Porphyrins are organic pigments, of both natural and synthetic origin, all of which contain the porphyrin ring as part of their structure. In addition, porphyrin chemistry deals with various analogues and derivatives of porphyrins and, particularly, with their metal complexes.

1. PORPHYRINS AND IT'S
CLASSIFICATION
BY
JYOTI REKHA PATRA

2. Porphyrin Definition:-
• A porphyrin is a large ring molecule consisting of 4 pyrroles, which are
smaller rings made from 4 carbons and 1 nitrogen. These pyrrole
molecules are connected together through a series of single and
double bonds which forms the molecule into a large ring.
• The technical name for 4 pyrroles connected together is
a tetrapyrrole.
• The ring is flat in space, and the distribution of electrons is fairly
equal around the circumference of the ring.
• For this reason, a porphyrin is considered an aromatic compound.
This means that a porphyrin molecule is very stable. The model of a
general porphyrin is called porphin.
• This molecule is only rarely found in nature as an intermediate

3. The blue parts of the molecule represent the aromatic ring which forms the base of all
porphyrin molecules.
The black molecules and bonds will eventually be substitutedfor complex side chains.
These molecules will allow the cellular machinery to attach to and use the porphyrin.
Porphyrins are also capable of absorbing certain wavelengths of light, especially when
associated with different ions. Porphyrins cause both the red color of blood and the green
color of plants.
Porphyrin molecules serve a number of purposes in animals, plants, and even bacteria. For
this reason porphyrin is considered an evolutionarily conserved molecule.

4. • General characterization :-
• Porphyrins are a class of macrocyclic aromatic compounds composed of
four pyrrole rings connected by methine bridges. Porphyrins are ubiquitous
in nature, as a heme cofactor of hemoglobin, cytochromes, and other redox
active enzymes, and, as more saturated analogs, in the photosynthetic
apparatus in plants and bacteria.
• Tetrapyrrolic macrocycles have been widely examined for their unique
optical and redox properties.

5. • Porphyrins have a unique electronic structure that results in a
complex absorption spectrum.
• Simple porphyrins (such as tetraphenylporphyrin) exhibit a very
strong (with ɛ ∼ 500,000 M–1 cm–1) absorption band around 400
nm, a series of much weaker bands in the visible region (500–650
nm), and a very weak absorption band in red spectral window (∼ 650
nm).170 Porphyrins possess also moderate fluorescence quantum
yields (∼ 0.1).170
• Although simple porphyrins are not suitable for in vivo fluorescence
imaging because of their weak absorption in red/near-IR spectral
window

6. • The precursor pyrrole and
the parent porphin
nucleus of porphyrins.
Sites of isomeric
substitutions are given as
circled numbers and the
pyrrole rings as letters. A
schematic representation
is also given.

7. • The classification of the porphyrins is based on the synthetic porphyrin, etioporphyrin
(ETIO), in which two different radicals are substituted at positions 1 through 8. The
substituted radicals are four methyl (M) and four ethyl (E) groups. The number of
structural isomers possible with these eight substituted radicals is four, as shown at the
top of Figure 8-2. The naturally occurring porphyrins are only those in which the
positioning of their substituted radicals correspond to isomer I or III of etioporphyrin,
ETIO I and ETIO III. This observation led Fischer to speak of a “dualism” of porphyrins in
nature, which is in essential agreement with present knowledge of the biosynthesis of
the porphyrin isomers as proceeding along parallel and independent paths.
• The uroporphyrins also contain two different radicals, acetic (A) and propionic (P) acids,
and four each of these are arranged to correspond to either isomer ETIO I or ETIO III (Fig.
8-2). In this case, A corresponds to M and P corresponds to E. Therefore, these are
designated uroporphyrin I (URO I) or uroporphyrin III (URO III). Similarly, the
coproporphyrins contain four M and four P groups and are designated coproporphyrin I
(COPRO I) and coproporphyrin III (COPRO III). The protoporphyrin of heme (iron-
protoporphyrin, the prosthetic group of hemoglobin) corresponds to the series III isomer.
In this case, however, three different radicals instead of two are substituted. These
consist of four M, two P, and two vinyl (V) radicals. With three different radicals, 15
isomers are possible, but the protoporphyrin of heme is the only naturally occurring
isomer known. This isomer was designated protoporphyrin IX because it was the ninth in
the series of protoporphyrin isomers synthesized by Fischer. The arrangement of the
methyl groups of this isomer as shown in Figure 8-2 corresponds to that of a type III
etioporphyrin isomer and more properly should be called protoporphyrin III. However, by
convention, the name protoporphyrin IX (PROTO IX) is the designation for this porphyrin.

