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1.
Hydrophilic β-cyclodextrin (β-CD) and its derivatives are not soluble in organic liquids but they are highly soluble in water and can interact with enantiomers
selectively to form diastereomeric complexes which enable their use as chiral selectors in chiral solvent extraction. In this
paper, terbutaline enantiomers were extracted by hydrophilic β-CD derivatives in an aqueous/organic biphasic solvent system with racemic terbutaline in the organic phase and β-CD in the aqueous phase. Five β-CD derivatives, namely: methyl-β-cyclodextrin (Me-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD), 2-hydroxyethyl-β-cyclodextrin (2-HE-β-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and (4-sulfobutylether)-β-cyclodextrin (SBE-β-CD) were used as hydrophilic selectors, respectively. Process variables affecting extraction efficiency were investigated,
namely influence of the type of organic solvents and β-CD derivatives, concentrations of selectors and terbutaline enantiomers, pH, and temperature. Experimental results show that
the efficiency of extraction depends, often strongly, on process variables. All five β-CD derivatives studied preferentially extract the more biologically active (R)-terbutaline from the organic phase; HP-β-CD has the strongest recognition ability. The maximum enantioselectivity (α) of 1.42 was achieved under optimal conditions: pH 7.0 and temperature of 5°C. Utilization of the extraction method for separation
of terbutaline enantiomers is expected to be cheap and easy to scale up to commercial scale. 相似文献
2.
Yan-Min Yu Wensheng Cai Xueguang Shao 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):225-235
The inclusion complexes of α-, β- and γ-cyclodextrin (CD) with three isolated phospholipid (PI – phosphatidylinositol; PS – phosphatidylserine; and PE – phosphatidylethanolamine) headgroups were studied using a flexible docking algorithm FDOCK based on molecular mechanics (CFF91 force filed). In the three phospholipid headgroups, PI headgroup exhibits the strongest affinity for CD, and the affinity of PS headgroup is greater than that of PE headgroup. By investigating the energy distribution and the complex structure in the inclusion procedure, it can be found that the van der Waals force is the main driving force responsible for the complexation. For the α-CD complex of PI headgroup, more than one inclusion complex should coexist due to the steric hindrance, which is reasonably consistent with the experimental results. Furthermore, analyses of the complex of PS and PE headgroup with α-CD also show that two or three possible complexes may appear in the inclusion process, and the complex structure with full inclusion is of the lowest energy and should be the most stable structure in the mixture. For β-␣and γ-CD, the energies of the most stable complexes structures for the three phospholipids headgroups were also discussed. 相似文献
3.
Tze-Loon Neoh Hidefumi Yoshii Takeshi Furuta 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):125-133
Encapsulation and release of carbon dioxide (CO2) into and from α-cyclodextrin (α-CD) was studied. Initial moisture content of α-CD and CO2 pressure were found to have affected the encapsulation behavior. The increase of CO2 pressure has constantly accelerated the encapsulation rates and increased the maximum inclusion ratio, whereas the increase of initial moisture content showed no consistent effect. The saturated α-CD solution produced the inclusion complex crystal of similar inclusion ratio to solid α-CD. The release characteristics of inclusion complexes were also monitored at various relative humidities at 25 °C. Predominantly, increase in storage humidity accelerated the release of CO2. The inclusion complex crystal prepared from saturated α-CD solution showed the most stable release characteristic at all storage humidities investigated. The encapsulation and the release characteristics were analyzed using the first-order reaction equation and the Avrami’s equation respectively, in order to estimate the rate processes of encapsulation and release. The FT-IR spectra of inclusion complexes presented an absorption band at wavenumber around 2338 cm−1, indicating CO2 molecules resided inside the α-CD cavities in gaseous state rather than being bound to the hydroxyl groups of α-CD. Powder X-ray diffractometry was carried out to investigate the crystal lattice structure of α-CD and inclusion complexes. Scanning electron microscopy was also performed for morphological examination. 相似文献
4.
