Molecular Encapsulation E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 947

Veröffentlichungsjahr: 2011

Beschreibung

The inclusion of small guest molecules within suitable host compounds results in constrained systems that imbue novel properties upon the incarcerated organic substrates. Supramolecular tactics are becoming widely employed and this treatise spotlights them. Often, the impact of encapsulation on product formation is substantial. The use of constrained systems offers the means to steer reactions along desired pathways. A broad overview of various supramolecular approaches aimed to manipulate chemical reactions are featured. The following topics are covered in detail: - general concepts governing the assembly of the substrate with the reaction vessel - preparation of molecular reactors - stabilization of reactive intermediates - reactions in water, in organic solvents, and in the solid state - photochemical reactions - reactions with unusual regioselectivity Molecular Encapsulation: Organic Reactions in Constrained Systems is an essential guide to the art of changing the outcome and the selectivity of a chemical reaction using nano-sized reaction vessels. It will find a place on the bookshelves of students and researchers working in the areas of supramolecular chemistry, nanotechnology, organic and pharmaceutical chemistry, and materials science as well.

Leseprobe

Contents

Preface

List of Contributors

1 Reaction Control by Molecular Recognition–A Survey from thePhotochemical Perspective

1.1 Introduction

1.2 Photochemical Reactions Mediated by Macrocyclic Compounds

1.3 Photochemical Reactions with Biomolecules

1.4 Photochemical Reactions with Confined Cages Based on Inorganic and Organic–Inorganic Hybrid Materials

1.5 Photochemical Reactions with other Artificial Hosts

1.6 Photoreaction Control by External Variants

1.7 Conclusions

Acknowledgements

References

2 Cyclodextrins

2.1 Introduction

2.2 Acylations of the Cyclodextrins by Bound Substrates

2.3 Catalytic Reactions in Cyclodextrin Cavities: Aromatic Substitution

2.4 Other Solvents than Water

2.5 Catalytic Reactions Produced by Cyclodextrins With Covalently Attached Catalytic Groups

2.6 Binding by Cyclodextrins and their Dimers and Trimers

2.7 Mimics of Enzymes that Use Thiamine Pyrophosphate as a Co-Enzyme

2.8 Aldol Condensations Catalysed by Cyclodextrin Derivatives

2.9 Mimics of Enzymes Using Coenzyme B12 as a Cofactor

2.10 Mimics of Cytochrome P-450

Acknowledgements

References

3 Cyclodextrins as Molecular Reactors

3.1 Introduction

3.2 Regiocontrolled Electrophilic Aromatic Substitutions

3.3 Catalysis of Hydrolytic Reactions

3.4 A Molecular Reactor for the Synthesis of Indigoid Dyes

3.5 Manipulation of Cycloadditions

3.6 Conclusion

Acknowledgements

References

4 Reactions Mediated by Cyclodextrins

4.1 Introduction

4.2 The Inclusion Phenomena of Cyclodextrins

4.3 Origin of Microvessels as Molecular Flasks

4.4 Organic Reactions Mediated by CD in Water

4.5 Conclusion

References

5 Reactions in Zeolites

5.1 The Confinement Effect

5.2 Superelectrophilic Activation in Zeolites

5.3 Huisgen [3+2]-Cycloadditions

5.4 Multicomponent Reactions

5.5 Conclusion

References

6 Chemistry in Self-Assembled Nanoreactors

6.1 Introduction

6.2 Self-Assembled Nanocapsules

6.3 Encapsulation Effects in Catalysis

6.4 Hydrogen Bonded Capsules

6.5 Capsules Based on Metal–Ligand Interactions

6.6 Tetrahedral Cages Based on Octahedral M3+ Ions

6.7 Octahedral and Square Pyramidal Cages Based on Square-Planar M2+ Ions

