Supramolecular systems, laboratory

In the mid-1990s an alternative approach to the generation of functional supramolecular systems, dynamic comhinatorial chemistry (DCC), was conceived and developed by several groups, with the earliest publications coming from the Sanders, Lehn, and Miller laboratories [14—16], In DCC (Scheme 4.1), a series of building blocks (e.g., Aj-A, are mixed together and... 

One of the points made in Schwenz and Moore was that the physical chemistry laboratory should better reflect the range of activities found in current physical chemistry research. This is reflected in part by the inclusion of modem instrumentation and computational methods, as noted extensively above, but also by the choice of topics. A number of experiments developed since Schwenz and Moore reflect these current topics. Some are devoted to modem materials, an extremely active research area, that I have broadly construed to include semiconductors, nanoparticles, self-assembled monolayers and other supramolecular systems, liquid crystals, and polymers. Others are devoted to physical chemistry of biological systems. I should point out here, that with rare exceptions, I have not included experiments for the biophysical chemistry laboratory in this latter category, primarily because the topics of many of these experiments fall out of the range of a typical physical chemistry laboratory or lecture syllabus. Systems of environmental interest were well represented as well. 

Most, if not all, of the examples of supramolecular synthons given here are amenable for use in undergraduate laboratories and may form the basis of further study. The analytical methods likewise are applicable to a wide variety of supramolecular systems and computational methods are limited only by the resources available to the students. 

The titration method, based on rapidly varying the injection speed of reagent stock solutions into the mass spectrometer via a microreactor, offers a valuable alternative to more conventional laboratory-scale methodologies, provided that the selected supramolecular system is suitable to be studied by ESI-MS.60 The most important advantages of this approach are the limited sample... 

In our laboratory we are currently investigating several types of supramolecular systems which can play a role of artificial light-harvesting antennae or charge-separation devices. 

In an attempt to construct a rigid supramolecular systems capable to exhibit the above described type of behavior, Belser, et have synthesized compound 11 which contains the classical Ru(bpy)3 moiety fused with a quinone unit. In acetonitrile or water-acetonitrile solution 11 exhibits a visible absorption spectrum practically identical to that of Ru(bpy)3 , but no luminescence. This can be accounted for by electron transfer quenching from the MLCT excited state of the Ru(bpy)3 + unit to the quinone moiety. In CH2CI2 solution, however, where electron transfer is expected to be less favorable, 11 shows the usual Ru(bpy)3 luminescence. Electrochemical, photochemical and photophysical investigations on this and related complexes are under way in our laboratories. 

This book is aimed at providing the newcomers of the field with an overview of the potential offered by the photophysical and photochemical techniques applied to supramolecular systems and nanoobjects. Indeed, it provides the basic concepts, without introducing too many technical and mathematical details, with the aid of self-explicative figures and sehemes, and discusses the methodology to correctly perform a photochemical experiment, as well as the most critical aspects of the laboratory application. It is of interest also to scientists already involved in the field because it offers technical and operative details useful in the laboratory, as well as references to current research, pioneering contributions, and review articles on specific aspects. 

In addition to hydrogen-bonded host molecules, like the hacky sacks, tennis balls, and softballs described above, metal ions have been widely used to stitch together nanoflask capsules. In contrast to early supramolecular systems, where metal ions are the guest species (e.g., crown ethers, cryptands), in many of the newer systems, the metal ions are a key part of the host molecule. Many people have contributed to this area of metal-driven supramolecular capsules, and one of them was my PhD advisor. Professor Kenneth N. Raymond. When I started my PhD at the University of California, Berkeley, in 1994, Professor Raymond was just starting to work in this area. I did not personally work on this subject while I was earning my PhD, but I was witness to its development in Professor Raymond s laboratory, and it gave me a great perspective on the subject. 

In the early 1990s, Moore et al. reported the syntheses of a tremendous variety of meffl-connected PAMs [5 b, 36]. They recognized that the structural rigidity of systems like 8 could be useful in supramolecular chemistry. The convergent, stepwise approach of linear oligomeric phenylacetylene sequences developed in the Moore laboratory permitted absolute control over chain length, order of... 

Over the past 5 years, a number of researchers have started to explore and mimic these approaches in the laboratory. Enzyme-assisted formation of supramolecular polymers has several unique features. These include selectivity, confinement and catalytic amplification, which allow for superior control as observed in biological systems. These systems are finding applications in areas where supramolecular function is directly dictated by molecular order, for example in designed biomaterials for 3D cell culture, templating, drug delivery, biosensing, and intracellular polymerisations to control cell fate. Overall, biocatalytic production of supramolecular polymers provides a powerful new paradigm in stimuli-responsive nanomaterials. 

Such a high level of organization of multiple components is still very challenging, but several elegant examples of self-assembly are reported in the literature, and an examination of these systems reveals the underlying principles of supramolecular architecture and assembly. With this goal, we discuss selected examples from our laboratory as well as from literature to examine the role of molecular assemblies in various photoprocesses. 

For a general review on supramolecular chemistry with dendrimers, the reader is referred to an excellent paper of Zimmerman et al. [18]. Because of our acquaintance with the polylpropylene imine) dendrimers, we will restrict ourselves in this Chapter to some examples of supramolecular behaviour of these systems as investigated in our laboratory. Three systems will be discussed (Figure 1) the dendritic box, which can encapsulate guest molecules, the polystyrene-poly(propy-lene imine) block copolymer superamphiphiles, and alkyl-decorated dendrimers, which function as unimolecular micelles, and show surprising aggregation behaviour. However, first the synthesis and properties of the poly(propylene imine) dendrimers will be discussed to demonstrate some typical dendrimer features. 

Laboratory of Supramolecular Polymer Chemistry, Department of Chemical Engineering and Chemistry, Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands e-mail r.p.sijbesma tue.nl... 

Another supramolecular MR contrast agent based on the biotin-avidin system designed to increase agent sensitivity was developed by the Aime laboratory. Mono- and bis-biotinylated Gd + complexes were synthesized, with the mono-biotinylated probes exhibiting better relaxivity when bound to avidin (fourfold increase over the free complex). 

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