ISMSC 2007 - Università degli Studi di Pavia

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Carbon Dioxide and Supramolecular Chemistry Dmitry M. Rudkevich Department of Chemistry & Biochemistry, The University of Texas at Arlington, Arlington, TX 76019-0065, USA Carbon dioxide (CO2) is the major greenhouse gas. It constantly circulates in the environment through a variety of processes known as the carbon cycle. Extensive CO2 circulation in the atmosphere, industry and agriculture requires not only its systematic monitoring under a variety of conditions, but more importantly, necessitates the development of improved methods of the CO2 fixation and chemical utilization. We employ methods and techniques of supramolecular chemistry for these purposes. In particular, we explore the dynamic covalent chemistry between CO2 and primary amines. [1] Our progress will be highlighted in the following directions: 1. Switchable supramolecular polymers and peptide-based nanoscale architectures from CO2 and their further functionalization. [2,3] 2. Reversibly formed carbamate materials for selective entrapment, separation and storage of guest ions and molecules of biological and industrial interest. [4,5] 3. Supramolecular sensors for CO2 and its toxic derivatives. [6,7] [1] D. M. Rudkevich and H. Xu, Chem. Commun., 2005, 2651-2659 (review). [2] V. Stastny, A. Anderson and D. M. Rudkevich, J. Org. Chem., 2006, 71, 8696-8705. [3] H. Xu and D. M. Rudkevich, Chem. Eur. J., 2004, 10, 5432-5442. [4] V. Stastny and D. M. Rudkevich, J. Am. Chem. Soc., 2007, 129, 1018-1019. [5] H. Xu and D. M. Rudkevich, Org. Lett., 2005, 7, 3223-3226. [6] E. M. Hampe and D. M. Rudkevich, Tetrahedron, 2003, 59, 9619-9625. [7] H. Zhang and D. M. Rudkevich, Chem. Commun., 2007, 1238-1239. IL 1 Mechanistic Aspects of Threading of Polymers in Processive Rotaxane Catalysts Ruud G.E. Coumans, Pilar Hidalgo Ramos, Alexander B.C. Deutman, Johannes A.A.W. Elemans, Roeland J.M. Nolte, Alan E. Rowan Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands. Email: A.Rowan@science.ru.nl IL 2 Natural processive enzymes, such as -exonuclease or DNA polymerase III, operate by threading a DNA strand in a pseudo-rotaxane topology and subsequently slide along the chain performing several rounds of catalysis before they dissociate. 1 These highly efficient biocatalysts have inspired us to develop the first example of a synthetic processive rotaxane catalyst: 2 manganese porphyrin-containing macrocycle was threaded onto a polybutadiene strand and mimicked the catalytic action of a natural processive enzyme by catalyzing the epoxidation of the double bonds of the polymer while sliding along its chain. In order to investigate this threading in more detail a series mono functionalized polymers was synthesized which contain a blocking N,N’-dialkyl-4,4’-bipyridinium trap at one side of the polymer chain and an open end at the other side. 3 The macrocycles are unable to slip over the blocking group and therefore they have to traverse the whole polymer chain before they reach the bipyridine trap which quenches the fluorescence of the macrocycle. Fluorescence emission studies revealed that the kinetics of threading followed a second order process and that the rate of threading was found to dependent on the polymer length with a length-dependent barrier of 61 J/nm which increase to 93 J/nm when a larger more flexible macrocycle was used. The thermodynamics of threading revealed that for all polymers H ‡ on was positive and S ‡ on strongly negative with the absolute value of S ‡ on increasing with polymer length. These results are supportive of the nucleation mechanism proposed by Muthukumar, 4 resembling the transportation of DNA through the opening in a virus particle. These studies have provided direct evidence that macrocyclic compounds can readily thread onto polymeric chains and slide along. The time needed to reach the blocked end of the polymer is related to polymer length, and the rate-limiting step involves a barrier of entropic origin in which a certain part of the open end of the polymer has to stretch and unfold. Recent studies describing how this threading rate can be controlled using a metallated porphyrincontaining macrocycle, will also be discussed. 5 [1]. Wang, J.; Sattar, A.; Wang, C. C.; Karam, J. D.; Konigsberg, W. H.; Steitz, T. A. Cell 1997, 89, 1087. [2]. Thordarson, P.; Bijsterveld, E. J. A.; Rowan, A. E.; Nolte, R. J. M. Nature 2003, 424, 915. [3]. Coumans, R. G. E.; Elemans, J. A. A. W.; Nolte, R. J. M.; Rowan, A. E. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 19647. [4]. Muthukumar, M. Phys. Rev. Lett. 2001, 82, 3188. [5]. Hidalgo Ramos, P.; Coumans, R. G. E.; Deutman, A. B. C.; Smits, J. M. M.; de Gelder, R.; Elemans, J. A. A. W.; Nolte, R. J. M.; Rowan, A. E. J. Am. Chem. Soc. 2007, 129(17) 5699.
