Enantiomeric resolution of persistent compounds of technical toxaphene (CTTs) on t-butyldimethylsilylated β-cyclodextrin phases

Summary Eight of the most important single compounds of technical toxaphene were separated on t-butyldimethylsilylated β-cyclodextrin (β-BSCD) diluted in a medium polar phase using gas chromatography with electron capture detectors (GC-ECD). The enantiomeric resolution of all compounds was obtained in one GC run. The β-BSCD phase also separated the enantiomers of oxychlordane, cis- and trans-chlordane as well as α-HCH. Problems in the enantioselective determination of CTTs in biological samples are discussed. Finally, the enantioselective determination of the two most recalcitrant CTTs in biological samples was achieved using electron capture negative ionization mass spectrometry (GC-ECNI-MS) in the single ion monitoring (SIM) mode. Presented at the 21^st ISC held in Stutgart, Germany, 15^th–20^th September, 1996.     

Separation and Determination of the Structural Isomers of Madecassoside by HPLC Using β-Cyclodextrin as Mobile Phase Additive

A reversed phase HPLC method has been investigated for separation and determination of the structural isomers of madecassoside (madecassoside and asiaticoside-B). The isomeric compounds can be isolated with high resolution by adding β-CD in mobile phase on a C₁₈ column. The effect of β-CD concentration on resolution is discussed. The functional group in the separation process is investigated. The correlation coefficient (R ²) of the calibration was 0.9995 over the range of 0.1–5.0 mg mL⁻¹. The method was successfully applied to characterize and determine the madecassoside in Centella extract.     

Effect of strontium substitution on the composition and microstructure of sol–gel derived calcium phosphates

Sr-doped calcium phosphates have been prepared by sol–gel chemistry. All samples exhibit two phases: hydroxyapatite (HAp) and tricalcium phosphate (β-TCP). With respect to undoped sample, the Sr-doped samples exhibit higher proportion of β-TCP phase but the quantity appears to be quite independent of the doping level. To explain the mismatch with the nominal stoichiometry, the presence of amorphous CaO and SrO compounds have been postulated and their proportions evaluated. The insertion of Sr²⁺ ions in the two crystalline phases HAp and β-TCP is almost total for low doping levels but quite incomplete for the highest doping level. The majority of the inserted Sr²⁺ ions are in the β-TCP phase. Considering the acknowledged beneficial effect of Sr²⁺ on the bone regeneration process, the effective partial substitution of Sr in biphasic calcium phosphate makes these materials very interesting for clinical applications. The Sr-substituted HAp and β-TCP cell parameters agree fairly well with the Vegard’s law and Sr²⁺ ions substitute preferentially for Ca²⁺ in the Ca2 site for hydroxyapatite and in the Ca4 site for β-TCP. The microstructural parameters confirm the previous observation and give a new evidence of clear stabilizing effect of Sr²⁺ ions towards the β-TCP structure.     

Relationship between structure and nonlinear optical properties of new bisazo chromophores. Theoretical and experimental study

Two new bisazo chromophores—derivatives of bis-2,2-(4-hydroxyphenyl)propane (bisphenol A), heterocyclic amines (2-aminobenzothiazole, and 2-amino-6-nitrobenzothiazole) and aniline—were synthesized. Nonlinear optical properties of these chromophores were studied by solvatochromic method (obtained compounds have β_CT value ∼10⁻²⁹ esu). Dependence among the structure of molecules, their dipole moments, and first hyperpolarizabilities was considered on the basis of semi-empirical calculations. A correlation between the measured and calculated β values was studied. The NLO chromophores were used as special monomers to synthesize copolyarylates. The basic characterization of obtained polymers was carried out.     

