Geared molecules

A gear-shaped molecule spins freely on a copper metal surface. A molecular soccer ball nestles snugly in a cavity on a protein. It sounds like science fiction, but these creations are real developments in the blossoming field of nanotechnology. The term nanotechnology refers to science carried out at the nanometer scale (lmn = 10 m). 

Manzano C, Soe WH, Wong HS, Ample F, Gourdon A, Chandrasekhar N, Joachim C (2009) Step-by-step rotation of a molecule-gear mounted on an atomic-scale axis. Nat Mater 8 576... 

Unfortunately, the dynamic correlation energy is not constant for a given molecule but may vary considerably between different electronic states. Thus, any procedure geared towards quantitative accuracy in predicting excited-state energies must in some way account for these variations. The most economical way to achieve this is to introduce a number of parameters into the model. By scaling those to a set of experimental data... 

Ethanol is both an inducer and substrate of CYP2E1. Indeed, CYP2E1 seems to be structurally geared to favor small volatile molecules such as ketones, aldehydes, alcohols, halogenated alkenes, and alkanes as substrates (36). Moreover, many of these same compounds, like ethanol, are inducers of the enzyme. A major mechanism by which this diverse group of compounds appears to initiate induction is by inhibiting normal enzyme degradation. 

It may be pertinent to mention here a recent criticism of the gear effect by methyl groups, since most of the known examples used in the study of the gear effect are in aromatic molecules. Based on dynamic NMR data on the internal rotation of the 9-methyl group in 42, which indicated a far lower barrier for 42a than for 42b, Oki... 

While it is true that microarray technology is gearing up for proteomics, it is perhaps still too early to predict what role microarrays will ultimately play. Proteins are much more complex molecules than nucleic acids and the suggestion has been made that additional tools and approaches will be needed. Microfluidic devices (electrophoresis, flow cytometry) with miniaturized detectors may also be applicable. 

This result is in general agreement with an extensive analysis of the electron scattering of multiple rotor molecules by J. Karle206, who studied the effect on the intensity and the RD-curve in cases with low barrier and geared motion. 

Two molecules presenting the same kind of torsional problems, are C(CF3)4 and Ge(CF3)4380. The C-F distance is found to be nearly the same for the two compounds, but of course the distance from the central atom to the CF3 carbon is considerably larger for the latter molecule. The C-C distance is found to be 156.2 pm, and the Ge-C distance is found to be 198.9 pm. This leads to a noticeable difference in the torsional motion of the two molecules. In C(CF3)4 the torsional barrier is estimated to be about 10 kJ/mol from the electron-diffraction study, while a CNDO/2 calculation estimated a barrier of about 3 kJ/mol. For Ge(CF3)4 the electron-diffraction data suggest free rotation. For these molecules the geared motion has not been considered as was the case for (CF3)3CH, previously discussed (p. 136). 

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