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  • 1
    Electronic Resource
    Electronic Resource
    Bacterial uptake of octyl ethanolamine increases with pH (1992)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 91 (1992), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The uptake of octyl ethanolamine (C8EA) by Pseudomonas pseudoalcaligenes was determined at pH 7.1–10.0. At pH 9.1 the total uptake was nearly three times higher, and at pH 10.0 four times higher than at pH 7.1. Also the initial rate of uptake was lowest at pH 7.1. At pH 7.1 five to ten times higher concentrations of C8EA were needed than at pH 9.1 to achieve the same degree of leakage of cytoplasmic constituents. The results support the hypothesis that penetration of the bacterial cytoplasmic membrane by C8EA in its uncharged form is favoured. This takes place particularly with high pH in the suspending medium. In the cytoplasm, the pH is lower, and C8EA becomes more protonated. This will prevent back diffusion, promote accumulation and enhance membrane interaction and toxicity at high pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1992.tb05200.x
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  • 2
    Electronic Resource
    Electronic Resource
    Liquid chromatographic resolution of cyclic sulfoximides and their sulfoxide precursors on an N,N′-diallyl-L-tartardiamide-based chiral stationary phase (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 167-172 
    Details
    ISSN: 0899-0042
    Keywords: chromatographic resolution ; enantiomers ; sulfoximide ; sulfoximine ; sulfoxide ; hydrogen bonding ; DATD-based CSP ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two O,O′-diaroyl derivatives of an N,N′-diallyl-L-tartardiamide-based CSP, 3,5-dimethylbenzoyl (CSP I) and 4-tert-butylbenzoyl (CSP II), have been investigated and compared with respect to retention behaviour and resolving capabilities of a series of endocyclic sulfoximides of the 1-R-3-oxo-benzo[d]-isothia (IV)-azole 1-oxide type (R = methyl, octyl, 2′-carboxyphenyl, and 2′-carbethoxyphenyl) and their corresponding sulfoxide precursors. For the sulfoximides, selectivities of 1.44, 1.27, 1.28, and 1.20, respectively, were found on CSP II when eluted with 15% 2-propanol in hexane. Both the sulfoximide compounds and their sulfoxide precursors are well resolved by CSPs I and II. The retention was larger on the former phase, indicating that the molecular skeletons of the analytes studied interact, through hydrogen bonding, more strongly with CSP I than CSP II. Chirality 9:167-172, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Inversion barriers in sulfoxide functions studied by enantioselective liquid chromatography and chiroptical methods (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 9 (1997), S. 638-642 
    Details
    ISSN: 0899-0042
    Keywords: sulfoxide function ; stereoinversion ; enantiomerization barriers ; enantioselective chromatography ; chiroptical methods ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of 2-substituted 1,3,2-benzodithiazole 1-oxides has been synthesized and the compounds resolved into enantiomers by semipreparative enantioselective liquid chromatography. The low enantiomerization barriers have been determined by chiroptical techniques and were found to be relatively independent of the 2-substituent used. The kinetic results are consistent with a pyramidal inversion mechanism and a reduced barrier due to electronic effects, favouring the transition state over the pyramidal ground state. This mechanistic rationale was further supported by data obtained from molecular modelling using AM1 geometry optimization. The absolute configurations have been determined via a comparison of their CD-spectra with those of analogs with previously determined configuration. Chirality 9:638-642, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Some mechanistic aspects on chiral discrimination of organic acids by immobilized bovine serum albumin (BSA) (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 24-29 
    Details
    ISSN: 0899-0042
    Keywords: organic acids ; enantiomers ; BSA ; chiral discrimination ; hydrophobic interaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Although chiral anionic compounds, notably a large number of organic acids, have been found to be readily separated into enantiomers on BSA-based columns, the structural requirements for an efficient enantiomer discrimination by the protein is still not very well known. Since it is often observed that very hydrophobic acids, like many of the antiinflammatory “profens,” can be resolved with large separation factors for the enantiomers, a systematic study of a series of racemic α-substituted alkanoic acids was made. The series of analytes was prepared from α-amino acids, RCH(NH2)CO2H (where R = C1-C6), by reaction with N-(chloroformyl)-carbazole. A rapid increase in the capacity ratios of both enantiomers was found with increasing length of R. The effect, however, was larger for the last eluted enantiomer, leading to a substantial increase in the separation factor; this being 7.3 for R = C6 in 20 mM phosphate buffer (pH 8.0) with 30% of acetonitrile. Further, the separation factor also increased with decreasing organic modifier content. Thus when the R = C6-analyte