Proton cryptates. Kinetics and thermodynamics of protonation of the [1.1.1] macrobicyclic cryptand

Smith, Patrick B.; Dye, James; Cheney, John; Lehn, Jean Marie

doi:10.1021/ja00410a009

Cited by 93 publications

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“…in a controlled way inside a reaction vessel. [1.1.1]Cryptand [16][17][18] was used as a variable-pH device to carry out variable-pH kinetic (VpHK) experiments and obtain, in a single run, the pH-rate profile of a drug. [14] Acetic anhydride was used as a variable-temperature device to carry out a variable-temperature kinetic (VTK) experiment and obtain, in a single run, the activation parameters of a reaction of a metal-organic complex.…”

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“…Scheme 1 describes the three chemical systems present in the reaction vessel in which our apparatus was used. A) The VpH-KMD [1.1.1]cryptand acts as a molecular titrator hydrolysing rapidly and reversibly and then reacting slowly and irreversibly to give a protonentrapped species, [16][17][18] generating an almost linear increase of pH for about 2-3 pH units in the range 4-11. [2,14,19] B) Bromothymol blue (BTB) acts as a pH meter that, changing the equilibrium between its acid and basic forms by detecting the pH modulated by the cryptand, gives an absorbance signal directly linked to the pH.…”

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Molecular Apparatus for Automatic Titrations

Alibrandi

Vecchio

Villari

et al. 2010

Chemistry A European J

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Molecular Apparatus for Automatic Titrations

Alibrandi

Vecchio

Villari

et al. 2010

Chemistry A European J

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“…This is the case for [1.1.1]cryptand (4,10,15-trioxa-1,7-diazabicyclo[5.5.5]heptadecane), which behaves as a proton sponge that can capture hydrogen ions from solution equilibria in a selective, slow, and irreversible way. [2][3][4] It was for this reason that [1.1.1]cryptand was recently used, many years after it was initially reported, as a chemical device for variable-pH kinetic (VpHK) experiments. Use of [1.1.1]cryptand enabled the kinetic experiment of a pH sensitive reaction to be carried out while the pH was changed in a controlled way, and was thus an alternative to a physical device (an autoburette).…”

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“…4 to give pH i = 6.5, and one drop of a concentrated solution of phenol red (ca. 1 10 À4 m in the cuvette).…”

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[1.1.1]Cryptand: A Molecular Automatic Titrator

2009

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Old dog, new tricks! The pH value of a solution changes slowly and irreversibly over time when [1.1.1]cryptand is used as an automatic molecular titrator. The pKa value of phenol red was determined spectrophotometrically in a completely automatic run, without the need for external input adjustments (see picture, A=absorption, Acalcd=theoretical absorption). The experiment is proposed as a model for the automatic determination of thermodynamic parameters.

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“…Cryptand 111 (4,10,15-trioxa-1,7-diazabicyclo[5.5.5]heptadecane) is a good candidate as a chemical device for VpHK experiments. [7] It was synthesized by Lehn and Cheney [15] and kinetically characterized by Dye et al [16] The peculiarity of this "proton sponge" is that it abstracts the H + ion in solution not in a fast and reversible way but slowly and irreversibly.…”

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Cryptand 111: A Chemical Device for Variable‐pH Kinetic Experiments

Alibrandi

2008

Angew Chem Int Ed

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A device is a machine or tool used for a specific task.[1] A chemical device is a molecular species capable of performing a function at the molecular level, for example, as a drug carrier, an enzyme, or a molecular switch.[2] During my studies aimed at developing variable-parameter kinetics [3][4][5][6][7][8][9][10][11][12][13] (VPaK) I thought of exploring the possibility to use chemical systems, instead of physical ones, to change, in a known way, the value of an environmental parameter (pH, temperature, ionic strength I, concentration of a nuleophile C Nu , etc.) inside a reaction vessel.Variable-parameter kinetics enables one to obtain the dependence of the specific rate of a reaction on a physical parameter (pH, T, I, C Nu , etc.) in a single experiment. It consists of measuring kinetics while varying the value of the parameter and fitting the obtained kinetic profiles to suitably modified kinetic equations. For a general reaction in which a species A reacts to give products, the mathematical model describing these experiments is given by Equation (1), where C is the molar concentration of species A and k obs is the specific rate function of the parameter i varying with time. k obs (Par i ) is the dependence function [8] describing how k obs depends on the parameter; Par i (t) is the modulating function [8] describing how the parameter changes with time.For example, in a variable-temperature kinetic (VTK) experiment carried out by applying a linear increase of temperature with time, a sigmoidal kinetic profile is usually obtained, as described by Equation (2) (integral form) where C 0 is the molar concentration of A at the start of the reaction, the dependence function is the Eyring equation, [14] and the modulating function is T(t) = T 0 + at.By fitting the VTK experimental data to Equation (2), the activation parameters DS°and DH°, and then the k obs (T) profile, can be obtained. For a variable-pH kinetic (VpHK) experiment, the model is given by Equation (3), where the dependence function is given by the pH-rate profile and the modulating function describes how the pH changes with time.Several methods have been devised to produce the effects described by the modulating functions, but they always involve physical devices and external inputs to change the composition or the thermodynamic parameters of the solution (autoburettes to change the concentration of the nucleophile with time, [3,10] pH, [7,11] ionic strength; [12] temperature programmers to change the temperature [4][5][6]9] ). To change the pH inside the reaction vessel, for example, an autoburette was used to release a concentrated solution of NaOH into a reaction environment containing 0.01m CH 3 COOH, 0.01m H 3 PO 4 and 0.01m H 3 BO 3 to give an actual concentration of base in solution ofand V/L are, respectively, the release rate, the concentration of NaOH, and the reaction volume) and an almost linear increase of pH in the range 3-10. [7] Here I introduce for the first time the use of a chemical species as the origin of the variable-parameter ...

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Proton cryptates. Kinetics and thermodynamics of protonation of the [1.1.1] macrobicyclic cryptand

Cited by 93 publications

References 0 publications

Molecular Apparatus for Automatic Titrations

Molecular Apparatus for Automatic Titrations

[1.1.1]Cryptand: A Molecular Automatic Titrator

Cryptand 111: A Chemical Device for Variable‐pH Kinetic Experiments

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