MCrick_ACS Poster

1
Introduction Methods and Materials Introduction Halogen-containing volatile organic compounds are important carriers of fluorine, chlorine, bromine, and iodine within the planet’s biogeochemical cycling for the Group VII elements. Small, naturally occurring haloorganic compounds, mainly containing chlorine and bromine are either produced by living organisms or formed during processes such as volcanic eruptions, forest fires, and geothermal transformations (Gribble 2003). These compounds are usually benign, having relatively short lifetimes, being transformed either by hydrolysis, consumed as co-factors in microbial metabolism or by photochemical decomposition in the lower troposphere (Mohn et. Al. 1992). However, commercial use of anthropogenic chloro- fluoroanated saturated alkanes (CFCs) in cleaning solvents, aerosols, flame-retardants, refrigerants etc. has greatly affected these natural cycles. The carbon halide bond is strong, making the molecules very stable, but when haloorganics reach the Stratosphere, photolysis of the carbon-halide bond occurs due to the strong ultraviolet radiation. The X halogen anion destroys ozone molecules in the atmosphere by reacting in catalytic cycles in which one chlorine or bromine atom can destroy thousands of ozone molecules before its converted into a form that is harmless to ozone, all the while acting as greenhouse gases, leading to global warming. While current production and consumption controls have decreased the atmospheric concentration of synthetic haloorganics, and ozone recovery has been observed, there is still a negative effect on global warming. Studies have been conducted to determine the fate of halocarbons in the marine environment by both microorganisms (Häggblom 2003) and abiotic processes (Kriegman-King, 1994), where abiotic processes are considered slow in comparison with Abstract Results Biomimetic CFCs Degradation: an Insight into Biotic Halogen Cycling Mitchell Crick & Stephen K. O’Shea Department of Chemistry, Roger Williams University, Bristol, RI Understanding the marine microbial metabolic degradation pathways of natural halo-carbons is important not only from a climate perspective but also for what it reveals about the overall balance of biotic halo-carbons cycling and their release into the ecosystem, of which there is currently only limited knowledge. This research aims to discern the scope and mechanism for the oxidation and reduction of iron porphyrins by volatile halo-carbons as biomimetic models of marine heme systems. Furthermore, understanding the roles of marine iron porphyrin reductive dehalogenation in the transformation of halo-carbons gives insight into potential routes of anthropogenic chlorofluorocarbons marine decomposition and their metabolites potential impact on the halo-carbons global budget. Understanding the mechanism of reaction of reductive dehalogenation of these halo-carbons is important because eventually this chemistry could be used to rid the environment of these potentially harmful and robust compounds by converting them into simpler, less harmful ones. By understanding the redox potential of these porphyrins, it may be possible to use other similar pentadentate ligand complexes the achieve the same results. Rates of reaction were determined by monitoring the change in the UV-Vis absorption spectra. Products were determined in situ and from head-space analysis of the reaction mixtures by GC-MS compared to authentic standards. It was determined that the redox of the carbon-halo bond regulates the rate of reaction, where the iodo reactions were found to have higher kinetic rates in comparison to those of the fluoro- organics. Schemes References Reaction of a haloorganic with an Iron complex. In the first step, a radical results, the iron complex is oxidized, and the halogen is removed. In the second step, under acidic conditions the radical reacts with another iron(II) complex. The radical is protonated, and the iron center is oxidized Mechanisms of dehalogenation of a general haloorganic as well as for iodoethane and iodoform. Formation of the alkene occurs naturally