Translate this page into:
Synthesis of PAMAM dendrimers with porphyrin core and functionalized periphery as templates of metal composite materials and their toxicity evaluation
⁎Corresponding author. raqe_caz@hotmail.com (Raquel E. Hernández Ramírez)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Experiments were performed for the synthesis of meso-substituted tetraphenyl porphyrins in order to obtain growth active points for PAMAM branches and a functionalized periphery with thiazole groups for increasing the metal complexation activity. Characterization by 1H and 13C NMR, mass spectrometry and infrared spectrometry confirmed the produced dendrimeric nanostructures; the chemical reduction of metallic Ag and Cu inside the dendrimer was proved by XPS. Finally, the toxicity of the metal-dendrimer complex was analyzed by means of the bacterial respiration test.
Keywords
Porphyrin
PAMAM-dendrimers
Metal complex
Metal species
1 Introduction
The synthesis and investigation of the properties of macrocycles gave rise to what would be known as supramolecular chemistry, which Jean-Marie Lehn defined as the chemistry beyond the molecule. In these compounds, the most common types of interactions are intermolecular van der Waals forces, electrostatic attractions, hydrogen bonding, CH-π, π-π, π-n, etc. (Wilkison, 1975; Churchill and Wormald, 1969). It should be noted that most of these interactions can be used as resources of molecular chemistry for the design or “architecture” of a molecule involving non-covalent interactions in order to form a supramolecule with its own characteristics (Kealy and Pauson, 1951).
Intermolecular interactions are the basis of molecular recognition processes, reactivity, and inhibition of transport processes, which are all highly specific. For example, enzymatic reactions, protein complexation, operon systems, transduction and transcription processes, nucleic acid replication and neurotransmission (Miller et al., 1952).
The formation of supramolecular complexes, however, results in very low yields because the purification processes are often difficult and the complexes can be broken, making so hard the preparation of a large amount of these products. These limitations have not allowed the further development of this chemistry area (Wilkinson et al., 1952).
Moreover, the design and synthesis of host molecules require the proper handling of energy parameters and stereochemistry, which is called “the architecture of the molecule”, to achieve adequate intermolecular interactions, and build new macromolecules with very different and interesting physicochemical properties (Fisher and Pfab, 1952; Dunitz, 1993). Under these requirements, various cyclic macromolecules such as crown ethers, calixarenes, resorcinarenes, cyclophanes and porphyrins have been synthesized (Salzer, 1999; Wilkinson, 1956; Westman and Rinehart, 1962).
Porphyrins are important structural components in the design and preparation of model systems in chemistry and materials because it is possible to obtain various substituents and different specific patterns around the periphery of the macrocycle (Lindsey, 1994). The synthetic control of the molecular entities attached to the periphery facilitates the design and synthesis of porphyrins for specific applications. In this sense, the synthesis of porphyrins is the first step in many research projects (Medforth and Porphyrin Handbook, 2000; Kim et al., 1979). The demand for the creation of new complex structures has prompted the development of specialized methods for the synthesis of porphyrins with specific substitution patterns for the preparation of more complex materials such as dendrimers (Bhyrappa et al., 1996).
Dendrimers are organic macromolecules formed with a cyclic center surrounded by periphery ramifications with a perfectly defined structure and a wide variety of functional groups which can be coupled during the synthesis (Fréchet and Tomalia,).
Dendrimers are used as templates to complex metals due to their globular and controlled structure (Gorman, 1998). So, metallodendrimers are becoming of interest from a materials science perspective because of their unique physical properties, leading to potential photophysical and catalytic applications. Metallodendrimers show a substantial structural diversity and their properties and applications are wide-ranging. Metallodendrimers are classified according to where the metal appears in the dendrimer: at the centre, as connectors, as branching units, or as peripheral dendrimer units (Süleyman et al., 2014). The metal may be bound to a surface site on the dendrimer (exo-receptor) or to a site within the dendrimer internal cavities (endo-receptor) Newkome et al., 1999.
Previous works have reported PAMAM dendrimers modified with a porphyrin core for the complexation of heavy metal cations such as Hg(II), Co(II), Cd(II), Fe(II), Cr(II) and Pb(II) in aqueous solutions, with retentions of 60–99% (Hernández et al., 2015). Furthermore, the modification of PAMAM dendrimers with a CdTe/CdS core/shell, successfully synthesized in aqueous solution with adequate biocompatibility and sensitive photoluminescence as response in brain tumor cell imaging, has been reported (Bai et al., 2015).
