Toward the Synthesis of a Stable Water-Soluble Manganese(II) Porphyrin

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TOWARD THE SYNTHESIS OF A STABLE WATER-SOLUBLE

MANGANESE(II) PORPHYRIN

RESEARCH CONDUCTED & REPORT PREPARED BY:

Nicholas O. Gober

Undergraduate Student (B.S., Biochemistry, 2016)

Georgia Institute of Technology

College of Sciences, School of Chemistry & Biochemistry

901 Atlantic Drive NW, Atlanta, GA 30318, USA

P: (404) 894-4002 | F: (404) 894-7452

PRINCIPAL INVESTIGATOR: SPONSORING INSTITUTIONS:

Rosalie A. Richards, Ph.D.

Associate Provost for Faculty Development

& Professor of Chemistry and Education

Stetson University, Office of the Provost and

Academic Affairs

421 N. Woodland Blvd., Unit 8358

DeLand, FL 32723, USA

[email protected] | (386)-822-7906

Project Funding:

ACS Project SEED Program

American Chemical Society

1155 Sixteenth Street NW, Room 833

Washington, DC 20036, USA

[email protected] | (800)-227-5558 ext. 4380

Laboratory Facilities:

Georgia College and State University

Dept. of Chemistry, Physics, & Astronomy

301 Herty Hall, Campus Box 82

Milledgeville, GA 31061, USA

(478)-445-5769 | [email protected]

Toward the Synthesis of a Stable Water-Soluble Manganese(II) Porphyrin Gober, N. O.

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TABLE OF CONTENTS

Abstract........................................................................................................................................................................3

Introduction..............................................................................................................................................................4

Porphyrin Chemistry & Problem...................................................................................................................6

Literature Overview & Hypothesis...............................................................................................................7

Reagents & Instrumentation............................................................................................................................8

Synthetic & Proposed Methods.......................................................................................................................9

1. Synthesis of Cu(II)TMPyP4+ from H2TMPyP4+........................................................................................................................9 2. β-Chlorination of CuTMPyP4+ to yield CuTMPyPCl84+......................................................................................................10 3. Synthesis of NiTMPyP4+ from H2TMPyP4+............................................................................................................................13 4. Metathesis I: Synthesis of NiTMPyP4+ as Cl- salt.................................................................................................................14 5. β-Chlorination of NiTMPyP4+ as Cl- salt to yield NiTMPyPCl84+ using NCS...............................................................15 6. Metathesis II: Synthesis of NiTMPyP4+ as PF6- salt............................................................................................................16 7. β-Chlorination of NiTMPyP4+ as PF6- salt to yield NiTMPyPCl84+ using SOCl2.........................................................17

Results: Spectroscopic Observations........................................................................................................19

Discussion & Future Outlook.........................................................................................................................20

Acknowledgements............................................................................................................................................21

References...............................................................................................................................................................21


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ABSTRACT

Recent research conducted on manganese porphyrins (MnPs) has shown that these complexes have

a wide array of prospective medicinal applications that extend far beyond original assertions. To date,

however, only water-insoluble (i.e., non-employable in vivo) MnP derivatives have been synthesized. The

central challenge with synthesizing a stable water-soluble MnP derivative like MnTMPyPCl85+, our target

molecule1 , is halogenation of the porphyrin’s eight β-carbons—full β-chlorination must occur before

insertion of the Mn2+ ion. Here, we describe attempts at β-chlorination of two pre-cursor metalloporphyrins,

Cu(II) and Ni(II) complexes, using three separate chlorinating agents—NCS, SOCl2, and Cl2 (g)—by

widely varying reaction conditions, with close monitoring of structural changes via ultraviolet-visible (UV-

Vis) absorption spectroscopy. The largest Soret-band (λmax) shifts were exhibited by the Ni(II) complex,

the most drastic of which occurred after refluxing NiTMPyP4+ (as PF6- salt) with SOCl2 (Δλmax = 26.5 nm)2.

This result suggests that complete halogenation (i.e., λmax ≈ 456 nm) is likely feasible after few minor

reaction-system modifications. The Cu(II) complex, nor either metallo-complex when Cl2 and NCS were

employed as chlorinating agents, showed no significant Δλmax. Elemental analysis will be performed on the

Ni(II) compound to determine its actual degree of chlorination; accordingly, to elucidate the optimum

conditions under which full β-halogenation may be successfully achieved, future work will place concerted

efforts on experimental designs in which the Ni(II) complex is allowed to react with SOCl2 under several

varying conditions.

