in black and white
Main menu
Share a book About us Home
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics

The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
Previous << 1 .. 185 186 187 188 189 190 < 191 > 192 193 194 195 196 197 .. 240 >> Next

the meso-aryl groups. There are three types of doublestrapped porphyrins
derived from one-pot syntheses (Figure 6). An alternative, more versatile
synthesis, is attachment of the bridging strap after chromatographic
separation of atropisomers of we.vo-tetrakis-(2-aminophenyl)porphyrin.
= Porphyrin Framework
Figure 6. Three types of double-strapped porphyrins.
Some porphyrins strapped with multifunctional groups were found to be
suitable hosts for multi-interaction with particular guests. Hamilton,
Lehn and Sessler have reported that strapped porphyrins including two
crown ethers 11 trap alkyl diammonium salts, + ^(2),^3 * ( = 8~10)
via an ionic interaction 41 Rebek and his coworkers have prepared a
porphyrin host having two Kemp triacids 12 as interaction sites to
accommodate bipyridine through strong hydrogen bonding.42 In these
examples, porphyrin frameworks were utilized as platforms to fix
functional groups to accept small organic guest molecules. Binding of
guest molecules in the porphyrin plane cavity is confirmed by the large
upfield shift in the 'H NMR spectra of protons of the guest due to the
porphyrin ring current.
Two zinc(II) porphyrin complexes strapped by highly rigid
phenanthroline 13 show selective binding of fifth-axial imidazoles. An
NMR investigation showed that 2-methyli-midazole is on the hindered
strapped side and ALmethyli-midazole is on the open unstrapped side.
Hydrogen bonding between the imidazole N-H and phenanthroline nitrogen
determines the fashion of ligand coordination from the strapped side or
open side.43
E. OLIGOPORPHYRINS 1. Acyclic Oligoporphyrins
Syntheses of oligoporphyrins have targeted the construction of model
systems to mimic the assembly of chlorophylls in photosynthesis of green
plants and bacteria. In earlier times, a chlorophyll dimer was considered
the key unit of antenna systems which gather sunlight for production of
carbohydrate. Many model systems that elucidate the mechanism of
photoinduced electron-transfer reaction of photosynthesis have been
reported and well documented in many reviews. Syntheses of covalently
linked electron donors and acceptors have been extended to model
compounds appended to successive electron acceptors such as quinone
2. Dimeric Porphyrins
In 1972, Dolphin and coworkers reported the first covalently linked
porphyrin dimer 44 Reaction of the porphyrin having monofunctional groups
and a bifunctional linker molecule gives the bis-porphyrin. Another
approach is the reaction of
46/Porphyrins and Metalloporphyrins as Receptor Models
bis-dipyrromethene linked with spacer with dipyrro-methene. Flexibility
of the porphyrin dimer depends upon the structure of the spacer. For
example, if a phenyl group is accommodated as linker at the meta
positions in the dimer, the position of two porphyrins is fixed tightly.
Its metal complex 14 has two interaction sites to bifunctional substrates
such as diamine derivatives in its inner cavity.45
3. Cyclic Porphyrin Oligomers
The first cyclic porphyrin dimer (cyclophane porphyrin) linked with two
ester groups 15 was synthesized as a model of antenna chlorophyll dimer
by condensation of a 2,12-dipropionate porphyrin and a 2,12-bis-(3-
hydroxypropyl) porphyrin in high dilution in 1977 46 In order to clarify
the mechanism of electron-transfer reactions in biological systems, a
variety of porphyrin dimers have been reported as model systems of parts
of the photosynthetic apparatus in the last two decades. The first
synthesis of cyclic porphyrin oligomers was reported by Hamilton, Lehn
and Sessler in 1986.41
Sanders and coworkers have developed syntheses of rather rigid cyclic
oligoporphyrins (porphyrin-linker),, (n = 2~4) by catalytic-coupling
reactions of acetylene derivatives with copper salts. In particular,
incorporation of metal ions into cyclic porphyrin oligomers provides the
multi-interaction sites necessary to tightly bind heterocyclic compounds
in the inner cavity (see section IV).15-36 Rigidity of host molecules is
controlled by the structure of the linkage moieties.
1. Extrinsic Chiral Porphyrins and Metalloporphyrins
Chiral porphyrins47 have long been useful because of how their catalytic
organic reactions might mimic highly enantioselective reactions for
hydroxylation and epoxida-tion of organic substrates catalyzed by the
metalloenzyme cytochrome P450.48-52 Extrinsic chiral hosts consist of an
achiral porphyrin and chiral elements. There are two synthetic
approaches; the first involves attachment of a chiral group to the
functional groups of the porphyrin; the second starts from pyrroles
linked with a chiral group. The first chiral porphyrin 16 was prepared by
Previous << 1 .. 185 186 187 188 189 190 < 191 > 192 193 194 195 196 197 .. 240 >> Next