Production,isolation and structural characterization of [92]fullerene isomers

High-resolution 13C NMR has been used to structurally characterize a single isomer possessing C2 molecular symmetry as well as an inseparable mixture of other isomers of [92]fullerene, produced from dysprosium arc-burned soot, separated and isolated via multi-stage recycling HPLC.     

Synthesis and isolation of homeomorphous isomers of P-containing cryptands

The novel isomeric phosphite cryptands 2, 3, and 4 could be synthesized by a simple one-pot tripod capping method starting from bisphenol 1 and PCl3. The assembling of five components led to the formation of a macrobicyclic structure, which probably requires an appropriate preorganization of the reactants. In contrast to the NMR spectra of 2, 3, and 4 in solution, the X-ray structures of 2 and 3 reveal that these molecules have no C3 symmetry in the solid state. In the 31P NMR spectra, both in- and out-P atoms have remarkably different chemical shifts due to a distorted geometry around the in-phosphorus. Phosphorus atoms in the inposition have a decreased reactivity. They are, therefore, more slowly oxidized by cumene hydroperoxide than out-P atoms. A stepwise synthesis was developed for phosphite/phosphatecryptands (5, 7, 9, and 15) via the monoprotected bisphenol 11 and the phosphate 14. In addition, the cylindrical macrotricycle 16 was isolated as a mixture of diastereomers from the crude product of this reaction.     

Reactivity of triazolyl Schiff bases with Ru(II)-2,2′-bipyridyl: Synthesis,spectroscopic characterization of isomers and their photo-physical properties

The condensation of 3-amino-1H-1,2,4-triazole with benzaldehyde and terephthalaldehyde provides the bidentate and tetradentate Schiff bases 1,2,4-triazolo-3-imino-benzene L¹H and 1,4-bis(1,2,4-triazolo-3-imino)benzene L²H₂, respectively. The well characterized Schiff bases were allowed to react with cis-Ru(bpy)₂Cl₂ · 2H₂O. Isomers of the mononuclear complexes Ru(bpy)₂L¹]PF₆ · NH₄PF₆ (1a, N4) and [Ru(bpy)₂L¹]PF₆ · 0.5NH₄PF₆ (1b, N2), and the dinuclear Ru(II) complexes [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₂ · NH₄PF₆ (2a, N4N4), [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₂ · NH₄PF₆ · 2H₂O (2b, N2N2) and [Ru(bpy)₂L²Ru(bpy)₂](PF₆)₃ · NH₄PF₆ (2c, Ru(II)-Ru(III)) were separated by column chromatography and characterized by their elemental analysis, FAB mass and spectral (IR, NMR, UV–Vis) data. The data obtained suggest that the ligands are bound to the metal centre via the N4 and N2 atoms of the triazole moiety along with the N (imine) atom. The complexes display metal-to-ligand charge-transfer (MLCT) transitions in the visible region from the dπ(Ru^II) → π^∗L transition. Highly intense ligand-based π→π^∗ transitions are observed in the UV region. A dual emission occurs from the N2 and N2N2 isomers.     

Synthesis and characterization of tetrakis-silylated C60 isomers

A photochemical reaction of C(60) with disilane in a 2:3 ratio affords the isomer mixture of the tetrakis-adduct of C(60)((t)BuPh(2)Si)(4) as the major product. The use of a three-stage HPLC separation system isolated three of their isomers. Their structural assignments were based on FAB mass, UV-vis, NMR, and cyclic voltammetry (CV) measurements. The CV analysis showed that the terakis-adduct has lower oxidation and higher reduction potentials than the bis-adduct C(60)((t)BuPh(2)Si)(2) and the parent C(60).     

Synthesis and characterization of norbornanediol isomers and their fluorinated analogues

[reaction: see text] Fluorinated norbornene monomers exhibit the requisite properties for inclusion in 157 nm photoresists, but traditional addition and radical polymerizations with these monomers have failed. Norbornanediols provide an alternate route to these materials via condensation polymerization, and methods have been developed for the efficient synthesis of the exo-2-syn-7- and endo-2-exo-3-dihydroxynorbornanes. Synthesis of the fluorinated analogues is complicated by steric and electronic effects; however, a high-yielding synthesis of endo-2-exo-3-dihydroxynorbornane bearing a 5-endo-[2,2-bis(trifluoromethyl)hydroxyethyl] substituent is reported.     