This work reports the synthesis of tetraphenyl porphyrins as core with PAMAM branches and periphery modification using thiazole groups for the complexation of Ag(I) and Cu(II) and their chemical reduction; furthermore, their toxicity is also studied.
2 Results and discussion
2.1 Synthesis and characterization of porphyrins
The synthesis of porphyrins was carried out using the conventional methods developed by Adler and Lindsey through the condensation of pyrrole and p-anisaldehyde with the subsequent oxidation of the precursors. Finally, the deprotection reaction using BBr3 was performed as shown in Scheme 1.
Synthesis of porphyrins.
The porphyrins were characterized by 1H NMR and the following signals were observed in Fig. 1 for Compound 3: a singlet at −2.75 ppm was assigned to two pyrrolic protons inside the macrocycle; another singlet at 4.09 ppm was assigned to twelve protons of methoxy groups in the periphery. To 16 protons of aromatic rings in meso positions in the porphyrin macrocycle was assigned a triplet at 7.25–7.30 ppm and a multiplet at 8.11–8.22 ppm was assigned. Finally, a singlet at 8.86 ppm was assigned to 8 pyrrole protons.
1H NMR spectrum of Compound 3.
In addition, the structure of Compound 3 was confirmed by the determination of the molecular ion at 759 m/z by MALDI-TOF Mass Spectrometry as shown in Fig. 2.
MALDI-TOF spectrum of Compound 3.
2.2 Synthesis and characterization of functionalized dendrimers
The synthesis of the functionalized PAMAM dendrimers with porphyrin core was carried out by the divergent approach. This method includes three steps: firstly, a 0.5 type dendrimer was synthesized with methyl bromoacetate in acetone for 24 h; secondly, amine groups were introduced in order to obtain the first generation PAMAM dendrimers (Compound 7); and thirdly, active centers were introduced using ethyl 2-(2-chloroacetamido)-4-thiazoleacetate, obtaining Compound 9 according to Scheme 2 with a yield of 90%.
Synthesis of functionalized dendrimers with porphyrin core and PAMAM branches.
Fig. 3 shows the 13C NMR spectrum of Compound 9, where the following signals were indexed: an ethoxy group in the dendrimer periphery was observed at 13.59 ppm for the methyl group and at 60.20 ppm for the methylene group; signals at 150.58 and 164.24 ppm were assigned to the thiazole ring; methylene groups between amines were reported at 36.60 and 41.54 ppm; benzene rings were identified at 113.91 ppm; at 121.84 and 143.18 ppm, pyrrole rings were assigned and methine bridges were identified at 110.16 ppm.
13C NMR spectrum of Compound 9.
Additional characterization by 1H NMR, IR, MALDI-TOF mass spectrometry and elemental analysis confirmed the reported dendrimeric structures.
2.3 Metal-dendrimer complexation and chemical reduction
Compound 9 (0.0001 mmol) was added to 50 mL of AgNO3 at 5 ppm of Ag+ and 50 mL of CuSO4 at 5 ppm of Cu2+ in aqueous solution for the complexation. The addition of NaBH4 in excess causes the reduction in the dendrimer-metal complexes according to the mechanism depicted in Scheme 3.
Metal complexation and chemical reduction to metallic species.
Compound 9 was analyzed by infrared spectrometry, Fig. 4a, where a stretching broad band at 3420 cm−1, corresponding to N—H bonds of the primary amine groups on the periphery can be seen; at 3080 cm−1, a stretching band corresponding to the C—H bonds of aromatic rings can be identified; at 2991 cm−1, a stretching band corresponding to aliphatic C—H can be observed. The stretching band at 1734 cm−1 belongs to C⚌O groups and the deformation band at 1658 cm1 corresponds to N—H of primary amines. To C⚌C of bonding aromatic rings, stretching bands at 1587 and 1434 cm−1 are assigned. For N—H of secondary amines, a deformation band appears at 1542 cm−1; for C—O bonds, stretching bands at 1340 cm−1 (asymmetric) and 1038 cm−1 (symmetric) are observed. Finally, the stretching bands observed at 1210 and 738 cm−1 belong to C—N and C—S bonds, respectively. Table 1 shows the infrared spectrometry data of dendrimer-metal complexes (Fig. 4b and 4c), where a shift of the bands corresponding to the dendrimer amine groups is observed. Due to the formation of coordination bonds with metal cations, it is possible to observe a band shifting at 1210 cm−1 from C—N to C—N-met and at 1237 cm−1 for C—N—Ag; in addition, in the fingerprint region, the bands are also shifted because of the presence of metals in the organic template.
