Branched arrays

Even among nonlinear polymers, many of the materials of interest are composed of a preponderance of bifunctional units with only a minority of polyfunctional units. This applies to vulcanized rubber where no more than about 1 or 2 percent of the isoprene units are cross-linked. It also applies to the amylopectin fraction of starch which consists of chains composed of an average of about 20 glucose units, these chains being connected to one another by trifunctional units to yield an irregular branched array to wool consisting of poly-... 

Figure 12.7 Various architectures of the porphyrin arrays for light harvesting, (a) Cyclic array with peripheral acceptor (b) cyclic array with integral acceptor (c) tri-branched array with central acceptor (d) starburst array with central acceptor. FB denotes the free base porphyrin and Zn the zinc-porphyrin complex. (Adapted from Van Patten et al. [71])...

Recent work has investigated the potential to control the partitioning of charge in branched arrays [230]. This has many potential applications to the development of photoactive networks and dendritic systems capable of electron transfer. Compounds 17 and 18 employ 1,3,5-triaminobenzene as the central branch point. In each molecule ANI is attached to the 1 position and serves as the electron donor. The electron acceptors again are NI and PI, and are attached to the 3 and 5 positions, respectively in compound 17. Excitation of ANI with 400 nm laser pulses results in electron transfer exclusively to the NI branch. This is due to the 0.3 V... 

Figure 13.33. Linear and branched arrays with BODIPYs as primary energy donors. The ON/OFF states are a function of the oxidation state of the MgP.

Lest I leave the erroneous impression here that colloid science, in spite of the impossibility of defining it, is not a vigorous branch of research, I shall conclude by explaining that in the last few years, an entire subspeciality has sprung up around the topic of colloidal (pseudo-) crystals. These are regular arrays that are formed when a suspension (sol) of polymeric (e.g., latex) spheres around half a micrometre in diameter is allowed to settle out under gravity. The suspension can include spheres of one size only, or there may be two populations of different sizes, and the radius ratio as well as the quantity proportions of the two sizes are both controllable variables. Crystals such as AB2, AB4 and AB13 can form (Bartlett et al. 1992, Bartlett and van... 

Combinatorial chemistry constitutes a branch of the molecular sciences, providing an array of concepts and methods to solve molecular optimization problems (in drug research and beyond) more rapidly and efficiently than classical synthetic approaches. 

An impressive achievement of this strategy has been the construction of three-dimensional structures. Utilizing branched phenylacetylene sequences, double cyclization yielded macrobicyclic arrays 54 and 55 [43]. The zenith of Moore s approach is macrotricycle 56, a freely hinged system with a sizable 36xl2xl2A molecular cavity [44]. 

Formation of DNA Periodic Arrays Based on Branched Motifs Heid Together by Sticky Ends... 

Despite the fact that Milner s theory was originally developed for miktoarm-star copolymers, it can also be adopted for more complex branched structures. This empirical concept termed constituting-block copolymers approximates the architecture of branched molecules to be composed of an array of A2B and A2B2 miktoarms. This approach is capable of predicting the morphology of architectures as complex as centipedes or barbed wires, as shown in a very recent publication [125]. 

An extensive array of chiral phosphine ligands has been tested for the asymmetric rhodium-catalyzed hydroboration of aryl-substituted alkenes. It is well known that cationic Rh complexes bearing chelating phosphine ligands (e.g., dppf) result in Markovnikoff addition of HBcat to vinylarenes to afford branched boryl compounds. These can then be oxidized through to the corresponding chiral alcohol (11) (Equation (5)) ... 

Fig. 5. Illustration of the real and superficial current density. Top Current ditribution over lines on an inert substrate. Middle Current distribution over an array of trenches. Bottom Current distribution over a branching aggregate.

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