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  • Organic Chemistry  (916)
  • 2010-2014
  • 2005-2009
  • 1990-1994  (916)
  • 1985-1989
  • 1970-1974
  • 1992  (916)
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  • 2010-2014
  • 2005-2009
  • 1990-1994  (916)
  • 1985-1989
  • 1970-1974
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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: With the aid of a thermochemical cycle consisting of acidity and new redox data in dimethyl sulfoxide (DMSO) solution, homolytic N—H bond dissociation energies (ΔBDE values) relative to acetamide (1) (where the N—H BDE for 1 is defined as 0 kcal mol-1) were determined for diacetamide (0), biuret (+ 1), 3,3-dimethylglutarimide (-3), diacetylhydrazine (-16), 4,4-dimethylpyrazolidine-3,5-dione (- 25), 4-dimethylurazole (-29), hydrazoic acid (-15), succinimide (-15) and 1,2-dimethylurazole (-13) (all values in kcal mol-1). These ΔBDE data provide (a) additional evidence for the minimal N—H bond weakening effects of adjacent carbonyl groups, (b) evidence for relatively large N—H bond weakening effects of adjacent  - NHC(O)R moieties in both cyclic and acyclic hydrazides and (c) evidence suggesting that urazolyl radicals are more stable than pyrazolidinedionyl radicals, relative to their hydrogenated precursors. Inserting the appropriate acidity and redox data for hydrazoic acid into a thermochemical cycle that includes a constant that permits comparison of DMSO solution BDEs with gas-phase BDEs yields estimates of 93 kcal mol-1 for the homolytic strengths of the N—H bonds present in succinimide and H—N3. The DMSO N—H BDE determined in this way for H - N3 is in remarkable agreement with a determination of its gas-phase value, whereas the DMSO N—H BDE for succinimide places it intermediate between three published estimates of its gas-phase value.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 3
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular recognition properties of 18 acyclic imides were studied to evaluate the relative contributions of conformational, hydrogen bonding and crystal packing forces to the stabilization of specific aggregate patterns in the solid state. The crystal structure of diisobutyramide and the aggregate patterns of the 18 imides are presented. The stabilization by hydrogen bonding was found to override the conformational preferences of imides, while packing forces often precluded the formation of the most stable hydrogen bonded aggregate. The aggregate patterns of imides were also found to be a function of the type of substituents present as R groups. Imides with R groups of similar shape and size prefer to pack as bifurcated hydrogen bonded chains, whereas dimers or singly hydrogen-bonded chains form when the R groups have significantly different spatial requirements. Analysis of imide aggregate patterns revealed the similar spatial requirements of isopropyl and phenyl groups. The molecular recognition properties of acyclic imides are summarized as a set of hydrogen bond rules, which can be used to design new imide aggregates.
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  • 4
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of loss of NO2- from the radical anions of 2-(4-nitrophenyl)-2-nitropropane (α,p-dinitrocumene) and 2-phenyl-2-nitropropane (α-nitrocumene) were compared by three different methods. The rate constant for the apparently heterolytic process (DN) undergone by the radical anion of the dinitrocumene was measured by pulse radiolysis to be 2 × 103 s-1 in dimethylformide at 25°C. This value is in reasonable agreement with values estimated from an indirect chemical method and from cyclic voltammetry at low temperature. The rate for the formally homolytic dissociation process (DR) undergone by the radical anion of the mononitrocumene could not be determined by pulse radiolysis but could be shown to be between 50 and 1000 times faster than the dinitro case using the other two methods. Possible reasons for the faster rate for the DR process are discussed with reference to related systems for which the DR process had been found to be unexpectedly slow.
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  • 5
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction between α-tocopheroxyl radical (VE·) and ascorbic acid (VC) and its lipophilic derivatives ascorbyl-6-caprylate (VC-8), 6-laurate (VC-12) and 6-palmitate (VC-16) was studied by stopped-flow ESR spectroscopy in cetyltrimethylammonium bromide (CTAB) micelles. The second-order rate constants for the reaction were found to be 9 · 0, 3 · 0, 0 · 7 and 0 · 03 × 105 1 mol-1 s-1 for VC, VC-8, VC-12 and VC-16, respectively, indicating a remarkable influence of the aliphatic side-chain on the reactivity. The lifetime of the reaction intermediate, ascorbate radical anion, was greatly enhanced by the lipophilic side-chain, being 0 · 4, 5 and 110 s for VC-8-., VC-12-. and VC-16-. respectively. Kinetic analysis shows that the inter- and intramicellar diffusion may be the rate-limiting steps for the reaction carried out in micelles.
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  • 6
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Long-lived trapped radicals produced during the photopolymerization of butane-1, 4-diol diacrylate (BDDA) were studied by EPR and ENDOR spectroscopy and their thermal decay was followed by EPR measurements at different temperatures (40-120 °C) for kinetic study. The EPR signal showed the superimposition of two different patterns, a three-line and a single-line spectrum. Both EPR patterns decayed following first-order kinetics in the investigated temperature range. Activation parameters of the decay were obtained. The EPR patterns were attributed to the same radical species situated in fluid and in cross-linked regions of the photopolymerized BDDA. Radicals of the latter kind undergo electron spin exchange strong enough to wash out the hyperfine splitting. The single-line width is mainly determined by electron spin dipole-dipole interactions. The ENDOR response is only of the matrix kind, typical of radicals in a solid phase. The present model was also compared with recent literature reports.
