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Chiral Recognition (chiral + recognition)
Terms modified by Chiral Recognition Selected AbstractsDicopper(II) Complexes with the Enantiomers of a Bidentate Chiral Reduced Schiff Base: Inclusion of Chlorinated Solvents and Chiral Recognition of1,2-Dichloroethane Rotamers in the Crystal LatticeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006Vamsee Krishna Muppidi Abstract Bisphenoxo-bridged dicopper(II) complexes [Cu2Ln2Cl2] {1 (n = 1) and 2 (n = 2)} with the N,O-donor reduced Schiff bases N -(2-hydroxybenzyl)-(R)-,-methylbenzylamine (HL1) and N -(2-hydroxybenzyl)-(S)-,-methylbenzylamine (HL2) have been synthesised and characterised. In both 1 and 2, the bidentate chiral ligands coordinate the metal centres through the secondary amine N atom and the bridging phenolate O atom. The chloride ion occupies the fourth coordination site and completes a slightly distorted square-planar NO2Cl environment around each copper(II) centre. Magnetic susceptibility measurements in the solid state suggest a strong antiferromagnetic interaction between the metal centres in both complexes. Both 1 and 2 readily form 1:1 host-guest compounds with chlorinated solvents such as CH2Cl2, CHCl3 and Cl(CH2)2Cl. All the host-guest compounds crystallise in noncentrosymmetric space groups. 1·CH2Cl2 and 2·CH2Cl2 crystallise in the P21 space group while 1·CHCl3, 2·CHCl3, 1·Cl(CH2)2Cl and 2·Cl(CH2)2Cl crystallise in the P212121 space group. In these inclusion crystals, the C,H···Cl interactions between the guest and the host molecules are primarily responsible for enclatheration of the chloroalkane molecules. In the case of CH2Cl2, one of its Cl atoms acts as the acceptor. On the other hand, for CHCl3 and Cl(CH2)2Cl, the metal coordinated Cl atom of the host complex acts as the acceptor. The structures of 1·(P)-Cl(CH2)2Cl and 2·(M)-Cl(CH2)2Cl provide rare examples for chiral recognition of the right handed (P) and the left handed (M) gauche forms of Cl(CH2)2Cl in molecular assemblies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Calix[4]arene-Based Chromogenic Chemosensor for the ,-Phenylglycine Anion: Synthesis and Chiral RecognitionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2006Guang-Yan Qing Abstract Calix[4]arene-based two-armed chiral anion receptors 3a and 3b have been synthesized and examined for their chiral anion-binding abilities by UV/Vis absorption and 1H NMR spectroscopy. The results of nonlinear curve fitting indicate that 3a and 3b form 1:1 stoichiometric complexes with the L - or D -,-phenylglycine anion by multiple hydrogen-bonding interactions and exhibit good enantioselective recognition for the enantiomers of the ,-phenylglycine anions (3a: Kass(L)/Kass(D) = 4.76; 3b: Kass(D)/Kass(L) = 2.84). The marked colour changes observed for the complexation of 3a with the chiral anions and the good enantioselective recognition reveal that receptor 3a could be used as a good chiral chromogenic chemosensor for the enantiomers of the ,-phenylglycine anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Chiral Recognition by Resorcin[4]arene Receptors: Intrinsic Kinetics and DynamicsCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Andrea Tafi Prof. Abstract Molecular recognition of representative amino acids (A) by a chiral amido[4]resorcinarene receptor (1L) was investigated in the gas phase by ESI-FT-ICR mass spectrometry. The ligand displacement reaction between noncovalent diastereomeric [1L,H,A]+ complexes and the 2-aminobutane enantiomers (B) exhibits a distinct enantioselectivity with regard to both the leaving amino acid A and the amine reactant B. The emerging selectivity picture, discussed in the light of molecular mechanics and molecular dynamics calculations, points to chiral recognition by 1L, as determined by the effects of the host asymmetric frame on the structure, stability, and rearrangement dynamics of the diastereomeric [1L,H,A]+ complexes and the orientation of the amine reactant B in encounters with [1L,H,A]+. The results contribute to the development of a dynamic model of chiral recognition of biomolecules by enzyme mimics in the unsolvated state. La spettrometria di massa ESI-FT-ICR è stata impiegata per lo studio del riconoscimento chirale di alcuni amminoacidi rappresentativi (A) da parte di un ammido[4]resorcinarene chirale (1L). La reazione di rilascio dell,amminoacido A dai complessi diastereomerici non covalenti [1L,H,A]+ a seguito dell,attacco degli enantiomeri del 2-amminobutano (B) mostra una distinta enantioselettività sia per quanto riguarda la molecula