium ions (mMe, dMe, tMe, mEt, dEt, tEt, dBu, and dHex) was studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Interactions of the noncovalent complexes were investigated by means of competition experiments, collision-induced dissociation (CID) experiments, ion-molecule reactions with tripropylamine and gas phase H/D-exchange reactions with deuteroammonia. Gas phase ion-molecule reactions gave especially valuable information about the structure and properties of the complexes. Resorcarene 1 formed relatively stable 1:1 complexes with all aliphatic alkyl ammonium ions. Steric properties of the alkyl ammonium ions and proton affinities of the conjugate amines noticeably affected the complexation properties, indicating the importance of hydrogen bonding in these complexes. According to the competition experiments, the thermodynamically most stable host-guest complexes were formed with alkyl ammonium ions that were most substituted and had the longest alkyl chains. In CID experiments, release of an intact free guest ion or dissociation of the host was observed to depend on the proton affinity of the amine and the strength of the hydrogen bond that was formed. In ion-molecule reactions with tripropylamine, a guest exchange reaction occurred with all alkyl ammonium ion complexes with reaction rates mostly dependent on the steric properties of the original guest ion. In H/D-exchange reactions the N-H hydrogen atoms of the guest ion were exchanged with deuterium, whereas the resorcinol hydrogen atoms remained unchanged.

Reversible Change in Optical Rotation by Phtochromism of Diarylethenes in the Stretched DNA–Quaternary Ammonium Ion Complex Films

Abstract Transparent stretched films of DNA–dimethyldioctadecylammonium ion complex incorporating a photochromic diarylethene exhibited large change in optical rotation by its photochromic reactions. As the stretched films at the photostationary state of UV-irradiation showed the dichroism, it was suggested that the diarylethene molecules are partly intercalated between the DNA base pairs.

Ammonium ion mediated resorcarene capsules: ESI-FTICRMS study on gas-phase structure and ammonium ion affinity of tetraethyl resorcarene and its per-methylated derivative

The ammonium ion binding affinities of tetraethyl resorcarene ( 1) and its per-methylated derivative ( 2) were studied by electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Ten different ammonium ions were tested as guests for the resorcarenes. A strong tendency for complex formation was observed with all ammonium ions of size and charge distribution suitable for noncovalent interactions with the cavities of the resorcarene hosts 1 and 2. Although differences in ammonium ion affinities were observed between 1 and 2 due to the dissimilar conformations, the overall tendency was that increase in the degree of substitution and the length of carbon chain of the ammonium cation facilitated the complex formation until the sterical hindrance impeded the complexation. Dimeric as well as monomeric ammonium ion complexes were formed with resorcarene 1, but resorcarene 2 was unable to form the dimeric capsules because of the lack of H-bond donor possibilities. The nature of binding of the guest was further investigated with ion–molecule reactions and by determination of the single crystal X-ray structure of host 1 complexed with tetramethyl ammonium bromide.

Thermodynamics of Complexation of 18-Crown-6 with NH4+ Ion in Water-Dioxane Mixtures

The stability constants of 1 : 1 complexes of ammonium ion with 18-crown-6 in water and aqueous dioxane (dioxane weight fraction 0.2, 0.4, 0.6, and 0.8) in the range 283-318 K were determined electrometrically, and the thermodynamic parameters of the complexation were calculated. The stability of the complexes is determined by the enthalpy factor. The contributions from the Gibbs energy of solvation of NH4 + ion, 18-crown-6·NH4 + complex, and free 18-crown-6 to stabilization of the complex with increasing content of dioxane in the mixed solvent were estimated. The thermodynamics of complexation of ammonium, sodium, and potassium ions with 18-crown-6 in aqueous-organic solvents, such as water-2-propanol, water-acetone, and water-dioxane, were compared considering the effects of reactant solvation. The variations of the conformational component of the Gibbs energy of solvation of 18-crown-6 and the parameters of selective solvation of the reactants were evaluated. The influence of the dielectric permittivity and donor-acceptor properties of mixed aqueous-organic solvents on the Gibbs energy of complexation and solvation of the cations and 18-crown-6 was subjected to correlation analysis.

Electrospray ionization mass spectrometric investigation of ammonium ion complexes with anomeric 2,3-O-isopropylidene-1alpha- and -1beta-D-ribofuranosyl azides: anomeric and kinetic isotope effects in ammonium affinities.