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  • 7
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The application of cavity theories of solution and linear solvation energy relationships to the interpretation of enthalpy of solution values of tert-butyl halides in hydroxylic media, measured at 25 °C and infinite dilution, is deserted, in order to define the intermolecular forces acting between solutes and solvents. It is concluded that solvent dipolarity and solvent HBD acidity effects dominate the solution process. An empirical equation relating the enthalpies of solution with selected properties of both solvents and solutes is proposed. New experimental Δ Hs∞ values for tert-butyl iodide in 13 alcohols are reported.
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  • 8
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclopropylmethoxycarbene undergoes ambiphilic-nucleophilic intermolecular reaction with alkenes and methanol, but its intramolecular chemistry (1,2-carbon migration) is suppressed (k 〈 3 × 103 s-1) by the α-methoxy substituent.
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  • 9
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 10, 10-Dimethyl-9-anthrylidene (DMA) was studied by laser flash photolysis (LFP) techniques. LFP of the requisite diazo precursor in pentane or carbon tetrachioride produced transient spectra attributed to the hydrocarbon and monochlorinated diarylmethyl radicals, respectively. In the presence of pyridine and oxygen, ylides were formed upon LFP of 10, 10-dimethyl-9-diazoanthrone. However, ylides are not formed in acetonifrile or acetone. The carbene itself was not detected by transient absorption spectroscopy. The absolute rate constants for reaction of DMA with pyridine, methanol and triethylsilane are 1·96 × 109, 1·8 × 1010, and 1·0 × 108 I mol-1 s-1, respectively. It is concluded that the singlet and triplet states of DMA are essentially degenerate.
    Additional Material: 6 Ill.
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  • 10
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The different possible sources of the intraannular hydrogens in the dehydroxylated calixarenes obtained by reductive cleavage of the calix [4] arene diethyl phosphate esters 2 and 6 are analysed. Two calixarene diethyl phosphate esters (4 and 5) full deuterated in the ethyl groups were synthesized. Reductive cleavage of 4 and 5 (potassium-ammonia) resulted in the formation of the OH-depleted calixarenes 3 and 7, respectively, which did not incorporate any deuterium at the intraannular positions, as judged by integration of the NMR signals. Quenching with D2O of the reaction mixture of either 2 or 6 and potassium-ammonia did not result in any deuterium incorporation in the products. The labelling experiments rule out the possibility that the source of the intraannular hydrogens is the diethyl phosphate ester groups or the quencher. It is concluded that the most probable sources of the hydrogen atoms in the OH-depleted calixarenes is the ammonia molecule.
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  • 11
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Peroxymonosulfate ion (HSO5-) rapidly oxidizes 2-chloroethyl phnyl sulfide (1). Dilute micelle-forming cationic surfactants slightly speed the reaction but the reaction rate decreases sharply with increasing surfactant concentration. Rate-surfactant concentration profiles in solutions of cetyltrimethylammonium hydrogensulfate can be treated quantitatively by estimating concentrations of 1 and HSO5- at the micellar surface with allowance for competition between HSO5- and HSO4-. The second-Order rate constant in the micellar pseudo-phase is lower that in water by a factor of ca 400. Similar rate-surfactant concentration profiles were observed for the oxidation of di-n-propyl sulfide by periodate ion in solutions of cetyltrimethylammonium bromide, chloride and mesylate, and second-order rate constants in the micellar pseudo-phases are lower than in water by factors of ca 400. These oxidations are slowed by a decrease in the water content of aqueous acetonitrile and solvent, and micellar rate effects are consistent with transition states in which positive charge builds up on sulfur.
    Additional Material: 6 Ill.
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  • 12
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydrogen-bond pattern of 4-mercaptopyridine-4-thiopyridone in solution and in the solid state consists of extended chains of 4-thiopyridone associated through NH…S hydrogen bonds. The solution structure in chloroform was studied by UV-visible spectrometry and vapor pressure osmometry. A tautomerization constant of 1 · 8, favoring 4-thiopyridone, and a self-association constant of 2600 ml-1 were determined. Over 50% of the sample is aggregated near saturation with significant amounts (〉15%) of the sample present as oligomers containing four or more 4-thiopyridone monomer units. In its crystal structure, 4-mercaptopyridine-4-thiopyridone is composed of infinite chains of 4-thiopyridone associated by NH…S hydrogen bonds between glide related molecules, with N…S = 3 · 219(3) Å, H…S = 2 · 42(4) Å, N - H…S angle = 175(4)° and H…S = C angle = 96(1)°. Relationships between solution aggregation, crystal nucleation, and crystal propagation are discussed. Crystal data are as follows: space group = P21/c, a = 7 · 183(5) Å, b = 6 · 132(5) Å, c = 11 · 618(7) Å, β = 90 · 51(5)°, Z = 4, Dc = 1 · 44 g cm-3, 1623 reflections, R = 0 · 050, Rw = 0 · 072.
    Additional Material: 9 Ill.
