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Trapp O, Pearce EW, Kimmel JR, Yoon OK, Zuleta IA, Zare RN. A soft on-column metal coating procedure for robust sheathless electrospray emitters used in capillary electrophoresis-mass spectrometry. Electrophoresis 2005; 26:1358-65. [PMID: 15759300 DOI: 10.1002/elps.200410152] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
An on-column metal coating procedure was developed for sheathless electrospray emitters, based on Justus von Liebig's electroless silver mirror reaction followed by electrochemical deposition of gold onto the silver layer. The coating procedure is straightforward, mild, inexpensive, and can be performed with standard laboratory equipment. A long-term (600 h) stability investigation of the conductive coating was carried out by continuous electrospray in the positive electrospray mode, and no degradation in performance was found. The simplicity of the coating procedure and the robustness of the spray tips makes the spray tips highly suitable to couple delicate wall-coated or monolithic capillary columns to mass spectrometry. Peptide mixtures were separated by capillary electrophoresis and injected into either a Hadamard-transform time-of-flight mass analyzer or a commercial quadrupole mass analyzer using the described sheathless electrospray emitters. The performance was judged to be excellent.
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202
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Trapp O. Direct calculation of interconversion barriers in dynamic chromatography and electrophoresis: Isomerization of captopril. Electrophoresis 2005; 26:487-93. [PMID: 15657905 DOI: 10.1002/elps.200410235] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Dynamic capillary electrophoresis (DCE) and direct calculation of the rate constants of isomerization has been applied to determine the cis-trans isomerization barriers of the angiotensin-converting enzyme inhibitor captopril. The separation of the rotational cis-trans isomeric drug has been performed in an aqueous 50 mM borate buffer at pH 9.3. Interconversion profiles featuring plateau formation, peak-broadening, and peak coalescence were observed. To determine the rate constants of the forward and backward reaction (k(cis-->trans) and k(trans-->cis)) of the isomerization process in dynamic capillary electrophoresis, a novel straightforward calculation method using the experimental parameters plateau height, h(plateau), peak width at half height w(h), the total migration times of the cis-trans isomers t(R) and the electroosmotic break-through time t(0) as well as the peak ratio of the cis-trans isomers is presented for the first time. From temperature dependent measurements the rate constants k(cis-->trans) and k(trans-->cis) and the kinetic activation parameters DeltaG( not equal), DeltaH( not equal), and DeltaS( not equal) of the cis-trans isomerization of captopril were obtained. From the activation parameters the isomerization barriers of captopril at 37 degrees C under basic conditions were calculated to be DeltaG( not equal) (cis-->trans) = 90.3 kJ.mol(-1)and DeltaG( not equal) (trans-->cis) = 90.0 kJ.mol(-1*).
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Trapp O, Kimmel JR, Yoon OK, Zuleta IA, Fernandez FM, Zare RN. Kontinuierliche flugzeitmassenspektrometrische Zweikanaldetektion von Elektrospray-Ionen. Angew Chem Int Ed Engl 2004. [DOI: 10.1002/ange.200461240] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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204
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Trapp O, Kimmel JR, Yoon OK, Zuleta IA, Fernandez FM, Zare RN. Continuous Two-Channel Time-of-Flight Mass Spectrometric Detection of Electrosprayed Ions. Angew Chem Int Ed Engl 2004; 43:6541-4. [PMID: 15578763 DOI: 10.1002/anie.200461240] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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205
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Trapp O. Evaluation and Prediction of Stereoisomerizations in Comprehensive Two-Dimensional Chromatography. ACTA ACUST UNITED AC 2004; 44:1671-9. [PMID: 15446825 DOI: 10.1021/ci049899k] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conformational and configurational changes such as isomerizations, epimerizations, diastereomerizations and, enantiomerizations are important for the investigation of a large variety of processes ranging from protein folding to the stereostability of drugs. Under optimized conditions, these processes lead to an elution profile characterized by a plateau formation between the two interconverting species in chromatographic separations in a certain temperature range. By temperature-dependent measurements and subsequent computer simulation of the experimental chromatograms, the forward and backward rate constants k1 and k(-1), the Gibb's energy DeltaG++, activation enthalpy DeltaH++, and entropy DeltaS++ can be obtained. Due to its high efficiency two-dimensional chromatography is able to resolve the time-dependent distribution of the two species in the second dimension, thereby yielding the precise ratio of stereoisomers. An algorithm for the simulation and evaluation of two-dimensional chromatographic experiments has been developed, based on the theoretical plate model, which allows the determination of rate constants and barriers of isomerization, epimerization, and enantiomerization processes from two-dimensional chromatographic experiments. In the present article a detailed description of the extended theoretical plate model required for the simulation, the methods available, and examples for the evaluation of complex experimental data and the prediction of the separation conditions to observe isomerization, epimerizations, and enantiomerizations in two-dimensional chromatography are given.
