In Search of Molecular Ratchets

Abstract

COMMUNICATIONS tural feature of these (TMPDO),TCNE arrays is rectangular four-site 0 -C binding at the TCNE olefinic carbon atoms, which appear to interact through their K* lobes. The topological requirement for DA complexation at the N-oxide center is more flexible, allowing the formation of both ladder and web (crosslinked ladder) DA arrays in the (TMPDO),TCNE crystals as the N-0-C angle flexes. TMPDO (2.58 g, 69%, m.p. 498 K (493 K 1221) was prepared by treatment of 2,3,5,6-tetramethylpyrazine (2.95 g, Aldrich) in CH,CI, (50 mL) with potassium peroxomonosulfate (66.6 g, 5 equiv; OXONE, Aldrich) in H,O (400 mL) with vigorous stirring at 298 K for 24 h. TCNE (Aldrich) was purified by multiple sublimation (373 K, 0.05 mmHg) through activated charcoal. Conditions for the Benesi-Hildebrand analysis: [TMPDO] = 1 . 9 0 m~; [TCNE] =18.7, 34.0, 51.1, 66.4, 75.7, and 9 0 . 6 m~. Purple crystals of (TMPDO),TCNE were prepared by cooling a mixture of TMPDO ( 4 0 m~) and TCNE ( 2 0 m~) in CH,CN to 253 K for 2-5 h. Red prismatic crystals of (TMPDO),TCNE were prepared analogously, after 2-3 d crystallization. Crystal X-ray diffraction was performed on a Siemens SMART diffractometer with CCD area detection at 293 (purple (111) and 173 K (red 1131) with monochromatic Mo,.radiation ( A = 0.71073 8,). Solution and refinement (against were performed with SHELXTL. No absorption correction was employed. Hydrogen atoms were placed in calculated positions (0.95 8, from the methyl carbon atom with tetrahedral angles). They were given torsional freedom and their thermal parameters were set to 1.2 x Oc, of the bonded carbon atom. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100438. Copies of the data can be obtained free of charge on application to ). Powder Cu,. X-ray spectra were obtained on a Rigaku powder diffractometer. Experimental Section

An autonomous chemically fuelled small-molecule motor

“…22 Their designs culminated in a system that employed chemical reactions to bias a 120 degree rotation of a triptycene residue in one direction, 23 but attempts to extend this approach to repetitive 360 degree directional rotation proved unsuccessful. 24 Light-driven rotary molecular motors based on overcrowded alkenes 12,13 and imines 14,16 have been developed by the groups of Feringa and Lehn, while our group 25,26 and others [27][28][29] have made molecules in which the components can be rotated directionally step-wise by repetitively carrying out several chemical reactions in sequence.…”

Unidirectional rotary motion in a liquid crystalline environment: Color tuning by a molecular motor

“…Among the fascinating structures designed to induce mechanical motions are shuttles, muscles, ratches, pseudorotaxanes, and switches (5)(6)(7)(8)(9)(10)(11)(12). Recently, the first examples of unidirectional rotary motors were reported (13,14), and it was shown that the rate of the rotary motion in the light-driven motors could be tuned by structural modification (15).…”

Molecular dynamics of a grid-mounted molecular dipolar rotor in a rotating electric field

“…Molecular rotors driven unidirectionally by light (8), or bidirectionally by heat (9)(10)(11)(12) or chemically (13,14) have been synthesized. Alternating electric field has been used to affect intramolecular motion (15), and intense laser field of rapidly rotating linear polarization has been used to drive the rotation of a chlorine molecule (16).…”