uscente A che per quanto riguarda il reagente B. Il quadro di reattività ottenuto, discusso alla luce di calcoli di meccanica e dinamica molecolare, indica che il riconoscimento chirale da parte di 1L è determinato dall,effetto della struttura asimmetrica dell, ammido[4]resorcinarene sulla struttura, la stabilità, e la dinamica di riarrangiamento dei suoi complessi diastereomerici [1L,H,A]+ e dall, orientamento dell,ammina reagente B nel complesso di collisione con [1L,H,A]+. I risultati ottenuti contribuiscono allo sviluppo di un modello dinamico per il riconoscimento chirale di biomolecole da parte di enzimi artificiali allo stato non solvatato. [source] Chiral Recognition of Carboxylic Acids by Chiral Nitrogen Containing Calix[4]areneCHINESE JOURNAL OF CHEMISTRY, Issue 10 2005Yan-Song Zheng Abstract Chiral nitrogen-containing calix[4]arene was easily synthesized by the reaction of 25,27-di(2-bromoethoxy)-26,28-dihydroxy-5,11,17,23-tetrakis(t -butyl)calix[4]arene with S -((,)-1-phenylethylamine in excellent yield, and showed good ability to recognize the enantiomers of mandelic acid and 2,3-dibenzoyltartaric acid. This finding has potential application to assay and separation of enantiomers of the carboxylic acids. [source] Chiral recognition of the Schiff bases by NMR spectroscopy in the presence of a chiral dirhodium complex.MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2007Deuterium isotope effect on 13C chemical shift of the optically active Schiff bases, their dirhodium adducts Abstract The dirhodium method has been successfully applied in chiral recognition of the optically active Schiff bases, derivatives of ortho -hydroxyaldehydes existing in the NH-form. or at tautomeric equilibrium. The position of the equilibrium of Schiff bases as well as their adducts has been established on the basis of measurements of deuterium isotope effects on 13C chemical shifts. The presence of the proton transfer equilibrium or NH-tautomer has promoted the adduct formation. At the equilibrium state, formation of the adducts has shifted the proton transfer equilibrium towards the NH-form. The binding site was the oxygen atom of the proton donor group. Copyright © 2007 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] Chiral recognition of dipeptide methyl esters by an anionic ,-cyclodextrinCHIRALITY, Issue 8 2001Koji Kano Abstract Chiral recognition of dipeptide methyl esters by anionic heptakis[6-carboxymethylthio-6-deoxy]-,-cyclodextrin (per-CO2, -,-CD) was studied in D2O at pD 7.0 by means of 1H NMR spectroscopy. The methyl esters of alanylalanine (Ala-Ala-OMe), alanylleucine (Ala-Leu-OMe), alanyltryptophan (Ala-Trp-OMe), glycyltryptophan (Gly-Trp-OMe), valyltryptophan (Val-Trp-OMe), leucyltryptophan (Leu-Trp-OMe), and tryptophylalanine (Trp-Ala-OMe) were used as the dipeptides. The binding constant (K) determined from NMR titration increases in the order Ala-Ala-OMe < Ala-Leu-OMe < Ala-Trp-OMe, suggesting that van der Waals interactions between the host and the guest participate in complexation. Coulomb interactions between the protonated dipeptide methyl esters and the anionic host seem to be another attractive force. Per-CO2, -,-CD interacts with the (R,R)-enantiomers of the dipeptide methyl esters more strongly than the (S,S)-enantiomers. Such enantioselectivity corresponds to that for ,-amino acid methyl esters such as Leu-OMe and Trp-OMe, whose (R)-enantiomers are the preferable guests. The enantioselectivity is mainly dominated by amino acid residue at the C -terminal and chirality at the N -terminal residue plays an assistant role. An asymmetrically twisted shape of the host cavity may be essential for chiral recognition. Chirality 13:474,482, 2001. © 2001 Wiley-Liss, Inc. [source] Dicopper(II) Complexes with the Enantiomers of a Bidentate Chiral Reduced Schiff Base: Inclusion of Chlorinated Solvents and Chiral Recognition of1,2-Dichloroethane Rotamers in the Crystal LatticeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006Vamsee Krishna Muppidi Abstract Bisphenoxo-bridged dicopper(II) complexes [Cu2Ln2Cl2] {1 (n = 1) and 2 (n = 2)} with the N,O-donor reduced Schiff bases N -(2-hydroxybenzyl)-(R)-,-methylbenzylamine (HL1) and N -(2-hydroxybenzyl)-(S)-,-methylbenzylamine (HL2) have been synthesised and characterised. In both 1 and 2, the bidentate chiral ligands coordinate the metal centres through the secondary amine N atom and the bridging phenolate O atom. The chloride ion occupies the fourth coordination site and completes a slightly distorted square-planar NO2Cl environment around each copper(II) centre. Magnetic susceptibility measurements in the solid state suggest a strong antiferromagnetic interaction between the metal centres in both complexes. Both 1 and 2 readily form 1:1 host-guest compounds with chlorinated solvents such as CH2Cl2, CHCl3 and Cl(CH2)2Cl. All the host-guest compounds crystallise in noncentrosymmetric space groups. 