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Marriott P, Aryusuk K, Shellie R, Ryan D, Krisnangkura K, Schurig V, Trapp O. Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography. J Chromatogr A 2004; 1033:135-43. [PMID: 15072298 DOI: 10.1016/j.chroma.2004.01.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Comprehensive two-dimensional gas chromatography (GC x GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC x GC allows sufficient retention duration on the second column, which permits the typical plateau-shape recognised for the interconversion process to be observed. The extent of interconversion depends on prevailing temperature, retention time, and the phase type. Polyethylene glycol-based phases were found to result in high interconversion kinetics, although terephthalic acid-terminated polyethylene glycol had a lesser extent of interconversion. Much less interconversion was seen for phenyl-methylpolysiloxane and cyclodextrin phases. This suggests that for the oximes, interconversion largely occurs in the stationary phase. Examples of different extents of interconversion in both dimensions are shown, including peak coalescence on the first column with little interconversion on the second column.
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Wheeler AR, Trapp G, Trapp O, Zare RN. Electroosmotic flow in a poly(dimethylsiloxane) channel does not depend on percent curing agent. Electrophoresis 2004; 25:1120-4. [PMID: 15095455 DOI: 10.1002/elps.200305784] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Poly(dimethylsiloxane) (PDMS) microfluidic devices were prepared from different ratios of "curing agent" (which contains silicon hydride groups) to "base" (which contains vinyl-terminated noncross-linked PDMS), to determine the effect of this ratio on electroosmotic flow (EOF). In fabricating devices for this purpose, a novel method for permanently enclosing PDMS channels was developed. As a supplement to the microfluidic method, the inner walls of capillaries were coated with PDMS formed from varying ratios of curing agent to base. EOF was found to be constant for PDMS formed with each ratio, which implies that the negative surface charges do not arise from chemical species present only in the base or the curing agent.
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208
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Kemmer TP, Trapp O. Adrenal insufficiency in patients after severe brain injury. Exp Clin Endocrinol Diabetes 2004. [DOI: 10.1055/s-2004-819174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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209
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Trapp O, Schurig V, Kostyanovsky RG. The Control of the Nitrogen Inversion in Alkyl-Substituted Diaziridines. Chemistry 2004; 10:951-7. [PMID: 14978821 DOI: 10.1002/chem.200305494] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
For the first time the nitrogen inversion barriers in 3,3-unsubstituted trans-diaziridines, such as 1,2-di-tert-butyldiaziridine (1) and 1,2-di-n-butyldiaziridine (2) were determined. Enantioselective stopped-flow multidimensional gas chromatography was used to investigate the enantiomerization barrier of 1 between 126.2 and 171.0 degrees C (DeltaG ++ gas (150.7 degrees C) = 135.8+/-0.2 kJ mol(-1), DeltaH++ gas = 116.1+/-2.5 kJ mol(-1), DeltaS ++ gas == -46+/-2 J K(-1) mol(-1)). The separation of the enantiomers has been achieved in presence of the chiral stationary phase (CSP) Chirasil-beta-Dex with a high separation factor (alpha = 1.44 at 80 degrees C). In a complementary approach, the enantiomerization barriers of 1,2-di-tert-butyldiaziridine (1), 1,2-di-n-butyldiaziridine (2), 1-n-butyl-3,3-dimethyldiaziridine (3), and 1,2,3,3-tetramethyldiaziridine (4) were determined for comparison by enantioselective dynamic chromatography (DGC) and computer simulation of the dynamic elution profiles. The enantiomerization barrier of 2 was shown to be the highest among the nonsterically hindered diaziridines studied so far, whereas 1 exhibited the highest value found for strained nitrogen-containing rings, that is, aziridines, diaziridines and oxaziridines.
