The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M-1. Affinities close to 105 M-1 are found for polyazacryptands (3 and 4) exhibiting F-/Cl- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes.

The kinetics of ATP-induced phosphorylation and K+ binding of Na,K-ATPase has been investigated at different pressures by applying the fluorescence stopped-flow method. For both type of reactions, a conformational transition is considered to act as rate-limiting reaction step. These transitions are characterized by large activation volumes up to +100 ml mol−1. The significance of the determined values in terms of Kramers’ theory is discussed. A molecular interpretation related to solvation changes and cavity formation in the transmembrane domain of the protein is suggested. A large negative reaction volume is found upon ATP binding (—100 ml mol−1). The selective binding of Na+ and K+ leads to smaller, but positive values.

The first variable-temperature and variable-pressure stopped-flow spectrophotometric study of the sequential threading of alpha-cyclodextrin (alpha-CD) onto the guest dye Mordant Orange 10, S, is reported. Complementary (1)H one-dimensional (1D) variable-temperature kinetic studies and two-dimensional (2D) rotating-frame nuclear Overhauser effect spectroscopy (ROESY) and EXSY NMR studies are also reported. In aqueous solution at 298.2 K, the first alpha-CD threads onto S to form a 1:1 complex S.alpha-CD with a forward rate constant k(1,f) = 15 200 +/- 200 M(-1) s(-1) and dethreads with a reverse rate constant k(1,r) = 4.4 +/- 0.3 s(-1). Subsequently, S.alpha-CD isomerizes to S.alpha-CD (k(3,f) = 0.158 +/- 0.006 s(-1), k(3,f) = 0.148 +/- 0.006 s(-1)). This process can be viewed as a thermodynamically controlled molecular shuttle. A second alpha-CD threads onto S.alpha-CD to form a 1:2 complex, S.(alpha-CD)(2), with k(2,f) = 98 +/- 2 M(-1) s(-1) and k(2,r) = 0.032 +/- 0.002 s(-1). A second alpha-CD also threads onto S.alpha-CD to form another 1:2 complex, S.(alpha-CD)(2), characterized by k(4,f) = 9640 +/- 1800 M(-1) s(-1) and k(4,r) = 61 +/- 6 s(-1). Direct interconvertion between S.(alpha-CD)(2) and S.(alpha-CD)(2) was not detected; instead, they interconvert by dethreading the second alpha-CD and through the isomerization equilibrium between S.alpha-CD and S.alpha-CD. The reaction volumes, DeltaV(0), were found to be negative for the first three equilibria and positive for the fourth equilibrium. For the first three forward and reverse reactions, the volumes of activation are substantially more negative, indicating a compression of the transition state in comparison with the ground states. These data were used in conjunction with DeltaH, DeltaH degrees, DeltaS, and DeltaS degrees data to deduce the dominant mechanistic threading processes, which appear to be largely controlled by changes in hydration and van der Waals interactions, and possibly by conformational changes in both S and alpha-CD. The structure of the four complexes were deduced from (1)H 2D ROESY NMR studies.

The first volume profiles for complex formation of α-cyclodextrins (α-CD) with diphenyl azo dyes (S) are presented as a new approach in understanding inclusion phenomena. The following dyes were selected:  sodium 4-(4-diethylaminophenylazo)benzenesulfonate (1), sodium 4-(3-carboxy-4-hydroxy-5-methylphenylazo)benzenesulfonate (2), sodium 4-(4-hydroxy-3,5-dimethylphenylazo)benzenesulfonate (3), and sodium 2-hydroxy-3-methyl-5-(4-sulfamoylphenylazo)benzoate (4). The behavior of the dyes alone were first studied in aqueous solutions to rule out any competition reaction. Under the experimental conditions used for the stopped-flow kinetic studies, it has been proved that only monomeric species are present (no aggregation of the dye is formed by π−π stacking interactions). NMR experiments and kinetic evidences have shown that only directional binding of the dye via the sulfonate/sulfonamide group through the wide rim of the α-cyclodextrin was possible. The 1:1 complex was the only stoichiometric species formed. ...

The full volume and entropy profiles of the inclusion reaction between alpha-cyclodextrin and the guest molecule, mordant yellow 7, are constructed from variable pressure and temperature kinetic experiments, showing a two-step mechanism where both steps involve contracted transition states.

The development of a stopped-flow instrument that operates over a temperature range of -40 to +100 °C and up to 200 MPa is described. The system has been designed so that measurements can be performed in absorbance and fluorescence modes simultaneously, without dismantling the unit. It can easily be combined with an optical system of a conventional ambient pressure setup by using light guides. Optimum optical performance and a wide operating wavelength range (220-850 nm) are achieved as the light is not passing through the pressurizing fluid. A special design for the pistons has been developed; thus, the apparatus has proven to be leak-free, even under extreme conditions (high pressure, low temperature, various solvents). The dead time of the system is found to be less than 2 ms at 298 K and is pressure independent up to 200 MPa. We examined the kinetics for the formation of the Mg(2+)-8-hydroxyquinoline chelate in aqueous solutions at pH 8.0 in order to develop a convenient alternative test method for high-pressure stopped-flow spectrometers with absorption and fluorescence detection.

The full volume and entropy profiles of the inclusion reaction between ?-cyclodextrin and the guest molecules, ethylorange (1) and mordant yellow 7 (2), have been constructed from variable-pressure and -temperature stopped-flow kinetic experiments.

First order global analysis consists of linking common parameters across series of measurements, e.g., reaction kinetics measured at different wavelengths where the rate constants are the same for all kinetic traces at individual wavelengths. This approach is taken a step further in second order globalisation. A series of measurements is linked together by a new superimposed model which encompasses the individual measurements. The mathematics for the non-linear least-squares fit of the global parameters is presented. Two modes are possible depending on whether the linear parameters (absorption spectra) are constant or changing across the series. Factor analysis is incorporated for multivariate measurements. The procedures are exemplified with applications of activation analysis in chemical kinetics. Global analysis of complete temperature and pressure dependences results directly in the activation parameters of interest, i.e., activation enthalpies, entropies and volumes. Due to a significant decrease in the number of parameters to be fitted, the robustness is considerably improved.

The kinetics of the monocomplex formation and dissociation of [Co(Cl-phen)]2+ and [Ni(Cl-phen)]2+ (Cl-phen=2-chloro-1,10-phenanthroline) in aqueous solution have been studied as a function of temperature, pressure and excess metal ion. The dissociation of these complexes was followed by adding Cu2+ to a solution of the complex [Co(Cl-phen)]2+ or [Ni(Cl-phen)]2+. The rate constants, activation enthalpies, entropies and volumes, and the corresponding thermodynamic parameters obtained for [Co(Cl-phen)]2+ (and for [Ni(Cl-phen)]2+) are as follows: k298f (M−1 s−1)=5.7x104 (1.3x103); k298r (s−1)=7.1 (0.025); ΔH‡f (kJ mol−1)=47.1 (53.5); ΔH‡f (kJ mol−1)=59.2 (80.7); ΔS‡f (J K−1 mol−1)=+4 (−6); ΔS‡f (J K−1 mol−1)=−30 (−5); ΔV‡f (cm3 mol−1)=+6.6 (+6.0); ΔV‡r (cm3 mol−1)=+0.2 (+2.1); log K298 (M−1)=3.91 (4.71); ΔHo (kJ mol−1)=−12.1 (−27.2); ΔSo (J K−1 mol1)=+34 (−1); ΔVo (cm3 mol−1)=+6.4 (+3.9). It is concluded that the complex formation reactions on both metal ions take place via dissociative interchange Id mechanisms.