A Validated Chiral HPLC Method for the Determination of Enantiomeric Purity of R-β-amino-β-(4-methoxyphenyl) Propionic Acid

A normal phase chiral LC method for chiral purity evaluation of β-amino-β-(4-methoxyphenyl) propionic acid was developed on donor–acceptor (pirkle) column. The chiral stationary phase used was a 250 × 4.6 mm (R, R) Whelk-01 with 5 μm particle size, which was accompanied with a 1 cm long guard column. The “hybrid” pi-electron donor–acceptor based stationary phase (R, R) Whelk-01 was found to be enantiomeric selective for (R) and (S) enantiomers of β-amino-β-(4-methoxyphenyl) propionic acid with a resolution >2.5. The concentration of 2-propanol and TFA in the mobile phase plays an important role on the chrmatographic efficiency and resolution between the enantiomers. The limit of detection and limit of quantification of (S) enantiomer was 0.3 and 1.0 μg mL^-1 for 20 μL injection volume. The percentage RSD of the peak area of six replicate injections of (S) enantiomer at LOQ concentration was 4.5. The percentage recovery of (S) enantiomer from (R) enantiomer samples ranged from 92 to 100. The test solution was observed to be stable up to 24 h after the preparation. The developed method was also checked by different analysts and on different lots of columns, reagents and it was proved to be rugged. The developed normal phase chiral LC method can be used for the determination of the enantiomeric purity of R-β-amino-β-(4-methoxyphenyl) propionic acid.     

Triangular ruthenium acetate clusters containing the bis(pyridyl)propane ligand and their inclusion chemistry with β-cyclodextrin

The triruthenium carboxylate cluster [Ru₃O(OAc)₆(py)₂(bpp)]⁺ (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru₃O(OAc)₆(py₂)}₂(μ-bpp)]²⁺ were synthesized in order to investigate their inclusion compounds with β-cyclodextrin (β-CD). Characterization of the complexes was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion complexes was evaluated using ¹H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational isomers and their possible role in the host–guest chemistry with β-CD. Instead of observing the formation of inclusion compounds with different stoichiometries, we observed the formation of 1:1 bpp/β-CD compounds in which the bpp ligand assumes different conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the ¹H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and β-CD.     

Enantiomer separation by CEC

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (βCD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R8) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2crn packed length. Efficiency of 45 000 theoretical plates per meter andR8 of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R₈ of 2.60. (ii) 75 μm I.D. capillary was packed with octadecylsilica particles (ODs). Chiral separation of a basic drug, propranolol, was studied with chiral agent, via addition of the dimethyl-β-cyclodextrin (DM β-CD) directly into the mobile phase on this column. Baseline separation and efficiency of 81 000 theoretical plates per meter were achieved for propranolol. Project supported by the Natural Science Foundation of Liaoning Province, China, the National Natural Science Foundation of China (Grant No.29875030), and the Excellent Young Scientist Award from the National Natural Science Foundation of China. (Grant No.29725512).     

Ethylenediaminetetraacetic acid (EDTA) as an auxiliary tool in the electrospray ionization mass spectrometry analysis of native and derivatized β-cyclodextrins,maltoses, and fructans contaminated with Ca and/or Mg

The effect of Ca²⁺ (and Mg²⁺) and the disodium salt of ethylenediaminetetraacetic acid (EDTA), a well known Ca²⁺ (and Mg²⁺) chelating agent, on the volatilization/ionization of carbohydrates by using electrospray ionization mass spectrometry has been studied. Model compounds such as maltoses (maltose to maltoheptaose), β-cyclodextrins (β-cyclodextrin, methyl-β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin, heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, and 2-hydroxypropyl-β-cyclodextrin) and fructans (sucrose, 1-ketose, nystose, and 1F-fructofuranosylnystose) were used.     