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

Separation,interconversion, and insecticidal activity of the cis‐ and trans‐isomers of novel hydrazone derivatives

A series of cis‐ and trans‐isomers of hydrazone derivatives were separated and analyzed through HPLC with diode‐array detection and HPLC‐MS/MS using ESI and ion trap MS. Two single crystals (A‐5‐1 and C‐2‐1) of the trans‐isomers were obtained and determined using X‐ray crystallography data, and the cis‐ to trans‐isomerization under different conditions was discussed. Both of the cis‐ and trans‐isomers of A‐4 and A‐5 exhibited good insecticidal activities against Plutella xylostella.     

Direct separation and quantitative determination of glimepiride isomers by high performance liquid chromatography

A simple and sensitive high‐performance liquid chromatographic procedure for the determination of the trans isomer of glimepiride is reported. Chromatography accomplished direct separation of the cis and trans isomers of glimepiride on a Dikmonsil C18 (250×4.6 mm, 5 μm) column with a mobile phase consisting of methanol‐acetonitrile‐NH₄Ac buffer solution (1.5 mol L^–1, pH = 4.5) (1.1 : 1.3 : 1.0, v/v) at a flow rate 0.5 mL min^–1. The resolution (R_S) was 1.73 with a retention time of 24.885 and 23.018 min for the cis and the trans isomer, respectively. A standard linear calibration curve was established for the trans isomer of glimepiride over the range of 4.95–198.00 μg mL^–1 with a correlation coefficient of 0.99997. This method has been successfully used to analyze four different kinds of glimepiride product.     

Separation of isomers of dienoic acids by electromigration techniques

Different capillary electromigration techniques were employed to resolve geometrical isomers of sorbic acid, decadienoic acid, and ethyl sorbate. Since these substances differ in their polarity, shape, and size, various electromigration approaches were investigated to separate the four geometrical isomers of each compound. With capillary electrophoresis (CE) modified with a cyclodextrin (β‐CD) the four isomers of sorbic acid were separated using a buffer that consists of 60 mM tetraborate and 8 mg/mL β‐CD. The separation of decadienoic acid geometrical isomers was not possible, even at elevated tetraborate and cyclodextrin concentrations. The four isomers of decadienoic acid were successfully separated using micellar electrokinetic chromatography (MEKC) with a buffer consisting of 30 mM tetraborate and 100 mM SDS and microemulsion electrokinetic chromatography (MEEKC). Ethyl sorbate is the least polar of all the studied substances and its isomers could not be separated by MEKC or MEEKC. The resolution was improved and isomers were fully separated using capillary electrochromatography (CEC) with ODS stationary phase and a mobile phase consisting of 10 mM boric acid in 50% acetonitrile. Minor differences in the polarity and the shape of isomers and high resolving power of the applied techniques were sufficient for separation of very similar compounds. We have shown that versatile electromigration techniques can be applied for separation of geometrical isomers of dienoic acids and their esters.     

HPLC separation of isomers of tetrahydro-1,5-benzothiazepines and tetrahydro-1,5-benzodiazepines

Summary Separation of positional and cis-trans-isomers of tetrahydro-1,5-benzothiazepines and tetrahydro-1,5-benzodiazepines was studied using reversed-phase chromatography and liquid-solid chromatography. The selection of solvent was based on the selective triangle for solvents. Systems of separation consisted of C₁₈ columns and methanol, THF or acetonitrile in water for the reversedphase method; it was suitable for the separation of positional isomers only but the liquid-solid method was suitable for separation of cis-trans-isomers as well as positional isomers using a silica column and ethyl ether, chloroform or ethyl acetate as the mobile phase respectively.     

Synthesis, isolation and structural characterization of optically active planar chiral cyclomercurated ferrocenylimines

Asymmetric cyclomercuration of chiral ferrocenylimines (+)-(R)-2 and (−)-(S)-2 with mercuric acetate and subsequent treatment by lithium chloride gave two different pairs of diastereomeric cyclomercurated ferrocenylimines. The four enantiomerically pure compounds with both planar and central chirality were isolated from the two pairs by thin layer chromatography. The structures and absolute configurations of these complexes were determined by single-crystal X-ray analysis and characterized by IR, ¹H NMR, specific rotation and elemental analysis.     