6.8 Hydrophobic Effects as the Driving Force for the Self-Assembly of Nanocapsules

6.9 Ligand Template Approach Using Lewis Acid/Base Interactions

6.10 Virus Capsids, Proteins and Micellar Systems

6.11 Micellar Systems

6.12 Conclusions and Outlook

Acknowledgements

References

7 Concave Reagents

7.1 Introduction

7.2 Classes of Concave Reagents

7.3 Reactions and Catalyses

7.4 Summary and Outlook

References

8 Reactivity Control by Calixarenes

8.1 Introduction

8.2 Calixarenes as Hosts

8.3 Calixarenes as Molecular Platforms

8.4 Concluding Remarks

References

9 Reactions Inside Carcerands

9.1 Introduction

9.2 Types of Inner Phase Reactions

9.3 Probing the Properties of the Inner Phase Cyclohexanes

9.4 Through-Shell Reactions

9.5 Intramolecular Thermal Reactions

9.6 Inner Phase Photochemistry

9.7 Conclusions and Outlook

Acknowledgements

References

10 Encapsulation of Reactive Intermediates

10.1 Introduction

10.2 Encapsulation of Labile Species

10.3 Isolation of Non-covalently Bonded Aggregates

10.4 Inclusion of Reactive Intermediates

References

11 Dye Encapsulation

11.1 Introduction

11.2 Reversible Dye Encapsulation Inside Organic Container Molecules

11.3 Reversible Dye Encapsulation by Biological Receptors

11.4 Permanent Dye Encapsulation Inside Rotaxanes

11.5 Permanent Encapsulation Inside Inorganic Matrices

11.6 Conclusion

Acknowledgements

References

12 Organic Cations in Constrained Systems

12.1 Introduction

12.2 Host–guest Complexes with Organic Cations

12.3 Extended Hosts and Capsules

12.4 Cucurbiturils

12.5 Complex Systems and Applications

12.6 Conclusions

References

13 Proteins as Host for Enantioselective Catalysis: ArtificialMetalloenzymes Based on the Biotin–Streptavidin Technology 361

13.1 Introduction

13.2 The Biotin–Avidin Technology

13.3 Artificial Hydrogenases

13.4 Artificial Allylic Alkylases

13.5 Artificial Transfer Hydrogenase

13.6 Enantioselective Sulfoxidation Based on Vanadyl-loaded Streptavidin

13.7 Conclusions and Outlook

Acknowledgements

References

14 Chemical Reactions with RNA and DNA Enzymes

14.1 Introduction

14.2 Catalysis by Naturally Occurring Ribozymes

14.3 How to Generate Artificial RNA and DNA Catalysts

14.4 The Catalytic Spectrum of Artificial Ribozymes

14.5 Deoxyribozymes–DNA Molecules with Catalytic Properties

14.6 Catalysis of C—C Bond Formation by Diels–Alderase Ribozymes

14.7 Conclusion

References

15 Reactions in Supramolecular Systems

15.1 Introduction

15.2 The Single Micellar Systems: Factors of Concentration and Micellar Microenvironment 398

15.3 The Role of the Structural Factor in Supramolecular Catalytic Systems 402

15.4 Binary Surfactant Systems

15.5 Polycomponent Catalytic Systems Based on Amphiphiles and Polymers 408

15.6 Conclusions

Acknowledgements

Dedication

References

16 Encapsulation Processes by Bilayer Vesicles

16.1 Introduction

16.2 Catalysis by Vesicles. Encapsulation of Reactants

16.3 Liposomal Encapsulation in Drug Delivery

16.4 Vesicle–Nucleic Acid Interactions: Gene Transfer Using Lipoplexes 438

References

17 Reactions in Liposomes

17.1 Introduction

17.2 Lipid Vesicles (Liposomes)

17.3 Experimental Strategies and Theoretical Aspects

17.4 A Theoretical Framework for Complex Reactions in Liposomes

17.5 Four Cases of Compartmentalized Reactions

17.6 Conclusion

Acknowledgements

Abbreviations

References

Index

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Library of Congress Cataloging-in-Publication Data

Molecular encapsulation: organic reactions in constrained systems / editors, Udo H. Brinker, Jean-Luc Mieusset.p. cm.

