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The advent of conformational analysis, or the study of [[Conformational isomerism|conformer]]s to analyze complex chemical structures, in the 1950s gave rise to the idea of understanding and controlling relative motion within molecular components for further applications. This led to the design of "proto-molecular machines" featuring conformational changes such as cog-wheeling of the aromatic rings in [[triptycene]]s.<ref name="kay2015">{{cite journal |last1=Kay |first1=E. R. |last2=Leigh |first2=D. A. |title=Rise of the molecular machines |journal=Angewandte Chemie International Edition |date=2015 |volume=54 |issue=35 |pages=10080–10088 |doi=10.1002/anie.201503375}}</ref> By 1980, scientists could achieve desired conformations using external stimuli and utilize this for different applications. A major example is the design of a photoresponsive [[crown ether]] containing an [[azobenzene]] unit, which could switch between ''[[Cis–trans isomerism|cis]]'' and ''trans'' isomers on exposure to light and hence tune the cation-binding properties of the ether.<ref>{{cite journal |last1=Shinkai |first1=S. |last2=Nakaji |first2=T. |last3=Nishida |first3=Y. |last4=Ogawa |first4=T. |last5=Manabe |first5=O. |title=Photoresponsive crown ethers. 1. Cis-trans isomerism of azobenzene as a tool to enforce conformational changes of crown ethers and polymers |journal=Journal of the American Chemical Society |date=1980 |volume=102 |issue=18 |pages=5860–5865 |doi=10.1021/ja00538a026}}</ref> In his seminal 1959 lecture ''[[There's Plenty of Room at the Bottom]]'',
Though these events served as inspiration for the field, the actual breakthrough in practical approaches to synthesize artificial molecular machines took place in 1991 with the invention of a "molecular shuttle" by [[Fraser Stoddart|Sir Fraser Stoddart]].<ref>{{cite journal |last1=Anelli |first1=P. L. |last2=Spencer |first2=N. |last3=Stoddart |first3=J. F. |title=A molecular shuttle |journal=Journal of the American Chemical Society |date=1991 |volume=113 |issue=13 |pages=5131–5133 |doi=10.1021/ja00013a096}}</ref> Building upon the assembly of mechanically linked molecules such as [[catenane]]s and [[rotaxane]]s as developed by [[Jean-Pierre Sauvage]] in the early 1980s,<ref>{{cite journal |last1=Dietrich-Buchecker |first1=C. O. |last2=Sauvage |first2=J. P. |last3=Kintzinger |first3=J. P. |title=Une nouvelle famille de molecules : les metallo-catenanes |journal=Tetrahedron Letters |date=1983 |volume=24 |issue=46 |pages=5095–5098 |doi=10.1016/S0040-4039(00)94050-4 |trans-title=A new family of molecules: metallo-catenanes |language=French}}</ref><ref>{{cite journal |last1=Dietrich-Buchecker |first1=C. O. |last2=Sauvage |first2=J. P. |last3=Kern |first3=J. M. |title=Templated synthesis of interlocked macrocyclic ligands: the catenands |journal=Journal of the American Chemical Society |date=May 1984 |volume=106 |issue=10 |pages=3043–3045 |doi=10.1021/ja00322a055}}</ref> this shuttle features a rotaxane with a ring that can move across an "axle" between two ends or possible binding sites ([[hydroquinone]] units). This design realized the well-defined motion of a molecular unit across the length of the molecule for the first time.<ref name=kay2015/> In 1994, an improved design allowed control over the motion of the ring by [[pH]] variation or [[electrochemistry|electrochemical]] methods, making it the first example of an artificial molecular machine. Here the two binding sites are a [[benzidine]] and a [[biphenol]] unit; the cationic ring typically prefers staying over the benzidine ring, but moves over to the biphenol group when the benzidine gets protonated at low pH or if it gets electrochemically oxidized.<ref>{{cite journal |last1=Bissell |first1=R. A |last2=Córdova |first2=E. |last3=Kaifer |first3=A. E. |last4=Stoddart |first4=J. F. |title=A chemically and electrochemically switchable molecular shuttle |journal=Nature |date=1994 |volume=369 |issue=6476 |pages=133–137 |doi=10.1038/369133a0}}</ref>
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