8. • The isomeric porphyrins.
The nomenclature of the
porphyrins URO, COPRO,
and PROTO is based on
the isomeric structure of
the etioporphyrins

9. • Synthesis of Porphyrins and Heme:-
• The initial steps in the pathway for porphyrin and heme biosynthesis begins
with the incorporation of the methyl carbon (C-2) and nitrogen atom of
glycine into the porphyrin ring and ultimately into the heme of hemoglobin.
• The methyl carbons (C-2) of glycine supply 8 of the 34 carbons of
protoporphyrin: one for each of the four methene bridges and one for each of
the pyrrole rings (Fig. 8-3). The carboxyl carbon atom of glycine is given off as
CO2 and is not incorporated into the protoporphyrin molecule (Fig. 8-3). The
direct incorporation of the nitrogen or the methyl carbon glycine into the
heme of hemoglobin has been the basis for a useful technique to label the
erythrocyte and to measure its survival time. After administering 15N-glycine,
the concentration of 15N in heme rises rapidly, remains constant for a time,
and then falls.
• The remaining carbons of protoporphyrin are supplied by the tricarboxylic acid
(TCA) cycle intermediate

11. • Types of Porphyrins
• Porphyrins in Animals
• A major use of porphyrin molecules in animals is in the construction
of heme groups. These molecules are simply a porphyrin molecule with various
side-chains substituted around the main ring. In a heme, the porphyrin ring
serves an important function. The nitrogen molecules at the center of the ring
are capable of “hosting” an iron molecule. It is this porphyrin structure, holding
iron, which gives blood its red color.
• The red blood cells have the protein hemoglobin, which holds the heme in
place.
• Another heme-holding molecule, myoglobin, functions as the oxygen
transporting molecule within the muscle cells. This heme is also made from
porphyrin, and hosts iron. Myoglobin has different side-chains than
hemoglobin. As such, it can interact with the machinery of muscle cells, and
deliver oxygen from the surface of the cell to the mitochondria which need the
oxygen of oxidative phosphorylation.

12. • Porphyrins in Plants
• plants have also mastered a different configuration of porphyrin molecule,
which allows them to capture the energy in sunlight. Chlorophyll is a special
molecule designed around a porphyrin base. Seen below, the chlorophyll
molecule has several unique side-chains off of the porphyrin molecule. It also
has a really long side chain, seen coming off the bottom. These side-chains
slightly change the shape and configuration of the base porphyrin.

13. • Applications
• Photodynamic therapy
• Porphyrins have been evaluated in the context of photodynamic therapy (PDT)
since they strongly absorb light, which is then converted to energy and heat in
the illuminated areas.[18] This technique has been applied in macular
degeneration using verteporfin.[19]
• Organic geochemistry
• The field of organic geochemistry had its origins in the isolation of porphyrins
from petroleum. This finding helped establish the biological origins of
petroleum. Petroleum is sometimes "fingerprinted" by analysis of trace
amounts of nickel and vanadyl porphyrins.
• Toxicology
• Heme biosynthesis is used as biomarker in environmental toxicology studies.
While excess production of porphyrins
indicate organochlorine exposure, lead inhibits ALA dehydratase enzyme.[22]

14. THANK YOU