Supramolecular chirality of hydrogen-bonded rosette assemblies Mercedes Crego-Calama To cite this version: Mercedes Crego-Calama. Supramolecular chirality of hydrogen-bonded rosette assemblies. Supramolecular Chemistry, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2007, 19 (01-02), pp.95-106. 10.1080/10610270600981716. hal-00513491 HAL Id: hal-00513491 https://hal.archives-ouvertes.fr/hal-00513491 Submitted on 1 Sep 2010 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Supramolecular Chemistry For Peer Review Only Supramolecular chirality of hydrogen-bonded rosette assemblies Journal: Supramolecular Chemistry Manuscript ID: GSCH-2006-0028 Manuscript Type: Review Date Submitted by the 31-May-2006 Author: Complete List of Authors: crego-calama, mercedes; University of Twente, SMCT Supramolecular chirality, noncovalent synthesis, amplification of Keywords: chirality, diastereomeric synthesis, enantiomeric synthesis Note: The following files were submitted by the author for peer review, but cannot be converted to PDF. You must view these files (e.g. movies) online. tif.sit URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Page 1 of 20 Supramolecular Chemistry 1 2 3 4 5 Supramolecular chirality of hydrogen-bonded 6 7 rosette assemblies 8 9 10 Socorro Vázquez-Campos, Mercedes Crego-Calama*, and David N. Reinhoudt* 11 12 13 14 Laboratory of Supramolecular Chemistry and Technology, MESA+ Institute for 15 Nanotechnology and Faculty of Science and Technology, University of Twente, P.O. 16 ForB oPeerx 217, 7500 AReviewE Enschede, The Ne tOnlyherlands 17 18 19 20 Abstract 21 22 The control of chirality in synthetic self-assembled systems remains challenging 23 because of their lower stability and their higher susceptibility to racemization when 24 25 compared to covalent systems. In this review, we describe the supramolecular chirality 26 of noncovalent hydrogen-bonded assemblies formed by multiple cooperative hydrogen- 27 bonds between calix[4]arene dimelamines and cyanurates or barbiturates derivatives 28 (rosette assemblies). It is shown that the amplification of chirality (a high enantiomeric 29 or diastereomeric excess induced by a small initial amount of chiral bias) of double and 30 31 tetrarosette assemblies is influenced by bulky substitution on their components and 32 electronic properties of the substituents as well as their proximity to the rosette core. In 33 absence of chiral centers in their components, the assemblies form as a racemic mixture 34 of both enantiomers (P and M). The synthesis of enantiomerically pure rosette 35 assemblies is conducted via induction of chirality using chiral barbiturates, followed by 36 substitution of the chiral components for achiral cyanurates (“chiral memory” concept). 37 38 The addition of an external auxiliary to a racemic mixture of P and M assemblies 39 leading to the formation of one of the two possible diastereomeric assemblies is also 40 described. Moreover, chiral resolution of self-assembled nanostructures on highly 41 oriented pyrolytic graphite (HOPG) surfaces is also discussed. 42 43 44 Graphical Abstract 45 46 A brief description of the supramolecular chirality of noncovalent hydrogen-bonded 47 rosette assemblies is presented. This overview includes diastereomeric and enantiomeric 48 noncovalent synthesis of rosette assemblies, chiral amplification and a brief discussion 49 on the chiral resolution of these aggregates on surfaces. 50 51 52 Keywords 53 54 Supramolecular chirality, noncovalent synthesis, amplification of chirality, 55 diastereomeric synthesis, enantiomeric synthesis, hydrogen-bonds 56 57 58 59 60 URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Supramolecular Chemistry Page 2 of 20 1 2 3 4 5 1. Introduction 6 7 The three dimensional arrangement of atoms in molecules defines the molecular 8 stereochemistry. In the case of supramolecular structures, the supramolecular 9 stereochemistry1 comes from the spatial arrangement of their molecular components 10 which are held together by weak interactions. Supramolecular chirality plays an 11 2 12 important role in life; nearly all biological polymers are optically pure meaning that all 13 their components have the same handedness. All amino-acids in proteins are “left 14 handed” while all sugars in DNA, RNA and in the metabolic pathway are “right 15 handed”. Therefore, the control of supramolecular chirality has become an important 16 issue to undForerstand b ioPeerlogical proce ssReviewes such as protein