1 Structure of MnTMPyPCl85+ complex shown directly above and in Fig. 1 on page 6. 2 See Fig. 17 on page 18, Fig. 18-B on page 19, and Table 1 (Sample 21) on page 19.

MnTMPyPCl85+


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INTRODUCTION

Motivation. An extensive, diverse array of various porphyrin complexes have become increasingly

studied in recent years. One porphyrin class that has received a considerable amount of attention,

predominantly within the last decade, is the metalloporphyins—specifically, manganese porphyrins

(MnPs)—which are characterized by the presence of a metal ion bonded within their structural core.

Promising research has shown that MnPs likely have many medicinal applications, including: use in

treatments for certain diseases, such as diabetes[1] and amyotrophic lateral sclerosis (ALS);[2] use in

treatments for specific conditions, including hepatic ischemia;[3] and as agents to improve the effectiveness

of some cancer treatments.[4] Additionally, MnPs have been show to prolong the half-life of an ‘oxidation-

prone’ compound and have been patented for treating or preventing injury due to: exposure to a ‘reactive

species’, erectile dysfunction caused by surgery, lung disease, hyperoxia, myocardial damage during

cardioplegia, and cardiovascular disease.[5]

Moreover, a certain type of modified MnP, β-octa-brominated MnPs, that have been synthesized

in GCSU laboratories[6] have been implicated in other research as mimics of superoxide dismutase[7], an

enzyme responsible for the removal of peroxide moieties (O22-) from the body, thus preventing excessive

build-up of toxins. Although the properties of β-chlorinated MnPs appear to be similar to brominated

derivatives, the chloro- species has not been nearly as thoroughly investigated as potential treatments or

mimics;[8] as such, we have initiated studies on both the synthesis and likely medicinal applications of β-

chlorinated MnPs.

Diabetes background. Diabetes, a disease associated with high levels of blood glucose resulting

from defects in insulin production, causes sugar to accumulate in the body excessively. It is the seventh

leading cause of death in the United States and can cause serious health complications, including: heart

disease, blindness, kidney failure, and lower-extremity amputations, among others. There are

approximately 24 million people in the U.S. alone, 8% of the current total population, who have been

diagnosed with diabetes at some point in their lives, an increase of more than 3 million individuals in

roughly only two years. Moreover, an estimated 57 million Americans have pre-diabetes, a condition in

which the earliest stages of diabetes have materialized.[9]

Diabetes medicinal implications. In an experiment conducted at Kuwait University in 2005,[1]

certain manganese porphyrin complexes were shown to decrease mortality rate and markedly extend the

life-span of diabetic rats. Specifically, the MnTMPyP5+ complex suppressed diabetes-induced oxidative

stress, which presumably accounts for its beneficial effect on the life-span of the diabetic rats. The results

seem to indicate that MnPs possess considerable potential to be used as potent therapeutic agents against

diabetes.


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ALS background. Although the recent increase in resources, funding, and time invested into

medicinal-related research and development has been quite substantial, a person diagnosed with ALS

(commonly referred to as Lou Gehrig’s disease) today essentially receives a death sentence. ALS is a

rapidly progressive, invariably fatal neurological disease that attacks the neurons responsible for controlling

voluntary muscles. The disease belongs to a group of disorders known as motor neuron diseases, which are

characterized by the steady degeneration and death of motor neurons. The disorder causes muscle weakness

and atrophy throughout the body as both the upper and lower motor neurons degenerate, gradually ceasing

to send messages to muscles. Unable to function, the muscles consistently weaken and develop contractions

because of denervation, leading to eventual atrophy; subsequently, the patient may, in due course, lose the

ability to initiate and control all voluntary movement, ultimately becoming permanently paralyzed.[10]

ALS medicinal implications. To date, no cure has been found for ALS. Indeed, the FDA approved

the first drug treatment, under the trade name Rilutek®, for the disease in 1995.[11] Yet, unfortunately,

Rilutek® only prolongs the patient’s life-span for several months.[10] During a 2005 study at the University

of Arkansas,[2] certain MnPs were tested on mice that had a disease similar to that of ALS. These mice

underwent manganese porphyrin-therapy and lived three times longer than those in the control group—

thus, it is highly likely that these drugs will have some type of substantial effect on the human condition.

Hepatic ischemia background and medicinal implications. Hepatic ischemia is a condition in

which the liver does not receive enough blood or oxygen, causing injury to liver cells. It has been known

to cause liver failure, a critical, life-threatening condition, in many patients.[12] In a 2007 study conducted

by Wu et al.,[3] rats suffering from injuries leading to hepatic ischemia were treated with MnPs. The

researchers observed that, ultimately, the effects of the condition were lessened, allowing more oxygenated

blood to flow to the liver.