1·CH2Cl2 and 2·CH2Cl2 crystallise in the P21 space group while 1·CHCl3, 2·CHCl3, 1·Cl(CH2)2Cl and 2·Cl(CH2)2Cl crystallise in the P212121 space group. In these inclusion crystals, the C,H···Cl interactions between the guest and the host molecules are primarily responsible for enclatheration of the chloroalkane molecules. In the case of CH2Cl2, one of its Cl atoms acts as the acceptor. On the other hand, for CHCl3 and Cl(CH2)2Cl, the metal coordinated Cl atom of the host complex acts as the acceptor. The structures of 1·(P)-Cl(CH2)2Cl and 2·(M)-Cl(CH2)2Cl provide rare examples for chiral recognition of the right handed (P) and the left handed (M) gauche forms of Cl(CH2)2Cl in molecular assemblies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] NMR Enantiodiscrimination of Polar and Apolar Substrates by Multifunctional CyclodextrinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2005Gloria Uccello-Barretta Abstract Mixed methylated/carbamoylated cyclodextrins constitute a new class of chiral complexing agents for NMR spectroscopy, which are able to induce anisochrony of enantiomeric mixtures of apolar trisubstituted allenes and polar derivatized compounds most of which are endowed with a ,-acidic 3,5-dinitrophenyl ring. The differing contribution to enantiorecognition phenomena of the nature and location of the functional groups on the two cyclodextrin rims was shown. Some interesting aspects of the complexation phenomena, which are the basis of chiral recognition, have been underlined by NMR spectroscopic investigations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Mechanism of Selective and Unselective Enclathration by a Host Compound Possessing Open, Flexible Host FrameworksEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2003Kazunori Nakano Abstract Molecular recognition of o -, m -, and p -xylenes (oX, mX, and pX) through enclathration of cholic acid (CA) is described. All of the xylenes give lattice inclusion crystals with CA, and crystallographic studies reveal that they are included in different open host frameworks. In particular, oX has two polymorphs, depending on the recrystallization temperatures. Competitive recrystallization from mixtures of xylenes resulted in selective enclathrations and the formation of racemic mixed crystals. In the presence of an equimolar amount of oX, CA selectively includes mX or pX in the host frameworks, which are identical to those obtained from the pure mX or pX, respectively. The low affinity of oX is explained in terms of a lower stability of CA·oX than of the other two complexes, as judged from the low PCcavity, the volume ratio of the guest compound to the host cavity. Meanwhile, mixtures of mX and pX yield inclusion crystals that accommodate both of the guests. These have the same open host framework as obtained from pure mX, and the guest components are disordered statically in the host cavity. The ratios of the xylene mixtures in the single crystals are similar to those in the original recrystallization mixtures, and also in the bulk crystals, indicating that CA forms mixed crystals of mX and pX. This non-selectivity is attributed to the similar stabilities of CA·mX and CA·pX, according to the moderate PCcavity. The inclusion behavior of CA from mixtures of xylenes is quite similar to chiral recognition by diastereomer-salt methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Chiral polymers for resolution of enantiomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2009Yoshio Okamoto Abstract In 1979, the formation of one-handed helical poly(triphenylmethyl methacrylate) (PTrMA) was found through the helix-sense-selective polymerization of methacrylate using chiral anionic initiators, and the existence of a stable helical polymer without chiral side chains was proved. The chiral polymer exhibited unexpected high chiral recognition of various racemic compounds when used as the chiral packing material (CPM) for HPLC, which was commercialized in 1982 as the first chiral column based on an optically active polymer. This success encouraged us to develop further useful commercial chiral packing materials (CPMs) based on polysaccharides, cellulose, and amylose. By using these polysaccharide-based CPMs, particularly phenylcarbamate