Isolation and purification of two antioxidant isomers of resveratrol dimer from the wine grape by counter‐current chromatography

Resveratrol dimers belong to a group of compounds called stilbenes, which along with proanthocyanidins, anthocyanins, catechins, and flavonols are natural phenolic compounds found in grapes and red wine. Stilbenes have a variety of structural isomers, all of which exhibit various biological properties. Counter‐current chromatography with a two‐phase solvent system composed of n‐hexane/ethyl acetate/methanol/water (2:5:4:5, v/v/v/v) was applied to isolate and purify stilbene from the stems of wine grape. Two isomers of resveratrol dimers trans‐ε‐viniferin and trans‐δ‐viniferin were obtained from the crude sample in a one‐step separation, with purities of 93.2 and 97.5%, respectively, as determined by high‐performance liquid chromatography. The structures of these two compounds were identified by ¹H and ¹³C NMR spectroscopy. In addition, their antioxidant activities were assessed by 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) assay. The antioxidant activities of trans‐δ‐viniferin were higher than that of trans‐ε‐viniferin in this model. This work demonstrated that counter‐current chromatography is a powerful and effective method for the isolation and purification of polyphenols from wine grape. Additionally, the DPPH radical assay showed that the isolated component trans‐δ‐viniferin exhibited stronger antioxidant activities than trans‐ε‐viniferin and a little bit weaker than vitamin E at the same concentration.     

Carbon-carbon double bond in pillar[5]arene cavity: Selective binding of cis/trans-olefin isomers

The binding behavior of pillar[5]arenes (P5As) towards a series of olefin guests ((E)-1,4-dichlorobut-2-ene (1E), (Z)-1,4-dichlorobut-2-ene (1Z), (E)-but-2-ene-1,4-diol (2E), and (Z)-but-2-ene-1,4-diol (2Z), as well as an alkyne derivative 1,4-dichlorobut-2-yne (3)) have been studied in organic solution. P5As exhibit considerable selectivities for the trans-olefin isomers (1E and 2E) over their cis-isomers (1Z and 2Z). The cis/trans-selective interactions hold the potential of utilizing P5As to separate olefin isomers.     

Synthesis of 1,1,1,7,7,7-hexafluoroheptane-2,4,6-trione, the simplest fluorinated 1,3,5-triketone

A simple, convenient and effective method to synthesize 1,1,1,7,7,7-hexafluoroheptane-2,4,6-trione, the simplest fluorinated 1,3,5-triketone, on a preparative scale was developed. The title compound was obtained by a Claisen-type double condensation of acetone with trifluoroacetic acid ethyl ester and isolated as a solid monohydrate from the reaction mixture. Subsequent dehydration proceeds smoothly to produce the desired compound as an individual substance. Its peculiar tautomeric (keto-enol, ring-chain) features in various solvents are discussed.     

A new gas chromatographic stationary phase: Polysiloxane with β-cyclodextrin side chain for the separation of chiral and positional isomers

Summary A new stationary phase [bikis(2,6-di-O-pentyl-3-O-hex-6-enyl)-pentakis(2,6-di-O-pentyl-3-O-methyl)-β-CD-polysiloxane] was synthesized and successfully applied in GC for the separation of chiral and achiral isomers. It possesses high column efficiency and exhibits excellent separation ability for disubstituted benzenes. Some typical enantiomers and optical isomers are well separated. The separation behavior of this new phase is characterized and discussed.     

Energetic analysis of 24 C20 isomers

Twenty-four individual geometric structures of the 20-carbon system are investigated using hybrid Hartree–Fock/density functional theory (DFT-B3LYP) in combination with the 6-31G and 6-311G* basis sets. These computations are carried out in order to evaluate the relative energies of the various C₂₀ isomers utilizing both geometry optimization and single-point energy calculations. The relative energies of the three most widely studied C₂₀ isomers (ring, bowl, and cage) are compared to the energies of other cyclic, bowl-like, and miscellaneous isomers. Although the ring and the bowl isomers are predicted to be the two most stable species, we have identified three to four additional cyclic structures that are predicted to be energetically competitive with the fullerene structure.     

Effect of gamma-irradiation on the levels of total and cis/trans isomers of beta-carotene in dehydrated parsley

Ionizing radiation is a method for preservation of foods that use the high energy of gamma rays or accelerated electrons, thereby ionizing molecules. The most important precursor of vitamin A is β-carotene, a carotenoid with pro-vitamin A activity. The highly unsaturated chain confers the instability of β-carotene, and some reactions, as isomerisation, can reduce the characteristics of pro-vitamin A. The present study investigated whether increasing doses of 0, 10 and 20 kGy lower the total β-carotene level and if an enhancement of cis-isomers occurred on samples of dehydrated parsley. No differences were observed of either fractions analyzed at doses applied in this study, nor did it contribute to the decrease of vitamin A.