Enantiomeric Separation of Alcohols by Gas Chromatography Using Cyclodextrin Derivatives as Stationary Phases

Enantiomeric Separation of Alcohols by Gas Chromatography Using Cyclodextrin Derivatives as Stationary Phases
Author: Ornuma Konghuirob
Publisher:
Total Pages: 216
Release: 2004
Genre: Alcohol
ISBN: 9789745314641

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Enantiomeric separations of 70 alcohols were studied by means of capillary gas chromatography using heptakis(2,3-di-O-¬methyl-6-O-tert-butyldimethylsilyl)cyclomaltoheptasose (or BSiMe) and octakis(2,3-di-O-¬methyl-6-O-tert-butyldimethylsilyl)cyclomaltooctaose (or GSiMe) as chiral stationary phases. The influence of analyte structure, e.g. the type and position of substituent, alcohol chain length, the position of chiral center, and main-structure of alcohols, on retention and enantioselectivity was systematically investigated. Thermodynamic data were also calculated to clarify the strength of analyte-stationary phase interaction and enantioselectivity towards the selected group of alcohols. All of alcohols studied, except for 35F and 2oct, were successfully separated with either BSiMe or GSiMe, or both of them. Generally, BSiMe phase exhibited grater enantioseparation towards most analytes than GSiMe phase. On both columns, the structure of alcohol analytes plays an important role on separation. Changing the position of substituent or chiral center causes changes in the interaction and enantioselectivity. The type and size of substituent also significantly affect enantioselectivity. In addition to the analyte structure, the size of cyclodextrin molecules greatly affects enantioselectivity.

ENANTIOMERIC SEPARATION OF ALCOHOLS BY GAS CHROMATOGRAPHY USING BETA-CYCLODEXTRIN DERIVATIVE AS STATIONARY PHASE

ENANTIOMERIC SEPARATION OF ALCOHOLS BY GAS CHROMATOGRAPHY USING BETA-CYCLODEXTRIN DERIVATIVE AS STATIONARY PHASE
Author: Morrakot Jongjitwattana
Publisher:
Total Pages: 174
Release: 2014
Genre: Alcohol
ISBN:

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Enantiomeric separation of forty alcohols based on 1-phenylethanol was studied by gas chromatography using heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-ß-CD (or BSiAc) as a chiral stationary phase. Factors affecting analyte retentions and enantioselectivities were studied: column temperature, alcohol structure (type and position of substitution) as well as type of alcohol derivatization (trifluoroacetyl (TFA) and trimethylsilyl (TMS)). The number of underivatized alcohols that could be separated into their enantiomers was higher than those of derivatized forms. Temperature affected enantioselectivities of meta-substituted underivatized alcohols more than para- or ortho-isomers, while it affected enantioselectivities of para-substituted derivatized alcohols more than other isomers. However, derivatization could improve enantioseparation of some alcohols and may provide more symmetrical peak shapes. In addition, many TFA derivatives showed complete enantioseparation in shorter analysis time than their corresponding underivatized alcohols. In this study, enantiomeric separation of all analytes, either underivatized or derivatized form, could be observed. The shortest analysis time for complete enantioseparation was observed for 18-TFA.

Modified Cyclodextrins for Chiral Separation

Modified Cyclodextrins for Chiral Separation
Author: Weihua Tang
Publisher: Springer Science & Business Media
Total Pages: 266
Release: 2013-05-24
Genre: Science
ISBN: 3642376487