derivatives, nearly 90% of chiral compounds can be resolved not only analytically but also preparatively, and several chiral drugs have been produced using the CPMs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1731,1739, 2009 [source] Preparation, characterization, and chiral recognition of optically active polymers containing pendent chiral units via reversible addition-fragmentation chain transfer polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2007Jian Wang Abstract Optically active polymers bearing chiral units at the side chain were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in the presence of 2,2,-azobisisobutyronitrile (AIBN)/benzyl dithiobenzoate (BDB), using a synthesized 6- O - p -vinylbenzyl-1,2:3,4-Di- O -isopropylidene- D -galactopyranose (VBPG) as the monomer. The experimental results suggested that the polymerization of the monomer proceeded in a living fashion, providing chiral group polymers with narrow molecular weight distributions. The optically active nature of the obtained poly (6- O - p -vinylbenzyl-1,2:3,4-Di- O -isopropylidene- D -galactopyranose) (PVBPG) was studied by investigating the dependence of specific rotation on the molecular weight of PVBPG and the concentration of PVBPG in tetrahydrofuran (THF). The results showed the specific rotation of PVBPG increased greatly with the decrease of the concentration of the PVBPG homopolymer. In addition, the effect of block copolymers of PVBPG on the optically active nature was also investigated by preparing a series of diblock copolymers of poly(methyl methacrylate) (PMMA)- b -PVBPG, polystyrene (PS)- b -PVBPG, and poly(methyl acrylate) (PMA)- b -PVBPG. It was found that both the homopolymer and the diblock copolymers possessed specific rotations. Finally, the ability of chiral recognition of the PVBPG homopolymer was investigated via an enantiomer-selective adsorption experiment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3788,3797, 2007 [source] Preparation of HPLC chiral packing materials using cellulose tris(4-methylbenzoate) for the separation of chrysanthemate isomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2006Chiyo Yamamoto Abstract We investigated the separation of chrysanthemate isomers (1), particularly the (1R)-trans form, by high-performance liquid chromatography (HPLC) using polysaccharide derivatives, such as the phenylcarbamates and benzoates of cellulose and amylose, as the chiral stationary phases (CSPs). The chiral packing materials (CPMs) having a high chiral recognition for the chrysanthemic acid ethyl ester (1a) were prepared by coating cellulose tris(4-methylbenzoate) (2a) dissolved in solvents containing methyl benzoate or acetophenone as an additive on silica gel. The separation factor for 1a significantly depended on the preparation conditions of CPM 2a, such as the coating amount of 2a and the type and amount of additives. The chiral recognition ability created by imprinting the additives was lost when the CPM was heated at a high temperature, and was recovered by contacting it with the additive in a packed column. The structural change in 2a during these treatments was not clearly detected by spectroscopic methods. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5087,5097, 2006 [source] New mathematic model for predicting chiral separation using molecular docking: Mechanism of chiral recognition of triadimenol analoguesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2009Guoqing Zhang Abstract The purpose of this paper was to study the enantioseparation mechanism of triadimenol compounds by carboxymethylated (CM)-,-CD mediated CE. All the enantiomers were separated under the same experimental conditions to study the chiral recognition mechanism using a 30 mM sodium dihydrogen phosphate buffer at pH 2.2 adjusted by phosphoric acid. The inclusion courses between CM-,-CD and enantiomers were investigated by the means of molecular docking technique. It was found that there were at least three points (one hydrophobic bond and two hydrogen bonds) involved in the interaction of each enantiomer with the chiral selectors. A new mathematic model has been built up based on the results of molecular mechanics calculations, which could analyze the relationship between the resolution of enantioseparation and the interaction energy in the docking area. Comparing the results of the separation by CE, the established mathematic model demonstrated good capability to predict chiral separation of triadimenol enantiomers using CM-,-CD mediated CE. [source] Extended application of a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to