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  • 13
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ESR spectra of 2-arylindan-1,3-dionyl radicals in various solvents at 343 K were obtained and assignments of the hyperfine structures were made. The hyperfine coupling constant (hfcc) of the dimethylamino nitrogen increases whereas the 2',6'-hydrogen hfcc decreases as the ET value, a solvent polarity parameter, increases. MO calculations were made according to the semi-empirical procedure of Rieger and Fraenkel; the nitrogen and oxygen Coulomb integrals were adjusted so that the calculated spin density on the nitrogen atom agrees with that estimated from its hfcc. It is found that the π-moment of the radicals increases from 9·13 D in toluene to 9·85 D in acetic acid. The solvent dependence of the equilibrium between the radicals and its dimer has been explained in terms of the solventinduced π-moment in polar solvents.
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  • 14
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The protonation of diphenyl sulfoxide and several substituted diphenyl sulfoxides was probed by the MNDO-PM3 method to gain a theoretical insight into the experimentally observed preference for stable diphenyl sulfoxonium ion formation (O-protonation) in 1:1 FSO3H - SbF5 (Magic Acid) - SO2. In agreement with solution studies, O- protonation is uniformly favored (by ca 17 kcal mol -1) over S-protonation. The differences in the heats of formation of protonated and unprotonated diphenyl sulfoxides are increased by electron-withdrawing substituents (F, CF3) and decreased by electron-donating groups (Me, OMe). Variations in the SO bond length and bond order in the onium ions are compatible with simple resonance arguments and the oxonium/sulfonium character of both the O- and S-protonated onium ions. Surprisingly, the O- and S-protonated dibenzothiophene S-oxides are predicted to have identical energetics as compared with the corresponding protonated diphenyl sulfoxides. On structure optimization dibenzothiophene S-oxide itself, if the initial geometry is somewhat twisted, rearranges by ring expansion to give a new heterocycle with lower energy. A rotational barrier study on the parent O-protonated diphenyl sulfoxide showed two minima, separated by 1.3 kcal mol-1, at HOSC dihedral angles of 60° and 240°. The two conformations correspond to syn and anti orientations of the OH proton relative to the aromatic rings, and support the lowtemperature solution observations of the presence of two distinct sulfoxonium ions in solution. The rotational barriers for diphenyl sulfoxonium cation are compared with those of O-protonated dimethyl sulfoxide.
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  • 15
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The first direct determination of a 1,2-chlorine atom shift in a chlorobenzylcarbene was achieved by nanosecond laser flash photolysis. Arrhenius activation parameters of Eact = 3.39 ± 0.14 kcal mol-1 and log [A(s-1)] = 10.98 ± 0.14 were obtained for 1,2-chlorine migration in α-methyl-α-chlorobenzyl(ch1oro)carbene. The lifetime of this carbene is considerably longer than previously estimated and the measured Eact, is in excellent agreement with that determined by product analysis.
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  • 16
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction between 1-fluoro-2,4-dinitrobenzene and n-butylamine in toluene shows a two-step plot of kobs, values vs the initial values of the concentration of the amine. The usual base-catalysis mechanism for HF elimination from the zwitterionic intermediate hardly explains this kinetic behaviour and the kinetic effect of addition of salts (and of 2-hydroxypyridine) to the reaction mixtures at different initial values of the concentration of n-butylamine. In contrast, the kinetic behaviours are easily explained by the presence of substrate-amine (or catalyst) interactions on the pathway of the substitution reaction.
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  • 17
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 21-23 
    ISSN: 0899-0042
    Keywords: protein binding ; affinity chromatography ; resolution ; allosteric interaction ; increased enantioselectivity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of phenprocoumon enantiomers on the stereoselective binding of 3-substituted 1,4-benzodiazepines to human serum albumin (HSA) was studied by chromatography on HSA-Sepharose column. (S)-Phenprocoumon exerts stereoselective allosteric interaction on the binding of benzodiazepines. The structural requirements of enhanced stereoselectivities are similar to those found previously with (S)-warfarin.
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  • 19
    ISSN: 0899-0042
    Keywords: opioids ; piperidines ; 1,2,3,4-tetrahydroisoquinolines ; antinociception ; binding affinity ; QSAR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two novel series, Ia,b and IIa,b, of kappa opioid antinociceptive agents have recently been described. 2a,b,3a,b,c The biological activities of 16 racemic compounds and their corresponding (-) enantiomers are now compared in a battery of tests. Enantiomers of unsubstituted piperidines Ia were synthesized starting from S(-) pipecolic acid, whereas the enantiomerically pure substituted piperidines (Ib), tetrahydroisoquinolines (IIa), and thienopiperidines (IIb) were, in general, obtained after diastereomeric crystallization of the corresponding tartrate salts. The absolute stereochemistry of one representative enantiomer from series IIa was determined to be (1S) by X-ray crystallographic analysis. Antinociceptive activity in the mouse abdominal constriction and tail-flick tests following subcutaneous administration, and binding affinity for κ and μ receptors, were found to reside predominantly in the (-) enantiomers. Consequently, racemic compounds showed approximately half potency of the corresponding enantiomers. This potency difference was less clear after oral administration presumably due to small differences in bioavailability of the two corresponding enantiomers.For compounds with some affinity also for μ receptors (Ki 〈1,000 nM), the κ/μ selectivity was maintained within each enantiomeric pair, in contrast to results found for other κ agonists.