Includes bibliographical references and index. ISBN 978-0-470-99807-6 (cloth: alk. paper)

1. Nanochemistry. 2. Microencapsulation. I. Brinker, Udo H. II. Mieusset, Jean-Luc. QC176.8.N35M653 2010 547′.2–dc222010004249

A catalogue record for this book is available from the British Library.

ISBN 9780470998076

Set in 10 on 12 pt Times by Toppan Best-set Premedia Limited.

Preface

The inclusion of small guest molecules within suitable host compounds results in constrained systems that imbue novel properties upon the incarcerated organic substrates. For example, the chromophoric nature of dye molecules is considerably altered upon complexation. And the targeted delivery of active pharmaceutical ingredients can be facilitated in vivo. So, understandably, supramolecular tactics are becoming widely employed and this treatise spotlights them. Indeed, the knowledge gleaned from constructing such assemblies can be applied to develop innovative molecular devices. Insofar as molecular constraint influences chemical reactivity, including chemo -, regio -, and stereoselectivity, new synthetic routes become plausible. Often, the impact of encapsulation on product formation is substantial. Therefore, special attention must be paid to the stabilization and chemistry of short-lived, high-energy intermediates, since they are key compounds that govern the outcome of reactions. Common among these transient species is their ability to subsequently undergo an array of reaction mechanisms that include the generation of unusual or strained products. However, the conventional drawback has been that high product yields are sacrificed due to a lack of selectivity across low-energy barriers. The use of a constrained system, however, offers the means to solve this problem by steering the reaction trajectory along a desired pathway. In general, we provide a broad overview of many different approaches that aim to manipulate chemical reactions. We anticipate that this endeavor will be thought provoking and ultimately facilitate the exchange of ideas between various scientific disciplines.

This volume comprises 17 chapters. It is spearheaded by an account of molecular recognition being used to precisely control photochemical reactions and foster enantiomeric excess. The supramolecular reaction proceeds under mild conditions, wherein a highly reactive excited-state intermediate readily generates products that are difficult to obtain thermally. Such inductions of enantioselectivity by chiral auxiliary are especially appealing. The following three chapters expound upon the cyclodextrin macrocyclic hosts, whose wide availability and ability to form inclusion complexes makes them miniature reaction vessels par excellence. Chapter 2 deals with the use of natural and derivatized Schardinger dextrins to accelerate reactions, such as transesterifications and Diels–Alder reactions, and to mimic enzymes, e.g., ribonucleases and transaminases. Chapter 3 focuses on the development of molecular reactors. The primary role of these containers is to increase the selectivity of a chemical transformation, which also may occur by decreasing the overall rate of the process. In chapter 4, special cyclodextrin -mediated reactions are discussed. Since guest complexation offers the possibility of performing organic reactions in aqueous media, microsolvent effects are feasible, the protection of water-sensitive intermediates is achieved, and conformational control during the reaction is realized. Indeed, this approach has great appeal for environmental chemistry. Chapter 5 demonstrates the potential of nanoreactor technology, using zeolites as an example. These inorganic inclusion compounds are widely used on an industrial scale during petroleum refining, for example, because they catalyze the isomerization and oligomerization of alkenes. The utility of these materials is due to the presence of active sites in well-defined cavities that enable customized control of reaction selectivity. And though these natural catalysts are readily available, easily reusable, and therefore cost -effective, the facile preparation of a container of sufficient size suitable for the regulation of a chemical reaction is an ongoing challenge. To fashion cages as appropriate nano -reactors, a novel approach avoiding tedious multistep synthesis is becoming widespread. It entails the self-assembly of noncovalent capsules. The results obtained using these organized media are highlighted in chapter 6.