the resolution of N -(substituted benzoyl)-,-amino acid amidesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2006Guanghui Tan Abstract A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N -(substituted benzoyl)-,-amino acid amides and esters. N -(Substituted benzoyl)-,-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01 : 0.05 : 100, v/v/v) as an optimum mobile phase while N -(substituted benzoyl)-,-amino acid esters were not resolved at all. In contrast, both N -(substituted benzoyl)-,-amino acid amides and esters were not resolved at all or resolved very poorly on another CSP (CSP 2), which lacks the two N,H hydrogens of the amide tethers of CSP 1. Among the substituents on the benzoyl group of analytes, the nitro group was the best for good resolution of analytes on CSP 1. From these results, the two N,H hydrogens of the amide tethers of CSP 1, the carbonyl oxygen of the amide group of analytes, and the nitro group on the benzoyl group of analytes were concluded to play significant roles in chiral recognition. In addition, various N -(3,5-dinitrobenzoyl)leucine amides with different lengths of N -alkylamide chains were resolved on CSP 1 and N -(3,5-dinitrobenzoyl)leucine N -propylamide was found to show the best chiral recognition in terms of the separation (, = 1.30) and the resolution factor (RS = 3.17). [source] Thermodynamic origin of the chiral recognition of tryptophan on teicoplanin and teicoplanin aglycone stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 5 2005Mohamed Haroun Abstract The D-, L-tryptophan binding and the chiral recognition properties of the teicoplanin and teicoplanin aglycone (TAG) chiral stationary phase (CSPs) were compared at various column temperatures. The solute adsorption isotherms (bi-Langmuir model) were determined for both the two CSPs using the perturbation method. It was demonstrated that the sugar units were involved in the reduction of the apparent enantioselectivity through two phenomena: (i) the inhibition of some enantioselective contacts with low-affinity binding regions of the aglycone and (ii) a decrease in the stereoselective properties of the aglycone high-affinity binding pocket. The phenomenon (ii) was governed by both a decrease in the ratio of the enantiomer adsorption constant and a strong reduction of the site accessibility for D- and L-tryptophan. In addition, a temperature effect study was performed to investigate the chiral recognition mechanism at the aglycone high-affinity pocket. An enthalpy-entropy compensation analysis derived from the Grunwald model as well as the comparison with the literature data demonstrated that the enantioselective binding mode was dependent on an interface dehydration process. The change in the enantioselective process observed between the TAG and teicoplanin CSP was characterized by a difference of ca. 2,3 ordered water molecules released from the species interface. [source] A Self-Assembling Polythiophene Functionalised with a Cysteine MoietyMACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2003Adele Mucci Abstract A new copolymer bearing a cysteine moiety, designed for molecular interaction, metal-ion detection, and chiral recognition, was synthesised starting from the dibromo derivative of methyl N -(tert -butoxycarbonyl)- S -thien-3-ylcysteinate and distannylthiophene through a Stille coupling reaction. UV-vis spectroscopy, circular dichroism, NMR spectroscopy, and gel permeation chromatography analyses evidenced that this polymer is able to form self-assembling structures, through the formation of a hydrogen-bond network, not only in the solid state but also in solution. [source] Chiral recognition of the Schiff bases by NMR spectroscopy in the presence of a chiral dirhodium complex.MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2007Deuterium isotope effect on 13C chemical shift of the optically active Schiff bases, their dirhodium adducts Abstract The dirhodium method has been successfully applied in chiral recognition of the optically active Schiff bases, derivatives of ortho -hydroxyaldehydes existing in the NH-form. or at tautomeric equilibrium. The position of the equilibrium of Schiff bases as well as their adducts has been established on the basis of measurements of deuterium isotope effects on 13C chemical shifts. The presence of the proton transfer equilibrium or NH-tautomer has promoted the adduct formation. At the equilibrium state, formation of the adducts has shifted the proton transfer equilibrium towards the NH-form. The binding site was the oxygen atom of the proton donor group. