Trend In Affinity Research Articles

The role of multivalent cations in determining the cross-linking affinity of alginate hydrogels: A combined experimental and modeling study

This study explores the development of a comprehensive mathematical model to predict the cross-link density of alginate hydrogels using varying concentrations of divalent and trivalent ions. By systematically investigating the effects of Ca²⁺, Ba²⁺, Cu²⁺, Sr²⁺, Mg²⁺, Fe3⁺ and Al³⁺, the research describes the relationship between ion concentration and cross-link density. Experimental data reveals that the type and concentration of these ions critically influence the mechanical properties of the resulting hydrogels, with trivalent ions such as Fe³⁺ forming stronger, triple cross-links that significantly enhance the hydrogel's mechanical strength. Among the divalent ions, the trend in binding affinity is as follows: Ba²⁺ with the highest affinity followed by Sr²⁺, Ca²⁺ and Cu²⁺, while Mg²⁺ stands out with the lowest affinity, significantly differing from the others. The deviation of Cu²⁺ (transition metal ion) from the expected trend in ion interactions suggests that coordination chemistry, along with ionic radius, valence, and cation coordination abilities, plays a significant role in determining interaction strength with alginate. The proposed model, enhanced with fitting parameters k1 and k2 to account for ion-specific effects, leverages the unique binding affinities and coordination chemistry of each ion to tailor alginate hydrogels for specific applications. The parameter k1 reflects the affinity of the ions for the alginate chains, while k2 captures the coordination abilities and cross-linking efficiency. This work not only advances the understanding of ion-mediated cross-linking in alginate systems but also offers a valuable tool for the design and optimization of hydrogels with precise mechanical properties governed by various applications.

Assessing the response of marine fish communities to climate change and fishing.

Globally, marine fish communities are being altered by climate change and human disturbances. We examined data on global marine fish communities to assess changes in community-weighted mean temperature affinity (i.e., mean temperatures within geographic ranges), maximum length, and trophic levels, which, respectively, represent the physiological, morphological, and trophic characteristics of marine fish communities. Then, we explored the influence of climate change and fishing on these characteristics because of their long-term role in shaping fish communities, especially their interactive effects. We employed spatial linear mixed models to investigate their impacts on community-weighted mean trait values and on abundance of different fish lengths and trophic groups. Globally, we observed an initial increasing trend in the temperature affinity of marine fish communities, whereas the weighted mean length and trophic levels of fish communities showed a declining trend. However, these shift trends were not significant, likely due to the large variation in midlatitude communities. Fishing pressure increased fish communities' temperature affinity in regions experiencing climate warming. Furthermore, climate warming was associated with an increase in weighted mean length and trophic levels of fish communities. Low climate baseline temperature appeared to mitigate the effect of climate warming on temperature affinity and trophic levels. The effect of climate warming on the relative abundance of different trophic classes and size classes both exhibited a nonlinear pattern. The small and relatively large fish species may benefit from climate warming, whereas the medium and largest size groups may be disadvantaged. Our results highlight the urgency of establishing stepping-stone marine protected areas to facilitate the migration of fishes to habitats in a warming ocean. Moreover, reducing human disturbance is crucial to mitigate rapid tropicalization, particularly in vulnerable temperate regions.

Flavonoid Derivatives as Potential Cholinesterase Inhibitors in Scopolamine-Induced Amnesic Mice: An In Vitro, In Vivo and Integrated Computational Approach.

Flavonoids are one of the most exciting types of phenolic compounds with a wide range of bioactive benefits. A series of flavone derivatives (F1–F5) were previously synthesized from substituted O-hydroxy acetophenone and substituted chloro-benzaldehydes. The titled compounds F1–F5 in the present study were evaluated for their anticholinesterase potential (against AChE and BuChE). The obtained results were then validated through a molecular docking approach. Compound F5 was found to be the most potent inhibitor of AChE (IC50 = 98.42 ± 0.97 µg/mL) followed by compound F4, whereas compound F2 was found to be the most promising inhibitor of BuChE (IC50 = 105.20 ± 1.43 µg/mL) among the tested compounds. The molecular docking analysis revealed a similar trend in the binding affinity of compounds with the targeted enzymes and found them to be capable of forming highly stable complexes with both receptors. The selected compounds were further subjected to in vivo assessment of cognitive function in a scopolamine-induced amnesic animal model, in which almost all compounds F1–F5 significantly attenuated the amnesic effects as evaluated through Y-Maze Paradigm and novel object discrimination (NOD) tasks, findings that were further supported by ex vivo experimental results. Among (F1–F5), F5 showed significant anti-amnesic effects in scopolamine-induced amnesic models and ameliorated the memory loss in behavioral model studies as compared to counterparts. In ex vivo study, noteworthy protection from oxidative stress in the brains of scopolamine-induced amnesic mice was also recorded for F5. These findings also confirmed that there were no significant differences among the in vivo and ex vivo results after administration of F1–F5 (7.5 or 15 mg/kg) or donepezil (2 mg/kg). These synthesized flavonoids could serve as potential candidates for new neuroprotective and nootropic drugs. However, further studies are needed to validate their observed potential in other animal models as well.