was run at a mobile phase concentration of 20% acetonitrile and a flow rate of 1.5 ml/min, the time difference between the two eluted enantiomers exceeded 20 hr.A reasonable interpretation of our results seems to be that enantioselectivity is promoted by increased hydrophobic interaction. Since the anionic charge of the analyte is also taking part in the retention mechanism, a tight binding of the analyte will result from simultaneous electrostatic and hydrophobic interaction. When the latter is increased, less conformational freedom will be left for the analyte and the steric configuration at the α-carbon atom will become more and more important. Steric hindrance by the α-substituent in the first eluted enantiomer will counteract the tight binding caused by the combined binding interactions and lead to a smaller increase in the capacity ratio.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530040107
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  • 5
    Electronic Resource
    Electronic Resource
    Enantioselectivity of lipase-catalyzed hydrolysis of some 2-chloroethyl 2-arylpropanoates studied by chiral reversed-phase liquid chromatographySecond International Symposium on Chiral Discrimination, May 27 - 31, 1991, Rome, Italy. (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 98-102 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective hydrolysis ; lipase ; 2-chloroethyl esters ; 2-arylpropanoic acids ; chiral liquid chromatography ; enantiomer separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A technique based exclusively on chiral reversed-phase liquid chromatography has been shown to greatly facilitate studies of enantioselectivity in lipase-catalyzed hydrolysis of chiral organic esters. Only two sets of experimental data are needed to calculate the enantioselectivity (E) of a kinetically controlled enantiomer-differentiating reaction of this kind, viz. the enantiomeric excess of the product (eep) or substrate (ees), and the degree of substrate conversion (c). The product enantiomers are well separated on a BSA-based column, giving eep directly. In addition, separation of the (unresolved) ester substrate from the enantiomeric products gives c by integration. Via an optimization of the mobile phase used in the chiral chromatographic system, both these parameters can often be determined in a single run. Highly precise and detailed kinetic studies of the enzymatic reaction can thus be performed. In this way, E-values have been determined for a series of 2-chloroethyl 2-arylpropanoates hydrolyzed in the presence of a Candida cylindracea lipase at pH 6.0 and 7.1. Effects on the E-values from a partial purification and further processing of the lipase have also been studied.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530040206
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  • 6
    Electronic Resource
    Electronic Resource
    Enantioselective lipase-catalyzed ester hydrolysis: Effects on rates and enantioselectivity from a variation of the ester structure (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 154-158 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective hydrolysis ; lipase ; esters ; substituent effects ; chiral liquid chromatography ; enantiomer separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to make a preliminary study of substituent effects on the rate and enantioselectivity obtained in esterolytic reactions catalyzed by a lipase from Candida rugosa, a series of racemic esters, derived from some α-alkyl and α-halo phenylacetic acids, were prepared. The reactions were studied at pH 6.0 and 50°C under which conditions uncatalyzed hydrolysis was relatively slow. Reaction samples were studied at different points of time by means of analytical chiral reversed-phase liquid chromatography, which permitted the simultaneous determination of product enantiomeric excess and of the degree of total ester hydrolysis. These data were then used to calculate initial rates as well as enantioselectivity. An increase of the steric bulk of the α-substituent was found to highly decrease the rate of the reaction. On the other hand, rates were higher for the p-nitrophenyl esters than for the corresponding 2-chloroethyl esters. Consistently, the enantioselectivity was found to be higher for the latter type of ester. The esters of the α-halo (bromo and chloro) phenylacetic acids gave mandelic acid as the final product. This was caused by a rapid solvolysis of the α-halo phenylacetic acid initially formed. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050309
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  • 7
    Electronic Resource
    Electronic Resource
    Chiral discrimination by albumin: A mechanistic study of liquid chromatographic optical resolution of nonaromatic carboxylic acids (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 295-299 
    Details
    ISSN: 0899-0042
