Self-assembly of bisurea compounds in organic solvents and on solid substrates

被引:247
作者
vanEsch, J [1 ]
DeFeyter, S [1 ]
Kellogg, RM [1 ]
DeSchryver, F [1 ]
Feringa, BL [1 ]
机构
[1] KATHOLIEKE UNIV LEUVEN, DEPT CHEM, B-3001 LOUVAIN, BELGIUM
关键词
gels; electron microscopy; scanning tunneling microscopy; self-assembly; ureas;
D O I
10.1002/chem.19970030811
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
New low molecular weight gelators based on the structure R-NHCONH-X-NHCONH-R have been synthesized and tested for their ability to cause gelation of organic solvents. Compounds 2 (R = n-dodecyl, X = -(CH2)(9)-), 3 (R = n-dodecyl, X = -(CH2)(12)-), 4 (R = n-dodecyl, X = 4,4'-biphenyl), and 5 (R = benzyl, X = -(CH2)(9)-) form thermoreversible gels with a wide range of organic solvents, at concentrations well below 10 mg mL(-1). Depending on the nature of the R and X groups, the solvents that undergo gelation include hexadecane, p-xylene. 1-octanol, n-butyl actetate, cyclohexanone, and tetralin. The gels are stable up to temperatures well above 100 degrees C, but are easily disrupted by mechanical agitation. Light microscopic investigations revealed that compounds 2-5 spontaneously aggregate to form thin flat fibers, which can be several hundreds of micrometers long and only 2-10 mu m wide. Depending on the solvent, multiple twists in the fibers are observed. In the gels, these fibers form an extended three-dimensional network, which is stabilized by multiple mechanical contacts between the fibers. Electron microscopy and X-ray powder diffraction revealed that the fibers consist of stacks of sheets. The thickness of the sheets is 3.65 and 3.85 nm for 2 and 3, respectively. Scanning tunneling microscopic investigations of 2 absorbed on graphite showed that 2 forms ion ribbons with a width of 5.0 nm. In the ribbons the molecules have a parallel arrangement, with the long molecular axis perpendicular to the long ribbon axis. The two urea groups within a given molecule are each part of mutually parallel extended chains of hydrogen bonds, Based on these observations a model is proposed for the arrangement of the molecules in the fibers, In this model the bisurea molecules aggregate through hydrogen-bond formation into long ribbons, which assemble into sheets. In these sheets the ribbons are tilted. Finally, the sheets stack to form lone thin fibers. This model is supported by molecular dynamics simulations.
引用
收藏
页码:1238 / 1243
页数:6
相关论文
共 41 条
  • [1] ANIA F, 1981, MAKROMOL CHEM, V183, P235
  • [2] [Anonymous], 1992, THERMOREVERSIBLE GEL
  • [3] GROMACS - A MESSAGE-PASSING PARALLEL MOLECULAR-DYNAMICS IMPLEMENTATION
    BERENDSEN, HJC
    VANDERSPOEL, D
    VANDRUNEN, R
    [J]. COMPUTER PHYSICS COMMUNICATIONS, 1995, 91 (1-3) : 43 - 56
  • [4] A NON-AQUEOUS LYOTROPIC NEMATIC GEL
    CAMPBELL, J
    KUZMA, M
    LABES, MM
    [J]. MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 1983, 95 (1-2): : 45 - 50
  • [5] AN APPROACH TO THE DESIGN OF MOLECULAR-SOLIDS - STRATEGIES FOR CONTROLLING THE ASSEMBLY OF MOLECULES INTO 2-DIMENSIONAL LAYERED STRUCTURES
    CHANG, YL
    WEST, MA
    FOWLER, FW
    LAUHER, JW
    [J]. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1993, 115 (14) : 5991 - 6000
  • [6] STM investigations of organic molecules physisorbed at the liquid-solid interface
    Cyr, DM
    Venkataraman, B
    Flynn, GW
    [J]. CHEMISTRY OF MATERIALS, 1996, 8 (08) : 1600 - 1615
  • [7] DEFEYTER S, UNPUB
  • [8] SUPRAMOLECULAR SYNTHONS IN CRYSTAL ENGINEERING - A NEW ORGANIC-SYNTHESIS
    DESIRAJU, GR
    [J]. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH, 1995, 34 (21): : 2311 - 2327
  • [9] SMALL DEPSIPEPTIDES AS SOLVENT GELATORS
    DEVRIES, EJ
    KELLOGG, RM
    [J]. JOURNAL OF THE CHEMICAL SOCIETY-CHEMICAL COMMUNICATIONS, 1993, (03) : 238 - 240
  • [10] FONTELL K, 1974, LIQUID CRYSTALS PLAS, V2, P80