A. A. Abdoh M. B. Zughul J. Eric. D. Davies A. A. Badwan 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):503-510
Guest–host interactions were examined for neutral diclofenac (Diclo) and Diclofenac sodium (Diclo sodium) with each of the
cyclodextrin (CD) derivatives: α-CD, β-CD, γ-CD and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), all in 0.05 M aqueous phosphate
buffer solution adjusted to 0.2 M ionic strength with NaCl at 20 °C, and with β-CD at different pHs and temperatures. The
pH solubility profiles were measured to obtain the acid–base ionization constants (pK
as) for Diclo in the presence and absence of β-CD. Phase solubility diagrams (PSDs) were also measured and analyzed through
rigorous procedures to obtain estimates of the complex formation constants for Diclo/CD and Diclo sodium/CD complexation in
aqueous solutions. The results indicate that both Diclo and Diclo sodium form soluble 1:1 complexes with α-, β-, and HP-β-CD.
In contrast, Diclo forms soluble 1:1 Diclo/γ-CD complexes, while Diclo sodium forms 1:1 and 2:1 Diclo/γ-CD, but the 1:1 complex
saturates at 5.8 mM γ-CD with a solubility product constant (pK
sp = 5.5). Therefore, though overall complex stabilities were found to follow the decreasing order: γ-CD > HP-β-CD > β-CD > α-CD,
some complex precipitation problems may be faced with aqueous formulations of Diclo sodium with γ-CD, where the overall concentration
of the latter exceeds 5.8 mM γ-CD. Both 1H-NMR spectroscopic and molecular mechanical modeling (MM+) studies of Diclo/β-CD indicate the possible formation of soluble isomeric 1:1 complexes in water. 相似文献
5.
Takayoshi Kimura Takashi Yukiyama Masao Fujisawa 《Journal of Thermal Analysis and Calorimetry》2012,108(2):695-704
In order to investigate the contribution of the hydrophilic parts of guest molecules of aliphatic complexes to the inclusion
reaction, the thermodynamic properties of inclusion complexes of cyclodextrin (α-CD) with aliphatic nitriles [H(CH2)
n
CN: n = 1–8] into the α-CD cavity in dilute aqueous solutions were measured by a micro-calorimeter at 298.15 K. The thermodynamic
properties of inclusion for the octane nitrile system were different from those of others. The inclusion process of aliphatic
nitriles to α-CD has two kinds of major driving force of enthalpy and entropy driven inclusion. The interaction energies of
inclusion complexes of α-CD and aliphatic nitriles were determined by DFT calculation (B3LYP/6-31++G (d,p)) in water and compared
with the experimental results. DFT calculations were performed on the inclusion complexes of α-CD with seven nitriles of each
conformer. Both the gas phase interaction and solvent effect were taken into consideration. Also non-polar interactions between
aliphatic nitriles + α-CD in aqueous solution were calculated and herein the inclusion energy is discussed. 相似文献
6.
Summary Capillary electrophoresis (CE) has been successfully applied to the separation of the enantiomers of venlafaxine (Vx) and
its main active metabolite,O-desmethylvenlafaxine (ODV), by use of a mixture of two cyclodextrins (CDs) added to the background electrolyte (BGE). The
use of carboxymethylated β-cyclodextrin (CMB) enabled the enantioseparation of both Vx and ODV, although separation of all
four enantiomers was not achieved. Addition of a second cyclodextrin (α-CD) to the BGE resulted in the simultaneous resolution
of the enantiomers of both compounds. In this system, α-CD enabled discrimination between Vx and ODV whereas CMB enabled the
enantioseparation. Resolution was strongly influenced by the ratio of the concentrations of the two complexing agents. Baseline
resolution of Vx and ODV was achieved in an uncoated capillary. Addition of organic modifiers to the BGE had a substantial
effect on the interaction of the analytes with the α-CD. 相似文献
7.
P. Fini L. Catucci M. Castagnolo P. Cosma V. Pluchinotta A. Agostiano 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):663-668
The interaction of Rose Bengal (RB) with hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and
hydroxypropyl-γ-cyclodextrin (HP-γ-CD) has been studied in water and in acetate buffer at pH 4.5 by UV–Vis absorption, fluorescence
spectroscopy and Induced Circular Dichroism at 298 K. Evidence of the complex formation between the RB and all HP-CDs have
been obtained both in water and in buffer. Binding constants and stoichiometry of RB/HP-CD complexes in water have been determined
by applying the modified Benesi-Hildebrand equation to the fluorescence measurements. 相似文献
8.
