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MOLECULAR-LEVEL MACHINES: THE CLOCKWORK MODEL


Crystalline phases and solutions of the flexible complexes ROC(O)CH_2Co(CO)_3PPh_3 contain enantiomeric pairs of chiral conformers characterized by two forms of the PPh_3 ligand of opposed helical chirality, each of which is accompanied by only one conformation of the ester fragment. The interconversion amongst enantiomers is very fast and the stereoselectivity is high. No diastereomers have been detected so far. A member of this family, [(etoxycarbonyl)methyl]cobalt tricarbonyl triphenylphosphine (I) was chosen as a model to study the mechanism of the highly specific selection of the si,M and re,P enantiomers found in the crystalline phase. The results of semi-empirical calculations, molecular graphical studies, MM conformation analyses show that correlated motions of co-axial rotors, coupled bevel gear-like rotors with different periodicity and the first example of a coupled conrotation identified in a molecular system provide the mechanism of the inversion. These dynamic gearings, originating mainly in non-bonded interactions, govern the preferred spatial disposition and carry far-reaching conformational information through the molecular system. The partial rotation of the ester group and its impact on the coupled structural elements are identical to those of the escapement wheel in a clock. The Co(CO)_3 rotor acts as an anchor, its two carbonyl ligands form an OC-Co-CO fork that function as pellets. The role of the third coordinated carbonyl of this 'molecular anchor', also assisted by the other two, is to convey the impulse to the phenyl rings, thus acting as a balance-wheel flipping over to their phase enantiomeric configuration. Both the macroscale and (here) the molecular scale escapements transform into their phase isomeric (mirror image) configuration when their action is completed. This is a clockwork analogue unimolecular machine, which can exist in two enantiomeric forms. The two swithchable digital states '1' and '0', might represent the elementary constituent of a computer, operating on the activity of a single molecule. The amplitude of movements is large enough, without the danger of permanent chemical changes as a consequence of appropriate external stimuli. Beside thermal activation, asymmetric impact such as polarized light might be easily envisaged for fuelling and reading the operation of our bistable, molecular-level machines. Extensive preparative and theoretical studies over twenty derivatives of the [(alkoxycarbonyl)methyl]cobalt tricarbonyl triphenylphosphine type molecules are carried out in our laboratories to develop new molecular building blocks for nanomechanical devices.......

【作者名称】: LAJOS BENCZE, GYULA PALYI, ROBERT KURDI
【作者单位】: University of Veszprem, Mueller (Computational Chemistry) Laboratory Egyetem u.10. Veszprem, H-8200 Hungary
【关 键 词】: concerted rotations, mechanochemiacal clockwork, simulation, bistable molecular machine, organocobalt complex, force field
【会议名称】: NATO Advanced Study Institute on Metal-Ligand Interactions: Molecular, Nano-, Micro-, and Macro-Systems in Complex Environments; 20020901-20020912; Cetraro; IT
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 101,777,892
【摘要长度】: 2,659
【会议地点】: Cetraro(IT)
【会议组织】: University of Veszprem, Mueller (Computational Chemistry) Laboratory Egyetem u.10. Veszprem, H-8200 Hungary
【会议时间】: 2002
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