Synthesis of Rotaxanes by Brief Melting of Wheel and Axle Components

Abstract

COMMUNICATIONS out in the same way. but without the addition of enzyme. Oxidation of amines: 2-, 3-, or 4-chloroaniline (78 FM), H,O, (44.4 p~) , and 1 M sodium acetate buffer (pH 4.5) The reaction was started by the addition of 0.5 u (determined by the monochlorodimedone assay) CPO-P or CPO-T to 1 mL of the mixture. The reaction was carried out at 30 C (3-chloroaniline: 30 min; 2.. 4-chloroaniiine. 50 min). The products were identified by HPLC-coinjection. O.Yidrriion.s wirh peruci'iii' u c i d Under identical experimental conditions, peracetic acid was used instead of H, O, enzyme. (200 pnol CH,CO,H instead of 150 Fmol H,O,). In the monochlorodimedone assay, peracetic acid was used in a concentration of 72 p~ (instead of 7200 p~ H,O,).'iiiutii irm~forinutioii ofperacetic acid hy mass spectrometry: sectorfield mass spectrometer Jeol JMS-700 MS, high-resolution CI-MS with isobutane as reactant gas. positile ion mode, resolution R = 8000. accumulation of 5-10 scans of the accelerating voltage (m/r 56-90,s s per cycle), quasi-molecular ion [ M + HIi (calcd. for C,H,O, 77.0239, found: 77.0261), internal mass calibration with ions derived from isobutane and the solvent. Aliquots (2.5 mL) of a 37 mM solution of peracetic acid in 1 M \odium acetate buffer (pH 5.5) were a) incubated with 5.5 mg (ca. 50 u) CPO-T for 10 min at room temperature (RT). b) incubated with 5.5 mg trypsin for 1 h at RT. or c) kept at RT without the addition of enzyme. The solutions were then acidified with H,SO, to pH 1 and extracted with ether (1 mL). The extracts were concentrated to approximately 50 pL in a stream of N, and introduced into the mass spectrometer through the reference inlet. Whereas peracetic acid was clearly present in approximately the same concentration in experiments (b) and ( c ) , no peracetic acid could be detected by MS in the extract from (a). Furthermore. whereas the pungent smell of peracetic acid persisted in the experiments (h) and (c). this typical odor vanished immediately after the addition of enzyme in experiment (a) Hydrolow uriiviti f t~~~~i c u l~. i p e r~~n e n / .~~.The enzymes were added to a solution of 0.1 pmol p-nitrophenylacetate in 2.0 mL 1 M sodium acetate buffer (pH 5.5) and 10 pL trri-but$ alcohol. The reaction was followed by the decrease of extinction at i = 317 nm. Inliihifion rrperinimr.\' In a typical experiment, 0.04 u CPO-T (determined by the rnonochlorodimedone assay) in 500 pL of water or sodium acetate buffer (pH 5.5, various concentrations) were incubated with a solution of PMSF (4 pmol) in tertbutyl alcohol (20 wL) at 50 C. The remaining enzymatic activity was determined at various incubation times as described above.

Squaring cooperative binding circles

“…V2 has a di-tertbutylphenyl moiety attached to one side that cannot be traversed by Zn1 and a cyclohexyl moiety attached to the other side, which can be passed over via a slippage (26)(27)(28)(29) process. The kinetics of this complex formation can be monitored accurately with the help of fluorescence spectroscopy.…”

“…1). These compounds also affect the kinetics of pseudorotaxane formation [slippage (26)(27)(28)(29) experiments] between Zn1 and a stopper functionalized viologen derivative. The present study aims at providing a simple and efficient procedure for deriving cooperative binding effects from experimentally obtained kinetic and thermodynamic data to be used as a guide in other artificial and natural cooperative binding systems.…”

Templated Synthesis of Interlocked Molecules

“…The free energy of activation was observed to increase upon reducing the size of the cavity of the macrocycle and/or enlarging the bulk of the stoppers. Rotaxanes have also been synthesized [146][147][148] by slippage using other well-known recognition motifs. For example [146], the interaction of secondary dialkylammonium ions with commercially available dibenzo [24]crown-8.…”

“…For example [146], the interaction of secondary dialkylammonium ions with commercially available dibenzo [24]crown-8. In 1997, Vögtle [148] reported the synthesis of the first amide-type rotaxane using the slippage approach. The rotaxane-like structure was achieved by briefly melting the macrocycle and dumbbell components together in order to overcome the high energy of activation for the slippage process.…”

“…This approach has led to the preparation of rotaxanes by either threading-followedby-stoppering [152,[182][183][184] or slippage [135][136][137][138][139][140][141][142][143][144][145][146][147][148] protocols. However, in 2001, the Stoddart group [185] reported a simple and highly effective dynamic procedure (Scheme 10) for the formation of a [2]rotaxane by the clipping of a diamine with a dialdehyde, as the precursor components of a [24]crown-8-like macrocycle, around a dialkylammonium center that also acts as a template.…”