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  • 20
    ISSN: 0899-0042
    Keywords: optical resolution ; enantioselectivity ; chromatography ; dissociation constants ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a chromatographic method for the separation and determination of the optical purity of the enantiomers of WB 4101 [(±)-1], one of the most potent and selective α1-adrenoreceptor antagonists. (±)-1 was converted into the amide of N-tosyl-(S)-proline. The two diastereoisomers were separated on silica gel and analysed by HPLC reversed phase. The analytical method described is both accurate and sensitive and allows the optical purity to be determined at very low concentrations and to obtain WB 4101 enantiomers with a purity of more than 99.95%.
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  • 21
    ISSN: 0899-0042
    Keywords: tyrosine chiral selector ; enantiomeric separations ; chiral stationary phases ; HPLC ; subFC ; β-blockers ; 1,2-amino-alcohols ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel chiral stationary phase (CSP) derived from tyrosine is evaluated with regard to the first generation commercially available (S)-ChyRoSine-A CSP, under normalphase or reversed-phase liquid chromatographic (NPLC or RPLC) and subcritical fluid chromatographic (SubFC) conditions. The complete scope of application of these CSPs is reviewed. The novel CSP, which bears a bulkier functional group, displays a higher enantiorecognition ability than previously described (S)-ChyRoSine-A toward about 15 families of racemates, whatever the mobile phase conditions.The direct enantiomeric separation of 1,2-amino-alcohols (β-blockers) is carried out on both CSPs. Facile separations are achieved within short analysis times using SubFC mode, whereas very poor separations are obtained using NPLC mode. These results disagree with previous theories (interchangeability between NPLC and SubFC modes).
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  • 22
    ISSN: 0899-0042
    Keywords: dopamine agonist ; direct chiral separation ; cellulose carbamate stationary phase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of the enantiomeric impurity, i.e., the percentage of (+) N-0437 (= N-0924) in several batches of (--) N-0437 (= N-0923) by chiral HPLC is described. Enantiomeric impurities were calculated based on the peak areas of the two baseline separated enantiomers in the chromatogram. The enantiomeric impurities found in different batches ranged from 0.02% to 0.11%. Calibration curves of the two isomers of N-0437 (Fig. 1,) were made twice to study the reproducibility and linearity of the method. The absorbance ratio, N-0923/N-0924, was found to be 1.02 with a relative standard deviation (RSD) of 9% over the whole concentration range used for the calibration curves.
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  • 23
    ISSN: 0899-0042
    Keywords: aging ; β-adrenergic blocking agent ; enantiomers ; propranolol ; protein binding ; stereoselective pharmacokinetics ; tissue binding ; tissue concentrations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of aging on the pharmacokinetics and the tissue distribution of (R)- and of (S)-propranolol was studied in 3-, 12-, and 24-month-old rats. After both iv and oral administration of rac-propranolol, the plasma concentrations were higher for the (R)- than for the (S)-enantiomer. For the tissue concentrations, the reverse was true. The free fraction of (S)-propranolol in plasma was about 4 times larger than that of (R)-propranolol, and this is the main factor responsible for the differences in kinetics between the two enantiomers. There was a suggestion for a difference in tissue binding between the two enantiomers. With aging, the plasma and tissue concentrations of both enantiomers increase, probably due to a decrease in blood clearance. Tissue binding did not change much with aging. Notwithstanding the marked differences between the kinetics of the propranolol enantiomers, the changes which occur with aging affect both enantiomers to the same degree.
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  • 24
    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.
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  • 25
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 1-7 
    ISSN: 0899-0042
    Keywords: product enantioselectivity ; aliphatic hydroxylation ; 6-n-propylchromone carboxylic acid ; chiral HPLC ; chiral shift 1H-NMR ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-n-Alkylchromone-2-carboxylic acids are metabolized solely by aliphatic oxidation. In the rabbit, the 6-n-propyl congener (PCCA) undergoes ω-1 hydroxylation exclusively. Following administration of PCCA to female Dutch rabbits (500 μmol/kg), some 77% of the dose was excreted in the urine, 41% as PCCA and 36% as 6-(2'-hydroxy-n-propyl)chromone-2-carboxylic acid. Since this metabolite is chiral, we have examined the stereochemistry of the excreted material. Diastereoisomeric (as camphanate and α-methoxy-α-(trifluoromethyl)phenylacetate esters) and direct chiral HPLC and chiral lanthanide shift NMR have each shown the S:R ratio of the excreted metabolite to be 76:24. When rabbits were dosed with the racemic metabolite, excretion of the compound was not stereoselective. The regio- and stereo-selectivity of the aliphatic hydroxylation of PCCA are thus reflections of the selectivities of the enzyme systems responsible for its formation and suggest PCCA to be an appropriate probe compound for the study of prochiral-chiral hydroxylations.
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  • 26
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 24-29 
    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.
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  • 27
    ISSN: 0899-0042
    Keywords: simultaneous stereodifferentiation of γ(δ)-lactones ; chiral monoterpenes ; stereoselective analysis ; modified cyclodextrins ; genuineness of flavours and essential oils ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The simultaneous stereodifferentiation of all aromarelevant 4(5) alkylsubstituted γ(δ)-lactones is described, using enantioselective multidimensional gas chromatography (MDG), and the column combination OV 1701/octakis(3-O-butyryl-2,6-di-O-pentyl)-γ-cyclodextrin. The method is applicated to the lactone flavour compounds of fruits, indicating the advance to the analytical differentiation between “natural” and “nature-identical” aromas. Modified cyclodextrins are also proved to be powerful tools in the chirospecific CGC analysis of monoterpenoid constituents of essential oils. Optical purity control is discussed as an indicator for their natural origin.
