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Physicochemical characterization, and relaxometry studies of micro-graphite oxide, graphene nanoplatelets, and nanoribbons.

Paratala BS, Jacobson BD, Kanakia S, Francis LD, Sitharaman B - PLoS ONE (2012)

Bottom Line: The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research.In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn(2+) ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds.The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America.

ABSTRACT
The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn(2+) ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

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Room temperature EPR spectra of solid (a) oxidized micro-graphite, (b) oxidized graphene nanoplatelets, (c) reduced graphene nanoplatelets and (d) graphene nanoribbons.
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pone-0038185-g003: Room temperature EPR spectra of solid (a) oxidized micro-graphite, (b) oxidized graphene nanoplatelets, (c) reduced graphene nanoplatelets and (d) graphene nanoribbons.

Mentions: Figure 3a–d show the EPR spectra of the oxidized micro-graphite, oxidized graphene nanoplatelets, reduced graphene nanoplatelets and graphene nanoribbons, respectively (the blank EPR spectrum of the quartz EPR tube and DPPH standard is shown in in the Figure S5). The g values, EPR line widths at half heights (ΔH1/2, Gauss) and electron relaxation time (T2e) of each EPR spectra are listed in Table 1. All samples show broad peak (ΔH1/2) at their respective g values. However, graphene nanoribbons show ΔH1/2 values 2.6 times greater than oxidized micrographite, oxidized graphene nanoplatelets and reduced graphene nanoplatelets, which have similar ΔH1/2 values. The large line width indicates short electron relaxation time (T2e), and the calculated T2e values were between 0.19–21 nanoseconds for oxidized micrographite, oxidized graphene nanoplatelets, and reduced graphene nanoplatelets. Graphene nanoribbons have T2e values 0.072 nanoseconds; at least 2.9 times shorter than the other compounds. The EPR spectra of the graphene nanoribbons samples also shows a narrow peak in the center, which indicates presence of free radical species, possibly due to defect centers in the nanoribbon structures as reported by Tour et al. [33]. The free radical species have g of 2.007, and line width of 1.2 Gauss, and thus have very long electron relaxation time (T2e) of 88.2 nanoseconds. The large line broadening in all the compounds indicates significant manganese-to-manganese dipolar interaction. A reduction in the amount of manganese in the sample should decrease the line broadening, and resolve the 6-line manganese hyperfine structure in the EPR spectrum, and consequently, decrease the electron relaxation time.


Physicochemical characterization, and relaxometry studies of micro-graphite oxide, graphene nanoplatelets, and nanoribbons.

Paratala BS, Jacobson BD, Kanakia S, Francis LD, Sitharaman B - PLoS ONE (2012)

Room temperature EPR spectra of solid (a) oxidized micro-graphite, (b) oxidized graphene nanoplatelets, (c) reduced graphene nanoplatelets and (d) graphene nanoribbons.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369907&req=5

pone-0038185-g003: Room temperature EPR spectra of solid (a) oxidized micro-graphite, (b) oxidized graphene nanoplatelets, (c) reduced graphene nanoplatelets and (d) graphene nanoribbons.
Mentions: Figure 3a–d show the EPR spectra of the oxidized micro-graphite, oxidized graphene nanoplatelets, reduced graphene nanoplatelets and graphene nanoribbons, respectively (the blank EPR spectrum of the quartz EPR tube and DPPH standard is shown in in the Figure S5). The g values, EPR line widths at half heights (ΔH1/2, Gauss) and electron relaxation time (T2e) of each EPR spectra are listed in Table 1. All samples show broad peak (ΔH1/2) at their respective g values. However, graphene nanoribbons show ΔH1/2 values 2.6 times greater than oxidized micrographite, oxidized graphene nanoplatelets and reduced graphene nanoplatelets, which have similar ΔH1/2 values. The large line width indicates short electron relaxation time (T2e), and the calculated T2e values were between 0.19–21 nanoseconds for oxidized micrographite, oxidized graphene nanoplatelets, and reduced graphene nanoplatelets. Graphene nanoribbons have T2e values 0.072 nanoseconds; at least 2.9 times shorter than the other compounds. The EPR spectra of the graphene nanoribbons samples also shows a narrow peak in the center, which indicates presence of free radical species, possibly due to defect centers in the nanoribbon structures as reported by Tour et al. [33]. The free radical species have g of 2.007, and line width of 1.2 Gauss, and thus have very long electron relaxation time (T2e) of 88.2 nanoseconds. The large line broadening in all the compounds indicates significant manganese-to-manganese dipolar interaction. A reduction in the amount of manganese in the sample should decrease the line broadening, and resolve the 6-line manganese hyperfine structure in the EPR spectrum, and consequently, decrease the electron relaxation time.

Bottom Line: The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research.In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn(2+) ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds.The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, United States of America.

ABSTRACT
The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn(2+) ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents.

Show MeSH