Dendrimers and Dendrons: Controlled Macromolecular Structure According to Dendritic Branching Rules and Principles

among others, this virtually universal art reached its zenith in the Celtic culture. The magnificent illuminations consisting of extremely complex interlaced designs and knots in the Book o f Kelk give evidence of the fascination that braids, wreaths and knots exert on human beings . In this famous manuscript, the work of Irish monks during the eighth century, geometrical figures were converted into marvelous representations. Later, superb interlaced designswere created by Albrecht Diirer and Leonard0 da Vinci. In relation to the graphic arts, mathematical topology and biology, the creation of knots at the molecular level (using the tools of synthetic chemists) is an especiallychallenging objective. Despite many early difficulties, our group’s results over the course of the last few years has opened the door to the preparation of knots constructed around transition-metal ion templates. Our strategyis shown in Fig. 3. Toward the goal of preparing a trefoil knot, we extended the synthetic concept that had already proved successfulin the synthesis of catenanes (i.e. interlocking ring molecular systems, Fig. 3, top). In the strategy toward a trefoil knot, we exploited the three-dimensional (3D) template effect induced by two transition metals.As shown in Fig. 3 (bottom), two molecular threads A can be interlaced on two transition metal centers (black dot), leading to a double helix B.After cyclizationto C and demetalation, a knotted system D is obtained. I will not describe here in detail the experimental work done along the strategy of Fig. 3 (bottom) for synthesizinga molecular knot. Simply, severalyears of research were necessary (performed mostly by C. Dietrich-Buchecker and myself ) in order to achieve the preparation of the first chemical trefoil knot using copper atoms as templates (black circles in Fig. 3) and relatively complicated molecular threads interlaced by coordination to the two copper centers. The chemical structure and the X-ray structure (crystallography) of the molecular knot actuallyprepared are represented in Fig. 4 (left and right, respectively). of our research team to the field of chemical topology has been to introduce new synthetic concepts based on the template effect of transition metals and allowing the intertwining of molecular strings at will before incorporating them into target molecular systems. Although classical organic chemists had In conclusion, the main contribution developed elegant synthetic procedures in the past for making interlocking rings (catenanes), the syntheses used prior to our work were tedious and low yielding. In fact, the research domain of catenanes was slowly vanishing. After we proposed efficient templated synthetic strategies (1983-1984), the research area underwent a spectacular revival, as has been testified by the many research laboratories who have joined the field in recent years and by the numerous publications on catenanes and related systems appearing regularly in scientificjournals. Our scientific contribution to topology at the molecular level culminated with the first synthesis of a chemical knot (a molecular trefoil knot, 1989) and its full characterization by X-ray crystallography (1990). Interestingly, chemical knots had been envisaged for almost 30 years before actually being made-long before biologists had demonstrated that DNA-based knots (and other interlaced or interlocking structures ) are very frequent in nature. DENDRIMERS AND DENDRONS: CONTROLLED STRUCTURE ACCORDING TO DENDRITIC BRANCHING RULES AND PRINCIPLES Donald A. Tomalia, Michigan Molecular Institute, 1910 W. St. Andrews Road, Midland, MI 48640, U.S.A. The work reported in this Abstract was awarded a I996 LVMH Vinci of Excellence Prize. It is well known that critical macromolecular design parameters (CMDPs) such as size, shape, surface chemistry, topology and flexibilityare exquisitely controlled in nature, especially in life processes. This problem was solved some 4.5 billion years ago during the course of our natural molecular evolution . Prime examples include structurecontrolled biopolymers such as proteins, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).DNA may be thought of as a one-dimensional (1D) template that transcribes molecular information through a cascade of intermediates and ultimately translates this genetic information into 1D protein sequences in the polymerization reactors (ribosomes) of various cells. The size of these proteins is determined by the length of the polypeptide MACROMOLECULAR chain; unique shapes, topologies and surfaces result from sequence-induced foldings that are directed by the side chains-of the 20 natural amino...