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  • 28
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 68-70 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 29
    ISSN: 0899-0042
    Keywords: improving enantioselectivity ; lipase ; enantioselective biocatalysis ; enantiomerically pure compounds ; dihydropyridines ; enantioselective inhibition ; cis-3-hydroxy-6-acetoxy-cyclohex-1-ene ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Different approaches to improve the enantioselectivity of biocatalytic systems are presented. These methodologies have been successfully applied to the preparation of optically active dihydropyridine, calcium antagonists, and cis-3-hydroxy-6-acetoxy-cyclohex-1-ene, a valuable chiral building block for natural products synthesis. The phenomenon of enantioselective inhibition is described and several new heterocyclic amines have been shown to be effective enantioselective inhibitors in the Candida lipase system.
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  • 30
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 103-109 
    ISSN: 0899-0042
    Keywords: dihydrocinnamic acid derivatives ; hydroxy azido acids ; hydroxy amino acids ; enantioselective hydrolysis ; Pseudomonas fl. lipase ; Candida cyclindracea lipase ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of some acyloxy-methoxy-cinnamic acid derivatives, azidohydroxy butanoates, and azidohydroxy butanedioates in enantiomerically pure form is presented. Racemic diastereomerically pure educts were prepared in few steps. These racemates are resolved with lipases from Candida cylindracea (CC) and Pseudomonas fluorescens (P).
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  • 31
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 122-124 
    ISSN: 0899-0042
    Keywords: 4-acetoxy-2-azetidinone ; antibiotics ; carbapenem ; HPLC ; chiral stationary phases ; cellulose tris(1-phenylethylcarbamate) ; amylose tris(1-phenylethylcarbamate) ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical resolution of six β-lactams was examined by HPLC using chiral stationary phases consisting of tris((R)-, (RS)-, and (S)-1-phenylethylcarbamate)s of cellulose and amylose. All β-lactams were optically resolved at least by one of the carbamates. Amylose tris((S)-1-phenylethylcarbamate) showed high optical resolving abilities for some β-lactams.
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  • 32
    ISSN: 0899-0042
    Keywords: 2-arylpropionic acids ; nonsteroidal antiinflammatory drugs ; stereoselective ; coenzyme A thioesters ; chiral inversion ; oxidative phosphorylation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of the enantiomers of ibuprofen (0.25 and 0.50 mmol/kg b.w.) and flurbiprofen (0.01, 0.03, and 0.06 mmol/kg b.w.) on the β-oxidation of palmitate were investigated in the rat. The mean cumulative exhalation of 14CO2 after ip administration of [U-14C]palmitic acid was significantly reduced over 6 h by ibuprofen at the higher dose but not at the lower dose for either enantiomer. There was no difference between the enantiomers, the reduction over 6 h being 31.3 and 33.0% for (R)- and (S)-ibuprofen, respectively. There was also a significant inhibition of β-oxidation by flurbiprofen at all 3 doses. Again, there was no stereoselectivity evident in this inhibition. Flurbiprofen was much more potent than ibuprofen in eliciting this effect, the 0.01mmol/kg dose giving a similar reduction in β-oxidation as observed for the 0.50 mmol/kg dose of ibuprofen. The data support the hypothesis that inhibition of the in vivo β-oxidation of palmitate by ibuprofen and flurbiprofen is primarily via a nonstereoselective noncoenzyme A-dependent mechanism. © 1992 Wiley-Liss, Inc.
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  • 33
    ISSN: 0899-0042
    Keywords: polarimetry ; circular dichroism spectra ; optical purity ; thermal interconversion of enantiomers ; optically active sorbents ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Qualitative and quantitative use of polarimetry at one wavelength for detection during liquid chromatography is briefly reviewed. Acquisition of circular dichroism spectra by stopped-flow and nonstop measurements has been further developed. Reasons are given why the angle of rotation, i.e., the polarimeter, is preferred for monochromatic use and differential absorbance, i.e., the dichrograph, for polychromatic requirements. Both methods are demonstrated by novel applications, mainly to enantiomers which interconvert thermally via intramolecular processes. © 1992 Wiley-Liss, Inc.
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  • 34
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 205-215 
    ISSN: 0899-0042
    Keywords: cyclodextrins ; molecular mechanics ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparison of α-, β and γ-cyclodextrins in the solid state is made. Monomeric features analyzed include orientations of primary hydroxyl groups and pyran ring pucker. Macromolecular features examined include planarity of the oligomer, tilting of pyran rings, and, deviation from Cn symmetry where n = number of monomers. The mean values and standard deviations of these shape descriptors are given for cyclodextrins with and without guests embedded in their interiors. Molecular mechanics calculations using the MM2, AMBER, and CHARMM force fields show that most solid state cyclodextrins are trapped in high-energy conformations relative to the most stable forms found in this study. © 1992 Wiley-Liss, Inc.
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  • 35
    ISSN: 0899-0042
    Keywords: NSAID ; chirality ; enantiomers ; protein binding ; equilibrium dialysis ; fluorescent specific markers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protein binding of etodolac enantiomers was studied in vitro by equilibrium dialysis in human serum albumin (HSA) of various concentrations varying from 1 to 40 g/liter, by addition of each enantiomer at increasing concentrations. In the 1 g/liter solution, at the lowest drug levels, the (R)-form is more bound than its antipode, the contrary being observed at the highest drug levels. For higher albumin concentrations, S was bound in a larger extent than R. Using the displacement of specific markers of HSA sites I and II, studied by spectrofluorimetry, it was suggested that R and S are both bound to site I, while only S is strongly bound to site II. © 1992 Wiley-Liss, Inc.