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210
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Kostyanovsky RG, Schurig V, Lyssenko KA, Trapp O, Kadorkina GK, Kostyanovsky VR, Averkiev BB. Stereochemisty of 3,3-disubstituted 2-methoxy-1,2-oxazolidines. MENDELEEV COMMUNICATIONS 2004. [DOI: 10.1070/mc2004v014n06abeh002036] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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211
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Trapp O, Trapp G, Schurig V. Determination of thecis-trans isomerization barrier of enalaprilat by dynamic capillary electrophoresis and computer simulation. Electrophoresis 2004; 25:318-23. [PMID: 14743484 DOI: 10.1002/elps.200305746] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Dynamic capillary electrophoresis (DCE) and computer simulation of the elution profiles with the stochastic model has been applied to determine the isomerization barriers of the angiotensin converting enzyme inhibitor enalaprilat. The separation of the rotational cis-trans isomeric drug has been performed in an aqueous 20 mM borate buffer at pH 9.3. Interconversion profiles featuring plateau formation and peak broadening were observed. To evaluate the rate constants k(cis-->trans) and k(trans-->cis) of the cis-trans isomerization from the experimental electropherograms obtained by dynamic capillary electrophoresis, elution profiles were analyzed by a simulation with iterative convergence to the experimental data using the ChromWin software which requires the total migration times of the individual isomers t(R), the electroosmotic break-through time t(0), the plateau height h(plateau), the peak widths at half height of the individual isomers w(h), as well as the peak ratio of the isomers as experimental data input. From temperature-dependent measurements between 0 degrees and 15 degrees C the thermodynamic parameters Delta G, Delta H and Delta S, the rate constants k(cis-->trans) and k(trans-->cis) and the kinetic activation parameters Delta G*, Delta H*, and Delta S* of the cis-trans isomerization of enalaprilat were obtained. From the activation parameters the isomerization barriers at 37 degrees C were calculated to be Delta G* (trans-->cis) = 87.2 kJ.mol(-1) and Delta G*(cis-->trans) = 91.9 kJ.mol(-1).
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212
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Holder E, Trapp O, Trapp G, Marin V, Hoogenboom R, Schubert US. Synthesis, complete characterization, and enantioselective electrokinetic separation of functionalized ruthenium complex enantiomers. Chirality 2004; 16:363-8. [PMID: 15190581 DOI: 10.1002/chir.20042] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Electrokinetic chromatography was employed to separate the enantiomers of two novel functionalized ruthenium(II) complexes with different polypyridyl coordination spheres. The use of anionic carboxymethyl-beta-cyclodextrin as chiral mobile phase additive resulted in maximum efficiency and resolution for the enantiomer separation of both transition metal complexes. The syntheses of the [4-(3-hydroxypropyl)-4'-methyl-2,2'-bipyridine]-bis(2,2'-bipyridine)rethenium(II)-bis(tetrafluoroborate) and [4-(3-hydroxypropyl)-4'-methyl-2,2'-bipyridine]-bis(4,4'-dimethyl-2,2'-bypyridine)ruthenium(II)-bis(tetrafluoroborate) complexes and their complete characterization by means of two-dimensional (1)H and (13)C[(1)H] NMR techniques ((1)H-(1)H COSY and (1)H-(13)C HMQC) as well as elemental analyses and MALDI-TOFMS are described in detail. The functionalized complexes can be used as building blocks for further reactions with polymers, biopolymers, surfaces and nanoparticles.
