研究目的
Investigating the physical properties, mesomorphic behavior, dielectric anisotropy, and structural selectivity of supramolecular 4-(ω-hydroxyalkyloxy)-4’-cyanoazoxybenzenes as stationary phases for gas chromatography.
研究成果
The supramolecular 4-(ω-hydroxyalkyloxy)-4’-cyanoazoxybenzenes exhibit enhanced nematic mesomorphism, increased dielectric anisotropy, and high structural selectivity in gas chromatography due to hydrogen bonding and self-assembly. They stabilize mesophases when used as additives and show promise for analytical separations of structural isomers, with entropy factors playing a crucial role in selectivity. Future work could explore broader applications and further modifications.
研究不足
The high temperature of mesophase existence complicates the application of compounds in pure form; purification methods did not change the isomer ratio due to structural features and strong specific interactions; the study is limited to specific homologs and sorbates, and may not generalize to all liquid crystals or isomers; experimental errors include ±0.1°C for temperature, 1% for dielectric constant, 3% for dielectric anisotropy, and 0.5-1.0% for birefringence.
1：Experimental Design and Method Selection:
The study involved synthesis and purification of 4-(ω-hydroxyalkyloxy)-4’-cyanoazoxybenzenes homologs, structural elucidation using NMR spectroscopy (1H, 13C, 15N, and HMBC experiments), investigation of mesomorphic properties via polarization thermomicroscopy (PTM) and differential scanning calorimetry (DSC), measurement of dielectric properties and birefringence, and gas-liquid chromatography (GLC) to assess selectivity and thermodynamic parameters.
2：Sample Selection and Data Sources:
Samples included synthesized azoxybenzene homologs (Ia-e), commercial 4-pentyloxy-4’-cyanobiphenyl (5OCB), and reference compounds like 4,4’-dimethoxyazoxybenzene (LC-1) and 4-propyloxy-4’-cyanoazoxybenzene (LC-2). Sorbates for GLC were structural isomers such as xylenes, methylanisoles, lutidins, picolines, and cresols.
3：2). Sorbates for GLC were structural isomers such as xylenes, methylanisoles, lutidins, picolines, and cresols. List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: NMR spectrometer (Bruker Avance III-500), polarization microscope (Polam L211 with temperature stage), DSC calorimeter (DSC 204 F1 Phoenix), balances (Мр 20 and Sartorius Genius ME215 P), dielectric measurement cell with LCR-817 instrument, Abbe refractometer, gas chromatograph (Shimadzu GC-2014 with flame ionization detector and autosampler AOC-20i), and software (Shimadzu GC-solution, PC GAMESS, Chem Craft). Materials included solvents (CDCl3, ethanol, chloroform), stationary phase support (Chromaton N-AW), and carrier gas (helium).
4：Experimental Procedures and Operational Workflow:
Purification by recrystallization and vacuum incubation; NMR spectra acquisition in CDCl3; PTM and DSC for phase transition temperatures; dielectric constant measurement using a calibrated cell; birefringence measurement with oriented specimens; GLC column preparation by coating stationary phase, conditioning, and measuring retention times of sorbates; thermodynamic parameter calculation from retention data; quantum-chemical simulation of hydrogen bond complexes.
5：Data Analysis Methods:
NMR data interpretation for structure elucidation; phase transition analysis from PTM and DSC curves; dielectric anisotropy and birefringence calculation; GLC data used to compute structural selectivity coefficients and thermodynamic parameters (enthalpy, entropy) using Antoine equation and statistical methods; DFT simulations for bond energy estimation.
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NMR Spectrometer
Avance III-500
Bruker
Used for 1H, 13C, and 15N NMR spectroscopy to elucidate the structure of synthesized compounds.
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Gas Chromatograph
GC-2014
Shimadzu
Used for gas-liquid chromatography to measure retention times and study selectivity.
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Autosampler
AOC-20i
Shimadzu
Used to apply sorbate samples to the gas chromatograph column.
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Software
GC-solution Chromatography Data System Version 2.4
Shimadzu
Used for setting parameters and data analysis in gas chromatography.
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Polarization Microscope
Polam L211
Used for polarization thermomicroscopy to study mesomorphic properties and phase transitions.
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DSC Calorimeter
DSC 204 F1 Phoenix
Used for differential scanning calorimetry to measure phase transition temperatures and enthalpies.
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Balance
Мр 20
Used for weighing mixtures with an accuracy of 0.05 mg.
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Balance
Sartorius Genius ME215 P
Sartorius
Used for weighing mixtures with an accuracy of 0.01 mg.
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LCR Meter
LCR-817
INSTEK
Used to measure capacitance for dielectric constant calculations.
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Refractometer
Abbe refractometer
Used to measure refractive indexes for birefringence calculations.
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Software
PC GAMESS
Used for quantum-chemical simulations (DFT method) to study hydrogen bond complexes.
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Software
Chem Craft
Used for data input preparation and results processing in quantum-chemical simulations.
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