Protonation of noncyclic and cyclic diamines in aqueous solution

Dantz, D. A.; Buschmann, Hans‐Jürgen; Schollmeyer, Eckhard

doi:10.1016/s0040-6031(97)00036-1

Cited by 12 publications

(4 citation statements)

References 36 publications

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“…The pH was adjusted at 25 °C to 7.0−7.3 by direct addition of the azacrown ether, whereas in the absence of the ether, pH was adjusted to 6.9−7.4 with NaOH. (Because the p K a 1 of 4,13-diaza-18-crown-6 is 7.94 at 25 °C, we utilized the azacrown ether to buffer the reaction pH. As expected, pre- and postreaction measurements revealed minimal pH drift; Table .)…”

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confidence: 66%

Unprecedented Acceleration of Zirconium(IV)-Assisted Peptide Hydrolysis at Neutral pH

et al. 2004

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confidence: 66%

Unprecedented Acceleration of Zirconium(IV)-Assisted Peptide Hydrolysis at Neutral pH

et al. 2004

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“…The protonation of the N 1 and N 2 atoms of the macrocycle influenced the basicity of the ligands, which is known to decrease from secondary to tertiary amines. 104 Among the two competing effects, Lewis acidity and nucleophile activation, the latter was found to dominate the activities of these complexes.…”

Section: Resultsmentioning

confidence: 99%

“…These results suggested that the doubly deprotonated form of the N 2 O 4 core containing complex ( I DN2O4 ) hydrolyzed the peptide bond with the lowest barrier (30.6 kcal/mol). The protonation of the N 1 and N 2 atoms of the macrocycle influenced the basicity of the ligands, which is known to decrease from secondary to tertiary amines . Among the two competing effects, Lewis acidity and nucleophile activation, the latter was found to dominate the activities of these complexes.…”

Section: Results and Discussionmentioning

confidence: 99%

Effects of Ligand Environment in Zr(IV) Assisted Peptide Hydrolysis

Zhang

Sharma

Paul

et al. 2017

J. Chem. Inf. Model.

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In this DFT study, activities of 11 different NO, NO, and NO core containing Zr(IV) complexes, 4,13-diaza-18-crown-6 (I'), 1,4,10-trioxa-7,13-diazacyclopentadecane (I'), and 2-(2-methoxy)ethanol (I'), respectively, and their analogues in peptide hydrolysis have been investigated. Based on the experimental information, these molecules were created by altering protonation states (singly protonated, doubly protonated, or doubly deprotonated) and number of their ligands. The energetics of the I', and I' and their analogues predicted that both stepwise and concerted mechanisms occurred either with similar barriers, or the latter was more favorable than the former. They also showed that the doubly deprotonated form hydrolyzed the peptide bond with substantially lower barriers than the barriers for other protonation states. For NO core possessing complexes, Zr-(NO)(OH)(HO/OH) for n = 1-3, the hydroxyl group containing molecules were found to be more reactive than their water ligand possessing counterparts. The barriers for these complexes reduced with an increase in the coordination number (6-8) of the Zr(IV) ion. Among all 11 molecules, the NO core possessing and two hydroxyl group containing I' complex was found to be the most reactive complex with a barrier of 28.9 kcal/mol. Furthermore, barriers of 27.5, 28.9, and 32.0 kcal/mol for hydrolysis of Gly-Glu (negative), Gly-Gly (neutral), and Gly-Lys (positive) substrates, respectively, by this complex were in agreement with experiments. The activities of these complexes were explained in terms of basicity of their ligand environment and nucleophilicity of the Zr(IV) center using metal-ligand distances, charge on the metal ion, and the metal-nucleophile distance as parameters. These results provide a deeper understanding of the functioning of these complexes and will help design Zr(IV)-based synthetic metallopeptidases.

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“…The p K a values of diaza‐crown ethers are about 9 , so that the compounds are protonated at the pH values studied. Interestingly, none of the analytes could be detected at pH 2.5 in the presence of Kryptofix® 22 under both, normal and reversed polarity of the separation voltage.…”

Section: Resultsmentioning

confidence: 99%

Capillary electrophoresis separation of peptide diastereomers that contain methionine sulfoxide by dual cyclodextrin‐crown ether systems†

Zhu

Heinemann

Schönherr

et al. 2014

J of Separation Science

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A dual-selector system employing achiral crown ethers in combination with cyclodextrins has been developed for the separation of peptide diastereomers that contain methionine sulfoxide. The combinations of the crown ethers 15-crown-5, 18-crown-6, Kryptofix® 21 and Kryptofix® 22 and β-cyclodextrin, carboxymethyl-β-cyclodextrin, and sulfated β-cyclodextrin were screened at pH 2.5 and pH 8.0 using a 40/50.2 cm, 50 μm id fused-silica capillary and a separation voltage of 25 kV. No diastereomer separation was observed in the sole presence of crown ethers, while only sulfated β-cyclodextrin was able to resolve some peptide diastereomers at pH 8.0. Depending on the amino acid sequence of the peptide and the applied cyclodextrin, the addition of crown ethers, especially the Krpytofix® diaza-crown ethers, resulted in significantly enhanced chiral recognition. Keeping one selector of the dual system constant, increasing concentrations of the second selector resulted in increased peak resolution and analyte migration time for peptide-crown ether-cyclodextrin combinations. The simultaneous diastereomer separation of three structurally related peptides was achieved using the dual selector system.

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Protonation of noncyclic and cyclic diamines in aqueous solution

Cited by 12 publications

References 36 publications

Unprecedented Acceleration of Zirconium(IV)-Assisted Peptide Hydrolysis at Neutral pH

Unprecedented Acceleration of Zirconium(IV)-Assisted Peptide Hydrolysis at Neutral pH

Effects of Ligand Environment in Zr(IV) Assisted Peptide Hydrolysis

Capillary electrophoresis separation of peptide diastereomers that contain methionine sulfoxide by dual cyclodextrin‐crown ether systems†

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