Jiří Horský Bedřich Porsch 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):97-102
With polymer substrates, the continuous variation method based on monomer unit concentration underestimates the number of
monomer units covered by a low-molecular-weight ligand. Accordingly, gel permeation chromatography confirms that an α-cyclodextrin
(α-CD) molecule occupies more than previously claimed two ethylene glycol units in solid α-CD/poly(ethylene glycol) inclusion
complexes. Consequently, the poly(ethylene glycol) chain cannot be modeled as an array of distinct binding sites corresponding
to two monomer units and no preferred positions, i.e., no distinct binding sites probably exist on the chain for α-CD threading.
The effect of such binding delocalization can be assessed using the theory of binding large ligands to a finite one-dimensional
lattice [I.R. Epstein: Biophys. Chem. 8, 327 (1978)]. Binding delocalization slightly decreases the average occupancy with highly occupied chains but strongly promotes
the occupancy in the case of weak binding. This may be an additional reason for observed high yields of precipitated CD/polymer
complexes. 相似文献
9.
H. Krajian N. Mofaddel D. Villemin P. L. Desbène 《Analytical and bioanalytical chemistry》2009,394(8):2193-2201
Enantioseparation of 6,6′-dibromo-1,1′-binaphthyl-2,2′-diol (DBBD) by cyclodextrin-modified capillary zone electrophoresis
(CD-CZE) was studied using the three native α, β, and γ cyclodextrins, the three hydroxypropylated cyclodextrins (2-hydroxypropyl-α,
β, and γ), heptakis-2,6-di-O-methyl-β-CD (DM-β-CD), and heptakis-2,3,6-tri-O-methyl-β-cyclodextrin (TM-β-CD). First, the acidity constants of DBBD were determined using capillary electrophoresis, before
performing enantioseparation. The influence of the concentrations of the studied cyclodextrins on the enantioseparation was
explored and the experimental optimal concentrations were determined and compared to the theoretical optimal concentrations.
Moreover, the apparent complexation constants between each studied cyclodextrin and the two DBBD enantiomers were evaluated
using a non-linear curve fitting method and three linear plotting methods (x-reciprocal, y-reciprocal and double reciprocal). For TM-β-CD, the order of migration of the enantiomers of DBBD reversed as a function
of TM-β-CD concentration. The influence of the nature of methylated cyclodextrin derivatives (methyl-β-CD (M-β-CD) and DM-β-CD)
was then studied. Inversion of the order of migration of the enantiomers of DBBD was observed for DM-β-CD, whereas the S enantiomer of DBBD always migrated first for M-β-CD. 相似文献
10.
Summary The simultaneous separation of isomeric α-and β-aspartyl peptides as well as their enantiomers by capillary electrophoresis
was investigated. Resolution of the enantiomers of the peptides α/β-AspPhe-NH2 and α/β-AspPhe-OMe was achieved with 18-crown-6-tetracarboxylic acid (18C6H4) in untreated fused silica capillaries in the acidic pH range. Baseline resolution for the dipeptides was obtained using
polyacrylamide (PAA)-coated capillaries. The selectivity of the crown ether is compared with the selectivity of another chiral
selector, namely the negatively charged CD derivative carboxymethyl-β-CD (CM-β-CD). 相似文献
11.
Irina V. Terekhova Rosario De Lisi G. Lazzara Stefania Milioto Nicola Muratore 《Journal of Thermal Analysis and Calorimetry》2008,92(1):285-290
Density and heat capacity of the water+cyclodextrin (CD), water+nicotinic acid (NA) and water+CD+NA mixtures were determined
at 298.15 K. CDs with different cavity size and alkylation were selected. From the experimental data the apparent molar properties
were calculated. Assuming the formation of inclusion complexes of 1:1 stoichiometry, these properties were modeled and provided
the stability constants of CD/NA inclusion complexes and the corresponding property change. The binding of NA with the smallest
sized α-cyclodextrin (α-CD) generates more stable complexes accompanied by the lower volume and the heat capacity changes.
These results are in agreement with earlier proposed binding mode according to which deep insertion of NA into α-CD takes
place and it is governed by the hydrophobic-hydrophilic forces. The volume and the heat capacity changes caused by the interactions
of CDs with NA were interpreted in terms of cosphere overlap model and the release of water molecules from the CD cavity due
to the NA incorporation. 相似文献
12.