Study on the Inclusion Compounds of Eugenol with α-, β-, γ- and Heptakis (2,6-di-O-methyl)-β-cyclodextrins

Several host–guest inclusion compounds of eugenol as a guest molecule and cyclodextrins (α-,β-,γ-CD) and heptakis (2,6-di-O-methyl)-β-cyclodextrin (DMβ-CD) as hosts were investigated in the solid state and in aqueous solution. The one-to-one solid inclusion compounds of eugenol and β-CD or γ-CD were prepared, but those of eugenol with α- or DMβ-CD were not obtained under the same condition. However, the UV-visible absorption spectroscopy data indicated that the liquid guest could form a 1:1 inclusion compound with all four hosts respectively in aqueous solution. The two solid inclusion compounds were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The association constants (K), calculated from the modified Benesi–Hidebrand equation, of eugenol with α-, β-, γ- and DMβ-CD is 4.95 × 10⁴, 3.96 × 10⁵, 1.47 × 10⁵ and 9.33 × 10⁴ mol⁻¹ dm³, respectively.     

Dehydration Reaction of Manganese(II) Oxalate Dihydrate in the Solid State New Method in the Study of Non-isothermal Kinetics

A new method was proposed for determining the most probable mechanism function of a solid phase reaction. According to Coats-Redfern's integral equation E_β→0 was calculated by extrapolating β to zero using a series of TG curves with different heating rates. Similarly, E_α→0 was calculated according to Ozawa's equation. The most probable mechanism function of the solid phase dehydration of manganese(II) oxalate dihydrate was confirmed to be G(α)=(1-α)^1/2 by comparing E_α→0 with E_β→0. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polyfunctional fluoroalkyl-containing carbonyl compounds in the synthesis of heterocycles

Efficient procedures for the regioselective synthesis of fluoroalkyl-containing threefive-, six-, and seven-membered heterocycles as well as of related fused compounds, namely, α,β-epoxyketones, α,β-aziridinylketones, pyrazoles, pyrazolines, isoxazolines, 1,2-dithiolenes, amino- and mercaptopyrimidines, Δ^3,5-2-thioxo-1,3,2-thiazaphosphorines, Δ^3,5-2-thioxo-1,3,2-oxazaphosphorines, 2,3-dihydro-1,4-diazepines, azirino[1,2-a]quinoxalines, benzo[b]-and naphtho[2,3-b]-1,4-diazepines, and triazolopyridazines, which have been developed by the authors and coworkers, are summarized. The α- and β-functionalized fluoroalkylcontaining carbonyl compounds (β-diketones, β-ketoesters, their salts, regioisomeric β-aminovinyl ketones, β-aminovinylthiones, β-hydroxyketones, α,β-enones, and their halogen derivatives) were used as synthons in the processes of formation of the above-mentioned heterocycles. Dedicated to the memory of Academician I. Ya. Postovskii on his 100th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1279–1286, July, 1998.     

Improvement of Steroid Biotransformation with Hydroxypropyl-β-Cyclodextrin Induced Complexation

The inclusion complexes induced by cyclodextrins and its derivates have been shown previously to enhance the biotransformation of hydrophobic compounds. Using hydroxypropyl-β-cyclodextrin (HP-β-CD; 20% w/v), the water solubility of cortisone acetate increased from 0.039 to 7.382 g L⁻¹ at 32 °C. The solubilization effect of HP-β-CD was far superior to dimethylformamide (DMF) and ethanol. The dissolution rate also significantly increased in the presence of HP-β-CD. The enzymatic stability of Δ¹-dehydrogenase from Arthrobacter simplex TCCC 11037 was not influenced by the increasing concentrations of HP-β-CD contrary to the organic cosolvents which negatively influenced in the order DMF > ethanol. The activity inhibition effect caused by HP-β-CD was not so conspicuous as ethanol and DMF. Inactivation constants of ethanol, DMF, and HP-β-CD were 5.832, 4.541, and 1.216, respectively. The inactivation energy (E _a) was in the order of HP-β-CD (55.1 kJ mol⁻¹) > ethanol (39.9 kJ mol⁻¹) > DMF (37.1 kJ mol⁻¹).     