    Keywords: enantiomers ; BSA ; N-alkanoyl-leucines ; chiral recognition ; radiolabeling ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to get further insight into the mechanism by which bovine serum albumin (BSA) discriminates between enantiomers of organic acids, some radioisotopically labeled, nonaromatic carboxylic acids were studied under varying mobile phase conditions. It was found for a series of N-alkanoyl-DL-[3H]leucines that the D-enantiomers were much more strongly retained and that the composition of the mobile phase could be adjusted to give very large (α 〉 20) enantiomeric separation factors. The elution order was consistent with what has been found earlier for other N-acyl derivatives as well as for N-arylcarbamoyl derivatives of simple aliphatic amino acids. A marked increase in the hydrophobic interaction of the D-enantiomers with the chiral phase was found upon a lowering of the mobile phase strength, conditions under which the L-form was only slightly influenced. These and other results are consistent with a chiral recognition model by which inclusion of the compound in a hydrophobic chiral cavity of BSA with simultaneous charge interaction is assumed to take place and whereby discrimination is determined by the steric bulk and orientation of the α-substituent. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050503
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  • 8
    Electronic Resource
    Electronic Resource
    Estimation of the number of enantioselective sites of bovine serum albumin using frontal chromatography (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 5 (1993), S. 513-515 
    Details
    ISSN: 0899-0042
    Keywords: enantioselective retention ; albumin ; bilangmuir adsorption model ; frontal analysis ; saturation capacity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On a column with bovine serum albumin (BSA) immobilized covalently to silica, the adsorption isotherms of the enantiomers of mandelic acid, tryptophan, 2-phenylbutyric acid, and N-benzoylalanine are measured using a buffered mobile phase. Knowing the amount of BSA immobilized on the column (36 mg), the ratio of the number of enantiomer molecules needed to saturate the enantioselective retention mechanism to the number of BSA molecules is determined. The mean of the set of eight enantiomers is 0.28. These data confirm that at most one enantioselective site exists for each BSA molecule for the kind of enantiomers studied. © 1993 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530050707
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  • 9
    Electronic Resource
    Electronic Resource
    A new class of network-polymeric chiral stationary phases (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 248-256 
    Details
    ISSN: 0899-0042
    Keywords: chiral discrimination ; chiral stationary phase ; network polymer ; DATD ; hydrogen bonding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A strategy based on the use of homo bi- and multifunctional building blocks for the synthesis of a new class of network-polymeric chiral stationary phases has been evaluated. The key steps comprise acylation of N,N′-diallyl-L-tartardiamide (DATD) and reaction with a multifunctional hydrosilane, yielding a network polymer incorporating the bifunctional C2-symmetric chiral selector. Covalent bonding to a functionalized silica takes place during the latter process. Many of these chiral sorbents show interesting enantioselective properties toward a wide variety of racemic solutes under normal-phase (hexane-based) conditions. The retention is mainly caused by the hydrogen-bonding ability of the analyte, which is regulated by mobile phase additives like alcohol or ether cosolvents. The most interesting chiral stationary phases, in terms of broad enantioselectivity, were obtained from O,O′-diaryol-DATD-derivatives, particularly those containing the 3,5-dimethylbenzoyl and the 4-(tert-butyl)benzoyl moieties. Since high column efficiencies can be obtained with these chiral sorbents, an α-value of ca. 1.2 is usually sufficient to produce baseline separation. A large number of neutral as well as acidic or basic drug racemates are resolved without derivatization. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070411
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  • 10
    Electronic Resource
    Electronic Resource
    Chromatographic resolution of some cyclic sulfoximides derived from prochiral and chiral sulfoxides (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 541-546 
    Details
    ISSN: 0899-0042
    Keywords: chiral liquid chromatography ; chromatographic resolution ; cyclic sulfoximides ; reaction stereochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three endocyclic sulfoximides of the 1-aryl- and 1-alkyl-3-oxo-benzo[d]-isothia (IV)-azole 1-oxide type (1-substituent = 2′-carboxyphenyl, 2′-carbethoxyphenyl, and octyl, respectively) were found to be well resolved on a chiral phase derived from bovine serum albumin (BSA). Selectivities (α) of 1.74, 1.12, and 1.44, respectively, were obtained. The retention behaviour of 1-octyl-3-oxo-benzo[d]isothia(IV)-azole 1-oxide was further investigated in some detail as a function of the mobile phase composition and the elution order was established from optically active material obtained from the enantiopure sulfoxide precursor. An enantiomeric excess of 85.4% was obtained in the cyclocondensation reaction of the octyl-substituted sulfoxide precursor with hydrazoic acid to the corresponding endocyclic sulfoximide. © 1995 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070708
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