foOnlylding or the expression and 17 18 transfer of genetic information. Supramolecular chirality results from both the 19 properties of the components and the way in which they associate. Therefore, the 20 chirality of the system at the supramolecular level can be formed by the association of 21 chiral components3, 4 as well as by a dissymmetric interaction of achiral components.5-17 22 Self-assembly of supramolecular structures occurs via non-covalent interactions such as 23 hydrogen bonding, coordination, aggregation, and electrostatic interactions. Especially 24 18, 19 25 hydrogen bonding interactions contribute in the selectivity of processes such as 26 molecular recognition, self-assembly, biomimicking as well as supramolecular 27 chirality.20-24 28 Clear examples of stereochemical selectivity in noncovalent synthesis can be observed 29 in the rosette assemblies. These are obtained by the combination of building blocks with 30 complementary hydrogen bonding motifs (three melamines and three isocyanuric acid 31 25-27 32 (CYA) or barbituric acid (BAR)) (Figure 1). This rosette motif forms large and 33 well-defined hydrogen-bonded structures. The formation of double rosette assemblies is 34 induced by mixing calix[4]arene derivatives, diametrically substituted with two 35 melamine units at the upper rim, with two equivalents of BAR or CYA (Figure 1).28 36 Extended tetra-, hexa- and octarosettes are obtained when calix[4]arene dimelamine 37 29-31 38 units are covalently linked. The rapid increase of number of hydrogen bonds 39 (double rosette = 36, tetrarosette = 72, hexarosette = 108 and octarosette = 142) in these 40 extended assemblies renders a high thermodynamic stability (Figure 1). 41 In this review, the control of the chirality of hydrogen-bonded assemblies based on 42 rosette motif at three different levels is described. Amplification of chirality (“Sergeant 43 44 and soldiers” principle), which takes place when the achiral building blocks of the 45 assemblies follow the helicity induced by the chiral components even when the chiral 46 molecules are present in very small amounts. Enantioselective noncovalent synthesis 47 (memory of supramolecular chirality) is also described where the use of a chiral 48 building block interacts stereoselectively to give preferentially one of the two possible 49 diastereomeric forms (P or M-helix). After the replacement of the chiral building block 50 51 by an achiral analog the induced chirality is preserved leading to the synthesis of 52 enantiomerically enriched double rosette assemblies. Furthermore, diastereomeric and 53 enantiomeric noncovalent synthesis of double rosettes can be achieved by the 54 introduction of a chiral guest; therefore inducing the formation of one specific helicity 55 of the rosette assemblies. The studies on enantioselectivity and amplification of chirality 56 57 in extended systems, tetrarosette assemblies, are also presented. Moreover, the induction 58 of chirality observed for these hydrogen-bonded rosette assemblies on highly oriented 59 pyrolytic graphite (HOPG) surfaces is also reviewed? 60 2 URL: http:/mc.manuscriptcentral.com/tandf/gsch Email: [email protected] Page 3 of 20 Supramolecular Chemistry 1 2 3 4 5 2. Rosette assemblies: Formation and characterization 6 7 Double rosette assemblies 13•(DEB)/13•(CYA)6 are held together by a total of 36 8 hydrogen bonds. The assemblies are formed spontaneously by mixing calix[4]arene 9 dimelamines 1 with 2 equivalents of either barbituric acid (BAR) or cyanuric acid 10 (CYA) derivatives in apolar solvents such as chloroform, benzene or toluene (Figure 11 28, 32 12 1). Three conformational isomers of double rosette assemblies can be formed D3-, 33, 34 13 C3h- and Cs-isomers (Figure 2). The assemblies with D3-symmetry, which is the 14 predominant isomer, are chiral due to the staggered (antiparallel) orientation of the two 15 melamine on each calix[4]arene unit, leading to a twist of the two different rosette 16 planes, whiForch can e ithPeerer adopt a cReviewlockwise ((P)-isome r)Only or counterclockwise ((M)- 17 18 isomer) conformation. In both C3h- and Cs-isomers, the two melamines on each 19 calix[4]arene unit adopt an eclipse (parallel) conformation and are therefore achiral. The 20 difference between the C3h- and Cs-isomers is the 180° rotation of one of the 21 calix[4]arene dimelamines. 22 Double rosette assemblies can conveniently be characterized by 1H-NMR spectroscopy 23 in solution.32 Upon formation