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Synthesis of double-clickable functionalised graphene oxide for biological applications.

Mei KC, Rubio N, Costa PM, Kafa H, Abbate V, Festy F, Bansal SS, Hider RC, Al-Jamal KT - Chem. Commun. (Camb.) (2015)

Bottom Line: Fourteen-percentage increase in azide content was found, after pre-treatment of GO with meta-chloroperoxybenzoic acid (mCPBA), determined with elemental analysis.No effect on A549 cell viability was found, up to 100 μg mL(-1) and 72 h of incubation, determined with the modified lactate dehydrogenase (mLDH) assay.The final conjugate was characterised with ATR-FTIR and TGA.

View Article: PubMed Central - PubMed

Affiliation: Institute of Pharmaceutical Science, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK. khuloud.al-jamal@kcl.ac.uk.

ABSTRACT
Azide- and alkyne-double functionalised graphene oxide (Click(2) GO) was synthesised and characterised with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and Raman spectroscopy. Fourteen-percentage increase in azide content was found, after pre-treatment of GO with meta-chloroperoxybenzoic acid (mCPBA), determined with elemental analysis. No effect on A549 cell viability was found, up to 100 μg mL(-1) and 72 h of incubation, determined with the modified lactate dehydrogenase (mLDH) assay. Two sequential copper(i) catalysed azide-alkyne cycloaddition (CuAAC) reactions were performed to conjugate the propargyl-modified blood-brain barrier targeting peptide Angiopep-2, and a bis-azide polyethylene glycol (MW = 3500), to the Click(2) GO. The final conjugate was characterised with ATR-FTIR and TGA.

No MeSH data available.


Infrared-transmittance spectra of GO-N3 derivatives and Click2 GO derivatives. (A) GO-N3 derivatives. The introduction of azide groups was confirmed at 2120 cm–1 (GO-N3 –mPCBA), 2122 cm–1 (GO-N3 +mCPBA). (B) Click2 GO derivatives. (Click2 GO +mCPBA). Enhanced C–OH peaks (3200 cm–1, 1227 cm–1 and 1036 cm–1) were observed. Full description of the peak locations can be found in ESI.†
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fig1: Infrared-transmittance spectra of GO-N3 derivatives and Click2 GO derivatives. (A) GO-N3 derivatives. The introduction of azide groups was confirmed at 2120 cm–1 (GO-N3 –mPCBA), 2122 cm–1 (GO-N3 +mCPBA). (B) Click2 GO derivatives. (Click2 GO +mCPBA). Enhanced C–OH peaks (3200 cm–1, 1227 cm–1 and 1036 cm–1) were observed. Full description of the peak locations can be found in ESI.†

Mentions: GO-N3 was then prepared using NaN3 and 1,2-epoxide ring opening reaction as described in ESI,† Methods (Scheme S2). GO-N3 was characterised by Raman spectroscopy and attenuated total reflectance Fourier transform infrared (ATR-FTIR) using the methods described in SI. A unique azide peak at 2121 cm–1 was found when azide groups were introduced on GO. Free azide peak was detected at 2053 cm–1 when the purification was not properly performed (Fig. S5, ESI†). All the oxygen functionalities found in GO were also observed in GO-N3 except that the intensity of hydroxyl related peaks was higher (3200, 1227, and 1036 cm–1) than that in GO (Fig. S6A, ESI†). The presence of a single azide peak at 2121 cm–1 confirmed the elimination of free azides. Raman spectra were normalised to the G peak (intensity equals 1) (Fig. S6B, ESI†). Higher ID/IG (peak height) ratio was obtained for GO-N3 (1.30 ± 0.05, n = 3) than GO (1.25 ± 0.01, n = 3). The difference, however, was not significant with t(2) = –1.62, p-value = 0.246. The presence of azide group was further confirmed by Staudinger-Ninhydrin assay (ESI,† Methods, Scheme S3, Fig. S6C).36,37 In order to increase the azide group content on GO-N3, m-chloroperoxybenzoic acid (mCPBA), a strong oxidising reagent, commonly used to epoxidise alkenes was used to introduce more epoxide groups on GO. Epoxidation of GO is generally not required as epoxides are known to be naturally present when graphite is oxidised to GO.38,39 Direct epoxidation of GO with H2O2, however, has been reported to generate ultra-small graphene quantum dots (GQD) via epoxide ring opening.40–42 To the best of our knowledge, direct epoxidation of GO with mCPBA has not been reported in the literature. In this work, mCPBA was therefore used to enrich epoxide content on GO surface to form epo-GO. Methods of epo-GO preparation is summarised in ESI,† Methods and presented in Scheme S4. Elemental analysis (C, H, N, O) was performed to determine N% in GO and GO-N3 derivatives (Table S3, ESI†). The N% for GO, GO-N3 (–mCPBA), and GO-N3 (+mCPBA) were <0.10, 0.71, and 0.81%, respectively. The mCPBA pre-treatment increased the azide content by 14%. The IR spectra of GO and GO-N3 (±mCPBA) are shown in Fig. 1A. The azide peak at 2120 and 2122 cm–1 was found for GO-N3 (–mCPBA) and GO-N3 (+mCPBA), respectively.