Cancer medicinal implications. During an experiment conducted at Duke University in 2005,[4]

rodents infected with tumors were exposed to MnTMPyP5+ in vitro and examined for viability and

radiosensitivity in a controlled environment. Additionally, tumors were exposed to simultaneous treatment

of both radiation and MnTMPyP5+; the effects of tumor growth and vascularity were monitored, and the

two approaches were compared for overall effectiveness. In vitro, MnTMPyP5+ was not significantly

cytotoxic. However, combined treatment with radiation and in vivo injection of MnTMPyP5+ achieved

synergistic tumor devascularization, with a 78.7% reduction in vascular density observed within 72 hours

of radiotherapy. Moreover, co-treatment of tumors resulted in synergistic antitumor effects, extending the

delay of tumor growth by nine days. This study suggests that it is not unreasonable to investigate the

potential in vivo use of MnPs in humans as agents to enhance the responsiveness of cancerous tumors to

various radiation therapies.


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Research goal. The overarching aim of this project is to synthesize the β-chlorinated water-soluble

manganese(II) porphyrin complex MnTMPyPCl85+, shown in Fig. 1 below, and to harness its medicinal

applications as a potential life-saving drug.

FIGURE 1: Chemical structure of the fully octa-chlorinated water-soluble metallo-complex of 4-N-methylpyridylporphyrin, MnTMPyPCl85+, the target molecule. All chlorine atoms are bonded to the β-carbons of the porphyrin ring (one such β position is indicated here with an arrow).

PORPHYRIN CHEMISTRY & PROBLEM

Significance. Our interest is in MnPs since porphyrins and their derivatives are currently being

explored for applications as drugs which could treat, help prevent, or even cure many life-threatening

conditions and diseases. Porphyrins are particularly great candidates for medicinal application because they

are ubiquitous to nature, forming the structural basis of both heme and chlorophyll (Fig. 2-A).[13]

Structurally, porphyrins are derived from the parent molecule porphine and are comprised of four

alternating pyrrole rings joined by four methine bridges at their alpha-carbons (α-carbons), which include:

C1, C4, C6, C9, C11, C16, and C19 (see Fig. 2-B).[13] Porphyrin is different to porphine when various

groups are substituted for hydrogens on the outer beta-carbons (β-carbons), a phenomenon that can occur

any time after the actual porphyrin is synthesized. In Fig. 2-B, the β-carbons include: C2-3, C7-8, C12-13,

and C17-18. Metal ions can be substituted for the hydrogen atoms found within the porphyrin’s core to

form metalloporphyrins (see Fig. 2-A), a class of heterocyclic macrocycles that are highly conjugated and,

therefore deeply colored, which allows them to exhibit optimal spectra with very intense transitions at ~400

nm (known as Soret-bands). Similarly, most porphyrins exhibit several less-intense Q-bands in the visible

region at ~500-700 nm.[15]

MnTMPyPCl85+


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Predominant challenge. MnPs have the propensity to be life-saving molecules—the primary hope

is that medicine capable of treating humans can be derived from these complexes; however, the feasibility

of this goal is very much dependent upon the synthesized complexes being water-soluble. To date,

unfortunately, only water-insoluble complexes have been successfully synthesized—if these insoluble

complexes were to be used by humans as drugs, there would be a significant risk of the body rejecting them,

which would, in turn, cause even more health complications for an already vulnerable, weakened body.

Conversely, a water-soluble porphyrin would most likely easily be both absorbed and excreted by the body.

Problem statement. β-octa-chlorination of water-insoluble porphyrins has been demonstrated in

prior studies, but, to date, β-octa-chlorination of water-soluble porphyrins has yet to be reported.

FIGURE 2: (A) Chemical structure of chlorophyll (left) and heme (right). Note the magnesium (Mg2+) and iron (Fe2+) ions within the core of the chlorophyll and heme metallo-complexes, respectively. (B) Chemical structure of porphine, the parent molecule of all porphyrin complexes.

LITERATURE OVERVIEW & HYPOTHESIS

Literature background. For the challenge of chlorinating the porphyrin, our method of attack is

based on three separate studies, and, therefore, three different chlorinating agents: thionyl chloride (SOCl2),

N-chlorosuccinimide (NCS), and chlorine gas (Cl2).