Another promising method to augment selectivity is described in chapter 7 and is based on the concept of concave reagents whose reactive moiety is situated inside a cleft or macrocycle and thereby sterically shielded. Another popular group of hosts used to control reactions are the calixarenes (chapter 8). Their appeal derives from the ease of the macrocyclic ring-closure during their synthesis and the capability of performing selective derivatization to both increase the size of the cavity and introduce functional groups. Using this method, a cage can be built wherein the reacting guest is completely imprisoned and may only escape at elevated temperatures. These hosts, known as hemicarcerands, have allowed isolation and spectroscopic observation of traditionally ephemeral intermediates. Remarkable results are presented in chapter 9. In chapter 10, an overview is given regarding the generation and associated change in reactivity of highly reactive intermediates, like radicals, carbenes, and nitrenes, within cavitands. This exposition is further elaborated by a presentation of the actual developments in dye encapsulation where improvements in the photoproperties and chemical stability are especially prized (chapter 11) and by a description of research on organic cations (chapter 12).

The subsequent chapters concern methodologies that are not only inspired by biology and enzyme mimicry, but actually employ modified biopolymers to achieve catalysis. In the first approach, the goal is to improve the enantioselectivity of a classic organometallic catalyst through its incorporation into a host protein that generates a secondary coordination sphere environment responsible for a rise in selectivity. These artificial metalloenzymes are showcased in chapter 13. The second technique is summarized in chapter 14 and details the generation of artificial RNA enzymes that are able to catalyze various chemical reactions, including the Diels–Alder reaction.

Finally, the assembly of more complex systems requires that the exact supramolecular reaction site be known. For this purpose, micelles and liposomes are very attractive due to the sequestering of reagents, the possibility of conducting various reactions in a confined space, and the similarity with living cells. These particular organized media are examined in detail in chapter 15, which describes the catalytic effect of micelles and supramolecular systems based on cyclophanes. In addition, the encapsulation process of vesicles and their catalytic effect on organic reactions is outlined in chapter 16. And, finally, chapter 17 previews efforts to assemble a semi-synthetic cell.

Many authors contributed chapters for this book, whose scope covers an expansive interdisciplinary area. We are profoundly grateful for their input and expertise. Indeed, we expect that this monograph will be useful to students and researchers alike who want to be informed about the latest developments in the burgeoning field of supramolecular chemistry. Not only will it help them to master established reactions, but new synthetic opportunities and exciting applications of these methodologies will surely arise.

Vienna, January 2010Udo H. Brinker Jean-Luc Mieusset

List of Contributors

Werner Abraham, Institut für Chemie, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany

Easwaran Arunkumar, Molecular Targeting Technologies Inc, PA 19380, USA

Ronald Breslow, Department of Chemistry, Columbia University, New York, NY 10027, USA

Udo H. Brinker, Institut für Organische Chemie, Universität Wien, A–1090 Wien, Austria

Roberta Cacciapaglia, IMC CNR Sezione Meccanisma di Reazione, c/o Dipartimento di Chimica, Università La Sapienza, I-00185 Roma, Italy

Stefano Di Stefano, IMC CNR Sezione Meccanisma di Reazione, c/o Dipartimento di Chimica, Università La Sapienza, I-00185 Roma, Italy

Christopher Easton, Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia

Jan B.F.N. Engberts, Stratingh Institute of Chemistry, University of Groningen, 9747 AG Groningen, The Netherlands

Jeremiah J. Gassensmith, Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556, USA

Lutz Grubert, Institut für Chemie, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany

Yoshihisa Inoue, Department of Applied Chemistry, Osaka University, Suita 565-0871, Japan

Andres Jäschke, Institut für Pharmazie und Molekulare Biotechnologie (IPMB), Universität Heidelberg, D-69120 Heidelberg, Germany