[Methanol + ammonium acetate] solutions of anomeric 2,3-O-isopropylidene-1alpha- and 1beta-ribofuranosyl azides were investigated by electrospray ionization mass spectrometry (ESI-MS). The compounds included d6-labeled and/or unlabeled isopropylidene groups that enable the identification of peaks characteristic of the ammonium-attached monomeric (MNH4(+)), ammonium-bound homodimeric ([M]2NH4(+)) and heterodimeric ([MNH4M1](+)) complex ions in ESI mass spectra of solutions of a pair of compounds. The intensities of the product ion peaks obtained by the collisionally activated ammonium-bound dimeric ions are related to the secondary isotope effect k(alpha)/k(alphad6) = 0.88 and k(beta)/k(betad6) = 1.25 or to isotope plus anomeric effects k(alpha)/k(betad6) = 1.43 and k(beta)/k(alphad6) = 0.59 in the ammonium affinities of these compounds. The calculations of solely anomeric effects in the ammonium affinities of alpha and beta anomeric compounds obtained from the data presented previously give two series of values: k(alpha)/k(beta) = (k(alpha)/k(alphad6))(k(alphad6)/k(beta)) = 1.49 and k(alphad6)/k(betad6) = (k(alphad6)/k(beta))(k(beta)/k(betad6)) = 2.12 or k(alpha)/k(beta) = (k(alpha)/k(betad6))(k(betad6)/k(beta)) = 1.14 and k(alphad6)/k(betad6) = (k(alphad6)/k(alpha))(k(alpha)/k(betad6)) = 1.63. The disparities of these results indicate the different structures of hydrogen bonding in ammonium-bound dimeric complexes which decompose to monomeric ions with different rate constants. Comparison of experimental results obtained by the qualitative approach of the kinetic method and ammonium affinities of these compounds calculated by the semi-empirical molecular orbital method (AM1) show that the [MNH4M1](+) dimeric complex ions dissociate to the most stable MNH4(+) and M1NH4(+) monomeric ions. The obtained relative order of ammonium affinities of these compounds is: alphad6 > alpha > beta > betad6.

Application of the membrane technology to control ammonia in surface water

Amnonium ion is effectively removed by Reverse Osmosis membranes (Brackish water, BW; Saline water, SW). The removal efficiency of ammonium ion from a solution containing ammonium ion which is not complexed is varying in the range of 5–60%. On the contrary, ammonium ion forms complexes with other ions in water and wastewater removal efficiency was as high as 99% for the synthetic solution which contained a complex of iron and ammonium ion. Elmali reservoir which is one of the water sources of the Istanbul city is suffering from high ammonia content due to discharges of untreated wastewater. Application of the BW membrane to Elmali Reservoir water resulted in ammonia removal efficiency of about 95%. The permeate ammonia concentration of 0.2 mg/l was achieved. High removal ratio of ammonia ions in complex form is due to increased molecular diameters of the ammonium ion complexes. Increased pH values were observed in parallel to increase the ammonium ion concentrations when ammonium ion was not in complex form. Ammonium ion removal efficiency decreased with increasing pH. On the other hand, when the concentration of ammonium ion complexed with iron was increased, pH value was decreased. In parallel to the decreasing pH, an increase of removal efficiency was observed. Membrane types did not significantly affect the flux. No fouling problems were observed during the test runs and thus fluxes were practically constant throughout the experimental run. The total estimated cost of treatment will be in the range of $0.95 to $1.06/m3 for the investigated drinking water source.

Kinetic study of ligand release promoted by ammonium ion on bis( N-alkylsalicylaldiminato)zinc(II) complexes in aprotic solvent

The reaction between ammonium ion and bis( N-alkylsalicylaldiminato)zinc(II) complexes [Zn(R-sal) 2] (R-sal=anion of N-alkylsalicylaldimine; R=H, n-Bu=n-butyl, t-Bu=tert-butyl, i-Pr=iso-propyl, Et=ethyl) in dry acetonitrile, leads to the release of the ligand. The reaction was studied kinetically at different temperatures and an analysis by mean of a multi-wavelength stopped-flow technique evidences a first-order kinetic as a general rule, and a two exponential profile for the t-butyl substituted complex for the release of one of the bidentate ligands of the Zn(II) complexes. Kinetic and 1H NMR data indicate that the first step of the release reaction of the ligand is the OZn bond breaking.