Metallointercalators-DNA Tetrahedron Supramolecular Self-Assemblies with Increased Serum Stability.

Self-assembly of metallointercalators into DNA nanocages is a rapid and facile approach to synthesize discrete bioinorganic host/guest structures with a high load of metal complexes. Turberfield's DNA tetrahedron can accommodate one intercalator for every two base pairs, which corresponds to 48 metallointercalators per DNA tetrahedron. The affinity of the metallointercalator for the DNA tetrahedron is a function of both the structure of the intercalating ligand and the overall charge of the complex, with a trend in affinity [Ru(bpy)2(dppz)]2+ > [Tb-DOTAm-Phen]3+ ≫ Tb-DOTA-Phen. Intercalation of the metal complex stabilizes the DNA tetrahedron, resulting in an increase of its melting temperature and, importantly, a significant increase in its stability in the presence of serum. [Ru(bpy)2(dppz)]2+, which has a greater affinity for DNA than [Tb-DOTAm-Phen]3+, increases the melting point and decreases degradation in serum to a greater extent than the TbIII complex. In the presence of Lipofectamine, the metallointercalator@DNA nanocage assemblies substantially increase the cell uptake of their respective metal complex. Altogether, the facile incorporation of a large number of metal complexes per assembly, the higher stability in serum, and the increased cell penetration of metallointercalator@DNA make these self-assemblies well-suited as metallodrugs.

Abnormal Association between Metal-Organic Cages and Counterions Regulated by the Hydration Shells.

A unique trend in the binding affinity between cationic metal-organic cages (MOCs) and external counteranions in aqueous media was observed. Similar to many macroions, two MOCs, sharing similar structures but carrying different number of charges, self-assembled into hollow spherical single-layered blackberry-type structures through counterion-mediated attraction. Dynamic and static light scattering and isothermal titration calorimetry measurements confirm the stronger interactions among less charged MOCs and counteranions than that of highly charged MOCs, leading to larger assembly sizes. DOSY NMR measurements suggest the significance of thick hydration shells of highly charged MOCs, inhibiting the MOC-counterion binding and weakening the interaction between them. This study demonstrates that the greater role played by hydration shell on ion-pair formation comparing with charge density of MOCs.

A Walk Across the Lanthanide Series: Trend in Affinity for Phosphate and Stability of Lanthanide Receptors from La(III) to Lu(III).

The trend in affinity of two 1,2-hydroxypyridinonate lanthanide(III) receptors-LnIII-2,2-Li-HOPO and LnIII-3,3-Gly-HOPO (LnIII = LaIII, PrIII, NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, ErIII, TmIII, YbIII, and LuIII)-for phosphate across the series was investigated by luminescence spectroscopy via competition against the central europium(III) analog. Regardless of the ligand, the rare earth receptors display a steep and continuous increase in affinity for their phosphate guest across the series, with the later lanthanides displaying the highest affinity for the oxyanion. This trend mirrors that of the stability of the lanthanide receptors, which also increases significantly and continuously from LaIII to LuIII. For these two ligands, the ionic radius of a rare earth, a parameter directly linked to its Lewis acidity, correlates strongly with its affinity for anions, regardless of whether that anion is the one coordinating it (in this case the 1,2-hydroxypyridinonate ligand) or the guest targeted by the lanthanide receptor (in this case phosphate). These observations are indicative of a lack of steric hindrance for coordination of phosphate. Advantageously, increased efficacy of the lanthanide receptor comes with increased stability. The remarkably high stability of LuIII-2,2-Li-HOPO, combined with its high affinity for phosphate, makes it a particularly promising candidate for translational application to medical or environmental sequestration of phosphate since the higher stability will further reduce the risk of the rare earth leaching during anion separation. The unusually large difference in stability between lanthanide complexes (the LuIII complex of 2,2-Li-HOPO is at least 7 orders of magnitude more stable than the LaIII one) bodes well for potential applications in rare earth separation.