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  • 36
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    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 323-332 
    ISSN: 0899-0042
    Keywords: chiral separation ; chiral counterion ; ion-pair chromatography ; N-benzyloxycarbonylglycyl-L-proline ; quinine ; indirect detection ; porous graphitic carbon ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of porous graphitic carbon as adsorbing phase for direct separation of enantiomeric acids and amines using chiral ion-pair chromatography is described. The enantiomeric amines were separated as diastereomeric ion pairs with N-benzyloxycarbonylglycyl-L-proline, N-benzyloxycarbonylglycylglycyl-L-proline, or captopril as the chiral counterion. High enantioselectivities were obtained for amines having a hydrogen bonding function in the vicinity of the asymmetrical carbon atom. Quinine was the chiral counterion used to separate the enantiomeric acids. The strongly UV-absorbing quinine improved detection of solutes having low UV-absorbing properties, e.g., (R,S)-2-chloropropionic acid, by “indirect detection.” Retention and stereoselectivity of enanticmeric acids were regulated by the quinine concentration and by the addition of carboxylic acids as well as polar modifiers, e.g., methanol and 2-propanol, to the mobile phase. © 1992 Wiley-Liss, Inc.
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  • 37
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992) 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 38
    ISSN: 0899-0042
    Keywords: H-1 antihistamines ; chiral HPLC ; β-cyclodextrin-inclusion complexes ; NMR ; circular dichroism ; affinity constants ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The resolution of the H-1 antihistamines chloropheniramine, dimethindene, carbinoxamine, and mebrophenhydramine is described. The optical purity of antipodal products is investigated by chiral HPLC (use of α1 -acid glycoprotein and β-cyclodextrin columns) and NMR (spectra of β-cyclodextrin inclusion complexes). Configurational relationships among the group are reviewed and assignments are confirmed and extended by circular dichroism evidence. Affinity constants of antipodal pairs for guinea pig ileum and cerebellum sites, determined by gut bath and binding experiments respectively, are reported together with some in vivo tests in man for central effects. Results are discussed in terms of configurational requirements for activity and variations in antipodal potency ratios within the group. © 1992 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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  • 39
    ISSN: 0899-0042
    Keywords: enantiomeric separations ; polymeric CSPs ; enthalpy ; entropy ; H-bonding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and a preliminary chromatographic evaluation of a novel polymeric chiral stationary phase (CSP) derived from (1R;2R)-diaminocyclohexane (DACH) are presented. A radical copolymerization process has been employed to generate a silica-based chiral sorbent, showing considerable high chemical and thermal stability and stereoselectivity toward racemic compounds capable of H-bonding (3-hydroxy-benzodiazepin-2-ones, chlorthalidone, atropoisomeric sulfur compounds, etc.); in the present paper we present the investigation on the resolution of racemic dihydroxy biarylic atropoisomers; the effects of eluent composition and of temperature on the separation ability of the CSP have been studied in order to elucidate the recognition mechanism operating in these chiral separations. © 1992 Wiley-Liss, Inc.
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  • 40
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 406-406 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 41
    ISSN: 0899-0042
    Keywords: GSH conjugate ; pharmacokinetics ; biliary excretion ; chiral ; 2-bromo-3-phenyl propionic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glutathione (GSH) conjugation of the chiral compound 2-bromo-3-phenylpropionic acid (BPP) was studied in vitro and in the rat in vivo. GSH conjugation of BPP, catalyzed by a mixture of glutathione-S-transferases (GST's) from rat liver cytosol in vitro, was stereoselective: at a substrate concentration of 250 μM, (R)-BPP was more rapidly conjugated than (S)-BPP (R/S-ratio = 2.6). The blood elimination kinetics of the separate BPP enantiomers and the biliary excretion kinetics of the corresponding GSH conjugates were studied in the rat in vivo after administration of (R)- or (S)-BPP at a dose level of 50 μmol/kg. Elimination of (R)-BPP from blood was faster than that of (S)-BPP: half lives were 9 ± 2 min for (R)-BPP and 13 ± 1 min for (S)-BPP. The biliary excretion rate of the GSH conjugate of (R)-BPP declined monoexponentially, while that of the GSH conjugate of (S)-BPP displayed a biphasic profile. Half lives of excretion were 13 ± 1 for the GSH conjugate of (R)-BPP, and 11 ± 2 for the GSH conjugate of (S)-BPP (second phase). The first phase in the biliary excretion of the GSH conjugate of (S)-BPP could not be attributed to capacity limitation of biliary transport carriers as higher excretion rates were attained upon administration of higher doses (100 and 200 μmol/kg) of ((S)-BPP). The blood elimination profiles of (R)- and (S)-BPP differed greatly from the biliary excretion profiles of the corresponding GSH conjugates. This suggests that the kinetics of BPP conjugate excretion are determined by other processes than hepatic GSH conjugation. © 1992 Wiley-Liss, Inc.