in soil. Methane and ethylene products were successfully produced from the iron complexes shown below. Gribble G.W., 2003 Chemosphere 52, (2), pp 289-297 Mohn W.W. and Tiedje J.M. Microbiological Reviews, 1992, 56, (3), pp 482-507. Häggblom M.M., Fennell D.E., Ahn Y, Ravit B. and Kerkhof L.J. 2006 Twardowska (eds.), Soil and Water Pollution Monitoring, Protection and Remediation, pp 3-23. Springer. Kriegman-King M.R. and Reinhard M. 1994 Environmental Science and Technology., 28, (4), pp 692-700 Fahey, D.W., and M.I. Hegglin. “The Ozone Hole-Ozone Destruction.” The Ozone Hole-Ozone Destruction. Web. 09 Apr. 2015 Murphy B.L. and Morrison R.D. 2007 Introduction to Environmental Forensics 2 nd edition Academic Press. Matsumoto, K.; Gruber, N. (2005). “How accurate is the estimation of anthropogenic carbon in the ocean? An evaluation of the DC*method”. Global Biogeochem. Cycles Acknowledgements Structure of simple iodinated substrates of interest. It is observed that iodo reactions occurred fastest, followed by chloro and then bromo. Reactions with a vicinical dihalide produces an alkene. Iodoethane and iodoform were reacted with Iron(II) complexes in acidic conditions. Headspace was analyzed using Gas Chromatography. RWU Provost Foundation for Undergraduate Research and Roger Williams University Student Senate for travel support. This material is based upon work supported in part by the National Science Foundation EPSCoR Cooperative Agreement #EPS-1004057. Funding was received from the RWU Foundation for faculty sponsored undergraduate research. Thanks to Jim Lemire for poster printing. Ligand Structure E 1/2 (mV ) λ (nm ) Octaethyl Porphyrin -241 540 Phthalocyanine +208 658 Cyclam -57 360 White-Chen Catalyst a 386 Triflate +72 330 Acetate +75 332 250 300 350 400 450 500 0 0.5 1 1.5 2 2.5 3 Fe (II) acetate Wavelength (nm) Absorbance (AU) 300 400 500 600 700 800 900 0 0.2 0.4 0.6 0.8 1 1.2 Fe (III) phthalocyanine Wavelength (nm) Absorbance (AU) 250 300 350 400 450 500 550 0 0.5 1 1.5 2 2.5 3 Fe (II) cyclam Wavelength (nm) Absorbance (AU) 250 300 350 400 450 500 550 600 650 700 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Fe (II) White- Chen Wavelength (nm) Absorbance (AU) 200 250 300 350 400 450 500 550 600 650 700 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Fe (II) triflate Wavelength (nm) Absorbance (AU) Fe (II) OEP Fe (III) OEP UV-Vis spectra of Iron(II) and iron(III) complexes. Oxidation of the complexes were monitored at the specific wavelengths indicated by blue arrows and the table to the right. The complexes were dissolved in 50:50 DMF/acetic acid. Gas chromatograms of headspace taken from reaction vessel of iron(II) phthalocyanine and iodinated substrates. Note the elution of the products methane and ethylene that demonstrates the dehalogenation Cyclic voltammogram of OEP Fe(III)/(II) in NMP Glassy carbon electrode Ag/AgCl reference electrode and Pt auxiliary Iron complexes were reacted with iodinated substrates in acidic conditions with 50:50 DMF/Acetic acid as solvents. All Iron complexes were purchased, except for iron cyclam which was prepared in situ by the addition of cyclam to a boiling acetonitrile solution of iron trifluoromethanesulfonate. The solution was refluxed for 30 minutes, and then a hot ethanolic solution containing NH 4 PF 6 was added. Precipitation of crude product was brought about by azeotropic distillation of the acetonitrile with ethanol. Product was collected by filtration and recrystallized from acetonitrile and ethanol. UV-vis spectroscopy was used to monitor the change from iron (II) to iron (III). Monitored wavelengths are shown in the table below, as well as reduction potentials and the structures of the complexes of interest. O 2 , CH 4 CH 3 COOH DMF CHI 3 O 2 ,CH 2 CH 2 CH 3 CH 2 I DMF CH 3 CH 2 I The reactions between iron and the iodo molecules are fully completed within two hours The reaction products were characterized by GC-MS, eliciting the step-wise dehalogenation Wavelength of the reaction kinetics were determined, the relationship to the redox potential can be investigated a To be determined. Due to ligand exchange