Understanding the Localization of Berylliosis: Interaction of Be2+ with Carbohydrates and Related Biomimetic Ligands.

The interplay of metal ions with polysaccharides is important for the immune recognition in the lung. Due to the localization of beryllium associated diseases to the lung, it is likely that beryllium carbohydrate complexes play a vital role for the development of berylliosis. Herein, we present a detailed study on the interaction of Be2+ ions with fructose and glucose as well as simpler biomimetic ligands, which emulate binding motives of saccharides. Through NMR and IR spectroscopy as well as single‐crystal X‐ray diffraction, complemented by competition reactions we were able to determine a distinctive trend in the binding affinity of these ligands. This suggests that under physiological conditions beryllium ions are only bound irreversibly in glycoproteins or polysaccharides if a quasi ideal tetrahedral environment and κ4‐coordination is provided by the respective biomolecule. Furthermore, Lewis acid induced conversions of the ligands and an extreme increase in the Brønstedt acidity of the present OH‐groups imply that upon enclosure of Be2+, alterations may be induced by the metal ion in glycoproteins or polysaccharides. In addition the frequent formation of Be‐O‐heterocycles indicates that multinuclear beryllium compounds might be the actual trigger of berylliosis. This investigation on beryllium coordination chemistry was supplemented by binding studies of selected biomimetic ligands with Al3+, Zn2+, Mg2+, and Li+, which revealed that none of these beryllium related ions was tetrahedrally coordinated under the give conditions. Therefore, studies on the metabolization of beryllium compounds cannot be performed with other hard cations as a substitute for the hazardous Be2+.

Distinctive Trend of Metal Binding Affinity via Hydration Shell Breakage in Nanoconfined Cavity

We report a distinctive trend in the binding affinity of metal cations when they interact with lacunary Keggin-type polyoxometalate K7[α-PW11O39] clusters in aqueous media. The binding affinity of metal cations follows the special trends of Li+ > Na+ > K+ for monovalent cations and Mg2+ > Ca2+ > Sr2+ > Ba2+ for divalent cations, completely reversed from the common trends of Li+ < Na+ < K+ and Mg2+ < Ca2+ < Sr2+ < Ba2+ for macroion–counterion ion-pair formation in dilution solution. Isothermal titration calorimetry and NMR measurements confirm that the hydration shells of metal cations are significantly broken during the interaction in the nanoscale cavity, making the binding affinity stronger for the cations with smaller ionic sizes instead of hydrated sizes. The same phenomenon is also observed for the lacunary Dawson-type clusters, which contain well-defined cavity in their structures as well, demonstrating the universality of this reverse trend and its connection to nanoconfinement effect in small subm...

Alkali Metal Cation Affinities of Anionic Main Group-Element Hydrides Across the Periodic Table.

We have carried out an extensive exploration of gas-phase alkali metal cation affinities (AMCA) of archetypal anionic bases across the periodic system using relativistic density functional theory at ZORA-BP86/QZ4P//ZORA-BP86/TZ2P. AMCA values of all bases were computed for the lithium, sodium, potassium, rubidium and cesium cations and compared with the corresponding proton affinities (PA). One purpose of this work is to provide an intrinsically consistent set of values of the 298 K AMCAs of all anionic (XHn-1- ) constituted by main group-element hydrides of groups 14-17 along the periods 2-6. In particular, we wish to establish the trend in affinity for a cation as the latter varies from proton to, and along, the alkali cations. Our main purpose is to understand these trends in terms of the underlying bonding mechanism using Kohn-Sham molecular orbital theory together with a quantitative bond energy decomposition analyses (EDA).