Chenfeng Ke, Department of Chemistry, Nankai University, Tianjing, China

Tehila S. Koblenz, Supramolecular and Homogeneous Catalysis, Van‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1018 WV Amsterdam, The Netherlands

Alexander Konovalov, A.E. Arbuzov Institute of Organic and Physical Chemistry of the Russian Academy of Science, 420088 Kazan, Russia

Ludmila Kudryavtseva, A.E. Arbuzov Institute of Organic and Physical Chemistry of the Russian Academy of Science, 420088 Kazan, Russia

Yu Liu, Department of Chemistry, Nankai University, Tianjing, China

Pier Luigi Luisi, Biology Department, University of Roma Tre, 00146 Rome, Italy

Ulrich Lüning, Otto-Diels-Institut für Organische Chemie, D-24098 Kiel, Germany

Luigi Mandolini, IMC CNR Sezione Meccanisma di Reazione, c/o Dipartimento di Chimica, Università La Sapienza, I-00185 Roma, Italy

Jincheng Mao, Department of Chemistry, University of Basel, CH-4056, Basel Switzerland

Jean-Luc Mieusset, Institut für Organische Chemie, Universität Wien, A–1090 Wien, Austria

Alla Mirgorodskaya, A.E. Arbuzov Institute of Organic and Physical Chemistry of the Russian Academy of Science, 420088 Kazan, Russia

Hideki Onagi, Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia

Joost N. H. Reek, Supramolecular and Homogeneous Catalysis, van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1018 WV Amsterdam, The Netherlands

Bradley D. Smith, Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, IN 46556, USA

Jean Sommer,Faculté de Chimie, Université Louis Pasteur, Strasbourg, F-67008 Strasbourg, France

Pasquale Stano, Biology Department, University of Roma Tre, 00146 Rome, Italy

Marc C.A. Stuart, Groningen Biomolecular Sciences and Biotechnology Institute and Stratingh Institute of Chemistry, University of Groningen, 9747 AG Groningen, The Netherlands

Keiko Takahashi, Department of Nanochemistry, Faculty of Engineering, Tokyo Polytechnic University, Atsugi, Kanagawa 243-0297, Japan

Jarl Ivar van der Vlugt, Supramolecular and Homogeneous Catalysis, Van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1018 WV Amsterdam, The Netherlands

Thomas R. Ward, Department of Chemistry, University of Basel, CH-4056 Basel, Switzerland

Ralf Warmuth, Rutgers The State University of New Jersey, Department of Chemistry and Chemical Biology, Piscataway, NJ 08854, USA

Jeroen Wassenaar, Supramolecular and Homogeneous Catalysis, Van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, 1018 WV Amsterdam, The Netherlands

Stéphane Walspurger, Energy Research Centre of The Netherlands, Petter, The Netherlands

Cheng Yang, PRESTO (JST) and Department of Applied Chemistry, Osaka University, Suita 565-0871, Japan

Lucia Zakharova, A.E. Arbuzov Institute of Organic and Physical Chemistry of the Russian Academy of Science, 420088 Kazan, Russia

Elena Zhiltsova, A.E. Arbuzov Institute of Organic and Physical Chemistry of the Russian Academy of Science, 420088 Kazan, Russia

1

Reaction Control by Molecular Recognition–A Survey from the Photochemical Perspective

Cheng Yang1, Chenfeng Ke2, Yu Liu2, and Yoshihisa Inoue1

1 PRESTO (JST) and Department of Applied Chemistry, Osaka University, Suita 565-0871, Japan2 Department of Chemistry, Nankai University, Tianjing, China

1.1 Introduction

Molecular recognition through non-covalent interactions between two or more molecules has attracted much attention from a broad spectrum of chemists for a long period of time and has already found many applications in various areas of science and technology. The concept of molecular recognition was first developed for biomolecular systems such as enzyme, antibody and DNA, which can selectively bind the specific target molecules through non-covalent weak interactions, including hydrogen bonding, van der Waals, dipole–dipole, charge–dipole and hydrophobic interactions.1–3 Recent studies on artificial host–guest systems have revealed that molecular recognition is the essential conceptual basis for supramolecular chemistry and nanotechnology.4,5

