Nanoscale molecular rotors that can be driven in the solid state have been realized in Cs2([18]crown-6)3[Ni(dmit)2]2 crystals. To provide interactions between the molecular motion of the rotor and the electronic system, [Ni(dmit)2]- ions, which bear one S=1/2 spin on each molecule, were introduced into the crystal. Rotation of the [18]crown-6 molecules within a Cs2([18]crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2]- ions and molecular rotation. Furthermore, braking of the molecular rotation within the crystal was achieved by the application of hydrostatic pressure.
Pitrilysin from Escherichia coli was overproduced, purified, and analyzed for enzymatic activity using 14 peptides as a substrate. Pitrilysin cleaved all the peptides, except for two of the smallest, at a limited number of sites, but showed little amino acid specificity. It cleaved -endorphin (-EP) most effectively, with a K m value of 0.36 M and a k cat value of 750 min À1 . -EP consists of 31 residues and was predominantly cleaved by the enzyme at Lys 19 -Asn 20 . Kinetic analyses using a series of -EP derivatives with N and/or C-terminal truncations and with amino acid substitutions revealed that three hydrophobic residues (Leu 14 , Val 15 , and Leu 17 ) and the region 22-26 in -EP are responsible for high-affinity recognition by the enzyme. These two regions are located on the N-and C-terminal sides of the cleavage site in -EP, suggesting that the substrate binding pocket of pitrilysin spans its catalytic site.
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