Synthesis of Multivalent [Lys8]-Oxytocin Dendrimers that Inhibit Visceral Nociceptive Responses

Peptide dendrimers are a novel class of precisely defined macromolecules of emerging interest. Here, we describe the synthesis, structure, binding affinity, receptor selectivity, functional activity, and antinociceptive properties of oxytocin-related dendrimers containing up to 16 copies of [Lys8]-oxytocin or LVT. These were generated using a copper(i)-catalyzed azide–alkyne cycloaddition (CuAAc) reaction with azido-pegylated LVT peptides on an alkyne–polylysine scaffold. 2D NMR analysis demonstrated that each attached LVT ligand was freely rotating and maintained identical 3D structures in each dendrimeric macromolecule. The binding affinity Ki at the oxytocin receptor increased approximately 17-, 12-, 3-, and 1.5-fold respectively for the 2-, 4-, 8-, and 16-mer dendrimeric LVT conjugates, compared with monomer azido-pegylated LVT (Ki = 9.5 nM), consistent with a multivalency effect. A similar trend in affinity was also observed at the related human V1a, V1b, and V2 receptors, with no significant selectivity change observed across this family of receptors. All LVT dendrimers were functionally active in vitro on human oxytocin receptors and inhibited colonic nociceptors potently in a mouse model of chronic abdominal pain.

The Effect of Hydration on the Cation-π Interaction Between Benzene and Various Cations

The effect of hydration on cation-π interaction in M q+ B m W n (B= benzene; W= water; M q+= Na+, K+, Mg2+, Ca2+, Al3+, 0 ≤ n,m ≤ 4,1 ≤ m + n ≤ 4) complexes has been investigated using ab initio quantum chemical methods. Interaction energy values computed at the MP2 level of theory using the 6-31G(d,p) basis set reveal a qualitative trend in the relative affinity of different cations for benzene and water in these complexes. The π–cloud thickness values for benzene have also been estimated for these systems. Effect of hydration on cation-π interaction

Polymer-Supported Aminomethylphosphinate as a Ligand with a High Affinity for U(VI) from Phosphoric Acid Solutions: Combining Variables to Optimize Ligand–Ion Communication

ABSTRACTAminomethylphosphinic acid (AMPA) is immobilized onto cross-linked polystyrene beads and found to have a high affinity for the uranyl ion, especially from solutions as acidic as 6 M H3PO4. The trend in uranyl affinity by different ligands is AMPA > phosphinic > phosphonic > sulfonic. For example, the percent sorbed from 6 M H3PO4 is 89.5% (AMPA), 44.8% (phosphinic), 5.38% (phosphonic), and 2.60% (sulfonic). The high affinity shown by AMPA is due to the decreased hydrogen bonding in the phosphinic acid ligand as well as synergistic coordination of the uranyl ion by a proximate P=O of a second phosphinate ligand. AMPA contacted with synthetic wet process phosphoric acid solution sorbed 72.2% uranium compared to 0.14% for a commercially available sulfonic acid.

Gas-phase acid-base properties of 1-aminocycloalkane-1-carboxylic acids from the extended kinetic method

The gas-phase proton affinities (PA) and gas-phase acidities (GA) for the non-protein amino acids 1-aminocyclopropane-1-carboxylic acid (1), 1-amino-1-cyclobutane-carboxylic acid (2), cycloleucine (3) and 1-amino-1-cyclohexane (4) have been determined using the extended kinetic method in ESI-tandem mass spectrometers. These non-protein amino acids are found in a variety of foods and can compete with other aliphatic amino acids in a variety of biochemical processes. We find a positive trend in proton affinity with an increasing ring size for the four amino acids. Experimental proton affinities of 896±8.0, 913±8.0, 931±8.0, and 933±8.0 were determined for 1–4, respectively. Hybrid density functional theory calculations at the B3LYP/6-311++G(d,p)//B3LYP/6-31+G(d) level of theory give predictions for the proton affinities of 1–4 that are in excellent agreement with the measured values and support the positive trend. In contrast, we find that the gas-phase acidities (ΔHacid) for 1–4 are the same within error. Acidities of 1425±8kJ/mol, 1424±8kJ/mol, 1428±10kJ/mol, and 1423±8kJ/mol were determined for 1–4. Theoretical predictions for the acidities for 1–4 are in excellent agreement with the measured acidities and support the conclusion that there is no trend with changing ring size.

