Daniel A. Laufer

The complexation chemistry of cyclohexaamyloses: Adducts with 1-adamantanecarboxylic acid and anion

Abstract A study is reported of complexation reactions of cyclohexaamylose (Cy) with 1-adamantanecarboxylic acid and its anion using conductometry, pH potentiometry, and 13 C nmr spectrometry. Binary and ternary (2 mol Cy/mol substrate) complexes are detected with both the acid and anion, and standard entropies and enthalpies of complexation are determined from the temperature dependences of the formation constants for all except the very weak ternary complex with the anion. Both the 13 C nmr results and the entropy of complexation confirm the earlier suggestion that the anion in binary complexation is structured with the adamantanyl group in proximity to, but not penetrating, the Cy cavity. However, a negative Δ S o for formation of this complex is reported which casts doubt on an earlier proposal that the adamantyl binary complex binding mode involves an “apolar” mechanism accompanied by loss of solvated water molecules. Values are also reported for p K a , Δ H o , and Δ S o for the aqueous dissociation of 1-adamantanecarboxylic acid.

Carbon-13 nuclear magnetic resonance spectra ofp-aminobenzoic acid oligomers: Range dependence of additive substituent effects

Abstract Analysis of13C chemical shifts ofp-aminobenzoic acid oligomers indicates that13C NMR additivity rules of 1,4-phenylene derivatives are distorted by interaction among substituents. These interactions are sharply attenuated, and additivity rules become more exact, as the substituents are placed farther apart. Additivity deviation terms of amino-substituted monomeric and dimeric series are correlated with corresponding terms of analogous nitro-substituted series.

13 C nuclear magnetic resonance study of acid–base tautomeric equilibria

Acid–base tautomerisation equilibria are reported for o-, m-, and p-aminobenzoic acids, p-aminophenylacetic acid, pyridine-3-carboxylic (nicotinic) acid, and pyridine-4-carboxylic (isonicotinic) acid. These equilibria are determined by modelling the displacements of 13C n.m.r. chemical shifts of each carbon due to protonation of basic sites. The models are based on the corresponding displacement due to protonation of as many as twelve related compounds. Each such model compound yields several independent estimates of the tautomeric partitioning ratio corresponding to the several carbon resonances. It is observed that the mean tautomeric partitioning ratio and its estimated uncertainty are independent of the nature or the location of ring substituents and are unaffected by heteroatom substitution in the aromatic ring. This observation has led to the development of generic models for 13C n.m.r. chemical shift protonation displacements based on collections of similar model compounds. The use of generic models summarises and simplifies the determination of tautomeric equilibria.

Adamantan-1-ylamine and adamantan-1-ylamine hydrochloride complexes with cycloamyloses

Using both pH potentiometry and spectrophotometry, aqueous complex formation constants have been measured over a range of temperatures for both cyclohexa-amylose (α-cyclodextrin) and cycloheptaamylose (β-cyclodextrin) with substrates amantadine (adamantan-1-ylamine) and amantadine hydrochloride. Both forms of cycloamylose complex with either amantadine or the hydrochloride with 1:1 stoicheiometry and cyclohexa-amylose complexes with amantadine with 2:1 stoicheiometry also. The formation constants for the cyclohepta-amylose adducts are unusually strong, ca. 1 × 105 and 1 × 104 for amantadine and the hydrochloride, respectively. Enthalpies and entropies of formation are estimated for each complex from the temperature dependence of the equilibrium constants. These ΔH° and ΔS° values together with measurements of 13C n.m.r. chemical shift displacements of carbons on both host and substrate species lead to speculation about the structures and binding mechanisms of the complexes. The spectrophotometric experiments also yielded complex formation constants of both cycloamyloses with acidic and basic forms of the indicator Methyl Orange. ΔH° and ΔS° values of these complexes are also calculated.

Aqueous complexation constants of cyclohexaamylose with p-iodoaniline and p-iodo anilinium ion☆

Abstract Formation constants for binary complexes of cyclohexaamylose (Cy) with p -iodoaniline (B) and p -iodoanilinium cation (BH + ) were determined by means of pH potentiometric experiments at 10–45°. The temperature dependences of these constants yielded the following thermodynamic parameters: Δ H ° CyB = −8.2 ± 0.5 kcal · mol −1 , Δ S ° CyB = −12.1 ± 1.8 cal · mol −1 · K −1 ; and Δ H ° CyBH Psu+ = −6.3 ± 0.7 kcal · mol −1 , Δ S ° CyBH + = −7.6 ± 2.2 cal · mol −1 . K −1 . Enthalpic and entropic contributions to the overall complexation of BH + are discussed in terms of partial desolvation of the cationic center upon binding. A 13 C-n.m.r. investigation confirmed a configuration of the Cy · BH + complex reported earlier.