Stoddart Mechanostereochemistry Group

 

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fraser stoddart

 

 

 

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research chronicle

 

Contributions to Self-Assembly Processes and Molecular Nanotechnology

 

from the
SHEFFIELD | BIRMINGHAM | UCLA
days

 

2007.  In collaboration with Jim Heath at Caltech, Stoddart describes a 160,000-bit molecular electronic memory circuit based on bistable [2]rotaxane and fabricated at a density of 100,000,000,000 bits per square centimeter – that is roughly analogous to the dimensions of a DRAM circuit projected to be available in 2020. The entire 160,000-bit cross-bar, described in a letter in Nature (#775) is approximately the size of a white blood cell.

2007.  With a judicious choice of ions and solvents, it is possible to amplify a molecular Solomon link by kinetically controlled crystallization from a dynamic combinatorial library of molecular knots that includes the molecular Borromean rings. By incorporating mixed-metal ion templates into the usual protocol employed in the synthesis of the molecular Borromean rings, the Stoddart group has obtained a molecular Solomon link as the only crystalline product. Its crystal structure graces the inside front cover of Issue 1 for 2007 of Angewandte Chemie. See #773

2006.  In collaboration with the Balzani group in Bologna, the Stoddart group has described an autonomous nanomotor powered by solar energy in the Proceedings of the National Academy of Sciences (#739).  It is autonomous because it can work continuously without external interference: it is powered by an inexhaustible energy source (sunlight) and operates without consuming or generating chemical fuels or waste.  The system operates according to a four-stroke cycle which is reminiscent of an internal combustion engine in a motor car.  A full cycle is carried out in less than one thousandth of a second which means that the motor can operate at a frequency of 1000 Hertz – a speed that is equivalent, using the car engine analogy to 60,000 RPM.

2006.  The Stoddart group reports on the kinetics and thermodynamics associated with electrochemically driven molecular mechanical switching of a bistable rotaxane perched in its lower-conducting ground-state on the brink between being ON and OFF, and after writing, in its fully conducting metastable state.  The nuances of this indecisive molecular switch lend credence to the postulated mechanism of action of such switches.  Science is so beautiful!  The implications of these findings are displayed on the front cover of Issue 1 for 2006 of Chemistry – A European Journal.  See #737.

2006.  The Stoddart group describes structure control at the organic-solid interface in a review (#738) in the Journal of Materials Chemistry.  The research is highlighted on the front cover of the first issue in 2006.

2005.  The Stoddart group describes a rational design of molecular switches and sensors from a tool-kit of chemical building blocks in a review (#735) in Topics in Current Chemistry.

2005.  The Stoddart group explores dynamics and stereochemistry in mechanically interlocked compounds in a lengthy review (#731) in the Collection of Czechoslovak Chemical Communications.

2005.  In collaboration with Bjfrnholm, Goddard and Heath, the Stoddart group provides structural evidence for the mechanical switching of amphiphilic bistable rotaxanes in Langmuir monolayers at air water interfaces.  The experimental results, which are described in a communication (#732) in Angewandte Chemie, are supported by monolayer dynamics simulation: see a full paper (#725) published in the Journal of the American Chemical Society.

2005.  The design of an electronic paper display, working in conjunction with Bill Goddard, is announced by the Stoddart group in a communication (#726) in the Journal of the American Chemical Society.

2005.  In reflective mood, the Stoddart group traces, in an article published in Pure and Applied Chemistry (#722), the hurly-burly life of a scientific nomad through thick and thin from the Athens of the North to the City of Angels with brief and not so brief interludes on the edge of the Canadian Shield, in the Socialist Republic of South Yorkshire, on the plains of Cheshire beside the Wirrall, and in the Midlands in the heartland of Albion.

2005.  The Stoddart group reviews the concepts of multivalency and cooperativity in supramolecular chemistry in Accounts of Chemical Research (#721).