Theory and Methodology for Determining Nanoparticle Affinity for Heteroaggregation in Environmental Matrices Using Batch Measurements

In this study, we present a method for determining the relative affinity of nanoparticles (NPs) for an ensemble of other particles in a complex, heterogeneous suspension. We evaluated this method for NPs heteroaggregating with suspended solids present in activated sludge. A relationship was derived between the heterogeneous affinity coefficient, α, and measurements over time of the distribution coefficient, γ, of NPs measured in supernatant versus those removed by heteroaggregation and subsequent settling. Application of this method, which uses a mathematical relationship to determine α from experimentally measured γ values, to a series of metal and metal oxide NPs heteroaggregated with activated sludge indicated a relative affinity in the order of pristine CeO2, TiO2 NPs, and ZnO NPs>Ag(0) NPs surface-modified with polyvinylpyrrolidone (PVP)>citrate-functionalized CeO2 NP>Ag(0) NPs surface-modified with gum arabic. This trend in relative affinity followed the observed trend in removal such that higher affinity corresponded to higher removals of NPs. Values of α were calculated from measured relative affinities using average diameter and concentration of the activated sludge particles. The value calculated for PVP-stabilized Ag(0) NPs was comparable to a value previously reported for the attachment of these same NPs to a biofilm. Calculations also yielded size dependence of α in the case of the two Ag(0) evaluated that may be linked to NP dissolution.

From Catalytic Mechanism to Rational Design of Reversible Covalent Inhibitors of Serine and Cysteine Hydrolases

AbstractMechanistic studies of catalysis and the inhibition of serine and cysteine proteases afford new and sometimes surprising insights, challenging conventional dogmas in enzymology. The intrinsic source of the difference in the catalytic mechanisms of serine and cysteine hydrolases, the origin of the stability of the enzymeinhibitor complex in serine proteases, and the structures and mechanisms of catalysis and inhibition in cysteine proteases are not just intellectually interesting; our findings provide a mechanistic basis to understand the trend in the binding affinity of “warheads” of reversible covalent (reaction coordinate analogue, RCA) inhibitors. The theoretically derived covalent descriptors W1 and W2 differentiate serine and cysteine hydrolases and account for the energetic contribution of the new covalent bond in the enzymeinhibitor complex. The W1 and W2 descriptors are at the heart of our enzyme mechanism based method (EMBM); a new computer‐assisted drug design tool for the filtration of inhibitor warheads by activity. EMBM is unique because it accounts for both covalent and noncovalent interactions of RCA inhibitors with their target enzymes.

QM-polarized ligand docking accurately predicts the trend in binding affinity of a series of arylmethylene quinuclidine-like derivatives at the α4β2 and α3β4 nicotinic acetylcholine receptors (nAChRs)

Compounds containing a quinuclidine scaffold are promising drug candidates for pharmacological management of the central nervous system (CNS) pathologies implicating nAChRs. We have carried out binding affinity and in-silico docking studies of arylmethylene quinuclidine-like derivatives at the α4β2 receptor using in-vitro receptor binding assay and comparative modeling, respectively. We found that introducing a hydrogen-bond acceptor into the 3-benzylidene quinuclidine derivative resulted in a 266-fold increase in binding affinity and confers agonism properties. By contrast, addition of a phenyl group to 3-benzylidene quinuclidine derivative only results in an 18-fold increase in binding affinity, without conferring agonism. We also found that docking into the orthosteric binding site of the α4β2 nAChR is consistent with the fact that the basic nitrogen atom donates a hydrogen-bond to the carbonyl group of the highly conserved Trp-149, as initially observed by Dougherty and co-workers.1 The experimentally-observed trend in binding affinity at both α4β2 and α3β4 nAChRs was accurately and independently confirmed by quantum mechanics (QM)-polarized docking. The reduction in binding affinity to the α3β4 subtype primarily results from a dampening of both coulombic and cation–π interactions.