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  • 42
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    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 439-442 
    ISSN: 0899-0042
    Keywords: trans-nor-pentazocine ; Sigma ; PCP ; NMR analysis ; GC analysis ; chiral derivatizing reagents ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient resolution of (±)-trans-2'-hydroxy-5,9-dimethyl-6,7-benzomorphan has been developed employing ( - )-(R)- and (+)-(S)-O-acetylmandelic acids. Measurement of optical rotations on the resolved bases, NMR analyses of diastereomeric urea derivatives, as well as gas chromatographic analyses of diastereomeric amide derivatives indicate a net improvement over previous resolution methodology and an enantiomeric excess ≥ 99%. © 1992 Wiley-Liss, Inc.
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  • 43
    ISSN: 0899-0042
    Keywords: enantioseparation ; reverse-phase chiral HPLC ; organic-inorganic chiral stationary phases ; polymeric CSPs ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An overall view on some new chiral stationary phases based on (trans)-1,2-diaminocyclohexane is illustrated. The selected chiral moiety, derivatized with different aroyl groups, has been linked to a silica matrix in order to give chiral stationary phases (CSPs) enabling them to be used efficiently in the normal and reverse phase, both for analytical and preparative purposes. In addition new polymeric CSPs have been prepared by using the same selector, suitably modified, as monomer. The new chiral stationary phases have been characterised by physicochemical methods and used for the resolution of various racemic compounds classes such as α-aryloxyacetic acids, alcohols, sulfoxides, selenoxides, phosphinates, tertiaryphosphine oxides, benzodiazepines etc. without prederivatization or as amines, amino acids, amino alcohols, nonsteroidal antiinflammatory agents in a derivatized form. The separated solutes structural variety suggests that multiple interaction sites are involved in the recognition process: some thermodynamic data relative to the CSPs - selectands interactions are also illustrated. © 1992 Wiley-Liss, Inc.
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  • 44
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 45
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 46
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Fusion of the Journals „Journal für praktische Chemie “ and „Chemiker-Zeitung“ A Historical AccountThe fusion of the journals „Journal für praktische Chemie“ (founded in 1828 in Leipzig) and „Chemiker-Zeitung“ (founded in 1877 in Köthen) is the background for a historical study on the journals' development.„Journal für praktische Chemie“ was founded by O.L. Erdmann in Leipzig and is the oldest German chemical journal; its original title was „Journal für technische und ökonomische Chemie“. It has always been a scientific journal while „Chemiker-Zeitung“ in its beginnings mainly provided information about practical applications. Its founder and first editor was the chemist G. Krause from Köthen (until 1905). In the 1950s the editors decided to publish a journal with a higher scientific orientation, the result of which was the wellknown „Chemiker-Zeitung“.
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  • 47
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evaporated dye layers are gaining in importance in modern information and energy storage systems due to their specific optical and electrical properties. The photophysical properties decisively depend on the structure of layers, e.g., on a kind of aggregation, degree of crystallinity and crystal modification. These parameters and, therefore, the properties can be strongly manipulated by technological parameters (kind and temperature of substrate, evaporation rate, annealing) and by coevaporated admixtures of inorganic (metal halides or oxides) or organic (dyes or others) compounds.On the basis of recent investigations of evaporated merocyanine and phthalocyanine dyes, some results of the relationship between deposition are presented technology, structure and photophysical properties and evaluated with regard to their usefulness in organic solar cells.
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  • 48
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    New York, NY : Wiley-Blackwell
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, high yield synthesis of [Pd2Cl2(m̈-dmpm)2] (dmpm = bis(dimethylphosphino)methane), which avoids the use of the ill-defined, polymeric substance [PdCl(CO)]n as a starting material, is described. The procedure involves ligand metathesis of [Pd2Cl2(m̈-dppm)2] (dppm = bis(diphenylphosphino) methane) with dmpm using a solvent in which both [Pd2Cl2(m̈-dppm)2] and [Pd2Cl2(m̈-dmpm)2] are only sparingly soluble. Yields of 〉 98% are routinely obtained.
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  • 49
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    New York, NY : Wiley-Blackwell
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Norcamphor (1) was anodically oxidized at Pb/PbO2 anodes in 1 M · H2SO4, MeCN/H2O (V/V = 1/1). 3-Oxocyclopentaneacetic acid (3) and oxabicyclo[3.3.0]octan-3-one (4) were obtained with material yields up to 76% and 42%, respectively. The effects of electrode materials, current densities and concentrations were studied. A possible anodic oxidation mechanism was proposed.
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  • 50
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thienoanneleted 6aλ4-Thia-1,6-diazapentalenes by Baseinduced Dimerisation of 5-Methyl-isothiazolium SaltsIsothiazolium salts 2 and 3 are easily available by reaction of (Z/E)-β-thiocyanatovinyl aldehydes with primary aliphatic and aromatic amines in acetic acid or with aromatic amine hydrochlorides, respectively. Preparative advantages of this reaction are demonstrated and discussed. Reaction of 3 with secondary amines results in an unexpected formation of 6aλ4-thia-1,6-diazapentalenes 5, a new typ of thiadiazapentalenes anellated with a heterocyclic ring system. The structure of 5 was evidenced by IR, UV, 1H-, 13C-n.m.r. spectral data and supported by elemental analysis. By means of 15N- and 13C-n.m.r. spectroscopy the synthesized thiadiazapentalenes were found to be stable towards protonation.