2005.  In collaboration with Jeff Zink, the Stoddart group reports on a reversible molecular valve using beads of mesoporous silica coated with a switchable [2]rotaxane.  This nanovalve system, which can be recycled many times, was described in an article published in the Proceedings of the National Academy of Sciences (#720).

2005.  The Stoddart group has shown that borohydride reduction of the parent Borromean linked complex containing six zinc (II) ions and 12 imine bonds results in its demetallation producing a neutral Borromean link compound and also its free macrocycle.  This intellectually satisfying proof of the chemical topology of the Borromean link compound is summarized in Chemical Communications (#719).

2005.  By employing atom labels on one of the ligand precursors, the lability of at least some of the 30 dative and 12 imine bonds stabilizing and constituting the three rings of a metallo-Borromean (Borromeate) linked compound is demonstrated by the Stoddart group in acidic methanolic solution.  The demonstration of dynamic nanoscale Borromean links is recorded in Chemical Communications (#718).

2005.  The Stoddart group announces the making of donor-acceptor pretzelenes in Angewandte Chemie (#714).  See also #727 and #733.

2005.  The Stoddart group describes the powering of the 1993 supramolecular machine with a photoactive molecular triad in the first issue of the new journal Small (#705).  See also #724.

2004.  The Stoddart group (and Heath) publish a perspective in Science (#703) entitled “Whence Molecular Electronics?’ It transpires that the metastable to ground state relaxation times of the bistable molecular switches in solution (#702) are much shorter than they are in the polymer matrix (#699) and in the ‘half-device’ by an order of magnitude.  By the same token, the relaxation times in the ‘full devices’ are longer than they are in the polymer matrices and in the ‘half-device’ by an order of magnitude.  In terms of the activation barriers to get from the metastable back to the ground state, a value of around 16 kcal/mol in the polymer matrices and ‘half-device’ and finally up to around 22 kcal/mol in the ‘full-device’ have been noted.  The metastable state of a switch in a ‘full-device’ decays back to the ground state during a period of 10-60 minutes.

2004.  The Stoddart group describes in Applied Physics Letters (#697) the use of a donor-acceptor doubly bistable, palindromic [3]rotaxane, tethered through its two rings to gold-coated cantilevers in a series of experiments that demonstrate the transduction of chemical into mechanical energy.  For a detailed description of these linear artificial molecular muscles, see the full paper in the Journal of the American Chemical Society (#723).

2004.  The Stoddart group demonstrates that the relative mechanical movements between the components of bistable switchable catenanes and rotaxanes can be stimulated (i) chemically in condensed phases, e.g., Langmuir films and Langmuir-Blodgett monolayers (#686, #697, #711, and #725) and (ii) electrochemically in a highly viscous polymer matrix (#699), as well as (iii) electrochemically in a ‘half-device’ as a self-assembled monolayer on gold (#671 and #709) and (iv) electronically in a ‘full device’ within solid-state molecular switch tunnel junctions (#582, #618, and #631).

2004.  In collaboration with Jeremy Sanders, the Stoddart group describes the template-directed synthesis of some neutral bistable rotaxanes in a communication in the Journal of the American Chemical Society (#689).  Their switching behavior is discussed in the subsequent full paper published in Chemistry – A European Journal.  See #701.

