No abstract

The formation of complex monolayers between gemini surfactants (CsH2s-R,ω-(CmH2m+1N + (CH3)2Br -)2, abbreviated as C12-Cs-C12, s ) 3, 4, 6, 8, 10, 12) and DNA at the air-water interface was systematically investigated. The polyion-complex monolayers formed in situ through the electrostatic attraction between the ammonium groups of gemini surfactants and the phosphate groups of DNA. The effect of surfactant spacer length on the surface properties was investigated. A turning point of the surface properties (extrapolated molecular area and collapse pressure) of the gemini surfactant/DNA complex monolayers appears when the surfactant spacer is above a certain length (s ) 6). The gemini surfactant spacer taking a reverse U-shape conformation at the air-water interface is proposed to interpret the turning point. A quantitative kinetic analysis of the decay curves further confirms that the turning point appears at the surfactant spacer above its critical length, s ) 6. Moreover, the surface topographies of the gemini surfactant/ DNA complex monolayers were controlled by the spacer length of the gemini surfactants, which may be important in surface patterning and nanofabrication.

Ever since the axial chiral catalysts were developed for asymmetric reactions with excellent chiral discrimination and high efficiencies, the interest in the supramolecular catalyst has also been extensively investigated. Here, with a hint from the typical molecular catalyst, we developed a series of metal-coordinated nanotube (M-helical nanotube, M-HN) catalysts for asymmetric reactions. The M-HN catalyst was fabricated on the basis of the self-assembly of an l-glutamic acid terminated bolaamphiphile, which formed a single-walled nanotube. On one hand, through the coordination of transition metal ions with the carboxylic acid groups on the nanotube surface, a wide variety of single-walled M-HN catalysts could be fabricated, in which the coordination sites could serve as the catalytic sites. On the other hand, using a slight amount of these catalysts, significant reactivity and enantioselectivity were realized for certain asymmetric reactions under mild conditions. Remarkably, Bi(III)-HN could catalyze the asymmetric Mukaiyama aldol reaction with high enantioselectivity (up to 97% ee) in an aqueous system; Cu(II)-HN catalyzed the asymmetric Diels-Alder reaction with up to 91% ee within 60 min. It was suggested that a synergetic effect of the aligned multicatalytic sites and stereochemical selectivity of the M-HN lead to an excellent catalytic performance. Through this work, we proposed a new concept of a single-walled nanotube as catalyst and showed the first example of nanotube catalysts presenting high reactivity and enantioselectivity that rivaled a chiral molecular catalyst.