YOSHINORI TAKASHIMA KAZUYA SAKAMOTO YOSHIFUMI OIZUMI HIROYASU YAMAGUCHI SHIGEHIRO KAMITORI AKIRA HARADA 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):45-53
Cyclodextrins (α-CD, β-CD and 2,6-di-O-dimethyl-β-CD (DM-β-CD)) were found to form inclusion compounds with thiophenes (thiophene (T), bithiophene (2T)) in water and in crystalline states. The structures of α-CD–T, β-CD–2T, and DM-β-CD–2T inclusion complexes were determined by X-ray crystallography. DM-β-CD forms a 1:1 cage type complex with 2T. In contrast, β-CD formed 2:3 (CD:guest) complexes with thiophene and α-CD formed 2:3 complexes, both of the channel type. These inclusion complexes were found to polymerize by FeCl3 in the inclusion compounds in water. The products were formed poly-pseudo-rotaxane between cyclodextrins and poly(thiophene) characterized by IR, 1H-NMR and 13C CP/MAS NMR. The molecular weights of the poly-pseudo-rotaxanes with poly(thiophene) were determined by the MALDI-TOF mass spectra to be 3000–5000. In comparison between poly-pseudo-rotaxane (DM-β-CD–poly(thiophene)), authentic poly(thiophene) and the washed DM-β-CD–poly(thiophene) which was washed with DMF to dethread DM-β-CD, these poly-pseudo-rotaxane was characterized by Raman, UV–vis and fluorescence spectra. The maximum emission band of DM-β-CD–poly(thiophene) shifted to a shorter wavelength. The hypsochromic shift was derived from poly-pseudo-rotaxane with DM-β-CD. 相似文献
13.
Matioli Graciette Zanin Gisella M. De Moraes Flávio F. 《Applied biochemistry and biotechnology》2001,91(1-9):643-654
The enzyme cyclod extringly cosyltransferase (CGTase), EC2.4.1.19, which produces cyclodextrins (CDs) from starch, was obtained
from Bacillus firmus strain no. 37 isolated from Brazilian soil and characterized in the soluble form using as substrate 100 g/L of maltodextrin
in 0.05 M Tris-HCl buffer, 5 mM CaCl2, and appropriate buffers. Enzymatic activity and its activation energy were determined as a function of temperature and pH.
The activation energy for the production of β- and γ-CD was 7.5 and 9.9 kcal/mol, respectively. The energy of deactivation
was 39 kcal/mol. The enzyme showed little thermal deactivation in the temperature range of 35–60°C, and Arrhenius-type equations
were obtained for calculating the activity, deactivation, and half-life as a function of temperature. The molecular weight
of the enzyme was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, giving 77.6k Da. Results for CGTase
activity as a function of temperature gave maximal activity for the production of β-CD at 65°C, pH 6.0, and 7 1.5 mmol of
β-CD/(min·mg of protein), whereas for γ-CD it was 9.1 m mol of γ-CD/(min·mg of protein) at 70°C and pH 8.0. For long contact
times, the bestuse of the enzymatic activity occurs at 60°C oratalower temperature, and the reaction pH may be selected to
increase the vield of a desired CD. 相似文献
14.
B. Malaekeh-Nikouei H. Nassirli N. Davies 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):245-250
Cyclodextrins (CDs) are cyclic oligosaccharides that form inclusion complexes with lipophilic molecules through their hydrophobic
central cavity. In this study, the effect of α-CD, hydroxylpropyl-β-CD (HP-β-CD) and mixtures of these two CDs on the aqueous
solubility of cyclosporine A (CyA) was investigated. Infrared spectroscopy and thermal analysis were used to confirm CyA-CD
complex formation. CyA aqueous solubility was increased by 10 and 80 fold in the presence of α-CD and HP β-CD, respectively.
The phase-solubility profile for HP-β-CD was linear while that for α-CD had positive deviation from linearity. In the presence
of constant concentration of α-CD (15% w/v), aqueous solubility of CyA was further increased upon addition of HP-β-CD up to
a concentration of 20% w/v. At higher HP-β-CD concentrations, aqueous solubility of CyA was observed to decrease. Addition
of sodium acetate (up to 5% w/v) to aqueous solutions containing 20% w/v HP-β-CD and increasing concentrations of α-CD resulted
in a significant reduction in CyA solubility. Complex formation between CyA and both α-CD and HP-β-CD was confirmed by differential
scanning calorimetry (DSC). No significant changes were observed in the IR spectra of either CyA or CD following complex formation
suggesting chemical interaction between CyA and the CD was unlikely. Phase-solubility studies showed that α-CD had a much
greater effect on the solubility of CyA than HP-β-CD. Addition of HP-β-CD to aqueous solutions of α-CD affected the solubility
of CyA in these systems. A mixture of 15% w/v α-CD and 20% w/v HP-β-CD was optimal for increasing aqueous solubility of CyA. 相似文献
15.
