Evaluation of the Effect of Citronellol Group on Functionalized Mesogenic Materials by Capillary GC

In this paper, the effects of functionalization with terpenes on two new liquid-crystalline stationary phases for gas chromatography (GC) are described. Citronellol was used as the terminal group in the first material, and tetrahydrogeraniol was used with a second material. Inverse GC showed that the new materials have wide liquid-crystalline ranges (mesophases), 371–500 and 395–501 K, respectively. Moreover, they show good thermal stability up to 523 K and good potential as stationary phases for capillary GC. To clarify the effects of the liquid crystal structures and functional groups on retention and separation, the chromatographic behaviors of the two stationary phases were compared by eluting alkylbenzenes, polycyclic aromatic hydrocarbons, aromatic compounds, and terpenoids. The selectivities for a wide range of analytes achieved using the citronellol column were significantly better than those obtained using the tetrahydrogeraniol column. The columns showed different retention behaviors and fine resolutions for some of the main constituents of essential oils. Introduction of the double bond of citronellol greatly improved the polarization interactions involved in the shape recognition of the liquid-crystalline state for isomers. The new citronellol liquid-crystalline stationary phase, therefore, has a high affinity for natural compounds.

     

An elliptic system modeling two subpopulations

In this paper we study an elliptic system modeling two subpopulations of the same species competing for resources. We show the existence and uniqueness of coexistence states of the system by giving necessary and sufficient conditions.     

Original formation of benzyl benzoates by TDAE strategy

We report herein an original photoinduced electron transfer reaction between an aromatic aldehyde and TDAE in the presence of chloromethyl-dimethoxybenzenes. Thus, the reaction of 1-chloromethyl-2,5-dimethoxy-3,4,6-trimethylbenzene (1), dichlorides 4 and 5 with a series of aromatic aldehydes, in the presence of TDAE and under light catalysis, gave the corresponding benzyl benzoates.     

Computational studies of 1:2 complex between retinol propionate and β cyclodextrin

[M05-2X/6-31G*:PM3MM] and [B3LYP/6-31G*:PM3] ONIOM2 methods have been used to investigate the vitamin A propionate/β cyclodextrin complex with 1:2 stoichiometry. Both methods give almost the same lowest energy minimum. The minimum energy structure of the complex is found in good agreement with experimental data. In this configuration, the major structure of propionate of vitamin A (PVA) is embedded inside the two cavities of βCD while the propionate group is kept outside. However, the three methyl groups of PVA are positioned in the free space between both βCD molecules. The driving forces for complexation are dominated by Van der Waals interactions between PVA and the βCD molecules assisted with multiple hydrogen bond interactions between the two cyclodextrin molecules. These interactions were investigated using the natural bond orbital approach.     

Quantum chemical investigations on hydrogen bonding interactions established in the inclusion complex β-cyclodextrin/benzocaine through the DFT,AIM and NBO approaches

Structure and stability of an inclusion complex formed by Benzocaine (BZC) and β-cyclodextrin (β-CD) were investigated computationally using different levels of theory. The conformational research based on PM6 method allowed reach two minimum-energy structures: model A and model B. The lowest conformers have been exposed to fully geometry optimization employing four DFT functionals: B3LYP, CAM-B3LYP, M05-2X and M06-2X. The performed DFT calculations have identified the model B, in which the amino group is located at the primary face of β-CD, as the most stable complex by an amount up to ?40 kcal/mol. Further, the greater stabilization of model B in respect to model A, has been ascertained through AIM and NBO analyses which clarified the main hydrogen bonds HBs interactions governing the reactivity of BZC inside the hydrophobic cavity of β-CD. Finally, the estimated isotropic ¹H nuclear magnetic shielding constants generated from the gauge-including-atomic-orbital calculation have been analyzed and then compared with the available experimental data.     

Functionalization of 6-nitrobenzo[1,3]dioxole with carbonyl compounds via TDAE methodology

We report herein the synthesis of substituted 2-(6-nitrobenzo[1,3]dioxol-5-yl)-1- aryl ethanols and 2-(6-nitrobenzo[1,3]dioxol-5-yl)-propionic acid ethyl esters from the reaction of 5-chloromethyl-6-nitrobenzo[1,3]dioxole with various aromatic carbonyl and alpha- carbonyl ester derivatives using the tetrakis(dimethylamino)ethylene (TDAE) methodology.     

A new long-chain unsaturated ester and other constituents of Hypericum tomentosum

Three long-chain unsaturated esters (1-3), a fatty acid (4), a fatty ester (5), phytone (6) and a phloroglucinol (hyperfoliatin) (7) were isolated from the light petroleum extract of the endemic species Hypericum tomentosum L. (Clusiaceae). Compound 2, 8,10,13-trimethyltetradecanoic acid (2E)-3-methylhexadec-2-enyl ester, which we named tomentosate, is reported for the first time. The structures of the identified compounds were established on the basis of physical and spectroscopic analysis, and by comparison with literature data.     

Three Nematogen Azobenzene-Based Stationary Phases for Capillary GC: Synthesis and Comparative Study

In this paper, three laterally substituted liquid crystals termed LCC₁, LCC₃ and LCC₄ were synthesized. Characterization of these substances was carried out by ¹H NMR and ¹³C NMR; they possess similar core and differ in their lateral substituents. Their thermal stability was conducted by thermogravimetric analysis and showed decomposition beginning at 212, 233 and 264 °C related to LCC₁, LCC₃ and LCC₄, respectively. Thermal properties were determined by differential scanning calorimetry, thermomicroscopy and inverse gas chromatography. The three novel compounds exhibited a nematic mesophase at a defined range of temperatures, which varied from 81 to 55 °C. Lengthening of the lateral substituent seemed to affect the nematic range by decreasing it. Fused-silica capillary columns (30 m × 0.32 mm) were employed for the analytical study. Numerous mixtures of components of various properties were injected. Particular attention was given to the selectivity towards the close-boiling isomers. These investigations indicated that lateral attached groups had considerable effect on the thermal and chromatographic properties of the liquid crystal compounds. These interesting results may guide in improving the development of new type of liquid crystals with desired properties for a widespread application.