In one study conducted in 2000, SOCl2 was used as the chlorinating agent for Pd, Ni, and Cu

metalloporphyrins.[8] In these experiments, octa-chlorination occurred at the β-carbons of each

metalloporphyrin after each complex was refluxed in SOCl2 for various amounts of time. However, all of

the porphyrins used by Mironov et al.[8] were insoluble in water, while our main goal is to synthesize a

stable water-soluble porphyrin. Still, there is a possibility that SOCl2 will prove to be successful at β-

chlorination while maintaining the solubility of the porphyrin; thus, SOCl2 will be investigated as one

potential chlorinating agent in our study.

B A


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In a separate study undertaken in 1990, NCS was used as a chlorinating agent for H2TPP analogues

under certain refluxing conditions.[16] Octa-chlorination occurred after these porphyrin complexes were

refluxed in chloroform for different durations of time. Based on the success at β -chlorination in this study,

it is probable that NCS will successfully β-chlorinate Cu(II) and/or Ni(II) metalloporphyrins, and that the

complexes will remain both stable and water-soluble. Because of this likelihood, NCS will be explored as

a prospective chlorinating agent.

Finally, during a third study performed in 1995, an Fe(III)TPP complex underwent facile

perchlorination of its porphyrin ring when treated with Cl2 (g).[17] It is likely that this technique can also be

used to octa-chlorinate a Cu(II) complex because of the high level of similarity in the properties of both

metal-ion complexes—accordingly, Cl2 (g) will be investigated as a possible chlorinating agent for Cu(II)

complexes. Moreover, as reported in the same aforementioned study,[17] a Ni(II)TPP complex reacted with

10-12 equivalents of NCS to give Ni(II)TPPCl8 in 75% yield—based on these observations, it is highly

possible that NCS can be used to β-chlorinate a water-soluble Ni(II) complex, so this approach will be

explored as well.

Hypothesis statement. It is hypothesized that the synthesis of the β-octa-chlorinated derivative of

the water-soluble 4-N-methyl-pyridylporphyrin manganese complex, MnTMPyPCl85+, can be successfully

undertaken by modifying the solvent conditions to enable solubility of both the porphyrin and chlorinating

agent. Any potential structural transformation(s) of the porphyrin will be monitored via UV-Visible

absorption spectroscopy.

REAGENTS & INSTRUMENTATION

The octa-chlorinated water-soluble manganese porphyrin complex, MnTMPyPCl85+ (see Figure

1), will be prepared via the synthesis of metallo-derivatives of meso-tetrakis(N-methyl-4-pyridyl)porphyrin,

or H2TMPyP4+ (see Fig. 3). Reaction progress will be monitored with UV-Vis absorption spectroscopy via

a Shimadzu UV-2401PC Ultraviolet-Visible Spectrophotometer (Shimadzu Corporation; Nakagyō-ku,

Kyoto, Japan).

The meso-tetrakis(N-methyl-4-pyridyl)porphyrin starting complex (H2TMPyP4+) was purchased

directly from Frontier Scientific, Inc. (Logan, UT 84321, USA) and used without further purification.

Thionyl chloride (SOCl2); N-chlorosuccinimide (C4H4ClNO2); cupric(II) acetate (Cu(CH3COO)2);

nickel(II) sulfate heptahydrate (NiSO4·7H2O); sodium acetate (CH3COONa); tetra-n-butylammonium

chloride (TBAC; NBu4Cl); ammonium hexafluorophosphate (NH4PF6); methanol (CH3OH); acetone

(CH3COCH3); sulfuric acid (H2SO4); N, N-dimethylformamide ((CH3)2HCON); hydrochloric acid (HCl);


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sodium hypochlorite (NaClO); and acetonitrile (CH3CN) were all purchased directly from Sigma-Aldrich

Co. LLC (St. Louis, MO 63103, USA) and used without any further purification.

SYNTHETIC & PROPOSED METHODS

The attempted synthesis of the MnTMPyPCl85+ complex was approached using several different

synthetic steps, all of which are identified and described below.

1. Synthesis of Cu(II)TMPyP4+ from H2TMPyP4+. A Cu2+ ion was inserted into into the core

of the H2TMPyP4+ complex by refluxing porphyrin (100 mg) with cupric acetate (50 mg) in

methanol (20 mL) and DI water (5 mL) for 4 h (Fig. 3); the reaction was subsequently monitored

by UV-Visible spectroscopy (Fig. 4).

FIGURE 3: Reaction mechanism of Cu2+ ion insertion into core of H2TMPyP4+ complex (left) to yield CuTMPyP4+ metalloporphyrin complex (right).