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  • 51
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Gas Chromatographic Investigation of Stereoisomeric Cyclotrideca-1,5,9-trienesUsing achiral phases of different polarity in capillary gas chromatography on the one hand and a chiral cyclodextrine phase on the other hand it is demonstrated, that a ring-enlargement sequence starting from (E, E, Z)-cyclododeca-1,5,9-triene yields five of the six theoretically possible isomeric cyclotrideca-1,5,9-trienes and (E, Z)-trans-bicyclo[10.1.0]trideca- 4,8-diene. With all achiral phases only three of the isomeric trienes and the bicyclic isomer were separated from each other; (E, Z, E)- and (Z, E, Z)-cyclotrideca-1,5,9-triene are eluated in only one (the fifth) peak, these isomers were separated on the cyclodextrine phase. Moreover, this chiral phase separates the enantiomers of the bicyclic isomer.
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  • 52
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: T-2 toxin dissolved in CDCl3 and C6D6 and T-2 triol in CDCl3 were studied by 1D and 2D n.m.r. spectrometric methods. Comprehensive n.m.r. spectral parameters are reported. Iterative analysis of the isovaleroxy proton resonances of T-2 toxin in C6D6 and T-2 triol in CDCl3 was carried out. The assignments of the proton and carbon resonances of the ace-toxy groups and of the H-13 and H-15 resonances of T-2 toxin are given. The known conformation of the trichothecene ring system was confirmed by NOESY.
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  • 53
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: HPLC-Electrochemical Detector with a Carbon Fiber Working ElectrodeThe paper describes an electrochemical detector with carbon fibers as the working electrode placed perpendicularly to the flow direction. The detector performance was characterized by the detection limit for selected phenolic compounds, reproducibility, linearity and the signal dependence on the flow rate. An electrochemical in situ pretreatment of the working electrode improves sensitivity and long term stability.
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  • 54
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Regioselectivity of the Reaction of Methallyl Isothiocyanate with Monosubstituted HydrazinesMethallyl isothiocyanate 1 reacts with substituted aryl hydrazines to 1,4- respectively 2,4-disubstituted thiosemicarbazides 4 and 5 in dependence on the reaction conditions and the nature of the aryl group. The influence of the substituents is discussed. The novel N′-mono- and disubstituted N-methallylic thioureas 2 and 3 are synthesized.
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  • 55
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexes of N-Heterobases and Carbonic Acids in Non-Aqueous Media. Structural Investigations by FTIR Spectroscopy and Factor AnalysisA series of FTIR spectra of different concentration ratios of dichloroacetic acid and i-chinoline was investigated by factor analysis. The best results were obtained for difference spectra, in which the dominating bands of the main constituents have been eliminated prior to factor analysis.The component spectra, computed by factor analysis, showed a band of a strong OH…N complex. No evidence was found for O…HN species, i.e., proton transfer does not occur in the investigated system. The formation of complexes of higher order or of dichloroacetic acid dimers has not been ovserved.
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  • 56
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystal and Molecular Structure of 4,5-Dibenzoylseleno-1,3-diselenole-2-seloneThe crystal and molecular structure of 4,5-dibenzoylseleno-1,3-diselenole-2-selone is described. The compound crystallizes in the monoclinic space group P21/c with a = 9.704, b = 10.839, c = 17.726 [Å], β = 93.43° and Z = 4. The structure is compared with that of the analogous „all-sulfur“ compound. The crystal packing of the heterocycle studied shows surprisingly short intermolecular distances between neighbouring selone groups.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton Exchange in the NH3 · HCl Gas Phase ComplexThe cyclic proton exchange in NH3 · HCl is studied by quantum chemical ab initio calculations in order to characterize the chemical flexibility of the NH3 · HCl gas phase system, and to present a model for studying electrophilic substitution reactions. In contrast to the hydrogen bonded molecular complex, the cyclic structure II (C2v) is found to be highly ionic.It represents the transition structure of the proton exchange within the isolated complex. The potential barrier (ΔEpot = EII - EI) of the reaction can only sufficiently be described when including correlation energy. The C3v cage III is also ionic and similar in energy in comparison with the transition structure II.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 58
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Substituted 2-Aminoquinoline-1-oxides by Reductive Cyclization of Substituted 3-(2-Nitrophenyl)acrylonitrilesAn approach to the class of 2-aminoquinoline-1-oxides is given based on reductive cyclization of appropriate substituted 3-(2-nitrophenyl)acrylonitriles. Thus, 2-nitrobenzylidene compounds 1 a - d have been reductively cyclized by H2/PtO2 or H2/Pd-C under normal conditions to form N-oxides 2 a - d. 1H-NMR data show that 1 d has to be regarded as ethyl(Z)-2-cyano-3-hydroxy-3(2-nitrophenyl)acrylate.The analogous (2-nitrobenzoyl)acetonitrile 3, however, did not cyclize under the same conditions, but yielded anthraniloylacetonitrile 4. The results are discussed in comparison with the reaction behaviour of structural related nitronitriles under comparable conditions. A short survey of reactions leading to heterocyclic N-oxides by reductive cyclization of nitro compounds is given.
    Additional Material: 1 Tab.
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  • 59
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 60
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Ethane-1,2-bis[tris(chlormethyl)-phosphoniumchloride]
    Type of Medium: Electronic Resource
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  • 61
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simple Synthesis of 2,3-Diamino-quinoline-3-carbonitriles
    Additional Material: 2 Tab.
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