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Modified Cyclodextrins for Chiral Separation offers a review of the latest advances in developing modified cyclodextrins as chiral selectors for various chromatographic and electromigration techniques. Over the years, many descriptions of chiral separation have appeared in academic journals and books, but most of them have been devoted to either the development of analytical methods and protocols or the summary of different chiral selectors, including cyclodextrins for chiral separation applications. This is in marked contrast to this volume which focuses on the research endeavors concerning the development of cyclodextrin derivatives specifically as either chiral mobile phases for capillary electrophoresis, or chiral stationary phases for various chromatographic techniques including gas chromatography, or high-performance liquid chromatography and supercritical fluid chromatography. The ongoing thread in this book is the synthesis of structurally-defined cyclodextrin derivatives and their applications in enantiomer separation by means of different analytical techniques. Modified Cyclodextrins for Chiral Separation is intended for those who are interested in expanding their knowledge of cyclodextrin chemistry and chiral separation, and in what cyclodextrin modification can be made to suit the needs of chiral selectors for different analytical techniques. It primarily focuses on the state-of-the-art cyclodextrin chemistry which is the basis for all chiral selectors used in these chiral separation techniques. Weihua Tang, PhD, is a professor at the Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, Nanjing University of Science and Technology, China. Siu-Choon Ng, PhD, is a professor at the Division of Chemical and Biomedical Engineering, School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore. Dongping Sun, PhD, is a professor at the Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, Nanjing University of Science and Technology, China.

Enantiomeric Separation of Epoxides by Gas Chromatography Using Derivatized Beta-cyclodextrin as Stationary Phase

Enantiomeric Separation of Epoxides by Gas Chromatography Using Derivatized Beta-cyclodextrin as Stationary Phase
Author:
Publisher:
Total Pages:
Release: 2004
Genre: Cyclodextrins
ISBN: 9789741761289

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Eanatiomeric separations of aromatic epoxides were studied by means of capillary gas chromatography using heptakis(2,3,di-O-methyl-6-O-tert-butyldi methylisilyl)cyclomaltoheptaose (or BSiMe) and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsiloyl)cyclomaltoheptaose (or BSiAc) as chiral stationary phases. The effects of substitution types and position of styrene oxide derivatives on retention and enantioselectivity have been investigated. Thermodynamic data on the interaction of enantiomers with chiral stationary phases were collected in detail in order to clarify the strength of analyte-stationary phase interaction and enantioselectivity towards the selected groups of epoxides. All eposides with different substitution type and position were successfully separated with either BSiMe or BSiAc, or otherwise both of them. On both columns, the number, type, and position of analyte substitution have a strong influence on enantioselectivity. The type of substituent on cyclodextrin molecule (BSiMe vs.BSiAc) also affect enatioselectivity of epoxides greatly. Both columns can be used to compliment one another as their resolving abilities are quite opposite.

Gas Charomatographic Enatiomeric Separation of Alcohols Using Derivatized Alpha-cyclodextrin Stationary Phase

Gas Charomatographic Enatiomeric Separation of Alcohols Using Derivatized Alpha-cyclodextrin Stationary Phase
Author:
Publisher:
Total Pages: 224
Release: 2006
Genre: Cyclodextrins
ISBN:

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Enantiomeric separations of 90 alcohols were studied by means of capillary gas chromatography using hexakis (2,3-di-O-methyl-6-O-tert-butyldimethylisilyl)cyclo-maltohexaose (or ASiMe) as chiral stationary phase. The influence of type, position and number of substituent, position of chiral center, and main-structure of alcohols, on retention and enantioselectivity was systematically investigated. Thermodynamic data and molecular docking calculation were also acquired to clarify the strength of analyte-stationary phase interaction and the mechanism of chiral recognition towards the selected groups of alcohols. The gas chromatographic results indicated that all tested analytes, except for 12,15,17, 4OMe, 4OMeBen and 2but, could be successfully enantioseparated with ASiMe. Among 90 alcohols studied, the best enantioseparation was observed on 1-(2,5-difluorophenyl)-ethanol. The effect of position of substituent towards enantioseparation was clearly seen from mono-substituted 1-phenylethanols. The enantioseparation increased as the position of substituent was in the order of para-

Design and Synthesis of Novel [beta]-cyclodextrins and Their Application as Chiral Stationary Phases for Gas Chromatography

Design and Synthesis of Novel [beta]-cyclodextrins and Their Application as Chiral Stationary Phases for Gas Chromatography
Author: Tiffany R. Turner Hayden
Publisher:
Total Pages:
Release: 2010
Genre:
ISBN:

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Enantiomers can be directly separated only with use of systems containing a chiral selector. Cyclodextrins (CDs) and modified cyclodextrins have been used as chiral selectors for their ability to form host-guest complexes with various analytes. The scaffold of the CD allows for assembly of functional groups with controlled geometry. CDs can be readily modified through substitution of the hydroxyl groups, giving rise to derivatives with significantly different properties, especially increased solubility and controlling the hydrophobicity of the cavity. Even though CDs can be readily modified, the syntheses can be tedious and complicated with various protecting group strategies to control the reactivity of the various alcohols. The preparation of modified cyclodextrins for use as chiral stationary phases (CSP) for gas chromatography (GC) is the focal point of this research. Our effort to identify useful new [beta]-CD derivatives involved attempts to make bridged (annulated) derivatives, could increase the thermal stability of the derivatives, and change the length, width and polarity of the CD cavity. To date, there are no reports of annulated CD derivatives in the chemical literature. In the process of evaluating a wide range of electrophiles that could accomplish annulation, several new [beta]-CD derivatives, i.e., per(6-O-TBS-2,3-O-cyclodimethylsilyl)- [beta]-CD, per(6-O-TBS-2,3-O-cyclodiphenylsilyl)- [beta]-CD, per(6-O-Pivaloyl-2,3-O-cyclodimethylsilyl)-[beta]-CD, per(6-deoxy-2,3-O-methyl)- [beta]-CD, and per(6-deoxy-2,3-O-allyl)- [beta]-CD, were synthesized. Two of the new derivatives were evaluated as components of stationary phases for GC, per(6-O-TBS-2,3-Ocyclodimethylsilyl)-[beta]-CD and per(6-deoxy-2,3-O-methyl)-[beta]-CD. Overall, this work resulted in five new CD derivatives.

Modified Cyclodextrins as Chiral Stationary Phases for Capillary Gas Chromatographic Separation of Enantiomers

Modified Cyclodextrins as Chiral Stationary Phases for Capillary Gas Chromatographic Separation of Enantiomers
Author:
Publisher:
Total Pages:
Release: 2002
Genre:
ISBN:

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Cyclodextrin (CD) derivatives are widely used as chiral stationary phases in capillary gas chromatography. Their performance depends substantially on the side chains attached to the hydroxyl groups of the glucose moieties. In this study new classes of CD-derivatives suitable for gas chromatographic (GC) separation of enantiomers were synthesized by introducing (i) acetal functions and (ii) chiral acyl moieties at positions 2 and 3 of the glucose units. Octakis(2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl)-g-cyclodextrin (2,3- MOM-6-TBDMS-g-CD) obtained by reaction of 6-O-TBDMS-g-cyclodextrin with methoxymethylchloride (MOM-Cl) was synthesized as first representative of cyclodextrin GC stationary phases containing alkoxymethyl side chains. The structure was confirmed by NMR and mass spectrometry. The suitability of the material diluted in polysiloxane as GC stationary phase was shown. Enantioseparations could be achieved for a broad spectrum of chiral volatiles from various chemical classes. Structural influences of the analytes on the enantiodifferentiations were demonstrated. High separation factors were observed for the hydroxyketone acetoin (a = 1.8) and some methyl branched ketones. Pronounced enantioseparations were also determined for cyclic pentenolone and furanone derivatives. To investigate the impact of the size of the CD torus, the 2,3-MOM-derivatives of the b- and a-CD analogs were synthesized. The spectrum of compounds for which enantiomers could be separated on 2,3-MOM-6-TBDMS-b-CD was more limited and the enantioseparations achieved were generally less pronounced compared to the g-CD derivative. However, for 2-alkyl esters unusually high separation factors (a up to 4.31) were observed. Using 2-pentyl acetate as example, phenomena underlying the enantioseparation were investigated by determining thermodynamic parameters. The data showed that only one enantiomer is retained significantly on the chiral stationary phase whereas the other one behaves.