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213
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Cousin H, Trapp O, Peulon-Agasse V, Pannecoucke X, Banspach L, Trapp G, Jiang Z, Combret J, Schurig V. Synthesis, NMR Spectroscopic Characterization and Polysiloxane-Based Immobilization of the Three Regioisomeric Monooctenylpermethyl-β-cyclodextrins and Their Application in Enantioselective GC. European J Org Chem 2003. [DOI: 10.1002/ejoc.200300108] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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214
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Trapp O, Shellie R, Marriott P, Schurig V. Simulation of Elution Profiles for Two-Dimensional Dynamic Gas Chromatographic Experiments. Anal Chem 2003; 75:4452-61. [PMID: 14632049 DOI: 10.1021/ac0301144] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The interconversion of E and Z isomers of acetaldoxime 1 and butyraldoxime 2 have been investigated by comprehensive two-dimensional dynamic gas chromatography (DGCxDGC) and computer simulation. Time-resolved cryogenic modulation is capable of revealing the precise isomeric ratio as a fine structure under the dynamic elution profile, which is characterized in one-dimensional experiments by a plateau formation or peak coalescence caused by interconversion of the isomers during the separation process. The chromatographic theoretical plate model has been extended for the computer simulation of comprehensive two-dimensional dynamic chromatographic experiments. A novel program, ChromWin 2D, based on the new algorithm has been developed for computer simulation to evaluate and predict the elution profiles of DGCxDGC experiments. ChromWin 2D allows the determination of rate constants and barriers of isomerization, epimerization, and enantiomerization processes occurring during chromatographic separations. The Eyring activation parameters of the E/Z and Z/E isomerization barriers in the presence of the stationary phase BP21 (poly(ethylene glycol) terephthalate terminated) were determined by temperature-dependent experiments between 80 and 90 degrees C for 1 and 70 and 130 degrees C for 2. The thermodynamic Gibbs free energy of the E/Z equilibrium of the isomers has been determined from the time-resolved chromatograms by cryogenic modulation. The method described here constitutes a new and important tool for the determination of isomerization barriers, which are of great interest, for example, for the quantitative determination of derivatized aldehydes, such as dinitrophenylhydrazine derivatives, in trace analysis.
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Trapp O, Trapp G, Schurig V. Direct calculation and computer simulation of the enantiomerization barrier of oxazepam in dynamic HPLC experiments--a comparative study. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 2002; 54:301-13. [PMID: 12543506 DOI: 10.1016/s0165-022x(02)00118-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Dynamic chromatographic methods constitute a versatile approach to the rapid and precise determination of enantiomerization barriers of stereolabile drugs. In the present study enantioselective dynamic high-performance liquid chromatography (DHPLC) was employed to determine the enantiomerization barrier of oxazepam. Dynamic elution profiles, exhibiting plateau formation and/or peak broadening between 20 and 60 degrees C at pH 2.6 and pH 8 were obtained in the presence of the chiral stationary phase (CSP) Nucleodex-beta-PM (permethylated beta-cyclodextrin chemically bonded to silica) using a 6:4 mixture of phosphate buffer and methanol as mobile phase. Evaluation of the experimental chromatograms was performed by the novel approximation function (AF) (without computer simulation), and by the stochastic model implemented in the ChromWin simulation software (with computer simulation) furnishing the respective apparent forward rate constants, k(1)(app)(T). From the rate constants, k(1)(app)(T), measured at variable temperatures, the kinetic Eyring activation parameters, deltaG(T)(#), deltaH(#) and deltaS(#), of the enantiomerization of oxazepam were obtained. By variation of the flow rate of the mobile phase, the expected independence of the enantiomerization barrier from the chromatographic time scale was demonstrated for the first time.
