Chiral Ethylene Oxide Derivatives in Supramolecular Assemblies

Chiral ethylene oxide derivatives in supramolecular assemblies Citation for published version (APA): Janssen, H. M. (1997). Chiral ethylene oxide derivatives in supramolecular assemblies. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR494055 DOI: 10.6100/IR494055 Document status and date: Published: 01/01/1997 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 07. Oct. 2021 Chiral Ethylene Oxide Derivatives in Supramolecular Assemblies Chiral Ethylene Oxide Derivatives in Supramolecular Assemblies PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. M. Rem, voor een commissie aangewezen door het College van Dekanen in het openbaar te verdedigen op maandag 23 juni 1997 om 16.00 uur. door Henricus M. Janssen geboren te Meijel Dit proefschrift is goedgekeurd door de promotoren: prof.dr. E.W. Meijer en prof.dr. R.J.M. Nolte CIP-DATA LffiRARY TECHNISCHE UNNERSITEIT EINDHOVEN Janssen, Henricus M. Chiral ethylene oxide derivatives in supramolecular assemblies / by Henricus M. Janssen. - Eindhoven: Technische Universiteit Eindhoven, 1997. Proefschrift. - ISBN 90-386-0918-3 NUGI813 Trefw.: amfifielen / chiraliteit / macrocyclische verbindingen Subject headings: amphiphiles / chirality / macrocyclic compounds Contents Chapter 1: General introduction 1 1.1 mtroduction 1 1.2 Synthesis, properties and applications of polyethylene oxides 2 1.3 Crown ethers and podands 4 1.4 Ethylene oxide derivatives in supramolecular chemistry 8 1.5 Amphiphilicity, hydrophobic effect and non-ionic amphiphilic polymers 13 1.6 Chirality in ethylene oxide derivatives 15 1.7 Chiroptical spectroscopy in conformational studies 18 1.8 Aim and scope of the thesis 19 1.9 Outline of the thesis 19 Chapter 2: The synthesis and polymerization of oxo-crown ethers 25 2.1 mtroduction 25 2.2 Results and discussion 26 Synthesis of the precursors of oxo-crown ethers 1-3 26 Cyclization to oxo-crown ethers 1-3 27 Polymerization of oxo crown ethers 1-3 30 2.3 Conclusion 33 Experimental 34 Chapter 3: Unconventional amphiphilic polymers based on chiral polyethylene oxide derivatives 41 3.1 mtroduction 41 3.2 Results and discussion 44 Synthetic approaches to polymers 1-3 44 The synthesis of the alkyl-modified oxo-crown ethers (SS)-4 - (S)-6 45 Stereochemical analysis of the synthetic route to (SS)-4, (S)-5 and (S)-6 49 The preparation of polymers 1-3 51 ES-MS characterization of polymers 1-3 53 Polymers 1-3: a new class of amphiphilic polymers 55 3.3 Conclusion 59 Experimental 60 Chapter 4: Ordering and assembly of chiral polyethylene oxide derivatives 81 4.1 Introduction 82 4.2 Results and discussion 84 Approach 84 Synthesis of the reference components 84 Ordering processes of polymers 1-3 in aqueous solutions? An ORD-analysis 87 The complexation of chiral ethylene oxide derivatives with alkali salts 90 Microscopy studies on polymers 1-3 94 4.3 Conclusion 96 Experimental 97 Chapter 5: Constitutionally asymmetric and chiral [2)pseudorotaxanes 105 5.1 Introduction 105 5.2 Results and discussion 107 The synthesis of the molecular components 107 IH NMR spectroscopy 110 Stability constants of [2]pseudorotaxanes 113 X-ray crystallography 114 CD-measurements 119 5.3 Conclusion 121 Experimental 122 Chapter 6: Polyrotaxane Inclusion complexes of ethylene oxide derivatives and cyclodextrins - a preliminary study - 139 6.1 Introduction 140 6.2 Results and discussion 141 The complexation of glycol derivatives 1--4 with CDs 141 Characterization of the a-CD-t, a-CD-2 and a-CD--4 complexes 142 X-ray powder diffraction of the a-CD and the y-CD inclusion complexes 146 6.3 Conclusion and concluding remarks 147 Experimental 149 Summary Samenvatting Curriculum vitae Dankwoord Chapter 1 General introduction 1.1 Introduction Ethylene oxides - also named ethylene glycols - are water soluble, hydrolytically stable and conformationally flexible compounds with a chelating capacity towards cations. Charles Pedersen discovered that cyclic ethylene oxides which he named crown ethers have a pronounced affinity for particularly alkali metal ions [I]. The stable complexes that are produced are based on non-covalent interactions, and therefore Pedersen's discovery is regarded as the beginning of supramolecular chemistry, or - more accurately - the beginning of a more fundamental interest in "the chemistry beyond the covalent bond" [2]. Supramolecular chemistry is a science in which researchers investigate the basic 'recognition motifs' [3] that are employed by assembling molecules. The main strategy in this relatively young discipline of research involves the design, synthesis and examination of (aesthetically appealing [4]) molecular architectures. Supramolecular chemists find inspiration in natural systems, because in these systems the assembly of molecules is precisely regulated, leading to, for instance, biological materials [5]. Hair is an example of such a material. On a molecular level, peptides form hydrogen bonded triple helices (collagen). In the next ordering stages, the collagen threads form nanoscopic filaments and microscopic fibres. The hierarchical construction pattern is concluded by the assembly of the fibres to macroscopic 'hair'. Synthetic systems can also assemble to well-defined, higher-order structures, but also for these systems, the understanding of the various stages of assembly is limited [6]. Nevertheless, one can imagine that the efforts in the area of supramolecular chemistry lead to new materials, devices or applications, although, up to date, the research still has a rather fundamental character [7]. The presence of chirality is often the difference - generally observed by comparison between natural systems and systems designed by mankind. Nature employs chirality in most of its 'recognition motifs', whereas chiral building blocks are only sparsely used in synthetic supramolecular systems. From one viewpoint, true mimicking of natural systems requires the use of chirality. This can cause severe though challenging - synthetic problems, as routinely observed in natural product synthesis [8]. From another perspective, chirality can be a tool in the examination of synthetic supramolecular architectures. When chirality is introduced in a molecule or in a well-defined assembly of molecules, chiroptical techniques can give information on the system under investigation [9]. Thus, chiroptical techniques such as circular dichroism (CD) spectroscopy and optical rotatory dispersion (ORD) spectroscopy are powerful tools in supramolecular chemistry. Chapter 1 The work described in this thesis focuses on the use of the alkyl-substituted ethylene oxide unit in the construction and examination of supramolecular assemblies. Particularly, this [C*HR-CH20]-unit has been employed to synthesize unconventional amphiphiles; i.e. by combining apolar alkyl-substituted ethylene oxide units with polar ethylene oxide units, non ionic amphiphilic polymers with a stereoregular and regioregular design are obtained. Furthermore, the enantiomerically pure [C*HR-CH20]-unit has been used as a chiroptical probe in the study of several supramolecular architectures. In this Chapter, a short literature survey is presented in which the synthesis and properties of ethylene oxides are discussed and in which their role in supramolecular chemistry and polymer chemistry is addressed. The use of CD and ORD-spectroscopy in the fields of interest is also briefly discussed. Finally, the aim and scope of the work described in this thesis will be outlined. 1.2 Synthesis, properties and applications of polyethylene oxides [1011,11] Ethylene oxide a cyclic compound that is obtained by passing ethylene and oxygen over a silver-based oxidation catalyst - is the monomer from which polyethylene oxides (PEOs) are prepared (Figure 1.1). Polymerization

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