2004.  The total synthesis of molecular Borromean rings employing dynamic covalent chemistry (DCC) is reported in an article in Science (#683).  It represents the highest level of sophistication so far achieved in synthesis by templation methods in the Stoddart laboratories.  Guided by intuition and an appropriate amount of molecular modeling, the Stoddart group combines the equilibrium-based methods of imine formation with the templation power of zinc (II) to effect a one-step total synthesis of a molecular Borromean link in over 90% yield for 18 precursors.  The strategy uses a set of six endo- and six exo-oriented ligands designed to form an oriented trigonal bipyramidal unit around the zinc ions, six of which are incorporated into the Borromean link topology.  In a recent review, Daryle Busch, the “father’ of templation in chemistry has commented – “The achievement was remarkable in a number of ways. It involved what is probably the most complicated template in the chemical literature, based on six zinc(II) ions and both convergent (or endo-directed) and divergent (or exo-directed) molecular turns. In contrast to the overall complexity of the templating system, the reactants were relatively simple. The divergent component was a dipyridyl while the convergent component was an a,a'-diiminopyridyl unit formed by a thermodynamic, or equilibrium, templating process. Top of the outstanding characteristics of the template is the fact that it involves both kinetic and thermodynamic template components, a combination that should become common. Both of these distinctive template types were used in their fully modern contexts. The combination is extremely powerful; the components of the kinetic template hold the subjugated components in place while the thermodynamic components find their final disposition at equilibrium. In the classic equilibrium template the reactants form their normal distribution of products and the anchoring/selecting factor (often a metal ion) selects the product that binds best, combines with it and shifts the equilibrium accordingly.  Only the authors know the extent to which alternative components were selected and rejected in failure, but their final choices contain still another special feature.  The choice of zinc as the template anchor provided a second opportunity for flexibility in the reacting system because zinc, being a spherical ion, is adaptable when it comes to coordination numbers and coordination geometries. So, this template system allowed the chemistry to determine critical features both in the Schiff base reaction steps and in the basic stereochemistry of the metal ion anchor. Further, the yield in this scientific triumph was 90%. The success over the enormous challenge of synthesizing the molecular embodiment of the Borromean link suggests that the science of using the molecular template has reached a level of maturity from which scientists may be expected to produce new molecular entanglements and interlocked structures of profound significance, despite the equally profound challenges they represent.”The all-in-one synthetic strategy (#729) for the making of nanoscale Borromean links combines (#707) all the virtues of reversibility, proof reading, and error checking that we associate with DCC (#623), together with the geometrical guidance and precision we entrust to coordination chemistry.  It is the template-directed protocol (#629 and #717), working in chemical synthesis with such a vengeance, that tells us that much more is possible. The making of the Borromean links by supramolecular assistance to covalent synthesis (#454) heralds the beginning of a new era in topological chemistry.

2004.  The Stoddart group, in collaboration with Vincenzo Balzani, describes the design, construction and operation of a molecular elevator, operated by changing pH, in an article in Science (#676).  This mechanically interlocked molecule represents one of the most complex artificial molecular machines described in the literature to date.  See also #726.

2004.  The Stoddart group, in collaboration with Jeff Zink, reports an operational supramolecular nanovalve in a communication published in the Journal of the American Chemical Society (#675).  It is operated by redox chemistry and is based on the attachment of the supramolecular machine described back in 1993 to beads of mesoporous silica.

2004.  The metastable co-conformation (MSCC) of a bistable [2]rotaxane monolayer self-assembled onto a gold electrode is identified electrochemically by the Stoddart group.  In an article published in ChemPhysChem (#671), an activation barrier of just under 18 kcal/mol is obtained for the spontaneous decay of the MSCC back to the ground-state co-conformation (GSCC) as a result of performing many experiments at different scan rates and temperatures.  This research on a ‘half-device’ represents a compelling vindication of the proposed electromechanical switching mechanism between the MSCC and the GSCC in the self-assembled monolayer SAM of a surface-bond bistable [2]rotaxane.

2003.  A semiconducting single-walled carbon nanotube (SWNT) based molecular switch tunnel junction (MSTJ) is shown by the Stoddart group, in an article published in ChemPhysChem (#668), to sustain a remnant molecular signature arising from within a bistable [2]catenane containing diazapyrenium units that are believed to complex to the sides of SWNTs.

2003.  The concepts of displaying lactosides in a multivalent fashion by tethering them to cyclodextrins that are threaded onto polymer chains is announced by the Stoddart group in Organic Letters (#665).  These self-assembled multivalent pseudopolyrotaxanes show considerably enhanced binding for galectin-1.

