Porphyrins positive“ template

Zhu et al. [94] reported the synthesis of Sn02 semiconductor nanoparticles by ultrasonic irradiation of an aqueous solution of SnCLj and azodicarbonamide under ambient air. They found that the sonochemically synthesized Sn02 nanoparticles improved remarkably the performance of Li ion batteries such that there was about threefold increase (from 300 to 800 mAh/g) in the reversible capacity in the first lithiation to delithiation cycles. Similarly the irreversible capacity also increased by about 70% (from 800 to 1400 mA h/g). Wang et al. [95] reported the synthesis of positively charged tin porphyrin adsorbed onto the surface of silica and used as photochemically active templates to synthesise platinum and palladium shell and... 

The direct attachment of adequately substituted mexo-arylporphyrin to the saccharide units has been another synthetic strategy. Mexo-tetraaryl-porphyrins were used as templates to append, directly or by a spacer, several sugar units at the ortho, meta or para positions of the phenyl ring (Fig. 1). 

A porphyrin template has also been used by DeGrado and coworkers [35] for developing a well-defined four a-helix structure (41) that has proton channel activity (see Sect. 3.2). Following modeling studies, they used a tetraphenyl porphyrin with four carboxylic acids at the meta positions as attachment points for the peptide segments. 

Templates possessing two hydrogen bonding subunits bind two substrates forming a ternary complex in which the substrates are positioned so as to facilitate bond formation between them [5.64a]. In a related way, the rate and stereoselectivity of a bimolecular Diels-Alder reaction are substantially increased by binding both the diene and the dienophile within the cavity of a tris-porphyrin macrocycle [5.64b]. 

In such a design, deprotonation of the four pyridines causes the loss of the positive charges (Fig. 14) and consequently the disassembly of the supramolecular complex re-protonation would lead to reassembly of the aggregate, but what about the chiral information Indeed, to reassemble the chiral supramolecular structure after the chiral template removal is the crucial and most tricky step of the whole erase and rewrite process. In fact, apparently, switching on the electrostatic interactions by re-protonating the four meso basic groups (Fig. 14) should lead to the achiral complex between the two porphyrins because the chiral information should be lost after the erase reaction (Scheme 2, route a). 

Template synthesis has become a classic technique for the synthesis of tetra-benzoporphyrin metal complexes which, like [Mg(L580)] and [Mg L581)], occupy an intermediate position between porphyrins and phthalocyanines. Thus complexes [M(L588)], where M = Zn or Mg are obtained by condensation of 3-carboxy-... 

Synthesis of cyclic porphyrin tetramer 4 from linear tetramer 6 using y4Porph and Bipy as positive cyclisation templates. 

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