Infrared analysis for metal complexes.
Functional group
Bonding
Dendrimer without metal
(a) Wavenumber cm−1
Dendrimer-Ag
(b) Wavenumber cm−1
Dendrimer-Cu
(c) Wavenumber cm−1
Amine
N—H
υ
3420
3420
3364
Aromatic ring
C—H
υ
3080
3080
3080
Aliphatic
C—H
υ
2991
2918
2994
Carbonyl
C⚌O
υ
1734
Amine
N—H
δ
1658
1663
1658
Aromatic
C⚌C
υ
1587
Amine
N—H
δ
1542
1545
1542
Aromatic
C⚌C
υ
1434
1439
1443
Ester
C—O
υas
1340
Amine
C—N
υ
1210
1237
1223
Ester
C—O
υs
1038
Thiazole
C—S
υ
738
734
737
2.4 Analysis of composite materials
In this work, the analysis of high resolution XPS shows Ag peaks, and the addition of NaBH4 allows the chemical reduction in the cation to its metallic state. In Fig. 5, the doublet at 368.18 and 374.19 eV corresponds to Ag0 present at 86.88%. In addition, an AgO doublet at 367.34 and 373.27 eV was also observed at 13.12%.
High resolution XPS spectrum of Compound 10.
The high-resolution XPS analysis for Cu in Fig. 6 shows a doublet at 932.75 and 952.35 eV, which corresponds to Cu2O with an abundance of 73.7%; a doublet at 932.2 and 951 eV for Cu0 species is also observed, which was found in 26.4% of abundance in the sample.
High resolution XPS spectrum of Compound 11.
2.5 Evaluation of dendrimer toxicity
Respirometry tests were performed. This technique allows the study of biodegradability, treatability and inhibition of contaminants in water. The percent inhibition (ID) is determined by Eq. (1) according to the maximum value of SOUR (Specific Oxygen Uptake Rate). Fig. 7 shows the respirometry results.
Results of respirometry tests for Compounds 9 and 10.
By applying Eq. (1), inhibition rates of 5.07% for the dendrimer without metal (Compound 9) and 11.01% for the composite dendrimer with Ag0 (Compound 10) were obtained with a remarkable increase due to the antibacterial properties of Ag. The results obtained by respirometry allow a real quantification of the dendrimer toxicity. Based on the obtained results, the dendrimer with Ag0 cannot be considered as toxic according to the minimum inhibition index of 15%, for this poses a risk neither for health nor for the environment.
3 Experimental section
3.1 Materials and equipment
Solvents and reagents were purchased as reagent grade and used without further purification. Acetone was distilled over calcium chloride. 1H and 13C NMR were recorded on a Varian-Unity-300 MHz with tetramethylsilane (TMS) as an internal reference. Infrared (IR) spectra were recorded on a Perkin Elmer FT-IR spectrophotometer. The elemental analyses were determined by Chemical Analysis Laboratories at IMP México. MALDI-TOF mass spectra were recorded on a Micromass TofSpec instrument. The surface analyses of the composites were performed on a Thermo Scientific K-Alpha spectrometer.
3.1.1 Synthesis and deprotection of porphyrins
A p-anisaldehyde solution (5 mmol) in 50 mL of methylene chloride was added with trifluoroacetic acid (1.30 mmol) at 70 °C with constant stirring and reflux for 2 h. Subsequently, the solution temperature was lowered to 0 °C in order to add slowly 5 mmol of pyrrole, Compound 1, with constant stirring for 30 min. By thin layer chromatography, the presence of porphyrin was confirmed; afterward, the solution was immobilized on silica gel to promote the oxidation of the formed compounds. Finally, purification was performed by column chromatography using silica gel as stationary phase. As mobile phase, mixtures of hexane-ethyl acetate 2:1 and methylene chloride-methanol 1:1 were used, and porphyrins were isolated. The solution was evaporated under vacuum and precipitated with methylene chloride-hexane.
Compound 3: 0.04 mmol, 1% yield, purple powder and m.p. > 300 °C.
