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Titolo:
Thermodynamics of binding of (R)- and (S)-dinitrobenzoyl leucine to cinchona alkaloids and their tert-butylcarbamate derivatives in methanol: Evaluation of enantioselectivity by spectroscopic (CD, UV) and microcalorimetric (ITC) titrations
Autore:
Lah, J; Maier, NM; Lindner, W; Vesnaver, G;
Indirizzi:
Univ Ljubljana, Fac Chem & Chem Technol, Ljubljana 1000, Slovenia Univ Ljubljana Ljubljana Slovenia 1000 Technol, Ljubljana 1000, Slovenia Univ Vienna, Inst Analyt Chem, A-1090 Vienna, Austria Univ Vienna ViennaAustria A-1090 st Analyt Chem, A-1090 Vienna, Austria
Titolo Testata:
JOURNAL OF PHYSICAL CHEMISTRY B
fascicolo: 8, volume: 105, anno: 2001,
pagine: 1670 - 1678
SICI:
1520-6106(20010301)105:8<1670:TOBO
Fonte:
ISI
Lingua:
ENG
Soggetto:
NUCLEAR-MAGNETIC-RESONANCE; BETA-CYCLODEXTRIN; PROPRANOLOL ENANTIOMERS; CHIRAL RECOGNITION; ALPHA-CYCLODEXTRIN; ANION-EXCHANGERS; CHROMATOGRAPHY; SEPARATION; CELLULASE; CONSTANTS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
23
Recensione:
Indirizzi per estratti:
Indirizzo: Vesnaver, G Univ Ljubljana, Fac Chem & Chem Technol, Askerceva 5, Ljubljana 1000, Slovenia Univ Ljubljana Askerceva 5 Ljubljana Slovenia 1000 , Slovenia
Citazione:
J. Lah et al., "Thermodynamics of binding of (R)- and (S)-dinitrobenzoyl leucine to cinchona alkaloids and their tert-butylcarbamate derivatives in methanol: Evaluation of enantioselectivity by spectroscopic (CD, UV) and microcalorimetric (ITC) titrations", J PHYS CH B, 105(8), 2001, pp. 1670-1678

Abstract

Isothermal calorimetric titrations (ITC), circular dichroism (CD), and UV spectroscopy have been employed to investigate and quantify binding of the enantiomers of N-3,5-dinitrobenzoyl-leucine (DNB-Leu) and nonchiral N-3,5-dinitrobenzoyl-glycine (DNB-Gly), denoted as selectands (SAs) to the following chiral selectors (SOs): quinine (QN), quinidine (QD) and their derivatives O9-tert-butylcarbamoyl quinine (t-BuCQN) and O9-tert-butylcarbamoyl quinidine (t-BuCQD). The results reveal that DNB-Leu binds to all SOs in a 1:1 association mode. Although DNB-Leu exhibits higher affinity for QN and QD than for t-BuCQN and t-BuCQD, no preferential binding of any of the two DNB-Leu enantiomers to QN or QD was observed. By contrast, t-BuCQN binds (S)-DNB-Leu with high enantioselectivity (K-b,K-S/K-b,K-R approximate to 10), whereas the t-BuCQD derivative shows similarly high selectivity for the (R)-DNB-Leu enantiomer (K-b,K-R/K-b,K-S approximate to 10). The results of optical (CD, UV) titrations of t-BuCQN with (S)-DNB-Leu and t-BuCQD with (R)-DNB-Leu are fully consistent with those obtained from the corresponding calorimetric titrations. The induced CD spectra of (S)-DNB-Leu-t-BuCQN and (R)-DNB-Leu-t-BuCQD ionic complexes display bands of opposite sign indicating thatbinding of DNB-Leu enantiomers within the SOs molecules occurs at well-defined domains in a "pseudo-enantiomeric fashion" (Lammerhofer and Lindner, J. Chromatog. 1996, 741, 33). The relative binding constants derived from ITC, UV, and CD titrations are in good agreement with the enantioseparation factors observed with the corresponding immobilized SO versions under HPLC conditions in prior studies. The thermodynamic analysis shows that the ion-pair formation between cinchona alkaloid type SOs and DNB-leucine is a strongly enthalpy-driven process (DeltaH(b)(o) up to -38 KJ/mol), accompanied byunfavorable entropic contributions ( T DeltaS(b)(o)T DeltaS(b)(o) up to -15 kJ/mol). The observed highly exothermic DeltaH(b)(o) values result most likely from the attractive noncovalent intermolecular interactions, such as van der Waals interactions, hydrogen bonding and pi-pi interactions, whereas the negative entropy contributions apparently reflect the generation of highly ordered bimolecular ionic associates.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 07/04/20 alle ore 04:13:01