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1.
C. Álvarez J. A. Sánchez-Brunete S. Torrado-Santiago R. Cadórniga J. J. Torrado 《Chromatographia》2000,52(7-8):455-458
Summary An easy and rapid enantioselective separation for assay of racemic thalidomide on an immobilized α1-acid glycoprotein chiral stationary phase (GPA CSP) is described. The effects of tetrahydrofuran (THF) as organic modifier,
buffer concentration to control the ionic strenth, and mobile phase pH were studied. These variations have consequences in
terms of chromatographic retention (k), resolution (R
s), selectivity (α), and peak asymmetry (USP tailing factor). The main condition affecting chromatographic retention was mobile
phase pH. At pH 4.5, no separation of thalidomide enantiomers was achieved whereas at pH 7.9 chiral separation was optimum.
Peak tailing was directly related to changes in pH and to addition of THF as mobile phase modifier. Results also indicated
that the resolution factor is THF concentration-dependent, and that the separation factor (α) is the best parameter for evaluating
enantioselectivity. The best mobile phase was pH 7.0, 30 mM ammonium acetate containing 0.3% THF. Under these conditions validation
including linearity, recovery, and precision was performed. The suitability of this method has been successfully proved in
a limited in-vivo study after intravenous administration of thalidomide to a New Zealand male rabbit. 相似文献
2.
R. Berkecz I. Ilisz A. Ivanov-Sztojkov I. Szatmári F. Fülöp D. W. Armstrong A. Péter 《Chromatographia》2007,65(5-6):337-341
The enantiomers of 1-(α-aminobenzyl)-2-naphthol and 2-(α-aminobenzyl)-1-naphthol analogs were separated isothermally on a 3,5-dimethylphenylcarbamoylated β-cyclodextrin-based chiral stationary phase (Cyclobond DMP), with an n-hexane/alcohol modifier as mobile phase. Optimization of the separation was achieved by variation of combinations of the
polar mobile phase additives ethanol and methanol. The nature and position of the α-aminobenzyl substituent of the 1- and 2-naphthol analogs influenced the retention and the selectivity. 相似文献
3.
Pengyan Liu Lei Liu Li Zhang Ning Jiang Zhanli Liu Yun Wang 《Frontiers of Chemistry in China》2008,3(4):378-383
A molecularly imprinted polymer (MIP), with special molecule recognition properties of ciprofloxacin (CIP), was prepared by
thermal polymerization in which ciprofloxacin acted as template molecule, α-methacrylic acid (MAA) acted as functional monomer and trimethylolpropane trimethylacrylate (TRIM) acted as crosslinker.
The optimized ratio was determined to be n(CIP): n (MMA):n(TRIM)51:6:16 by investigation of the effects of different concentrations of functional monomer and the crosslinker on the
MIP’s recognition properties. Equilibrium binding experiment was used to investigate the adsorption dynamics, the binding
ability to template molecule and the substrate selectivity. Scatchard analysis was used to study the MIP’s binding characteristic
to template molecule. The results indicated that MIP has higher adsorption ability and selectivity. The equilibrium distribution
coefficient K
D was 41.64 and the separation factor α was 1.62. Scatchard analysis showed that two different kinds of binding sites were produced in the polymer matrix and their
dissociation constants were calculated to be K
d1 = 5.249 × 10−5 mol·L−1, K
d2 = 2.237 × 10−3 mol·L−1.
__________
Translated from Chemistry, 2008, 71(2): 132–137 相似文献
4.
Summary Using reversed phase liquid chromatography (RPLC), this paper investigates the enantioselectivity variations, in a series
of weak polar R, S-imidazole derivatives, with β-cyclodextrin concentration in the mobile phase over a wide range of column
temperatures. These compounds are used for the treatment of onychomycosis. The selectivity data obtained were assessed using
a chiral recognition model, based on the formation of complexes between the solute molecule and the cyclodextrin cavity. Gibbs
Helmholtz parameters (Δ(ΔH), Δ(ΔS)) between R- and S- enantiomers were determined from the logarithm of the separation factor, α, versus the reciprocal
of the temperature plots. The thermodynamic results predicted that the enantioselectivity mechanism was related to both the
solute's bulkiness and the asymmetric carbon atom configuration. 相似文献
5.
Summary The analysis of α, β, γ, δ-tocopherols, trienols, α-tocopheryl acetate and nicotinate (vitamin E) in complex matrices was
carried out using a new liquid chromatographic (HPLC) method giving better separation efficiency, selectivity and sensitivity
than that described in the literature. The use of normal-phase (NP)-HPLC on silica gel with issoctane-diisopropylether-1,4-dioxane
as optimized mobilepphase yielded higher resolution than conventional reversed-phase (RP)-HPLC using methanol mobile phase.