Computational Study of the Coordination of Methane to First Row Transition Metal Dication Complexes

The coordination of methane, the first step in methane activation, to coordinately unsaturated first row transition metal dication complexes has been studied computationally to determine the most stable metal-methane interaction. The geometries and the vibrational frequencies of the encounter complexes [M(pyridine)2(CH4)](2+) have been determined using density functional theory with the ωB97XD hybrid functional and triple-ζ basis sets. The structure is dependent on the metal center; for the early transition metals η(3) coordination is favored, whereas η(2) is more favorable for the later transition metals. The periodic trend in methane binding energies in the [M(pyridine)2(CH4)](2+) complexes follows the trend in electron affinity until the Mn complex but then exhibits decreasing energies from Fe to Zn. This is attributed to increasing Pauli repulsion and ligand-ligand repulsion. For the most stable complex, [Cr(pyridine)2(CH4)](2+), the structures, energies, and spin states of the key intermediates and products in the oxidative addition/reductive elimination pathway have been investigated. It is found that the reaction is thermodynamically favorable and indicates that two-state reactivity may play an important role in lowering the energy of the hydridomethyl intermediate.

Pharmacological properties and predicted binding mode of arylmethylene quinuclidine-like derivatives at the α3β4 nicotinic acetylcholine receptor (nAChR)

We have carried out a pharmacological evaluation of arylmethylene quinuclidine derivatives interactions with human α3β4 nAChRs subtype, using cell-based receptor binding, calcium-influx, electrophysiological patch-clamp assays and molecular modeling techniques. We have found that the compounds bind competitively to the α3β4 receptor with micromolar affinities and some of the compounds behave as non-competitive antagonists (compounds 1, 2 and 3), displaying submicromolar IC50 values. These evidences suggest a mixed mode of action for these compounds, having interactions at the orthosteric site and more pronounced interactions at an allosteric site to block agonist effects. One of the compounds, 1-benzyl-3-(diphenylmethylene)-1-azoniabicyclo[2.2.2]octane chloride (compound 3), exhibited poorly reversible use-dependent block of α3β4 channels. We also found that removal of a phenyl group from compound 1 confers a partial agonism to the derived analog (compound 6). Introducing a hydrogen-bond acceptor into the 3-benzylidene quinuclidine derivative (compound 7) increases agonism potency at the α3β4 receptor subtype. Docking into the orthosteric binding site of a α3β4 protein structure derived by comparative modeling accurately predicted the experimentally-observed trend in binding affinity. Results supported the notion that binding requires a hydrogen bond formation between the ligand basic nitrogen and the backbone carbonyl oxygen atom of the conserved Trp-149.

Thermodynamics of the DNA binding of biogenic polyamines: Calorimetric and spectroscopic investigations

The thermodynamics of the reaction of biogenic polyamines spermine, spermidine, putrescine and cadaverine with calf thymus DNA was studied by thermal melting, differential scanning calorimetry and isothermal titration calorimetry experiments. These results were supplemented by ethidium bromide displacement and circular dichroism experiments. Melting studies show enhanced stabilization of DNA melting temperature by spermine (17K)>spermidine (11K)>putrescine (7K)>cadaverine (6K). The binding affinity of the polyamines to DNA as determined from calorimetry experiments was in the order, spermine>spermidine>putrescine>cadaverine with KiSPM=6.20×105M−1, KiSPD=3.10×105M−1, KiPUT=1.80×104M−1, and KiCAD=1.60×104M−1 at T=293.15K, which correlated with their increasing number of positive charges. The trend in the binding affinity was also in agreement with the IC50 values of ethidium bromide displacement ability and circular dichroism perturbations. Absorbance and circular dichroism studies showed perturbation of DNA conformation within the B-form by spermine to be the highest and that by cadaverine to be the least. The binding of all the four polyamines was entropy driven with small enthalpy contributions that were unfavourable. Electrostatic interaction is judged to be the major contributing force to the Gibbs energy term. The heat capacity values denote some extent of hydrophobic interaction between the polyamines and DNA.

Steric effects on alkyl cation affinities of maingroup‐element hydrides

We have carried out an extensive exploration of gas-phase alkyl cation affinities (ACA) of archetypal anionic and neutral bases across the periodic system using zeroth order regular approximation-relativistic density functional theory at BP86/QZ4P//BP86/TZ2P. ACA values were computed for the methyl, ethyl, i-propyl and t-butyl cations and compared with the corresponding proton affinities (PA). One purpose of this work is to provide an intrinsically consistent set of values of the 298 K ACA of all anionic (XH (n-1)(-)) and neutral bases (XH(n)) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (group 18) along the periods 1-6. Another purpose is to determine and rationalize the trend in affinity for a cation as the latter varies from proton to t-butyl cation. This undertaking is supported by quantitative bond energy decomposition analyses. Correlations are established between PA and ACA values.