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216
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Trapp O, Trapp G, Kong J, Hahn U, Vögtle F, Schurig V. Probing the stereointegrity of Tröger's base--a dynamic electrokinetic chromatographic study. Chemistry 2002; 8:3629-34. [PMID: 12203289 DOI: 10.1002/1521-3765(20020816)8:16<3629::aid-chem3629>3.0.co;2-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Under acidic conditions the enantiomers of Tröger's base 1 (2,8-dimethyl-6 H,12 H-5,11-methanodibenzo[b,f][1,5]diazozine) are subject to enantiomerization. During enantioselective dynamic electrokinetic chromatography using 10 mM hydroxypropyl-beta-cyclodextrin as the chiral mobile phase additive in 50 mM tris/phosphate buffer at pH 2.2, enantiomerization of Tröger's base gives rise to characteristic elution profiles featuring plateau formation and peak broadening. Introduction of a permanent positive charge attributed to quaternization in the monobenzylated derivative of Tröger's base 2 (5-benzyl-2,8-dimethyl-6 H,12 H-5,11-methanodibenzo[b,f][1,5]diazozinium bromide) decreases the enantiomerization barrier significantly. To determine the rate constants of enantiomerization the experimental chromatograms were evaluated by a direct calculation method and by using the computer simulation program ChromWin. From temperature-dependent measurements the Eyring activation parameters for 1 and 2 were determined: 1: DeltaG( not equal ) (298 K)=100.9+/-0.5 kJ mol(-1), DeltaH( not equal )=89.5+/-2.0 kJ mol(-1), DeltaS( not equal )=-42+/-10 J K(-1) mol(-1); 2: DeltaG( not equal ) (298 K)=90.2+/-0.5 kJ mol(-1), DeltaH( not equal )=91.4+/-2.0 kJ mol(-1), DeltaS( not equal )=9.8+/-10 J K(-1) mol(-1).
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217
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Trapp O, Schurig V. Novel direct access to enantiomerization barriers from peak profiles in enantioselective dynamic chromatography: enantiomerization of dialkyl-1,3-allenedicarboxylates. Chirality 2002; 14:465-70. [PMID: 12112339 DOI: 10.1002/chir.10089] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The axially chiral allenes dimethyl-1,3-allenedicarboxylate 1 and diethyl-1,3-allenedicarboxylate 2 show characteristic plateau formation during enantioselective GC separation on the chiral stationary liquid phase Chirasil-beta-Dex. The elution profiles, obtained from temperature-dependent dynamic GC (DGC) experiments (1: 100-140 degrees C; 2: 110-150 degrees C) were evaluated with the recently derived approximation function (AF) k1(approx) = f(t(R)(A),t(R)(B),w(h)(A),h(plateau), N) to yield the enantiomerization rate constant directly k(1). These values were compared with those obtained by computer-aided simulation with ChromWin. The Eyring activation parameters of the experimental interconversion profiles were determined to be: DeltaG(#)(298.15 K) = 103.6 +/- 0.9 kJ mol(-1), DeltaH(#) = 44.7 +/- 0.4 kJ mol(-1), DeltaS(#) = -198 +/- 7 J K(1) mol(-1) for dimethyl-1,3-allenedicarboxylate 1, and DeltaG(#)(298.15 K) = 103.5 +/- 1.1 kJ mol(-1), DeltaH(#) = 44.7 +/- 0.5 kJ mol(-1), DeltaS(#) = -197 +/- 9 J K(-1) mol(-1) for diethyl-1,3-allenedicarboxylate 2. The approximation function (AF) presented here allows the fast determination of rate constants k(1) and activation barriers of enantiomerization DeltaG(#) from chromatographic parameters without extensive computer simulation.
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218
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Trapp O, Schoetz G, Schurig V. Stereointegrity of thalidomide: gas-chromatographic determination of the enantiomerization barrier. J Pharm Biomed Anal 2002; 27:497-505. [PMID: 11755751 DOI: 10.1016/s0731-7085(01)00573-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Enantioselective chromatographic methods, representing the most commonly used techniques for the determination of enantiomeric ratios, can also be used for the evaluation of stereochemical integrity. In the present study, two chromatographic methods, dynamic gas chromatography (DGC) and stopped-flow gas chromatography (SFGC) were used to determine the enantiomerization barrier of thalidomide. In the presence of a chiral stationary phase (CSP), the enantiomers of thalidomide produced characteristic elution profiles exhibiting plateaus and/or peak broadening which were observed between 190 and 220 degrees C in DGC. To obtain the enantiomerization barrier of thalidomide from experimental data, the fast and efficient simulation program ChromWin was used to simulate the elution profiles and obtain kinetic activation parameters. From temperature-dependent measurements the rate constants k(1) and k(-1) and the kinetic activation parameters DeltaG#, DeltaH# and DeltaS# of the enantiomerization of thalidomide were obtained by DGC. The enantiomerization barrier DeltaG# was determined to be 154+/-2 kJ/mol with DGC and 150+/-3 kJ/mol with the sfGC technique at 200 degrees C, respectively. The concept of the retention increment R' has been applied to separate the enantiomerization barrier of thalidomide in the dissolved and complexed state of the CSP.