Identification of peaks was by UV-absorbance at 295 nm, diode array, or fluorescence detection (λ
ex = 295 nm,λ
ex = 330 nm). The latter was found to be more selective and ten times more sensitive than UV-absorbance detection. A quadrupole,
ion-trap mass spectrometer with an atmospheric-pressure ionization (APCl) interface was used to detect vitamin E constituents
in the femtomole range. With collision-induced dissociation (CID) in the ion source, which gave characteristic fragmentation,
the identity of the investigated compounds could be confirmed. Plots of peak area versus amount injected allowed quantitation
of α, β, γ, δ-tocopherols and-trienols, α-tocopheryl acetate and nicotinate in real samples such as peanut, almond, spinach,
spelt grain bran, latex and tablets. The method described offers fast identification and quantitation of vitamin E constituents
of complex biological origin.
Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65th birthday. 相似文献
6.
Summary The proportion of organic modifier and the pH of the acetonitrile-water mixtures used as mobile phases were optimized in order
to separate a group of diuretic compounds covering a wide range of physyco-chemical properties. The Linear Solvation Energy
Relationship (LSER) formalism based either on the multiparameter π*, β and α scales or the single solvent polarity parameterE
T
N
, have been used to predict their chromatographic behaviour as a function of the percentage of acetonitrile in the eluent.
Moreover, correlation established between retention and pH of the aqueous-organic mobile phases have been used to predict
the chromatographic behaviour of the diuretic compounds studied as a function of the eluent pH. Linear correlation between
a function of the eluent pH. Linear correlation between the chromatographic retention and theE
T
N
polarity parameter of mobile phases containing different percentages of organic modifier has been obtained Based on the knowledge
of the acid-base dissociation constant the relation between retention and mobile phase pH has also been linearized. These
relationship allowed an important reduction of the experimental retention data needed for developing a given separation and
a great improvement in chromatographic optimization schemes. 相似文献
7.
Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize
the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA. 相似文献
8.
A. Slováková X. Freiin von Maltzan B. K. Patel A. F. Drake A. J. Hutt 《Chromatographia》1998,48(5-6):369-376
Summary The chromatographic resolution of the enantiomers of sulindac has been achieved using a Chiralpak AD CSP (10 μm, 250×4.6 mm)
with a mobile phase of hexane: ethanol (85∶15 v/v) containing trifluoroacetic acid (0.05% v/v) at a flow rate of 1.0 mL min−1. Under these conditions the enantiomers eluted with separation and resolution factors of 1.43 and 2.46 respectively. Semipreparative
isolation of the enantiomers and their characterization by circular dichroism spectroscopy and NMR, in the presence of a chiral
shift reagent, indicated that the elution order was (−)-(S)- before (+)-(R)-sulindac. The enantiomeric composition of sulindac in urine following administration of the racemic drug to man was determined
by sequential achiral-chiral chromatography. Achiral analysis was carried out using a Spherisorb S5 ODS2 stationary phase
(5 μm, 250×4.6 mm) and a mobile phase of aqueous acetic acid (2% v/v; pH 3.5): acetonitrile: THF (50∶48∶2 by volume) at a
flow rate of 1.0 mL min−1. The HPLC eluate containing sulindac (retention time 4.9 min) was collected and following workup, the enantiomeric composition
of the drug was determined using the CSP. Over the 24 h collection period sulindac was excreted predominantly as theR-enantiomer, but the enantiomeric composition was found to vary markedly with time which is presumably associated with the
complex metabolism of the drug. 相似文献
9.
The K-stearate/glycerol (KC18/Gl) binary system was studied at mole fractions of stearate of x
KC18 = 0.10, 0.25, 0.30 and 0.50. Small- and wide-angle X-ray diffraction (XRD) measurements were combined with differential scanning
calorimetry (DSC) measurements at different temperatures. The investigations were intended to verify the previously published
phase diagram and were targeted at the confirmation of the gel-like (G1) phase and the isotropic (I) phase. The XRD and DSC measurements lead to the conclusion that the G1 phase as well as the I phase, the existence of which had been proposed from texture observations, do in fact not exist. Consequently,
a correction of the preliminary phase diagram is given. This corrected phase diagram reveals the crystalline phase (C) ⇆ gel
phase (G) ⇆ hexagonal phase (Hα) ⇆ isotropic, micellar phase phase transitions for low KC18 concentrations of x
KC18 = 0.15–0.3 and the C ⇆ G ⇆ lamellar phase (Lα) phase transitions for concentrations about or higher than x
KC18 = 0.35. The C, G, Lα and Hα phases have been further characterized by structural parameters (characteristic d values) as a function of temperature. The phase transitions C ⇆ G, G ⇆ Lα and G ⇆ Hα correlate with sharp shifts in the d value of the first small-angle reflections.