2003.  The Stoddart group discovers that a collection of donor-acceptor [2]catenanes containing elements of axial, planar and helical chiralties, exhibit a keen selectivity for just one of up to eight diastereoisomers.  The research is described in a full paper in Chemistry – A European Journal.  See also #656 and #704.

2002.  The Stoddart group reports solubilization of single-walled carbon nanotubes (SWNTs) in an aqueous solution of the starch-iodine complex.  These starched carbon nanotubes are a result of a ‘disproportionation reaction’ in which amylose in a helical conformation wraps itself around the SWNTs.  The communication, reported in Angewandte Chemie (#634) and already cited 100 times, acts as an incentive to other scientists to use carbohydrates, proteins and nucleic acids to bind SWNTs in aqueous media, thus integrating an important nanoscopic material with the world of biology.  See also #687.

2002.  The Stoddart group describes two-dimensional molecular electronic circuits based on amphiphilic bistable [2]rotaxanes in an article (#631) published in ChemPhysChem and already cited over 130 times.  This piece of research has been extended as far as the realization of a 64 K-bit memory with a density of 1011 bits per square centimeter which corresponds to 2028 on the semiconductor roadmap.

2002.  An Angewandte Chemie review (#623) on ‘Dynamic Covalent Chemistry’ is published and is cited over 150 times.  This review gives substance to the rapidly growing importance of thermodynamic control in the chemical synthesis of unnatural products.

2002.  As part of a long-standing interest in making the molecular counterpart of the Borromean links, the Stoddart group reports a ring-in-ring complex in Angewandte Chemie (#622).

2001.  In collaboration with Jeff Zink, the Stoddart group describes in Angewandte Chemie (#610) working supramolecular machines trapped in glass and mounted on a film surface.  This work is important in as far as it shows, qualitatively at least that mechanical motion, observed in a [2]pseudorotaxane in solution (#305), is actually carried over into condensed phases and also remains true to form at interfaces.  From the point of view of harnessing the potential of artificial molecular machines in devices, this is an important observation.

2001.  The Stoddart group reports in Angewandte Chemie (#599) the preparation and properties of single-walled carbon nanotubes wrapped with conducting polymers.  This communication is cited almost 200 times.  See also #624, #635, and #651.

2001.  The extremely efficient (near quantitative) template-directed synthesis of a [2]rotaxane by clipping under thermodynamic control of a crown ether-like macrocycle incorporating two imine bonds around a dialkylammonium ion center is described (#604; see also #661).  This observation is used subsequently to make multiply mechanically interlocked molecules under thermodynamic control (#713 and #716).

2000.  The Stoddart group reports the template-directed synthesis of the first of several generations of amphiphilic bistable [2]rotaxanes incorporating tetrathiafulvalene and dioxynaphthalene recognition sites for the cyclobis(paraquat-p-phenylene) ring (#590; see also #598, #603, #627, #659, #662).  Many of these amphiphilic bistable [2]rotaxanes are subsequently incorporated into crossbar memory devices and also become the focus of in-depth quantitative studies (kinetic and thermodynamic) in condensed phases as well as in solutions. Vide infra.

2000.  The Stoddart group describes the first-steps towards synthesizing mechanically interlocked molecules beyond catenanes and rotaxanes (#583).  In, as yet, unpublished work, interlocked molecules, for which Stoddart has coined the name suitanes, have been synthesized by a combination of templation and dynamic covalent chemistry that relies on the formation of multiple imine bonds, cf. #580 where the formation of dynamic hemicarcerands and hemicarceplexes involving multiple imine bond formation is described.