UV–vis CH3OH nm: 247, 291, 410, 515, 565, 597 and 649
IR KBr, cm−1: 3330, 1603, 1501, 1240, 1170, 998 and 750
1H NMR CDCl3, 300 MHz, δ ppm: −2.75 (s, 2H, pyrrole int), 4.09 (s, 12H, O—CH3), 7.25–7.30 (t, 8H, Ar), 8.11–8.22 (m, 8H, Ar), 8.86 (s, 8H, pyrrole)
13C NMR DMSO, 75 Hz, δ ppm: 56.2 (O—CH3), 99.13 (methine), 111.4 (Ar), 119.9 (Ar), 120.7 (pyrrole), 120.9 (Ar), 128.9 (Ar), 142.1 (pyrrole), 156.65 (Ar-porphyrin ring), 161.1 (pyrrole)
MALDI TOF 734 (m/z)
Anal. Calc for: C48H38N4O4 C, 78.45%; H, 5.21%; N, 7.62% Found: C, 76.86%; H, 5.10%; N, 7.34%
A solution of Compound 3 (0.13 mmol) in 50 mL of dichloromethane was heated at 100 °C with reflux until a homogeneous solution was obtained. Then, it was cooled to 0 °C by adding BBr3 (0.54 mmol). The reaction occurred under constant stirring for 24 h. The product was dried in a rotary evaporator and then precipitated with dichloromethane-hexane.
Compound 5: 0.12 mmol, 97% yield, deep purple powder and m.p. > 300 °C
UV–vis CH3OH nm: 263, 327, 434, 524, 576, 601 and 657
IR KBr, cm−1: 3580, 1603, 1501, 1240, 1070, 998 and 750
1H NMR CDCl3, 300 Hz, δ ppm: −2.82 (s, 2H, pyrrole int), 5.35 (s, 4H, O—H), 7.15–7.24 (m, 8H, Ar), 7.65–7.79 (m, 8H, Ar), 7.98–8.15 (m, 8H, pyrrole)
13C NMR CDCl3, 74 Hz, δ ppm: 99.13 (methine), 111.4 (Ar), 119.9 (Ar), 120.7 (pyrrole), 120.9 (Ar), 128.9 (Ar), 142.1 (pyrrole), 156.65 (Ar-porphyrin ring), 161.1 (pyrrole)
MALDI TOF 678.23 (m/z)
Anal. Calc. for C44H30N4O4 C, 77.86%; H, 4.46%; N, 8.25% Found: C, 77.95%; H, 4.26%; N, 8.29%.
3.1.2 Synthesis of 0.5 generation dendrimers
A solution of Compound 5 (0.45 mmol) in 50 mL of dry acetone was added with methyl bromoacetate (1.7 mmol) and cesium carbonate (1.53 mmol). The reaction was heated with reflux and stirred vigorously under nitrogen atmosphere for 18 h. Afterward, the mixture was filtered to remove the catalyst. The filtrate was evaporated to dryness under vacuum. The organic layer was evaporated to dryness and the mixture was purified by dilution in dichloromethane; then, hexane was added, thus obtaining a precipitate, Compound 5.
Compound 6: 0.28 mmol, 64% yield, purple powder with metallic shine, and m.p.>300 °C,
UV–vis CH2Cl2 nm: 230, 255,303, 421, 452, 518, 554, 595, and 685.
IR KBr, cm−1: 3448, 3314, 3116, 3034, 2950, 2911, 2851, 1756, 1603, 1506, 1210, and 1175.
1H NMR CDCl3, 300 Hz, δ ppm: −2.74 (s, 2H, pyrrole int.), 3.94 (s, 12H, O—CH3), 4.91 (s, 8H, CH2⚌O), 7.24–7.28 (m, 8H, Ar), 8.09–8.12(m, 8H, Ar), and 8.84 (s, 8H, pyrrole).
13C NMR CDCl3, 300 Hz, δ ppm: 52.42 (O—CH3), 65.65 (CH2—O), 112.95 (Ar), 119.47 (Ar), 127.87 (methine), 130.99 (pyrrole), 135.61 (C—Ar), 135.71 (pyrrole), 140.18 (pyrrole), 157.69 (C—O), and 169.51 (C⚌O).
MALDI TOF 967 (m/z).
Anal. Calc. for C56H46N4O12: C, 69.58%; H, 4.79%; and N, 5.79%. Found: C, 69.98%; and H, 4.81%; N, 5,27%.
3.1.3 Synthesis of first generation dendrimers
To a solution of Compound 6 (0.40 mmol) in 400 mL of benzene-methanol 1:1, ethylendiamine (1.65 mmol) was added. The reaction was carried out at 90 °C with constant stirring for 24 h. Next, the solvents were evaporated under vacuum, and the obtained solid was dissolved in dichloromethane and precipitated with hexane, producing Compound 7.