Received: 20 April 1999 Accepted: 28 July 1999 相似文献
10.
L. I. Belen'kii T. G. Kim I. A. Suslov N. D. Chuvylkin 《Russian Chemical Bulletin》2005,54(4):853-863
Data on the relative reactivities (substrate selectivity) of five-membered heterocycles in electrophilic substitution reactions
and positional selectivity (α : β ratio) in these reactions were analyzed. Unlike the substrate selectivity (pyrrole ≫ furan
> selenophene > thiophene) determined by the position of heteroatoms in the Periodic Table, the positional selectivity decreases
in the order corresponding to the change in the relative stability of the onium states of the elements (O+ < Se+ ≤ S+ < N+) and reflects the predominant role of heteroatoms in the stabilization of σ complexes formed upon β-substitution. These differences
in the positional selectivity of the parent heterocycles have a substantial effect on the orientation in electrophilic substitution
reactions in their derivatives and the corresponding benzoannelated systems. This interpretation was confirmed by ab initio quantum chemical calculations (RHF/6–31G(d) and MP2/6– 31G(d)//RHF/6–31G(d)) and density functional theory calculations (B3LYP/6–31G(d)).
Quantum chemical calculations were performed by the above-mentioned methods for model N-R-pyrroles (R = Me, Et, Pri, But, CH=CH2, C≡CH, Ph, PhSO2, and 4-O2NC6H4) and their α- and β-protonated σ complexes. The results of these calculations demonstrated that it is the steric factors
and charges on the β-C, α-C, and N atoms and the substituents at the N atom (the kinetic control), as well as the nature of
the electrophile, rather than the difference in the relative stabilities of the onium states of N+ (which depends on the nature of the substituent at the N atom and reflects the role of the heteroatom in stabilization of
σ complexes formed via β-substitution; the thermodynamic control) that are responsible for the type of orientation (α or β) that prevails.
Dedicated to Academician V. I. Minkin on the occasion of his 70th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 837–846, April, 2005. 相似文献
11.
Analogously to the aqueous K-soap/water systems already examined, the five glycerol · (Gl)-containing systems KC
n
/Gl (n = 12, 14, 16, 18, 22) also built up hexagonal (Hα), lamellar (Lα), isotropic micellar (S), gel-like (G) and crystalline phases (C). These phases were identified by texture observations with
a polarizing microscope, by differential scanning calorimetry measurements and by X-ray diffraction investigations. The appertaining
phase regions were plotted in the binary phase diagram. Binary Gl-containing K-soap systems have the following properties.
The Hα phase is built up at low soap concentration. The Lα phase is formed at high soap concentrations. The temperature of the phase transition Hα ⇆ S runs through a maximum. Increasing the chain lengths of the soaps shifts the formation of the Hα phase to lower soap concentration. A strong correlation between the chain length of K-soaps and the d values of Lα, Hα, G and C phases is found. Based on the comparison of the X-ray diffractograms of the G phase a structural model is proposed.
The G phase consists of two groups of domains with two different dimensions.
Received: 9 August 1999/Accepted in revised form: 20 September 1999 相似文献
12.
The kinetics of the isothermal adsorption of ethanol from an aqueous solution onto a hydrophobic zeolite of the NaZSM-5 type
in the temperature range 298–333 K was investigated. Specific shape parameters of the adsorption degree curves were determined.
The changes in the specific shape parameters of the adsorption degree curves with temperature were determined. The kinetic
parameters of ethanol adsorption (Ea,ln A) were determined by the initial rate, the saturation rate and the maximum rate methods as well as from the Johnson, Mehl
and Avramy equation. The kinetic model of ethanol adsorption kt=[1−(1−α)1/3] was determined by the “model fitting” method.
Ethanol adsorption from aqueous solution onto NaZSM-5 is a kinetically controlled process limited by the rate of three-dimensional
movement of the boundary layer of the adsorption phase. A model for the mechanism of ethanol adsorption onto NaZSM-5 is suggested
on the basis of the kinetic model. Ethanol molecules in aqueous solution are associated in clusters. The activation energy
of the adsorption process corresponds to the energy required for the detachment of an ethanol molecule from a cluster and
its adsorption onto the zeolite. 相似文献
13.
