Ion affinity

An artificial metalloenzyme (26) was designed by Breslow et al. 24). It was the first example of a complete artificial enzyme, having a substrate binding cyclodextrin cavity and a Ni2+ ion-chelated nucleophilic group for catalysis. Metalloenzyme (26) behaves a real catalyst, exhibiting turnover, and enhances the rate of hydrolysis of p-nitrophenyl acetate more than 103 fold. The catalytic group of 26 is a -Ni2+ complex which itself is active toward the substrate 1, but not toward such a substrate having no metal ion affinity at a low catalyst concentration. It is appearent that the metal ion in 26 activates the oximate anion by chelation, but not the substrate directly as believed in carboxypeptidase. 

All alkyl ions tested demonstrate a comparable behaviour independent of the sign of their charges. The decrease of the reaction enthalpies AH (11) with the change from the methyl to the ethyl cation (AAH (ll) = 165 kJ mol-1) and from the ethyl to the but-2-enyl cation (AAH°(11) = 117 kJ mol-1) corresponds to the increase of stability of these carbenium ions, which are expressed by the difference of their heats of formation (AAH f = —118 and AAHj = —42 kJ mol-1 90)) and of their hydride ion affinity (AHIA = 176 and 126 kJ mol-1 91)), respectively. 

This reaction corresponds to the basic process during the initiation of cationic polymerizations by RX/MtXn and when reversed is the termination reaction. It will be handled more in detail in part 4.2. When X = H, the reaction enthalpy of the previous equation is equal to the hydride ion affinity (HIA) which is shown for various relevant... 

That means The higher the proton affinity of the monomer, the lower the hydride ion affinity of its cation, that is, the more stable this cation (see part 4.1.3). 

Other Ion Affinities Binding affinities for many different types of ions to neutrals are defined analogously to hydride affinity, as the 298 K enthalpy required to dissociate the complexed species. The ion can be a cation or an anion. Conversely, ion affinities can be described in terms of the dissociation. 

In principle, the equilibrium approach can be used to measure any of the thermochemical properties listed above. However, in practice, it is most commonly used for the determination of gas-phase acidities, proton affinities, and electron affinities. In addition, equilibrium measurements are used for measuring ion affinities, including halide (F, Cl ) and metal ion (alkali and transition metal) affinities. 

Energy-resolved CID can be used to measure bond dissociation energies directly, and therefore is readily applicable for the determination of ion affinities. However, Graul and Squires have also described a method for measuring gas-phase acidities using CID of carboxylates. ° Upon CID, carboxylate ions, RCO2, undergo decarboxylation to form the alkyl anions, R, ... 

Li, S. and Dass, C., Iron(III)-Immobilized Metal Ion Affinity Chromatography and Mass Spectrometry for the Purification and Characterization of Synthetic Phosphopeptides, Anal. Biochem., 270, 9, 1999. 

Amini, A., Chakraborty, A., Regnier, F.E. (2002). Simplification of complex tryptic digests for capillary electrophoresis by affinity selection of histidine-containing peptides with immobilized metal ion affinity chromatography. J. Chromatogr. B 772, 35-44. 

Bouchonnet, S., and Y. Hoppiliard. 1992. Proton and Sodium Ion Affinities of Glycine and Its Sodium Salt in the Gas Phase. Ab Initio Calculations. Qrg. Mass Spectrometry 27, 71-76. 

Porath, J. (1992) Immobilized metal ion affinity chromatography. Protein Expr. Purif. 3, 263-281. 

Porath, J., and Olin, B. (1983) Immobilized metal ion affinity adsorption and immobilized metal ion affinity chromatography of biomaterials. Serum protein affinities for gel-immobilized iron and nickel ions. Biochemistry 22, 1621-1630. 

Reid, R. T., Live, D. H., Faulkner, D. J. and Butler, A. (1993). A siderophore from a marine bacterium with an exceptional ferric ion affinity constant, Nature, 366, 455-458. 

Comment on heats of formation of fluoro-anions, and electron and fluoride-ion affinities of neutral fluorides, measured mass spectropho-tometrically (57,185,216,222) or derived from salt values obained by conventional calorimetry (32, 45, 46, 105) needs to be reserved until better agreement is reached between methods. However, from measurements on heats of formation of the predominantly ionic xenon fluoride adducts it has been possible to show the trend to increasing ionic-ity with pentafluoride partners Nb < Ta < Sb, which parallels the increasing Lewis acidity of these fluorides found by independent methods (44). 

Cao P. and Stults J.T. (1999), Phosphopeptide analysis by on-line immobilized metal-ion affinity chromatography-capillary electrophoresis-electrospray ionization mass spectrometry, J. Chromatogr. 853(1-2), 225-235. 

IMAP (immobilized metal ion affinity-based fluorescence polarization) Molecular Devices Trivalent metal ion containing beads bind to phosphorylated peptide producing FP signal change... 

Simple linear equations could also be developed for the other three systems of Figure 4, PA of aldehydes and ketones(4e), and their hydride ion affinities, both of the neutral (4f) and protonated forms (4g), However, in addition to effective polarizability and electronegativity, hyperconjugation had also to be used as a parameter, as p-orbitals carrying a partial positive charge are involved in the reactions 4e to 4g (26),... 

Reid RT, Live DH, Faulkner DJ, Butler A (1993) A Siderophore from a Marine Bacterium with an Exceptional Ferric Ion Affinity Constant. Nature 366 455... 

LCA toward amino acids and nucleic bases has also been measured. Wesdemiotis and Cerda measured the alkali metal ion affinities of nucleobases in the gas phase from the dissociation of metal ion-bound heterodimers [nucleobase + B]M+, in which B represents a reference base of known affinity and M is an alkali metal. By assessing the dimer decomposition for two different internal energies, entropy is deconvoluted from enthalpy and LCA values are obtained. For guanine, cytosine, adenine, thymine and uracil, the corresponding Li+-nucleobase bond energies are as follows 57.2, 55.5, 54.1,... 

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