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FIGURE 4: UV-Vis spectrum acquired of H2TMPyP4+ (purple line) starting material (λmax = 422 nm in CH3OH; 4 Q-bands observed) overlaid with spectrum acquired of the synthesized CuTMPyP4+ (red line) metallo-complex (λmax = 425 nm in CH3OH; 2 Q-bands observed).

Formation of the Cu(II) metallo-complex was necessary so that the four nitrogen atoms

within the core of the H2TMPyP4+ complex, all of which bonded with the Cu2+ ion, would be

protected from ensuing chlorination. Metallation of H2TMPyP4+ was evidenced by the observed

decrease in lower-energy Q-bands from four to two (see Fig. 4). The solvent was removed via

distillation, and the purple solid was collected, vacuum-dried, and used in subsequent syntheses

without any further purification.

2. β-Chlorination of CuTMPyP4+ to yield CuTMPyPCl84+. N-chlorosuccinimide (NCS) and

chlorine gas (Cl2) were used as chlorinating agents for the Cu(II) complex. Two different methods

using NCS were chosen in our attempts to octa-chlorinate the water-soluble porphyrin complex: in

separate approaches, the variables of 1) temperature and 2) form of combination were manipulated.

a. β-Chlorination of CuTMPyP4+ using NCS. CuTMPyP4+ (5 mg) was added to N,

N-dimethylformamide (20 mL; DMF) containing NCS (5 mg). Before the porphyrin was

added, the solution was heated for no more than five minutes at which point the desired

temperature was reached. The CuTMPyP4+ was then added to the DMF containing the NCS

at both 80° (Fig. 5) and 90°C. The samples were allowed to react for 15 minutes, during

which time the solutions changed from dark-red in color to a dark greenish-yellow. The

reaction was monitored with UV-Visible spectroscopy (spectrum acquired of 80°C sample

shown in Fig. 7-A).


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Additionally, two separate combination-based experimental approaches, both of

which involved the exact same reagent amounts aforementioned in the preceding

paragraph, were undertaken: 1) reflux of CuTMPyP4+ and NCS in DMF for a total of 4 h,

and 2) vigorous stirring (with no heating) of porphyrin and NCS in DMF for the same

amount of time (Fig. 6). During both experimental approaches, a change in color of the

reaction mixture from dark-red to light-brown was observed after ~3 h of reaction time.

Again, the transformation of the complex was closely monitored by UV-Visible

spectroscopy (spectrum acquired of sample subjected to stirring shown in Fig. 7-B).

FIGURE 5: Reaction mechanism showing theoretical octa-chlorination of the CuTMPyP4+ complex (left) to yield the hypothetical CuTMPyPCl84+ complex (right) via heat-based manipulations (i.e., significant temperature increases) to the system.

FIGURE 6: Reaction mechanism showing theoretical octa-chlorination of CuTMPyP4+ complex (left) to yield the hypothetical CuTMPyPCl84+ complex (right) via manipulation of the amount (i.e., intensity) of induced perturbation (i.e., forceful stirring at relatively high speed) to the system.


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FIGURE 7: (A) UV-Vis spectrum obtained after CuTMPyP4+ complex reacted with previously-heated (80°C) NCS in DMF for 15 min (λmax = 435 nm in DMF; 2 Q-bands observed; dark green-yellow color observed post reaction). (B) UV-Vis spectrum obtained after CuTMPyP4+ complex and NCS vigorously stirred in DMF for 4 h, with no added heat (λmax = 431.5 nm in DMF; 1 Q-band observed; light-brown color observed post reaction).

b. β-Chlorination of CuTMPyP4+ using Cl2. Chlorine gas, which was generated by

reacting hydrochloric acid (HCl) with sodium hypochlorite (NaClO), was also employed

as a chlorinating agent for the Cu(II) complex (Fig. 8). Contact with Cl2 induced an

immediate color change in the CuTMPyP4+ solution (in CH3OH), which changed from a

light-red color to a dark blackish-brown color. The reaction was allowed to take place for

no more than 5 s, and it was monitored using UV-Visible spectroscopy (Fig. 9).

FIGURE 8: Reaction mechanism showing theoretical octa-chlorination of CuTMPyP4+ complex (left) to yield the hypothetical CuTMPyPCl84+ complex (right) via subjection to Cl2 (g) for a duration of 5 s.

A B


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FIGURE 9: UV-Vis spectrum of the (theoretically) chlorinated CuTMPyPCl84+ complex acquired after 5 s contact with Cl2 (g). Two Q-bands, labeled 1 and 2 (located at 543 and 629 nm, respectively) were observed (λmax = 428 nm in CH3OH).