W. Zielenkiewicz I. V. Terekhova A. Marcinowicz M. Koźbial J. Poznanski 《Journal of Thermal Analysis and Calorimetry》2008,93(2):365-372
Interactions of native and modified α- and β-cyclodextrins with nicotinic acid, pyridoxine and pyridoxal were studied by isothermal
titration calorimetry, solution calorimetry, and 1H NMR spectroscopy at 298.15 K and pH 6.8. Weak 1:1 complex formation was found only between α-cyclodextrin and nicotinic
acid. The stability constant and corresponding thermodynamic parameters of complex formation (Δc
G, Δc
H and Δc
S) were calculated using the calorimetric data. The 1H NMR data indicate the shallow insertion of the carboxylic group of the nicotinic acid molecule into α-CD cavity. For all
other compounds the weak interactions, not accompanied by complex formation, were characterized by the enthalpic virial coefficients
calculated on the basis of McMillan-Mayer approach. The obtained thermodynamic parameters were analyzed in the terms of influence
of the solutes’ structure on the selectivity of intermolecular host-guest interactions. 相似文献
14.
Abul K. Mallik Kaori Shingo Usha Ghimire Gautam Tsuyoshi Sawada Makoto Takafuji Hirotaka Ihara 《Analytical and bioanalytical chemistry》2010,397(2):623-629
Poly(2-N-carbazolylethyl acrylate) with terminal trimethoxysilyl groups was prepared as an organic phase and immobilized onto silica.
The retention behavior of the column packed with this carbazole-based polymer-immobilized silica (Sil-CEA) was investigated
by using various estrogenic steroids and corticoids in both reversed-phase and normal-phase liquid chromatography. As a result,
complete separation was confirmed for eight kinds of steroids with Sil-CEA. The most specific separation with Sil-CEA can
be emphasized by the high separation factor (e.g., α = 1.39 in methanol–water (7:3, v/v) at 35 °C) for 17α and 17β-estradiols, one of the most difficult pairs of isomers in chromatographic separation, whereas
for two kinds of commercially available polymeric ODS columns as references α = 1.01, only, under the same conditions. Because the excellent separation and retention order with Sil-CEA was maintained
even in a normal-phase mobile phase such as a hexane–2-propanol, it is estimated that the CEA phase has multiple interaction
mechanisms through stronger interactions such as dipole–dipole, carbonyl–π, and hydrogen bonding interactions than the hydrophobic
effect expected with ODS. 相似文献
15.
Thermodynamic parameters for acid dissociation of the conjugate acids of poly(N-vinylimidazole) and polyallylamine have been determined in the presence of sodium chloride and sodium nitrate. Even though
the plots of ΔG
0 against the degree of dissociation, α, are highly dependent on the added salt concentration levels, the concentration effect
has never been observed for the corresponding ΔH
0 versus α plots. The effect on the ΔG
0 versus α plots has been attributed to the entropy change of the counterions between a polyelectrolyte phase and a bulk solution
phase. The α dependency of ΔH
0 is affected remarkably by the kinds of cationic polymers and counter-anions. Each ΔH
0 value at completely neutralized conditions is quite close to the corresponding ΔH
0 value of the monomer analog. The difference in the ΔH
0 values at fully charged conditions has been explained by the heats due to
The ion-pair formation of chloride anion to the conjugate acids of poly(N-vinylimidazole) and polyallylamine has been supported by 35Cl NMR measurement. It has also been suggested that chloride anions bind the basic polymer molecules even at fully neutralized
conditions.
Received: 2 June 1999/Accepted in revised form: 19 July 1999 相似文献
16.
G. Sugihara A. A. Nakamura T. -H. Nakashima Y. -I. Araki T. Okano M. Fujiwara 《Colloid and polymer science》1997,275(8):790-796
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, the differential
conductivity (∂κ/∂C)
T
,
P
vs. square root of concentration (√C) was employed in order to determine not only CMC but also the limiting molar conductance (Λ0) and the molar conductance of micellar species (ΛM).
Based on the data of the degree of counterion binding to micelles (β) determined previously at different temperatures ranging
15–50 °C at every 5 °C, the experimental values of the degree of dissociation (ionization) of a micelle (αEX) were calculated by regarding as αEX=1−β. The ratio ΛM/Λ0 corresponding to the ratio of slopes below and above CMC in the curve of specific conductivity (κ) vs. concentration (C), which has been often assumed to be the degree of ionization of micelles (α), was compared with the present αEX. However, the ratio ΛM/Λ0 (=α) was found to have a correlationship with αEX (=1−β) as αEX≈0.40×(ΛM/Λ0), or strictly, αEX=0.40 (ΛM/Λ0)+0.08, indicating that the simple ratio of the slopes below and above CMC in κ vs. C curve is not true for αEX=1−β. On the other hand, the method proposed by Evans gave a value closer to αEX compared with the simple ratio.