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Rau H, Schauer R, Zimmermann A, Angele MK, Trapp O, Schildberg FW. [Surgical therapy of advanced gallbladder carcinoma]. KONGRESSBAND. DEUTSCHE GESELLSCHAFT FUR CHIRURGIE. KONGRESS 2002; 119:79-81. [PMID: 12704874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/20/2023]
Abstract
The use of surgery for the treatment of advanced gall bladder cancer is controversially discussed. This retrospective study included 204 patients who were subjected to surgery due to advanced gall bladder cancer at the Klinikum Grosshadern. Mean survival time of all patients was 4.5 months. Advancement of the tumor stage resulted in a decreased percentage of possible R0 resections (T3 n = 48, R0 31%, T4 n = 87, R0 13%). Nonetheless, R0 resections of T3 tumors significantly increased the survival rate compared to R1 and R2 resections (mean survival 20.2 vs. 4.5 months). R0 resections of T4 tumors also significantly attenuated the survival rate (18.1 vs. 2.4 months compared to R1 and R2 resections). Thus, diagnostic procedures have to focus on identifying patients with possible R0 resections and perform extensive resections on those patients.
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220
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Kostyanovsky RG, Schurig V, Trapp O, Lyssenko KA, Averkiev BB, Kadorkina GK, Prosyanik AV, Kostyanovsky VR. Chiral 1-alkoxyaziridines: resolution, nitrogen inversion, stucture and diastereomeric transformations. MENDELEEV COMMUNICATIONS 2002. [DOI: 10.1070/mc2002v012n04abeh001612] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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221
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Schoetz G, Trapp O, Schurig V. Determination of the enantiomerization barrier of thalidomide by dynamic capillary electrokinetic chromatography. Electrophoresis 2001; 22:3185-90. [PMID: 11589278 DOI: 10.1002/1522-2683(200109)22:15<3185::aid-elps3185>3.0.co;2-v] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Enantioselective chromatographic methods, representing the most commonly used techniques for the determination of enantiomeric ratios, can also be used for the evaluation of stereochemical integrity. In the present study, dynamic capillary electrokinetic chromatography (DEKC) was employed to determine the enantiomerization barrier of thalidomide. In the presence of the chiral mobile phase additive carboxymethyl-beta-cyclodextrin, the interconverting enantiomers of thalidomide produced characteristic elution profiles exhibiting plateaus and/or peak broadening between 25 and 55 degrees C at pH 8. To obtain the enantiomerization barrier of thalidomide from experimental data, the fast and efficient simulation program ChromWin was used to simulate the experimental interconversion profiles and to obtain the apparent rate constants k1app(T). Additionally, these values were compared with the novel approximation function for the direct calculation of enantiomerization barriers from chromatographic parameters of elution profiles. From the rate constants k1app(T) of temperature-dependent measurements the kinetic activation parameters deltaG(T)#,deltaH#, and deltaS# of the enantiomerization of thalidomide were obtained. At 25 degrees C, the enantiomerization barrier deltaG# was determined to be 102 +/- 1 kJ/mol at pH 8 in the dynamic electrokinetic chromatographic experiment.