Permethylated 6I-alkenoylamino-6I-deoxy β-cyclodextrin derivatives as modifiers of photoluminescence sensor response of porous silicon

A set of permethylated 6^I-(ω-alkenoyl)-6^I-amino-6^I-deoxy-β-cyclodextrin derivatives with different chain length of the alkenoyl group (used as a spacer) was synthesized. These derivatives were attached by photochemically activated hydrosilylation reaction to the surface of porous silicon. Photoluminescence response of the modified PS to controlled concentrations of various molecules in gas phase revealed strong host-guest interactions between β-cyclodextrin and the detected molecules. The strongest interaction was observed for aromatic molecules, which have the optimal size to fit into the β-cyclodextrin molecular cavity.     

Processing of β-BaB2O4 Thin Films Through Metal Organics

β-BaB₂O₄ (β-BBO) thin films were successfully synthesized by the sol-gel method using metallo-organic compounds. A stable BBO precursor solution was prepared from barium metal and boron triethoxide or 2,4,6-triethoxycyclotriboroxane in a mixture solvent of ethanol and 2-ethoxyethanol. As-precipitated powder formed by hydrolysis of the precursor solutions crystallized to ψ phase, which was transformed to β phase at higher temperatures. The transformation temperatures of powders from ψ to β phase of the ethoxide system and the boroxane system were 600 and 680°C, respectively. The calcination of precursor films in a mixture gas of water and oxygen was found to decrease the crystallization temperature of β-BBO films on Pt sheet substrates. The precursor films prepared from the ethoxide system and the boroxane system crystallized to β-BBO on Pt (111)/glass substrates at 500 and 550°C, respectively. The BBO films on Pt(111)/glass substrates showed the strong (006) preferred orientation. The β-BBO films on Pt(111)/glass substrates showed the second harmonic generation (SHG) of the 532 nm light on irradiation with 1064 nm light. The SH power from the BBO films was correlated with the fundamental power through the square-law proportionality based on the theory. The SHG efficiency of the BBO films was dependent upon the film thickness.     

Can cyclodextrins really improve the selectivity of extraction of BTEX compounds?

Solubility of BTEX compounds was determined in aqueous solutions of natural CDs (α-, β-, γCD) as well as of some industrial βCD derivatives (RAMEB, HPBCD, AcβCD) measured by UV photometry. From the phase solubility diagrams the complex association constants were determined. The βCD derivatives increased the solubility of individual monoaromatic compounds, depending on the structure of the guest molecule. We have found that RAMEB (randomly methylated βCD) and AcβCD (partially acetylated βCD) are the most effective solubilizers while the effect of natural CDs is not significant because the complexes precipitate from the solutions. Extraction experiments were performed to see how the complexation of components influences the extraction using a mixture modeling the composition of these pollutants in soil. We have found that although the soluble CD derivatives are not as selective as expected based on complex association constants, they increased the efficacy of extraction by 4–6 times. The reason of the low selectivity is that the concentration ratio of certain BTEX compounds in CD solutions is smaller than in water. CD derivatives seem to have an equalizing effect: the solubility of the least soluble p-xylene is improved in the highest extent, but that of benzene the least. This result, however, is an advantage in the application of these CD derivatives in soil remediation (the availability of each BTEX compounds will be enhanced).     

Confirmatory determination of organochlorine pesticides in surface waters using LC/APCI/tandem mass spectrometry⋄