Transcript of MCrick_ACS Poster

Page 1: MCrick_ACS Poster

IntroductionMethods and Materials Introduction

Halogen-containing volatile organic compounds are important carriers of fluorine, chlorine, bromine, and iodine within the planet’s biogeochemical cycling for the Group VII elements. Small, naturally occurring haloorganic compounds, mainly containing chlorine and bromine are either produced by living organisms or formed during processes such as volcanic eruptions, forest fires, and geothermal transformations (Gribble 2003). These compounds are usually benign, having relatively short lifetimes, being transformed either by hydrolysis, consumed as co-factors in microbial metabolism or by photochemical decomposition in the lower troposphere (Mohn et. Al. 1992). However, commercial use of anthropogenic chloro-fluoroanated saturated alkanes (CFCs) in cleaning solvents, aerosols, flame-retardants, refrigerants etc. has greatly affected these natural cycles. The carbon halide bond is strong, making the molecules very stable, but when haloorganics reach the Stratosphere, photolysis of the carbon-halide bond occurs due to the strong ultraviolet radiation. The X− halogen anion destroys ozone molecules in the atmosphere by reacting in catalytic cycles in which one chlorine or bromine atom can destroy thousands of ozone molecules before its converted into a form that is harmless to ozone, all the while acting as greenhouse gases, leading to global warming. While current production and consumption controls have decreased the atmospheric concentration of synthetic haloorganics, and ozone recovery has been observed, there is still a negative effect on global warming.

Studies have been conducted to determine the fate of halocarbons in the marine environment by both microorganisms (Häggblom 2003) and abiotic processes (Kriegman-King, 1994), where abiotic processes are considered slow in comparison with marine biotic microbial pathways. Transformations are catalyzed by reduction and oxidation by cytochrome P450s. (Mohn et. al. 1992, Häggblom et. al. 2006). Cytochrome P450s are a class of iron-centered hemeproteins that are an integral part of the respiratory sequence of all aerobic and facultative marine organisms. Despite their importance and ubiquitous nature, the redox chemistry of these units is not well defined within the protein matrix. Therefore, a better understanding of the processes that are responsible for the removal of halocarbons from the oceans before returning to the atmosphere is required.

Abstract Results

Biomimetic CFCs Degradation: an Insight into Biotic Halogen Cycling

Mitchell Crick & Stephen K. O’SheaDepartment of Chemistry, Roger Williams University, Bristol, RI

Understanding the marine microbial metabolic degradation pathways of natural halo-carbons is important not only from a climate perspective but also for what it reveals about the overall balance of biotic halo-carbons cycling and their release into the ecosystem, of which there is currently only limited knowledge. This research aims to discern the scope and mechanism for the oxidation and reduction of iron porphyrins by volatile halo-carbons as biomimetic models of marine heme systems. Furthermore, understanding the roles of marine iron porphyrin reductive dehalogenation in the transformation of halo-carbons gives insight into potential routes of anthropogenic chlorofluorocarbons marine decomposition and their metabolites potential impact on the halo-carbons global budget. Understanding the mechanism of reaction of reductive dehalogenation of these halo-carbons is important because eventually this chemistry could be used to rid the environment of these potentially harmful and robust compounds by converting them into simpler, less harmful ones. By understanding the redox potential of these porphyrins, it may be possible to use other similar pentadentate ligand complexes the achieve the same results. Rates of reaction were determined by monitoring the change in the UV-Vis absorption spectra. Products were determined in situ and from head-space analysis of the reaction mixtures by GC-MS compared to authentic standards. It was determined that the redox of the carbon-halo bond regulates the rate of reaction, where the iodo reactions were found to have higher kinetic rates in comparison to those of the fluoro-organics.

Schemes

References

Reaction of a haloorganic with an Iron complex. In the first step, a radical results, the iron complex is oxidized, and the halogen is removed. In the second step, under acidic conditions the radical reacts with another iron(II) complex. The radical is protonated, and the iron center is oxidized

Mechanisms of dehalogenation of a general haloorganic as well as for iodoethane and iodoform. Formation of the alkene occurs naturally in soil. Methane and ethylene products were successfully produced from the iron complexes shown below.