3. Synthesis of NiTMPyP4+ from H2TMPyP4+. After failed octa-chlorination of the

CuTMPyP4+ complex, a Ni(II) complex was synthesized using the same starting material and

methods. A Ni2+ ion was inserted into H2TMPyP4+ by reflux of porphyrin (200 mg) with nickel(II)

sulfate heptahydrate (100 mg) and sodium acetate (50 mg) in DMF (50 mL) for 3 h (see Fig. 10).

The reaction was subsequently monitored by UV-Vis absorption spectroscopy (Fig. 11).

FIGURE 10: Reaction mechanism of Ni2+ ion insertion into core of H2TMPyP4+ complex (left) to form NiTMPyP4+ metalloporphyrin complex (right).

2 1


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FIGURE 11: Overlaid UV-Vis spectra acquired of H2TMPyP4+ (red line) starting material (λmax = 422 nm in CH3OH; 4 Q-bands observed) and the synthesized NiTMPyP4+ (black line) metallo-complex (λmax = 420.5 nm in DMF; 2 Q-bands observed).

Formation of the Ni(II) complex was necessary to protect the nitrogen atoms in the core of

the porphyrin complex from ensuing chlorination. Metallation of H2TMPyP4+ was evidenced by

the replacement of four lower energy Q-bands by two. After cooling, the solvent was removed via

distillation. The black solid was then collected and vacuum-dried, and it used in subsequent

syntheses without any further purification.

4. Metathesis I: Synthesis of NiTMPyP4+ as Cl- salt. Solubility testing of the Ni(II) complex

was performed using several different solvents, including: acetone, acetonitrile, methanol, and DI

water. Test results indicated that the Ni(II) porphyrin complex was completely insoluble in acetone

and acetonitrile while being moderately soluble in both methanol and DI water. Consequentially, a

metathesis on the NiTMPyP4+ complex was performed to increase its overall solubility, with the

goal of synthesizing a fully water-soluble, stable complex (Fig. 12). Tetra-n-butylammonium

chloride (30 mg), or TBAC, was added to DMF (20 mL) containing the Ni(II) complex (30 mg).

Upon addition of the TBAC, a black solid precipitated out of the solution, which was subsequently

collected via suction filtration and allowed to air dry.


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FIGURE 12: Illustration of Cl- salt metathesis performed on NiTMPyP4+ complex using TBAC (Cl- salt addition indicated in enlarged circle as ‘X’).

5. β-Chlorination of NiTMPyP4+ as Cl- salt to yield NiTMPyPCl84+ using NCS. Two

different methods using NCS were chosen in our attempts to octa-chlorinate the Ni(II) porphyrin

complex. One approach involved manipulations with both stirring and heating, and the other

approach employed reflux techniques.

The Ni(II) complex as the chloride salt (5 mg; see Figure 12) and NCS (5 mg) were added

to methanol (10 mL), and the solution was simultaneously heated to a boil and stirred (Fig. 13). As

it boiled, the solution turned from a dark-brown to a dark greenish-yellow color. In less than 10

min, the solution had completely evaporated, leaving only a thin layer of a black jelly-like substance

that was stuck to the bottom of the vial. Methanol (10 mL) was poured onto the black substance,

and the liquid immediately turned brown. A sample was taken and monitored by UV-Visible

spectroscopy (Fig. 14-A).

Additionally, the Ni(II) complex (10 mg) as the chloride salt (see Fig. 12) and NCS (10

mg) were added to methanol (20 mL), and the solution was allowed to reflux for 1 h. The solution

changed from a dark-brown color to a deep yellow color. Structural transformation was monitored

by UV-Vis spectroscopy (Fig. 14-B).


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FIGURE 13: Reaction mechanism showing theoretical octa-chlorination (using NCS) of the NiTMPyP4+ complex as the Cl- salt (left) to hypothetically yield the CuTMPyPCl84+ complex (right) via stirring/heating manipulations (i.e., significant temperature increases) to the system.

FIGURE 14: (A) Spectrum obtained after NiTMPyP4+ complex as Cl- salt and NCS stirred/heated in CH3OH for < 10 min until complete CH3OH evaporation (λmax = 441.5 nm in CH3OH; 3 Q-bands observed; brown color observed post reaction). (B) Spectrum obtained after NiTMPyP4+ complex and NCS refluxed in CH3OH for 1 h (λmax = 419 nm in CH3OH; no Q-bands observed; dark yellow color observed post reaction).

