Topological control

Some of the more remarkable examples of this form of topologically controlled radical polymerization were reported by Percec et cii.231 234 Dendron maeromonomers were observed to self-assemble at a concentration above 0.20 mol/L in benzene to form spherical micellar aggregates where the polymerizable double bonds are concentrated inside. The polymerization of the aggregates initiated by AIBN showed some living characteristics. Diversities were narrow and molecular weights were dictated by the size of the aggregate. The shape of the resultant macroniolecules, as observed by atomic force microscopy (ATM), was found to depend on Xn. With A, <20, the polymer remained spherical. On the other hand, with X>20, the polymer became cylindrical.231,232... 

J. A. Swift, M. D. Ward, Cooperative Polar Ordering of Acentric Guest Molecules in Topologically Controlled Host Frameworks , Chem. Mater. 2000,12,1501-1504. 

Homochiral molecules readily available from inexpensive sources are useful synthetic building blocks and chiral auxiliaries. 1,4-01-0-benzyl-L-threitol has been used in construction of homochiral crown ethers that are useful as enzyme model systems. Topologically controlled diastereoselective delivery of the Simmons-Smith reagent for 2-cycloalken-l-one 1,4-d1-0-benzyl-L-threitol ketals was recently reported. ... 

Guilera, G., Steed, J. W., Topological control in coordination polymers by non-covalent forces. Chem. Commun. 1999, 1563-1564. 

Iedema, P.D. and Hoefsloot, H.C.J. (2001) Synthesis of branched polymer architectures from molecular weight and branching distributions for radical polymerisation with long-chain branching, accounting for topology-controlled random scission. Macromol. Theor. Simul., 10, 855. 

The kinetic complexity seen in oriented micelles persists in inverse micelles. The distribution of electron transfer quenchers within the water pool follows Poisson statistics and enables the kinetic data to describe migration rates to and from the aqueous subphase [65]. These orientation effects also make possible topological control of non-electron transfer photoreactions occurring within AOT micelles [66]. 

Topological control of the position of the carbonyl groups on the properties of 4-azaazulenones 4-8 has been studied by self-consistent field (SCF) calculations and a frontier orbital model was proposed based on dipolar structures of oxo derivatives, such as 4a and 6a (85MI2, 85UP1). 

Utamapanya, S. and Rajca, A. (1991). Topological control of electron localization in re-conjugated polyarylmethyl carbopolyanions and radical anions. J. Am. Chem. Soc. 113, 9242-9251... 

Co-Conformational and Topological Control of Interlocked and Interpenetrated (Super)Molecules... 

It is clear from these results that the AOT reversed micelles have more than a concentrating effect upon the stilbazolium cations. Changes In the size of the water pool have a profound effect upon the outcome of the dimerization reaction. The interface not only concentrates the monomers but aisp orients the cations in such a way as to force a nonpreferential association between the stilbazolium molecules. These results indicate that it is possible to exert topological control over the... 

The presence of "excimer" fluorescence at coverage levels as low as 11% indicates the concentrating effect of Nation s interface. However, in order to investigate whether the interface could exert topological control over the reactivity, the films were irradiated and the photoproducts were extracted (three times with a 5M pyridinium... 

Table I shows that, in every reaction examined, the hydration (or transfer) products formed from an enitol have the same configuration as the hydrolytic (or transfer) products formed by the same enzyme from its more reactive chiral substrates. The conservation of stereochemical outcome holds whether the enzyme protonates the enitol from the same or opposite direction than its glycosidic substrates. The finding that a given glycosylase can create, de novo, a particular product configuration from a prochiral substrate indicates that the stereochemical outcome of all its reactions could be under topological control.

The topological control of such polymerization reactions has been the subject of recent extensive reviews,52 and the same phenomenon in 2,5-distyrylpyrazine has been further discussed.53 The true photopolymerization process discussed here is typified by the u.v.-induced polymerization of AW -polymethylenebis-(maleimides) discussed above,51 and a complete study of the kinetics of the process is included in this series of papers. The conclusion is reached that the triplet state of the chromophore is the reactive species this can be quenched by the addition of ferrocene or 3,3,4,4-tetramethyl-l,2-diazetine 1,2-dioxide. The kinetics of a further example of true photopolymerization, the reductive photocopolymerization of diaryl ketones, have been compared with those of the photoreduction of the model compound benzophenone and found to be similar.53 The photoreductive poly-recombination of the diaryl ketones shown in Schemes 2 and 3 has been studied extensively.54... 

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