Notes Bull. Korean Chem. Soc. 2009, Vol. 30, No. 7 1641 The Role of the Neutral and Cationic Gelators from (1S,2S)-(-)-Diphenylethylenediamine for the Preparation of Silica Nano Tubes Myung Ho Hyun, † Min Seob Shin, †,‡ Tae Kyu Kim, †,‡ Ok-Sang Jung, † Jong Pil Kim, ‡ Hyun Jin Kim, ‡ Euh Duck Jeong, ‡,* and Jong Sung Jin ‡,* † Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea ‡ High-Technology Components & Materials Research Center & Busan Center, Korea Basic Science Institute (KBSI), Busan 609-735, Korea. * E-mail: edjeong@kbsi.re.kr and jsjin@kbsi.re.kr Received April 1, 2009, Accepted May 13, 2009 Key Words: Silica nano tube, Gelators, (1S,2S)-(-)-Diphenylethylenediamine, Sol-gel transcription 1R = CH3 2R = N(CH3)3 + Br ‑ Table 1. The gelation ability of gelator 1, gelator 2 and the mixed gelator (1 + 2, 1:1 wt% mixture). a Solvent Gelator 1 Gelator 2 1 + 2 (1:1 wt%) Ethanol G S G Acetonitrile G S G n-Butanol G Gp G Tetrahydrofuran G I I Chloroform S I I Hexane I I I Ethyl acetate G I I Methanol C S C a Gelator concentration: 5.0 wt% /vol, G = stable gel at room temperature, S = solution, I = insoluble, C = crystallize, Gp = partial gel. Many scientists have recently been interested in the synthesis of helical silica nano tubes by using the self assemblies of chiral organic gelators as templates. As organic gelators, for example, sugar-integrated geloators 1 or cholesterol-based gelators 2 based on chiral compounds readily available from natural environments in an optically active form have been used for the preparation of silica nano tubes. Chiral trans- 1,2-cyclohexanediamine derivatives have also been known as excellent gelators that can harden a wide variety of organic fluids. Trans-(1R,2R)- or trans-(1S,2S)-1,2-di(undecylcar- bonylamino)cyclohexane derivatives were reported to self- assemble into left-handed and right-handed helical organogel fibers, which are stabilized by inter molecular hydrogen-bonds through amide groups. 3 The chiral self-assemblies based on these organic gelators have been successfully utilized as excellent templates for the sol-gel polycondensation of tetra- ethoxysilane (TEOS) into helical silica nano tubes. 4 In order to transcribe the organogel structure into the silica structure, it was noticed that the cationic charge in the gelators is indis- pensable in the sol-gel polycondensation of TEOS, but the cationic gelators tend to lose the high gelation ability and rarely result in the helical structure. 5 To overcome this dilemma, the mixture of the neutral and the cationic gelators have been utilized to form stable organogels supported by the helical fiber structure. 5 However, it is not clear how the neutral and cationic gelators are integrated into the organogels while it is known that cationic charge is necessary for the sol-gel trans- cription in order to adsorb anionic silica particles onto the organogels. 1 In order to explore how the neutral and cationic gelators are integrated into the organogels and to explore the role of the neutral and cationic gelators in forming silica tubes, in this study, we prepared two organic gelators 1 and 2 starting from (1S,2S)-(-)-diphenylethylenediamine via the method utilized for the preparation of organic gelators from optically active trans-diaminocyclohexane. 5 The structures of the two gelators prepared in this study were confirmed by the 1 H-, 13 C-NMR, FT-IR spectral data and melting points. Gelation abilities of neutral and cationic gelators (1 and 2) were tested in various solvents and the results are summarized in Table 1. Neutral gelator 1 can gelate ethanol, acetonitrile, n-butanol, tetrahydrofuran and ethyl acetate among eight solvents tested while cationic gelator 2 can partially gelate n-butanol only. However, when gelator 2 was mixed with gelator 1, the mixed gelator (1 + 2, 1:1 wt% mixture) was found to gelate ethanol, acetonitrile and n-butanol. In order to see the morphological structures of organogels prepared in ethanol, the organogels prepared from gelator 1 and the mixed gelator were diluted with ethanol. The ethanol solution of gelator 2 was also diluted with ethanol. And then the partially dissolved organogels and the ethanol solution of gelator 2 were taken on the carbon grids five times. The carbon grids were frozen in liquid nitrogen and then were lyophilized. The resulting carbon grids were subjected to scanning electron microscopy (SEM). SEM results are shown in Figure 1. In the case of neutral gelator 1, rod-shaped structure is shown (Figure 1a), the thickness of the rods being in the rage of 70 ~ 90 nm. In the case of cationic gelator 2, does not have any regular morphology (Figure 1b) even though gelator 2 does not gelate ethanol under usual condition as shown Table 1.