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Schoetz G, Trapp O, Schurig V. Determination of the cis-trans isomerization barrier of several L-peptidyl-L-proline dipeptides by dynamic capillary electrophoresis and computer simulation. Electrophoresis 2001; 22:2409-15. [PMID: 11519944 DOI: 10.1002/1522-2683(200107)22:12<2409::aid-elps2409>3.0.co;2-c] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Dynamic capillary electrophoresis (DCE) and computer simulation of the elution profiles with the theoretical plate and the stochastic model has been applied to determine the isomerization barriers of the three dipeptides L-alanyl-L-proline, L-leucyl-L-proline, and L-phenylalanyl-L-proline. The separation of the rotational cis-trans isomers has been performed in an aqueous 70 mM borate buffer at pH 9.5. Interconversion profiles featuring plateau formation and peak broadening were observed. To determine the rate constants k1 and k(-1) of the cis-trans isomerization in dynamic capillary electrophoresis, equations have been derived for the theoretical plate model and stochastic model. The electropherograms were simulated with the ChromWin software which uses the experimental data plateau height h(plateau), peak width at half height Wh, the total migration times of the cis-trans isomers tR and the electroosmotic break-through time t0 as well as the peak ratio [cis]/[trans]. From temperature-dependent measurements, the rate constants k1 and k(-1) and the kinetic activation parameters deltaG#, deltaH# and deltaS# of the cis-trans isomerization of the three dipeptides were obtained.
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Trapp O, Schoetz G, Schurig V. Determination of enantiomerization barriers by dynamic and stopped-flow chromatographic methods. Chirality 2001; 13:403-14. [PMID: 11466759 DOI: 10.1002/chir.1052] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In recent years, dynamic chromatography and stopped-flow chromatographic techniques have become versatile tools for the determination of enantiomerization and isomerization barriers. Increasing demands for the stereochemical safety of chiral drugs contributed to the rapid development of new techniques. New computer-aided evaluation systems allow the on-line determination of interconversion barriers from the experimental chromatograms. Both dynamic chromatography and stopped-flow chromatography have been applied to the entire range of chromatographic methods (GC, SFC, HPLC, CE).
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224
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Trapp O, Caccamese S, Schmidt C, Böhmer V, Schurig V. Enantiomerization of an inherently chiral resorcarene derivative: determination of the interconversion barrier by computer simulation of the dynamic HPLC experiment. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s0957-4166(01)00246-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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225
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Mariott P, Trapp O, Shellie R, Schurig VG. Time-resolved cryogenic modulation reveals isomer interconversion profiles in dynamic chromatography. J Chromatogr A 2001; 919:115-26. [PMID: 11459297 DOI: 10.1016/s0021-9673(01)00778-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The dynamic chromatographic study of interconversion of E and Z forms of oximes has been investigated by using a novel cryogenic modulation method in a two-dimensional gas chromatographic array. The primary column is a conventional capillary GC column on which the molecular interconversion proceeds. In this case, the molecular dynamical process leads to a peak profile describing the kinetics and thermodynamics of the interconverting molecules during its chromatographic elution. Thus an interconversion region intercedes the elution of the individual stereoisomers of the reaction. Since the molecules are isomers, classical molecular identification methods such as gas chromatography-mass spectrometry are unable to study the individual instantaneous amounts of each of the compounds. Hence the infinitesimal profiles of interconversion along the entire column have never been experimentally observed; rather the total profile is normally subjected to mathematical modelling studies in order to match experiment with theory, and to gain the kinetic parameters of the process. In the present study, an instantaneous ratio of the individual isomers can be found during the chromatographic elution by direct measurement. This is achieved by using a cryogenic zone focussing process, with rapid longitudinal modulation of a cold trap and continual pulsing of collected zones into a fast-analysis high-resolution capillary column on which isomer interconversion is minimized. The data can be displayed as a two-dimensional contour plot to demonstrate the individual isomer profiles. The two-dimensional analysis also allows easy measurement of the peak ratios of the two isomers which is an indicator of the extent of interconversion that has taken place. Two model systems, acetaldoxime and butyraldoxime, were chosen to illustrate the use of the cryogenic modulation procedure. It is anticipated that the procedure could be applied to other molecules which exhibit gas-phase isomerizations or reactions.
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