Compound 7: 0.34 mmol, 96% yield, purple powder, and m.p. >300 °C.
UV–vis CH2Cl2 nm: 230, 256, 304, 421, 519, 556, 596, 650, 695, 716, and 772.
IR KBr, cm−1: 3360, 3316, 3065, 2931, 2867, 1661, 1603, 1504, 1229, 1177, 1057, 965, 799, 732, and 555.
1H NMR CDCl3 + DMSO, 300 Hz, δ ppm: −2.84 (s, 2H, pyrrole int), 2.98 (t, 8H, NH2, J = 6 Hz), 3.50–3.56 (m, 16H, NH—CH2—CH2—NH2), 4.81 (s, 8H, CH2—C⚌O), 7.38–7.41 (m, 8H, Ar), 7.82 (br, 4H, NH), 8.11–8.14 (m, 8H, Ar), and 8.84 (s, 8H, pyrrole).
13C NMR CDCl3 + DMSO, 75.4 Hz, δ ppm: 39.82 (CH2—NH2), 40.60 (CH2—NH), 67.22 (CH2—C⚌O), 112.80 (Ar), 118.970 (Ar), 124.34 (pyrrole), 134.99 (methine), 143.92 (pyrrole), 157.15 (C—O), 159.51 (Ar), and 168.05 (C⚌O).
MALDI TOF 1079 (m/z).
Anal. Calc. for C60H62N12O8: C, 66.77%; H, 5.79%; and N, 15.57%. Found: C, 67.02%; H, 5.76%; N 15.32%.
3.1.4 Synthesis of functionalized dendrimers
The synthesis of Compound 9 was carried by means of an SN2 reaction between Compound 7 (0.09 mmol) and ethyl 2-(2-chloroacetamido)-4-thiazoleacetate, Compound 8 (0.37 mmol), in 40 mL of benzene as the reaction medium. The reaction was brought to room temperature at constant stirring and the coupling was instantaneous. Afterward, the solvents were evaporated under vacuum, and the obtained solid was dissolved in dichloromethane and precipitated with hexane.
Compound 9: 0.08 mmol, 91.2% yield, copper red powder and m.p. > 300 °C.
IR KBr, cm−1:3420, 3102, 3080, 2991, 1734, 1658, 1587, 1410, 1210, 1172, 1038, 966, 876, 738, 640 and 613.
1H NMR CDCl3 + DMSO, 300 MHz, δ ppm: −2.74 (s, 2H, pyrrole int.), 1.28 (s, 12H, CH2—CH3), 2.58 (s, 8H, NH—CH2), 2.86 (an, 8H CH2—C⚌O), 3.68 (s, 16H, CH2—C⚌O, CH2—NH), 4.13 (s, 8H, CH2—CH3), 4.86 (s, 8H, CH2—C⚌O), 6.82 (s, 4H, N—CH, thiazole) 7.31 (s, 8H, Ar), 7.51 (s, 8H, Ar), 7.97 (s, 8H, pyrrole), 9.81 (an 12H, NH).
13C NMR CDCl3 + DMSO, 75 MHz, δ ppm: 13.59 (CH2—CH3), 36.6 (CH2C⚌O), 39.77 (NH—CH2), 40.05 (CH2—NH), 51.4 (CH2—C⚌O), 60.2 (CH2—CH3), 66 (CH2—C⚌O), 112.4 (methine), 122 (CH, anillo-CH2), 128 (Ar), 134.6 (CH⚌CH, thiazole), 143.8 (pyrrole), 145 (Ar), 151 (pyrrole) 157.03 (C—O), 161 (N—CH—S, ring), 164.24 (C⚌O), 169.55 (C⚌O), 173 (C⚌O).
MALDI TOF 1997.67 m/z.
Anal. Calc. for C97H104N20O20S4 C, 58.30%; H, 5.25%; N, 14.02%. Found: C, 58.45%; H, 5.41%; N, 13.71%.
3.1.5 Synthesis of metal composite materials
For the synthesis of metal species, 0.0001 mmol of Compound 10 was added to a volume of 50 mL of Ag+ and 50 mL of Cu2+ aqueous solutions. The complexation reaction was carried out with constant stirring and room temperature for 2 h for silver and 3 h for copper. Finally, dendrimer-metal complexes were formed in the same aqueous solution. Subsequently, 40 mg of NaBH4 was added, and the reaction went on for 3 h under N2 atmosphere at room temperature and constant stirring for silver and 5 h for copper under the same conditions. The solutions were filtered with nylon membranes with 0.45 μm of pore size to recover the composites.