Cleber P. A. Anconi Clebio S. Nascimento Jr. Wagner B. De Almeida Hélio F. Dos Santos 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(1-2):25-33
Supramolecular complexes consisting of cyclic molecules, such as cyclodextrins (CD), and polymeric chains have attracted considerable
attention, being addressed in literature as novel molecular assembly. The so-called molecular tube (MT), synthesized by cross-linking
adjacent α-CD in a polyrotaxane, is expected to act as host for large molecules in inclusion processes. In addition, these
tubes can also be used as building-blocks in the formulation of novel materials. Molecular tubes constructed with α-cyclodextrin
are obtained as a mixture containing entities with various molecular weights, and the molecular features determining the tube
size distribution are not completely understood. In this paper, we propose the use of a statistical procedure based on binary
numbers to examine the MT formation process. A complete analysis of the distinct orientations between cyclodextrin’s units
was made and, in the light of the approximations of our model, we pointed out, on quantitative basis, that the molecular weight
distribution of α-cyclodextrin MTs can be explained assuming imperfections in the cross-linking process due to the existence
of head-to-tail (HT) arrangements in the polyrotaxanes employed in synthesis. 相似文献
16.
Tze-Loon Neoh Yasuhiro Noda Hidefumi Yoshii Takeshi Furuta 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(1-2):117-123
The effect of cyclodextrins (CDs) on water solubility of iodine was investigated. Modified CDs greatly enhanced the solubility of iodine. On the contrary, enhancement by natural CDs was rather moderate whereby the solubility was only doubled at the highest β-CD concentration examined. Desorption experiment of iodine from solution was carried out with addition of various CDs to study the effect of CDs on iodine retention. α-CD was the most efficient in retarding iodine desorption. Later, various concentrations of α-CD were used in the desorption experiment to observe its volatile suppression effect and determine the stability constant of iodine/α-CD complexation. At α-CD concentration of 10.3 mM, no lost of iodine from the solution was detected. A model was developed for desorption of iodine from the solution based on mass transfer theory. The stability constant K given by this model was 3.28×104 M−1 which was in the same order as the value estimated in this study by solubility method and as well those reported by other authors. In release experiments of solid state inclusion complexes, stability of inclusion complex powders decreased in the order of α-CD>β-CD>randomly methylated β-CD (RM-β-CD). 相似文献
17.
Abdulilah A. Dawoud Nathir Al-Rawashdeh 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):293-301
The inclusion complexes of selected imidazoline-derived drugs, namely Antazoline (AN), Naphazoline (NP) and Xylometazoline
(XM) with β-cyclodextrin (β-CD) were investigated using steady-state fluorescence spectroscopy, differential scanning calorimetry
(DSC), and molecular mechanics (MM) calculations and modeling. The modified form of the Benesi-Hildebrand relation was employed
for estimating the formation constant (Kf) of the 1:1 inclusion complexes, which was applied based on measuring the variation in the fluorescence intensity of the
guest molecule as a function of growing β-CD concentration. On the other hand, the formation of the inclusion complexes was
verified by analyzing solid samples of the complexes using DSC. The thermodynamics of the inclusion complexation, standard
enthalpy (ΔH°) and entropy changes −(ΔS°) were obtained from the temperature-dependence of Kf. Obtained values of ΔH° and ΔS° indicated that the inclusion process favorably proceeds through enthalpy changes that was
sufficiently predominant to compensate for the unfavorable entropy changes. MM calculations revealed that the proposed drugs
molecules can form 1:1 inclusion complexes with β-CD that are stabilized predominantly through van der Waals forces. In addition,
MM calculation provided the energetically favored configuration of the inclusion complexes, where NP and XM can be included
inside the β-CD cavity through its wide rim, whereas AN can penetrate through the narrow rim of the β-CD cavity. 相似文献
18.