2000.  In collaboration with Jim Heath, the Stoddart group reports a bistable [2]catenane-based solid-state electronically reconfigurable switch in Science (#582).  The article, which presents the experimental evidence of an electromechanical mechanism of switching by the bistable [2]catenanes molecules between open (OFF) and closed (ON) states that are, respectively, of lower (ground-state) and higher (metastable-state) conductivities, is cited almost 400 times.  See also #601, #604, #606, and #618.  The proposed mechanism is subsequently supported by first-principles modeling of the switching in the device by the Goddard Group at Caltech.  See Phys. Rev. Lett. 2005, 94, 156-801.

2000.  The Stoddart group reports an extremely stable interwoven supramolecular bundle (#570) formed between a tris-crown ether and a tris-ammonium trication.  On further elaboration (#674, #678, and #685), the concepts of multivalency and cooperativity in binding are exposed and discussed subsequently in a review (#721) on ‘Multivalency and Cooperativity in Supramolecular Chemistry’ published in Accounts of Chemical Research.

2000. The post-assembly covalent modification of triphenylphosphonium-stoppered [2]rotaxanes using the Wittig reaction allows surrogate stoppers to be exchanged in [2]rotaxanes (#560; see also #566 and #640).  This rare example of the subsequent chemical modification of rotaxanes makes possible the highly controlled synthesis of higher order rotaxanes, molecular shuttles, dendritic rotaxanes, and polyrotaxanes.

2000.  The Stoddart group reports a strategy in Langmuir for molecular information storage materials by introducing [2]catenanes into Langmuir monolayers and Langmuir-Blodgett films (#555).  This piece of research anticipated the need to self-assemble molecular switches on solid substrates (electrodes) and becomes increasingly important in the subsequent fabrication of crossbar devices.  See also #581.

1999.  Both hydrogen-bond based and donor-acceptor rotaxanes are formed under thermodynamic control using imine formation and exchange in relation to functional groups present in their dumbbell components (#552 and #553).

1999.  By employing amphiphilic molecules (rotaxanes and dumbbells) containing bipyridinium units, electronically configurable molecular-based logic gates were constructed in collaboration with Jim Heath.  This Science article has been cited almost 500 times.  See also #575.

1999.  The template-directed synthesis of the first rotacatenane is reported (#539).

1998.  The Stoddart group reports the self-assembly of supramolecular daisy chains in Angewandte Chemie (#484 and #499; see also #613).  This first publication, relating to this particular recognition motif, is cited more than 70 times.

1998.  A chemically and electrochemically switchable [2]catenane incorporating tetrathiafulvalene and dioxynaphthalene units is reported in Angewandte Chemie (#472; see also #563).  This approximately one nanometer cube switch is subsequently employed in solid-state devices as a molecular switch.

1997.  The template-directed synthesis of the first donor-acceptor molecular trefoil knot is reported by the Stoddart group (#463).

1997.  A review on synthetic supramolecular chemistry appears in Accounts of Chemical Research (#454) and is subsequently cited over 270 times.

1997.  The Stoddart group announces the template-directed synthesis of an acid-base switchable [2]rotaxane (#453) which is employed subsequently to construct a nanoscale elevator (#676; see also #726).  This research describes the first quantitatively switchable rotaxane based on orthogonal recognition motifs – namely, hydrogen bonding and donor-acceptor interactions.

1996.  As a result of a collaboration with Helmut Ringsdorf, the Stoddart group describes the first Langmuir monolayers and Langmuir Blodgett multilayers incorporating mechanically threaded molecules (#417).

1996.  The Stoddart group describes his first synthesis of carbohydrate containing dendrimers (#403; see also #429, #435, #441, #488, #496, #504, #578, #595, #632, #638, #639, #664, #665, and #690).  This research represents yet another set of remarkable feats in chemical synthesis by the Stoddart group.  It has been exploited subsequently in the context of carbohydrate recognition in biological systems and has led to some fundamental questions being asked about the nature of cooperativity and multivalency.  See also #685 and #721.

