Fabrication of Carbon-Like, π-Conjugated Organic Layer on a Nano-Porous Silica Surface

This paper presents a new type of black organic material-porous silica composite providing an extremely highly selective adsorption surface. This black composite was prepared by lamination on nano-sized pores with a carbon-like, π-extended structure, which can be converted via the on-site polymerization of 1,5-dihydroxynaphthalene with a triazinane derivative and a thermally induced condensation reaction with denitrification. This bottom-up fabrication method on porous materials had the great advantage of maintaining the pore characteristics of a raw porous material, but also the resultant black surface exhibited an extremely high molecular-shape selectivity; for example, that for trans- and cis-stilbenes reached 14.0 with the black layer-laminated porous silica, whereas it was below 1.2 with simple hydrophobized silica.

High-performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles

The optimization of a porous structure to ensure good separation performances is always a significant issue in high-performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high-performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high-performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high-performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36,000 m(-1). Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans-stilbene with separation factor as 7 and theoretical plate number as 76,000 m(-1) for cis-stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long- established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.

Retention mechanism of l-glutamide-derived noncrystalline stationary phases in reversed-phase high-performance liquid chromatography and application for separation of nucleic acid constituents

Double alkylated L-glutamide-derived noncrystalline stationary phases Sil-DSG and Sil-DBG have been prepared by coupling N',N''-dioctadecyl-N-[4-carboxybutanoyl]-L-glutamide (DSG) and N',N'',-dibutyl-N-[4-carboxybutanoyl]-L-glutamide (DBG) with aminopropylated silica (Sil-APS). TEM observations of DSG and DBG showed that lipid DSG can aggregate in organic solvents (methanol, chloroform, toluene, etc.) and self-assembled nano fibers are observed while such fibrous aggregations are not observed for DBG. The resulting chromatographic data have been provided information about its selective interaction with guest molecules (PAHs) in RP-HPLC. We have observed that the carbonyl groups in Sil-DSG exist in ordered state by forming a condensing thin layer over silica surface while DBG cannot form such an ordered state due to its lower order of short alkyl chain. The ordered carbonyl groups present in Sil-DSG promotes multiple carbonyl pi-benzene pi interactions with guest PAHs isomers which enhance the selectivity for these compounds. The contribution of pi-pi interactions was also supported by the substantial effects on the selectivity of benzene and nitrobenzenes. The effect of pi-electron containing solvent on the retention behavior of the PAHs was also studied. The selectivity for nucleic acid constituents, i.e. nucleosides and its bases were also evaluated by Sil-DSG and the selectivity for these compounds on Sil-DSG was compared with the selectivity of conventional polymeric ODS phase. It has been found that Sil-DSG provided higher selectivity for nucleic acid constituents than polymeric ODS and that HPLC packing materials can be efficiently employed for routine analysis of these compounds. The effect of methanol content on the separation behavior of nucleosides was also studied.

Conformational Effect of Silica-supported Poly(octadecyl acrylate) on Molecular-Shape Selectivity of Polycyclic Aromatic Hydrocarbons in RP-HPLC

Poly(octadecyl acrylate) with a terminal reactive group was synthesized by radical telomerization in various solvents. The polymers were grafted onto porous silica for use in RP-HPLC, and the molecular recognition ability was investigated along with the selectivity for the structural isomers of polycyclic aromatic hydrocarbons. The mechanism of selectivity was also investigated with differential scanning calorimetry and NMR spectroscopic observations.

Retention versatility of silica-supported comb-shaped crystalline and non-crystalline phases in high-performance liquid chromatography

Silica-supported comb-shaped polymer (Sil-ODA18) provided a specific selectivity towards aromatic and non-aromatic solutes. Selectivity of Sil-ODA18 and ODS (polymeric and monomeric) columns towards polycyclic aromatic hydrocarbons and geometric isomers have been discussed in respect of molecular shapes and sizes. The retention versatility of this phase arises from the orientation change on transition from the ordered crystalline to the less ordered non-crystalline state. Selectivity in the crystalline and non-crystalline regions of Sil-ODA18 is similar to that of polymeric and monomeric ODS phases, respectively. Sil-ODA18 column also exhibited the characteristic temperature dependency of liquid-crystalline phases, i.e., an increase in retention with increasing temperature on transition from crystalline to isotropic state.