3.1.6 Respirometry test
A Surcis respirometer with one liter of capacity, temperature control (±1 °C), recirculation and medium stirring was used to determine the toxicity of Compounds 9 and 10. A sensor was used in line to measure the dissolved oxygen (DO) (5–19 mgO2 L−1) every 2 s. Prior calibration was performed to determine the DO in the medium, which remained constant; the sensor baseline indicated parameter variability. An active sludge from a wastewater treatment plant was used; this sludge was conditioned with constant air flow (1.7 ml/min); to promote the endogenous sludge, phase nutrients were not added. In a first test, the respiration rate was measured by means of a biodegradable substrate (CH3COONa, 100 mg/L), which represents the benchmark for the evaluation of dendrimers in Compounds 9 and 10. For the second and third tests, each analyzed dendrimer (10 mg/L) and the substrate was added with the same proportion.
4 Conclusions
The chemical reduction in dendrimer-metal complexes was determined by XPS, where 86.88% of Ag and 26.4% of Cu cations were reduced to the metallic phase.
PAMAM dendrimers with porphyrin core are adequate materials for the synthesis of metallic species, because the synthesis is possible under normal conditions of temperature, pH and pressure; moreover, their application in aqueous solutions for the complexation reaction is possible. The time required for the complex formation is decreased because porphyrin is a molecule with the property of forming complexes with metal cations.
Biological studies by means of respirometry techniques for quantifying the toxicity of dendrimers and dendrimer-Ag°Complexes were performed, using activated sludge from a tertiary process for wastewater treatment as biomass. The obtained inhibition rate was 5% for the dendrimer without metal and 11% for the dendrimer with Ag0, indicating that microorganisms are capable of metabolizing the dendrimers, which shows that these compounds do not pose a health risk because they have an inhibition index below 15%. The results suggest that the obtained dendrimers may have a potential application in the field of medicine as possible drug carriers due to the properties of porphyrins, which can be used as markers for the identification of metastasis.
Dendrimers are innovative materials that allow high control of the design and construction at every stage of their synthesis. Their chemical properties can be exploited for doping with compounds of electrophilic character (metals), obtaining new compounds capable of having specific properties to be used in different research fields, for when used in small amounts, these compounds maintain the same characteristics.
Acknowledgments
The authors would like to acknowledge the support provided by SIP-IPN 20171270.
References
- Appl. Sci.. 2015;5:1076-1085.
- J. Am. Chem. Soc.. 1996;118:5708-5711.
- Inorg. Chem.. 1969;8:716-1939.
- In Organic Chemistry: Its language and its state of the art 1993:9-23.
- J. Chem. Sci.. 1952;7:377-379.
- Fréchet, J.M.J., Tomalia, D.A. Dendrimers and Other Dendritic Polymers. Wiley, New York.
- Adv. Mater.. 1998;10:295-309.
- J. Inc. Phenom. Macrocycl. Chem.. 2015;84(1):49-60.
- Nature. 1951;168:1039-1040.
- Kim, J.B., Longo, F.R., 1979. Porphyrin Chemistry Advances. In: Longo, F.R., (Ed.), Ann Arbor Science Publishers Inc, Michigan, p. 305.
- Metalloporphyrins Catalyzed Oxidations. The Netherlands: Kluwer Academic Publishers; 1994. p. :49-86.
- Medforth, C.J., 2000. Porphyrin Handbook. In: Kadish, K.M., Smith, K.M., Guilard, R. (Eds.), Vol. 5, Academic Press, San Diego, p. 3.
- J. Chem. Soc. 1952:632-635.
- Chem. Euro. J.. 1999;5:1445-1451.
- Pure Appl. Chem.. 1999;8:1557-1585.
- Polym. Int.. 2014;63(4):778-787.
- Acta Chem. Scan.. 1962;16:1199-1205.
- Org. Synth.. 1956;36:31.
- Organometal. Chem.. 1975;100:273-278.
- J. Am. Chem. Soc.. 1952;74:2125-2126.
Appendix A
Supplementary material
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.arabjc.2017.01.013.
Appendix A
Supplementary material
Supplementary data 1
Supplementary data 1