1996.  The first cyclo-oligomerizations of disaccharides which crystallize to form carbohydrate nanotubes are announced (#381; see also #442, #444, #449, #488, and #497).  This research represents a remarkable feat in chemical synthesis by the Stoddart group.  It awaits development and exploitation.

1996.  Numerous articles describing the prototypes of molecular machines, switches and devices in solution are published (#379 and #380; see also #426, #464, #500, #509, #519, #522, #533, #569, #587, #588, #614, #625, #643, and #653).  In this remarkable series of publications, many of them carrying the name of Vincenzo Balzani as a co-author, the Stoddart group introduces the concept of molecular machinery in the context of the relative movements, both circumrotational and linear, undergone by the component parts of bistable catenanes and rotaxanes when stimulated either (i) chemically (e.g., pH change), (ii) electrochemically, or (iii) photochemically.  In so doing, he gives the concept of translational isomerism, introduced by Schill, real practical expression and finds it necessary to introduce the term co-conformation (and co-conformer) to describe the relative movements of the components in interlocked molecules.  This substantial body of research identifies Stoddart as one of the very first chemists to see the potential applications for mechanically interlocked molecules.  Essentially, he recognizes their importance in addressing memory and logic in molecular electronics, as well as the central role they can play in the fabrication of nanoelectromechanical systems (NEMS).

1996.  The Stoddart group writes an authoritive review which receives over 260 citations, on self-assembly in natural and unnatural systems for Angewandte Chemie (#383).

1995.  The Stoddart group publishes a review of interlocked and intertwined structures in Chemical Reviews (#365) which is cited over 720 times during the following decade.  Presently, it is the Stoddart’ group's most highly cited publication.

1995.  The Stoddart group describes the forerunners to a new family of interlocked molecules templated by the hydrogen bonding of dialkylammonium ions within crown ether macrocycles containing at least 24 ring atoms (#355 and #356; see also #392, #523, and #592).  This discovery – which is made coincidentally at around the same time by Daryle Busch in Kansas – leads to a blossoming of research on catenanes and rotaxanes (also polyrotaxanes) in many laboratories around the world, employing this easy-to-use recognition motif.

1995.  The Stoddart group reports the first branched [n]rotaxanes (#343) and bis[2]catenanes (#347), respectively the building blocks for dendrimers and mechanically linked polymer chains (#356; see also #368).

1994.  The synthesis of the [5]catenane, olympiadane, which can be achieved in two successive template-directed steps via a [3]catenane intermediate, is reported with full characterization, including a solid-state structure, in Angewandte Chemie by the Stoddart group (#323; see also #314, #460, and #485).  This synthesis is epoch-making as well as symbolic.  The very fact that these compounds can be made in good quantities demonstrates the remarkable power of supramolecular assistance to covalent synthesis in the making of mechanical bonds.  Between them, these four articles are cited more than 220 times.

1994.  The first chemically and electrochemically switchable [2]rotaxane is described in Nature by the Stoddart group and Kaifer (see #322).  This article, which is cited nearly 400 times, marks the beginning of research into bistable rotaxanes (and catenanes) as molecular switches and motors, using a range of different structural types including the metal-based rotaxanes and catenanes (catenates) reported earlier by Sauvage.

1994.  The template-directed synthesis of the first optically-active donor-acceptor catenane is described by the Stoddart group (#319).

1993.  The Stoddart group, in collaboration with Balzani, describes the first photochemically driven supramolecular machine in Angewandte Chemie (#305; see also #473).  This particular supramolecular machine becomes a favorite one to probe the movements of components of molecular machinery in condensed phases.  This communication is cited over 140 times.

1993.  The control of translational isomerism in non-degenerate donor-acceptor [2]catenanes is discussed by the Stoddart group for the first time in a full paper published in the New Journal of Chemistry (#306; see also #304, #311, #329, and #340).