Synthetic Strategies and Structural Aspects of Metal-Mediated Multi- Porphyrin Assemblies Elisabetta Iengo, † Ennio Zangrando, Enzo Alessio Department of Chemistry, University of Trieste, 34127 Trieste, Italy. † Current address: University of Cambridge, Chemical Laboratories, Lensfield Road, Cambridge CB2 1EW, UK. Porphyrins play a major role as active chromophores in artificial systems mimicking the natural photoinduced processes. The formation of coordination bonds between peripheral donor sites on the porphyrins and external metal fragments has proved to be an efficient alternative to covalent synthesis for the construction of multi-porphyrin assemblies, whose complexity and beauty gradually approach those of the multichromophore systems found in Nature. In a modular approach, relatively simple metal-mediated porphyrin adducts, owing to their thermodynamic and kinetic stability, can be exploited as building blocks in the construction of higher order architectures. Thus multichromophore systems become accessible on demand, with a limited synthetic effort. The collection of solid state structures that will be reported demonstrates that the flexibility of the porphyrins and of the metal junctions, combined with the conformational freedom of the coordination bonds, may lead to assemblies with hardly predictable architectures. Examples in which X-ray structural determination was essential for establishing the real composition and geometry of the multiporphyrin assemblies, such as the slipped-cofacial porphyrin macrocycle shown in the figure, will be highlighted. Some recent references of our contributions to this field are given below [1-4]. [1] F. Scandola, C. Chiorboli, A. Prodi, E. Iengo, E. Alessio, Coord. Chem. Rev., 2006, 250, 1471-1496. [2] E. Iengo, F. Scandola, E. Alessio, Struct. Bond., 2006, 121, 105-144. [3] E. Iengo, E. Zangrando, E. Alessio, Acc. Chem. Res., 2006, 39, 841-851. [4] A. Prodi, C. Chiorboli, F. Scandola, E. Iengo, E. Alessio, ChemPhysChem, 2006, 7, 1514- 1519. IL 3 Cyclodextrin-based Supramolecular Architectures and Dynamics Akira Harada, Hiroyasu Yamaguchi, Yoshinori Takashima, Yasushi Okumura Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. E-mail: harada@chem.sci.osaka-u.ac.jp Cyclodextrins (CDs) have been extensively used as host molecules for small molecules. We found that CDs form inclusion complexes with some polymers selectively to give pseudo-polyrotaxanes.[1] Recently, we found that CD rings pass through some groups unidirectionally (Figure1) [2]. In addition, we found that the threading process could be monitored by using a CD with a PEG chain by way of a cinnamoyl group in the presence of a competitive guest. (Figure 2) [3] When each end of the polymer chain of the pseudo-polyrotaxane is blocked by large stopper groups, polyrotaxanes were obtained. [4] One or two CD rings could be moved by using an STM tip along a polymer chain. [5] When neighbouring CD units were linked by short binding agents, followed by removing bulky stopper groups at both ends of the polymer chain, tubular polymers were obtained. [6] The molecular tube includes long molecules like 1,6-diphenylhexatriene to give highly fluorescent inclusion complexes. When a guest part was attached to a cyclodextrin host, they formed intramolecular or intermolecular complexes to give supramolecular assemblies. When a cinnamoyl group was attached to one of 6-OH groups by an ester linkage, they formed a cyclic trimer (cyclic daisy chain). When a cinnamoyl group was attached by an amide bond, they formed a Figure 1. Unidirectional threading Figure 2. Conformational switching Figure 3. α-,β-CD alternating copolymer IL 4 cyclic dimer. When a cinnamoyl group was attached to one of the secondary hydroxyl groups, they formed linear oligomers, when the t-Boc group was attached to the cinnamoyl group, they formed longer helical supramolecular polymers. In addition we have prepared α−,β-CDalternating supramolecular polymers and [2]rotaxane polymers.[7] Supramolecular catalytic system [8], stimuli-resposive systems[9], and supramolecular sensors have been developed. [1] Chem. Commun., 1990, 1332. Macromolecules, 23, 2823 (1990). [2] J. Am. Chem. Soc., 2005,127, 12186: J. Phys. Condens. Matter 2006, 18, S1809; Chem.Euro. J., in press.; J. Am. Chem. Soc., 2000, 122, 3797. [3] J. Am. Chem. Soc., 2006, 128, 8994; Macromolecules, in press. [4] Nature, 356, 325 (1992). J. Am. Chem. Soc., 1994, 116, 3192. [5] J. Am. Chem. Soc. ,2000, 122, 5411; 2003, 125, 5080 [6] Nature, 364, 516 (1993), 370, 126 (1994). [7] J. Am. Chem. Soc., 2000, 122, 9876; 2004, 126, 11418; 2005, 127, 2034; 2005, 127, 2984. [8] J. Am. Chem. Soc., 2004, 126, 13588; Macromolecules, in press. [9] J. Am. Chem. Soc., 2006, 128, 2226; Angew. Chem., Intl. Ed., 2006, 4605.
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PSB 61 Molecular Recognition of Ele
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Novel ditopic probes for different
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PSB 81 Tripodal polyamines as anion
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PSB 85 Templated Synthesis of Large
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