Received: 17 September 1996 Accepted: 8 April 1997 相似文献
17.
The electronic structure and absorption spectra properties of the complex 8-((trimethoxysilyl)methylthio)quinoline⋅ZnCl2 in the gas phase and in acetonitrile (MeCN) have been investigated by means of DFT/TD-DFT calculations. Calculation results
indicate that the broad and weak experimentally observed absorption bands of the complex in MeCN at 335.6 nm originates from
spin-forbidden singlet-triplet transitions, but the other experimentally observed absorption bands at 318.5 nm, 310.6 nm and
237.5 nm arise from spin-allowed singlet-singlet transitions. Inclusion of MeCN as solvent leads to dramatic changes in the
electronic structures and energy levels of the frontier molecular orbitals of the complex, and hence transition mechanisms
of the absorption bands are also changed. For the complex, whether in the gas phase or in MeCN, the metal Zn does not participate
in the transitions involved, in the gas phase the calculated lowest-energy absorption band of the complex comes from π→π
∗ mixed with n→π
∗ transitions with LLCT (ligand-to-ligand charge transfer) character, while in MeCN, the calculated lowest-energy absorption
band is of LLCT/ILCT (intra-ligand charge transfer) character. 相似文献
18.
A simple, isocratic, normal phase chiral HPLC method was developed and validated for the enantiomeric separation of repaglinide,
(S)-(+)-2-ethoxy-4-N [1-(2-piperidinophenyl)-3-methyl-1-butyl] aminocarbonylmethyl] benzoic acid, an antidiabetic in bulk drug substance. The
enantiomers of repaglinide were resolved on a ChiralPak AD-H (amylose based stationary phase) column using a mobile phase
consisting of n-hexane: 2-propanol:trifluoroacetic acid (95:5:0.2 v/v/v) at a flow rate of 1.0 mL min−1. The resolution between the enantiomers was found to be not >3.5 in optimized method. The presence of trifluoroacetic acid
in the mobile phase played an important role, in enhancing chromatographic efficiency and resolution between the enantiomers.
The developed method was extensively validated and proved to be robust. The calibration curve for (R)-enantiomer showed excellent linearity over the concentration range of 900 ng mL−1 (LOQ) to 6,000 ng mL−1. The limit of detection and limit of quantification for (R)-enantiomer were 300 and 900 ng mL−1, respectively. The percentage recovery of the (R)-enantiomer ranged between 98.3 and 101.05% in bulk drug samples of repaglinide. Repaglinide sample solution and mobile phase
were found to be stable up to 48 h. The developed method was found to be enantioselective, accurate, precise and suitable
for quantitative determination of (R)-enantiomer in bulk drug substance. 相似文献
19.
234U/238U α-activity ratios determined by α-spectrometry (AS) and those calculated from the atom ratio data using the half-life values
are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For α-spectrometry, electrodeposited
sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm2) was used for recording the α-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry
(TIMS) and the recommended half-life values of234U and238U were used to calculate the α-activity ratio. It is observed that234U/238U α-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared
to the α-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination
of the half-life values of234U and238U. 相似文献
20.
V. Yu. Rudyak V. G. Avakyan V. B. Nazarov N. I. Voronezheva 《Russian Chemical Bulletin》2006,55(8):1337-1345
The structures and energies of formation of α-cyclodextrin (α-CD) dimers formed according to the “head-to-head” (HH), “head-to-tail”
(HT), and “tail-to-tail” (TT) modes, harmonic vibrational frequencies, and intensities of IR bands of the IR transitions were
calculated by the DFT/PBE density functional method with full geometry optimization without symmetry restrictions. The spectral
data were transformed into spectral patterns. An α-CD molecule can exist in two isomeric forms close in energy, namely, α-CD− and α-CD+, with different directions of the ring intramolecular hydrogen bonds. Among the three α-CD− dimers, the highest dimerization energy (E
d/kcal mol−1) belongs to the HH− (68.9), TT− (43.4), and HT− (24.8) dimers. The strength of the α-CD+ dimers decreases in the series: TT+ (56.7), HT+ (49.4), and HH+ (42.4). The energies E
H of hydrogen bonds were calculated from the low-frequency shifts of bands of stretching vibrations of the OH groups involved
in the formation of these hydrogen bonds. The E
H value for each dimer correlates with E
d. A possibility of formation of intermolecular hydrogen bonds is a driving force of association of α-CD molecules in aqueous
solutions.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1289–1296, August, 2006. 相似文献