1993.  The practice of slippage is popularized by the Stoddart group as an alternative method to clipping or threading-followed-by-stoppering for the self-assembly of rotaxanes under thermodynamic control (#301 and #302; see also #478, #495, #506, and #589).  The procedure allows many rotaxanes to be accessed that would otherwise be difficult to synthesize: it finds wide applicability in many other research laboratories.

1993.  The first template-directed synthesis of catenated cyclodextrins is announced in Angewandte Chemie (#293; see also #341).  Since the first reported (and failed) attempt in the literature to make a [2]catenane away back in 1958 involved a cyclodextrin as one of the two interlocked rings, this research is of considerable historical significance.

1992.  In a series of three back-to-back communications (#278, #279, and #280) published in Synlett, the design and synthesis of the first non-degenerate molecular shuttles are described by the Stoddart group.  They are the forerunners to the first molecular switch based on a bistable [2]rotaxane published two years later.

1992.  The Stoddart group publishes the first (#264) of a long series of full papers on “Molecular Meccano” in the Journal of the American Chemical Society and also discusses, in Chemistry in Australia, the prospect of ‘Whither and Thither Molecular Machines’ for the first time in the context of mechanically interlocked molecules.  This series of scholarly papers does much to establish the nature of the mechanical bond in chemistry.  The first full paper in the series is cited over 500 times.

1991.  The Stoddart group coins the term [2]pseudorotaxane (#247 and #253) to describe the self-assembly of the ring and rod components that precede either catenation or the formation of a rotaxane (see also #260 and #261).

1991.  The use of molecular recognition, self-assembly, and template-directed synthesis in the making of mechanically interlocked molecular compounds is outlined by the Stoddart Group in a review (#250) and two communications (#251 and #252) published in Synlett.  The review is cited over 240 times.

1991.  The first degenerate donor-acceptor [2]rotaxane – dubbed a molecular shuttle by the Stoddart –group is described in a communication (#249) in the Journal of the American Chemical Society.  This publication marks the beginning of the development of artificial linear molecular motors based on the [2]rotaxane constitution.  It captures the imaginations of many other researchers, stimulating an enormous amount of activity along conceptually similar lines in countless other research laboratories around the world.  It is illustrated and discussed at length in the Fourth Edition of Jerry March’s Advanced Organic Chemistry published in 1992.  The advent of the molecular shuttle opens up the possibility of constructing controllable molecular switches that can be employed as memory and logic in electronic devices.  There is every reason to believe that these molecular switches will have a profound impact on the new communications-based technologies of the next few decades.  The communication is cited over 210 times.

1991.  The Stoddart group announces the synthesis and characterization of the per-3,6-anhydrocyclodextrins (#240; see also #262) as receptors for cationic substrates in organic solvents.

1989.  In a seminal contribution published in Angewandte Chemie (#218), the Stoddart group announces the template-directed synthesis, under kinetic control, of a degenerate donor-acceptor [2]catenane in an impressive 70% yield.  The work describes the prototype for the subsequent design and development of bistable molecular switches.  Also, as the first all-organic catenane to be made in gram quantities, it opens up the search for more examples, e.g., the Hunter-Vögtle-Leigh amide-based catenanes (and rotaxanes) where hydrogen bonding is the molecular recognition motif that is exploited.  This class of mechanically interlocked molecular compounds is now being studied in a highly creative manner by David Leigh in Edinburgh.  The communication is cited over 180 times.

1988.  The Stoddart group reports, in two back-to-back Angewandte Chemie communications (#201 and #202), the synthesis of cyclobis(paraquat-p-phenylene), a tetracationic cyclophane which subsequently gains notoriety as ‘the little blue box’ because of its voracious appetite to complex with π-electron rich guests (see also #248, #259, and #413).  This one compound is to dominate research in the Stoddart group right up to the present day and undoubtedly beyond into the future!  The two communications are cited over 250 times.