A confirmatory method for the determination of organochlorine pesticides (OCPs) and their metabolites (endrin, α-endosulfan, β-endosulfan, endosulfan sulfate, heptachlor, heptachlor epoxide, 2,4′-DDD, 4,4′-DDD, 2,4′-DDE 4,4′-DDE, 2,4′-DDT, and 4,4′-DDT) in surface waters using liquid chromatography /APCI/tandem mass spectrometry has been developed. Chromatographic separation was carried out on a ChromSpher 5 Pesticide column using a gradient elution with mobile phase 1mM ammonium acetate-acetonitrile. Endrin, α-endosulfan, β-endosulfan , endosulfan sulfate, heptachlor and heptachlor epoxide were determined in the negative ionization mode, while the rest compounds in positive ionization mode. For the identification of the analytes, two multireaction monitoring transitions were selected per compounds except for the heptachlor which selected ion monitoring was used. The linearity of the optimized method ranges after SPE concentration, from 0.009 to 30.60 μgL⁻¹ with correlation coefficients greater than 0.99. The method recovery values varied from 72 to 119 % for the different fortification levels . The developed method was successfully applied to determine OCPs and their metabolites in surface water samples collected near paddy fields in growing season of rice, at year 2005 in Pathumthani province, Thailand. Endosulfan sulfate was detected in five out of seven samples and three of them could be quantitated in the range of 0.31to 0.50 μgL⁻¹.     

The role of β-cyclodextrin and hydroxypropyl β-cyclodextrin in the secondary chemical equilibria associated to the separation of β-carbolines by HPLC

The use of cyclodextrins (CDs) in HPLC as mobile phase additives provides a flexible alternative for the separation of chemically related compounds because these separations can be performed on conventional columns and are economically advantageous over the use of chiral stationary phases. The present paper describes the influence of the presence of β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) on the separation of the β-carboline alkaloids norharmane, harmane and harmine. The nature of the stationary phase (reverse phases C₁ and C₁₈) affects the chromatographic separations and also the stability of the inclusion complexes that are developed. The changes in the proportion of the organic solvents at constant concentration of CDs (3 mM for β-CD and 15 mM for HPβ-CD) modify the retention factors (k′) for all alkaloids studied. The nature of the organic solvent in the mobile phase also changes the chromatographic parameters. The logarithm of the capacity factor (k′) is linearly increased with the proportion of water in the hydro-organic mobile phase (ethanolic or methanolic) but the slopes obtained vary depending on the CD added to the mobile phase. The role of competitive equilibria, i.e., chromatographic distribution and inclusion complexes formation is discussed. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May, 14–17, 2006     

Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids with ɛ–β-fish-like phase diagram

The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr), or 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced interfacial layer (A ^S), and the solubilities of ionic liquid (S ^O) and alcohol (A ^O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion stabilized by both C₁₂mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained.     

Bifonazole-β-cyclodextrin Inclusion Complexes. Thermal analysis and X-ray powder diffraction study

The complexation of bifonazole, an antimycotic hydrophobic imidazole derivative, with β-cyclodextrin (β-CD) was investigated in solid phase, using the following complementary techniques: differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and X-ray powder diffractometry. The β-CD-bifonazole samples were prepared in both aqueous medium by coprecipitation and in solid state by kneading method and the β-CD-bifonazole binary diagrams were drawn. The experimental results demonstrate the formation of two binary compounds, β-CD-bifonazole and (β-CD)_x bifonazole (x =2 or 4). The first compound may be an inclusion compound and the second a crystallized compound, in which the bifonazole is not necessarily included in the cyclodextrin internal cavity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhancement of aqueous solubility of tricyclic acyclovir derivatives by their complexation with hydroxypropyl-β-cyclodextrin

Solubilities of tricyclic acyclovir derivatives in buffered aqueous solutions of hydroxypropyl-β-cyclodextrin (HP-β-CD) at pH 5.5 and 7.0 were determined at 25 and 37 °C. Complexation of these compounds with HP-β-CD resulted in a noticeable increase of their solubility; nevertheless it was limited to tricyclic derivatives of acyclovir carrying an aryl substituent. Combination of ¹H NMR and DSC techniques demonstrated the existence of inclusion complexes between acyclovir derivatives and HP-β-CD. The stability constants, estimated using the Higuchi–Connors method, were found in the range of 10–100 M⁻¹. Additionally, the pK _a values at 25 °C and molar extinction coefficients in aqueous buffered solutions were also determined for all studied compounds.