Synthesis of double-clickable functionalised graphene oxide for biological applications.

Mei KC, Rubio N, Costa PM, Kafa H, Abbate V, Festy F, Bansal SS, Hider RC, Al-Jamal KT - Chem. Commun. (Camb.) (2015)

Infrared-transmittance spectra of GO-N3 derivatives and Click2 GO derivatives. (A) GO-N3 derivatives. The introduction of azide groups was confirmed at 2120 cm–1 (GO-N3 –mPCBA), 2122 cm–1 (GO-N3 +mCPBA). (B) Click2 GO derivatives. (Click2 GO +mCPBA). Enhanced C–OH peaks (3200 cm–1, 1227 cm–1 and 1036 cm–1) were observed. Full description of the peak locations can be found in ESI.†
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4594119&req=5

fig1: Infrared-transmittance spectra of GO-N3 derivatives and Click2 GO derivatives. (A) GO-N3 derivatives. The introduction of azide groups was confirmed at 2120 cm–1 (GO-N3 –mPCBA), 2122 cm–1 (GO-N3 +mCPBA). (B) Click2 GO derivatives. (Click2 GO +mCPBA). Enhanced C–OH peaks (3200 cm–1, 1227 cm–1 and 1036 cm–1) were observed. Full description of the peak locations can be found in ESI.†
Mentions: GO-N3 was then prepared using NaN3 and 1,2-epoxide ring opening reaction as described in ESI,† Methods (Scheme S2). GO-N3 was characterised by Raman spectroscopy and attenuated total reflectance Fourier transform infrared (ATR-FTIR) using the methods described in SI. A unique azide peak at 2121 cm–1 was found when azide groups were introduced on GO. Free azide peak was detected at 2053 cm–1 when the purification was not properly performed (Fig. S5, ESI†). All the oxygen functionalities found in GO were also observed in GO-N3 except that the intensity of hydroxyl related peaks was higher (3200, 1227, and 1036 cm–1) than that in GO (Fig. S6A, ESI†). The presence of a single azide peak at 2121 cm–1 confirmed the elimination of free azides. Raman spectra were normalised to the G peak (intensity equals 1) (Fig. S6B, ESI†). Higher ID/IG (peak height) ratio was obtained for GO-N3 (1.30 ± 0.05, n = 3) than GO (1.25 ± 0.01, n = 3). The difference, however, was not significant with t(2) = –1.62, p-value = 0.246. The presence of azide group was further confirmed by Staudinger-Ninhydrin assay (ESI,† Methods, Scheme S3, Fig. S6C).36,37 In order to increase the azide group content on GO-N3, m-chloroperoxybenzoic acid (mCPBA), a strong oxidising reagent, commonly used to epoxidise alkenes was used to introduce more epoxide groups on GO. Epoxidation of GO is generally not required as epoxides are known to be naturally present when graphite is oxidised to GO.38,39 Direct epoxidation of GO with H2O2, however, has been reported to generate ultra-small graphene quantum dots (GQD) via epoxide ring opening.40–42 To the best of our knowledge, direct epoxidation of GO with mCPBA has not been reported in the literature. In this work, mCPBA was therefore used to enrich epoxide content on GO surface to form epo-GO. Methods of epo-GO preparation is summarised in ESI,† Methods and presented in Scheme S4. Elemental analysis (C, H, N, O) was performed to determine N% in GO and GO-N3 derivatives (Table S3, ESI†). The N% for GO, GO-N3 (–mCPBA), and GO-N3 (+mCPBA) were <0.10, 0.71, and 0.81%, respectively. The mCPBA pre-treatment increased the azide content by 14%. The IR spectra of GO and GO-N3 (±mCPBA) are shown in Fig. 1A. The azide peak at 2120 and 2122 cm–1 was found for GO-N3 (–mCPBA) and GO-N3 (+mCPBA), respectively.

Bottom Line: Fourteen-percentage increase in azide content was found, after pre-treatment of GO with meta-chloroperoxybenzoic acid (mCPBA), determined with elemental analysis.No effect on A549 cell viability was found, up to 100 μg mL(-1) and 72 h of incubation, determined with the modified lactate dehydrogenase (mLDH) assay.The final conjugate was characterised with ATR-FTIR and TGA.

View Article: PubMed Central - PubMed

Affiliation: Institute of Pharmaceutical Science, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK. khuloud.al-jamal@kcl.ac.uk.

ABSTRACT
Azide- and alkyne-double functionalised graphene oxide (Click(2) GO) was synthesised and characterised with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA) and Raman spectroscopy. Fourteen-percentage increase in azide content was found, after pre-treatment of GO with meta-chloroperoxybenzoic acid (mCPBA), determined with elemental analysis. No effect on A549 cell viability was found, up to 100 μg mL(-1) and 72 h of incubation, determined with the modified lactate dehydrogenase (mLDH) assay. Two sequential copper(i) catalysed azide-alkyne cycloaddition (CuAAC) reactions were performed to conjugate the propargyl-modified blood-brain barrier targeting peptide Angiopep-2, and a bis-azide polyethylene glycol (MW = 3500), to the Click(2) GO. The final conjugate was characterised with ATR-FTIR and TGA.

No MeSH data available.