Reaction control through complexation of substrate by supramolecular host is a relatively new idea compared to the conventional approaches that involve simple collisional attack or coordination of substrate to metal. Multiple non-covalent interactions in supramolecular assembly bind and locate a site-specific substrate in the right position, orientation and conformation near the catalyst or active site, stabilize the high-energy transition state, and eventually make the reaction faster and more selective. Typical examples are found in enzymatic reactions, which proceed with high specificity and efficiency in aqueous solutions under mild conditions. These observations in natural systems have inspired researchers to develop novel research areas such as supramolecular chemistry, biomimetic chemistry and bio-inspired materials science and technology.6,7

Contrary to the thermal counterpart, photochemical reactions in supramolecular system have been less investigated and therefore of current interest. Photochemistry is a powerful tool in synthetic chemistry as a complementary method for achieving compounds that are difficult to obtain through thermal reactions due to high strain, low stability, and orbital symmetry reasons. Unlike thermal reactions, photoreactions deal with excited-state molecules that are usually short-lived but experience much lower energy barriers and exhibit high reactivities even at low temperatures. As a consequence of these features, the precise control of a photoreaction is more difficult to achieve than that of thermal one. This is one of the reasons why most asymmetric photoreactions result in only relatively low enantioselectivities. In this context, supramolecular approaches to the photochemical asymmetric synthesis enable the more precise control of the orientation and conformation of substrates and, as a result, the enantioselectivity of photoproducts, by utilizing the non-covalent interactions in both ground and excited states.

Supramolecular photochemistry is a relatively new interdisciplinary area of science and may be tracked back to the work in early 1980s, where the spectroscopic properties of ions were manipulated by crown ethers.8–10 The rapid development of supramolecular chemistry in the last two decades accelerated the application of supramolecular systems to organic photochemistry 11,12 and more recently to asymmetric synthesis, 13,14 leading to a great number of publications on reaction control by molecular recognition. Consequently, not all of these areas will be covered, but the concentration will be rather on the representative supramolecular photoreactions conducted primarily in solution. This will help idenitify the crucial concepts, strategies and conclusions as well as the major factors and mechanisms that govern the supramolecular photochemistry in different systems, and also provide the possible applications and future perspectives of this interesting area of supramolecular chemistry.

1.2 Photochemical Reactions Mediated by Macrocyclic Compounds

1.2.1 Supramolecular Photoreactions with Crown Ethers

Crown ethers, a family of cyclic oligomers of ethylene oxide, are artificial macrocyclic hosts which have been synthesized and utilized since the early days of supramolecular chemistry.15,16 Besides various metal ions that are complexed by crown ethers mainly through ion–dipole interaction, primary and secondary organic ammonium ions also form stable complexes with larger sized crown ethers through ion–dipole and hydrogen-bonding interactions. Stoddart and co-workers used crown ethers that can simultaneously bind two organic ammonium guests to facilitate photodimerization. forms a doubly encircled, doubly threaded 2: 2 complex with bis--phenylene-34-crown-10 to give a centrosymmetric [4]pseudorotaxane in the solid state. In addition to the hydrogen-bonding interactions between and , the complex is also stabilized by – stacking interactions between the two -stilbene units with mean interplanar and centroid-centroid separations of 3.57 and 4.33 Å, respectively. The close arrangement of stilbenes accelerates the photodimerization upon irradiation to As illustrated in , -stilbene derivative exclusively give a single cyclobutane isomer with a –– conformation, as confirmed by X-ray crystallographic analysis. A control experiment showed that no photodimerization but only -to- isomerization took place in the absence of crown ether .