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multinuclear magnetic resonance study of chiral mesoionic oxa- and thiatriazole and tetrazole derivatives: adducts with dirhodium complexes and chiral recognition,MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2003Jaroslaw Ja Abstract Mesoionic compounds 1,8 were synthesized and their 1H, 13C, 14N, 15N and 17O NMR spectra recorded in the absence and presence of the chiral dirhodium complex Rh*. It is shown that the enantiomers of the mesoionic compounds could be differentiated satisfactorily (,dirhodium method'). Copyright © 2003 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] Control of helix sense in protein-mimicking backbone by the noncovalent chiral effectTHE CHEMICAL RECORD, Issue 3 2007Yoshihito Inai Abstract We have reviewed our previous work regarding induction or control of a peptide helix sense through chiral stimulus to the peptide chain terminus. An optically inactive 310 -helix designed mainly with unusual ,-amino acid residues was commonly employed. Such an N-terminal-free peptide generates a preferred helix sense by chiral acid molecule. A helix sense pre-directed in chiral sequence is also influenced or controlled by the chiral sign of such external molecule. Here free amide groups in the 310 -helical N-terminus participate in the formation of a multipoint coordinated complex. The terminal asymmetry produces the noncovalent chiral domino effect (NCDE) to influence the whole helix sense. The NCDE-mediated control of helicity provides the underlying chiral nature of protein-mimicking helical backbones: notably, chiral recognition at the terminus and modulation of helical propensity through chiral stimulus. The above items from our previous reports have been outlined and reviewed together with their significance in biopolymer science and chiral chemistry. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 191,202; 2007: Published online in Wiley Inter-Science (www.interscience.wiley.com) DOI 10.1002/tcr.20116 [source] Chiral interaction in Gly-capped N-terminal motif of 310 -helix and domino-type induction in helix senseBIOPOLYMERS, Issue 4 2006Naoki Ousaka Abstract Chiral interaction of helical peptide with chiral molecule, and concomitant induction in its helix sense have been demonstrated in optically inactive nonapeptide (1) possessing Gly at its N-terminus: H,Gly,(,ZPhe,Aib)4,OCH3 (1: ,ZPhe = Z-dehydrophenylalanine; Aib = ,-aminoisobutyric acid). Spectroscopic measurements [mainly nuclear magnetic resonance (NMR) and circular diochroism (CD)] as well as theoretical simulation have been carried out for that purpose. Peptide 1 in the 310 -helix tends to adopt preferentially a right-handed screw sense by chiral Boc- L -amino acid (Boc: t -butoxycarbonyl). Induction in the helix sense through the noncovalent chiral domino effect should be derived primarily from the complex supported by the three-point coordination on the N-terminal sequence. Thus the 310 -helical terminus consisting of only ,-amino acid residues enables chiral recognition of the Boc-amino acid molecule, leading to modulation of the original chain asymmetry. Dynamics in the helix-sense induction also have been discussed on the basis of a low-temperature NMR study. Furthermore, the inversion of induced helix sense has been achieved through solvent effects. © 2006 Wiley Periodicals, Inc. Biopolymers 83:337,351, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Homochirality as a Consequence of Thermodynamic Equilibrium?CHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2006Joaquim Crusats Dr. Abstract Recent results on the crystallisation/dissolution equilibrium of enantiomorphic crystals of NaClO3 lead to the conclusion that liquid-phase systems composed of achiral or fast racemising compounds yielding enantiomorphic solid phases (racemic conglomerates) can derive spontaneously to a single homochiral solid phase. This is a thermodynamically driven total resolution, which can only occur when the system is so perturbed that chiral recognition between the species of the system becomes feasible. Resultats recents sobre l'equilibri de cristal.lització/dissolució de cristalls enantiomòrfics de NaClO3 duen a la conclusió següent. El sistemes composats per solucions o fases líquides de compostos aquirals que racemitzen ràpidament i cristal.litzen en fases sòlides enantiomòrfiques (conglomerats racèmics) poden derivar espontàniament cap a l'homoquiralitat. Es tracta d'una ressolució total que ve control.lada termodinàmicament i que només es pot produir quan el sistema és perturbat de manera que