Moussa Mbaye Mame Diabou Gaye Seye Atanasse Coly Alphonse Tine Jean-Jacques Aaron 《Analytical and bioanalytical chemistry》2009,394(4):1089-1098
The photochemically induced fluorescence (PIF) spectral properties of α-cypermethrin in organic solvents (hexane, dichloromethane,
acetonitrile, ethanol) and in cyclodextrin aqueous solutions (β-CD and 2-hydroxypropyl-β-CD, 2-HP-β-CD) were investigated.
The photolysis kinetics of α-cypermethrin were evaluated in the various media. The PIF signal was found to be significantly
enhanced in the CD media relative to the organic solvents. The stoichiometry and the formation constants of the α-cypermethrin
inclusion complexes formed with the CDs were determined. The analytical performances of the PIF method were improved in the
presence of HP-β-CD relative to the other media, and a CD-enhanced PIF analytical method was developed. The limits of detection
and limits of quantification ranged, respectively, between 6 and 98 ng/mL and between 24 and 343 ng/mL, depending on the medium.
Application to the analysis of tap water and Senegal natural water samples collected close to agricultural areas and spiked
with α-cypermethrin yielded satisfactory recoveries going from about 77% to 98%. An interference study of foreign species,
including pesticides and inorganic ions likely to be present in natural waters, was also carried out.
Figure Photolysis reaction of α-cypermethrin in presence of HP-β-CD 相似文献
19.
Kim Lambertsen Larsen Stig Bruse Andersen Anne Louise Mørkbak Reinhard Wimmer 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):185-190
The inclusion complexes between fusidate, 3-keto fusidate, 11-keto fusidate and 11-deoxy fusidate and α-, β-, and γ-cyclodextrin
(CD) were studied using capillary electrophoresis. By monitoring the changes in mobility of the negatively charged compounds
in the presence of varying amount of CD the stability constants of the complexes formed could be obtained. In the case of
α- and β-CD the obtained results could be modelled to a simple model assuming 1:1 stoichiometry, revealing, not surprisingly,
that β-CD formed a stronger complex compared to α-CD. A model assuming 1:2 (fusidate:CD) stoichiometry could be fitted to
the data obtained with γ-CD. The results showed that the different fusidanes formed very strong 1:1 complexes with γ-CD as
well as a quite weak 1:2 complex. 3-keto-, 11-keto- and 11-deoxy-fusidate formed stronger complexes compared to fusidate,
probably due to an decrease in hydrophilicity caused by the reduced number of hydroxyl groups. The complex between γ-CD and
fusidate was studied by use of 2D-NMR spectroscopy. The results showed that most of the hydrogen atoms of fusidate show interactions
with the hydrogen atoms in the cavity of γ-CD. The interaction pattern suggests that fusidate may be fully embedded in the
cavity of γ-CD. No interactions between fusidate and the hydrogen atoms situated at the outside of the CD were found. 相似文献
20.
Gasparrini F Pierini M Villani C Filippi A Speranza M 《Journal of the American Chemical Society》2008,130(2):522-534
The structure, stability, and reactivity of proton-bound diastereomeric [M x H x A]+ complexes between some amino acid derivatives (A) and several chiral tetra-amide macrocycles (M) have been investigated in the gas phase by ESI-FT-ICR and ESI-ITMS-CID mass spectrometry. The displacement of the A guest from the diastereomeric [M x H x A]+ complexes by reaction with the 2-aminobutane enantiomers (B) exhibits a distinct enantioselectivity with regards to the leaving amino acid A and, to a minor extent, to the amine reactant B. The emerging selectivity picture, discussed in the light of molecular mechanics calculations, provides compelling evidence that the most stable conformers of the selected chiral tetra-amide macrocycles M may acquire in the gas phase a different conformation by induced fit on complexation with some representative amino acid derivatives A. This leads to the coexistence in the gas phase of stable diastereomeric [M x H x A]+ eq-eq and ax-ax structures, in proportions depending on the configuration of A and M and characterized by different stability and reactivity toward the 2-aminobutane enantiomers. The enantioselectivity of the gas-phase A-to-B displacement in the diastereomeric [M x H x A]+ complexes essentially reflects the free energy gap between the homo- and heterochiral [M x H x A]+ complexes, except when the tetra-amidic host presents an additional macrocycle generated by a decamethylene chain. In this case, the measured enantioselectivity mostly reflects the stability difference between the relevant diastereomeric transition structures. 相似文献