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Diastereomeric Complexes (diastereomeric + complex)
Selected AbstractsMolecular modeling of chiral-modified zeolite HY employed in enantioselective separationCHIRALITY, Issue 6 2007Siricharn S. Jirapongphan Abstract Insight into enantioselective separation utilizing chiral-modified zeolite HY could be useful in designing a chiral stationary phase for resolving pharmaceutical compounds. A model was employed to better understand the enantioseparation of valinol in zeolite HY that contains (+)-(1R;2R)-hydrobenzoin as a chiral modifier. This model incorporates the zeolite support and accounts for the flexible change. Results from grand canonical Monte Carlo and molecular dynamics simulations indicate that the associated diastereomeric complex consists of a single (+)-(1R;2R)-hydrobenzoin and a single valinol molecules located in the zeolite HY supercage. Supercage-based docking simulation predicted an enantioselectivity of 2.6 compared with that of 1.4 measured experimentally. Also, the supercage-based docking simulation demonstrated a single binding motif in the S complex, and two binding motifs in the R complex. The multiple binding modes in the R complex resulted in its lower stability. This is hypothesized to be the origin of the weaker binding between (,)-(R)-valinol and the chiral modifier, and explains why (+)-(R)-valinol is retained more in the chiral-modified zeolite system studied. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source] Recent advances in enantioseparations of peptides by capillary electrophoresisELECTROPHORESIS, Issue 22-23 2003Gerhard K. E. Scriba Abstract The present review summarizes peptide enantioseparations by capillary electrophoresis with the focus on recent developments. These include the application of new chiral selectors and systematic studies involving series of di- and tripeptides with either common features or with a variety of structures. One section emphasizes mechanistic aspects of the migration order of the enantiomers in cyclodextrin-assisted chiral separations with respect to the complexation constants and the mobilities of the transient diastereomeric complexes. In addition, short paragraphs on the application of chiral capillary electrophoresis to the determination of the stereochemical purity of peptidomimetics and on chiral separations of peptides by capillary electrochromatography have also been included. [source] Expanding the Range of "Daniphos"-Type P,P- and P,N-Ligands: Synthesis and Structural Characterisation of New [(,6 -arene)Cr(CO)3] ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2007Elisabetta Alberico Abstract New P,P- and P,N-ligands have been synthesised whose core structure is an [(,6 -arene)Cr(CO)3] unit. These new ligands, which extend the range of "Daniphos" ligands, are endowed with central and planar chirality and have been prepared through a stereoselective synthetic strategy from optically pure benzylamines bearing a second substituent on the arene other than the benzyldimethylamino group. Because the two faces of unsymmetrically 1,2- and 1,3-disubstituted benzylamine are diastereotopic, which means that diastereomeric complexes arise upon coordination of theCr(CO)3 fragment to either of these two faces, the synthetic plan has been adjusted by exploiting the trimethylsilyl group as a temporary steric modulator in order to access both complexes with high diastereoselectivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Ferrocenyl-Aryl Based trans -Chelating Diphosphine Ligands: Synthesis, Molecular Structure and Application in Enantioselective HydrogenationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Raffael Schuecker Abstract Potentially trans -chelating diphosphine ligands based on a ferrocenyl-aryl backbone were synthesised in a four-step sequence and the molecular structures in the solid state of two representatives were determined by X-ray diffraction. High throughput screening of these ligands in rhodium-, ruthenium- and iridium-mediated hydrogenations of a variety of alkenes and ketones revealed that these ligands can deliver high enantioselectivity for alkenes (up to 98% ee) but are less selective when ketones are used as the substrates. The coordination behaviour of one ligand in its square planar palladium and platinum dichloride complexes was studied by 31P,NMR and only trans -chelated complexes, together with oligomeric by-products, were observed. Reaction with the (p -cymene)ruthenium dichloride dimer, [RuCl2(p -cymene)]2, resulted in a mixture of diastereomeric complexes. [source] Chiral discrimination in hydrogen-bonded complexes of 2-methylol oxirane with hydrogen peroxideINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Guiqiu Zhang Abstract A systematic quantum chemical study reveals the effects of chirality on the intermolecular interactions between two chiral molecules bound by hydrogen bonds. The methods used are second-order Møller,Plesset perturbation theory (MP2) with the 6-311++g(d,p) basis set. Complexes via the OH···O hydrogen bond formed between the chiral 2-methylol oxirane (S) and chiral HOOH (P and M) molecules