Gribble G.W., 2003 Chemosphere 52, (2), pp 289-297Mohn W.W. and Tiedje J.M. Microbiological Reviews, 1992, 56, (3), pp 482-507.Häggblom M.M., Fennell D.E., Ahn Y, Ravit B. and Kerkhof L.J. 2006 Twardowska (eds.), Soil and Water Pollution Monitoring, Protection and Remediation, pp 3-23. Springer.Kriegman-King M.R. and Reinhard M. 1994 Environmental Science and Technology., 28, (4), pp 692-700Fahey, D.W., and M.I. Hegglin. “The Ozone Hole-Ozone Destruction.” The Ozone Hole-Ozone Destruction. Web. 09 Apr. 2015Murphy B.L. and Morrison R.D. 2007 Introduction to Environmental Forensics 2nd edition Academic Press.Matsumoto, K.; Gruber, N. (2005). “How accurate is the estimation of anthropogenic carbon in the ocean? An evaluation of the DC*method”. Global Biogeochem. Cycles

Acknowledgements

Structure of simple iodinated substrates of interest. It is observed that iodo reactions occurred fastest, followed by chloro and then bromo. Reactions with a vicinical dihalide produces an alkene. Iodoethane and iodoform were reacted with Iron(II) complexes in acidic conditions. Headspace was analyzed using Gas Chromatography.

RWU Provost Foundation for Undergraduate Research and Roger Williams University Student Senate for travel support. This material is based upon work supported in part by the National Science Foundation EPSCoR Cooperative Agreement #EPS-1004057. Funding was received from the RWU Foundation for faculty sponsored undergraduate research. Thanks to Jim Lemire for poster printing.

Ligand Structure E1/2(mV)

λ (nm)

Octaethyl Porphyrin -241 540

Phthalocyanine +208 658

Cyclam -57 360

White-Chen Catalyst a 386

Triflate +72 330

Acetate +75 332

250 300 350 400 450 5000

0.5

1

1.5

2

2.5

3

Fe (II) acetate

Fe (III) acetate

Wavelength (nm)

Abso

rban

ce (A

U)

300 400 500 600 700 800 9000

0.2

0.4

0.6

0.8

1

1.2

Fe (III) phthalocyanine

Fe (II) phthalocyanine

Wavelength (nm)

Abso

rban

ce (A

U)

250 300 350 400 450 500 5500

0.5

1

1.5

2

2.5

3

Fe (II) cyclamFe (III) cyclam

Wavelength (nm)

Abso

rban

ce (A

U)

250 300 350 400 450 500 550 600 650 7000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Fe (II) White-Chen

Fe (III) White-Chen

Wavelength (nm)

Abso

rban

ce (A

U)

200 250 300 350 400 450 500 550 600 650 7000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Fe (II) triflateFe (III) triflate

Wavelength (nm)

Abso

rban

ce (A

U)

Fe (II) OEP

Fe (III) OEP

UV-Vis spectra of Iron(II) and iron(III) complexes. Oxidation of the complexes were monitored at the specific wavelengths indicated by blue arrows and the table to the right. The complexes were dissolved in 50:50 DMF/acetic acid.

Gas chromatograms of headspace taken from reaction vessel of iron(II) phthalocyanine and iodinated substrates. Note the elution of the products methane and ethylene that demonstrates the dehalogenation

Cyclic voltammogram of OEP Fe(III)/(II) in NMP Glassy carbon electrode Ag/AgCl reference electrode and Pt auxiliary

Iron complexes were reacted with iodinated substrates in acidic conditions with 50:50 DMF/Acetic acid as solvents. All Iron complexes were purchased, except for iron cyclam which was prepared in situ by the addition of cyclam to a boiling acetonitrile solution of iron trifluoromethanesulfonate. The solution was refluxed for 30 minutes, and then a hot ethanolic solution containing NH4PF6 was added. Precipitation of crude product was brought about by azeotropic distillation of the acetonitrile with ethanol. Product was collected by filtration and recrystallized from acetonitrile and ethanol. UV-vis spectroscopy was used to monitor the change from iron (II) to iron (III). Monitored wavelengths are shown in the table below, as well as reduction potentials and the structures of the complexes of interest.

O2 , CH4

CH3COOH

DMF

CHI3O2 ,CH2CH2

CH3CH2I

DMF

CH3CH2I

• The reactions between iron and the iodo molecules are fully completed within two hours • The reaction products were characterized by GC-MS, eliciting the step-wise dehalogenation• Wavelength of the reaction kinetics were determined, the relationship to the redox potential can be investigated

a To be determined. Due to ligand exchange