Isotope effects in liquid chromatography of imipramine and desmethylimipramine

Kudelin, B. K.; Gavrilina, L. V.

doi:10.1016/0021-9673(93)80237-3

Cited by 9 publications

(3 citation statements)

References 9 publications

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“…The conclusion that the observed isotope effects are due to ionization finds precedent in the literature. The p K a of a basic group is invariably increased by the introduction of vicinal hydrogen isotopes (see refs −26). This was seen as accelerated elution of isotopomers of N -methyl labeled benzazepines during reversed-phase chromatography; increased p K a or basicity of the amino group led to a greater proportion of charged molecules, which elute more quickly under these conditions.…”

Section: Discussionmentioning

confidence: 99%

Isotope Effect-Mapping of the Ionization of Glucose Demonstrates Unusual Charge Sharing

Lewis

Schramm

2003

J. Am. Chem. Soc.

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Isotopic substitution is known to affect kinetic rate constants and equilibrium constants in chemistry. In this study, we have used tritium substitution and high pH to probe the glucose left harpoon over right harpoon glucose(-) + H(+) equilibrium. Passing partially ionized mixtures of [(3)H]- and [(14)C]glucose over anionic exchange resin has permitted the detection of subtle differences in pK(a). We have found that, at pH 11.7 in an anionic exchange system, [(3)H]glucose always elutes ahead of the [(14)C]glucose, and we report isotope effects of 1.051 +/- 0.0007, 1.012 +/- 1.0005, 1.014 +/- 0.0004, 1.024 +/- 0.0003, 1.014 +/- 0.0004, and 1.015 +/- 0.0014 for [1-(3)H]-, [2-(3)H]-, [3-(3)H]-, [4-(3)H]-, [5-(3)H]-, and [6,6-(3)H(2)]glucose, respectively, as compared to either [2-(14)C]-or [6-(14)C]glucose. The elevated isotope effects at H1 and H4 imply unusual charge sharing in anionic aqueous glucose. Base titration of (13)C-chemical shift changes demonstrates the dominance of pyranose forms at elevated pH, and ab initio isotope effect computations on gas-phase glucose anions are presented.

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Section: Discussionmentioning

confidence: 99%

Isotope Effect-Mapping of the Ionization of Glucose Demonstrates Unusual Charge Sharing

Lewis

Schramm

2003

J. Am. Chem. Soc.

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“…The steric imposition of an active site group directly upon a CH bond causes an inverse isotope effect on the binding equilibrium constant. Normal effects occur on full or partial deprotonation of neighboring groups. − The latter result is due to increased potential energy of heteroatom electron lone-pairs, which become more free to donate density to the antibonding orbital of the CH of interest through an increase in n−σ* hyperconjugation. A similar mechanism has been used to explain CH bond effects due to hydroxyl torsional angle changes in 2-propanol …”

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confidence: 99%

Glucose Binding Isotope Effects in the Ternary Complex of Brain Hexokinase Demonstrate Partial Relief of Ground-State Destabilization

Lewis

Schramm

2003

J. Am. Chem. Soc.

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Isotope effects can yield detailed information about contacts made between a bound compound and its host receptor or enzyme. In this study, we have measured isotope effects upon the equilibrium constant for the association of glucose and human brain hexokinase [E.C.2.7.1.1] in the presence of beta,gamma-CH(2)-ATP and compared these with data for the same equilibrium in the absence of ATP-analogue. We have found isotope effects of 1.012, 0.929, 1.031, 1.052, 0.998, and 1.032 for the competitive binding of [1-(3)H]-, [2-(3)H]-, [3-(3)H]-, [4-(3)H]-, [5-(3)H]-, or [6,6-(3)H(2)]- and either [2-(14)C]- or [6-(14)C]glucose to brain hexokinase. We observed changes only at H1, H5, and H6, and we attribute these to a slight change in the position of Asn683 and Glu742 due to nucleotide binding and to partial satisfaction of activated OH6 by the terminal nucleotide phosphorus.

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“…This phenomenon was observed with isotopically labeled compounds such as simple ammonium ions [19], for which the high isotopic influence enables chromatographic separation. It has also been observed for deuterated [20], tritiated [21], and carbon-labeled compounds [22].…”

Section: Isotope Fractionationmentioning

confidence: 73%

Liquid chromatographic enrichment ofN-acetylmethionine from casein hydrolysates for stable-isotope-ratio analysis of sulfur

Lamprecht

Haberhauer²

2001

Chromatographia

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Key WardsColumn liquid chromatography Sulfur stable-isotope-ratio analysis Isotope-fractionation Casein N-Acetylmethionine SummaryA chromatographic method has been developed for enrichment of methionine-bouncl sulfur ~n casein, for stable-isotope analysis. Casein is precipitated from milk samples and cleaved by acid hydrolysis in 6 M hydrochloric acid at 95 ~ The amino acids released are converted into their N-acetyl derivatives by addition of acetic acid anhydride. After lyophihzation, N-ace@-methionine is separated from the accompanying components on octaclecylsilica by use of a gradient prepared from 0.02 M formic acid and methanol. The fractions containing N-ace@-methionine are pooled and freeze dried. Procedures for hydrolysis and clerivatization were optimized to furnish the highest yields. The influence of the abundance ratio on the chromatographic separation is shown and discussed. From 1.0 g casein 16.5 mg N-acetylmethionine were isolated.

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Isotope effects in liquid chromatography of imipramine and desmethylimipramine

Cited by 9 publications

References 9 publications

Isotope Effect-Mapping of the Ionization of Glucose Demonstrates Unusual Charge Sharing

Isotope Effect-Mapping of the Ionization of Glucose Demonstrates Unusual Charge Sharing

Glucose Binding Isotope Effects in the Ternary Complex of Brain Hexokinase Demonstrate Partial Relief of Ground-State Destabilization

Liquid chromatographic enrichment ofN-acetylmethionine from casein hydrolysates for stable-isotope-ratio analysis of sulfur

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