Study Of Novel Bis-amide Bond-containing Polar Silanes And Poar-modified Stationary Phases

High performance liquid chromatography(HPLC) is currently the fastest growing, most widely used analytical separation technique across many fields due to its efficiency, speed, and sensitivity. C18 reversed-phase bonded silicas have become the most popular packing in many fields. However, C18 columns have several drawbacks including ineffective separation of polar and basic compounds, column degradation under highly aqueous mobile phase conditions, poor resolution and peak tailing for basic compounds, etc. Importantly, an urgent need for new stationary phases has emerged due to the growing number of polar compounds that are found in separation tasks. Polar-embedded phases are well-suited for the separation of polar and basic compounds, and can run under highly aqueous mobile phase conditions. The study of these polar silanes and stationary phases is the main focus of the study described herein.AimsThe main objective of this study is to develop novel polar chromatography silanes, which are the bottleneck in developing new polar stationary phases. The specific research tasks include:1. Design and synthesis of eleven polar silanes with bis-amide bonds2. Study of the synthetic methodology3 Scale-up of the bis-amide bond-containing polar silanes to pilot scale4. Preparation of a series of novel stationary phases using polar silanes5. Evaluation of column performance using internationally recognized testsMethods and Results1. Design and synthesis of nine polar silanes with bis-amide bonds, studies of their synthetic methodology. Two preparation methods were studied:A. The first method is a mixed anhydride method(isobutyl chloroformate method). Acid chloride reacts initially with amino acid in an aqueous sodium hydroxide solution; this is followed by neutralization and subsequent reaction with 3-aminopropyltrimethoxysilane in the presence of triethylamine and isobutyl chloroformate to obtain polar silane. The products were characterized by mass spectrometry, nuclear magnetic resonance spectroscopy and elemental analysis. The yields of eleven silanes are in the range of 84-89%.B. The second method is the acid chloride method. Acid chloride reacts with amino acid in the presence of triethylamine to obtain intermediate acid. Thionyl chloride is then added dropwise into this solution to obtain a new acyl chloride. This solution was further reacted with 3-aminopropyltrimethoxysilane in the presence of triethylamine to yield polar silane. The products were characterized by mass spectrometry, nuclear magnetic resonance spectroscopy and elemental analysis. The yields of eleven silanes are in the range of 75-80%.Comparing the two synthesis methods, the mixed acid anhydride method provides a high purity and high yield product that can be conveniently purified by recrystallization. The acid chloride method is quicker and less costly. Overall, both are effective methods for the synthesis of polar silane.2. Scale-up of the bis-amide bond-containing polar silanes to pilot scale.3. Preparation of novel stationary phase using polar silane. The pretreated silica gel was reacted with an excess of bis-amide bond-containing polar silane in toluene in the presence of triethylamine; the resulting solid was washed with various organic solvents. The product was then hydrolyzed and washed with acetone and methanol, and then dried to give the bonded phase. The material was further reacted with hexamethyldisilazane in toluene. The mixture was filtered, washed and dried to obtain stationary phase.4. Evaluation of column performance using internationally recognized tests including column efficiency test, base deactivation test, hydrogen bonding and metal chelating test at low p H, ion interaction at high p H conditions. The stationary phase exhibits high column efficiency and sensitivity, and excellent selectivity and resolution.These results show that the synthesis processes of new polar silanes are simple, stable and reliable. They can be effectively used for the development of novel chromatographic stationary phases. All synthesis methods have industrialization prospects.