Silver's Effect On Porphyrin

Introduction Tetraphenylporphyrin will be synthesized and metallated with silver acetate. After purification and NMR and UV-visible spectra was taking for the original porphyrin synthesized and the silver porphyrin. From this data obtained we will talk about silver’s effect on porphyrin.
Theory
Porphyrin is important to study because it plays keys roles in biological process; they are responsible for giving plants and blood their colors green and red respectively. Porphyrins have the iron chelate in hemoglobin and myoglobin for carrying oxygen. Metallated porphyrins and their other forms are also evident in cytochrome c which is an important aspect to the electron transport chain and vitamin B12 which is used keep the body’s nerve, make DNA,
and blood cells healthy.

Figure 1. Provides the molecular structure for hemoglobin and chlorophyll.
The aromatic ring and its size allows for pi-pi* transitions to occur in the visible region of the electronic spectrum.
For instance non-metallated porphyrin exhibits a deep purple color, but after metalation different physical properties become amended. In this case more specifically silver will produce a less stable porphyrin a different yet similar color to porphyrin. Figure 2 shows the structure of unmetallated and metallated porphyrin. Figure 2. Chemical tructures of, H2TPP (A) & metallated tetraphenylporphyrins, (B).

The Adler-Longo method will be used to synthesize tetraphenylporphyrin. This method includes pyrrole and benzaldehyde heated in propionic acid which is conveyed in first reaction scheme. The expected yield range for this experiment is around 10-20 percent.
Reaction Scheme 1 Metalation is done by heating the metal salt in a distillation tube until it refluxes in DMF which is shown in the second scheme. The silver metal has +2 oxidation state and is stabilized with the porphyrin, but it is light sensitive so experimentation will have to be carried out in the dark.
Reaction Scheme
2 Purification is of porphyrins is best done with chromatography for the most part except with MnTPPCl because it has +3 oxidation state that will strongly attach to the silica gel. NiTPP has very little solubility in regards to most solvent so it is a poor choice for separation through a column. However for this experiment we are focusing on silver we are with using a column for separations. The compounds will be moved with DMF to remove impurities. Proton NMR: For the proton NMR should exhibit fills downfield around 6.5-8.5 parts per million and a deshielding signal around 3 part per million due to located on both nitrogens. The spectra is fairly simple because how symmetrical the compound which relates to the nearest neighboring protons in each environment. From the NMR spectra conclusions can be formed about magnetic properties. Electronic Properties: We can corroborate for obtaining by looking UV-visible spectra for porphyrin which absorb around 390-425 nanometers for the Soret Band, but if Q band is around 480 and 700 nm then extinction coefficient will be around 10,000 and 50,000 M-`1cm-1. They Q Band should be about 10 times the magnitude of the Soret Band. The Q Bands should be originally four prior to purification and should convey about two bands after purification. The Q and Soret Bands arise from symmetry. With the purpose of continuing experimentation, we are making the porphyrin more symmetrical. Originally the four nitrogens in the structure of porphyrin are not the same because two are protonated and the other two are not. Consequently the Q bands are split into four bands: Qx(0,0), Qy(0,0), Qx(1,0), Qy(1,0). It is the pi to pi* transitions on the porphyrin which enables us to view the Q and Soret Bands from forming on the UV-visible spectrum. The a1u() to eg(*) electronic transition and the a2u() to eg(*) electronic transition occur respectively for Soret and Q Bands. More than one Q band is observed from coupling of vibrational transitions to electronic pi to pi* transition as demonstrated in Figure 3. For metallated porphyrin these transitions are better known as Q (0,0) and Q (0,1) to represent the vibrational level excited and ground state respectively. The reason for the absorption and fluorescence of MTPP is caused by conjugated porphyrin p system.
The energies effect metal dp orbitals that possess the same symmetry. Dxz a Dyz have the egp symmetry which have the ability to overlap eg(p*). This effect is similar to pi backbonding where the electron density is donated by a metal to a ligand with p* orbitals. When these orbitals interact with each other, porphyrin eg(p*) orbitals are lowered in energy, but metal dp orbtials are raised in energy due the orbitals having the same symmetry. This is evident when the Q and Soret bands shift on the UV-vis spectrum. MTPP compounds are also known as hyper porphyrins because they are less than half way filled. Hyper porphyrins show additional bands around 320 – 420 nm which occur under charge transfer transition between the porphyrin and metal. Figure 4.
In contrast, the later d-block metal d orbitals are filled and have lower energy than the porphyrin eg(*) orbitals. Again, these orbitals interact, but the porphyrin eg(*) orbitals are raised in energy and the metal d orbitals are lowered in energy (Fig. 4B). This results in shifting the Soret and Q bands to higher energies. These are referred to as hypso porphyrins and tend to contain metals from later in the d-block which are more than half filled (d6 – d9) such as Ni(II), Pt(II) and Pd(II). Thus the energies of the Soret and Q bands can be correlated with the position of the metal in the periodic table.

Experimental Procedure
To make H2TPP, a reflux condenser was attached to 250 mL round bottom flask under a heating mantle with a stir bar to bring 80 mL of propionic acid to reflux. The heating mantle was removed and then 3.3 mL (32 mmol) of benzaldehyde and 2 mL (29 mmol) was put through the top of the reflux condenser. The reflux condenser was also washed again with 20 mL of propionic acid. The reaction was refluxed for thirty minutes. The mixture was filtered with a glass frit and was rinsed with methanol until the filtrate ran clear. The crystals were dried for at least 20 minutes before weighing and recording the yield for experimentation.
Metallation of TPP. 0.50 g (0.81 mmol) of porphyrin in 100 mL of dimethylformamide(DMF) was put into a 250 mL rbf (round bottom flask) and a metal salt was added as directed by table 4. The solution was heated so it could reflux and react. From there, the progress of the reaction was monitored using UV-vis spectroscopy every 30 minutes until a Q-band region was observed at 514, 549, 590, and 647 nanometers in methylene chloride. The metallated complex were expected to have 1-3 Q bands due to an increase from C2v to D4h. Once the metalation appears to be complete by UV-vis spectroscopy, the reaction was put into an ice bath for 15 minutes. MnTPPCl requires the isolation procedure of the experimental procedure. For all others procedures, the solution was poured into 200 mL of water in a 500 mL Erlenmeyer flask and eventually the porphyrin precipitated.
Metalation AgTPP. In the dark the porphyrin, DMF, and water mixture was filtered through a glass frit and the solid was washed with 250 mL of 0.5 M acetic acid followed by water in excess. The solid was dried for about 15 minutes before the yield was recorded.
Purification (done in the dark)
H2TPP, CoTTP, CuTPP, ZnTPP. The MTPP solid was stirred in 100 mL of CH2Cl2 for 15 minutes and filtered to remove any undissolved porphyrin. The resulting filtrate was chromatographed on a silica gel column. The first major band observed is what was desired and therefore collected. The solution was concentrated to approximately 50 mL through the use of a rotor vap and precipitated by using 50 mL of MeOH. The solid was filtered and washed with MeOH and dried for 15 minutes before the yield was recorded.