have been investigated, which lead to four diastereomeric complexes. The nomenclature of the complexes used in this article is enantiomeric configuration sign corresponding to English letters. Such as: sm, sp. The relative positions of the methylol group and the hydrogen peroxide are designated as syn (same side) and anti (opposite side). The largest chirodiastaltic energy was ,Echir = ,1.329 kcal mol,1 [9% of the counterpoise correct average binding energy De(corr)] between the sm-syn and sp-anti in favor of sm-syn. The largest diastereofacial energy was ,1.428 kcal mol,1 between sm-syn and sm-anti in favor of sm-syn. To take into account solvents effect, the polarizable continuum model (PCM) method has been used to evaluate the chirodiastaltic energies, and diastereofacial energies of the 2-methylol oxirane···HOOH complexes. The chiral 2,3-dimethylol oxirane (S, S) is C2 symmetry which offers two identical faces. Hence, the chirodiastaltic energy is identical to the diastereomeric energy, and is ,Echir = 0.563 kcal mol,1 or 5.3% of the De(corr) in favor of s,s-p. The optimized structures, interaction energies, and chirodiastaltic energies for various isomers were estimated. The harmonic frequencies, IR intensities, rotational constants, and dipole moments were also reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Deuterium isotope effects observed during competitive binding chiral recognition electrospray ionization,mass spectrometry of cinchona alkaloid-based systemsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2006Kevin A. Schug Abstract Deuterium isotope effects are reported for binding between tert -butylcarbamoyl-quinine/quinidine chiral selectors and isotopomeric quasienantiomers of N -(3,5-dinitrobenzoyl)leucine measured using electrospray ionization-mass spectrometry (ESI-MS) and competitive binding. Evaluation of mixtures of each selector with one labeled and one unlabeled enantiomeric selectand of identical configuration showed a significant difference in measured ion abundances of diastereomeric complexes between the selector and each selectand. It was found that in some cases, the complex containing the nondeuterated selectand was 15% more abundant than its deuterated counterpart. On the basis of an assessment of solution- and gas-phase isotope effects reported in the literature, a series of control experiments were performed to study the origin of the effects. On the basis of these measurements, our preliminary conclusion is that the differing gas-phase physicochemical nature of the deuterated versus nondeuterated selectand represents the strongest contribution to the observed effect in this chiral molecular recognition system. Copyright © 2006 John Wiley & Sons, Ltd. [source] Enantiomer discrimination of peptides by tandem mass spectrometry: influence of the peptide sequence on chiral recognitionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Christoph Czerwenka The enantiomer discrimination of peptides by electrospray ionization tandem mass spectrometry is described. A cinchona alkaloid derivative, tert -butylcarbamoylquinine, is used as chiral selector. The chiral selector forms diastereomeric complexes with the peptide enantiomers in the liquid phase (methanolic solution), which are then transferred to the gas phase, where their dissociation behaviour is studied in an ion-trap mass spectrometer. Different degrees of dissociation of the diastereomeric complexes allow for the discrimination of the peptide enantiomers. The influence of the peptide sequence on enantiomer discrimination is discussed and molecular recognition information is derived by comparing the results obtained for related peptides. For dipeptides, small amino acid residues at the N-terminus and bulky side chains at the C-terminus were found to enhance chiral recognition, while for tripeptides the effects were rather irregular. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determination of the enantiomeric excess of an M3 antagonist drug substance by chemometric analysis of the IR spectra of different guest-host complexesCHIRALITY, Issue 5 2006Lili Zhou Abstract A novel approach for the potential on-line determination of the enantiomeric excess (ee) of an M3 antagonist drug substance combining attenuated total reflectance infrared (ATR-IR) spectroscopy, guest-host complexes, and chemometric data analysis is described. Chiral recognition through a formation of diastereomeric complexes was measured by ATR-IR. Small changes on the IR spectra reflect the interaction between the guest (M3) and host (chiral selector). These changes are measured as a function of M3 enantiomer excess. The standard error of prediction is 1.3 ee%. The prediction results based on the IR method were in good agreement with the gravimetric method. The robustness of the calibration model was evaluated by varying the concentration of the chiral selector, the pH of the solution, and the organic solvents. The stability of the calibration model was also demonstrated through measuring different sets of samples on different days. Chirality, 2006. © 2006 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||