1987.  The Stoddart group announces the structure-directed synthesis of molecular belts and collars in Angewandte Chemie using tandem Diels-Alder reactions (#169; see also #196, #214, #215, #216, #289, and #291), leading to the development of the concept of ‘Molecular Lego’ (#203; see also #271, #284, #287, and #298).

1987.  A series of six back-to-back communications is published in Chemical Communications, describing the complexation of paraquat (and diquat) by bisparaphenylene[34]crown-10.  This work is important since it demonstrates for the first time that organic dications can be threaded through crown ethers: the stage is now set from here on to develop the chemistry of the mechanical bond in all-organic systems based on the self-assembly of donor macrocycles and threaded acceptor dications (#160, #161, #162, #163, #164, and #165).  The fourth of the six communications, which points the way forward to the first synthesis of the first (degenerate) donor-acceptor [2]catenane, is reported (#218) in Angewandte Chemie two years later and is cited over 125 times.

1986.  A seminal review on second-sphere coordination, which has been highly cited, is published in Angewandte Chemie (#151; for subsequent reviews, see #200 and #406).  At this stage, the Stoddart group essentially leaves the field after five years for other researchers to develop further.  The review is cited over 200 times.

1985.  The isolation of an adduct between the anti-cancer drug cisplatin and [18]crown-6 is described (#129) and the concept of second-sphere coordination is extended to the use of cyclodextrins as second sphere ligands for transition metal ammines including the anti-cancer drug carboplatin (#139, #140, and #141; see also #221).  The work becomes the subject of a patent with Johnson-Matthey who supports the research at Sheffield.

1983.  Donor-acceptor interactions are extended beyond second-sphere coordination to their complex formation between dibenzo crown ethers and the diquat dication in a seminal paper published in Chemical Communications (#111; see also #131 and #136).  This communication draws attention to the importance of [C–H···O] interactions, in addition to the donor-acceptor interactions, in stabilizing 1:1 complexes of this type.

1981.  The Stoddart group describes the use of donor-acceptor interactions between a cationic platinum complex carrying a bipyridyl ligand and dibenzo[30]crown-10 in a seminal communication published in Angewandte Chemie (#94, see also #130, #184, and #212).  The X-ray crystal structure solved by David Williams at Imperial College graces the front cover of the journal and heralds the beginning of the establishment of self-assembly processes for making donor-acceptor complexes.

1981.  The Stoddart group reports on the investigation of the second-sphere coordination of neutral and cationic transition metal ammines by crown ethers (#90, #91, #92, and #93; see also #109 and #152).  This research represents the first really successful attempt to illustrate a phenomenon about which Werner had speculated over half a century ago.

1979.  The Stoddart group writes a much-cited review "From Carbohydrate to Enzyme Analogues" for Chemical Society Reviews (#73).  This article, which coincides with Stoddart's leaving Sheffield for the first time to join the Imperial Chemical Industries (ICI) Corporate Laboratory, marks the end of an era where the research goals had included supramolecular catalysis.  It is cited over 180 times.

1979.  The Stoddart group describes the complexation of primary alkylammonium salts by asymmetric [18]crown-6 derivatives incorporating the 4,6-O-benzylidene unit in some methyl D-glycopyranosides for the first time (#67, #68, and #69).  This research line is subsequently pursued vigorously by researchers in Eastern Europe and Japan.

1977.  The complexation of secondary dialkylammonium salts by 1,7-diaza[12]crown-4 is reported (#58).  Some 18 years later many of the same salts are found to thread through [24]crown-8 derivatives.  See #354.

1975.  The chiral recognition by configurationally chiral cryptands synthesized from carbohydrate precursors is described (#40 and #41).

1974.  The Stoddart group describes the first synthesis of macrobicyclic polyethers with carbon bridgeheads (#30; see also #52).

1969.  Stoddart describes the synthesis and characterization of medium and large heterocyclic rings from cyclic carbohydrate precursors (#11 and #17).

   

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