faci possible el reconeixement quiral entre les espècies del sistema. [source] Chiral Recognition by Resorcin[4]arene Receptors: Intrinsic Kinetics and DynamicsCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Andrea Tafi Prof. Abstract Molecular recognition of representative amino acids (A) by a chiral amido[4]resorcinarene receptor (1L) was investigated in the gas phase by ESI-FT-ICR mass spectrometry. The ligand displacement reaction between noncovalent diastereomeric [1L,H,A]+ complexes and the 2-aminobutane enantiomers (B) exhibits a distinct enantioselectivity with regard to both the leaving amino acid A and the amine reactant B. The emerging selectivity picture, discussed in the light of molecular mechanics and molecular dynamics calculations, points to chiral recognition by 1L, as determined by the effects of the host asymmetric frame on the structure, stability, and rearrangement dynamics of the diastereomeric [1L,H,A]+ complexes and the orientation of the amine reactant B in encounters with [1L,H,A]+. The results contribute to the development of a dynamic model of chiral recognition of biomolecules by enzyme mimics in the unsolvated state. La spettrometria di massa ESI-FT-ICR è stata impiegata per lo studio del riconoscimento chirale di alcuni amminoacidi rappresentativi (A) da parte di un ammido[4]resorcinarene chirale (1L). La reazione di rilascio dell,amminoacido A dai complessi diastereomerici non covalenti [1L,H,A]+ a seguito dell,attacco degli enantiomeri del 2-amminobutano (B) mostra una distinta enantioselettività sia per quanto riguarda la molecula uscente A che per quanto riguarda il reagente B. Il quadro di reattività ottenuto, discusso alla luce di calcoli di meccanica e dinamica molecolare, indica che il riconoscimento chirale da parte di 1L è determinato dall,effetto della struttura asimmetrica dell, ammido[4]resorcinarene sulla struttura, la stabilità, e la dinamica di riarrangiamento dei suoi complessi diastereomerici [1L,H,A]+ e dall, orientamento dell,ammina reagente B nel complesso di collisione con [1L,H,A]+. I risultati ottenuti contribuiscono allo sviluppo di un modello dinamico per il riconoscimento chirale di biomolecole da parte di enzimi artificiali allo stato non solvatato. [source] Immobilization and chiral recognition of 3,5-dimethylphenylcarbamates of cellulose and amylose bearing 4-(trimethoxysilyl)phenylcarbamate groupsCHIRALITY, Issue 1 2010Shouwan Tang Abstract A small amount of 4-(trimethoxysilyl)phenyl groups was randomly introduced onto the 3,5-dimethylphenylcarbamates of cellulose and amylose by a one-pot method. The obtained derivatives were then effectively immobilized onto silica gel as chiral packing materials (CPMs) for high-performance liquid chromatography through intermolecular polycondensation of the trimethoxysilyl groups. The effects of the amount of 4-(trimethoxysilyl)phenyl groups on immobilization and enantioseparation were investigated. Also, the solvent durability of the immobilized-type CPMs was examined with the eluents containing chloroform and tetrahydrofuran. When these eluents were used, the chiral recognition abilities of the CPMs for most of the tested racemates were improved to some extent depending on the compounds. Chirality 2010. © 2009 Wiley-Liss, Inc. [source] Chirality and chemical processes: A few afterthoughtsCHIRALITY, Issue 1 2008Pedro Cintas Abstract Chirality and chiral have become terms that pervade a wide range of disciplines in physical and life sciences. Although such terms are precisely defined, their use often engenders confusion and ambiguity. Perhaps, the most improper use of chirality, yet widely accepted, is related to its association with stereodynamics and physico-chemical transformations, such as chiral discrimination, chiral resolution, chiral recognition, chiral synthesis, and so on. Even though this conceptual perversion has been highlighted by renowned stereochemists, it has become a recurring keyword and a hot message in modern literature. It is timely to renew the correct use and context in forums such as the present journal, adding further reflections that may help both beginners and practitioners. This short article is not intended to criticize or highlight errors, but rather to encourage a level of rigor and the use of statements, which should be universally correct. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source] Enantiomeric separation of imidazolinone herbicides using chiral high-performance liquid chromatographyCHIRALITY, Issue 3 2007Kunde Lin Abstract Chiral high-performance liquid chromatography (HPLC) is one of the most powerful tools to prepare enantiopure standards of chiral compounds. In this study, the enantiomeric separation of imidazolinone herbicides, i.e., imazethapyr, imazapyr, and imazaquin, was investigated using chiral HPLC. The enantioselectivity of Chiralpak AS, Chiralpak AD, Chiralcel OD, and Chiralcel OJ columns for the three analytes was compared under similar chromatographic conditions. Chiralcel OJ column showed the best chiral resolving capacity among the test columns. The resolved enantiomers were distinguished by their signs of circular dichroism detected at 275 nm and their structures confirmed with LC-mass spectrometric analysis. Factors affecting the chiral separation of imidazolinones on Chiralcel OJ column were characterized. Ethanol acted as a better polar modifier than the other alcohols including 2-propanol, 1-butanol, and 1-pentanol. Although the acidic modifier in the mobile phase did not influence chiral recognition, it was necessary for reducing the retention time of enantiomers and suppressing their peak tailing. Thermodynamic evaluation suggests that enantiomeric separation of imidazolinones on Chiralcel OJ column is an enthalpy-driven process from 10 to 40°C. This study also shows that small amounts of pure enantiomers of imidazolinones may be obtained by using the analytical chiral HPLC approach. Chirality 19, 2007. © 2006 Wiley-Liss, Inc. [source] Enantioseparation by HPLC using phenylcarbonate, benzoylformate, p -toluenesulfonylcarbamate, and benzoylcarbamates of cellulose and amylose as chiral stationary phasesCHIRALITY, Issue 6 2005Tomoyuki Ikai Abstract Phenylcarbonate, benzoylformate, and p -toluenesulfonylcarbamate of cellulose and five new benzoylcarbamate derivatives of both cellulose and amylose were synthesized and their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). Cellulose benzoylcarbamate has a higher chiral recognition ability compared to phenylcarbonate, p -toluenesulfonylcarbamate, and benzoylformate of cellulose. The benzoylcarbamate derivatives exhibited a characteristic chiral recognition for the racemates, which bear a hydrogen atom capable of hydrogen bonding to the carbonyl group of the benzoylcarbamates. The structures of the benzoylcarbamates were investigated by CD spectroscopy. Chirality 17:299,304, 2005. © 2005 Wiley-Liss, Inc. [source] Chiral stationary phase covalently bound with a chiral pseudo-18-crown-6 ether for enantiomer separation of amino compounds using a normal mobile phaseCHIRALITY, Issue 3 2005Keiji Hirose Abstract In order to apply the excellent chiral recognition ability of chiral pseudo-18-crown-6 ethers that we developed to chiral separation, we prepared a chiral stationary phase (CSP) by immobilizing a chiral pseudo-18-crown-6-type host on 3-aminopropyl silica gel. A chiral column was prepared by the slurry-packing method in a stainless steel HPLC column. A liquid chromatography system using this CSP combined with the detection by mass spectrometry was used for enantiomer separation of amino compounds. A normal mobile phase can be used on this CSP as opposed to conventional dynamic coating-type CSPs. Enantiomers of 18 common natural amino acids were efficiently separated. The chiral separation observed for amino acid methyl esters, amino alcohols, and lipophilic amines was fair using this HPLC system. In view of the correlation between the enantiomer selectivity observed in chromatography and the complexion in solution, the chiral recognition in host,guest interactions might contribute to this enantiomer separation. Chirality 17:142,148, 2005. © 2005 Wiley-Liss, Inc. [source] Preparation and enantioseparation characteristics of two chiral stationary phases based on mono(6A -azido-6A -deoxy)-perphenylcarbamoylated ,- and ,-cyclodextrinCHIRALITY, Issue 9 2004Xiang-Hua Lai Abstract Two chiral stationary phases, ph-,-CD and ph-,-CD, were prepared from mono(6A -azido-6A -deoxy)perphenylcarbamoylated ,- and ,-cyclodextrin immobilized onto silica gel via the Staudinger reaction. The chromatographic characteristics of these two chiral stationary phases were evaluated. The influence of different cyclodextrins (CDs) on the enantioselectivities was also investigated in this study. Compared to ph-,-CD, ph-,-CD exhibited quite good enantioselectivity toward the analytes with bulky molecular structures. It was found that the formation of inclusion complex might play a quite important role in the chiral recognition not only under reverse phases but also under normal phases. Chirality 16:592,597, 2004. © 2004 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||