Supramolecular systems

K. Kurihara, Direct Measurement of Surface Forces of Supramolecular Systems Structures and Interactions, in Microchemistry, H. Masuhara et al., Elsevier Science, 1994. 

Boulas P L, Gomez-Kaifer M and Echegoyen L 1998 Electrochemistry of supramolecular systems Angew. Chem. Int. Edn. Engl. 37 216-47... 

Electrochemistry of supramolecular systems with heterocyclic fragments as host molecules (porphirinoids, complexes on the basis of 2,2 -bipyridine and 2,2, 2"-terpyridine, hetero- and heteracyclophanes) 98AG(E)216. 

Eunctionalized supramolecular systems based on monolayers of bioactive compounds (macrocyclic ionophoric peptides, crown ethers, nucleoside derivatives) 98MI12. 

Template effect and incapsulation in macroheterocyclic supramolecular systems 97T15911. 

The transition state of concerted Diels-Alder reactions has stringent regio- and stereochemical requirements and can assume settled configurations if the reaction is carried out in a molecular cavity. Cyclodextrins, porphyrin derivatives and cyclophanes are the supramolecular systems that have been most investigated. 

Juris A (2001) In Balzani V (ed) Electron transfer in chemistry. Biological and artificial supramolecular systems. Wiley-VCH, Weinheim, Germany, vol 3, p 655... 

Electrochemistry of Functional Supramolecular Systems, Margherita Venturi, Paola Ceroni, and Alberto Credi... 

This relationship is illustrated in Figure 1. The science of solids is the science of supramolecular systems in which the three-dimensional solid structure is held together by covalent bonds... 

Toufar H, Baekelandt BG, Janssens GOA, Mortier WJ, Schoonheydt RA (1995) Investigation of supramolecular systems by a combination of the electronegativity equalization method and a Monte-Carlo simulation technique. J Phys Chem 99(38) 13876—13885... 

One of the most successful approaches to the synthesis of metalla-supramolecular systems has been by templated self-assembly processes. Most of the templating agents used by synthetic chemists are either cationic or neutral species. Anions, on the other hand, have only fairly recently been successfully utilized as templates. The new metalla-macrocycles [Pd2Ni2(atu)4(PPh3)4X]3+ (atu = deprotonated amidinothiourea, X = C1, Br, I) have been prepared using anion templated syntheses. Only in the presence of each of these three halides are the metalla-macrocycles... 

Since 1982 there have been enormous developments in metal-based chemistry, particularly the emergence of supramolecular chemistry - chemistry beyond the molecule, molecular architecture, and molecular engineering. Comprehensive Supramolecular Chemistry was published in 1996, a survey which contains much of interest to coordination chemists. Consequently in this volume review material relating to supramolecular systems is mainly restricted to developments since 1990. 

Within this approach, clathrates (for a definition see Chapter 1 in Vol. 140 of this series) and related lattice-type aggregates may be considered as multi-supramolecular systems where guest molecules are included in a crystal matrix. They allow a great many applications which have been specified in Vol. 140, first of all the separation of enantiomers by enantioselective recognition and inclusion of racemic guest molecules. 

After more than 20 years, Walde et al. (1994) returned in a way to coacervate experiments, although using other methods. Walde (from the Luisi group) repeated nucleotide polymerisation of ADP to give polyadenylic acid, catalysed by polynucleotide phosphorylase (PNPase). But instead of Oparin s coacervates, the Zurich group used micelles and self-forming vesicles. They were able to demonstrate that enzyme-catalysed reactions can take place in these molecular structures, which can thus serve as protocell models. Two different supramolecular systems were used ... 

Materials Science and Engineering C Biomimetic and Supramolecular Systems, 26, 328—333. 

Self-Assembled Metallo-Supramolecular Systems Incorporating P-Diketone Motifs as Structural Elements David J. Bray, Jack K. Clegg, Leonard F. Lindoy and David Schilter... 

D-B-A Donor-molecular bridge-acceptor supramolecular system... 

Several natural and synthetic helical macromolecules such as DNA, polypeptides, and polyisocyanates form, in the appropriate solvent, cholesteric meso-phases. Also self-assembled supramolecular systems formed by guanosine derivatives 2 and 3 (G-wires), which are essentially four-stranded helices (Figure 7.8), behave in a similar way.35... 

Dynamics of guest binding to supramolecular systems techniques and selected examples... 

Supramolecular systems have the capability of achieving functions not accessible by using molecular components.1,2 Supramolecular chemistry provides the framework to move from the molecular world to the nano- and meso-scale world. In this respect, the development of supramolecular systems provides a bottom-up approach for the construction of nanoscale objects where complexity is paramount to achieve multi-step function. Detailed knowledge of the system s thermodynamics and dynamics is required to rationally design new structures and to modify known ones. 

The building blocks of supramolecular systems are held together by intramolecular interactions and these systems are reversible. This intrinsic property is not only a consequence of the more labile interactions within supermolecules, compared to covalent bonds in molecules, but reversibility is essential for the function expressed by supramolecular systems. Kinetics can never be inferred from thermodynamic studies. For example, the knowledge of a host-guest equilibrium constant does not... 

The dynamics of a supramolecular system are defined by the association and dissociation rate constants of the various components of the system. The time-scale for the dynamic events is influenced by the size (length-scale) and by the complexity of the system. The fastest time for an event to occur in solution is limited by the diffusion of the various components to form encounter complexes. This diffusion limit provides an estimate for the shortest time scale required for kinetic measurements. The diffusion of a small molecule in water over a distance of 1 nm, which is the length-scale for the size of small host systems such as CDs or calixarenes, is 3 ns at room temperature. In general terms, one can define that mobility within host systems can occur on time scales shorter than nanoseconds, while the association/dissociation processes are expected to occur in nanoseconds or on longer time scales. The complexity of a system also influences its dynamics, since various kinetic events can occur over different time scales. An increase in complexity can be related to an increase in the number of building blocks within the system, or complexity can be related to the presence of more than one binding site. 

Laser flash photolysis experiments48,51 are based on the formation of an excited state by a laser pulse. Time resolutions as short as picoseconds have been achieved, but with respect to studies on the dynamics of supramolecular systems most studies used systems with nanosecond resolution. Laser irradiation is orthogonal to the monitoring beam used to measure the absorption of the sample before and after the laser pulse, leading to measurements of absorbance differences (AA) vs. time. Most laser flash photolysis systems are suitable to measure lifetimes up to hundreds of microseconds. Longer lifetimes are in general not accessible because of instabilities in the lamp of the monitoring beam and the fact that the detection system has been optimized for nanosecond experiments. 

Methods using excited states to measure the dynamics of supramolecular systems have the additional dimension that the excited state has a lifetime and this decay has to be considered in the kinetic treatment of the data. The decay processes are parallel... 

The kinetic information for NMR experiments is contained in the line broadening observed for a nucleus that resides in two different magnetic environments, and values for rate constants can be obtained using line-shape analysis.28,68,69 Line broadening experiments obtained using ID NMR is the method of choice when analyzing the kinetics of a molecule in two sites. 2D NMR techniques, such as 2D EXYS are employed when the kinetics are sequential, i.e. more than one step, or multiple sites are analyzed.69 For example in the case of supramolecular systems this technique was employed to measure the exchange kinetics in capsules.70... 

---