Cascade macromolecules

A fractal notation has been proposed by Mendenhall17,81 to address the complexity of cascade macromolecules, since they possess a high degree of molecular symmetry. This highly condensed description of a symmetrical molecule possessing a fractal architecture can be generalized in the following form ... 

Aharoni and coworkers characterized 59 Denkewalter s cascade macromolecules 4 by employing classical polymer techniques viscosity determinations, photo correlation spectroscopy (PCS), and size exclusion chromatography (SEC). It was concluded that at each tier (2 through 10) these globular polymers were, in fact, monodisperse and behaved as nondraining spheres. The purity of these molecules was not ascertained and the dense packing limits were either not realized or simply not noted. 

Treatment of a dendritic polyester 5 with a dendritic polyamine 6 is perhaps the simplest example of coupling between two dissimilar cascade macromolecules.178-801 Scheme 9.2 illustrates some potential products (i.e., 7 and 8) available by this general procedure, as well as a continuation of surface amidation to afford polymeric species such as random network 9. As envisioned, it would be difficult to stop this procedure after the formation of a single amide bond, due to the close proximity of adjacent ester—amine groups. 

Dendrimer electrokinetic capillary chromatography unimolecular micellar behavior of carboxylic acid terminated cascade macromolecules. [S. A. Kuzadal, C. A. Monnig, G. R. Newkome, C. N Moorefield, J. Chem. Soc., Chem. Commun. 1994, 2139-2140] [ 638]. 

Smart cascade macromolecules. From arborols to unimolecular micelles and beyond [G. R. Newkome, G. R. Baker, in Molecular Engineering for Advanced Materials, Eds. J. Becher, K. Schaumburg, Kluwer, The Netherlands, 1995, pp. 59-75]. 

Laferla, R. Conformations and dynamics of dendrimers and cascade macromolecules. Journal of Chemical Physics, 106, 688-700 (1997). 

Nonetheless, it was a fairly short step from octopus compounds to dendrimers, and the step was taken by Vogtle in the late 1970s when he attempted to use a cascade reaction to prepare a molecule of the dendrimer type that would now be considered a dendron rather than a fully developed dendrimer. It began with the addition of acrylonitrile to an anfine, followed by reduction of the nitrile to amine. This was followed by a further reaction with acrylonitrile, and the process was repeated several times to yield highly branched macromolecules. There were initially problems with the reduction step but these were overcome, and the preparation of these poly(propylene imine) dendrimers was later commercialized. 

At elevated temperatures (80°C in DMF), the acetyl azide group rearranges to form an isocyanate that can react with hydroxyl-containing molecules to form a urethane linkage (Figure 9.38). The Cascade Blue urethane derivatives of macromolecules are extremely fluorescent and can be detected down to femtogram quantities (Takadate et al., 1985). 

Phosphoryl group transfer reactions add or remove phosphoryl groups to or from cellular metabolites and macromolecules, and play a major role in biochemistry. Phosphoryl transfer is the most common enzymatic function coded by the yeast genome and, in addition to its importance in intermediary metabolism (see Chapter 5), the reaction is catalysed by a large number of central regulatory enzymes that are often part of signalling cascades, such as protein kinases, protein phosphatases, ATPases and GTPases. 

MaUcoch M, Thibault RJ, Drockenmuller E, Messerschmidt M, Voit B, RusseU TP, Hawker CJ. Orthogonal approaches to the simultaneous and cascade functionaUzation of macromolecules using cUck chemistry. J Am Chem Soc 2005 127 14942-14949. 

Newkome GR, Young JK, Baker GR, Potter RL, Audoly L, Cooper D, Weis CD, Morris K, Johnson CS Jr. Cascade polymers. 35. pH dependence of hydrodynamic radii of acid-terminated dendrimers. Macromolecules 1993 26 2394-2396. 

Young JK, Baker GR, Newkome GR, Morris KF, Johnson CS Jr. Smart cascade polymers. Modular syntheses of four-directional dendritic macromolecules with acidic, neutral, or basic terminal groups and the effect of pH changes on their hydrodynamic radii. Macromolecules 1994 27 3464 -3471. 

I personally wish to thank these authors for their time and effort to complete their contributions to this series and wish them continued success in their further endeavor in the field. Future volumes in this series will continue to highlight the research efforts of others in the field of cascade/dendritic and related hyperbranched macromolecules. 

Once the electrical signal has arrived at a chemical synapse (see Fig 4.2) a cascade of events is triggered with the arrival of an electrical impulse (an action potential), a chemical compound known as a neurotransmitter is released from the presynaptic side into the synaptic cleft. The released neurotransmitter then reaches the membrane of the second cell (postsynaptic membrane) where it interacts with a macromolecule, a so-called receptor. It is this neurotransmitter receptor interaction that triggers another cascade of (chemical) reactions within the second cell and this ultimately leads to the generation of an electrical signal within this cell. This signal then is transferred along this second cell s axon towards another synapse. 

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