6. Metathesis II: Synthesis of NiTMPyP4+ as PF6- salt. A second metathesis was performed

because β-chlorination of the Ni(II) complex as the chloride salt was unsuccessful. Here, instead

of Cl- (Fig. 15), the tosylate salt was replaced with PF6- via ammonium hexafluorophosphate

(NH4PF6). NH4PF6 (30 mg) was added to H2O (20 mL) containing the Ni(II) porphyrin (30 mg).

Upon addition of NH4PF6, a black solid precipitated out of the solution, which was later collected

via suction filtration and allowed to air dry.

A B


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FIGURE 15: Illustration of PF6- salt metathesis performed on NiTMPyP4+ complex using NH4PF6 (PF6- salt addition indicated in enlarged circle as ‘X’).

7. β-Chlorination of NiTMPyP4+ as PF6- salt to yield NiTMPyPCl8

4+ using SOCl2. Two

different methods using thionyl chloride (SOCl2) as the chlorinating agent were employed in

attempt to octa-chlorinate the Ni(II) complex. First, the Ni(II) complex as the PF6- salt (10 mg) was

added to stirring SOCl2 (20 mL), and heat was applied (Fig. 16)—almost instantaneously, the

solution turned dark brownish-green in color. The reaction was stopped when the temperature of

the system reached 75°C. Transformation was monitored by UV-Vis spectroscopy (Fig. 18-A).

Second, the Ni(II) complex as the PF6- salt (10 mg) was refluxed in SOCl2 (20 mL) for 2 h

before being stopped (Fig. 17); a color change from a light-brown color to a very deep greenish-

brown color was observed post reaction. The extent of the reaction was monitored using UV-

Visible spectroscopy (Fig. 18-B).


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FIGURE 16: Reaction mechanism showing theoretical octa-chlorination (using SOCl2) of the NiTMPyP4+ complex as the PF6- salt (left) to hypothetically yield the CuTMPyPCl84+ complex (right) via stirring/heating manipulations (i.e., significant temperature increases) to the system.

FIGURE 17: Reaction mechanism showing theoretical octa-chlorination (using SOCl2) of the NiTMPyP4+ complex as the PF6- salt (left) to hypothetically yield the CuTMPyPCl84+ complex (right) by reflux.


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FIGURE 18: (A) Spectrum obtained after NiTMPyP4+ complex as PF6- salt and SOCl2 stirred and heated to 75°C (λmax = 446.5 nm in SOCl2; 3 Q-bands observed; brown color observed post reaction). (B) Spectrum obtained after NiTMPyP4+ complex as PF6- salt refluxed in SOCl2 for 2 h (λmax = 447.5 nm in SOCl2; 2 Q-bands observed; dark green-brown color observed post reaction).

RESULTS: SPECTROSCOPIC OBSERVATIONS

TABLE 1: Soret-band positions exhibited by significant spectra of various porphyrin complexes studied both in this study and in previous experiments. All data obtained from previous work is in bolded rows (i.e., Samples 11-14, 22-23), and specific literature references are given in the λmax column. All spectroscopic data reported here was acquired via ultraviolet-visible absorption spectroscopy.

Sample Solvent Porphyrin Species Reaction Conditions λmax (nm) 1 H2O H2TMPyP4+ -- 422 2 CH3OH

CuTMPyP4+

H2TMPyP4+ reflux w/ Cu(CH3COO)2, 4 h 425 3

DMF

Reflux w/ NCS, 4 h 422.5 4 Heated w/ NCS, 90°C, 15 min 423.5 5 Reflux w/ NCS, 2 h 425 6 Heated/stirred w/ NCS, 80°C, 1 h 425.5 7 Heated/stirred w/ NCS, 80°C, 2 h 426 8 CH3OH Contact w/ Cl2 (g), 5 s 428 9

DMF Heated/stirred w/ NCS, 90°C, 1 h 431.5

10 Heated w/ NCS, 80°C, 15 min 435 11 C7H14 ZnTF5PPCl8 Cl2 (g) 442[10] 12 SOCl2 Cu(TPPs)Cl8 Reflux, 1 h 463-69[8] 13 CH2Cl2 CuTPPCl8 NCS 456[9] 14 CH3CN CuTMPyPBr8

4+ Contact w/ Br2 in DMF at RT 456[6] 15 DMF NiTMPyP4+ H2TMPyP4+ reflux w/ NiSO4, 4 h 420.5 16

CH3OH NiTMPyP4+

(Cl- salt)

Heated/stirred w/ NCS, 140°C, 15 min 418.5 17 Reflux w/ NCS, 1 h 419 18 Heated/stirred w/ NCS to evap. 441.5 19

SOCl2 NiTMPyP4+ (PF6- salt)

Heated/stirred, 55°C 439.5 20 Heated/stirred, 70°C 446.5 21 Reflux, 2 h 447.5 22 CH2Cl2 NiTPPCl8 Cl2 (g) 449[9] 23 DMF NiTMPyPBr84+ Contact w/ Br2 in DMF at RT 446[6]

A B


20

DISCUSSION & FUTURE OUTLOOK

The results of the initial experiments suggest that our attempts at β-chlorination using the Cu(II)

complex with NCS and Cl2 as chlorinating agents were not particularly successful. According to previous

studies[8], [15], when using NCS to octa-chlorinate a Cu(II) complex, the ideal position of the Soret-band is

in the range of 463-469 nm. The most successful experiment conducted using the Cu(II) complex was

heating the porphyrin with NCS to 80°C, resulting in an observed Soret-shift of 10 nm, from 425 to 435

nm (see Table 1, Sample 10); still, despite this approach yielding the most promising result, the Soret-band

was 28 nm away from the optimal position, a discrepancy considered to be too large to suggest that full

octa-chlorination of the Cu(II) complex was achieved.

Alternatively, the Ni(II) complex, with SOCl2 employed as its chlorinating agent, proved to be

much more successful at attaining β-chlorination of the porphyrin ring. When the NiTMPyP4+ complex (as

PF6- salt) was refluxed with SOCl2, a Soret-shift from 421 to 447.5 nm was observed (see Table 1, Sample

21). According to previous studies, Ni(II) complexes that have been fully octa-chlorinated via SOCl2 should

exhibit a Soret-band around 456 nm—our porphyrin sample demonstrated a Soret-band that was a mere 8.5

nm away from said optimum position. Still, however, our porphyrin must undergo further analysis to

determine its exact degree of chlorination. Nonetheless, indeed, although much more work is needed, these

preliminary results appear to support our hypothesis.

At the conclusion of our study, Ni(II)TMPyP4+ remains synthesized. The complex has been

partially chlorinated, but a full octa-chlorination has yet to take place; future work will focus on experiments

with Ni(II) water-soluble complexes. Investigations into alternate techniques that could potentially be

executed to achieve full β-chlorination of the porphyrin ring have been initiated. One such approach

involves the use of an insoluble porphyrin (i.e., H2TPyP) as the starting material, with subsequent solubility

modifications via a methylating agent, such as methyl triflate (C2H3F3O3S).

Regardless of the manner in which it is accomplished, successful octa-chlorination of the porphyrin

would be consequently followed with the replacement of the Ni2+ ion in the core of the NiTMPyP4+ complex

with a Mn2+ ion, a two-step procedure consisting of: 1) demetallation of the porphyrin via a strong acid

(i.e., H2SO4), yielding H2TMPyPCl85+; and 2) insertion of the Mn2+ ion into the core of the complex via

reflux with manganese chloride (MnCl2), as per the methods laid out by Richards et al.[6]


21

ACKNOWLEDGEMENTS

First and foremost, I thank the American Chemical Society for giving me the opportunity and

privilege to participate in its Project SEED Program, which, ultimately, was an invaluable, life-changing

experience, not just intellectually and professionally, but also emotionally and personally, as an individual.

I also thank my family, namely my mother, Shannon, and friends for their endless, unwavering support

throughout the entirety of this project; I send an abundance of my love and sincere wishes of well-being to

each and every one of you—may you each experience the best possible outcome in each and every one of

your future endeavors.

I also thank two of my collaborators and fellow Project SEED participants, Mr. Jah-Wann M.

Galimore and Mr. Alvin P. Huff, for their countless contributions to this project, all of which are highly

valued and held to the highest esteem. I have the utmost respect for each of you, both as professional

colleagues and personal friends—with the high-quality character that you each possess, I am certain that

both of you will find much happiness and success in life, of which you deserve nothing less.

Additionally, I extend much gratitude not only to the GCSU Dept. of Chemistry, Physics, &

Astronomy for allowing me to use its facilities and supplies located in Herty Hall, but to the entire team of

faculty and staff members who comprise the department and make its existence possible.

And, finally, I express legitimately endless gratitude to my mentor and genuine friend, Dr. Rosalie

A. Richards, for her guidance, instruction, understanding, support, and for being there for me every step of

the way, in both professional and personal purposes alike, as I continue to navigate what is simply referred

to as life.

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22

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